Surface Iridium Single‐Atom Engineering Enables a Highly Stable RuO ₂ Catalyst for Efficient Acidic Water Oxidation

Efficient and stable electrocatalysts for acidic water oxidation are pivotal to proton exchange membrane water electrolyzer (PEMWE). Ruthenium dioxide (RuO 2 )‐based catalysts demonstrate exceptional activity for the acidic oxygen evolution reaction (OER), however, their practical application in PEMWE is hindered by poor durability at industrial‐level current density. Herein, a KCl‐etching strategy is developed to embed Iridium (Ir) single atoms and grain boundary (G) within the RuO 2 matrix (Ir SAC ‐G‐RuO 2 ) to enhance its stability for the acidic OER. The as‐prepared Ir SAC ‐G‐RuO 2 catalyst exhibits excellent acidic OER activity with a low overpotential of 189 mV at 10 mA cm −2 and high stability with negligible degradation over 1000 h at 50 mA cm −2 . In situ electrochemical spectroscopy analyses verify that the asymmetric Ru‐O‐Ir sites lower activation energy, promote OH* generation, and suppress lattice oxygen participation, thereby enhancing both activity and stability. A PEMWE electrolyzer equipped with Ir SAC ‐G‐RuO 2 catalyst achieves a high current density of 1.0 A cm −2 at 1.61 V and maintains stable operation over 200 h at 1 A cm −2 , underscoring its significant potential for large‐scale green hydrogen production. This work establishes a viable strategy for anchoring Ir single atoms onto RuO 2 surface, addressing the critical trade‐off between Ir usage and durability in PEMWE.