Preparation And Electrochemical Performances Of Graphene-based Carbon/carbon Composites

With rapid development of economy and over-extraction of energy,such problems as energy shortage and environment pollution become increasingly serious.In this context,the supercapacitor comes into being,which is a new energy storage device.The most core component of supercapacitor is electrode material.Therefore,it is particularly important to develop an electrode material with excellent properties.Graphene is considered as a preferred electrode material of supercapacitor,for its excellent performance.However,graphene reunites easily by van der Waals force between graphene layers,reducing the effective utilization of specific surface area and influencing the electrochemical property of graphene.In this thesis,in order to resolve the reunion of graphene,carbides with different morphologies regarded as spacers are inserted into graphene layers.Besides,doping modification and hole forming are implemented to adjust the physical and chemical properties of graphene.The details are as follows:1)Polyaniline-lignosulfonate composite(PL)was firstly synthesized from aniline monomers using lignosulfonate(LS)as a surfactant through a static in-situ polymerization at room temperature.Then,graphene-wrapped nitrogen-containing carbon spheres(PLG)were prepared by co-pyrolysis of graphene oxide and the polyaniline-lignosulfonate composite through high temperature carbonization process.The results showed that the optimized value of LS in PL was 30 wt.%,and the carbon spheres in pyrolysis product PLG30 exhibited uniform morphology structure and distributed homogeneously,and the graphene in PLG30 were very thin.Besides,when the temperature of carbonization was 800 ?,the material obtained the highest capacitance.A high specific capacitance of the PLG30 presented to be 203.5 F·g-1 at a current density of 1 A·g-1 and increased to 103.8%after 1000 cycles,showing an excellent performance as a supercapacitor electrode.2)Porous nitrogen-doped graphene/carbon nanotubes composite(PNGC)was prepared by pyrolysis of graphene oxide,with carbon nanotubes(CNTs)as spacers,LS as surfactants and urea as nitrogen source.Besides,the influence of CNTs feed content on electrochemical properties was explored.The results are as follows:it was optimized that the CNTs feed content was 20 mg,and the CNTs in PNGC distributed homogeneously,and the graphene in PNGC were very thin and fluffy.Under combined action of LS and urea,porous structure formed on the graphene nanosheets.PNGC exhibits a high specific capacitance of 213 F·g-1 at a current density of 1 A g-1 and high stability(96.5%of capacitance retention ratio after 2000 cycles at 100 mV·s-1),indicating an excellent performance of PNGC.