Solid state ionics: advanced concepts and devices

Resume : The integration of highly crystalline (lithium-based) oxide thin films on silicon substrates is essential in order to fabricate high performance solid-state devices, especially for microbattery and memristor applications. However, growing epitaxial oxide films directly on silicon requires high deposition temperatures (~600°C) and often high oxygen partial pressures, which leads to undesirable species (e.g. SiO2 and silicates) that compromise the crystal quality of the oxide. To overcome this, 3 nm of γ-Al2O3 was used as a passivation layer prior to the growth of the desired oxide on Si(111) substrates. Li4Ti5O12 (LTO) was chosen as a representative oxide for use in both batteries and memristors. XPS as well as in- and out-of-plane XRD measurements confirmed the sharp heterostructure interface and the high quality of the epitaxial LTO films. Excellent electrochemical cycling was also achieved for the stack against lithium metal in a conventional liquid electrolyte. In order to make a solid-state microbattery, a solid electrolyte (LiPON) was first sputtered on the LTO/Al2O3/Si stack followed by deposition of metallic lithium or amorphous silicon (a-Si) as the counter electrode. For the latter, LTO was successfully chemically lithiated beforehand, since as-deposited LTO and a-Si do not structurally possess mobile lithium ions. Beyond microbatteries, we will discuss the promising attributes of a stack consisting of chemically lithiated LTO with a-Si for memristive devices.

Resume : The interface between 8% mol yttria stabilized zirconia (YSZ) and acceptor doped ceria has important technological applications as these two oxides are usually coupled in high temperature solid oxide fuel cells (HT-SOFC) to improve the stability of the electrolyte at the interface with the cathode. Thin films and multilayers are useful model systems to study interface effects which can affect the conductivity, such as strain, space charge effect and interdiffusion. In this work, multilayers of YSZ and samaria doped ceria (SDC) are grown by pulsed laser deposition, increasing the number of layers and consequently of interfaces and keeping the thickness constant. While no structural variation is observed between bulk and interface, electron energy loss spectroscopy highlights the reduction of cerium ions in a 2 nm thick layer at each interface with YSZ. Concurrently, the conductivity measured in plane, decreases increasing the number of interfaces, suggesting the progressive confinement of the ionic conduction to the YSZ layers. The analysis of the conductivity data indicates the formation of an insulating layer of about 2 nm at each interface. At these interlayers both ionic and electronic conduction are very small compared to YSZ and SDC bulk.

Resume : Proton-conducting ceramics, such as yttrium doped barium zirconates/cerates referred to as BZCY, are studied for intermediate temperature applications, including protonic-ceramic fuel/electrolysis cells, electrochemical compressors, or catalytic membrane reactors. In the presence of steam, the material hydrates with the consumption of oxygen vacancies and the formation of protonic defects. Hydration-induced chemical expansion (lattice expansion upon protonic defect formation) can be critical during the sample preparation and testing. Techniques for thermal and chemical expansion measurements will be presented together with challenges associated with analysis and interpretation. A short overview of the literature data on the expansion in proton-conducting ceramics will be provided. While all these measurements are performed in a single atmosphere, it is important to predict the expansion with different gas compositions on both sides of the membrane, thus representing real device applications. To do so, we developed a computational model based on a Nernst-Planck-Poisson formulation and included a chemo-thermo-mechanical component. Examples of crack formation due to uncontrolled hydration on symmetrical cells (BZCY-NiO//BZCY//BZCY-NiO) prepared by tape-casting will be shown.

Resume : Proton conducting ceramic electrolyte possesses attractive features – higher ionic conductivity than oxygen ion conductor and lower activation dependency on the temperature – and enables SOFCs to operate at lower temperatures (400 – 600oC). In addition, higher fuel utilization and carbon coking resistance can be achieved. However, crucial technical challenges on cell fabrication, especially establishing a chemically homogeneous and physically thin electrolyte layer, have been limiting its commercial implementation. These challenges mainly stem from the refractory nature of the proton-conducting electrolytes. It makes the densification behavior of the electrolyte in PCFCs difficult to control and in most cases, negatively impacts on its ionic conductivity. As a result, protonic ceramic fuel cells has been demonstrated a frustrating performance and scalability (an anode support size of at most 3cm^2). Here, we present breakthroughs in the performance and scalability of PCFCs: a high peak power density of 1.3 W/cm^2 in a size of 5x5 cm^2 was obtained at 600°C. The advances stem from an anode-assisted facile densification of a proton-conducting electrolyte on a structurally and compositionally uniform anode support. We show that an internal supply of sintering aid from the anode to the electrolyte as well as an excess shrinkage force driven by the anode effectively promote the densification of the very thin electrolyte (less than 5 μm thick) of BaCe0.55Zr0.3Y0.15O3-δ at much lower temperature of 1350°C while retaining initial chemical composition, leading to a low area-specific ohmic resistance of 0.09 ohm·cm^2. Furthermore, since all of the utilized fabrication processes are cost-effective, consistent, and readily scalable, our results fulfill the requirements of high performance, scalability, and cost efficiency for achieving commercial feasibility of PCFCs as cooler ceramic fuel cells.

Resume : 3D printing of ceramic functional materials has been a breakthrough for ceramic manufacturing technologies. Additive manufacturing allow to generate complex designs while reducing the wasted material bringing clear advantages in terms of functional ceramic materials fabrication. This freedom of design allows to propose high surface area geometries for the electrolytes. Performances of energy devices such as Solid Oxide Cells (fuel cell and electrolyser) show a direct dependence with their active surface area. In this work, yttria stabilized zirconia electrolytes of solid oxide fuel cells and electrolysers have been produced by additive manufacturing technology (SLA) and electrochemically tested. Here presented approach propose new complex geometries of the electrolytes that enhance the active surface (ca. +60%) per projected area. The produced cells show improvements of the final performance (maximum power density and injected current) proportional to the promoted enhance of the area by using the advantages og the 3D printing. The study of the I-V polarizations curves, on SOFC and SOEC modes, and the electrochemical impedance spectroscopy (EIS) results are presented to discuss the described improvements.

Resume : Introducing cathode materials with high oxygen reduction reaction (ORR) activity is one of the best ways to lower the operating temperature of solid oxide fuel cells with sustaining high performance. La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) can be a candidate with high ORR activity, but it reacts with yttrium-stabilized zirconia (YSZ) electrolyte, forming an insulating layer. As a result, forming a gadolinium-doped ceria (GDC) barrier layer is essential. Problems still remain such as delamination due to discrepancy of thermal expansion coefficient between YSZ electrolyte and GDC barrier layer, the formation of insulating layer at the high annealing temperature. In this study, we describe a well-designed structure with a thin GDC barrier layer and a nano-web-structured LSCF thin-film layer (NW-LSCF) via introducing a facile spin-coating method. A dense GDC barrier layer with a thickness of approximately 400nm was coated on a YSZ electrolyte without delamination at a low annealing temperature. In addition, the introduction of NW-LSCF layer enhanced ORR owing to an increased triple-phase boundary length. Cells employing a GDC barrier layer and NW-LSCF interlayer showed excellent electrochemical performance and stable operating behavior. The peak power density reached 2.14 W/cm2 and the voltage degradation rate measured under galvanostatic mode was below 0.025% per hour at an operating temperature of 650oC.

Resume : Global warming and its consequences over environment have boosted the investigation of alternative energy sources for the reduction of CO2 emissions, and consequently, the dependence on fossil fuels. In addition, the scientific community efforts have focused on the CO2 transformation into added value chemicals and fuels. H2 is a flexible energy carrier and can be produced from water, with a low CO2 footprint. Among the technologies employed for H2 production, water electrolysis, is an efficient, green and commercial technology and if combined with CO2 electrolysis comes up as promising clean route for synthetic fuel production, such as CH4. Thus, in this work we have evaluated CH4 production via co-electolysis focusing on the selection of the most suitable catalyst for a high CH4 yield. Firstly, Ce0.9Gd0.1O2-δ-Ni (GDC-Ni) composite electrode was developed to ensure a proper electronic and ionic conductivity, and to guarantee a good porosity and electrode-electrolyte adhesion. In that direction, different Ce0.9Gd0.1O2-δ:Ni ratios and sintering temperatures were assessed. In a second step, a fixed-bed reactor was employed for the methane catalyst selection. The GDC-Ni powder was impregnated with different metal (Cr, Cu, Ni, Rh, Ru, Pd and Mo) precursors and tested in the co-electrolysis conditions to select the catalyst with the highest yield and selectivity to CH4. Finally, a fully-assembled co-electrolysis cell consisting of Sc doped Yttria as electrolyte and GDC-Ni and LSM-GDC as cathode and anode, respectively, was manufactured. Different current densities and temperatures were selected to study the methane production. The exhaust gas was monitored by a mass spectrometer and gas chromatograph.

Resume : Micro-tubular type solid oxide fuel cells are considered as the advantage of short gas sealing line and higher thermal stability. A micro-tubular type solid oxide cell was prepared by using a tubular type NiO-Y2O3 stabilized ZrO2 (NiO-YSZ) fuel electrode substrate and La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte film which was prepared by dip-coating and co-sintering method. Since IR loss and overpotential was still larger than those expected, the effects of insertion Ni-based fuel electrode functional layer on NiO-YSZ tubular substrate and rare earth oxide infiltration into NiO-YSZ tube was further studied. The result indicated that the cell using Ni-Fe functional layer and infiltration of CeO2 into the substrate shows a higher maximum power density. The electrolysis performance of the prepared tubular cell under reversible operation was also studied. The reasonably large current density was also realized in electrolysis mode on the optimized cell. The results indicated that the cell using CeO2 infiltration and Ni-Fe layer was highly effective for increasing the power density due to much decreased IR loss and overpotential of fuel electrode, in particular at low temperature. In addition, cyclic SOFC and SOEC operation, which means SORC performance was also successfully demonstrated.

Resume : Thin-films deposited by Pulsed Laser Deposition (PLD) have enabled the fabrication of cathodes for solid oxide cells (SOC) to possess various microstructures, crystalline states and surface chemistry. These films are often subjected to various post-thermal treatments which influence the chemical activity and stability of the films. Here, we investigate how the catalytic activity is affected by the thermally induced surface restructuring in complex transition metal oxides, in particular, La0.6Sr0.4CoO3-δ (LSC) thin films grown by PLD. To this end, the influence of substrate temperature during PLD as well as post-annealing treatments on the film microstructure and surface chemistry were studied. In comparison to high-temperature grown films, the post-annealed low-temperature grown ones showed 2-times lower degradation rate in long-term electrochemical tests at 500 °C. The differences in the electrochemical activity were found to be related to the initial microstructure and morphology of the films. After long-term tests at 500 °C, the low-temperature grown film showed localised Sr-segregation into protruding particles, leaving the remaining surface with catalytically active stoichiometry. On the other hand, the high-temperature grown films showed a fully covered surface with Sr-rich particles, which continued to thicken with time. Here we emphasise the importance of thermal treatments on catalytic activity and stability of the SOC electrode films and propose that it should be considered as among the main pillars in the design of the active surface.

Resume : BaFeO3-δ perovskites with mobile oxygen vacancies, holes, and protons, can be used as cathode material for Protonic Ceramic Fuel Cells (PCFC). Their mixed conductivity including protons is important to activate the whole cathode surface for the oxygen reduction. The proton concentration in such cathode perovskites was determined by thermogravimetry. [1,2] Crystal structure, symmetry and local lattice distortions have an important impact on the proton uptake. Partial substituion of Fe by redox-inactive and oversized Zn2+ or Y3+ is beneficial for proton uptake. [2] This can be assigned to local lattice distortions decreasing the covalency of Fe-O bonds, and thus enhancing the basicity of oxygen ions. The local environment and bonding of the cations and of O2- is probed using Extended X-Ray Absorption Fine Structure (Fe,Zn,Y K-edges) and X-Ray Raman Scattering (O K-edge) for oxidized ("Fe4+"), reduced ("Fe3+") and hydrated samples. The rather small Fe edge shift between reduced and oxidized samples and strong pre-edge features at the O K-edge indicate that electron holes are largely delocalized to oxygen states. [3] Together with the EXAFS analysis of the lattice distortions without and with Zn2+ ,Y3+ , this yields a comprehensive understanding of proton uptake in PCFC cathodes, and indicates possibilities to optimize them. [1] D.Poetzsch et al. Phys.Chem.Chem.Phys.16,16446(2014) [2] R.Zohourian et al. Adv.Funct Mater.28,1801241(2018) [3] G. Raimondi et al., to be submitted

Resume : Hydration of double perovskite (DP) BaLnCo2O6-δ for a large range of lanthanides is investigated by Thermogravimetry (TG), Secondary Ion Mass Spectroscopy (SIMS), Neutron Diffraction (ND), and atomistic modelling. The relationship between structure, electronic configuration, and cation composition is investigated by use of ND, Synchrotron Radiation Powder X-ray Diffraction (SR-PXD), X-ray Photoelectron Spectroscopy (XPS), and Scanning Transmission Electron Microscopy (STEM). Incorporation of protons in the hydrating DP compositions is a sluggish, multi-step process involving oxidation or reduction, depending on temperature and atmosphere / atmospheric history. Conductivity measurements in combination with TG with H2O/D2O exchange give indications of the proton incorporation mechanism and the interplay between electronic states and hydration. XPS gives information about electronic states, SIMS gives concentration profiles of 2H from surface to bulk, and STEM shows cation disorder upon hydration and gives indication of charge ordering in the Co layers, possibly affecting the stability of protons through the basicity of the adjacent oxide ions. The screening of lanthanides has given a new insight to the prerequisites for incorporation of protons in DP cobaltites suitable as electrode materials in Proton Ceramic Electrochemical Cells. Financial and scientific contributions from the Research Council of Norway (Grant nᵒ 272797 “GoPHy MiCO”) through the M-ERA.NET Joint Call 2016.

Resume : Accepter doped ceria, Ce1-xRExO2-d, where RE = rare earth, has been widely investigated for its oxide-ion and electronic conduction properties, while the transport of other ionic charge carrier species is less well understood. The diffusivity and surface catalytic properties of oxide-ions and protons has been investigated by means of isothermal isotopic exchange depth profile using secondary ion mass spectrometry (IEDP-SIMS) and electrochemical impedance spectroscopy (EIS). Over an intermediate temperature range (500 – 800oC), diffusion analysis has identified that tracer exchange and transport rates of the protonic species were dependent on both the pH2O and pO2 of the exchange atmosphere. The EIS and exchange data were found to be in excellent agreement. This paper will therefore discuss the fundamental and novel mechanistic insights into the solid/gas interfacial kinetics and ion transport through rare earth doped ceria.

