Preparation And Electrochemical Properties Of MOFs Based Porous Carbon Materials

In recent years,with the rapid development of science,technology and economy,the global energy consumption has been gradually accelerated,and the natural environment on which human beings depend for survival has been irreparably damaged.In order to avoid resource crisis and environmental degradation,we must find advanced energy conversion and storage technology.As a new type of green electrochemical energy storage element,super capacitor has many advantages,such as high power density,wide range of applicable temperature,fast charge and discharge speed,high efficiency,strong stability,large current,long cycle life,environmental protection,no pollution and so on,compared with traditional capacitor,which has gradually attracted people's wide attention.However,it has the disadvantage of low energy density.In order to solve this problem,it is necessary to explore new electrode materials with high specific capacitance.Metal organic framework is a kind of porous material with periodic network structure formed by self-assembly with central metal ions or metal clusters as nodes and organic ligands as connection units under the action of coordination bonds.Because of its advantages of large specific surface area,high porosity,adjustable pore size,structural diversity and strong stability,MOFs is a kind of porous material with periodic network structure,It has potential application value in the field of battery electrode materials.The transformation of MOFs materials into nano porous carbon materials by pyrolysis can not only retain the original structural characteristics of MOFs materials,but also solve the problems of too many micropores and less mesopores and the existence of half pores or pore plugging,so that it have larger specific surface area and reasonable pore size distribution,which is conducive to improving their electrochemical performance.In this paper,two kinds of iron-based MOFs were synthesized by hydrothermal method,which were used as carbon precursor.Porous carbon materials were prepared by one-step carbonization method.The microstructure was characterized by XRD,TGA,Raman,SEM,TEM,bet and XPS.The effects of different carbonization temperature,activator and nitrogen doping on the electrochemical properties of porous carbon materials were investigated.The main research work of this paper includes the following aspects:?1?The metal-organic framework[Fe₃O?1,4-bdc?₃?H₂O?₃]Cl?H₂O?_x was synthesized by hydrothermal method.The porous carbon material MC101-T was prepared by one-step carbonization in an inert gas atmosphere.The effects of carbonization temperature,activator and nitrogen doping on its microstructure and electrochemical properties were investigated.The results show that when the carbonization temperature is 800°C and the carbonization time is 2 h,the specific surface area of the porous carbon material MC101-800 is 300.85 m² g^-1.In the three electrode system,6 M KOH is used as the electrolyte,and the specific capacitance reaches 130 F g^-11 when the current density is 1.0 A g^-1.When the current density is 2.0A g^-1,the capacitance retention is 64.62%after 5000 times of constant current charging and discharging,showing good electrochemical performance and cycle stability.When MC101-800:KOH=1:3,the prepared porous carbon material MC101-800-1:3 has the best electrochemical performance.In the 6 M KOH electrolyte,when the current density is 1.0 A g^-1,its specific capacitance is 181 F g^-1.When MC101-800:urea=1:4,the prepared porous carbon material NMC101-800-1:4has the best electrochemical performance.In the electrolyte of 6 M KOH,when the current density is 1.0 A g^-1,its specific capacitance is up to 160 F g^-1.?2?The metal organic framework[Fe₃O?1,4-BDC?₃?DMF?₃][FeCl₄]?DMF?₃]was synthesized by hydrothermal method.As a carbon precursor,porous carbon material MC235-T was prepared by one-step carbonization in inert gas atmosphere.The effects of carbonization temperature and activator on its microstructure and electrochemical properties were investigated.The results show that when the carbonization temperature is 800°C and the carbonization time is 2 h,the specific surface area of the porous carbon material MC235-800 is 303.59 m² g^-1.In the three electrode system,the specific capacitance is 124 F g^-11 when the current density is 1.0 A g^-1.When the current density is 2.0 A g^-1,the capacitance retention rate is 62.10%after 5000 times of constant current charging and discharging,showing good electrochemical performance and cycle stability.When MC235-800:KOH=1:3,the prepared porous carbon material MC235-800-1:3 has the best electrochemical performance.In the 6 M KOH electrolyte,when the current density is 1.0 A g^-,its specific capacitance is 170 Fg-1.