To speed up the water splitting process, extremely efficient electrocatalysts for the oxygen evolution reaction (OER) must be developed. Herein, we successfully incorporated Mo into NiCo LDH on the surface of nickel foam (NF) using a hydrothermal approach (NiCoMo LDH/NF), and then used an electrodeposition method to deposit FeOOH uniformly on the surface of ternary NiCoMo LDH/NF to configure an FeOOH–NiCoMo LDH/NF electrocatalyst. The synthesized nanoarray exhibits excellent electrocatalytic performance for oxygen evolution reaction (OER) both in alkaline medium (1.0 M KOH) and simulated alkaline seawater (1.0 M KOH and 0.5 M NaCl aqueous solution), the overpotential is 256 mV and 272 mV at the current density of 50 mA cm⁻², respectively. In addition, the long-term stability is evaluated for 50 h at 50 mA cm⁻² and only a 0.07% increase is observed. The enhanced OER activity is attributed to: (I) the defect - rich structure of holey nanobrush arrays, which increases the number of electrocatalytic active sites; (II) the incorporation of high-valence Mo into the LDH structure, which can tune the electronic structure to reduce the reaction resistance; (III) the improved kinetics from synergistic coupling of FeOOH with ternary NiCoMo LDH.