Insights on Dual-Functional Ionic Liquid Interfacial Layer for Efficient CO2 Electroreduction to C2+ Products in Acid.

Electrocatalytic CO2 reduction reaction (CO2RR) in acidic electrolyte is hindered by severe hydrogen evolution reaction (HER) and inefficient C-C coupling, leading to poor selectivity toward multicarbon (C2+) products. Here, we construct a dual-functional interfacial layer by modifying a CuO catalyst with the ionic liquid choline triazole ([Cho][Triz]). This interfacial layer simultaneously regulates the active hydrogen (*H) supply pathway to suppress HER and stabilizes key C-C coupling intermediates, thereby promoting C2+ product formation. Comprehensive in situ spectroscopic characterizations and theoretical simulations reveal that the ionic liquid interfacial layer disrupts the continuous hydrogen-bond network of interfacial water, suppresses hydronium (H3O+) transport from the bulk electrolyte, and accelerates water dissociation to generate *H species, thereby promoting intermediate hydrogenation and inhibiting HER. Meanwhile, the hydroxyl groups in the ionic liquid stabilize the *CHO intermediate and facilitate the energetically favorable asymmetric *CHO-*CO coupling pathway. Benefiting from this dual-functional regulation, the [Cho][Triz]-modified CuO catalyst delivers a C2+ Faradaic efficiency of 81.1% at 800 mA cm-2 in 1 M KCl/0.05 M H2SO4 electrolyte. Notably, the Faradaic efficiency of ethanol is approximately 2.2 times higher than that of CuO.