Enhanced Acidic CO 2 ‐to‐C 2+ Reduction via Ionic Liquid Layer Modification

Abstract Acidic CO 2 electroreduction reaction (CO 2 RR) garners significant attention as a promising approach for cutting carbon density, as it effectively mitigates CO 2 loss by suppressing carbonate species formation. Unfortunately, achieving efficient multi‐carbon products (C 2+ ) production in acidic media remains challenging due to two main limitations: weak CO adsorption on Cu sites and competitive H* adsorption caused by the high concentration protons (H + ). To overcome these challenges, a cation‐anion‐modification strategy is proposed using an ionic liquid layer—1‐Propyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([PMIM][NTf 2 ])—on Cu surface. Density functional theory calculations predict that PMIM + cation strengthens *CO adsorption through quasi‐hydrogen bonding, while NTf 2 − anion creates a hydrophobic environment, effectively reducing H* coverage and promoting *CO adsorption. Resistance tests demonstrate that [PMIM][NTf 2 ] modification effectively reduced proton diffusion. Attenuated total reflection infrared spectroscopy (ATR‐IR) confirmed the reinforcement of *CO adsorption on the modified Cu surface. As a result, the [PMIM][NTf 2 ] modified Cu catalyst achieved a remarkable partial current density of ≈640 mA cm −2 for C 2+ products, with exceptional faradaic efficiency of 80.1% and durability of ≈20 h at a partial current density exceeding 500 mA cm −2 in a flow cell. This study highlights the potential of cation‐anion modification strategies for significantly enhancing CO 2 RR in acidic media.