Fabrication And Electrochemical Properties Of The Graphene Based Composites As Supercapacitor Electrode Materials

As a new type of energy storage device,supercapacitor has a wide range of applications in mobile devices,new energy storage and many other fields because of its large specific capacitance,high power density and long cycle life.In order to realize the practical application of the supercapacitor,broaden its scope of application,research and development of high performance electrode materials has become a hot topic in supercapacitors.Graphene is an ideal matrix material for supercapacitors due to its large specific surface area,excellent physical and mechanical properties.Combined graphene with pseudocapacitive materials can take advantage of the performance advantages of both materials at the same time.It is expected to obtain electrode materials with high specific capacitance,high energy density,power density and excellent cyclic stability.However,the agglomeration of graphene has always been the main factor affecting its performance improvement,which limits the further application of the materials.In this paper,the main subject is fabrication supercapacitor electrode materials with excellent electrochenmical performance.Three kinds of graphene matrix composites with different structures were prepared,and their morphologies and electrochemical properties were studied.The main contents are follows:Ni（OH）₂ and graphene oxide nanosheets were prepared by a hydrothermal and Hummers method,respectively.Ni（OH）₂ nanosheets treated by cationic surfactants and graphene oxide with negative charges were mixed by electrostatic self-assembly.After annealing,hybrid two-dimensional NiO-reduced graphene oxide nanosheets（NiO-graphene）were obtained.Because of the unique lamellar structure of NiO and the improvement of electrical conductivity by graphene,the composite exhibits excellent electrochemical properties.The maximum specific capacity of the composite electrode can reach 686 F/g at 1 A/g.It also has excellent rate performance（77%）and cycle stability（80%）.Directly used as composite electrodes to assemble symmetrical supercapacitor,the maximum energy density 5.4 Wh/kg is obtained at the power density is 430 W/kg.Moreover,the assembled supercapacitor exhibits excellent cycling performance with 92%of the specific capacitance maintained after 1000 cycle tests at 10 A/g.A graphene foam was prepared by CVD using nickel foam as template and methane as carbon source.Then,polyaniline nanowire arrays（PANI NWAs）were grown on the surface of graphene foam by in-situ polymerization to obtain the PANI NWAs/graphene foam composite.Because of the excellent properties of graphene foam and the unique structure of PANI NWAs,the composite exhibits excellent electrochemical properties,which obtain a high specific capacitance of870 F/g at 1 A/g.The specific capacity of 813 F/g can be obtained when the current density is 10 A/g,and retanied 80%capacitance after 1000 cycles at the current density of 6 A/g.In addition,the symmetric supercapacitor based on PANI NWAs/graphene foam composite electrodes exhibits an energy density of8.3 Wh/kg at a power density of 410 W/kg.Moreover,the assembled supercapacitor also shows a good cycling stability,which retains 70%of its initial specific capacitance after 1000 cycles.With the aim to improve the strength of three-dimensional graphene materials,we prepared uniform size nickel nanoparticles by chemical reduction method,and used it as a template to prepare a novel three-dimensional graphene by CVD.A high strength three-dimensional graphene is obtained because of its smaller pore size and three-dimensional interconnection structure.Then,PANI NWAs was grown on the surface of three-dimensional graphene by in-situ polymerization.Due to the synergistic effect of three-dimensional graphene and PANI NWAs,which exhibits a high specific capacitance（680 F/g at 1 A/g）,good rate capability（85.8%）and excellent cycle stability（76%）.Furthermore,a two electrode symmetric supercapacitor based on composite electrodes demonstrates an energy density of 6.43 Wh/kg at the power density is 400 W/kg.Moreover,the supercapacitor exhibits excellent cycling stability,the specific capacity can reach78%of its initial capacitance after 1000 cycles at 10 A/g.