Study On The Supercapacitor Of Iron/Manganese Oxide And Graphene Composites

As the thinnest two-dimensional material, graphene is a honeycomb-like sheet of carbon just one atom thick with a number of unique physical properties, has captured enormous attention since it was discovered in2004. Graphene supercapacitor is typical electrochemical double-layer capacitors (EDLCs) with the advantages of long cycle life and stability, which has the shortcoming of low energy density, while pseudo-capacitors can make up these shortages. Hence, the combination of graphene and metallic oxide, could improve the conductivity of metallic oxide, and in addition, the existence of metallic oxide could bring extra pseudo capacitance for the supercapacitor. Besides, using the hydrothermal method to synthesize graphene and their compounds has the potential of large scale production, and the advantage of low cost and high efficient.This paper has investigated the synthesis and reduction procedure of graphene, the hydrothermal method of synthesizes the compounds of FeOOH/MnOx and graphene, and the formation mechanism of the compounds, the influence of the raw material and graphene to the nanorods, and the influence of the ratio of graphene to the electrochemical performance of the electrodes.The results showed that:during formation of FeOOH/rGO materials by hydrothermal method. the GO played an important role as not only the oxidizer to oxidize Fe2+to Fe3+but also the base planes on which the FeOOH crystallines to grow, the nanorods growing on the surface of GO to form a3D network structure, which greatly improved the specific area of the compounds. The existence of CH3COONa could greatly improve the growth and crystallization of the nanorods but not essential. Simultaneously, there were many oxygen functional groups on the surface of GO, such as-COOH,-OH, in the existence of CH3COONa, the hydrolysis of CH3COONa and GO would create OH-to the solution, then caused an increase of pH value, and this alkaline environment would prevent the high local supersaturation of Fe2+and lead to nucleation of the nanorods, then the crystal nucleus started growing on the GO sheets to form the intermediates. The length of the nanorods increased to200nm with time, at last, the oxygen functional groups on the surface of GO would be gradually consumed, hence, the GO has been reduced into rGO by Fe2+. The electrical performance of the FeOOH/rGO materials depends on the quantity of rGO and the combination. An increase of rGO and decrease of the crystal size and could apparently improve the specific capacitance. The FeOOH/rGO electrodes exhibited high specific capacitance of537.14F/g and reached a2.6times improvement maximumly compared to the rGO electrode at the current destiny of2A/g. The FeOOH/rGO electrode supercapacitor can contain specific capacitance of92.56%after400cycles.Besides, this paper investigated the compounds of MnOx and graphene, the results showed:during the hydrothermal procedure within the rGO, the small pieces of rGO in the suspension could provide the base planes on which the MnOx crystallines to grow. The mass ratio of rGO and MnO2has crucial influence to the results. When the ratio was rGO:MnO2=1:3, the nanorods were MnOOH, while the ratio was rGO:MnO2=1:1, the nanospheres were Mn3O4. The nanospheres on the compounds of Mn3O4/rGO were uniformly grown on the wrinkles of the rGO, could get maximal contact area with rGO. When Mn3O4/rGO used as the electrode of the supercapacitor, the rGO could act as the electric skeleton of the compounds, and form a huge electric conduction grid, so that the Mn3O4could release pseudo capacitance greatly. With the combination of the pseudo capacitance and the double layer capacitance, the supercapatior could exhibit excellent electrochemical performance. The Mn3O4/rGO electrode exhibited specific capacitance of297.14F/g at the current destiny of2A/g.