Resume : The utilization of mesoporous CGO came to the fore as scaffold material for Solid Oxide Cell (SOC) applications, because of its ability to furnish a high surface-active area (BET~100m2/g). The large pore volumes and good thermal stability are essential prerequisites to design optimal infiltration of the scaffold by mixed ion-electron conductor (MIEC) perovskites such La1-xSrxCo1-yFeyO3-δ (LSCF). [1] However, the mesoporous CGO scaffolds suffer of some drawbacks like SiO2 contamination, derived by the followed nanocasting hard template method by KIT 6. [2] In addition, the fabrication process is limited by the sintering temperature of the scaffold that can promote the collapse of the nanostructure. [3] A twofold strategy is proposed to overcome the presented issues: firstly, the removal of residual silica by an optimized chemical etching process leading to an improvement of the ionic conductivity of the scaffold. Secondly, the use of Co oxide nanoparticles as sintering aid allows a fine tune of the sintering temperature that ensures the attaching maintaining a nanostructured scaffold. The effectiveness of this approach was demonstrated by a series of complementary techniques such: SEM, XRD, SAXS, ICP-MS, BET, TPR and by impedance spectroscopy measurements.[4] A complete SOC was electrochemically measured to prove such enhancements in terms of performances. 1 E. Hernández, F. Baiutti, A. Morata, M. Torrell and A. Tarancón, J. Mater. Chem. A, 2018, 6, 9699–9707. 2 P.-S. Cho, Y. H. Cho, S.-Y. Park, S. B. Lee, D.-Y. Kim, H.-M. Park, G. Auchterlonie, J. Drennan and J.-H. Lee, J. Electrochem. Soc., 2009, 156, B339. 3 L. Almar, T. Andreu, A. Morata, M. Torrell, L. Yedra, S. Estradé, F. Peiró and A. Tarancón, J. Mater. Chem. A, 2014, 2, 3134. 4 S. Anelli, F. Baiutti, A. Hornés, L. Bernadet, M. Torrell and A. Tarancón, J. Mater. Chem. A, 2019, 3, 10031–10037.

Resume : Within the Ruddlesden-Popper (RP) series Lnn+1BnO3n+1, the first order (n=1) RP-type rare earth nickelates with Ln=La, Nd, Pr and B=Ni are known for their high oxygen diffusivities as well as good electronic as well as ionic conductivities. A drawback for their application as air electrode in solid oxide fuel and electrolyser cells is the low oxygen surface exchange kinetics. In order to improve this property, partial substitution of Ni by Co on the B-site in Pr2NiO4+δ (PNO) was recently investigated [1]. Electrochemical impedance spectroscopy (EIS) measurements were performed on microelectrodes fabricated from dense thin films to obtain oxygen surface exchange rates of Pr2NiO4+δ and Pr2Ni0.9Co0.1O4+δ between 550 and 800°C. Compared to Pr2NiO4+δ, Pr2Ni0.9Co0.1O4+δ showed increased oxygen surface exchange rates especially at lower oxygen partial pressures [2]. In order to understand the oxygen nonstoichiometry δ of Pr2NiO4+δ and Pr2Ni0.9Co0.1O4+δ as function of pO2 and T, a defect chemical analysis was performed for both compounds. Cell tests with Pr2Ni0.9Co0.1O4+δ / GDC composites as SOEC air electrode on anode supported cells were performed for water electrolysis up to current densities of 1000 mA cm-2 at 800°C. [1] C. Berger et al., Solid State Ionics 2018, 316, 92. [2] C. Berger et al., J. Electrochem. Soc. 2019, 166 (14), F1088.

Resume : Memristive devices are attracting a great deal of attention for memory, logic and sensing applications due to their simple structure, high density integration, low-power consumption, and fast operation. In particular, multi-terminal structures controlled by active gates would certainly provide novel concepts for reconfigurable electronic systems with engineered functionality. In this work we will show the potential of reversible field-induced metal-insulator transition (MIT) in strongly-correlated metallic oxides for the design and obtention of multi-terminal memristive transistor-like devices [1, 2]. We have studied the highly correlated cuprate YBa2Cu3O7-δ as a model system, which is able to display non-volatile volume MIT, driven through local oxygen migration. In this way, vertical and lateral oxygen mobility may be modulated, at the micro- and nano-scale, by tuning the applied bias voltage and operating temperature. The key advantage of this material is the possibility to homogeneously modulate the oxygen vacancy diffusion not only in a confined filament or interface, as observed in widely explored insulating strongly correlated oxides, but also toward the whole film thickness. We will show different device configurations in which the lateral conduction of a bridge is controlled by active gate-tunable volume resistance changes. Large design flexibility can be obtained by changing the switching performance of different gates, thus offering the possibility to locally adjust the conductance response as required for non volatile memories and neuromorphic functionalities. References [1] A. Palau et al. ACS Applied Materials & Interfaces. 10, 30522, 2018 [2] J.C. Gonzalez-Rosillo et al. Adv. Elect. Mater. 1800629, 2019

Resume : The chemo-mechanical effect in solids refers to dimensional change due to change in stoichiometry. Dimensional change due to electrochemically-induced compositional change has been termed the electro-chemo-mechanical (ECM) effect. The chemical instability inherent in this effect is clearly deleterious for batteries or fuel cells, but, as recently suggested, has potential for use in actuation[1]. The structure of the actuator device that operates on the ECM principle is a micrometer thick solid electrolyte (SE) sandwiched between two ECM-active layers (ActLs). An electrochemical reaction must occur in these layers, causing them to expand or contract. In order to facilitate the ECM response, these layers must have mixed ionic and electronic conductivity and a large chemical expansion coefficient. We have constructed a thin film, ECM actuator comprising 20mol% Gd doped CeO2 (20GDC) as the SE and [Ti oxide\20GDC] composite as the ActL. Selected area electron diffraction measurements showed the composite to be nanocrystalline, a morphology that enables interfacial oxygen ion diffusion. Synchrotron X-ray absorption measurements of the ActL identified the chemical composition to be a mixture of Ce3 /Ce4 and Ti3 /Ti4 oxidation states. The deformation of the ECM actuator was determined to be in the bending regime producing large vertical displacements (~2 μm) and more than ~8 MPa stress. [1] J. G. Swallow et al., Nat. Mater. (2017) 16, 749

Resume : Wide band gap semi-conductors such as SrTiO3 (STO) have attracted high interest for photoelectrochemical water splitting and as part of photovoltaic cells. However, the impact of UV irradiation on the composition (e.g. the oxygen content) of STO and Fe doped STO (Fe:STO) at elevated temperatures has hardly been studied. In this contribution, we show that exposure to UV light at ca. 350 °C in air causes a filling of oxygen vacancies in STO. An chemical potential equal to a p(O2) in the range of GPa can be realized in Fe:STO. Due to this oxygen incorporation and subsequent electron hole formation, UV irradiation thus leads to an increase of the in-plane bulk conductivity by up to a factor of 10^3 in STO. These thermodynamic effects but also their kinetic counterparts (chemical diffusion coefficients) were examined in dependency of temperature and p(O2) using an electrochemical oxygen pump. Moreover, space charge effects leading to photovoltages and additional semicircles in the impedance spectra are discussed.

Resume : Due to their well-defined, tunable nanoporous structure and their long-range order, crystalline metal-organic frameworks (MOFs) present an ideal model system for the investigation of the ionic mobility under nanoconfinement. Here, the dynamic properties of room-temperature ionic liquids (IL) in the nanopores of MOF thin films are investigated. The experimental data supported by molecular dynamic simulations show that the percentage of pore filling of a prototype IL ([BMIM][NTf2]) in MOFs of type HKUST-1 has a tremendous impact on the dynamic IL properties.[1] The conductivity and ion mobility decreases by three orders of magnitude when the pores of the MOFs are filled with IL. Detailed investigation unveil that mutual pore blockage of the cation and anion results in transient pore jamming, responsible for the conductivity drop. Moreover, it will be presented that photochromic molecules can be incorporated in the MOF structure, resulting in photoswitchable nanoporous materials. There, the ionic conduction of protons[2,3] and ionic liquids in the nanopores can be photomodulated. [1] A.B. Kanj, R. Verma, M. Liu, J. Helfferich, W. Wenzel, L. Heinke Nano Lett. 19 (2019) 2114-2120. [2] K. Müller, J. Helfferich, F. Zhao, R. Verma, A.B. Kanj, V. Meded, D. Bléger, W. Wenzel, L. Heinke Advanced Materials 30 (2018) 1706551. [3] A.B. Kanj, A. Chandresh, A. Gerwien, S. Grosjean, S. Bräse, Y. Wang, H. Dube, L. Heinke Chem. Sci., 2020, DOI: 10.1039/c9sc04926f.

Resume : Heat flux and temperature are key parameters to measure in order to regulate any physical, chemical, and biological processes. New emerging technologies, e.g. electronic-skin and interactive buildings, are in the need of accurate temperature or heat flux sensors, that are also mechanically flexible and easily projected onto large areas. Thermopiles can provide accurate and stable heat flux and temperature reading but the technology today is based on inorganic materials that have low Seebeck coefficient (100 µV K–1) and are brittle and difficult to scale up to large areas. Recently, polymer electrolytes have been proposed for thermoelectric devices because the ionic thermodiffusion in such materials can lead to giant ionic Seebeck coefficient. [1, 2] Here we introduce a solid “ambipolar” ionic liquid polymer gel showing a giant negative ionic Seebeck coefficient (-4,000 µV K–1). The Seebeck coefficient can be tuned from negative to positive (up to +14,000 µV K–1) by adjusting the polymer matrix composition. Nuclear magnetic resonance spectroscopy, Raman and infrared spectroscopy analysis shows that the interaction between the ion and the polymer is the key factor in controlling the sign and magnitude of the ionic Seebeck coefficient. The ionic thermodiffusion in the polymer gel can be combined with pyroelectric response to enhance the heat detecting performance. [3] The presented integrated concept provides both rapid initial response upon heating and stable synergistically enhanced signals upon prolonged exposure to heat stimuli. 1. Zhao, D., Wang, H., Khan, Z. U., Chen, J. C., Gabrielsson, R., Jonsson, M. P., Berggren, M., Crispin, X., Ionic thermoelectric supercapacitor, Energy Environ. Sci., 9, 1450-1457 (2016). 2. Zhao, D., Fabiano, S., Berggren, M., Crispin, X., Ionic thermoelectric gating organic transistors, Nat. Commun., 8, 14214 (2017). 3. Chaharsoughi, M. S., Zhao, D., Crispin, X., Fabiano, S., Jonsson, M. P., Adv. Funct. Mater. 29, 1900572 (2019).

Resume : The traditional Li-ion chemistry is approaching its physicochemical limit. In order to power up the electro-mobility of the future, a paradigm shift is required at the fundamental materials level. Traditional intercalation electrode materials simply act as host for Li-ions, while in conversion and alloying chemistries they “actively” participate to the charge storage mechanism causing severe volume changes and ultimately poor cycle life. In my talk, I will discuss electro-chemo-mechanical and interfacial challenges common to conversion and alloying materials, using phosphorous, lithium and iron(II) fluoride as model material systems.

Resume : Na metal all-solid-state batteries could bring a solution to three objectives for next-generation batteries: an improved safety, a higher energy density and a reduced environmental impact. Safety wise, the absence of an organic liquid electrolyte makes solid-state batteries less flammable; the energy density increase in solid-state batteries originates from the use of high capacity Na metal anodes and high voltage cathodes; the reduced environmental impact comes from the replacement of Li (a limited and geographically poorly distributed resource) by abundant, easily accessible (and therefore cheap) Na. Early work in the field of solid-state batteries has focused on improving the ionic conductivity of solid electrolytes to match the ionic conductivity of liquid electrolytes. Among good Na conducting ceramic solid electrolytes, the family of Na SuperIonic CONductors (NaSICON) of composition Na1 xZr2SixP3-xO12 (0 ≤ x ≤ 3) has long been recognized for its remarkably high ionic conductivity. In recent work, a total ionic conductivity of 5.0 mS.cm-1 at room temperature has been reported for the composition Na3.4Zr2Si2.4P0.6O12 1. Combining this highly conductive solid electrolyte with Na metal anodes however raises some challenges. The Na metal/NaSICON interface is indeed characterized by a large Area Specific Resistance (ASR) 1,2; the stability of Na metal versus NaSICON and the formation of a resistive Solid-Electrolyte Interface (SEI) still has to be more fundamentally understood. This work addresses the challenge of minimizing the large Na metal / NaSICON interfacial resistance. Two routes to achieve low ASR have been identified: 1. Improving the contact between the anode and electrolyte by applying uniaxial pressure during cell assembly; 2. Altering the NaSICON surface chemistry to improve its wettability. The influence of applied pressure and of surface treatments (rough polishing, fine polishing, post-polishing annealing) on the ASR was analysed by Electrochemical Impedance Spectroscopy (EIS). The samples’ surface chemistry was analysed by X-ray Photoelectron Spectroscopy (XPS), Low Energy Ion Scattering (LEIS) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The samples’ surface roughness was measured by light interferometry to interpret the observed differences between fine and roughly polished samples.

Resume : Sodium (Na) metal is an appealing anode material for Na batteries because of its high theoretical specific capacity of 1166 mAh g-1 and low electrochemical potential of -2.71 V versus standard hydrogen electrode.[1] However, the long-standing issue of dendrite growth during repeated Na plating and stripping hinders the practical use of Na-metal anodes for high energy density batteries. Rational assembly of Na metal with 3D hosts has been proven to be an effective way to accommodate the large volume changes arising from Na plating/stripping and reduce the local current density so as to mitigate the Na dendrite growth.[2] Unfortunately, Na metal tends to deposit on the top part of 3D hosts near the separator, known as the “top-growth” mode, leading to poor utilization of internal voids. Here, we report the fabrication of 3D sodiophilic-sodiophobic gradient hosts, Au/CF, by sputter coating of Au on the bottom part of melamine-derived carbon foam scaffold, which can guide a “bottom-up” deposition. As a result, the Na@Au/CF composite anodes can run for 1000 h with a steady overpotential of ~20 mV at a current density of 2 mA cm-2 in symmetric cells, illustrating its great potential in stabilizing Na deposition. In addition, the Na@Au/CF anode exhibits much better electrochemical performance than the Na@CF host without Au coating when coupled with a Na3V2(PO4)2F3 and sulfurized polyacrylonitrile cathode. The sodiophilic-sodiophobic gradient structure paves a new avenue for stable Na metal, which can also be extended to other types of metal anodes.

