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2019 Spring Meeting



Latest advances in solar fuels

This symposium will provide an interdisciplinary forum for the latest R&D activities on sustainable solar hydrogen generation by addressing the latest advances in fundamental understanding as well as performance and stability of efficient catalytic systems by bringing together top world-wide academic scientists and engineers.


Staggering air pollution worldwide, now chronic in certain major cities in Asia and in the Western world, has become one of the most important problems that humanity is facing. It is therefore crucial to transition to new societies where environmental, energy, and economic policies are no longer based on fossil fuel technologies to substantially decrease our environmental and health impact. Without a doubt, using the two most abundant, free, and geographically balanced resources available on Earth, that is the sun and seawater, to make an unlimited amount of clean H2 is The way forward. Indeed, it will provide a clean and sustainable energy resource while releasing only H2O in the atmosphere as an emission product from combustion and/or fuel cell use. With several decades of research, the scientific community still encounters great academic and technological challenges to efficiently generate hydrogen from water with sunlight at large scale and low cost. Recent developments based on novel system designs have led to significant advances in the fundamental understanding of light-induced charge dynamics and related interfacial chemical reactions and efficiencies as well as long term performance and stability of such new systems. This symposium aims to gather the most significant advancements in recent years for a sustainable generation of hydrogen from solar energy.

Hot topics to be covered by the symposium:

  • Latest improvements in photoelectrode design and performance for (sea)water splitting and CO2 reduction
  • Novel hybrid molecular-semiconductor catalytic systems
  • Progress in operando/in-situ spectroscopic techniques for energy science
  • Advances in materials design for efficient plasmonic/hot electron/multiple exciton generation
  • Status of long term performance and stability strategies and assessments
  • Latest development in low cost and large scale fabrication techniques
  • Atomic-scale understanding of mechanism and structural-performance relationships
  • Multi-time scale dynamics of photogenerated charges and defects
  • Modeling and simulation of photo(electro)catalytic solar fuels generation
  • National and international solar fuel energy systems, projects, and networks

Confirmed list of invited speakers:

  • Alceo Macchioni, Univ. Perugia, Italy
  • Antoni Llobet, ICIQ, Spain
  • Artur Braun, EMPA, Switzerland
  • Bruce Koel, Princeton Univ., USA
  • Bruce Parkinson, Univ. Wyoming, USA
  • Chengxiang Xiang, California Institute of Technology, USA
  • Chung-Li Dong, Tamkang Univ., Taiwan
  • Clemens Heske, Karlsruhe Institute of Tech., Germany
  • Daniel Esposito, Columbia Univ., USA
  • Emily Carter, Princeton Univ., USA
  • Gary Brudvig, Yale Univ., USA
  • Gerko Oskam, CINVESTAV, Mexico
  • Ghim Wei Ho, Natl Univ. Singapore
  • Harry Tuller, Massachusetts Institute of Technology, USA
  • Hicham Idriss, SABIC, Saudi Arabia
  • Ian Sharp, TU Munich, Germany
  • Jae-Sung Lee, UNIST, Korea
  • Jan Augustynski, Warsaw Univ., Poland
  • Jennifer Leduc, Koln Univ., Germany
  • Jin Zhang, UC Santa Cruz, USA
  • Jinghua Guo, Lawrence Berkeley Natl. Lab., USA
  • Jozsef Pap, MTA, Hungary
  • Juan Ramon Morante, IREC, Spain
  • Kazunari Domen, Univ. Tokyo, Japan
  • Kevin Sivula, EPFL, Switzerland
  • Lianzhou Wang, Univ. Quensland, Australia
  • Mahendra Sunkara, Univ. Louisville, USA
  • Mohammed Huda, UT Arlington, USA
  • Ooman Varghese, Univ. Houston, USA
  • Prashant Kamat, Notre Dame Univ., USA
  • Renata Solarska, Warsaw Univ., Poland
  • Shaohua Shen, Xi’an Jiaotong Univ., China
  • Song Jin, Univ. Wisconsin, USA
  • Tim Lian, Emory Univ., USA
  • Victor Batista, Yale Univ., USA
  • Victor Klimov, Los Alamos Natl. Lab., USA
  • Wolfram Jägermann, TU Darmstadt, Germany
  • Yanfa Yan, Univ. Toledo, USA
  • Yasuhiro Tachibana, RMIT, Australia
  • Zetian Mi, Univ. Michigan, USA

Confirmed list of scientific committee members:

  • Thomas Hamann, Michigan State Univ., USA
  • Nick Wu, West Virginia Univ. USA
  • Yat Li, UC Santa Cruz, USA
  • Heinz Frei, LBNL, USA
  • Frank Osterloh, UC Davis, USA
  • Kirk Bevan, McGill Univ., Canada
  • Dongling Ma, INRS, Canada
  • Csaba Janaky, Univ. Szeged, Hungary
  • Liejin Guo, Xi’an Jiaotong Univ., China
  • Ana Flavia Nogueira, IQ-UNICAMP, Brazil


  • Solar Energy Materials and Solar Cells (Impact Factor 2016: 4.784) (Approved)
  • Journal of Materiomics (Approved)
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Latest Advances in Solar Fuels I : Lionel Vayssieres
Authors : Kazunari DOMEN
Affiliations : Shinshu University The University of Tokyo

Resume : Sunlight-driven photocatalytic water splitting has attracted much attention as a means of renewable hydrogen production on a large scale. Water splitting systems must be both efficient and scalable for practical application. Development of particulate photocatalysts driving overall water splitting efficiently has a significant impact because such systems can be spread over large areas using inexpensive solution processes. The author’s group has developed photocatalyst sheets consisting of La- and Rh-codoped SrTiO3:La,Rh and Mo-doped BiVO4 embedded into a conductor layer by particle transfer for Z-scheme water splitting. The conductor layer transfers photogenerated carriers between photocatalyst particles efficiently. The photocatalyst sheet based on a carbon conductor exhibits a solar-to-hydrogen energy conversion efficiency (STH) of 1.0% at an ambient pressure, which is outstanding among particulate photocatalyst systems. The author’s group has also been developing panel-type reactors that accommodate photocatalyst sheets effectively in view of large-scale application. Al-doped SrTiO3 photocatalyst sheets contained in a panel-type reactor split water and release gas bubbles at a rate corresponding to a STH of 10% under intense UV illumination even when the water depth is merely 1 mm. A 1-m2-sized photocatalyst panel reactor splits water under natural sunlight irradiation without a significant loss of the intrinsic activity of the photocatalyst sheets.

Authors : Jae Sung Lee
Affiliations : School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919 Korea

Resume : About 400 semiconductor solids are known to have photocatalytic activity for water splitting. Yet they could not satisfy all the requirements for practical use: i) suitable band gap energy (~ 2 eV) for high efficiency, ii) proper band position for reduction/oxidation of water, iii) long-term stability, iv) low cost, v) high crystallinity, and vi) high conductivity. Among these requirements, we considered that the long term durability and low cost are most important for practical applications. Thus, we have selected intrinsically stable metal oxide semiconductors made of earth-abundant elements. But because of their poor charge mobility, we employ multiple modifications strategy to minimize recombination of generated photoelectrons and holes, and extract full potential of the materials.[1] Finally, we construct a stand-alone solar fuel production system by combining with a solar cell in tandem, which provides bias voltage needed for unassisted solar fuel production utilizing only solar energy.[2] Due to the rapid materials development in the field during the last two decades, it is the time now to consider practical applications of the technology. The presentation will be concluded by providing a perspective on the scale-up and dissemination of the solar hydrogen production technology.

09:30 Coffee Break    
Authors : Emily A. Carter
Affiliations : School of Engineering and Applied Science, Princeton University, Princeton, New Jersey 08544-5263, United States

Resume : Electrochemically based water splitting to produce sustainable hydrogen remains impractical because of the dearth of inexpensive electrocatalysts that can efficiently carry out the more difficult half-reaction of water oxidation. Even more difficult is carbon dioxide reduction to useful products. This lecture will discuss structural and mechanistic characterization of (photo-)electrocatalysis at complex semiconductor electrodes, as derived from quantum mechanics calculations. High fidelity modeling of the water-semiconductor interface is crucial. I will present my group’s recent work identifying the most probable active crystal facets and key surface species involved in water oxidation at doped NiOOH electrodes, along with our latest findings related to photo-electro-reduction of carbon dioxide at functionalized compound semiconductor electrodes.

Authors : Artur Braun
Affiliations : Empa

Resume : Atmospheric oxygen that we live on is the result of a fundamental evolutionary step in photosynthesis which occurred on Earth 2-3 billion years ago [Biello 2009]. The water oxidation in natural photosystem II accounts for 50% of this oxygen. The man-made analog to this natural process is water oxidation in photoelectrochemical cells - one of the most complex processes in physical chemistry. I will showcase how modern x-ray spectroscopy methods have assisted in the understanding of the molecular processes which occur in natural [Bora 2013, Ralston 2000, Visser 2001] and in man-made "photosystems". The operando and in situ analyses of the aforementioned processes is still a major technical challenge. A most recent example is the element and orbital specific identification of transient electron holes in iron oxide [Braun 2012], chemical surface intermediates [Bora 2011] and changes in the water molecules in the electrochemical double layer during photoelectrochemical water oxidation [Braun 2016]. I will also demonstrate how the electronic structure evolution is quantitatively paralleled by the electric transport properties of the electrodes during operation. [Biello 2009] Biello D: The Origin of Oxygen in Earth's Atmosphere. In Scientific American 2009. [Bora 2011] Bora DK et al. Journal of Physical Chemistry C 2011, 115:5619-5625. [Bora 2013] Bora DK et al. J. Electr. Spec. Rel. Phenom. 2013, 190:93-105.[Braun 2012] Braun A et al. Journal of Physical Chemistry C 2012, 116:16870-16875. [Braun 2016] Braun A et al. Catalysis Today 2016, 260:72-81. [Ralston 2000] Ralston CY et al. Journal of the American Chemical Society 2000, 122:10553-10560. [Visser 2001] Visser H et al. Journal of the American Chemical Society 2001, 123:7031-7039.

Authors : Jan Augustynski
Affiliations : Centre for New Technologies, University of Warsaw, Poland

Resume : Photo-electrochemical water splitting using semiconductor electrodes is a widely investigated approach to the direct chemical storage of solar energy. Besides optoelectronic properties of the photo-materials, i.e. the range of the absorbed solar wavelengths and energetic positions of the band-edge levels, the principal issue is the long-term stability of the employed electrodes. This presentation will focus on recent improvements in photo-electrochemical properties of tungsten trioxide WO3 thin films achieved in our laboratory. Use of appropriate mixtures of of tungstic acid and organic structure-directing agents that form the WO3 film precursor, combined with a two-step annealing, allows the formation of highly crystalline (of monoclinic structure) electrodes with controlled porosity. Both are the key features that allow reducing photogenerated charge recombination in the fabricated photo-material and obtaining large photo-oxidation currents that attain the saturation point at potentials around 1 V vs reversible hydrogen electrode. Photo-electrolysis experiments employing synthetic sea water electrolyte in a two compartment cell demonstrated dominant formation of chlorine at the WO3 photo-anode with remarkably stable photocurrents exceeding 4.5 mA cm-2.

Authors : Yasuhiro Tachibana
Affiliations : 1 School of Engineering, RMIT University, Bundoora, VIC 3083, Australia 2 Project Research Center for Fundamental Sciences, Faculty of Science, Osaka University

Resume : Solar water splitting is one of the most attractive energy generation reactions to utilize solar energy. Light generated hydrogen is clean energy source, since their consumption for energy generation produces only water. Moreover, it can be stored and used whenever required. Semiconductor TiO2 is known as a photocatalyst and was investigated for solar water splitting reactions over the last several decades. TiO2 has still been employed to assess the capability of photocatalysis reactions. The water splitting kinetic reaction mechanism at the TiO2 surface has been elucidated, particularly employing transient absorption spectroscopy, however detailed understanding of the mechanism remains to be clarified. In this presentation, we will demonstrate quantitative assessment of photocatalytic water splitting mechanism at the TiO2 surface by employing a series of transient absorption spectroscopies covering from fs to 10 s over UV-VIS-NIR wavelength ranges. The reaction paths and their dynamics at the charge trap states will be discussed. This work was partly supported by JSPS KAKENHI Grant Number 16K05885, Japan. We also acknowledge supports from ARC DP fund (DP180103815) and ARC LIEF fund (LE170100235), Australia, and Office for Industry-University Co-Creation at Osaka University.

12:00 Lunch    
Latest Advances in Solar Fuels II : Lionel Vayssieres
Authors : Ian D. Sharp
Affiliations : Walter Schottky Institute and Physics Department, Technical University of Munich

Resume : The capture of sunlight and its direct conversion to chemical fuels in artificial photosystems provides a promising route for sustainably meeting future energy demands. However, progress has been hindered by a lack of materials that are simultaneously stable, efficient, and scalable. To address this gap, international research efforts have intensively targeted transition metal oxide semiconductors as potentially stable light harvesting compounds and recent work has led to the discovery of a remarkable range of new materials. However, the energy conversion efficiencies from these systems often fall far short of thermodynamic limits. Using bismuth vanadate and copper vanadate as a representative materials systems, we discuss the physical factors that limit solar-to-chemical conversion, the challenges of integrating these materials into monolithic photosystems, and prospects for enhancing performance characteristics. Among these approaches, we introduce a new device architecture, the hybrid photo-electrochemical and -voltaic cell, that provides a route to overcome the problem of mismatched tandem component performance by adding a third electrical terminal to the bottom sub-cell. This third contact allows photogenerated charge carriers that are not consumed by the chemical reaction to be collected as electrical current, thereby producing electrical power at the same time that chemicals are produced. This ability to overcome efficiency losses associated with current mismatches provides a route to creating efficient and functional systems from the existing set of semiconductor light absorbers.

Authors : Minmin Gao, Liangliang Zhu, Connor Kangnuo Peh, Min-Quan Yang, Ghim Wei Ho*
Affiliations : Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore. Engineering Science Programme, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore

Resume : Using readily available renewable resources i.e. solar energy and seawater to secure sustainable fuel and freshwater for humanity is an impactful quest. The utilization of photothermal materials with broad solar absorption, in parallel to engineered evaporator designs, offers new approach to achieve efficient solar light conversion. Here, we have designed solar thermal collector nanocomposites that possess efficient photothermic properties for highly targeted interfacial phase transition reactions that are synergistically favorable for catalysis, vaporization and energy generation. The photothermic effect arises from plasmonic metal, semiconductor and carbon nanomaterials exhibit localized interfacial heating which directly triggers surface-dominated catalysis and steam generation processes, with minimal heat losses, reduce thermal masses and optics implementation. The solar thermal collector nanocomposites are photo stable for practical solar conversion to simultaneously produce clean energy, water and electricity. Finally, proof-of-concept prototypes demonstrate the viability of sustainable photothermic driven catalysis, desalination/distillation and energy generation under natural sunlight. Furthermore, the opportunities of solar water evaporation should be explored beyond silos so as to conjointly address the interlinked water, energy and environmental nexus.

Authors : Sacha Corby, Ernest Pastor, Laia Francas, Michael Sachs, Shababa Selim, Andreas Kafizas and James R. Durrant
Affiliations : Imperial College London

Resume : Using transient absorption spectroscopy over a broad range of timescales, we observe the generation, reaction/collection and competing recombination of charge carriers in WO3 under catalytic conditions. We find this material oxidises water faster than other commonly studied transition metal oxides. By varying the electrolyte and applied potential, we facilitate changes to surface band-bending and monitor a reduction in bulk recombination, which ultimately result in increased charge extraction at longer timescales. These results provide valuable insight into the timescales of recombination processes in operando and highlight some material challenges that need be addressed if metal oxides are to achieve their maximum catalytic potential.

Authors : Andre L M Freitas; Renato V Gonçalves; Flavio L Souza
Affiliations : Universidade Federal do ABC-UFABC; Universidade de São Paulo - USP - IFSC; Universidade Federal do ABC - UFABC

Resume : Hydrogen generation via water splitting using hematite as photoanode remains unsolved challenge over decades. One crucial step toward the progress is related to the importance of high annealing temperature in the hematite surface activation.(1) Moreover, preventing damages in the substrate-hematite interface may lead an improved performance.(2) This work aimed to investigate how high annealing temperatures affect the FTO (fluorine-doped tin oxide) substrate and FTO-hematite semiconductor interface performance. The pure commercial FTO and FTO covered by iron oxide layer (photoanode) product of microwave-assisted hydrothermal synthesis were submitted to three different temperatures 400, 750 and 800°C, at fast (low-time exposure) and slow (long-time exposure) conditions. It was observed that 750°C synthesized photoanodes represents the superior photocurrent performance for all designed hematite achieving 0.54 mA cm-2 at 1.23 VRHE and cathodically shiffiting onset potential around 200 mV. By UV-visible, XPS and EIS measurements were determined that this temperature represents a balance to preserve the substrate nature as much as possible and satisfactory to hematite PEC performance. Moreover, it was defined that synergy among the Sn-diffused species amount from the substrate, lower F-losses and exposure time at high temperatures are the key factors to produce efficient photoanodes to water splitting applications. (1) Phys. Chem. Chem. Phys., 2017, 19, 25025 (2) J. Phys. Chem. C (2015), 119, 3810−3817 The authors acknowledge the financial support from the Brazilian agency FAPESP (Grants 2014/11736-0 and 2017/25935-3), Capes and CNPq. F. L. S. and R. V. G. gratefully acknowledge support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation.

