Role of the anion on the Interfacial Structure of Ionic Liquids Binary Mixtures at Mercury Interfaces

Electrified double-layer (EDL) of ionic liquids electrode interfaces have been attracting considerable interest both from the fundamental and applied points of view. So far from the large set of ionic liquids synthetized only a very limited number has been electrochemically studied. As a consequence, the effect of complex shape and chemical properties of the ions and surface morphology on the structure and mechanism of formation of EDL is far from being understood. Binary mixtures of ionic liquids with a common cation (1-ethyl-3-methylimidazolium) paired with two different anions (bis(trifuoromethylsulfonyl) imide, [Tf N-2](-) and tris(pentafluoroethyl)trifluorophosphate, [FAP](-)) were prepared and their molecular mixing behavior was followed through the changes in their vibrational structure by Fourier transform infrared (ATR-FT-IR) spectroscopy. The interface at Hg and each of the binary mixture was followed by electrochemical impedance spectroscopy and drop time measurements. Differential capacitance and charge-potential curves were obtained and compared with those corresponding to the pure liquids. The data is interpreted as suggesting the coexistence at the interface of a mixture of two limiting structures each of which containing essentially one of the anions and sharing the common cation in a co-network. (C) 2016 Elsevier Ltd. All rights reserved.