Synthesis Of Few-layered Graphene By Arc Discharge Method And Study On Their Electrochemical Properties

Graphene is a two-dimensional （2D） crystal consisting of a single layer of sp²hybridized carbon atoms arranged in six-membered rings. It has fascinated the almostmaterial scientific community due to its extraordinary properties and potentialapplications.Firstly, we have explored the optimum conditions of the synthesis of few-layeredgraphene. According to the characterization results of SEM and XRD, we can findthat the efficient exfoliation of the graphite requires a higher current density in H2-Hebuffer gases. However, when the arc current is too much high, the samples are easy tosinter and agglomerate, and as-obtained graphene have a large thickness andinhomogeneity. Only when the volume content of hydrogen ranges from25%to75%in containing H2buffer gases, fewer-layerd graphene nanosheets with high qulity canbeen achieved by arc discharge method. In addition, total pressure have little effect onthe morphology and structures of the graphene in H2-He buffer gases, only somedifferences in the size of the graphene nanosheets, and the less total pressure, thesmaller size.Secondly, we have investigated the influence of different buffer gases onsynthesis of graphene. To begin with, few-layered graphene sheets were synthesizedby direct current arc discharge using different buffer gases. Then, A variety ofcharacterizations of the samples were conducted, such as SEM, TEM, AFM, Raman,BET and TGA （thermogravimetric analysis） et. al. Moreover, the hydrophobility andthe field emission properties of the sprayed-coating graphene films prepared by adirect solution process were studied. As a result, the generation of graphene sheetsshows strong dependence on the composition of buffer gases and containing H2buffergases are necessary to prepare few-layered graphene sheets. The graphene sheetsproduced in H₂-He buffer gases have better crystallinity and higher specific surfacearea compared with those produced in others containing H₂buffer gases. Theas-obtained graphene sheets are mainly no more than5layers and their lateraldimensions are about40-200nm. The graphene sheets show excellent thermalstability and there is only less than3wt.%weight loss up to800oC in N2atmosphere.The graphene sheets can be easily dispersed into ethanol and the as-obtainedsuspension can be stable for more than two months. The sprayed graphene films show good hydrophobility and a typical cold cathode field emission behavior.Lastly, we have studied the electrochemical properties of graphene and nitric-acid-treated graphene. And arge-scale synthesis of graphene nanosheets （GNSs） withgood crystallinity and high electrical conductivity (1680S·m^-1) is achieved by arcdischarge method. In order to increase the surface active sites of electrochemicalreactions and promote the wettability of the GNSs in aqueous electrolyte, a surfacechemical modification has been carried out on the GNSs by nitric acid treatment.Furthermore, the nitric-acid-modified GNSs （H-GNSs） as electrode material have thelargest specific capacitance of65.5F·g^-1 at a current density of0.5A·g^-1 in2M KOHelectrolyte, about30times higher than that of original GNSs. In addition, the H-GNSselectrode shows good cycling stability. Therefore, the H-GNSs may be an attractivecandidate as an electrode material for supercapacitors.