-CH3 Mediated Pathway for the Electroreduction of CO2 to Ethane and Ethanol on Thick Oxide-Derived Copper Catalysts at Low Overpotentials

Oxide-derived copper is known for its unique ability to catalyze the selective electroreduction of CO2 to C-2 and higher carbon compounds at low overpotentials. To understand this phenomenon, mechanistic studies typically chose ethylene (C2H4) as the model compound. The pathways to form other C-2 compounds such as ethane (C2H6) and ethanol are then generally considered to be similar to that of C2H4. However, regular detection of C2H6 or ethanol on thick oxide derived Cu at low overpotentials, often with selectivities exceeding that of C2H4, raises an important question: does the formation of these two C-2 molecules really share a common route with C2H4? In this work, through an investigation of CO2 electroreduction on oxide-derived Cu of different thicknesses and oxidation states, we show that the formation of C2H6 and ethanol on thick oxide-derived Cu films could proceed through routes distinct from that of C2H4 at low overpotentials. Investigations using select molecular precursors such as diacetyl [(CH3CO)(2)] suggest that the formation of C2H6 on thick oxide-derived Cu surfaces is likely to originate from the dimerization of -CH3 intermediates. We attribute the higher selectivity for C2H6 and ethanol to a higher population of Cu+ sites in the thick oxide-derived Cu films, which helped to stabilize the -CH3 intermediates.