The Mechanism and Enhancement of Imidazolium-Mediated CO2 Reduction on Silver in Non-Aqueous Electrolytes

Electrocatalysis of carbon dioxide reduction reaction (CO 2 RR) is known to proceed at lower overpotentials with the presence of ionic liquids (ILs) in the electrolyte. However, the role of ILs in modulating CO 2 RR, even for the most studied 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF 4 ]) remains unclear. In this study, the electric field and the hydrogen bonding effects induced by [EMIM][BF 4 ] and hydrogen bond donors (HBDs), including water and a series of alcohols, in acetonitrile were examined on Ag. By employing voltammetry, in-situ enhanced Raman spectroscopy (SERS), and density functional theory (DFT) calculations, we reveal that the initial electron transfer to CO 2 occurs at reduced overpotentials when it is confined between the [EMIM] + ring planes and the electrode surface. This confinement of CO 2 stabilizes it at the interface and enables its conversion to CO, accompanied by the generation of carbene and water as by-products. Furthermore, our findings suggest water (< 0.5 M) acts as the hydrogen bond donor as opposed to serving as the primary source of free protons. Based on this finding, we further show how the extend of hydrogen bonding as varied by various alcohols alter the microenvironment in synergy with [EMIM] + at the electrode-electrolyte interface for fine tuning of the thermodynamics of CO 2 RR. The clarified role of the imidazolium based ILs and hydrogen bond donors, and the demonstrated enhancement in CO 2 RR will advance non-aqueous electrolyte development and inform future kinetic studies.