Insight into the Kinetics of Water Photooxidation on CuWO ₄ Electrodes

Photooxidation of water on semiconductors is a promising approach for solar fuel production. Among the semiconductors, CuWO 4 has been identified as a candidate photoanode for water oxidation due to its ability to absorb visible light up to 550 nm and to be highly stable in neutral and slightly basic solutions. Although the water photooxidation on this material has been intensively studied, the pathway of photoexcited hole transfer to solutions and the rate law are not fully understood yet. Here, these issues were investigated by a combination of multiple (photo-)electrochemical techniques. We found that the kinetics of CuWO 4 water oxidation by photogenerated holes in potassium phosphate buffer at pH 7.0 solutions can be described by a model of surface state mediating charge transfer and recombination. The kinetic parameters under various applied potentials and light intensities were quantified, and the rate law, in terms of steady-state photocurrent, is the product of the surface hole density exponential dependent rate constant and the surface hole density for all the surface hole densities studied. In addition, the rate law was compared to those for other popular photoanodes and is discussed. This study may thus be beneficial for designing more efficient CuWO 4 photoanodes and for further understanding the reaction mechanism.