High-rate electroreduction of carbon monoxide to multi-carbon products

Carbon monoxide electrolysis has previously been reported to yield enhanced multi-carbon (C2+) Faradaic efficiencies of up to ~55%, but only at low reaction rates. This is due to the low solubility of CO in aqueous electrolytes and operation in batch-type reactors. Here, we present a high-performance CO flow electrolyser with a well controlled electrode–electrolyte interface that can reach total current densities of up to 1 A cm–2, together with improved C2+ selectivities. Computational transport modelling and isotopic C18O reduction experiments suggest that the enhanced activity is due to a higher surface pH under CO reduction conditions, which facilitates the production of acetate. At optimal operating conditions, we achieve a C2+ Faradaic efficiency of ~91% with a C2+ partial current density over 630 mA cm–2. Further investigations show that maintaining an efficient triple-phase boundary at the electrode–electrolyte interface is the most critical challenge in achieving a stable CO/CO2 electrolysis process at high rates.