Crosslinked ethyl phosphoric acid grafted polybenzimidazole and polybenzimidazole blend membranes for high-temperature proton exchange membrane fuel cells

Our previous work illustrated that blending 10-30 wt.% of ethyl phosphoric acid-grafted PBI (PBI-EPA, 12 mol% degree of grafting) in the PBI membrane enhances the phosphoric acid doping level (PA(dop)) and proton conductivity sigma of the membrane. On the other hand, the mechanical properties were decreased, and the membrane was highly dissolved in an 85 wt.% H3PO4 aqueous solution, while the PBI-EPA concentration in the PBI/PBI-EPA blend membrane was greater than 50 wt.%. To improve the mechanical properties of the PBI/PBI-EPA blend membrane, crosslinked PBI/PBI-EPA membranes with a PBI-EPA concentration higher than 50 wt.% were prepared by blending epoxy resin as a crosslinker. These crosslinked blend membranes demonstrated greater PA(dop) and sigma and better fuel cell performance than the neat-PBI and epoxide-crosslinked PBI membranes.