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 the 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 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 applications. At 400 °C, MoO₃ spreads as a thin layer of surface polymeric molybdates on NiCo₂S₄ as seen in the XRD pattern. Significantly, it delivers the 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, the 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 the synthesis temperature on the functional character of ternary sulfide/oxide composite materials for charge storage applications.