Solar Hydrogen Production by Photo-oxidation of Water from Doped Iron Oxide Photoanodes

Content Provider	Semantic Scholar
Author	Kleiman-Shwarscetin, Alan
Copyright Year	2010
Abstract	Iron Oxide Photoanodes Alan Kleiman-Shwarsctein, Yong-Sheng Hu, Arnold J. Forman, Galen D. Stucky and Eric W. McFarland Materials Department, University of California Santa Barbara, CA, 93106, USA. Dept. of Chemical Engineering University of California Santa Barbara, CA, 93106, USA. Dept. of Chemistry and Biochemistry, University of California Santa Barbara, CA, 93106, USA. *mcfar@engr.ucsb.edu (corresponding author) Introduction High efficiency photoelectrochemical material systems, for the production of hydrogen from water and sunlight, have been proposed and demonstrated; unfortunately, the costs of these systems far exceeds any commercially acceptable value for large volume, low value, fuel production. Unfortunately, the abundant and inexpensive metal oxides such as TiO2, ZnO, and WO3 have wide bandgaps and are therefore limited in overall terrestrial solar energy efficiency to less than ~4%. Metal oxides based on iron including, α-Fe2O3 (hematite), have several advantages for photoelectrocatalytic chemical conversions using sunlight compared to alternatives. Hematite is an n-type semiconductor with a bandgap of 22.2 eV which can capture approximately 40% of the energy in incident sunlight, it is stable in most electrolytes at pH > 3, and it is abundant, inexpensive, non-toxic and environmentally benign. However, as a Mott-insulator it has several inherent disadvantages which give rise to poor charge transfer and high recombination rates for the photogenerated electrons and holes which limit the efficiency of the pure-phase material. In addition, for water photoelectrolysis, the rate of the oxygen evolution reaction (OER) on hematite is relatively slow. Finally, the energy of the conduction band relative to the redox level of the H2/H is too low (~ 0.2 V vs. NHE) to efficiently drive the hydrogen evolution reaction. In order to use hematite as a photocatalyst in large scale solar applications, the factors that limit its performance must be overcome without adding significantly to the cost.
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