Performance enhancement of polybenzimidazole based high temperature proton exchange membranes with multifunctional crosslinker and highly sulfonated polyaniline

Polybenzimidazole (PBI) based high temperature proton exchange membranes were prepared by covalent cross-linking with triglycidylisocyanurate (TGIC) and doping with highly sulfonated polyaniline (SPAN). Insoluble SPAN with high degree of sulfonation was synthesized as the proton conductor. SPAN was homogeneously dispersed in the PBI-TGIC matrix. The composite membranes presented good thermal, dimensional, mechanical and oxidative stability for fuel cell applications. Since TGIC was a tri-functional cross-linker, with a relatively low cross-linking degree (CLD), the mechanical strength, dimensional stability and oxidative resistance of the composite membranes were improved. The low CLD also allowed high doping level of SPAN and consequently high proton conductivity. The proton conductivity of PBI-TGIC(5%)/SPAN(50%) and PBI-TGIC(10%)/SPAN(50%) at 180 °C and 100% RH was 0.13 and 0.12 S cm−1, respectively. At 180 °C and 50% RH, the proton conductivity of these two PEMs was 0.064 and 0.058 S cm−1, respectively. At 180 °C and 0% RH, the proton conductivity of them was 0.018 and 0.016 S cm−1, respectively. The methanol resistance and membrane selectivity of PBI-TGIC/SPAN were also good and thus the membranes could be well applied in direct methanol fuel cells.