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2018 Spring Meeting



Theoretical searches for innovative materials for energy harvesting and storage

Evolution towards a renewable future demands application-specific materials. Hence, targeted in silico searches across chemical space are emerging as critical tools for accelerated materials discovery. This symposium covers all aspects of those efforts, focusing on technologically paramount areas.


In the context of our civilization’s growing dependence of technology, the prediction of global shortages of natural resources - both oil and critical raw materials – is among the gravest concerns facing humanity. The situation calls for a rapid transition towards renewable energies and more resource-efficient technologies in critical areas like electricity generation and transportation. Furthermore, technological development in new areas like the Internet of Things, and advances in nanotechnology, require energy harvesting and storage at scales far removed from current mainstream solutions.

Ushered by advances in statistics and computational power, a new kind of dynamics between theory and experiment is emerging in materials science, with the potential to accelerate materials discovery to meet the increased demand for task-specific materials. This new approach enables the exploration of large areas of chemical space in search of good candidate materials with optimal values of a target property. The heightened demand for automation, advanced analysis and predictive capabilities inherent to this new method put it in an exciting crossroads between chemistry, mathematics and computational science.

This transversal multidisciplinary approach is the key ingredient of the European Energy oriented Centre of Excellence (EoCoE) which aims to accelerate the transition to a reliable low carbon energy supply exploiting the ever-growing computational power of HPC (High Performance Computing) infrastructures. The ambitious goal of the Materials4Energy community, one of EoCoE’s pillars, is to harness the synergies between disciplines to attain groundbreaking materials design for energy applications.

The symposium aims to bring together key researchers in all fields of study related to theoretical discovery of materials for energy applications to exchange achievements and develop future collaborations. The selection of speakers reflects a desire to turn this symposium into an interdisciplinary meeting point: the organizers believe that the unusual blend of researchers working on solid crystals, organic liquids, and pure methodology will set the event apart from more typical meetings.

All aspects of theoretical materials discovery fall within the scope of the symposium, including: predictive calculation of material properties, computational thermodynamics, generation of descriptors, materials databases, machine-learning methods, and specific applications.

Hot topics to be covered by the symposium:

The symposium will be divided in sessions, dedicated to materials discovery in connection with specific applications, including but not limited to: batteries and other electrochemical devices, hydrogen storage, carbon capture, solar power, small scale energy harvesting/scavenging (thermoelectrics, piezoelectrics…)

List of invited speakers:

  • S. Curtarolo (Duke University, Durham, USA),
  • R. Ramprasad (University of Illinois, USA),
  • C. Wolverton (Northwestern University, Evanston, USA),
  • J. Even (INSA-Rennes, CNRS, France),
  • F. Giustino (University of Oxford, UK),
  • A. De Vita (King’s College, London, UK),
  • A. Igartua, (TEKNIKER, Spain),
  • C. Massobrio (IPCMS-CNRS, Strasbourg, France)

Scientific committee members:

  • M. Buongiorno Nardelli (University of North Texas, Texas, USA),
  • N. A. Katcho (CIC Energigune, Minano, Alava, Spain),
  • W. Li (Shen Zhen University, China),
  • S. Sanvito (CRANN, Trinity College, Dublin, Ireland),
  • I. Savic (Tyndall Institute, Cork, Ireland),
  • C. Schröder (Institute of Biological Chemistry, University of Vienna, Austria),
  • L.M. Varela Cabo (University of Santiago de Compostela, Spain),
  • A. Walker (University of Bath, UK),
  • N. Novakovic (University of Belgrade, Serbia),
  • P. Pochet (INAC, CEA Grenoble, France),
  • M. Salanne (CNRS, Pierre et Marie Curie University, France),
  • U. Aeberhard (FZJ, Jülich, Germany),
  • F. Stassin (EMIRI, Energy Materials Industrial Research Initiative, Belgium),
  • A. Di Carlo (University of Tor Vergata, Rome, Italy),
  • S. Fabris (Centro Democritos, CNR-IOM, Italy),
  • P. Asinari (Politecnico di Torino, Italy)


A single Best Student Presentation Award will be granted by the symposium and its sponsors, either to a poster or to an oral presentation. The winner will be nominated on the last day of the symposium.


The papers will be published in a special issue of Computational Materials Science (Elsevier) to which all invited speakers will be asked to contribute.


This symposium is supported by the European Energy oriented Centre of Excellence (EoCoE), grant agreement number 676629, funded within the Horizon2020 framework of the European Union.

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Photovoltaic and Optical Materials (I) : M. Celino
Authors : Feliciano Giustino
Affiliations : Department of Materials, University of Oxford, and Department of Materials Science and Engineering, Cornell University

Resume : During the past six years halide perovskites have revolutionised the landscape of photovoltaic research. With solar-to-electricity power conversion efficiencies above 22%, perovskites are the first solution-processable technology to outperform even multicrystalline silicon [1]. As perovskite solar cells progress steadily towards market applications and the research arena is expanding towards LEDs and consumer electronics, there is a pressing need for addressing two engineering challenges: the long-term material stability and the toxicity of lead. During the past few years at Oxford we have been combining first-principles computational design with experimental synthesis and characterisation in order to design stable, lead-free perovskites as potential alternatives to the lead halides. In this talk I will review our work in this area, and describe how we discovered three new double perovskites: Cs2BiAgCl6 [2], Cs2BiAgBr6 [3], and Cs2BiInCl6 [4]. In all cases the compounds were first designed on the computer and then synthesised in the lab. I will also describe our recent attempts at developing lead-free double perovskites which are specifically designed to have a band structure similar to methylammonium lead tri-iodide [5]. [1] ACS Energy Lett. 2016, 1, 1233 (2016); [2] J. Phys. Chem. Lett. 7, 1254 (2016); [3] J. Phys. Chem. Lett. 7, 2579 (2016); [4] J. Phys. Chem. Lett. 8, 772 (2017); [5] J. Phys. Chem. Lett., 8, 3917 (2017).

Authors : Feng Li (1), Philippe Czaja (1), Simone Giusepponi (2), Michele Gusso (3), Massimo Celino (2), and Urs Aeberhard (1)
Affiliations : (1) IEK-5 Photovoltaik, Forschungszentrum Jülich, Germany; (2) ENEA, C. R. Casaccia, Italy; (3) ENEA, C.R. Brindisi, Italy

Resume : Heterojunction devices with hydrogenated amorphous passivation layers hold the efficiency record among silicon solar cells. The exact configuration of the interface region, especially the density and energy of defects, but also the band offsets and doping induced band bending plays a crucial role in transport and recombination across the interface and, in consequence, for the overall device performance. In our contribution, we investigate the electronic structure and transport at amorphous-crystalline silicon interfaces by means of first principle calculations. Both a-Si:H/c-Si and a-SiOx/c-Si interfaces are created using ab-initio molecular dynamics, and the electronic structure is analyzed with density functional theory. Special attention is given to the characterization of localized defect states at the interface. Ab-initio electronic transport from maximally-localized wannier functions is investigated on the level of ballistic transmission based on the electronic structure using the NEGF formalism, in order to assess the role of subgap states in the charge transfer across the hetero-interface. The transmission function of the interface region is compared to the mobility gap as defined by the spread of the wave functions in the amorphous region.

Authors : Prashun Gorai, Rachel Kurchin, Tonio Buonassisi, Vladan Stevanovic
Affiliations : Colorado School of Mines, National Renewable Energy Laboratory; Massachusetts Institute of Technology; Massachusetts Institute of Technology; Colorado School of Mines, National Renewable Energy Laboratory

Resume : Defect tolerance is the resilience of electronic transport properties, in particular the charge carrier lifetimes, to the presence of defects in semiconductors. The tolerance to defects is a consequence of the fact that defects in these materials introduce only shallow defect levels. Recently, defect tolerance has garnered considerable interest largely due to the rise of hybrid lead halide perovskites as photovoltaic (PV) absorbers. Hybrid perovskites exhibit remarkable PV efficiencies despite their synthesis via solution-based methods that introduce large concentrations of defects. However, concerns surrounding lead toxicity as well as long-term stability of these materials has motivated a search for perovskite-inspired materials that might share the same extraordinary electronic properties as perovskites. Through extensive first-principles defect calculations, we have identified specific structural and chemical features in binary and pseudo-binary compounds that promote defect tolerance. Specifically, we have identified two classes of structures that promote shallow anion vacancies. This includes the CsCl-type structure and structures with low anion coordination. We have also found that the presence of partially-oxidized cations such as Pb2+, Tl1+ promotes shallow cation vacancies. With these structural and chemical features as guiding principles, we have searched crystal structure databases to identify new binary and ternary compounds that are likely to be defect-tolerant semiconductors. The findings of this work will pave the way for the discovery of novel pervoskite-inspired materials.

Authors : A. Crovetto, K. Kuhar, M. Pandey, K. Thygesen, B. Seger, P. Vesborg, O. Hansen, I. Chorkendorff, K. Jacobsen
Affiliations : DTU Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark

Resume : One of the current key challenges in solar photovoltaics and solar-driven water splitting is to identify an efficient, stable, and inexpensive material to be used as a high-band gap (1.6-2.0 eV) photabsorber in tandem device configurations. To identify promising candidates that have not been considered before, we have computationally screened 705 compounds with the ABS3 formula (A,B = metals; S = sulfur). Only 15 compounds pass all the screening rounds, which include criteria such as phase stability, suitable band gap, low effective mass, and defect tolerance. The list of 15 compounds includes the previously synthesized materials BaZrS3 and SrZrS3, as well as a number of other compounds that have not yet been reported experimentally. We have therefore combined computational screening with targeted synthesis of a few of such novel ABS3 compounds [1]. Among them, the compound LaYS3 is confirmed by experiment to a stable and especially attractive high-band gap photoabsorber. In this contribution, we will focus particularly on how the materials properties predicted by theory can be effectively used to interpret experimental characterization results from the synthesized compounds. From the perspective of an experimental researcher such as the presenting author, first-principles calculations have proven to be an invaluable tool for speeding up the development of new materials. [1] Kuhar, Crovetto et al., Energy Environ. Sci. 10, 2579 (2017).

Authors : Ailbhe L. Gavin, Graeme W. Watson
Affiliations : School of Chemistry and CRANN, Trinity College Dublin, Dublin 2, Ireland

Resume : Transparent conducting oxide (TCO) materials possess conductivity greater than 1000 S cm–1, carrier concentrations in the region of 10^20-10^21 cm^–3 and an optical band gap of greater than 3 eV, allowing them to transmit visible light. p-type semiconductors present a challenge, as in many wide gap binary oxides, the top of the valence band consists primarily of O 2p states, resulting in formation of deep holes localised on oxygen sites when p-type defects are introduced. However, in perovskite oxides, such as LaCrO3, the top of the valence band can consist of O 2p and transition metal 3d states. Sr doping of LaCrO3 is reported to dope holes into the top of the valence band, with an increase in p-type conductivity with increase in Sr content.[1] Defect analysis of pure LaCrO3 Sr-doped LaCrO3 has been carried out using PBEsol + U calculations.[2] The chemical potential dependence of defect formation, and defect stabilities have been investigated, by calculating formation energies and transition levels for each of the defects. This allows us to understand the origin of the improvement in electronic conductivity and optical properties observed experimentally. The Sr defect on a La site has low formation energy under oxygen-rich conditions and synthesis conditions, with a very shallow transition level, indicating the potential of Sr-doped LaCrO3 as a p-type TCO. [1] Zhang et al., Adv. Mater, 27, 5191-5195 (2015) [2] J. P. Perdew et al., Phys. Rev. Lett., 2008, 100, 136406

Materials for Electrochemical Devices (I) : F. Giustino
Authors : Aldo Glielmo (1) , Claudio Zeni (1) , Alessandro De Vita (1,2)
Affiliations : (1) Physics Department, King's College London, Strand, London WC2R 2LS, UK (2) Department of Engineering and Architecture, Universtity of Trieste, I-34127, Trieste, Italy

Resume : Machine learning force fields (ML-FFs) that try to reproduce reference QM forces in materials systems are becoming increasingly available. Appealingly, ML-FFs do not involve parametrised functional forms (P-FFs) that have to be carefully tuned for each system, and are difficult to validate [1]. However, their use is not as yet fully mainstream, as they typically can achieve good accuracy and high generality only at a considerable speed-of-execution cost, given that the force-prediction time grows with both the training database size and the chosen representation?s complexity. In this talk I will review and elaborate on the above, and describe how ?covariant? Gaussian Process kernels [2] equivalent to ?n-body? interatomic potentials can be defined and practically constructed. I will further describe how these ML-FFs can be further ?mapped? onto non-parametric n-body fields (?M-FFs?) of optimal complexity, whose execution cost is independent of the database size, making them as fast (while still more accurate) than traditional P-FFs [3]. Finally, while no fixed force field will extrapolate well to new chemically complex situations [4], M-FFs could provide a natural way to tackle the validation problem. This is because for any given database the expected error on the GP-predicted forces on atoms can be easily calculated and mapped, effectively producing a classical force field capable of ?warning? the user if any dangerous extrapolation is likely to be occurring during use. [1] F. Bianchini, J.R. Kermode, and A. De Vita, Modell. Simul. Mater. Sci. Eng. 24, 045012 (2016). [2] A. Glielmo, P. Sollich, and A. De Vita, Physical Review B 95, 214302 (2017). [3] A.Glielmo, C.Zeni and A.De Vita, (2018), arXiv:1801.04823 [4] Z. Li, J. R. Kermode and A. De Vita, Phys. Rev. Lett., 114, 096405 (2015).

Authors : J. M. Otero-Mato, H. Montes-Campos, B. Docampo-Alvarez, V. Gómez-González, O. Cabeza, D. Diddens, A. Ciach, L. J. Gallego, L. M. Varela
Affiliations : Grupo de Nanomateriales, Fotónica y Materia Blanda, Departamento de Física de Partículas, Facultade de Física, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain; Departamento de Física e Ciencias da Terra, Facultade de Ciencias, Universidade da Coruña, Campus A Zapateira s/n E-15071, A Coruña, Spain; Institute of Physical Chemistry, University of Münster, Corrensstrasse 28/30, 48149 Münster, Germany; Helmholtz-Institute Münster (HI MS), Ionics in Energy Storage, Forschungszentrum Jülich GmbH, Corrensstraße 46, 48149 Münster, Germany; Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland;

Resume : We perform molecular dynamics (MD) simulations on the structure of the electric double layer (EDL) in ionic liquids (ILs) and their mixtures with alcohols (methanol, ethanol) close to graphene walls. We study the charge oscillations close to neutral and charged graphene walls in the direction normal to the walls. Specifically, we report results for the density and potential of the mean force profiles of the different species in solution, and for the vibrational density of states of the solute molecules or ions, analyzing in detail the lateral structure of the layers closest to the walls. The results are compared to those previously reported for mixtures with other molecular cosolvent (water) and 1:1 (lithium and potassium) and 1:2 (magnesium) salts. Structural transitions between different mesophases (stripes, hexagons) at the interfacial layer are seen to be induced by perturbations coupling to the charge density at the innermost layer of the EDL (composition of the mixtures, electrode’s voltage, structural defects in the electrode surface, etc.). The occurrence of preferential adsorption and desorption of the different species at the electrochemical interface is analyzed and the universality of the patterns proved by means of A study of the IL-vacuum interface. Finally, the 3D structure of the EDL is studied analyzing the structural patterns in the three layers closest to the electrode, observing a gradual transition from ordered hexagonal phase to bulk disorder.

Authors : N.A. Kabanova
Affiliations : Samara Center for Theoretical Materials Science (SCTMS), Samara University, Samara, Russia

Resume : For attaining a high ion migration in crystal structures, the presence of open channels and sufficient number of vacancies is necessary and the search for the compounds with optimal structure parameters is a topical question. One of the promising methods for solving this problem is the geometric-topological approach, based on Voronoi partition theory and implemented in the program package ToposPro [1]. This method is well proven by the study of Li+, Na+ and K+-conductive solid electrolytes [2, 3]. The ion migration map constructed with this method describes all possible ion transition pathways, including those through vacancies. Our investigation was devoted to the analysis of oxygen conductivity in the compounds with the perovskite-like structure (brownmillerite and aurivillius structure types), containing Bi, Hf, In, Cd, Zr or Sc. Based on the Voronoi and DFT analysis of known oxygen-conductive structures, we determined the geometric (radius of migration channels >2.2 Å) and energetic (difference between the energy of vacancy formation of the adjacent migration positions ?EVF < 0.10 eV) criteria for proper transport characteristics. Further, using these criteria, we screened the database ICSD (version 2017/2) and selected the structures, which contain Bi, Hf, In, Cd, Zr or Sc and possess 1D, 2D or 3D migration map of oxygen anions. As a result, among approximately 6000 compounds, we revealed 10 compounds, which had not been treated as oxygen ion conductors; these compounds can be proposed as new prospective candidates for oxygen conductive materials. [1] V. A. Blatov, A. P. Shevchenko, et al. // Cryst. Growth Des. 2014. V. 14. N. 7. P. 3576-3586. [2] N. A. Kabanova, V. A. Blatov, et al. // J. Phys. Chem. C, 2017, 121 (39), pp 21128?21135 [3] F. Meutzner, N.A. Kabanova, et al. // Chem. Eur. J. 2015. V. 21. N. 46. P.16601-16608.

Authors : Ivano E. Castelli, Dusan Strmcnik, Thomas Østergaard, Filippo Maglia, Byron K. Antonopoulos, Nenad M. Markovic, Jan Rossmeisl
Affiliations : Department of Energy Conversion and Storage, Technical University of Denmark; Materials Science Division, Argonne National Laboratory; Nano-Science Center, Department of Chemistry, University of Copenhagen; BMW Group, Battery Cell Technology; BMW Group, Battery Cell Technology; Materials Science Division, Argonne National Laboratory; Nano-Science Center, Department of Chemistry, University of Copenhagen

Resume : Understanding the formation of the SEI layer is a key-point for improving the lifetime of Li-ion batteries for the automotive industry, as well as predict novel anode materials with improved properties. This understanding can also be used to formulate designing principles for the formation of the SEI layer and to design better anode materials. Here, we explain the formation of inorganic Li-compounds (LiF, LiO2, LiOH) in the SEI layer in the LP57 electrolyte, on metal single crystals and carbon systems combining density functional theory (DFT) with ab-initio molecular dynamics to model the solid-liquid interface and interpret experimental cyclic-voltammetries at the atomic-scale level. We show that the presence of Li at the interface is required, in order to split HF and H2O, and to form LiF and Li-oxide compounds. We also show that the adsorption potential of Li on the anode is correlated with different quantities, such as the measured first-electrochemical response, and this can be used as a designing principle for the development of novel anode materials.

Authors : Gergely Juhasz
Affiliations : Chem. Dept., Tokyo Institute of Technology, Japan

Resume : Electrochemical and photochemical reactions on TiO2 surfaces have been extensively studied. Recently, Yamauchi and her group recently showed that anatase-type TiO2 electrodes can be used for electrochemical reduction of carboxylic acids to alcohols [1]. So far this reaction has several limitations, as it has been demonstrated only for oxalic acid with an efficiency very sensitive to the preparation conditions of the anatase electrode. One possible explanation of such sensitivity electrochemical activity to preparation conditions is that the morphology of the surface has a deep impact on the electrochemical processes. To improve the efficiency as well as to understand what factors limit the reduction of other acids, we studied the effect of morphology on the electronic structure of anatase nanoparticles using Density Functional Tight Binding (DFTB) method. Based on experimental data, we focused on models of nanoparticles with a size of 2-4 nm and dominantly 101 and 100 faces. Our studies showed a significant decrease of bandgap in models, as well as the localization of low energy LUMO orbitals around edges and corners. These low energy orbitals can be partially explained by the 4- and 5- coordinated Ti(IV) ions located in those edges, which can also be responsible for the smaller band gap and strong reactivity of the particles. We performed extensive calculations to study the water and acid absorption on the edges and faces of nanoparticles to identify the most probable coordination environment of these Ti(IV) ions. This computational work offers new understanding for optimization of titania electrode surfaces for electrochemical reaction and shows the importance of studying the surface reactions beyond the standard slab models for ideal surfaces. The work was supported by CREST, JST and the computations were partially performed using Research Center for Computational Science, Okazaki, Japan. Reference: [1] R. Watanabe, M. Yamauchi, M. Sadakiyo, R. Abe and T. Takeguchi, Energy Environ. Sci., 2015, 8, 1456–1462

Materials for Electrochemical Devices (II) : A. De Vita
Authors : Aysenur Gencer, Gokhan Surucu
Affiliations : Middle East Technical University, Department of Physics ; Middle East Technical University, Department of Physics, Ahi Evran University, Department of Electric and Energy, Gazi University, Photonics Application and Research Center

Resume : The energy sources and storage techniques are important with the world’s technology development. The mostly used source is fossil fuels which release greenhouse gases. Therefore, renewable energy sources are investigated to get a reliable and efficient source. Renewable energy sources depend on weather conditions that require energy storage. Thus, hydrogen being the most abundant element, has a high mass energy content. So, hydrogen can be stored as gas, liquid or solid state. Gaseous storage needs high pressure tanks while liquid storage needs energy to liquefy hydrogen. Different from gaseous and liquid storage, the solid state hydrogen storage could be more efficient and could be a long-term solution. In literature, metal hydrides and complex hydrides have been commonly investigated materials for solid state storage. In addition to hydrides, perovskite materials could be proposed as an alternative candidate for the solid state storage applications. For this purpose, structural, mechanical, electronic, vibrational and thermal properties of BaScO3 have been calculated. As well as, the hydrogen storage properties in BaScO3Hx has been analyzed and will be presented. All of the simulations in this work were performed by the self-consistent density functional theory (DFT) with a plane-wave pseudopotential approach implemented in the VASP code. PBE parametrization of the GGA was used for the exchange-correlation terms in the electron-electron interaction.

Authors : Christian Hänsel, Dipan Kundu
Affiliations : Multifunctional Materials, Departement of Materials, ETH Zurich, Switzerland

Resume : Owing to high capacities alkali metal batteries (Li, Na) present exciting opportunities to push the energy limits of rechargeable battery devices. However, low Coulombic efficiency and dendrite growth at the alkali electrode during battery operation hinder their practical application.1 In traditional binary salt electrolytes, both cations and anions are mobile, which can lead to the build-up of ion concentration gradient, and consequent polarization losses. Non-uniform anion distribution has also been predicted to cause ramified metal deposition. Thus, it is necessary to eliminate the free movement of anions, and one way to achieve that is by covalently tethering the anions to a polymer backbone. These unique conductors, also known as ionomers, have achieved considerable success toward stabilizing lithium deposition and preventing dendritic growth,2 but report on Na ionomer is nonexistent. Here, we report on the development of a novel Na ionomer derived from an inexpensive and chemically robust polymer. The microporous ionomer membranes infused with liquid organic carbonates display Na+ transference number close to unity, high conductivities (>10-5 S cm-1 at room temperature) over a wide temperature window, and good chemical, thermal and mechanical stabilities, resulting in stable sodium plating stripping and excellent full cell performance at room temperature. 1. Lin, D. et al. Nat. Nanotechnol. 2017, 12, 194–206. 2. Lu, Y. et al. Adv. Energy Mater. 2015, 5, 1402073.

Authors : Zineb Kerrami, Anass Sibari, Omar Mounkachi, Abdelilah Benyoussef, Mohammed Benaissa
Affiliations : La.M.C.Sc.I, Faculty of Sciences, Mohammed V University Rabat, Morocco; Institute of Nanomaterials and Nanotechnology MAScIR Rabat, Morocco.

Resume : Photocatalytic water splitting technology has recently received extensive attention as a promising method to produce hydrogen, which has generated an urgent need to find alternative photocatalytic materials for such technique. In the present study, the electronic and photocatalytic properties of SnO2 under uniaxial strain have been examined, based on Density functional theory (DFT), showing that under tensile strain the band gap energy decreases, while an opposite behavior is demonstrated in the case of compression. Band edge alignments of unstrained SnO2 shows that the VBM is more positive than the redox potential of O2/H2O (1.23V) while the CBM for pH = pH(pzc) lies above the redox potential of H /H2 (0V), which mean that the pure SnO2 cannot be used for hydrogen evolution reaction (HER). Applying compressive strain, the CBM edge position decreases gradually as the strain percent increases, in other hand under tensile strain the CBM edge position could be corrected for pH ≥ 10. Which clearly reveals the ability of mechanical strain to modulate the band structure and the photocatalytic properties of SnO2 in order to improve its suitability as a photo-electrochemical material for water decomposition.

Authors : Asma Marzouk (a) , Fernando A. Soto (b) , Kie Hankins (b), Perla B. Balbuena (b), Fedwa El-Mellouhi (a)
Affiliations : (a) Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University, PO BOX 34110, Doha, Qatar ; (b) Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, United States

Resume : The complexity of the Solid Electrolyte Interphase (SEI) at Li-ion batteries on graphitic electrodes, has triggered extensive deal of research due to its crucial properties for the long life of the battery. The SEI layer is composed by organic and inorganic species and results from the electrolyte decomposition on the electrode upon the first cycling of the battery. A stable SEI layer is crucial to maintain the chemical and mechanical stability of the electrode and the electrochemical stability of the electrolyte in order to prevent the irreversible capacity loss. This work uses computational crystal structure prediction genetic evolutionary algorithm to simulate the nucleation, growth and the aggregation of the inorganic SEI products forming the SEI mosaic film. In depth investigation of the growth mechanisms of LiF and Li2CO3 starting from the first nucleation seed is undertaken. The energetics of the resulting cluster growth mode in compared to layer by layer growth mode at the graphite surface in different lithiation and surface termination states. Acknowledgment: This work in supported by the Qatar National Research Fund (QNRF) through the National Priorities Research Program: NPRP 7-162-2-077.

