Blend membranes from poly(2,5-benzimidazole) and poly(styrene sulfonic acid) as proton-conducting polymer electrolytes for fuel cells

Polymer electrolyte membranes were fabricated by blending of poly(2,5-benzimidazole) (ABPBI) and poly(styrene sulfonic acid) (PSSA) at several molar ratios with respect to repeating units. Fourier transform infrared spectroscopy was used to elucidate inter-polymer interactions. Surface morphology was studied through scanning electron microscope. Thermal properties of the membranes were investigated by thermogravimetric analysis and differential scanning calorimetry. The spectroscopic measurements and water uptake (WU) studies indicate a complexation between ABPBI and PSSA where the swelling behavior of membranes increases with the PSSA content. Proton conductivities of the anhydrous and humidified samples were measured using impedance spectroscopy. Proton conductivity of ABPBI:PSSA bend with (1:4) molar ratio was detected as around 10⁻³ S/cm at higher temperatures under anhydrous conditions. On the other hand, the membrane ABPBI:PSSA (1:2) showed the proton conductivity of 0.02 S/cm (ambient temperature, RH = 50%) which is at least five-order of magnitude higher than the anhydrous material.