Functionalization Of The Graphene Surface And Its Supercapacitor Performance

Supercapacitor is a new type of electrochemical energy storage electronic component based on the interface of double electric layer.Compared with the traditional capacitor and accumulator,it has higher power density,longer cycle life,large capacity,little environmental pollution and low cost.In 2004,graphene was discovered for the first time,and because of its high specific surface area and excellent electrical conductivity,it is widely used as a carrier for various nanomaterials and is also an ideal candidate electrode material for energy storage devices.Therefore,in this thesis,graphene is used as a carrier.By functionalizing its surface,loading a transition metal compound on its surface,and compounding it with a preferred base material,a supercapacitor electrode material with excellent performance is prepared.The specific content is as follows:1.By grafting polydopamine on the surface of graphene,then using the rich amino groups of polydopamine to adsorb transition metal cobalt ions,and then pyrolyzing at high temperature to obtain highly dispersed Co₃O₄ nanocube-supported nitrogen-doped porous carbon composite material.A simple hydrothermal method was used to prepare nanocomposites with the help of polydopamine.Electrochemical tests show that the specific capacitance of the Co₃O₄@PDA-rGO composite is 1183 F g^-1at a current density of 1 A g^-1.In this work,we use polydopamine to combine graphene oxide and Co₃O₄,which can effectively improve the dispersion of Co₃O₄ on the surface of graphene,ensure the full utilization of Co₃O₄nanocrystals,and introduce nitrogen atoms on the surface of carbon materials,so as to improve the hydrophilicity of the materials.At the same time,it also contributes to the pseudo capacitance,which makes the Co₃O₄@PDA-rGO composite show excellent electrochemical performance.When the power density is 1125 W kg^-1,the energy density is 65 W h kg^-1,and it retains 73.2%of its initial capacitance after 3,000charge and discharge cycles.2.The core-shell structure of Cu₂O@Co₃O₄/PC composite was obtained by using Cu?OH?₂ self-template method,which encapsulated Co₃O₄ in Cu₂O nano cubic crystal and anchored on porous carbon?PC?.Electrochemical tests show that the specific capacitance of Cu₂O@Co₃O₄/PC composite is 1096 F g^-1 at a current density of 1 A g^-1.An asymmetric supercapacitor device was assembled using Cu₂O@Co₃O₄/PC as the positive electrode and rGO as the negative electrode.The electrochemical test results show that the Cu₂O@Co₃O₄/PC//rGO device has a specific capacitance of 116 F g^-1 at a current density of 1 A g^-1,and the contribution rate of the device is 56.5%at the scanning rate of 50 m V s^-1.When the power density is 700 W kg^-1,the energy density is 32.1 W h kg^-1,and it retains 78%of its initial capacitance after 3,000 charge and discharge cycles.3.Hollow NiMoO₄@V₂CT_x/rGO MXenes positive electrode materials and hierarchical nanostructured Fe₂O₃@Mo O₂/PC negative electrode materials were successfully prepared by using ionic liquid-assisted hydrothermal method and electrodeposition method,and a solid-state V-MXenes//FMC-ASC device was assembled.Electrochemical tests show that the maximum energy density of the super capacitor is 56.1Wh kg^-1 at 800 W kg^-1,and the maximum power density is 8000 W kg^-1 at an energy density of 31.6 Wh kg^-1.In addition,it maintained 81.8%of the initial capacity after 3,000cycles,showing good cycle stability.The exploration and synthesis of NiMoO₄@V₂CT_x/rGO MXenes electrode materials provide new strategies for the development of other two-dimensional MXenes materials.