MoO₃ thin layers on NiCo₂S4 substrate for efficient electrochemical charge storage.

Ternary oxides/sulfides have long been investigated as promising electrode materials for charge storage applications. However, it is important to rationally design nanostructured hybrid composites for superior charge storage performance as electrodes in devices. In this work, MoO3@NiCo2S4 hybrid composites materials are synthesized by hydrothermal method followed by annealing at different temperatures. The charge storage properties of these materials are tested by cyclic voltammetry, galvanostatic charge-discharge curves and electrochemical impedance spectroscopy. It is found that the structure of the hybrid composite material not only assists the electron and charge transportation but also precisely control the volume expansion during redox reactions, contributing to superior electrochemical behavior. Among all the electrodes, the electrode fabricated with MoO3@NiCo2S4 composite material annealed at 400 °C (MoO3@NiCo2S4-400) is the best for charge storage application. At 400 °C MoO3 spreads as a thin layer of surface polymeric molybdates on NiCo2S4 as seen in the XRD pattern. Significantly, it delivers highest capacitance of 1622 F g‒1 at 1 A g‒1 in 2 M aqueous KOH electrolyte compared to other hybrid composite electrodes, NiCo2S4 (962 F g‒1), MoO3@NiCo2S4-500 (1412 F g‒1) and MoO3@NiCo2S4-600 (970 F g‒1) under the same measurement conditions. Furthermore, MoO3@NiCo2S4-400 hybrid electrode shows better cyclic stability with 93% capacitance retention after 3000 charge-discharge cycles at 8 A g‒1. The synergistic effect of two components and annealing temperature plays important role in enhancing the charge storage performance. This work shows the importance of synthesis temperature on the functional character of ternary sulfide/oxide composite materials for charge storage applications.