Despite the criticality of photocarrier injection from semiconductor-based photocatalysts to cocatalysts in photocatalytic water splitting, carrier dynamics within cocatalysts remain poorly understood. To overcome the limitations of existing methods, which fail to separate semiconductor and cocatalyst signals, we used synchrotron-based time-resolved X-ray absorption fine structure spectroscopy to observe the injection of photoexcited holes from a semiconductor photocatalyst (TiO2) to a cocatalyst (IrOx) in real time. The oxidation of the Ir centers in IrOx supported on TiO2 or N,F-codoped TiO2 (TiO2:N,F) after excitation by ultraviolet light provided direct evidence for hole injection dynamics. The decay kinetics of the transferred holes in IrOx revealed that the hole lifetime in IrOx/TiO2:N,F was ∼16 times longer than that in IrOx/TiO2, which was directly correlated with the higher photocatalytic water oxidation activity of the latter system. Our findings highlight the importance of the interfacial energy landscape in the design of photocatalyst systems, as it critically influences carrier lifetime in cocatalysts and promotes efficient charge separation to enhance photocatalytic performance.
Kanazawa et al. (Wed,) studied this question.