Electrochemical properties of PEM fuel cells based on Nafion-polybenzimidazole-imidazole hybrid membranes

Proton exchange membranes based on perfluorosulfonic acid (PFSA, Nafion-115) and fluorine-containing polybenzimidazole (PBICF3), and imidazole (Im) were prepared by immersion of Nafion-115 into PBICF3, Im and both of them. Fluorine-containing polybenzimidazole was synthesized from 3,3′-diaminobenzidine and 2,2-bis-(4-carboxyphenyl)hexafluoropropane. Obtained four membranes (PFSA-PBICF3-Im, PFSA-PBICF3, PFSA-Im and PFSA) were used to assemble single polymer fuel cells. All membranes were characterized by FT-IR spectroscopy, TGA (DTG) analyses and water content. For Nafion-115 membrane immersed in PBICF3-Im, the increase of water uptake in the range from 1.6 to ca. 3% in comparison to unmodified electrolyte was found. Constructed PEM single cells were investigated by electrochemical impedance spectroscopy, polarization curves and two voltammperometric methods (LSV and CV). Influences of PBICF3, Im and mixture of both of them in defined conditions, on the thermal and electrochemical properties of Nafion-115, were analyzed in details. The maximum power density of 124 mW/cm2 at the current density of 347 mA/cm2 was detected for PFSA-Im membrane. The immersion of Nafion-115 in PBICF3, Im and PBICF3-Im caused an increase of ionic conductivity from 2.16 mS/cm (for Nafion-115) to 3.48 mS/cm for PFSA-Im.