Resume : Complex hydrides are a fascinating class of materials that were deeply investigated for solid-state hydrogen storage. The interest of the scientific community on those chemicals has been recently drawn again since it was shown that, in particular conditions, they allow fast cationic conduction. However, elevate ionic motion occurs only after a structural phase change, which is generally far from room temperature (rt). Many efforts have been made in order to decrease the phase transition temperature, which has been found also influenced by the nature, size and shape of the hydride's anion. Therefore, frustrating the anion sublattice, either by anion replacing or anion mixing, is an effective strategy to stabilize towards rt the fast conductive phase, taking into account that interesting ionic conductivity for practical purpose should be above 1 mS cm-1 at 25°C. Lying on this approach, we recently develop a new group of fast Na+ conductors, obtained by mechanical mixing of different closo- and carbacloso-borates. Among them, Na4(CB11H12)2(B12H12) features a superior ionic conductivity of 2 mS cm-1 at rt, with a low activation energy of 314 meV. Temperature-dependent synchrotron powder X-rays diffraction shows neither further phase transitions nor decomposition up to 500°C. Electrochemical stability has been studied by means of CV and resulted in an operational voltage window up to 4.1 V vs. Na+/Na. Interestingly, such value matches the decomposition value that has been measured for the B12H122--containing salts in acetonitrile. This evidence leads to speculate that the oxidative stability of the solid electrolytes obtained by anion mixing is limited by the electrochemical stability of the less stable anion. To elucidate this aspect, CV of different closo and carbacloso-borates binary mixtures have been compared, revealing a decomposition trend that confirms the aforementioned hypothesis. To get further insights into the decomposition products generated at high voltage, XPS on the electrode’s surface and on-line MS analysis have been carried out. Reductive stability was also investigated. As a case study, Na4(CB11H12)2(B12H12) has been proved to be stable toward Na symmetrical Na||Na cell operating at rt: reversible Na plating/stripping has been achieved, with a steady and limited polarization, starting from ±8.5 mV that further decreases, stabilising around ±6 mV for more than 500 operating hours. Interfaces evolution has been also studied by means of in situ EIS, confirming the good compatibility between Na and the solid electrolyte. The superior electrochemical properties of this solid electrolyte even at rt have been also demonstrated with galvanostatic tests on Na batteries, towards NaCrO2 as positive electrode (120 mAh g-1 theoretical capacity). The cell delivers more than 90% of the theoretical capacity with a CE above 99% up to C/5, with an average operating voltage of 3.0 V vs. Na+/Na. Promising results have also been obtained with the 3.8 V electrode Na2Fe2(SO4)3, demonstrating the compatibility of Na4(CB11H12)2(B12H12) with different class of electrode materials.

Resume : Email: tinehinane.bounazef@univ-littoral.fr Abstract: Sodium glassy/glassy ceramic chalcogenide systems exhibit high ionic conductivity values making particularly promising for application as inorganic solid electrolytes in all solid state sodium ion batteries. However, in contrast to their silver counterparts, the ion transport and structural information related to sodium systems is scarce. To this end, glass sample compositions in the quasi-binary Na2S-As2S3 chalcogenide system and over a large concentration range (up to 4 orders of magnitude in the sodium content) are synthesized and characterized for the first time. The glass-forming region, determined by X-ray diffraction, for the (Na2S)x(As2S3)1-x extends up to x = 0.35. Macroscopic properties such as density, mean atomic volume, and glass characteristic temperatures (the glass transition, Tg and the crystallization Tx) were measured. Both Tg and Tx decrease with increasing sodium content x. The glasses belong to Na+ ionic conductors and their room temperature conductivity increases by 5 orders of magnitude from 2.2010-16 S.cm-1 to 4.610-11 S.cm-1 over 4 orders of magnitude in the sodium content y, between ymin = 0.004 at.% Na (x = 10-4) and ymax 16.3 at.% Na (x = 0.35). Meanwhile, the conductivity activation energy shows an overall decrease by 5 factors from 1.05 eV (x = 0.0) to 0.56 eV (x = 0.35). Two different ion transport regimes were distinguished: (a) critical percolation domain at low sodium content (≤ 1-2 at.% Na) and (b) modifiercontrolled domain at highsodium content. The structural investigations were carried out using Raman scattering and neutron diffraction measurements and ion transport changes in Na2S-As2S3 glasses in relation to structural changes are studied.

Resume : Different charge compensation mechanisms are known for ionic solids. Among them are the formation of compensating defects such as electronic or ionic defects, the valence changes of atoms and the segregation of dopants. In principle, the introduction of positive charges by donor doping or reduction results either in the compensation by electrons, negatively charged intrinsic acceptors as metal vacancies, the reduction of a one of the species in the compound, or in the segregation of the dopant species. The situation is reversed for the addition of negative charges. While the different mechanisms are well-documented for different materials, predicting the prevailing compensation mechanism in a material is hardly possible. It is a common perception that the Fermi energy is determined by the defect concentrations. However, it is also possible to describe the concentration of defects as a function of the Fermi energy. This reveals Brouwer diagrams, which are identical to those obtained using standard defect chemistry calculations. In addition, it enables a direct comparison of the different compensation mechanisms.

Resume : Protonic ceramic fuel cells (PCFC) attract growing interest, since BaZr1-xYxO3-x/2 electrolytes offer a higher ionic conductivity compared to oxide ion conductors < 600°C. Optimized cathode materials with mixed protonic and electronic conductivity (e.g. (La,Ba,Sr)(Co,Fe,Zn,Y)O3-delta [1]) are crucial for PCFC performance. However, they generally show lower degrees of hydration compared to BaZr1-xYxO3-x/2. We perform density functional calculations based on the Hubbard (PBE+U) model and hybrid PBE0 exchange-correlation functional (using VASP and CRYSTAL codes) for La1-xSrxFeO3-delta [2], Ba1-xSrxFeO3-delta [3], including preliminary data for BaCoO3-delta. We present a detailed analysis of the density of states, volume and local geometry changes, oxidation and hydration energies as a function of oxygen deficiency (nominal Fe oxidation state, hole concentration). The hydration energy is more negative for Ba1-xSrxFeO3-delta than for La1-xSrxFeO3-delta, which can be assigned to the larger oxide ion basicity. The hydration energy becomes less negative with increasing hole concentration, which is related to hole delocalization to the oxide ions. Thus, we achieve a comprehensive understanding of water incorporation in mixed protonic-electronic conductors. [1] R. Zohourian, R. Merkle, G. Raimondi, J. Maier, Adv. Funct. Mater. 28 (2018), 1801241 [2] D. Gryaznov, R. Merkle, E. A. Kotomin, J. Maier, J. Mater. Chem. A 4 (2016), 13093 [3] M. Hoedl, D. Gryaznov, R. Merkle, E. A. Kotomin, J. Maier, J. Mater. Chem. A submitted

Resume : Cation diffusion in fluorite-type AO2 polycrystals has been observed experimentally in diverse studies to occur much faster along grain boundaries than in the bulk phase (Dgb >> Db). In many cases, the corresponding activation enthalpy (?Hgb) is seemingly unphysical: ?Hgb approaches ?Hb or even exceeds it. In this study we examined the possibility of cation-defect accumulation, in space-charge layers adjacent to a grain boundary, giving rise to accelerated grain-boundary diffusion. Using continuum-level simulations, we predicted defect distributions in space-charge layers from thermodynamic driving energies, allowed cation diffusion to occur parallel to the interface, and analysed the resultant diffusion profiles to obtain the product of wgb, the effective boundary width, and Dgb. Our results show that the presence of space-charge layers at a boundary can give rise to ?Hgb as high as ?Hb but not exceeding it. Furthermore, we demonstrate, through derivation of an empirical relationship, that wgb·Dgb can be predicted from knowledge of boundary space-charge potential and Db.

Resume : Sulfide solid electrolytes (SE) comprise promising materials for the usage in Li all-solid-state batteries due to high Li ion conductivities and easy processing. Especially the argyrodite materials within Li6PS5X (X = Cl, Br, I) stand out with ionic conductivities in the range of 1 mS/cm competing with those of conventional liquid electrolytes. For the Li6PS5Br it was found that a S/Br site-disorder in the range of 10-40% can be induced depending on the synthesis protocol. Furthermore, it was found that the ionic conductivity increases with increasing site-disorder. In order to understand the underlying dependence between structure and ionic transport we performed density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations on a variety of Li6PS5Br structures with different degrees of site-disorder. In line with the experiment, we will present results from AIMD simulations proving the necessity of S/Br site-disorder to enable sufficient Li transport at low temperatures [1]. A detailed analysis of the influence of the local structure on the Li transport is carried out and relations between the S/Br site-disorder and other properties such as the thermodynamical stability or lattice constants are presented. The results can be used to develop improved materials and synthesis protocols. [1] A. Gautam, M. Sadowski et al., Chem. Mater. 31 (24) 10178-10185 (2019), https://doi.org/10.1021/acs.chemmater.9b03852

Resume : Halide perovskites have attracted great interest as light absorbers for photovoltaic applications. Among these materials, hybrid organic-inorganic systems based on methylammonium (MA) and/or formamidinium (FA) lead iodide have shown the highest performances in solar cell devices. Such hybrid compositions, however, suffer from high instability under operation. One currently explored alternative is to move to the fully inorganic CsPbX3 (with X=I, Br), as these compounds could potentially fulfill both performance and stability criteria. However, many aspects regarding the stability of these inorganic materials, as well as the influence of ionic defects on their properties have yet to be thoroughly investigated experimentally and theoretically: We discuss here [1] the first principles DFT hybrid functional calculation of the atomic and electronic structure of perfect CsPbI3 and CsPbBr3 crystals and defects therein. The decomposition energies into binary compounds (CsX and PbX2) are calculated and compared with experimental data. Calculated temperature dependences of the heat capacities are also in good agreement with experimental data. It is shown that interstitial halide atoms in CsPbBr3 do not tend to form di-halide dumbbells Br_2(-) while such dimers are energetically favorable in CsPbI3, similar to the H-centers in alkali halides. Instead, in the case of CsPbBr3, a loose trimer configuration (Br_3(2-) is energetically favorable. The effects of crystalline symmetry and bond covalency are discussed as well as the role of defects in recombination process. [1]. R. A. Evarestov, E. A. Kotomin, A. Senocrate, R. K. Kremer, J.Maier, PCCP, 2020, in press

Resume : All solid-state batteries are of considerable current interest because they are a potential route to the use of lithium metal anodes while avoiding dendrite formation.[1] Among the variety of lithium solid-state electrolytes studied, sulphides show among the highest Li ion conductivity. For instance, members of the thio-LISICON family[2] and the Li-argyrodites Li6PS5X (X = Cl, Br, I)[3] have superior ionic conductivities, σ ~ 1-20 mS cm-1 at RT and low activation energies, Ea, ~ 0.20 eV. With the goal of finding new lithium solid electrolytes by a combined computational-experimental method, the exploration of the Li-Al-O-S phase field resulted in the discovery of a new sulphide Li3AlS3. This compound was made via the solid state reaction of Li2S and Al2S3 in sealed ampoules. The structure of the new phase was determined through an approach combining synchrotron X-ray and neutron diffraction with 6Li and 27Al magic angle spinning nuclear magnetic resonance spectroscopy, and revealed a highly ordered cationic polyhedral network within a sulphide anion hcp-type sublattice. The originality of the structure relies on the presence of Al2S6 repeating dimer units consisting of two edge-shared Al tetrahedra. We find that, in this structure type consisting of alternating tetrahedral layers with Li-only polyhedra layers, the formation of these dimers is constrained by the Al/S ratio of 1/3. Moreover, by comparing this structure to similar phases such as Li5AlS4 and Li4.4Al0.2Ge0.3S4 ((Al+Ge)/S = 1/4),[4,5] we discovered that the Al2S6 dimers not only influence atomic displacements and Li polyhedral distortions, but also determine the overall Li polyhedral arrangement within the hcp lattice, leading to the presence of highly ordered vacancies in both the tetrahedral and Li-only layer. AC-impedance measurements revealed a low lithium mobility (σbulk =1.3(1)·10-8 S·cm-1 at room temperature), which is strongly impacted by the presence of ordered vacancies. A potential diffusion pathway was proposed through the use of the bond valence sum mapping method which showed the dimensionality of the conduction and confirmed that ordered vacancies act as road block for diffusion. Finally, a composition-structure-property relationship understanding was developed to explain the extent of lithium mobility in this structure type. [1] Xu, W.; Wang, J.; Ding, F.; Chen, X.; Nasybulin, E.; Zhang, Y.; Zhang, J.-G. Lithium Metal Anodes for Rechargeable Batteries. Energy Environ. Sci. 2014, 7 (2), 513–537. [2] Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; et al. A Lithium Superionic Conductor. Nat. Mater. 2011, 10 (9), 682–686. [3] Rao, R. P.; Adams, S. Studies of Lithium Argyrodite Solid Electrolytes for All-Solid-State Batteries. Phys. Status Solidi A 2011, 208 (8), 1804–1807. [4] Lim, H.; Kim, S.-C.; Kim, J.; Kim, Y.-I.; Kim, S.-J. Structure of Li5AlS4 and Comparison with Other Lithium-Containing Metal Sulfides. J. Solid State Chem. 2018, 257, 19–25. [5] Leube, B. T.; Inglis, K. K.; Carrington, E. J.; Sharp, P. M.; Shin, J. F.; Neale, A. R.; Manning, T. D.; Pitcher, M. J.; Hardwick, L. J.; Dyer, M. S.; et al. Lithium Transport in Li4.4M0.4M′0.6S4 (M = Al3+, Ga3+, and M′ = Ge4+, Sn4+): Combined Crystallographic, Conductivity, Solid State NMR, and Computational Studies. Chem. Mater. 2018, 30 (20), 7183–7200.

Resume : Substitution doped lithium lanthanum zirconium oxide (LLZO) garnets are promising Li ion conductors to replace current liquid electrolytes in Li ion batteries. Experimental results show that the introduction of aliovalent elements generally improves ionic conductivity. This improvement is attributed to an increased lattice parameter and changes in the lithium stoichiometry. However, quantitative predictive models of these effects are lacking and their development could contribute to the rational development of solid electrolytes. We will present ab initio molecular dynamics simulations of Li transport in LLZO-based materials to characterize the role of the dopant on transport. An analysis of residence time of the Li ions on the tetrahedral and octahedral sites of the crystal provides new insight into the mechanisms behind the improvement in conductivity. Furthermore, models based on these calculations explain the optimal level of doping. In addition, to guide the design of new garnets with improved properties, we used machine learning to develop predictive models from all published conductivities for over a hundred different compositions. Using existing data and these models, we will show that sequential learning can cut down on the number of experimental trials to achieve an optimal solution by approximately 60%.