15:30 Coffee Break    
Authors : Jin Zhong Zhang
Affiliations : Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States

Resume : Organo-metal halide perovskites show excellent promise for applications due to their unique optoeletronic properties. Perovskite quantum dots (PQDs) provide additional advantages including tunable optical and electronic properties. However, insulating ligands used to stabilize PQDs limit their charge transfer and transport properties in the solid form for device applications including solar cells and LEDs. One solution to this problem is to use short conductive aromatic ligands to allow delocalization of the electronic wave function from the PQDs and facilitate charge transport between PQDs by lowering the energy barrier. We have demonstrated using methylammonium lead bromide (MAPbBr3) and iodine (MAPbI3) QDs prepared using conjugated ligands such as benzylamine (BZA) and benzoic acid (BA). Optimized BZA-BA-MAPbBr3 QDs are highly stable and show very high photoluminescence (PL) quantum yield (QY). More importantly, the BZA-BA-MAPbBr3 QD film exhibits higher conductivity and more efficient charge extraction compared to PQDs with insulating ligands based on electrochemical measurements and transient photocurrent and photovoltage spectroscopy. In addition, we have explored different anchoring groups, such as phosphonic acids, of the ligands with the objective to improve bonding of the ligands with the PQD core.

Authors : Victor I. Klimov
Affiliations : Center for Advanced Solar Photophysics, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Resume : Quantum-confined semiconductor nanocrystals, or “quantum dots,” are promising materials for applications in a range of solar-energy technologies from low-cost solar cells and photocatalysis to luminescence solar concentrators. They feature size/shape-tunable optical spectra, as well as a variety of novel physical properties that can enable fundamentally new schemes for solar energy conversion. This presentation provides an overview of fundamental and applied studies of quantum dots conducted in the context of photoconversion with focus on advanced concepts such as carrier multiplication (generation of multiple excitons by single photons) and up-conversion of infrared light. The specific topics will include recent progress in understanding of carrier multiplication in quantum confined materials, demonstration of a significant enhancement of multiexciton yields by implementing the control of intra-band relaxation, and applications of engineered quantum dots in energy up-conversion via confinement-enhanced Auger processes.

Authors : Carlota Bozal-Ginesta(a), Laia Francàs(a), Camilo A. Mesa(a), A. Reynal(c), Daniel Antón García(b), Erwin Reisner(b), James R. Durrant(a)
Affiliations : (a) Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, UK; (b) Christian Doppler Laboratory for Sustainable SynGas, Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK

Resume : The sequential transfer of electrons from a semiconductor (TiO2) to surface-bound molecules (the organometallic cobaloxime catalyst for proton reduction CoP2) have been studied by photo-exciting TiO2 in acetonitrile and following the catalyst spectroscopic signal. This research is necessary to understand catalysis requiring multiple charges, and to make efficient photo-driven water reduction possible. Spectroelectrochemistry and time-resolved absorption spectroscopy have been used to monitor the catalyst signal and the kinetics of consecutive electron transfers. The second electron transfer, necessary to reduce protons into hydrogen, has been observed to occur in 1 ms, three orders of magnitude slower than the first electron transfer to the catalyst, thus limiting catalysis efficiency and the turnover frequency.

Latest Advances in Solar Fuels Poster Session : Flavio de Souza / Sanjay Mathur / Samuel Mao
Authors : Yuhang Wang, Junlang Liu, Yifei Wang, Yonggang Wang, Gengfeng Zheng
Affiliations : Laboratory of Advanced Materials, Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai, China

Resume : The ever-changing sunlight illumination on the earth presents a substantial impediment of maintaining high (photo)electrocatalytic efficiency and stability for the practical applications of solar fuels. Inspired by green plant photosynthesis with the separation of light reaction and carbon fixation (dark reaction), we have developed a redox medium-assisted system that proceeds water oxidation with a nickel-iron hydroxide1 electrode under light illumination and CO2 reduction with a gold nanocatalyst.2 The Zn/Zn(II) redox couple mimics the ATP/ADP in green plants to store the electrons for carbon fixation which can be controllably released to reduce CO2 into CO spontaneously under dark condition. We have achieved a solar-to-CO efficiency peaking at 15.6% under 1-sun intensity without external bias.3 Our system further allows the tuning of activity and selectivity with various CO2 reduction catalysts targeting at different products which suggest new opportunities in the manufacture of non-renewable fossil fuels from CO2 and sunlight via this redox medium-assisted approach. (1) M. Gong, Y. Li, H. Wang, Y. Liang, et al., J. Am. Chem. Soc., 2013, 135, 8452–8455. (2) M. Liu, Y. Pang, B. Zhang, P. De Luna, et al., Nature, 2016, 537, 382–386. (3) Y. Wang, J. Liu, Y. Wang, Y. Wang, et al., Nat. Commun., 2018, 9, 5003.

Authors : Dávid Lukács, József S. Pap, Miklós Németh, Levente Illés
Affiliations : Dávid Lukács, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences H-1121 Budapest, Konkoly-Thege street 29-33; József S. Pap, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences H-1121 Budapest, Konkoly-Thege street 29-33; Miklós Németh, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly-Thege street 29-33; Levente Illés, Institute of Technical Physics and Material Science, Centre for Energy Research, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly-Thege street 29-33

Resume : Cost, efficiency and technical flexibility are all important factors to be considered when new, noble metal free solutions are sought for the chemical storage of renewable energy by water splitting. This work concerns the water oxidation half-cell reaction with the use of abundant first row transition metal complexes, specifically, with an in situ assembled, peptide containing copper(II)-diglycyl-glycine complex. Its catalytic activity in the oxygen evolving reaction could be revealed as well as its capability of behaving either as homogeneous catalyst or precursor for the preparation of electroactive CuO coatings by simply changing the pH or the total concentration of the applied borate buffer. The dynamics of the two-faced behaviour of this low cost, easily accessible and biocompatible complex were investigated by spectro-electrochemical and pure electrochemical techniques. On standard indium tin oxide electrodes XPS and SEM analysis revealed well controllable, nanostructured coatings of operando fabricated CuO even from very low concentrations of the peptide complex precursor. This work is financed by the NKFI-128841 grant, and the VEKOP-2.3.2-16-2016-00011 grant supported by the European Structural and Investment Funds. J. S. Pap is grateful for the J. Bolyai Research Scholarship from the Hungarian Academy of Sciences.

Authors : Xue Han
Affiliations : Xue Han, Imperial College London

Resume : With the rapid development of the world, human energy demand gets huge. Solar energy and corresponding technologies attracts much researchers’ interest among the wide range of the energy for decades. Organic solar cell would take more occupation of industry market in the future, with its solution-based, low temperature manufacture processing. The non-fullerene acceptor has gradually replaced the fullerene derivatives in solar cell. The power conversion efficiency improved by blending with non-fullerene acceptor. Altering acceptor/donor in Non-Fullerene Acceptor would optimize the solar cell and improve the efficiency.

Authors : Lingyu Zou
Affiliations : Hyojung Cha; James R Durrant

Resume : Natural photosynthesis plays an important role in solar harvesting and the extended technique of artificial photosynthesis is promising for charge separation and producing hydrogen as future energy source. Recently, focus on hydrogen generating materials has transferred from inorganic semiconducting materials to organic systems for their wider spectrum absorptions and improved scalability. However, the hydrogen yields of organic materials are still far from satisfactory due to their short lifetime and inefficient charge separation rate resulted from unexpected recombination, which emphasizes the necessity to work on the fundamental dynamics during the process of proton reduction. IDTBR is a kind of organic photovoltaics and it can achieve a maximum 6.4% quantum efficiency with P3HT as an electron donor. Herein, in this project we mainly explore the potential performances of IDTBR and its derivatives for generating hydrogen. With the technique of transient absorption spectroscopy, we try to understand each step included in the mechanism of proton reduction happening in IDTBR system, which include both platinum as co-catalyst and ascorbic acid as sacrificial electron donor. Additionally, we also carry out research on the effects of different components in tested systems on achieved hydrogen evolution rate. The conclusion on kinetics of proton reduction can be very helpful for analysing the potential defects in materials and improving hydrogen evolution rate of this system.

Authors : Jongwon Ko, Se Jin Park, Hyomin Park, Soohyun Bae, Yoonmook Kang, Hae-Seok Lee, Donghwan Kim
Affiliations : Department of Materials Science and Engineering, Korea University, Seoul, Korea;Department of Materials Science and Engineering, Korea University, Seoul, Korea;Department of Materials Science and Engineering, Korea University, Seoul, Korea;Department of Materials Science and Engineering, Korea University, Seoul, Korea;KU·KIST Green School, Graduate School of Energy and Environment, Korea University, Seoul, Korea;KU·KIST Green School, Graduate School of Energy and Environment, Korea University, Seoul, Korea;Department of Materials Science and Engineering, Korea University, Seoul, Korea

Resume : Solar energy is attracting attention as an alternative to conventional energies. Among them, solar cells that produce electricity using solar light are considered as important renewable energy. As the installed capacity of photovoltaic modules around the world is increasing worldwide, there is also a growing interest in disposal and recycling methods of end-of-life photovoltaic modules. Conventional photovoltaic module recycling technology is usually performed through the grinding or firing process of the module. In this case, it is considered that it is not effective in terms of recycling efficiency and material yield. In this study, proposed method to easily separate the glass and EVA by delaminate the FTO layer by inserting FTO layer into the glass-EVA interface in the general silicon photovoltaic module structure of glass-EVA-solar cell-EVA-back sheet. Experiments under various conditions of temperature, humidity and voltage showed that the FTO layer was delaminated and the glass and EVA were easily separated. XRD analysis confirmed the change of the preferred orientation of the FTO.

Authors : Carina Faber, Vincent Artero, Antoni Llobet, Artur Braun, Huub De Groot
Affiliations : Carina Faber, UCLouvain, Belgium; Vincent Artero, University of Grenoble, CEA & CNRS, France; Antoni Llobet, ICIQ, Spain; Artur Braun, Empa, Switzerland; Huub de Groot, Leiden University, Netherlands;

Resume : SUNRISE is one of the candidates for a future European large-scale research initiative. We propose a sustainable alternative to the fossil-based, energy-intensive production of fuels and base chemicals. The needed energy will be provided by sunlight, the raw materials will be molecules abundantly available in the atmosphere, such as carbon dioxide, oxygen and nitrogen. Our proposal for a coordination and support action (CSA) has been successfully selected by the European Commission at stage one and two of the FETFLAG-01-2018 call. The CSA project will start in spring 2019 and will be funded with €1M for preparing the full SUNRISE initiative addressing the S&T challenge of converting solar energy into fuels and commodity chemicals with high solar energy to product yield. The main objectives of the CSA are to: (i) Develop the Scientific and Technological (S&T) roadmap of the Flagship; (ii) Build the community for carrying out the Flagship roadmap including scientific, industrial and general public stakeholders; and (iii) Establish an effective Flagship governance scheme. This contribution will provide details about the project's vision and mission, its partners and supporters and will serve as gathering point for those interested in reinforcing the SUNRISE community.

Authors : Filip Chymo 1, Karol Fröhlich 2,3, Kristína Hušeková 2,3, Ivan Kundrata 2,3, Ladislav Harmatha 1, Miroslav Mikolášek 1
Affiliations : 1 Institute of Electronics and Photonics, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava, Slovakia 2 CEMEA SAS, Dúbravská cesta 5807/9, 841 04, Bratislava, Slovakia 3 Institute of Electrical Engineering SAS, Dúbravská cesta 9, 841 04, Bratislava, Slovakia

Resume : The silicon based metal-insulator-semiconductor (MIS) photoanode has the ability to provide a high photocurrent for oxidation of water in water splitting applications. Recently, we have shown superior performance of RuO2/SiO2/n-Si compared to Ni/SiO2/n-Si based MIS structure, which was achieved due to the high catalytic activity, good transparency and good interface properties of RuO2 [1]. In this paper, we focus on the stabilization of the RuO2 based MIS structure by a thin TiO2 protection layer. Prepared TiO2/RuO2/SiO2/n-Si structures were characterized in 1M H2SO4 (pH=0) and 0.5M Na2SO4 (pH=6) electrolytes. A photocurrent in saturation of 25 mA/cm2, and a low overpotential of 0.15 V required to achieve 10 mA/cm2 photocurrent at a thermodynamic water oxidation potential were achieved in 1M H2SO4 (pH=0) under AM15 illumination. Photoanode testing revealed stable operation in 0.5M Na2SO4 solution for over 10 hours at 1.5 V vs. RHE. The paper will discuss the impact of the top TiO2 layer on the stability, catalytic efficiency of RuO2 and performance of the TiO2/RuO2/SiO2/n-Si photoanode in order to achieve long term water oxidation. Acknowledgements This research was funded by APVV (project APVV-17-0169) and VEGA (project 1/0651/16). References [1] Mikolasek, M. et al., Silicon based MIS photoanode for water oxidation: A comparison of RuO2 and Ni Schottky contacts. Applied Surface Science 461 (2018) 48-53.

Authors : Prangya P. Sahoo, Peter Cendula
Affiliations : Institute of Aurel Stodola, Faculty of Electrical Engineering, University of Zilina, Liptovsky Mikulas, kpt. Nalepku 1390, 03101, Slovakia

Resume : The photoelectrolysis of water has drawn a significant amount of recent research interest because of the potential to produce hydrogen as a renewable fuel source, using only sunlight and water. This generated hydrogen could become the central energy carrier of a hydrogen-based energy economy, replacing the role of fossil fuels. Cu2O is a well-studied earth abundant, low-cost, and non-toxic material for the generation of hydrogen as fuel from photocatalytic water splitting under visible light irradiation. Preparation of Cu2O thin films by electrodeposition method allows the thin films to grow directly on the conducting substrate. Thin films of different thickness, orientation, and crystallinity could be obtained by manipulating different synthetic variables such as pH, temperature, and composition. In this work, the Cu2O thin films were electrodeposited on to fluorine doped tin glass from an alkaline electrolyte solution containing copper sulfate and lactic acid. The resulting electrodes were subjected to different characterization techniques such as powder X-ray diffraction, Scanning and Transmission Electron Microscopy, and Raman Spectroscopy. The band gaps were measured by UV-Visible diffuse reflectance spectroscopy. The new copper oxide photoelectrodes were utilized for different photoelectrochemical measurements such as Mott-Schottky plots, current-voltage curves and chronoamperometric experiments under chopped visible light irradiation.

Authors : He Sun 1.3, Nobuyuki Nishiumi 1, Hidenobu Shiroishi 2, Yuta Matsushima 1, Philipp Stadler 3, Tsukasa Yoshida 1
Affiliations : 1 Department of Chemistry and Chemical Engineering, Faculty of Engineering, Yamagata University, Jonan 4-3-16, Yonezawa. Yamagata 992-8510, Japan; 2 Department of Chemical Science and Engineering, National Institute of Technology, Tokyo College, 1220-2 Kunugida-machi, Hachioji, Tokyo 193-0997, Japan; 3 Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, A-4040 Linz, Austria;

Resume : Among various metal oxides previously tested, Co3O4 is known to be one of the best catalysts for oxygen evolution reaction (OER). In this study, doping of Co ions into nanocrystals of zinc oxide (ZnO) has been achieved by microwave (MW) assisted hydrothermal reaction to form catalytic surface sites for OER combined with highly conductive and stable ZnO for flexible catalyst design and potential enhancement of the catalytic activity. MW-assisted hydrothermal reaction has successfully yielded Co-doped ZnO nanocrystals at a low reaction temperature of 160ºC and in a short reaction time of 30 min. Partial replacement of 4-coordinated Zn(II) ions of ZnO with Co(II) ions up to about 10at% has been suggested from evaluation of the products by UV-Vis absorption spectra, morphological observations and X-ray diffraction. The higher addition of Co resulted in its phase-separated precipitation as Co(OH)2. While mesoporous electrode processed from ZnO nanocrystals was totally inactive, that of Co-doped ZnO exhibited a good catalytic activity to achieve about 1 mA cm-2 current of OER with an overvoltage of 0.545 V in a neutral aqueous KCl solution, which in fact was far superior to a Co3O4 electrode known to suffer from its limited conductivity. The doped Co ions are only expected to act as reaction centers for charge transfer on the very surface in contact with the electrolyte, while ZnO acts as a highly conductive and chemically stable host matrix to support the catalyst.

