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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).