基于柔性主链的新型碱性聚合物电解质研究

Alkaline polymer electrolytes (APEs) is the key component of alkaline polymer electrolyte fuel cells. Recent studies demonstrated that the chemical stability of APEs can be improved by removing the polar groups in conventional aromatic ether backbones. However, the membranes based on polyphenylene backbones without any polar groups were always brittle due to the poor flexibility. As a result, a trade-off between the high chemical stability and excellent mechanical properties was observed. In addition, polyphenylene based APEs possess high glass transition temperature, which makes the hot pressing process cannot work well during the preparation of membrane electrode assembles. To resolve these issues, alkaline polymer electrolyte based on flexible backbone without polar groups, e.g., polyolefin, will be synthesized. The influence of backbone structure on the mechanical properties will be studied by the computational and experimental combined approaches. In this study, mechanically tough backbone structure with both high tensile strength and flexibility will be obtained. Post functionalization method will be used to modify the backbone. APEs with distinct microphase separation will be formed to solve the low conductivity problem that caused by the poor hydrophilicity of the backbone. The initial discharge performance and durability of APEFCs based on the new developed APE materials will be evaluated. This project will provide the ideas on the rational design of flexible backbone based APEs, which possess high chemical stability, high mechanical properties, high conductivity, and low glass transition temperature, so as to boost the development of fuel cell technology.

碱性聚合物电解质(APE)是碱性聚电解质燃料电池的关键材料。最新研究发现，减少芳基醚类主链极性基团可以提高APE化学稳定性，但是膜材料的柔韧性能明显降低，导致APE高化学稳定性和高机械性能难以兼具，此外，这类APE玻璃化转变温度高，不利于膜电极组件的热压。针对这一挑战，本申请项目拟合成基于不含极性基团的柔性聚烯烃主链的新型APE。通过计算与实验相结合的手段探索主链结构对机械性能的影响机制，优化出刚柔并济的主链，采用后功能化反应解决主链不易被改性的难题，然后在APE结构中构建高速离子通道，解决APE因为亲水性差而导致其离子电导率低的难题，最后测试APE在燃料电池器件中的放电功率及运行寿命。本项目的实施有望为获得同时具备高化学稳定性、高机械性能、高物理性能和低玻璃化转变温度的柔性APE提供新的结构设计思想，推动燃料电池技术的发展。

碱性聚电解质（APEs）作为碱性聚电解质燃料电池的关键材料，直接影响燃料电池的性能。研发具有高离子电导率、优异机械性能和高化学稳定性的APEs十分必要。然而，要合成优秀的APEs存在三个方面的挑战。第一，理想稀溶液中，OH−离子迁移率仅是H+离子迁移率的0.57倍，氢氧根离子传导能力天生低于质子。第二，氢氧根是一种强碱性亲核试剂，APEs的阳离子以及主链容易受到OH−进攻而发生降解。第三，传统提高离子电导率（提高离子交换容量）和化学稳定性（主链不含极性基团）的方法会导致材料机械性能变差。针对这些问题，本项目做了系统且深入的研究。首先，向APEs中引入疏水侧链，促进离子通道形成，提高APEs的离子传导效率。通过分子结构设计，考察了侧链接枝位置以及侧链长度对APEs离子传导性能的影响。疏水侧链接枝在主链上优于接枝在阳离子上，A8SB-QAPPO在80 oC的氢氧根离子电导率为101.2 mS/cm，而A8SC-QAPPO的离子电导率仅为56.1 mS/cm。疏水侧链长度为5的季铵化聚砜相较其他样品离子电导率最高，80 oC时，a5-QAPS的离子电导率为75.5 mS/cm，而a1-QAPS，a3-QAPS，a7-QAPS的离子电导率分别为38.4，54.5，38.8 mS/cm。其次，研究发现有序相分离的形成可以抑制APEs过度溶胀和吸水，从而降低OH−的进攻能力，提高材料耐碱性。憎水侧链接枝的sQAPSF，sQAPPSU和sQAPPO相较于各自原始QAPSF，QAPPSU和QAPPO，主链及阳离子化学稳定性均有明显提高。还发现，APEs的离子传导性能和化学稳定性可以通过提高材料的含水量来提高，单独研究阳离子或者主链的性质来判断他们在APEs中的应用不具备实际意义。最后，自聚集型离子交联策略可以实现APEs兼具高机械性能、高离子电导率和高化学稳定性的目的。acS8QAPSF在80 oC的OH−电导率为90.5 mS/cm，溶胀仅为10.0%。25 oC时，湿态下的抗拉强度和断裂伸长率分别为23.9 MPa和21.1%。在80 oC 1M NaOH溶液中浸泡30天之后，acS8QAPSF的主链质量损失为8.0%，其IEC和IC的保留百分比分别为92.0%和90.5%。而QAPSF在30天稳定性测试结束之后，降解成碎片，无法测试相关性能。此外，将acS8QAPSF作为电池