Synthesis and Characterization of Carbon-Supported Platinum-Molybdenum and Platinum-Tungsten Catalysts for Methanol Oxidation in Direct Alcohol Fuel Cells

Abstract

A series of carbon-supported bimetallic catalysts with different metallic loadings was synthesized, using platinum as the principal active phase and molybdenum or tungsten as promoting phases. The materials were prepared by organometallic precursor thermolysis and characterized by direct current electrochemical methods, transmission electron microscopy, scanning electron microscopy and x-ray diffraction. Electrodes were elaborated with each catalyst and their electrochemical performances were studied by cyclic voltammetry. These results show an increased activity of the catalysts with small amounts of Mo or W, towards oxidation of methanol with respect to the catalyst containing only platinum. XRD results reveal the presence of molybdenum or tungsten bronzes (HxMoO3, HxWO3) that are responsible for the increase in activity. It is believed that the bronzes participate in a spillover effect by promoting the removal of protons from the platinum surface. It was found that the presence of molybdenum in this type of catalyst prevents the platinum phase from sintering during the thermal treatment and allows them to keep platinum particles with mean sizes between 2 and 8 nm. The proposed catalysts are adequate for methanol oxidation in liquid-fuel alcohol fuel cell systems, since it was found that oxidation potentials are lower than those observed with platinum catalysts.