Z. Naturforsch. 68a, 101 – 111 (2013)
Molecular Simulations of Hydrated Proton Exchange Membranes: the Structure
Gabriel Marchand1,2, Philippe A. Bopp2, and Eckhard Spohr1
1 Lehrstuhl für Theoretische Chemie, Fakultät für Chemie, Universität Duisburg-Essen, Campus Essen (S05 V06 E15), Universitätsstraße 5, DE-45141 Essen
2 Department of Chemistry, Université de Bordeaux, 351 Cours de la Libération Bât A12, FR-33405 Talence CEDEX
Received September 27, 2012 / published online February 15, 2013
Reprint requests to: P. A. B.; E-mail: philippebopp@yahoo.com
The structure of two hydrated proton exchange membranes for fuel cells (PEMFC), Nafion® (Dupont) and Hyflon® (Solvay), is studied by all-atom molecular dynamics (MD) computer simulations. Since the characteristic times of these systems are long compared to the times for which they can be simulated, several different, but equivalent, initial configurations with a large degree of randomness are generated for different water contents and then equilibrated and simulated in parallel. A more constrained structure, analog to the newest model proposed in the literature based on scattering experiments, is investigated in the same way. One might speculate that a limited degree of entanglement of the polymer chains is a key feature of the structures showing the best agreement with experiment. Nevertheless, the overall conclusion remains that the scattering experiments cannot distinguish between the several, in our view equally plausible, structural models.

We thus find that the characteristic features of experimental scattering curves are, after equilibration, fairly well reproduced by all systems prepared with our method. We thus study in more detail some structural details. We attempt to characterize the spatial and size distribution of the water rich domains, which is where the proton diffusion mostly takes place, using several clustering algorithms.

Key words: Molecular Dynamics; Nafion; Equilibration; Structure; Clustering.
PACS numbers: 61.20Gy; 61.20Ja; 61.20.Qg; 61.25.H-
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