Investigation of surface morphology, structure and electrocatalytic properties for O2 evolution of titanium based IrO2+Ta2O5 coatings

Titanium based IrO2+Ta2O5 oxide anodes with different compositions and pyrolysis temperatures were prepared by thermodecomposition method. By using X-ray diffraction (XRD), the structure and texture coefficient of the coatings. TC(hkl), of IrO2 rutile crystal have been tested. It showed that, the crystallization processes of IrO2 and Ta2O5 in IrO2+(100-x) Ta2O5 (x is in mol%) films affect and confine each other. In the mixed system, IrO2 rutile phase exists as a solid solution with Ta, and attains the maximum solubility when x=70 mol%, i.e. for the coating of 70% IrO2+Ta2O5. For the coatings of low iridium content or at low preparing temperature, (110) and (101) preferred orientations are dominant. However, preferred growth of IrO2 weakened with increasing either iridium content or temperature. Three typical surface morphologies were observed by using scanning electron microscopy (SEM). The crystallite size of the mixed oxide coatings are finest for the film of 70%IrO2+30%Ta2O5, and decreases with the pyrolysis temperature. As the results of the finest crystallite segregating on surface and the maximum solid solubility of Ir and Ta component in deposits, the coatings with the composition of 70%IrO2Y+Ta2O5 prepared at 450 °C present the maximum electrocatalytic activity for O2 evolution in 0.5 M H2SO4 solution. Up to 550°C, Ti base suffers to oxidation resulting in decreasing anode conductivity, therefore, coatings perform a low activity.