物理化学学报 >> 2019, Vol. 35 >> Issue (4): 378-384.doi: 10.3866/PKU.WHXB201805031

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醇/水混合溶剂中碱性聚合物电解质独特的溶解行为

吕康杰1,彭燕秋1,肖丽1,*(),陆君涛1,庄林1,2,*()   

  1. 1 武汉大学化学与分子科学学院，化学电源材料与技术湖北省重点实验室，武汉 430072
    2 武汉大学高等研究院，武汉 430072
  • 收稿日期:2018-04-09 发布日期:2018-09-13
  • 通讯作者: 肖丽,庄林 E-mail:chem.lily@whu.edu.cn;lzhuang@whu.edu.cn
  • 基金资助:
    国家重点研发计划(2016YFB0101203);国家自然科学基金(91545205);国家自然科学基金(21633008)

Atomistic Understanding of the Peculiar Dissolution Behavior of Alkaline Polymer Electrolytes in Alcohol/Water Mixed Solvents

Kangjie LYU1,Yanqiu PENG1,Li XIAO1,*(),Juntao LU1,Lin ZHUANG1,2,*()   

  1. 1 Hubei Key Lab of Electrochemical Power Sources, College of Chemistry and Molecular Sciences, Wuhan 430072, P. R. China
    2 Institute for Advanced Studies, Wuhan University, Wuhan 430072, P. R. China
  • Received:2018-04-09 Published:2018-09-13
  • Contact: Li XIAO,Lin ZHUANG E-mail:chem.lily@whu.edu.cn;lzhuang@whu.edu.cn
  • Supported by:
    the National Key Research and Development Program of China(2016YFB0101203);the National Natural Science Foundation of China(91545205);the National Natural Science Foundation of China(21633008)

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摘要：

自聚集型季铵化聚砜(aQAPS)是一种高性能的碱性聚合物电解质(APE)，已被应用于碱性聚合物电解质燃料电池(APEFCs)中。长期以来，N, N-二甲基甲酰胺(DMF)一直被作为溶解aQAPS的最佳溶剂，但DMF的高沸点使其难以彻底除尽并可能会毒化电催化剂。在我们最近的实验中发现，虽然aQAPS不能溶解于乙醇、正丙醇或水中，但它可以溶解在这些醇和水的混合物中。这种尚未被理解的独特溶解行为能够极大地促进APEFCs中膜电极组件(MEA)的制备。本工作使用分子动力学(MD)模拟的方法研究了aQAPS在不同溶剂中的溶解行为，包括水、甲醇、乙醇、正丙醇、DMF以及这些非水溶剂与水的混合物。aQAPS链在单一溶剂中的构象与其在实验中观察到的溶解行为一致，但在含有水的混合溶剂中，aQAPS链往往处于更加蜷缩的状态。模拟结果进一步揭示了混合溶剂中的水扮演着双重角色。一方面，由于疏水作用，aQAPS链在加水时被压缩至收缩状态；另一方面，水可以驱动反离子(Cl−)的离解，从而导致溶质-溶剂相互作用能的增强，促进aQAPS的溶解。在大多数混合溶剂中，这两种相互作用的总效果是增大了总的溶质-溶剂相互作用能，在能量上有利于aQAPS的溶解。本研究不仅能够加深我们对聚电解质溶解行为的基本认识，而且对于开发性能更优的APEFCs也具有技术指导作用。

关键词: 碱性聚合物电解质, 溶解, 醇/水混合溶剂, 分子动力学模拟

Abstract:

Self-aggregated quaternary ammonium polysulfone (aQAPS) is a high-performance alkaline polymer electrolyte that has been applied in alkaline polymer electrolyte fuel cells (APEFCs). For a long time, N, N-dimethyl formamide (DMF) has been considered the best solvent to dissolve aQAPS, but the high boiling point of DMF makes it hard to remove from the electrodes, which potentially poisons the electrocatalysts. Our recent experiments have shown that although aQAPS is unable to dissolve in ethanol, n-propanol, or water, it can dissolve in the mixture of these alcohols and water. This peculiar dissolution behavior significantly facilitates the fabrication of the membrane electrode assembly (MEA) for APEFCs, even though it has not been understood. In this work, atomistic molecular dynamics (MD) simulations were employed to study the dissolution behavior of aQAPS in different solvents, including water, methanol, ethanol, n-propanol, DMF, and the mixture of these non-aqueous solvents and water. The conformation of the aQAPS chain in pure solvents agreed well with the dissolution behavior observed in the experiments, even though in the water-containing mixed solvents, the aQAPS chain tended to be in a more contracted state. The simulations further revealed that the water component in the mixed solvents played dual roles. On one hand, the hydrocarbon chain of aQAPS was compressed to a contracted state upon the addition of water, because of the hydrophobic effect. On the other hand, water can drive the dissociation of the counterion (Cl–­ ­ ­ ), which led to an enhancement in the solute-solvent interaction energy and thus facilitated the dissolution of aQAPS. In most mixed solvents, the compensation of these two interactions resulted in a general increase in the total solute-solvent interaction energy; therefore, the addition of water was energetically favorable for the dissolution of aQAPS. This study not only furthers our fundamental understanding of the dissolution behavior of polyelectrolytes but also is technologically significant for the development of better APEFCs.

Key words: Alkaline polymer electrolyte, Dissolution, Alcohol/water mixed solvents, Molecular dynamics simulation