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

以1，4，5，8-萘四甲酸二酐（NTDA）、4，4 '-双（4-磺基苯氧基）联苯-3，3'-二磺酸（BAPBDS）和双（3-磺基丙氧基）联苯胺（BSPBs）两种磺化二胺和普通非磺化二胺为原料，通过统计缩聚反应合成了两种磺化共聚聚酰亚胺（co-SPI）。BSPB基共-SPI膜具有明显的微相分离结构，由亲水区和疏水区组成，但亲水区之间的连接较差。另一方面，基于BAPBDS的co-SPI膜没有显示出如此清晰的微相分离。co-SPI膜在323 K下在水中显示出0.10-0.16 S/cm的高质子传导率，这与Nafion 112（0.13 S/cm）相当。共-SPI膜的甲醇渗透率几乎不依赖于进料组成。它们比Nafion 112小两倍多。结果，共SPI膜显示出两倍多的大小 ...更多信息 在燃料电池运行条件下，水和甲醇通过膜的渗透不是由质子输运引起的电渗控制，而是由活性差异引起的扩散控制。这与全氟磺酸膜（例如Nafion）的情况截然不同，并对燃料电池性能产生了有利影响。SPI膜在较高甲醇浓度（20-50 wt %）的DMFC体系中表现出更高的性能，上级Nafion膜，在中温（310-350 K）下具有很大的应用潜力。随着相对湿度从0%RH增加到90%RH，NTDA-BAPHFDS（H）聚酰亚胺的透气性增加了一个数量级以上。另一方面，非磺化聚酰亚胺的透气性随着湿度的增加而略微降低。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