Single-site decorated copper enables energy- and carbon-efficient CO 2 methanation in acidic conditions.

Renewable CH 4 produced from electrocatalytic CO 2 reduction is viewed as a sustainable and versatile energy carrier, compatible with existing infrastructure. However, conventional alkaline and neutral CO 2 -to-CH 4 systems suffer CO 2 loss to carbonates, and recovering the lost CO 2 requires input energy exceeding the heating value of the produced CH 4 . Here we pursue CH 4 -selective electrocatalysis in acidic conditions via a coordination method, stabilizing free Cu ions by bonding Cu with multidentate donor sites. We find that hexadentate donor sites in ethylenediaminetetraacetic acid enable the chelation of Cu ions, regulating Cu cluster size and forming Cu-N/O single sites that achieve high CH 4 selectivity in acidic conditions. We report a CH 4 Faradaic efficiency of 71% (at 100 mA cm -2 ) with <3% loss in total input CO 2 that results in an overall energy intensity (254 GJ/tonne CH 4 ), half that of existing electroproduction routes.