Carbon Monoxide Reduction Reaction to Produce Multicarbon Products in Acidic Electrolytes Using Gas Diffusion Electrode Loaded with Copper Nanoparticles

The synthesis of multi-carbon products (C2+) by electrochemical CO2 reduction reaction (CO2RR) is a promising technology that will contribute to the realization of a carbon-neutral society. In particular, efficient CO2RR to produce C2+ in acidic electrolytes is desirable because the conversion of CO2 to inert (bi)carbonate can be suppressed under acidic conditions, thereby increasing the efficiency of substrate CO2 utilization. Herein, since C2+ products are produced via the dimerization of carbon monoxide, an intermediate in CO2RR, the focus is on the carbon monoxide reduction reaction (CORR). A gas diffusion electrode loaded with copper nanoparticles is used in acidic electrolytes to investigate the conditions necessary for efficient C2+ production. The faradaic efficiency and partial current density for C2+ production attained 75% and 280 mA cm-2 in a pH 2.0 solution, and they reached up to 66% and 260 mA cm-2 even in a pH 1.0 solution. Numerical simulations showed that increasing the alkalinity of the electrode surface to greater than pH 7 by consuming protons is necessary to facilitate the production of C2+ during the CORR. When the desired level of alkalinity is achieved, the concentration and type of alkali cations present at the electrode surface have an impact on the selectivity for C2+ production. Multicarbon production by CO reduction reactions in highly acidic solutions is achieved. A local alkalinity with a pH exceeding 7 at the electrode surfaces is essential for multicarbon production. The local pH is predominantly determined by the bulk pH and the applied current density. The types and concentrations of alkali cations influence the selectivity after alkalization.image