Synthesis of nickel sulfide–graphene oxide composite microflower structures to enhance supercapacitor performance

NixSy in various crystal phases (NiS, NiS2, and Ni3S4) was synthesized on thermally reduced graphene oxide (TRGO) by a one-step hydrothermal process. Microstructures and morphologies of as-prepared NixSy–TRGO composites were characterized. NixSy was formed as microflowers with average size of 1.1–2.3 µm, which grew homogeneously on the curved TRGO nanosheets. Electrochemical performance of NixSy–TRGO was revealed with high specific capacitance of 1602.2 F g−1 at 1 A g−1 and favorable cycling retention of 90.81% after 3000 cycles at 5 A g−1. An asymmetric supercapacitor device based on NixSy–TRGO||TRGO exhibited a superior energy density of 39.78 Wh kg−1 at the power density of 0.75 kW kg−1 with an cycling stability of 91.2% capacitance retention after 3000 cycles. Thus, the as-prepared NixSy–TRGO could be an advanced supercapacitor electrode material.