Synergistic Interface Engineering of Ni _0.2 Mo _0.8 N/MoO ₂ Heterostructure Catalysts for Accelerated Hydrogen Evolution in Alkaline Water and Seawater

Abstract The development of efficient and durable electrocatalysts for the hydrogen evolution reaction (HER) in alkaline seawater electrolytes remains a formidable challenge, hindered by sluggish reaction kinetics and chloride‐induced corrosion. Herein, a synergistic interface engineering strategy is developed to fabricate hierarchical Ni _0.2 Mo _0.8 N/MoO ₂ heterostructured rod arrays composed of nanoparticle assemblies. This design integrates conductive Ni _0.2 Mo _0.8 N domains with MoO ₂ phases, leveraging metal–support interactions to enhance water adsorption/dissociation kinetics and proton adsorption/activation capacity. Consequently, this catalyst achieves ultralow overpotentials of 30/212 mV (alkaline freshwater) and 44/217 mV (alkaline seawater) to drive current densities of 100/1000 mA cm ⁻² , respectively, outperforming commercial Pt/C and state‐of‐the‐art transition metal‐based catalysts. Notably, in chloride‐containing alkaline seawater, it demonstrates remarkable stability by sustaining 200 mA cm ⁻² for 550 h. Theoretical calculations reveal that the Ni _0.2 Mo _0.8 N/MoO ₂ heterointerface effectively modulates the electronic structure, significantly lowering the energy barriers for water dissociation and optimizing the adsorption/desorption capacity of hydrogen intermediates, ultimately enhancing catalytic performance. This work may provide a novel design framework for in situ construction of heterojunction catalytic systems, enabling industrial‐scale energy conversion.