Synthesis And Electrochemical Performance Of Graphene And Doped Graphene

Graphene, a single-atom-thick sheet with a honeycomb lattice of carbon atoms,has generated tremendous attention in recent years. However, graphene is easy to reunite, and the chemical exfoliation of graphite to graphene via oxidation and reduction will introduce many defects into graphene sheets. In addition, graphene is a zero bandgap semiconductor, which hindered the application of graphene in electrical devices. It can effectively adjust the electronic structure of graphene by chemical doping, which improved its physical and chemical properties, and then optimized electrochemical performance of graphene. In order to solve these issues, looking for a suitable method to prepare graphene is putting on the schedule. In this paper, severial feasible methods are developed to prepare graphene and doped graphene with graphite and fluorinated graphite, and the influence of dispersion stability, the structure,electric conductivity and electrochemical performance were investigated. The main research contents and results are as follows:(1) Three chemical oxidation reduction methods, including Hummers method,modified Hummers method, and improved method, were used to prepare GOs and graphene sheets. The influence of preparation methods on the structure, dispersion stability in organic solvents, and electrochemical properties of graphene sheets were investigated. The results showed that the amount and kind of oxidizing agent, may be varied the oxidation degree of GO. In addition, graphene prepared by improved method exhibits excellent dispersity and stability in organic solvents without any additional stabilizer or modifier, which is attributed to the completely exfoliation and regular structure. Moreover, cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS) measurements showed that graphene prepared by improved method exhibits superior electrochemical properties than that prepared by the other two methods.(2) One of the key problems with the chemical exfoliation of graphite to graphene via oxidation and reduction, is the excessive oxidation of graphite and incomplete reduction of graphene oxide, which introduce many defects into graphene sheets. Therefore, fluorinated graphite (FGi) was chosen to prepare graphene sheets,ultrasonic method, static method and refluxing method are selected. The results showed that graphene prepared by refluxing method emerges outstanding crystal structure and electrochemical properties.(3) A series of Nitrogen-doped graphene sheets (N-Gr) with discrepant electrochemical performance were prepared through a high-temperature solid state reaction method by controlling reaction temperature on reaction reagent of fluorinated graphite and urea. Nitrogen was successfully doped into graphene with three forms of pyrrolic nitrogen, pyridinic nitrogen and graphitic nitrogen. The results showed that N-Gr-500 presented the best crystal structure, and largest CV curve area. As a contrast,the mixture of GO and urea is employed to produce Nitrogen-doped reduction of graphene oxide (N-RGO). The most dramatic discovery of this study is that the electric conductivity of N-Gr-500 achieved 9475 S/m, whlie the electric conductivity of N-RGO-500 was only tested to be 200 S/m.(4) Another experiment is regard to the synthesis of Sulphur-doped graphene sheets (S-Gr) and its electrical properties. A sequence of Sulfur reagents, such as NaHSO3, Na2S2O3·5H2O, Na2SO3 and Na2S·9H2O were selected for reductants and dopants to prepare S-Gr at 500?. The doped materials were characterized by XPS and demonstrated that sulfur in the form of C-S-C and C-SOx-C successfully doped into graphene, and the sulfur content of sulfur doped graphene prepared by Na2S·9H2O (S-Gr-4) is reach to 3.35%. Furthermore, S-Gr-4 exhibits superhigh electric conductivity. The electric conductivity of S-Gr-4 is 21720 S/m.