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Enhancement of Water Oxidation Kinetics at Semiconductor Photoanodes: Development of IrO2 Nanoparticle Catalysts P. Bomroongsakulsawat, S. Dennison, K. Hellgardt and G. Kelsall Department of Chemical Engineering Imperial College London, London SW7 2AZ UK [email protected] Solar photoelectrolysis is a potentially important approach to the generation of hydrogen from water in the development of systems for developing the hydrogen economy. A key component of a photoelectrolyser is the photoanode, which must both absorb solar energy efficiently (in the visible part of the solar spectrum) and be an efficient catalyst for the oxidation of water to oxidation. Poor O2 evolution kinetics is a drawback for a number of materials which have been identified as candidates for photoelectrodes, since this limits H2 evolution. Both Fe2O3 and WO3 (Eg ~ 2.2 and 2.6eV respectively) are materials with useful optical properties for the absorption of solar radiation, but which have slow oxidation evolution kinetics. Acceleration of O2 evolution has the potential to reduce the effect of other problems, such as recombination losses. We have selected IrO2 as an oxygen evolution catalyst for semiconductor photoanodes. It is known to be an effective catalyst for O2 evolution (exchange current density = 4 x 10-9 Am-2); it is stable in acid and alkali, so will operate over the whole pH range likely to be encountered in water photoelectrolysis. Routes for the decoration of thin-film semiconductors (WO3 and Fe2O3) with nanoparticulate IrO2 have been developed. The (photo)electrochemical properties of the resulting composite films have been determined. These data are correlated with further physical characterisation of the films (SEM, XRD).