Resume : Garnet-type materials such as Li7La3Zr2O12 (LLZO) are promising candidates as solid-state electrolytes in Li-ion batteries, the dominant power supplies for portable electronics, energy storage and electric vehicles. LLZO is characterised by high ionic conductivity, negligible electronic transport and good chemical stability with respect to metallic Li. In the cubic phase (Ia-3d) the ionic conductivity of LLZO is two orders of magnitudes higher than in the tetragonal phase (I41/acd), 10-3 S/cm vs 10-6 S/cm The cubic structure is formed of ZrO6 octahedra linked by LaO8 dodecahedra; Li atoms occupy interstitial sites, which can be classified as the tetrahedral 24d sites (Li1) and distorted octahedral 96h sites (Li2). The fractional occupation of the Li sites and the consequent occupational disorder play an important role in the Li ion migration. Periodic quantum mechanical simulations within the density functional theory will be performed by using the range separated hybrid functional HSE06, as implemented in the CRYSTAL17 program. The aim of this study is to investigate the possible influence of both intrinsic and extrinsic defects (in particular Li vacancies, O vacancies and substitutional dopants on Li sites) on the structural and electronic properties of this material and to explore what role these play in the observed nucleation and propagation of Li-dendrites within the electrolyte in operando.

Resume : The lithium ionic conductor argyrodite Li6PS5Cl with high conductivity is a promising candidate as an electrolyte in all-solid-state lithium-ion batteries (LIBs) at room temperature. However, it owns several drawbacks such as poor mechanical property, unstable interface with important electrode active materials, e.g. Li metal, is limiting practical energy storage applications. The novel hybrid solid electrolyte PVdF-HFP/Li6PS5Cl is prepared to overcome such drawbacks. It is fabricated with different percentages of PVdF-HFP from 5 to 50 %, and ionic conductivity is improved by adding Li salt, LiCF3SO3. The hybrid solid electrolyte PVdF-HFP/Li6PS5Cl obtains excellent ionic conductivity closed to 10-3 Scm-1 at 30 oC with improved mechanical property. An all-solid-state cell LTO| PVdF-HFP/Li6PS5Cl|NMC was successfully operated at 30 oC with high reversibility. The performance of the half cells with Li metal also exhibits compatibility of the electrolyte with Li.

Resume : The search for next-generation solid-state superionic conductors has attracted significant attention. Among Na superionic conductors, Na11Sn2PS12 has been reported to have a room temperature ionic conductivity of 1.4 mS/cm. In this study, we employ density functional theory to study the stability of Na11Sn2PS12 and further explore the substitution of Sn with Ge. Our results indicate that Na11Ge2PS12 is more stable than Na11Sn2PS12. Furthermore, substituting Sn with Ge increases the band gap, improves the room temperature ionic conductivity by a factor of 2, and lowers the activation energy of Na hopping. Statistical analysis suggests that Na11Ge2PS12 has a faster diffusion along the ab-plane compared to the c-axis. The Na diffusion in Na11Ge2PS12 appears to occur with two different mechanisms depending on temperature: 1) an ion hopping process at lower temperatures (<800 K); 2) a fluid-like distribution of Na ions at higher temperatures (>1000 K). The computations suggest that Na11Ge2PS12 is a promising candidate as a solid Na electrolyte due to its high room temperature ionic conductivity and phase stability. In light of these simulation results, we expect to stimulate further experimental studies on Na11Ge2PS12.

Resume : Redox-based based memristive devices are one of the most attractive candidates for future non-volatile memory applications and neuromorphic circuits. For the most common memristive band insulators, resistive switching is induced by the formation of oxygen vacancies and the resulting valence change on the cation sublattice. However, manganites, cobaltites and ferrates undergo a topotatic phase transition between the perovskite and the brownmillerite structure upon reduction that might also be induced during resistive switching. Due to the spatially confined redox-process, experimental proofs of topotactic phase transitions in memristive devices are very rare. By employing X-ray absorption spectromicroscopy, we demonstrate that the reversible topotactic phase transition between the insulating brownmillerite phase, SrFeO2.5, and the conductive perovskite phase, SrFeO3, gives rise to resistive switching of SrFeOx memristive devices. Interestingly, we found that the electric field induced phase transition spreads over a large area in (001) oriented SrFeO2.5 devices, where oxygen vacancy channels are ordered along the in-plane direction of the device. In contrast, (111) grown SrFeO2.5 devices with out-of-plane oriented oxygen vacancy channels, reaching from bottom to the top electrode, show a localized phase transition. We attribute this difference in the extension of the topotactic phase transition to the anisotropic oxygen ionic conduction in the brownmillerite structure.

Resume : We use atomistic modelling and Density Functional Theory calculations to investigate how electron injection from metal electrodes into thin HfO2 films under voltage bias causes changes of their resistance. The results suggest that electron and hole injection can facilitate the formation of Frenkel defects in monoclinic as well as amorphous HfO2 films and stimulate diffusion of O ions. In both crystalline and amorphous HfO2, electrons and holes localize and form bi-polarons [1,2], which facilitate the formation of pairs of Frenkel defects [3,4]. The electron trapping causes strong Hf–O bond weakening and facilitates thermally activated formation of Frenkel defects: neutral O vacancies and interstitial O2- ions. The barriers for these processes in a-HfO2 are about 1.5 eV and reduced by bias application. We show that more O vacancies can be produced near pre-existing vacancies if they become negatively charged after electron trapping. It is found that the third vacancy formation energy is, on average, 0.2 eV lower than the second and the barrier for vacancy formation is also reduced significantly. Holes also form bi-polaron states in a-HfO2 which reduce barriers for formation of V2+ oxygen vacancies and interstitial O atoms. These results provide insights into the interplay between electronic and ionic processes in crystalline and amorphous HfO2 films in memristive devices. [1] D. Munoz Ramo, et al., Phys. Rev. Lett. 99, 155504 (2007). [2] M. Kaviani, J. Strand, V. V. Afanas’ev, A. L. Shluger, Phys Rev B. 94, 020103 (2016) [3] S. R. Bradley, A. L. Shluger and G. Bersuker, Phys. Rev. Appl. 4, 064008 (2015)

Resume : Two-dimensional (2D) materials have been introduced to the field of memristors to achieve novel properties that are not shown in the traditional ones, such as high transparency and flexibility, controllable volatile and non-volatile switching. However, most 2D materials based memristors are fabricated by mechanical exfoliation which is not a scalable method, or via chemical vapor deposition although this method requires a complex transfer. Instead, inkjet printing exhibits large-scalability, mask and residue free, versatility and cost-effectiveness properties which make it a promising technique for the future electronic industry demands. In this work, we introduce inkjet printing technology to fabricate 2D materials based memristors. We have first formulated proper printable inks and afterwards produced fully inkjet printed Ag/hexagonal boron nitride (h-BN)/Ag structure (device size 300 μm × 300 μm). The devices show stable bipolar resistive switching behavior with acceptable endurance and retention and an operation voltage around ±1 V, characterized by applying both ramped voltage stresses and pulsed voltage stresses. The devices can also show the potentiation for multilevel storage, which may be attributed to the multilayer of 2D material flake caused by inkjet printing. The results from this study will bring insight to the use of inkjet printing to construct 2D materials based memristors on papers, plastic or clothes, as well as the potential for commercialization.

Resume : Memristive devices based on the valence change mechanism (VCM) are intensively studied for non-volatile redox-based resistive random access memory (ReRAM) as well as for artificial synapses in beyond-von Neumann computing architectures. The relatively simple cell structure consists of a resistive switching metal oxide layer sandwiched between an inert, high-work function metal forming a Schottky-type contact and a chemically reactive metal forming an ohmic-type contact and enabling oxygen exchange across this interface. Starting from insulating transition metal oxides, the devices require an electroforming step comparable to a controlled breakdown that enables the formation of a conductive filament consisting of a chain-type percolation of oxygen deficient metal oxide material. The extension of the filament towards the two electrodes can be switched by application of voltages of opposite polarity resulting in the high and low resistive states. Beside the oxygen vacancy drift and diffusion process in the filament the effect of oxygen exchange across the metal oxide /metal electrode interface becomes more pronounced, especially for small devices of reduced dimensions. The importance of oxygen exchange reactions at the interface of the metal oxide and the chemically reactive electrode has been demonstrated recently. Here, we will focus on the effect of the structure of the materials, TMO and metal, being either amorphous or crystalline, close to the interface. Further, effects of charge compensation by means of impurity-ion segregation will be addressed. The results contribute to a deeper understanding of the competition between oxygen ion drift/diffusion vs. oxygen exchange reactions and of the role of material structure and impurity segregation on the device performance.

Resume : The Fermi energy determines the charge state of impurities, the concentration of electrons and holes and interfacial charge transfer processes. In a semiconductor, the Fermi energy can often be freely controlled across the whole energy gap by doping. This is not the case in oxides, where different mechanisms exist, which limit the range of the Fermi energy. In order to understand the limits of the Fermi energy in BiFeO3, photoelectron spectroscopy has been used to quantitatively determine the Fermi energy position in differently treated BiFeO3 thin films and ceramics. This is also related to the discussion whether the material is more a p- or more a n-type conductor. Different reducing and oxidizing treatments and interface formation with low and high work function oxides have been applied to raise or lower the Fermi energy. All treatments and interface formation were performed in-situ without breaking vacuum. The experiments reveal a lower and an upper limit of the Fermi energy of 0.5 eV and 1.75 eV above the valence band maximum, respectively. As also observed previously for Fe2O3 [1], the upper limit of the Fermi energy is related to a change of the valence of Fe from 3+ to 2+. The energies at which the valence change of Fe occurs is the same in Fe2O3 and BiFeO3. In contrast to the upper limit, there is no clear spectroscopic signature at low Fermi energies, which can be used to identify whether the lower limit is also fundamental. In addition to the limits of the Fermi energy, the energy level of the Co2+/3+ transition in Co-doped thin films could be identified to be at 0.8 eV above the valence band maximum using our approach. References [1] C. Lohaus, A. Klein und W. Jaegermann, Nature Commun. 9, 4309 (2018).

Resume : Resistive switching memory has been conceived as next-generation memory by fast information storage, large information storage and low energy consumption. Recently, organometal halide perovskite materials for use as resistive switching memory has received a great deal of attention owing to low operation voltage and high ON/OFF ratio. However, resistive switching memory based on the organometal halide perovskite materials have shown the poor endurance property such as endurance of 350 cycles. In this presentation, we exploited 2D/3D perovskite heterointeface structure by forming 2D phenylethylamine lead iodide ((PEA)2PbI4) endurance property of about 3000 cycles compared to the bare 3D perovskite layer whose endurance property was about 350. The excellent endurance property was explained in terms of presence of many reversible. This study provides another strategy for improving endurance property of perovskite based resistive switching memory devices.

Resume : The need for clean and efficient energy conversion systems has stimulated tremendous research activities in the area of energy systems. Solid oxide fuel cells stand out because of their high efficiency and low emissions. In spite of the promise, to commercialize solid oxide fuel cells the operating temperature needs to be reduced below 800 °C. Unfortunately, at such low temperatures the oxygen reduction reactions taking place at the cathode side of the solid oxide fuel cells are typically sluggish. Ferrites have recently shown that they can overcome this challenge. However, the conductivity of these materials is typically low. Here, we introduce P in the Fe site of Ba0.95La0.05FeO3-δ to make a novel cathode material, Ba0.95La0.05Fe0.95P0.05O3-δ. We observe that Ba0.95La0.05Fe0.95P0.05O3-δ has higher electronic conductivity and better electrocatalytic activity compared to Ba0.95La0.05FeO3-δ. We also show by density functional theory calculations that introducing P in the Fe site lowers both the O vacancy formation and vacancy migration energies and promotes the creation of PO4 groups. These factors contribute to improving the diffusional properties and oxygen reduction reaction performance. In light of these results, we suggest that non-metal element doping is an effective strategy for the design of new ferrites.

Resume : Li-ion batteries (LIBs) are widely used in the development of renewable energy technologies. However, most easily accessible lithium reserves are in either geographically remote or politically sensitive areas. This has raised concerns whether or not the global lithium resources can match the demand of upcoming electric and hybrid electric cars.[1] Developing Na-ion batteries (NIBs) for large-scale electric energy (ESS) systems has become a growing interest in recent years due to the low-cost, environmentally benign and natural abundance of sodium resources. In this regard, Prussian white (PW), Na2-xFe[Fe(CN)6]1-y·nH2O (x = y = n = 0) has received great attention due to its potential high capacity for 2 Na+ storage (~170 mAh/g), facile synthesis, and inexpensive Earth abundant elements.[2] However, in the literature the compound has been reported with a range of different compositions such as Fe(CN)6 vacancies, sodium and water content, leading to inconsistent electrochemical performance.[3] In addition to these parameters, it is also extremely important to understand the conditions under which the electrodes should be processed, handled and stored prior to inclusion in an electrochemical cell to ensure their long-term cycling stability. In this work, we demonstrate for the first time the critical effect of exposing hydrous monoclinic Prussian white (M-PW) and anhydrous rhombohedral Prussian white (R-PW) electrodes to 55% relative humidity (RH). Both the M-PW and R-PW electrodes exhibit reversible capacity at C/10, but there are significant differences in their electrochemical behavior. Humidity has considerable influence on the initial capacity of M-PW electrodes such that ~21% is lost from 61 mAh/g to 48 mAh/g for pristine and 55% RH exposed, respectively. While in the case of R-PW electrodes the loss in the initial capacity is ~16%, from 148 mAh/g to 141 mAh/g for pristine and 55% RH exposed, respectively. This study is considered a potential roadmap to proper processing and storage of moisture sensitive electrode materials before building batteries for practical applications. Reference [1] Tarascon, J.-M. Is lithium the new gold? Nat. Chem. 2, 510 (2010). [2] Wang, L. et al. Rhombohedral Prussian White as Cathode for Rechargeable Sodium-Ion Batteries. J. Am. Chem. Soc. 137, 2548–2554 (2015). [3] Brant, W. R. et al. Selective Control of Composition in Prussian White for Enhanced Material Properties. Chem. Mater. 31, 7203–7211 (2019).

Resume : Rutile (TiO2), a semiconductor with a wide bandgap, is prevalent due to its essential applications; for example, as gas sensor and as a photocatalyst in solar cells. In order to tailor electrical properties, engineering of zero dimensional point defects plays an important role. However, the solubility limit of the dopant constrains this tool for tailoring material properties significantly. In the present work, we demonstrate how one dimensional defects alter the electrical properties of rutile by inducing dislocations via controlled mechanical deformation. This is based on an approach reported by Adepalli et al. [1]. However, we improved the high temperature deformation in order to arrange the dislocations so that their influence on electrical properties could be studied utilizing knowledge about alignment and dislocation type. Results from electrical measurements across and along the induced dislocation network are discussed. Furthermore, the change in defect chemistry at several temperatures and the effect of changing the oxygen partial pressure (pO2) on high temperature conductivity are shared. This way, the topic of dislocation induced change in functional properties is presented based upon an experimental approach combining micromechanics and solid state ionics concepts. [1] Adepalli, Kiran Kumar, et al. "Influence of line defects on the electrical properties of single crystal TiO2."Advanced Functional Materials" 23.14 (2013): 1798-1806.

