Electronic Modulation of Cu Catalytic Interfaces by Functionalized Ionic Liquids for Enhanced CO₂ Reduction

The electrocatalytic CO₂ reduction reaction (CO₂RR) into value-added multi-carbon C₂₊ products holds significant promise for sustainable chemical synthesis and carbon-neutral energy cycles. Among the various strategies developed to enhance CO₂RR, the use of ionic liquids (ILs) has emerged as a powerful approach for modulating the local microenvironment and electronic structure of Cu-based metal catalysts. In this study, to unravel the molecular-level mechanisms underlying these enhancements, density functional theory calculations (DFTs) were employed to systematically explore how ILs with different terminal groups modulate the electronic reconstruction of the Cu surface, further affecting the *CO-*CO coupling and product selectivity. Electronic structure analyses reveal that ILs bearing polar moieties (-SH, -COOH) can synergistically enhance the interfacial electron accumulation and induce an upshift of the Cu d-band center, thereby strengthening *CO adsorption. In contrast, nonpolar IL (CH₃) exhibits negligible effects, underscoring the pivotal role of ILs' polarity in catalyst surface-state engineering. The free energy diagrams and transition state analyses reveal that ILs with polar groups significantly lower both the reaction-free energy and activation barrier associated with the *CO-*CO coupling step. This energetic favorability selectively inhibits the C₁ product pathways and hydrogen evolution reaction (HER), further improving the selectivity of C₂ products. These theoretical insights not only unveil the mechanistic origins of IL-induced performance enhancement but also offer predictive guidance for the rational design of advanced IL-catalyst systems for efficient CO₂ electroreduction.