Authors : Tomiko M. Suzuki, Takeo Arai, Shunsuke Sato, Keita Sekizawa, *Takeshi Morikawa
Affiliations : Toyota Central R&D Labs., Inc.

Resume : The development of catalysts incorporating earth abundant elements for oxygen evolution reaction (OER) is important for the artificial photosynthesis to generate useful chemicals such as hydrogen and organic compounds. Here, we report a highly crystalline, 10 nm-sized red rust OER catalyst composed of pure β-phase FeOOH(Cl) nanorods doped with Ni ions (β-FeOOH:Ni) [1] and surface-modified with amorphous Ni(OH)2, which can be synthesized by a facile one-pot process at room temperature. An electrode composed of β-FeOOH:Ni/Ni(OH)2 nanorods, in which there is interaction between Fe atoms and Ni species, generates an OER current of 10 mA/cm2 at an overpotential of 430 mV in 0.1 M KOH (without subtracting the iR drop). This performance is superior to those exhibited by Fe-rich oxide and oxyhydroxide catalysts [2]. We subsequently demonstrated photoelectrochemical CO2 to CO reduction with 3.4 % solar-to-chemical conversion efficiency by combination with earth-abundant catalysts; the β-FeOOH:Ni/a-Ni(OH)2 catalyst and a Mn-complex polymer for CO2 reduction [3] were connected with polycrystalline silicon photovoltaic cells around neutral pH in a single-compartment reactor [4]. References [1] T. M. Suzuki, et al., Sustainable Energy Fuels, 2017, 1, 636-643, [2] T. M. Suzuki, et al., Bull. Chem. Soc. Jpn., 2018, 91, 778-786, [3] S. Sato, et al., ACS Catal., 2018, 8, 4452-4458, [4] T. Arai, et al., Chem.Commun., 2019, 55, 237-240

Authors : Sahir M. Al-Zuraiji, Tímea Benkó, József S. Pap
Affiliations : Sahir M. Al-Zuraiji, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary, Doctoral School on Materials Sciences and Technologies, Óbuda University, Bécsi út 96/B, 1034 Budapest, Hungary; Tímea Benkó, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary; József S. Pap, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary

Resume : Finding efficient, low cost and “green” alternatives to the noble metal based catalysts for water oxidation (WOCs) has become a major challenge for scientists in the field of artificial photosynthesis. Its low cost, low toxicity and high natural abundance made iron a promising metal to be used in molecular WOCs, however, the generally labile metal-ligand interactions often undermine stability. The aim of this work was to compare the electrochemical and -catalytic properties of two selected Fe compounds under both homogeneous and heterogeneous conditions. The 2,2’-bipryidyl like ligands, 2-(2'-pyridyl)benzimidazole (PBI), and 2-(2'-pyridyl)benzoxazole (PBO) provided the structurally characterized [Fe(PBI)3](OTf)2 and [Fe(PBO)2(OTf)2] compounds (OTf- = trifluoromethyl sulfonate anion). The electrocatalytic activity of these complexes was investigated in homogeneous water/acetonitrile mixtures and kinetic analysis revealed considerable activity for both compounds. Due to their hydrophobic properties the additive-free layering of the complexes onto ITO semiconductor surface could be done and the evolution of O2 in aqueous buffer could be sustained for long periods with the modified electrodes. Inspection of the ITO surface after use clearly showed the operando stability of [Fe(PBI)3](OTf)2 and the degradation of [Fe(PBO)2(OTf)2]. Financial support of the NKFI-128841 and the VEKOP-2.3.2-16-2016-00011 grant supported by the European Structural and Investment Funds, and a J. Bolyai Research Scholarship by MTA (J. S. Pap) are gratefully acknowledged.

Authors : Sergei Piskunov, Maxim Sokolov, Aleksejs Gopejenko, Janis Kleperis
Affiliations : Institute of Solid State Physics, University of Latvia, 8 Kengaraga str., Riga LV-1063, Latvia

Resume : Substitution of fossil fuel-based chemical processes by the combination of electrochemical processes driven by sources of renewable energy and parallel use of CO2 from exhausts as a carbon source must direct the chemical production of bulk chemicals and fuels. The main goal of our study is development and design of cathode material based on graphene decorated with copper nanoclusters for CO2-reduction to ethylene in electro-catalytic process In the current presentation, we report the atomistic 2D graphene-based models with periodically distributed copper nanoclusters of different configurations, both neutral and charged to be used as a catalyst for the electrochemical CO2 reduction. We have performed the first principles simulations, which result in slight deflection of graphene monolayer under Cu nanoparticle and charge transfer from the latter to substrate (~0.4 e per copper atom). We have also estimated dependence of the total charge in the vicinity of Cu/graphene interface on the potential applied to it and its influence to the CO2 reduction. Funding from European Union`s Horizon 2020 Research and Innovation Programme project under grant agreement No 768789 is greatly acknowledged.

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Latest Advances in Solar Fuels III : Sanjay Mathur
Authors : Song Jin
Affiliations : Department of Chemistry University of Wisconsin-Madison

Resume : Due to the intermittent nature of most renewable energy sources (such as solar and wind), practical large scale renewable energy utilization demands both efficient energy conversion and large scale energy storage or alternative usage. Earth-abundant but highly active electrocatalysts need to be developed to enable efficient and sustainable production of energy using electrocatalytic and photoelectrochemical (PEC) water splitting. We developed earth-abundant nanoscale electrocatalysts, such as exfoliated nanosheets of MoS2, for enhancing hydrogen evolution reaction (HER). We established nanotructures of ternary pyrite-type cobalt phosphosulfide (CoPS) as the best earth-abundant HER catalyst in acidic conditions to date. Our recent efforts on the conversion of biomass derived molecules utilizing the increasingly affordable renewable electricity to value-added chemicals will be discussed. Efficient photoelectrochemical hydrogen generation systems that integrate these earth-abundant electrocatalysts with efficient semiconductor materials have been rationally designed and demonstrated. I will also discuss novel hybrid solar-charged storage devices that integrate photoelectrochemical solar cells and redox flow batteries (RFBs). In these integrated solar flow batteries (SFBs), converted solar energy is used to directly charge up the redox couples without external electric bias; which can be discharged to generate the electricity when electricity is needed.

Authors : Yanfa Yan
Affiliations : University of Toledo

Resume : Direct photoelectrochemical (PEC) splitting of water into hydrogen and oxygen remains a promising route for producing sustainable and renewable hydrogen fuel. From chemical stability concerns, metal oxides are the desirable photoelectrodes. Unfortunately, most metal oxides have too large bandgaps to effectively absorb the main portion of the sunlight spectrum. Through density-functional theory (DFT) and experimental synthesis, we demonstrate a new approach to effectively engineer the bandgap of barium bismuth niobate double perovskites (Ba2BiNbO6) (BBNO). We find that the film with the composition of Ba2Bi1.4Nb0.6O6 forms single pure phase and exhibits a nearly direct bandgap of about 1.64 eV, which is small enough to absorb visible light at wavelengths below 756 nm. We further find that the PEC activity of BBNO-based electrodes can be dramatically enhanced by coating thin BBNO layers on tungsten oxide (WO3) nanosheets to solve the poor conductivity issue while maintaining strong light absorption. The PEC activity of BBNO/WO3 nanosheet photoanodes can be further enhanced by applying Co0.8Mn0.2Ox nanoparticles (CoMnO NPs) as a co-catalyst. A photocurrent density of 6.02 mA cm-2 at 1.23 V (vs. RHE) is obtained using three optically stacked, but electrically parallel BBNO/WO3 nanosheet photoanodes. The BBNO/WO3 nanosheet photoanodes also exhibit excellent stability in a high-pH alkaline solution; the photoanodes are stable with negligible photocurrent density decay for more than 7 h. Our work suggests a viable approach to improve the PEC performance of BBNO absorber-based devices.

09:30 Coffee Break    
Authors : Dereck N. F. Muche1*, Saulo A. Carminati2, Maurício A. Melo2, Renato V Gonçalves3, Ana F. Nogueira2, Flavio L Souza1*,
Affiliations : 1Universidade Federal do ABC, Santo André-São Paulo, Brazil. 2Universidade de Campinas, Instituto de Quimica, Campinas, SP, Brazil 3Universidade de São Paulo, Instituto de Física de São Carlos, São Carlos, SP, Brazil

Resume : The seek for the most promising renewable energy source, brings hematite (α-Fe2O3) photoelectrode a promising candidate for hydrogen production via water splitting induced by sunlight irradiation. However, its poor electronic characteristics together with its complex scale-up engineering production have prevented its commercial applications. This work describes different approach for improving hematite nanocrystalline structure / transparent conductor oxide substrate (TCO) interface and also, hematite nanocrystalline surface for chemical reactions with controlled addition of Tin (Sn). Herein, α-Fe2O3 electrodes were obtained by coating deposition of an alcoholic solution composed of Fe3+ complexed polymeric solution synthesized via Pechini method and annealed at 750 oC for 30 min under N2 atmosphere. Modified electrodes were obtained by 2 different routes: i) In the route here named (Sn-R1), 20 µL of a 5 µmol SnCl4 alcoholic solution was added on top of the unmodified α-Fe2O3 calcined films followed by re-calcination at 750 ⁰c for 30 min under N2 atmosphere. ii) In the second route named (Sn-R2), 1% excess of SnCl4 were added into the synthesized α-Fe2O3 Pechini solution, followed by spin-coating deposition and the same annealing protocol. Unmodified hematite films showed considerable enhancement on photocurrent density J, increasing from a range of ~ 30 µ [1, 2] up to 0.127 at 1.23 VRHE, with the onset of the photocurrent curve starting at 0.8 VRHE. Such improvement has been mainly attributed to a better uniformity of the films and an improved interfacial adherence of the hematite thin film to the TCO provoked primarily by the substitution of water to ethanol as a solvent into the polymeric deposition solution. When modified with Sn, hematite films showed an increasing in photocurrent density up to ~ 40% at 1.23 VRHE in both Sn-R1 and Sn-R2 routes. Specifically, in Sn-R1 route, (SnCl4 added dropwise on top of the electrode), a slight alteration in the onset of the curve were observed followed by a significant change upright on the slope. Likewise, in Sn-R2 route (when Sn are added into the Pechini solution), a pronounced alteration on the onset of the photocurrent curve, moving towards anodic direction from ~0.8 VRHE for unmodified electrode to ~0.95 VRHE has been observed, together with a change on the slope to upright direction, where surfaces effects are predominant [3] . Although increasing in photocurrent are shown in both routes, Sn-R2 provides more homogenous Sn addition through the hematite film nanostructure, enabling single-step preparation process in addition of better reproducibility. Acknowledgments The authors acknowledge the financial support from the Brazilian agency FAPESP (Grants 2015/23775-3), Capes and CNPq. D. N. F. M., F. L. S., M. A. M., R. V. G and A. F. N gratefully acknowledge support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. [1]. F. L. Souza, K. P. Lopes, P. A. Nascente and E. R. Leite, Solar energy materials and solar cells, 2009, 93, 362-368. [2]. D. A. Bellido-Aguilar, A. Tofanello, F. L. Souza, L. N. Furini and C. J. L. Constantino, Thin Solid Films, 2016, 604, 28-39. [3]. B. Yao, J. Zhang, X. Fan, J. He and Y. Li, Small, 2018, 1803746.

Authors : Camilo A. Mesa1*, Laia Francàs1*, Ke Yang2, Pablo Garrido2,3, Ernest Pastor1, Yimeng Ma1, Andreas Kafizas1, Timothy E. Rosser4, Matthew Mayer5, Erwin Reisner4, Michael Grätzel5, Victor Batista2 and James Durrant1
Affiliations : 1 Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom 2 Department of Chemistry and Energy Sciences Institute, Yale University, New Haven, Connecticut 06520-8107, United States 3 Institute of Chemical Research of Catalonia (ICIQ), Avinguda Països Catalans 16, E-43007 Tarragona, Spain 4 Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom 5.Laboratory of photonics and interfaces, EPFL, CH-1015, Laussane, Switzerland *These authors contributed equally.

Resume : Natural photosynthesis has served as inspiration for solar driven fuels synthesis (e.g., hydrogen) as a potentially inexpensive technology to store solar energy into chemical bonds via photoelectrochemical water splitting. Water oxidation is still considered the bottleneck of the overall water splitting process due to its slow kinetics, however the mechanism of reaction and its kinetic consequences remains not yet well understood. Despite the 4 photogenerated holes this reaction requires to complete, recently, we have found that 3 of such species are required to diffuse together at a hematite surface to overcome the rate determining step of the water oxidation reaction. [1,2] In this talk, recent advances on the kinetics of water oxidation taking place on different metal-oxide photoanodes will be presented, focusing particularly on hematite photoanodes. A detailed mechanistic analysis will be presented by the study of the water oxidation rate law under different physicochemical conditions. Here we employed light-induced spectroelectrochemical techniques to investigate the photogeneration, recombination and reaction of the photogenerated holes and the correlation between surface density and the current densities produced. The experimental results combined with DFT calculations enabled us to propose a detailed molecular water oxidation mechanism on hematite, which is found to have parallels with proposed mechanisms for Photosystem II (PSII) in the natural photosynthesis. [3] These findings suggest that understanding the natural photosynthesis may lead to further developments in the artificial photosynthesis field. References [1] Le Formal, F. et al. Rate Law Analysis of Water Oxidation on a Hematite Surface. J. Am. Chem. Soc. 2015, 137, 6629–6637. [2] Francàs, L. et al. Rate law analysis of water splitting photoelectrodes. in: Advances in photoelectrochemical water splitting: Theory, experiment and systems analysis. Ed: Royal Society of Chemistry 2018. [3] Mesa, C. A. et al., Multihole catalysis of water oxidation on metal oxide photoanodes: Insights from in operando light-induced spectroelectrochemistry and density functional theory, Nature Chem., Under Revision.

Authors : Aafke C. Bronneberg, Richard van de Sanden, Anja Bieberle-Hütter
Affiliations : Dutch Institute for Fundamental Energy Research (DIFFER), Eindhoven, 5612AJ, The Netherlands

Resume : Photocatalytic water splitting is a promising route to store solar energy in the form of hydrogen. The exact mechanism of photocatalytic water splitting remains a largely unexplored area. However, knowledge on surface intermediates and catalytic sites will allow fabrication of photoelectrodes with a maximum number of catalytic sites and higher water splitting efficiencies. Here, we report on a novel approach to study the surface intermediates using operando IR spectroscopy. An ZnSe internal reflection element (IRE) serves as substrate for the photoelectrode. This approach has several advantages over geometries in which a thin electrolyte layer separates the photoelectrode from the IRE [1,2]. Firstly, the surface groups are probed from the “back” which avoids IR absorption by the electrolyte. Secondly, since the IRE is not in contact with the electrolyte, the pH of the electrolyte is not limiting regarding the chemical stability of the IRE. Thirdly, the IR operando cell geometry is similar to conventional PEC cells. We will demonstrate the working principle of this approach using Fe2O3 as case study material. We will confirm the intermediate species predicted by simulations [3,4]. We will discuss different OER mechanisms and address implications for material design. [1] Zandi et al. Nat. Chem. (2016) [2] Zhang et al. J. Am. Chem. Soc. (2018) [3] Zhang, Bieberle-Hütter et al. J. Phys. Chem. C (2016) [4] George, Bieberle-Hütter et al. (2018) submitted

12:30 lunch    
Latest Advances in Solar Fuels IV : Sanjay Mathur
Authors : Chung-Li Dong
Affiliations : Department of Physics, Tamkang University, Taiwan

Resume : Energy issues have recently become globally important. Low-carbon green energy will have a key role in the Third Industrial Revolution. To reduce global greenhouse gas emissions in response to globalization and increasingly strict carbon emission policies, green energy technologies must be developed. A new age of human demand for green energy is coming and material scientists are devoted to finding new functional materials to produce clean and sustainable energy. Improving the energy conversion/generation/storage efficiency of energy materials has always been a great challenge. Monitoring the atomic/electronic structures close the interface in many important energy materials, such as nanostructured catalysts, artificially photosynthesizing materials, smart materials, and energy storage devices, is of great importance. Designing such a material with improved performance without understanding its fundamental properties, such as chemical states, atomic and electronic structures, and their changes under operating conditions, is difficult. Understanding and controlling the interfacial electronic structures of energy conversion/storage materials require in-situ/operando characterization tools, of which synchrotron x-ray spectroscopy is one with many unique features. The last decade has witnessed a golden age of operando and in situ synchrotron x-ray spectroscopy for energy materials. X-ray absorption spectroscopy can be used to determine local unoccupied electronic structures (conduction band) while X-ray emission spectroscopy can be utilized to examine the occupied electronic structure (valence band). The additional use of resonant inelastic X-ray scattering reveals inter- or intra-electric transitions (d-d or f-f excitation or charge transfer excitation) that reflect the chemical and physical properties of the material. The in situ/operando approach enables modifications of atomic and electronic structures of an energy material in an operational environment to be tracked. This presentation will report recent studies and perspectives of the application of in situ/operando synchrotron x-ray spectroscopy to energy materials. It will also introduce the Tamkang University (TKU) end-station, which was constructed at the Taiwan Photon Source (TPS) 45A beamline for the in situ/operando x-ray spectroscopic investigation of energy materials.

