Covalency Regulation of Ru‐Based Solid Solutions by Iridium for Durable Proton Exchange Membrane Water Electrolysis at 2 A cm −2

Abstract Ruthenium dioxide (RuO 2 )‐based catalysts are widely recognized as the most active for the acidic oxygen evolution reaction (OER), yet overoxidation and dissolution of Ru species hinder their application in proton exchange membrane water electrolyzers (PEMWEs). Herein, a stabilization strategy is presented in which the remarkable stability of Ru‐based solid solutions is achieved by the introduction of iridium (Ir) to regulate Ru─O covalency. The Ru 8 Ir 1 O x catalyst exhibits a low overpotential of 177 mV at 10 mA cm −2 and demonstrates stable performance exceeding 850 h at 100 mA cm −2 with negligible degradation. Operando spectroelectrochemical measurements and X‐ray absorption fine structure (XAFS), combined with theoretical calculations, reveal that the participation of lattice oxygen and the leaching of Ru species are suppressed due to weakened Ru─O covalency, which results from Ru─O bond elongation and reduced hybridization upon Ir introduction, ultimately enhancing the stability of RuO 2 ‐based catalysts. PEMWE assembled using Ru 8 Ir 1 O x exhibits a voltage of only 1.76 V to reach 3 A cm −2 and maintains stable performance for 350 h at 2 A cm −2 . This study provides a feasible solution for the practical application of RuO 2 ‐based catalysts in PEMWE.