Preparation of laminated composite membranes by impregnation of polypropylene with styrene in supercritical CO2 for direct methanol fuel cells

Composite membranes were formed by grafting styrene using supercritical carbon dioxide (scCO-2) impregnation and polymerization procedures. A polypropylene membrane, styrene monomer, divinylbenzene (DVB), and 2,2′-Azoisobutyronitrile (AIBN) were placed in a reactor, and CO−2 was injected into the reactor at 38 ‡C for the scCO−2 impregnation process. After impregnation, the polymerization process was carried out at 78 ‡C. The grafted membranes were sulfonated in concentrated sulfuric acid at 95 ‡C. These polypropylene grafted polystyrene sulfonic acid (PP-g-pssa) membranes were characterized by using various methods. The morphology and structure of the PP-g-pssa membranes were analyzed with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and energy dispersive spectrometer (EDS). The ion conductivity and methanol permeability were also measured. The ion conductivity of the PP-g-pssa membranes was higher and the methanol permeability of the laminated membrane was lower than that of Nafion membranes. The performance of the PP-g-pssa/Nafion laminated membranes was evaluated in a DMFC unit cell at 90 ‡C.