Revealing the Role of Defective Sulfur Sites in Constructing Interfacial Potential Barriers for Photocatalytic CO ₂ Reduction Coupled With Water Oxidation

ABSTRACT Defect engineering represents a powerful strategy for alleviating the global energy crisis and CO ₂ emissions, although the role of defective sites in CO ₂ reactions is still not fully elucidated. Herein, a sulfur‐vacancy‐engineered CdS/BCN heterojunction photocatalyst was successfully constructed via a solvothermal approach. The synergistic effects of sulfur‐vacancy engineering and potential barrier construction enable directional charge separation, prolonged carrier lifetime, and accelerated interfacial charge transfer, collectively overcoming the intrinsic limitations of photocatalysts, namely severe charge recombination and sluggish reaction kinetics. Notably, the sulfur vacancies in CdS _0.5 /BCN act as electron reservoirs, facilitating efficient CO ₂ reduction and H ₂ O dissociation, achieving a CO production rate of 58.79 µmol g ⁻¹ h ⁻¹ under light irradiation for 6 h. Mechanistic investigations reveal that the presence of vacancies promotes the CO ₂ activation and ^* COOH intermediate formation, thereby facilitating CO generation. Density functional theory calculations further demonstrate that sulfur vacancies in CdS effectively modulate the interfacial electronic structure, reduce the CO ₂ activation energy barrier, and optimize the reaction pathway toward CO generation. This work not only introduces an efficient photocatalyst for solar‐driven CO ₂ conversion but also provides fundamental insights into defect‐ induced charge transfer, presenting a promising strategy to overcome challenges in photocatalytic CO ₂ reduction systems.