Keywords: particles, polymer matrix, composite membranes, proton conduction, metal alkoxides, sol gel, nanoparticles, nanotechnology, titania phosphate, fuel cells
Proton conductive composite membranes
In this work we investigated the synthesis of composite organic and inorganic membranes for proton conduction. Particles derived from metal alkoxides (M(OR)n) sol-gel processes (Ti, Zr, W with phosphoric acid) were embedded in polymeric matrices of poly-vinyl alcohol, (3-glycidoxypropyl)-trimethoxysilane and ethylene glycol. The structure of the composite membranes was complex as several IR peaks were convoluted, indicating the assignment of several functional groups. However, the peaks assigned to OH groups reduced in intensity in the composite membranes, indicating that cross-linking of hydroxyl groups in the organic and inorganic phases of the membrane may have occurred. The particles allowed for re-arrangement of the polymer matrix, as crystallinity was reduced compared to a polymer blank membrane. The composite membrane process resulted in homogeneous dispersion of nanoparticles into the polymer film. Proton conduction of the inorganic phase was mainly dominated by titania. Binary mixtures of titania phosphate (sample name TiP) resulted in proton conduction of 7.15 ? 10−2 S.cm−1, one order of magnitude higher than zirconia phosphate (ZrP). The addition of Zr and W to TiP forming ternary or quaternary phases also led to lower proton conduction as compared to TiP. Similar trends were also observed for the composite membranes, though the TiP composite membrane proton conduction reduced after several hours of testing at 50?C, which was mainly attributed to acid leaching.