Preparation And Energy Storage Properties Of Covalent Organic Framework Materials Based On Triazine Ring

With the proposal of my country’s "dual carbon" goal,the search for clean.and sustainable energy has become a rigid need for current economic development.As a new type of energy storage device,supercapacitors have broad development prospects in the energy field due to their unique functional properties.Covalent organic frameworks(COFs)are a new class of crystalline polymer materials with periodic porous framework structures formed by the precise connection of designable organic building units through covalent bonds.As a new type of electrode material,one of the problems of COFs is the poor conductivity of the material.The introduction of redox building blocks into the molecular structure of COFs can provide pseudocapacitive properties for the materials,which can further improve the electrical conductivity of the materials.Or by compounding COFs materials with other substances(conductive polymers,carbon materials,nanowires,etc.),the synergistic effect between materials can also be used to improve the electrical conductivity of materials.In this study,the triazine ring-based covalent organic framework material was firstly constructed,then composited with nickel nanowires and modified graphene,and finally applied in supercapacitor electrode materials.1.Covalent organic framework materials with triazine ring structure and periodic π arrays can provide pseudocapacitance and good electronic conductivity for electrode materials.In Chapter 3,we prepared a kind of COFs material with triazine ring structure(TPT-COFs)by solvothermal method.The results showed that the material has good chemical stability,high specific surface area and abundant nitrogen atomic sites.The hexagonal pore structure of TPTCOFs was constructed with the help of Chemdraw and Materials Studio.Through performance testing in different electrolytes,TPT-COFs exhibited better electrochemical performance in sulfuric acid electrolyte.2.When TPT-COFs are used as supercapacitor electrode materials,the conductivity needs to be further improved.Nickel nanowires have a large aspect ratio and have the high electrical conductivity that metal materials should have.In Chapter 4,we improved the electrical conductivity of materials by introducing different contents of nickel nanofibers(NiNWs).It was found that th e specific capacitance of the composite electrode material could reach 343 F/g(0.1 A/g)when 15%NiNWs was added.At a current density of 5 A/g,the material exhibited a capacitance retention of 107%and a Coulombic efficiency of 109%.By assembling symmetric and asymmetric supercapacitor devices,it was found that the specific capacitance of the symmetric supercapacitor device could reach 53 F/g at 0.1 A/g;when the power density was 2970 W/kg,the energy density was 3.7 Wh/kg;The specific capacitance of the symmetric supercapacitor device at 0.1 A/g could reach 76 F/g;when the power density was 10945 W/kg,the energy density was 12.8 Wh/kg.3.Due to strong van der Waals interactions,graphene nanosheets are stacked together,resulting in low charge storage efficiency,which seriously affects their performance as supercapacitor electrode materials.The TPT-COFs prepared in this paper are ideal spacers as a new type of conductive polymer,but their conductivity has certain limitations.To improve the conductivity of TPT-COFs and the stacking effect of graphene,we tried to introduce highly conductive graphene into the system.In Chapter 5,we firstly modified graphene,and then composited TPT-COFs with modified reduced graphene oxide.Taking advantage of the excellent electrochemical performance of modified graphene and the abundant mesopores in TPT-COFs,the efficient transport process of electrolyte ions in the composite electrode material was realized.Comparing the properties of the composites before and after modification,it was found that the modified composites had larger specific surface area,higher thermal stability and electrochemical performance.At a current density of 0.1 A/g,the specific capacitance of the material could reach 299 F/g.After 10,000 cycles at a current density of 5 A/g,the material had a capacitance retention rate of 120%and a Coulombic efficiency of 110%,showing excellent cycling stability.At the same time,the electrochemical impedance results showed that the material had a smaller solution contact resistance(2.1Ω),which contributed to the improvement of the material conductivity.By assembling symmetric and asymmetric supercapacitor devices,it was found that the specific capacitance of the symmetric supercapacitor device could reach 46 F/g at 0.1A/g;when the power density was 5184 W/kg,the energy density was 3.6 Wh/kg.The specific capacitance of the asymmetric supercapacitor device at 0.1 A/g could reach 66 F/g;when the power density was 12360 W/kg,the energy density was 10.3 Wh/kg.