Preparation And Pseudocapacitive Behavior Studies Of Cobalt Nickel Sulfide For Supercapacitors

Supercapacitors as a new type of energy storage device are widely studied in recent years, it has advantages of short charging time, high charging efficiency, long cycle life and other characteristics, those advantages make it promising in solar energy, wind energy storage, new energy automotive, consumer electronics and other markets. The performance of supercapacitors mainly depend on electrode materials.In this thesis, Dandelion-like Co9S8 nanotubes have been fabricated by a mild two-step hydrothermal method. Through the observing of electrochemical characterizations and morphology transmutations at different charge-discharge stages, an unusual activation process of the as-prepared electrode is revealed with the help of different kinds of characterization methods including SEM, TEM, FT-IR, cyclic voltammetry, galvanostatic charge-discharge methods. During the initial charge-discharge process, intermediate product Co9S8 OH nanosheets are formed and accumulated on the Co9S8 nanotubes, turning into a core-shell structure, which can largely enhance the contact surface area between electrode and electrolyte and result in an improvement of specific capacitance. After activation, the specific capacitance can be significantly increased by 9.2%. During the preparation of electrode, the dosage of reactants and loading mass will also have some effect on the supercapacitor performance. By changing the dosage of reactants and loading mass, the material morphology size and specific capacitor can be easily controlled.Nickel and cobalt-nickel sulfide in the same morphology are also fabricated and studied by the same mild method. The comparison results show that cobalt-nickel sulfide electrode can combine the advantages of cobalt sulfide and nickel sulfide because of its multiple redox in the supercapacitor. At the same current density of 1A/g, the specific capacitor of cobalt-nickel sulfide is as high as 773 F/g, 77% higher than the cobalt sulfide and 24% higher than the nickel sulfide. The results above proving that cobalt-nickel sulfide is a promising electrode material in supercapacitors.