Praparation Of RGO/Fe₂O_3-x And RGO/Co₃O_4-x By Hydrothermal Method And Their Electrochemical Properties

Supercapacitor is an efficient energy-storage device with high power density,long cycle life,wide operating temperature range,maintenance-free and environment protection.In many energy-storage devices,it exhibits excellent electrochemical performance.But its energy density is far less than that of rechargeable battery.So now researchers have to break through the key is to ensure that power density does not attenuate while increasing energy density.Metal oxides have remarkable effects on improving the energy density of supercapacitors.Iron trioxide and cobalt oxide are considered to have great potential as pseudocapacitor electrode materials due to their low cost,high theoretical specific capacity and easy preparation.But their conductivity is low,this study improves their shortcomings by introducing oxygen vacancies.Graphene has greatly specific surface area and ion conductivity,which is an excellent double layer capacitor material in energy-storage devices.In summary,we synthesized reduced graphene oxide/oxygen vacancies Fe₂O_3-x and Co₃O_4-xcomposites by hydrothermal method to obtained excellent electrochemical properties.In this thesis,two kinds of transition metal oxides/reduced graphene oxide composites were prepared by one-step hydrothermal synthesis and subsequent processes such as freeze drying and grinding,and they were studied on structure and morphology by various characterization methods.Assemble symmetrical supercapacitors and analyze their electrochemical properties.The work is as follows:1.The reduced graphene oxide/iron oxide(rGO/Fe₂O_3-x)composite electrode material was prepared by hydrothermal method using graphene and iron（ⅲ）nitrate nonahydrate as experimental materials.The results of scanning electron microscopy and transmission electron microscopy showed that Fe₂O_3-x was grows uniformly on the porous network structure of rGO in a spherical shape.The fitting peak area ratio of Fe³⁺and Fe²⁺was 0.869:1,and the x figure was0.535.At a scan rate of 2 m V/s,the specific capacitance based on Fe₂O_3-x is as high as 1745.5 F/g.The composite electrode material was assembled into a symmetrical supercapacitor,and the energy density was 39.2 Wh/kg at the power density of 120 W/kg.The capacitance retention rate after 10000 electrochemical cycles was 96.23%.Symmetrical supercapacitors exhibit good rate performance and cycle stability.2.A three-dimensional reduced graphene oxide/cobaltosic oxide(3D rGO/Co₃O_4-x)composite electrode material containing oxygen vacancies was prepared by one-step hydrothermal synthesis using graphene oxide（GO）and cobalt nitrate hexahydrate（Co（NO₃）₂·6H₂O）as experimental materials.The fitting peak area ratio of Co³⁺and Co²⁺was calculated to be 3:5 to the XPS results,and the x value of Co₃O₄-_x was 0.44.The uniform distribution of linear and spherical-shaped Co₃O_4-x on the 3D rGO with porous network structure was displayed by scanning electron microscopy and transmission electron microscopy,indicating the successful preparation of 3D rGO/Co₃O_4-x composites.At a scan rate of 2 m V/s,the specific capacitance based on Co₃O_4-x was 635.7 F/g.A symmetrical supercapacitor was assembled using the composite electrode material,which exhibited an energy density of 10.6 Wh/kg at a power density of 100 W/kg.After 10000 electrochemical cycles,the capacitance retention rate was as high as 98.15%.The excellent electrochemical performance of symmetrical supercapacitors was attributed to the large specific surface area,good porosity of graphene,and the synergistic effect between Co₃O_4-x and graphene.