Heteroatoms-doped Porous Carbons:Preparation And Their Application As Electrode Materials For Supercapacitor

Porous carbon materials are widely used in electrode materials of supercapacitors because of their good electrical conductivity,chemical stability,low cost and high specific surface area.However,the energy density of traditional porous carbon-based materials is relatively low,which limits their further application in high performance supercapacitors.Therefore,how to improve the energy density of porous carbon-based materials has received special attention in recent years.This thesis aims at developing high performance heteroatom-doping porous carbon materials based on the previous advances on the improvement of the electrochemical properties of nitrogen-doped porous carbon?NDPC?materials,and attempts to solve the bottleneck problem of the carbon-based materials in high performance supercapacitors.The electrochemical performances of nitrogen and sulfur co-doped porous carbon?NSDPC?materials prepared from different calcination temperatures as electrode active materials for supercapacitors are firstly studied.The correlation between the physical and electrochemical performances of these materials indicated that the calcination temperature has a great influence on the structure properties and electrochemical performance of the NSDPC-based materials.That is,the higher the temperature,the higher the graphitization degree but the lower the nitrogen content of the NSDPC-based materials.In addition,the micropore volume and total pore volume firstly increase then decrease with the increase of the temperature.The sample achieved at 800 ^oC displays superior electrochemical performances than those of the samples obtained at 700 and 900 ^oC.Under the optimum calcination temperature,NDPC and NSDPC materials with similar pore structure and specific surface area are prepared by using urea as nitrogen source and thiourea as nitrogen source and sulfur source,respectively.Compared with the electrochemical performance of the NDPC,it is found that the additional doping of sulfur into the NDPC sample can enhance its hydrophilicity and pseudo-capacitance,and thus improve the electrochemical performance of the final N,S-codoped porous carbon.A series of NSDPCs samples are prepared by changing the mass ratio of thiourea and calcium chloride.The structure and compositions of the materials are characterized by various physical mesurement methods.And the effects of specific surface area,pore structure and N,S-codoping content on the electrochemical properties of these materials are also discussed in detail.Under the condition of constant CaCl₂ content and with the increase of the mass of thiourea,the average pore size and total pore volume of the as-obtained samples decrease,while the nitrogen content,micropore volume,disordered degree,specific surface area and the ratio of V_micropore/V_total increase.Furthermore,the excessive V_micropore/V_total ratio is not beneficial to the rate performance of the NSDPC-based materials.Under the condition of constant thiourea content and with the increase of calcium chloride,the nitrogen content and disorder degree of the as-obtained samples decrease,but the mesoporous and macroporous volume and average pore diameter increase,which result in the superior rate performance of the NSDPC-based materials.Based on the analysis of these results,it is suggested that a reasonable microporous ratio and moderate nitrogen content can effectivly increase the energy and power density of NSDPC-based materials.A novel and environmentally friendly route for the preparation of NDPCs was proposed.This route can avoid the production of highly toxic substances?KCN?in the traditional route for the synthesis of NDPCs,in which the alkaline activators?KOH and/or K₂CO₃?are used.Also,the NDPC sample prepared by adding proper amount of CaCl₂ as auxiliary activators shows more reasonable pore structure and higher nitrogen content,exhibiting high specific capacitance,excellent rate performance and good cycle stability as an electrode material for high performance supercapacitors.