Achieving efficient and durable nonprecious hydrogen evolution reaction (HER) catalysts for scaling up alkaline water/seawater electrolysis is desirable but remains a significant challenge. Here, a heterogeneous Ni‐MoN catalyst consisting of Ni and MoN nanoparticles on amorphous MoN nanorods that can sustain large‐current‐density HER with outstanding performance is demonstrated. The hierarchical nanorod–nanoparticle structure, along with a large surface area and multidimensional boundaries/defects endows the catalyst with abundant active sites. The hydrophilic surface helps to achieve accelerated gas‐release capabilities and is effective in preventing catalyst degradation during water electrolysis. Theoretical calculations further prove that the combination of Ni and MoN effectively modulates the electron redistribution at their interface and promotes the sluggish water‐dissociation kinetics at the Mo sites. Consequently, this Ni‐MoN catalyst requires low overpotentials of 61 and 136 mV to drive current densities of 100 and 1000 mA cm−2, respectively, in 1 m KOH and remains stable during operation for 200 h at a constant current density of 100 or 500 mA cm−2. This good HER catalyst also works well in alkaline seawater electrolyte and shows outstanding performance toward overall seawater electrolysis with ultralow cell voltages.

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Electrochemical reconstruction is a powerful tool for generating highly active oxygen evolution reaction (OER) catalysts. Utilizing electrochemical reconstruction to fabricate an OER active catalyst based on a hydrogen evolution reaction...