Seawater electrolysis could address the water scarcity issue and realize the grid-scale production of carbon-neutral hydrogen, while facing the challenge of high energy consumption and chloride corrosion. Thermodynamically more favorable hydrazine oxidation reaction (HzOR) assisted water electrolysis is efficiency for energy-saving and chlorine-free hydrogen production. Herein, the MoNi alloys supported on MoO₂ nanorods with enlarged hollow diameter on Ni foam (MoNi@NF) are synthesized, which is constructed by limiting the outward diffusion of Ni via annealing and thermal reduction of NiMoO₄ nanorods. When coupling HzOR and hydrogen evolution reaction (HER) by employing MoNi@NF as both anode and cathode in two-electrode seawater system, a low cell voltage of 0.54 V is required to achieve 1,000 mA·cm⁻² and with long-term durability for 100 h to keep above 100 mA·cm⁻² and nearly 100% Faradaic efficiency. It can save 2.94 W·h to generate per liter H₂ relative to alkaline seawater electrolysis with 37% lower energy equivalent input.