ZIFs-derived Carbon And Its Composite Material With Zn-Co Hydroxide For Supercapacitors Application

Supercapacitors?SCs?have attracted much attention as an energy storage device with high power density and stable cycle performance.While energy-using equipments such as new energy vehicles require high-performance ion batteries,supercapacitors can act as a complementary energy storage device to offer high power.Electrode is one important part of supercapacitors,but still suffer some urgent problems,such as,the low electrochemical activity of cathode materials,the high cost and poor electrochemical performance for commercial carbon anode materials.In recent years,metal-organic frameworks?MOFs?materials has attracted more and more attentions due to their unique high porosity and high specific surface area.SC s as an energy storage device that relies on the surface reaction between the electrode materials and electrolyte to store energy.Hence,the MOFs material is a potential high-performance supercapacitor electrode material candidate.The ZIFs materials is one of the representative categories metal organic frameworks material.In this thesis,the ZIFs?sod?material with excellent pore size distribution and high specific surface area is synthesized.Next,the ZIFs derived carbon and Zn Co-ZIFs composite are prepared and applied in electrodes of SCs.The main achievements are list as follows:?1?Fe-modified ZIF-derived carbon supercapacitor anode materialIn order to improve the graphitization degree of organic compounds derived carbon material.During the synthesis process of the zeolitic imidazolate frameworks-8?ZIF-8?,a certain proportion of iron acetylacetone?Fe?acac?₃?was added to precursor solution.Subsequently,the Fe modified ZIF-8 compound was carbonized under high-temperature to prepare the derived carbon material.As the ligand metal element Zn?boiling point is 907??in the ZIF-8 will evaporate at a high temperature?950??.And Fe element will promote the conversion of the ZIF-8 compound to a higher conductive carbon at high temperature.After the introducing of Fe element,the electrochemical performance of the derived carbon materials presents present more excellent than that of no Fe modified ones.(The derived carbon?the ratio of Zn:Fe is2.5?has the best rate performance.The capacitance of the nano carbon-0.4?NC-0.4?could retain 53.0%from 1 to 50 A g^-1 and the capacitance remains 96.9%after 25,000cycles).The reason is that graphitized carbon materials have higher electrical conductivity than that of amorphous carbon materials.?2.1?Zn Co LDH cathode material coated with ZIFsIn order to improve the low electrochemical activity of the Zn Co layered hydroxide nanosheets?Zn Co LDH?cathode material.The different array density and length of the Zn Co LDH nanosheets were synthesized under different hydrothermal temperature.Since the Zn Co element on the surface of Zn Co LDH nanosheets can react with 2-methylimidazole vapor under high temperature and pressure conditions.In the subsequent,a layer of porous ZIFs was grown on the surface of the Zn Co LDH nanosheets by chemical vapor deposition.The results show that the Zn Co-ZIFs present better electrochemical performance than that of the Zn Co LDH nanosheets.(The sample,which prepared at hydrothermal temperature of 130°C for 6 h and subsequent chemical vapor deposition for 10 hours,presents excellent electrochemical properties.The electrochemical capacity of the Zn Co-130-ZIFs-10h can reach 2068 F g^-1 at 1 A g^-1.And its capacity can still maintain at 92.6%of the initial capacity after 10 000 GCD cycles).?2.2?The Zn-Co-130-ZIFs-10h//NC-950 deviceThe Zn Co-130-ZIFs-10h//NC-950 supercapacitor device was prepared by adjusting the quality of the positive electrode material?Zn Co-130-ZIFs-10h?and the negative electrode material?NC-950?.The results show that the capacity of the Zn-Co-130-ZIFs-10h//NC-950 can reach 106,97.2,85.2,67.9 and 52 F g^-1 when the scan rates are 0.5,1,2,5 and 10 A g^-1,respectively.The relationship between the energy density and power density of the device was further calculated and the results show that the device can achieve an energy density of 42.5 Wh kg^-1 when the power density is 424 W kg^-1.