This study reports the development of a three-dimensional (3D) core-shell metal-nitride catalyst, NiMoN@NiFeN, for efficient and durable alkaline seawater electrolysis. The catalyst consists of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam. This design addresses the challenges of chloride corrosion and low current densities in seawater electrolysis. The 3D core-shell structure provides a large surface area, numerous active sites, and efficient charge transfer, leading to excellent oxygen evolution reaction (OER) performance. The catalyst achieves current densities of 500 and 1000 mA cm⁻² at record-low voltages of 1.608 and 1.709 V, respectively, for overall alkaline seawater splitting at 60 °C. Additionally, the catalyst exhibits superior stability and can be driven by various power sources, including an AA battery and a commercial thermoelectric module. The discovery significantly advances the development of seawater electrolysis for large-scale hydrogen production.This study reports the development of a three-dimensional (3D) core-shell metal-nitride catalyst, NiMoN@NiFeN, for efficient and durable alkaline seawater electrolysis. The catalyst consists of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam. This design addresses the challenges of chloride corrosion and low current densities in seawater electrolysis. The 3D core-shell structure provides a large surface area, numerous active sites, and efficient charge transfer, leading to excellent oxygen evolution reaction (OER) performance. The catalyst achieves current densities of 500 and 1000 mA cm⁻² at record-low voltages of 1.608 and 1.709 V, respectively, for overall alkaline seawater splitting at 60 °C. Additionally, the catalyst exhibits superior stability and can be driven by various power sources, including an AA battery and a commercial thermoelectric module. The discovery significantly advances the development of seawater electrolysis for large-scale hydrogen production.