Ionic Liquids as Interfacial Media for Metal-Free Electrochemical CO<sub>2</sub> Reduction in Water.

Abstract

The electrochemical carbon dioxide reduction reaction (CO₂RR) in water offers a sustainable pathway to mitigate carbon emissions while generating value-added chemicals. Most conventional CO₂RR systems rely heavily on metal-based catalysts. Beyond traditional metal-based catalyst design, attention has increasingly shifted to understanding how the electrochemical microenvironment and the electrode-electrolyte interface influence CO₂RR. Ionic liquids (ILs), widely regarded as green solvents, have previously been employed as electrolytes or cocatalysts in metal-catalyzed systems. Yet, the ability of ILs to facilitate CO₂RR at metal-free interfaces in aqueous media remains underexplored. Here, we demonstrate that ILs polarize CO₂ and facilitate CO₂ electrochemical response at a glassy carbon interface under aqueous conditions, while simultaneously functioning as electrolytes. Spectroscopic, electrochemical, and computational analyses reveal that ILs interact with CO₂, thereby increasing its dipole moment. This interaction suggests a favorable environment for CO₂ polarization that correlates with the observed electrochemical response. The response efficiency depends on the chemical identity of the ILs, highlighting the tunability of this IL-based system. These findings redefine the functional role of ILs in CO₂RR, establishing IL-induced molecular polarization as a potential strategy for promoting the reactivity of otherwise inert molecules. More broadly, this work introduces IL-driven dipole modulation as a general approach for enabling reactivity of nonpolar small molecules, with implications for sustainable chemical synthesis.