–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 CO 2 to C 2 and higher carbon compounds at low overpotentials. To understand this phenomenon, mechanistic studies typically chose ethylene (C 2 H 4 ) as the model compound. The pathways to form other C 2 compounds such as ethane (C 2 H 6 ) and ethanol are then generally considered to be similar to that of C 2 H 4 . However, regular detection of C 2 H 6 or ethanol on thick oxide-derived Cu at low overpotentials, often with selectivities exceeding that of C 2 H 4, raises an important question: does the formation of these two C 2 molecules really share a common route with C 2 H 4? In this work, through an investigation of CO 2 electroreduction on oxide-derived Cu of different thicknesses and oxidation states, we show that the formation of C 2 H 6 and ethanol on thick oxide-derived Cu films could proceed through routes distinct from that of C 2 H 4 at low overpotentials. Investigations using select molecular precursors such as diacetyl [(CH 3 CO) 2 ] suggest that the formation of C 2 H 6 on thick oxide-derived Cu surfaces is likely to originate from the dimerization of −CH 3 intermediates. We attribute the higher selectivity for C 2 H 6 and ethanol to a higher population of Cu + sites in the thick oxide-derived Cu films, which helped to stabilize the −CH 3 intermediates.