Insights on Dual‐Functional Ionic Liquid Interfacial Layer for Efficient CO 2 Electroreduction to C 2+ Products in Acid

ABSTRACT Electrocatalytic CO 2 reduction reaction (CO 2 RR) in acidic electrolyte is hindered by severe hydrogen evolution reaction (HER) and inefficient C–C coupling, leading to poor selectivity toward multicarbon (C 2+ ) 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 C 2+ 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 (H 3 O + ) 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 C 2+ Faradaic efficiency of 81.1% at 800 mA cm −2 in 1 M KCl/0.05 M H 2 SO 4 electrolyte. Notably, the Faradaic efficiency of ethanol is approximately 2.2 times higher than that of CuO.