Design And Synthesis Of Cobalt Oxide Composite Electrode Materials And Their Supercapacitor Performance

With the increasing of energy crisis and environmental pollution,it is urgent to develop some sustainable and pollution-free energy storage equipments.As a kind of energy storage device with long cycle life,supercapacitor has attracted one’s much attention.Electrode material is a key factor for the improvement of the electrochemical performance of supercapacitors.Therefore,it is of great significance to develop electrode materials with high electrochemical performance.Among them,cobalt oxide shows large theoretical specific capacitance,multiple variable valence states,environmental friendliness and low price.However,the low conductivity limits its application.In this thesis,the prepared multi-level composite nanomaterials are investigated such as the growth mechanism of the material and the energy storage mechanism.Through the synergistic effect between the materials,the conductivity and structural stability are improved,thereby which enhances the electrochemical performance of the electrode material.The main contents of the thesis are as follows:（1）Metal-organic frameworks（MOFs）are used as sacrificial templates to prepare Co₃O₄porous nanosheets by high-temperature calcination.Co₃O₄ porous nanosheets grown under different solution concentration are studied.Reasonable pore size distribution helps to increase the specific surface area and facilitates the full contact between the electrode material and the electrolyte.The results show the prepared material possesses a large specific capacitance(156F·g^-1 at 0.5 m V s^-1).After 6000 cycles,it can still maintain its initial specific capacitance of80%.After assembled into the device,the power density can reach 1500 W kg^-1 when the energy density is 17.5 Wh kg^-1.After 8000 cycles,its specific capacity retention rate is 83%.（2）Three-dimensional Co₃O₄@NiMoO₄ core-shell nanomaterials are prepared by a hydrothermal method.The obtained sample delivers a specific capacitance of 1200 F g^-1 at 1A g^-1.After 10,000 cycles,it still maintains a specific capacitance of 98.2%compared to the initial capacitance.As a cathode material for asymmetric supercapacitors,the assembled Co₃O₄@NiMoO₄//AC device presents an energy density of 36.1 Wh kg^-1 at a power density of 2700 W kg^-1.After 10,000 cycles,the specific capacitance still maintains a retention rate of84.4%.Meanwhile,the flexibility of the device is investigated by bending at different angles.The results show it possesses excellent compression resistance and mechanical flexibility.（3）The Co₃O₄@CoMoO₄structure is synthesized by a two-step hydrothermal method,and then an amorphous polypyrrole is deposited on its surface by electrodeposition.Electrical conductivity and electrochemical performance are explored after the introduction of organic conductive polymer PPy.This material can not only improve the conductivity of the electrode material,but also stabilize the structure.The results show it is helpful to improve the electrochemical performance.The prepared electrode material delivers a specific capacitance of 1564 F g^-1 at the current density of 1 A g^-1,and it can still maintain 80%of the initial specific capacitance at the current density of 8 A g^-1,showing its excellent rate performance.After10,000 cycles,92%of the specific capacitance can still be kept,demonstrating its excellent durability.The assembled device shows a power density of 751.9 W kg^-1 at the energy density of 37.8 Wh kg^-1.When the energy density is 30 Wh kg^-1,the power density can reach 6002 W kg^-1.（4）Using Co₃O₄ as the host material,three-dimensional CoP@C@Ni（OH）₂ multi-level nanomaterials are obtained.when the current density is 1 A g^-1,the specific capacitance of the prepared samples can reach 1884 F g^-1,and even if the current density is expanded to 8 A g^-1,the specific capacitance can still reach 1312 F g^-1.The prepared CoP@C@Ni（OH）₂ three-dimensional arrays is used as the positive electrode,several devices are assembled.At a power density of 749.3 W kg^-1,the energy density can reach 41.9 Wh kg^-1.After connecting the devices in series,a blue LED with 2 V voltage is lightened for 4 minutes.