| The construction of ecological civilization has stimulated the development of environmentally friendly energy sources such as solar and wind power,so it is crucial to prepare equipment that can store and release the clean energy efficiently.In energy storage systems,supercapacitors can store electric energy in the form of electric charges,which have been studied continuously due to their excellent power density and fast charge-discharge performance.Transition metal oxides as electrode materials have rich electrochemical activities,but their effects are limited by high electrical resistance and structural instability.Transition metal oxides combined with other materials to form nanocomposites can improve the specific charge capacity,charge and discharge and ion diffusion kinetics,as well as the cyclicity of devices.Among them,the metal oxide-carbon nanocomposite electrode combines the advantages of the two components.In this composite electrode,the carbon nanostructure not only acts as the physical carrier of the metal oxides,but also provides a channel for charge transmission,and its high conductivity is conducive to improving the rate capacity and power density.As the main source of charge and energy storage,the high specific capacitance and high energy density of the composite electrode are determined by the electrical activity of metal oxides.Carbon nanotubes(CNTs),as a new material,have high chemical stability and specific surface area(up to 1300 m2/g),which are helpful to establish a large electrolytic-electrode interface and achieve a large amount of energy storage.Compared with traditional heating methods,microwave method uniformly converts electromagnetic energy into heat energy inside the material,thus achieving rapid reaction and low energy consumption,which is conducive to sustainable energy development.Therefore,in this paper,a one-step microwave method was adopted to prepare high-performance transition metal oxide/carbon nanotube composite electrode by taking CNTs as conductive substrate and microwave absorbent and composite with CuO and MnO2.The main work is as follows:(1)Using Cu(NO3)2·3H2O as the copper source,CNT with different masses was put into the microwave oven,and the microwave power was set at 400/600/800 W and the heating time was 30/60/90 s to prepare CuO/CNT nanocomposites.The structure test shows that the CuO nanoparticles are uniformly distributed on CNT,and the electrode material prepared under the conditions of C30:Cu50,600 W,60 s has the best performance,the specific capacitance reaches164.54 F g-1,and the cycling stability reaches 10,000 times.The capacitance of the prepared CuO/CNT//AC asymmetric supercapacitor(ASC)is 51.4 F g-1 and can be cycled up to 30,000times.At a power density of 0.775 k W kg-1,the highest energy density of ASC is 17.08 Wh kg-1.(2)In order to improve the electrochemical performance of MnO2,the MnO2/CNT nanocomposite was successfully prepared in 60 s with CNT as the substrate and Mn(NO3)2·4H2O as the metal oxide precursor under the action of CNT absorption microwave.Various structural tests showed that MnO2 with poor crystal shape was prepared and uniformly distributed on CNT.Through the exploration of the reaction conditions,the material has the best performance under the conditions of 600 W and 60 s,and the specific capacitance has been greatly improved(1250 Fg-1),7000 GCD cycles show that the cycle performance has a small improvement,and through the analysis of the kinetic behavior,it is found that the capacitor process is dominant.The MnO2/CNT//AC ASC capacitance value reaches 94.26 F g-1(1 A g-1),the cycling performance can reach 10,000 times,and the energy density can reach33.51 Wh kg-1(power density is 0.4 k W kg-1). |
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