X-RAY PHOTOELECTRON-SPECTROSCOPY AND ELECTROCHEMICAL SURFACE CHARACTERIZATION OF IRO2 + RUO2 ELECTRODES

IrO2 + RuO2 layers on Ti prepared by thermal decomposition at 400-degrees-C of the chlorides dissolved in acid aqueous solution have been characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), energy dispersion X-ray (EDX), inductively coupled plasma emission spectroscopy (ICPES), and cyclic voltammetry (VA) as a function of composition. The surface analysis carried out by XPS showed surface enrichment with Ir while the in-depth composition profile by AES indicated homogeneous distribution of components below the surface. The AES atomic ratio was found to be in agreement with the nominal one as confirmed by ICPES. The voltammetric curves show features which can be used to quantitatively analyze the surface as sensitively as XPS. While in XPS the positions of Ir and Ru photoelectron lines do not change for different mixed oxides, redox transition potentials in voltammetric curves do not vary linearly with surface composition, thus pointing to some possible "synergistic" effects. Surface charges were obtained by integration of voltammetric curves. Their variation with composition and with potential scan rate provides some insight into the morphology and texture of the oxide layers. Reasons for the actual surface composition and for the bulk structure are discussed.