Preparation And Electrochemical Properties Of Heteroatom-doped Carbon Spheres

In recent years,supercapacitors have received extensive attention and research due to their advantages such as high power density,fast charge and discharge rates,long cycle life,and environmental friendly,and are expected to become a new generation of energy storage devices.Electrode material is the main factor that affects the performance of supercapacitor.Due to its high specific surface area,excellent chemical stability,good conductivity and low price,carbon material is one of the most promising electrode materials for supercapacitors.In this thesis,resorcinol thiourea formaldehyde(RTF)spheres were synthesized by the extension St?ber method with resorcinol formaldehyde resin as carbon source,thiourea as nitrogen source and sulfur source.The effects of the experimental parameters on the morphology and particle size of the spheres were investigated in detail.Then,RTF resin spheres were used as precursors to prepare N/S co-doped hierarchical porous carbon spheres by one-step KOH chemical activation method,and their electrochemical performance in supercapacitors was investigated.The specific research content is as follows:The experimental parameters investigated during the preparation of resorcinol-thioureaFormaldehyde(RTF)resin spheres mainly include: the concentration of ammonia and reactants,the molar ratio of thiourea/resorcinol(T/R),ethanol/water volume ratio and alkyl chain length of alcohol.By changing the experimental parameters,the particle size of RTF resin spheres can be adjusted in the range of 280 ~ 2650 nm,and the particle size is mainly distributed between 400 ~ 650 nm.Subsequently,the RTF resin spheres were carbonized at 600?,700? and 800?,respectively,to obtain monodispersed N/S co-doped carbon spheres(NSCSs).As the NSCSs-800 carbonized at 800 ? has higher graphitization degree,it showed excellent electrochemical performance,and its specific capacitance can reach 157.5 F/g at the current density of 0.5 A/g.Then,the N/S co-doped hierarchical porous carbon spheres(NSHPCSs)were prepared by one-step KOH chemical activation method with RTF resin spheres as the precursor.At the same time,we investigated the effects of different activation methods and different precursors on the product morphology and electrochemical performance.It is found that when the precursor are all RTF resin spheres,different activation methods can produce N/S co-doped carbon spheres with different pore structures.One-step KOH chemical activation method can prepare N/S co-doped hierarchical porous carbon spheres(NSHPCSs)containing micropores,mesopores and macropores.The samples(NSPCSs)obtained by the two-step KOH chemical activation method(pre-carbonization followed by activation)only contain micropores.When one-step KOH chemical activation method is used,samples with RTF resin spheres as the precursor have more abundant pore structure than those with resorcinol formaldehyde(RF)resin spheres as the precursor.Unique hierarchical porous structure and nitrogen and sulfur doping give rise to a remarkable electrochemical performance of NSHPCSs.As shown,the specific capacitance of NSHPCSs electrode is up to 295 F/g at a current density of 0.5 A/g,even at a higher current density of 20 A/g,the specific capacitance can reach 232 F/g,so it has good rate performance.And even excellent stability of only 4.8% capacitance loss after 5000 cycles at 10 A/g.Furthermore,the symmetrical supercapacitor device delivers a high energy density of 7.36 Wh/kg at a power density of 100 W/kg.And a commercial yellow light-emitting diode(LED)can be driven successfully.