Synthesis Of Three-dimensional Graphene Materials From The One-step Carbonization Of PEG200 And Research Of Their Electrochemical Application

Graphene has great application potential in super capacitors,lithium ion batteries(LIB)and other fields due to its advantages such as large theoretical specific surface area and high electrical conductivity.However,the formation of wrinkles and stacks caused by structural thermodynamic instability makes the electrochemical performance of graphene in practical applications much lower than expected.Therefore,we need to carry out effective functional design of graphene materials.Among numerous methods,the construction of three-dimensional graphene material can increase pore structure and specific surface area,which is beneficial for the transport of ions and electrons.In addition,doping treatment of graphene material,such as N atom doping,can improve the surface wettability and conductivity of material,thereby improving its electrochemical performance.In this thesis,a series of three-dimensional graphene materials were synthesized by using magnesium oxide(MgO)as catalyst and template,polyethylene glycol 200(PEG200)as carbon source,and their electrochemical applications were subsequently studied.The main work of this paper is as follows:In this dissertation,we firstly used MgO as a catalyst,PEG200 as carbon source to synthesize three-dimensional graphene materials by one-step carbonization.By using scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),N2 adsorption/desorption test,cyclic voltammetry(CV)and galvanostatic charge-discharge(GCD)and other methods,the surface morphology and microstructure of carbon products were characterized,and the electrochemical performance of carbon materials prepared at different carbonization temperatures and different mass ratios of PEG200 and MgO was compared.The results show that the carbon products prepared have large specific surface area and abundant pore structure.When the carbonation temperature is 1000? and the mass ratio of PEG200 and MgO is 4:1.5,the carbon material obtained,FG-4:1.55 has the largest specific surface area and the best electrochemical performance.In the application of supercapacitor,the specific capacity of FG-4:1.5 in the CV test with a scanning rate of 2 mV/s is 222 F/g and the specific capacity retention after 10,000-cycle CV test with a scanning rate of 200 mV/s can reache 92%;In the application of LIB,the reversible discharge specific capacity of FG-4:1.5 at a current density of 0.2C is 734 mAh/g and cyclic stability is up to 98%.In this dissertation,MgO was then used to catalyze PEG200/melamine for the synthesis of N-doped three-dimensional graphene materials.Through SEM,TEM,XPS,N2 adsorption/desorption,CV,GCD and other tests,we analyzed the surface morphology and microstructure of carbon products.And the electrochemical properties of carbon materials synthesized under different addition amounts of melamine and different carbonization temperatures were studied and compared.The results show that carbon products behave large specific surface area and rich pore structure.When the amount of melamine added is 10%and the carbonization temperature is 900?,the carbon material,NFG-900,has the largest specific surface area and the best electrochemical performance.The specific capacity in GCD test at a current density of 0.5 A/g is 324 F/g and cycle stability can reach 90%.In the last part of this dissertation,MgO was used to catalyze PEG200/triazine carbon-forming agent(CFA)to synthesize N-doped three-dimensional graphene materials.Under the help of SEM,TEM,XPS,N2 adsorption/desorption,CV,GCD and other measurements,we have studied the surface morphology and microstructure of carbon materials.And the electrochemical performances of carbon materials obtained under different CFA additions and different carbonization temperatures were compared.The results show that carbon products possess a high specific surface area and a large number of pore structure.When the amount of CFA added is 10%and the carbonization temperature is 900?,the carbon material obtained,CNFG-900,has the largest specific surface area and the most excellent electrochemical performance.The specific capacity in GCD test at a current density of 0.5 A/g is 347 F/g.And after consecutive CV test of 10000 cycles at a scanning speed of 200 mV/s,the specific capacity can still reach 90%of the initial value.