Synthesis of hollow carbon nanoshells and their application for supercapacitors

This work is devoted to the study of the synthesis, the description of the structure, and the use of hollow carbon nanoshells 3–5 nm in size. Hollow carbon nanoshells were synthesized by thermolysis of a mixture of nickel acetate and citric acid in the temperature range of 500–700$^\circ$C. During the chemical reaction, nickel nuclei $\sim$3–5 nm in size are formed, separated from each other by carbon layers. At an annealing temperature of 600$^\circ$C, the most ordered, close-packed structure is formed, evenly distributed throughout the sample. The etching of nickel with nitric acid resulted in hollow carbon nanoshells with a high specific surface area ($\sim$1200 m$^2$/g) and a homogeneous structure. Raman spectroscopy shows that the graphene-like structure of carbon nanoshells is preserved before and after the etching of nickel, and their defect density does not increase, which enables them to be subjected to new processing (functionalization) in order to obtain additional physical properties. The resulting carbon nanoshells were used as active material of the supercapacitor electrodes. The conducted electrochemical measurements showed that the specific capacitance of the supercapacitor did not fall below 120 F/g at a current density of 0.3 to 3 A after 800 charge/discharge cycles.