Atomically dispersed hexavalent iridium oxide from MnO₂ reduction for oxygen evolution catalysis

Hexavalent iridium (Ir^VI) oxide is predicted to be more active and stable than any other iridium oxide for the oxygen evolution reaction in acid; however, its experimental realization remains challenging. In this work, we report the synthesis, characterization, and application of atomically dispersed Ir^VI oxide (Ir^VI-ado) for proton exchange membrane (PEM) water electrolysis. The Ir^VI-ado was synthesized by oxidatively substituting the ligands of potassium hexachloroiridate(IV) (K₂IrCl₆) with manganese oxide (MnO₂). The mass-specific activity (1.7 × 10⁵ amperes per gram of iridium) and turnover number (1.5 × 10⁸) exceeded those of benchmark iridium oxides, and in situ x-ray analysis during PEM operations manifested the durability of Ir^VI at current densities up to 2.3 amperes per square centimeter. The high activity and stability of Ir^VI-ado showcase its promise as an anode material for PEM electrolysis.