Supported single-atom catalysts (SACs) demonstrate exceptional catalytic performance, atom efficiency, and selectivity, as a result, they are the potential candidates used in oxygen evolution reaction (OER). However, stabilizing monodispersed noble-metal atoms is challenging. This is especially true for two-dimensional (2D) layered double hydroxide (LDH) nanostructures. Here, we report the successful stabilization of ruthenium (Ru) single atoms (SAs). These SAs are located within a defective NiFe LDH nanosheet grown on the nickel foam (NF). This material is named Ru SAs/D-NiFe LDH@NF and formed through the hydrothermal reaction followed by etching. The resulting catalyst exhibits outstanding OER performance in alkaline media, achieving an exceedingly low overpotential (206 mV) at 50 mA·cm⁻², which remarkably decreases relative to the overpotential in pristine NiFe LDH (311 mV). Ru SAs regulate the electron distribution near defects, optimizing the Ru-NiFe hydroxide interaction and diminishing energy barrier for forming $\ast \mathrm{O}\mathrm{O}\mathrm{H}$ intermediates, as revealed by density functional theory (DFT) calculations. Moreover, the catalyst demonstrates remarkable stability in Zn-air batteries (ZABs), delivering the maximal power density (170 mW·cm⁻²). Furthermore, it maintains stable operation for 350 h, highlighting its practical viability. This work provides a versatile strategy for integrating single-atom sites into NiFe LDH, paving the way for the design of next-generation SACs for energy conversion applications.