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

Abstract

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 a new 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 450oC. 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 VRHE in a neutral electrolyte, without requiring additional modifications or doping. Moreover, we demonstrate that the incorporation of a cobalt phosphate (Co-Pi) co-catalyst into the BiVO4 photoanode significantly enhances the lifetime of photogenerated holes by a factor of nine, 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 co-catalyst. Our fabrication approach opens up a new facile route for producing large-scale, highly efficient BiVO4 photoanodes for PEC water splitting technology.