Synthesis, characterization and electrocatalytic performance of W surface modified, carbon supported Pt anode catalysts for low-temperature fuel cell applications

摘要

Novel, tungsten, surface modified Pt catalysts supported on carbon, (Pt-W(1 wt%)/C, Pt-W(10 wt%)/C), involving Selective surface modification of the active Pt nanoparticles, have been prepared and characterized with respect to their Structure, electrochemical properties and their performance as anode fuel cell catalyst, far the oxidation of CO contaminated H? feed gases. Selective surface modification is achieved by adsorption and thermal decomposition of W(CO)( on ligand-stabilized Pt nanoparticles and their subsequent deposition on Vulcan XC-72. Transmission electron microscopy (TEM), X-ray photo-electron, spectroscopy (XPS) and X-ray diffraction (XRD) measurements show that the surface modification has little effect on the particle size / particle size distribution and that W deposition leads to islands of tungsten oxides (WO,,) on the surface of the Pt nanoparticles rather than to surface alloy formation. This conclusion is supported by electrochemical and mass spectrometric measurements (differential electrochemical mass spectrometry (DEMS)). DEMS measurements on COad pre-covered catalyst electrodes monitoring Faradaic current, CO2, formation and H-2 consumption: and quasi-stationary (v = 1 m,V(.)s(-1)) rotating disk electrode (RDE) measurements in, electrolyte saturated unth, CO/H-2 mixtures with, different CO concentrations (250 ppm, - 2% CO) show that compared to unmodified commercial Pt/C catalysts the HOR activity is significantly improved at relevant, low potentials on the largely COad covered, W-modified catalysts, where < 2000 ppm. The high HOR activity under these conditions is explained by a combination of several effects, a high HOR activity on the unmodified Pt surface areas, an improved activity of the WOx deposit for the generation of oxygen species and reaction with COad on neighboring Pt sites, and a low mobility of COad species, leaving COad free Pt areas for the HOR around the deposited WOx islands.