Polybenzimidazole and benzyl-methyl-phosphoric acid grafted polybenzimidazole blend crosslinked membrane for proton exchange membrane fuel cells

•–C6H5CH2PO3H2 (BP) graft polybenzimidazole (PBI) has higher H3PO4 doping than PBI.•PBI membrane conductivity is improved by grafting –C6H5–CH2–PO3H2 side chain.•Crosslink PBI/PBI-BP blend membrane shows better fuel cell performance than PBI.

We synthesize polybenzimidazole (PBI; Mw = 1.65 × 105 g mol−1) and benzyl-methyl-phosphoric acid grafted PBI (PBI-BP; 24 mol% degree of grafting). We demonstrate that blending 20 to −40 wt.% PBI-BP in the PBI membrane enhances the H3PO4 doping level, proton conductivity, and mechanical strength. However, the membrane is highly dissolved in an 85 wt.% H3PO4 aqueous solution as the PBI-BP content in the blend membrane is larger than 50 wt.%. To prevent PBI-BP from being dissolved out of the blend membrane by the H3PO4 aqueous solution, we fabricated a PBI/PBI-BP/epoxy (8/2/1.23 by wt.) crosslinked membrane. The crosslinked membrane demonstrated good fuel cell performance and excellent stability after a 23 on/off (12 h on at 160 °C with a current density of 200 mA cm−2 and 12 h off at room temperature) fuel cell cycle test with an unhumidified H2/O2.