1-Alkyl-3-methylimidazolium bis(perfluoroalkylsulfonyl)imide water-immiscible ionic liquids - The effect of water on electrochemical and physical properties

The electrochemical and physical properties of a class of 1-n-alkyl-3-methylimidazolium (C(n)mim) bis(perfluoroalkylsulfonyl)imide room-temperature ionic liquids (RTILs) is reported. By varying the chain length on the cation (n = 6, 8, and 10) and the perfluorinated carbon chains of the imide anions, -CF3 (BMSI) to -CF2CF3 (BETI), the effect on water content, viscosity, conductivity, and potential window has been examined. The water content of the RTILs, both ambient and water-equilibrated, varies linearly with the imidazolium alkyl chain length. The viscosities of the water-equilibrated BMSI- and BETI-based RTILs were accurately calculated using a linear combination of the viscosity of water and the ambient RTILs. The conductivities for this series ranges from 2.9 mS/cm (C(6)mimBMSI) to 0.92 mS/cm (C(10)mimBETI) and were accurately estimated based on the viscosity, density, and molecular weight. The potential windows of the ambient RTILs are 4.3 and 4.9 V for the BMSI and BETI salts, respectively. The window is reduced to 3.9 and 4.3 V upon equilibration with water. The reversible electrochemistry of ferrocene (DeltaE(p) = 70 mV) and decamethylferrocene (DeltaE(p) = 63 mV) has been measured in water-equilibrated imide-based RTILs with as much as 23 mol% H2O. (C) 2004 The Electrochemical Society.