Novel radiation grafted membranes based on fluorinated polymers for proton exchange membrane fuel cell

Official URL: http://risc01.sabanciuniv.edu/record=b1640588 (Table of Contents)

In the first part of this thesis a facile method for preparing poly(vinylidene fluoride) (PVDF)-gpoly( styrene sulfonate acid) (PSSA) membranes by radiation induced graft polymerization is reported. Sodium styrene sulfonate (SSS) monomer has been used for the grafting of SSS from PVDF powder in aqueous dimethyl sulfoxide (DMSO) solution, and it precipitated after synthesis. Later on, the resultant PVDF-g-PSSS graft copolymer membranes were prepared by means of vapor induced phase separation (VIPS) technique at 60% relative humidity (RH), and dried under vacuum at high temperature to achieve PVDF-g-PSSA proton conducting nano-porous membranes. It was found that these membranes exhibit encouraging results in terms of higher conductivity and better mechanical properties compared to Nafion® NR-211. In the second part of thesis, the effect of divinylbenzene (DVB) as a cross-linker on the graft polymerization of 4-vinylpyridine (4-VP) from poly(ethylene-co-tetrafluoroethylene) (ETFE) films was studied. The resulted films were doped with phosphoric acid (PA), and examined for mechanical properties and fuel cell performance. The cross-linked membrane obtained from grafting a mixture of 4- VP with 1% DVB improved the polymerization kinetics, and resulted in 50% graft level (GL). The resulted membrane additionally exhibited proton conductivity as high as 75 mS/cm at 50% relative humidity and 120 °C, besides doubling the power output of fuel cell comparing to a non-cross-linked membrane.