Synthesis and characterization of proton conducting polymer membranes for fuel cells

Commercial polymers with aryl backbones such as polystyrene (PS), polycarbonate (PC), polysulfone (PSf) and poly (phenylene oxide) (PPO) were sulfonated using suitable reagents, and assessed for their potential to serve as proton exchange membranes (PEM) in fuel cells (FCs). The membranes thus synthesized were characterized by Fourier transform infra-red (FTIR) and 1H NMR to verify sulfonation and to identify the sites available for proton conduction. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) studies were carried out to investigate the thermal stability of the sulfonated membranes. Surface morphology and tensile strength were evaluated by scanning electron microscopy (SEM) and UTM, respectively. Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion exchange capacity (IEC), which is a measure of proton conductivity, and the degree of substitution (DS) were evaluated and found to be comparable with the commercially available Nafion membranes. Sulfonated polycarbonate (SPC) was found to possess all the requisite properties of a PEM; namely, high IEC (0.57 meq./g), tensile strength (157 N/mm2) and thermal stability (Tg=120 °C) besides low affinity towards methanol (%sorption=2.97). The study reveals the possibility of developing inexpensive and sturdy fuel cell membranes, which could provide attractive alternatives to substitute the expensive commercially available membranes.