Preparation And Electrochemical Performance Of Functionalized Graphene Based Materials

Supercapacitors are the new energy storage system with long cycle life,low cost and environmental friendliness.As a practical application of energy storage device,the extensive research were further developed on efficient supercapacitor,which has become the new research topic.The performance of the supercapacitor depends on the electrode materials.However,the key of enhancement about energy storage density is to explore new electrode materials.It is also the difficult point to obtain the electrode materials with high capacitance and excellent stability.Graphene is a newly discovered carbon materials,comprised of the high specific surface area,high conductivity and a series of excellent properties.It will be an ideal material for supercapacitor electrode materials.Moreover,the performance of the graphene sheets were severely inhibited by the adhesion attributing to the strong Van der Waals' force.The functionalization of graphene in chemical reaction focus on overcoming the restacking of graphene sheets.And then the graphene-based electrode materials with good performance and stable structure were obtained after the process of reduction.In this paper,the graphene oxide with large area and high quality was obtained by Hummers' method.Besides,graphene-based materials with different functional-groups were synthetized by regulating experimental conditions and methods.The graphene/polypyrrole composite materials were synthetized by in-situpolymerization.The solvent with different ratios of water to alcohol were changed in the process of graphene oxide and pyrrole monomer blend.The morphology and structural analysis found that polypyrrole was closely combined on the surface of reduced graphene oxide.The results showed that ethanol influence the distribution of polypyrrole.Furthermore,a small amount of ethanol not only promote the combination of pyrrole monomer and GO,but also make the polypyrrole uniformly distribute in the surface of graphene.However,companying the increase of dosage of ethanol,a large number of pyrrole monomer prone to polymerize in activity points,which limited the distribution of polypyrrole on the surface in graphene.By electrochemical tests,the composite with 9:1water alcohol ratio showed the outstanding electrochemical performances and excellent stability.Graphene quantum dots(GQDs)with uniform sizes of less than 5 nm were synthesized by a novel top-down strategy.The C-C bond of GO was destroyed by ultrasonic fracturing and strong acid cutting under the ultrasonic and hydrothermal process.Moreover,the oxygen-containing functional groups which introduced in the stage of acid oxidation were removed by heat treatment.Both nanoscale size and edge effect of GQDs improve their abundant active sites and restrain the restack of graphene nanosheets,and further promote the diffusion of ions within the material and electrolyte.At the same time,the electrochemical performance tests showed the ideal performance of electrochemical double-layer capacitors behavior and exceptional cycle stability.The properties of GQDs proved the potential applications in the field of supercapacitor electrode materials.Nitrogen-doped graphene(NG)with wrinkled and bubble-like texture was fabricated via the coordination of acid and treatment.Especially,a novel sonicationassisted pretreatment with nitric acid is used to further oxidize GO and its binding with melamine molecules.The special morphology of NG was obtained because of the pyrolysis of nitrogen source and deoxidation of GO under hyperthermia.There are many hollow bubble-like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets.Such characteristic bubble-like texture can effectively overcome the restacking of nanosheets and increase the active area between the nanosheets and electrolyte ions,which can provide more channels to promote the access of electrons into the inter-space.Therefore,NG demonstrates desirable characteristics as the electrode of supercapacitors: high specific capacitance,superior cycle stability and excellent energy density.The results indicate the potential use of NG as graphenebased electrode material for energy storage devices.