Petal-like NiFe2O4/Fe2O3 heterostructure nanoarrays as bifunctional electrocatalyst for highly efficient alkaline overall water splitting

• Petal-like NiFe 2 O 4 /Fe 2 O 3 heterostructure nanoarrays are constructed on IF. • Synergistic effect between NiFe 2 O 4 and Fe 2 O 3 promotes electrochemical kinetics. • The NiFe 2 O 4 /Fe 2 O 3 hybrid exhibits superior bifunctional HER and OER performances. • The electrolyzer demonstrates robust durability throughout a week-long period. Exploring high-performance and cost-effective nonprecious metal-based electrocatalysts for overall water splitting is the key to sustainable renewable energy. Herein, petal-like NiFe 2 O 4 /Fe 2 O 3 heterostructure nanoarrays were constructed on iron foam (IF) surface by spontaneous galvanic displacement reaction and subsequent thermal oxidation. This in-situ grown integrated architecture is binder-free and useful for exposing accessible active sites, improving mass transfer and heightening the release of gases produced during water electrolysis. More importantly, the synergistic effect between NiFe 2 O 4 and Fe 2 O 3 effectively modulates the electronic structure of catalytic active sites, thereby promoting electrochemical kinetics. Accordingly, the optimal Ni-FeOx/IF 3 electrocatalyst exhibits remarkably enhanced catalytic activity in alkaline solution with only 230 and 82 mV to reach 10 mA cm −2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The electrolyzer composed of Ni-FeOx/IF 3 as both the anode and cathode attain a current density of 10 mA cm −2 at a cell voltage of only 1.58 V for overall water splitting, with robust durability for 168 h in continuous water electrolysis, outperforming most reported NiFe-based catalysts. This work demonstrates a feasible and simple method to synthesize integrated electrodes with outstanding stability and high-performance for overall water splitting and provides an inspiration for future design of efficient bifunctional electrocatalysts.