A RESISTOMETRIC STUDY OF THE OXIDE LAYER FORMATION ON THIN-FILM IRIDIUM ELECTRODES IN AN ACIDIC SOLUTION

The composition of a thin-film iridium electrode as well as its electr ical and corrosion properties at different stages of oxidation in 0.5 M H2SO4 were investigated using resistometric and potentiodynamic tech niques, X-ray photoelectron spectroscopy, infrared spectrophotometry, and atomic-absorption spectroscopy. When the Ir electrode was cycled u p to E(r) = 1.35 V (RHE), the potential dependence of its resistance w as similar to that of other metals of the platinum group. When E(r) wa s increased to 1.45 V, the layer of a nonstoichiometric hydrated oxide was formed on the electrode surface, which led to a significant chang e in the electrical properties of the electrode. The contribution of i ridium dissolution to an increase in the film resistance was evaluated . Our results were quantitatively discussed on the basis of the oxidat ion model, which presumes that the oxide gradually ''intergrows'' into the bulk of the film at separate active centers.