Authors : Ahmed Sodiq, Lagnamayee Mohapatra, Fathima Fasmin, Sabah Mariyam, Rachid Zaffou, Belabbes Merzougui
Affiliations : Ahmed Sodiq; Sabah Mariyam, College of Science and Engineering, Lagnamayee Mohapatra; Fathima Fasmin; Rachid Zaffou; Belabbes Merzougui, Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Doha, Qatar

Resume : Electrical Energy Storage (EES) is projected to play an important role in the integration of renewable energy sources with electricity grid or off-grid. Grid-scale energy storage particularly for renewable energy applications has been a challenging task due to its cost and the intermittent nature of renewable energy sources. Redox Flow Batteries (RFBs), among other options, is uniquely suited for large-scale EES due to many advantages over the conventional sealed batteries (i.e., lead-acid and Li-ion batteries). Owing to its design flexibility, flow batteries can meet a wide range of commercial-scale EES applications with varying power-to-energy ratios. In addition, flow batteries have excellent life-cycle. Furthermore, as a result of their simple thermal management, which is provided by the circulating reactant solutions, and their low sensitivity to crossover (no thermal runaway reactions), flow batteries are considered to be inherently safer compared to conventional sealed batteries. Despite its attractiveness and demonstrated performances, flow battery technology still suffers from high system capital cost (which limits its potential deployment into grid storage applications) and low energy density of the reactant fluids (which leads to large footprint and makes it impractical for EES applications with confined space). A number of studies have reported an estimated cost of flow battery system at large-scale (MW) that exceeds $500/ [1]. For an energy storage system to be economically feasible, the United States Department of Energy (DOE) set the cost target for its large-scale deployment at $100/ [2]. Therefore, to deploy flow batteries for EES applications for mass market, the high system cost and the large footprint issues must be addressed. These challenges can only be met if high energy density and cheaper battery materials are developed. An attractive approach has been introduced recently [3], where the active materials in conventional RFB system are mixed with carbon particles to create a flowable suspension (otherwise known as slurry electrode). This approach has attracted attention due to its potential applications in energy storage devices. Slurry electrode is defined as “a suspension of particles with large double-layer capacity, such as activated carbon, in an electrolyte solution”. These particles transfer charge from an electrochemical cell to an external reactor, where a substance is oxidized or reduced, and are recharged in the cell [4]. Unlike conventional RFB system, the semi-solid approach uses flowable electrodes that are electronically conductive. Slurry electrodes are characteristically dynamic, particles continuously move and collide with each other. Percolation theory defines a critical loading, fc, above which there are enough particles in the slurry that, at any point in time, a constant network of particles is formed that spans the distance from one boundary to another [5]. It is due to these continuum of particles that slurries are able to conduct electrons out into the electrode and away from the current collector to utilize the high surface area of the particles for electrochemical processes [6]. Other advantages of slurries involve their ability to have high surface areas, simple assembly, and ease of maintenance through filtering. In this work, electrochemical behavior of different carbon materials in slurry form with redox systems, (such as Sulfide/Carbon and FeCl3/Carbon), conductivity of flowable electrodes (such as FeCl3/HCl/carbon and Na2S/NaOH/carbon) and cell performance of the system, (FeCl3/HCl/carbon as catholyte and Na2S/NaOH/carbon as anolyte) will be presented and discussed. Also, we will shed lights on challenges and opportunities of slurry based flow batteries. References [1] Z. Yang, et al., "Electrochemical energy storage for green grid," Chemical reviews, vol. 111, pp. 3577-3613, 2011. [2] Z. Li, et al., "Aqueous semi-solid flow cell: demonstration and analysis," Physical Chemistry Chemical Physics, vol. 15, pp. 15833-15839, 2013. [3] M. Duduta, et al., "Semi‐Solid Lithium Rechargeable Flow Battery," Advanced Energy Materials, vol. 1, pp. 511-516, 2011. [4] B. Kastening, et al., "Design of a slurry electrode reactor system," Journal of applied electrochemistry, vol. 27, pp. 147-152, 1997. [5] L. Gao, et al., "Effective thermal and electrical conductivity of carbon nanotube composites," Chemical Physics Letters, vol. 434, pp. 297-300, 2007. [6] T. J. Petek, et al., "Characterizing Slurry Electrodes Using Electrochemical Impedance Spectroscopy," Journal of The Electrochemical Society, vol. 163, pp. A5001-A5009, 2016.

Poster Session I : J. Carrete Montana
Authors : NACHTANE Mourad,TARFAOUI Mostapha
Affiliations : 1ENSTA Bretagne, FRE CNRS 3744, IRDL, F-29200 Brest, France Phone number: +33(0) 298348705, e-mail:

Resume : The systems used in EMR applications are very strongly impacted by environmental conditions during their installation, operation or maintenance phase. The optimization of their functioning and their dimensioning can only be done by controlling the interaction between the medium and the components or structures of the systems. Thus, the development of numerical and experimental tools and methodologies capable of simulating the impact of wind, wave, current and behavior of these systems in a coupled way constitutes a major dimensioning challenge. The validation of these sizing processes is made possible by in-situ measurement, which requires a strategy adapted to the application envisaged. This aspect constitutes a major stake at the dawn of the deployment of pilot farms of fixed and laid wind turbines and prototype of hydro-turbines. Indeed, the aim of this phase is to validate the choice of a solution and to identify the optimization paths that will allow to go on the commercial phase with a substantial gain of LCOE (Levelized Cost of Energy). The recovery of energy from the kinetics of marine or river currents is particularly interesting because it constitutes an immense and almost inexhaustible source. By installing marine or inland waterways, it is possible to recover some of this kinetic energy. During operation and taking into account the fluid - structure couplings, the machines are generally stressed by cyclic mechanical forces, repeated shocks and / or progressive rotation. The goals of structural service, machine efficiency and turbine performance pose significant challenges for designers, mechanics of solids and fluids. Wind turbines and hydro-wind turbines are the two most advanced technologies, but the hydro-turbines still require optimization studies. In particular, the blades and the nozzle are on the critical path of machine life. Thus, they should be designed as safely as possible and be able to withstand the applied loads and the hostile environment. It has become common practice to find structural parts of composite materials such as blades, nozzles, etc. on energy recovery techniques. Moreover, the behavior of composites in service (shock, fatigue) remains difficult to predict. The aim is to equip design departments with the dimensioning of composite structures with tools enabling them to choose materials (fiber / matrix), fibrous architectures (tablecloth, fabrics), stacking sequence of strata minimizing sensitivity to applied loads of working structures.

Authors : Xin Li, Haijun Wu, Abdelnaby Mohamed Kotb Elshahawy, Ling Wang, Stephen J. Pennycook, Cao Guan, and John Wang
Affiliations : Department of Materials Science and Engineering, National University of Singapore, 117574 Singapore.

Resume : To effectively enhance the energy density and overall performance of electrochemical capacitors (ECs), we propose a strategy to increase both the intrinsic activity of active sites and their density via tuning the composition and structure of the electrode. A self-supported NiCoP/NiCo-OH nanocomposite electrode with 3D cactus-like porous architecture is assembled on carbon cloth substrate via a hydrothermal process followed by phosphorization. The nanocomposite electrode material is designed to offer multiple advantages. Firstly, the nanocomposite exhibits cactus-like 3D flakes supporting a high density of nanospines offering numerous edge and surface sites, integrating the advantages of a 1D structure that can form an efficient pathway for charge transport, with those of a 2D structure that exhibits mechanical stability and strength. Secondly, the nanocomposite structure allows for a synergistic combination of NiCoP and NiCo-OH. The partially phosphorized nanocomposite (NiCoP/NiCo-OH) is designed to consist of a hydroxide matrix to stabilize the overall structure, on which phosphide nanocrystallites are distributed uniformly, leading to higher activity and capacitance. After thoroughly investigating the unique cactus-like 3D structure and its dependence on the processing parameters involved, we establish a model for the growth mechanism of the hierarchical architecture. Through properly tuning the NiCo-OH to NiCoP ratio, it can result in a high-specific capacitance of ≈1100 F g−1, which is around a 7-fold increase compared to that of NiCo-OH alone (≈150 F g-1 at 1 A g-1). In addition, the nanocomposite possesses ≈90% capacitance retention after 1000 cycles, benefitting from the excellent stability of NiCo-OH. The corresponding asymmetric supercapacitor full cell of NiCoP/NiCo-OH//MOF-derived porous carbon (PC) is demonstrated with a high energy density of ≈34 Wh kg-1 at a power density of 775 W kg-1, a comparable specific capacitance of ≈101 F g-1 at 1 A g-1, and excellent electrochemical cycling stability. The nanocomposite electrode presents a great potential for ECs, and is also promising for other functional applications such as in catalysts and batteries, owing to the unique structures and properties demonstrated.

Authors : C.Azahaf1, H.ZAARI1* , A.G. El Hachimi1, A. Benyoussef1, 2, A. El Kenz1
Affiliations : 1 Laboratoire de Matière Condensée et Sciences Interdisciplinaires (LaMCScI), Facultés des Sciences P.B. 1014, Université Mohammed V Rabat, Morocco, (PPR15), 2 Materials and Nanomaterials Center, MAScIR Foundation, Rabat Design Center Rue Mohamed Al Jazouli - Madinat Al Irfane , Rabat 10 100, Morocco

Resume : We present a systematic first-principles study of the structural, magnetic and optical properties of perovskite-structure EuTiO3. Our calculations of the high symmetry cubic structural prototype show G type of antiferromagnetic order. Comparing the formation energy between tetragonal and cubic structures, the system has a tendency to symmetry lowering structural deformations composed of rotations of the oxygen octahedra, specially the I4/mcm phase is the most stable structure. We discuss the dynamical stability of Pm-3m, P4mm and I4-mcm structures, and the influence some parameters on the magnetic coupling and the electrical polarization. Key word: multiferroic, magnetic coupling, polarization, WIEN2K

Authors : Romeo Malik*, Melanie J. Loveridge*, Qianye Huang*, Krishna N. Manjunatha**, Shashi Paul**, Paul R. Shearing*** and Rohit Bhagat*
Affiliations : * Electrochemical Engineering Group, Warwick Manufacturing Group, University of Warwick, Coventry, CV4 7AL, UK ** Emerging Technologies Research Centre, De Montfort University, The Gateway, Leicester, LE1 9BH, UK *** Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK

Resume : This study investigates modes of degradation in hybrid silicon-tin anodes for Li-ion batteries, with emphasis on the electrode architecture. In recent years, considerable studies have shown that crystalline Si is a promising negative electrode candidate, with a specific capacity of 3579 mAh/g which is ca. 10 times the specific capacity of graphite. However, Si still has major performance issues associated with it, predominantly the volume expansion (up to 280%) which can result in cracking and pulverization of active particles. Addition of tin to the silicon-based anode enhances performance by way of the decreased resistance from metallic tin improving cycling stability and charge capacity. The electrode macro and micro-cracking in the silicon-based electrodes results in disintegration of the electrode architecture and leads to the formation of ?dead spots? (or loss of active materials). Incorporation of tin into the system is thought to help in reducing these electrically separated dead spots due to its conductive properties. The performance synergy between silicon and tin outperforms the individual contribution of each material alone. It is imperative to comprehensively understand the fundamental degradation mechanisms inside anode microstructures and at their interfaces. X-ray computed tomography (CT), FIB-SEM tomography in conjunction with impedance spectroscopy and associated physical characterization, will be employed to capture and quantify key aspects of the evolution of internal morphology and resistance build up. This includes characterization of SEI growth, porosity changes and conductive network breakdown during charge-discharge operation. The study will also include in-situ and operando tomography and diffraction experiments for clearer insights into key degradation processes, such as delamination, initiation, and propagation of particle cracking as well as time-resolved identification of phase transformations. Tomography has been proven to be an effective tool to explore the hierarchical structure of battery electrodes and for diagnosing battery failure mechanisms at multiple- length scales. This approach will enable us to observe and quantify failures in Li-ion batteries at the electrode level, and thus facilitate construction of better electrode architectures. This study aims to characterize electrode structures to be able to develop and correlate microstructural architecture with performance. It is anticipated that this study will influence major improvements in the design of Li-ion battery materials and their processing which in turn positively impact cell performance.


Resume : Materials play very important role in the technological advancement of lithium-ion batteries. In this work, the state-of-the-art ab initio method based on density functional theory was used to investigate the adsorption of lithium ions on layered vanadium disulfide. The adsorption energy, structural and electronic properties were computed using both the local density approximation and the generalized gradient approximation for comparison. The preliminary results indicate that single-layered vanadium disulfide is a candidate anode material for lithium-ion batteries with enhanced gravimetric capacity.

Authors : Guang Yang,a,b Bowei Zhang,b Jianyong Feng,b Zhiqiang Wang,b Vanchiappan Aravindan,a,b Muthiah Aravind,a,b Jilei Liu,*c Srinivasan Madhavi,*a,b Zexiang Shen,a,b,c and Yizhong Huang*a
Affiliations : aSchool of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore b Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Research Techno Plaza, 50 Nanyang Drive, Singapore 637553 cDivision of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore

Resume : The sharp proliferation of electric automotive and regenerative electric energy storage system (EES) drives the search of high-performance power sources that have high energy density and power density. Stable Li+ ion intercalation chemistry of graphite ensures the success of LIBs over the past decades. However, challenges facing graphite anode such as limited specific capacity (372 mAh g-1) and safety issue related to Li dendrite formation upon Li+ ion intercalation at low potential (close to 0 V), especially at high rates, promote urgent demands for novel anode alternatives with both large capacities and more positive intercalation voltages (vs. Li+/Li). Spinel Li4Ti5O12 has been exploited since it operates with zero strain, high reversibility, and good rate performance. Nevertheless, its low specific capacity (~150 mAh g-1) and relatively high operating potential (about 1.5 V vs. Li+/Li) sacrifices the overall cell performance. In addition to insertion type anodes, conversion-type anodes (i.e., transition metal oxide and metal sulfides etc.), and alloying-type anodes (e.g., Si and Sn-based materials) have been also investigated. The conversion-type anodes generally deliver a specific capacity of 2-3 times of that of graphite. Since the theoretical value is determined by the oxidation state of metal ions. However, they suffer from poor kinetics, low energy efficiency and large polarization associated with the energy barrier to trigger the cleavage of the metal-oxygen and/or sulfur bonds. The alloying-type anodes can deliver ultra-high capacities, but at the expense of huge volume change and poor cycling performance. Given the improved specific capacity and appropriate intercalation potential, intercalation-type anodes are intrinsically attractive from the perspective of highly reversible Li+ insertion/extraction and negligible volume change upon cycling. More recently, Zhou et al reported such a material, -Li3VO4 (LVO), with high reversible capacity (394 mAh g-1, based on Li3VO4 + xLi+ + xe-  Li3+xVO4, 0  x  2) and suitable Li+ ion intercalation potential (0.5 V  1.0 V, vs. Li+/Li). The orthorhombic LVO exhibits hollow lantern-like 3D framework consisting of a regular array of corner-shared VO4 tetrahedra and LiO4 tetrahedrons, which provides lots of empty sites and intercalation channels for Li+ ion. Moreover, the high ionic conductivity of LVO (10-4 10-6 s cm-1) ensures fast Li+ ion diffusion. Ex-situ XRD results revealed that the insertion of Li+ into LVO starts with a solid-solution step and follows with a two-phase reaction. Theoretical calculations also showed that the reversible phase transformation from Li3VO4 to Li5VO4 is energetically favorable (with a biphasic reaction at 0.7 V, vs. Li+/Li) upon 2 Li insertion/extraction process. Nonetheless, for one more Li insertion, this process is difficult as manifested by the low predicated voltage (0.14 V, vs Li+/Li) and the major structural rearrangements (20% volume variation). However, experimental results demonstrate the practical feasibility of the third Li insertion although the underlying mechanism is still unclear. For example, a high reversible specific capacity of 540 mAh g-1 (about 2.7 Li) was reported for Li3VO4/C composite at a current density of 150 mA g-1. The carbon-coated LVO prepared by solid-state method delivers a reversible capacity of 547.1 mAh g-1 based on GITT tests and in-situ XRD characterizations. Further work has also shown that the synthesis method, crystallinity and the morphology greatly affect the electrochemical properties of electrode materials. For example, micro-sized LVO (0.8 - 2.0 m) prepared by solid-state method delivers the first discharge and charge capacity of 345 and 258 mAh g-1, respectively. These values rise up to 469 and 326 mAh g-1 for hollow cuboid LVO (0.8-2.0 m) synthesized by a sol-gel method, and 624 and 481 mAh g-1 for nano-sized LVO (10-100 nm) produced by a hydrothermal method. Despite significant progresses have been made in synthetic optimization, morphology tailoring, surface modification, and/or electrode hybridization so far, LVO is still far from practical applications due to the lack of understanding in i) a comprehensive relationship between materials structure properties with electrochemical characteristics, and ii) the fundamental electrochemistry. Herein, we synthesized a series of LVO with controlled morphologies from spherical-assembly, single-crystal nanorods, flower shape, to bulk by a solvothermal approach using different alcohols. To investigate the morphology effect on the anodes, XRD, SEM, FITR, Raman CV and galvanostatic charge/discharge were employed to examine their physical properties with electrochemical characteristics. The results reveal that single-crystal LVO nanorods show the best performance in terms of rate performance and cyclability. This enhanced electrochemical performance can be ascribed to i) the high surface area of the porous rod-shaped structure that offers favorable ion diffusion and electron transfer, and ii) the small particle size that reduces the diffusion length. Moreover, further improvement in the electrochemical performance was achieved using carbon coating on the single-crystal LVO nanorods. The as-prepared LVO/C delivers a high reversible capacity of 430 mA g-1 at a current of 100 mA g-1, along with good rate performance and cycling stability.

Authors : Najebah M. Alsaleh, Nirpendra Singh, and Udo Schwingenschlgl
Affiliations : King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Divison (PSE), Thuwal 23955-6900, Saudi Arabia

Resume : The electronic and transport properties of bulk and monolayer CuSbS2 and CuSbSe2 are determined using density functional theory and semi-classical Boltzmann transport theory, in order to investigate the role of the interlayer coupling for the thermoelectric properties. The calculated band gaps of the bulk compounds are in agreement with experiments and significantly higher than those of the monolayers, which thus show lower Seebeck coefficients. Since also the electrical conductivity is lower, the monolayers are characterised by lower power factors. Therefore, the interlayer coupling is found to be essential for the excellent thermoelectric response of CuSbS2 and CuSbSe2 even though it is weak.

Authors : Anass Sibari, Zineb Kerrami, Abdelkader Kara, Abdelilah Benyoussef, Omar Mounkachi, Mohammed Benaissa
Affiliations : LaMCScI, B.P. 1014, Faculty of Science-Mohammed V University, Rabat, Morocco; Department of Physics, University of Central Florida, Orlando, Florida 32816, USA; Institute of Nanomaterials and Nanotechnology, MAScIR Rabat, Morocco; Hassan II Academy of Science and Technology, Rabat, Morocco

Resume : A computational examination of the structural and electronic properties of monolayer, bilayer and trilayer phosphorene as subjected to uniaxial strain is reported. Our calculations using various approximations showed that the Perdew−Burke−Ernzerhof (PBE) functional, as derived from the generalized gradient (GGA) approximation with taking into account the effect of van der Waals (vdW) interactions, best describes the crystalline structure of free-standing phosphorene. The calculations based on the variation of the bandgap as a function of either an armchair or a zigzag strain reveal that a compressive strain results in the reduction of the bandgap while a tensile strain is firstly seen to increase it to reach a maximum value before starting to decrease until a metallic transition occurs. While unstrained phosphorene exhibits a p-type semiconducting, we demonstrated that a uniaxial strain can clearly switch the conduction type in phosphorene to an n-type semiconductor and vice versa to a p-type semiconductor. Those findings strongly suggest that by means of strain, the bandgap and electronic properties of 2D phosphorene can be easily modulated leading its integration to different applications such as in photovoltaics.

Authors : Daniel Stoeffler
Affiliations : Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 23 rue du Loess, BP 43, 67034, STRASBOURG Cedex 2, France

Resume : Multiferroic oxides, such as Bi2FeCrO6 (BFCO) presenting a band gap of 2.0 eV, were recently reported to be potentially suited for photovoltaic applications. Morever, it has been shown that some properties of BFCO films like the bandgap can be tuned by acting on the concentration of Fe-Cr antisite defects during the growth process [1]. In this work, the relation between the Fe/Cr ordering and the bandgap is investigated using the Density Functional Theory implemented into the VASP code by combining hybrid HSE and GGA+U functionals. Imperfect configurations are built by varying the Fe-Cr stacking order relative to the ideal structure into a 30 atoms cell derived from the R3 cell of BFCO. Using the HSE functional, it is shown that the presence of antisite defects leads to an increase of the bandgap by about 0.25 eV with respect to the one obtained in the ideal structure. It is also shown that the saturation magnetization is strongly reduced along with the difference between the Fe and Cr Born Effective Charges (BEC) when the Fe/Cr local disorder is increased. It is also shown that the GGA+U approximation allows to nicely reproduce the HSE electronic structure by varying Ueff from 4 to 7 eV when focussing on properties depending on the occupied states or on the bandgap width. This allows to determine and to discuss the oxydation state of the Fe and Cr atoms from polarization calculations [2]. 1. Nature Photonics 9 (2014), 61-67. 2. Phys. Rev. Lett. 108 (2012), 166403.

Affiliations : 1 Laboratoire de Matière Condensée et Sciences Interdisciplinaires (LaMCScI), Facultés des Sciences P.B. 1014, Université Mohammed V Rabat, Morocco., (PPR15), 2Institute of Nanomaterial’s and Nanotechnology, MAScIR, Rabat, Morocco 3 Hassan II Academy of Science and

Resume : BiFeO3 has been studied extensively due to its room temperature multiferroic features and has been proven as a promising candidate for device applications. The cubic perovskite BHO have a large band gap equal to 6 eV, it has a considerable value of polarization allow us to consider this material as a ferroelectric, the combination of ferroelectric and magnetic properties in such material has attract a great interest, thus, a heterostructures approach of two compound present good solution to have multiferroic systems. In this work, BiFeO3 (in cubic and R3c structure) and BaHfO3 with a good lattice matching was studied and optical and electronic properties were studied, using the first principles calculations with Full Potential Linear Augmented Plane Wave method (FP-LAPW), implemented in the Wien2k code. The combination between an insulator material BHO and a metallic BFO, show that the cubic heterostructures (BaHfO3)/ (BiFeO3) with GGA approximation has a metallic behavior, but using the mBJ correction, the (BHO)/(BFO) in both cases (cubic and pseudo cubic) gives a semiconductor nature with gap energy equal to 2.1 eV, however a cubic structure is unstable, in contrary to pseudo cubic BFO combined with BHO. based on these results we can conclude that this combination of two material allow as to exploit the electric and semiconductor behavior in photovoltaic application by reducing the gap energy to have good absorption in visible light.

Authors : Mainul Akhtar, S.B. Majumder
Affiliations : Materials Science Centre, Indian Institute of Technology Kharagpur

Resume : In present scenario, most widely used electrochemical energy storage systems for consumer electronics are Li-ion batteries and supercapacitors. Conventional cathodes used in lithium ion rechargeable cells cannot meet the requirements of batteries required in electrical vehicles. Bi-material cathodes, comprise of battery and super-capacitors composites, yield high energy as well as high power density rechargeable cells. In this work, we demonstrated that microwave assisted hydrothermally grown carbon coated Na3V2(PO4)3@C (NVP@C) –activated carbon (AC) hybrid electrodes are excellent cathode material for lithium ion rechargeable cell. The as synthesized NVP@C (battery component) and commercially available AC (supercapacitor component) were mixed (40/60 weight ratio) to fabricate bi-material cathode. The electrochemical characteristics of NVP@C, AC, and bi-material electrode (NVP@C/AC) were evaluated using 1(M) LiPF6 in EC:DEC (3:7) in half cell configuration using lithium metal counter electrode. For selected cells full cell characteristics were also studied using Li4Ti5O12 counter electrode. The cells were characterized by cyclic voltammograms, electrochemical impedance spectroscopy, rate capabilities and cycleability. At low specific currents (50 mAg-1), the NVP@C, AC and NVP@C/AC deliver specific capacities of 105, 36 and 66 mAhg-1 with 83%, 93% and 99% capacity retentions respectively after 100 cycles. At high specific currents (700 mAg-1), the NVP@C/AC outperforms both and delivers specific capacity as high as 58 mAhg-1 as compared to 35 and 27 mAhg-1 for NVP@C and AC respectively. The synergistic effect of the bi-material electrode was confirmed by comparing cyclic voltammograms, electrochemical impedance spectra and galvanostatic charge–discharge profiles of these electrodes.

Authors : Ahmed Sodiq, Fathima Fasmin, Lagnamayee Mohapatra, Rachid Zaffou, and Belabbes Merzougui*
Affiliations : Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar

Resume : Energy storage area is witnessing great upturns in the recent decade due to the increased demand on renewables, such as solar and wind energy. Several options of energy storage systems have been developed. Among them, electrochemical systems, which are not geographically limited as in the case of hydro and compressed air, have gained attention, especially for mobile and off-grid applications. Redox flow battery, however, has been seen as the best option for multi-hours applications because of its flexibility in scaling up the energy independently from the power. Yet, flow battery still suffers from large footprint and high cost as results of low energy density. Slurry electrode based flow battery concept, where the electroactive species and carbon are mixed together and stored in tanks outside the battery box, is an emerging approach to improve the energy density. In this work, we will present some of the experimental and theoretical findings related to a slurry electrode based on high surface area carbon, Black Pearls (BP). In particular, slurry conductivity, redox behavior, and cell performance will be presented and discussed. We will also shed lights on the challenges and opportunities of slurry electrode for electrochemical energy storage applications.*************************************************************************************** "Acknowledgement: This work was made possible by NPRP grant 9-158-1-029 from the Qatar National Research Fund, Qatar Foundation".