Resume : The realization of artificial synapses for neural networks require analog weights to be programmable as the device conductance via blind update and access operations. However, most electrostatic memory devices are bi-stable in nature which are only useful for digital single bit storage. Memristors and memdiodes belong to the class of iontronics which utilizes ion-assisted switching mechanisms to achieve programmable device conductance. Non-stoichiometric tin oxide thin films are utilized in a rich repertoire of iontronics due to the low oxygen vacancy defect energy. In this study, atomic layer deposition was utilized to deposit ultrathin conformal SnOx thin films for synaptic applications. First, we design and evaluate a resistive switching anodic metal/oxide (Al/SnOx) interface under high electric field. The reversible formation of interfacial aluminium oxide is believed to enable the stability of intermediate resistance states. To utilize the interface as an artificial synapse, we optimize the analog programmability and propose a proof-of-concept ternary switching memristor. A spectroscopic study conducted on the chemical states of Sn after set and reset bias suggests that the resistive switching was oxide ion-assisted in nature. Subsequently, the defective oxide/oxide Schottky barrier interface (ITO/SnOx) is explored as a photoactive memdiode synapse. The photo-activity of the memdiode in the visible spectrum can be attributed to the photon-assisted discharging of the intermediate defect states, lowering the energy barrier and device resistance. Harnessing the electric field-assisted exchange of oxide ions between the two oxide films, we demonstrate that the persistence of photoconductivity can be modulated with bias voltage known as priming pulses. Such priming activities are important device functionalities to implement bio-realistic synaptic weight updates. In this study, the oxygen deficient tin oxide thin films demonstrated promising ion-assisted switching and photomemory characteristics. An interface with an anodic metal generates a memristive device capable of achieving non-volatile analog weight changes crucial for artificial synapses. Interchanging the metal with an oxide electrode, the memdiode exhibits photoconductivity with high persistence and modulability with field-assisted defect priming.

Resume : Yttrium doped BaCeO3 (BCY) enhances the proton conductivity of BaCeO3 (BCO) at intermediate-high temperatures. The addition of Yttrium increases the concentration of proton defect and the proton concentration. It is also known that the strain engineering can also be used to modify and improve the properties of proton conducting materials as the proton mobility may be enhanced by introducing strain and, therefore, changing the molecular structure (unit cell and lattice symmetry) and its properties. In this work BCO and BCY (1µm thickness) are prepared by e-beam vapor deposition at 12Å/s deposition rate at 700oC and 800oC. At those technological parameters crystallization of BCO is observed, the surface morphology is homogenous, and high density is achieved. Different substrates (alloy 600, stainless steel, Invar, and glass sealing alloy) with different thermal expansion coefficients are used to induce strain to the films and investigate the influence of strains on protonic conductivity. The research was financially supported by project no. 2017/27/L/ST5/03185 founded by the National Science Centre, Poland and Research Council of Lithuania (LMTLT), agreement No S-LL-18-3.

Resume : Transition metal oxides attract a growing interest due to their exceptionally broad range of functionalities. For example, NiO has a function of steam reforming to generate H2. Furthermore, by reducing NiO passivation layers on Ni substrates, an alternative catalyst of Pt for exhaust gases of motor vehicles is expected for the clean Ni surface. In this study, therefore, the oxidation and reduction reaction kinetics on Ni(111) surface was investigated by X-ray photoelectron spectroscopy using synchrotron radiation (hv = 1100 eV) at BL23SU, SPring-8, to explore in real time the oxygen uptake and oxidation states. By analyzing the time evolution of NiO thickness, dNiO, the reduction reaction mechanism of rapid-temperature-rising annealing as well as the NiO growth reaction model based on Ni vacancies and holes is considered. When the reduction was conducted in vacuum with no H2 supply, a significant decrease of dNiO from 2 nm to ~1 nm was caused by the rapid temperature rising from 350 to 700℃, whereas dNiO remained at ~ 1nm for a long period of 3×104 s during the subsequent isothermal annealing even at 700℃, while the rapid-temperature-raising-induced decrease of dNiO under H2 atmosphere was almost the same as that in vacuum, indicating that reduction of NiO during the rapid temperature rising is governed by the diffusion of O2- enhanced by the tensile stress due to the difference in thermal expansion coefficient between Ni and NiO. In contrast, the NiO films were completely removed by the isothermal annealing at 700℃ under H2 atmosphere. This is because H2 dissociative adsorption is caused at Ni metal clusters on NiO surface, leading to H2O desorption.

Resume : As the operating temperature of solid oxide fuel cells (SOFCs) continues to decrease, they are now low enough to use stainless steel (SS) as an interconnector material. However, when the stainless is used for a long time at around 700~800 oC, Cr2O3 can be formed on the surface which significantly degrades the performance of SOFCs. In order to prevent the oxidation of SS, various kinds of coatings of spinel or perovskite structured oxides have been adopted as the anti-oxidants on the surface of SS. In this study, Mn1.5Co1.5O4 (MCO) spinel is employed for coating. The MCO powder was synthesized by the solid-phase synthesis method and pulverized into fine powders by attrition milling. The specific surface area and Zeta potential of the MCO powders were analyzed and the thermal expansion coefficient of the MCO sintered body was measured and compared with that of the SS. An appropriate amount of iodine (I2) was added to the MCO slurry for EPD coating and the microstructures of the coated films were observed. A dense film was obtained through a sintering process in which the coated film was reduced at high temperature in a reducing atmosphere and then re-oxidized in an oxidizing atmosphere. The electrical conductivity, microstructure, compositional stability of the MCO layer were analyzed after a long-term (1000 h) operation.

Resume : Recently, lithium-ion batteries (LIBs) have been applied to large-scale devices such as electric vehicles and energy storage systems (ESSs), requiring high energy density and long cycle life. The use of organic electrolytes in lithium ion batteries in such large-scale devices has some safety issues. Organic electrolytes have a high ionic conductivity, but there are many risks of leakage, explosion and ignition due to the decomposition reaction of the electrolyte. As a promising solution to this issues, the use of a solid electrolyte have been proposed. In contrast to organic-based liquid electrolytes, all-solid-state lithium batteries (ASLBs) with a solid electrolyte are considered safe because of their non-flammability. These solid electrolytes have the advantages of high stability and high energy density, but they have a disadvantage of very low ionic conductivity at room temperature. In this work, we prepared sheet-type Li6PS5Cl-infiltrated electrode that has high capacity, even though it has high loading value. We propose two solutions to ensure that SE materials are evenly distributed and sufficiently infiltrated into the porous structures of LIB electrode. First, we aimed to reveal the effects of solid electrolyte solution vaporization on the solid electrolyte content in the thick electrode for ASSBs. The performance of the cells at different temperatures were compared. The electrochemical performance of ASSBs employing the LPSCl-infiltratred SEs is dependent on the LPSCl content, and it is noticeably high at higher temperatures that cause molecular motion. Therefore, it should contain more LPSCl in cathode. The NCM622 electrode infiltrated LPSCl at 90oC show reversible capacity of 177mAhg-1(5.5mg/cm2) and 136mAhg–1(17mg/cm2) at 0.05C, 55oC. We also prepared three different active materials having different particle size. The porous electrode which is made by mixing different sized active materials(DS-AM) absorbs SE solution. This absorb effects explain the capillary phenomena. The mixed DS-AM electrode demonstrated higher capacity than non-mixed DS-AM electrodes due to the improved ion transport path.

Resume : Cubic fluorite structures of lanthanum strontium manganite (La0,7Sr0,3)0,95MnO3-/8YSZ (LSM) thin films are deposited on Pulsed laser Deposition (PLD) at 500C and 600C, at different number of pulses (90.000 pulses for 8YSZ and 100.000 pulses for (La0,7Sr0,3)0,95MnO3-) like cathode for µSofc and sensing electrode for potentiometric oxygen sensor on different substrates (Si(100) and Ti). The microstructure, the composition and the crystalline/ phase of the films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS); optical properties, electrical and electrochemical measurements are used to optimize the performance of such subansamblies. It was obtained uniform cubic crack free structures with good adhesion on cathode /electrolyte. Keywords: Lanthanum Strontium Manganite (LSM), Thin film cathode, Pulsed laser Deposition (PLD), Cubic Fluorite Structure, Electrochemical devices.

Resume : For fuel cell application, we investigated Proton conducting composite membranes of sulfonated polyether ether ketone (s-PEEK) reinforced by two various clays (a commercial montmorillonite and a home purified one) which we introduced at various clay Wt%; varying from 0 to 20Wt% of clay. We conducted various physic-chemical characterizations such as X-Ray diffraction (XRD), Scanning electron microscopy (SEM), ion exchange capacity (IEC), water uptake (WU), ionic conductivity measurements at various relative humidity conditions. The XRD patterns showed typical peaks of the clay confirming the effective introduction and the stability of the clay even after the thermal and the acid treatment of the membranes. The IEC measurements showed increased values by introducing the clay at around 5 wt% and a progressive reduction occurs with the increase of the clay amount. The WU reported at different temperatures showed different behaviours depending on the clay used. The ionic conductivity showed better values for the 15 Wt% sample for both types of clay. Fuel cell tests have been conducted with the 15 Wt% clay s-PEEK membranes. For this we used home-made electrodes by spraying the catalytic ink onto a commercial gas diffusion layer (GDL) and we made the Membrane-Electrodes Assemblies at 10Nm. Fuel cell tests, were carried out in a commercial 25cm2 single cell at 80°C, and with humidified H2/air (75-100% RH). The performance of the fuel cell are in agreement with the proton conductivity results, in fact the recast membrane reaches the best performance followed by the composite membranes which present comparable performance. The reduced performance of composite membranes is attributed to the increase of the cell resistance, in accordance with the proton conductivity measurements. It is to notice that reducing the relative humidity from 100% to 75% maintains the trend of the cell resistance and the open circuit voltage (OCV); the composite membranes have higher cell resistance and lower OCV than the pure s-PEEK membrane. The 15% home purified Clay based membrane maintains the performance quite the same, meaning a less sensitivity to the reduction of relative humidity.

Resume : New materials or advanced functional films are always dedicated for specific aplications. Very often either the substrate material or the film material are strongly sensitive against normal environmetal conditions. Even if the components of such deposition are not sensitiv against such attac, the interfacing between substrate and film is effected from such influence. The solution in material research for such problems is an isolation of such substrate under strongly controlled atmosphere, which can be achieved with the use of glove boxes with integrated gas cleaning systems. The user interacts via isolation gloves to handle sensitive materials in the glove box wich are introduced to it via integrated load lock ports. The combination of such controlled work bench to any kind of deposition system is a problem, because normally no easy way exist to transfer such materials from a glove box into separate deposition systems. Only a fully protected connection from such glove box to the deposition system allows an undisturbed transfer. But standard deposition systems are not prepared for such transfer. SURFACE offers now fully integrated process systems which have a complete glovebox built in. In addition the complete design of such system recognizes the reduction of handling performance of the user caused by the thick gloves and its limited taktile sensitivities. Any services on such deposition system is generated from the atmosphere side, without disturbing the conditions of the contolled atmoshere in the glove box. The fully integrated style of the glove box reduces also the necessary floor space of such comlete set-up in the lab. As an excample : the total foot print of a complet PLD Glove Box system including big Excimer laser, its gas cabinet, the process automation system with user interface, the vacuum chamber, cooling chiller and the gas control cabinet fits to a floor space of 2,5m x 0,8m and includes already the glove box workstation with a working width of 1 to 1,5 m. Exambles for such integrated systems are presented.

Resume : Revealing the detailed atomistic and electronic structures at the solid-liquid electrified interface has been a major focus in electrochemistry and theoretical investigations through computational simulation. However, previous simulations are largely limited in investigating single aspects of electrochemical transformation at the interface and cannot provide a comprehensive and realistic modelling of the interface nanostructure. My project focuses on improving the depiction of the electronic structure of the electrified interface and overcoming the difficulty for applying higher level DFT hybrid functionals for simulations in complex system due to high computational cost. The first stage of the project focuses on improving the accuracy of density description of an already-generated PBE-level ab initio molecular dynamic simulation on a realistic and large system of the interface. Sample snapshots are taken from the AIMD simulation and a survey of various hybrid functionals, such as B3LYP and PBE0, are applied to the sample snapshots. With the higher accuracy density profile, a DFT+U correction is applied to the system to gain more insights of the electronic structure. The resulting new description of the electronic structure is then compared with experimental spectroscopic data, including FTIR. The future prospect of the work will include performing constrained DFT AIMD for the complex system with the newly generated high accuracy density profile.

Resume : Electrochromic material devices (ECDs) development aims to decrease power consumption while increasing the variety of desired colors. Electrochromic smart windows can be used in cars or buildings to adjust brightness or in spacecraft to moderate the intense thermal fluctuations by switching between light/infrared transmission and reflection. Electrochromic materials and devices change their optical properties in a reversible and persistent way under an applied voltage. Organic polymers show high color efficiency and a huge range of colors but suffer from limited stability, particularly when exposed to the ambient environment. Using metal-organic frameworks (MOFs) as an electrochromic material, MOFs offer enormous structural and chemical diversity being constructed from metal/metal cluster centers and organic linkers in countless combinations. The deliberate insertion of redox-active naphthalene diimide (NDI) ligands into the versatile family of metal-organic frameworks, MOF can be switched reversibly from transparent to dark. Zinc (Zn) metal center is integrated with the NDI and viologen moiety. MOFs, known to be porous coordination polymers, are crystalline coordination networks consisting of metal ions/clusters and organic linkers. Due to its porosity ions can easily mobilize, this motion increases the scope of multicolor functionality, quick response and reversibility. While typical MOF has one reduction state, our viologen-functionalized NDI may give rise to multi reduction states, which means multiple colors can be observed. These MOF films were deposited on ITO substrate which exhibit cycling stability unrivaled by organic linkers to significant optical contrast in a lithium-based electrolyte.

Resume : The characterization of three electrode cells with a properly placed reference electrode (RE) offers the possibility of measuring I-V-curves and impedance spectra of a single electrode. This technique is widely used in aqueous electrochemistry, but is rather difficult to apply in solid state electrochemical cells. There, most designs presented in literature suffer from artefacts due to inevitable small imperfections in fabrication, or frequency-dependent current distributions. In this contribution, we present a newly developed cell design, with the RE placed onto a protrusion of the electrolyte. This approach minimizes artefacts, and sample fabrication is comparatively simple. Here, we use this design to characterize model cells with porous La0.6Sr0.4FeO3-δ (LSF) electrodes. Half-cell spectra were acquired in different oxidizing and reducing atmospheres, and under electrochemical bias. Data quality allows fitting the spectra analytically with a transmission-line type equivalent circuit, that delivers information on the surface catalytic properties, chemical capacitance, and ionic conductivity of the material. The obtained results are consistent with literature data of LSF, thus demonstrating the strength of the chosen cell geometry. In conclusion, we can provide guidelines for fabrication and material selection for three-electrode cells with solid electrolytes to obtain artefact-free I-V-curves and impedance spectra under electrochemical polarization of single electrodes.

