Design and development of noble metal-free, active and bifunctional electrocatalysts is crucial for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the full water splitting process. Herein, an amorphous cobalt–cobalt oxide/cobalt selenide composite film (CoO_x–CoSe) has been fabricated directly on a three-dimensional macro-porous Ni foam (NF) substrate by a facile electrodeposition method, which shows remarkable activity and good long-term stability as an efficient bifunctional electrocatalyst for the OER and HER under alkaline conditions. In 1.0 M KOH, this catalyst as a robust 3D O₂-evolving anode can achieve 100 mA cm⁻² and 500 mA cm⁻² only at overpotentials of 300 mV and 380 mV, respectively. When used as a HER catalyst, similarly, this electrode shows excellent catalytic performance, which needs an overpotential of 90 mV to deliver 10 mA cm⁻². This bifunctional electrode can allow an alkaline electrolyzer to obtain a water-splitting current density of 20 mA cm⁻² at a cell voltage of around 1.66 V, which offers potential applications in the field of water splitting.