Novel fabrication of Ni₃S₂/MnS composite as high performance supercapacitor electrode

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.