Resume : Recently partially substituting oxygen with nitrogen in ternary transition metal oxides is of growing interest because introducing a nitride anion (N3-) within the oxide anionic (O2-) sublattice can result in interesting modification of properties [1], e.g. optical properties, magnetic properties, electronic, dielectric and thermoelectric behavior etc. Among the oxynitrides, the perovskite-type system has received the most attention due to its structural flexibility and many investigations have been conducted on this structure type AB(O,N)3, where A = Rare Earth, B = Transition Metal. CeNbO4+δ (δ = 0, 0.08, 0.25 and 0.33), because of the wide range of oxygen non-stoichiometries, has attracted considerable interest as a fast oxide ion conductor in solid oxide fuel cells (SOFCs) [2]. Oxynitride formation of the CeNbO4+δ precursor, which has not been reported in literature, may modify the optical properties as well as the electronic and ionic transport properties of the materials. Thus, this Ce-Nb-(O,N) system could be of particular interest for compositional, optical and electrical studies. In this work single phase cerium niobium oxynitride has been successfully synthesised via the thermal ammonolysis method and a variety of characterisation techniques have been performed to study its crysatallographic structure, physical and chemical properties. Complex multi-stage redox processes of this material was observed at elevated temperature and the band gap found to decrease significantly due to the incorporation of nitrogen into the oxygen sublattice, theoretically and experimentally confirmed, which indicated it could be a promising candidate for photocatalytic applications. References [1] A. Fuertes, J. Mater. Chem., 22 (2012) 3293 [2] R. J. Packer and S. J. Skinner, Adv. Mater., 22 (2010) 1475

Resume : In recent years, there have been important applications envisioned that would require small-scale devices to be implemented. An example of such are microelectromechanical systems (MEMS) used as energy harvesters. A significant challenge in the realisation of such devices is finding novel ways of lubrication, due to the high friction and wear present. In this work, Room Temperature Ionic Liquids (RTILs) are proposed as a solution to this problem, due to their numerous tuneable properties. The vapour pressure of ionic liquids is also very low, thus almost no liquid is lost due to evaporation. Additionally, their ionic behaviour is a topic with major scope for enhancing or controlling the compound’s properties through applied electric fields. Finally, these liquids are also able to be characterised through molecular simulations. In order to explore the friction properties at the nanoscale of RTILs, a MEMS tribometer has been developed. This consists of a miniature thrust pad bearing interface, manufactured using semiconductor fabrication techniques. Furthermore, this experimental rig is to be modified to apply charge on the system. In this way, the charged behaviour of RTILs can be studied. Thanks to previous molecular simulation work done at Imperial, the experimental results can be compared and validated. Following the conclusions of this work, applications will be explored in the nanoscale lubrication properties for MEMS devices and energy harvesters.

Resume : Complex non-stoichiometric oxides with doubled perovskite-like structure attract much attention due to a combination of such functional properties as electrical and ionic conductivity, magnetic properties, and oxygen exchange. Coexistence of oxygen vacancies with transition metals promotes these compounds to be sensitive even to slight changes in temperature and gas-phase composition. Thus oxygen content affecting to defect equilibrium and crystal structure becomes a crucial factor to form the required characteristics of oxides. Therefore a comprehensive study of defect formation processes by number of theoretical and experimental methods is essential to govern the desired properties. In the present work solid solutions based on PrBaM2O6–δ, with M=Co or Mn, were obtained through the glycerol-nitrate precursors. Coulometric titration data were utilized in order to simulate the isothermal dependences of oxygen content in oxides vs. partial pressure. Equilibrium concentrations of the corresponding defects were calculated from the model proposed. Experimental data on high-temperature magnetic susceptibility combined with the defect structure were applied to explain some features of electric transport properties. In particular, the phenomenon of the so-called “spin blockade” was established at high temperatures. This work was supported by the Russian Science Foundation under grant №19-79-10147

Resume : In situ exsolution of nanocatalysts to enhance the catalysis of fuel in solid oxide fuel/electrochemical cells (SOFCs and SOCs) is an increasingly favored strategy. Here we report nonmetal cations (Silicon and Phosphorus) as a secondary dopant in the B-site of the strontium titanate perovskite, improving the electrochemical performance and exsolution of transition metal. Using ab initio computations, the energetics and the diffusional properties of the materials were studied. The improved exsolution predicted in theoretical studies agrees with the excellent area-specific resistance of 0.050 Ωcm2 (5% Si-doped) and 0.047 Ωcm2 (5% P-doped), measured for the optimum compositions (Sr0.8Ti0.85Ni0.1(Si/P)0.05O3-δ. Additionally, these materials showed excellent electrochemical and thermal stability, performing steadily at the low polarization resistance for over 100 hours in the imitated fuel environment (3% humidified H2). XPS studies reveal simultaneous oxidation of the nonmetal dopants during exsolution (or reduction) of Ni, which aids the exsolution process. The exsolved nanoparticles were characterized using SEM and EDS. This work proposes a cost-efficient improvement which was previously done through expensive rare earth metal dopants, which hindered exsolution as a trade-off to electrical conductivity improvements. This is the first time, to our knowledge, nonmetal dopants in perovskite were utilized as an ‘exsolution-helper’.

Resume : Ultraviolet (UV)-crosslinked solid-state polymer electrolyte system (SSPE) based on poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block co-polymer was developed for applications in all solid state batteries. Cross-linkable polymeric precursors with four functionality were synthesized by reacting terminal end groups of PEO-PPO block co-polymer (Tetronic 90R4) and 4-vinylbenzyl chloride. The crosslinked SSPEs were obtained by solvent free UV initiated polymerization of the mixtures containing cross-linkable polymeric precursors, divinyl benzene (DVB), and photo-initiator. In order to achieve a good balance between electrochemical and mechanical properties, the number of PEO-PPO units and the feed ratios of DVB and liquid electrolyte in the SSPEs were precisely controlled. The resulting SSPE showed high ion conductivity of 1.62 mS/cm at room temperature. Thermal stability of the crosslinked SSPEs were evaluated by thermogravimetric analysis (TGA) and different scanning calorimetry (DSC). An Na-Na symmetric cell assembled with SSPE exhibited good electrochemical performance.

Resume : Forming the La0.6Sr0.4CoO3-δ (LSC) nanoparticles on the cathode surface has been intensively explored since this enables the high performance of solid oxide fuel cells by enhancing the charge conductivity. However, the 0D structure still has limitations such as inefficient charge conducting path or fading the reaction site due to the excessive loading level for ensuring the continuity of La0.6Sr0.4CoO3-δ (LSC) nanoparticles. In this study, we report the uniformly grown ultrathin 2D La0.6Sr0.4CoO3-δ nanosheet for effectively enhancing the cathode performance. Continuous 2D figure more efficiently enlarges the reaction site with low loading level compared to the conventional 0D figure. 2D nanosheet structure is ideal figure for enlarging the charge conducting path because it has more contact with cathode scaffold compared with any other structures. Solid oxide fuel cell with 2D La0.6Sr0.4CoO3-δ nanosheet exhibit quite enhanced power density of 1.2 W cm-2 at 600 oC by facilitating the conductivity of charge within the cathode. Our strategy provides the instructions for the high-performance solid oxide fuel cells through the cathode structure design.

Resume : Formation of the gadolinium-doped ceria electrolyte layer on the yttria-stabilized zirconia electrolyte layer as a protection layer has been researched for its use at low operation temperature. The dense gadolinium-doped ceria barrier layer could reduce the diffusion of Sr from the cathode material such as La0.6Sr0.4Co0.2Fe0.8 and enables stable and high performance. However, the limited sintering temperature to avoid side reactions between the two electrolytes incurs the low density of the electrolytes. In this study, we report a facile method for the fabrication of dense gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolyte at low sintering temperatures. Even at 1250 °C, a thin and highly dense bilayer electrolyte structure could be achieved by employing an isostatic pressure process on the dip-coated electrolyte layers and anode support substrate. This dense bilayer electrolyte system exhibits high power density of 1.251Wcm−2 at 650 °C and high stability for 100 h. These improvements in performances are attributed to the greatly reduced porosity (< 2.5%) of the bilayer electrolyte.

Resume : In recent years, the ceramic oxygen transport membranes have attracted substantial attention due to their high selectivity and permeability for oxygen separation from air. A lot of efforts have been dedicated to the development of the single-phase membrane with ABO3 structure due to their outstanding oxygen permeability. Despite these great efforts, perovskite materials cannot be applied commercially due to their thermo-mechanical and chemical instabilities and gradual deterioration of performance when CO2 is used as sweep gas. To overcome these obstacles, many researches have shown increased attention in dual-phase membranes based on fluorite structure material since the fluorite oxides used as an electrolyte of solid oxide fuel cell are mechanically and chemically stable under the real operating atmosphere. However, in terms of the oxygen permeability, oxygen permeation flux produced by dual-phase membrane is noticeably lower than 5- 10 mL∙cm-2∙min-1 that is required to ensure the industrail target of oxygen transport membrane. In this study, the membrane comprises a mixture of gadolinium doped ceria (Ce0.9Gd0.1O2-δ, GDC) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with a volume ratio of 70:30. The perovskite structure is applied as the active materials of ceria-based membrane to enhance the surface exchange reaction on the membrane surface. The highest oxygen permeation flux of up to 10 mL∙cm-2∙min-1 was achieved with the dual-phase membrane at 1000 oC at the air/He condition. The excellent stability was also observed in time dependence of oxygen permeation test where pure CO2 was used as the sweep gas.

Resume : The production of hydrogen has been extensively studied since hydrogen is an ideal energy, high quality and clean energy carrier. Currently, the hydrogen is mainly produced by the fossil fuels or other carbon-based fuels. However, the production technology of hydrogen via the fossil fuels causes global warming by emitting environmental pollutions such as CO, CO2, and CH4. Thus, a lot of efforts have been dedicated to the production of hydrogen through the clean renewable energy sources such as water, biomass. Among these technologies, an alkaline water electrolysis has been considered as the promising candidate for the green hydrogen technology. The high catalytic activity and durability of the electrodes should be guaranteed for commercialization of alkaline water electrolysis. Platinum group metals have the best catalytic activity for alkaline water electrolysis, but it is a limitation to commercialization due to high cost and their dissolution during the oxygen evolution reaction (OER). To overcome the problems, nickel-based metals that are stable during OER have been investigated as electrodes for alkaline water electrolysis. The perovskite oxides are also attractive candidates as catalysts to overcome the low current density and durability. In this study, metal/oxides composite electrode with high activity and durability was fabricated by high-temperature processing. The effects of metal/oxides composite electrode on OER and HER has been systematically studied via the electrochemical measurement analysis.

Resume : In this study, we obtained experimental results similar to the isotope substitution effect by using the proton irradiation of K(H0.47D0.53)2PO4 (DKDP) ferroelectric single crystals. Temperature dependence of dielectric constants showed that the ferroelectric phase to paraelectric phase transition temperature increased from 175 K to 195 K of approximately 20 K after the proton beam irradiation. It was observed that the vibration mode P(OD)2 was changed from 893 to 884 cm-1 in Raman spectroscopy. In 1H Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, the isotropic chemical shift after proton irradiation decreased from 14.46 to 14.32 ppm, which is indicative of the change of the O-H…O the equilibrium distance of hydrogen bonds estimated as 1.60066 Å and 1.62228 Å before and after the proton irradiation, respectively. It was observed that the Full width at half maximum (FWHM) line width also decreased from 563 to 244 Hz in 1H MAS spectral line shape, which is indicative of obeying the displacive phase transition model.

Resume : Solid oxide cells (SOCs) are key elements for hydrogen-based energy storage in a future sustainable energy system. In order to design reliable devices, a detailed understanding of their potential failure mechanisms is needed. In particular, when SOCs are operated in electrolysis mode, the presence of gradients in the electrical and chemical potential can lead to local reduction or segregation which would limit the lifetime of the cells. Using single crystals of the mixed electronic-ionic conductor SrTiO3 and the ionic conductor Y-stabilized ZrO2 (YSZ) as model materials for SOC electrodes and electrolyte, we analyze electroreduction effects under vacuum conditions. We demonstrate that in SrTiO3 single crystals, dislocations act as easy reduction sites thus establishing filamentary conductance paths during electroreduction, while in YSZ an inhomogeneous reduction front evolves following the electric field lines. When prolonged electroreduction is applied in Hebb-Wagner type geometry, a stoichiometry polarization of the oxygen activity is established in both investigated materials. In SrTiO3, this leads to the sublimation of Sr from the surface close to the cathode leaving behind nanoporous TiOx thus revealing a significant degradation mechanism which has not been considered in detail before. Also in YSZ, the ongoing electroreduction results in segregation phenomena related to the evolution of new oxygen-depleted ZrOx phases on the nanoscale eventually altering the oxide’s properties irreversibly.

Resume : Ion-conducting electrolyte accounts for safety and energy density of hybrid-flow and all-solid state batteries. Since liquid electrolytes are highly flammable, ceramic electrolytes attract research attention due to relatively high ionic conductivity and stability. However, ceramics lack mechanical integrity and flexibility during cycling. Therefore, we propose using composite membranes based on conductive ceramics and polymer binder. We selected polyvinylidene fluorine (high electrochemical stability window) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics (facile synthesis; ionic conductivity up to 7·10-4 S cm-1) as a components of composite electrolyte. We optimized the synthesis procedure of the material and studied in detail electrochemical characteristics varying membranes’ composition and outer factors (temperature, working environment). The composite membranes possess the ionic conductivity up to 10-5 S cm-1 at 23 °C in dry from which may be further improved up to 10-4 S cm-1 at 23 °C during soaking in appropriate solvent, the electronic conductivity is 10-10 S cm-1 and the electrochemical stability window is 1.9 – 4.7 V vs. Li/Li+. The samples are applicable as an electrolyte in all-solid-state batteries and lithium hybrid-flow batteries due to sufficient ionic conductivity and high mechanical integrity and flexibility.

