| Co-Investigator(Kenkyū-buntansha) |
OKAMOTO Ken-ichi Yamaguchi University, Faculty of Engineering, Professor emeritus, 工学部, 教授(特命) (20029218)
KITA Hidetoshi Yamaguchi University, Faculty of Engineering, Professor, 工学部, 教授 (10177826)
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| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2004: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
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
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