Synthesis and Properties of Ion-Exchange Membranes Based on Porous Polytetrafluoroethylene and Sulphonated Polystyrene

Novel ion-exchange membranes based on a commercial porous polytetrafluoroethylene film and sulfonated polystyrene are synthesized. To form porous polytetrafluoroethylene–polystyrene composites, thermal polymerization of styrene sorbed in the pores of the matrix-film from the monomer solution is used. The use of porous matrix makes it possible effectively obtaining the composites, used as precursors of the ion-exchange membranes. The sulfonating of the porous polytetrafluoroethylene–polystyrene composites forms the membranes with ion-exchange capacity up to 2.8 mmol/g. The composition and ground physicochemical properties of the new proton-conducting composite membranes are investigated. The developed membranes were shown to have good transport properties. The proton conductivity of water-saturated membranes is as high as 0.13 S/cm at room temperature; the hydration number is 30. Comparative tests of the synthesized membranes and the commercial Nafion-115 membrane in a direct methanol fuel cell at 60°C showed the characteristics of the fuel cell with the developed membranes being at least not inferior to those of a Nafion-115-based cell.