Preparation and proton conductivity of phosphoric acid‐doped blend membranes composed of sulfonated block copolyimides and polybenzimidazole

A series of phosphoric acid ( PA )‐doped blend membranes composed of block or random sulfonated polyimides ( SPIs ) and polybenzimidazole ( PBI ) were prepared with similar PA contents to investigate the influence of chemical structures of SPIs on proton conductivity. The proton conductivity of a PA ‐doped blend membrane containing block‐type SPI , PA‐bSPI (80/20)/ oPBI , was higher than that of the corresponding pristine block‐type SPI , PA‐SPI / PBI containing random‐type SPI and Nafion membranes over a wide temperature range, and reached 0.37 S cm −1 at 90 °C and 98% relative humidity. The PA‐bSPI (80/20)/ oPBI membrane also showed distinct proton conductivity even at low humidity due to a new proton transport pathway among PA and sulfonic acid groups. Also, the novel PA ‐doped blend membrane showed higher proton conductivity than Nafion at both above 100 °C and below 0 °C under low relative humidity conditions.