Preparation Of Covalent Organic Frameworks Derived Materials And Research On Its Electrocatalytic Oxygen Evolution Performance

With the growing concern about climate change,environmental protection and the demand for green energy supply,the development of clean energy technologies,advanced energy conversion and storage technologies has become the most important issues in the development of the world today.Hydrogen is a non-polluting,clean energy source with non-toxic,zero greenhouse emissions,and a promising fuel of the future because of its ultra-high energy density and environmental friendliness.Electrocatalytic hydrolysis is an important conversion technology for hydrogen storage process,however,in the presence of multiple electron transfer processes at the anode,the slow kinetics of the oxygen evolution reaction（OER）is the main reason limiting its industrial application.The OER process has been achieving favorable kinetic behavior mainly through noble metal-based electrocatalysts.However,these noble metal-based electrocatalysts have obvious defects such as poor durability,low selectivity,susceptibility to intermediate toxicity,as well as high cost and scarcity,which greatly hinders its expansion at scale.Thus,the development of non-precious metal-based electrocatalysts for OER processes is of great importance in the electrolytic water to hydrogen industry.The aim of this thesis is to design and synthesize based on covalent organic frameworks（COFs）derived materials for alkaline electrolyte oxygen evolution reactions.The details of the study are as follows.（1）Efficient OER electrocatalysts based on COFs-derived carbon layers as carriers for immobilization of active bimetallic Fe/Co nanoparticles applications.The triazine-based COFs（Schiff base network SNW-1）were obtained by the condensation reaction of melamine（MA）and terephthalaldehyde（TA）,and the Fe/Co ion ratio was optimized to enter the SNW-1 pore to effectively suppress the ion agglomeration and migration during the pyrolysis.The SNW-1 derived Fe Co（1:3）@SNC presented abundant micro-and mesoporous structures to enhance the catalytic activity specific surface area,nitrogen doping content and electrolyte permeability.The results show that a current density of 10m A cm^-2 can be achieved with an overpotential of 288 m V in strongly alkaline solutions,with a corresponding Tafel slope of 40 m V dec^-1,and the better OER performance than that of commercial Ru O₂.It has remarkable stability after 20 hours of continuous electrolysis and the performance of the catalyst slightly decreases after 2000 CV cycles.This work provides an effective idea and approach method for the development of superior OER electrocatalysts using COFs.（2）An ideal platform based on the composite of COFs and carbon nanotubes（CNT）anchored Ni/Co bimetallic nanoparticles as efficient OER electrocatalysts.Among them,the highly ordered network structure of SNW-1 provides channel for the doping of metal active components,and CNT serves as conductive substrate to enhance the conductivity of the catalyst.In addition,the SNW-1 derived carbon layer on the CNT surface can provide more pores for ion diffusion transport in the electrolyte and modify the CNT with high nitrogen doping.The good electrolyte permeability and abundant nitrogen content of this catalyst are favorable to enhance the OER activity of the catalyst.The results show that the optimized catalyst Ni Co-SNW-1@CNT400 has a low overpotential of 290 m V and a small Tafel slope of 74 m V dec^-1 at a current density of 10 m A cm^-2,and the catalyst maintains good catalytic activity after 20 h of continuous testing and 2000 CV cycles.This work provides new insights and strategies for the development of COFs-based applications in energy conversion technologies.（3）ZIF-67 was used as precursor,which was derived by pyrolysis to graphitic carbon（GC）.In this process,Co ions were transformed into metal nanoparticles embedded in the GC framework.Then SNW-1 was covered on the GC surface in situ,and after secondary pyrolysis,the SNW-1 covered on the GC surface was converted into nitrogen-rich porous carbon,which was used to achieve the effective integration of COFs and MOFs-derived GC to form a well-defined structure of GC@SNW-1 core-shell structure.The composites have high electrical conductivity,layered pore structure and abundant and uniform metal and carbon edge sites.In addition,the COFs layers plays a protective role for the metal active component inside and forms a strong interfacial interaction with the MOFs-derived GC,which contributes to the OER performance enhancement and catalytic stability of the material.The results showed a low overpotential of 308 m V,a small Tafel slope of 74m V dec^-1 at a current density of 10 m A cm^-2.In addition,continuous testing by chronopotentiometric method at different current densities for 20 h and 2000 CV cycles showed favorable catalytic stability.This work provides some insights for the combination of MOFs and COFs for electrocatalysis applications.