Carbon Monoxide Reduction to Multi-Carbon Products at Ampere-Level Current Densities: A Comparative Assessment with CO2 Reduction Reactions

The electrochemical reduction of CO2 is a promising approach for achieving a closed carbon cycle. An increase in the current density is essential for the practical implementation of this technology. As CO2 electrolysis technology for CO production is approaching industrial practicality, there is now an increasing demand for electrolysis technologies that convert the produced CO into higher-valued multicarbon (C2+) products under high-current-density conditions. Herein, we report a substantial enhancement of the partial current density for the reduction of CO to C2+ products over Cu nanoparticles supported on gas diffusion electrodes in 1 M KOH, achieving a record value of 1.6 A cm−2 for C2+ formation at a total current density of 3 A cm−2. This high-current-density CO electrolysis was enabled by the extremely large triple-phase interface area in our electrode, which maximized CO transport. Notably, the partial current density for acetate reached 519 mA cm−2 at −1.74 V vs. Ag/AgCl, with a Faradaic efficiency of 26.0%. The selectivity for acetate in the CO reduction reaction was several times higher than that in the CO2 reduction reaction over the wide total current density range from 0.2 to 3 A cm−2. The coupling between adsorbed reduced species and gaseous CO is expected to form an intermediate for acetate. Under high CO partial pressures, the formation of this intermediate is favored in CO reduction reactions over CO2 reduction reactions. In addition, high-current-density electrolysis increases the surface pH at the electrode, promoting the insertion of OH− into the adsorbed precursor, thereby facilitating acetate formation, as suggested by the analysis of the simulated surface pH.