Conductive ceramic oxides based on Ir and Ta are commonly used in the fabrication of dimensionally stable anodes for many electrochemical systems requiring high chemical stability and electrocatalytic activity in aggressive environments. In this paper, the degradation of IrO₂-Ta₂O₅ (35.6 wt%  Ir and 26.3 wt% Ta ) coated titanium mesh anodes in 2 M sulfuric acid solutions will be discussed. The Ir-Ta oxide coated electrodes were prepared by brush coating Ti mesh samples with an organic solvent system containing H₂IrCl₆ and TaCl₅followed by firing at approximately 450 deg. C. The thickness of the oxide coating was ~ 4.8 to 6.9 microns.

The electrochemical properties of the prepared electrodes were studied by performing galvanostatic accelerated life tests and anodic polarization. The accelerated life test consisted of subjecting the sample to a current density in the range of 0.54 to 1 A/cm² in 2 M sulfuric acid solution in a customized flow through cell with a titanium mesh cathode for a period lasting over five hundred hours. The degradation of the coating was followed by monitoring the cell potential. A PARSTAT 2273 Potentiostat system equipped with a PowerSuite^®software was used for these experiments. The acid concentration was maintained at 2M by adding the required amount of water to compensate for the decomposition of water to oxygen at the anode. The lifetime test was interrupted periodically to conduct anodic polarization experiments and determine changes in the potential for oxygen evolution. The morphology and chemical composition of the coatings at different stages of the accelerated life test were characterized by SEM and energy dispersive X-ray spectroscopy (EDS).

The as-prepared sample had numerous cracks and displayed amorphous and crystalline features. Localized thinning as well as complete removal of the oxide coating were evident in samples subjected to accelerated life testing (see Figure). EDS analysis indicated selective removal of IrO₂ from the oxide coating. The presentation will discuss the results of the electrochemical and morphological investigations and propose a degradation mechanism for the Ir-Ta oxide coating in acidic environment.