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

We synthesize polybenzimidazole (PBI; M-w = 1.65 x 10(5) g mol(-1) and benzyl-methyl-phosphoric acid grafted FBI (PBI-BP; 24 mol% degree of grafting). We demonstrate that blending 20 to -40 wt.% PBI-BP in the FBI 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 degrees 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. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.