Preparation And Supercapacitor Performance Investigation Of ZIF-derived Porous Carbons

Porous carbon materials prepared by using metal organic framework materials as precursors,especially the nitrogen-doped porous carbon materials prepared by using ZIF-8 as precursor,have been widely used in supercapacitors.But there still exists some problems with porous carbons derived from direct carbonization of ZIF-8,these carbons have a single pore structure,a low utilization efficiency of micropores and a low graphitization degree,which limit the further improvement of the specific capacitance and rate performance.In this paper,we took ZIF-8 as the precursor,and tried to use the microwave heating method to prepare porous carbon materials.Then the structure and capacitance performance of the as-synthesized carbon materials were fully studied by using scanning electron microscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy,N2adsorption-desorption test and electrochemical workstation and so on as the testing methods.In addition,because Co has the effect of improving the graphitization degree of carbon materials,so the Co-doped ZIF-8 with different Co²⁺/Zn²⁺ were synthesized and used as precursors to prepare a series of porous carbon materials,then the influence of Co doping on the capacitance performance of porous carbon materials was studied.Series of nitrogen-doped porous carbon materials were obtained from the carbonization of ZIF-8 by using microwave heating method,then the influence of carbonization temperature and particle size of ZIF-8 on the structure and capacitance performance of carbon materials were studied.The results revealed that,when the carbonization temperature was higher than800?,the graphitization degree of carbon materials became higher and there appeared some mesoporous and macroporous structure that derived from the body linking of carbons,and with the increase of the particle size of ZIF-8,it was found that the degree of the body linking increased first,then decreased,and carbons with larger particle size were difficult to link and form mesoporous and macroporous structure,the Carbon-M-100 nm had the best linking degree.Therefore,Carbon-M-1000?Carbon-M-100nm?showed the highest specific capacitance value of 207.7F/g at a current density of 0.1A/g,and had the best rate performance?when the current density is at 10A/g,the specific capacitance still retained66.5% of initial capacitance?.Carbon-T-1000 were prepared by direct carbonization of ZIF-8 in a tube furnace,compared with Carbon-M-1000,Carbon-T-1000 had a larger specific surface area and pore volume,but Carbon-M-1000 had a higher graphitization degree and nitrogen content.Furthermore,Carbon-M-1000 can form a mesoporous and macroporous pore structure derived from body linking while Carbon-T-1000 was composed of microporous structure mainly.Which made Carbon-M-1000 had a better rate performance,its specific capacitance retention was 66.5% at a current density of 10A/g,higher than that of 60.3% of Carbon-T-1000.Co-doped ZIF-8 with different Co²⁺/Zn²⁺ were designed and synthesized,then a series of nitrogen-doped porous carbon materials were obtained by the direct carbonization of these Co-doped ZIF-8 at a high carbonization temperature.the structure and capacitance properties of these carbons were studied,and the results showed that,with the increase of Co²⁺/Zn²⁺,the graphitization degree of carbon materials increased gradually,the mesoporous structure increased gradually,but the surface area decreased gradually,while the nitrogen content increased first and then decreased.Carbon-Z-0.2 exhibited the highest specific capacitance of313.6 F/g at a current density of 0.1A/g,and the specific capacitance still retained 61.5%when the current density increased to 10A/g.