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

以1，4，5，8-萘四甲酸二酐、两种磺化二胺4，4‘-bis(4-sulfophenoxy)biphenyl-3，3’-disulfonic酸(BAPBDS)和双(3-磺基丙氧基)联苯(BSPB)为原料，通过统计缩聚反应合成了两种磺化共聚酰亚胺(co-SPI)。基于BSPB的共-SPI膜具有明显的微相分离结构，由亲水和疏水结构域组成，但亲水结构域之间的连接较差。另一方面，基于BAPBDS的共聚SPI膜没有表现出如此清晰的微相分离。当温度为323K时，膜在水中的质子电导率为0.10~0.16 S/cm，与Nafion112的质子电导率(0.13 S/cm)相当。共-SPI膜的甲醇透过率几乎不受进料组成的影响。它们比Nafion 112的体积小两倍多。结果，共-固相离子交换膜的…要大两倍以上质子电导率与甲醇渗透率的比值高于Nafion，表明直接甲醇燃料电池具有很大的应用潜力。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传输引起的电渗透控制的，而是由活度差异引起的扩散控制的。这与全氟磺化膜如Nafion的情况有很大不同，并导致了对燃料电池性能的有利影响。在甲醇浓度较高(20-50wt%)的DMFC体系中，SPI膜表现出较高的性能，优于Nafion，在中温(310-350K)下具有很大的应用潜力。当相对湿度从0%RH增加到90%RH时，NTDA-BAPHFDS(H)聚酰亚胺的气体渗透率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湿度的增加而略有下降。较少

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