CHARACTERIZATION OF TIO2 FILMS MODIFIED BY PLATINUM DOPING

TiO2-Pt films were prepared through galvanostatic platinum deposition from acidic H2PtCl6 solutions, followed by potentiodynamic TiO2 growth in Na2SO4 Solutions. The characterization of the doped films was carried out by means of Auger electron spectroscopy and X-ray photoelectron spectroscopy (XPS) in combination with argon bombardment. The dopant concentration profiles and the valence states of the elements present within the films were also determined. The predominant species present is metallic platinum, although oxidized species probably make some contributions. Titanium changed from TiO2 to lower oxidation states in going from the surface to the film depth. XPS indicates the presence of hydrated oxides at the surface. Scanning electron microscopy (SEM) analyses indicate that platinum deposition occurs preferentially on grain boundaries. At high platinum content, clusters are evident and the substructure of titanium substrate is reproduced. At low platinum content, SEM cannot detect its presence at the surface in spite of the electrochemical evidence. The electrochemical behaviour of modified oxide films was also analysed. The potentiodynamic response correlates with the response of a polycrystalline platinum electrode. Electron transfer reactions reveal a catalytic effect due to the platinum incorporated into the TiO2 layer. The oxygen evolution reaction was investigated using impedance as a function of both the platinum content and the thickness of the TiO2 layer. Finally, an approximate physical model for the system is proposed.