New polymer electrolyte membranes for low temperature fuel cells

Partially fluorinated proton exchange materials were synthesised by pre-irr adiation grafting of styrene into poly(vinylidene fluoride) films with subs equent sulfonation. The grafted and sulfonated membranes, PVDF-g-PSSA membr anes, have been studied with respect to water uptake, ion and water cluster ing, ion conductivity and water diffusion coefficients. Water associates wi th the membranes in three different ways: bound non-freezable water, freeza ble bound water and freezable free water. The proton conductivity of the me mbrane is strongly dependent on the hydration, it decreases more rapidly th an the water self diffusion with decreasing water content. Ion clusters wit h a Bragg distance of 25 Angstrom form the conducting channels in the membr anes.