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Abstract This study examines the activity of chemisorbed CO2 species in the microenvironment formed by bifunctional ionic liquids (ILs) in the reactive capture and conversion (RCC) of CO2 to CO on silver. Comparative electroanalytical measurements with imidazolium based ILs were performed to probe the impact of electrostatic interactions, anion and cation basicity, and hydrogen bonding on RCC. Particularly, ILs with 1-ethyl,3-methylimidazolium ([EMIM]+) and 1-ethyl, 2,3-methylimidazolium ([EMMIM]+) cations and aprotic heterocyclic anions of 2-cyanopyrrolide ([2-CNpyr]) and 1,2,4-triazolide ([1,2,4-Triz]) were examined for RCC. It was found that anion–CO2 carbamate complexes facilitate RCC at significantly lower overpotentials compared to cation–CO2 carboxylate complexes. Additionally, [EMIM]+ was found to better stabilize anion–CO2 complexes than [EMMIM]+. Furthermore, it was found that 2-CNpyrH that naturally forms in CO2 absorption competes for electrode surface adsorption with the anion–CO2 carbamate complex, thereby reducing the electrochemical activity of the anion–CO2 complex. These results highlight the importance of IL structure in tuning the interfacial interactions and suggest that ILs with anion-dominated CO2 chemisorption enhances CO2 utilization in RCC applications. 

Abstract Electrochemical CO₂reduction (CO₂RR) on copper (Cu) shows promise for higher‐value products beyond CO. However, challenges such as the limited CO₂solubility, high overpotentials, and the competing hydrogen evolution reaction (HER) in aqueous electrolytes hinder the practical realization. We propose a functionalized ionic liquid (IL) which generates ion‐CO₂adducts and a hydrogen bond donor (HBD) upon CO₂absorption to modulate CO₂RR on Cu in a non‐aqueous electrolyte. As revealed by transient voltammetry, electrochemical impedance spectroscopy (EIS), and in situ surface‐enhanced Raman spectroscopy (SERS) complemented with image charge augmented quantum‐mechanical/molecular mechanics (IC‐QM/MM) computations, a unique microenvironment is constructed. In this microenvironment, the catalytic activity is primarily governed by the IL and HBD concentrations; former controlling the double layer thickness and the latter modulating the local proton availability. This translates to ample CO₂availability, reduced overpotential, and suppressed HER where C₄products are obtained. This study deepens the understanding of electrolyte effects in CO₂RR and the role of IL ions towards electrocatalytic microenvironment design. 

The roles of the ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), and water in controlling the mechanism, energetics, and electrocatalytic activity of CO2 reduction to CO on silver in nonaqueous electrolytes were investigated. The first electron transfer occurs to CO2 at reduced overpotentials when it is trapped between the planes of the [EMIM]+ ring and the electrode surface due to cation reorientation as determined from voltammetry, in situ surface-enhanced Raman spectroscopy, and density functional theory calculations. Within this interface, water up to 0.5 M does not induce significant Faradaic activity, opposing the notion of it being a free proton source. Instead, water acts as a hydrogen bond donor, and the proton is sourced from [EMIM]+. Furthermore, this study demonstrates that alcohols with varying acidities tune the hydrogen bonding network in the interfacial microenvironment to lower the energetics required for CO2 reduction. The hydrogen bonding suppresses the formation of inactive carboxylate species, thus preserving the catalytic activity of [EMIM]+. The ability to tune the hydrogen bonding network opens new avenues for advancing IL-mediated electrocatalytic reactions in nonaqueous electrolytes. 

Formation of C‐N bonds through the electrochemical utilization of CO2 and nitrogen containing compounds (N‐compounds) is appealing for the purpose of converting waste and readily available sources or pollutants into value added chemicals at ambient conditions. Existing research predominantly explores these electrochemical reactions independently, often in aqueous electrolytes, leading to challenges associated with competitive hydrogen evolution reaction (HER), low product selectivity, and yield. Functional electrolytes such as those containing ionic liquids (ILs) present selective solubility to the solute reactants and present unique interactions with the electrode surface that can suppress the undesired side reaction HER while simultaneously co‐catalyzing the conversion of CO2 and N‐compounds such as N2, NO, NO2, andNO3. In this concept paper, we discuss how the microenvironment enabled by ILs can be  leveraged to stabilize reaction intermediates at the electrode‐electrolyte interface, thereby promoting C‐N bond formation on an active electrode surface at reduced overpotential, with the case study of CO2 and N‐compounds co‐catalysis to generate urea. 

Ionic liquids (ILs) and deep eutectic solvents (DESs) have tremendous potential for reactive capture of CO₂, due to their highly properties, including a wide electrochemical stability window, low volatility, and high CO₂solubility.