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

Abstract

Ethylene is well known as the primary product of CO 2 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 C 2 oxygenates; however, the mechanisms for C 2 product selectivity are not well established. This work considers selectivity trends of Cu-P 0.065 , Cu-Sn 0.03 , and Cu 2 Se electrocatalysts made using a standard one pot synthesis method. Results show that Cu-P 0.065 electrocatalysts (Cu δ + = 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 CO 2 reduction product at Cu-Sn 0.03 (Cu δ + = 0.27) electrocatalysts shifts to ethanol (FE = 48% at 350 mA cm −2 ) while CO 2 reduction at Cu 2 Se (Cu δ + = 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.