Ultrathin nanosheets-assembled NiCo₂S₄ nanocages derived from ZIF-67 for high-performance supercapacitors

The design and synthesis of new microstructure electrodes with large surface area and high electrochemical response play an essential role in advanced supercapacitors. Herein, NiCo₂S₄ hollow nanocages assembled by ultrathin nanosheets were synthesized through a facile solid-state chemical sulfuration method derived from the sacrificial template of Co-based zeolitic imidazolate frameworks (ZIF-67). The obtained hollow NiCo₂S₄ possess inner cavities and largely ultrathin nanosheets for both short ion diffusion distance and rich interfacial active sites which can dynamically speed up faradaic reactions. A specific capacitance of 1232 F g⁻¹ is obtained at a current density of 2.0 A g⁻¹ for the NiCo₂S₄ electrode. Notably, compared with Co–Ni LDH, NiCo₂S₄ electrode yields impressive rate capability and excellent cycling stability (80% capacitance retention after 8000 charge–discharge cycles), mainly due to its robust porous architecture and good electronic conductivity. The electrochemical reaction mechanism is studied by in situ XRD, indicating that NiCo₂S₄ exhibits a single-phase OH⁻ insertion/extraction behavior. The aqueous asymmetric supercapacitor assembled with NiCo₂S₄ as positive electrode also delivers high energy density of 41.4 Wh kg⁻¹ at power density of 689.5 W kg⁻¹. This work demonstrates that the well-designed NiCo₂S₄ is promising electrode materials for high-performance supercapacitors.