HighlightsA hierarchical interconnected NiMoN (HW-NiMoN-2h) was successfully prepared based on a rational combination of hydrothermal and water bath processes.HW-NiMoN-2h exhibited high hydrogen evolution reaction (HER) activity due to its large specific surface area and good stability due to its enhanced mechanical strength.In 1 M KOH seawater, HW-NiMoN-2h delivered current density of 1 A cm−2for HER at an overpotential of 130 mV and showed excellent stability over 70 h at 1 A cm−2.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01129-y.