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

Hexavalent iridium (IrVI) oxide is predicted to be more active and stable than any other Ir oxide for the oxygen evolution reaction in acid; however, its experimental realization remains challenging. Here, we report the synthesis, characterization, and application of atomically dispersed IrVI oxide (IrVI-ado) for proton-exchange membrane (PEM) water electrolysis. The IrVI-ado was synthesized by oxidatively substituting the ligands of K2IrCl6 with manganese oxide. The mass-specific activity (1.7 × 105 A gIr-1) and turnover number (1.5 × 108) exceeded those of benchmark Ir oxides, and in-siu X-ray analysis during PEM operations manifested the durability of IrVI at current densities up to 2.3 A cm-2. The high activity and stability of IrVI-ado showcase its promise as an anode material for PEM electrolysis., Nafion 115 polymer membranes were used to fabricate the membrane electrode assembly (MEA). Prior to use, the Nafion membrane was boiled sequentially for 1 h each in 3 wt.% H2O2, Milli-Q water, 1.0 M H2SO4, and Milli-Q water to remove possible contaminants and ensure that the membrane was completely protonated. IrVI-ado samples with loading amounts of 0.02, 0.04, and 0.08 mgIr cm-2 were used as an anode and coated with 10 wt. % Nafion ionomer before being assembled into the MEAs. Pt/C catalyst (20 wt% Pt on carbon black, Fuel Cell Earth) coated on hydrophobic carbon paper (TGP-H-060, Toray) with a loading amount of 0.2 mgPt cm-2 was used as a cathode. The Pt/C catalyst slurry used for coating was prepared by mixing Pt/C, water, ethanol, and Nafion solution (10 wt% in H2O, Sigma-Aldrich) with a Pt/C to Nafion ionomer ratio of 3:1. The MEAs with an active area of 1 cm2 were prepared by hot-pressing the anode and cathode on a Nafion membranes at 135 °C at a mold clamping force of 2 MPa for ..., , # Atomically dispersed hexavalent iridium oxide from MnO2 reduction for oxygen evolution catalysis

[https://doi.org/10.5061/dryad.bg79cnpjc](https://doi.org/10.5061/dryad.bg79cnpjc)

## Description of the data and file structure

Dataset1: Cell voltages of IrVI-*ado* in PEM cell with a mass-specific activity of 50000 A gIr-1. The dataset shows the variations in cell voltage (E) over time (t).

Dataset2: Cell voltages of IrVI-*ado* in PEM cell with a mass-specific activity of 25000 A gIr-1. The dataset shows the variations in cell voltage (E) over time (t).

Dataset3: Cell voltages of IrVI-*ado* in PEM cell with a mass-specific activity of 12500 A gIr-1. The dataset shows the variations in cell voltage (E) over time (t).

Dataset4: Cell voltages of IrVI-*ado* in PEM cell with a mass-specific activity of 22500 A gIr-1. The dataset shows the variations in cell voltage (E) over time (t).