Atomically dispersed hexavalent iridium oxide from MnO 2 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) (K ₂ IrCl ₆ ) with manganese oxide (MnO ₂ ). The mass-specific activity (1.7 × 10 ⁵ amperes per gram of iridium) and turnover number (1.5 × 10 ⁸ ) 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.