The activity origin of C-N-Cu electrocatalysts for ethanol formation in the CO₂ reduction reaction under working conditions

Cu-anchored N-doped carbon (C-N-Cu) catalysts have been experimentally shown to exhibit high activity for the conversion of CO₂ to ethanol. It is believed that reversible Cu agglomeration on C-N-Cu catalysts under operating conditions is responsible for the high activity, but exploring their intrinsically catalytically active sites faces great challenges since the transient Cu cluster structure can't be effectively detected using in situ techniques. Here, adopting a developed constant potential method and considering the electrode potential and solvation effect, we theoretically unveil the active sites of C-N-Cu catalysts under working conditions. As a negative potential is applied on the C-N-Cu catalyst, electrons tend to occupy the anti-bonding states of Cu-N bonds, driving the leaching of Cu atoms for Cu cluster formation. An aggregated C-N-Cu₅ cluster configuration is identified as natural active sites, exhibiting a well-aligned catalytical performance with experimental reports. The d-band center, charge distribution, and multiple active sites of C-N-Cu₅ guarantee its configuration as a promising platform for CO₂ reduction. Based on this active site, we further elucidated the reaction mechanism and key intermediates of ethanol formation on the C-N-Cu₅ catalysts, revealing that the adsorbed CHO species act as the reactants for C-C coupling.