Studies of bibenzimidazole and imidazole influence on electrochemical properties of polymer fuel cells

Binary and ternary membranes were prepared by immersion of Nafion-115 in 2,2′-bis(4-aminophenyl)-5,5′-bibenzimidazole (BAPBI) or/and in imidazole (Im) and were used in proton exchange membrane fuel cells (PEMFCs) with Pt/C gas diffusion electrodes and graphite single-serpentine monopolar plates. Membranes were activated in 0.2 M H2SO4. BAPBI was synthesized in poly(phosphoric) acid and the chemical structure was confirmed by 1H, 13C NMR and ATR-FTIR spectroscopy. Membranes were characterized by FTIR spectroscopy, TGA, AFM techniques. Also the water uptake was determined. PEMFCs were investigated by electrochemical impedance spectroscopy, polarization curves, cyclic voltammetry and linear sweep voltammetry taking into consideration the kind of imidazole applied and the temperature used (25 or 60 °C). The maximum power density of 146 mW/cm2 at the current density of 345 mA/cm2 was detected for Nafion-115-BAPBI membrane. For all constructed PEMFCs the efficiency at 0.6 V was found about 41%. The immersion of Nafion-115 in Im, BAPBI or BAPBI-Im increased the thermal stability and mechanical properties of membranes. The Nafion-115-BAPBI membrane showed good prospective for application in PEMFCs while in opposite to Nafion-115-Im, the poisoning effect on Pt catalyst was not observed.