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

Photocatalytic CO2 reduction reaction (CO2RR) is usually constrained by sluggish kinetics and low product selectivity. Herein, a Cu-doping multi-tier hierarchical S-scheme heterostructure Cu-ZnIn2S4/ZIF-67 was fabricated, achieving highly efficient photocatalytic CO2RR under visible light without additional thermal input. At low pressure (absolute pressure 40 kPa), the optimized catalyst 2Cu-ZISF demonstrated a CH4 yield of 22.27 μmol g−1h−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 CO2RR 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 CH4 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.