Surfactant-Enhanced Formation of Ethylene from Carbon Monoxide Electroreduction on Copper Catalysts

Surface functionalization has been found to be promising for enhancing the electrochemical CO2 reduction reaction (CO2RR) to C2+ products on copper catalysts, typically by suppressing the parasitic hydrogen evolution reaction and increasing the local concentration of CO2 at the electrode. Expanding upon this approach, we developed surface-functionalized catalysts for CO reduction (CORR) to C2+ products with high activity and selectivity. Using an oxide-derived copper (OD-Cu) catalyst coated with tetrabutylammonium cations (TBA+), CO was reduced at −0.65 V vs RHE to C2+ products with a Faradaic efficiency (FE) of 78% (j C2+ = –765 mA cm–2), of which the FE ethylene was 40%. In contrast, unmodified OD-Cu catalysts achieved lower FEs of C2+ products (60%) and ethylene (27%). Our mechanistic study to explore the above product distribution, which involved performing CORR at different CO partial pressures, in situ Raman spectroscopy, and the use of other surfactants, reveals that the enhanced selectivity of C2+ products in the presence of TBA+, especially ethylene, is attributed to heightened CORR activity and increased ethylene production rather than HER suppression. Optimization of the mass loading of the TBA+-coated Cu catalysts and applied potentials enabled a j C2+ exceeding −1 A cm–2 (j ethylene = −694 mA cm–2).