具有强耐碱性聚芳醚类阴离子交换膜的分子设计及结构性能研究

Anion exchange membrane fuel cells （AEMFCs） show some unique characteristics. The most significant advantage is the inherently faster kinetics of the oxygen reduction reaction, which allows using non-noble and low-cost metal electrocatalysts in the AEMFCs.However,the usual anion exchange membranes reported in the references exhibit some disadvantages, such as low ionic conductivity, the poor alkali stability, the requirement of the chloromethyl ether and other carcinogenic reagents for the synthetic procedure. Moreover, less investigation is focusing on the relationship between the properties of the anion exchange membrane and the structure of polymer chemistry and microstructure. In this project,we will attach bromine atoms onto the benzyl groups using N-bromosuccinimide as the bromination agent.It is a quantitative, rapid, and selective method for production of anion exchange membranes without the use of chloromethyl ether. We will synthesize a new type of polymer electrolyte of which the quaternary ammonium groups are located on the side chain.Locating the electrolyte groups on the side chain and introducing conjugated π bond in the main-chain are two important strategies to prepare polymer electrolyte membranes with enhanced performances. Side-chain-type structures can help to enhance the separation of the hydrophilic regions and the hydrophobic polymer backbone, which results in improved conductivity and stabilities.As is well known, quaternary phosphonium and imidazolium hydroxide moieties are more stable than quaternary ammonium hydroxide moieties under alkaline environment. We will prepare anion exchange membranes based on poly (aryl ether) containing quaternary phosphonium groups or imidazolium groups based on poly (aryl ether)s containing dipropenyl groups. This project aims to balance the ionic conductivity and the mechanical properties, improve the stability in an alkaline environment, and establish the relationship between the structure and properties of anion exchange membranes.

阴离子交换膜应用于碱性直接甲醇燃料电池中，可避免贵重金属Pt催化剂的使用，明显降低成本。但目前文献报道的阴离子交换膜存在着离子传导率较低、耐碱性差、合成需要氯甲醚等致癌试剂等缺点，尚不清楚阴离子交换膜的宏观性能与聚合物化学结构及微观结构之间的内在关系。本项目针对这两个基本问题，拟合成含苯甲基或丙烯基等侧链基团的聚芳醚类聚合物，利用苄基位的溴甲基化反应、季铵或季鏻化反应制备阴离子交换膜。该方法具有反应迅速，条件温和，无需氯甲醚且溴代位置和溴化度均可控的优点。拟通过在聚合物主链中引入共轭结构、推电子基团及长侧链结构，提高阴离子交换膜的综合性能，平衡离子传导率与机械性能的关系，增加在碱性环境里的稳定性，为设计更加优异的稳定的碱性阴离子交换膜提供思路。

目前商业化的阴离子交换膜主要应用于电渗析等电化学领域，大多通过辐射接枝制备，品种相对单一。应用于燃料电池中存在着离子传导率低、季铵基团在碱中易降解等问题，难以满足实际工况下长期稳定使用的要求。因此，寻求具有优良的导电性能兼具高的化学与机械稳定性的阴离子交换膜日益成为国内外科学家关注的热点。本项目针对离子传导率低和耐碱稳定性差这两个基本问题，通过在聚合物主链中引入共轭结构、推电子基团及长侧链结构，旨在提高聚芳醚类阴离子交换膜的综合性能。为此，本项目合成了一系列含苯甲基或丙烯基等侧链基团的聚芳醚类聚合物，利用苄基位的溴甲基化反应、季铵或季鏻化反应制备阴离子交换膜。该方法具有反应迅速，条件温和，无需氯甲醚且溴代位置和溴化度均可控的优点。并利用聚合物主链上残余的双键或苄基溴进行交联改性，研究了交联程度对阴离子交换膜性能的影响。通过本项目的研究，制备出了具有高的氢氧根离子传导率（>0.02 S/cm），适当的水溶胀率（30%），良好的热稳定性（>250℃），良好的耐碱稳定性的新型阴离子交换膜材料。发表了标注基金项目的SCI论文21篇，培养硕士研究生4名，博士研究生7名。本项目的完成有利于解决阴离子交换膜离子传导率与机械强度之间的矛盾，提出了改善阴离子交换膜在碱性环境中稳定性的策略，为设计更加优异的稳定的碱性阴离子交换膜提供了思路。