Abstract In an anion exchange membrane, OH− conduction is closely related to the affinity of the functional group and membrane morphology. This relationship can change when the water uptake of the membrane varies. To explore the effect of the water uptake on the affinity of the functional group to OH− and the membrane morphology, a series of molecular dynamics simulations based on an all-atom force field were performed for the imidazolium-grafted PPO (Im-g-PPO) membranes with different water uptakes. The simulation results of the membrane density, water and OH− self-diffusivity, and OH− conductivity verify the accuracy of the simulation systems. The local distributions of OH− and water around the imidazolium group indicate that increasing water uptake enhances the hydration structure of the imidazolium group and weakens the affinity of the imidazolium group to OH−. The critical water saturation of imidazolium group could produces suitable affinity to the surrounding OH−. When the imidazolium group is water saturated, further increasing water uptake is not conducive to retaining the affinity to OH−. As a result, the critical water saturation of the imidazolium group balances between the affinity to OH− and the transfer of OH− in the hydrated Im-g-PPO membrane. Furthermore, it also produces a percolated hydrophilic channel and maintains a relatively high mechanical strength of the Im-g-PPO membrane. Therefore, the imidazolium groups should be maintained under the critical water saturation, where two and eight water molecules are retained in the first and second hydration shells, respectively. This work provides a molecular-level understanding of the effect of the hydration structure of the imidazolium group on OH− conduction and the morphology of the Im-g-PPO membrane. It also provides potential guidance for maintaining high performance in anion exchange membrane fuel cells.

中文翻译：

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通过分子动力学模拟了解水合咪唑鎓-g-PPO 膜中用于羟基阴离子传导的咪唑鎓基团水合和聚合物结构

摘要 在阴离子交换膜中，OH-传导与官能团的亲和力和膜形态密切相关。当膜的吸水量变化时，这种关系会发生变化。为了探索吸水对官能团对 OH− 的亲和力和膜形态的影响，对咪唑鎓接枝的 PPO（Im-g- PPO) 具有不同吸水率的膜。膜密度、水和 OH− 自扩散率以及 OH− 电导率的模拟结果验证了模拟系统的准确性。OH- 和水在咪唑鎓基团周围的局部分布表明，增加吸水量会增强咪唑鎓基团的水合结构并削弱咪唑鎓基团对 OH- 的亲和力。咪唑鎓基团的临界水饱和度可以对周围的 OH-产生合适的亲和力。当咪唑鎓基水饱和时，进一步增加吸水量不利于保持对 OH- 的亲和力。因此，咪唑鎓基团的临界水饱和度平衡了对 OH- 的亲和力和水合 Im-g-PPO 膜中 OH- 的转移。此外，它还产生渗透的亲水通道并保持 Im-g-PPO 膜的相对较高的机械强度。因此，咪唑鎓基团应保持在临界水饱和度下，其中两个和八个水分子分别保留在第一个和第二个水化壳中。这项工作提供了对咪唑鎓基团的水合结构对 OH-传导和 Im-g-PPO 膜形态的影响的分子水平的理解。它还为保持阴离子交换膜燃料电池的高性能提供了潜在的指导。