Properties and fuel cell applications of polybenzimidazole and ethyl phosphoric acid grafted polybenzimidazole blend membranes

•12 mol% imidazole –NH groups of PBI are grafted with ethyl phosphoric acid.•PBI toughness improved by blending with 10–20 wt% ethyl phosphoric acid grafted PBI.•PBI conductivity increased by blending with 10–30 wt% ethyl phosphoric acid grafted PBI.•PBI fuel cell performance increased by blending with 10–30 wt% ethyl phosphoric acid grafted PBI.

Polybenzimidazole doped H3PO4 (PBI/H3PO4) membrane is considered as one of the most promising proton exchange membranes for high temperature proton exchange membrane fuel cells (PEMFCs). However, the brittleness of PBI membrane limits its applications. In this study, we synthesize ethyl phosphoric acid grafted PBI (PBI-EPA; 12.0 mol% degree of grafting) and prepare PBI/PBI-EPA blend membranes. The PBI/PBI-EPA blend membrane has a lower tensile stress and a larger tensile strain than the neat-PBI membrane when the PBI-EPA content is ~10–20 wt% in the blend membrane. The H3PO4 doping level, proton conductivity, and fuel cell performance at 160 °C with nonhumidified H2/O2 and H2/air fuel gases are also enhanced by blending 10–30 wt% of PBI-EPA in the PBI/PBI-EPA blend membranes.