Comparison of the Hydration and Diffusion of Protons in Perfluorosulfonic Acid Membranes with Molecular Dynamics Simulations
Comparison of the Hydration and Diffusion of Protons in Perfluorosulfonic Acid Membranes with Molecular Dynamics Simulations
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DOI：
10.1021/jp8039803
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发表时间：
2008-10-23
影响因子：
3.3
通讯作者：
Edwards, Brian J.
中科院分区：
文献类型：
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作者：
Cui, Shengting;Liu, Junwu;Edwards, Brian J.
通过经典分子动力学（MD）模拟，确定了两种不同全氟磺酸（PFSA）膜的水合形态和水合离子扩散系数随水含量的变化规律。比较了具有较长全氟醚侧链的1143等效重量（EW） Nafion与短侧链（SSC） PFSA离子单体在EW为977时的结构和输运性质。在主链中含有-(CF(2))(15)-单元的两种离聚体中，侧链的分离保持均匀，水化程度从5 - 20重量%的水不等。MD模拟结果表明，在低含水量条件下，水团在SSC电离层中的分布更加分散，导致了一个更连通的水渠网络。这表明，SSC离聚体可能更倾向于形成跨越样品的水畴，通过这些水畴可以进行水和质子的传输。计算水合水平为4.4时水合氢离子和水分子的扩散系数。6.4, 9.6和12.8 H(2)O/SO(3)H为每个离子角。与实验质子扩散系数相比，这表明随着水含量的增加，质子跳跃对质子扩散的贡献增加。
Classical molecular dynamics (MD) simulations were performed to determine the hydrated morphology and hydronium ion diffusion coefficients in two different perfluorosulfonic acid (PFSA) membranes as functions of water content. The structural and transport properties of 1143 equivalent weight (EW) Nafion, with its relatively long perfluoroether side chains, are compared to the short-side-chain (SSC) PFSA ionomer at an EW of 977. The separation of the side chains was kept uniform in both ionomers consisting of -(CF(2))(15)- units in the backbone, and the degree of hydration was varied from 5 to 20 weight % water. The MD simulations indicated that the distribution of water clusters is more dispersed in the SSC ionorner, which leads to a more connected water-channel network at the low water contents. This suggests that the SSC ionomer may be more inclined to form sample-spanning aqueous domains through which transport of water and protons may occur. The diffusion coefficients for both hydronium ions and water molecules were calculated at hydration levels of 4.4. 6.4, 9.6, and 12.8 H(2)O/SO(3)H for each ionorner. When compared to experimental proton diffusion coefficients, this suggests that as the water content is increased the contribution of proton hopping to the overall proton diffusion increases.