Resume : The development of miniaturized and flexible energy storage devices have been intensively studied for future electronics such as portable and wearable devices. However, since the conventional secondary batteries adopt a liquid or gel electrolyte, so that fabrication of the micro-sized batteries is limited. In this regard, all-solid-state Li-ion thin-film batteries (ASSB) with a solid electrolyte are liquid-free battery architecture to solve this problem. However, the process temperature of ASSBs is relatively high compared to conventional liquid electrolyte based batteries. Generally, flexible devices require low-temperature processes due to the low glass transition temperature of the plastic substrate. Moreover, interfacial characteristics between electrode and solid electrolyte need to be improved. In this study, the electrochemical properties of Li-ion batteries (Li4Ti5O12/electrolyte/Li) were investigated by changing the electrolyte type, as well as the presence and absence of polymer-based separator. Also, the effects of the Al2O3 interlayer between the electrode and solid electrolyte (LiPON) were studied. As a result, the improved electrochemical characteristics were obtained for the ASSB without a polymer-based separator. Despite the fabricated ASSBs showed low electrochemical performance due to large interfacial resistance compared to batteries with liquid electrolytes, but it was improved when the Al2O3 was adopted as an interlayer.

Resume : Although lithium ion batteries (LIBs) are the most fascinating systems for large scale energy storage, the conventional flammable organic liquid electrolyte limits the safety of the LIBs. In this regard, while solid state electrolyte provides the high energy density with high safety, the poor interfacial contact between electrode and electrolyte is the major issue for commercialization of the all-solid-state (ASS) LIBs. Solid polymer electrolyte (SPE) is a promising electrolyte for next generation ASSLIBs owing to their safety advantages. However, the insufficient ionic conductivity, mechanical strength, and electrochemical stability raise several queries for the practical application of SPEs. Thus, it is of immense importance to find novel SPE with superior electrochemical property and stability. The composite solid polymer electrolyte (CSPE) with poly(propylene carbonate) as host matrix with mesoporous silica nanoparticles as passive ceramic filler are capable to attain noteworthy properties. The prepared CSPE with 4wt.% of MSN filler exhibited high ionic conductivity of ~7.5×10-4 S cm-1, wide electrochemical potential window >4.8 V vs. Li/Li , high lithium transference number ~0.87, and good enough mechanical strength. Moreover, CSPE shows excellent stability with lithium metal for longer than 1000 h lithium stripping/plating cycles at 60 °C. Li/CSPE/LiFePO4 (LFP) cell delivered specific discharge capacity of 103 mAh g-1 even at high current of 1C and impressive stability over 200 cycles with small over potential. Moreover, Li/CSPE/LFP cell exhibited excellent rate capability up to 5C. Such notable electrochemical performance of CSPE is attributed to the uniform distributed highly mesoporous silica which allows large surface area for interaction with PPC matrix by forming intense polymer-ceramic phase for lithium transportation. The highly mesoporous silica reinforced CSPE offers opportunities for highly stable, lithium dendrite free-, and high energy density ASSLIBs.

Resume : The direct and converse magnetoelectric effect, i.e. switching of the polarization by a magnetic field and switching of the magnetization an electrical field, are highly interesting for a large variety of applications, e.g. as sensors or in data storage devices. Here, we report on multiferroic heterostructures consisting of BaTiO3 or Ba0.5Sr0.5Nb2O6 as ferroelectric component in combination with ferrimagnetic ferrite spinels MFe2O4 (e.g. M = Co, Ni) or ferromagnetic metals/alloys (Co, Ni, Co1/3Fe2/3). Different classical and soft-chemistry synthesis approaches have been applied leading to 0–3- (particles embedded in a matrix) and 3–3-heterostructures (interpenetrating networks). The samples have been investigated using a broad variety of characterization techniques including XRD, SEM/EDX, impedance spectroscopy and temperature- and field-dependent magnetic measurements. The magnetoelectric effect has been studied in detail with respect to different compositions, temperature, external magnetic field and frequency.

Resume : LiCoO2 is the most commonly used transition metal oxide cathode in lithium-ion batteries because of its high operating voltage (~ 4V), ease of synthesis, and good cycle life. However during fabrication and device operation Co and oxygen diffusion into the electrolyte occurs. This results in decreased energy and power density, and increased impedance. The issue is exacerbated in the case of thin-film solid-state electrolytes, which requires a heating step during fabrication (e.g. Li7La3Zr2O12). The interdiffusion of the electrolyte and the LiCoO2 forms a strongly ionically resistant interlayer. One way to suppress the chemical instability and reactivity with the electrolyte is to coat the surface of the cathode with inert oxides. An ALD process for Nb2O5 is presented, which acts as a coating for the thin-film LiCoO2 cathode fabricated by magnetron sputtering. To investigate the electrochemical performance, liquid electrolyte half-cells were assembled with Li foil as anode. In this first step, the focus lies on the power density of the modified cathodes. By investigating cathode and coating thickness, increased rate performance could be demonstrated. Such Nb2O5-coated LiCoO2 cathodes showed at 20 C charge rate, 80% capacity retention relative to 1 C, which for uncoated cathodes, no capacity remained at that rate.

Resume : CdTe-based compounds are recently studied with the intention to be used in the detection at room temperature of high energy radiation – X-rays and gamma-rays. For this application the uniformity of a crystal structure and an electric field within the bulk crystal is required. Tellurium inclusions are typical for CdTe obtained by the Bridgman method. In some of the crystals, grown under cadmium-excess, Cd inclusions were found. Pockels electro-optic effect studies present that in the vicinity of Te inclusions the internal electric field is disturbed, whereas Cd inclusions have no impact on this issue. Transmission infrared microscopy demonstrates that Te inclusion does not cause micro fractures in CdTe lattice. However, a Cd inclusion with a similar size as Te, generates micro cracks in the area which is few times bigger than the inclusion itself. Thus, Cd defect consists of the core (inclusion) and the six branches (cracks). We link the six directions of the cracks with the three easy-cleavage planes (110) in the zinc blende structure. SEM observations and the electron backscatter diffraction (EBSD) techniques allow for the detailed investigation of regions around the inclusions and other types of defects, like grain boundaries, as well as to determine changes in internal stresses in the vicinity of inclusions.

Resume : Improving the energy density of lithium-ion batteries by replacing a graphite anode with lithium metal anode is heavily desired.1 The garnet (LLZO) solid electrolytes are promising candidates to protect lithium metal due to their high lithium-ion conductivity and high elastic modulus, however, the interfacial chemistry between LLZO/Li is poorly understood.2-4 In this work, LLZO electrolytes of >98% theoretical density were prepared with Field Assisted Sintering Technology. The solid state electrochemistry of LLZO with lithium and blocking electrodes is characterized using electrochemical impedance spectroscopy. Further, investigation of interfacial phenomena between LLZO and Li metal using a suite of surface characterization techniques will be discussed in detail. References 1. Liu J., Bao Z., Cui Y., Dufek E. J., Goodenough J. B., Khalifah P., Li Q., Liaw B. Y., Liu P., Manthiram A., Meng Y. S., Subramanian V. R., Toney M. F., Viswanathan V. V., Whittingham M. S., Xiao J., Xu W., Yang J., Yang X. Q., and Zhang J. G., Nat. Energy, 4, 180 (2019). 2. Krauskopf T., Hartmann H., Zeier W. G., and Janek J. ACS Appl. Mater. Interfaces, 11, 14463 (2019). 3. Fu K., Gong Y., Liu B., Zhu Y., Xu S., Yao Y., Luo W., Wang C., Lacey S. D., Dai J., Chen Y., Mo Y., Wachsman E., and Hu L. Sci. Advances, 3, e1601659 (2017). 4. Sharafi A., Kazyak E., Davis A. L., Yu S., Thompson T., Siegel D. J., Dasgupta N. P., and Sakamoto J. Chem. Mater. 29, 7961 (2017).

Resume : This work is devoted to the preparation of three-component Ga1-xAlxAs and Ga1-xAlxP nanofilms by varying x on the surface of GaP and GaAs by ion implantation, and their composition, structure, and properties are studied. Single crystal GaP(111) and GaAs(111) samples were chosen as objects of study. Before ion implantation, GaP(111) was irradiated under ultrahigh vacuum (P = 10-7 Pa) at T = 900 K for ~4 hours. By implanting Al+ ions with E0 = 1 keV at different doses on the surface of a GaP(111) single crystal, nanocrystalline phases and Ga0.6Al0.4P grains were obtained and their composition, crystal structures, and properties were studied. It is shown that the type and lattice parameters of a three-component nanostructure are in good agreement with those for the substrate. An analysis of the change in the parameters of the bands shows that, at d≤35–40 nm, the quantum-size effects disappear in the nanocrystalline Ga0.6Al0.4P phases. The implantation of Al+ ions with Е0 = 1 keV at a dose of D = 1017 cm–2, as in the case of GaAs, led to the uniform incorporation of Al atoms in the middle part of the irradiated GaP surface. Moreover, the Al concentration on the surface was ~30-35 at.% And the entire irradiated surface was strongly disordered. After heating at T = 900 K, a three-component compound with an approximate composition of Ga0.6Al0.4P was formed on the surface.

Resume : Multiferroicity has great potential for the next generation electronic applications such as ferroelectric photovoltaics and next-generation memory devices. An epitaxially-grown antiferromagnetic BiFeO3 is representative material which shows the multiferroicity with single phase, while a ferromagnetic-electrically coupled material at room temperature has not been reported yet. In this presentation, we show a Pb-based perovskite which is magnetoelectrically coupled above even room temperature. Detailed x-ray absorption spectroscopy studies at both near (XAS and XMCD) and extended edges (EXAFS) have confirmed that the ferrimagnetic property of perovskite has been induced by the A-site substitution with Ni.

Resume : State of the art SOEC are complex structures requiring many fabrication steps and are still presenting durability issues. On one side, fuel electrodes, usually made with Ni YSZ (yttria stabilized zirconia Y2O3-ZrO2) cermets, suffer re-oxidation, Ni volatility and agglomeration and coking issues during pure CO2 electrolysis and co-electrolysis. On the other side, oxygen electrodes, usually made with La1 xSrxMO3 δ (LSM) YSZ composites or by mixed ionic-electronic conducting (MIEC) perovskite like La1 xSrxCo1 yFeyO3 δ (LSCF), are subject to delamination problem or inter-diffusion of ions. This work presents the study of symmetrical solid oxide cells made with Sr2Fe1.5Mo0.5O6−δ (SFM) electrodes. The symmetrical configuration allow a reduction of sintering steps and an improvement of the electrodes-electrolyte thermomechanical compatibility meanwhile the use of MIEC perovskite electrodes enables operations under steam electrolysis (SOEC) or co-electrolysis (co-SOEC) without the use of safe gas at the fuel electrode. YbScSZ tapes previously coated with a Ce1 xGdxO1.9 (GDC) barrier layer grown by pulsed laser deposition (PLD) were used as electrolyte supports. The sintering temperature of electrodes was optimized by means of electrochemical impedance spectroscopy (EIS) measurements in both air and H2 symmetrical atmosphere. The cell was then electrochemically characterized under SOEC and co-SOEC modes without the use of H2 as a safe gas reaching a maximum injected current density of 1.4 and 1.1 A·cm-2 respectively, at the thermoneutral voltage. The cells reversibility was proved by switching electrodes chambers composition between the cathode and anode.

Resume : Aqueous rechargeable zinc-metal batteries (ZMBs) are emerging as safe and promising electrochemical energy storage technology. However, cycle life of ZMBs are often hampered due to the formation of undesired dendrite-like structure on the metallic zinc anode. In the current work, we have addressed this issue by employing Zn2+-integrated Nafion ionomer membrane as the separator. The membrane created by coordinating Zn2+-ions with the sulfonated tetrafluroethylene polymer chain present in Nafion, furnishes the single ion conducting electrolyte feature. As a result, the ionomer membrane facilitates the mobility of Zn2+-ions during the charge/discharge cycles and directs the uniform electrodeposition of zinc on the anode. We have demonstrated the utility of Nafion membrane in ZMBs with two different transition metal oxide cathodes; V2O5 and MnO2. Compared to the traditionally used porous separators (glass fibre paper or Celgard separator), the Nafion-based cells could endure more than 1000 charge/discharge cycles with better capacity retention. The further characterization of the post-stability anodes reveals the smooth surface of the zinc anode coupled with Nafion membrane. On the other hand, the porous separators lead to nonuniform dendrite-like surface morphology of the cycled-anodes. This indeed highlights the critical role of ionomer membrane in stabilizing the metallic anode resulting improved cycling performance of ZMBs.

Resume : As we move towards next generation applications for supercapacitors, it is imperative to characterize their performance under non-ambient and/or inconvenient environments. These include: changing magnetic field, temperature, external shocks or vibrations, etc. I will discuss the effects of all these external parameters on the device performance, which can open a new direction in the field of supercapacitor research. The strategy of exposing the supercaps to magnetic field before their real application can enhance the deliverable specific capacitance. In supercapacitors, fabricated using ferromagnetic metal oxides such as Fe2O3, MnO2, etc., nearly 170% increase in energy density, at 1 A g−1, was observed by varying the magnetic field from 0 to 5 mT. In addition, a ten-fold increase in the power density can be obtained. The observations are attributed to the changing Lorentz force and/ or magneto-hydrodynamic effects. Therefore, one may argue that size of the electrolyte ion should also be considered. It is clearly shown that this hypothesis, which predicts ‘change in specific capacitance’ by varying electrolyte, is correct. Till date, a Nernstian relation across the electrode is used to explain the super capacitive behaviour of a cell. The theoretical formulations proposed in the Gouy Chapman or the Stern models have no parameters that consider the consequences of a varying magnetic field. It is shown that the net charge flux is essentially dominated by the diffusive transport of the ions. The modified theory leads to consistent results, which are corroborated with the experimental data. In B=0 limit, the model reduces to the earlier mentioned established theoretical postulates

Resume : Several non-stoichiometric transition metal complex oxides have been proposed for oxygen separation from air. Apart from the high concentration of oxygen vacancies, a favorable crystal structure with low energy migration pathways is required for high ionic conductivity at lower temperatures. Neutron diffraction having better sensitivity towards oxygen atoms can be exploited to probe the fractional coordinates and Debye-Waller factors of oxygen, even in the presence of relatively higher atomic number metals. This gives insight into the crystallographically distinct oxygen which is responsible for the high oxide ion mobility in the material under question. Herein, the structural analysis of the three different phases of strontium cobalt oxide has been performed to investigate the oxide ion mobility at room temperature in them. The three phases, namely Sr6Co5O15, SrCoO2.5 and SrCoO3-d were analyzed by means of neutron diffraction at room temperature. A combined Rietveld refinement of X-ray and neutron diffraction patterns was carried out to achieve a single structural solution. The crystallographically different oxygens which are responsible for oxide ion movement inside the lattice were identified and found to have lower fractional occupancy in addition to higher thermal parameters. Apart from diffraction studies, electrical conductivity measurements in different atmospheres were also used to characterize the oxide ion mobility in these oxides. The electrical conductivity of SrCoO2.5 was measured in air, nitrogen and oxygen atmospheres showing a difference in conductivity due to possible oxygen intake/release.

