Surface Hydroxyl Groups Enhance Ethylene Selectivity in Acidic CO2 Reduction Reaction

Acidic conditions can enable high single-pass conversion in electrochemical CO2 reduction (CO2R) reaction. However, the kinetically facile hydrogen evolution reaction (HER) prevails in acidic conditions and limits the energy efficiency for CO2R towards multi-carbon (C2+) products. By performing electrodeposition under CO2R conditions, we synthesized a copper catalyst (EC-Cu) that promotes selective CO2R to C2+ products in acidic conditions. We combine in situ spectroscopy, DFT calculations, and catalyst performance to show that co-adsorbed CO and OH on the catalyst surface promote C-C coupling, which we correlate with evidence of increased CO residence time. With optimization, the EC-Cu catalyst achieved a 60% faradaic efficiency for ethylene and 90% for C2+. Furthermore, when implemented in a slim flow cell, the EC-Cu catalyst can attain a 20% energy efficiency toward ethylene production.