Fundamental Studies on Ionic Liquids and Ion Gels for Functional Materials

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This study has aimed at understanding fundamental properties of ionic liquids and ion gels and at making new concept for their functionalization as new materials. Efforts have been focused on(1)Ion dynamics and "ionicity" of ionic liquids and ion gels(2)Development of thermally stable proton-conducting ionic liquids and ion gels under non-humid conditions and their application to fuel cells at > 1000C(3)Electron transporting ionic liquids and ion gels and their application to dye-sensitized solar cellsIon dynamics in common ionic liquids has been systematically explored by means of ionic conductivity measurements and pulsed-gradient spin echo NMR (pgse-NMR) measurements, and "ionicity" of the ionic liquids was proposed based on the both measurements. The ionicity corresponds to the self-dissociation degree of the ionic liquids and was found to closely correlate with Lewis acidity of the cations and Lewis basicity of the anions. It has been revealed by this study that the ionicity is lo … More wer than unity for the ionic liquids, indicating the formation of ionic clusters. Regarding to proton conducting ionic liquids, the existence of Grotthuss-type proton transfer through the hydrogen-bonding network formed in the ionic liquids was clearly demonstrated in this study for the first time, which greatly enhances the proton diffusivity and the proton transference number. Also it was discovered in this study that hydrogen oxidation and oxygen reduction occurs at the interface between the ionic liquids and Pt, which opens up the possible application of the proton conducting ionic liquids as electrolyte of fuel cells under non-humid and medium temperature operation. Thorough the investigation of more than 70 proton-conducting ionic liquids, diethylmethylammonium trifluoromethanesulfonate was found to exhibit excellent properties as fuel cell electrolyte in terms of high proton conductivity, high thermal stability, and facile electrochemical reactions at the interface. Furthermore, polyiodide ions in ionic liquids transport electron through electron self-exchange reactions, quite interestingly which is only observed in ionic liquids and not in molecular liquids. The ionic liquids containing polyiodide ions have been utilized in dye-sensitized solar cells, long-term stability of which is greatly enhanced, compared with solar cells using molecular solvents, without losing the photo-electron conversion efficiency. The ionic liquid electrolytes can be solidified by the addition of nanoparticle with the acceleration of the charge transport rate. Less