Phosphoric acid doped polybenzimidazole membrane for high temperature PEM fuel cell

In the present study, phosphoric acid doped polybenzimidazole (PBI) membranes with potential applications in high temperature PEM fuel cells were investigated. PBI was synthesized by polycondensation of 3,3'-diaminobenzidine and isophtalic acid in polyphosphoric acid. The formation of PBI was validated by H1-NMR and elemental analysis. PBI membranes were prepared by solution casting method and immersed in phosphoric acid in order to provide ionic conductivity. The phosphoric acid doped membranes were used to prepare membrane electrode assemblies (MEA) for PEMFC operation. Gas diffusion layer (GDL) spraying method was used to prepare the electrodes. In order to determine optimum electrode structure, the effect of electrode preparation technique on fuel cell performances was studied. Two methods were applied in which the binder differs in the catalyst ink. In the first method, 5 wt % PBI solution was used as the binder. In the second method, polyvinylidene fluoride (PVDF) was used in addition to PBI as the binder in the catalyst ink. The MEA were tested in a single cell operating at 100 degrees C without need for humidification of reactant gases. The observed maximum power output was increased considerably from 0.015 to 0.072 W/cm2 at 150 degrees C when the binder of the catalyst was changed from PBI to PBI and PVDF mixture (PVDF : PBI = 3 : 1). A single cell was operated up to 160 degrees C and the power outputs of 0.032 and 0.063 W/cm2 were obtained at operating temperatures of 125 and 160 degrees C, respectively. The PVDF : PBI ratio was 1 : 3 in the catalyst ink at both temperatures. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012