Authors : Katerina Dohnalova-Newell
Affiliations : Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands

Resume : Silicon nanoparticles (SiNPs) have unique advantages amongst other semiconductor nanoparticles - besides non-toxicity and abundant resources, they have covalently bonded ligands. Covalent bond between Si and C is one of the strongest bonds that cannot be chemically cut and hence, organically capped SiNPs, where the ligands are attached via Si-C bond, are one of the most stable nanoparticles available. This is reflected also in the great difficulties faced by chemists in synthesis of such materials. For us, the most important advantage is that Si-C attached ligands strongly contribute to the band structure of the nanoparticle either simply by strain [1], or by adding new energy levels leading to strong changes in the band structure and band gap [2,3]. In our previous studies [2,3], we have shown using simple tight binding simulations that direct bandgap-like "fuzzy" band structure can form as a result of electronegative ligands and environment. However, tight binding is a simplified model, plus we have not taken into account strain induced by the ligands, which, interestingly, has been shown by Kusova et al. in Ref. 1 to further enhance the directness of the bandgap. In our present work, we extend our studies to several types of electronegative organic ligands, taking into account various surface coverage of the dominating facets {111} and {100} and hence also strain, using atomistic simulations by Density Functional Theory (DFT). For this purpose we use cp2k programme and "fuzzy" band-structure approach implemented by Dr. Hapala [4]. In this way, we propose some specific SiNP structures with advantageous properties for photonics, energy and bio-applications.

Authors : Simone Giusepponi, Massimo Celino.
Affiliations : Simone Giusepponi; Massimo Celino: ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development C. R. Casaccia, Via Anguillarese 301, Rome, Italy.

Resume : In the next generation of nuclear reactors. the stainless steels will be widely used because to their high thermal conductivities, high resistance to swelling, low expansion coefficients, and so on. In accelerator driven systems, they are chosen as the structural materials and the containers for liquid heavy metals and alloys, such as lead and lead bismuth eutectic which are selected as the spallation target and the coolant. Heavy liquid metals are good candidates for core coolants and high-power spallation targets in accelerator driven systems, because of their low melting point, low vapor pressure, high neutron yield and good heat removal. These aspects permit to have fast heat exchange with enhanced energetically efficiency in nuclear reactors. However, stainless steels can be severely damaged if they are exposed to liquid metals. The so called liquid metal embrittlement by molten lead alloys in stainless steels poses a serious obstacle to the use of those materials in nuclear applications, and then, in the development of accelerator driven systems. Despite, many experiments have been carried out to evaluate the corrosion behavior, very few theoretical researches have been carried out on this problem. Also, the atomic-level mechanism for these effects are not fully understood. To have a better understanding into the corrosion phenomena at atomic-level, it is necessary to explore the interaction details of atoms at the interface. Specifically, how the liquid atoms deposit onto the surface, and how the deposited liquid atoms affect the escape of Fe atoms from the steel surface.

Authors : S. Giusepponi, M. Celino, M. Gusso, P. Czaja, U. Aeberhard, Feng Li.
Affiliations : S. Giusepponi; M. Celino; M. Gusso: ENEA, C. R. Casaccia, Via Anguillarese 301, Rome, Italy; P. Czaja; U. Aeberhard; Feng Li: IEK-5 Photovoltaik, Forschungszentrum Jülich, D-52425 Jülich, Germany

Resume : The silicon hetero-junction (SHJ) technology is very promising technology because it holds the current efficiency record (more than 25%) for silicon-based single junction solar cells. The high open-circuit voltages that can be achieved thanks to the passivation of contacts by thin films of hydrogenated amorphous silicon (a-Si:H) is a central point of this technology. However, the a-Si:H/c-Si interface is still not fully understood in terms of transport and recombination across this nanoscale region, especially concerning the role of the different localized tail and defect states in the a-Si:H and at the a-Si:H/c-Si interface and of the band offsets and band bending induced by the heterostructure potential and the large doping, respectively. A microscopic picture of the interface is provided by accurate atomic-scale modelling based on DFT approaches and the electronic process involved are characterized using structural properties like radial pair correlation function and coordination analysis. The high accuracy of the computed macroscopic quantities depends on the atomic scale models describing the interatomic forces and how they are implemented to exploit the High Performance Computing (HPC) technologies. This approach has been realized within the recently EC promoted Centre of Excellence EoCoE (Energy oriented Centre of Excellence for computing applications, EoCoE uses the tremendous potential offered by the ever-growing computing infrastructure to foster and accelerate the European transition to a reliable low carbon energy supply using HPC. Four pillars (Meteorology, Materials, Water and Fusion) are targeted to enhance their numerical modelling capabilities by a transversal multidisciplinary effort providing both high-end expertise in applied mathematics and access to high-end HPC infrastructures.

Authors : Jun-Ho Park†§, Kang Hee Lee†, Kwangjin Park∥, Byungjin Choi†, Seong Yong Park‡, Jin-Hwan Park† and Heung Nam Han§
Affiliations : † Energy Lab, Samsung Advanced Institute of Technology (SAIT), Electronic Materials Research Complex, 130 Samsung-ro, Gyeonggi-do, [16678], Republic of Korea; ‡ Analytical Department, Samsung Advanced Institute of Technology (SAIT), Electronic Materials Research Complex, 130 Samsung-ro, Gyeonggi-do, [16678], Republic of Korea; § Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, Seoul 151-744, Republic of Korea; ∥ Department of mechanical engineering, Gacheon University, 1342 Seongnamdaero, Sujeong-gu, Seongnam-si, Gyeonggi-do, [13120], Republic of Korea;

Resume : Ni-rich layered oxides for lithium-ion batteries are the most promising cathode material for use in electric vehicles (EVs) among layered-structured ternary cathode materials due to its prominent energy density over 200 mAh g-1and low cost. However, there are several issues, which are needed to overcome; Ni/Li cation mixing, gas evolutions during cycling from unreacted lithium source on the surface of the active material. Herein, a simple and novel approach for post treatment using a type of metal-organic framework (MOF), which has been known to be easily synthesizable and mass producible was applied. The MOF was introduced for the Ni-rich layered oxides having Ni contents over 80% among the transition metals of Li(NiCoMn)O2. As a result, considerable morphology and phase changes of the active materials were derived by the post treatment. The introduction of the MOF to the active materials is effectively influenced on the structure of the outer and inner primary particles on a molecular level. In addition, electrochemical performances and thermal stability are improved by this effective modification. The treated samples were characterized by surface analyses (X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy), thermal analyses (thermogravimetric analysis, differential scanning calorimetry) and electrochemical methods (AC impedance, half- and full-cell test).

Authors : Disha Gupta, Assoc Prof. ZhiLi Dong, Dr Timothy Hyde, Prof. Sankar Gopinathan, Dr Tom Baikie.
Affiliations : Disha Gupta, ZhiLi Dong - School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, 639798, Singapore Dr Timothy Hyde - Johnson Matthey Technology Centre, Blount's Court, Sonning Common, Reading, RG49NH, UK Prof. Sankar Gopinathan - Department of Chemistry, University College London, 20 Gordon Street, London, WC1H OAJ, UK Dr Tom Baikie - Energy Research Institute @ NTU (ERI@N) Nanyang Technological University, Research Techno Plaza, 50 Nanyang Drive, 637553, Singapore.

Resume : The aim of this research is to conduct X-ray and e beam characterization techniques on lithium-ion battery materials for the improvement of battery performance. The key characterization techniques employed are the synchrotron X-ray Absorption Spectroscopy (XAS) combined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to obtain a more holistic approach to understanding material properties. This research effort provides additional battery characterization knowledge that promotes the development of new cathode, anode, electrolyte and separator materials for batteries, hence, leading to better and more efficient battery performance. Both ex-situ and in-situ synchrotron experiments were performed on LiFePO4, one of the most common cathode material, from different commercial sources, and their structural analysis were conducted using Athena/Artemis software. This analysis technique was then further extended to study other cathode materials like LiMnxFe(1-x)PO4 and even some sulphate systems like Li2Mn(SO4)2 and Li2Co0.5Mn0.5(SO4)2. XAS data were collected for the all the possible edges, Fe, Mn, P and S K-edge. Analysis of EXAFS data for all these edges is demonstrated here, with emphasis given mostly on the phosphate systems since very little information is available about the P K-edge from previous studies. XANES studies of all these edges also give information about the oxidation state and electronic configuration around the absorbing atom. Finite Difference Method for Near Edge Structure (FDMNES) simulations was also conducted for various phosphate model compounds and compared with the experimental XANES data to understand mainly the pre-edge structural information of the absorbing atoms.

Authors : Hsin-Yuan Liu, Pin-Jen Huang, Chih-Hao Huang, Chi-Young Lee, Hsin-Tien Chiu
Affiliations : Hsin-Yuan Liu;Pin-Jen Huang;Chih-Hao Huang;Hsin-Tien Chiu-Department of Applied Chemistry, National Chiao-Tung University, Hsinchu, Taiwan, 30010, R.O.C. Chi-Young Lee-Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, 30010, R.O.C.

Resume : As a promising electrode material in Li-ion batteries, Si has the advantages of its high theoretical lithium storage capacity (3579 mAhg-1), numerous natural abundance and environmental friendly. Here, we report that via a simple vapor-solid reaction growth (VSRG) method to synthesize highly crystalline Si materials with different morphology at 1023-1223K. They were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman analysis. SEM images displayed four type of structures, including nanoparticles, nanowires (NWs), coral-like and flake-like solids. XRD and Raman spectra showed that all the data of the as-synthesized products were assignable to Si. The as-fabricated Si powders were mixed with Super P® and KS4 in order to improve their conductivities were applied for anodes in Li-ion batteries. The half cell consisted of Si-NWs showed a reversible capacity 308 mAhg-1 in EC/DMC/EMC electrolytes after 50 discharge/charge cycles at a current density of 420 mAg-1. Compared to commercial Si particles, which demonstrated a capacity 186 mAhg-1, the Si powders we synthesized exhibit higher reversible capacity and better cycle performance. We expect further improvements will enhance the performance significantly.

Authors : Pin-Jen Huang, Hsin-Yuan Liu, Yu-Liang Chen,Chi-Young Lee, Hsin-Tien Chiu
Affiliations : Pin-Jen Huang; Hsin-Yuan Liu; Yu-Liang Chen; Hsin-Tien Chiu- Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan. R.O.C. Chi-Young Lee- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan. R.O.C.

Resume : In this work, the gold nanowire (AuNW) structures are fabricated on flexible substrates by electrochemical deposition. Polymer composites of polypyrrole (PPy) and polyaniline (PANI) are fabricated by in situ chemical oxidation of pyrrole and aniline on the mercaptoethanol-modified AuNW. Two electrodes are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) to observe the morphology of nanostructures, element characterization and the coverage of polymer composites. The AuNW structures have an average width of 100 nm. Subsequently, two electrodes are applied in a battery system. The open circuit voltage and power density of the battery is characterized under simulated body fluids like sweat and blood plasma (0.9% (w/w) NaCl), which may have further application on biomedical devices.

Authors : Fathima Fasmin, Lagnamayee Mohapatra, Ahmed Sodiq, Rachid Zaffou, Belabbes Merzougui
Affiliations : Qatar Environment and Energy Research Institute, QEERI; College of Science and Engineering, Hamad Bin Khalifa University, Doha, Qatar.

Resume : Slurry electrodes are promising candidates for energy storage applications, such as flow batteries and capacitors. The slurries contain conducting carbon particles and electrochemical active species dispersed in suitable ionic electrolytes. Hence, slurry conductivity is due to both ion migration and flow of electrons. The electronic conductivity of the slurry electrodes is determined by the degree of particle to particle connectivity and the contact resistances. During operation, the slurry is pumped from an external reservoir to the electrochemical cell where the redox reactions occur and the resulting electrons flow through the current collector to the external circuit. Under flow conditions, the particles are solvated and moving continuously, making and breaking contact with each other. This can result in low electronic conductivity values (< 0.1 mS/cm) and may limit the electrochemical performance of the device. Therefore, accurate estimation and enhancement of electronic conductivity is an important step towards the development of robust slurry flow systems. Electrochemical impedance spectroscopy (EIS) is widely used to measure the slurry conductivity. However, researchers have employed multiple electrical equivalent circuits (EEC) and analysis methods to calculate conductivity from the measured impedance data. Therefore, there is a need to develop reliable impedance models to characterize the electrochemical properties of the slurry electrodes accurately. In this work, we will present the experimental impedance data and EEC model used to extract the ionic, electronic, and charge transfer resistances of aqueous carbon based slurries in flow battery systems. We will also present numerical simulation results (using MATLAB) showing the effect of various resistances on the impedance behavior of the slurry. ***************************************************************************************************** Acknowledgements: This report was made possible by NPRP grant 9-158-1-029 from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors

Authors : Najebah Alsaleh 1, Elvis Shoko 1, Muhammad Arsalan 2, and Udo Schwingenschlo ̈gl∗ 1
Affiliations : 1-King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Divison (PSE), Thuwal 23955-6900, Saudi Arabia 2-Saudi Aramco, Dhahran 31311, Saudi Arabia

Resume : The electronic and thermoelectric properties of the AB2Te4 (A = Pb, Sn and B = Bi, Sb) compounds are investigated in the pressure range from 0 to 8 GPa, using density functional theory combined with semi-classical Boltzmann theory. The spin-orbit coupling and van der Waals interaction are included in all calculations, because of the heavy elements involved and the layered crystal structure, respectively. The variation of the electronic band gap under hydrostatic pressure is analyzed in detail and its consequences for the material properties are discussed. The behavior of the power factor under hydrostatic pressure is explained in terms of the electronic band structure.

Authors : Emiliano Burresi, Massimo Celino
Affiliations : Emiliano Burresi ENEA, SSPT Department, PROMAS Division, MATAS Laboratory, C.R. Brindisi ; Massimo Celino ENEA, DTE Department, ICT Division, C.R. Casaccia, Rome

Resume : Computational methods have been widely employed in several aspects of materials science, to perform electronic and structural characterization, to compute response properties to the external fields and more generally to design advanced materials with improved features to face mechanics and thermal applications. In this contest, the ab initio molecular dynamics, based on accurate quantum approaches, can provide a reliable description of the material reproducing thermodynamical experimental conditions. Cadmium sulfide is a II-IV semiconductor with direct band gap studied and employed as emitting material in solar cell devices, for photocatalytic applications and also as luminescent material in the led technology. Quantum confinement in nanostructured semiconductors allows the tunability of the band gap versus nanoparticle dimensions, making the CdS nanocrystal a very interesting and suitable material for application in several technologies. In this work structural, electronic and energetic properties of a cadmium sulfide nanostructured cluster were investigated by means of ab initio molecular dynamics. In particular, the ab initio molecular dynamics method was used to simulate this nanostructure under a temperature program, performing the structural characterizations following all the trajectories at different temperatures. The analysis of the electronic structure reveals the strong localization on the surface of the orbitals with energy around the Fermi energy. The analysis of the electronic behaviour reveals also that a delocalization of the HOMO orbital from superficial atoms towards atoms localized inside the nanoparticles are determinant for the stabilization of the structure at higher temperature. References Burresi E, Celino M (2012) Methodological approach to study energetic and structural properties of nanostructured cadmium sulfide by using ab-initio molecular dynamics simulations. Solid State Science 14:567-573 Burresi E, Celino M (2013) Surface states and electronic properties for small cadmium sulfide nanocluster. Nanoscience and Nanotechnology Letters 5:1182-1187

Authors : Avinash Kumar, Amartya Chowdhury
Affiliations : Centre for Energy and Environment, Malaviya National Institute of Technology J.L.N. Marg, Jaipur India -302 017

Resume : Crystalline silicon (c-Si) solar cell efficiency decreases by 0.4% for each oC increase of its operating temperature. Use of active power consuming cooling mechanism round the year is not financially viable and possible. So, one of the easiest cooling method is to use a visibly transparent passive radiative cooling layer on top of solar cell. In this work we have used COMSOL software to analyse the cooling effects of materials like Si3N4, SiO2, MgF2, Al2O3 and HfO2 on top of c-Si wafer as well as solar cell. All of these materials are almost transparent in the working wavelength range of c-Si solar cell i.e. 350 -1100 nm. The efficiency gain of the c-Si solar cell has been estimated for incorporation of the above layers considering the positive effect of temperature reduction as well as the negative effect of optical absorption in it. Our simulation shows that Single layer SiO2 can reduce the c-Si temperature by about 10oC and Al2O3 can reduce that by about 6-8 oC. The above layers may also be used as anti-reflection coating (ARC) of the solar cell and thus replace the original ARC of solar cell. Overall the best suitable combination will be investigated and power conversion efficiency improvement due to operating temperature reduction of solar cell under AM 1.5 spectra will be reported.

Authors : Ying-Ru Chen, Chun-Yu Su, Chao-Wu Chu, Cheng-Han Chiang, Hsin-Tien Chiu and Chi-Young Lee
Affiliations : Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan; Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan

Resume : In this work, flower-like CuO grown on the carbon nanotube paper was prepared via aqueous-based chemical reaction using copper sulfate as copper source along with sodium hydroxide, and trisodium citrate as chelating agent. The as-prepared flower-like CuO is an about 300 nm petal like flake aggregate. Due to high surface area and multi-oxidation state of the flower-like CuO which can provide both electric double layer capacitance and pseudocapacitance, flower-like CuO/carbon nanotube paper was used as electrode for supercapacitor. The supercapacitance of the flower-like CuO on lightweight carbon nanotube paper was investigated by cyclic voltammetry, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy. Cyclic voltammetry showed redox potential between -0.5 V and 0.3 V in sodium sulfate. Lightweight carbon nanotube can reduce the electrode total weight. Furthermore, the BET surface area of the flower-like CuO (53.5 m2/g) was much larger than the commercial CuO nanopowder (~29 m2/g). To sum up, the flower-like CuO/carbon nanotube paper is a promising electrode for supercapacitors.

Authors : Young-Hwan Lee1, Min-gyeom Kim1, Jeong-heum Han1, Mi-Ra Shin2, Ji-Woong Shin2, Jin-Ju Bae2, Kyoung-Tae Kim2, Sang-Yub Park2, Jong-Tae Son2*, Tae-Hwan Hong1
Affiliations : 1. Department of Advanced Materials Engineering, Korea National University of Transportation, Chung-ju 380-702, Republic of Korea 2. Department of Polymer Science and Engineering, Korea National University of Transportation, Chung-ju 380-702, Republic of Korea * Presenting author

Resume : Recently, hydrogen (H_2) has become a growing concern as a clean energy source to replace fossil fuels with various problems. To utilize this hydrogen energy, a large quantity of hydrogen and a high purity of hydrogen is being created, and hydrogen separation membrane studies are being conducted. The membrane reactor for hydrogen fabricate needs high hydrogen permeability, selective permeability, heat and the stable mechanical membrane. Pd and Pd-alloy are usually used, but these have many problems with high prices and durability. Therefore, many researchers have been studying substances to replace Pd, Pd-alloy.[1] On the other hand TiN powder are great in resistance to acids and chemically steady under high operation temperature. it used in catalysts and fuel cell electrode application. Alumina (Al_2 O_3) is widely used as a high-tech material with excellent heat resistance, mechanical strength and corrosion resistance. In accordance Tin-Alumina was manufactured using Sol-gel. TiN?Alumina membrane was characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). TiN?Alumina membrane was estimated hydrogen permeability by Sievert's type hydrogen permeation membrane equipment.

Authors : Dae Su Kim1,2, Alexis Brenes3, Elie Lefeuvre3, Hyung-Won Kang1, Chan-Sei Yoo1, Chae Il Cheon2, Seung Ho Han1
Affiliations : 1Electronic Convergence Materials and Device Research Center, Korea Electronics Technology Institute, South Korea; 2Center for Nanoscience and Nanotechnology, Université Paris-Sud – CNRS, Université Paris-Saclay, France; 3Department of Materials Science and Engineering, Hoseo University, South Korea

Resume : Piezoelectric energy harvesting has attracted considerable attention because it can generate sufficient energy to power small electronic components such as wireless sensor nodes. Piezoelectric ceramic is the key element for the piezoelectric energy harvester (PEH), which should be able to generate large amount of electrical energy even for a small mechanical input energy. Although, there have been many reports on the figure-of-merits of the piezoelectric ceramics for the PEH, few studies were performed on the figure-of-merit of the electromechanical system, namely PEH itself. Therefore, it is necessary to investigate the influence of the figure-of-merits of the ceramics on the electromechanical figure-of-merit and final output power densities of the PEHs for appropriate materials selection in various PEH applications. In the study reported here, two kinds of unimorph cantilever-type PEH were fabricated using soft and hard PZT materials. Electromechanical figure-of-merits of the PEHs were obtained from theoretical modeling of frequency dependent admittance measured at different actuation amplitudes. The electric power of the PEHs was measured under their resonance frequencies, with optimal resistance loads, and at equivalent acceleration condition. Finally, the figure-of-merits of the ceramics were compared with electromechanical figure-of-merits and final output power densities of the PEHs.

Authors : Roberto Grena, Massimo Celino, Tommaso Crescenzi
Affiliations : C.R. ENEA Casaccia, DTE-STT, via Anguillarese 301, 00123 Roma; C.R. ENEA Casaccia, DTE-ICT, via Anguillarese 301, 00123 Roma; C.R. ENEA Casaccia, DTE-STT, via Anguillarese 301, 00123 Roma

Resume : Liquid nitrates are among the most interesting fluids for heat storage/transfer applications, given their low cost, low toxicity and good thermal properties. They are widely investigated as possible heat transfer / heat storage media for solar energy production (the mixture NaNO3/KNO3 is called “solar salt” for this reason), alone or with the addiction of nanoparticles. However, their characterization is far from complete. Few molecular dynamics studies can be found in literature, and none of them using ab-initio methods (to the authors’ knowledge). This paper presents the ab-initio simulation of the most common of these salts (NaNO3), in liquid phase at 500 °C. Besides showing the feasibility of such a simulation, physical quantities of interest (density, correlation functions, self-diffusion coefficients) are computed and compared to experimental quantities. These methods can also be applied to more complex systems, such as mixtures (e.g., the solar salt, or ternary mixtures containing LiNO3), and can be used to predict changes in physical properties following variations of the relative concentrations or of the temperature.

Authors : Guntars Zvejnieks, Leonid L. Rusevich, Denis Gryaznov, Eugene A. Kotomin
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga str., Riga LV-1063, Latvia

Resume : Recent progress in material engineering allows one to produce new complex materials with improved ferro- and piezo- properties. In this study, we considered theoretically composite perovskites in the form of both (Ba,Sr)TiO3 solid solutions and (BaTiO3)m/(SrTiO3)n heterostructure superlattices, which are promising candidates for replacement of lead-containing materials for electrical/mechanical energy conversion. Using first principles calculations within the linear combination of atomic orbitals (LCAO) approximation and advanced hybrid functionals (PBE0, B1WC) of the density functional theory (DFT) as implemented in the CRYSTAL code, we calculated the elastic and piezoelectric properties as well as polarization of solid solutions in ferroelectric phase [1] and heterostructures for different m/n layer ratios. We predict that piezoelectric properties are improved with increasing amount of Sr for both solid solutions and heterostructures, but solid solutions are more effective for the same chemical composition. However, for Sr/Ba ratio >0.3, when solid solution becomes paraelectric, the heterostructures demonstrate the existence of optimal m/n ratio for which piezoelectric properties of BaTiO3 considerably improved. These results are relevant for practical applications including energy harvesting. [1] L.L. Rusevich, G. Zvejnieks, A. Erba, R. Dovesi, E.A. Kotomin, J. Phys. Chem. A 2017, 121, 9409?9414.

Authors : Leonid L. Rusevich (1), Guntars Zvejnieks (1), Eugene A. Kotomin (1), Marjeta Maček Kržmanc (2), Špela Kunej (2), Ioana D. Vlaicu (3)
Affiliations : (1) Institute of Solid State Physics, University of Latvia, 8 Kengaraga str., Riga LV-1063, Latvia; (2) Advanced Materials Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia (3) National Institute of Materials Physics, 405A Atomistilor Street, Magurele-Ilfov, 077125-Romania

Resume : An enhancement of the electromechanical properties of lead-free materials, which allow conversion of mechanical energy into electricity and may be used for different commercial applications, including energy harvesting, is the challenging problem. Progress in material engineering allows producing new complex materials with improved ferroelectric and piezoelectric properties. For example, to optimize the electrical properties of the widely applicable BaTiO3 (BTO) perovskite, it can be used both the chemical substitutions of Ba ions by isovalent dopants (Sr or Ca) and the creation of the BaTiO3/SrTiO3 (BTO/STO) ferroelectric plates. In this work, we considered (Ba,Sr/Ca)TiO3 solid solutions and BTO/STO heterostructures. The results of the first-principles computations of electromechanical properties are presented and discussed. Calculations were performed with CRYSTAL14 code within the linear combination of atomic orbitals (LCAO) approximation, using three advanced hybrid functionals of the density-functional-theory (DFT). Different chemical compositions and spatial arrangements are considered for the ferroelectric phase. Calculated structural properties of solid solutions in tetragonal phase are compared with experimental data for lattice constants, c/a ratio and unit cell volumes. It is predicted that solid solutions and heterostructures improve the piezoelectric properties of bulk BTO, what is important for technological applications.

Authors : G. Mancini, M. Celino (2), A. Di Cicco, E. Covino
Affiliations : Università di Camerino Via Madonna delle Carceri 62032, Camerino (MC), Italy; (2) ENEA, Ente per le Nuove Tecnologie, l’Energia e lo Sviluppo Economico Sostenibile C. R. Casaccia, Via Anguillarese 301, 00123 Roma, Italy

Resume : Thanks to its higher electron and hole mobilities and its lower operating voltages, germanium is gaining increasing consideration for replacing silicon for less energy-demanding solid state devices. A series of first-principles molecular dynamics simulations have been carried out for a relatively large system consisting of 240 GeO2 atoms. We have covered the entire range 10-4000 K by ab-initio simulations using norm conserving, separable, dual-space gaussian pseudopotentials for the BLYP exchange–correlation functional. The high temperature results show structural properties which are in good agreement with experimental results allowing for further simulations at lower temperatures to get a representative GeO2 system.

