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Defects in the bulk and on surfaces and interfaces of metal oxides with photoelectrochemical properties: In-situ photoelectrochemical and resonant x-ray and electron spectroscopy studies

English title Defects in the bulk and on surfaces and interfaces of metal oxides with photoelectrochemical properties: In-situ photoelectrochemical and resonant x-ray and electron spectroscopy studies
Applicant Braun Artur
Number 132126
Funding scheme Project funding (Div. I-III)
Research institution Labor für Hochleistungskeramik EMPA
Institution of higher education Swiss Federal Laboratories for Materials Science and Technology - EMPA
Main discipline Condensed Matter Physics
Start/End 01.06.2011 - 31.05.2015
Approved amount 218'761.00
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All Disciplines (5)

Discipline
Condensed Matter Physics
Physical Chemistry
Material Sciences
Microelectronics. Optoelectronics
Inorganic Chemistry

Keywords (13)

parallel; solar energy; photoelectrochemistry; solar hydrogen; PEC; hematite; electron hole pair; defects; Gerischer; Butler; Gärtner; Schottky; flat band potential

Lay Summary (English)

Lead
Lay summary

Photoelectrochemical cells (PEC) can convert solar energy into clean hydrogen fuel by solar water Splitting. In this SNF project we investigate how metal oxides interact with the electrolyte in PEC cells at the molecular level by using advanced synchrotron x-ray and photoelectron spectroscopy methods.

In PEC anode materials, solar energy creates electron-hole pairs which separate under an external field; the holes diffuse to the anode-electrolyte interface into the electrolyte where they can oxidize water and generate oxygen gas; in return, an electron from the electrolyte enters the anode material, and at the cathode hydrogen is evolved which can be used as fuel.

Defects in the bulk of the electrode materials can cause premature recombination of the electron hole pairs and thus work against the efficiency of PEC electrodes. Hematite, an otherwise quite suitable PEC anode materials, has a very short hole diffusion length with a limited efficiency of the system.

Defects at the electrode surface can be beneficial, however. Our recent operando study of a PEC system under light and bias showed the existence of 2 different types of electron holes during PEC operation.

 

[1] A. Braun, S. Erat, X. Zhang, Q. Chen, F. Aksoy, R. Löhnert, Z. Liu, S.S. Mao, T. Graule, Surface and bulk oxygen vacancy defect states near the Fermi level in 100 nm WO3-δ/TiO2 (110) films: A resonant valence band photoemission spectroscopy study, J. Phys. Chem. C.

http://pubs.acs.org/doi/abs/10.1021/jp202375h

[2] D.K. Bora, A. Braun, S. Erat, R. Löhnert, A.K. Ariffin, R. Manzke, K. Sivula, T. Graule, M. Grätzel, E. Constable, Evolution of an oxygen NEXAFS transition in the upper Hubbard band in α-Fe2O3 upon electrochemical oxidation, J. Phys. Chem. C, 2011, 115 (13), 5619–5625.

http://pubs.acs.org/doi/abs/10.1021/jp108230r   http://arxiv.org/abs/1106.1089

[3] D. Bora, A. Braun, R. Erni, G. Fortunato, T. Graule, E. Constable, Hydrothermal treatment of a hematite film leads to highly oriented faceted nanostructures with enhanced photocurrents, Chem. Mater. 2011, 23, 2051–2061

http://pubs.acs.org/doi/abs/10.1021/cm102826n

[4] R. Solarska, A. Heel, J. Ropka, A. Braun, L. Holzer, J. Ye, T. Graule. Enhancement of Photocatalytic Performance of Calcium Bismuth Mixed Oxide by One-Step Flame Spray Synthesis. Applied Catalysis A 2010, 382(2) 190-196.

