Hierarchical NiCo2S4@NiMoO4 nanotube arrays on nickel foam as an advanced bifunctional electrocatalyst for efficient overall water splitting

The development of efficient and robust electrocatalysts for overall water splitting (OWS) has a crucial effect on alleviating energy and environmental issues. Herein, an integrated electrode of hierarchical NiCo2S4 nano-tube@NiMoO4 nanosheet arrays on nickel foam (NiCo2S4@NiMoO4/NF) is constructed via hydrothermal reac-tion. And the heterostructure can form the strong electron interaction and synergistic effect between NiCo2S4 and NiMoO4. Therefore, the NiCo2S4@NiMoO4/NF electrode exhibits prominent electrocatalytic performances with low overpotentials for oxygen and hydrogen evolution reaction (OER: 285 mV; HER: 197 mV) at the current density of 100 mA cm-2. Moreover, low potentials of 1.46, 1.63, and 1.75 V are needed to reach 10, 50, and 100 mA cm-2 and outstanding stability of 100 h is exhibited using NiCo2S4@NiMoO4/NF as a bifunctional electro-catalyst for OWS, which is superior over most of previously reported cobalt-and nickel-based electrocatalysts. These outstanding performances benefit from the unique hierarchical structure that combines the advantages of the nanosheet/nanotube and binder-free electrode, the specialty of NiCo2S4 and NiMoO4 in HER and OER, and the protective effect of the NiMoO4, which synergistically enhance the catalytic activity and stability of OWS.