Authors : Sergey Karabanov(1), Dmitriy Suvorov(1), Dmitriy Tarabrin(1), Evgeniy Slivkin(1), Oleg Belyakov(2), Andrey Karabanov(2), Andrey Serebryakov(1), Vladimir Klimakov(1)
Affiliations : 1- Ryazan State Radio Engineering University, Ryazan, Russia 2- Helios Resource Ltd., Saransk, Russia

Resume : Currently, the main technologies for solar-grade silicon production are based on the reduction of silicon hydrogen chloride compounds. These technologies use environmentally dangerous and explosive compounds in quantity. The paper provides the research of new ecologically friendly technology based on vacuum and plasma-chemical purification of metallurgical-grade silicon melt under the conditions of electromagnetic stirring by mathematical model using COMSOL Multiphysics software. The modeling was carried out for the direct crystallization system. The paper studies: - thermal conditions of the direct crystallization system; - electromagnetic stirring at various magnetic field configurations; - impurity diffusion in silicon melt under the conditions of electromagnetic stirring. The modeling results are as follows: - a mathematical model of thermal calculation of the direct crystallization system is developed; - various configurations of the magnetic field created by electromagnetic stirring have been investigated; - electromagnetic stirring modes providing an optimal rate of surface mass transfer in silicon melt for effective purification from impurities are determined; - the diffusion of various impurities in silicon melt are studied. The obtained theoretical results allow of developing the solar-grade silicon production technology that has a number of advantages: - ecologically friendly production; - low cost of produced silicon; - wide range of the process scalability.

Authors : Guillaume AH-LUNG, Cécile AUTRET, Fouad GHAMOUSS
Affiliations : Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l’Energie (PCM2E), EA 6299, Université François Rabelais, Tours, France ; Groupe de Recherche En Matériaux, Microélectronique, Acoustique et Nanotechnologies (GREMAN), UMR 7347, CNRS/Université François Rabelais, Tours, France ; Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l’Energie (PCM2E), EA 6299, Université François Rabelais, Tours, France

Resume : Nowadays, due to environmental issues and the depletion of fossil fuels, the fear concerning the energy security is increasing which lead to an imperative development of alternatives for the energy production, its storage and transport. Among these alternatives we denote ultracapitors. Yet, for safety issues and convenient considerations like electrolytes inflammability and the fabrication process cost, the development of aqueous ultracapacitors became attractive. In order to increase performances, the studies are about the electrode materials and electrolytes. The pseudocapacitive materials, as metal oxide and their composites with carbonaceous materials, appear like the best alternative to activated carbon, currently use as ultracapacitors electrodes. Consequently, due to its pseudocapacitance storage type, its low cost and an eco-friendly behaviour, the MnO2 constitutes an interesting alternative. However, this oxide is formed of amorphous structure and many crystal structures. Each structure has their own electrochemical properties. In a typical MnO2 synthesis, the final structure is not always controlled without using a thermal process. Herein, simple and rapid preparation process of amorphous and high crystallinity MnO2 will be presented and discussed in terms of morphology, structure and electrochemical performances. MnO2 materials were synthesized by a solvent-assisted method using glycerol, ethylene glycol, or ethanol. The combination of a high viscosity (Glycerol) and a basic media (KOH) leads to highly crystalline Birnessite materials, while low viscosity solvent (Ethanol) leads to mostly amorphous structure. Furthermore, specific surface and total porous volume trend to decrease by increasing the crystallinity of the oxide (from 200 m2/g to 20 m2/g). In term of theirs electrochemical performances, capacitance and impedance, the results fit well with the structural nature of the oxide, ie. Amorphous or crystalline as well as theirs specific surface. The redox pseudocapacitive peaks are more marked for the combination of a solvent with a high viscosity and the presence of KOH. The oxide materials have been also used for building aqueous asymmetric capacitors with carbonaceous anode materials (graphene, and activated carbon). Energy and power of such systems will be presented and discussed as function of MnO2 type and anode materials.

Authors : Jun-Ho Park 1, Suk-Gi Hong 1, Kwangjin Park 2*,
Affiliations : 1 Energy Lab, Samsung Advanced Institute of Technology (SAIT), Electronic Materials Research Complex, 130 Samsung-ro, Gyeonggi-do, [16678], Republic of Korea 2 Department of mechanical engineering, Gachon university, 1342 SeongnamDaero, Sujung-Gu, Seongnam-si,Gyeonggi-Do, Korea, 1320

Resume : The solvent evaporation method on the structural changes and surface chemistry of the cathode and the effect of electrochemical performance of Li1.0Ni0.8Co0.15Mn0.05O2 (NCM) has been investigated. After dissolving of Li residuals using minimum content of solvent in order to minimize the damage of pristine material and the evaporation time, the solvent was evaporated without filtering and remaining powder was re-heated at 700 °C in oxygen environment. Two kinds of solvent, de-ionized water and diluted nitric acid, were used as a solvent. The almost 40% of Li residuals were removed using solvent evaporation method. The NCM sample after solvent evaporation process exhibited an increase in the initial capacity (214.3 mAh/g) compared to the pristine sample (207.4 mAh/g) at 0.1C because of enhancement of electric conductivity caused by decline of Li residuals. The capacity retention of NCM sample after solvent evaporation process (96.0% at the 50th cycle) was also improved compared to that of the pristine NCM sample (90.6% at the 50th cycle). The uniform Li residual layer after solvent treated and heat treatment acted like a coating layer, leading to enhance the cycle performance. The NCM sample using diluted nitric acid showed better performance than that using de-ionized water.

Authors : Kwangjin Park_1
Affiliations : 1 Department of mechanical engineering, Gacheon University, 1342 Seongnamdaero, Sujeong-gu, Seongnam-si, Gyeonggi-do, [13120], Republic of Korea

Resume : The formation of lithium residuals in Ni-rich nickel cobalt manganese oxide is inevitable, due to of the cation mixing by Ni2+ and excess Li required for high energy density. The purpose of this study is to examine the role of Li content in such materials after the washing process, which could reduce Li residuals and enhance the electrochemical performance of lithium ion batteries containing Li1.xNi0.91Co0.0Mn0.03O2 (NCM) as the cathode. The washing process reduced the Li residuals on the surface as well as the Li in the NCM structure. When a low Li content is used in the NCM, the Li content remaining in its structure after washing is lower than 1 mole. This removal of Li residues from the surface after washing leads to a capacity drop in spite of the improved cycle retention. Therefore, a high Li content is required in order to obtain enhanced electrochemical performance of high-Ni NCM. This trend regarding the Li content is also shown for NCM with small particle size.

Authors : Shenghuang Lin1,†, Yang Liu1,†, Zhixin Hu2,†, Gongxun Bai1, Yanyong Li1, Huiyu Yuan1, Yunzhou Xue1, Lukas Rogée1, Jianhua Hao1, Xuming Zhang1,*, Shu Ping Lau1,*
Affiliations : 1 Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong SAR, P. R. China 2 Center for Joint Quantum Studies, Physics Department of Tianjin University, Tianjin, P. R. China

Resume : Methylammonium lead iodide perovskite (MAPbI3), as a new type of light absorber for optoelectronic devices, has attracted much interest and served as foundation for new device concepts. However, most studies to date are mainly focusing on the fabrication of MAPbI3-based solar cells and photodetectors. Here we report a facile method to prepare a large-scale MAPbI3 photocatalyst through atmospheric pressure physical vapor deposition. The photocurrent density of the MAPbI3 coated with an Au layer can reach 30.8 and 85.5 μA/cm2 in ethanol and H2SO4 electrolytes, respectively. Meanwhile, the strong interaction between H2O orbitals and the conduction band of MAPbI3 is revealed by density functional theory calculations. Our study opens a new pathway for the development of perovskite-based photo-electrochemical reaction systems.

Authors : Teng Ma1, Michio Niwano2, Ayumi Hirano-Iwata1,3
Affiliations : 1. WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Japan; 2. Kansei Fukushi Research Institute, Tohoku Fukushi University, Japan; 3. Research Institute of Electrical Communication, Tohoku University, Japan

Resume : The organometal halide perovskite solar cells (PSCs), as the strong candidate of the next generation photovoltaics, have demonstrated their strong potential in the past several years.[1] However, as the quantum efficiency of PSCs based on the sandwich structure approaching 100%, it became more and more difficult to improve the performance. To break the bottleneck, we propose that it is possible to further boost the power conversion efficiency (PCE) of PSCs by replacing the widely-used sandwich structure with an integrated-back-contacted structure. In this work, we examined whether and to what extent the structural optimization can improve the PCE of PSCs, and discussed the possible film deposition technique to realize the structure. Using a numerical simulation technique, we demonstrate that the PCE of PSCs can be improved from 20% (sandwich) to 22.8% (IBC) using optimized structural parameters.[2] Furthermore, a new deposition method is proposed to fabricate perovskite films with grain sizes larger than the contact width in the IBC structure to reduce the charge recombination at the grain boundaries.[3] [1] Best Research-Cell Efficiency. (accessed 15/1/2018). [2] T. Ma, et al. Submitted. [3] T. Ma, Q. Zhang, D. Tadaki, A. Hirano-Iwata, M. Niwano, J. Phys. Chem. Lett. 2017, 8, 720−726.

Authors : Joshua Shipman, Brian Riggs, Jianwei Sun, Douglas Chrisey
Affiliations : Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118, USA

Resume : The combination of nanoparticles with polymers into a composite dielectric capacitor can increase overall energy density (solving their key deficiency), but these nanoparticles also can create both a macroscopic and a nanoscale incoherent interface (causing higher breakdown than the neat polymer film). Extensive work has been done to minimize the macroscopic interface through the shape and size of the composite interface. Minimizing the effect of the nanoscale interface is the motivation of this work. We present a theoretical study of the electrical interface between polymer and nanoparticle, motivated by simulations showing that dipole traps would be an excellent way to reduce the breakdown of polymer-nanoparticle composites. We have modelled the interface between ceramic barium titanate nanoparticles and a set of alkene terminated silane surface functionalizations, using first principles Density Functional Theory (DFT) calculations to study the local dielectric constant. Additionally, we have modelled the dielectric constant and polarization of the functionalization molecules separately. We have used numerical analysis to weight and combine the interfacial data with the polarization data, allowing for a ranking of the different functioanlizations. We have experimentally tested our prediction, combining our functionalized nanoparticles with a modular system of thiol-ene click monomers to spin coat thin films. We created solid films using a xenon flash lamp curing system to create covalent bonds between all the components of the system, though a light mediated thiol-ene click reaction. Our testing has shown that our predicted best surface functionalization increases the capacitors’ overall energy density by more than 20% as compared with the worst surface functionalization. We believe our modelling technique could be transferred to other areas where interface control is paramount, such as supercapacitor electrodes and surface functionalization for organometallic perovskite solar cells and quantum dot solar cells.

Authors : J.-M Chiu and Y. Tai
Affiliations : Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan

Resume : Applications of lithium ion battery have been hampered by a lack of ideal anode materials in terms of capacity and stability. Metal chalcogenide based on conversion or alloying reactions have drawn much attention because of their significantly higher specific capacity than traditional insertion electrode materials. However, debate about the underlying mechanisms and overall appraisal of its usage in lithium ion battery system remains. Here, a comprehensive study on the energy storage mechanism of copper zinc tin sulfde (CZTS) nanowalls possessing ultrahigh rate capability (500 mAh g??1 charged within 60 s) is reported. Structural evolutions along with the accompanying changes in the oxidation state upon charge/discharge were monitored by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. During lithiation, lithium ion reacted with CZTS to form lithium sulfdes. At the same time, a sequential conversion reactions of copper, zinc and tin sulfdes enabled the CZTS nanowalls to achieve excellent electrochemical performance (1400 mAh g??1 at a current density of 1000mA g??1 over 400 cycles). Multi-element metal chalcogenides in conjunction with an adhesion-enhancing seed layer and a rational nanostructure design hold the key to such ultrahigh capacity and stable anode materials for next generation energy storage devices.

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Photovoltaic and Optical Materials (II) : Wu Li
Authors : Carlo Massobrio
Affiliations : Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, F-67034 Strasbourg, Frace

Resume : Understanding the structure of disordered materials is a prerequisite for further knowledge of their physico-chemical properties. A desirable target is to bridge the gap between fundamental science and potentially useful applications. In this talks , we shall present two examples of studies of ternary glasses prone to technological applications and yet very much interesting from the fundamental point of view because of their controversial structure. Our approach is based on a quantitative prediction of material properties obtained via first-principles molecular dynamics combined to a careful choice of the relevant parts of the theoretical framework (exchange-correlation functionals, inclusion of dispersion forces). The first example deals with the atomic stucture of glassy Ge2Sb2Te5, one of the most established and successful phase change materials. In the second example, devoted to Ga10Ge15Te75, we considered a system studied experimentally because of its exceptionally large infrared transparency window.

Authors : Dibyajyoti Ghosh,† Philip Walsh Atkins,‡ M. Saiful Islam,*,‡ Alison B. Walker,*,† and Christopher Eames‡
Affiliations : †Department of Physics, University of Bath, Bath BA2 7AY, U.K. ‡Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.

Resume : Metal halide perovskite solar cells have rapidly emerged as leading contenders in photovoltaic technology. Compositions with a mixture of cation species on the A-site show the best performance and have higher stability. However, the underlying fundamentals of such enhancement are not fully understood. Here, we report new atomic-scale insights into the local structures and dynamics of mixed A-cation compositions based on formamidimium lead iodide (CH(NH2)2PbI3 ) doped with Cs+, Rb+ and MA+. Our specific findings include the first indication that substitution of low concentrations of smaller cations on the A-site in CH(NH2)2PbI3 results in a global ‘locking’ of the PbI6 octahedra tilting and reduced lattice dynamics. A key impact of this feature is that the rotational or tumbling motion of the CH(NH2)2+ molecular ion in a locked cage is severely restricted. We discuss the impact of locking on the photovoltaic performance and stability. The results presented here provide key fundamental insights into the origin of the significant enhancements in solar cell performance achieved by using mixed A-site species in lead halide perovskites and will have wide impact on future design strategies. Reference : Ghosh et al. ACS Energy Lett. 2017, 2, 2424

Authors : V.-A. Ha; G. Yu; F. Ricci; M. J. van Setten; M. Giantomassi; G.-M. Rignanese and G. Hautier
Affiliations : Institute of Condensed Matter and Nanoscience (IMCN), Université catholique de Louvain (UCL), Chemin étoiles 8, bte L7.03.01, Louvain-la-Neuve 1348, Belgium

Resume : High performance p-type transparent conducting materials (TCMs) must exhibit a rare combination of different properties including high mobility, transparency and p-type dopability. The finding of high-mobility p-type TCMs is very essential for many applications such as solar cells, transparent electronic devices,... Up to now, oxides have been conventionally considered as a promising chemical space to dig out novel p-type TCMs. However, many other non-oxide compounds also show very low hole effective mass and might perform better than traditional p-type TCMs (oxides). In this work, we carried out a high throughput (HT) computational search for a large dataset of more than 30.000 compounds. We show that non-oxides present large opportunities for high performance TCMs and identify BP, CaTe and Li3Sb as very good p-type TCMs candidates. These materials are indirect semiconductors with band gaps smaller than 3.0 (eV) but show high transparency because of indirect and therefore weak optical transitions. Their p-type doping tendencies are verified through defect calculations. Our approach goes beyond the usual analysis based on effective masses and band gap as we also estimated directly carrier mobilities through the computation of electron-phonon coupling and Boltzmann transport theory and obtained very competitive mobilities in comparison with current n-type TCMs.

Authors : Daniele Rossi, Matthias Auf der Maur, Alessandro Pecchia, Aldo Di Carlo
Affiliations : Dipartimento di Ingegneria Elettronica, Università di Tor Vergata, Rome, Italy; Dipartimento di Ingegneria Elettronica, Università di Tor Vergata, Rome, Italy; Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), Consiglio Nazionale delle Ricerche (CNR), Rome, Italy; Dipartimento di Ingegneria Elettronica, Università di Tor Vergata, Rome, Italy;

Resume : This work is focused on understanding the role that ferroelectric domains in MAPbI3 have on perovskite solar cells performance. We study 2D and 3D systems considering different polarization domains patterns, by proposing a polarization model based on the knowledge of the crystalline structure, symmetry considerations and electrical simulations. We compute charge carrier transport by solving a drift-diffusion model, in which the Poisson equation for potential calculation includes the polarization model. We show that the presence of polarization domains has a strong impact on charge separation, thus leading to a decrease of recombination losses and current pathways formation at domains interfaces. In detail, the decrease of Shockley-Read Hall recombination losses improves the open-circuit voltage, while the high current pathways formation lead to an increase of the short-circuit current. The achieved results demonstrate that the presence of ordered ferroelectric domains, even with weak polarization magnitude, can actually affect the performance of the solar cell in terms of power conversion enhancement. Moreover, from the comparison between our results and experimental IV characteristics of MAPbI3(Cl) devices we conclude that the polarization model proposed can effectively reproduce the solar cell operation.

Authors : Marcelo A. Carignano, Jacky Even, Claudine Katan
Affiliations : Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, P.O. Box 14110, Doha, Qatar; Univ Rennes, INSA Rennes, CNRS, Institut FOTON - UMR 6082, F-35000 Rennes, France; Univ Rennes, ENSCR, INSA Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, F-35000 Rennes, France.

Resume : We have performed a systematic study of hybrid perovskite systems using first principles molecular dynamics on supercell models containing 64 units. Our research includes different cations (MA, FA and Cs), different halide atoms (I, Br and Cl) and different thermodynamics conditions. The picture that emerges is one with several common features across different systems. The high temperature phase displays some degree of anharmonicity in the kinetics of the halide which depends on the structure of the cation, while FAPbI3 behaves close to harmonic at 450 K, the MAPbI3 already show anharmonic modes at this high temperature. Reducing the temperature to 370 K enhances the anharmonic character for all studied systems. For the case of the MA cation, the molecular electric dipole plays an important role that significantly affects simulations performed in 444 supercells. Over correlation of the dipolar interactions across the periodic boundary conditions drives the system to a phase change from cubic to a phase with high dipolar coupling. At the low temperature orthorhombic phases, MAPbX3 (X=I, Br and Cl) behaves as a standard crystal experiencing atomic vibrations but no molecular rotations. As the system is heated above the tetragonal transition temperature the simulations show the activation of molecular degrees of freedom. As a consequence, the static hydrogen bonds of the orthorhombic phase became dynamics and short lived in the tetragonal phase.

Photovoltaic and Optical Materials (III) : C. Massobrio
Authors : J. Even;H. Tsai;W. Nie;J.-C. Blancon;A. Neukirch; L. Pedesseau;B. Traoré;M. Kepenekian;C. Stoumpos;M. Sfeir;J. Crochet;S. Tretiak;M. Kanatzidis;A. Mohite;C. Katan
Affiliations : FOTON, UMR 6082, CNRS, INSA Rennes, Rennes, France; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; FOTON, UMR 6082, CNRS, INSA Rennes, Rennes, France; ISCR, UMR 6226, CNRS, Université de Rennes 1, Rennes, France; ISCR, UMR 6226, CNRS, Université de Rennes 1, Rennes, France; Department of Chemistry, Northwestern University, Evanston, Illinois USA; Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; Department of Chemistry, Northwestern University, Evanston, Illinois USA; Los Alamos National Laboratory, Los Alamos, New Mexico, USA; ISCR, UMR 6226, CNRS, Université de Rennes 1, Rennes, France;

Resume : In the past five years, solution-processed organometallic perovskite based solar cells have emerged as a promising thin-film photovoltaic technology. Multilayered 2D Ruddlesden-Popper phases, composed of perovskites layers sandwiched between two layers of large organic cations, have recently demonstrated improved photostability under standard illumination as well as humidity resistance over 2000 hours, affording a conversion efficiency of 12.5 %.(1) For multilayered halide perovskites, intrinsic quantum and dielectric carrier confinements are afforded by the organic inner barriers, which leads to a stable Wannier exciton at room temperature.(2) However, solar cell and LED efficiencies are essentially related to extremely efficient internal exciton dissociation through edge states in layered 2D Ruddlesden-Popper perovskites, as shown from the investigation of both thin films and small single crystals.(3) These materials can be described as unconventional semiconductors. The spin-orbit coupling is giant and shows up in the conduction band, the band gap is direct with the critical wavevector located at one of the edges of the reference Brillouin zone, and among others, excitonic or Rashba-Dresselhaus effects play a crucial role.(4) The electronic band structure can be modeled using either Density Functional Theory calculations. However multilayered halide perovskites are very large systems beyond the possibilities of state of the art DFT codes to include many-body corrections or excitonic effects.(5) Empirical methods based on the effective mass or multiband k.p Hamiltonian are still very useful, provided they are properly combined with DFT results to account for the dielectric and quantum confinements.(6) References 1 H. Tsai et al, Nature 2016; C. M. M. Soe et al, Adv. Ener. Mat. 2 G. Lanty et al, J. Phys. Chem. Lett. 2014; M. Smith et al, Chem. Sci. 2017 ; J. C. Blancon et al, arXiv:1710.07653 3 J. C. Blancon et al, Science 2017, H. Tsai et al, Adv. Mat. 2017 4 J. Even et al, Phys. Rev. B 2012; J. Phys. Chem. C 2015; M. Kepenekian et al, ACS Nano 2015 5 C. Stoumpos et al, Chem 2017 ; C. M. M. Soe et al, J. Am. Chem. Soc. 2017 ; L. Mao et al, J. Am. Chem. Soc. 2017 ; 6 J. Even et al, ChemPhysChem 2014; D. Sapori et al, Nanoscale 2016 ; L. Pedesseau et al, ACS Nano 2016

Authors : W. Q. Jemmali*, N. Ajnef, M. M. Habchi, A. Rebey
Affiliations : University of Monastir, Faculty of sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications / Corresponding author : *

Resume : The BAC model coupled to k.p theory and Pikus-Bir theory was used to determine the electronic properties of GaNxAs1-x-yBiy strained highly electronegativity alloys. This investigation was performed at room temperature in terms of electronic band structure, energy levels and spin-orbit splitting energies and with a bismuth and nitrogen concentrations range varying from 0 to 12%. The incorporation of a small N or Bi content affects the strain types and induces a large variation in the properties of these semiconductors. As results, we note essentially that, for strained GaAsBi and GaAsN ternaries, a significant reduction of the bandgap energy E_g^c of about 54 meV/%Bi and 99 meV/%N were found, respectively. In addition, the spin-orbit splitting ∆_(0 )^cwas increased by 39meV/%Bi for GaAsBi and decreased by 5meV/%N for GaAsN. On the other hand, for typical concentrations (x = 4% ; y = 5%) of strained GaNxAs1-x-yBiy, the energies E_g^c, ∆_(so ) and the valence band splitting VBS are equal to 0.66 eV, 0.54 eV and 17 meV respectively. Finally, we applied these results in the investigation of GaAs/GaN.03As.90Bi.07/GaAs and GaAs/GaN.02As.93Bi.05/GaAs single quantum well structures under compressive stress emitting at 1.3 and 1.55 μm./ Key words : GaNAsBi/GaAs ; k.p theory ; BAC model; Strain structures ; 1.3 and 1.55 μm emissions

Authors : P. Wahnon (a), G. Garcia (a), P. Palacios (b), A. Montero-Alejo (c), E. Menéndez-Proupin (c), J. C. Conesa (d)
Affiliations : (a) Instituto de Energía Solar and Dept. TFB, E.T.S.I. Telecomunicación, Universidad Politécnica de Madrid, Spain; (b) Instituto de Energía Solar and Dept. FAIAN, E.I. Aeronáutica y del Espacio, Universidad Politécnica de Madrid; (c) Departamento de Física, Facultad de Ciencias, Universidad de Chile, Chile; (d) Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, Madrid, Spain.

Resume : We investigate the excellent photovoltaic properties, such as suitable bandgap, high optical absorption and long carrier lifetime of organic-inorganic lead halide perovskites (mainly CH3NH3PbI3). To explain the large recombination time we propose the hypothesis that the formation of ferroelectric domains can separate the diffusion pathways of electrons and holes. We have found that a two-dimensional hole confinement in CH3NH3PbI3 is possible under room temperature conditions and is enhanced by the deformation of the inorganic PbI3 sublattice. Beside, to improve their photovoltaic performance, we explore the impact of point defects on their electronic structure through sub-bandgap absorption. We report here the electronic structure of new CH3NH3PbI3 perovskite derivatives, in which narrow band were obtained by replacing Pb atoms by Cr atoms. To deal with the bandgap underestimation problem of common DFT methods, quasiparticle calculations have been applied via the GW approximation. The investigation of the electronic structure of new CH3NH3PbI3 perovskites suggests that the presence of point defects play an important role in the coupling of two low energy photons to achieve a higher energy electron excitation, which would maximize the photovoltaic performance

Authors : J. Zhou1, L. O. Le Cunff1, K. Nomenyo1, A. Vial1, T. Pauporté2 and G. Lerondel1
Affiliations : 1. Laboratoire de Nanotechnologie et d'Instrumentation Optique, Institut Charles Delaunay, CNRS UMR 6281, Université de Technologie de Troyes, 12 rue Marie Curie, CS 42060, 10004 Troyes Cedex, France 2. Chimie Paristech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), 11 rue Pierre et Marie Curie, 75005 Paris, France

Resume : A phenomenological model has been developed and is discussed. The model is able to describe the experimentally measured light transmission of nanowires arrays. A slab of nanospheres and rough layers with thickness waviness were combined to simplify the nanowires structure description. This phenomenological description was proven to be feasible by fitting experimental data. As a conclusion, light transmitted through randomly distributed nanowires can be explained by the combination of volume and surface scatterings using respectively Mie theory and rough Fresnel coefficients at the interfaces.

