Abstract Anion Exchange Membranes (AEMs) are nowadays used in a very wide range of different applications, from electrodialytic systems for water treatment, to Fuel Cells for energy generation. In many of these cases, the AEM is in contact with water molecules, either in aqueous or gas phase, which can strongly interact with the AEM polymer, thus affecting membrane properties. The role of water in fully swollen AEM and its effect on the diffusion of hydroxide is the focus of this work. Density Functional Theory (DFT) based calculations were merged with Molecular Dynamics (MD) simulations coming to a more accurate description of the ionic exchange capacity effect on the hydroxide ion diffusion in AEM. Hydration of the polysulfone-tetramethylammonium (PSU-TMA), one of the most studied systems in Alkaline anion exchange Membrane Fuel Cells (AMFC), was determined by DFT developing an efficient algorithm. The ab-initio calculations predicted water uptake, at different Ion Exchange Capacity (IEC), resulted in good agreement with the experimental data. The theory-experiment comparison identified a threshold range of 1.2–1.7 meq/g as critical IEC at which over-swelling of functionalized polymer matrix occurs. From this comparison, three IEC values were chosen to perform MD simulations in order to evaluate the hydroxyl diffusion coefficients as a function of the different IEC where the ab-initio water uptake and partial charges, utilized in the force-field, were adopted. Diffusion coefficients in the bulk of the membrane were calculated through the Mean Square Displacement (MSD) over 100 ns MD trajectories, and then compared with the values obtained by the analytical Mackie-Meares's model, finding good agreement between the two computational methodologies. In addition, the computed diffusion coefficients were compared with the experimental conductivity data with a fair agreement. It is worth noting that, thanks to the minimization of adjustable parameters, the present work can be easily adapted to study any type of Ion Exchange Membrane (IEM) and counter-ions diffusion.

中文翻译：

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离子交换容量和吸水量对 PSU-TMA 膜中氢氧化物传输的影响：DFT 和分子动力学研究

摘要 阴离子交换膜 (AEM) 现在被广泛应用于不同领域，从用于水处理的电渗析系统到用于发电的燃料电池。在许多情况下，AEM 与水分子或气相水分子接触，这会与 AEM 聚合物强烈相互作用，从而影响膜性能。水在完全溶胀的 AEM 中的作用及其对氢氧化物扩散的影响是这项工作的重点。基于密度泛函理论 (DFT) 的计算与分子动力学 (MD) 模拟相结合，可以更准确地描述离子交换容量对 AEM 中氢氧根离子扩散的影响。聚砜-四甲基铵 (PSU-TMA) 的水合，这是碱性阴离子交换膜燃料电池 (AMFC) 中研究最多的系统之一，是由 DFT 开发的有效算法确定的。ab-initio 计算预测了不同离子交换容量 (IEC) 下的吸水量，结果与实验数据非常吻合。理论-实验比较确定了 1.2-1.7 meq/g 的阈值范围作为功能化聚合物基质发生过度膨胀的临界 IEC。从这个比较中，选择了三个 IEC 值来执行 MD 模拟，以评估羟基扩散系数作为不同 IEC 的函数，其中采用了力场中使用的 ab-initio 吸水量和部分电荷。通过 100 ns MD 轨迹上的均方位移 (MSD) 计算大部分膜中的扩散系数，然后与分析 Mackie-Meares 模型获得的值进行比较，在两种计算方法之间找到良好的一致性。此外，计算的扩散系数与实验电导率数据进行了比较，具有相当的一致性。值得注意的是，由于可调参数的最小化，目前的工作可以很容易地适应研究任何类型的离子交换膜 (IEM) 和反离子扩散。