Electrodeposition of high-capacitance 3D CoS/graphene nanosheets on nickel foam for high-performance aqueous asymmetric supercapacitors

Electrochemical energy storage devices that encompass the capability of offering both excellent capacitance and rate performance have always be in high demand. Herein, we present a simple and green two-step electrodeposition process to fabricate a high-performance 3D CoS/graphene hybrid network with a nanosheet structure on Ni foam. The nanosheet-like CoS is tightly wrapped and anchored by the graphene layer and the two different material species are nicely integrated together, leading to increased conductivity and enlarged electroactive surface area of the electrode materials. The CoS/graphene composites exhibit an impressive specific capacitance of 3785 F g(-1) at a current density of 1 A g(-1), a favorable rate capability with 82% retention at 20 A g(-1). A CoS/graphene vertical bar vertical bar activated carbon asymmetric supercapacitor fabricated in 2 M KOH solution exhibits a maximum energy density of 29 Wh kg(-1) at the power density of 800 W kg(-1), and a power density of 40.0 kW kg(-1) (at the energy density of 11.0 Wh kg(-1)). Furthermore, 70% capacitance retention was obtained after 10 000 cycles within the potential window of 0-1.6 V. The excellent performance of the CoS/graphene composites demonstrated in this work has revealed the promising potential of adopting the CoS/graphene hybrid network for high performance supercapacitors.