Authors : P. Jäker (1,2), D. Aegerter (1), T. Kyburz (1), D. Koziej (1,2),
Affiliations : 1 ETH Zurich, Department of Materials, Laboratory for Multifunctional Materials, 8093 Zurich, Switzerland 2 University of Hamburg, Institutes of Nanostructure and Solid State Physics, Center for Hybrid Nanostructures, LuruperChaussee149, 22607 Hamburg, Germany

Resume : Photoelectrochemical (PEC) water splitting promises to deliver a carbon-free, high-energy density fuel but has not yet been commercialized. Partially, because we do not fully understand fundamental electronic processes occurring during PEC device operation. The operando methodology enables addressing these questions by studying devices in their actual working environment. Especially suited are hard X-ray absorption spectroscopies (XAS) offering high penetration depth and element selectivity. However, currently their broader application is limited due to lack of standard PEC cells compatible with X-ray methods. Here, we present an operando cell that simultaneously offers high X-ray detection efficiency and desired photoelectrochemical measures with low electrical noise. Most importantly, switching thin film materials for sequential operando measurements is realized in a standardized manner. We demonstrate the successful operation by collecting Fe K-edge spectra of hematite and ferrite oxide thin film photoelectrodes during water oxidation using high energy resolution fluorescence-detected (HERFD)-XAS. The cell enables to routinely conduct operando XAS experiments on photoelectrochemical thin films.

Authors : Woong Hee Lee, Yun Jeong Hwang, Byoung Koun Min, Hyung-Suk Oh
Affiliations : Clean Energy Research Center, Korea Institute of Science and Technology (KIST), Hwarangro 14-gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea

Resume : Electrochemical catalytic materials are a key component of various electrochemical devices for the storage of renewable electricity and low-carbon-footprint chemical production. For the oxygen evolution reaction (OER), it is applied to a variety of electrolysis systems. Their successful development and optimization require insight into the relations between the atomic-scale structure of the catalytic interface and the electrolyte to improve the catalytic activity and stability. In this presentation, we will focus on recent research on the design and understanding of Ir-oxide based materials and electronic structure by using in-situ/operando X-ray absorption spectroscopy technique. Based on these results, we will outline the preparation, characterization, and catalytic activity of Ir-oxide model catalysts for water splitting and discuss fundamental aspects of their structure-activity and -stability relationships.

15:30 Coffee Break    
Authors : Clemens Heske
Affiliations : Institute for Photon Science and Synchrotron Radiation (IPS) and Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT), Hermann-v.-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany; Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV), 4505 Maryland Parkway, Las Vegas, NV 89154-4003, USA

Resume : The purpose of this talk is to demonstrate how the combination of soft x-ray and electron spectroscopies (in particular using high-brilliance synchrotron radiation) can be used to gain insights into the electronic and chemical surface properties of candidate materials for solar water splitting. Focus will be placed on compound semiconductors, with particular emphasis of chalcopyrite-based material systems, and how ambient conditions and deliberate tailoring can modify and impact the surface of such materials. It will be shown that photoelectron spectroscopy (PES), x-ray-excited Auger electron spectroscopy (XAES), inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive band edge positions, band gaps, electronic level alignment, and insights into chemical stability, both with experiments in ultra-high vacuum, as well as under in situ and operando conditions.

Authors : Mahendra K. Sunkara 1,2 Hank Paxton 2 Sonia Calero-Barney 1 Madhu Menon 2 James Young 4 Todd Deutsch 4
Affiliations : 1. Chemical Engineering Department, University of Louisville, Louisville, KY 40292 2. Conn Center for Renewable Energy Research, University of Louisville, 216 Eastern Parkway, Louisville, KY 40292 3. Center for Computational Sciences, University of Kentucky, Lexington, KY 40506 4. National Renewable Energy Laboratory, Golden, CO 80401-3305

Resume : Photoelectrochemical water splitting cells comprising the alloys of III-V semiconductors hold record solar-to-hydrogen efficiencies. However, the performance of state-of-the art III-V alloy-based single absorber devices, particularly of InGaP2, InGaAs, GaPN, and GaAsN, comes short of unassisted water due to a) inadequate alignment of band edges with respect to the HER and OER redox potentials, b) insufficient photovoltage, and/or c) recombination. In this regard, we have been researching on III-V alloys involving GaN and GaP alloyed with antimony. Our recent results suggest that Sb alloying into GaN resulted in GaSbxN1-x alloys with band gaps ranging from 3.4 to 1.5 eV with appropriate band edge locations. Similarly, Sb alloying into GaP resulted in GaSbxP1-x alloys with band gaps ranging from 2.26 to 1.7 ev. In the case of GaSb0.03P0.97, a photovoltage in excess of 750 mV an onset potential of -0.5V vs RHE and a current density around 7 mAcm-2 under zero applied bias and 10 sun illumination was obtained. These promising results can be explained by the favorable direct (2.68eV) and indirect (2.26eV) energetic transitions and a sufficient negative conduction band edge at -0.7V vs RHE. This presentation will highlight recent advances with progress on both GaSbxN1-x and GaSbxP1-x materials and their growth using halide vapor phase epitaxy technique. The growth rates are modeled using a combination of thermodynamic and kinetic models and compared with experimental results.

Authors : Nicolas Gaillard
Affiliations : University of Hawaii

Resume : Photoelectrochemical (PEC) water splitting is an attractive method for efficient renewable hydrogen production. However, the cost, efficiency and durability of lab-scale systems are not yet at the level required to make this technology economically attractive. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promissing classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)(S,Se)2, Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of In2S3 n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.

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Latest Advances in Solar Fuels V : Flavio de Souza
Authors : Kevin Sivula
Affiliations : EPFL

Resume : The development of robust, inexpensive and high performance semiconducting materials are needed to make the direct solar-to-fuel energy conversion by photoelectrochemical cells economically viable. In this presentation our laboratory’s progress in the development new light absorbing materials and co-catalysts will be discussed along with the application toward overall solar water splitting tandem cells for H2 production. Specifically, this talk will highlight recent results with the ternary oxides (CuFeO2 and ZnFe2O4) 2D transition metal dichalcogenides, and organic (π-conjugated) semiconductors as solution-processed photoelectrodes. With respect to ternary oxides, in our recent work [1,2] we demonstrate state-of-the-art photocurrent with optimized nanostructuring and address interfacial recombination by the electrochemical characterization of the surface states and attached co-catalysts. In addition, we report an advance in the performance of solution processed two-dimensional (2-D) WSe2 for high-efficiency solar water reduction by gaining insight into charge transport and recombination by varying the 2D flake size[3]and passivating defect sites[4]. Finally, with respect to π-conjugated organic semiconductors, the main approaches for employing organic semiconductor-based devices towards solar H2 generation via water splitting are reviewed[1] and new benchmark results are described. [1] X. Zhu, N. Guijarro, Y. Liu, P. Schouwink, R. A. Wells, F. L. Formal, S. Sun, C. Gao, K. Sivula, Adv. Mater. 2018, 30, 1801612. [2] Guijarro, N.; Bornoz, P.; Prevot, M.; Yu, X.; Zhu, X.; Johnson, M.; Jeanbourquin, X.; Le Formal, F.; Sivula, K., Sustainable Energy Fuels 2018, 2, 103-117. [3] Yu, X.; Sivula, K., Chem. Mater. 2017, 29, 6863-6875. [4] Yu, X.; Guijarro, N.; Johnson, M.; Sivula, K. Nano Lett. 2018, 18, 215-222. [5] L. Yao, A. Rahmanudin, N. Guijarro, K. Sivula, Adv. Energy Mater. 2018, 1802585.

Authors : Giordano Gatto, Lucia Fagiolari, Gabriel Menendez Rodriguez, Cristiano Zuccaccia, and Alceo Macchioni
Affiliations : Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto, 8 – 06123 Perugia, Italy

Resume : Water oxidation (WO) is the ideal reaction to provide electrons and protons for the photo- and electro-synthesis of renewable fuels, generating exclusively oxygen as a benign by-product. Besides being demanding from the thermodynamic point of view, WO is also extremely difficult from the kinetic one. This has caused an explosion of interest for developing efficient water oxidation catalysts (WOCs) [1]. Parallel to the search for efficient non-noble metal WOCs [2], many efforts are directed forward noble-metal atom economy in WOCs [3]. Three strategies have been proposed to minimizing the atomic contents of noble metal: 1) exploiting molecular WOCs, under the assumption that all metal centres are catalytically active, differently from what happens in heterogeneous WOCs; 2) anchoring a well-defined molecular WOC onto a suitable support, thus obtaining a heterogenized WOC, combining the positive aspects of homogeneous and heterogeneous catalysis; 3) diluting active metal centres in a suitable material with features that maximize the metal-accessibility and performances. Herein, recent results of our efforts aimed at pursuing all three strategies for developing efficient WOCs based on iridium are reported [3]. [1] Kärkäs, M. D.; Verho, O.; Johnston, E. V.; Åkermark, B. Chem. Rev. 2014, 114, 11863. Blakemore, J. D.; Crabtree, R. H.; Brudvig, G. W.; Chem. Rev. 2015, 115, 12974. [2] Kärkäs, M. D.; Åkermark, B. Dalton Trans. 2016, 45, 14421. [3] Macchioni, A. Eur. J. Inorg. Chem. 2019, 7.

09:30 Coffee Break    
Authors : Antoni Llobet
Affiliations : Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology (BIST), Av. Països Catalans 16, E-43007 Tarragona, Spain

Resume : The replacement of fossil fuels by a clean and renewable energy source is one of the mostn urgent and challenging issues our society is facing today, which is why intense research is devoted to this topic recently. Nature has been using sunlight as the primary energy input to oxidize water and generate carbohydrates (a solar fuel) for over a billion years. Inspired but not constrained by nature, artificial systems [1] can be designed to capture light and oxidize water and reduce protons or other organic compounds to generate useful chemical fuels. In this context this contribution will present how molecular water oxidation catalysts can be anchored on solid supports to generate powerful hybrid electro- and photo-anodes for water splitting. [2] References: 1. S. Berardi, S. Drouet, L. Francàs, L.; C. Gimbert-Suriñach, M. Guttentag, C. Richmond, T. Stoll, A. Llobet, Chem. Soc. Rev., 2014, 43, 7501-7519. 2. (a) R. Matheu, M. Z. Ertem, J. Benet-Buchholz, E. Coronado, V. S. Batista, X. Sala, A. Llobet, J. Am. Chem. Soc. 2015, 137, 10786-10795. (b) J. Creus, R. Matheu, I. Peñafiel, D. Moonshiram, P. Blondeau, J. Benet-Buchholz, J. García-Antón, X. Sala, C. Godard, A. Llobet, A. Angew. Chem. Int. Ed. 2016, 55, 15382-15386. (c) R. Matheu, I. A. Moreno-Hernández, X. Sala, H. B. Gray, B. S. Brunschwig, A. Llobet, A; N. S. Lewis, J. Am. Chem. Soc. 2017, 139, 11345-11348.

Authors : Shaohua Shen; Tingting Kong
Affiliations : Xi'an Jiaotong University; Xi'an Shiyou University

Resume : Photocatalytic overall water splitting without using sacrificial agents is very appealing for converting solar energy into chemical fuels. Recently, polymer photocatalysts with tunable molecular structures have emerged as promising alternatives to inorganic photocatalysts for overall water splitting. Unfortunately, developing single-component photocatalysts for overall water splitting has been proven rather difficult, due to the fact that very few polymer photocatalysts possess suitable band structures with sufficient redox potentials to simultaneously drive water oxidation and proton reduction reactions. With inspiration from the natural photosynthesis, coupling two different polymer photocatalysts to form a Z-scheme structure could potentially lead to overall water splitting. The key for developing polymer-based Z-scheme systems lies mainly in identifying the H2-evolving and O2-evolving polymer photocatalysts with suitable band structures. Moreover, efficient charge transfer between the interfaces of heterostructures is crucial to achieve high photocatalytic activity. Herein, 1 nm-thick ultrathin graphitic carbon nitride nanosheets (CNNS) were firstly synthesized by a two-step ultrasonication-calcination method. With the unique structural features for efficient electron excitation and charge transport, the resultant ultrathin CNNS exhibited excellent activity for photocatalytic hydrogen evolution. Subsequently, by introducing homogeneous defect and dopant to CNNS via NaBH4 thermal treatment, we modulated the band structures of this ultrathin CNNS to achieve higher over potential for water oxidation. Finally, taking use of electrostatic self-assembly strategy, the photogenerated holes and electrons produced by CNNS and NaBH4 treated CNNS, respectively, could be promptly recombined at the interfaces of heterostructures whereas other excited electrons and holes were retained on different counterparts to drive redox reactions, leading to an efficient two-dimensional ultrathin Z-scheme photocatalytic system.

Authors : József S. Pap, Dávid Lukács, Miklós Németh, Łukasz Szyrwiel, Levente Illés, Béla Pécz, Shaohua Shen, Lionel Vayssieres
Affiliations : József S. Pap, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary; Dávid Lukács, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary; Miklós Németh, Surface Chemistry and Catalysis Department, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary; Łukasz Szyrwiel, European XFEL, Albert-Einstein-Ring 19, 22761 Hamburg, Germany; Levente Illés, Institute of Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary; Béla Pécz, Institute of Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences, H-1121, Konkoly-Thege street 29-33, Budapest, Hungary; Shaohua Shen, International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China; Lionel Vayssieres, International Research Center for Renewable Energy, State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

Resume : The true electrocatalyst of water oxidation in a number of cases proved to be an in situ developed CuO/OH film instead of (or beside) the original Cu complex itself, since the breaking of metal-ligand interactions and release of Cu ions under the applied conditions often successfully compete with the homogeneous process. The in situ decomposition of catalyst candidates is obviously unwanted; on the other hand, inexpensive and controllable precursor complexes represent an exciting platform to fabricate nanostructured CuO/OH coatings utilized in artificial photosynthesis. We investigated a family of low-cost and environmentally benign Cu-tripeptide complexes with tuned stability, but uniform {N,N,N,O}eq peptide binding mode throughout the surveyed pH range of 7 to 11. Boundary conditions were obtained for their alternating functioning between molecular catalyst and precursor to CuO, in borate buffers. At pH <8.5 and pH >10 homogeneous catalysis via an emblematic Cu(III)-peptide intermediate was confirmed, assisted by borate. In contrast, at pH 8.6-10 the development of robust CuO coatings consisting of nanoparticles occurs upon water oxidation on indium tin oxide. Importantly, a fine CuO coating could be also fabricated on a α-Fe2O3 nano-array without affecting its anisotropic morphology. We identified the interplay between the co-existent borate equilibrium species and the Cu complexes as the key factor to determine the dominant process. Financial support of the NKFI-128841 grant, the VEKOP-2.3.2-16-2016-00011 grant supported by the European Structural and Investment Funds, and the János Bolyai Research Scholarship from the Hungarian Academy of Sciences (J. S. Pap) are gratefully acknowledged.

Authors : Oomman K. Varghese, Ram Neupane, Maggie Paulose
Affiliations : Nanomaterials and Devices Laboratory, Department of Physics, University of Houston, Houston, TX 77204, USA.

Resume : The topic of generating fuels in a sustainable manner has never been more relevant than today. The pollution originating from hydrocarbon fuels has started causing obvious changes to the environment. Solar photoelectrochemical (PEC) fuel generation is a potential future green technology that utilizes the photocatalytic properties of semiconducting materials for converting energy in the ultraviolet to the near infrared region of the solar spectrum to fuels through processes such as water splitting. Although various materials and strategies have been developed for making the technology commercially feasible, low process efficiency and stability of the electrodes are still outstanding issues. Several of the stable photocatalysts do not have the ability for broad spectrum light absorption and hence, do not offer high solar-to-fuel conversion efficiency. We have recently demonstrated that the heterostructures formed by narrow and wide band gap low dimensional (0, 1 or 2D) materials could utilize solar photons in a broad energy range. When such heterostructured materials were used as electrodes in the PEC cell for water splitting, a significant enhancement in the performance was observed. The low dimensional materials facilitated even an uphill transfer of electrons at the hetero-interface. The advances in this work will be discussed in this presentation.

