Developing　nonmetallic　active　sites-based　catalysts　for　efficient　electrocatalytic　CO2　reduction　reaction　(CO2RR)　remains　challenging.　Active　N-heterocyclic　carbenes　(NHCs)　as　typical　nonmetal　catalysts　have　shown　high　efficiency　in　organic　catalysis　but　rarely　used　in　electrochemistry.　Herein,　we　report　for　the　first　time　using　the　CO2-masked　NHCs　functionalized　metal–organic　framework　(UiO-66-NHC-CO2)　as　efficient　electrocatalyst　for　the　CO2RR　towards　production　of　CO.　The　active　NHCs　sites　protected　by　the　COO−　group　in　the　UiO-66-NHC-CO2　can　activate　CO2　and　the　Faradaic　efficiency　of　CO　reaches　80.1%　at　−2.5　V　versus　Ag/Ag+,　outcompeting　current　metal-free　catalysts　with　well-defined　active　sites.　Experimental　results　and　DFT　indicate　that　the　NHCs　species　shielded　by　CO2　have　a　lower　adsorption　activation　energy　for　CO2　compared　to　imidazolium　salts,　making　it　easier　to　bind　and　activate　CO2,　thus　leading　to　easy　reduction　to　CO.　Therefore,　the　NHCs　portion　of　UiO-66-NHC-CO2　can　be　capable　of　activating　CO2　and　facilitating　its　reduction　to　CO.　This　discovery　provides　valuable　insights　for　the　preactivation　of　CO2　and　efficient　electrocatalytic　reduction　of　CO2　©　2024　Chinese　Chemical　Society.　All　rights　reserved.