Hybridization of Nafion membranes by the infusion of functionalized siloxane precursors

Polysiloxane-modified hybrid membranes were prepared by introducing in a pre-swelled commercial Nafion membrane a sol–gel precursor solution, consisting of a pre-hydrolyzed mixture of tetraethoxysilane and a mercaptan functionalized organoalkoxysilane. The structure of the polysiloxane network was changed by altering the ratio of the two silane components within the precursor solution. The mercaptosilane modifier was used to provide an additional source of acidic Bronsted sites through the oxidisation of the mercaptan groups to sulfonic acid groups.The physical and chemical properties of the hybrid membranes were examined by TGA, FT-IR and SEM–EDS analysis. The water vapor sorption and proton conductivity characteristics were evaluated at 40, 60 and 70 °C and with water activity in the region of 0.4–1.It was found that the polysiloxane network alters the water vapor sorption mechanism of the Nafion membrane, resulting in an increase in the equilibrium amount of water absorbed in the middle range of water activity (0.4–0.6). At the same time, the increased water sorption capability produced a concomitant increase in ionic conductivity at low water activities.