In Situ Soft X‐Ray Absorption Spectroscopy Investigation on Charge Transfer Mechanism in COF/CdS S‐Scheme Photocatalyst

Abstract Photocatalysis enabled by step‐scheme (S‐scheme) heterojunction has emerged as a promising strategy for addressing the global energy crisis and achieving carbon neutrality. However, mechanisms regulating the interfacial charge transfer dynamics of S‐scheme heterojunctions remain elusive. Herein, the electron transfer mechanisms are elucidated for a model S‐scheme heterojunction composed of cadmium sulfide and a covalent organic framework material using synchrotron‐based in situ soft X‐ray absorption spectroscopy, substantiating the well‐established in situ irradiated X‐ray photoelectron spectroscopy. The results, combined with theoretical calculations, reveal that interfacial Cd─N and Cd─S bonds act as the charge transfer channels within the heterojunction. The S‐scheme heterojunction exhibits high charge separation efficiency, as demonstrated by femtosecond transient absorption spectroscopy, which contributed to enhanced photocatalytic performance in coupled H ₂ O ₂ generation and organic transformation reactions. This study validates a new approach to characterizing S‐scheme heterojunctions and can guide the design of inorganic‐organic S‐scheme heterojunctions for practical photocatalytic applications.