Grafting of styrene on to Nafion membranes using supercritical CO2 impregnation for direct methanol fuel cells

Grafting of styrene on to Nafion membranes is carried out by impregnation and radical polymerization in supercritical carbon dioxide (scCO2) as a solvent and swelling agent. Styrene monomer and the initiator 2,2′-azoisobutyronitrile (AIBN) are first impregnated into Nafion membranes using scCO2 at 38 °C and 25 MPa. After releasing CO2, the polymerization is carried out at 80 °C and 10 MPa. The Nafion-grafted-polystyrene (N-g-ps) is sulfonated in concentrated sulfuric acid (98% H2SO4). The grafted membranes are characterized by measuring their ion-exchange capacities, ion conductivity and methanol permeation. The morphology and structure of these membranes are observed with Fourier transform infrared spectroscopy and scanning electron microscopy. The Nafion-grafted-polystyrene sulfonic acid (N-g-pssa) exhibits higher ion conductivity and lower methanol permeability than that of Nafion 115. The N-g-pssa membranes are tested as electrolytes in a direct methanol fuel cell.