Preparation Of The Hierarchically Heteroatom Doped Carbon And Their Electrochemical Performance For Supercapacitors

Supercapacitors were seen as one of the most promising clean energies due to high power density,high capacitances and excellent cyclic performance.The preparation of supercapacitor materials is a key step in the application of supercapacitors.At present,the main supercapacitor materials have carbon-based materials,metal oxides and hydroxides,and conducting polymers.Because carbon-based materials are much lower cost,simple synthesis and excellent cyclic performance than other materials used for supercapacitors,it has received much attention.Therefore,many researchers pay a lot of attentions to seek for high electrode performance and lower cost carbon-based materials for supercapacitors.This research chooses the hot materials in the present:carbon materials based on MOFs and BCs,adopting heteroatom-doping ways to improve electrode performance,for example,N-doping and O-doping.Meanwhile,we also investigate the material morphology,the construct of element,nano-structure,the group way of devices and electrochemical performance.The main contents as follows:(1)The composite materials ZIF8@BC were synthesized by the mutual interaction between Zn ion and-OH on cellulose and the complexation between Zn ion and 2-methlimidazole,using the bacterial cellulose as the template.Then,ZIF8@BC was carbonized on the condition of900?in order to form porous carbon aerogels NCNF with excellent mechanical strength.It can be use as self-standing electrode materials.The result of texting shows that these materials have excellent electrode performance.In the current density of 0.5 A/g,NCNF shows high mass specific capacitances of 220 F/g and area specific capacitances of 612 m F/cm~2,and it exhibits high mass specific capacitances of 149 F/g and area specific capacitances of 408 m F/cm~2 even at high current density of 10 A/g.The retention rate of capacitances is about 67%.Meanwhile,this material has a good cyclic performance after 10000 cycle(about 97%at current density of5 A/g).The symmetrical supercapacitors constituted of two same NCNF and PVA-KOH hydrogel also show excellent electrochemical performance.In the current density of 0.25 A/g,it exhibits the mass specific capacitances of 41.1 F/g(based on the total mass of NCNF)and the volumetric specific capacitances of 2.5 F/cm~3(based on total volume of device).It shows the mass specific capacitances of 20 F/g and the volumetric specific capacitances of 1.3 F/cm~3even at the high current density of 5 A/g.More importantly,it shows about 91%of retention rate of capacitances after 5000 cycle at current density of 2.5 A/g.Those performances show that NCNF are a promising material for supercapacitors.(2)The echinoid microspheres with high specific area,O-self doping,and third dimension structure(ECOM)were synthesized by the mutual interaction between MOF-74 and urea.It shows 2249 m~2/g of specific area and 5.01%of content of O.When it was used for the materials of supercapacitors,ECOM shows the mass specific capacitances of 287 F/g at current density of 0.5 A/g and the mass specific capacitances of 165 F/g even at high current density of 50 A/g.The retention rate of capacitances is about 58%.More importantly,it also exhibits about 98%of retention rate of capacitances after 10000 cycle at high current density of 20 A/g.In the condition of power density of 250 W/kg,the energy density of electrode is 39.86 Wh/kg.