Investigation on meta-polybenzimidazole blend with sulfonated PVdF-HFP proton conducting polymer electrolytes for HT-PEM fuel cell application

Sulfonated poly (Vinylidene Fluoride-co-hexafluoro propylene) (SPVdF-HFP) blended with varying concentrations of m-poly (Benzimidazole) (PBI) were prepared by solution casting techinque. The sulfonation of PVdF-HFP was carried out with fuming chlorosulfonic acid at 60 °C and the degree of sulfonation was found to be 2.48%. The addition of m-PBI into the hydrophilic sulfonated PVdF-HFP membrane has provided good chemical and thermal stability. And also the increases the physico-chemical characteristics such as the water uptake, ion exchange capacity and proton conductivity. An inter chain separation and specific interaction between the two polymers in the blends was observed by XRD and FT-IR analyses. The Fourier transform spectroscopy indicated the intense ionic bond between—SO₃H and N-basic group. The 25% of m-PBI based blend polymer electrolyte gives high proton conductivity (5.72 × 10⁻³ S/cm) at 160 °C and also the thermal stability. The temperature dependent proton conductivity of the polymer electrolyte follows an Arrhenius relationship and Grotthuss mechanism and it shows hopping of ions in the polymer matrix. It is noticed that the addition of m-PBI in the sulfonated PVdF-HFP enhances the mechanical, thermal and proton conductivity, which are sufficiently better for the use in HT-PEM fuel cell applications.