Ni–Co Bimetallic Sulfide Coated with Reduced Graphene Oxide and Carbon for High-Capacitance Supercapacitor

Ternary cobalt–nickel sulfide coated with carbon was successfully decorated on the surface of reduced graphene oxide (RGO) by a facile solvothermal route. The carbon encapsulated bimetallic sulfide nanoparticles can improve the electrochemical stability of the composite material, and load on the surface of graphene can further improve the electrical conductivity. The rational design and efficient synthesis of NiCo₂S₄/RGO-C with controlled compositions, shapes and micro-structures was applied as the electrode material for pseudocapacitors. Moreover, the as-fabricated electrode material exhibited a high specific capacitance of 1467 F g⁻¹ at a current density of 0.5 A g⁻¹,also had enhanced rate capability (up to 941 F g⁻¹ at 20 A g⁻¹). The electrode retained a high specific capacitance of 790 F g⁻¹ even after 10000 cycles at a current density of 20 A g⁻¹, showing excellent electrochemical stability with 83% capacitance retention. The ingenious design will be exceedingly prospective for other energy storage/conversion devices.