Highly selective and methanol resistant polypyrrole laminated SPVdF-co-HFP/PWA proton exchange membranes for DMFC applications

Abstract

A series of poly (vinylidene fluoride-co-hexafluoropropylene)/phosphotungstic acid/polypyrrole [SPVdF-co-HFP/PWA/PPY- n, where ‘n’ denotes the number of times the PPY coating process was repeated] composite proton exchange membranes (PEMS) were fabricated and studied for its suitability in direct methanol fuel cells (DMFCs). In situ polymerization was used for the lamination of polypyrrole (PPY) on the SPVdF-co-HFP/PWA membrane surface to diminish the leaching of phosphotungstic acid (PWA). FT-IR analysis confirmed the blending of PWA to SPVdF-co-HFP and the coating of PPY on the composite PEM. AFM study indicated that the surface roughness of the composite membrane was decreased by increasing in PPY layer. Ion exchange capacity, water uptake and swelling ratio of the SPVdF-co-HFP/PWA membranes were decreased whereas tensile strength was increased by increasing the PPY layer. The hydrophobic PPY leads to a substantial drop in methanol crossover with workable levels of proton conductivity. The methanol crossover of SPVdF-co-HFP/PWA/PPY-5 hybrid PEM was found to be 1.73 × 10−7 cm2s−1 and was much lower than Nafion-117 (63 × 10−7 cm2s−1). The selectivity ratio of SPVdF-co-HFP/PWA/PPY-5 was found to be high (2.77 × 104 Scm-3s). Thus, all the experimental results revealed that the SPVdF-co-HFP/PWA/PPY composite membrane could be an alternative to high-priced Nafion.