Molecular Dynamics Modeling of Proton Transport in Nafion and Hyflon Nanostructures
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- 作者：Jaanus Karo ; Alvo Aabloo ; John O. Thomas ; Daniel Brandell
- 刊名：Journal of Physical Chemistry B
- 出版年：2010
- 出版时间：May 13, 2010
- 年：2010
- 卷：114
- 期：18
- 页码：6056-6064
- 全文大小：406K
- 年卷期：v.114,no.18(May 13, 2010)
- ISSN：1520-5207
文摘
Classical molecular dynamics modeling studies at 363 K are reported of the local atomic-level and macroscopic nanostructures of two well-known perfluorosulfonic acid proton exchange polymer membrane materials: Nafion and Hyflon. The influence of the different side-chain lengths in the two polymers on local structure is relatively small: Hyflon exhibits slightly greater sulfonate-group clustering, while Nafion has more isolated side chains with a higher degree of hydration around the SO3− side-chain ends. This results in shorter mean residence times for water molecules around the end groups in Nafion. Hyflon also displays a lower degree of phase separation than Nafion. The velocities of the water molecules and hydronium ions are seen to increase steadily from the polymer backbone/water interface toward the center of the water channels. Because of its shorter side chains, the number of hydronium ions is 50% higher at the center of the water channels in Hyflon, and their velocities are 10% higher. The water and H3O+ diffusion coefficients are therefore higher in the shorter side-chain Hyflon system: 6.5 × 10−6 cm2/s and 25.2 × 10−6 cm2/s, respectively; the corresponding values for Nafion are 6.1 × 10−6 cm2/s and 21.3 × 10−6 cm2/s, respectively. These calculated values compare well with experiment: 4 × 10−6 cm2/s for vehicular H3O+ diffusion.