Roles of copper(I) in water-promoted CO2 electrolysis to multi-carbon compounds

The membrane electrode assembly (MEA) is promising for practical applications of the electrocatalytic CO 2 reduction reaction (CO 2 RR) to multi-carbon (C 2+ ) compounds. Water management is crucial in the MEA electrolyser without catholyte, but few studies have clarified whether the co-feeding water in cathode can enhance C 2+ formation. Here, we report our discovery of pivotal roles of a suitable nanocomposite electrocatalyst with abundant Cu 2 O−Cu 0 interfaces in accomplishing water-promoting effect on C 2+ formation, achieving a current density of 1.0 A cm −2 and a 19% single-pass C 2+ yield at 80% C 2+ Faradaic efficiency in MEA. The operando characterizations confirm the co-existence of Cu + with Cu 0 during CO 2 RR at ampere-level current densities. Our studies reveal that Cu + works for water activation and aids C‒C coupling by enhancing formations of adsorbed CO and CHO species. This work offers a strategy to boost CO 2 RR to C 2+ compounds in industrial-relevant MEA by combining water management and electrocatalyst design.