Proton-Conducting Properties of a Brnsted Acid-Base Ionic Liquid and Ionic Melts Consisting of Bis(trifluoromethanesulfonyl)imide a
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- 作者：Hirofumi Nakamoto ; Akihiro Noda ; Kikuko Hayamizu ; Satoshi Hayashi ; Hiro-o Hamaguchi ; Masayoshi Watanabe
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：January 25, 2007
- 年：2007
- 卷：111
- 期：3
- 页码：1541 - 1548
- 全文大小：362K
- 年卷期：v.111,no.3(January 25, 2007)
- ISSN：1932-7455
文摘
A novel protic ionic liquid and ionic melts consisting of a Br
nsted acid and base were prepared with thecombination of bis(trifluoromethanesulfonyl)imide (HTFSI) and benzimidazole (BIm) at various molar ratios.The thermal properties, ionic conductivities, 1H-NMR chemical shifts, Raman spectra, 1H and 19F self-diffusioncoefficients, and electrochemical polarization curves were explored. A mixture at the equivalent molar ratioformed a protic neutral salt, and its thermal stability was higher than 350 
C. The phase diagram of theBIm-HTFSI binary mixtures revealed that stoichiometric complexes other than the neutral salt were foundat [BIm]/[HTFSI] = 2/1 and 6/1. In these BIm excess compositions, fast proton exchange reactions betweenprotonated BIm (HBIm+) and free BIm were observed at 140 C, where BIm and HBIm+ were indistinguishableby 1H-NMR but were distinguishable by Raman spectroscopy. The proton transfer became faster and also theproton transference number increased with increasing BIm mole fraction. The neutral and base-rich BIm-HTFSI melts exhibited electroactivities for H2 oxidation and O2 reduction at a Pt electrode. The neutral saltwas hydrophobic and stable for the electrode reactions of H2 oxidation and O2 reduction even in the presenceof water at 150 C. The neutral and base-rich BIm-HTFSI melts can serve as H2/O2 fuel cell electrolytesunder entirely nonhumid conditions and at temperatures higher than 100 C. The polarization curves werecompared with those of conventional electrolytes, such as anhydrous H3PO4 and an aqueous H2SO4 solution;these indicate highly favorable characteristics of the BIm-HTFSI melts as fuel cell electrolytes.
nsted acid and base were prepared with thecombination of bis(trifluoromethanesulfonyl)imide (HTFSI) and benzimidazole (BIm) at various molar ratios.The thermal properties, ionic conductivities, 1H-NMR chemical shifts, Raman spectra, 1H and 19F self-diffusioncoefficients, and electrochemical polarization curves were explored. A mixture at the equivalent molar ratioformed a protic neutral salt, and its thermal stability was higher than 350 C. The phase diagram of theBIm-HTFSI binary mixtures revealed that stoichiometric complexes other than the neutral salt were foundat [BIm]/[HTFSI] = 2/1 and 6/1. In these BIm excess compositions, fast proton exchange reactions betweenprotonated BIm (HBIm+) and free BIm were observed at 140 C, where BIm and HBIm+ were indistinguishableby 1H-NMR but were distinguishable by Raman spectroscopy. The proton transfer became faster and also theproton transference number increased with increasing BIm mole fraction. The neutral and base-rich BIm-HTFSI melts exhibited electroactivities for H2 oxidation and O2 reduction at a Pt electrode. The neutral saltwas hydrophobic and stable for the electrode reactions of H2 oxidation and O2 reduction even in the presenceof water at 150 C. The neutral and base-rich BIm-HTFSI melts can serve as H2/O2 fuel cell electrolytesunder entirely nonhumid conditions and at temperatures higher than 100 C. The polarization curves werecompared with those of conventional electrolytes, such as anhydrous H3PO4 and an aqueous H2SO4 solution;these indicate highly favorable characteristics of the BIm-HTFSI melts as fuel cell electrolytes.