Defective core–shell NiCo₂S₄/MnO₂ nanocomposites for high performance solid-state hybrid supercapacitors

The roles of oxygen vacancies to enhance the electrochemical performance were not clearly explained in comprehensive research. Herein, the vertically oriented NiCo₂S₄/MnO₂ core–shell nanocomposites are in situ grown on the nickel foam (NF) surface and activated by oxygen vacancy engineering via a chemical reduction method. The scanning electron microscope (SEM) and transmission electron microscope (TEM) results show the shell-MnO₂ is well coated on the core-NiCo₂S₄. The hierarchical core–shell nanostructures synergistically increase conductivity and provide rich faradaic redox chemical reactions. Moreover, the density functional theory (DFT) calculations further indicate that the electronic properties and structure properties in NiCo₂S₄/MnO₂ electrode of reduction for 60 min (NiCo₂S₄/MnO₂-60) are effectively adjusted by introducing oxygen vacancies. Impressively, the NiCo₂S₄/MnO₂-60 electrode delivers substantially appreciable areal capacity of 2.13 mAh·cm⁻² couple with superior rate capability. The as-prepared high-performance electrode material can assemble into solid-state hybrid supercapacitor. The fabricated NiCo₂S₄/MnO₂-60//AC device exhibits an exceptional energy density of 43.16 Wh·kg⁻¹ at a power density of 384.21 W·kg⁻¹ and satisfactory cyclic stability of 92.1 % at current density of 10 mA·cm⁻² after 10,000 cycles. In general, the work demonstrates the significance of NiCo₂S₄/MnO₂-60 as a highly redox active electrode material for future practical application in supercapacitors.