File(s) under permanent embargo

Proton transport properties in zwitterion blends with brønsted acids

journal contribution
posted on 18.11.2010, 00:00 authored by M Yoshizawa-Fujita, Nolene ByrneNolene Byrne, Maria ForsythMaria Forsyth, D MacFarlane, H Ohno
We describe zwitterion, 3-(1-butyl-1H-imidazol-3-ium-3-yl)propane-1-sulfonate (Bimps), mixtures with 1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methanesulfoneamide (HN(Tf)2) as new proton transport electrolytes. We report proton transport mechanisms in the mixtures based on results from several methods including thermal analyses, the complex-impedance method, and the pulsed field gradient spin echo NMR (pfg-NMR) method. The glass transition temperature (Tg) of the mixtures decreased with increasing HN(Tf)2 concentration up to 50 mol %. The Tg remained constant at −55 °C with further acid doping. The ionic conductivity of HN(Tf)2 mixtures increased with the HN(Tf)2 content up to 50 mol %. Beyond that ratio, the mixtures showed no increase in ionic conductivity (10−4 S cm−1 at room temperature). This tendency agrees well with that of Tg. However, the self-diffusion coefficients obtained from the pfg-NMR method increased with HN(Tf)2 content even above 50 mol % for all component ions. At HN(Tf)2 50 mol %, the proton diffusion of HN(Tf)2 was the fastest in the mixture. These results suggest that Bimps cannot dissociate excess HN(Tf)2, that is, the excess HN(Tf)2 exists as molecular HN(Tf)2 in the mixtures. The zwitterion, Bimps, forms a 1:1 complex with HN(Tf)2 and the proton transport property in this mixture is superior to those of other mixing ratios. Furthermore, CH3SO3H and CF3SO3H were mixed with Bimps for comparison. Both systems showed a similar tendency, which differed from that of the HN(Tf)2 system. The Tg decreased linearly with increasing acid content for every mixing ratio, while the ionic conductivity increased linearly. Proton transport properties in zwitterion/acid mixtures were strongly affected by the acid species added.

History

Journal

Journal of physical chemistry B

Volume

114

Issue

49

Pagination

16373 - 16380

Publisher

American chemical society

Location

Washington, D.C.

ISSN

1520-6106

eISSN

1520-5207

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2010, American Chemical Society