Study On MnO₂/Co-ZIF Derived Porous Carbon Composites For Supercapacitors Performance

With the rapid development of society,the excessive consumption of traditional fossil fuels has caused serious deterioration of the ecological environment.Electrochemical supercapacitors?EC?,also known as supercapacitors,have high power density and excellent cycling performance,and play an important role in energy conversion and storage.However,the application of supercapacitors is limited due to their low energy density.We know that the energy density of supercapacitors depends on the material voltage window and specific capacitance.Therefore,finding an electrode material with a wide voltage window and high specific capacitance is an effective method to solve the problem of low energy density.MnO₂ has the advantages of rich natural reserves,environmental friendliness,wide voltage range?0-1.0 V?,and high theoretical specific capacitance(?1370 F g^-1),so it is favored by people.However,the poor electrical conductivity makes the actual specific capacitance and stability of manganese dioxide unsatisfactory.Therefore,it is of great significance to study how to improve the actual utilization of manganese dioxide.In this dissertation,a MnO₂composite electrode is constructed based on the performance-oriented porous carbon derived from Co-ZIF,and the goal of improving the capacitance performance of MnO₂is achieved by optimizing parameters.Our main research contents are as follows:First,carbon paper is used as a current collector to construct a ZIF-67 derived nanoporous carbon and MnO₂ composite structure?Na⁺-MnO₂/NPC?.The specific capacitance of the composite electrode reaches 217.0 F g^-1,which is significantly better than the specific capacitance of each single component.At a current density of 2-20 A g^-1,the capacitance remains 82.80%.After 5000 cycles,the capacitor retention rate was91%.In addition,the capacity retention rate of the device assembled using the Na⁺-MnO₂/NPC composite material after 3000 cycles was 82%.The composite electrode shows excellent performance.Second,a leaf-like Co-ZIF derived nanoporous carbon and MnO₂ nanosheet composite structure?MnMC/NF?was constructed on the basis of nickel foam.The composite electrode was obtained by annealing leaf-like Co-ZIF grown on nickel foam and treating with potassium permanganate.The optimal annealing temperature is 700°C.MnMC/NF 700 achieves a specific capacitance of 531F g^-1 at 1 A g^-1,and has a rate performance of 85.5%(456 F g^-1 at 20 A g^-1).The MnMC/NF 700 composite electrode has a capacity retention rate of 82%after 5000cycles,and has good long-term cycle stability.In addition,the assembled device has an energy density of up to 38.78 Wh kg^-1.The experimental results show that the composite structure of Co-ZIF derived porous carbon and manganese dioxide has excellent supercapacity and has potential application prospects.