12:00 lunch    
Latest Advances in Solar Fuels VI : Flavio de Souza
Authors : Bruce E. Koel
Affiliations : Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544-5263, USA

Resume : Lack of a highly active, stable, earth-abundant electrocatalyst for carrying out hydrogen evolution and oxidation reactions (HER and HOR) in strongly acidic conditions is a major technical challenge for developing economical polymer electrolyte membrane (PEM)-based electrolyzers and fuel cells. We have found that processing Hf oxide with an atmospheric N2 plasma forms an acid-insoluble hafnium oxynitride material. We propose that under electrochemical environments this material is transformed into an active oxynitride hydroxide that demonstrates unprecedented high catalytic activity and stability for both HER and HOR in strong acidic media for earth-abundant materials. The zero onset potentials and high current densities demonstrate that this material is a promising alternative to Pt. This material demonstrates excellent HER and HOR activities in acids using non-platinum group metal (PGM) catalysts, opening new opportunities to develop technologically and economically viable unitized regenerative fuel cell (URFC) systems and cost-effective PEM electrolyzers. Furthermore, these results have broad implications for using nitrogen incorporation (e.g. by N2 plasma treatment) to activate other non-conductive compounds and films to form new active electrocatalysts.

Authors : Daniel V. Esposito
Affiliations : Columbia University

Resume : This talk describes emerging electrocatalyst and photoelectrode architectures for which the active sites for electrochemical reactions are encapsulated by nanomembrane overlayers that are permeable to the electroactive species of interest. These overlayers can be thought of as multifunctional exoskeletons that can be engineered to enhance the stability, charge transfer rates, and/or reaction selectivity of electrodes used in solar fuels generators. Here, I will present several case studies based on work from our lab that demonstrate each of these benefits using silicon oxide (SiOx) nanomembranes coated onto Pt-modified Si photocathodes and Pt thin films. We show that well-defined thin film electrodes are especially useful for quantifying transport properties of these nanomembranes and developing a deeper mechanistic understanding about (photo)electrocatalysis that occurs at buried interfaces. Importantly, these studies also show that properties of oxide nanomembranes can be highly tunable, providing new control knobs that be used to optimize the stability and efficiency of solar fuels generators for a variety of electrochemical reactions.

Authors : G. Zafeiropoulos1, H. Johnson2, S. Kinge2, M.C.M. van de Sanden1, M.N. Tsampas1
Affiliations : 1 Dutch Institute For Fundamental Energy Research - DIFFER, Eindhoven, 5612AJ, the Netherlands 2 TOYOTA MOTOR EUROPE NV/SA, Hoge Wei 33, 1930 Zaventem, Belgium

Resume : Solar hydrogen is a promising sustainable energy vector for mobility and power generation, and steady progress has been made towards the development of efficient water splitting materials. While most demonstrated solar water splitting systems run on liquid water, the idea of using water contained in ambient air is very appealing. Capturing water from the air implies that no liquid water is needed for operation. This potentially enables the construction of free-standing devices, in areas which don’t usually have a nearby water supply i.e. near to roads or remote areas. Since no ambient air testing protocols exist, we have developed a solid-state PEM-PEC cell inspired by the polymeric electrolyte membrane (PEM) electrolysers. In the PEM-PEC cell, the two electrochemical half-reactions are separated by a solid electrolyte. In this design the hydrogen generation and water dissociation are taking place in different compartments, allowing the exposure of the photoanode to ambient air. We show here how the functionalisation of porous TiO2 or WO3 photoanodes with ionomers enables the capture of water from ambient air. Functionalised photoanodes operating at 60-80% RH were able to recover 60-70% of the performance obtained when water is introduced in liquid phase. In addition long term experiments have shown remarkable stability at 60% RH for 80h of cycling (8h continuous illumination - 8h dark) demonstrating that the concept can be applicable outdoors.

Authors : Michael Sachs, Reiner Sebastian Sprick, Drew Pearce, Sam J. Hillman, Adriano Monti, Anne A. Y. Guilbert, Nick J. Brownbill, Stoichko Dimitrov, Frédéric Blanc, Martijn A. Zwijnenburg, Dave J. Adams, Jenny Nelson, James R. Durrant, and Andrew I. Cooper
Affiliations : M. Sachs; S. Dimitrov; J. R. Durrant: Department of Chemistry and Centre for Plastic Electronics, Imperial College London, U.K. R. S. Sprick; N. J. Brownbill; F. Blanc; D. J. Adams; A. I. Cooper: Department of Chemistry and Materials Innovation Factory, University of Liverpool, U.K. D. Pearce; S. J. Hillman; A. A. Y. Guilbert; J. Nelson: Department of Physics and Centre for Plastic Electronics, Imperial College London, U.K. A. Monti; M. A. Zwijnenburg: Department of Chemistry, University College London, U.K.

Resume : While the field of sunlight-driven fuel generation has traditionally been dominated by inorganic materials, organic photocatalysts are have sparked intense research interest - particularly due to their much higher synthetic flexibility. While some parallels can be drawn to organic photovoltaics, the fundamental understanding of photocatalytic processes has stayed behind the rapid development of more efficient materials. In this study,[1] we investigate a series of polymers with strikingly different hydrogen evolution activity, including some of the highest performing photocatalysts reported to date in this class of materials. A comparison to structurally related polymers with significantly lower activity allows us to identify the key determinants of hydrogen evolution activity in this series. To this end, we use transient absorption spectroscopy to monitor photogenerated reaction intermediates on time sales of femtoseconds to seconds after light absorption and correlate the type and yield of observed intermediates with the hydrogen evolution activity of the respective polymer. Computational simulations and calculations build on this transient data and extend the observations to the role of the solvent environment in the photoinduced reaction sequence. The presented results can provide design strategies with implications for the development of new and more efficient organic photocatalysts. References [1] Sachs, M.; Sprick, R. S.; et al. Nat. Commun. 2018, 9 (1), 4968.

15:30 Coffee Break    
Authors : K. Katsiev, H. Idriss
Affiliations : SABIC-Corporate and Research Center (CRD), King Abdullah University for Science and Technology (KAUST), Saudi Arabia

Resume : In an effort to probe into the fundamentals of charge carriers dynamics relevant to photo-catalytic materials, we have performed femtosecond time resolved spectroscopy (TRS) on anatase and rutile single crystals in the gas phase as well as in aqueous environment. By studying the effect of pump fluence, differences in charge carrier recombination rates and nature between both crystals were observed. The time constants for carrier recombination are two orders of magnitude slower for anatase (101) when compared to those of rutile (110) single crystal. Bulk defects introduced by sample reduction via annealing in ultra-high vacuum resulted in faster recombination rates for both polymorphs. Both surfaces (fresh and reduced) probed by pump fluence dependence measurements revealed that the major recombination channel in fresh and reduced anatase and reduced rutile is the first-order Shockley–Reed mediated. The effect of a hole trapping agent (ethanol) and of electron trapping agents (Ag+ and Ce4+ cations) is investigated over TiO2(110) rutile single crystal. Ethanol adsorption resulted in increasing the transient absorption signal in the 700-950nm with a slight decrease of their lifetime. No change was seen in the 500nm region commonly attributed to the presence of holes. The decay of the 700-950 nm signal mainly composed of two components is considerably perturbed by the presence of Ag+ or Ce4+ cations, which may indicate its surface origin. Work in progress to extract kinetic information from the study of the concentration effect of these metal cations in both the “nominally” hole and electron transient absorption regions

Authors : J.R.Morante
Affiliations : 1 Institut de Recerca en Energia de Catalunya (IREC), E-08930 Sant Adrià del Besòs, Spain; 2 Universitat de Barcelona, Barcelona, Spain

Resume : Nowadays, the circular economy of carbon dioxide constitutes one of the major world challenges. The conversion of CO2 into value-added chemicals and/or fuels, using renewable energy and earth-abundant elements as well as environmental friendly materials is a key priority. Under this scenario, carbon dioxide can give rise to different reduction reactions pathways with several sub products. Consequently, catalyst materials are essentials for increasing selectivity and productivity towards determined sub product such as CO, syngas, formic gas, methanol or even methane or double bonded carbon molecules. So, aside of the system design constraints, parameters as the over-potential values or charge transfer resistances are determining the final energy balance as well as the overall efficiency and productivity. In this presentation, the influence of the catalyst characteristics on the final performances, energy balances and final productivity will be presented and discussed considering over-potentials, Tafel plots and the overall characteristics of the selected catalyst according to the target CO2R products and used electrolytes. Catalyst mechanisms considering bimetallic, metal combination with P, S or Se or the role of individual catalyst atoms using metal organic frameworks, MOF, will be discussed in order to design the more adequate catalyst for enhancing the electrode performances. Special attention will also be paid on the conditions for diminishing as much as possible the overall cell voltage. For it, aside the development of highly efficient cathode catalysts, the development of high-performance catalysts for the oxygen-evolution reaction (OER) is also of paramount importance for achieving a cost-effective conversion of renewable electricity to fuels and chemicals. Considering these boundaries, we will demonstrate industrial feasibility and competitiveness of the electrochemical conversion of CO2 as alternative for the future energy models considering solar and dark refineries as energy paradigms delivering high current densities at low voltage cells or under bias free conditions, improving energy balance with high stability.

Authors : Mauricio A. Melo, Jr.,(1) Dereck N. F. Muche,(2) Flavio L. Souza,(2) Renato V. Gonçalves(1)
Affiliations : (1) São Carlos Institute of Physics, University of São Paulo, São Carlos, São Paulo, Brazil; (2) Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo, Brazil.

Resume : Iron titanate has recently surfaced as a promising photocatalyst for the O2-generating water splitting half reaction. Compared to other photocatalysts, it shows improved structural and photochemical features, which result in better conductivity, smaller band gap, longer charge carriers diffusion and adequate valence band energy. It is also cheap and non-toxic. However, Fe2TiO5 has been scarcely explored for the solar energy conversion into fuels, especially as the main absorber. In this investigation, orange phase-pure nanosized Fe2TiO5 (30 to 100 nm), with band gap of 2.0 eV, was obtained through a hydrothermal method. The nanoparticles were suspended in water and irradiated by a Xe lamp (λ>400 nm), producing 59.2 μmol h-1 g-1 of O2, using NaIO4 as electron scavenger. This is the first time O2 production using suspended Fe2TiO5 is reported. The evolution was boosted to 92.4 μmol h-1 g-1 after the loading of 1 wt% NiO nanoparticles as cocatalysts. Further loading impairs the reaction yield. Photoelectrochemical measurements in phosphate buffer (pH 7) corroborate these observations. For example, overpotentials of 0.34 and 0.18 on the water oxidation potential ( 0.82 V vs NHE) were observed for pristine and Fe2TiO5 loaded with 1wt% NiO. Thus, NiO leads to lower energetic barrier for the minority charge extraction, also favoring the charge carriers separation. Overall, this work illustrates how structural alterations of newly discovered photocatalysts can improve photochemical energy conversion. The authors acknowledge support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation.

Authors : Maciej Gryszel, Eric D. Głowacki
Affiliations : Linköping University

Resume : One of the biggest challenges of sustainable development is efficient solar energy harvesting and storage. Huge progress in photovoltaics enabled economically feasible solar-driven electricity generation, however an issue of the energy storage remains unresolved. One emerging possibility is photocatalytic oxygen reduction to the high-energy product hydrogen peroxide. Hydrogen peroxide is easier to store than hydrogen. Herein we present our recent work on photocatalysis and photoelectrocatalysis with organic semiconductors which efficiently produce hydrogen peroxide. When the organic semiconductor is in contact with oxygenated aqueous solution, the light driven 2-electron/2-proton redox cycle leads to photoreduction of oxygen to hydrogen peroxide. We show examples of n type, p type, and ambipolar organic semiconductors performing photochemical oxygen reduction, both as stand-alone photocatalysts and as components in photoelectrochemical cells. Many of these catalytic systems are stable and effective in a wide pH range from 2-12. This demonstration of efficient organic semiconductors as aqueous photocatalysts possibly opens new avenues for their catalytic applications.

Authors : Jan Kosco, Michael Sachs, Robert Godin, Mindaugas Kirkus, Laia Francas, Matthew Bidwell, Muhammad Qureshi, Dalaver Anjum, James R. Durrant, Iain McCulloch
Affiliations : J. Kosco, Dr. M. Kirkus, Prof. I. McCulloch Department of Physical Sciences and Engineering KAUST Solar Centre (KSC) 4700 KAUST, 23955 Thuwal, Saudi Arabia M. Sachs, Dr. R. Godin, Dr. L. Francas, M. Bidwell, Prof. J. R. Durrant, Prof. I. McCulloch Department of Chemistry and Centre for Plastic Electronics Imperial College London South Kensington Campus, London SW7 2AZ, UK M. Qureshi, Dr. D. Anjum Department of Physical Sciences and Engineering KAUST Catalysis Centre (KCC) 4700 KAUST, 23955 Thuwal, Saudi Arabia

Resume : Conjugated polymer (CP) semiconductors can be used to photocatalytically produce hydrogen from water using solar radiation. Most organic semiconductors have required a metal co-catalyst, usually photodeposited Pt, to produce quantifiable amounts of H2.(1) It is accepted that Pt accelerates the hydrogen evolution reaction (HER) by facilitating electron extraction from the semiconductor and subsequent electron transfer to protons in the aqueous phase.(2) However, many CPs contain significant levels of residual Pd, originating from their synthesis via Pd catalyzed polymerization.(3) There are conflicting views in the literature about the role of residual Pd in CP photocatalytic systems, which impedes the development of guiding structure–property relationships for efficient polymer design. In this presentation the effect of residual Pd on the hydrogen evolution activity in CP photocatalytic systems is discussed using CP nanoparticles as a model system. Residual Pd is observed in the form of homogeneously distributed nanoparticles within the polymers, and in the absence of additional co-catalysts is essential for any hydrogen evolution to be observed from the polymers. Low Pd concentrations (<40 ppm) are sufficient to have a significant effect on the HER rate, which increases linearly with increasing Pd concentration from <1 ppm to approximately 100 ppm, at which point the HER rate begins to saturate. Transient absorption spectroscopy experiments suggest that residual Pd mediates electron transfer from the F8BT nanoparticles to protons in the aqueous medium, thereby acting as a proton reduction co-catalyst. Because the morphology and distribution of residual Pd within CPs cannot effectively be controlled, its presence can make it impossible to make rational comparisons between the photocatalytic performance of different CPs. Furthermore, the presence of Pd could hinder a range of reduction chemistries, including CO2 reduction, as it will act as an electron trap, promoting proton reduction at the expense of the species of interest. Purification methods are presented that remove residual Pd from CPs, enabling rational comparisons between different organic semiconductor photocatalysts to be made. References: (1) Banerjee, T.; Gottschling, K.; Savasci, G.; Ochsenfeld, C.; Lotsch, B. V. H 2 Evolution with Covalent Organic Framework Photocatalysts. ACS Energy Lett. 2018, 3 (2), 400–409. (2) Yang, J.; Wang, D.; Han, H.; Li, C. Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis. Acc. Chem. Res. 2013, 46 (8), 1900–1909. (3) Krebs, F. C.; Nyberg, R. B.; Jørgensen, M. Influence of Residual Catalyst on the Properties of Conjugated Polyphenylenevinylene Materials: Palladium Nanoparticles and Poor Electrical Performance. Chem. Mater. 2004, 16 (7), 1313–1318.

19:00 Graduate Student Award ceremony followed by the social event    
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Latest Advances in Solar Fuels VII : Samuel Mao
Authors : Renata Solarska
Affiliations : Centre of New Technologies University of Warsaw

Resume : Solar energy conversion to different types of energy which might be subsequently released in diverse ways remains an unsaturated need, since the global demand for energy is continuously growing and will continue to rise. However, currently the field of renewable energy suffers from lack of an ideal material able to drive conversion of the solar energy with high efficiency and being stable enough to provide a long-term productivity. Therefore, multi-directional efforts including development of new materials and catalysts, incorporation of plasmonic nanostructures or creation of low-level sub- stoichiometry through different approaches are continuously undertaken and devoted to minimisation of the required bias voltage, improvement of light capture or charge transport properties. Our recent achievements regrading employment of different in structure polyoxometalates as catalysts, sub-stochiometric semiconducting oxides, newly designed and engineered crystal structures in solar driven arrangements as well as their performance for photo- induced processes will be presented and discussed in detail. Besides the extensive characterization of the above-mentioned systems, the kinetic assessment of the transient absorption phenomena will be approached. Use of transient absorption spectroscopy to study charge carrier behaviour in semiconductors-based systems allows to relate a photoelectrode architecture to the charge carrier origin, separation, collection, trapping, lifetime and therefore final efficiency. Therfore, comparison of the charge carrier dynamics occurring in semiconducting systems: bare, modified as well as mixed, are particularly useful in clarifying the observed differences in their photoelectrochemical performance.

