Preparation Of 3d Graphene And Its Application

Graphene is a two-dimensional nanomaterial with a honeycomb-like lattice structure composed of carbon atoms through sp2 hybridization.Graphene has unique electronic,thermal,optical and mechanical properties.Graphene has to be assembled into desired three-dimensional macro-architecture with porous structure to expand the application of graphene in the field of energy storage.The three-dimensional graphene is macro-architecture with porous structure based on graphene,compared with the two-dimensional graphene,has a higher specific surface area,high conductivity and high mechanical properties and so on.Three dimensional graphene has great potential in the field of supercapacitors.As a pseudocapacitive material,MnO2 has many advantages,such as high theoretical capacitance,environmental friendly and low cost.The combination of three-dimensional graphene and MnO2 has a synergistic effect,and it is expected to obtain higher energy storage performance.In this study,three-dimensional graphene was prepared by chemical vapor deposition(CVD)and oxidation-reduction method respectively.The effects of nickel foil,copper foil and nickel foam substrate on the quality of graphene prepared by chemical vapor deposition were discussed.The preparation of three-dimensional graphene/MnO2 composites was carried out by using constant current electrodeposition technique and the effect of electrodeposition on the capacitive performance of the composites was investigated.The rGO/MnO2 composite hydrogel was prepared by hydrothermal method and the effect of MnO2 loading on the performance of composite hydrogel was studied.The morphology and structure of graphene,MnO2 and its composites were characterized by optical microscopy(OM),scanning electron microscopy(SEM),Raman spectroscopy(Raman),transmission electron microscopy(TEM)and X-ray diffraction(XRD),and the electrochemical workstation was used to test the composite material capacitive performance.The main results are as follows:(1)Three-dimensional graphene was prepared through CVD system on the foam nickel substrate,when the growth time is 10 min and the methane concentration are in the range of experimental design(1 vol%,2 vol%,4 vol%),a three-dimensional conductive network of multilayer graphene with high structural strength was obtained.(2)A smooth surface of the copper foil was obtained by electrochemical polishing.CVD was used to prepare the graphene on the smooth surface which can reduce the nonuniform nucleation of graphene and improve the crystallinity of graphene.When the flow rate of H2/CH4 is 20,the crystallinity of graphene is poor,and when the H2/CH4 flow ratio is 40,the regular hexagonal monolayer graphene is obtained on the surface of polished copper foil.(3)MnO2/three-dimensional graphene composites were prepared by constant current electrodeposition which can effectively reduce the equivalent series resistance of the composite material.When the constant current electrodeposition time is 15min,the best specific capacitance and rate performance of the composites were obtained.When the current density is 1.5 Ag-1,the specific capacitance is 265 Fg-1,and the specific capacitance decreases 6.4%when the current density increases to 4 Ag-1.(4)The hydrothermal synthesis of rGO hydrogel and the rGO/MnO2 composite hydrogel are simple,environmental friendly and easy to operate.When the MnO2 loading is 10 mg,the composite hydrogel has the highest specific capacitance and best rate performance,the specific capacitance of the composite hydrogel under the condition of 1.5 Ag-1 is 175 Fg-1.With the increasing of MnO2 loading,MnO2 agglomerates,resulting in the decrease of the utilization of the active species,which leads to the decrease of the specific capacitance of the composite hydrogel.