Fabrication and performances of solid superacid embedded chitosan hybrid membranes for direct methanol fuel cell

This study reports the fabrication and performances of hybrid proton-conducting membranes by dispersing nanosized solid superacid inorganic fillers, TiO2-SO42- (STiO2), into chitosan (CS) matrix. Fourier transform infrared spectra demonstrate intermolecular interactions between STiO2 and chitosan segmental chains. High resolution scanning electron microscope characterization reveals an essentially homogeneous dispersion of the solid superacid fillers within chitosan matrix. The incorporation of the superacid fillers leads to a reduced fractional free volume (FFV) of the hybrid membranes as confirmed by positron annihilation lifetime spectroscopy (PALS) analysis. This reduced FFV and more tortuous pathway significantly enhance the methanol diffusion resistance through the membranes, resulting in a decreased methanol crossover. Under identical conditions, compared with TiO2 embedded membranes, the STiO2-filled hybrid membranes exhibit simultaneously improved methanol barrier and proton transport properties due to the enhanced interfacial interaction and proton conductive ability. Moreover, compared with Nafion 117 membrane, all the STiO2-filled hybrid membranes display much lower methanol crossover whereas the proton conductivity of the membranes remains high enough for DMFC applications. Meanwhile, due to the interfacial interactions between STiO2 and chitosan chains, the hybrid membranes exhibit an enhanced mechanical strength and adequate thermal stability as verified by mechanical strength characterization and thermogravimetric analysis. (C) 2009 Elsevier B.V. All rights reserved.