Electrochemical Capacitors Using Fluorohydrogenate Ionic Liquid Electrolytes

Abstract

Electrochemical capacitors using fluorohydrogenate ionic liquids show a large voltage dependence of capacitance with a maximum at a charging voltage around 2.5 V, resulting in a larger capacitance than those using other typical ionic liquid electrolytes. The voltage dependence becomes less remarkable with decrease in the HF composition n in EMIm(FH)nF (EMIm: 1-ethyl-3-methylimidazolium). Cyclic voltammetry using an activated carbon working electrode revealed that two redox reactions occur at the higher and lower potentials against the rest potential in EMIm(FH)2.3F. These Faradaic processes contribute to the voltage dependence of capacitance.