Metal ion cycling of Cu foil for selective C–C coupling in electrochemical CO2 reduction

Electrocatalytic CO2 reduction to higher-value hydrocarbons beyond C1 products is desirable for applications in energy storage, transportation and the chemical industry. Cu catalysts have shown the potential to catalyse C–C coupling for C2+ products, but still suffer from low selectivity in water. Here, we use density functional theory to determine the energetics of the initial C–C coupling steps on different Cu facets in CO2 reduction, and suggest that the Cu(100) and stepped (211) facets favour C2+ product formation over Cu(111). To demonstrate this, we report the tuning of facet exposure on Cu foil through the metal ion battery cycling method. Compared with the polished Cu foil, our 100-cycled Cu nanocube catalyst with exposed (100) facets presents a sixfold improvement in C2+ to C1 product ratio, with a highest C2+ Faradaic efficiency of over 60% and H2 below 20%, and a corresponding C2+ current of more than 40 mA cm–2. Electrocatalytic reduction of CO2 to products containing multiple carbon atoms is useful for producing high-value chemicals and fuels. This work uses theory to predict the preferred copper surface for C–C coupling, and subsequent metal ion cycling to produce the desired facets results in a catalyst that is highly selective for C2+ products.