In situ self-assembly of Ni3S2/MnS/CuS/reduced graphene composite on nickel foam for high power supercapacitors

Abstract

Transition metal sulfides (TMS), as promising electroactive materials for asymmetric supercapacitors, have been limited due to their relatively poor conductivity and cycle stability. Here ternary Ni3S2/MnS/CuS composites were assembled in situ on nickel foam (NF) using a hydrothermal method via electrostatic adsorption of Ni+, Mn2+ and Cu2+ ions on a reduced graphene (rGO) nanosheet template. The chemical structure was characterized by various analytic methods. Ni3S2/MnS/CuS has spherical morphology assembled from closely packed nanosheets, while Ni3S2/MnS/CuS@rGO has a three-dimensional porous spherical structure with much lower diameter because rGO nanosheets can play the role of a template to induce the growth of Ni3S2/MnS/CuS. At a current density of 1 A g(-1), the specific capacitance was obtained to be 1028 F g(-1) for Ni3S2/MnS/CuS, 628.6 F g(-1) for Ni3S2/MnS@rGO, and 2042 F g(-1) for Ni3S2/MnS/CuS@rGO, respectively. Charge transfer resistance (R-ct) of Ni3S2/MnS/CuS@rGO (0.001 omega) was much lower than that of Ni3S2/MnS@rGO by 0.02 omega, and lower than that of Ni3S2/MnS/CuS by 0.017 omega. After 5000 cycles, the Ni3S2-MnS-CuS@RGO electrode maintains 78.3% of the initial capacity at 20 A g(-1). An asymmetric supercapacitor was subsequently assembled using Ni3S2/MnS/CuS@rGO as the positive electrode and rGO as the negative electrode. The specific capacitance of asymmetric batteries was maintained at 90.8% of the initial state after 5000 GCD.