Authors : El Mahdi ASSAID, Hicham EL ACHOUBY, Mhamed ZAIMI, Asmaa IBRAL, Safae AAZOU
Affiliations : Optics and Electronics of Semiconductor Nanostructures Team, Department of Physics, Faculty of Sciences, Chouaïb Doukkali University; Moroccan Foundation for Advanced Science, Innovation and Research (MAScIR), Optics and Photonics Center, Rabat, Morocco

Resume : In this paper, we present three methods to extract physical parameters of single diode electronic circuit modeling photovoltaic solar module. The physical parameters are photocurrent Iph, saturation current Is, ideality factor η, series resistance Rs and shunt conductance Gp. The first method uses the exact solution of module characteristic equation, the second one utilizes the exact expression of dynamic conductance and the third one uses the exact expression of the integral of I-Is. In these methods, we perform fitting of experimental data of current, dynamic conductance and area under I-Is with appropriate analytical expressions to extract model physical parameters in standard test conditions (STC). We then consider these values as initial conditions to derive exact analytical expressions describing the effects of incident solar irradiance and temperature on model physical parameters using temperature coefficients available in module datasheet as well as irradiance coefficients extracted from current-voltage curves set. The analytical expressions derived for model physical parameters are tested on Shell SQ80 photovoltaic module under different conditions of irradiance and temperature and very good agreements between experimental and predictive analytical characteristics are then raised.

Cathode Materials : J. Even
Authors : Chris Wolverton
Affiliations : Northwestern University, Dept. of Materials Science and Eng.

Resume : The energy density of many lithium metal oxide battery cathodes is limited by redox reactions associated with the transition metal alone. Anionic redox reactions are affording new opportunities to increase this energy density. Here, we present results from first-principles density functional theory (DFT) calculations aimed at understanding the combined cation/anion redox of Li-rich materials, and designing new materials that will enable high-capacity, reversible cycling with minimal oxygen evolution. We illustrate this approach on three Li-rich compounds: Li5FeO4, Li4Mn2O5, and Li2MnO3. Li5FeO4: Initial removal of Li is accompanied by Fe migration to form a disordered rocksalt structure. A local Li6-O coordination of oxygen, identified by DFT calculations, raises the O 2p band and enables reversible O-/O2- redox behavior, previously unknown in this material. This insight leads to the prediction and subsequent experimental demonstration of anionic and cationic redox reactions with good reversibility and without any obvious O2 gas release. Li4Mn2O5: We study the recently-reported, high-capacity, disordered rocksalt-type Li4Mn2O5 compound and also determine the ground state ordered structure of Li4Mn2O5 via a DFT-based enumeration method. DFT calculations show that the delithiation process occurs via a three-step reaction pathway involving the complex interplay of cation and anion redox reactions: i) Mn3+ ➝ Mn4+ (LixMn2O5, 4 > x > 2), ii) O2− ➝ O1− (2 > x > 1), and iii) Mn4+ ➝ Mn5+ (1 > x > 0) concomitant with Mn migration from the original octahedral site to the adjacent tetrahedral site. Finally, we predict that alloying with M = V and Cr in Li4(Mn,M)2O5 would produce new stable compounds with substantially improved electrochemical properties. Li2MO3: We catalog the family of Li2MO3 compounds as active cathodes or inactive stabilizing agents using high-throughput density functional theory (HT-DFT). With an exhaustive search based on design rules that include phase stability, cell potential, resistance to oxygen evolution, and metal migration, we predict a number of new Li2MIO3–Li2MIIO3 active/inactive electrode pairs, in which MI and MII are transition- or post-transition metal ions, that can be tested experimentally for high-energy-density lithium-ion batteries.

Authors : Mauricio R. Bonilla (1), Ariel Lozano (2), Bruno Escribano (1), Javier Carrasco (3), Elena Akhmatskaya (1,4)
Affiliations : 1 - Basque Center for Applied Mathematics, Alameda de Mazarredo 14 (48009) Bilbao, Spain 2 - Montefiore Institute, University of Liège, Allée de la découverte, 4000 Liège, Belgium 3 - CIC EnergiGUNE, Albert Einstein 48 (01510) Miñano, Spain. 4- IKERBASQUE, Basque Foundation for Science (48013) Bilbao, Spain

Resume : Today's commercial rechargeable batteries rely on Li-ion technology. Yet the expansion of the battery market towards electric vehicles and large-scale grid storage is likely to lead to a steep increase in the lithium price [Tarascon, 2010]. As a consequence, intense efforts have been devoted to find a suitable alternative. From a chemical perspective, sodium is positioned immediately below lithium in the periodic table and, therefore, it is its natural surrogate. Added to this, the high abundance, environment-friendly nature, and low cost of sodium have made research in Na-based batteries a topic of high interest in recent years [Slater, Kim et al., 2013]. From a Li-based viewpoint, LiFePO4 shows stand-out features such as great stability, remarkable rate capability, and sustained high voltage throughout the whole discharge cycle. In principle, one could expect NaFePO4 to inherit these properties from its isostructural lithium counterpart. Therefore, there has been a recent flurry of interest in NaFePO4 [Landa-Medrano, Li et al., 2016; Saracibar, Carrasco et al., 2016]. However, atomistic simulation of partially sodiated NaFePO4 has been hindered by (i) the lack of interatomic potentials for crystals having simultaneously Fe2+ and Fe3+ (both present in the partially sodiated structure) and (ii) the significant energy barriers associated with diffusion in this system, for which traditional molecular dynamics is not suitable. In this work we tackle both issues by developing a new, polarizable force-field for olivine NaxFePO4 (0 < x < 1) and combining it with an advanced atomistic sampling technique to simulate the diffusion of Na+ through the structure. In order to train the parameters of the proposed force field, we build a DFT-based dataset of configurations at several sodium concentrations. In this regard, our proposal goes beyond all previously suggested interatomic potentials for NaFePO4, which were specifically derived to simulate fully sodiated structures [Whiteside, Fisher et al., 2014]. We show that the new force field outperforms existing alternatives in terms of accuracy and thermal stability. Combining the new force field with a novel, in-house enhanced sampling methodology, the Randomized Shell Mass Generalized Shadow Hybrid Monte Carlo Method (RSM-GSHMC) [Akhmatskaya, Reich, 2008; Escribano, Akhmatskaya et al., 2015], we study with unprecedented level of detail the Na-ion diffusion in Na0.66FePO4. We confirm that the main diffusion mechanism involves single Na-ion hops through the one-dimensional channels along the [010] crystallographic direction. Furthermore, we identify the novel Na-ion diffusion dynamics involving the formation and annihilation of Na/Fe antisite defects, which effectively facilitate the migration of Na-ions between adjacent [010] channels. In principle, similar ion migration mechanisms could operate in other olivine framework compounds as well. The presented study provides an in-depth understanding of Na-ion mobility in olivine NaxFePO4, a promising alternative to the commercially available LiFePO4 cathode material for Na-ion batteries, and paves the way to unveil fundamental aspects of ion dynamics in polyanionic materials, in general. References Akhmatskaya, E.; Reich, S. GSHMC: An efficient method for molecular simulation. Journal of Computational Physics 2008, 227, 4934 – 4954. Escribano, B.; Lozano, A.; Radivojević, T.; Fernández-Pendás, M.; Carrasco, J.; Akhmatskaya, E. Enhancing sampling in atomistic simulations of solid-state materials for batteries: a focus on olivine NaFePO4. Theoretical Chemistry Accounts 2017, 136, 43. Landa-Medrano, I.; Li, C.; Ortiz-Vitoriano, N.; Ruiz de Larramendi, I.; Carrasco, J.; Rojo, T. Sodium–Oxygen Battery: Steps Toward Reality. The Journal of Physical Chemistry Letters 2016, 7, 1161–1166. Saracibar, A.; Carrasco, J.; Saurel, D.; Galceran, M.; Acebedo, B.; Anne, H.; Lep- oitevin, M.; Rojo, T.; Casas Cabanas, M. Investigation of sodium insertion-extraction in olivine NaxFePO4 (0 ≤ x ≤ 1) using first-principles calculations. Phys. Chem. Chem. Phys. 2016, 18, 13045–13051. Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S. Sodium-Ion Batteries. Advanced Functional Materials 2013, 23, 947–958. Tarascon, J. M. Is lithium the new gold? Nature Chemistry 2010, 2. Whiteside, A.; Fisher, C.; Parker, S.; Islam, M. S. Particel shapes and surface structures of olivine NaFePO4 in comparison to LiFePO4. Phys. Chem. Chem. Phys. 2014, 16, 21788–21794.

Authors : Hayk A. Zakaryan, Alexander G. Kvashnin, Artem R. Oganov
Affiliations : Yerevan State University Skolkovo Institute of Science and Technology Moscow Institute of Physics and Technology Northwestern Polytechnical University

Resume : One of the most studied materials for catalysis, sensing and energy applications is the rutile-type RuO2, especially its (110) surface [1]. Structure, chemical composition, and properties of the surface depend on external conditions. Using the evolutionary prediction method (USPEX), we found stable reconstructions of the (110) surface [2]. Two stable reconstructions, RuO4–(2×1) and RuO2–(1×1), were found, and the surface phase diagram was determined. The new RuO4–(2×1) reconstruction is stable in a wide range of environmental conditions, its simulated STM image perfectly matches experimental data, is more thermodynamically stable than previously proposed reconstructions, and explains well pseudocapacitance of RuO2 cathodes. References (1) Over, H. Surface chemistry of ruthenium dioxide in heterogeneous catalysis and electrocatalysis: from fundamental to applied research. Chem. Rev. 112, 3356–3426 (2012). (2) Zakaryan. H. A.; Kvashnin A. G.; Oganov A. R. Stable reconstruction of the (110) surface and its role in pseudocapacitance of rutile-like RuO2. Sci. Rep., 7, 10357 (2017)

Authors : Jin Hyun Chang, Juan Maria García-Lastra, Tejs Vegge
Affiliations : Department of Energy Conversion and Storage, Technical University of Denmark; Department of Energy Conversion and Storage, Technical University of Denmark; Department of Energy Conversion and Storage, Technical University of Denmark

Resume : Cluster expansion (CE) [1,2] is an effective method for studying metal alloys and oxides where a thorough exploration of all possible atomic configurations is practically impossible due to the high computational costs of first-principles calculations. CE dramatically reduces the computational cost of the exploring the configuration space by mapping the first-principles calculation results on to a much faster Hamiltonian. Especially with the emerging new cathode materials for Li-ion batteries based on lithium transition metal oxyfluorides [3,4], CE is becoming a relevant method in exploring and evaluating energy materials. This family of new cathode materials also presents new challenges such as a large number of constituting element types (four and a vacancy) and structural deformation upon delithiation, to list a few. We have implemented a CE code as a part of a popular Atomic Simulation Environment (ASE) package [5]. The implemented code includes necessary tools to evaluate complex battery materials while taking a generalized approach to allow the CE modeling of materials in any space group. We demonstrate our approach and its features with the Li2VO2F cathode as an example. 1. J. M. Sanchez, F. Ducastelle, and D. Gratias, Phys. A, 128, 334–350 (1984). 2. J. M. Sanchez, Phys. Rev. B, 81, 224202 (2010). 3. R. Chen et al., Adv. Energy Mater., 5, 1–7 (2015). 4. R. Chen et al., RSC Adv., 6, 65112–65118 (2016). 5. A. H. Larson et al., J. Phys. Condens. Matter, 29, 273002 (2017).

Authors : Roberta Pigliapochi, Ieuan Seymour, Céline Merlet, Andrew Pell, Denissa Murphy, Siegbert Schmid, Clare Grey
Affiliations : Department of Chemistry, University of Cambridge; School of Chemistry, University of Sydney

Resume : Titanium doping in lithium manganese oxide spinels was shown to be beneficial for the structural stability of the potential Li-ion battery cathode materials LiTixMn2-xO4, 0.2 < x < 1.5, yet the distribution of Li/Ti/Mn in the structure and the cation oxidation states, both pivotal for the electrochemical performance of the material, are not fully understood. Our work investigates the changes in the local ordering of the ions throughout this series by using a combination of 7 Li NMR spectroscopy and ab initio density functional theory calculations. The 7 Li NMR shifts are first calculated for a variety of Li configurations with different numbers and arrangements of Mn ions in the first metal coordination shell and then decomposed into Li?O?Mn bond pathway contributions to the shift. These Li?O?Mn bond pathways are then used to simulate and assign the experimental NMR spectra of different configurations and stoichiometries beyond those in the initial subset of configurations via a random distribution model and a reverse Monte Carlo approach. This methodology enables a detailed understanding of the experimental 7Li NMR spectra, allowing the variations in the local ordering of the ions in the structure to be identified. A random distribution of Ti4+ ? Mn3+/4+ sites is found at low Ti content (x = 0.2); an inhomogeneous lattice of Mn4+ ? rich and Ti4+ ? rich domains is identified for x = 0.4, and single-phase solid solution is observed for x = 0.6 and 0.8. A mixed Li? Mn2+ tetrahedral and Li?Mn3+/4+ ?Ti octahedral configuration is determined for the x = 1.0 case. A specific cation ordering in the partially inverse LiTi1.5Mn0.5O4 case is found, which transforms into a two-phase network of disordered Mn3+ ? rich and ordered Mn 2+ ? rich domains for x = 1.1?1.4.

Anode Materials : C. Wolverton
Authors : Zakhar I. Popov, Maxim A. Visotin, Natalia S. Mikhaleva
Affiliations : National University of Science and Technology MISiS, 4 Leninskiy prospekt, Moscow, 119049, Russian Federation; Siberian Federal University, 79 Svobodny av., Krasnoyarsk, 660041, Russian Federation; Kirensky Institute of Physics, 50/38 Akademgorodok, Krasnoyarsk, 660036, Russian Federation

Resume : Two-layer freestanding heterostructure consisting of VS2 monolayer and graphene was investigated by means of density functional theory computations as a promising anode material for lithium-ion batteries (LIB). We have investigated lithium atoms’ sorption and diffusion on the surface and in the interface layer of VS2/graphene heterostructure with both H and T configurations of VS2 monolayer. The theoretically predicted capacity of VS2/graphene heterostructures is high (569 mAh/g), and the diffusion barriers are considerably lower for the heterostructures than for bulk VS2, so that they are comparable to barriers in graphitic LIB anodes (∼0.2 eV). Our results suggest that VS2/graphene heterostructures can be used as a promising anode material for lithium-ion batteries with high power density and fast charge/discharge rates.

Authors : Ali Kachmar1, William A. Goddard III2
Affiliations : 1Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar 2Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, United States

Resume : Sodium Ion Batteries (SIBs) are the most cost-effective alternative to current generation lithium ion batteries (LIBs), [1-3] but Na is known to deliver very low energy capacity for sodium intercalation compared to Lithium. In order to improve the performance for SIB, we want to understand at the atomistic level how the metal ion changes its coordination to the solvent in positioning itself for insertion into graphite or adding at the metal surface [4,5]. Previous studies (force fields with fixed charges) ignored the coupling of electronic states with the changing charge and solvation. We report here Density Functional Theory molecular metadynamics simulations [6-8] to obtain the free energy landscape including changes in the electronic coupling as a sodium ion in Dimethyl sulfoxide solvent intercalates into graphite, the first step in understanding how the local environment affects the free energy of solvation [9]. We analyze the free energy landscape for all the possible sodium solvation scenarios, while quantifying their free energy barriers [10]. Our simulations indicate that solvent plays an important role in stabilizing the sodium intercalation into graphite through shielding of the sodium while modulating the interaction of the solvent with the graphite sheets. In order to facilitate this intercalation, we propose solvents with negatively charged groups and aromatic cores (e.g., cyclic ethers) that could allow a greater rate of anion exchange to increase Na mobility. References 1. Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research development on sodium-ion batteries. Chem. Rev. 2014, 114, 11636-11682. 2. Kubota, K.; Komaba, S. Review-Practical Issues and Future Perspective for Na-Ion Batteries. J. Electrochem. Soc. 2015, 162 (14), A2538-A2550. 3. Hwang, J. Y.; Myung, S. T.; Sun, Y. K., Sodium-Ion Batteries: Present and Future. Chem. Soc. Rev. 2017, 46, 3529-3614. 4. Kim, H.; Hong, J.; Yoon, G.; Kim, H.; Park, K. Y.; Park, M. S.; Yoon, W. S.; Kang, K. Sodium Intercalation Chemistry in Graphite. Energy Environ. Sci. 2015, 8, 2963−2969. 5. Jache, B.; Binder, J. O.; Abe, T.; Adelhelm, P. A Comparative Study on the Impact of Different Glymes and Their Derivatives as Electrolyte Solvents for Graphite Co-Intercalation Electrodes in Lithium-Ion and Sodium-Ion Batteries. Phys. Chem. Chem. Phys. 2016, 18, 14299-14316. 6. CP2K version 2.6.2 (Development Version), CP2K is freely available from 7. Laio, A.; Parrinello, M. Escaping free-energy minima. Proc. Natl. Acad. Sci. 2002, 99, 12562-12566. 8. Iannuzzi, M.; Laio, A.; M. Parrinello, M. Efficient Exploration of Reactive Potential Energy Surfaces Using Car-Parrinello Molecular Dynamics. Phys. Rev. Lett. 2003, 90, 238302. 9. Kachmar, A.; Carignano, M.; Laino, T.; Iannuzzi, M.; Hutter, J. Mapping the Free Energy of Lithium Solvation in the Protic Ionic Liquid Ethylammonuim Nitrate: A Metadynamics Study. ChemSusChem. 2017, 10, 3083-3090. 10. Kachmar, A.; Goddard III, W. A. The Role of Solvent for Sodium Intercalation into Graphite, submitted.

Authors : Takalign Terfa Debela and Hong Seok Kang
Affiliations : Institute for Application of Advanced Materials, Jeonju University, SOUTH KOREA Department of Nano & Advanced Materials, Jeonju University, SOUTH KOREA

Resume : First, we will describe our recent investigation on the origin of high charge capacity of a composite of transition metal chalcogenides with graphite in lithium ion battery. This is done by crystal structure prediction, ab initio NPT simulation followed by structure optimization, and graphene intercalation. Second, we propose two-dimensional (2D) GeP2 in the tetragonal (T) phase never observed for other group IV-V compounds. Our HSE06 calculation shows that its few-layers are a semiconductors with band gaps in the visible region. Band offset with respect to the Fermi levels of appropriate half-reactions shows that its n-type few-layers can be useful in photocatalyzed CO2 splitting to CO as well as in photocatalyzed water splitting, specifically under acidic conditions. Other recent calculations on the energy applications of 2D materials will be also discussed.

Authors : Oier Arcelus,Unai Arrieta,Nebil A. Katcho,Javier Carrasco
Affiliations : CIC Energigune

Resume : The search for Si-based anodes capable of undergoing low volume changes during electrochemical operation in rechargeable batteries is ample and active. Here we focus on crystalline Si24 [1], a recently discovered open-cage allotrope of silicon, to thoroughly investigate its electrochemical performance using density functional theory calculations. In particular, we examine the phase stability of NaxSi24 along the whole composition range (0 ? x ? 4), volume and voltage changes during the (de)sodiation process, and sodium ion mobility. We show that NaxSi24 forms a solid solution with minimal volume changes. Yet sodium diffusion is predicted to be insufficiently fast for facile kinetics of Na-ion intake. Considering these advantages and limitations, we discuss the potential usefulness of Si24 as anode material for Na-ion batteries. [1] Arrieta et. al., Scientific Reports, 7, 5350 (2017)

Authors : Dominik Bauer, Teutë Bunjaku, Mathieu Luisier
Affiliations : Integrated Systems Laboratory, Department of Information Technology and Electrical Engineering, ETH Zürich, Gloriastrasse 35, 8092 Zürich, Switzerland

Resume : The Li-ion battery (LIB) technology is expected to play an important role in the future of electrical vehicles for which sufficiently high energy storage capabilities are needed. Research on alternative electrode materials is essential to improve the performance of LIBs, but it is not possible to explore the large available design space only experimentally. Our goal is therefore to simplify the search with the help of computer aided design tools. Ab-initio calculations have become a well-established approach to study the structural properties of electrode materials in LIBs. Here, we will present results for lithiated SnO2 anodes, which stand out due to their high lithium storage capacity. Instead of restricting ourselves to the atomic configuration of Li-SnO2, we will further investigate the electrical transport characteristics of this compound since they also affect the underlying charge/discharge processes. For that purpose, a scheme based on maximally localized Wannier functions and non-equilibrium Green's functions has been developed. With this ab-initio quantum transport method we can not only determine the total current flowing through the considered structures, but also reveal the preferred current trajectories and their dependence on specific atomic alignments. Our study makes it possible to draw precise conclusions on the quality of a material in terms of lithium storage as well as on its limitations when it comes to electron transport.

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Thermoelectrics and Thermal Storage (I) : I. Savic
Authors : A.Igartua, B. Coto, J. Barriga, E. Aranzabe
Affiliations : IK4-TEKNIKER

Resume : IK4-TEKNIKER develop new materials and advanced manufacturing processes for energy conversión and storage systems, offering solutions that start at laboratory scale and can finalize in the industrialization of the product at customer level. In particular: • The phase change materials (PCM) sopported with inorganic matrix with capacity of thermal storage for transport, building applications or automotion. In particular, composite materials with porous support and organic or inorganic PCMs, and development of encapsulation pathways by means of sol gel technology for in situ encapsulation of organic or inorganic PCMs. • Thin layer solar cells with different type of substrates with high efficient energy conversión ratio of solar energy and competitive production processes, as for example, development of new photovoltaic absorvers based con chalcopyrite, or development of transparent outer metallic contacts for solar cells, and finally buffer thin layers (semiconductor type n). • Functional coatings for solar thermal collectors, increasing the yield of electricity generation plants as for example, development of selective coating on steel tubes with high absortive and emisivity, and development of mirrors with high reflexion capability. • Functional coating with high resistance to corrosion for bipolar plates and catalyst based on nanoparticles. • Advanced functional coatings with self cleaning, biocides and anfifouling properties • Nanoadditive materials as for example thermal fluids containing nanofluids, salts for thermal storage and PCM based slurries.

Authors : Annalisa Cardellini, Matteo Alberghini, Matteo Fasano, Eliodoro Chiavazzo, Pietro Asinari
Affiliations : Politecnico di Torino

Resume : Due to a continuous and inevitable depletion of fossil fuels, the use of renewable energy sources is gaining an increasing interest. Particularly, novel nanostructured materials are under investigation to enhance the technical and economic feasibility of solar thermal absorption, storage, and transport. In this presentation, we will particularly focus on thermal solar energy at low/medium temperature, and will report on some recent investigations on fundamental modelling and numerical tools for i) designing optically engineered nano-suspensions for sunlight volumetric absorption and for ii) predicting main properties of water sorption nano-porous materials for thermal energy storage applications. First, we show a novel Multi-Scale (MS) model able to predict the stability and aggregation of nanoparticle suspensions in aqueous solution. The strategy developed herein allows the incorporation of nanoscale phenomena into the dynamics of suspended NPs, thereby bridging the challenging gap between nanoscopic and macroscopic scales, and providing the first accurate dynamics of suspended NPs. By synergistically integrating molecular dynamics simulations, stochastic dynamics simulations, and macroscopic theory, the proposed model offers a well-founded platform to predict suspension stability, timescales for NP aggregation, and macroscopic performance indicators of NP suspensions. Second, because of the inconstant availability of solar irradiance, thermal storage devices are becoming crucial to the exploitation of solar source. From the point of view of seasonal storage energy, the most promising technology is represented by sorption thermal batteries, which allow storing energy without heat loss with time. The improvement of thermal batteries design is related to a better understating of heat and mass transport phenomena occurring in the adsorption/desorption phases. In this context, both molecular dynamics and Monte Carlo simulations are used to properly predict the adsorption isotherm and heat of some recently commercialized zeolites with non-trivial behavior.

Authors : Najebah M. Alsaleh, Elvis Shoko, and Udo Schwingenschlgl
Affiliations : King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Divison (PSE), Thuwal 23955-6900, Saudi Arabia

Resume : The pressure-dependence of the electronic and thermoelectric properties of four ternary chalcogenides with space group Pnma, namely, Cu(Sb,Bi)(S,Se)2 , is investigated up to 8 GPa using density functional theory combined with semiclassical Boltzmann theory. The effects of the van der Waals interaction are included in all calculations, since these compounds have layered structures. They all have indirect band gaps that decrease monotonically with increasing pressure except for CuBiS2 , for which an indirect-indirect band gap transition occurs around 3 GPa leading to conduction band convergence with concomitant increase in the Seebeck coefficient (20%) and power factor (45%). These enhanced thermoelectric properties result from a complex interplay between multivalley and multiband effects as well as band effective masses, driven by hydrostatic pressure. Our results suggest that ongoing developments in high-pressure science may open new opportunities for the discovery of more efficient thermoelectric materials.