Authors : Jianwu Sun,* Hao Li, Jingxin Jian, Yuchen Shi, Mikael Syväjärvi, Rositsa Yakimova
Affiliations : Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183, Linköping, Sweden. *E-mail:

Resume : Abstract: Photoelectrochemical (PEC) water splitting offers a promising way to convert the intermittent solar energy into the renewable and storable hydrogen energy. However, the most studied semiconductor photoanodes generally exhibit a poor PEC performance due to sluggish water oxidation. In this work, we demonstrate that the bottleneck of PEC water oxidation can be overcome via atomic manipulating proton-transfer on polar surfaces of silicon carbide (SiC) photoanodes [1]. On the typical carbon-face SiC, where proton-coupled electron transfer governed the interfacial hole transfer for water oxidation, substantial energy loss was inevitable due to the highly-activated proton-transfer steps. Via preferentially exposing the silicon-face, we enabled the surface-catalyzed barrierless O-H breaking with a facile proton exchange and migration character. In particular, we show that among SiC polytypes, cubic SiC (3C-SiC) is a very promising semiconductor for PEC water splitting due to its relatively small bandgap of 2.36 eV, which is close to the hypothetical ideal bandgap of 2.03 eV for the theoretical maximum of the solar water splitting efficiency. [1] Hao Li, Huan Shang, Yuchen Shi, Rositsa Yakimova, Mikael Syvajarvi, Lizhi Zhang and Jianwu Sun*, “Atomically Manipulated Proton-Transfer Energizes Water Oxidation on Silicon Carbide Photoanodes”, Journal of Materials Chemistry A, 6, 24358, (2018).

09:30 Coffee Break    
Authors : Shababa Selim,* Ernest Pastor,* Michael Sachs,* Laia Francàs,* Sacha Corby,* Miguel García-Tecedor,** Benjamin Moss,* Sixto Gimenez,** Andreas Kafizas,*** Artem Bakulin,* James R. Durrant*
Affiliations : *Imperial College London, Department of Chemistry, South Kensington Campus, London, SW7 2AZ, UK. **Institute of Advanced Materials (INAM), Universitat Jaume I, 12006, Castelló de la Plana, Spain. ***The Grantham Institute, Imperial College London, South Kensington, London SW7 2AZ, UK

Resume : Metal oxides are prone to oxygen deficiencies, which can have significant impact on photoanode performance. Bismuth vanadate has demonstrated the highest performing photoanodes to date, yet, the role these deficiencies play on charge carrier dynamics and thus the overall photocatalytic process remains controversial. In this talk, we will discuss the in situ modulation of the redox state associated with these defect induced sub-bandgap states through electrochemical, optical and thermal approaches, and explore the resulting impact on charge carrier dynamics and photocatalysis. The redox states of these defects are not only found to be essential for driving holes to the surface for water oxidation, but they are also associated with advantageous electron trapping. These trapped electrons are subsequently transported through the material facilitated by redox-mediated electron transport channels, giving rise to photocurrent generation. On the other hand, holes trapped into these states are rendered redundant to surface oxidation processes. As such, we show how incorporating the control of defect redox state in the photoelectrode fabrication and design process can be instrumental to optimising the overall performance.

Authors : Abdullah Kahraman,1,2,3* Mahsa Barzgar Vishlaghi,1,2,3 Işınsu Baylam,3,4 Alphan Sennaroglu,1,2,3,4 and Sarp Kaya1,2,3,5
Affiliations : 1 Material Science and Engineering, Koç University, Istanbul 34450, Turkey 2 Koç University TUPRAS Energy Center (KUTEM), Koç University, Istanbul 34450, Turkey 3 KoçUniversity Surface Science and Technology Center(KUYTAM), Koç University, Istanbul 34450, Turkey 4 Physics Department, Koç University, Istanbul 34450, Turkey 5 Chemistry Department, Koç University, Istanbul 34450, Turkey

Resume : BiVO4 is one of the most promising materials used as a photoanode for photoelectrochemical water splitting. The carrier recombination dynamics of BiVO4 is one of the main obstacles for the water oxidation reaction and it is commonly addressed employing the Ultrafast Transient Absorption Spectroscopy (UTAS). The aim of this study is two-folded: to understand the details of carrier recombination dynamics of BiVO4 and to reveal the impacts of surface engineering that leads to enhanced water oxidation activity. The proposed models for the recombination dynamics of BiVO4 are usually referred to UTAS investigations on TiO2 and Fe2O3, and the absorption spectra are interpreted in terms of excited state absorption, hole absorption, and ground state bleach. The electronic structure of BiVO4, therefore the possible optical pump induced transitions in the conduction and valence bands, are different from the TiO2 and Fe2O3, and more comprehensive analysis is required. In this study, we investigate the charge carrier dynamics of bare and modified BiVO4 (e.g. CoOx/BiVO4 and N-doped BiVO4) through UTAS and transient photocurrent spectroscopy (TPS). UTAS investigations in air, in different media (i.e. hole scavenger), and the numerical modelling help us to offer two promising dynamical models for BiVO4. The operando UTAS is utilized to identify the role of the interface on the catalytic activity and on the suppression of the carrier recombination. The co-catalyzed BiVO4 shows better activity which is associated to longer carrier life-time. TPS becomes handy to determine the change of depletion width and hole-diffusion length between engineered and bare BiVO4.

Authors : Thi Hiep Nguyen, Mengyuan Zhang, Wilman Septina, Joel Ming Rui Tan, Lydia H. Wong
Affiliations : School of Materials Science & Engineering, Nanyang Technological University, 639798, Singapore

Resume : The demand for utilization of clean and renewable energy has motivated many researchers to study on various possible strategies for harvesting solar energy. Among them, solar water splitting, which generate usable hydrogen from water and sunlight using photoelectrochemical (PEC) system is a promising approach towards generation of clean fuel. The PEC water splitting system based on photoelectrodes of photoanode and photocathode and electrolyte with the main component is the semiconductor photolectrodes. In general, metal oxides with high stability for photoelectrocatalytic water oxidation are often used as photoanodes [1]. Recently, by using high throughput calculations and experiments, a list of promising VO4-based ternary vanadate photoanodes was reported. Among them, FeVO4 which contains earth abundant elements of Fe and V, with favourable bandgap of 2.06 eV is a potential candidate for photoanode [2]. However, the PEC performance reported is still low due to its low carrier mobility [3]. This motivated us to explore alteration of multiple properties of the FeVO4 by metal alloying or doping to improve its photoelectrochemical performance. In order to find effective metal doping for FeVO4 photoanode, we use combinatorial synthesis and high-throughput characterizations of libraries of materials. FeVO4 thin films was fabricated using inkjet printing machine; with its drop-on-demand feature, this is a versatile method which enables printing a material with certain composition at a desired area while allowing deposition of multiple compositions on a single substrate. In our study, we explore doping of Fe-V oxides by adding Mo, Ni, Bi, Cr, Zn or W. After that, we perform scanning droplet cell to our photoanode materials as a quick assessment method of their photoelectrochemical behaviour. The best photoresponse to date was obtained from Fe-V-Cr oxide with 7% doping ratio of Cr/(Fe +V). Other samples with Mo, Bi, or W doping also showed higher current density compared with undoped FeVO4. This result opens a direction for further improvement of photoanode efficiency of PEC system for accelerating toward practical application. [1] B. D. Alexander, P. J. Kulesza, I. Rutkowska, R. Solarska and J. Augustynski, J. Mater. Chem., 2008, 18, 2298-2303. [2] Q. Yan, J. Yu, S. K. Suram, L. Zhou, A. Shinde, P. F. Newhouse, W. Chen, G. Li, K. A. Persson, J. M. Gregoire and J. B. Neaton, PNAS, 2017, 114, 3040-3043. [3] M. Zhang, Y. Ma, D. Friedrich, R. V. D. Krol, L. H. Wong, F. F. Abdi, J. Mater. Chem. A, 2018, 6, 548–555

Authors : Zhen Qiu, Gunnar A Niklasson, Tomas Edvinsson
Affiliations : Department of Engineering Sciences, Solid State Physics, Uppsala University, Box 534, 75121 Uppsala, Sweden

Resume : Investigating the influence of iron on nickel oxide nanosheets for enhanced overall water splitting through in-situ Raman and impedance spectroscopy Zhen Qiu, Gunnar A Niklasson, Tomas Edvinsson Department of Engineering Sciences, Solid State Physics, Uppsala University, Box 534, 75121 Uppsala, Sweden Contact email:, Mixed iron-nickel-based systems with tuned microstructure have recently emerged as promising non-noble electrocatalysts for alkaline water splitting. The understanding of interfacial reaction induced charge-transfer mechanisms and active phases, however, is still limited in overall water splitting. Herein, we report a detailed investigation of active surface phases and mechanisms during both the oxygen evolution (OER) and hydrogen evolution (HER) reactions in an alkaline electrolyte through in-situ Raman and impedance spectroscopy. The frequency response of electrical behaviour is interpreted by a full theoretical equivalent circuit model and is related to the Raman spectra. The results show that the reaction resistance exhibits a strong dependence on applied bias and electrode materials in natural correlation with the reaction rate under both OER and HER process. The presence of iron (Fe) results in a less inductive feature observed in HER impedance spectroscopy, which is associated with the coverage relaxation of involved adsorbed intermediates. By in-situ Raman spectroscopy, it is clear to see that the main function of nickel (Ni) and Fe sites are dependent on the applied energy. When the Femi level shifts to more negative potentials, the hydroxyl groups are prone to adsorb on Fe3 sites to form Fe oxyhydroxides, whereas the hydrogen groups show the tendency to adsorb (or migrate) to Ni sites, which accelerates water reduction and thus enhances HER activity. Moreover, the presence of Fe promotes the formation of high Ni valency (γ-NiOOH), leading to an improved OER catalytic performance. Our findings provide insights into the active phases formed in-situ under both the HER and OER reactions and are expected to be valuable for design strategies for efficient and earth-abundant Ni-Fe based catalytic systems.

Authors : Giulia Alice Volpato, Francesco Rigodanza, Serena Berardi, Stefano Caramori, Marcella Bonchio, Maurizio Prato, Andrea Sartorel
Affiliations : Dipartimento di Scienze Chimiche, University of Padova; CNR-ITM; Department of Chemistry and Pharmaceutical Sciences and CNR-ISOF, University of Ferrara; Department of Chemistry and Pharmaceutical Sciences and CNR-ISOF, University of Ferrara; CNR-ITM and Dipartimento di Scienze Chimiche, University of Padova; Center of Excellence for Nanostructured Materials (CENMAT) and INSTM, Department of Chemical and Pharmaceutical Sciences, University of Trieste; CNR-ITM and Dipartimento di Scienze Chimiche, University of Padova

Resume : Photoelectrochemical water oxidation still represents a major obstacle toward efficient solar fuel generation. In this regard, dye sensitized photoanodes embedding molecular water oxidation catalysts (WOC) are promising candidates to match solar emission spectrum at low energy radiation while combining fast catalysis. In the present work, poly-cationic perylene bisimides (PBIs) dyes have been used in combination with the deca-anionic tetra-ruthenium polyoxometalate (Ru4POM) WOC: the former feature a strong and broad absorption in the Vis range, great oxidizing power and stability toward oxidation; the latter consists of a tetra-ruthenium(IV) core, favouring sequential holes accumulation, stabilized by oxidation resistant POM ligands. The combination of electrostatic interactions with the pi-stacking ability of the dye offers a simple non-covalent approach for the assembly of these two components onto semiconducting metal oxides. When nanostructured WO3 is used, the resulting photoelectrodes show extended absorption up to 600 nm and light harvesting efficiency up to 40%, and show promising results in photoelectrochemical water oxidation, with quantitative faradaic yield towards O2 and absorbed photon to current efficiency (APCE) up to 1.4%. Further studies aim at improving the stability of the molecular assembly onto the semiconducting substrate. Bonchio et al., Nat. Chem. 2019. DOI: 10.1038/s41557-018-0172-y

12:15 lunch    
Latest Advances in Solar Fuels VIII : Samuel Mao
Authors : Benjamin Moss, Qian Wang, Andreas Kafizas, Robert Godin, Takashi Hisatomi, Anna Regoutz, David Payne, Kazunari Domen, Ludmilla Steier and James Durrant
Affiliations : Imperial College London; Cambridge University; Imperial College London; University Of British Columbia; Shinshu university; Imperial College London; Imperial College London;

Resume : Photocatalytic Z-Scheme water splitting uses a low-cost dispersion of two types of semiconducting particles to split water. Although simple and cost effective, this design strategy typically sufferers from low efficiencies. An improved design, known as the photocatalyst sheet, embeds particles in a conducting medium to facilitate inter-particle electron transfer. With appropriate co-catalysts, this highly scalable device architecture can split water unassisted with an quantum efficiency of 26 %. However, the key factors behind this remarkable efficiency are not yet fully understood. Herein, we focus on the proton reducing semiconductor in the Z-Scheme, La,Rh:SrTiO3 and present the first in-operando study of charge carrier dynamics of this material. Using photocatalyst sheet half-electrodes, we find that that in the absence of La, a re-organisation of the electronic structure of Rh:SrTiO3, via the reduction of Rh(IV) is a necessary prerequisite to observe the accumulation of persistent electrons. These can then be utilised by the co-catalyst to drive proton reduction. One way to achieve such Rh(IV) reduction is by applying a strong negative bias. This induces in-situ the reorganisation of electronic structure necessary to accumulate charge, however, such potentials are inaccessible in the complete photocatalyst sheet device. A different strategy must therefore be deployed in order to accumulate persistent electrons in Rh:SrTiO3.

Authors : Matthew T. Mayer
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie

Resume : Driving chemical reactions with renewable energy is a pathway to sustainable and carbon-neutral society. Combining photoabsorber and electrocatalytic components into integrated devices, we developed copper oxide-based photocathodes for water reduction to hydrogen [1,2], as well as carbon dioxide reduction to carbon monoxide [3], in demonstrations of efficient solar-to-fuels conversion. Such devices exhibit benchmark efficiencies among metal oxide based photoelectrodes.   Recently, oxide-derived copper emerged as an intriguing electrocatalyst for the conversion of carbon dioxide (CO2) into hydrocarbon products. In an effort to modify the product selectivity of copper oxide nanowire arrays, we used atomic layer deposition to apply conformal monolayers of tin oxide to the electrode surface. This copper-tin-oxide hybrid exhibited nearly unity selectivity for carbon monoxide (CO) as CO2 reduction product, deviating significantly from the behavior expected for copper or tin alone, neither of which typically produce CO at high selectivity. This result suggests atomic layer composition modification of electrode surfaces can be a powerful strategy for tuning electrocatalyst selectivity. (Work performed at previous affiliation: Ecole polytechnique fédérale de Lausanne EPFL, Switzerland)   1. L. Pan, J. H. Kim, M. T. Mayer, M-K Son, A. Ummadisingu, J. S. Lee, A. Hagfeldt, J. Luo, M. Grätzel, Nature Catalysis, 2018, 1, 412. 2. P. Dias, M. Schreier, S. D. Tilley, J. Luo, J. Azevedo, L. Andrade, D. Bi, A. Hagfeldt, A. Mendes, M. Grätzel and M. T. Mayer, Adv. Energy Mater., 2015, 5, 1501537. 3. M. Schreier, J. Luo, P. Gao, T. Moehl, M. T. Mayer and M. Grätzel, J. Am. Chem. Soc., 2016, 138, 1938. 4. M. Schreier, F. Héroguel, L. Steier, S. Ahmad, J. S. Luterbacher, M. T. Mayer, J. Luo and M. Grätzel, Nature Energy, 2017, 2, 17087.

Authors : Mariam Barawi, Elena Alfonso, Alba García, Carmen G López-Calixto, Marta Liras and V. A. de la Peña O´ Shea.
Affiliations : Photoactivated Proceses Unit IMDEA Energy Institute, Móstoles Technology Park, Av. Ramón de la Sagra 3, 28935 Móstoles, Madrid, Spain.

