The Synthesis Of Heteroatom-Doped Porous Carbon Materials And Its Application In The Aspect Of Electrochemical Performance

Graphene,a novel two-dimensional carbon material,has fascinating electrical,mechanical and thermal properties.The study about porous carbon is earlier than graphene.Heteroatom?such as N,S and P?doped graphene or porous carbon have been fabricated and applied in electrochemical aspect to really modify their electronic property,chemical reactivity and electrochemical performance.In this project,S-doped,N-doped,P-doped and dual-doped porous graphenes were successfully synthesized by chemical vapor deposition?CVD?process.Porous carbon with high S concentration was synthesized by the template method using asphalt and sucrose as precursor.This thesis includes the following aspects of the work progress.?1?Basic magnesium carbonate microspheres with a RBC-like appearance and diameters of ³ ?m were synthesized by amphiphilic molecule-participated self-assembly under hydrothermal conditions using SDBS,NH3.H2 O and MgSO4 as starting materials.Porous?RBC?-like MgO microspheres were obtained by calcining basic magnesium carbonate microspheres at 700 oC.Graphene microspheres with a red blood cell?RBC?-like appearance were synthesized by template-directed CVD using RBC-like basic magnesium carbonate microspheres as templates.As electrode for supercapacitors,RBCG electrode exhibits a specific capacitance of 343 F g^-1 at 1 mV s^-1.?2?Few-layered graphene networks composing of phosphorus and nitrogen dual-doped porous graphene?PNG?are synthesized via a MgO-templated CVD using?NH₄?₃PO₄ as N and P source.Raman spectra show that the amount of defects or disorders increases after P and N atoms are incorporated into graphene frameworks.As anodes for lithium ion batteries?LIBs?,the PNG electrode exhibits high reversible capacity(2250 m A h g^-1 at the current density of 50 mA g^-1),excellent rate capability(750 mA h g^-1 at 1000 mA g^-1).Three-dimensional networks composing of S and N dual-doped graphene?SNG?were synthesized by a chemical vapor deposition approach using MgSO4-containing whiskers as templates and S source and NH3 as N source.The SNG,as an anode material for LIBs,exhibits extremely high capacity(3525 mA h g^-1 at the current density of 50 m A g^-1)and superior rate capability(870 mA h g^-1 at 1000 mA g^-1).The enhanced conductivity,the three-dimensional porous network with many disorders have led to the excellent electrode performance of the SNG networks.?3?S-doped nanomesh graphene?SNMG?and S-doped carbon nanotures?SCNTs?were synthesized by the post-treatment approach.As electrode for supercapacitors,the SNMG exhibits better capacitive property.The SCNTs derived from the same methodology exhibit higher conductivity and better hydrophily as compared to the pristine CNTs.?4?The synthesis and application of S-doped porous carbon.S-doped porous carbon with an S content as high as 14.0 atom% are synthesized by carbonization of sucrose using magnesium sulfate whiskers as templates and S source.Raman spectra demonstrate that the amount of defects rise with the increase of S content.When sucrose was substituted by asphalt,S-doped porous carbon derived by the same approach was employed as anode for LIBs.Removal of functional groups or highly active C atoms during the S doping has led to formation of much thinner solid-electrolyte interface layer and hence significantly enhanced the coulombic efficiency in the first cycle from 39.6 %?for the undoped porous carbon?to 81.0 %.In conclusion,this project mainly concentrated on the synthesis of heteroatom-doped porous carbon materials based on CVD process,post-treatment approach and template method.The influence of heteroatom doping on the properties of porous carbon materials and electrochemical performance was investigated.The as-obtained heteroatom-doped porous carbon materials are promising electrode materials for LIBs and supercapacitors.