Core-shell nanostructured MnO₂@Co₉S₈ arrays for high-performance supercapacitors

Manganese dioxide (MnO₂) with large theoretical capacity, low cost and rich reserves has been considered as one of the most promising advanced electrode materials of supercapacitors, but the shortage of electrochemical active sites and the inherent defects of electrical conductivity hinder its widespread application in high-performance supercapacitors. Herein, the hierarchical core-shell nanostructure has been rationally designed by coating highly electrically conductive Co₉S₈ on MnO₂ arrays on Ni foam (MnO₂@Co₉S₈/NF) using a simple solution-based method. The prepared MnO₂@Co₉S₈/NF exhibits a high specific capacitance of 643.3 C g⁻¹ at 3 mA cm⁻², which is 3.4 and 10.1 times higher than the Co₃O₄@MnO₂ and pristine MnO₂ electrodes, respectively. Moreover, the asymmetric supercapacitor (ASC) with MnO₂@Co₉S₈ composite electrode provides a high areal capacitance of 1540 mC cm⁻² and a maximum energy density of 346.5 μW h cm⁻² (35 Wh kg⁻¹) at the power density of 2376 μW cm⁻² (240 W kg⁻¹). Importantly, the excellent cycling life with a capacitance retention of 97.5% after 36,000 cycles indicates the good stability of the core-shell structure of the composite electrode. These superior electrochemical properties of current materials are comparable to the most advanced MnO₂-based electrodes for supercapacitors.