Reaction Selectivity of IrO2-Based Nano/Amorphous Hybrid Oxide-Coated Titanium Anodes in Acidic Aqueous Solutions: Oxygen Evolution and Lead Oxide Deposition

Abstract

The present study demonstrated that novel IrO2-Ta2O5/Ti anodes prepared by thermal decomposition at a low temperature of 380 °C have high reaction selectivity for oxygen evolution and metal oxide deposition in acidic aqueous solutions. Conventional IrO2-Ta2O5/Ti anodes are generally prepared at a temperature between 450 °C and 500 °C. However, if Pb(II) ions are present as an impurity in the electrolyte, the oxidation of Pb(II) ions occurs as an anodic side reaction, leading to deposition of PbO2 onto the conventional anodes. Herein, we prepared IrO2-Ta2O5/Ti anodes by thermal decomposition at the low temperature of 380 °C and investigated their crystallographic structure, surface morphology, and polarization behaviors for oxygen evolution as well as their suppression effect for anodic PbO2 deposition in sulfuric acid/lead sulfate solutions. SEM observations with low accelerated incident electrons revealed that the nano/amorphous hybrid structure consisting of nanosized IrO2 particles highly dispersed in the amorphous Ta2O5 matrix can be prepared at 380 °C. Oxygen evolution was accelerated with an increasing Ir ratio in the anodes prepared at 380 °C in sulfuric acid solutions. Anodic PbO2 deposition on the anodes prepared at 380 °C in lead sulfate solutions, which assumed the conditions of practical use, was completely suppressed.