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

Abstract

We synthesize polybenzimidazole (PBI; M w = 1.65 × 10 5 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 H 3 PO 4 doping level, proton conductivity, and mechanical strength. However, the membrane is highly dissolved in an 85 wt.% H 3 PO 4 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 H 3 PO 4 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 H 2 /O 2 . • –C 6 H 5 CH 2 PO 3 H 2 (BP) graft polybenzimidazole (PBI) has higher H 3 PO 4 doping than PBI. • PBI membrane conductivity is improved by grafting –C 6 H 5 –CH 2 –PO 3 H 2 side chain. • Crosslink PBI/PBI-BP blend membrane shows better fuel cell performance than PBI.