BACKGROUNDFabricating high‐performance bifunctional electrocatalysts remains challenging to promote the development of electrocatalytic water‐splitting.RESULTA heterostructure Fe‐Ni3S2@CoSx/NF was successfully synthesized using an interfacial engineering strategy. Benefiting from the strong synergistic effect between highly active cobalt sulfide (CoSx) and iron‐doped trinickel‐disulfide (Ni3S2) (Fe‐Ni3S2), Fe‐Ni3S2@CoSx/NF exhibited outstanding bifunctional performance, with low overpotentials of 77 and 217 mV for the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), respectively, at 10 mA cm−2.CONCLUSIONThe CoSx nanoarrays and Fe‐Ni3S2 nanosheets respectively served as HER and OER active centers. When Fe‐Ni3S2@CoSx/NF was used as both cathode and anode for overall water‐splitting, a low voltage of 1.52 V was required to reach the current density of 10 mA cm−2 with nearly 100% Faradic efficiency and outstanding durability. © 2024 Society of Chemical Industry (SCI).