Switching the Reaction Pathway to the Oxide Path for High‐Efficiency Acidic Oxygen Evolution

Abstract Understanding dynamic structure–activity relationships in the oxygen evolution reaction (OER) remains challenging due to electrocatalysts’ structural complexity. Here, we employ Ca 2 IrO 4 —a model catalyst with exclusively edge‐sharing IrO 6 octahedra forming 1D chains—to decode mechanistic evolution through synergistic interplay between corrosion‐resistant (110) and electrochemically activable (001) facets. With low (110) and (001) facet ratios, Ca 2 IrO 4 (L‐H‐CIO) undergoes electrochemical activation to form an adaptively reconstructed structure, ultimately achieving exceptional OER performance—demonstrating a low overpotential of 279 mV at 10 mA cm −2 and 200‐h stability without decay. The L‐H‐CIO‐based PEMWE exhibits high electrocatalytic activity (1.78 V @ 2.0 A cm −2 , 80 °C, 0.11 mg Ir cm −2 ) at ampere‐level current densities while demonstrating sustained stability beyond 500 h at 1.0 A cm −2 . In situ characterization and theoretical calculations reveal that adaptive surface reconstruction drives a mechanistic transition from the adsorbate evolution mechanism (AEM) to the oxide path mechanism (OPM). This shift is structurally anchored by edge‐sharing IrO 6 octahedra reconstruction (Ir–Ir 2.8 Å) of the (001) surface, which simultaneously downshifts the Ir d‐band center away from the Fermi level. The resultant weakened metal‐intermediate covalency optimizes the adsorption–desorption equilibrium, conferring thermodynamic and kinetic advantages to OPM. Our work establishes adaptive coordination reconstruction as a universal strategy to engineer pre‐catalysts that evolve into high‐efficiency OER phases, providing a roadmap for next‐generation catalyst design.