Band Structure Engineering of BiVO ₄ by Copper and Sulfur Codoping for Efficient Photoelectrochemical Water Oxidation

Bismuth vanadate (BiVO4) is a promising photoanode for photoelectrochemical (PEC) water splitting, but its performance is still limited by insufficient light absorption and charge separation. Here, we report that codoping BiVO4 with metallic copper (Cu) and nonmetallic sulfur (S) enables significant modulation on the electronic band structure. Spectroscopic and electrochemical analyses reveal a notable upward shift of the valence band (VB) upon incorporating Cu and S, which narrows the band gap and strengthens visible-light absorption. Theoretical calculations attribute this band structure modulation to the formation of the O–Cu–S species with strong orbital hybridization among the O 2p, Cu 3d, and S 2p states. Besides, Mott–Schottky measurements show that the codoping results in an increasing charge carrier density and decreasing space charge layer width, which is beneficial to charge separation. This codoping strategy is effective for BiVO4 photoanodes synthesized by both hydrothermal and electrochemical methods. Particularly, in the presence of NiFe layered double hydroxide (LDH) cocatalyst, electrochemically synthesized Cu,S@BiVO4 exhibits a photocurrent density of 3.01 mA·cm–2 at 1.23 V vs RHE, 2.2 times greater than pristine BiVO4 (1.38 mA·cm–2) and surpassing most reported BiVO4-based photoanodes. This work offers mechanistic insights into metal/nonmetal codoping and presents a viable pathway for designing efficient, low-cost, and stable PEC electrodes with desirable band structures.