Boosting photocatalytic CO2 reduction by tuning photogenerated carrier kinetics in two-dimensional WOx/BiOCl S-scheme heterojunction with oxygen vacancies

Photocatalytic CO2 reduction driven by sustainable solar energy is a highly desirable route to achieve carbon recycling, to which charge separation in photocatalysts holds the key. In this work, two-dimensional (2D) WO3·H2O nanosheets with rich oxygen vacancies (Vo-WOx) were combined with 2D BiOCl nanosheets to form a 2D/2D Vo-WOx/BiOCl S-scheme heterojunction by a self-assembly process. The 2D/2D stacked structure combined with the introduction of oxygen vacancies in Vo-WOx could improve the light harvesting of the designed photocatalytic system. The dual transfer pathways in the S-scheme junction were induced by the fact that the photogenerated electrons on the conduction band and defect energy level of the Vo-WOx transfer across the interface to combine with the BiOCl, leading to an improved kinetic process of photogenerated carriers. Moreover, the S-scheme configuration can retain a strong redox potential for satisfying the thermodynamic requirement of CO2 reduction. As a result, the optimized 30Vo-WOx/BiOCl composite can achieve the highest CO yield rate of 8.82 μmol h−1 from CO2 reduction without any sacrifice reagents, which was 4.69 and 3.08 times higher than that of pure BiOCl and WO3/BiOCl without oxygen vacancy. This work provides a new view of defect engineering in S-scheme heterojunction for pursuing a highly efficient photocatalytic CO2 reduction system.