A facile and effective approach for fabricating a 3D nanostructured catalyst based on nonprecious metals for water splitting is reported. The Ni-Fe foam (NFF) is pretreated by a dielectric barrier discharge (DBD) plasma under ambient conditions, resulting in numerous microtrenches on the NFF surface. Meanwhile, some NiO and Fe2O3 spots appear on the NFF foam upon exposure to hot filaments generated in DBD plasmas in air. Cross linked 3D CoS/Ni3S2-FeS nanopetals emerge on plasma treated NFF surface (PNFF) through sulfurization of Co nanosheets electrodeposited on PNFF. The produced CoS/Ni3S2-FeS/PNFF nanocomposite exhibited high electrocatalytic activity and stability for the overall water splitting. Benefiting from the 3D hierarchical nanoarchitecture of CoS/Ni3S2-FeS/PNFF with a large surface area, fast electron transport, and low free energy for adsorption, a current density of 10 mA cm(-2) is achieved for the HER and OER with ultralow overpotentials of 75 mV and 136 mV, respectively. The amounts of H-2 and O-2 produced at a normalized current density of 10 mA cm(-2) in 1 M KOH are about 680 mu mol h(-1) and 1230 mu mol h(-1), respectively. These values are very competitive compared with the state-of-the-art results reported for noble metal-free electrodes in alkaline media.