Enhanced Acidic CO2-to-C2+ Reduction via Ionic Liquid Layer Modification.

Acidic CO2 electroreduction reaction (CO2RR) garners significant attention as a promising approach for cutting carbon density, as it effectively mitigates CO2 loss by suppressing carbonate species formation. Unfortunately, achieving efficient multi-carbon products (C2+) 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][NTf2])-on Cu surface. Density functional theory calculations predict that PMIM+ cation strengthens *CO adsorption through quasi-hydrogen bonding, while NTf2 - anion creates a hydrophobic environment, effectively reducing H* coverage and promoting *CO adsorption. Resistance tests demonstrate that [PMIM][NTf2] 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][NTf2] modified Cu catalyst achieved a remarkable partial current density of ≈640 mA cm-2 for C2+ 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 CO2RR in acidic media.