Influence of Imidazolium Pyrrole-2-Carbonitrile on the Electrochemical Reduction of CO₂ on Silver Metal in Acetonitrile

Abstract

Electrochemical reduction of CO2 into value-added fuels or chemical feedstocks is one of several viable strategies for mitigating carbon dioxide waste. However, CO2 is thermodynamically stable molecule requiring high energy to activate it making this process energy demanding. Therefore, selective catalysts and stable electrolytes with high CO2 solubility are desired. Ionic liquids (ILs) are versatile solvents with tunable properties including high CO2 solubility and electrochemical stability. Literature suggests that ILs co-catalyze the CO2 reduction reaction and can alter the reaction route through its specific interactions with CO2 and reaction intermediates. Therefore, in this study, we examined the influence of 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]) IL on CO2 reduction in acetonitrile on Ag surface. [EMIM][2-CNpyr] has the carbene, N-heterocyclic, and amine functionalities to complex with CO2. The performed linear sweep voltammetry experiments shows the onset potential of CO2 reduction is -1.82 V (vs. Ag/Ag+) in the presence of the IL. This is confirmed to be due to the presence of the IL when compared to the control experiments with tetraethylammonium perchlorate which is a non-reactive supporting salt. The bulk electrolysis with 1.5 M [EMIM][2-CNpyr] in acetonitrile over Ag cathode showed reduction of CO2 to carbon monoxide (CO) with high selectivity (>80 %) at -2.1 V (vs. Ag/Ag+) and stable current density (~ 6 mA·cm−2) for at least 12 h without any electrolyte decomposition as confirmed by NMR analysis. The fundamental understanding of the interfacial microenvironment is needed and spectro-electrochemical studies are currently underway to probe these interfaces and to develop similarly high performing electrolytes for implementation of combined carbon capture and utilization in the future.