Studies on Understanding and Reducing Fuel Permeation through Polyelectrolyte Membranes for Fuel Cells

以1,4,5,8-萘四羧酸二酐（NTDA）、4,4'-双（4-磺苯氧基）联苯-3,3'-二磺酸（BAPBDS）和双（3-磺丙氧基）联苯胺（BSPBs）两种磺化二胺以及常见的非磺化二胺为原料，通过统计缩聚反应制备了两种磺化共聚亚胺（co-SPIs）。基于bspb的co-SPI膜具有清晰的由亲水和疏水结构域组成的微相分离结构，但亲水结构域的连接较差。另一方面，基于bapbds的co-SPI膜没有表现出如此明显的微相分离。在323 K时，共spi膜在水中的质子电导率为0.10 ~ 0.16 S/cm，与Nafion 112 （0.13 S/cm）相当。co-SPI膜的甲醇渗透性几乎不受饲料组成的影响。它们比nationon112的体积小了两倍多。结果表明，co-SPI膜的质子导电性和甲醇渗透率比Nafion高出两倍以上，表明其在直接甲醇燃料电池中的应用潜力很大。在燃料电池运行条件下，水和甲醇通过膜的交叉不是由质子传输的电渗透控制，而是由活性差异引起的扩散控制。这与Nafion等全氟磺化膜的情况大不相同，并对燃料电池性能产生有利影响。SPI膜在甲醇浓度较高（20-50 wt %）的DMFC系统中表现出更高的性能，优于Nafion，并且在中等温度（310-350 K）下具有很高的DMFC应用潜力。测量了磺化均聚亚胺的透气性，并与具有相同聚合物骨架的非磺化均聚亚胺的透气性进行了比较。当相对湿度从0% RH增加到90% RH时，NTDA-BAPHFDS(H)聚酰亚胺的透气性增加一个数量级以上。另一方面，非磺化聚酰亚胺的透气性随湿度的增加而略有下降。少

Two types of sulfonated copolyimides (co-SPIs) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), two types of sulfonated diamines, namely, 4,4'-bis(4-sulfophenoxy)biphenyl-3,3'-disulfonic acid (BAPBDS) and bis(3-sulfopropoxy)benzidines (BSPBs), and common nonsulfonated diamines via statistical polycondensation reaction. The BSPB-based co-SPI membranes had a clear microphase-separated structure composed of hydrophilic and hydrophobic domains but the connection of hydrophilic domains was rather poor. On the other hand, the BAPBDS-based co-SPI membranes did not show such a clear micro-phase separation. The co-SPI membranes showed high proton conductivities of 0.10-0.16 S/cm in water at 323 K, which was comparable to that of Nafion 112 (0.13 S/cm). The methanol permeabilities of the co-SPI membranes hardly depended on feed composition. They were more than two times smaller than those of Nafion 112. As a result, the co-SPI membranes showed more than two times larger … More ratios of proton conductivity over methanol permeability than Nafion, suggesting high potential for direct methanol fuel cell application.The water and methanol crossover through membrane under the fuel cell operation conditions is not controlled by electro-osmosis due to proton transport but by diffusion due to activity difference. This is quite different from the case of perfluorosulfonated membranes such as Nafion and results in the advantageous effects on fuel cell performance. SPI membranes displayed higher performances in DMFC systems with higher methanol concentration (20-50 wt %), which is superior to Nafion and have high potential for DMFC applications at mediate temperatures (310-350 K).Gas permeability for sulfonated homopolyimides were measured and compared to those of the non-sulfonated homopolyimide having the same polymer backbone. With increasing relative humidity from 0% RH to 90% RH, the gas permeability for NTDA-BAPHFDS(H) polyimide increased by more than one order of magnitude. On the other hand, the gas permeability for the non-sulfonated polyimide slightly decreased with increasing humidity. Less