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Electrochemical hydrogen evolution reaction (HER) with cost‐effectiveness, high performance, and repeatable scale‐up production hold promises for large‐scale green hydrogen generation technology. Herein, a convenient method for scaling up Cu2S@NiS@Ni/NiMo electrocatalysts on Cu foam with high geometric area over 100 cm2 is presented. The hybrid electrode exhibits high hydrogen evolution activity with 190 and 250 mV overpotential at 1000 mA cm−2 and superior stability with negligible overpotential loss after over 2000 h at 500 mA cm−2 under steady‐state conditions in both artificial seawater and real seawater. Detailed characterizations and simulations demonstrate that high intrinsic activity resulting from the unique boundary interface, enhance mass transport resulting from superaerophobic nanoarray architecture, and corrosion resistance resulting from polyanion‐rich passivating layers together lead to the outstanding performance. The practicability is also demonstrated in an alkaline seawater electrolyzer coupling with the hybrid electrode and stable commercial anode. [ABSTRACT FROM AUTHOR]