Designing Surface-Defect Engineering to Enhance the Solar-Driven Conversion of CO₂ to C₂ Products over Zn₃In₂S₆/ZnS

The manipulation of electronic structure and prevention of photogenerated carriers from being quenched in bulk defects during the photocatalytic CO₂ reduction reaction (CRR) have been effectively demonstrated through surface vacancy and defect engineering. In this work, the electronic structure on the surface of Zn₃In₂S₆/ZnS (ZIS/ZnS) is significantly modified by the introduction and control of the surface S vacancies (S_V) through Ar-plasma treatment. EPR and XPS analyses confirmed that S_V was exclusively present on the ZIS/ZnS surface. The resulting ZIS/ZnS heterojunction photocatalysts demonstrate an impressive 46.6% selectivity toward C₂ products even in the absence of cocatalysts. The mechanism of photocatalytic CRR is further elucidated through in situ analysis. Theoretical calculations demonstrate that the presence of In and Zn atoms adjacent to S_V significantly enhances the adsorption of CO₂ and facilitates C-C coupling.