Nanostructured BiVO₄ Photoanodes Fabricated by Vanadium-Infused Interaction for Efficient Solar Water Splitting

Bismuth vanadate (BiVO₄) has emerged as a highly prospective material for photoanodes in photoelectrochemical (PEC) water oxidation. However, current limitations with this material lie in the difficulties in producing stable and continuous BiVO₄ layers with efficient carrier transfer kinetics, thereby impeding its widespread application in water splitting processes. This study introduces an accessible fabrication approach that yields continuous, monoclinic nanostructured BiVO₄ films, paving the way for their use as photoanodes in efficient PEC water oxidation for hydrogen production under solar light conditions. The fabrication involves the intercalation of vanadium (V) ions into Bi₂O₃ films at 450 °C. Upon interaction with V ions, the film undergoes a transformation from tetragonal Bi₂O₃ to monoclinic scheelite BiVO₄. This synthesis method enables the fabrication of single monoclinic phase BiVO₄ films with thicknesses up to 270 nm. The engineered monoclinic BiVO₄ film, devoid of any pinholes that could cause carrier loss, exhibits a robust photocurrent of 1.0 mA/cm² at 1.23 V_RHE in a neutral electrolyte, without requiring additional modifications or doping. Moreover, we demonstrate that the incorporation of a cobalt phosphate (Co-Pi) cocatalyst into the BiVO₄ photoanode significantly enhances the lifetime of photogenerated holes by a factor of 9, resulting in a further elevation of the photocurrent to 2.9 mA/cm². This remarkable PEC enhancement can be attributed to the surface state passivation by the Co-Pi cocatalyst. Our fabrication approach opens up a facile route for producing large-scale, highly efficient BiVO₄ photoanodes for PEC water splitting technology.