Abstract: Heteroatom doping-induced breaking of the intrinsic electronic symmetry in metal sulfides is an attractive strategy for promoting charge separation. In this work, Co-doped CdS (CoCdS) nanoparticles were synthesized via a hydrothermal method and coupled with 2D graphdiyne (GDY) to construct GDY/CoCdS S-scheme heterojunctions for efficient broad-spectrum photocatalytic hydrogen evolution. Co doping induces local asymmetric charge redistribution in CdS, weakens S-H interaction, and lowers the hydrogen desorption energy barrier, thereby accelerating the surface hydrogen evolution reaction. Meanwhile, Co doping also creates a local built-in electric field that significantly enhances the intrinsic charge separation within CdS and synergistically facilitates interfacial charge transfer in the S-scheme heterojunction. In situ X-ray Photoelectron Spectroscopy (XPS) analysis and differential charge density calculations confirm the S-scheme charge transfer mechanism at the GDY/CoCdS heterointerface, which greatly accelerates the separation and migration of photogenerated carriers. Moreover, GDY endows the composite with extended light response and enhanced reaction kinetics owing to its broad-spectrum light harvesting and photothermal effect. As a result, the 15%GDY/CoCdS exhibits a prominent hydrogen evolution amount of 4.8 mmol g^-1 within 4 h under visible light irradiation, which is approximately 9.6 and 48 times higher than that of pure CoCdS and GDY. This work offers a reliable strategy of Co-doping induced asymmetric charge modulation in S-scheme heterojunction toward highly efficient broad-spectrum photocatalytic hydrogen evolution.

Key words: S-scheme heterojunction, Photocatalytic hydrogen evolution, Graphdiyne, Photothermal effect, Asymmetric charge redistribution