Electrocatalytic activity of platinum nanoparticles supported on different phases of tungsten carbides for the oxygen reduction reaction

Carbon-supported tungsten carbides with cubic (β-WC1-x/C) and hexagonal (α-WC/C) are evaluated as support materials of Pt-nanoparticles, to be used as electrocatalysts for the oxygen reduction reaction (ORR) in acid media. The produced materials are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes are employed for the electrochemical investigations. It is seen that all Pt-α-WC/C catalysts present specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C), while for the Pt-β-WC1-x/C composites the specific activitiy is 3.6 times higher than that of Pt/C, when a carbide-to-carbon load of 40 wt% is used. These differences in reactivity for the ORR may be associated to differences in the binding energy of adsorbed oxygen on Pt, introduced by the tungsten carbide substrates. Pt XANES results for the β-WC/C1-x materials evidence a small increase in the Pt 5d band occupancy, which may lead to a weaker Pt-OHx interaction, increasing the ORR kinetics.