Enhancing the local electron density at active sites to promote the selective conversion of CO2 into C2H6†

Abstract

Metal–covalent organic frameworks (M-COFs) have exhibited great potential in photocatalytic CO₂ reduction. However, challenges persist in generating C₂ products and their low selectivity. Here, we incorporated electron-rich and conjugated benzotrithiophene (BTT) into aldehyde monomers to synthesize a hydrazone-linked COF. Copper (Cu) atoms coordinate with the hydrazone bonds, forming Cu sites with high charge density. Notably, the high charge density at the Cu sites not only facilitates CO₂ activation but also creates a suitable microenvironment for the stability of *CO intermediates, thereby increasing their concentration and enhancing C–C coupling. As a result, Cu@BTT-DMTH-COF exhibits a C₂H₆ evolution rate of 34.5 μmol g⁻¹ h⁻¹ with a selectivity of 72.5%, and its C₂H₆ electron selectivity is 1.72 times higher than that of a hydrazone-linked metal COF composed of pyrene units. In summary, this work serves as an ideal model for achieving photocatalytic conversion of CO₂ into ethane using metal-based COF materials.