Unraveling the Kinetics of Photocatalytic Water Oxidation on WO3

Understanding the reaction kinetics of photocatalytic water splitting is important for the solar energy conversion field. Particularly, identifying the main obstacle in solar water oxidation is intriguing for efforts to promote the energy conversion efficiency. Herein, we take WO3 and cesium treated WO3 as prototypical models to disclose the reaction kinetics of photocatalytic water oxidation and found that the lack of long-lived surface holes is the bottleneck in the photocatalytic process. Analysis of the kinetic barriers of the surface catalytic reactions indicates that the water oxidation on WO3 is kinetically fast, whereas surface treatment of WO3 with cesium carbonate would enlarge the reaction energy barrier but unexpectedly increase the photocatalytic water oxidation rate. A further comparison of the charge dynamics by surface photovoltage and intensity modulated photocurrent spectroscopy reveals that the increased surface hole density due to the suppression of charge recombination accounts for the improvement in the photocatalytic activity.