Resume : Manganites in the form of thin films can present functional properties that vary largely in comparison to their intrinsic bulk properties. There is thus a large interest in understanding and controlling the influence of different parameters, such as epitaxy, substrate-induced strain and grain boundary effects, for the use of manganites in applied miniaturized functional devices for resistive switching (RS) memories, spintronic sensors, micro solar cells and micro solid oxide fuel cells. In this study we have selected LaMnO3±δ (LMO) due to its large oxygen reduction catalytic activity as a suitable material for applications such as solid oxide fuel cells cathode or catalyst for oxidation reactions. With these applications in mind, epitaxial LMO films were grown by Pulsed-Injection Metalorganic Chemical Vapor Deposition on two different substrates (SrTiO3 and LaAlO3) with different degree of strain, thickness and morphology. Their oxygen exchange and diffusion properties were measured at the temperature range of interest (500°C- 600°C) by the Isotope Exchange Depth Profile methodology combined with Time-of-Flight Secondary Ion Mass Spectrometry and the influence of strain and vertical dislocations on the oxygen ion transport across the films has been evaluated. Here we will show how the incorporation of oxygen into the LMO film and the ion transport down to the bottom interface can be maximized by a combination of strain engineering and film nanoarchitecturing.

Resume : Manganite thin films exhibit interesting properties for applications such as resistive switching (RS) memories or cathodes for Solid Oxide Fuel Cells. In thin films, the functional properties depend on the microstructure and composition. In particular, for valence change memories the resistance change relies on the oxygen vacancies drift, so the RS phenomena are expected to be tunable by varying the film nanostructure. With the two above-mentioned applications in mind strontium substituted LaMnO3 (La1-xSrxMnO3, LSM) was selected to study the structure-properties relation and their impact on the oxygen exchange kinetics and RS response. LSM thin films were grown by Pulsed Injection Metal-Organic CVD optimizing the deposition conditions to obtain dense films with different Sr substitution, i.e. x=0.20 and 0.50. LSM films were grown polycrystalline (on a Si3N4 substrate) and epitaxial (on LaAlO3 single crystals) and their electrical conductivity was studied as a function of film microstructure and Sr content. To understand the oxygen content structural changes and oxygen exchange in-situ Raman characterization was combined with simultaneous conductivity measurements at different temperatures and oxygen partial pressures. These experiments will set the grounds to understand the role of composition (strontium and oxygen content) and microstructure (role of the grain boundaries) in the oxygen exchange kinetics and resistive switching properties.

Resume : Bulk nanostructured simple oxides, such as TiO2, ZrO2 and CeO2, obtained through fast sintering approaches, have been shown to present a significant proton conductivity in presence of humidity. This conductivity is associated to a conduction process confined to surface of residual nanoporosity present in these materials. These ceramic materials might represent an interesting alternative to polymeric protonic conductors for low temperature applications, due to their low-toxicity, high chemical stability, high melting point and low cost. Optimization of the nanostructure and of the surface chemistry is required in order to enhance their conductivity. Doping with sulfur resulted to be particularly effective, but not on all the oxides. In this work the protonic conductivity of three undoped and sulfur-doped oxides was investigated. Nanopowders of the oxides, presenting a grain size around 10-20 nm were obtained. The nanopowders were densified by HP-FAST under 500-700 °C and a pressure of 400-600 MPa for 5 minutes. The conductivity measurements were performed at 80°C at different values of relative humidity. In all cases the conductivity is enhanced by the increase sulfur content. In the case of CeO2 the increase is very limited. On the contrary S-doped ZrO2 and S-doped TiO2 show a substantial enhancement in the protonic conductivity. Samples of TiO2 with the higher content of sulfur reach conductivity values of 0.1 S·cm-1, close to the ones reported for perfluorinated polymer-based protonic exchange membranes.

Resume : High entropy oxides (HEO) represent a new class of materials where a large number of cations are randomly and homogeneously distributed on few crystallographic sites, producing a significant entropic contribution and a reversible solid-state transformation between multiphase and single-phase states. In this study we investigated the compositional stability range of the high entropy oxide (CoxCuyMgzNiwZnk)O with (x+y+z+w+k=1), presenting a rock-salt structure, using the experimental design of mixtures. The first objective was to investigate the field of existence of the single-phase HEO and then determine how the electrical properties are affected by the composition. Since the number of possible compositions is high also for mixture design we decided to simplify the system grouping together the component oxides which present similar solid structure. The choice of the compositions to investigate, the so call candidate points, was done through the D-optimal design. The oxides were synthesized by solid-state reaction from the component simple oxides (CoO, CuO, MgO, NiO and ZnO) using an HP-FAST apparatus. The electrical properties were characterized by EIS until 500°C. It has been evidenced that this HEO phase presents a fairly wide compositional range. Within this range the electrical properties present significant modifications. The influence of compositional parameters on the overall electrical properties has been identified by principal component analysis (PCA) investigation.

Resume : In the novel layered perovskite-related material, BaNdInO4, the solubility of calcium ions on the Nd3+ site and the electrochemical properties of these doped material were investigated. All BaNd1-xCaxInO4-x/2 (x=0.0, 0.05, 0.10, 0.15, 0.20, 0.25) samples were synthesized through a solid-state reaction method. The structure analysis of those materials confirmed a monoclinic crystal structure with P21/c symmetry as reported in the previous literature[1]. A shrinkage in the unit cell volume and the lattice parameters was observed as the calcium content in the system increased. According to the electrochemical impedance spectroscopy(EIS), an increase in total conductivity of 1-2 orders of magnitude was achieved in the 10 mol% and 20 mol% calcium doped samples compared with the parent material. Among all calcium doped samples, BaNd0.8Ca0.2InO3.90 yielded the highest total conductivity σ(total) of 1.143×10-3 S˖cm-1 under lab air at 973K which was 20 times higher than that of parent material, BaNdInO4 (σ(total)=5.07×10-5 S˖cm-1 at 973K). These results agree with the previous reference[2]. The potential of these materials being used as protonic conductors was also investigated by measuring the electrochemical properties of these materials under wet conditions using the EIS technique. An increase in total conductivity was observed in both 10 mol% and 20 mol% calcium doped samples, which implied the presence of proton conductivity in these materials. The 20% calcium doped sample exhibits a total conductivity of 2.45×10-4 S˖cm-1 at 500℃, which is higher than most of the state-of-the-art proton conducting electrolytes[3] except for the BaZrO3 or BaCeO3 based perovskite conductors[4]. Besides, a unique controlled-atmosphere system was used to measure the resistivity of these Calcium doped samples under different atmosphere. Clear evidence of these materials being a protonic conductor was observed, such as mass increase and resistivity decrease as the atmosphere changed from dry to humid air. The transport of oxygen ions within both the parent material and the calcium doped sample was investigated by the isotope exchange depth profiling (IEDP)[5] technique. The kinetic parameters gained by these measurements were then compared with the ionic conductivity of these materials obtained in the EIS experiments under controlled atmosphere.

Resume : Lead-based perovskite structure materials with high dielectric constant value have wide applications in electronic devices, but due to the toxic nature of lead, a search of lead-free materials begins. Barium iron niobate (BaFe0.5Nb0.5O3, BFN), lead-free double perovskite structured ferroelectric material, shows high dielectric constant value. Here we studied the dielectric properties (impedance and modulus) of polycrystalline BFN sample between 20 to 300 K temperatures. The high value of the dielectric constant is due to the Maxwell –Wagner (space charge) type polarization at the grain boundary region. The origin of the dipolar polarization is due to the displacement of the cation (Fe3+ and Nb5+) with respect to the oxygen octahedra. It follows the non Debye type relaxation with relaxation straight of 3560. Activation energy calculated from the dielectric and modulus formalism is 17.26 meV and 2.74 meV corresponds to the motion of Fe3+ and Nb5+ ions in the oxygen octahedra. Temperature dependent impedance study shows the BFN is a potential candidate for direct application as low-temperature NTC thermistors.

Resume : Amorphous oxide semiconductors (AOS) are industrially applied in pixel driver thin film transistors of flat panel displays. The realization of AOS based memdiodes allows straight-forward integration towards hardware artificial intelligence systems on panel. Here, a comparative study of charge transport in various AOS based memdiodes with different Schottky contacts is presented. The studied resistive switching layers are either based on indium-gallium-zinc-oxide (IGZO) or indium-free zinc-tin-oxide (ZTO).[1] Besides platinum and gold, a novel non-noble Schottky contact is reported, based on an intentionally oxidized molybdenum bottom contact interface. All memdiodes have area-dependent characteristics and the rectification is preserved during switching events. Resistance state dependent changes to the barrier height and other parameters characterizing the diode forward current are presented, as well as evidence for ion migration during electroforming. Reference: 1: N. Casa Branca, J. Deuermeier, J. Martins, E. Carlos, M. Pereira, R. Martins, E. Fortunato, A. Kiazadeh, Advanced Electronic Materials 2019, DOI: 10.1002/aelm.201900958

Resume : Nano-scale 3D imaging techniques have enabled the multiphase microstructures of fuel cell and battery electrodes to be captured in detail. However, the resulting voxelised datasets are often very large and difficult to manipulate. This geometrical data is typically used to calculate a few key homogenised metrics (such as volume fractions, surface areas and tortuosity factors), which can then be inserted into low dimensional models. However, previous work by the authors have shown that microstructures with identical homogenised parameters, may still lead to a variety of electrochemical responses [REF]. Furthermore, improving electrode performance may depend strongly on the arrangement of the phases, which may not be captured by the standard microstructural metrics. Multiphysics modelling at the nano-scale can offer some insight into which configurations are optimal based on simulations performed within synthetic microstructural data. However, for this to be a useful tool, it is necessary to constrain the search space to include only those electrodes that are manufacturable. A variety of techniques have been employed over the years attempting to generate relevant structures, but often they bear little resemblance to real data. Deep convolutional generative adversarial networks (DC-GANs) are a powerful new approach to encoding imaging data. By training a DC-GAN on real image data from a variety of processing routes, it enables the user to then generate microstructures that have targeted properties intermediate to those in the training set, but still closely resembling real electrodes. This talk will introduce the approach and explore some of the more exciting implications for electrode characterisation and design.

Resume : Niobium, titanium-niobium, and niobium-tungsten oxides with crystallographic shear structures have shown excellent high-rate performance as electrodes for lithium-ion batteries [1]. The electronic structure, lithium insertion mechanism, and lithium dynamics of these compounds is largely unexplored due to their novelty and complexity. In this contribution, I will present recent first-principles density-functional theory (DFT) calculations by our group on the lithium intercalation and lithium diffusion mechanisms of crystallographic shear phases in the Wadsley-Roth family, specifically mixed-metal niobium-tungsten oxides. Our work has explored the electronic structure [2,3] with implications for electronic transport within lithiated shear structures and provided a unified mechanistic picture for the local and long-range structural changes in the family of crystallographic shear phases [3], focussing on the link between local distortion relaxation and buffered volume expansion. Simulations of lithium diffusion using transition state search techniques and ab initio molecular dynamics show effectively one dimensional diffusion with a clear hierarchy of activation barriers. Structure-property relationships that follow from these simulations will be discussed. [1] K. J. Griffith et al., Nature 559, 556-563 (2018) [2] Can P. Koçer, Kent J. Griffith, Clare P. Grey, Andrew J. Morris, Phys. Rev. B, 99, 075151 (2019) [3] Can P. Koçer, Kent J. Griffith, Clare P. Grey, Andrew J. Morris, J. Am. Chem. Soc, 141, 15121-34 (2019)

Resume : Garnet-type electrolytes have received great attention in the development of the next generation of solid state batteries based on Li-metal anodes because of their Li conductivity (greater than 1 mS/cm at room temperature) and stability against Li metal. However, their applicability has been hindered due to major issues related to stability and degradation phenomena that need understanding and addressing. The wide-ranging literature and lack of consensus with respect to the performance of garnets, in particular the Li conductivity, interfacial resistance with Li metal and critical current density for dendrite formation can be correlated to a lack of consistency in controlling the processing conditions for the material. This has a knock-on effect on the microstructure, local chemical composition of bulk, surfaces and grain boundaries and can also induce degradation phenomena such as segregation of secondary phases and moisture reactivity. All these parameters have a direct impact on the Li-ion dynamics in these systems, leading to significant implications on the cell performance in terms of power density and cycle life. In this work, we use a combination of Li-6 isotopic labelling, surface analysis techniques and electrochemistry to understand factors limiting the performance of garnet electrolytes when using Li metal as an anode. The effect of local chemical inhomogeneities will be explored and an introduction to the use of isotopic labelling for analysing Li-ion mobilities within grain, grain boundaries and interfaces will be given.

Resume : The degradation of LLZO-type garnets and, as a consequence thereof, the formation of resistive layers, such as Li2CO3, limits the application of garnets as solid-state electrolytes. Although, some studies on the underlying H+/Li+ exchange already exist, a complete fundamental understanding is still missing. This lack of knowledge mainly originates from the usage of polycrystalline materials having different grain sizes and, therefore, a varying bulk-to-surface ratio. Here, we used Li6La3ZrTaO12 single crystals to investigate their degradation behaviour in humid atmosphere. Ion exchange was carried out in distilled H2O for various time spans ranging from 1 to 31 days. The amount of Li+ exchange and the site preferences of the two cations, Li+ and H+, was studied via single-crystal neutron diffraction. Additionally, we investigated the influence on overall (ionic) conductivity by broadband impedance spectroscopy. Via 7Li and 1H Nuclear Magnetic Resonance (NMR) spectroscopy we separated the contribution of both ions to the overall conductivity and, furthermore, shed light on the diffusion pathway of H+ through the crystal.

Resume : In comparison to bulk Gd-doped ceria (GDC), little is known about the electrical grain boundary properties in thin films. This lack of knowledge arises from the small cross-sectional area of thin films, which makes separation of impedance features rather challenging. Here, we use embedded interdigitating Pt electrodes with spacing of few micrometers to separate grain and grain boundary conductivity of GDC thin films and characterise the effect doping and atmosphere. Since the used embedded Pt thin film electrodes are blocking for oxygen ions and reversible for electrons, they allow determination of partial electronic and ionic conductivities, with interesting results: Although the bulk vacancy concentration remains dominated by the extrinsic acceptor doping, the ionic conductivity of the films increases by up to one order of magnitude when going from oxidising to reducing atmosphere. By comparing conductivities of GDC thin films with 5 and 10 mol % Gd content, we find that the much lower ion conductivity of 5 % doped GDC is almost exclusively caused by a significantly higher grain boundary resistance. This finding is in line with the widely accepted grain boundary space charge model. The results are of high relevance for optimising the properties of GDC in anodes and electrolytes for solid oxide fuel cells, as well as for understanding electrostrictive and memristive devices, for which oxygen partial pressure dependent ionic conductivity is an important new aspect.