Kinetic Difference in Water Photooxidation between TiO₂ and WO₃ Electrodes by Rate Law Analysis

The photocarrier interfacial kinetics is often considered to be a bottleneck for water photooxidation on semiconductors and has attracted extensive attention in recent years. Although tremendous efforts have been devoted into the kinetic study for a certain semiconductor, there are few works focused on the dynamic differences in water oxidation between various kinds of semiconductors. In this study, the kinetics of water oxidation on WO 3 and TiO 2 electrodes was investigated by a combination of photoelectrochemical techniques and then compared using the electrodes’ rate law. It was found that the water oxidation on WO 3 is faster than the that of TiO 2 electrodes under the same surface hole density and the basic origin for this kinetic difference is attributed to greater charger transfer rate constant ( k ct ). The greater k ct is due to the fact that the WO 3 electrodes have a smaller Helmholtz layer capacitance ( C H ), a larger space charge layer capacitance ( C SC ), and a greater charge transfer rate constant at flatband potential ( k ct 0 ). These finding provide a better understanding of the photocarrier transfer dynamics and may enlighten rational design on exploiting the metal oxide semiconductors to achieve a higher solar conversion efficiency.