Lattice Strain and Charge Transfer Induced by the Ru@RuO 2 Core–Shell Heterostructure Enable Efficient and Durable Acidic Water Oxidation

ABSTRACT Ru‐based electrocatalysts are promising for low‐cost proton exchange membrane (PEM) electrolyzers, but their stability is severely limited by the overoxidation of Ru sites during the acidic oxygen evolution reaction (OER). Herein, we propose a synthetic approach to convert the typical Ru/RuO 2 heterostructure into a well–defined Ru@RuO 2 core–shell structure, with preferential exposure of the (020) plane of RuO 2 . Such a core–shell design not only shields the metallic Ru core from direct contact with the oxidative catalytic environment, thereby suppressing metallic Ru overoxidation, but also maximizes the surface with abundant active sites on the (020) plane, leading to enhanced durability and intrinsic activity. Ru@RuO 2 achieves a low overpotential of 165 mV at 10 mA·cm −2 and operates stably for over 1500 h. In a PEM electrolyzer, it delivers a current density of 1.0 A·cm −2 at 1.606 V and maintains stable operation for more than 200 h at 500 mA·cm −2 . This study highlights metal–oxide core–shell heterostructures as a new paradigm for designing highly active and stable RuO 2 ‐based catalysts for acidic OER.