Well-defined hollow tube@sheets NiCo₂S₄ core-shell nanoarrays for ultrahigh capacitance supercapacitor

Reasonable design of electrodes with well-defined nanostructure is the central aspect in the practical application of high-performance supercapacitors. Herein, hollow tube@sheets NiCo₂S₄ core-shell nanoarrays are rationally constructed to the free-standing electrode by in situ growing ZIF-67 on Co-precursor nanorods array and sequentially performing anion-exchange (S^2-) and cation-exchange (Ni²⁺). The well-defined nanostructures can shorten the ion transport path in the charging-discharging process, increase the specific surface area and electrochemical active cites, which help in improving electrochemical performance. Therefore, the unique tube@sheets NiCo₂S₄ core-shell nanoarrays exhibit intriguing electrochemical performance and show excellent areal capacitance of 11.3 F cm^-2 (3227.94 F g^-1) at a current density of 2 mA cm^-2 (2 A g^-1). The assembled asymmetric supercapacitor device delivers a high energy density of 0.42 mW h cm^-2 at a power density of 2.1 mW cm^-2 and displays outstanding cyclic stability (90.2% retention after 5000 cycles). Consequently, the well-defined nanostructure engineering strategy is beneficial for designing active electrode materials for efficient energy storage devices.