Electric double layer studies at the interface of mercury–binary ionic liquid mixtures with a common anion

Abstract

To gain deeper insight into the structure of the electrode–ionic liquid interface differential capacitance–potential curves have been acquired through electrochemical impedance measurements at the mercury electrode. Understanding the role of the nature and size of the ionic species in the ionic liquid, namely the influence of different lengths of alkyl side chains of the imidazolium cation on the structure of the double layer, is the aim of the work being carried out. Differential capacitance–potential curves were obtained at the mercury electrode in contact with various mixtures of room-temperature ionic liquids of varying cation chain length (1-alkyl-3-methylimidazolium, [C_nMIM]⁺ where n = 2, 6 and 12) with the same anion (bis(trifluoromethylsulfonyl)imide, [Tf₂N]⁻). For comparison purposes we have also carried out electrochemical measurements of the pure ionic liquids under the same conditions. Systematic variations in the electrocapillary drop-time curves and capacitance were found with increasing amounts of the cation with longer alkyl chains in the mixture. The electrocapillary curve results may be interpreted as indicating the preferential adsorption of the longer alkyl group on the mercury surface.