Authors : Riccardo Rurali, Martí Raya-Moreno, Hugo Aramberri, Juan Antonio Seijas-Bellido, Xavier Cartoixà
Affiliations : Institut de Ciència de Materials de Barcelona (ICMAB–CSIC), Campus de Bellaterra, 08193 Bellaterra, Barcelona, Spain; Departament d’Enginyeria Electrònica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

Resume : Recent progresses in the synthetic growth of Si nanowires (NWs) [1] have given access to phases such as the hexagonal diamond one that in bulk is only observed under extreme pressure conditions. Hexagonal forms of bulk Si become stable at a pressure of around 16 GPa, while local domains of hexagonal Si in NWs [2] or hexagonal Si shell around a GaP NW core [3] have been reported at atmospheric pressure. A reliable experimental characterization of these polytypes is still lacking, and first-principles calculations play an important role in their prediction. Nevertheless, while several works on the electronic properties exist, no study deals with their thermal properties. Hexagonal Si, however, could be of potential interest for phonon manipulations and thermoelectric applications. This situation is common to several III-V semiconductors that, in NW form, can be selectively grown as cubic zincblende or hexagonal wurtzite. We present a predictive estimate of the thermal conductivity of the cubic and hexagonal polytypes of Si and of a few III-V compound (GaP, GaAs, GaN, InAs), obtained solving the Boltzmann Transport Equation with force constants computed from first-principles density-functional calculations. We report a significantly lower value for the hexagonal crystals and argue that it is a general feature of cubic vs hexagonal polytypes deriving from the enhanced anharmonic scattering due to optical phonons in the mid-frequency range [4]. [1] R. Rurali, Rev. Mod. Phys. 82, 427 (2010) [2] F. J. Lopez et al., ACS Nano 5, 8958 (2011) [3] H. I. T. Hauge et al., Nano Lett. 15, 5855 (2015) [4] M. Raya-Moreno et al., Appl. Phys. Lett. 111, 032107 (2017)

Authors : Brahim MARFOUA 1*/ Hamza LIDJICI 1, 3, / Brahim LAGOUN 2,/ Pascal Boulet 4, / Marie-Christine Record 5
Affiliations : 1: Laboratoire d?étude et développement des matériaux semi-conducteurs et diélectriques, Université de Laghouat, Route de Ghardaïa B.P.37G. Laghouat. Algérie. 2: Laboratoire de physique des matériaux, Université de Laghouat, Route de Ghardaïa B.P.73G. Laghouat. Algérie. 3: Laboratoire des Matériaux et Procédés, Université de Valenciennes et du Hainaut-Cambrésis, Z.I du Champ de l?Abbesse 59600 Maubeuge, France. 4: MADIREL, Aix-Marseille University and CNRS, Avenue Normandie-Niemen, 13397 Marseille cedex 20, France. 5: IM2NP, Aix-Marseille University and CNRS, Avenue Normandie-Niemen, 13397 Marseille cedex 20, France.

Resume : The semiconductors with the formula Mg2X (X= Si and Sn), have attract attention as potential high-performance thermoelectric materials, and their electronic, and thermal properties have extensively investigated [1-6]. They are an indirect band gap semiconductor. We carried in this work an ab initio study based on the density functional theory to calculate structural, electronic properties of Mg2X(X=Si and Sn). The FP-LAPW method was used with TB-mBJ exchange-correlation potential where give the best result for the lattice parameter, and the best estimation of the band gap energy. The thermoelectric transport properties like electrical conductivity (?), Seebeck coefficient (S), power factor (S2.?) and electronic thermal conductivity (Ke), have been obtained by solving the linearized Boltzmann, our results are in good agreement with experiment and other theoretical results. REFERENCE: 1. Morris R G, Redin R D, Danielson G C. Phys Rev, 1958, 109: 1909. 2. Redin R D, Morris R G, Danielson G C. Phys Rev, 1958, 109: 1916. 3. Hauser J J. Phys Rev B, 1975, 11: 3860. 4. Zaitsev V K, Fedorov M I, Gurieva E A, et al. Phys Rev B, 2006, 74: 045207. 5. Stella A, Brothers A D, Hopkins R H, et al. Phys Stat Sol, 1967, 23: 697. 6. Lott A, Lynch D W. Phys Rev, 1966, 141: 681.

Thermoelectrics and Thermal Storage (II) : A. Igartua
Authors : Stefano Curtarolo
Affiliations : Duke University USA; Fritz-Haber Institute, Berlin, Germany

Resume : Superhard materials are found with entropy descriptors.

Authors : J.D. Querales-Flores (1), J. Cao (1), R. Murphy (1,2), S. Fahy (1,2) and I. Savic (1).
Affiliations : (1) Tyndall National Institute, Cork, Ireland. (2) University College Cork, Cork, Ireland.

Resume : PbTe is an important thermoelectric material for power generation applications due to its high conversion efficiency and reliability [1]. PbTe shows a shift of the electronic bandgap with temperature that is opposite to the majority of direct gap semiconductors, i.e. the gap increases with temperature [2]. In this work, we study the temperature dependence of the electronic structure and thermoelectric properties of PbTe. We perform density functional theory and density functional perturbation theory calculations [3] in the local density approximation to calculate electronic and phonon bands. We use Wannier interpolation scheme to calculate electron-phonon matrix elements [4]. Using this information, we build accurate models of electronic and phonon bands, and deformation potentials from first principles. By solving the Boltzmann equation in the momentum relaxation time approximation, we calculate the mobility and thermoelectric transport properties of PbTe. Our results are in good agreement with experiments. We find that the temperature dependence of the gap has a substantial effect on thermoelectric transport in PbTe. [1] Y. Pei, X. Shi, A. LaLonde, et al., Nature 473, 66 (2011). [2] Z. Gibbs, H. Kim, H. Wang, et al., Appl. Phys. Lett. 103, 26 (2013). [3] S. Baroni, S. de Gironcoli, A. Dal Corso, and P. Giannozzi, Rev. Mod. Phys. 73, 515 (2001). [4] F. Giustino, M. L. Cohen, and S. G. Louie, Phys. Rev. B 76, 165108 (2007). F. Giustino, Rev. Mod. Phys. 89, 015003 (2017).

Authors : Marco Arrigoni, Jesús Carrete, Natalio Mingo, Georg K. H. Madsen
Affiliations : Institute of Materials Chemistry, TU Wien, A-1060 Vienna, Austria, Institute of Materials Chemistry, TU Wien, A-1060 Vienna, Austria, CEA, LITEN, 17 rue des Martyrs, F-38054 Grenoble, France, Institute of Materials Chemistry, TU Wien, A-1060 Vienna, Austria

Resume : Random semiconductor alloys find application in several technological devices, such as light emitting diodes, quantum cascade lasers, multi-junction concentrator solar cells and high-temperature thermoelectrics. Thermal management plays an essential role in these systems and methods able to predict their thermal conductivity are increasingly sought. The combination of first-principles calculations with the Boltzmann transport equation has proved to be an efficient and accurate method in determining the lattice thermal conductivity of semiconductor single crystals. The approaches commonly employed for their alloys consider the disordered mixture as a mass perturbation affecting an underlying non-structural effective medium. While such approximation shows a good predictive power for a limited set of compounds, it fails for general III-V semiconductor alloys. This failure is not surprising as several experimental studies have shown that these materials are characterized by a complex atomic-scale structure. In this contribution, taking In1-xGaxAs as a model material, we analyze the shortcomings of such models and show that a considerable improvement can be achieved by employing a structural description of the alloy and including the effects of local disorder through the introduction of a force-constant perturbation. We then present a first-principles method [arXiv:1712.02577] which implements these ingredients and finally demonstrate its ability to accurately predict the thermal conductivity of general semiconductor alloys.

Authors : Peter Kratzer and Maedeh Zahedifar
Affiliations : Faculty of Physics, University of Duisburg-Essen

Resume : Three ab initio approaches to the band structure of ANiSn and ACoSb half-Heusler compounds (A= Ti, Zr,Hf) are compared and their consequences for thermoelectric properties explored. The GW calculations confirm the trend of a smaller band gap (0.75 to 1.05eV) in ANiSn compared to the ACoSb compounds (1.13 to 1.44eV) already expected from the DFT calculations. While in ANiSn materials the GW band gap is 20% to 50% larger than in HSE, the fundamental gap of ACoSb materials is smaller in GW compared to HSE. Using the calculated band structures and scattering rates taking into account the band effective masses, the Seebeck coefficients, thermoelectric power factors and figures of merit ZT are predicted for all six half-Heusler compounds. Comparable performance is predicted for the n-type ANiSn materials, whereas clear differences are found for the p-type ACoSb materials. Using the most reliable GW electronic structure, ZrCoSb is predicted to be the most efficient material with a power factor of up to 0.07 W/(K^2 m) at a temperature of 600K. We find strong variations among the different ab initio methods not only in the prediction of the maximum power factor and ZT value of a given material, but also in comparing different p-type thermoelectric materials. We conclude that the most elaborate, but also most costly GW method is required to perform a reliable computational search for the optimum material.

Poster Session II : N. Mingo
Authors : Hyun Young Jung, Sung Mi Jung
Affiliations : Gyeongnam National University of Science and Technology, Korea Institute of Toxicology

Resume : Improved energy storage is inevitably needed to improve energy efficiency and to be environmentally friendly to chemical processes. Ionic liquids (ILs) can play a crucial role in addressing these needs due to inherent adjustable properties including low volatility, low flammability, inherent conductivity, wide liquid range, broad electrochemical window, high thermal stability and recyclability. Here, binary mixtures of ILs were prepared with fumed silica nanoparticles and characterized to obtain ILs with conductivity and electrochemical properties optimized for use in energy storage devices. The solutes were prepared by varying the size and the weight percent concentration of the nanoparticles and made up 10 % of the binary mixture by weight. We report on the physical and electrochemical properties of the individual ILs and their binary mixtures.

Authors : Avinash Kumar, Amartya Chowdhury
Affiliations : Centre for Energy and Environment, Malaviya National Institute of Technology J.L.N. Marg, Jaipur India -302 017

Resume : Crystalline silicon (c-Si) solar cell power conversion efficiency and lifetime reduces with increase in its operating temperature. In hot countries like India, in summer months solar cell temperature reaches 70oC. If one deposits material like SiO2, Al2O3 and HfO2 on top of c-Si wafer or solar cell than the temperature of it reduces due to passive radiative cooling. Thin films of the above materials are almost transparent in working wavelength range of solar cell and highly emissive in 8-13 µm wavelength range. Due to these properties our simulations show that one can achieve 10 to 15 oC reduction in operating temperature. This implies 4% to 6% increase in power output from an un-encapsulated c-Si solar cell. Based on reports, this temperature reduction will also increase the c-Si solar cell lifetime operating in hot climatic condition by twice. In this present work we have used the combination of above layers to act as 1) passive radiative cooling layer as well as 2) anti-reflection coating layer (ARC). The properties of the ARC layers requires that the thickness of the total combination of ARC layers should be below or equal to 100 nm. Our simulation shows that SiO2 with the combination of HfO2 having higher emission in the range of 9-10µm, similarly Al2O3 with HfO2 shows higher emission in the range of 11-13µm. This shows the possibility to reduce the temperature of the solar cell up to 10-15oC during real time operation with the help of all the above three materials.

Authors : Byung Hoon Park, Kwang Bum Kim
Affiliations : Department of Materials Science and Engineering, Yonsei University

Resume : With rapidly increasing demands of high-performance portable electronics and electric vehicles, lithium-ion batteries (LIBs) with high-energy density and high-power density have been intensively pursued. Conventional graphite anodes are able to charge and discharge at very low operating voltage (~0.1 V vs. Li/Li ), however, they have rather small specific capacity (~372 mA h g−1). Alternatively, silicon has long been considered one of the most promising anode materials for replacing graphite in LIBs because of its superior theoretical capacity (~3587 mA h g−1), attractive operating voltage and natural abundance. However, a large volume change of Si during charge/discharge causes severe fading in the reversible capacity. In order to overcome such disadvantages of Si-based electrodes, Si-X compound systems (X = Li-inactive/active element) have been suggested. Although these approaches have exhibited improved electrochemical performances compared to pure-Si electrode, the complex synthetic procedures and high fabrication costs have prevented their commercialization. In this study, we prepared for SiP2/CNT composite by a simple ball milling of silicon and phosphorous powders at room temperature, and we demonstrated its potential to be used as a promising anode for Li-ion batteries. It exhibits not only enhanced rate performance but also superior cycling performance, owing to the formation of electrical conductive buffer matrix. More details will be discussed at the meeting.

Authors : Byung Hoon Park, Kwang Bum Kim
Affiliations : Department of Materials Science and Engineering, Yonsei University

Resume : Li-ion batteries (LIBs) are considered the most promising power sources for portable electronic devices, clean transportation, and renewable energy storage facilities. However, conventional graphite anode has a limitation to applications which demand high energy density property. Therefore, to meet the demands of the rapidly increasing market, various high capacity anode materials are being intensively researched. Among various anode materials investigated for use in LIBs, silicon and phosphorous have been widely studied as anode materials in LIBs due to their high theoretical capacities of 3587 mA h g−1 and 2500 mA h g−1 respectively, however, poor cycling stabilities are remained challenging. Recently, SiP2 have been suggested as a new promising anode material which exhibited a high theoretical capacity of 2900 mA h g-1 and has three-step lithiation mechanism. However, its severe fading in the reversible capacity still have prevented their commercialization. In this study, we prepared for SiP2/CNT composite by a simple ball milling of SiP2 and pristine CNT powders at room temperature, and we demonstrated its potential to be used as a promising anode for Li-ion batteries. It exhibits not only enhanced rate performance but also superior cycling performance, owing to the formation of electrical conductive buffer matrix. More details will be discussed at the meeting.

Authors : Geon-Woo Lee , Young-Hwan Kim, Ha-Kyung Roh, Byung Hun Park, Kwang Bum Kim
Affiliations : Department of Materials Science and Engineering, Yonsei University, 134 Shinchon- Dong, Seodaemoon-gu, Seoul 120-749, Republic of Korea

Resume : As for sodium-ion (Na-ion) and potassium-ion (K-ion) are in the similar position in the periodic table, both Na-ion and K-ion batteries share the same ‘‘rocking chair’’ principle of electrochemical operation of Lithium ion battery (LIBs). Thus extensive efforts have been made to sodium-ion battery (SIBs) in the last few years, however, SIBs have relatively high standard hydrogen potential (−2.71 V vs E°) compared to LIBs (−3.04 V vs E°) makes the energy density of SIBs relatively low and limits their potential industrial applications. Comparatively speaking, potassium ion battery (PIBs) have lower standard hydrogen potential of K (−2.93 V vs E°) than that of Na and closer to that of Li, thus PIBs is expected to have the high energy density due to its wide working potential. [ref] Although PIBs have the potential to be an alternative post-LIBs energy storage devices, PIBs are still in the initial stage of development. It becomes significant to explore and develop novel and effective electrode materials for PIBs. Herein, we for the first time report on the electrochemical performance of TiO2 for anode materials for PIBs. To increase the intrinsic low electronic conductivity of TiO2, we incorporate CNT on TiO2 host materials through spray drying method. More details on the synthetic procedure, electrochemical and structural properties will be presented at the meeting.

Authors : Geon-Woo Lee, Young-Hwan Kim, Ha-Kyung Roh, Byung Hun Park, Kwang Bum Kim
Affiliations : Department of Materials Science and Engineering, Yonsei University, 134 Shinchon- Dong, Seodaemoon-gu, Seoul 120-749, Republic of Korea

Resume : Lithium-ion batteries (LIBs) are primarily used for advanced portable electronic devices and automotive electrical energy storage (EES) systems. However, the cost disadvantage and global scarcity of lithium resources restrict the LIBs for widespread and cost efficient large scale applications. Recently, sodium-ion (Na-ion) and potassium-ion (K-ion) batteries have received considerable attention as a potential post-lithium ion energy storage device due to their low cost and abundance. Anatase titanium dioxide (TiO2) is widely used as an anode material in commercial LIBs due to its reasonably low insertion potential (~ 1.7 V vs. Li/Li+), relatively high capacity (335.6 mAh/g) and small volume change (< 4%) upon the Li-ion insertion reaction. And also in NIBs, TiO2 anode materials have achieved a huge success with quiet good cycling stability and relatively high rate performance. Considering TiO2’s encouraging success on Li-ion and Na-ion battery can give inspiration to use of anode materials for potassium-ion batteries. Herein, we for the first time report on the potassium ion storage mechanism of TiO2 for anode materials for PIBs. More details on the synthetic procedure, electrochemical and structural properties will be presented at the meeting.

Authors : Jun Hui Jeong, Byung-Hoon Park, Geon-Woo Lee, and Kwang-Bum Kim*
Affiliations : Department of Material Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea

Resume : Spinel Li4Ti4O12 (LTO) has been demonstrated to be one of the most promising electrode materials for lithium-ion batteries due to relatively high and flat operating voltage of 1.55V (vs. Li/Li+), high reversible capacity (175 mAh g-1), and near-zero structural changes during repeated charge-discharge processes. However, the practical application of LTO is still largely restrained by the low intrinsic electrical conductivity (10-13 S cm-1) and lithium diffusion coefficient (10-13 to 10-10 cm2 s-1) Recently, duplex phase LTO-TiO2 composites have been reported to show better electrochemical performance than pure LTO. The improved electrochemical properties are attributed to the unique advantages of LTO-TiO2 composites as follow: 1) the higher lithium diffusion coefficient of TiO2 phase (~ 10-6 cm2 s-1) could improve lithium insertion/extraction kinetics. 2) The presence of Ti3+ in LixTiO2 during the discharge process could enhance the entire electric conductivity. 3) The high theoretical capacity of TiO2 phase (~336 mAh g-1) could increase specific capacity. In this study, dual phase core-shell structure consisting of LTO core and TiO2 shell were synthesized using chemically treated LTO particles. The fraction of TiO2 shell was controlled by tuning the condition of chemical treatment of LTO and heat treatment. It exhibits not only enhanced rate performance but also higher specific capacity comparing pure LTO. More details will be discussed at the meeting.

Authors : Jun Hui Jeong, Byung-Hoon Park, Geon-Woo Lee, and Kwang-Bum Kim*
Affiliations : Department of Material Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea

Resume : To date, numerous efforts have been devoted to improving the rate capabilities of spinel Li4Ti5O12 (LTO) by decreasing lithium-ion diffusion length and increasing the electronic conductivity. They reported improved rate capability of LTO. However, LTO is not considered the most preferable choice for large-scale applications by the power industries mainly due to severe gassing during charge/discharge cycles and storage, especially at elevated temperatures. It has been reported that the interfacial reactions between LTO and organic electrolyte solution may be the root cause for the gassing behavior. The construction of a barrier layer like a carbon layer is found effective in suppressing the gassing during interfacial reactions. Unfortunately, the carbon materials have high reactivity with electrolyte solutions at elevated temperature, which brings great safety concern. Thereby, finding a coating layer with little interfacial reactivity with electrolyte is urgent for the wide application of LTO in high power LIBs In this study, we developed SiOx coated LTO composite by a chemical process. Since SiOx is an inactive material in LTO operating voltage, SiOx coating layer blocked the interfacial reactions between LTO and organic electrolyte solution resulting in suppressing the gassing. It exhibits ultra-long cycle performance at elevated temperature. More details will be discussed at the meeting.

Authors : Yeon Jun Choi, Myung Seong Kim, Jun Hui Jeong, Young Hwan Kim, and Kwang-Bum Kim
Affiliations : Department of Material Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemoon-gu, Seoul, 120-749, South Korea

Resume : As one of the most applicable energy storage devices, lithium-ion batteries (LIBs) have been widely used in hybrid electric vehicles and portable electronic devices because of their high energy density. SnO2 has been studied as a promising candidate for anode material owing to its high theoretical capacity. However, low conductivity and large volume expansion of SnO2 during repeated cycles significantly limit its practical applications to LIBs. One of the most strategies to overcome the limits of the SnO2 is incorporation of graphene to limit aggregation of particles and improve cycle performance by mitigating the internal stress from the volume expansion. Recently, porous graphene have been reported to provide more diffusion channels for Li-ions and provides more edge sites enhancing Li-ion storage. Furthermore, the porous structure of graphene might accommodate the large volume expansion of the SnO2. For these reasons, there have been several reports about incorporation of the SnO2 into porous graphene. However, there is no study about the effects of the pores on the electrochemical activities of the SnO2 or Li-ion storage performance according to the characteristics of pores such as locations of the pores. In this work, we synthesized SnO2/NPG microball which is a unique design of SnO2/graphene structure with nanoperforations located underneath the SnO2 to analyze the effect of nanoperforations on the electrochemical activity of SnO2 or the Li–ion storage performance.

Authors : Yeon Jun Choi, Myung Seong Kim, Jun Hui Jeong, Young Hwan Kim, and Kwang-Bum Kim
Affiliations : Department of Material Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemoon-gu, Seoul, 120-749, South Korea

Resume : As one of the most applicable energy storage devices, lithium-ion batteries (LIBs) have been widely used in hybrid electric vehicles and portable electronic devices because of their high energy density. SnO2 has been studied as a promising candidate for anode material owing to its high theoretical capacity. However, low conductivity and large volume expansion of SnO2 during repeated cycles significantly limit its practical applications to LIBs. One of the most strategies to overcome the limits of the SnO2 is incorporation of graphene to limit aggregation of particles and improve cycle performance by mitigating the internal stress from the volume expansion. In this work, we synthesized SnO2/NPG microball which is a unique design of SnO2/graphene structure with nanoperforations located underneath the SnO2 to analyze the effect of nanoperforations on the electrochemical activity of SnO2 or the Li–ion storage performance. This unique design of SnO2/NPG microball has several advantages in lithium storage performance: I) Improvement in rate capability by decreasing the diffusion length of Li-ions and increased reaction site of SnO2 through introduction of nanoperforations underneath the SnO2 and II) increase in capacity through insertion/extraction of Li-ion from the edge sites, III) advancement in cycle performance by accommodating the volume expansion of SnO2.

Authors : 1 Youssef Dabaki;1, 2 Mohamed Tliha;1 ChokriKhaldi;3 NouredineFenineche; 4 Omar ElKedim; 1JilaniLamloumi
Affiliations : 1 University of Tunis, Laboratory of Mechanics, Materials and Processes, Group of Metal Hydrides, ENSIT, Tunisia 2Department of Physics, University Faculty, Umm-Alqura University, Al-Qunfudah, Saudi Arabia. 3 FEMTO-ST, MN2S, UTBM, Site de Sévenans, 90010 Belfort Cedex, France. 4 IRTES-LERMPS/FR FCLAB, UTBM, Site de Sévenans, 90010 Belfort Cedex, France. * E-mail:

Resume : Ni - MH batteries are characterized by important features such as light weight, good thermal performance, long cycle life, configurable design, low maintenance and high power. In fact, Hydrogen storage alloys are crucial in Ni - MH battery power service life and inn defining the battery electrochemical characteristics. LaNi5, having CaCu5 crystal structure, is characterized by almost all these properties and especially fast hydrogen kinetics. In recent years, CaNi5 has been considerably investigated because of its low cost, good kinetic properties and important hydrogen storage capacity. Nevertheless, the major limitation of its application is its extremely low cycle life. [1-4] Our study aims at providing a more stable structure with improved electrochemical capacity by the different milling time. In this work, the hydrogen storage characteristics of the single substituted CaNi4.7Mn0.3, prepared by applying Ni partial substitution, were valuated methodically at various milling times (2, 10, 20, 30, 40, 50 and 60 hours). Obviously, the cells, assembled by employing the obtained active material as anode, were cycled for both charging and discharging. Consequently, the measurement of the hydrogen storage capacity, ranging from 76 to120 mAh/g, was carried out electrochemically. However, compared to pure CaNi5, none of the various milling time improved noticeably the cycling stability. Besides, the alloys X-ray diffraction patterns showed that the hexagonal CaCu5 structure of a true AB5 alloy was maintained just in some cases. References [1]C. Khaldi, H. Mathlouthi, J. Lamloumi,A comparative study, of 1 M and 8 M KOH electrolyte concentrations, used in Ni–MH batteries, Journal of Alloys and Compounds, 469, 464–474, (2009). [2] Xiangrong Chen, Haiyan Wang, Shuping Zhu, Fangfang Li, Yougen Tang, Zuming Liu, Effect of magnetic field on the microstructure and electrochemical performance of rapidly quenched La0.1Nd0.075Mg0.04Ni0.65Co0.12 alloy, Journal of Alloys and Compounds, 617, 722–728,(2014). [3] H Mathlouthi, C. Khaldi, M Ben Moussa, J Lamloumi, A Percheron-Guégan, Electrochemical study of mono-substituted and poly substituted intermetallic hydrides, Journal of Alloys and Compounds, 375, 297–304, (2004). [4] Y. Dabaki, S. Boussami, C. Khaldi, H. Takenouti, O. ElKedim, N. Fenineche, J. Lamloumi, The effect of ZnO addition on the electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 electrode used in nickel metal-hydride batteries, Journal of Solid State Electrochemistry, 21, 1157-1164, (2017). Keywords: Ni-MH batteries, hydrogen storage materials, CaNi5.

