Benzimidazole effect on the performance of polyelectrolyte membranes based on sulfonated hydrocarbon resin

In this work, anhydrous proton conducting membranes consisting of poly(vinyl alcohol) (PVA) and sulfonated hydrocarbon resin (SR) are obtained, and the effect of benzimidazole (BZ) as a protogenic agent on membrane performance is investigated. The membranes (PVA/SR–BZ) with different BZ concentrations were prepared by solvent casting and characterized by infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The membrane properties are comparatively evaluated by their water uptake, ionic exchange capacity (IEC) and proton conductivity by electrochemical impedance spectroscopy (EIS). The results show that the BZ interacts mainly with the SR polyelectrolyte and increases the thermal stability of the sulfonic groups of the membrane. The membrane conductivity analyzed under anhydrous conditions is susceptible to the presence of the protogenic compound; membranes with 5 wt% of BZ (PVA/SR–5BZ) presents the best results. This susceptibility is attributed to the strong interchain interaction through the basic benzimidazole and sulfonic acid groups. On the other hand, the increase of BZ content in the membrane decreases water uptake and depresses the membrane conductivity, thereby, promoting a change in the membrane properties.