Water-induced accelerated ion diffusion: voltammetric studies in 1-methyl3-[2,6-(S)-dimethylocten-2-yl]imidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids

The electrochemical properties of the room temperature ionic liquids 1-buty l-3-methylimidazolium tetrafluoroborate (BMIM+BF4-), 1-butyl-3-methylimidaz olium hexafluorophosphate (BMIM+PF6-) and 1-methyl-3-[2,6-(S)-dimethylocten -2-yl]imidazolium tetrafluoroborate (MDIM+BF4-) as solvents have been studi ed using micro-samples, with a volume of 10 muL, of the ionic liquids under vacuum conditions and under conditions with controlled gas and moisture su pplies. The impact of water-absorbed into the ionic liquid in a controlled manner from the gas phase-on the voltammetry of dissolved redox systems and on the accessible potential window of the ionic liquids was investigated. The diffusion coefficients for three representative redox systems, the oxid ation of neutral N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), the reduc tion of cationic methyl viologen (MV2+) and reduction of anionic hexacyanof errate(III), Fe(CN)(6)(3-), have been determined as a function of the water content of the ionic liquids. Water is shown to have a much more dramatic acceleration effect on the diffusion of the ionic compounds compared to its effect on neutral species in ionic liquids. A model based on nanoscale str uctural features of wet ionic liquid materials is proposed. The novel metho dology, which employs redox-active compounds dissolved or partitioned in mi crodroplets of ionic liquid, uses conditions suitable for the study of ioni c liquids for applications in electrochemical gas phase reactors and gas se nsor systems.