• • FeCoNiMnZn HELDH achieves an overpotential of only 306 mV at 100 mA cm−2, outperforming conventional LDHs and approaching noble-metal benchmarks, directly addressing the kinetic bottleneck for industrial water electrolysis.
• • The catalyst sustains stable operation for 200 h with no degradation, and even shows increasing current output, indicating exceptional durability under continuous OER conditions—critical for long-term renewable energy systems.
• • Zn leaching creates abundant cation vacancies that optimize adsorption energies of OER intermediates, as validated by DFT, providing a mechanistic basis for the enhanced intrinsic activity.
• • In zinc-air battery tests, the FeCoNiMnZn HELDH cathode maintains stable operation for over 400 h at 10 mA cm−2, demonstrating practical viability for energy storage applications.