Synthesis And Supercapacitive Properties Of Graphene And Graphene-based Composites

Graphene, a new type of carbon materials, has a broad application prospect on superconductingmaterials, nano electronic device, electrode materials and other fields because of its excellentelectrical, mechanical and thermodynamics properties. The preparation and performances study ofgraphene and its composite materials have become a new research topic in field of physics, chemistry,biology and many other disciplines. In this thesis, metallic sodium was used as a new reductant ofreducing graphite oxide. The graphene products were found to exhibit good specific capacitances.Graphene-Co₃O₄, NiO, NiCo₂O₄nanocomposites were prepared by using hydrothermal and lowtemperature heat-treatment method. And graphene-CoS₂composite materials were obtained by onestep hydrothermal method and its super capacitor performance was studied.Recently, we report a simple solvothermal method for preparing graphene from graphite oxideusing metallic sodium as reduction. And in this process, tetrahydrofuran was a favorable solvent. TheFT-IR indicates that the functional groups on the graphite oxide have been decomposited except asmall number of residual groups. TEM reveals that the graphene was transparent thin paper shape ofgraphene layers, almost no folds and accumulation. The results of electrochemical tests show thespecific capacitance is about153F/g at the current density of1A/g, indicating that the grapheneexhibits excellent supercapacitive behaviors.Graphene-CoOOH composites were prepared by using thermally exfoliated graphene as carrierthrough hydrothermal method. Then, the Graphene-Co₃O₄composites were obtained by lowtemperature heat treatment. The SEM images show the Co₃O₄nanoparticles were dispersed on thegraphene sheets uniformly. The cyclic voltammetry （CV） and galvanostatic charge-discharge （GC）test show good supercapacitor performance. The specific capacitance is about320F/g at thedischarging current of1A/g, which is much higher than the simple hydrothermal method preparationof Co₃O₄nanoparticles without graphene. It indicates that Co₃O₄nanoparticles have a higherelectrochemical contribution value after adding graphene. Graphene-NiO composites were obtainedby the similar method. The SEM images show the NiO has a hexagonal lamellar structure. N2adsorption-desorption analysis shows the samples have nano-scaled channels or pores, which are goodfor the transmission of electrolyte. The results of electrochemical tests indicate that the compositesexhibit excellent supercapacitive behaviors. Graphene-NiCo₂O₄composites have been prepared by hydrothermal and low temperature heattreatment method. The electrochemical properties of the sample were examined by CV and GC, theresult show the specific capacitance value of the sample is about360F/g at the current density of1A/g in2mol/L KOH.Graphene-CoS₂composites were prepared by one step hydrothermal method. In this process,thioacetamide （TAA） were used as the sulfur sources. Meanwhile, graphene-CoS₂was prepared usingsodium sulfide reduction method. At the same time, sulfide cobalt particles on the graphene sheetswere obtained by the reaction of cobalt acetate and sodium sulfide. The electrochemical test resultsindicate the samples have typical pseudocapacitance properties. This new composites material can bedeemed to a potential electrode material.