Effects of Oxide Composition on Structure, Surface Morphology, and Oxygen Evolution Behaviors of IrO₂-Ta₂O₅/Ti Anodes Prepared at a High Temperature

Abstract

Catalytic coatings comprising a mixture of IrO₂ and Ta₂O₅ were prepared at 50–80 mol% Ir by thermal decomposition at 470°C, and the crystallographic structures and surface morphologies were investigated. XRD analysis and high-resolution SEM observation using low accelerated incident beam revealed that decreasing Ir ratio made a phase transition of IrO₂ from crystalline to partly amorphous, and nano IrO₂ particles of 10 nm or less and nano chains made of them, which were uniformly dispersed on the flat area of the coating, were generated at 50–60 mol% Ir. The relationship between nano-scale surface morphology of the coating and electrocatalysis for oxygen evolution in H₂SO₄ solutions was also investigated. The active surface area and oxygen evolution current increased with reducing Ir ratio. The electrocatalysis of the IrO₂-Ta₂O₅ coatings for oxygen evolution is possible to be attributed to nano IrO₂ particles.