Pseudocapacitive behaviour of RuO 2 in a proton exchange ionic liquid

Abstract

We studied the electrochemical behaviour of a thermally-prepared RuO 2 electrode in a protic ionic liquid made from 2-methylpyridine and trifluoroacetic acid to determine if the current obtained on such electrode originates from double-layer charging or from pseudocapacitance. A thorough comparison of the electrochemical behavior in the ionic liquid and in aqueous electrolyte confirmed that pseudocapacitance is observed. The shape of the cyclic voltammograms obtained for the RuO 2 electrode in the protic ionic liquid is similar to that obtained in H 2SO 4 and shows distinct redox peaks attributed to Faradaic reactions across the electrolyte∣electrode interface, which give rise to pseudocapacitance. The specific capacitance of the electrode in the protic ionic liquid (83 F g −1) is in the same order of magnitude to that obtained in water-based electrolyte but is ten times higher than that in an aprotic ionic liquid composed of 1-ethyl-3-methylimidazolium tetrafluoroborate. Our observations lead to the conclusion that pseudocapacitance can occur on a ruthenium dioxide electrode in an ionic liquid. Our results could be of interest to develop new metal oxide electrochemical capacitors based on non-aqueous electrolytes.