Construction of porous hierarchical NiCo₂S₄ toward high rate performance supercapacitor

Developing high-performance supercapacitors is an effective way to satisfy the ever-increasing energy storage demand for emerging devices, but the inferior rate performance of battery-type supercapacitors limits their large-scale utilization. Herein, porous hierarchical nickel cobalt sulfide (NiCo₂S₄) was constructed by a novel strategy that the synthesized nickel cobalt oxide nanosheets as chemical template for hydrothermal method. Furthermore, the backbone of nickel cobalt oxide nanosheets can finally convert to NiCo₂S₄, which both plays the role of matrix to buffer the volume variation and enhances entire conductivity. Benefiting from high specific area (79.9 m² g⁻¹), suitable nanopores for KOH electrolyte, high conductivity, and multiple Co/Ni valence, the hierarchical NiCo₂S₄ electrode delivers a high specific capacity of 1035.1 F g⁻¹ at the current density of 1 A g⁻¹, and an ultrahigh rate performance of 80.9% capacitance retention at 20 A g⁻¹ was obtained. The assembled asymmetric supercapacitor device could achieve the maximum capacity of 102.4 F g⁻¹ at 5 mV s⁻¹ and maintain at 80.5 F g⁻¹ at 50 mV s⁻¹, indicating its superior rate ability. In addition, the highest energy density of 35.4 Wh kg⁻¹ can be obtained at a power density of 0.4 kW kg⁻¹. These results indicate that the porous hierarchical NiCo₂S₄ could be served as high rate performance electrode materials for advanced supercapacitors.