A novel Cu-based covalent organic framework with Cu-N2O2 single sites for efficient CO2 electroreduction to methane

Single-site catalysts (SSCs) are useful for CO2 electroreduction (CO2ER) to methane (CH4), but their selectivities for CH4 are still unsatisfactory due to the lack of efficient active sites. Herein, a novel Cu-based covalent organic framework (CuN2O2-COF) with Cu-N2O2 single sites was synthesized by the Schiff base reaction and used in CO2ER to improve CH4 generation for the first time. Compared with typical SSCs containing Cu-N-4 or Cu-O-4 sites, CuN2O2-COF exhibited superior CH4 production efficiency in CO2ER: the Faradaic efficiency of CH4 was as high as 85.4%, and the CH4 partial current density reached 313 mA.cm(-2) at -1.3 V, which exceeded those of most electrocatalysts reported thus far. Theoretical calculations indicated that compared with the Cu-N-4 or Cu-O-4 sites in typical SSCs, the new Cu-N2O2 configuration in CuN2O2-COF increased the d-band center of the Cu sites and enhanced the adsorption of key intermediates (*COOH and *CHO) required for CO2ER to CH4.