侧链型高温质子交换膜的微观结构调控、性能与离子传输机制

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have attracted extensive research interest due to their significant advantages over PEMFCs operating at room temperature, such as improved impurities tolerance of electrolyte and simplified water and heat management. As one of the key components of HT-PEMFCs, HT-PEM is a crucial factor in determining the cost, lifetime, and output performance of PEMFCs. However, the application of current HT-PEM in FCs is limited because it’s challenging to combine the satisfied ionic conductivity and mechanical properties. To break the bottlenecks of HT-PEM, this work is proposed to introduce nitrogen-containing functional groups (eg. N-heterocycl) as phosphoric acid anchoring sites to the side chains of polyaromatic ether or polysulfon by chemical grafting, to obtain the micro-phase separation structures of the polymer backbones and side chains with functional groups and modulate the performance of as-prepared membrane, to obtain practical HT-PEMs with both outstanding ionic conductivity and mechanical properties. The proposed study is to investigate the influence of the chemical structure and grafted degree of functional groups in the polymer side chains on the micro-structure of membranes and the influence of micro-structure on the performance of membrane, to illustrate the relationships among chemical structure of side chain, micro-structure and performance of the HT-PEMs. This work is also to explore the influence of components, grafted degree of pendant N-containing groups as well as micro-structure of the membrane on the proton transferring mechanism and performance in elevated temperatures. Finally the electrochemical behavior and durability of as prepared side-chain-type membranes in HT-PEMFCs would be investigated. In short, the implementation of this proposal will provide the fundamental and technical guidance for design and controllable preparation of novel HT-PEM and HT-PEMFC devices with satisfied comprehensive performance.

高温质子交换膜燃料电池由于具有强的催化剂抗毒化能力和简化的水热管理系统等突出优点而成为聚合物膜燃料电池的研究热点。高温质子交换膜作为其核心部件，直接决定着电池的输出性能、成本及寿命。现有高温质子交换膜存在力学性能和离子导电性能难以协同兼顾等难题，并且对其构效关系缺乏深度认识。本项目拟通过侧链接枝的方法，将锚定磷酸的功能基团（如含氮杂环）引入至高分子聚合物的侧链，对高温膜的微观结构进行调控；研究侧链功能基团的化学结构、接枝度等对膜微观聚集形态、离子输运机制等的影响及规律；阐明高温膜中侧链结构-微观形貌-宏观性能的内在联系，实现对高温膜离子传输与力学性能等宏观性能的协同提升。该研究将为新型高温质子交换膜的设计与高性能燃料电池器件的研发奠定理论与实验基础。

高温质子交换膜燃料电池由于电极具有高的一氧化碳耐受性而可以直接采用甲醇重整气等作为燃料、简化的水热管理等优点而成为聚合物膜燃料电池的研究热点。作为高温质子交换膜燃料电池的关键材料，高温质子交换膜直接决定着电池的输出性能、成本及寿命。现有高温质子交换膜存在力学性能和离子导电性能难以兼顾等问题，严重阻碍了其在电池中的应用。本项目针对上述的问题，本项目通过傅克反应和点击化学方法将锚定磷酸的含氮功能基团（如乙烯基咪唑、2,4,6-三(二甲氨基甲基)苯酚、聚乙烯亚胺等）接枝到聚砜、聚苯醚等聚合物分子链，获得系列具有不同侧链结构聚合物高分子材料。研究结果表明侧链结构有利于磷酸掺杂高温质子交换膜微观相分离结构的形成，侧链结构上的含氮功能基团吸收磷酸后形成亲水离子团簇，与憎水的主链形成微观相分离结构，该结构一方面为质子的传输提供快速通道，另一方面由于磷酸在亲水区的聚集降低了磷酸分子对高分子主链的塑化作用，使膜材料同时具有良好的力学性能，实现了质子传递性能和力学性能的共赢。此外，本项目研究结果还表明侧链结构的组成、侧链的长度和空间结构对磷酸掺杂后形成的离子团簇尺寸有显著影响。一般而言，离子团簇尺寸越大，离子传输能力越强，但同时氢渗透电流也越大。此外，侧链含氮基团的pKa值也对所获得的高温质子交换膜的离子传导能力和保酸能力有较大影响，适中的pKa能同时保证膜材料具有较高的电导率和保酸能力。在实际高温质子交换膜燃料电池的测试结果表明，本项目所制备的侧链结构膜材料展示出了良好的电池输出性能和运行稳定性，表明了本项目设计思想的正确性。本项目的研究结果表明通过将吸收磷酸的含氮功能基团引入到高分子链上获得侧链结构聚合物有利于掺杂磷酸后形成微相分离结构可有效解决磷酸掺杂高温质子交换膜的力学性能与传递性能难以兼顾的问题。本项目的研究成果为高温质子交换膜材料的设计和高温质子交换膜燃料电池的发展提供了新的思路。