(Invited) Probing Electrochemical Ionic Liquid Interfaces

Abstract

Ionic liquids are known to be excellent solvents but their relatively high viscosities can inhibit electrochemical reactions. We describe mixtures of two common ionic liquids, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM OTf) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM OTf), with two common molecular solvents, water and acetonitrile. We analyze the solution viscosity and correlate this to the dynamic response of the electrochemical double layer by recording current vs. time and voltage vs. time transients upon (de)polarization of the electrode. We also test the effects of the added co-solvents in the context of the electrochemical reduction of carbon dioxide. We find that adding water to the ionic liquid significantly reduces the overpotential for the reduction, and that adding acetonitrile significantly increases the current density, matching some of the best performance data currently reported for this reaction. Our results suggest that a three-part mixture of ionic liquid, water, and acetonitrile may lead to further improvements in reaction efficiency.