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论文类型：期刊论文

发表时间：2018-12-31

发表刊物：CHEMICAL ENGINEERING SCIENCE

收录刊物：SCIE、Scopus

卷号：192

页面范围：1167-1176

ISSN号：0009-2509

关键字：Imidazolium-grafted PPO; Molecular dynamics simulation; Hydroxide ion; Hydration structure; Affinity

摘要：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 main- taining high performance in anion exchange membrane fuel cells. (C) 2018 Elsevier Ltd. All rights reserved.