Studies On Preparation And Electrochemical Performance Of Husk-based Porous Graphitized Carbon Materials

At present,the continuous consumption of non-renewable energy has brought serious energy crisis and environmental pollution,and more and more attention has been paid to renewable green energy.Renewable energy has the characteristics of instability,such as the change of sun day and night,natural wind changes with the season,etc.Therefore,the development of stable and efficient energy storage devices to solve the intermittent and unstable problems in the process of renewable energy generation is of great significance to the adjustment of energy structure.As a new type of energy storage device,supercapacitor has attracted much attention because of its advantages of high charge and discharge efficiency,stable cycle performance and high power density.The performance and cost of supercapacitors are greatly affected by the electrode materials,among which carbon materials have been widely used in commercial applications due to their high specific surface area,good electrical conductivity and non-toxicity.As a kind of biomass raw material with a wide range of sources,rice husk contains a large amount of carbon element.The inherent silica component in rice husk can act as a perfect template skeleton in the process of conversion to carbon material,so it is an ideal raw material for preparing carbon material.In the process of converting rice husk and other biomass into carbon materials,most of the activators currently used are concentrated on corrosive compounds such as KOH,K2CO3,H3PO4 and Na OH,which do great harm to the environment.At the same time,most of the high temperature treatment method is used to increase the graphitization degree of carbon materials,which leads to low yield and high cost.And the pore structure of the carbon material is not developed.In this paper,different metal salts were used as activators and graphitization catalysts to systematically analyze the morphology,pore structure and graphitization degree of the prepared carbon materials at different activator dosages and activation temperatures.The prepared activated carbon was assembled into supercapacitors to explore its electrochemical performance.At the same time,the effects of different modification methods on the structure and electrochemical properties of the prepared activated carbon were investigated.The research results will provide a new idea for the preparation of biomaterial-based multi-pore graphitized carbon materials.The results show that different metal salts have different activation mechanisms and synergistic effects.Mg Cl2·6H2O and Ca Cl2 are easy to form mesopores during activation,while KCl is more active and easy to form micropores.The addition of Fe Cl3can not only increase the graphitization degree of carbon materials,but also increase the specific surface area when mixed with other metal salts.According to the results of nitrogen adsorption and desorption test,the specific surface area of carbon materials increased first and then decreased with the increase of the amount of activator KCl.When the mass ratio of rice husk and KCl was 1:2,the specific surface area of carbon materials obtained reached the maximum of 1881.2 m~2/g.Increasing the activation temperature is conducive to the formation of pore structure.When the temperature rises to 900℃,the specific surface area of the carbon material is 2003.5 m~2/g.However,excessive activation temperature generates excessive microporous structure,and the micropore rate is as high as 96.1%,which is not conducive to the storage and transportation of electrolyte ions.X-ray diffraction and Raman spectroscopy analysis results show that too much activator is not conducive to the formation of graphitic carbon structure,but increasing activation temperature is conducive to the transformation of amorphous carbon into graphitic carbon structure under the catalysis of iron.When KCl was used as the activator,Fe Cl3 was used as the graphitization catalyst,the mass ratio of rice husk,KCl and Fe Cl3 was 1:2:1,and the activation temperature was 800℃,the obtained carbon material had a higher specific surface area and graphitization degree.When the current density was 0.2 A/g,the specific capacitances of 288.2 F/g and 324.5 F/g were obtained under the two-electrode and three-electrode test systems,respectively,showing excellent electrochemical performance.The morphology,pore structure and graphitization degree of carbon materials were changed after the modification of carbon materials by means of desilication,pickling and hydrothermal modification.Nitrogen adsorption and desorption test results show that pickling and hydrothermal treatment are beneficial to increase the specific surface area of carbon materials.After desilication treatment,the specific surface area of carbon materials decreases,but the microporosity decreases,and the total pore volume increases.The results of X-ray diffraction and Raman spectrum analysis show that desilication and hydrothermal treatment are not conducive to the formation of graphite structure of carbon materials,and pickling is beneficial to improve the graphitization degree of carbon materials.According to the results of electrochemical test,the electrochemical properties of the chemically modified carbon materials have been improved,and the hydrothermal treatment has the most significant improvement.The specific capacitance has been increased from 288.2 F/g to 335.5 F/g,increasing by16.4%.