Surface hydroxide promotes CO(2) electrolysis to ethylene in acidic conditions

Performing CO(2) reduction in acidic conditions enables high single-pass CO(2) conversion efficiency. However, a faster kinetics of the hydrogen evolution reaction compared to CO(2) reduction limits the selectivity toward multicarbon products. Prior studies have shown that adsorbed hydroxide on the Cu surface promotes CO(2) reduction in neutral and alkaline conditions. We posited that limited adsorbed hydroxide species in acidic CO(2) reduction could contribute to a low selectivity to multicarbon products. Here we report an electrodeposited Cu catalyst that suppresses hydrogen formation and promotes selective CO(2) reduction in acidic conditions. Using in situ time-resolved Raman spectroscopy, we show that a high concentration of CO and OH on the catalyst surface promotes C-C coupling, a finding that we correlate with evidence of increased CO residence time. The optimized electrodeposited Cu catalyst achieves a 60% faradaic efficiency for ethylene and 90% for multicarbon products. When deployed in a slim flow cell, the catalyst attains a 20% energy efficiency to ethylene, and 30% to multicarbon products.