Atomic-level Cu active sites enable energy-efficient CO2 electroreduction to multicarbon products in strong acid

Electrochemical CO2 reduction provides a promising strategy to synthesize C2+ compounds with reduced carbon intensity; however, high overall energy consumption restricts practical implementation. Using acidic media enables high CO2 utilization and low liquid product crossover, but to date has suffered low C2+ product selectivity. Here we hypothesize that adjacent pairs of atomic-copper active sites may favour C-C coupling, thus facilitating C2+ product formation. We construct tandem electrocatalysts with two distinct classes of active sites, the first for CO2 to CO, and the second, a dual-atomic-site catalyst, for CO to C2+. This leads to an ethanol Faradaic efficiency of 46% and a C2+ product Faradaic efficiency of 91% at 150 mA cm-2 in an acidic CO2 reduction reaction. We document a CO2 single-pass utilization of 78% and an energy efficiency of 30% towards C2+ products; an ethanol crossover rate of 5%; and an ethanol product concentration of 4.5%, resulting in an exceptionally low projected energy cost of 249 GJ t-1 for the electrosynthesis of ethanol via the CO2 reduction reaction. Tandem electrocatalysts are developed for acidic CO2 electroreduction. The catalyst contains planar-copper for CO2 reduction to CO, and a dual-copper-active-site layer for CO reduction to C2+ products. An ethanol Faradaic efficiency of 46% and a C2+ Faradaic efficiency of 91% are achieved in acidic electrolyte at 150 mA cm-2.