http://dx.doi.org/10.1016/j.apcata.2010.04.043

[5] A. Braun, K.K. Akurati, G. Fortunato, F.A. Reifler, A. Ritter, A.S. Harvey, A. Vital, T. Graule, Nitrogen doping of TiO2 photocatalyst forms a second eg state in the Oxygen (1s) NEXAFS pre-edge, J. Phys. Chem. C, 2010, 114 (1), 516–519

http://pubs.acs.org/doi/pdf/10.1021/jp908875t  http://arxiv.org/abs/1106.1026  

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
A nanocomposite photoelectrode made of 2.2 eV band gap copper tungstate (CuWO4 and multi-wall carbon nanotubes for solar-assisted water splitting
Gaillard Nicolas, Chang Yuancheng, DeAngelis Alexander, Higgins Scott, Braun Artur (2013), A nanocomposite photoelectrode made of 2.2 eV band gap copper tungstate (CuWO4 and multi-wall carbon nanotubes for solar-assisted water splitting, in INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 38(8), 3166-3176.
Artificial Photosynthesis for Solar Fuels – an Evolving Research Field within AMPEA, a Joint Programme of the European Energy Research Alliance
A. Thapper S. Styring G. Saracco A. W. Rutherford B. Robert A. Magnuson W. Lubitz et al. (2013), Artificial Photosynthesis for Solar Fuels – an Evolving Research Field within AMPEA, a Joint Programme of the European Energy Research Alliance, in GREEN, 3(1), 43-57.
Formation of an electron hole doped film in the alpha-Fe2O3 photoanode upon electrochemical oxidation
Gajda-Schrantz Krisztina, Tymen Simon, Boudoire Florent, Toth Rita, Bora Debajeet K., Calvet Wolfram, Graetzel Michael, Constable Edwin C., Braun Artur (2013), Formation of an electron hole doped film in the alpha-Fe2O3 photoanode upon electrochemical oxidation, in PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 15(5), 1443-1451.
Spectroscopic assessment of the role of hydrogen in surface defects, in the electronic structure and transport properties of TiO2, ZnO and SnO2 nanoparticles
Flak Dorota, Braun Artur, Mun Bongjin Simon, Park Jong Bae, Parlinska-Wojtan Magdalena, Graule Thomas, Rekas Mieczyslaw (2013), Spectroscopic assessment of the role of hydrogen in surface defects, in the electronic structure and transport properties of TiO2, ZnO and SnO2 nanoparticles, in PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 15(5), 1417-1430.
Iron Resonant Photoemission Spectroscopy on Anodized Hematite Points to Electron Hole Doping during Anodization
Braun Artur, Chen Qianli, Flak Dorota, Fortunato Giuseppino, Gajda-Schrantz Krisztina, Graetzel Michael, Graule Thomas, Guo Jinghua, Huang Tzu-Wen, Liu Zhi, Popelo Anastasiya V., Sivula Kevin, Wadati Hiroki, Wyss Pradeep P., Zhang Liang, Zhu Junfa (2012), Iron Resonant Photoemission Spectroscopy on Anodized Hematite Points to Electron Hole Doping during Anodization, in CHEMPHYSCHEM, 13(12), 2937-2944.
Observation of Substrate Orientation-Dependent Oxygen Defect Filling in Thin WO3-delta/TiO2 Pulsed Laser-Deposited Films with in Situ XPS at High Oxygen Pressure and Temperature
Braun Artur, Akgul Funda Aksoy, Chen Qianli, Erat Selma, Huang Tzu-Wen, Jabeen Naila, Liu Zhi, Mun Bongjin S., Mao Samuel S., Zhang Xiaojun (2012), Observation of Substrate Orientation-Dependent Oxygen Defect Filling in Thin WO3-delta/TiO2 Pulsed Laser-Deposited Films with in Situ XPS at High Oxygen Pressure and Temperature, in CHEMISTRY OF MATERIALS, 24(17), 3473-3480.
Effect of Thermal Treatment on the Crystallographic, Surface Energetics, and Photoelectrochemical Properties of Reactively Cosputtered Copper Tungstate for Water Splitting
Chang YC, Braun A, Deangelis A, Kaneshiro J, Gaillard N (2011), Effect of Thermal Treatment on the Crystallographic, Surface Energetics, and Photoelectrochemical Properties of Reactively Cosputtered Copper Tungstate for Water Splitting, in JOURNAL OF PHYSICAL CHEMISTRY C, 115(51), 25490-25495.
Surface and Bulk Oxygen Vacancy Defect States near the Fermi Level in 125 nm WO3-delta/TiO2 (110) Films: A Resonant Valence Band Photoemission Spectroscopy Study
Braun A, Erat S, Zhang XJ, Chen QL, Huang TW, Aksoy F, Lohnert R, Liu Z, Mao SS, Graule T (2011), Surface and Bulk Oxygen Vacancy Defect States near the Fermi Level in 125 nm WO3-delta/TiO2 (110) Films: A Resonant Valence Band Photoemission Spectroscopy Study, in JOURNAL OF PHYSICAL CHEMISTRY C, 115(33), 16411-16417.
A dip coating process for large area silicon-doped high performance hematite photoanodes
Y. Hu D.K. Bora F. Boudoire F. Haussler M. Graetzel E.C. Constable. A. Braun, A dip coating process for large area silicon-doped high performance hematite photoanodes, in JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY.
Between photocatalysis and photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation
Bora DK, Hu Y, Thiess S, Erat S, Feng X, Mukherjee S, Fortunato G, Gaillard N, Toth R, Gajda-Schrantz K, Drube W, Grätzel M, Guo J, Zhu J, Constable EC, Sarma DD, Wang H, Braun A, Between photocatalysis and photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation, in Journal of Electron Spectroscopy and Related Phenomena.
Direct Observation of Two Electron Holes in a Hematite Photo-Anode During Photo-Electrochemical Water Splitting
Artur Braun Kevin Sivula Debajeet K Bora Junfa Zhu Liang Zhang Michael Grätzel Jinghua Guo an, Direct Observation of Two Electron Holes in a Hematite Photo-Anode During Photo-Electrochemical Water Splitting, in Journal of Physical Chemistry C.
High Surface Area Porous Platinum Electrodes for Enhanced Charge Transfer
Yelin Hu Aswani Yella Stefan Guldin Francesco Stellacci Michael Grätzel Morgan Stefik, High Surface Area Porous Platinum Electrodes for Enhanced Charge Transfer, in Advanced Energy Materials.
The electronic, chemical and electrocatalytic processes and intermediates on iron oxide surfaces during photoelectrochemical water splitting
A.Braun Y.Hu F.Boudoire D.K. Bora D.D. Sarma M. Graetzel C.M. Eggleston, The electronic, chemical and electrocatalytic processes and intermediates on iron oxide surfaces during photoelectrochemical water splitting, in Catalysis Today.

