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 CO2 reduction reaction (CO2RR) to multi-carbon (C2+) 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 C2+ formation. Here, we report our discovery of pivotal roles of a suitable nanocomposite electrocatalyst with abundant Cu2O-Cu0 interfaces in accomplishing water-promoting effect on C2+ formation, achieving a current density of 1.0 A cm-2 and a 19% single-pass C2+ yield at 80% C2+ Faradaic efficiency in MEA. The operando characterizations confirm the co-existence of Cu+ with Cu0 during CO2RR 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 CO2RR to C2+ compounds in industrial-relevant MEA by combining water management and electrocatalyst design.