Synthesis And Capacitive Performance Of Intercalated Graphene And Graphene-based Nanofibers

With the development of green energy(such as solar energy, wind energy, water energy, and etc), the problem of energy storage and convertion has attracted lots of interests. As a very promising energy storage device, supercapacitor has attracted much attention in recent years. The studies of supercapacitor mainly focus on electrode materials. In this work, we synthesized different series of graphene-based materials for supercapacitor, which provide a route to preparation of the high performance materials. This thesis mainly contains the following contents:1. Studies the capacitance properties of diaminoalakane-intercalated graphene: A series of diaminoalkane-intercalated graphene materials were prepared by intercalation reactions, followed by hydrazine reduction at room temperature. The as-prepared intercalated graphite oxides(DIGOs) and their reduced products were characterized using a variety of approaches such as X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and elemental analysis. Structural characterizations have confirmed that the diaminoalkanes were intercalated effectively into both DIGOs and DIGs. Moreover, the interlayer spacing of both DIGOs and DIGs can be controlled precisely by changing the number of methylene groups in diaminoalkanes. Electrochemical tests show that the specific capacitances of DIGOs and DIGs decrease as the interlayer spacing increases. After hydrazine reduction, the specific capacitances of DIGs become larger due to the increased electrical conductivity and micropore surface area. Kinetic studies demonstrate that ion adsorption onto both DIGOs and DIGs can be well fitted with pseudo-second-order kinetic equation. The ion diffusion rate constant is mainly determined by the interlayer pore sizes of DIGOs and DIGs. 2. Studies the capacitance properties of graphene-based carbon nanofibers: The graphene-based carbon nanofibers were prepared by electrospinning polyacrylonitrile(PAN) and N, N-dimethylformamide(DMF) solution containing dispersed oxidized graphene nanosheets which were prepared by Hummers method and improved method, followed by pre-oxidation at 280 oC in air for 1 h and carbonization at 800 oC in N2 for 1 h(the samples were named as HGCF and IGCF, respectively). The morphology and chemical structure of the samples were characterized by means of scanning electron microscopy(SEM), gas adsorption, element analysis(EA) and Fourier transform infrared spectroscopy(FT-IR). We found that GO which was prepared by the improved method were dispersed easily due to the excellent hydrophily, it can prevent graphene from restacking and was beneficial to the removal of oxygen-containing groups. Thus it can improve the conductivity and the specific surface area of IGCF. Electrochemical tests show that the specific capacitance of IGCF(156 F g-1, which is close to the ideal double electric layer capacitor) is larger than HGCF(108 F g-1) due to the higher conductivity and specific surface area.