The effect of Ir content on the service life of Ti/IrO₂-Sb₂O₅-SnO₂ DSA for O₂ evolution

Abstract

Ti/IrO₂-Sb₂O₅-SnO₂ dimensionally stable anodes (DSAs) were prepared using the thermal decomposition method. While the ratio of Sn to Sb was kept constant at 5.5, the nominal content of Ir was varied at 0, 10, 30, 50, 75, and 100%. Titanium rod was employed as the substrate. The metal oxides coating was maintained around 15 g/m². The surface coating of Ti/IrO₂-Sb₂O₅-SnO₂ DSA was found to be compact at low Ir content (<30%). Rough surface with tiny cracks can be found for coatings with higher Ir content (>50%). The three oxides formed solid solution with uniform distribution of their contents until Ir content is 50% when Ir metal can be detected in the coating. Accelerated life tests were conducted to characterize the service life of Ti/IrO₂-Sb₂O₅-SnO₂ DSA for O₂ evolution in 3 M H2SO₄ solution under a current density of 10,000 A/m² at 70°C. It was found that the service life increases with Ir content until 10%. The service life is similar for Ir content of 30%. Further increase in Ir content results in a decrease in the service life because of the change of coating surface properties. Optimal Ir content between 10 and 30% was found, for the first time, in terms of service life. At this optimal coating condition, the accelerated service life is found to be 1000 hours which is equivalent to over 44 years in the real industrial electroflotation under the normal operating conditions. The 10% and 30% Ir samples were less likely to lose their coating layers from detachment. The oxide coatings of high Ir content, 50% and 75%, were found easier to detach from the substrate resulting in the earlier end of their working life. It was found that the content of Sb dropped significantly during the life test, facilitating the deactivation of electrode especially at high Ir content. The non-conductive TiO₂ interlayer formation was found to be responsible for the deactivation of DSA at high Ir content resulting the peeling of the coating.

Date of Award	2013
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology