The physical-chemical properties and electrocatalytic performance of iridium oxide in oxygen evolution

► The calcination temperature mainly influenced the valence state of Ir. ► The activity of catalyst was influenced by the valence of Ir and crystallinity. ► Optimum condition was found at the thermo-decomposing temperature of 500 °C. ► Terminal voltage of water electrolysis was 1.72 V at 80 °C and 2 A cm−2.