Highly Active IrRuOx/MnOx Electrocatalysts with Ultralow Anode PGM Demand in Proton Exchange Membrane Electrolyzers

MnO_x-supported IrRuO_x exhibits outstanding OER performance in both liquid electrolytes and real cell environments. The MnO_x not only enhances the dispersion of IrRuO_x but also induces a compressive strain effect. The incorporation of Ru leads to surface reconstruction. Superior performance in single-cell tests is achieved with an ultralow (Ir + Ru) loading, making it a very promising catalyst for PEMWEs.

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 IrO₂ (C-IrO₂). 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.