Resume : The conversion of solar energy into fuels such as hydrogen through photoelectrochemical (PEC) cells is an attractive way to solve the storage problems present in renewable energies and also in transport applications.(1) Many advances have been made until today, but it is still necessary to develop new materials and cell configurations in order to take this technology to a commercial level. At the present, different materials as oxides, oxisulfides and metal chalcogenides are being investigated as photoelectrodes in PEC cells. However, achieving high STH (Solar To Hydrogen) by using a single material as photoelectrode is a very tricky objective. Therefore, hybrid materials are getting a lot of attention lately. (2) In this work, we present a tandem PEC cell composed by two hybrid photoelectrodes formed by the heterojunction of a novel synthesized organic conductive polymer (Nano-CMPDTT) and inorganic nanocrystals (TiO2 and CuI). Nano-CMPDTT is based on dithiothiophene moiety and was synthesized by Sonogashira cross coupling reaction from precursors in mini-emulsion conditions. In order to elucidate the electronic structure of this material, HOMO and LUMO orbital positions were determined by cyclic voltammetry and fermi level location through electrochemical impedance spectroscopy and XPS. The energy diagram shows an ideal position of the energy bands in order to use the synthesized polymer both as photocathode and as an electron injector to TiO2 in photocatalytic reactions (to former the photoanode). In this way, TiO2 NCs suspensions and Nano-CMPDTT has been deposited by spin coating in ITO glasses to build the photoanode and CuI (hole collector) and Nano-CMPDTT for the photocathode. The formed hybrid photoelectrodes have been characterized by X-ray diffraction, SEM, EDX and AFM. A series of photoelectrochemical measurements have been performed in a three electrode cell configuration, using the hybrid materials as working electrodes. The photoelectrodes presents high values of photovoltages and photocurrents. Electrochemical Impedance Spectroscopy (EIS) was performed to confirm the improved charge transfer observed when illuminating the hybrid photoelectrodes. Finally, we build a tandem PEC cell in a monolithic configuration and perform a series of photoelectrochemical measures in two electrode configuration and we test and quantify the hydrogen evolution reaction. References 1. Z. Chen, H. N. Dinh, E. Miller, Photoelectrochemical Water Splitting (Springer New York, New York, NY, 2013;, SpringerBriefs in Energy. 2. T. Bourgeteau et al., Enhancing the Performances of P3HT : PCBM − MoS3 ‑ Based H2 ‑ Evolving Photocathodes with Interfacial Layers. ACS Appl. Mater. Interfaces. 7, 16395 (2015).

Authors : Elena Alfonso González a, Mengjiao Wang b, Luca De Trizio b, Mariam Barawi a, Marta Liras a, Víctor A. de la Peña O'Shea a
Affiliations : a, IMDEA Energy Institute; b, Instituto Italiano di Tecnologia

Resume : Artificial photosynthesis is a very promising method to turn solar energy into fuels.(1) Photoelectrochemical (PEC) cells have led to some of the highest solar-to-hydrogen efficiencies achieved to date.(2) The setup of a successful PEC cell requires the preparation of stable photoelectrodes with high light absorption and efficient charge separation. Substoichiometric copper telluride, Cu2-xTe, is a very interesting material that, as far as we know, has not been used in a PEC cell yet. It has already been employed in photovoltaic cells due to its small band gap (around 1.5 eV) and its high conductivity.(3) In this work, we prepared thin films of Cu2-xTe nanocrystals synthesized by a colloidal method(4) on ITO coated glass and characterized them as photoelectrodes. In order to prepare these photoelectrodes and keep the original optical and electrical properties of Cu2-xTe, the organic capping was successfully removed by a ligand exchange method. XPS (Fermi level-to-valence band distance), linear sweep voltammetry (photocurrents, flat band potential) and UV-Vis-nIR spectroscopy (band gap) allowed us to build the bands energy diagram, which confirms the thermodynamic ability of this material to reduce water to hydrogen. This means that Cu2-xTe thin films are good candidates to be used as photocathodes, which was also confirmed by the measurement of H2 generation by water splitting in a two-electrode PEC cell connected to gas chromatography. A tandem PEC cell built with TiO2 and Cu2-xTe showed higher H2 generation than TiO2 or Cu2-xTe alone. Also, using Cu2-xTe as a photocathode and TiO2 as a photoanode enhances the photocurrent. The mechanisms and efficiency of these and other possible configurations will be discussed in the presentation. References (1) Kevin Sivula & Roel van de Krol, Semiconducting materials for photoelectrochemical energy conversion, Nature Reviews Materials 1, 1–16 (2016) (2) James L. Young, Myles A. Steiner, Henning Döscher, Ryan M. France, John A. Turner & Todd G. Deutsch, Direct solar-to-hydrogen conversion via inverted metamorphic multijunction semiconductor architectures, Nature Energy 2017, 17028, 1–8 (3) Nitiporn Rungtaweechai & Auttasit Tubtimtae, Cu2-xTe/MnTe co-sensitized near-infrared absorbing liquid-junction solar cells, Materials Letters 2015, 158, 70–74 (4) Enrico Mugnaioli, Mauro Gemmi, Renyong Tu, Jeremy David, Giovanni Bertoni, Roberto Gaspari, Luca De Trizio & Liberato Manna, Ab Initio Structure Determination of Cu2−xTe Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging, Inorganic Chemistry 2018, 57, 16, 10241-10248

Authors : Antonio Alfano, Alessandro Mezzetti, Francesco Fumagalli, Chen Tao, Annamaria Petrozza, Fabio Di Fonzo
Affiliations : Politecnico di Milano Physics Department, Center for Nano Science and Technology Istituto Italiano di Tecnologia; Center for Nano Science and Technology Istituto Italiano di Tecnologia; EU Joint Research Center Institute for Energy; Center for Nano Science and Technology Istituto Italiano di Tecnologia; Center for Nano Science and Technology Istituto Italiano di Tecnologia; Center for Nano Science and Technology Istituto Italiano di Tecnologia

Resume : Hybrid organic photoelectrochemical water splitting is gaining momentum in the field of solar conversion technologies. By taking advantage of organic semiconductors properties such as low cost, stability, tuneable electronic properties and ease of large area production, these materials can help to go beyond the limitations of standard inorganic photoelectrochemical water splitting. An efficient tandem cell must provide enough voltage to bias the overall water splitting reaction, overcoming the losses occurring in organic semiconductors-based systems. Therefore, we investigated the various donor and acceptor materials known from the field of OPV starting from electrochemical stability test. Complementary UV-Vis-NIR Absorption data are also collected for each D/A blend to assess the future integration in tandem systems. Hybrid photocathodes are then realized using different hole selective contacts and evaluating their effect on the performances. Materials belonging to the class of metal oxides, small molecules, and transition metal dichalcogenides are thereof studied and optimized for this peculiar application. Amongst the more promising architectures, PCDTBT:PC70BM based photocathodes delivered an open circuit potential of 0.85 V vs RHE, achieving a remarkable increase with respect to the benchmark P3HT:PCBM. The optimized architectures are then tested in organic-based tandem set-up with a perovskite solar cell to perform unbiased water splitting with STH efficiency above 2%.

15:30 Coffee Break    
Authors : Félix Urbain1*, Ruifeng Du1, Pengyi Tang1,2, Vladimir Smirnov3, Katharina Welter3, Teresa Andreu1,4, Friedhelm Finger3, A. Cabot1,5, Jordi Arbiol2,5, and Joan Ramón Morante1,6
Affiliations : 1 IREC, Catalonia Institute for Energy Research, Jardins de les Dones de Negre 1, 08930 Sant Adrià de Besòs, Barcelona, Catalonia, Spain 2 Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Catalonia, Spain 3 IEK-5 Photovoltaik, Forschungszentrum Jülich, D-52425, Jülich, Germany 4 Universitat Politècnica de Catalunya, Jordi Girona 1–3, 08034 Barcelona, Catalonia, Spain 5 ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Catalonia, Spain 6 Universitat de Barcelona, Martí i Franquès, 1, 08028 Barcelona, Catalonia, Spain

Resume : We report on a flow-cell type device for bias-free solar conversion of CO2 to syngas (H2 + CO), which by design, is integrated, scalable to large areas, and compatible with earth-abundant and cheap photovoltaics and electrocatalysts. The presented device was composed of a photocathode performing the CO2-to-CO conversion and a dark anode for the oxygen evolution reaction (OER). The photocathode consisted of a triple junction thin-film silicon solar cell, which was chemically protected and electrically connected to three-dimensional (3D) Cu foam, coated with bimetallic Ag-Zn catalyst nanostructures (<50 nm). For the coating process, co-electrodeposition of Ag and Zn on the Cu foam was applied, which has been optimized regarding catalyst size/distribution and complete coverage of the 3D foam. In the continuous flow-cell setup (dark conditions), stable and tunable H2:CO ratios between 4 and 0.1, reaching ±100% Faradaic efficiency for a wide range of low cathode potentials (< 1.0 V) have been demonstrated for the Ag/Zn-on-Cu foam electrode. Furthermore, high CO Faradaic efficiencies of up to 91 % and partial current densities of 47.5 mA cm2 were achieved. For the OER anode, we employed colloidal Co3O4 nanoparticles (<10 nm) loaded on Ni foam. This 3D electrode configuration resulted in impressively low overpotentials for the electro-oxidation process of 330 mV for current densities of 50 mA/cm2. Both optimized electrodes were finally integrated in a complete flow-cell for solar-driven CO2 conversion that applied a bipolar membrane to separate catholyte and anolyte compartments. In this configuration, we demonstrated a stable and bias-free operating current density of 6.1 mA/cm2, reaching 98 % Faradaic efficiency for syngas production.

Authors : Hyeong-Suk Oh, Da Hye Won, Yun Jeong Hwang
Affiliations : Clean Energy Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu Seoul, 136-791, Republic of Korea

Resume : To mitigate the increasing atmospheric CO2 concentration, CO2 utilization techniques have been recently highlighted. Among many of the CO2 utilization techniques, electrochemical CO2 conversion is promising because it can combined with renewable energy sources such as a solar cell, which is fossil-fuel free process. In nature, photosynthesis system absorbs sunlight and convert CO2 and H2O to produce valuable bio-chemicals with the assistance of the solar energy, from which it provides sustainable carbon recycle. At KIST research team have been developed a monolithic and stand-alone photoelectrochemical device to convert CO2 to valuable chemicals. The device is composed of a photovoltaic cell module which supplies the required energy for electrochemical CO2 reduction and water oxidation reactions. We demonstrated that cost-effective Si module can be applied for the photovoltaic cell to achieve ~ 8% of solar to CO conversion efficiency. In order to increase the conversion efficiency, the device design is especially important to decrease the series resistance as the current density increases. In addition, in order to increase the economic feasibility, the conversion efficiency as well as the CO2 conversion rate have to be considered. In this talk, several electrocatalysts would be also introduced for selective CO2 reduction to value-added chemicals. For CO production, Ag or Zn metal based nanostructured catalysts have been demonstrated the surface modification is important to achieve over 90% of Faradaic efficiency for CO production. We found that one of the critical challenges is how to suppress the hydrogen evolution reaction from the aqueous electrolyte. For selective C2+ chemical production, Cu-based mono or hybrid catalysts have been applied in order to increase C-C coupling reaction efficiency (up to ~ 70% of Faradaic efficiency). We found that introducing heterogeneity on the Cu surface can contribute to CO dimerization. In-situ spectroscopic studies were performed to understand the active species of the catalysts. Our series of studies suggests the modification of the metal nanoparticle surface by oxygen atom or surface mediated molecules/materials are effective strategies to develop efficient and durable electrocatalysts for CO2 reduction reaction.

Authors : Suhee Kang1, Joonyoung Jang1, Hyunsoo Nam1, Sung-Hoon Ahn2 and Caroline Sunyong Lee1,†
Affiliations : 1.Department of Materials and Chemical Engineering, Hanyang University, Ansan, South Korea ; 2.Department of Mechanical and Aerospace Engineering, Seoul National University, Seoul, South Korea

Resume : Titanium dioxide (TiO2) is the one of widely studied photocatalysts due to its non-toxicity and high chemical/physical stability. Nevertheless, it suffers through poor absorption in visible irradiation due to its large band gap energy of ~ 3.2 eV and high rate of recombination. Thus, bandgap engineering using doping or synthesizing with low band gap semiconductor materials is crucial to improve its photocatalytic properties. Recently, reduced TiO2 (TiO2-x) has received remote attention because of its wide light absorption ability as well as disordered structure, leading to better photocatalytic performances. Moreover, graphitic carbon nitride (g-C3N4), a non-metallic semiconductor having a bandgap of 2.6 eV, can be used to reduced its band gap energy as well as reducing recombination rates. This material has attracted much attention due to its easiness to manufacture as well as its environmentally benign and high thermal stability. Therefore, engineering heterostructure of reduced TiO2 and g-C3N4 would help enhancing photocatalytic evaluations. In the present work, we have tried to explore fabricating polymeric graphitic carbon nitride (g-C3N4) coating onto reduced TiO2 nanofibers via electrospinning followed by sintering method. Initially, TiO2 nanofibers were electrospinned and sintered by reducing nanofibers in H2/Ar atmosphere at 600 °C/4h. After that, as-fabricated reduced TiO2 nanofibers were sintered with thiourea solution at 520 °C/2h in air atmosphere to coat g-C3N4 structures onto reduced TiO2 nanofibers. This reduced TiO2 with g-C3N4 coating was analyzed to observe morphologies, its improvement in absorbance and reduction in recombination losses via different analytical techniques. Based on characterizations, CO2 photoreduction and H2 evolution photocatalytic measurements were performed to show better performance compared to that of the reduced TiO2 nanofibers only. Therefore, the optimized heterostructures were proven to be efficient photocatalytic materials which can be applied to artificial photosynthesis, solar cell, bio-applications.

Authors : Jeiwan Tan(1), Wooseok Yang(1), Yunjung Oh(1), Hyungsoo Lee(1), Jaemin Park(1), Joosun Kim(2), Jooho Moon(1)*
Affiliations : (1)Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Korea; (2)High-Temperature Energy Materials Research Center, Korea Institute of Science and Technology Seoul 02792, Korea

Resume : Understanding the degradation mechanism and improving the stability of photoelectrodes are essential to realize solar to hydrogen conversion via photoelectrochemical (PEC) devices. Although amorphous TiO2 layer has been widely employed as a protection layer on top of p-type semiconductors to implement durable photocathodes, a gradual photocurrent degradation was still unavoidable. Herein, we elucidate the photocurrent degradation mechanism of TiO2-protected Sb2Se3 photocathode and propose a novel interface modification methodology in which fullerene (C60) is introduced as a photo-electron transfer promoter for significantly enhancing the long-term stability. It is demonstrated that the accumulation of photo-electrons at the surface of TiO2 layer induces its reductive dissolution, accompanying the photocurrent degradation. In addition, the insertion of C60 photo-electron transfer promoter at Pt/TiO2 interface facilitates the rapid transfer of photo-electrons out of TiO2 layer, thereby enabling the enhanced stability. Our Pt/C60/TiO2/Sb2Se3 device revealed the high photocurrent density of 17 mA cm−2 at 0 VRHE and outstanding stability over 10 h-operation, representing the best PEC performance and stability as compared to previously reported Sb2Se3-based photocathodes. Our research not only provides in-depth understanding of the degradation mechanism for TiO2-protected photocathodes, but also suggests a new direction to achieve durable photocathodes for PEC water splitting.

Authors : Professor Antonio Tricoli
Affiliations : Nanotechnology Research Laboratory, College of Engineering and Computer Science, Australian National University

Resume : Chemical storage of solar energy by H2 production is an attractive approach for stabilization of the electrical grid and on-demand power generation. Currently the poor transparency of the thick low-cost catalyst layers required for water oxidation hinders the large-scale fabrication of efficient photo-electrochemical cells for artificial photosynthesis and hydrogen production. Flame synthesis is a scalable technology for the production of ultra-porous layers of photo-catalysts and optoelectronic devices [1]. Nevertheless, the fragility of this gas-phase self-assembly has limited their application in liquid environments with most studies requiring very high temperature sintering to obtain sufficient mechanical stability. Here, we report the multi-scale engineering of robust high performance photo- and electrocatalyst layers with tunable porosity and composition [2]. We discuss the critical parameters controlling the performance and present a flexible approach for their rapid in-situ mechanical and chemical stabilization. We apply this concept to the fabrication of photo-electrochemical cells for water splitting demonstrating high turn-over frequencies, controllable light absorption and efficient electron collection. We envision that this scalable synthesis approach can be readily implemented for the commercial production of low-cost devices for chemical energy storage and renewable fuel production. 1. N. Nasiri, A. Tricoli, et al., Adv. Mater. 2015, 27, (29), 4336 2. G. Liu, A. Tricoli, et al., Adv Energy Mater 2016, 6, (15).

