Efficient BiVO₄ Thin Film Photoanodes Modified with Cobalt Phosphate Catalyst and W-doping

Bismuth vanadate (BiVO₄) thin film photoanodes for light-induced water oxidation are deposited by a low-cost and scalable spray pyrolysis method. The resulting films are of high quality, as indicated by an internal quantum efficiency close to 100% between 360 and 450nm. However, its performance under AM1.5 illumination is limited by slow water oxidation kinetics. This can be addressed by using cobalt phosphate (Co-Pi) as a water oxidation co-catalyst. Electrodeposition of 30nm Co-Pi catalyst on the surface of BiVO₄ increases the water oxidation efficiency from ≈30% to more than 90% at potentials higher than 1.2V vs. a reversible hydrogen electrode (RHE). Once the surface catalysis limitation is removed, the performance of the photoanode is limited by low charge separation efficiency; more than 60% of the electron-hole pairs recombine before reaching the respective interfaces. Slow electron transport is shown to be the main cause of this low efficiency. We show that this can be remedied by introducing W as a donor type dopant in BiVO₄, resulting in an AM1.5 photocurrent of ≈2.3mAcm^-2 at 1.23V vs. RHE for 1% W-doped Co-Pi-catalyzed BiVO₄. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.