Preparation And Modification Of Coal-Based Nano-Fractured Porous Carbon And Characterization Of Its Supercapacitor Properties

To achieve both excellent electrochemical properties such as capacitance and outstanding electrolyte transport capabilities that increase the material’s rate performance and cycling stability,a porous carbon material containing a large number of nanocracks were preparaed by the KOH as activator and Xinyu coking coal’s heavy component（HC）as the carbon source using the high rank coking coal’s characteristic of easily generating cracked pores during pyrolysis.The porous carbon was then modified with sulfuric acid and ammonia to further improve the surface morphology and pore structure of the material,increase the mesopore volume,and enhance its electrochemical performance.The impact of the microscopic morphology,pore structure,and surface chemical properties of the nanocrack porous carbon on its electrochemical performance were studied using SEM,FTIR,XPS,Raman,and pore size and surface analysis instruments.The optimal process conditions,such as solventthermal temperature and the addition amount of sulfuric acid and ammonia,were investigated.The results showed that:（1）Using the heavy component of Xinyu coking coal as the carbon source and KOH as the activating agent,a one-step high-temperature carbonization and activation method was used to prepare porous carbon with ultra-high specific surface area and nanocracks（about5-20 nm）structure.It was found that the temperature had an important influence on the formation of nano-cracks:when the temperature was below 700°C,the formation of nanocracks was not obvious and the pores were relatively narrow;when the temperature was higher than 750°C,the nanocracks developed completely and the pores were relatively wide.Changing the amount of KOH only had a significant effect on the pore width of the nanocracks,which increased first and then decreased with the increase of KOH.When the activation temperature was 700°C and the KOH addition ratio was 4,the resulting porous carbon AHC-700-4 had a high specific surface area of 3438 m² g^-1,a specific capacitance of327 F g^-1 at 1 A g^-1,and it still maintained 63.5%of its capacitance at 20 A g^-1.After 10,000cycles of charge and discharge at a current density of 10 A g^-1,the specific capacitance could be maintained at 91.4%of its initial value.（2）The solvothermal temperature of sulfuric acid has a great influence on the pore width of nanocrack pores,and generally the pore width increases to varying degrees with increasing temperature.The sulfuric acid concentration has a small effect on the pore width when it is below 3 mol L^-1,but when it increases to 5 mol L^-1,the pore width is enlarged due to strong corrosion.Among them,the porous carbon with rich and well-developed nanocrack pore structure was formed when the solvothermal temperature was 120℃and the sulfuric acid concentration was 1 mol L^-1.The porous carbon S-AHC-1-120 modified from AHC-700-4 showed no significant changes in specific surface area and micropore volume,but the mesopore volume increased significantly.Its specific capacitance was 347.1 F g^-1 at 1 A A g^-1 and 279.6 F g^-1 at 20 A g^-1,and the rate performance improved from 63.5%to 80.6%.After 10,000 charge-discharge cycles at a current density of 10 A g^-1,the capacitance retention rate also increased from 91.4%to 96.5%.The significant improvement in rate performance and cycle stability is mainly due to the increase in mesopore volume brought about by the rich nanocrack pores,providing excellent transport channels for electrolyte ions under high current density.（3）Ammonia solvothermal modification can achieve more complete development of nano-crack pores in porous carbon.The solvent thermal temperature can greatly affect the pore width of nanocrack pores,and the pore width also increases with the increase of temperature,which can increase from unmodified 5 nm to 5-25 nm.The ammonia concentration has a small effect on pore width,and the average pore width is around 5 nm.Ammonia solvent thermal modification can also dope a certain amount of nitrogen atoms into porous carbon,and the nitrogen atom content increases from 0.66 at.%to 3.26 at.%.When the ammonia addition amount is 8 m L and the solvent-thermal temperature is 180℃,the modified porous carbon N-AHC-8-180 shows more nested pore structures.While the specific surface area and micropore volume remain almost unchanged,the mesopore volume significantly increases.The measured specific capacitance reaches 351.3 F g^-1 at 1 A g^-1 and289.8 F g^-1 at 20 A g^-1.Compared with AHC-700-4,the rate performance increases from63.5%to 82%,and the capacitance retention rate after 10 A g^-1cycling for 10000 times increases from 91.4%to 95.6%,demonstrating good rate performance and cycling stability.This thesis has 50 images,14 tables,and 92 references.