Enhanced solar water splitting of BiVO4 photoanodes by in situ surface band edge modulation

Abstract

Photoinduced charge separation and transfer has been recognized as one of the core factors affecting the photoelectrochemical (PEC) performance of BiVO₄ based photoanodes. To achieve a higher charge separation efficiency, modulating the surface band edge of BiVO₄-based photoanodes could be regarded as the best choice but still a challenge. Herein, first, it was confirmed by density functional theory (DFT) calculations that pristine BiVO₄ could form a type-II heterojunction with BiVO₄–V_Bi (replacing Bi sites with V in BiVO₄), which could be used to enhance carrier separation. Then we use a gas-phase cation exchange (CA) method to in situ modulate the surface band edge of the BiVO₄ photoanode by partially replacing Bi on the surface with V to form a V-rich surface. The charge separation efficiency of the optimized V-rich BiVO₄ (V/BVO) photoanode is significantly enhanced from 56.5% to 81.5% compared to pristine BiVO₄. As expected, it also displays a higher photocurrent density of 2.87 mA cm⁻² at 1.23 V vs. RHE (under AM 1.5G illumination), which is nearly 3.2 times higher compared with pristine BiVO₄. Upon further loading the FeOOH cocatalyst, the photocurrent of the V/BVO/FeOOH photoanode reached 4.26 mA cm⁻² due to the boosted surface water oxidation properties. This work sheds light on a simple strategy to regulate surface band edges for designing highly efficient photoanodes.