Inexpensive and accessible NiFe-based oxygen evolution reaction (OER) electrocatalysts show limitations for practical industrial applications owing to their activity and stability under industrial conditions. Herein, an FeNi₂S₄@NiFe–LDH heterostructure is constructed by the molten salt method and interfacial corrosion strategy, in which amorphous NiFe–LDH nanosheets grow in situ on the surface of crystalline FeNi₂S₄ with a nanograss structure. The introduction of amorphous NiFe–LDH can not only optimize the adsorption energy of OER intermediates, but also significantly improve the overall stability and activity of the catalyst by reducing the loss of the S element in FeNi₂S₄. At the same time, the OH⁻ produced by S ion hydrolysis can also promote the in situ construction of NiFe–LDH. Such an amorphous–crystalline structure gives full contribution to the advantages of each component, modulates the nanostructure, and promotes the electron transfer across the interfaces. Consequently, FeNi₂S₄@NiFe–LDH achieves large current density values of 500 and 1000 mA cm⁻² for the OER at overpotentials of only 283 and 306 mV in 1 M KOH (25 °C) without losing performance for at least 600 h at 500 mA cm⁻². Under the simulated practical industrial test conditions (6 M KOH, 70 °C), the same current densities of 500 and 1000 mA cm⁻² are delivered at the ultra-low overpotentials of 137 and 155 mV with long-term stability at high and low current densities. Such excellent catalyst performance shows its great industrial application prospects. This work also provides a strategy using Earth-abundant materials for realizing large-scale water splitting.