Preparation Of Graphene Sheets By Exfoliation Of Graphene In Supercritical Ethanol

Graphene has a very wide range of applications due to its excellent physical and chemical characteristics.Many methods have been explored for preparation of high-quality graphene efficiently.However,it still remains a great challenge for the scalable production of graphene with low cost.In this work,supercritical ethanol was employed as medium for the exfoliation of flake graphite and expanded graphite,respectively.And the influence of processing parameters on graphene yield were systematically investigated and discussed.The graphene sheets were characterized by Scanning Electron Microscopy?SEM?,Transmission Electron Microscopy?TEM?,Atomic Force Microscopy?AFM?,X-ray diffraction?XRD?and Raman Spectroscopy.The pure graphene film were fabricated on a ABS resin substrate using wire rod coating method in order to study its elelctrical properties.And the electrochemical performance of graphene as a supercapacitor electrode was also investigated.The graphene sheets were produced in supercritical ethanol using flake graphite as starting material,the suitable preparation conditions were as follows:the initial graphite concentration 0.32mg/ml,250^oC,26MPa and 0.5hour in exfoliation,in which the yield was about 12.49%.It could reach 21.32%at maximum after six times'of exfoliating under the optimum condition.AFM results suggested that 94%of the layers of graphene flakes were less than 8 layers,among which 6%were monolayers.The result of XRD and Raman showed that the graphene exhibits high quality and intact lattice structure.The graphene sheets were produced in supercritical ethanol using expanded graphite as starting material,the suitable preparation conditions were as follows:the initial graphite concentration 0.15mg/ml,250^oC,26MPa and 0.5hour in exfoliation,in which the yield could reach 11.5%.SEM and TEM results suggested that graphene sheets exhibit common morphologies of graphene including folding and wrinkles.Analysis of TEM and AFM results revealed that the large graphenes had been obtained,and the large graphenes had sizes up to 50?m×25?m.The results of XRD and Raman showed that the exfoliation process did not cause structural defects and guaranteed the high quality of graphene.Furthermore,electrical conducticity of the resultant pure graphene films using flake graphite and expanded graphite as starting material were 8.333×10⁴S/m and 1.033×10⁵ S/m,respectively.The cyclic voltammetry?CV?and galvanostatic charge-discharge tests?GCD?of G_?FG?electrode and G_?EG?electrode were carried out respectively.The results showed that both of the graphene sheets have good electrochemical performance.The cyclic voltammetry were carried out at a scanning rate of 100 mV/s,and the specific capacitance of the measured electrodes were 115 F/g and 130 F/g,respectively.Their specific discharge capacitance were78 F/g and 90 F/g between-1.0V and 0.4V potential at 16 A/g current density in 6M KOH solution.