Designed construction of hierarchical NiCo2S4@polypyrrole core–shell nanosheet arrays as electrode materials for high-performance hybrid supercapacitors

Abstract

In this work, we report the design and fabrication of hierarchical NiCo₂S₄@polypyrrole (PPy) core–shell hybrid nanosheet arrays on Ni foam as a novel battery-type electrode using a facile hydrothermal and electrodeposition strategy. The conductive and electroactive PPy layers are deliberately coated on the backbones of interconnected NiCo₂S₄ nanosheets to significantly boost the energy storage capacity. The resulting NiCo₂S₄@PPy hybrid electrode exhibits an enhanced areal capacity (800 μA h cm⁻² at 5 mA cm⁻²) and good rate capability. An aqueous hybrid supercapacitor (HSC) device is assembled by employing NiCo₂S₄@PPy and activated carbon as the positive and negative electrodes, achieving high energy density (60.8 W h kg⁻¹ at 200 W kg⁻¹) and high power density (4362 W kg⁻¹ at 31 W h kg⁻¹), as well as excellent cycling stability (98.3% retention over 3000 cycles at 20 mA cm⁻²). Moreover, two HSC devices can easily light 38 LEDs efficiently, demonstrating the great potential of this core–shell hybrid nanostructure toward practical applications in energy storage devices.