Three-dimensional NiCo2O4/NiCo2S4 hybrid nanostructure on Ni-foam as a high-performance supercapacitor electrode

Abstract

The spinel structured ternary mixed metal oxide NiCo₂O₄ and sulphide NiCo₂S₄ are considered as promising pseudocapacitive materials. In view of this, the present work involves the fabrication of NiCo₂O₄ nanosheets and a NiCo₂O₄/NiCo₂S₄ hybrid nanostructure on Ni-foam as a conductive substrate by a facile ammonia evaporation technique. The NiCo₂O₄/NiCo₂S₄ hybrid nanostructure exhibits remarkable supercapacitive performance compared to bare NiCo₂O₄ nanosheets due to its three dimensional open structure and synergistic effect of NiCo₂O₄ and NiCo₂S₄. The hybrid nanostructure exhibits a specific capacitance as high as 3671 F g⁻¹ at a current density of 1.8 A g⁻¹ and 2767 F g⁻¹ at 9 A g⁻¹ with a capacity retention value of 84% at 10 A g⁻¹ after 2000 cycles. Furthermore, the electrode composed of the NiCo₂O₄/NiCo₂S₄ hybrid nanostructure displays a noticeably high energy density as well as power density (8820 W kg⁻¹ at 41.65 W h kg⁻¹) compared to the NiCo₂O₄ nanosheets (5374.28 W kg⁻¹ at 20.90 W h kg⁻¹) with great flexibility. It is anticipated that the combination of materials and the special structural design lead to fast electrochemical redox reactions, fast electron/ionic transportation and mechanical integrity, which promote the NiCo₂O₄/NiCo₂S₄ hybrid nanostructure as a superior electrode in high performing flexible supercapacitors.