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 σ 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 σ and better fuel cell performance than the neat-PBI and epoxide-crosslinked PBI membranes.