Preparation And Electrochemical Properties Of Heteroatom Doped Porous Carbon Materials

With the exhaustion of fossil energy and the aggravation of environmental pollution,people urgently need to develop a kind of green high performance energy storage equipment.Supercapacitor is a new type of energy storage equipment,which has obvious advantages such as fast charging and discharging speed,long cycle life and high power density.The performance of supercapacitor is closely related to its electrode material.Among many electrode materials,porous carbon material can provide great specific surface area,adjustable pore structure,good electrical conductivity and electrochemical performance,which makes it an ideal electrode material for supercapacitor.Peanut shell is a common biological waste with high carbon content and can be used as a precursor of porous carbon materials for supercapacitors.However,lignocellulosic biomass exhibits a compact structure that inhibits the infiltration of activators,making pretreatment of biomass precursors necessary.Steam explosion is a kind of promising biomass pretreatment method.This is due to steam explosion pretreatment can break down the cell walls of biomass,induction of fiber dispersion,loose lining structure,produce porous biomass materials,increase the specific surface area of biomass material,therefore,it is beneficial to promote the contact between biomass and chemical substances used in the subsequent process and facilitate the subsequent reaction process.In addition,in order to improve the electrochemical performance of supercapacitors,we introduce phosphorus,sulfur,nitrogen as heteroatoms into carbon materials,which improve the electrical conductivity and wetability of electrode materials,and also provide more active sites.This project used steam explosion pretreated peanut shells as carbon source,introducing heteroatoms by one-step carbonization method,to prepare porous carbon materials with high specific surface area and rich content of heteroatoms for supercapacitors.The main work of this project is as follows:(1)Using steam explosion pretreated peanut shells as carbon precursor and potassium phosphate as activator and phosphorus source,phosphorus single doped porous carbon materials were prepared by one-step carbonization method.The effects of potassium phosphate content on the structure,morphology and electrochemical properties of porous carbon materials were investigated.The experimental results showed that the porous carbon material had the best electrochemical performance when the ratio of steam explosion pretreated peanut shells and potassium phosphate is 1:7.(2)On the basis of the above,the porous carbon material with high specific surface area(2046 m~2/g)and good pore structure was prepared by one-step carbonization method with steam explosion pretreated peanut shell as carbon precursor,potassium phosphate as activator and phosphorus source,and thiourea as nitrogen source and sulfur source.The effects of thiourea dosage on the structure,morphology and electrochemical properties of porous carbon materials were investigated.The results showed that the porous carbon material PSN-PSC-7-1 had the best electrochemical performance.The specific capacitance could reach334.7 F/g at the current density of 0.1 A/g.After 10,000 cycles in a three-electrode system,the capacitance retention of PSN-PSC-7-1 could reach 96%.(3)The mechanism of thiourea as dopant to improve the electrochemical performance of porous carbon was explored.By comparing the performance differences between porous carbon materials PSN-PSC-7-1 and PN-PSC-7-1 in terms of microstructure,specific surface area,elemental composition and electrochemical performance,it was concluded that the addition of thiourea was more conducive to the defect manufacturing and pore formation of porous carbon materials,and could provide large specific surface area.Moreover,the nitrogen atom in thiourea was easier to be doped into porous carbon material,which was beneficial to improve the electrochemical performance of the material.(4)PSN-PSC-7-1//PSN-PSC-7-1 symmetric capacitor was assembled using porous carbon material PSN-PSC-7-1 and its electrochemical performance was detected.The results showed that the specific capacitance of PSN-PSC-7-1//PSN-PSC-7-1 symmetric capacitor was 73.16 F/g at the current density of 0.1 A/g.Besides,as the power density increased from70 to 11016.51 W/k,the corresponding energy density was changing from 19.92 to6.43Wh/kg.The cyclic stability of PSN-PSC-7-1//PSN-PSC-7-1 symmetric capacitor was tested at a current density of 5 A/g.After 8000 cycles,the specific capacitance of the sample remained at 97.81%,showing good cyclic stability.