Studies On The Electrochemical Properties Of Graphene Modified By Amines And 3D Carbon Materials Containing Iron Oxidate

Supercapacitors are important devices for the storage and use of electric energy.Improving the energy density is the goal that people keep pursing.At present,various types of porous carbon with high specific surface area and good stability are the main components of electrode materials for supercapacitors.Therefore,developing new carbon materials with high specific capacitance for supercapacitors has become the main research direction.Graphene with two-dimensional nanostructures is an important cornerstone of building new carbon materials.Based on it,people are trying to build carbon materials with specific three-dimensional structure to achieve high specific capacitance.Graphene oxide,which is derived from natural graphite,is rich in a variety of functional groups and is convenient for chemical modification and batch preparation.The amine-modification technology of GO has been paid much attention for its advancement in regulating the structure of GO and improving the specific capacitance of the materials.In addition,polyaniline is cheap and easy to obtain with strong designability of morphology.After carbonization at high temperature,its original morphology is basically preserved,and it is also a carbon source often selected for the recent directional preparation of carbon materials.Carbon materials with three-dimensional graphitized structure are expected to be obtained by carbonization of polyaniline with iron oxide.In order to improve the specific capacitance of the electrode materials for supercapacitors,a new method of constructing three-dimensional carbon materials was explored in this dissertation.The modification of graphene oxide by amines and preparation of three-dimensional carbon materials containing iron oxidate,micro bowls and hollow spheres with graphitized carbon walls were successfully prepared.And the effects of preparation conditions on the morphology,structure and electrochemical properties of the carbon materials were characterized.Monoamines,diamines and multiamines were used as modifiers and reducers to prepare amine modified graphene oxide materials by hydrothermal method or solvothermal method.The effect of different amines on the specific capacitance of modified graphene oxide was characterized by cyclic voltammetry in a three-electrode electrochemical system with 0.5 mol/L sulfuric acid aqueous solution as the electrolyte.The results imply that 1,5-naphthalene diamine and p-phenylenediamine are both good modifiers,which can significantly improve the specific capacitance of the materials.The specific capacitance of 1,5-naphthalene diamine modified graphene oxide and p-phenylenediamine modified graphene oxide is 424.8 F/g and 379.5 F/g,respectively,both in 0.5 mol/L sulfuric acid aqueous solution and at the scan rate of 5 m V/s,tested by cyclic voltammetry technics.The studies also show that the modified molecules can effectively prevent the reaccumulation of graphene oxide layers after the reduction,so that the modified materials have multi-level porous structures,thus improving the specific capacitance of the materials.In addition,the molecular structures of the modifiers have a great influence on the specific capacitance of the products.Modifiers with specific conjugated structure,such as naphthalene diamine and p-phenylene-diamine,can significantly improve the specific capacitance of the materials.Then,different oligomers of aromatic amines were used as modifiers and reducers to prepare graphene oxide materials with three-dimensional structures under solvothermal conditions.The structure,morphology and specific capacitance of the materials were studied systematically.The results imply that oligomers of p-phenylenediamine,from which was heated at 60?for 48 h,have the greatest effect on the modification of graphene oxide.The specific capacitance of the material is 452.7 F/g in 0.5 mol/L sulfuric acid aqueous solution,at the scan rate of 5 m V/s,tested by cyclic voltammetry technics.A prototype supercapacitor was fabricated in a CR2032 cell case.Calculated by the active substance,the energy density of the cell is 6.8 W·h/kg,and the power density is 516.3 W/kg.And the retention is above 87.9%of its original charging/discharging process after 1 000 cycles.In addition,the mechanism of graphene oxide modified by oligomers of aromatic amines was explored,and the method of constructing modified graphene oxide materials with three-dimensional structures was proposed.In order to further improve the specific capacitance of the materials,the graphene oxide modified by oligomers of p-phenylenediamine was compounded with nanometer iron oxide by hydrothermal method or solvothermal method to prepare three-dimensional composites.The effects of reaction temperature,reactant mass ratio and solvent ratio on the morphology and the specific capacitance of the materials were investigated.The results show that,when the reaction temperature is 160?,the mass ratio of reactant is Fe Cl₃·6H₂O?GO=1?4,and the solvent of the mixed solution of 5m L water and 35 m L glycol is the best process condition.The specific capacitance of the prepared material is the highest,which is 443.9 F/g in 6 mol/L KOH aqueous solution,at the scan rate of 5 m V/s,tested by cyclic voltammetry technics.A prototype supercapacitor was fabricated in a CR2032 cell case.Calculated by the active substance,the energy density of the cell is 6.6 W·h/kg,and the power density is 560.1 W/kg.And the retention is above 79.6%of its original charging/discharging process after 1 500cycles.Furthermore,the three-dimensional graphitization mesoporous structure of polyaniline/Fe₃O₄ nanocomposites was obtained by carbonization and graphitization of the composites.Effect of graphitic temperature on morphology,pore structure and specific capacitance of the carbon were explored in detail.The research results show that the composites changes into porous carbon particles possessing irregular shapes when graphitic temperature changes from 800?to 1 000?.Some spheres with open mouths,like bowls,were found in samples when the composite being treated at1 200?.The wall of bowls is conformed by graphitic carbon layers.However,when the graphitic temperature was at 1 300?,only some hollow spheres were found in as-obtained carbon.Wall of the hollow spheres is formed by highly graphitic carbon-layers.By changing graphitic temperature of the composite,BJH adsorption average pore diameter and BET specific surface area of the mesoporous carbon can be easily adjusted in the range from 5.9 nm to 19.9 nm,and from 62.6 m²/g to 677.8 m²/g,respectively.Among all the as-prepared mesoporous carbon,the sample graphitized at800?has the best electrochemical performance,whose specific capacitance is 161.4F/g in 0.5 mol/L sulfuric acid aqueous solution,at the scan rate of 5 m V/s,tested by cyclic voltammetry technics.In summary,graphene oxide modified by oligomers of aromatic amines has three-dimensional and multi-layered porous structures,showing good specific capacitance.After compounding with iron oxide,the electrochemical energy storage properties of the materials are further improved.In addition,three-dimensional graphitized carbon materials can be prepared by iron oxide and polyaniline.This kind of carbon materials with three-dimensional structures has a broad application prospect in many fields such as energy storage.