Research On The Performance For Supercapacitors Of Transition Metal Framework Materials

Due to the severe energy situation,the study of novel energy conversion and storage has become an important research field.Supercapacitors,because of their fast charge and discharge ability,long-term cycle stability,low cost,clean safety and other characteristics have attracted wide attention.The research focus of supercapacitor is usually focused on the electrode material.The performance of the electrode material largely determines the performance of the supercapacitor.Framework materials are important research directions in recent years.The framework materials,including metal-organic framework materials（MOFs）and prussian blue analogs（PBA）,have controllable and adjustable components,abundant pore structure,and large specific surface area,and there are many derivatives that can be produced.These features are very attractive to supercapacitors.However,the widespread problems of framework materials such as poor conductivity greatly limit their further application in the direction of supercapacitors.Reasonable methods are adopted to improve the material and improve its capacitor performance while retaining its inherent advantages.In this paper,two framework materials,Ni-MOF and Co-Co PBA,were selected to improve on the basis of raw materials,and their electrochemical properties were tested and studied.The main work is as follows:（1）Bimetallic MOFs with Ni/Co ratios of 1:0,2:1,1:1,1:2 and 0:1 were in-situ grown on nickel foam by a simple solvothermal synthesis method.Compared with mono-metal MOFs,bimetallic MOFs not only have a strong improvement in electrical conductivity,but also the introduction of other transition metal ions also brings more redox active sites,and under the synergistic action of different components,the electrochemical performance of the material has been significantly improved.The in situ growth of the material on the foam nickel also avoids the negative effect of the binder on the conductivity of the electrode material.The uniformly oriented surface morphology of the material also contributes to the improvement of the bimetallic MOFs properties.The material exhibits the best electrochemical performance when the nickel-cobalt ratio is 2:1,and the Ni2Co1/NF electrode has a specific capacitance of 1600 F g^-1 at 1 A g^-1.After assembled with activated carbon,an energy density of 58.7 Wh kg^-1can be achieved at 1 A g^-1,resulting in a capacity retention rate of 86%after 1000 cycles.This indicates that Ni-Co bimetallic MOFs can be used as high performance supercapacitor materials.（2）The synthesized Co-Co PBA was treated with dopamine coating and selenization.Two surfactants,F127 and P123,were used for interfacial self-assembly of dopamine on the surface of PBA cube to form open microporous/mesoporous nitrogen-doped carbon core-shell materials.When the structure of nuclear material is fully exposed,the electrolyte can be fully permeated without affecting its own electrochemical performance.The introduction of carbon shell material is very beneficial to improve the electrical conductivity of the whole material.Then the composite material and selenium powder were calcined at high temperature in a tubular furnace to obtain porous carbon coated Co Se₂.At this time,due to etching during the formation of selenide,new mesoporous channels are generated on the material surface,which is conducive to electrolyte penetration and provides more active sites.CCS-700,a Co Se₂ core-shell material with a variety of pore sizes,was finally prepared.Charging and discharging tests at 1 A g^-1 produced a specific capacitance of 231.6 F g^-1.When assembled with active carbon,an energy density of 24.79 Wh kg^-1 can be obtained at 1A g^-1.After 1000 cycles,the capacity retention rate is 79%.This method also provides ideas for the preparation of other frame material derivatives.