AbstractExploring robust catalysts for water oxidation in acidic electrolyte is challenging due to the limited material choice. Iridium (Ir) is the only active element with a high resistance to the acid corrosion during water electrolysis. However, Ir is rare, and its large-scale application could only be possible if the intrinsic activity of Ir could be greatly enhanced. Here, a pseudo-cubic SrCo_0.9Ir_0.1O_3-δ perovskite, containing corner-shared IrO6 octahedrons, is designed. The Ir in the SrCo_0.9Ir_0.1O_3-δ catalyst shows an extremely high intrinsic activity as reflected from its high turnover frequency, which is more than two orders of magnitude higher than that of IrO₂. During the electrochemical cycling, a surface reconstruction, with Sr and Co leaching, over SrCo_0.9Ir_0.1O_3-δ occurs. Such reconstructed surface region, likely contains a high amount of structural domains with corner-shared and under-coordinated IrO_x octahedrons, is responsible for the observed high activity.