Effective Improvement\nof Thermodynamics and Kinetics\nof BiVO<sub>4</sub> Photoanode via CuI for Photoelectrochemical Water\nOxidation

The preparation of durable and efficient photoanodes\nfor photoelectrochemical\nwater oxidation is of great importance in promoting the development\nof green hydrogen production and artificial photosynthesis. Here,\nn-type BiVO<sub>4</sub> was combined with p-type CuI to construct\na CuI/BiVO<sub>4</sub> (CIB-1) p–n heterojunction photoanode.\nThe composite photoanode effectively overcame the drawbacks of BiVO<sub>4</sub>, such as low separation and injection efficiency of photogenerated\nelectron–hole pairs. As a result, the CIB-1 had the highest\nphotocurrent density of 1.98 mA cm<sup>–2</sup>, which was\n2.5 times higher than pure BiVO<sub>4</sub> with 0.79 mA cm<sup>–2</sup> at 1.23 V (vs RHE) under AM 1.5G light irradiation. The CIB-1 had\na lower Tafel slope of 23.2 mV decade<sup>–1</sup> compared\nto 47.9 mV decade<sup>–1</sup> for BiVO<sub>4</sub>, so the\nwater oxidation kinetics was remarkably advanced over CuI/BiVO<sub>4</sub>. Based on DFT calculations, the OER overpotential of 0.480\nV for CuI/BiVO<sub>4</sub> was significantly lower than that of 1.546\nV for BiVO<sub>4</sub> due to the lower free energy from OH<sup>–</sup> to oxygen over CuI/BiVO<sub>4</sub> compared to BiVO<sub>4</sub>.