Cu₂O as the hole extraction layer modified BiVO₄ photoanode to enhance charge separation and transfer

Photoinduced charge separation and transfer are the core factors affecting the photoelectrochemical performance of BiVO₄-based photoanodes. Herein, a hole extraction layer was inserted between a BiVO₄ photoanode and an oxygen evolution cocatalyst (OEC). The introduction of Cu₂O as a hole extraction layer between the OEC layer (FeOOH/NiOOH) and BiVO₄ optimized the migration paths and extended the lifetimes of the photogenerated holes, thus enhancing the photoelectrochemical performance of the photoelectrode. The charge separation efficiency of the optimized BiVO₄/Cu₂O/FeOOH/NiOOH photoanode was 92.0% significantly higher than the 70.6% efficiency for pure BiVO₄. As expected, this photoanode also displayed a high photocurrent density of 3.85 mA cm⁻² at 1.23 V_RHE (under AM 1.5G illumination), which was 2.77 times greater than that of pure BiVO₄. Our results indicate that electrodepositing a Cu₂O hole extraction layer is a simple and scalable method for increasing the photoelectrochemical activity of BiVO₄ photoanodes for solar water splitting.