Nanostructured nickel-cobalt sulfide grown on nickel foam directly as supercapacitor electrodes with high specific capacitance

• Ni–Co sulfide arrays are directly grown on Ni foam as supercapacitor electrodes.
• The capacitance increases to 314% of the initial value in the first 5000 cycles.
• Enlarging the potential range, the areal capacitance can further increase.

The synthesis of NiCo2S4/Co9S8 nanorod arrays directly grown on Ni foam and its application as a supercapacitor electrode were investigated. The electrode demonstrated a superior electrochemical performance and its capacitance could increase to 314% of the initial value after 5000 cycles due to a progressive activation. The highest areal specific capacitance could be 8.08 F cm−2 and the corresponding mass specific capacitance was 2068 F g−1 at the current density of 5 mA cm−2. Even after 10,000 cycles, its areal specific capacitance could be still 5.53 F cm−2, 190% of the initial capacitance. When the current density was increased, the areal capacitance would decrease usually. Through increasing the anode voltage, the areal specific capacitance could increase. The combination of high electrical conductivity, porous structure and the synergic effects of nickel and cobalt, played significant roles to obtain supercapacitor electrodes with excellent performances.