NMR Studies of Proton Transport in Anhydrous Polymer Electrolytes for High Temperature Fuel Cells

Authors

  • H. A. Every,

    1. Hydrogen and Clean Fossil Fuels, Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands
    2. Nanostructured Materials, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
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  • L. D. Ionescu,

    1. Hydrogen and Clean Fossil Fuels, Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands
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  • M. P. de Heer,

    1. Hydrogen and Clean Fossil Fuels, Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands
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  • Y. Álvarez-Gallego,

    1. Hydrogen and Clean Fossil Fuels, Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands
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  • G. J. M. Janssen

    1. Hydrogen and Clean Fossil Fuels, Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands
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  • Paper presented at the CARISMA workshop on ‘Ionomer Membranes for Medium and High Temperature Fuel Cells’, Stuttgart, 2007.

Abstract

This paper presents an NMR study of the dynamic processes related to proton transport in a new polymer consisting of two blocks – poly(2,6-diphenylphenol) (P3O) and an imidazole functionalised poly(2,6-dimethylphenol) (imi-PPE) – and subsequently doped with polyphosphoric acid (PPA). From 1H and 31P NMR relaxation and diffusion measurements of the individual homopolymers and block copolymer, it was observed that addition of PPA significantly enhanced the mobility of imi-PPE and the imi-block copolymer, but not of P3O. The similarity in 1H T2 values between imi-PPE and the imi-block copolymer suggests that the relaxation behaviour in the block copolymer is dominated by the imi-PPE phase. 1H diffusion in P3O and the imi-block copolymer were comparable to pure PPA, suggesting that the proton diffusion is similar in each case. For imi-PPE, the diffusion coefficients were several orders of magnitude lower, reflecting a restricted diffusion process that is not indicative of the proton mobility. For all three polymers, the 31P T2 relaxation behaviour and inability to measure 31P diffusion coefficients imply hindered translational motion of the phosphonate groups. From these results, it can be concluded that hydrogen bonds between the phosphoric acid and the polymer form a network that facilitates proton transport via a hopping mechanism.

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