Authors : Ioannis Deretzis 1), Antonino La Magna 1)
Affiliations : 1) CNR-IMM Zona Industriale VIII Strada 5 I 95121

Resume : Methylammonium lead tri-iodide (MAPbI3) is a polymorphic material with a remarkable potential for solar energy conversion. It is characterized by two temperature-induced phase transitions at about 165 K and 327 K, accompanied by an orthorhombic-to-tetragonal and a tetragonal-to-cubic lattice modification, respectively. Understanding the origins of these transitions as well as their implications on the crystal structure of the material could be important for its technological exploitation. Here, we use ab initio molecular dynamics to study the phase transitions of MAPbI3. We argue that the orthorhombic-tetragonal transition is characterized by an antiferroelectric to ferroelectric ordering through the partial rearrangement of the organic cations, which locally relaxes the stress arising from the thermal movement of atoms [1,2]. Besides, we propose a macroscopic model for the tetragonal phase that consists of rotated noncentrosymmetric domains where the MA ions are quasi-two-dimensionally confined around the a-b crystallographic plane. We finally show that the gradual disordering of the MA ions at higher temperatures triggers the tetragonal-to-cubic transition, resulting in a loss of the ferroelectric characteristics. [1] I. Deretzis, B.N. Di Mauro, A. Alberti, G. Pellegrino, E. Smecca, A. La Magna, Sci. Rep. 6, 24443 (2016) [2] I. Deretzis, A. La Magna, Nanoscale 9, 5896-5903 (2017)

Authors : Francesco Buonocore (a), Andrea Capasso (b), Nicola Lisi (a)
Affiliations : (a) ENEA, Casaccia Research Centre, I-00123 Rome, Italy; (b) Istituto Italiano di Tecnologia, Graphene Labs, Via Morego 30, Genova 16163, Italy

Resume : Graphene is a two-dimensional material that exhibits unique electrical, mechanical and optical properties. Derivatives of graphene recently became of large interest because of the possibility of adding new functionalities to graphene and tune its electronic properties. Among the possible derivatives, graphane - a graphene structure fully-hydrogenated on both sides of the lattice plane - and graphene oxide have attracted a great deal of attention in the last years. In this work we demonstrate via ab initio calculations that the formation of regular and short-period hydroxylated graphane is possible under suitable thermodynamic conditions. An application is shown where a graphene based derivative directly synthesized by chemical vapour deposition is used as hole transport layer in organic photovoltaic cells. Possibly, hydroxylated graphane could be applied as functional material in the fields of energy generation and storage. References [1] F. Buonocore, A. Capasso and N. Lisi, An ab initio study of hydroxylated graphane, Journal of Chemical Physics vol. 147, issue 10, 104705 (2017). [2] A. Capasso, L. Salamandra, G. Faggio, T. Dikonimos, F. Buonocore, V. Morandi, L. Ortolani, and Nicola Lisi, Chemical Vapor Deposited Graphene-Based Derivative As High-Performance Hole Transport Material for Organic Photovoltaics, ACS Appl. Mater. Interfaces 8 (36), pp 23844–23853 (2016).

Authors : A. EL Aouami (a), M. El Haouari (a,b), M. EL-Yadri(a), E. Feddi (a,b) and F. Dujardin (c)
Affiliations : (a) Groupe d'optoelectronique des boites quantiques des semiconducteurs, ENSET, Mohamed V University in Rabat, Morocco; (b) Centre Regional des Metiers de I'Education et de Formation (CRMEF), Tanger-Tetouan; (c) LCP-A2MC, Institut de Chimie, Physique et Matériaux Université de Lorraine, Metz, France;

Resume : The new generation of solar cells based on the intermediate bands within the energy gap of a semiconductor has been proposed as a way to increase photovoltaic solar cell efficiency. In this paper, we present a theoretical study of one intermediate-band solar cell (IBSC) formed by a multi-junction of InxGa(1-x)N/InN quantum dot supracrystals arrayed in the i layer of the p-i-n type structural cell. Based on Zhang's model [1], it is proposed to place the IB before the valence band (VB). Therefore we took into account electron-hole transitions. In order to determine the position and width of IB derived from the discrete quantized energy levels originating from QDs, the Kronig-Penny model was adopted to solve the Schrödinger equation. By taking into account the built in electric field generated at the junctions, we analyze the influence of the concentration x, mean size L and interdot spacing H of QDs on the position and width of IB. Thus the cell characteristic parameters such as IBSC efficiency, open circuit voltage (Voc), and short circuit current density (Joc) of InxGa (1-x) N/InN QD-IBSCs with single IB became clear. [1]: Q. Zhang, W. Wei, Appl Phys A (2018).

Authors : Danbi Lee, Youngho Oh, Eungjun Lee, Gibaek Lee*, Yongsug Tak*
Affiliations : Department of Chemical Engineering; Inha University

Resume : Energy storage system with high efficiency and capacity has attracted a great attention due to rapidly rising demand of an electric automobile, portable electric devices and internet of things. Lithium ion battery (LIB) has been used as a portable power supply device with high capacity. However, the problem including stability of electrode materials and limited supply of lithium sources has been raised because of chemical reactivity of Li and a limited resource reserves. Recently, alternative energy storage systems have been demanded. Among them, rechargeable aluminum-ion battery(AIB) is spotlight as an advanced-LIB. Aluminum metals can be used as an anode material because aluminum is relatively inexpensive from abundant reserve, high energy density with three-electron redox properties. Generally, ionic liquid is used as electrolyte for AIB, which exhibit high thermal stability, low vapor pressure, wide electrochemical window, high ion conductivity. However, ionic liquid could hinder the migration of charge carriers due to high viscosity. It causes formation of aluminum dendrite on the surface of Al electrode and unstable cycling performance at high current rates. In this work, we tried to figure out the correlation between viscosity and conductivity in electrolyte by adding benzene as organic solvent. According to Nernst-Einstein and Stokes-Einstein equations, conductivity is proportional to the number of charge carriers and inversely proportional to viscosity in electrolyte. But, addition of organic solvent decreases viscosity and reduces number of charge carriers as well. Accordingly, it is very important to set the suitable amount of organic solvent added to the ionic liquid. We prepared various electrolytes according to addition ratio of organic solvent and analyzed by electrochemical methods. (We used ionic liquid (AlCl3 / [EMIM]Cl) as electrolyte, and anhydrous benzene as additive to ionic liquid.) The reversible deposition and dissolution of aluminum and active reaction were investigated through cyclic voltammogram. Galvanostatic charge/discharge profiles were carried out using graphite as cathode for AIB. As a result, electrolyte with organic solvent is effective on stable cycling performance at a high current rate of 5Ag–1. We suggest that addition of organic solvent to ionic liquid can provide improved performance for rechargeable aluminum-ion battery.

Authors : I.Guizani, W.Q. Jemmali, M.M. Habchi, A. Rebey
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications, 5019 Monastir, Tunisia

Resume : We have theoretically investigated the 1.55 µm p-i-n GaNAsBi-based multiple quantum wells (MQWs) using a self-consistent calculation combined with 16x16 BAC model. Their performances are evaluated in terms of optical gain and radiative current density J_rad. We have found that J_rad reduces by increasing the well thickness〖 L〗_ω. The quantum confined Stark effect as well as the doping effect on spontaneous emission and radiative current density in ideal lasers are also discussed. The optical properties of the heterostructure are improved when the MQWs are doped. The optimization of well parameters can be used as a basis for GaNAsBi-based lasers intended for optical fiber telecommunication wavelength.

Authors : Krishna Manwani (1), J. Arout Chelvane (2), Emila Panda (1)
Affiliations : (1) Department of Materials Science and Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar 382355, Gujarat, India; (2) Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India

Resume : TbFe2 based magnetostrictive materials (owing to its larger magnetostriction value of 2500 ppm at RT) are of significant research interest due to their applications in defence in the form of microactuator, micromotor, sensor etc. However, its quality degradation due to oxidation poses an enormous challenge from being scaled up in a device. Understanding the microstructure of these oxide films is crucial as this would indicate about the loss of the constituent(s) from the bulk of the compound, thereby, giving direct information about the loss in the magnetic properties. In this context, a detailed study employing both theoretical and experimental methods was performed to understand the oxide-film overgrowth due to dry and thermal oxidation of TbFe2. The theoretical formalism predicted the overgrowth of Tb2O3, when there is no segregation of iron on the substrate, which is also experimentally validated. However, when the original surface of the TbFe2 substrate gets fully covered with iron atoms, formation of α − Fe2O3 become thermodynamically preferred over all other iron oxides. Experimentally, this was also found to co-exist with α − Fe2O3 at higher annealing temperatures. Moreover, both the model and the experimental data suggest segregation of Fe on TbFe2 substrate surface when annealed at higher temperatures. Understanding developed from this study would help in tuning the substrate constituents for higher temperature application, where oxidation of the compound is a major concern.

Affiliations : 1 Laboratory of chemistry and environmental chemistry L.C.C.E - University of Batna 1- Algeria 2 Faculty of Sciences- Department of Physics - University of Batna 2- 05000- Algeria

Resume : In this study, we used quantum chemistry calculations in order to determine some kinetic parameters of the isomerization reaction of the substituted icosadeca-ene. The studied molecules are: (C20H20, C20H10F10, C20H10Cl8, C20H10Br8 and C20H10I8) Cis and Trans. One of the adopted ways to access these parameters (activation energy, rate constant, etc ...) is looking for the transition state that is based on the exploration of intermediaries during the passage of Cis-Trans isomerization process. The study of a ten molecules series gives the following results: * The trans conformer is more stable than the Cis. * The activation energy changes very greatly depending on the size and nature of the substituent according to the reaction profile. * The constants of the isomerization reaction rates are in the following order: kC20H22 >> k C20H10F10 >> k C20H10Cl10 >>k C20H10Br10 >> k C20H10I10. * The geometrical parameters vary considerably according to intermediate products The calculation methods are DFT (TD-B3LYP) and Ab-initio methods at STO-3G*. Keywords: substituted icosadeca-ene, kinetics; isomerisation, HF (AM1+PM6), DFT

Authors : Tania Majumder, Subhasish Basu Majumder
Affiliations : Materials Science Centre, Indian Institute of Technology, Kharagpur-721 302, India

Resume : In commercial lithium ion batteries the most common anode material is graphite with a theoretical specific capacity is approximately 372 mAh/gm, but their low energy density and rate performance is poor. Therefore we have to improve the energy density as well as the specific capacity of anodes for powering electric vehicles. Most of the anode materials suffer from volume expansion and contraction during Li ion intercalation and de-intercalation processes, resulting in pulverization and poor stability of the electrodes in spite of having high storage capacity. In this investigation, we report the systematic study and synthesis of a novel perovskite Nickel Titanate (NiTiO3) by Sol–gel method. Nanosized powders annealed at 900 °C for 3 hours to form a crystalline structure and eliminate organic impurities. The phase and morphological properties were characterized by X-ray diffraction, Raman spectroscopy measurements, scanning electron microscopy, and transmission electron microscopy techniques. The pure-NTO electrode comprising a hexagonal crystal structure give a discharge capacity of approximately 550 mAh g−1 that corresponds to a coulombic efficiency of 67% in the first cycle, which further improved to ∼98% in the following cycles, at an applied specific current of 10 mAg−1, and stable cycling performance for 100 cycles. In the present work we demonstrate the importance of metal titanates, especially NTO, in terms of their applicability as an anode material for lithium ion batteries. Besides by engineering the microstructure and by making composites with carbonaceous materials these can also deliver effective lithiation/delithiation processes with better electrochemical performance.

Authors : O.O. Havryliuk, O.Yu. Semchuk
Affiliations : O.Chuiko Institute of Surface Chemistry NAS of Ukraine.

Resume : The film composite "Si nanocrystals in the matrix of amorphous Si" (nc-Si) is considered as a promising material for the next generation of solar cells (SC) at quantum dots. Among the main problems hampering the practical realization of the benefits of nc-Si is the lack of development of technology for controlling the size and concentration of Si nanocrystals at economically feasible film formation rates. One of the promising ways in this direction is the use of the phenomenon of metal induced crystallization (MIC) of amorphous silicon. An important role in the formation of nanocrystals in this structure is the distribution of temperature profiles that arises during laser irradiation. The temperature and time parameters of the MIC in the system a-Si-Sn are determined, as well as the prospects for using pulsed laser radiation to control the size and concentration of nanocrystals with induced tin crystallization of amorphous silicon. For this purpose, the finite element method was used to calculate the temperature distribution in the structure of a-Si-Sn-a-Si under the influence of different types of laser irradiation. The distribution of temperature profiles according to the intensity of pulsed radiation in the range of 15 KW/cm2 to 85 MW/cm2 with a duration of a single laser pulse of 10 ns and 150 μs (a laser with a wavelength of 535 nm and 1070 nm) is calculated. The difference between the temperature profiles in the structure with irradiated laser light with a length of 535 nm and 1070 nm is established.

Authors : R. I. Eglitis and A. I. Popov
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., Riga LV1063, Latvia; e-mail:

Resume : The results of ab initio calculations of polar YAlO3 (001) surfaces by means of a hybrid B3PW exchange-correlation functional as it is implemented in the CRYSTAL computer code are presented. Both polar YO and AlO2-terminations of the cubic YAlO3 (001) surface were considered. We performed relaxation of atoms on upper three layers of both YO and AlO2-terminated YAlO3 (001) surfaces using slabs containing 22 and 23 atoms and 9 layers, respectively. The Al-O chemical bond covalency change near the AlO2-terminated YAlO3 (001) surface relative to the YAlO3 bulk is discussed. YO and AlO2-terminated YAlO3 (001) polar surface energies are calculated and compared with ABO3 perovskite (001) surface energies [1,2]. Our B3PW calculated electronic band gaps near the YO and AlO2-terminated YAlO3 (001) surfaces are compared with the YAlO3 bulk band gap. 1. E. Heifets, R.I. Eglitis, E.A. Kotomin, J. Maier and G. Borstel, Phys. Rev. B 64, 235417 (2001) 2. R.I. Eglitis and A.I. Popov, J. Saudi Chem. Soc. (2018), in press

Authors : N. Ajnef, W. Q. Jemmali*, M. M. Habchi, A. Rebey
Affiliations : University of Monastir, Faculty of sciences Monastir, Unité de Recherche sur les Hétéro-Epitaxies et Applications / Corresponding author : *

Resume : Dilute bismide-nitride compound GaNAsBi is a promising candidate for use in GaAs-based optoelectronics devices in the near-infrared region. In this work, we report results of the electronic band structure of GaNAsBi/GaAs strained multiple quantum wells (MQWs). The band structure was modeled within the 16-band anti-crossing model, envelop function formalism and Bir-Pikus theory in conjugation with k·p Hamiltonian method. This investigation was used to describe the optoelectronics properties behavior of these structures such as band offsets, subband energies, strength of inter-band transitions and absorption coefficient spectra. We show that absorption coefficient spectra of GaN.04As.91Bi.05/GaAs strained single QWs has two maxima respectively located at 5,24 104 cm-1 for Τ_(e1-hh1) and 6, 37 104 cm-1 for〖 Τ〗_(e1-lh1). In addition, we have presented the results of the GaNAsBi-based strained double QWs (DQWs). We have deduced that the combined effects of strained and coupling between two wells enhance considerably the absorption coefficient compared to uncoupled DQWs. Keywords GaNAsBi-based strained QWs, Double QWs and coupling, Bir-Pikus theory, Absorption coefficient Optoelectronics properties

Authors : Stuart HANNAH*,Aravind RAVICHANDRAN, Marc RAMUZ, Sylvain BLAYAC
Affiliations : Stuart HANNAH*: presenting author; Aravind RAVICHANDRAN: Ph.D. student; Marc RAMUZ: Asst. Professor; Sylvain BLAYAC: Thesis director.

Resume : With the rapid development of wearable electronics and sensor networks, batteries cannot meet the sustainable energy requirements due to their limited lifetime, size and degradation. Ambient energies such as wind have been considered as an attractive energy source due to its copiousness, ubiquity, and feasible nature. With miniaturization leading to high-power and robustness, triboelectric nanogenerators (TENG) have been conceived as a promising technology by harvesting mechanical energy for powering small electronic systems. In this work, a state of the art TENG based on a wind venturi system is demonstrated for use in any complex environment. With the introduction of wind into the air channel of the TENG system, a thin flexible based film repeatedly contacts with and separates from the electrodes. Compound stacking not only amplifies the output power but also enables powering multiple sensor networks in remote area utilization. The system converts ambient mechanical energy to electricity with a 1.2kV peak amplitude by rapid super capacitor charging for powering an environmental sensor network. Different thin polymer materials are investigated by comparing the output power and mechanical stability performance. An autonomous sensor network system has been setup to monitor various environmental parameters and send real time signals for periodic analysis. The study also includes the influence of humidity and wind force under different environmental conditions. By considering these merits of simple fabrication, robust characteristics and outstanding performance, the TENG system could provide an autonomous detection system allowing clean and uninterrupted energy production.

Authors : Shuang Wu
Affiliations : Department of Chemistry, Imperial College London

Resume : Fuel cell powered by hydrogen from renewable sources is a clean and efficient way of energy utilization and has been developed rapidly over the past fifteen years. Fuel cells and electrolysers depend on electrocatalysis towards oxygen reaction and hydrogen reaction on their anode and cathode. However, the Oxygen Reduction Reaction (ORR) of a Fuel Cell and Oxygen Evolution Reaction (OER) of an electrolyser are kinetically sluggish. Hence, the loading of Platinum(Pt) electrocatalyst at the cathode is 10 times higher compared to that at the anode. The high cost and low earth availability has limit their application. Hence, this research aims to develop a clean and facile method for synthesis some non-precious metal phosphides as electrocatalysts for fuel cells and electrolysers. In this works, three different transition metal phosphides (Tungsten Phosphides, Chromium Phosphides and Tin Phosphides) will be synthesized by carbothermal synthesis and hydrothermal synthesis as catalyst supports, which will be followed by dispersion of Pt and Ir nanoparticles. Their electrochemical properties towards Hydrogen Reaction and Oxidation Reaction will be measured to investigate whether these catalysts can be applied to Fuel Cell efficiently.

Authors : Ziane mustapha, morad el baz, yassine hassouni
Affiliations : Um5 rabat

Resume : A direct measure of genuine entanglement in tripartite systems based on the volume of the negative part of Wigner function is proposed. We analyze comparatively this quantity and the dierent types of tripartite entanglement for two principal classes (GHZ and W class ) formed in coherent state basis.

Affiliations : 1 Laboratory of chemistry and environmental chemistry L.C.C.E - University of Batna 1- Algeria 2 Faculty of Sciences- Department of Physics - University of Batna 2- 05000- Algeria 3 Faculty of Sciences- Department of Chemistry - University of Biskra- Algeria

Resume : With the aim of finding an interpretation for the isomerization reaction of icosadeca-ene by quantum methods, we have studied a series of three molecules giving the following results: ? The studied segments (C20H20, C20H10F10, C20H10Cl8, C20H10Br8 and C20H10I8) are very stable. This stability is justified by the HOMO-LUMO found energy gap. However, examination of the stability of several conformations shows that the trans conformer is more stable than the cis conformer in the general assembly. ? According to the study of different reaction profiles, we noticed that the size and nature of the dopant plays a very important role on the evolution of the activation energy. ? From the obtained values of the activation energy, we find that the speed constants of the isomerization reaction are in the order: kC20H22 >> k C20H10F10 >> k C20H10Cl10 >> k C20H10Br10 >> k C20H10I10 ? The search for intermediate products during the transition Cis-Trans shows that the geometric parameters (angles and dihedral angles) are the most varied settings, this remark has been observed in the case of substituted and non-substituted icosadeca-ene. ? The methods of calculations performed in this work are the Ab-initio and DFT methods, with the bases (6-31G, 3-21G **). All these calculations are performed with the Hyperchem software, where parameters obtained are in a closer order to those obtained with the Gaussian 03W software ? Examination of different molecules obtained during the Cis-Trans isomerization reaction shows that the total energy of the resulting intermediate product is of the order of -10487.05 eV, corresponding to a 0.87eV activation energy (23.67 kcal / mol). ? With the same HF method (6-31G and 3-21 G**), a close geometry was obtained for the intermediate product in the isomerization reaction with a total energy of 0.93 eV (25.30 kcal/mole), which shows that the different values of the activation energy obtained by the HF and DFT methods at the 6-31G level can be compared to those obtained by Ito, Montaner and Bernier. Keywords: Ab-initio; DFT; kinetics; isomerisation; substituted icosadeca-ene

Authors : Minxia Liu, Wei Zhang , Geng Zhang, Dehai Zhu, Dongxiong Ling,Hongcheng Wang , Rui Zhang, Yi Li
Affiliations : Dongguan University of Technology

Resume : The discovery of 112-type Iron-based superconductors Ca1-xRExFeAs2 (RE= rare-earth elements) have attracted huge attention because of their various anomalous physical properties [1,2]. The temperature dependence of upper critical field for Ca0.83La0.17FeAs2 and Ca0.8La0.2Fe0.98Co0.02As2 single crystals are found to related to the two-band superconducting properties. To further understand the mechanism, the upper critical field for superconducting Ca0.83La0.17FeAs2 and Ca0.8La0.2Fe0.98Co0.02As2 crystals using the two band Ginzburg-Landau theory is calculated and analyzed. A two-parameter variables approach is utilized to obtain the upper critical field in arbitrary direction. The temperature and angular dependences of the upper critical field are carefully considered. It is found that the simulated two-band electronic structure for superconductors Ca1-xRExFeAs2 is well-fit with the experimental data in a broad temperature range [3]. The effect of impurity on the anomalous physical properties at superconductors Ca1-xRExFeAs2 (RE= rare-earth elements) is also reported. [1]. Yakita, H. et al. A New Layered Iron Arsenide Superconductor: (Ca,Pr)FeAs2. J. Am. Chem. Soc. 136, 846?9 (2014). [2]. Katayama, N. et al. Superconductivity in Ca1-xLaxFeAs2: A Novel 112-Type Iron Pnictide with Arsenic Zigzag Bonds. J. Phys. Soc.Jpn. 82, 123702 (2013). [3]. Xiangzhuo Xing et al. Two-band and pauli-limiting effects on the upper critical field of 112-type iron pnictide superconductors. Scientific reports. 7, 45943 (2017)

Authors : A.N. Sosa, A. Trejo, M. Cruz-Irisson
Affiliations : Instituto Politécnico Nacional

Resume : Currently many investigations focus in finding materials suitable as electrodes for the development of high capacity energy storage devices such as the lithium-ion batteries, specially germanium nanostructures have been considered as an attractive alternative for anodes due to its high theoretical charge capacity. To this end, one of the most promising nanostructures is the porous Germanium (PGe) since it overcomes limitations of crystalline bulk Ge such as the drastic volume expansion. However, the theoretical investigations of this material are scarce. In this work the effect of superficial Li on the electronic properties of PGe was investigated through the density functional theory and the supercell technique. The pores were modeled by removing columns of atoms from crystalline bulk Ge along [001] direction. The surface dangling bonds were passivated with H. To model the effects of superficial Li, H atoms were replaced by Li atoms until full coverage of the pore surface is achieved. Results shows that as the Li concentration increases at the surface, the electronic band gap decreases, favoring electronic conduction in these nanostructures which could be beneficial for use in lithium-ion batteries. Acknowledgment This work was supported by the computing facilities of LANCAD-CONACYT.

Authors : Hieu Trung Kieu, Adrian Wing-Keung Law
Affiliations : Environmental Process Modelling Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Interdisciplinary Graduate School, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

Resume : The rate of water evaporation as fundamental phase-change phenomenon is critically important to thermal processes in various industrial and manufacturing applications. With the development of nanotechnology, significant acceleration of evaporation rate process is now potentially feasible, which can lead to much higher efficiency, for example for thermal desalination. Recently, hollow and porous nanostructures have exhibited promising potential in the evaporation enhancement due to their capillary effect. However, the mechanism of water vapor transport through a capillary media at the nanoscale and the effect of surface properties remain unexplored. The present study investigates the evaporation behavior of water through the capillary channel of a graphene bilayer using molecular dynamics simulations, with tunable surface wettability by changing the surface charge states. The effects of both structural and environmental parameters, including the capillary channel distance and temperature, are also examined in details. The results show that significant enhancement of evaporation occurs when the graphene bilayer is brought into contact with the water surface. It is also found that the evaporation behavior is mainly controlled by two factors, namely, the morphology of the liquid-gas interface and the interaction energy between the water molecules and the graphene layer.

Authors : M.L. Grilli*, M. R. Mancini*, S. Stendardo * ,
Affiliations : ENEA, Casaccia Research Centre, Via Anguillarese 301, 00123 Rome (Italy)

Resume : The growing concern about CO2 impact on the environment pushes the researchers to the development of new materials with improved performances for CO2 capture and separation. Graphene oxide (GO) received recently a great attention and is recognized as one of the most promising materials for application in several fields such as solar cells, batteries, optoelectronic devices, energy storage, gas sorption and separation, gas sensing, etc.. The design of the GO structure and of its functionalization is of extreme importance for tailoring GO performances according to the requested applications. In this work we investigated the properties of graphene oxide obtained by modified Hummer’ method supported by CaO and not supported for application in CO2 capture.

Authors : William Yau
Affiliations : Imperial College London

Resume : Light Driven Organic Transformations to Enhance Hydrogen Production The water splitting reaction is a reaction that is kinetically and thermodynamically challenging to carry out. Alternative Hydrogen production involves the use of organic materials instead of water to facilitate hydrogen production. With the aid of Photo induced and Transient Absorption Spectroscopy along with the previous knowledge regarding the oxidation of methanol, the mechanism of the oxidation of organic waste is investigated. Using the oxidation of methanol to formaldehyde on a hematite electro catalyst under the irradiation of 365nm light as a platform to work from, we look to see if similar oxidation reactions of alcohols, glycerol and formation of epoxides work in a similar manner. Upon examination of the reactions of these organic substrates, one substrate will be selected to carry out further reactions. During these further reactions a pseudo steady state condition will be reached and then removed allowing for examination of rate of reaction and rate constants using Photo induced absorption spectroscopy. From this we can then seek to shine some light into the mechanism of this oxidation process. 1. Kinetics of Photoelectrochemical Oxidation of Methanol on Hematite Photoanodes Camilo A. Mesa, Andreas Kafizas, Laia Francàs, Stephanie R. Pendlebury, Ernest Pastor, Yimeng Ma, Florian Le Formal, Matthew T. Mayer, Michael Grätzel, and James R. Durrant Journal of the American Chemical Society 2017 139 (33), 11537-11543 DOI: 10.1021/jacs.7b05184 2. Kinetic Analysis of an Efficient Molecular Light-Driven Water Oxidation System Laia Francàs, Roc Matheu, Ernest Pastor, Anna Reynal, Serena Berardi, Xavier Sala, Antoni Llobet, and James R. Durrant, ACS Catalysis 2017 7 (8), 5142-5150, DOI: 10.1021/acscatal.7b01357 3. Jia, Jieyang, Linsey C Seitz, Jesse D Benck, Yijie Huo, Yusi Chen, Jia Wei Desmond Ng, Taner Bilir, James S Harris and Thomas F Jaramillo. (2016). "Solar water splitting by photovoltaic-electrolysis with a solar-to-hydrogen efficiency over 30%." Nature Communications 7: 13237.

