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

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 Al3+-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 RuO2 (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.