Unveiling the role of doping and intrinsic vacancies in BiVO4 for enhanced photoelectrochemical water splitting: a first-principles study

Monoclinic n-type bismuth vanadate (BiVO₄) is a leading photoanode material for photoelectrochemical water splitting, owing to its favorable band alignment with water redox potentials, high charge extraction efficiency, and ease of synthesis. However, its photoelectrochemical performance is hindered by a relatively wide band gap, low electronic conductivity, high recombination rates, and sluggish water oxidation kinetics. In this study, we use density functional theory to investigate the impact of non-metal doping, using nitrogen as a model, and intrinsic vacancies (Bi, V, O) on the photocatalytic properties of BiVO₄. Nitrogen doping reduces the band gap by ∼0.3 eV, increases charge carrier concentration, and improves mobility, leading to enhanced electron-hole separation. Among intrinsic defects, oxygen vacancies have the most significant effect on charge transport, while bismuth vacancies strongly influence light absorption. A charge-balanced N-doped BiVO₄ structure effectively combines reduced recombination with improved light harvesting. Our results highlight that the main contributions of doping and vacancies lie in enhancing light absorption and charge separation, rather than injection efficiency. These findings provide valuable guidance for the rational design of advanced BiVO₄-based photoanodes for efficient photoelectrochemical water splitting.