Enhanced photoelectrochemical water oxidation on bismuth vanadate by electrodeposition of amorphous titanium dioxide

n-BiVO₄ is a promising semiconductor material for photoelectrochemical water oxidation. Although most thin-film syntheses yield discontinuous BiVO₄ layers, back reduction of photo-oxidized products on the conductive substrate has never been considered as a possible energy loss mechanism in the material. We report that a 15 s electrodeposition of amorphous TiO₂ (a-TiO₂) on W:BiVO₄/F:SnO₂ blocks this undesired back reduction and dramatically improves the photoelectrochemical performance of the electrode. Water oxidation photocurrent increases by up to 5.5 times, and its onset potential shifts negatively by ∼500 mV. In addition to blocking solution-mediated recombination at the substrate, the a-TiO₂ film - which is found to lack any photocatalytic activity in itself - is hypothesized to react with surface defects and deactivate them toward surface recombination. The proposed treatment is simple and effective, and it may easily be extended to a wide variety of thin-film photoelectrodes.