Development of proton conducting polyimide membranes and their polymer electrolyte fuel cell applications

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The relationship between water stability of SPI membranes and their chemical structures were investigated. SPIs derived from 2,2' bis-(4-sulfophenoxy)benzidine (BSPOB) displayed high water stability of more than 500 h in water at 130℃ and reasonably high proton conductivity of 0.05 S/cm at 120℃ and 50%RH, indicating high potential for polymer electrolyte fuel cell applications above 100℃. Simple crosslinking method using sulfone linkage was developed, which significantly improved the water stability of membranes.MEAs with conventional catalyst electrodes and SPI membranes displayed high PEFC performance comparable to that for Nafion 112. A PEFC with BSPOB-based SPI membrane was operated at 90℃, 80-90%RH and a constant load current of 0.5 A/cm2 for 1600 h without any decrease in cell voltage and any increase in cell resistance, indicating reasonably high durability of the SPI membrane.MEAs with conventional catalyst electrodes and SPI membranes displayed high DMFC performance even for high methanol concentration of 50%, indicating that SPI membranes were superior to Nafion membranes because of much lower crossover of methanol and water.Novel SPIs suitable for ionomer in catalyst layer were developed. Using these SPIs, catalyst electrodes were prepared. MEAs composed of the catalyst electrode and BAPBDS-based SPI membrane showed low PEFC performance, but some problems to be solved became clear.