A Ni3S2/MnS composite with unique 3-D morphology was synthesized by a novel method consisting of etching and pre-oxidation of Ni foam followed by in situ hydrothermal method. The etching process created a flower-like structure with the Ni foam which was not only used as a substrate but also providing Ni source for subsequent growth of Ni3S2 and Ni3S2/MnS composite. The synthesized material showed hierarchical structure consisting of porous Ni3S2 which was coated with vertically grown MnS nanorods. The superior morphology enables the access of more active sites in the electrochemical charge/discharge process. In the meantime, the charges involved in redox reaction can be effectively transferred via Ni3S2 with relatively high conductivity to Nickel foam substrate, which improved the availability of MnS. Therefore, when the Ni3S2/MnS composite was used as a supercapacitor electrode, it showed a remarkable electrochemical performance of 6.70 mAh cm−2 which is over two-fold higher than that of the Ni3S2 (3.15 mAh cm−2) and MnS (2.34 mAh cm−2) at current density of 2 mA cm−2, respectively. Impressively, the specific capacity of Ni3S2/MnS still retained 6.41 mAh cm−2 with the capacity retention of 96.5% even after 1000 cycles. Further, the electrochemical properties of asymmetric supercapacitors (ACSs) deliver a maximum energy density of 0.47 mWh cm−2 at power density of 10 mW cm−2, together with 82.1% retention after long-term test.
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