Single-site decorated copper enables energy- and carbon-efficient CO2 methanation in acidic conditions

Renewable CH4 produced from electrocatalytic CO2 reduction is viewed as a sustainable and versatile energy carrier, compatible with existing infrastructure. However, conventional alkaline and neutral CO2-to-CH4 systems suffer CO2 loss to carbonates, and recovering the lost CO2 requires input energy exceeding the heating value of the produced CH4. Here we pursue CH4-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 CH4 selectivity in acidic conditions. We report a CH4 Faradaic efficiency of 71% (at 100 mA cm-2) with <3% loss in total input CO2 that results in an overall energy intensity (254 GJ/tonne CH4), half that of existing electroproduction routes.