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

Abstract

Metal-covalent organic frameworks have demonstrated great potential in photocatalytic CO2 reduction. However, challenges persist in the challenge of 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 covalent organic framework materials.