Molecular dynamics studies of the Nafion, Dow and Aciplex fuel-cell polymer membrane systems.
The Nafion, Dow and Aciplex systems--where the prime differences lies in the side-chain length--have been studied by molecular dynamics (MD) simulation under standard pressure and temperature conditions for two different levels of hydration: 5 and 15 water molecules per (H)SO(3) end-group. Structural features such as water clustering, water-channel dimensions and topology, and the dynamics of the hydronium ions and water molecules have all been analysed in relation to the dynamical properties of the polymer backbone and side-chains. It is generally found that mobility is promoted by a high water content, with the side-chains participating actively in the H(3)O(+)/H(2)O transport mechanism. Nafion, whose side-chain length is intermediate of the three polymers studied, is found to have the most mobile polymer side-chains at the higher level of hydration, suggesting that there could be an optimal side-chain length in these systems. There are also some indications that the water-channel network connectivity is optimal for high water-content Nafion system, and that this could explain why Nafion appears to exhibit the most favourable overall hydronium/water mobility.
Chemistry Department, Macromolecular and Interfaces Institute, Virginia Tech, Blacksburg, VA 24061, USA. brandell@vt.edu
Daniel
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Brandell
Jaanus
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Karo
Anti
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Liivat
John O
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Thomas
D003198:Computer Simulation; D011211:Electric Power Supplies; D004563:Electrochemistry / Q000295:instrumentation; D005465:Fluorocarbon Polymers / Q000737:chemistry; D007477:Ions; D008567:Membranes, Artificial; D008956:Models, Chemical; D008958:Models, Molecular; D008962:Models, Theoretical; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry
D005465:Fluorocarbon Polymers; D007477:Ions; D008567:Membranes, Artificial; D011108:Polymers; D014867:Water; C040402:perfluorosulfonic acid