Research On The Synthesis And Electrochemical Performance Of Covalent Organic Frameworks Derived Materials

At present,humanity’s primary energy is still traditional non-renewable energy sources such as coal,natural gas,and oil.The problems exposed to energy and the environment are becoming more and more serious.The exhaustion of limited resources has prompted people to urgently need to study a series of renewable energy sources as alternatives.Zinc-air batteries and fuel cells are the most promising directions related to new energy in the world,and it is vital to break through their technical problems.For traditional precious metal catalysts,the scarcity leads to high cost,which limits their application.Therefore,the development of efficient and economic OER/ORR catalysis has received extensive attention.COFs are ordered structures constructed by covalent bonds from organic monomers with atomic-level precision.They have excellent thermal stability,large specific surface area and low skeleton density.Their open and regular microporous structure promotes effective mass transfer in the reaction process,so they have excellent development prospects in electrocatalytic applications.In this paper,COFs are used as precursors to design synthetic composite materials,hierarchical porous materials and carbon materials.In addition to giving full play to the structural characteristics of COFs,they have all been further optimized.Derivative materials exhibit excellent electrocatalytic OER/ORR performance.Simultaneously,using COFs as a research platform provides a deeper understanding of the deep structure-activity relationship in electrocatalysis.The main contents of this article are as follows:（1）The research object is the composite material COF@CNT prepared by COFs in-situ coating of multi-walled carbon nanotubes（MWCNTs）.Through the fine control of the COFs layer.It is revealed that excellent catalytic performance is highly dependent on the appropriate amount of molecular catalyst loading on the carbon substrate.This balances the mass transfer and electron transfer in the catalytic process.Besides,the turnover frequency（TOF）calculation shows that the metal coordination of the COFs site has a moderate saturation characteristic.The diluted active site is more conducive to improving the overall catalytic performance.The relationship of competitive masking formed between active sites is proposed.Finally,similar studies were conducted with different types of COFs to verify the universal applicability of fine control of COFs.The prepared catalyst exhibits excellent OER electrochemical performance under alkaline conditions,and the overpotential at a current density of 10 m A cm^-2 is only 353 m V.The ideal platform composed of COFs and MWCNTs helps us understand the critical factors of COFs-based electrocatalysts in the OER mechanism.（2）Copper nanowires are used as hard templates.COFT with a tubular structure was obtained through in-situ growth of COFs and metal etching.The coordination of COFT and Co²⁺formed catalytically active sites.Observe the structure-activity relationship of the catalyst and demonstrate the benefits of introducing graphene（GF）.COFs with a tubular structure show high specific surface area and active site accessibility,but their charge conductivity is restricted instead.The synergistic effect of COFs with hierarchical porous structure and conductive carbon substrate can give full play to its electrocatalytic benefits.The composite GF@COFT-Co exhibits excellent electrocatalytic OER performance,with an overpotential of only 367 m V at a current density of 10 m A cm^-2 in an alkaline environment.Experiments show that the hierarchical porous structure of COFs and the line-to-surface contact with GF are the key to the high catalytic performance of composite materials.（3）Silver nanowires are used as hard templates.Precursors were prepared by in-situ synthesis and coating of COFs on the surface.The carbon nanotube structure is formed through calcination and acid washing.Through the amination/sulfurization treatment of secondary calcination,N/S heteroatom-doped and defect-rich carbon nanotubes were obtained.The ammoniating/vulcanization process will affect the existence of N atoms in the material.It is mainly manifested in the decrease of pyrrole N and graphite N and the increase of the relative content of pyridine N.At the same time,ammoniating/vulcanization treatment will lead to changes in the doping of N/S heteroatoms in the material.Asymmetric charges will be introduced into the carbon network,leading to the redistribution of local charge density and spin states.It will also promote the increase of carbon defects.The prepared catalyst COF-NS showed excellent electrochemical ORR performance.The half-wave potential and limiting current in 0.1M KOH electrolyte were 0.9 V vs.RHE and 5.8 m A cm^-2,respectively.Moreover,it has excellent stability.Derived carbon nanotubes prepared with COFs as precursors.The designable doping and arrangement of heteroatoms have the potential for extensive development and application.