Electrochemical behavior of IrO₂-Ta₂O₅/Ti anodes prepared with different surface pretreatments of Ti substrate

IrO₂-Ta₂O₅/Ti anodes were prepared by coating a Ti substrate with an Ir and Ta containing precursor, followed by oxidization at 450 °C for 30 min. Prior to coating the precursor, three different Ti-pretreatments including grinding with emery paper, etching in a 50 vol.% HCl solution and etching in a 19 g/L NH₄HF₂ + 5 vol.% HNO₃ solution were performed. The cyclic voltammetry (CV) behavior of the prepared IrO₂-Ta₂O₅/Ti anodes were tested in a 1 M H₂SO₄ solution, and their lifetime values were evaluated in a 1 M H₂SO₄ + 0.5 M Na₂SO₄ solution at 30 °C. The experimental results show that the lifetime of an IrO₂-Ta₂O₅/Ti anode is strongly affected by its Ti-pretreatment method. Whereas, the CV behavior of the IrO₂-Ta₂O₅/Ti anodes with different Ti-pretreatments were only slightly changed. A long lifetime and a relatively high voltammetric charge were detected for the IrO₂-Ta₂O₅/Ti anode with the Ti pretreatment of etching in the NH₄HF₂-based solution for 30 min. Delamination of the IrO₂-Ta₂O₅ layer from the Ti substrate was the main failure mode of an anode during the lifetime test. According to the transmission electron microscopy study, some parts of the IrO₂-Ta₂O₅ layer were detached from the Ti substrate pretreated with mechanical grinding. A high Ir concentration was detected in the IrO₂-Ta₂O₅ adjacent to the Ti substrate pretreated with etching in the 50 vol.% HCl solution. On the other hand, the segregation of Ir and interfacial detachment were not found in the IrO₂-Ta₂O₅ layer near the Ti substrate pretreated with etching in the NH₄HF₂-based solution. This pretreatment could be suitable for use to achieve a relatively long lifetime and high voltammetric charge on an IrO₂-Ta₂O₅/Ti anode.