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Molecular dynamics studies of the Nafion®, Dow® and Aciplex® fuel-cell polymer membrane systems
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
2007 (English)In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 13, no 10, 1039-1046 p.Article in journal (Refereed) Published
Abstract [en]

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)SO3 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 H3O+/H2O 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.

Place, publisher, year, edition, pages
2007. Vol. 13, no 10, 1039-1046 p.
Keyword [en]
Molecular dynamics, Nafion membrane, Proton exchange membrane fuel cell (PEMFC), Side-chain length
National Category
Chemical Sciences
URN: urn:nbn:se:uu:diva-13970DOI: 10.1007/s00894-007-0230-7ISI: 000248912300002PubMedID: 17665227OAI: oai:DiVA.org:uu-13970DiVA: diva2:41740
Available from: 2008-01-28 Created: 2008-01-28 Last updated: 2011-01-27Bibliographically approved
In thesis
1. The Rôle of Side-Chains in Polymer Electrolytes for Batteries and Fuel Cells
Open this publication in new window or tab >>The Rôle of Side-Chains in Polymer Electrolytes for Batteries and Fuel Cells
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The subject of this thesis relates to the design of new polymer electrolytes for battery and fuel cell applications. Classical Molecular Dynamics (MD) modelling studies are reported of the nano-structure and the local structure and dynamics for two types of polymer electrolyte host: poly(ethylene oxide) (PEO) for lithium batteries and perfluorosulfonic acid (PFSA) for polymer-based fuel cells. Both polymers have been modified by side-chain substitution, and the effect of this on charge-carrier transport has been investigated. The PEO system contains a 89-343 EO-unit backbone with 3-15 EO-unit side-chains, separated by 5-50 EO backbone units, for LiPF6 salt concentrations corresponding to Li:EO ratios of 1:10 and 1:30; the PFSA systems correspond to commercial Nafion®, Hyflon® (Dow®) and Aciplex® fuel-cell membranes, where the major differences again lie in the side-chain lengths.

The PEO mobility is clearly enhanced by the introduction of side-chains, but is decreased on insertion of Li salts; mobilities differ by a factor of 2-3. At the higher Li concentration, many short side-chains (3-5 EO-units) give the highest ion mobility, while the mobility was greatest for side-chain lengths of 7-9 EO units at the lower concentration. A picture emerges of optimal Li+-ion mobility correlating with an optimal number of Li+ ions in the vicinity of mobile polymer segments, yet not involved in significant cross-linkages within the polymer host.

Mobility in the PFSA-systems is promoted by higher water content. The influence of different side-chain lengths on local structure was minor, with Hyflon® displaying a somewhat lower degree of phase separation than Nafion®. Furthermore, the velocities of the water molecules and hydronium ions increase steadily from the polymer backbone/water interface towards the centre of the proton-conducting water channels. Because of its shorter side-chain length, the number of hydronium ions in the water channels is ~50% higher in Hyflon® than in Nafion® beyond the sulphonate end-groups; their hydronium-ion velocities are also ~10% higher.

MD simulation has thus been shown to be a valuable tool to achieve better understanding of how to promote charge-carrier transport in polymer electrolyte hosts. Side-chains are shown to play a fundamental rôle in promoting local dynamics and influencing the nano-structure of these materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 52 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 635
molecular dynamics, polymer electrolytes, side-chains, Li-ion batteries, proton exchange membrane fuel cell (PEMFC), PFSA membrane
National Category
Other Chemistry Topics Atom and Molecular Physics and Optics
Research subject
Materials Science
urn:nbn:se:uu:diva-100738 (URN)978-91-554-7499-7 (ISBN)
Public defence
2009-05-11, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2009-04-20 Created: 2009-04-06 Last updated: 2012-10-09

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