Preparation And Supercapacitor Properties Of Graphene-based MO_x-MnO_x Nanosheet Composites

Supercapacitor has been used in many fields widely and the world are sparing their efforts to research and application,The study found that the performance is an important factor in the electrode material.Graphene is a kind of single-carbon atomic layer two-dimensional nanomaterials,and its superior structural system gives a series of physical and chemical properties such as high specific surface area,excellent conductivity,good mechanical and chemical stability.In the field of supercapacitor,the graphene's theoretical capacity of the double layer capacitor is very good,but it is easy to agglomerate during the reduction process,which obviously limits its capacitance behavior and is difficult to meet the requirements of super capacitor electrode material.In order to solve this problem,people turn their attention to the transition metal oxide,among them,manganese,copper,zinc,these three oxides because of its good electrochemical properties of the electrode material has become a good choice.However,the conductivity of these oxides is poor,so that they are difficult to obtain ideal capacitance effect.In order to compensate for the shortcomings of the above two materials,this thesis will use physical or chemical means to combine the two materials,in combination with the advantages of the two materials mentioned above,On the basis of graphene and then load a transition metal oxide,Thereby preparing a graphene-based binary transition metal oxide nanomaterial to achieve the purpose of improving the capacitance of the electrode material.The following is the main research work:(1)Using natural graphite as raw material,Graphene oxide was prepared by simple Hummers'method.By using graphene oxide,potassium permanganate and zinc chloride as raw materials,the graphene as the substrate,binary transition metal oxide(Zn O/Mn O)nanosheet composite(ZM-GS)was prepared by low temperature hydrothermal method.Graphene-based manganese oxide nanosheet composites were prepared by the same method as a comparative material.The results of scanning electron microscopy(SEM)and transmission electron microscopy(TEM)and X-ray diffraction(XRD)show that the Zn O/Mn O composite nanosheets are grown on the surface of graphene by low temperature hydrothermal method.Because of the excellent conductivity and specific surface area of graphene and the unique lamellar structure of Zn O/Mn O,the contact area between the electrochemically active material and the electrolyte is greatly increased,which greatly enhances the electrochemical activity and energy of the composites density and so on.The electrochemical test results showed that the specific capacitance of ZM-GS was 325 F g^-1,which is significantly higher than that of M-GS.After 1000 cycles,ZM-GS showed excellent cycling stability.These results fully demonstrate the superiority of ZM-GS in the application of supercapacitor electrodes.(2)Graphene oxide was prepared by simple Hummers'method by using natural graphite as raw material.The oxidized graphite was reduced to graphene by low temperature hydrothermal method(120°C).the binary transition metal oxide nanosheets were grown on the surface of graphene during the hydrothermal treatment.GS-Cu₂O/Mn₃O₄ nanosheets were prepared with graphene as substrate by high temperature treatment.However,the comparative materials,due to the lack of copper raw materials,graphene-based manganese oxide(Mn O)nanocomposite was obtained.The change in valence of Cu₂O/Mn₃O₄ nanosheets is probably due to the fact that manganese ions lose the electrons and the copper ions get the electrons during heat treatment,The prepared graphene binary transition metal oxide(Cu₂O/Mn₃O₄)nanosheet composite(CM-GS),graphene,Cu₂O,Mn₃O₄ are extremely promising electrode materials.CM-GS showed excellent capacitance performance,capacitance up to 251 F g^-1;compared to GS capacitance density increased by 40%.After the 1000 s CM-GS cycle performance also received satisfactory results.This series of results fully demonstrates that CM-GS is a good supercapacitor electrode material.