Phosphoric Acid Doped Poly(2,5-benzimidazole)-Based Proton Exchange Membrane for High Temperature Fuel Cell Application

Undoped and doped poly(2,5-benzimidazole) (ABPBI) membrane was prepared by solvent casting method using methane sulfonic acid as a solvent and phosphoric acid (H3PO4) as a doping agent. The concentration of H3PO4 was varied from 0 to 60 vol% to enhance the proton conductivity of the ABPBI membrane at higher temperature. Wide angle X-ray diffraction analysis showed a decrease in crystallinity in ABPBI membrane with increase in H3PO4 doping concentration. The molecular signature and the presence of H3PO4 was observed in 1000-1500 cm(-1) in the Fourier transform infrared spectra, which was also supported by a corresponding weight loss at 180 degrees C-200 degrees C in the thermogravimetric analysis. Undoped ABPBI membrane registered the Young's modulus (E) and hardness (H) values of 2.46 and 0.92 GPa, respectively, and the corresponding E and H values for 1.65 doping level of 60 vol% H3PO4 doped ABPBI membrane were 0.14 and 0.067 GPa, respectively. The 60 vol% H3PO4 doped ABPBI membrane with doping level of 1.65 showed highest proton conductivity value of 2.2 x 10(-2) S/cm. The impedance spectroscopic analysis and the equivalent circuit model were discussed to understand the nature of proton conduction in H3PO4 doped ABPBI membrane. (C) 2016 Society of Plastics Engineers