Development of Fe-Ni-based electrocatalysts with high efficiency and stability remains a foremost challenge in the research for oxygen evolution reaction (OER) under high-current-density. Herein, a fast reduction strategy is developed for synthesis of strongly coupled crystalline alpha-Ni(OH)(2) with amorphous reduced FeOOH (r-FeOOH) heterostructure grown on Ni foam (r-FeOOH/alpha-Ni(OH)(2)/NF). The obtained r-FeOOH/alpha-Ni(OH)(2) with particle sizes around similar to 10 nm is coated orderly on the 3D NF surface in this hybrid. Benefitting from the strong coupling effects between r-FeOOH and alpha-Ni(OH)(2), low potentials of 1.62 and 1.66 Vat ultra-high current densities of 1,000 and 1,500 mA cm(-2), as well as a robust stability over 10 hat 1,500 mA cm(-2) in alkaline electrolyte are achieved in 3D r-FeOOH/alpha-Ni(OH)(2)/NF. Such a high OER performance is almost the best among all previously reported Fe-Ni-based OER electrocatalysts. Experimental results revealed that the NiOOH species is the real OER active phase in the 3D r-FeOOH/ alpha-Ni(OH)(2)/NF. Further, bifunctional 3D r-FeOOH/alpha-Ni(OH)(2) in alkaline electrolyzer delivers low cell voltages of 2.32 and 2.78 V to attain 500 and 1,000 mA cm(-2) toward the overall-water-splitting, surpassing the benchmark Pt/C-Ir/C/NF system. (C) 2020 Elsevier Inc. All rights reserved.