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Artur Braun1 Rita Toth1 Mmantsae Diale2 Debajeet Bora1 Jianjun Wang1 Edwin Constable3 Michael Grätzel4 Yelin Hu1 4 Florent Boudoire1 3 Minkyu Son1 4

1, Empa-Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, , Switzerland
2, University of Pretoria, Pretoria, Gauteng, South Africa
3, University of Basel, Basel, , Switzerland
4, EPFL, Lausanne, , Switzerland

Iron oxide has a long electroanalytical history as photoanode in photoelectrochemical water splitting cells (PEC) for solar hydrogen production 1. It is considered an environmentally benign material. In the last decades, steady progress was made in the photocurrent enhancement of iron oxide based photoanodes2. We present a PEC reactor which is based on hematite as basic electrode material. With various doping, nanostructure and heterostructure approaches we can steadily improve the photocurrent and efficiency of the system and arrive at a photocurrent of 3.3 mA/cm2 3. The reactor is made from repeating units with 10cm x 10cm large panes 4 and needs no electrolyte membrane and is operated outside in field tests. We discuss its use in decentralized hydrogen supply systems5 and its potential use in bio-based PEC systems6.

1. K.L. Hardee and A.J. Bard: SEMICONDUCTOR ELECTRODES .5. APPLICATION OF CHEMICALLY VAPOR-DEPOSITED IRON-OXIDE FILMS TO PHOTOSENSITIZED ELECTROLYSIS. Journal of the Electrochemical Society 123, 1024 (1976).
2. A. Kay, I. Cesar and M. Gratzel: New benchmark for water photooxidation by nanostructured alpha-Fe2O3 films. J Am Chem Soc 128, 15714 (2006).
3. J.-J. Wang, Y. Hu, R. Toth, G. Fortunato and A. Braun: A facile nonpolar organic solution process of a nanostructured hematite photoanode with high efficiency and stability for water splitting. J. Mater. Chem. A 4, 2821 (2016).
4. Y. Hu, D.K. Bora, F. Boudoire, F. Häussler, M. Graetzel, E.C. Constable and A. Braun: A dip coating process for large area silicon-doped high performance hematite photoanodes. Journal of Renewable and Sustainable Energy 5, 043109 (2013).
5. A. Braun, M.M. Diale, K.D. Maabong and R. Toth: Safe And Decentralised Hydrogen Fuel Production And Storage For Residential Building And Mobility Applications, in 6th International Disaster and Risk Conference 2016 - "Integrative Risk Management - towards resilient cities", edited by M. Stal, D. Sigrist, S. Wahlen, J. Portmann, J. Glover, N. Bernabe, D. M. d. Vitry and W. J. Ammann (Global Risk Forum GRF Davos, Davos, Switzerland, Davos, Switzerland, 2016), pp. 102.
6. D.K. Bora, A. Braun and E.C. Constable: "In rust we trust". Hematite - the prospective inorganic backbone for artificial photosynthesis. Energy & Environmental Science 6, 407 (2013).

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