Crosslinked polybenzimidazole containing branching structure with no sacrifice of effective N-H sites: Towards high-performance high-temperature proton exchange membranes for fuel cells

N-H sites are crucial to proton transportation for phosphoric acid (PA)-doped polybenzimidazole (PBI). However, these sites in crosslinked PBI are easily reacted by crosslinker, leading to a decreasing proton conductivity. Herein, a novel crosslinker is synthesized and a series of crosslinked PBIs containing branched structure without sacrifice of effective N-H sites are prepared using the special crosslinker. The branching structure can effectively elevate free volume and PA absorption of these membranes, while N-H sites in the PBIs still remain for efficient proton transport. The prepared membranes exhibit improved proton conductivity (0.073 S cm−1, 160 °C, anhydrous), mechanical performance and superior oxidative stability. In the case of actual usage in a single cell, a peak power density of 690 mW cm−2 is measured, single-cell performance under laboratory conditions at 160 °C with a constant current load (200 mA cm−2) is maintained for 200 h without membrane degradation, and H2 permeability remains almost unaffected during this test. The results indicate that the crosslinked PBIs containing branching structure with no sacrifice of effective N-H sites can potentially be used as high temperature proton exchange membrane.