High-valence metals play an important role in facilitating the oxidation cycles of 3d metals during the oxygen evolution reaction (OER), while maximizing atomic utilization efficiency is equally vital for further enhancing catalytic activity. Herein, we present a facile strategy to synthesize single-atom W confined within the lattice of CoFe-layered double hydroxide (CoFeW-LDH), which features an ultrathin (~ 5 nm) defect-rich nanosheet-assembled hollow cubic structure that serves as an efficient OER electrocatalyst. The introduction of W, characterized by significant differences in atomic radius and electronic structure, induces numerous lattice defects. This unique geometric structure and the modulated electronic structure endow it with low OER overpotentials of 263 mV at 10 mA·cm⁻² and remarkable durability exceeding 100 h at a high current density of 1 A·cm⁻² under alkaline conditions, outperforming most non-precious metal catalysts as well as commercial precious IrO₂ catalyst. Density functional theory calculations reveal that the incorporation of W reconfigures the electronic structure of the adjacent Co sites at defects in a manner conducive to enhancing OER kinetics and charge transfer. This work proposes an effective strategy for synthesizing lattice-confined, high-valence metal single-atom electrocatalysts with enhanced atomic utilization and OER activity.