Electrodeposition and Characterization of Three-Dimensional Tungsten(VI, V)-Oxide Films Containing Spherical Pt

Simultaneous reductive lectrodeposition f metallic platinum and tungsten(VI, V)-oxide aggregates was carried out by potential cycling in WOJchloroplatinate colloidal suspensions in H2SO4. The nonstoichiometric centers in the reduced WO3 deposits were found to mediate chloroplatinate electroreduction. Scanning electron microscopy was used to examine the morphology and distribution of Pt in the W(VI, V)-oxide supports. Auger electron spectrometry allowed detection of Pt, W, and C in films on graphite and was employed to characterize the elemental depth profiles. The spherical Pt micro-particles were randomly dispersed in the oxide matrix. The size and density of the particles were dependent on the rate of potential scan during electrodeposition. The Pt spheres tended to be larger and denser when they were formed from more concentrated chloroplatinate solutions. Absorption spectroscopy coupled with electrochemistry showed evidence for the partial reduction of the tungsten oxide support at-0.3V vs. SCE. Cyclic voltammetric experiments indicated that the tungsten-based redox transitions in the platinized oxide were essentially reversible and that their energetics were affected by dispersed Pt. The mutual metal-support interactions apparently involve desorption and spillover of H from Pt. This process eems to be coupled with the absorption of hydrogen by WO3 and apparently favors the formation of hydrogen W-bronzes. The long-term stability of the coating and the durability of the immobilized Pt were apparent from diagnostic experiments hat included sonication and prolonged cyclic oxidations and rereductions in 2M H2SO4