NiCo2S4 nanoparticles grown on reduced graphene oxides for high-performance asymmetric supercapacitors.

• rGO/NiCo 2 S 4 shows a maximum specific capacitance of 1059 F/g with good cycle life. • 3D of rGO/MnO is prepared and exhibits a maximun specific capacitance of 469 F/g. • The rGO/MnO//rGO/NiCo 2 S 4 ASC shows a high energy density of 38.8 Wh kg−1. The nanostructures of reduced graphene oxide (rGO)/NiCo 2 S 4 are prepared using the simple hydrothermal method and the thermal treatment process, which could provide good conductivity and ideal specific surface area. The rGO/NiCo 2 S 4 electrode shows a maximum specific capacitance of 1059 F g−1, excellent rate capability, and good cycle life. Furthermore, the three dimensional structures of rGO/MnO (3D rGO/MnO) are also synthesized by the hydrothermal method and the thermal treatment process, which have the high specific surface area and good conductivity. The rGO/MnO electrode exhibits a maximum specific capacitance of 469 F g−1. A rGO/MnO//rGO/NiCo 2 S 4 asymmetric supercapacitors (ASC) is assembled using 2 M KOH solution as electrolyte, rGO/NiCo 2 S 4 as positive electrode and rGO/MnO as negative electrode. The rGO/MnO//rGO/NiCo 2 S 4 ASC shows an energy density of 38.8 Wh kg−1 at a power density of 0.4 kW kg−1 and a good cycle life, which provides a possibility toward actual application in energy-storage systems. [ABSTRACT FROM AUTHOR]