Monitoring Electron Transfer Dynamics in WO 3 /CdS S‐Scheme Heterojunction by Near‐Infrared Femtosecond Transient Absorption Spectroscopy

Abstract To solve the problem of severe charge recombination in pure WO 3 , the construction of S‐scheme heterojunction is an effective approach. This work has successfully prepared WO 3 /CdS S‐scheme photocatalysts by electrostatic self‐assembly. In situ irradiated X‐ray photoelectron spectroscopy and in situ irradiated Kelvin probe force microscopy have provided evidence of steady‐state spectra of WO 3 /CdS S‐scheme heterojunction. To monitor the ultrafast S‐scheme interfacial electron transfer process, systematic femtosecond transient absorption spectroscopy (fs‐TAS) measurements are performed on pure WO 3 , CdS and WO 3 /CdS. Since pure WO 3 and CdS have similar negative fs‐TAS signals in the UV–vis wavelength range, it is difficult to resolve the electron dynamics of these two components in the WO 3 /CdS composite. To address this issue, this study effectively distinguishes the fs‐TAS signals of WO 3 and CdS by near‐infrared fs‐TAS for the first time. S‐scheme interfacial electron transfer mechanism is confirmed by resolving the quenching dynamics of trap state electrons in the WO 3 and CdS components of WO 3 /CdS composite. This work provides new ideas and references for systematic characterization of S‐scheme heterojunction photocatalysts.