Spatial Cascade Sites in Hierarchical COF-Based Photocatalyst Enable C─C Coupling for Selective CO₂ Photoreduction to...

The photoreduction of CO₂ into multi-carbon (C₂₊) products is a highly attractive route for CO₂ utilization; however, the yield and selectivity of C₂₊ products are seriously limited by slow multi-electron-proton transfer and sluggish C─C coupling kinetics. Herein, we construct a hierarchical tandem photocatalyst IS@COF-Ni by growing imine-pyridine covalent organic frameworks on non-stoichiometric indium sulfide and introducing isolated Ni single-atom sites at the interfacial edges. The synergistic effect between the spatially segregated sites promotes *CO dimerization, effectively lowering the kinetic barrier for high-rate ethylene (C₂H₄) generation. Thus, compared with its individual components, the IS@COF-Ni heterojunction achieves exceptionally high C₂H₄ productivity and selectivity in photocatalytic CO₂ reduction with water vapor in the absence of additives. In situ spectroscopic characterizations and theoretical calculations reveal that IS@COF-Ni establishes a low-energy pathway for electron and proton transfer, while the heterojunction interface effectively stabilizes the adsorbed CO (*CO) intermediate, facilitating C─C bond formation via coupling of adjacent *CO species to generate C₂H₄. This work provides a strategic approach for designing photocatalysts toward selective CO₂-to-C₂₊ conversion.