Tungsten and oxygen dual vacancies regulation of the S-scheme ZnSe/ZnWO4 heterojunction with local polarization electric field for efficient CO2 photocatalytic reduction

Inefficient separation and sluggish transfer of photogenerated charges on the photocatalyst is one of the bottlenecks for CO2 photocatalytic reduction. In this study, the ZnSe/ZnWO4 heterojunction with tungsten vacancies and oxygen vacancies (ZZ-30%-Vw,o) was synthesized by hydrothermal process and post-etching method for CO2 reduction. Various characterizations showed superior structural and optical properties of the ZZ-30%-Vw,o heterojunction; results of ESR and work function calculation demonstrated that the heterojunction conformed to S-scheme charge transfer mechanism. Results of various tests and density functional theory (DFT) calculation confirmed the existence of W and O vacancies, as well as the locally polarized electric field (PEF). The PEF and the built-in electric field (IEF) could not only accelerate carriers separation and transfer, but also enhance CO2 adsorption and activation, thus enhancing photocatalytic activity toward CO2 reduction. The ZZ-30%-Vw,o composite exhibited the highest CO yield of 96.91 µmol/g/h, approximately 21.0 times of the ZnSe. Moreover, the ZZ-30%-Vw,o possessed favorable structure-performance stability. The COOH* was the most important intermediate during CO2 reduction, and possible CO2 reduction pathways and mechanism were proposed. This work paves a feasible way for improving photocatalytic activity via introducing dual surface vacancies on heterojunction photocatalysts.