MOF-derived hierarchical core-shell hollow Co3S4@NiCo2O4 nanosheet arrays for asymmetric supercapacitors

Transition metal sulfides (TMSs) have been widely explored as electrode materials for supercapacitors (SCs). Nevertheless, the application of TMSs alone is limited due to their lattice expansion and dissolution in an alkaline electrolyte. To overcome these challenges, in this study, hierarchical core-shell hollow Co3S4@NiCo2O4 nanosheet arrays have been constructed on reduced graphene oxide/nickel foam (rGO/NF) through a metal-organic framework (MOF)-engaged strategy. The MOF-derived two-dimensional (2D) hollow Co3S4 nanosheets can offer rich electroactive sites and rapid charge transport paths. The 2D NiCo2O4 nanosheets with high electrochemical activity and a stable lattice can overcome the intrinsic defects of Co3S4 by coating on its surface. Besides, the binder-free configuration ensures good electronic conductivity and mechanical stability. Thus, the Co3S4@NiCo2O4/rGO/NF exhibits a significantly improved specific capacitance (6.34 F cm(-2) at 2 A cm(-2)), rate capability (57.9% at 50 mA cm(-2)) and cycling durability (70.9%, after 5000 cycles), compared with Co3S4/rGO/NF. Moreover, the Co3S4@NiCo2O4/rGO/NF and an activated carbon (AC) electrode have been constructed into an asymmetric supercapacitor (ASC), which exhibits an excellent energy density (35.7 W h kg(-1) at a power density of 799.3 W kg(-1)) and an outstanding cycling stability (85.7% capacitance retention after 10 000 cycles) and a high coulombic efficiency (95%). Two solid-state ASCs can power four green light emitting diode (LED) bulbs for 4 min, demonstrating the great potential of the Co3S4@NiCo2O4/rGO/NF electrode in practical applications.

Automated summary

In this study, hierarchical core-shell hollow Co3S4@NiCo2O4 nanosheet arrays were constructed on reduced graphene oxide/nickel foam (rGO/NF) through a metal-organic framework (MOF)-engaged strategy, which exhibited significantly improved specific capacitance, rate capability, and cycling durability compared with Co3S4/rGO/NF. Moreover, it was successfully applied in an asymmetric supercapacitor (ASC) with excellent energy density, cycling stability, and coulombic efficiency.