Nitrogen Doped Graphene Preparation And Super Capacitor Performance Research

Graphene, a novel two dimensional (2D) carbonaceous material, is composed of free-standing carbon atoms which are densely packed into a six-angle type honeycomb crystal structure. Due to their unusual electronic transport properties, outstanding mechanical properties and high specific surface area, graphene has attracted tremendous attention from both the experimental and theoretical scientific communities. Doping graphene with nitrogen is a practical way to tailor its electronic structure, improve its physical and chemical properties, and facilitate its practical applications. Among the many methods for producing graphene, chemical reduction is expected to the mass production, because of its low cost, high efficiency, and easy functionalization. Therefore, it’s still a great challenge of the research on graphene to look for the green and efficient chemical reducing agent and develop the new technology of doping graphene with nitrogen.In this paper, stable graphene aqueous suspensions and nitrogen-doped graphene were successfully achieved by chemical reduction method and hydrothermal method, respectively. The morphology, structure and component of the as-synthesized materials were characterized by the modern analysis methods, and the supercapacitive properties of the products were investigated using the electrochemical testes. The main contents can be summarized as follows:Highly stable graphene aqueous suspensions were synthesized by the chemical reduction method with graphene oxide (GO) as the raw materials and acetone oxime as reducing agents. To compare the reducing ability of acetone oxime, hydroxylammonium chloride or hydrazine hydrate was employed to chemically reduce GO under the same conditions. The possible mechanism for the chemical reduction of GO with acetone oxime was also studied. The as-synthesized materials were characterized by atomic force microscopy, field emission scanning electron microscopy, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis and electrical conductivity measurements. It is revealed that acetone oxime can reduce GO effectively and its reduction ability is equal to hydroxylammonium chloride or hydrazine hydrate. Interestingly, the doping of nitrogen into graphene plane is completed simultaneously as the GO is reduced and the atomic percentage of nitrogen is3.67%within the product. The supercapacitive properties of the materials were measured by cyclic voltammetry and galvanostatic charge-discharge measurements. Acetone oxime reduced graphene oxide and hydroxylamine hydrochloride reduced graphene oxide showed good capacitive behavior and cycling stability, the specific capacitance values were143and135F g"1, which can still maintain in135and125F g-1after1500cycle tests, respectively. Compared with GO, the specific capacitance of the two materials increased obviously.Nitrogen-doped graphene was synthesised through the hydrothermal method with GO as raw materials and urea as reducing-doping agents. The as-generated materials were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption analysis and electrical conductivity measurements. It’s revealed that nitrogen was doped into the graphene plane at the same time as GO sheets were reduced, and the content of nitrogen in the range of5.47-7.56at.%was obtained by adjusting the mass ratio of GO to urea. In addition, nitrogen-doped graphene achieved using our approach contain abundant pore structures. Cyclic voltammetry and galvanostatic charge-discharge measurements showed that doped graphene with different nitrogen content possessed different supercapacitive properties. The best performance and excellent long cycle life offer the promising prospects for the application of the doped graphene with the nitrogen content of7.50at.%as electrode materials in supercapacitors. The specific capacitance of191F g-1can be reached and only1.3%losses were found after1600cycles.