Collaboration

Group / person Country
Types of collaboration
Helmholtz Zentrum Berlin BESSY-II Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Universität Basel Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
EPFL Lausanne Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Lawrence Berkeley National Laboratory United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
University of Hawaii at Manoa United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Univ. of Pretoria, Phys. & Chem. Dept. South Africa (Africa)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Prof. Bongjin S. Mun, GIST Korean Republic (South Korea) (Asia)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Swiss-South Africa Nanotechnology Workshop at iTHEMBA LABS Talk given at a conference Swiss-South Africa Nanotechnology Workshop at iTHEMBA LABS 15.04.2014 Stellenbosch iThemba Labs Somerset, South Africa Braun Artur;
invited talk at Univ. of Pretoria Individual talk Iron oxide: towards a low‐cost and functional photo‐electrode for solar water splitting 14.03.2014 Pretoria, South Africa Braun Artur;
invited talk to iThemba Labs Individual talk Iron oxide: towards a low‐cost and functional photo‐electrode for solar water splitting 10.03.2014 Somerset, South Africa Braun Artur;
GSFMT Summer School 2013, Pühajärve Talk given at a conference Iron oxide: towards a low‐cost and functional photo‐electrode for solar water splitting 25.06.2013 Pühajärve, Estland, Estonia Braun Artur;
PEC DoE working Group Meeting Talk given at a conference Iron oxide: towards a low‐cost and functional photo‐electrode for solar water splitting 01.04.2013 Stanford University, United States of America Braun Artur;
Seminar gemeinsam mit dem Anorganisch‐chemischen Institut Individual talk Iron oxide: towards a low‐cost and functional photo‐electrode for solar water splitting 28.02.2013 Zürich, Switzerland Braun Artur;
Physikalisches Kolloquium Universität Konstanz Individual talk Solar hydrogen generation by water splitting in photoelectrochemical cells 29.01.2013 Konstanz, Deutschland, Germany Braun Artur;
SAOG 2013 Talk given at a conference Solar hydrogen generation by water splitting in photoelectrochemical cells 25.01.2013 Fribourg, Switzerland Braun Artur;
Recent Advances in Electrochemical Energy Materials and Devices Talk given at a conference Application of x-ray and electron spectroscopy to energy materials 24.07.2012 Indian Institute of Science Bangalore, India, India Braun Artur;
2nd Ertl Symposium on Surface and Interface Chemistry Talk given at a conference The role of defects in hematite in solar water splitting, and its experimental assessment with x-ray and photoelectron spectroscopy 24.06.2012 Stuttgart, Germany Braun Artur;
European X-ray Spectrometry Conference (EXRS 2012) Talk given at a conference Application of x-ray and electron spectroscopy to energy materials 19.06.2012 Vienna, Austria Braun Artur;
Fachtagung Prozessnahe Röntgenanalytik Talk given at a conference Application of x-ray and neutron methods for analysis of energy materials 25.11.2011 Berlin, Germany Braun Artur;
CECAM Workshop on X-ray Spectroscopy : Recent Advances in Modeling and New Challenges Talk given at a conference Application of x-ray and electron spectroscopy to energy materials 14.07.2011 Zürich, Switzerland Braun Artur;


