Rational design of spatial charge separation and targeted active site Cu for highly selective photocatalytic CO2 reduction to CH4

Photocatalytic CO 2 reduction reaction (CO 2 RR) is usually constrained by sluggish kinetics and low product selectivity. Herein, a Cu-doping multi-tier hierarchical S-scheme heterostructure Cu-ZnIn 2 S 4 /ZIF-67 was fabricated, achieving highly efficient photocatalytic CO 2 RR under visible light without additional thermal input. At low pressure (absolute pressure 40 kPa), the optimized catalyst 2Cu-ZISF demonstrated a CH 4 yield of 22.27 μmol g −1 h −1 with a selectivity of 94.7 %. In situ XPS and EPR confirmed that the photogenerated charge transfer obeys an S-scheme mechanism, with Cu sites serving as electron-rich centers, facilitating spatial charge separation. In situ DRIFT detected reaction intermediates of photocatalytic CO 2 RR mechanism, and Gibbs free energy calculations via Density Functional Theory revealed that Cu incorporation significantly stabilizes surface CO* species, thus reducing CO(g) production and facilitating hydrogenation, thereby acting as targeted active sites for CH 4 production. This work overcomes the limitations of slow reaction kinetics and offers an in-depth understanding of how to design effective S-scheme heterojunction photocatalysts and their charge transfer mechanisms.