Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper

Direct electrochemical conversion of CO2 to ethanol offers a promising strategy to lower CO2 emissions while storing energy from renewable electricity. However, current electrocatalysts offer only limited selectivity toward ethanol. Here we report a carbon-supported copper (Cu) catalyst, synthesized by an amalgamated Cu–Li method, that achieves a single-product Faradaic efficiency (FE) of 91% at −0.7 V (versus the reversible hydrogen electrode) and onset potential as low as −0.4 V (reversible hydrogen electrode) for electrocatalytic CO2-to-ethanol conversion. The catalyst operated stably over 16 h. The FE of ethanol was highly sensitive to the initial dispersion of Cu atoms and decreased significantly when CuO and large Cu clusters become predominant species. Operando X-ray absorption spectroscopy identified a reversible transformation from atomically dispersed Cu atoms to Cun clusters (n = 3 and 4) on application of electrochemical conditions. First-principles calculations further elucidate the possible catalytic mechanism of CO2 reduction over Cun.