Sulfonated Polyimide Membranes for Polymer Electrolyte Fuel Cells

Sulfonated polyimides (SPIs) bearing sulfophenoxy side groups were successfully prepared. Their uncross-linked and cross-linked membranes were evaluated as polymer electrolyte membranes for polymer electrolyte fuel cells (PEFCs). They maintained high mechanical strength and high proton conductivity after aging in water at 130 degrees C for 500 h, indicating their high water stability. PEFCs with the SPI membranes showed high performances at 90 degrees C and a high humidity (85 %RH) of supplied gases. They also showed fairly high performances even at a low humidity of 30%RH due to the back diffusion of water formed at the cathode. PEFCs with the cross-linked SPI membranes were operated under a constant current density of 0.5 A/cm(2) at 90 degrees C and 85 %RH for 1600 h without any reduction in cell performance, indicating their high fuel cell durability. The SPI membranes have high potential for PEFCs at higher temperatures above 80 degrees C.