Single‐Atom Defects Optimize Oxygen Evolution Performance of Monolayer NiFe‐Layered Double Hydroxides

ABSTRACT Precise control over atomic‐scale defects is crucial for elucidating structure‐activity relationships but remains a formidable synthetic challenge. Benefiting from the ordered distribution of trivalent cations within their host layers, layered double hydroxides (LDHs) offer an ideal platform for atomic‐scale defect engineering. Herein, we report an in situ Al 3+ ‐incorporation and selective etching strategy to introduce well‐defined single‐atom defects into monolayer NiFe‐LDH (mLDH) nanosheets. Free from layered lattice interference, these single‐atom‐defected mLDH (SAD‐mLDH) nanosheets serve as a well‐defined model system to probe intrinsic catalytic behaviors. Electrocatalytic evaluations in 1.0 M KOH demonstrate that SAD‐mLDH exhibits exceptional oxygen evolution reaction (OER) activity, requiring an overpotential of just 269 mV at 10 mA cm −2 , significantly outperforming defect‐free mLDH (300 mV) and commercial RuO 2 (340 mV). Mechanistic investigations reveal that the isolated single‐atom defects reconfigure the local coordination and electronic structure of the Ni and Fe centers. The upward shifts of the Ni and Fe d‐band centers, together with the site‐dependent redistribution of metal‐oxygen covalency revealed by M‐O ICOHP analysis, optimized the adsorption energetics of OER intermediates and reduced the thermodynamic free‐energy requirement of the rate‐determining *O‐to‐*OOH step. This work establishes a robust paradigm for designing high‐performance electrocatalysts via atomic defect engineering in 2D systems.