Authors : Dr. Khurram S. Joya
Affiliations : Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

Resume : For many catalytic processes, solar and chemical energy conversion, thin-film molecular and functional nanoscale materials and their surface assemblies are becoming increasingly significant. In this regard, developing robust and high activity electrocatalytic materials that are obtained from thin-film molecular and functional nanoscale materials and their synergistic interfacing with efficient light-harvesting modules is imperative for electro- and photo-electrocatalysis catalysis application in water oxidation and CO2 conversion, chemicals synthesis and solar fuels production. We have developed methods and exploited various functional thin film and nanoscale materials for catalytic water splitting, CO2 reduction, and recently for biomass catalysis, solar energy conversion and electrochemical sensing schemes. Now we implement several molecular nanoclusters, thin film, inorganic nanomaterials and metal-oxides displaying great potential to be used in surface chemistry and electrocatalysis. Their effective interfacing with semiconductor photo-responsive materials and/or CO2 reduction systems can provide a potential platform to make renewable energy supplies for a renewable and sustainable future. References: [1] K. S. Joya*, L. Sinatra, L. G. AbdulHalim, C. P. Joshi, M. N. Hedhili, O. M. Bakr and I. Hussain, Nanoscale, 8 (2016) 9695–9703. [2] K. S. Joya*, Y. F. Joya, H. J. M. de Groot, Adv. Energy Mater., 4 (2014) 1301929. [3] M. de Respinis, K. S. Joya, H. J. M. De Groot, F. D’Souza, W. A. Smith, R. van de Krol, B. Dam, J. Phys. Chem. C, 119 (2015) 7275–7281. [4] K. S. Joya*, H. J. M. de Groot, ACS Catal. 6 (2016) 1768–1771. [5] K. S. Joya*, N.K. Subbaiyan, F. D'Souza, H. J. M. de Groot, Angew. Chem. Int. Ed., 51 (2012) 9601–9605. [6] K. S. Joya*, N. Morlanés, E. Maloney, V. Rodionov, K. Takanabe, Chem. Commun., 51 (2015) 13481–13484. [7] K. S. Joya*, Y. F. Joya, K. Ocakoglu, R. van de Krol, Angew. Chem., 125 (2013) 10618–10630; Angew. Chem. Int. Ed., 52 (2013) 10426–10437.

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Latest Advances in Solar Fuels IX : Sanjay Mathur / Lionel Vayssieres / Flavio de Souza / Samuel Mao
Authors : Jinghua Guo
Affiliations : Advanced Light Source, Lawrence Berkeley National Laboratory, CA, USA

Resume : The energy materials and devices have been largely limited in a framework of thermodynamic and kinetic concepts or atomic and nanoscale. Soft x-ray spectroscopy characterization offers unique characterization in many important energy materials of energy conversion, energy storage and catalysis in regards to the functionality, complexity of material architecture, chemistry and interactions among constituents within. The presentation firstly gives some details on in situ/operando soft x-ray spectroscopy characterization of interfacial phenomena in energy materials and devices. It has been found that the microstructure and composition of materials as well as the microstructure evolution process have a great influence on performances in a variety of fields, e.g., energy conversion and energy storage materials, chemical and catalytic processes. However, it is challenging to reveal the real mechanism of the chemical processes. In-situ/operando x-ray spectra characterization technique offers an opportunity to uncover the phase conversion, chemical environment change of elements and other very important information of solid/gas and solid/liquid interfaces in real time. It will be shown how to use the powerful in-situ/operando soft x-ray spectroscopy characterization techniques, e.g. soft x-ray absorption spectroscopy (XAS) and resonant inelastic soft x-ray scattering (RIXS) to investigate the real electrochemical mechanism during the operation. A number of electrochemical liquid cells will be presented with success in revealing the catalytic and electrochemical reaction process at real time. The experimental results demonstrate that in-situ/operando soft x-ray characterization techniques can help researchers well understand the real reaction mechanisms.

Authors : Jennifer Leduc, Thomas Fischer, Sanjay Mathur
Affiliations : Institute of Inorganic Chemistry, University of Cologne, Cologne, Germany

Resume : Herein, we report on the role of electronically coupled phase boundaries on the water oxidation performance of hematite (-Fe2O3) photoanodes. Different metal oxides were tested as underlayer materials with regard to their absorption and charge-transfer properties. We demonstrate that uranium oxide (U3O8) underlayers grown by chemical vapor deposition or magnetite (Fe3O4) underlayers prepared via directed post-deposition plasma-chemical reduction of hematite effectively accelerate the OER in conjunction with -Fe2O3 overlayers through a built-in potential at the interface. We found that the differential chemical constitution and valence states of iron (Fe2+/Fe3+) and uranium (U5+/U6+) ions can enhance the charge separation and thus the overall electrical conductivity of the layer. Moreover, DFT simulations showed that the multivalence of U and Fe ions can induce the adjustment of the band alignment subject to the concentration of interfacial Fe ions. For both underlayer materials, a favored type II band edge alignment was calculated, which improves charge-transfer processes as supported by transient and X-ray absorption (TAS and XAS) spectroscopy.

09:30 Coffee Break    
Authors : Saulo Amaral Carminati; André do Nascimento Barbosa; André Luiz Martins de Freitas; Fernando Lázaro Freire Júnior; Flávio Leandro de Souza; Ana Flávia Nogueira
Affiliations : University of Campinas; Pontifical Catholic University of Rio de Janeiro; Federal University of ABC

Resume : The role of the single layer graphene (SLG) as overlayer on hematite (α-Fe2O3) photoanodes surface was investigated for water oxidation reaction via photoelectrochemical studies. SLG was synthesized by chemical vapour deposition (CVD) and transferred from the copper foil to the α-Fe2O3 photoanode surface. To ensure the purity and quality of SLG, elemental composition of the samples was determined in all steps and no metal (Cu) trace was found after the transference onto the photoanode surface. The photocurrent density of α-Fe2O3/graphene photoanode was increased from 1.25 to 1.64 mA cm-2 at 1.23 VRHE in comparison to bare α-Fe2O3 photoanode. The role of SLG added on α-Fe2O3 and the charge carrier dynamics were investigated combining transient absorption spectroscopy (TAS)[1] and surface photovoltage spectroscopy (SPS)[2]. These combined techniques revealed that the photogenerated holes had their lifetime increased as a function of applied bias and after the SLG deposition onto the α-Fe2O3 photoanode surface. As consequence, the photochemical separation and transfer of the photogenerated charge carriers became more efficient in the presence of SLG. The incorporation of SLG on α-Fe2O3 photoanode is believed to suppress the surface traps, enabling holes to diffuse into the solid-liquid interface and promoting water oxidation reaction driven by sunlight irradiation. [1] S. R. Pendlebury, M. Barroso, A. J. Cowan, K. Sivula, J. Tang, M. Grätzel, D. Klug, J. R. Durrant, Chem. Commun. 47 (2011) 716–718 [2] H. L. Tan, A. Suyanto, A. T. Denko, W, H. Saputera, R. Amal, F. E. Osterloh, Y. H. Ng, Part. Part. Syst. Charact. 34 (2017) 1600290

Authors : Rajiv Ramanujam Prabhakar1, Dennis Friedrich2, Thomas Moehl1 , Wei Cui1 and David Tilley1
Affiliations : 1. University of Zurich , Institute for Chemistry , Zurich , Switzerland 2. Helmholtz Zentrum, Institute for solar fuels , Berlin , Germany

Resume : Sb2Se3 has emerged as a promising photocathode for water splitting owing to its high photoelectrochemical performance (~ 15 mAcm-2) and resistance to photocorrosion in the absence of any protection layers. It has been demonstrated that sulfurization treatment of Sb2Se3 improves the onset potential and hence the photovoltage. However, the origin of such an improvement in the photovoltage is not fully understood in the literature. In this work, we employ 2 techniques to understand this phenomenon. Firstly, by in-situ surface potential sensing, the photovoltage was found to increase from 220 mV to 340 mV upon sulfurization treatment. Next, from time-resolved microwave conductivity (TRMC), although the carrier mobilities remained the same, there was an increase in the diffusion lengths upon sulfurization treatment. Interestingly, this increase was more pronounced in shorter wavelengths (400-700 nm) than longer wavelength (700-1100nm) suggesting that the sulfurization treatment primarily reduces the surface recombination rather than bulk recombination.

Authors : Jihye Suh, David Tilley
Affiliations : University of Zurich

Resume : SnS is a p-type semiconductor with a bandgap of 1.1-1.3 eV and large optical absorption coefficient in the visible. Its conduction band alignment is favorable for water reduction. Compare to CIGS (CuInGa(S,Se))or CdTe, tin and sulfur are both earth abundant and non-toxic elements. Thus, SnS is a promising photocathode material for low-cost water splitting. Solution-phase deposition of inorganic semiconductor thin films is facile and scalable method for manufacturing thin film photoelectrochemical (PEC) cells. In a binary solvent mixture of ethylenediamine (en) and 1,2-ethanedithiol(edt) in 10:1 vol/vol ratio, bulk SnS powder dissolves and form molecular Sn-S ink. Phase pure SnS thin film is then prepared by spin-coating the 0.5M Sn-S ink on Au (100nm) coated FTO (Fluorine doped Tin Oxide) and annealing in inert atmosphere at 350°C. Bare SnS shows very late onset potential for hydrogen reduction and is unstable in acidic conditions of PEC cell. To shift the onset voltage positively, n-type Ga2O3 (20nm) buffer layer was grown by Atomic Layer Deposition (ALD) to form a heterojunction. To improve the stability of the electrode, n-type TiO2 (50nm) was grown on Ga2O3 layer by ALD. As a hydrogen evolution catalyst, Pt nanoparticles were deposited on the surface of TiO2 by photoelectrodeposition. These photocathodes generates an onset voltage shift of 400mV and a photocurrent density of -0.8mA cm-2 at 0V versus reversible hydrogen electrode (RHE) for water splitting under 1 sun illumination. The photocurrent density does not decrease over time (30 min at 0V vs RHE) showing that the SnS/Ga2O3/TiO2/Pt structure device has improved stability for water splitting.

Authors : André E. Nogueira (a), Gelson T. S. T. Silva (a,b), Jéssica A. Oliveira (a,c), Juliana A. Torres (a), Mitchell Silva (b), Marcelo Carmo (d), Caue Ribeiro (a,d)
Affiliations : (a) Embrapa Instrumentation, Rua XV de Novembro, 1452, CEP: 13560-970, CP 741, São Carlos, SP,Brazil. (b) Department of Chemistry – Federal University of São Carlos, Via Washington Luiz, km 235, CEP: 13565-905, São Carlos, SP, Brazil. (c) Department of Chemical Engineering – Federal University of São Carlos, Via Washington Luiz, km 235, CEP: 13565-905, São Carlos, SP, Brazil. (d) Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-3): Electrochemical Process Engineering, 52425 Jülich, Germany

Resume : Cu-based materials (metal and related oxides) are among the most successful materials for CO2 photoreduction process, with some selectivity for CH4 production. However, the mechanism by that reaction takes place is still poorly understood, specially when using Cu oxides. Therefore we systematically investigated CO2 photoreduction catalyzed by CuO from different synthetic methods (solvothermal, coprecipitation and solid-state reaction) to understand which mechanism is prevailing for this reaction. The results showed that CuO acts as a reactant during CO2 reduction through copper carbonate formation rather than a catalyst, but the as-formed CuCO3.Cu(OH)2 (malachite) is active as catalyst for the same reaction. Significant CO2 conversion was observed during the CuO carbonation process, reducing to lower conversion levels after complete conversion to copper carbonate. To increase the stability of CuO, an heterojunction was proposed with Nb2O5, which was a candidate material with good performance in previous CO2 reduction studies. The heterojunction formation was also investigated for other reductive reactions, using electron and hole scavengers (sacrificial reactants) to understand the mechanisms. These results indicate that these catalysts are potential materials for solar fuel production trough CO2 reduction, as well as highlight the importance of adequate synthetic methods to produce them.

Authors : Ingrid Rodríguez-Gutiérrez 1,2,3, Jinzhan Su 2, Geonel Rodríguez-Gattorno 3, Flavio L. de Souza 1, Gerko Oskam 3
Affiliations : 1 Universidade Federal do ABC (UFABC), Centro de Ciências Naturais e Humanas (CCNH), Laboratório de Energia Alternativa e Nanomateriais (LEAN), CEP 09.210-170 Santo André-SP, Brazil. 2 International Research Center for Renewable Energy (IRCRE), State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, China. 3 Department of Applied Physics, CINVESTAV-IPN, Ant. Carr. a Progreso km 6, Mérida, Yucatán 97310, México.

Resume : Heterojunction configurations are particularly attractive for photoelectrochemical applications such as solar water splitting, based on the general idea that recombination can be partially prevented by increasing the charge separation efficiency; as a consequence, the current may increase and current onset may shift to more favorable potentials. The WO3/BiVO4 heterojunction system has previously been shown to generate a much larger photocurrent density than observed for the respective individual materials, by combining the better light harvesting ability of BiVO4 with the better electron conductivity of WO3, however, the exact nature of the charge carrier processes in the sandwich structure is still unclear. In this work, WO3/BiVO4 heterojunction thin films have been fabricated by spin coating in a variety of multilayer sandwich configurations, and the structure, morphology and photoelectrochemical properties have been characterized. Intensity-modulated photocurrent spectroscopy (IMPS) measurements illustrate that the balance between charge separation, surface recombination and hole transfer to the electrolyte can be optimized. The results are interpreted based on a simple model, and are compared to the results from electrochemical impedance spectroscopy (EIS). In addition, the individual materials are characterized in detail in order to explain the significant increase in efficiency for the heterojunction, and suggestions for further improvements are presented and discussed.

Authors : Lianzhou Wang
Affiliations : Nanomaterials Centre, School of Chemical Engineering and Australian Institute for Bioengineering and Nanotechnology, the University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia

Resume : Semiconducting materials hold the key for efficient photocatalytic and photoelectrochemical water splitting. In this talk, we will give a brief overview of our recent progresses in designing semiconductor metal oxides materials for photoelectrochemical energy conversion including photocatalytic solar fuel generation. In more details, we have been focusing the following a few aspects; 1) band-gap engineering of layered semiconductor compounds including layered titanate, tantalate and niobate-based metal oxide compounds for visible light phtocatalysis, and 2) facet-controlled TiO2, Fe2O3, WO3, BiVO4 as building blocks for new photoelectrode design,and 3) the combination of a high performance photoelectrode BiVO4 with perovskite solar cells can lead to unassisted solar driven water splitting process with unassisted solar-to-hydrogen conversion efficiency of >6.5%; The resultant material systems exhibited efficient visible light photocatalytic performance and improved power conversion efficiency in solar energy, which underpin important solar-energy conversion applications including solar fuel generation and simultaneous environmental application.

Authors : Victor S. Batista
Affiliations : Yale University, Department of Chemistry, New Haven, CT 06520-8107, U.S.A.

Resume : Proton coupled electron transfer (PCET) plays a fundamental role in the mechanism of water-splitting at the oxygen-evolving complex (OEC) of photosystem II (PSII). We address the underlying reaction mechanism by structural studies of catalytic intermediates. Many physical techniques have provided important insights into the OEC structure and function, including X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy as well as mass spectrometry (MS), electron paramagnetic resonance (EPR) spectroscopy, and Fourier transform infrared spectroscopy applied in conjunction with mutagenesis studies. However, experimental studies have yet to yield consensus as to the exact configuration of the catalytic metal cluster and its ligation scheme. Computational modeling studies, including density functional (DFT) theory combined with quantum mechanics/molecular mechanics (QM/MM) hybrid methods for explicitly including the influence of the surrounding protein, have proposed chemically satisfactory models of the fully ligated OEC within PSII that are maximally consistent with experimental results. The inorganic core of these models is similar to the crystallographic model upon which they were based, but comprises important modifications due to structural refinement, hydration, and proteinaceous ligation which improve agreement with a wide range of experimental data. The computational models are useful for rationalizing spectroscopic and crystallographic results and for building a complete structure-based mechanism of water-splitting assisted by PCET as described by the intermediate oxidation states of oxomanganese complexes. This talk summarizes recent advances on studies of the OEC of PSII and biomimetic oxomanganese complexes for artificial photosynthesis.


Symposium organizers
Flavio Leandro DE SOUZAUniversidade Federal do ABC

Avenida dos Estados, 5001, Santo Andre – SP, Brazil 09210-580

+5511 4996 8353
Lionel VAYSSIERESInternational Research Center for Renewable Energy-Xi’an Jiaotong University

School of Energy & Power Engineering; 28 Xianning West Rd; 710049 Xi’an, Shaanxi Province, China

+86 298 266 4665
Samuel S. MAOUniversity of California at Berkeley

Department of Mechanical Engineering; Etcheverry Hall, Hearst Ave, Berkeley, CA 94720, USA

+1 510 2258210
Sanjay MATHURDepartment of Chemistry, University of Köln

Institute of Inorganic and Materials Chemistry, Greinstraße 6, D-50939 Cologne, Germany

+49 221 470 4107/4657