Chemical and morphological characterization of a direct methanol fuel cell based on a quaternary Pt-Ru-Sn-W/C anode

Conventional and 'paste process' methods were investigated to fabricate the membrane/electrode assembly (M&E) for application in a vapour-feed direct methanol fuel cell. A quaternary Pt-Ru-Sn-W/C and a Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. The structure and chemical composition of the catalysts were investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). A crystalline Pt f.c.c. phase was found to prevail in both catalysts. Agglomeration and twinned particles were frequently observed in the Pt-Ru-Sn-W/C catalyst. Electrochemical investigations were performed by a.c.-impedance spectroscopy and galvanostatic polarization. The 'paste process' based assembly showed a significantly lower uncompensated resistance and an approximately two-fold power density increase with respect to the conventional assembly. According to the scanning electron microscopy analysis the observed results were attributed to improved bonding between catalysts and perfluorosulfonic membrane and to a larger extension of the three-phase reaction zone in the 'paste process' based assembly. © 1996 Chapman & Hall.