A Bifunctional Ionic Liquid for Capture and Electrochemical Conversion of CO₂ to CO over Silver

Electrochemical conversion of CO₂ requires selective catalysts and high solubility of CO₂ in the electrolyte to reduce the energy requirement and increase the current efficiency. In this study, the CO₂ reduction reaction (CO₂RR) over Ag electrodes in acetonitrile-based electrolytes containing 0.1 M [EMIM][2-CNpyr] (1-ethyl-3-methylimidazolium 2-cyanopyrolide), a reactive ionic liquid (IL), is shown to selectively (>94%) convert CO₂ to CO with a stable current density (6 mA·cm^-2) for at least 12 h. The linear sweep voltammetry experiments show the onset potential of CO₂ reduction in acetonitrile shifts positively by 240 mV when [EMIM][2-CNpyr] is added. This is attributed to the pre-activation of CO₂ through the carboxylate formation via the carbene intermediate of the [EMIM]⁺ cation and the carbamate formation via binding to the nucleophilic [2-CNpyr]^- anion. The analysis of the electrode-electrolyte interface by surface-enhanced Raman spectroscopy (SERS) confirms the catalytic role of the functionalized IL where the accumulation of the IL-CO₂ adduct between -1.7 and -2.3 V vs Ag/Ag⁺ and the simultaneous CO formation are captured. This study reveals the electrode surface species and the role of the functionalized ions in lowering the energy requirement of CO₂RR for the design of multifunctional electrolytes for the integrated capture and conversion.