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Issue 37, 2010
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Proton transport in choline dihydrogen phosphate/H3PO4 mixtures

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Mixtures of the plastic crystal material choline dihydrogen phosphate [Choline][DHP] and phosphoric acid, from 4.5 mol% to 18 mol% H3PO4, were investigated and shown to have significantly higher proton conductivity compared to the pure [Choline][DHP]. This was particularly evident from the electrochemical hydrogen reduction reaction and the proton NMR diffusion measurements, in addition to ionic conductivity measured from the impedance spectroscopy. The ionic conductivity was observed to increase by more than an order of magnitude in phase I (i.e. the highest temperature solid phase in [Choline][DHP]) reaching up to 10−2 S cm−1. The multinuclear NMR spectroscopy data suggest that, at least on the timescale of the NMR measurement, the H+ cations and [DHP] anions are equivalent in both phases. The pulsed field gradient NMR diffusion measurements of the 18 mol% acid sample indicate that all three ions are mobile, however the H+ diffusion coefficient is an order of magnitude higher than for the [Choline] cation or the [DHP] anion, and therefore conduction in these materials is dominated by proton conductivity. The thermal stability, as measured by TGA, is unaffected with increasing acid additions and remains high; i.e. no significant mass loss below 200 °C.

Graphical abstract: Proton transport in choline dihydrogen phosphate/H3PO4 mixtures

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Publication details

The article was received on 08 Apr 2010, accepted on 18 Jun 2010 and first published on 02 Aug 2010

Article type: Paper
DOI: 10.1039/C0CP00156B
Phys. Chem. Chem. Phys., 2010,12, 11291-11298

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    Proton transport in choline dihydrogen phosphate/H3PO4 mixtures

    U. A. Rana, P. M. Bayley, R. Vijayaraghavan, P. Howlett, D. R. MacFarlane and M. Forsyth, Phys. Chem. Chem. Phys., 2010, 12, 11291
    DOI: 10.1039/C0CP00156B

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