Effective Improvement of Thermodynamics and Kinetics of BiVO₄ Photoanode via CuI for Photoelectrochemical Water Oxidation

The preparation of durable and efficient photoanodes for photoelectrochemical water oxidation is of great importance in promoting the development of green hydrogen production and artificial photosynthesis. Here, n-type BiVO₄ was combined with p-type CuI to construct a CuI/BiVO₄ (CIB-1) p-n heterojunction photoanode. The composite photoanode effectively overcame the drawbacks of BiVO₄, such as low separation and injection efficiency of photogenerated electron-hole pairs. As a result, the CIB-1 had the highest photocurrent density of 1.98 mA cm^-2, which was 2.5 times higher than pure BiVO₄ with 0.79 mA cm^-2 at 1.23 V (vs RHE) under AM 1.5G light irradiation. The CIB-1 had a lower Tafel slope of 23.2 mV decade^-1 compared to 47.9 mV decade^-1 for BiVO₄, so the water oxidation kinetics was remarkably advanced over CuI/BiVO₄. Based on DFT calculations, the OER overpotential of 0.480 V for CuI/BiVO₄ was significantly lower than that of 1.546 V for BiVO₄ due to the lower free energy from OH^- to oxygen over CuI/BiVO₄ compared to BiVO₄.