Theory-guided Sn/Cu alloying for efficient CO2 electroreduction at low overpotentials

Electrochemical CO2 reduction to formate provides an avenue to reduce globally accelerating CO2 emissions and produce value-added products. Unfortunately, high selectivity in formate electrosynthesis has thus far only been achieved at highly cathodic potentials. Here we use density functional theory to investigate the effect of alloying Cu and Sn on the activity and selectivity towards formate. A theoretical thermodynamic analysis of the reaction energetics suggests that the incorporation of copper into tin could suppress hydrogen evolution and CO production, thus favouring formate generation. Consistent with theoretical trends, the designed CuSn3 catalysts by co-electrodeposition exhibit a Faradaic efficiency of 95% towards formate generation at -0.5 V versus RHE. Furthermore, the catalysts show no degradation over 50 h of operation. In situ Sn L-3-edge and Cu K-edge X-ray absorption spectroscopy indicate electron donation from Sn to Cu, which indicates positive oxidation states of Sn in CuSn3 under operating conditions.