PROTON EXCHANGE MEMBRANES BASED ON BLENDS OF POLY(BENZIMIDAZOLE) AND BUTYLSULFONATED POLY(BEZNIMIDAZOLE) FOR HIGH TEMPERATURE PEMFC

Phosphoric acid doped poly(benzimidazole) (PBI) is one of excellent candidates of proton exchange membranes for high temperature (150-180 degrees C) proton exchange membrane fuel cells (PEMFCs). However, the strong inter-polymer hydrogen bonds cause low elongation and brittleness of 13131 membranes. In this work, we synthesize poly(benzimidazole) (FBI) and butylsulfonated poly(benzimidazole) (PBI-BS), in which around 22 mole% of imidazole -NH groups of PBI are grafted with sulfonated butyl groups. We show the elongation, phosphoric acid doping level, and proton conductivity of PBI can be improved by blending similar to 20 wt% of PBI-BS in the FBI membrane, and the membrane electrode assembly prepared from PBI/PBI-BS (8/2 by wt) blend membrane has a better PEMFC performance at 140 degrees C similar to 180 degrees C than that prepared from PBI membrane. It is believed that the crosslink interactions of imidazole -NH and -N=C-groups with side chain -C(4)H(8)-SO(3)H groups of PBI-BS reduces the inter-PBI hydrogen bonds and increases the free volume of polymers, which leads to the enhancements of the membrane toughness and phosphoric acid doping level and the PEMFC performance.