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.