Selective and energy-efficient electrosynthesis of ethylene from CO2 by tuning the valence of Cu catalysts through aryl diazonium functionalization

Although progress has been made in producing multi-carbon products from the electrochemical reduction of CO2, the modest selectivity for ethylene (C2H4) leads to low energy efficiency and high downstream separation costs. Here we functionalize Cu catalysts with a variety of substituted aryl diazonium salts to improve selectivity towards multi-carbon products. Using computation and operando spectroscopy, we find that Cu surface oxidation state (δ+ where 0 < δ < 1) can be tuned by functionalization and that it influences the selectivity to C2H4. We report a Faradaic efficiency and a specific current density for C2H4 as large as 83 ± 2% and 212 mA cm−2, respectively, on partially oxidized Cu0.26+. Using a CO gas feed, we demonstrate an energy efficiency of ~40% with a C2H4 Faradaic efficiency of 86 ± 2%, corresponding to a low electrical power consumption of 25.6 kWh Nm−3 for the CO to C2H4 conversion reaction. Our findings provide a route towards practical electrosynthesis of C2H4 using valence engineering of copper. Achieving high selectivity towards the formation of a single type of multi-carbon product from CO2 electroreduction is difficult. Here Wu and colleagues show that the valence state of Cu can be tuned by functionalization of the catalyst surface with organic salts, boosting selectivity towards ethylene.