天然酚类抗氧化剂在车载燃料电池质子交换膜中的应用及其机理研究

Proton exchange membrane (PEM) is one of the key materials of membrane electrode assemblies (MEAs) as the core component of proton exchange membrane fuel cells (PEMFCs). The oxidative stability of PEMs is the primary cause influencing the lifetime of PEMFCs. The highest durability has attained or even exceeded 5000 hours internationally, however is only 3000 to 4000 hours domestically. And finding out methods to elongate the lifetime of fuel cells has become one of the key technologies of promoting the industrialization of PEMFCs. In this proposal, we plan to fabricate composite PEMs by combining natural phenolic antioxidants (NPAs), e.g. natural vitamin E (VE) with PEMs. We also propose to investigate the internal relationship of the entanglement between hydrophobic carbon chains of NPAs and backbones of PEMs, revealing the chemical causes of electrochemical windows of electro-oxidation reation between NPAs and PEMs in acidic solution to classify the possible protectable PEMs for NPAs. We will construct ccelerated stress test (AST) protocols to evaluate PEMs under complicated operation conditions, and majorly research the mechanism of the preferential reaction between NPAs and oxygen radicals under open circuit voltage (OCV) and complicated operation conditions of composite PEMs, and the antioxidation process and intrinsic reason of NPAs as radical scavengers protecting PEMs. We will also pursue on the regular influence of NPAs materials on the structural stability of molecules of PEMs while keeping the proton conductivity, and then apply such compounds in PEMs, e.g. PTFE/Nafion hybrid membranes. We will use our research results aiming to provide experimental foundation and theoretical guidance for future material design and performance improvements of organic antioxidants as oxygen radical scavengers used in PEMs.

质子交换膜（PEMs）是燃料电池核心部件膜电极（MEAs）的关键材料，其氧化稳定性是影响燃料电池寿命的主要原因之一。燃料电池寿命在国际上最长已到达5000小时，而国内燃料电池使用寿命仅有3000–4000小时。进一步延长燃料电池的使用寿命已成为推动燃料电池产业化的关键技术之一。本课题拟将天然维生素E（VE）为代表的天然酚类（NPAs）抗氧化剂与PEMs相结合，制备复合质子交换膜。探讨NPAs与PEMs在酸性条件下电化学窗口差异影响NPAs保护PEMs的化学机理，确认NPAs可保护的PEMs类别。建立复杂工况条件下对质子交换膜的快速评价方法（AST protocols）。探讨与NPAs类物质影响PEMs分子结构稳定性和保证其质子传导的基本规律，并将其使用在PTFE/Nafion等复合膜中，旨在为这类材料的材料设计和进一步性能提升提供实验基础与理论指导。

质子交换膜的化学腐蚀问题一直是制约燃料电池使用寿命的重要因素，研制高稳定性的质子交换膜对于燃料电池具有重要意义。自由基淬灭剂为一类能够清除体系内活性自由基的物质，能够有效地减缓质子交换膜的化学腐蚀，从而提升燃料电池的使用寿命。槲皮素、白藜芦醇都是种天然的抗氧化剂，普遍存在于植物的花、叶、果实中。本研究将槲皮素引入质子交换膜，采用浇铸方法合成了复合膜。扫描电子显微镜图片表明，Nafion膜与Nafion/1%槲皮素复合膜表面均没有任何的针孔或者裂纹。扫描电镜截面图表明，所制备的质子交换膜厚度大约为25.6μm，与商业的Nafion® 211膜（25.4μm）相当。加速老化测试（AST）表明，由Nafion膜组装的单电池在五个AST循环中有较为明显的性能下降，而用Nafion/1%复合膜组装的单电池在9个AST循环中的性能损失要明显低于由Nafion膜所组装的单电池。加速老化测试前后的MEA截面扫描电镜图表明，九个AST循环后的Nafion/1%槲皮素复合膜厚度要大于五个AST循环后Nafion膜的厚度，证明槲皮素的存在能有效的减缓质子交换膜的化学腐蚀。在复合膜中加入天然抗氧化剂白藜芦醇，以聚四氟乙烯(PTFE)为增强材料，制备了厚度更薄机械强度更强的复合膜。其中，采用聚多巴胺包覆的方法改善PTFE的亲水性。制备的膜的厚度为10μm，并采用加速老化试验进行稳定性测试。与不添加白藜芦醇的膜相比，添加1wt%白藜芦醇的复合膜氢渗透电流密度较低，复合膜寿命更长，同时其电池性能没有较大损失。