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

Understanding dynamic structure-activity relationships in the oxygen evolution reaction (OER) remains challenging due to electrocatalysts' structural complexity. Here, we employ Ca₂IrO₄-a model catalyst with exclusively edge-sharing IrO₆ 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, Ca₂IrO₄ (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 IrO₆ 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.