Electrochemical Reduction of CO2: A Common Acetyl Path to Ethylene, Ethanol or Acetate

Abstract Ethylene is well known as the primary product of CO2 reduction at Cu electrocatalysts using zero-gap membrane electrode assembly cells with gas diffusion cathodes. Other types of Cu electrocatalysts including oxide-derived Cu, CuSn and CuSe yield relatively more C2 oxygenates; however, the mechanisms for C2 product selectivity are not well established. This work considers selectivity trends of Cu-P0.065, Cu-Sn0.03, and Cu2Se electrocatalysts made using a standard one pot synthesis method. Results show that Cu-P0.065 electrocatalysts (Cuδ+ = 0.13) retain ethylene as a primary product with relatively higher Faradaic efficiencies (FE = 43% at 350 mA cm-2) than undoped Cu electrocatalysts (FE = 31% at 350 mA cm-2) at the same current density. The primary CO2 reduction product at Cu-Sn0.03 (Cuδ+ = 0.27) electrocatalysts shifts to ethanol (FE = 48% at 350 mA cm-2) while CO2 reduction at Cu2Se (Cuδ+ = 0.47) electrocatalysts favor acetate production (FE = 40% at 350 mA cm-2). Based on these results, we propose a common acetyl intermediate and a mechanism for selective formation of ethylene, ethanol or acetate based on the degree of partial positive charge (δ+) of Cu reaction sites.