XPS study of the state of iridium, platinum, titanium and oxygen in thermally formed IrO2+TiO2+PtOx films

Electrodes of nominal composition Ir0.3Ti(0.7-x)PtxO2 (x = 0; 0.4 and 0.7) have been prepared by thermal decomposition of mixtures of the chloride precursors. H2PtCl6 was used as Pt-precursor. A systematic study of the chemical composition and oxidation states of the elements of these electrodes was performed by XPS. XPS analysis showed that the surface of the PtOx-containing coatings are Pt enriched. Additionally, XPS revealed that the Ir signals are almost absent from the spectra of PtOx-containing electrodes, while the Ti signal is completely absent. On the basis of the XPS results it is possible to propose a model of the surface structure of these electrodes: the grains, composed almost exclusively of Ir Jr Pt, are Pt enriched and distributed in a matrix, which although having Ti in its composition, besides Ir and Pt, is also Pt enriched. This finding corroborates the electrochemical behaviour of these electrodes, which is characteristic of polycrystalline Pt. (C) 2000 Elsevier Science B.V. All rights reserved.