Self-organised

Title Date Place
MRS Spring 2013 Symposium D: From Molecules to Materials—Pathways to Artificial Photosynthesis 01.04.2013 San Francisco, California, United States of America

Communication with the public

Communication Title Media Place Year
Media relations: print media, online media Farbstoffsolarzellen. From DIY to Solar Chic - Die künstliche Fotosynthese "form" Ausgabe N° 254 (Verlag form GmbH & Co. KG) International 2014

Associated projects

Number Title Start Funding scheme
137868 Reaction-diffusion processes for the growth of patterned structures and architectures: A bottom-up approach for photoelectrochemical electrodes 01.03.2012 Project funding (Div. I-III)
147413 International Exploratory Workshop on Soft X-rays, Electrochemistry, and Energy Materials 01.05.2013 International Exploratory Workshops
121306 Fundamental Aspects of Photocatalysis and Photoelectrochemistry / Basic Research Instrumentation for Functional Characterization 01.07.2008 R'EQUIP
133944 Oxide heterointerfaces in assemblies for photoelectrochemical applications 01.11.2010 International short research visits
149031 Production of Liquid Solar Fuels from CO2 and Water: Using Renewable Energy Resources 01.03.2014 Bilateral programmes
161673 International Exploratory Workshop on Photoelectrochemistry, Catalysis and X-ray spectroscopy 01.07.2015 International Exploratory Workshops

Abstract

This experimental research project aims at elucidating the role of structural electronic defects in hematite a-Fe2O3 and heterostructures thereof with related metal oxides (WO3, TiO2, NiO) in intimate contact with each other and with electrolytes on their photoelectrochemical water splitting properties. The main body of the work will be carried out at Empa Dübendorf, Laboratory for High Performance Ceramics, and EPFL Lausanne, Laboratory for Photonics & Interfaces. The PhD student will be hosted for 12 months at a synchrotron radiation center, where s/he will do x-ray and electron spectroscopy experiments and also make pulsed laser deposited films and superlattices.Structure and transport properties of the aforementioned heterostructures (Fe2O3/WO3; Fe2O3/NiO, Fe2O3/TiO2) will be studied with respect to their defect density gradient and their photocurrent and optical incident photon to current conversion characteristic.The materials will be synthesized at Empa, in collaboration with partners at EPFL and USA, and will include single crystal model systems and porous photo-electrodes of nominally similar stoichiometry, employing pulsed laser and atomic layer deposition, and sol gel techniques.Selected samples will be subject to extensive element specific electron and x-ray spectroscopy methods with gradual surface and bulk probing depth sensitivity, including resonant photoemission spectroscopy and near-edge x-ray absorption fine structure spectroscopy, which are proven methods for the detection of defect states, such as arising from oxygen vacancies or substitution elements and interstitials. This will basically allow assigning particular defect states a specific depth in the probed sample, and also potentially assign them to particular elements, such as arising from Fe, Ti, Ni, or W.The availability of a novel ambient pressure XPS chamber will allow to perform the spectroscopy experiments under high (several hundreds mTorr) partial pressures of water, oxygen or hydrogen, and thus monitor the evolution of surface defects when the surface becomes wet/dry, and oxidized/reduced at temperatures from 300 k to 1200 K.The ultimate goal is to uncover the mechanism of the water molecule splitting process on a metal oxide semiconductor heterostructure or superlattice surface when struck by visible light, and the role of defects at the surface and in the bulk on the transport and electrochemical properties. A significant challenge as well as novelty in our approach is the combination of photoelectrochemical and ambient pressure XPS methods.
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