Research On Preparation And Electrochemical Properties Of Cottonseed Shell Porous Carbon

Supercapacitors play an important role in the field of energy storage by their advantages such as excellent charging and discharging efficiency,high energy density,and excellent reversibility.In the research of electrode materials for supercapacitors,porous carbon materials have received widespread attention due to their stable cycling performance,controllable microscopic morphological structure and pore size distribution.Biomass is the organic material that is accessible and contains a large amount of carbon itself.Therefore,biomass-based porous carbon materials can not only meet the pressing requirements of environmental pollution on the concept of green development,but also serve as new materials for long-term research on energy storage.In this thesis,cotton seed shell porous carbon was prepared by hydrothermal carbonisation with sulphuric acid and KOH activation with cotton seed shell as raw material,and the process conditions of hydrothermal carbonisation and activation phases were optimised.Porous carbon was prepared by direct carbonization,hydrothermal carbonization and hydrothermal carbonization with sulfuric acid,and the effects of different carbonization methods on porous carbon were compared.Nitrogen doping modification was carried out on the basis of sulfuric acid hydrothermal carbon material.The samples were subjected to SEM,XPS,and other characterisation methods to analyse the structural and chemical composition of the materials.CV,GCD and EIS in the three-electrode system,cycling performance tests in the two-electrode system,and other methods to analyse the electrochemical properties of the materials.The results were as follows:（1）Cotton seed shell porous carbon（CHPCs）was prepared by hydrothermal carbonization with sulphuric acid and activation with KOH.The effects of hydrothermal process conditions（concentration of H₂SO₄,hydrothermal temperature and time）and activation process conditions（mass ratio of hydrothermal carbon of sulfuric acid to activator,activation temperature and time）on the structure and electrochemical properties of CHPCs were investigated.The experimental results showed that porous carbon（CHPC）with carbon microsphere morphology was prepared by hydrothermal carbonization at 4 M sulfuric acid concentration at 150 ^oC for 12 h and an activation process at 700 ^oC and 60 min with a 1:1 mass ratio of sulfuric acid hydrothermal carbon to KOH.The specific surface area of CHPC was 1806.7 m² g^-1and a total pore volume of 1.111 cm³ g^-1,with a three-dimensional hierarchical pore structure.The morphology and pore structure parameters of porous carbon（CTPC or CPC）prepared by direct carbonization or hydrothermal carbonization under the same activation conditions were significantly different from those of CHPC（for example,the morphology of CTPC was honeycomb,and the morphology of CPC was spongy）,but all of them were amorphous carbon materials with a low degree of graphitization.（2）Electrochemical tests were conducted under a three-electrode system with 6 M KOH as the electrolyte.At 0.5 A g^-1,the specific capacitance of CHPC(390.2 F g^-1)was superior to CTPC(303.5 F g^-1)and CPC(381.1 F g^-1).The CTPC,CPC,and CHPC were assembled into symmetrical capacitive devices,and after 10000 cycles of testing at 1 A g^-1,the capacitance retention rates were 97.51%,98.56%,and 99.97%,respectively.In addition,when the power density of CHPC//CHPC was 2500 W kg^-1,the energy density was 5.07 Wh kg^-1.（3）Nitrogen-doped porous carbon（NCHPCs）was obtained by mixing sulfuric acid hydrothermal carbon with melamine for secondary hydrothermal carbonization and KOH activation reaction.The effects of mass ratio of sulfuric acid hydrothermal carbon to melamine,activation temperature and activation time on the structure and electrochemical properties of NCHPCs were investigated.The experimental results showed that the porous carbon material（NCHPC-5）prepared under the conditions of mass ratio of sulfuric acid hydrothermal carbon to melamine of 5:1,activation temperature of 700 ^oC,activation time of 60 min had a hierarchical porous structure.The specific surface area of NCHPC-5 was 3614.6 m² g^-1,the total pore volume was2.305 cm³ g^-1,and the pore size was 0.5-2 nm micropore and 3-5 nm mespore.The nitrogen elements in the material included pyridine-nitrogen,quaternary ammonium nitrogen and other forms,which improved the conductivity.In the three-electrode system,the specific capacitance of NCHPC-5 reached 437.8 F g^-1 at 0.5 A g^-1.NCHPC-5 was assembled into a symmetrical capacitor NCHPC-5//NCHPC-5.After 10000 cycle of testing at 1 A g^-1,the capacitor retention rate was 99.95%.In addition,NCHPC-5//NCHPC-5 had a higher energy density(6.25 Wh kg^-1)when the power density was2500 W kg^-1.There are altogether 70 figures,9 tables and 121 references in this thesis.