Highly Active IrRuO _x /MnO _x Electrocatalysts with Ultralow Anode PGM Demand in Proton Exchange Membrane Electrolyzers

Abstract Thrifting the rare iridium in proton exchange membrane water electrolyzer (PEMWE) anodes is an effective means to preempt undesired future iridium supply shortages aiding wider deployment of PEMWEs in coming years. This work explores a new family of MnO _x ‐supported IrO _x and IrRuO _x electrocatalysts for the acidic oxygen evolution reaction (OER). Comprehensive ex situ and in situ characterization uncovers synthesis‐structure‐activity relationships of the OER materials with insight into the origin of their exceptional activity: The MnO _x support provides beneficial dispersion while the introduction of Ru into IrO _x /MnO _x leads to a modulation of the chemical state of Ir coupled with a strong surface reconstruction. In half‐cell tests, IrRuO _x /MnO _x reveals an Ir mass activity of 964.7 A g _Ir ⁻¹ at 1.53 V _RHE , which is 36 times higher than that of the commercial IrO ₂ (C‐IrO ₂ ). It is also demonstrated that this promising catalytic OER activity translates into a realistic PEMWE performance. IrRuO _x /MnO _x and IrO _x /MnO _x thin catalyst layers are developed in low Ir‐loaded membrane electrode assemblies (MEAs) and an outstanding PEMWE cell performance is reported with cell voltages of 1.66 V at 2 A cm ⁻² . This translates into a favorable (Ir + Ru) platium group metal (PGM) demand of <0.05 g _PGM kW ⁻¹ at 70% voltage efficiency, meeting a 2035 technical demand target.