Oxygen‐Vacancy‐Mediated Coupling of Oxide‐Path and Lattice‐Oxygen Mechanisms in CoFeMo Oxyhydroxide for Efficient and Stable Water Oxidation

Efficient and stable oxygen evolution reaction (OER) electrocatalysts must accelerate O─O bond formation while avoiding sustained lattice degradation. However, lattice oxygen mechanism (LOM) often causes structural instability due to excessive consumption of lattice oxygen, whereas oxide‐path mechanism (OPM) requires geometrically and electronically matched dual‐site structural units, which are difficult to maintain during dynamic OER reconstruction. Here, we report an oxygen‐vacancy‐rich CoFeMo oxyhydroxide in which oxygen vacancies mediate dynamic OPM‐LOM cooperation. Density functional theory calculations show that oxygen vacancies reshape the local coordination, charge distribution, and spin polarization around Fe/Co sites, which stabilizes the M─O─O─M intermediate required for direct O─O coupling. Electrochemical activation of a (CoFe)MoO 4 precursor yields a reconstructed oxyhydroxide containing abundant oxygen vacancies and trace residual Mo. The catalyst delivers an overpotential of 226 mV at 10 mA cm −2 and sustains 1 A cm −2 operation for over 1000 h at 1.78 V in an anion‐exchange‐membrane water electrolyzer. In situ infrared spectroscopy, isotope‐labeling differential electrochemical mass spectrometry, and electrolyte‐dependent stability tests support a self‐regulated vacancy cycle, in which OPM serves as the dominant O─O coupling route, while moderate LOM participation regenerates oxygen‐vacancy motifs required for sustained OPM operation. These findings highlight defect‐pathway coupling as a useful strategy for designing durable OER electrocatalysts.