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.

Enhancement of activity of PtRh nanoparticles towards oxidation of ethanol through modification with molybdenum oxide or tungsten oxide

“…3 Scanning electron microscopy and EDS analysis of a PtRh/Vulcan, b MoO 3 -modifed PtRh/Vulcan, and c WO 3 -modifed PtRh/Vulcan nanoparticles the proposed electrocatalytic system due to possible dissolution of the MoO 3 from the surface of carbon-supported PtRh nanoparticles. In the literature, the stability of MoO 3 is still controversial [62][63][64][65][66][67]. However, we have not observed any time-dependent deactivation effect that may imply dissolution of MoO 3 .…”

Characterization and voltammetric behavior of Pt Mo O /C electrodes prepared by the thermal decomposition of polymeric precursors

“…However, the stability of this kind of catalysts is still controversial. While some studies report the occurrence of molybdenum dissolution after only a few cycles [11,16], other investigations have shown the presence of stable molybdenum species after several cycles at potentials between 0.0 and 1.2 V in 0.5 mol L −1 H 2 SO 4 [20,26,27].…”

A Voltammetry Study of Ethanol Oxidation on Carbon Supported, Non Alloyed Platinum-Tungsten Catalysts

“…The formulation of fuel cell catalysts with different tungsten promoting phases has been studied by several groups with promising results as a CO tolerant anode in the oxidation of ethanol and methanol. [23][24][25][26][27] While in Pt-Ru and Pt-Sn catalysts the activity enhancement is attributed to a combination of the bifunctional mechanism and the ligand effect, in the case of some tungsten-containing catalysts it has also been proposed that a hydrogen spillover effect may occur, continuously cleaning the platinum surface. 28 However, it is still not clear how this effect can play a role in the rate-determining step at the electrode potentials in which alcohol oxidation takes place.…”