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Promoting the self-reconstruction of NiFe-based catalysts represents a promising approach to facilitate seawater splitting, albeit with significant challenges. Herein, the redox cycle of Ni species is subtly regulated by decorating NiFe hydroxides with vanadium. Both experimental and theoretical studies demonstrate that the incorporation of V boosts the self-reconstruction of NiFe hydroxides and allows a superior OER performance on account of diminished propensity for chlorine adsorption and optimized binding energy of oxygen-containing intermediates. Consequently, the NiFeV/NF catalyst delivers 2.0 A cm−2 at an ultralow overpotential of 369 mV in 1.0 M KOH and exhibits exceptional stability for 720 h at 20 A in an alkaline membrane electrode assembly (MEA) electrolyzer. In alkaline seawater, it achieves prolonged stability, surpassing 240 h at 500 mA cm−2 with OER selectivity of 99 %. This work significantly advances the field of seawater electrolysis powered by marine renewables, paving the way for on-site hydrogen production. [Display omitted] • The redox cycle of Ni species is subtly regulated by decorating NiFe hydroxides with vanadium. • The incorporation of V diminishes the propensity of Cl− adsorption and optimizes the absorption of oxygen-containing species. • The NiFeV/NF delivers 2.0 A cm−2 at an overpotential of 369 mV and exhibits exceptional stability for 720 h at 20 A. • Deciphering the contributions of Cl* and OH* to the activity of seawater oxidation. [ABSTRACT FROM AUTHOR]