_______________________________________________ *Corresponding Author: roquero@unam.mx Electrocatalysis. may 2017, vol 8, issue 3, pp 261-269 / https://doi.org/10.1007/s12678-017-0361-2 The promoting role of tungsten oxides in the anodic oxidation of methanol on platinum-based catalysts D. Cíntora-Juárez a , A. L. Ocampo-Flores a , L.C. Ordóñez b , P. Roquero a * a: Facultad de Química, Universidad Nacional Autónoma de México. Avenida Universidad 3000. CP 04510 Ciudad de México. México b: Unidad de Energía Renovable, Centro de Investigación Científica de Yucatán. Parque Científico Tecnológico de Yucatán Carretera Sierra Papacal – Chuburná Puerto, km 5. Sierra Papacal, Yucatán, México. CP 97302 Abstract Carbon-supported Pt-WO 3 catalysts formulated with different proportions of platinum and tungsten were synthesized by thermal decomposition of metal carbonyl precursors. The activity of the PtWO 3 /C catalysts towards the methanol electrooxidation reaction (MOR) was evaluated in half-cell configuration and as anode catalyst in a direct methanol fuel cell device (DMFC) with a home-made membrane-electrode-assembly (MEA). The presence of WO 3 increase significantly the catalysts activity, expressed by higher oxidation currents at lower potential values than those obtained with Pt/C. DMFC power output is comparable to that obtained by using a commercial MEA containing twice of the Pt loading at the anode. Electron microscopy and X-Ray diffraction analysis (XRD) revealed that monoclinic WO 2.92 and hexagonal WO 3 phases coexist in the PtWO 3 /C catalysts. In samples with equal Pt loadings, the Pt particle size increase and its active area decreased as tungsten is added to the catalyst formulation. As the tungsten loading is increased and carbon content is diminished, hexagonal WO 3 appears as the predominant crystalline phase. Keywords. Direct Methanol Fuel Cell; electrocatalysts; platinum; tungsten trioxide; metal carbonyl precursor 1. Introduction Owing to its ease of storing and handling, as well as its high energy density, methanol is an attractive fuel to be directly electrooxidized in a fuel cell device as an alternative way to generate electric current for diverse applications. In this regard, very promising prototypes of vehicles and portable electronics running with direct methanol fuel cells (DMFC) have been described [1]. The complete electrooxidation of methanol to CO 2 on Pt-based electrodes involves the generation of partially oxidized species (H 2 CO, HCOOH, HCO, COH and CO) which strongly adsorb on the catalyst surface [2, 3]. This situation is the main responsible for the slow charge transfer kinetics at the anode surface, which causes the high overpotential required to bring the reaction to completion. The development of new anode catalysts that enhance the kinetics of methanol electrooxidation, together with the design of electrolyte membranes able