Thermoanalytical investigation on the formation of IrO₂-based mixed oxide coatings

Abstract

The formation reactions of IrO₂/TiO₂ mixed oxide films supported on titanium metal plate were followed by thermoanalytical (simultaneous TGA, DTG, DTA) and combined thermoanalyticalmass spectrometric (TGA-MS) techniques. The electrochemical characterization of the fired coatings was made by cyclic voltammetry. The thermal decomposition of the titanium precursor salt, titanium diisopropoxide bis-2,4-pentanedionate, shows a major change in the presence of hydrated iridium (iii) chloride. Due to the catalytic effect of the added noble metal, an almost complete conversion of the organic components of the precursor mixture to CO₂ and H₂O is observed in the combustion stage. Chlorine, from thermal decomposition of the iridium salt, is produced in a separate stage at higher temperatures, indicating that a sequence of steps occurs prior to the oxide formation. For iridium chloride alone a complexation between the metal ion and the solvent (isopropanol) is observed, leading eventually to H₂O and CO₂ production (combustion step) between 300 and 500° C. The cyclic voltammetry results indicate that the features of the precursor reaction affect the charge storage capacity of the oxide films.