Preparation Of MOFs-based Nitrogen-Doped Porous Carbon Materials And Graphene Composites For Electrochemical Storage

Supercapacitor is a new type of energy storage device between the traditional capacitor and the battery.It has the advantages of high power density,high charge and discharge speed,long cycle life,etc.It is widely used in the energy reserve technology field.As China enters a new era,the environmental requirements and the demand for high-power energy storage devices areincreasing.The development of the supercapacitor with a large capacity and long cycle life is a challenging task.The electrode material is the key for the supercapacitor.Double-layer energy storage electrode materials is the use of electrode and electrolyte interface double layer storage of electricity to achieve energy storage,with long cycle life,power density advantages,but the energy density needs to be improved;pseudocapacitor energy storage electrode materials is used to achieve energy storage using a reversible redox reaction arising on the electrode surface or in the bulk phase,which has the advantages of large energy density,but short cycle life.The development of electrode materials with double-layer and pseudocapacito energy storage is of great significance for improving the performance of supercapacitors.The nitrogen-doped carbon material can achieve a combination of electric double layer and tantalum capacitor energy storage.However,the development of high-performance nitrogen-doped carbon materials is a very challenging research work.There are two main methods for preparing nitrogen-doped carbon materials.One is to modify the surface of carbon materials by chemical modification.The process is cumbersome,the nitrogen content is low and the nitrogen-containing functional groups are mainly distributed on the surface,which will destroy or plug some pore structures of raw materials.The specific surface area is reduced;the other is the preparation of nitrogen-doped carbon materials by controlling carbonization and activating process,using nitrogen-rich precursors as raw materials,which can keep the nitrogen atoms contained in the carbon matrix.The original pore structure will not be destroyed.In view of the above problems,the specific research is as follows:1.The ZIF-8 of ZIFs series was chosen as the precursor.By using the large specific surface area of ZIF-8 and the rich theoretical nitrogen content up to 24.41%,the in situ nitrogen doping was carried out by accurately controlling the carbonization temperature and calcining under the condition of nitrogen gas at high temperature.Thus,nitrogen doped porous carbon materials were prepared to realize the combination of double layer and pseudo-capacitance energy storage.When applied to supercapacitors,under the conditions of6 M KOH electrolyte,three-electrode system,and the current density is 50 mA g^-1,the specific capacitance can reach 258.68 F·g^-1.2.graphene has large specific surface area and excellent conductivity,which is the best conductive material found at present.However,the van der Waals intermolecular force between graphene laminates can lead to the agglomeration of graphene.In the process of preparing ZIF-8,the ZIF-8 was prepared with graphene oxide.During the process of high temperature calcination,the space between graphene layers was supported by nitrogen doped carbon spheres,and the stacking of graphene layers was prevented.ZIF-8 based nitrogen-doped porous carbon spheres and graphene composites were prepared.The specific electric properties of supercapacitors were obtained when the current density was 50 mA g^-1in 6 M KOH electrolyte and three-electrode system.The maximum capacity can reach 292.22F·g^-1.The results show that the special pore structure and rich nitrogen content of ZIF-8 have high potential in the synthesis of electrochemical nitrogen-doped porous carbon electrode materials.The addition of graphene can also effectively improve the electrochemical performance of nitrogen-doped porous carbon materials.Nitrogen doped porous carbon and graphene composites based on MOFs have great potential for electrochemical energy storage as electrode materials for supercapacitors.