Boosting Oxygen Evolution Reaction Performance on BiVO4 Photoanode via Gradient Oxygen Vacancies

BiVO4 is extensively studied in photoelectrochemical water splitting systems. Its relatively large bandgap and low charge carrier mobility severely limit the solar-driven oxygen evolution reaction on BiVO4. A gradient distribution of oxygen vacancies can modulate the structural and electrical properties of BiVO4. However, the formation of oxygen vacancies remains a daunting challenge. Here, we propose a simple hydrothermal post-treatment method to deposit a thin amorphous BiOx layer (∼8 nm) with gradient oxygen vacancies on the surface of BiVO4 and enable directional hole migration. The resultant BiVO4/BiOx/NiFeOx photoanode achieves a high photocurrent density of 6.34 mA cm–2 at 1.23 V (vs RHE) in 1.0 M potassium borate solution. A solar-to-hydrogen conversion efficiency of 0.89% is obtained in a device using a BiVO4/BiOx/NiFeOx photoanode and a CuBi2O4 photocathode at zero bias. This work highlights a novel strategy for modulating the oxygen vacancy gradient and provides insights into the design of unbiased solar water splitting systems.