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Water splitting is widely considered to be a promising strategy for clean and efficient energy production. In this paper, for the first time we report an in situ growth of iron-nickel nitride nanostructures on surface-redox-etching Ni foam (FeNi3N/NF) as a bifunctional electrocatalyst for overall water splitting. This method does not require a specially added nickel precursor nor an oxidizing agent, but achieves well-dispersed iron-nickel nitride nanostructures that are grown directly on the nickel foam surface. The commercial Ni foam in this work not only acts as a substrate but also serves as a slow-releasing nickel precursor that is induced by redox-etching of Fe3+. FeCl2 is a more preferable iron precursor than FeCl3 for no matter quality of FeNi3N growth or its electrocatalytic behaviors. The obtained FeNi3N/NF exhibits extraordinarily high activities for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with low overpotentials of 202 and 75 mV at 10 mA cm-2, Tafel slopes of 40 and 98 mV dec-1, respectively. In addition, the presented FeNi3N/NF catalyst has an extremely good durability, reflecting in more than 400 h of consistent galvanostatic electrolysis without any visible voltage elevation. [ABSTRACT FROM AUTHOR]