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Nafion® Membranes: Molecular Diffusion, Proton Conductivity and Proton Conduction Mechanism

Published online by Cambridge University Press:  25 February 2011

Klaus-Dieter Kreuer
Affiliation:
Max-Planck-Institut für Festkörperforschung Heisenbergstr.1, W-7000 Stuttgart-80, Germany
Thomas Dippel
Affiliation:
Max-Planck-Institut für Festkörperforschung Heisenbergstr.1, W-7000 Stuttgart-80, Germany
Wolfgang Meyer
Affiliation:
Max-Planck-Institut für Polymerforschung, Ackermannweg 10 W-6500 Mainz, Germany
Joachim Maier
Affiliation:
Max-Planck-Institut für Festkörperforschung Heisenbergstr.1, W-7000 Stuttgart-80, Germany
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Abstract

H-PFG-NMR diffusion and proton conductivity data for NAFION® 117 is presented as a function of temperature and water content. From this, H2O diffusion on a molecular scale is concluded to be similar to the one in bulk water. But “geometrical” restrictions of diffusion lead to a decreasing pre-exponential factor, i.e. decreasing macroscopic diffusion coefficient with decreasing water content. It is shown that proton conductivity is correlated with water diffusion for low degrees of hydration (vehicle mechanism). With increasing hydration there is an increasing contribution from “structure diffusion” culminating in an amplification factor of A = 2.5 for fully hydrated protonic NAFION® 117 at room temperature. The bonding of water in NAFION® as well as the local environment (hydration) of the acidic proton are concluded to be similar as in acidic aqueous solutions.

Type
Research Article
Copyright
Copyright © Materials Research Society 1993

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