Hydroxide Ion Diffusion in Anion-Exchange Membranes at Low Hydration: Insights from Ab Initio Molecular Dynamics
Hydroxide Ion Diffusion in Anion-Exchange Membranes at Low Hydration: Insights from Ab Initio Molecular Dynamics
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DOI：
10.1021/acs.chemmater.9b01824
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发表时间：
2019-06
影响因子：
8.6
通讯作者：
Tamar Zelovich;Leslie Vogt-Maranto;M. Hickner;S. Paddison;Chulsung Bae;Dario R. Dekel;M. Tuckerman
中科院分区：
文献类型：
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作者：
Tamar Zelovich;Leslie Vogt-Maranto;M. Hickner;S. Paddison;Chulsung Bae;Dario R. Dekel;M. Tuckerman
阴离子交换膜 (AEM) 燃料电池 (AEMFC) 的运行会导致电池内产生梯度，从而导致电池内的低水合条件。因此，研究低水阳离子比（λ ≤ 4，λ=nH2O/ncation）的 AEM 中的氢氧根离子扩散非常重要。在这项工作中，提出了从头算分子动力学模拟，以探索低水合作用模型 AEM 中的氢氧根离子溶剂化络合物和扩散机制。通过改变 AEM 内的阳离子间距和水合程度，创建了六种不同的理想化 AEM 模型，其中水分布不均匀。结果表明，不同的水分布赋予独特的 OH- 扩散机制，分为三种状态。观察到的机制，非扩散、载体以及结构和载体扩散的混合，取决于氢氧根离子的第二溶剂化壳的存在或不存在以及局部水结构。结果表明，水分布更好...
Operation of anion-exchange membrane (AEM) fuel cells (AEMFCs) results in gradients in the cell that can lead to low-hydration conditions within the cell. It is therefore important to investigate hydroxide ion diffusion in AEMs with low water-to-cation ratios (λ ≤ 4, λ≡nH2O/ncation). In this work, ab initio molecular dynamics simulations are presented to explore hydroxide ion solvation complexes and diffusion mechanisms in model AEMs at low hydration. By changing the cation spacing within the AEM and the degree of hydration, six different idealized AEM models are created in which the water distribution is not uniform. It is shown that distinct water distributions impart unique OH– diffusion mechanisms that fall into three regimes. The observed mechanisms, nondiffusive, vehicular, and a mixture of structural and vehicular diffusion, depend on the presence or absence of a second solvation shell of the hydroxide ion and on the local water structure. The results suggest that the water distribution is a better...