Fabrication And Eletrochemical Property Of Manganese Oxide/Three Dimensional Graphene Composites

Graphene is recognized as a promising carbon material to be used as a supercapacitor because of its excellent properties. However, the relatively low capacitance and layers stack of graphene have limited the graphene capacitance applications. Therefore self-propagating high-temperature synthesis(SHS) and self-assembly methods were proposed for preparation of three dimensional(3D) graphene in this paper. 3D graphene was composited with manganese dioxide in order to obtain high performance electrode materials applied to SCs.In the paper the morphological structure of the three dimensional(3D) graphene is influenced by the carbon sources and dosage of reducing agent, and the mechanism of morphological changes is discussed. Furthermore, for preparation of high performance electrode materials applied in SCs, a new strategy was presented for the fabrication of the Mn O2/3D graphene by a reverse microemulsion(w/o) meterhod. For improving the electrochemical property of Mn O2/3D graphene, on the basis of reverse microemulsion(w/o) method, a novel approach for synthesizing a Mn O2/3D graphene composite was reported by an in situ growth reverse microemulsion method.Graphene with different micro three-dimensional(3D) structures can be quickly synthesized by the self-propagating high-temperature synthesis method which employed magnesium and various carbon sources. The morphological structures of micro three-dimensional graphene can be controlled by using different carbon sources. The electrochemical performance of graphene can be affected by the defect density and oxide content, which are as a result of various carbon sources. The graphene/Mn O2 was prepared by means of mechanical blending, and the electrochemical performance of graphene is further improved from 27.8 F/g to 147.2 F/g.By changing the dosage of reducing agent, the mechanism of self-assembly 3D graphene formation is investigated. The influence of the dosage of reducing agent on functional groups in self-assembly 3D graphene was investigated, and the optimized condition for preparation of 3D graphene with high electrochemical property was presented. The functional groups and pore structure of 3D graphene can be adjusted by the dosage of reducing agent in order to obtain high performance electrode materials for SCs.A new strategy for the fabrication of the Mn O2/3D RGO was presented by a reverse microemulsion(w/o) method. In this method, 3D RGO can be dispersed homogeneously in the oil of reverse microemulsion by its lipophilic property; and the Mn O2 nanoparticles, which were synthesized by the reaction between potassium permanganate(KMn O4) and manganese sulfate monohydrate(Mn SO4·H2O) dispersed in nano-reverse micelles, are prepared on the surface of macroporous of 3D graphene during reverse microemulsion reaction. Mn O2 nanorod and nanosphere can be fabricated by the templating effect of the surfactants. It is found that appropriate annealing conditions can improve hydrated content, crystallographic structure and pore structure of Mn O2, which can promote the electrochemical performance of Mn O2/3D RGO. After annealed at 150°C, the specific capacitance of Mn O2/3D RGO is increased from 222.5 F/g to 387.9 F/g at 0.5 A/g. After 1000 cycles, 90.4% of the initial capacitance value can be maintained, showing an excellent long-term stability.Based on the reverse microemulsion method, Mn O2/3D graphene composites were prepared by an in situ growth reverse microemulsion method. Mn O2 coating is prepared on the surface of micro 3D graphene by the reaction of potassium permanganate and carbon of graphene. Compared with reverse microemulsion method, in situ growth reverse microemulsion method can obtain Mn O2/3D graphene composite with excellent electrochemical property which was synthetized by one-step method. After morphological investigation, it is found that Mn O2 layers are uniformly coated on the surface of graphene sheets with the absence of large aggregates. This coating structure has contributed to the combination of Mn O2 and 3D graphene, which can take full advantage of high electrical conductivity of graphene. Compared with Mn O2/3D RGO composite which was fabericated by reverse microemulsion method, the specific capacitance of Mn O2/3D graphene composite is increased from 222.5 F/g to 479.6 F/g at 0.5 A/g, and the initial capacitance maintained value can be improved from 90.4% to 92.7% after 1000 cycles.