Authors : 1) Slimane Haffad, 2) Madani Samah, 3) Khaled Boufala
Affiliations : 1) Département de technologie, faculté de Technologie, université de Bejaia, Algerie; 2) Département de biologie, faculté de biologie, université de Bejaia, Algerie; 3) Département de physique, faculté des sciences exactes, université de Bejaia, Algerie

Resume : In this work, we employed density functional theory [1] to study the effect of ZnO thickness on the physical properties of ZnO/TiO2 core/shell nanostructures and their practical impacts when these structures are used in photocatalytic or photovoltaic systems [2]. We varied the thickness of the core from 4 to 16 A. The effect of the thickness on the electronic and mechanical properties was analyzed at GGA and GGA+U levels. The results show a non-uniform variation in the energy gap of the core/shell nanostructure suggesting a compensating mechanism due to the electronic defect states [3]. A larger energy gradient between the conduction band of ZnO and the conduction band of TiO2 was observed and favors the transfer of the excited electrons from ZnO to TiO2, in agreement with experiments [4]. However, the heterostructure shows a good resistivity even for a very fine core thickness. With such core/shell structures, the ratio of cells in surface area can be increased and demonstrate a good life time when they are used in dye sensitized solar cells (DSSCs) [2]. [1] W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965). [2] B. O. Regan and M. Graetzel Nature, 353, 737 (1991). [3] Haffad, arXiv:1702.02545v1 [physics.comp-ph]. [4] Fatma Kayaci, Sesha Vempati, Cagla Ozgit-Akgun, Inci Donmez, Necmi Biyikliab, and Tamer Uyar, Nanoscale, 6, 5735-5745 (2014).

Authors : N.A. Poklonski, A.N. Dzeraviaha, S.A. Vyrko
Affiliations : Belarusian State University, Physics Department, Nezavisimosti Ave. 4, Minsk 220030, Belarus,

Resume : The ionization equilibrium in n-type indium antimonide under external quantizing magnetic field is considered. The electroneutrality condition has the form: n(↑) + n(↓) + N(−1) = N(+1) = N − N(0,↑) − N(0,↓), where n(↑) + n(↓) is the concentration of c-band electrons which have parallel (↑) and antiparallel (↓) to the direction of magnetic field spin orientation, N = N(0,↑) + N(0,↓) + N(+1) is the concentration of all donors, N(0,↑) + N(0,↓) is the concentration of electrically neutral donors with “optical” electron, N(+1) and N(−1) are the concentrations of ionized donors and compensating acceptors. The calculation of electron concentrations n(↑) and n(↓) and electrically neutral donors concentrations N(0,↑) and N(0,↓) takes into account: 1) quantizing and spin-splitting of orbital movement energy (Landau levels) of c-band electrons; 2) spin-splitting of energy levels of impurity band; 3) c-band tail and distribution of impurity energy levels in the band gap; 4) electrostatic screening of impurity ions, percolation threshold and exchange interaction of c-band electrons [1]. The solution of electroneutrality condition gives the dependences of n(↑), n(↓), N(0,↑) and N(0,↓) on magnetic field, which are consistent with the theoretically unexplained experimental data on CW electron spin resonance in n-InSb [2]. The work was supported by the EU Programme Horizon 2020 (Grant Nos. H2020-MSCA-RISE-2015-691010 HUNTER and H2020-MSCA-RISE-2015-690968 NANOGUARD2AR). [1] N.A. Poklonski, S.A. Vyrko, A.I. Kovalev, A.N. Dzeraviaha. J. Phys. Commun. 2, 015013 (2018). [2] M.V. Kondrat’ev. Sov. Phys. Semicond. 20 (1986) [Fiz. Tekh. Poluprovodn. 20, 1485 (1986)].

Authors : Bojana Paskas*, Mamula, Nenad Ivanovic, Nikola Novakovic
Affiliations : VINCA Institute of nuclear sciences - University of Belgrade, POB 522, 11001 Belgrade, Serbia *Presenting author

Resume : Chemical bonding and stability of simple metal hydrides and transition metal doped MgH2 have been assessed by means of charge density topology analysis on the both local (Bader concept of atoms in molecules) and integral (concept of non covalent interactions) level. Trends in macroscopic properties (melting temperatures and overall thermodynamic stability, elastic properties etc.) observed in compound series such as alkali hydrides and halides, could be attributed to existence of subtle differencies in charge density topologies. These differencies on local level can be described using different number and distribution of charge density stationary (critical) points. On the broader scale, regions of bonding attraction and repulsion can be identified using non-covalent interactions concept. The local concept is insufficient to descibe topological transition between LiH ? NaH ? KH. Although LiH and NaH belong to different topological classes, non-local approach reveales that NaH is actually transition case, with attractive H-H charge concentrations not sufficient to fullfil bonding condition. Complex structure of NCI reduced charge density gradient in ionic MgH2 with first and second neighbor bonded atoms is replaced with more pronounced directional first neighbor bonding in transition metal doped MgH2.

Authors : Samah BOUDOUR1,2, Idris BOUCHAMA2,3, Moufdi HADJAB1, S. LAIDOUDI1,4
Affiliations : 1Research Center in Industrial Technologies CRTI, P.O. Box 64, Cheraga 16014, Algiers, Algeria. 2Electronic Department, Faculty of Technology, Mouhamed Boudiaf University of Msila, 28000, Msila - Algeria. 3Inorganic Materials Laboratory, Mouhamed Boudiaf University of Msila, 28000, Msila - Algeria. 4Laboratoire de Chimie, Ingénierie Moléculaire et Nanostructures, Université Ferhat Abbas-Sétif 1, Sétif 19000, Algérie

Resume : In the present work, we suggest on highlighting simulation study of a new structure ZnO/Si/Cu2O solar cell using Analysis of Microelectronic and Photonic Structures (AMPS-1D) computer simulator under solar spectrum AM1.5G illuminated from n-ZnO side. The inconveniences of using p-metal-oxide/n-metal-oxide (p-MO/n-MO) as a traditional PN junction in solar cells are more interface states for cell-based heterojunctions and high defects within MO layers which induce serious problems such as recombination and tunneling and hence deteriorate the cell performances. Considering widespread, robust and reliable Si materials in solar cell application, are performed to find optimized design structures based on n-ZnO and p-Cu2O MOs and crystalline p-type Si as a middle layer. The J-V characteristics as well as electric fields and quantum efficiencies (QE) of the new structure are investigated based on device design and input parameters such as band offsets, layers thickness and doping densities. Mutually optimization of the structure showed an appreciable improvement of conversion efficiency with an estimated value of ~13.4% compared to ~10.6% for n-ZnO/p-Cu2O two-layer structure. Key words: p-Si absorber, Cu2O, solar cell, AMPS-1D, J-V characteristics.

Authors : F. de Santiago, I. González, J. A. Santiago, A. Miranda, L. A. Pérez, M. Cruz-Irisson
Affiliations : Instituto Politécnico Nacional, ESIME-Culhuacán, Av. Santa Ana 1000, 04430 Ciudad de México, México; Instituto Politécnico Nacional, ESIME-Culhuacán, Av. Santa Ana 1000, 04430 Ciudad de México, México; Instituto Politécnico Nacional, ESIME-Culhuacán, Av. Santa Ana 1000, 04430 Ciudad de México, México; Instituto Politécnico Nacional, ESIME-Culhuacán, Av. Santa Ana 1000, 04430 Ciudad de México, México; Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, 01000 Ciudad de México, México; Instituto Politécnico Nacional, ESIME-Culhuacán, Av. Santa Ana 1000, 04430 Ciudad de México, México

Resume : The development of efficient means of hydrogen storage is essential for the adoption of hydrogen as fuel, since it would be cleaner and more available than fossil fuels. Storage by solid state materials provides advantages over compressed gas or liquefaction, and germanium and 2D materials have proven to be good adsorbents. In this work, we study the adsorption of H2 molecules in a germanene supercell, aided by a lithium, sodium or potassium atom decorating the monolayer. The analysis of the energies was carried out from calculations within density functional theory. It was discovered from geometrical optimization and energy calculations that all systems studied are structurally stable, and alkali atoms are chemically bonded with germanene. Up to seven H2 molecules can be physisorbed in the decorated germanene. Various adsorption sites for the molecules were analyzed. The results show that the site above the center of the hexagons of the lattice is the most energetically favorable for the adsorption of a H2 molecule, in all cases. The adsorption energy increases when the H2 is adsorbed through the alkaline atoms, K being the strongest adsorbent. As the H2 molecules are adsorbed on the K atom, the adsorption energy per molecule improves. The opposite happens in the cases of Li and Na. These results may be significant in the development of hydrogen storage systems based on solid state materials. Acknowledgements: Computing resources for this work were given by LANCAD project.

Authors : Chuangwei Liu,? Jie Zhang,? Yonggang Jin,? Chenghua Sun*,?
Affiliations : ? School of Chemistry, Faculty of Science, Monash University, Clayton, VIC 3800, Australia ? CSIRO Energy Flagship, PO BOX 883, Kenmore, QLD 4069, Australia ?Department of Chemistry and Biotechnology, Faculty of Science, Engineering & Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia

Resume : Electrocatalysts are essential to two key electrochemical reactions, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in renewable energy conversion and storage technologies such as regenerative fuel cells and rechargeable metal-air batteries. Density functional theory calculations were used to measure the free energy profile for OER on 2D boron monolayer, metal-free material, at room temperature in this work. Moreover, to rationally search for the best catalyst of boron sheet materials, we calculated the free energy and overpotential for elementary reactions of OER for all the possible active sites on 2D boron sheet doped with p-block elements. These calculations suggest that these materials have good performance of OER, which provide to a new class of low-cost, metal-free and efficient OER catalysts.

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Materials for Catalysis : M. Arrigoni
Authors : Antton Curutchet (1), Tangui Le Bahers (1), Amal BaQais (2,3), Ahmed Ziani(2), Hassan Ait Ahsaine (2), Sheikha Lardhi (2), Luigi Cavallo (2), Moussab Harb (2), Kazuhiro Takanabe (2), Philippe Sautet (4,5)
Affiliations : (1) Univ Lyon, ENS de Lyon, CNRS, Université Claude Bernard Lyon 1, Laboratoire de Chimie UMR 5182, F-69342 Lyon, France (2) KAUST Catalysis Center (KCC) and Physical Sciences and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), 4700 KAUST, Thuwal 23955-6900, Saudi Arabia (3) Department of Chemistry, College of Sciences, Princess Nourah bint Abdulrahman University (PNU), Riyadh 11671, Saudi Arabia (4) Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States (5) Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States

Resume : The search for novel efficient semiconductors for water splitting, that is photoelectrochemical conversion of water into O2 and high energetic H2, is an important and still growing field of research. To be efficient such semiconductors need to fulfil several requirements: Their bandgap (Eg) must be between 1.8 and 2.2 eV for efficient solar light absorption allowing sufficient photovoltage for water oxidation and reduction. layered materials, intensively studied for thermoelectric applications, would be excellent candidates if it wasn’t for their too small bandgap (at most 1.1eV for BiCuOS). To overcome to this issue, two options will be emphasized in this communication: In one hand, the lowering of valence band, driven by CuS layer, was investigated by simulating BiAgOS compound, with DFT calculations based on the HSE06 range-separated hybrid functional with inclusion of spin-orbit coupling. Resulting structure and electronic properties, in close agreement with the experimental values, confirmed the band gap increase. In the other hand, the conduction band was elevated by modifying BiO layer. To do so we designed Bi1-xRExCuOS solid solutions (RE = Y, La, Gd and Lu) that opened the door to bandgap tuning between pure BiCuOS value (Eg~1.1 eV) to pure RECuOS value (Eg~2.9 eV), reproducing experimental evidence for similar systems. The effect of Bi/RE mixing on the band positions and width, as well as charge transport properties, will be discussed in this presentation.

Authors : Hassan Ouhbi, Ulrich Aschauer
Affiliations : Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland

Resume : Photocatalytic water splitting on semiconductor surfaces is considered a promising route to produce clean hydrogen fuel. Since the discovery of this reaction by Fujishima and Honda using TiO2 under UV irradiation, various materials have been examined as visible light photocatalysts. Perovskite structured oxides hold particular promise due to their structural and chemical flexibility. Oxynitride perovskites additionally benefit from a smaller band gap compared to pure oxides, making them more promising for photocatalytic water splitting under visible light. In this work, we compare the surface chemistry of oxides and oxynitrides by investigating the oxygen evolution reaction with four proton-coupled electrons transfer steps on NaTaO3 (113) and SrTaO2N (001) surfaces. All free energy differences between reaction intermediates (OH*, O*, OOH*) are calculated using density functional theory (DFT) following Nørskov’s approach. Initially, we consider adsorption on a single reactive site. Our results predict a similar rate-determining step (formation of OOH*) for both surfaces, with a larger overpotential for the oxide than for the oxynitride. Following this, we establish the stable adsorbate coverage of each surface under photochemical conditions (pH, U) by computing the Pourbaix diagram and study the water oxidation steps under these conditions.

Authors : S.S. Gupta and M. A. van Huis
Affiliations : Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands

Resume : Metal-semiconductor (M-Sc) junctions have been a subject of wide scientific interest for their leading applications in electronics and photovoltaics. Over the last decade, these interfaces have also been exploited as a crucial component in nanoheterostructures, specifically for photocatalytic water-splitting and its important half-reaction of hydrogen evolution (HER). These semiconductor nanostructures have two physically crucial interfaces: one with the aqueous solution, and the other with the metal end. In our earlier work on the adsorption of water molecule-CdS surface [1], we had shown interesting cation vacancy motifs, which strongly chemisorb the water molecule. In the current work, we are focusing on the CdS-metal interface, which is solely responsible for enhancing the quantum efficiency of the photocatalytic mechanism, by physically separating the photogenerated charge carriers of the semiconductor. It is at this metal deposited end, that the important reduction reaction of obtaining hydrogen gas from liquid water takes place at room temperature. In our study, we have investigated the M-Sc interfaces of CdS (a very successful HER photocatalyst) with some of the relevant co-catalyst metal depositions using spin-polarised density functional theory calculations [2]. In the sub-nanometer size regime, many of the transition and noble metal clusters show unpaired electron density, for which a spin-polarized treatment becomes essential. These M-Sc interfaces were studied within the standard GGA-PBE functional, where we have exploited the fact that GGA-PBE already gives very accurate predictions of conduction band minima, and hence is suitable for predicting n-type Schottky barrier heights of these interfaces. Depositions of 13-atom and 55-atom clusters of Ni, Pd, Pt and Au were studied on the (1010) nonpolar CdS surfaces. Although these cluster sizes are in the non-scalable cluster regime, they were often shown to give optimal catalytic yield in HER experiments. For each metal, we selected a robust set of at least five metal clusters from the literature, with a wide range of (effective) coordination numbers, reactivity and stability, to study their isolated and interfacial properties. Depending on the chemical nature of the metal deposited on the CdS surface, interesting insights on cluster relaxation, atomic inter-diffusion, adhesion energies, n-type barrier heights could be made. Using the Sabatier principle for the HER, a criterium was drawn for the quality of the studied metal co-catalyst and CdS photocatalyst interfaces. Along with this, we also studied epitaxial depositions, which are also important as they resemble the various facets of the polycrystalline metal caps deposited on these nanostructures. The CdS-Metal interfaces with epitaxial mismatches smaller than 6% were studied. With such epitaxial modelling, we investigated the most stable epitaxial interface for different metal facets determining the initial stages of their epitaxial growth. In some cases, upon deposition of the metal overlayer on the substrate, spontaneous formation of extended row reconstructions were found to be the lowest-energy states, which can be experimentally tested. The barrier heights and the dipole strengths of the epitaxial interfaces were compared with the clustered depositions. From all these simulations, it becomes clear that the electronic properties and chemical reactivity of clustered or epitaxial CdS-metal interfaces are strongly dependent on both the size and morphology of metal clusters and on the epitaxial mismatches of the various metallic overlayers. Furthermore, in some cases, distinctly different behaviour was found when comparing the various metal depositions. This extensive modelling of the M-Sc interfaces with realistic sub-nanometre cluster sizes and extended epitaxial depositions has brought new insights into the physics and chemistry of these efficient nanoscale photocatalysts. [1] S.S. Gupta and M.A. van Huis, J. Phys. Chem. C, 2017,121 (18), pp 9815–9824 [2] S.S. Gupta, M.A. van Huis (in preparation).

Authors : Maria Bouri, Ulrich Aschauer
Affiliations : Department of Chemistry and Biochemistry, University of Bern, Switzerland

Resume : Solar water splitting is a promising process for green and renewable production of H2 as an energy carrier. Economic viability of this process however requires the discovery and design of materials with suitable photocatalytic properties. Oxides with the perovskite structure were shown to be potential candidates for photoelectrodes. However, their wide band gap restricts their photocatalytic activity to the UV part of the light spectrum. Substituting oxygen with less electronegative nitrogen narrows the band gap due to higher-energy nitrogen states, making oxynitrides suitable materials for solar water splitting. In addition, layered perovskites such as Ruddlesden-Popper (RP) phases are reported to have better photocatalytic properties than non-layered perovskites. This raises the question if layered oxynitrides will have an even better performance as photocatalysts than their non-layered counterparts. Although there are studies on layered bulk oxynitrides, the electronic features of their surfaces have not been studied to date. In present work, we investigate the structural and electronic properties of RP Sr2TaO3N bulk as well as its (001) and (100) surfaces by density functional theory (DFT) calculations. We focus on the electronic features of the surfaces and we show that the (001) TaON-terminated surface potentially exhibits promising photocatalytic properties due to the formation of nitrogen surface states that suppress electron-hole recombination.

Authors : Nathalie Vonrüti, Ulrich Aschauer
Affiliations : Department of Chemistry and Biochemistry, University of Bern, Switzerland; Department of Chemistry and Biochemistry, University of Bern, Switzerland

Resume : Perovskite oxynitrides are a promising class of material for photocatalytic water splitting under visible light, mainly due to their small band gaps. It has been shown for different oxynitrides that epitaxial strain can engineer the anion order as well as induce ferroelectricity, opening new possibilities to reach smaller overpotentials for the overall water splitting reaction. Using density functional theory, we analyse for the case of LaTiO2N as well as SrTaO2N the relationship between the anion order and polarity. We find a correlation between the two, which is caused by the larger ionic radii of nitrogen compared to oxygen. Further, we investigate changes in bandgaps for epitaxial strained oxynitrides with different anion orders in both the polar and nonpolar phase. We find the change in bandgap with epitaxial strain for oxynitrides to be intrinsically different compared to oxides. Most marked is the difference between polar oxides and oxynitrides: While for oxides polarity can increase the band gap up to 0.1 eV in a strain range of 4%, in oxynitrides polarity can increase the band gap in the same strain range by almost 1 eV. Therefore, especially for SrTaO2N, which we find to be polar already at zero strain, suppression of ferroelectric distortions, for example by increasing temperature, might significantly decrease the band gap and lead to a large increase in the photocatalyst's efficiency.

Authors : Heechae Choi, Sovann Khan, Seungchul Kim, So-Hye Cho
Affiliations : 1) Virtual Lab Inc.; 2)Korea Institute of Science and Technology

Resume : Seeking ideal heterostructured photocatalyst components is extremely time-consuming and ineffective way because of many requirements for being good photocatalysts in heterojunctions. In this talk, computational methods to select ideal photocatalytic materials using DFT calculations will be introduced. In addition, our recent successful computational and experimental works where predictions from DFT calculation guided real materials syntheses in cost-effective way.

Authors : D. Zagorac, J. Zagorac, H. Mueller, S. Rehme
Affiliations : D. Zagorac, J. Zagorac, Institute of Nuclear Sciences Vinča, Materials Science Laboratory, Belgrade University, Belgrade, Serbia and Center for the synthesis, processing and characterization of materials for use in extreme conditions “CEXTREME LAB”, Laboratory for Theoretical Investigation of Materials (L-TIM), Belgrade, Serbia; H. Mueller, S. Rehme, FIZ Karlsruhe – Leibniz Institute for Information Infrastructure, Karlsruhe, Germany

Resume : The Inorganic Crystal Structure Database (ICSD) is the world's largest database of fully evaluated and published inorganic crystal structure data mostly obtained from experimental results. However, the purely experimental approach is no longer the only route to discover new compounds and structures. In the past decades numerous computational methods for simulating and predicting structures of inorganic solids have emerged. On the other hand there are numerous problems with storing theoretical data, e.g. the great amount of (un)published work, discarding criterion, variety of methods/codes, no standardization, etc. Starting with the last year ICSD release, the scope of the database is extended to include theoretical structures. We would like to highlight that each theoretical structure has been carefully evaluated according to the several criteria and published in a peer review journal, while the theoretical CIF file has been upgraded and standardized, completely coherent with the experimental one. Furthermore, we show a complete systematics of theoretical methods for the first time, including additional categories (remarks) used for comparison of the experimental and theoretical data, e.g. predicted structures, excellent tool for synthesis planning, or optimized structures, excellent tool for properties investigation. Finally, we present keyword option, which in combination with previous features is another excellent tool in computational and experimental material science.

Authors : D. Selli,1,* G. Fazio,1 G. Seifert,2 C. Di Valentin 1
Affiliations : 1 Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Milano, Italy 2 Technische Universität Dresden, Institut für Theoretische Chemie, D-01062 Dresden, Germany

Resume : Among all the synthesized nano titania, high curvature nano-systems, e.g. nanospheres (NSs) or nanorods, are of prominent interest for TiO2 functionalization in photoapplications and biomedicine. TiO2 NSs are fundamental building blocks of technologies that operate in an aqueous environment, thus understanding their interaction with water is of extreme importance. Despite the great interest on TiO2 nanoparticles and their interaction with water, quantum chemical studies have been, so far, limited to low index TiO2 surfaces, due to the large size of realistic TiO2 NSs. However, titania flat surfaces are far to be representative of the real highly curved surface of nanospheres. We present an innovative computational approach, which allows to tackle the complexity of realistic TiO2 nanospheres (with a diameter of 2.2 nm) interacting with water multilayers, keeping a quantum chemical level of theory. First, we use an highly performing DFT-based semiempirical method, namely density functional tight-binding theory (SCC-DFTB), to obtain globally optimized NSs structure in vacuum. Second, we set up new SCC-DFTB parameters to simulate the interaction between TiO2 and water with an accuracy comparable to DFT. Finally, the static and dynamic interaction of the NSs with water is studied at both DFT (only static) and SCC-DFTB (static and dynamic) level of theory. This study gives a precious atomistic insight on the processes occuring at the TiO2 NS/water interface and on the influence of the aqueous medium on the NS structural and electronic properties.

Authors : J. Sjakste
Affiliations : Laboratoire des Solides Irradies, Ecole Polytechnique, CNRS UMR 7642, CEA-DRF-IRAMIS, Paris-Saclay University, 91128 Palaiseau, France.

Resume : Understanding hot carrier dynamics is crucial for the development of photovoltaic and optoelectronic devices. Electron scattering by phonons is one of the major processes that determine the relaxation dynamics iof hot carriers. Recently, we have developed a computational method, based on density functional theory and on interpolation of the electron-phonon matrix elements in Wannier space, for the calculation of the electron-phonon coupling in polar materials [1]. This method allowed us to successfully interpret the dynamics of hot electron relaxation in bulk GaAs, in excellent agreement with time- and angle- resolved photoemission experiment by the group of K. Tanimura (University of Osaka, Japan). We have demonstrated, for the relaxation of hot carriers in GaAs, the existence of two distinct relaxation regimes, one related with the momentum, and the other with energy relaxation [2]. Interestingly, the energy relaxation times become faster at lower energies. Furthermore, we will present our new results on hot electron relaxation dynamics in Ge and in InSe, which we compare to recent ARPES and transient optical spectroscopy experiments. [1] J. Sjakste, N. Vast, M. Calandra, and F. Mauri, Phys. Rev. B 92, 054307 (2015) [2] H. Tanimura, J. Kanasaki, K.Tanimura, J. Sjakste, N. Vast, M. Calandra, F. Mauri Phys. Rev. B 93, 161203(R) (2016)

Authors : Vijay Singh, Ambroise van Roekeghem, Natalio Mingo
Affiliations : CEA-Liten, Grenoble, France

Resume : Functional materials that intelligently adapt to changing environmental conditions, have long been the focus of scientific investigation because of the never-ending demand for smaller, cheaper, faster, and energy efficient devices. In this talk, I will first discuss basic concepts and mechanisms of several intelligent materials, focusing mainly on ferromagnetic shape memory alloys. I will present recent in silico studies that reveal the underlying physics behind these novel features. Thereafter, I will discuss the atomic and electronic structure of next-generation photovoltaic (PV) materials, such as hybrid-perovskites, kesterites, and all-inorganic perovskites solar cell materials. To elucidate the electronic, magnetic, optical and chemical bonding properties of these materials, we have employed first-principles density functional theory. The phononic properties (i.e. lattice dynamics) were investigated using first principles density functional perturbation theory and a direct, supercell force-constant approach. To treat anharmonic effects beyond perturbation theory, we have used our inhouse code, Self-consistent force constants (SCFCS). This talk will illustrate how theoretical results can highlight physical materials properties that might be important for the development of intelligent next generation functional materials.


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Symposium organizers
Jesús CARRETE MONTANAInstitute of Materials Chemistry, TU Wien

Getreidemarkt 9/165, A-1060 Vienna, Austria

+43 (0) 6803300610
Massimo CELINOEnergy Technologies Department, ENEA

C. R. Casaccia, Via Anguillarese 301, 00123 Rome, Italy

+39 0630483871
Natalio MINGOLaboratory for Innovation in New Energy Technologies and Nanomaterials, CEA Grenoble

17 rue des Martyrs, 38054 Grenoble, France

+33 (0) 438780160