Sequential catalysis enables enhanced C-C coupling towards multi-carbon alkenes and alcohols in carbon dioxide reduction: a study on bifunctional Cu/Au electrocatalysts

Electrochemical reduction of carbon dioxide (CO2) to multi-carbon products such as ethylene, ethanol and n-propanol offers a promising path for utilization of excessive CO2 and energy storage. Oxide-derived Cu electrodes are among the best electrocatalysts for the selective formation of ethylene and ethanol. However, a large fraction of the faradaic current still goes to hydrogen evolution, even at optimal conditions (electrolyte, potential, etc.). Here we employ the concept of sequential catalysis using judiciously designed CuAu bimetallic catalysts through galvanic exchange between Au3+ and Cu2O nanowires. By controlling the concentration of the Au3+ precursor and the exchange time, Au nanoparticles were evenly dispersed onto the Cu2O nanowires. The optimized oxide-derived CuAu catalyst showed remarkable improvement towards the formation of ethylene, ethanol and n-propanol, in terms of faradaic efficiency and current density. Our analysis of the electrochemical formation of carbon monoxide, ethylene and hydrogen suggests that the presence of Au, an electrocatalyst for CO2-to-CO conversion, helps enhance *CO-coverage on Cu, thus promoting the production of multi-carbon products and suppressing hydrogen formation on the CuAu catalyst. We propose promising strategies for designing electrochemical systems, which would enable the selective and scalable reduction of CO2 to ethylene and ethanol.