Improved stability of polycrystalline bismuth vanadate photoanodes by use of dual-layer thin TiO₂/Ni coatings

Ultrathin dual layers of TiO₂ and Ni have been used to stabilize polycrystalline BiVO₄ photoanodes against photocorrosion in an aqueous alkaline (pH = 13) electrolyte. Conformal, amorphous TiO₂ layers were deposited on BiVO₄ thin films by atomic-layer deposition, with Ni deposited onto the TiO₂ by sputtering. Under simulated air mass 1.5 illumination, the dual-layer coating extended the lifetime of the BiVO₄ photoanodes during photoelectrochemical water oxidation from minutes, for bare BiVO₄, to hours, for the modified electrodes. X-ray photoelectron spectroscopy showed that these layers imparted chemical stability to the semiconductor/electrolyte interface. Transmission electron microscopy revealed the structure and morphology of the polycrystalline BiVO₄ film as well as of the thin coating layers. This work demonstrates that protection schemes based on ultrathin corrosion-resistant overlayers can be applied beneficially to polycrystalline photoanode materials under conditions relevant to efficient solar-driven water-splitting systems.