Nafion/polyaniline/silica composite membranes for direct methanol fuel cell application

This work investigates the characterization and performance of polyaniline and silica modified Nation membranes. The aniline monomers are synthesized in situ to form a polyaniline film, whilst silica is embedded into the Nation matrix by the polycondensation of tetraethylorthosilicate. The physicochemical properties are studied by means of X-ray diffraction and Fourier transform infrared techniques and show that the polyaniline layer is formed on the Nation surface and improves the structural properties of Nation in methanol solution. Nation loses its crystallinity once exposed to water and ethanol, whilst the polyaniline modification allows crystallinity to be maintained under similar conditions. By contrast, the proton conductivities of polyaniline modified membranes are 3-5-fold lower than that of Nation. On a positive note, methanol crossover is reduced by over two orders of magnitude, as verified by crossover limiting current analysis. The polyaniline modification allows the membrane to become less hydrophilic, which explains the lower proton conductivity. No major advantages are observed by embedding silica into the Nation matrix. The performance of a membrane electrode assembly (MEA) using commercial catalysts and polyaniline modified membranes in a cell gives a peak power of 8 mW cm(-2) at 20 degrees C with 2 M methanol and air feeding. This performance Correlates to half that of MEAs using Nation, though the membrane modification leads to a robust material that may allow operation at high methanol concentration. (c) 2007 Elsevier B.V. All rights reserved.