Preparation Of Zn-based MOF Derived Carbon Materials And Study On Its Supercapacitor Performance

The proposal of the"double carbon"means that the demand for green and renewable energy in the whole society is further increased.As a green energy storage device,supercapacitors have attracted attention of researchers due to the high power density,excellent stability and long cycle life.The mechanism of electric double-layered supercapacitor（EDLC）to store energy is mainly through physical adsorption and desorption between carbon electrode and electrolyte.Carbon materials derived from MOF have the advantages of large specific surface area,adjustable pore structure and good stability.It can be used as ideal EDLC electrode materials.In this thesis,Zn-based MOF was used as the precursor.The structure of MOF and derived carbon were designed by simple and effective methods to optimize the electrochemical performance.The main contents and achievements of the thesis are as follows:（1）Zn-BTC was synthesized by solvothermal method,using pyromellitic acid（H₃BTC）as the organic ligand and zinc as the central metal.The environmentally friendly ethanol solvent was used to replace the traditional harmful solvent.The effects of different ethanol content on the morphology,pore distribution and electrochemical properties of Zn-BTC and derived porous carbon RTPC were emphatically studied and discussed.RTPC-50 synthesized in 50%ethanol displays a specific surface area up to 1930 m²g^-1and a specific capacity up to 287.2 F g^-1at1 A g^-1.The specific capacitance decays only 2.12%after 200000charge-discharge cycles at 50 A g^-1.This study provides an effective strategy for the synthesis of porous carbon for advanced supercapacitors.（2）This chapter provides an effective method to regulate the structure and properties of MOF and its derived carbon material by changing the carboxyl number of organic ligands.The results show that the more the number of carboxyl groups in ligands,the more micropores of MOF formed,and the corresponding derived carbon materials display larger specific surface area and excellent electrochemical properties.Zn-BTEC synthesized with zinc as the central metal and pyromellitic acid（H₄BTEC）as the organic ligand derived porous carbon PC with high specific surface area and rich pore structure through high-temperature carbonization and alkali washing.The electrochemical results show that the specific capacitance of PC can reach 333.3 F g^-1at 1 A g^-1in the three-electrode system.The specific capacitance remains 95%after 300000 charge-discharge cycles at a high current density of 50 A g^-1,showing excellent electrochemical stability.In addition,the assembled symmetrical capacitor shows a high energy density of 20.44 Wh kg^-1at696 W kg^-1.（3）In order to solve the problems of the destruction of the redox catalyst and the low instantaneous power of the discharge caused by the sudden drop of voltage during the discharge in Zn-Air battery,this study paralleled the capacitive carbon-based material with the redox catalyst to improve the power and stability of Zn-Air battery.The nitrogen-derived carbon material NC was derived from NH₂-Zn-MOF.The NC electrode and the Pt-C electrode were assembled in parallel to form a Zn-Air battery.In a 3-el system,the buffer times of platform voltage for Pt-C and Pt-C/NC are 13.5 s and 66.5 s,respectively at 1 m A cm^-2.At the same time,the voltage provided by Pt-C/NC is 1.497 V and 1.476 V when the discharge times are 0.1 s and 5 s,respectively.While Pt-C can only provide 1.494 V and 1.421 V voltages at 0.1 s and 5 s.The NC electrode provided a transmission channel for electrolyte ions in the initial discharge stage.It can effectively slow down the rapid drop of voltage and output more energy.Capacitive electrode can effectively protect the redox catalyst and improve the power performance.