Nafion膜表面不对称电荷聚电解质层层组装与过程调控

The proton exchange membrane acts as the key component in a direct methanol fuel cell (DMFC), which directly determines the performance of the battery. Nafion membrane has good proton conductivity but high methanol permeability. A layer-by-layer (LBL) assembly of a polyelectrolyte multilayer to modify Nafion is an effective method to reduce the methanol cross-over. Due to the electrostatic interaction between the anionic (sulfonic acid ions) and cations (ammonium ion) in the assembly layer, most of the SO3H groups in the polymer are engaged in ionic crosslinking, only a few of the SO3H groups in the polymer are relaxed (free SO3H), which could virtually transfer protons in a DMFC. Due to the decrease of the free SO3H groups in the assembled layers, the ionic crosslinking of polycations and polyanions on a Nafion membrane usually results in lower proton conductivity. To overcome these issues, the LBL assembly of an unbalanced charged rigid polyampholyte multilayer to modify Nafion is propose in this project by enhancing the content of free sulfonic acids to improve the proton conductivity, and by controlling the degree of crosslinking of the LBL membrane to hinder alcohol permeability. We will do much study on a variety of assembly conditions to control the performance of the LBL membrane. Preparing the well controlled structure, the best performance of the composite membrane and membrane electrode material, resolving the key issues of the DMFC, to promote the fluorinated sulfonic acid membrane to practical use as soon as possible.

质子交换膜是直接甲醇燃料电池（DMFC）的核心部件，其性能直接决定着电池的性能。含氟磺酸型质子交换膜（Nafion膜），具有良好的质子导电率，但是其甲醇渗透率较高。层层组装聚电解质多层膜对Nafion膜表面改性，可以在一定程度上降低甲醇的渗透。由于组装层中阴离子（磺酸离子）和阳离子（铵根离子）间的静电作用，大部分磺酸基团参与了离子交联，只有少量剩余的自由磺酸能传导质子，由于组装膜中缺乏自由磺酸，因此，组装膜的质子导电性比较低。针对上述问题，本项目将利用不对称电荷的刚性聚电解质，采用层层组装的方法，通过提高组装膜中自由磺酸的含量来提高质子导电率，通过控制交联程度提高Nafion膜的阻醇性能。系统研究各种组装条件对组装膜性能的调控规律。制备出结构可控、性能优异的复合膜及膜电极材料；解决目前DMFC所遇到的关键问题，推动含氟磺酸膜尽早走向实用化。

质子交换膜是直接甲醇燃料电池（DMFC）的核心部件，其性能直接决定着电池的性能。Nafion膜具有良好的质子导电率，但是其甲醇渗透率较高。层层组装聚电解质多层膜对Nafion膜表面改性，可以在一定程度上降低甲醇的渗透。为了提高膜的导电性及其与电极间的界面相容性，通过将区域集中型磺酸基团、柔性链段和氰基基团引入聚电解质，提供了一种解决膜与电极界面相容性的难题。.主要研究内容。.1）研究共价键交联驱动的不对称电荷聚电解质在质子交换膜表面的组装规律； 2）研究氧化石墨烯交联驱动的不对称电荷聚电解质在质子交换膜表面的组装规律；3）研究磺化质子交换膜中柔性链段和氰基的引入对电池组装性能的影响规律；4）研究区域集中性的磺酸分布对质子交换膜的导电性的影响。.重要结果、关键数据及其科学意义.1）采用不对称电荷聚电解质SPES-NH2和戊二醛的共价交联LBL组装法，改进了Nafion膜的阻醇性能。组装成单电池后的测试结果发现，组装膜的电池性能均优于原始Nafion膜的性能。.2）采用氧化石墨烯与SPES-NH2的组装构筑阻醇层，甲醇渗透降低10倍左右，但是质子导电率有不同程度的下降。由于交联结构的存在，组装膜与电极的界面相容性较差，无法组装成单电池。.3）在磺化质子交换膜中引入柔性链段和氰基基团，提高了膜与电极间的界面相容性。单电池的最大能量密度(24.5 mW cm-1)与Nafion 117膜的最大能量密度(24.3 mW cm-1) 相当。.4）区域集中的磺酸型聚电解质，协同含有氰基的柔性链段，不仅实现了质子导电率的提高，而且膜与电极间的界面相容性与较好，电池的能量密度高于Nafion膜。区域集中的磺酸膜协同柔性链段，具有更加优异的质子导电率和电极相容性，组装的单电池性能更加优良。