Faradaic impedance investigation of the deactivation mechanism of Ir-based ceramic oxides containing TiO2 and SnO2

Ti-supported IrO2/SnO2/TiO2 coatings were prepared by thermal decomposition of the chloride precursor mixtures (400 degrees C). The effect of the replacement of TiO2 by SnO2 on the service life of the Ti/IrO2 + TiO2 coating was investigated under galvanostatic polarization at 0.8 A cm(-2) in 1.0 mol dm(-3) HClO4. The deactivation mechanism of the electrodes, using OER as the reaction model, was investigated through the periodic recording of voltammetric curves (VC) and impedance spectra (EIS) as a function of the anodization time. Bulk composition and morphology of the electrode coatings were investigated by energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) before and after accelerated life tests. The service life showed a dependence on the electrode composition. Replacement of TiO2 by SnO2 in the Ir0.3Ti0.7O2 electrode led to a decrease in the service life of these systems above 30% mol SnO2 content. This behaviour is directly related to morphological factors and the absence of synergetic effects. The behaviour of the parameters supplied by the EIS, VC, SEM, and EDX analyses made it possible to describe the overall deactivation mechanism.