Non‐Precious Metals Enhance Hydrogen Evolution in COF/Cd _0.9 Cu _0.1 S S‐Scheme Heterojunctions: KPFM Reveals Charge Transfer Pathways

ABSTRACT Photocatalytic hydrogen production from water splitting is a promising strategy for sustainable and clean energy generation. However, the design of low‐cost, highly active photocatalysts remains a critical challenge. In this study, covalent organic frameworks (COFs) were loaded onto the surface of Cd 0.9 Cu 0.1 S to fabricate COF/Cd 0.9 Cu 0.1 S heterojunction. As a photocatalyst for hydrogen evolution, the optimized 10COF/Cd 0.9 Cu 0.1 S sample achieved a hydrogen evolution rate of 3398.3 μmol h −1 g −1 , representing 2.3‐fold and 3398.3‐fold enhancements compared with pristine Cd 0.9 Cu 0.1 S (1523.3 μmol h −1 g −1 ) and COF (almost nothing), respectively. The addition of Co 2+ as a co‐catalyst is a key factor in enhancing performance. Comprehensive photocatalytic tests, in situ X‐ray photoelectron spectroscopy, and transient absorption spectroscopy revealed that the charge–transfer process follows an S‐scheme mechanism. The covalent interaction between COF and Cd 0.9 Cu 0.1 S, coupled with favorable band alignment, induces a built‐in electric field at the heterojunction interface, thereby accelerating charge separation and suppressing recombination. This work provides an effective strategy for constructing efficient organic–inorganic heterojunctions, offering new insights into photocatalytic water splitting.