Exploration of the anion effect on the electrical conductivity of ionic liquids
Carlos F.P. Miranda, Luı́s M. N. B. F. Santos
Abstract
The effect of the anion on the electrical conductivity of ionic liquids was explored by a high-precision study of the temperature dependence (283–333 K) of the electrical conductivity of ten ILs based on the 1-butyl-3-methylimidazolium cation, [C 4 C 1 im] + . The following trend was observed for the molar conductivity at the reference temperature of 298.15 K: Ac < PF 6 − < BETI < OTf < TFA < BF 4 − < FAP < NTf 2 < FSI < DCA. The molar conductivity at infinite temperature, A Λ , and the energy barrier, E Λ , derived from the Vogel–Fulcher–Tammann equation (VFT) fitting were found to correlate well with the shape/size/dynamics and cohesive energy/charge localization of the studied ions. An extensive revision and comparison with the available experimental electrical conductivity data for the studied ionic liquids is also presented. Additionally, this work presents a detailed description, testing, and evaluation of performance results of a new system/methodology for the high-precision measurement of the electrical conductivity of ionic fluids, designed to minimize the size of the ionic liquid sample and in situ degassing of the sample. The measuring system is based on a high-precision LCR meter and a conductivity cell system designed to ensure the vacuum and gastightness of the sample container. The high-precision temperature control is ensured by a customized thermal chamber based on a heating and cooling Peltier system. The electrical conductivity data were corrected for the effect of solution polarization by extrapolating the resistance to infinite frequency. The accuracy and resolution of the system were evaluated by measuring the conductivity of the reference ionic liquid, [C 6 C 1 im][NTf 2 ] which was found to be in excellent agreement with the recommended data.