Prearation Of Covalent Organic Framework Materials Based On Metal Phthalocyanine And Electrocatalytic Performance

The increasingly prominent energy and environmental issues have led people to study green and sustainable energy conversion methods and storage devices.Zinc-air battery not only has the advantages of excellent safety and stability and low production cost,but also has a theoretical energy density of 1086 Wh·kg^-1,which becomes one of the potential energy conversion methods.However,the slow kinetics of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）on the air electrode of Zinc-air batteries have become the main bottleneck hindering the development of metal-air batteries.The development of high-activity dual-functional catalysts has become the current main mission.Although the precious metals Pt and Ir O₂/Ru O₂ are considered to have high ORR and OER activities,their limited reserves,high production costs,and poor stability and circulation have limited their future commercial applications.Therefore,the design and study of inexpensive,high-efficiency,and highly stable non-noble metal catalysts is of great significance to promote the development of metal-air batteries.Transition metal/nitrogen/carbon composite materials derived from covalent organic framework materials exhibit satisfactory performance in electrocatalysis due to their special microstructure,high specific surface area,and excellent electrical conductivity,and have great market application potential.In this thesis,based on carbon nanotubes,by loading covalent organic frameworks/covalent organic polymers on the surface of carbon nanotubes,a series of ORR/OER bifunctional electrocatalysts with high activity and excellent cycle stability have been designed and developed.Assemble Zinc-air battery to explore its practical application performance.The main work content is as follows:1.Using carboxylated multi-walled carbon nanotubes as a carrier,using tetraaminocobalt phthalocyanine（structural unit）and 4,4-biphenyl dicarbaldehyde（linking group）to grow Co-COFs structure in situ on the surface of carbon nanotubes,Prepared Co-COFs/CNT precursor;Utilizing the excellent electrical conductivity of carbon nanotubes,tetraaminocobalt phthalocyanine provides the nitrogen source and metal active center as well as the anchoring effect of the covalent organic framework.Pyrolysis under N₂ atmosphere produces Co-COFs/CNT-700catalyst for Co-N-C active sites.Characterization tests show that the existence of a covalent organic framework structure can not only anchor the metal Co and N elements to provide more catalytically active sites,but also improve the oxygen adsorption and transport capacity of the catalyst.In addition,the Co-COFs/CNT-700 catalyst contains active sites such as metal Co,Co O,and Co-N/C.Among them,pyridine N and Co O are beneficial to improve the OER performance of the catalyst,while the active sites of metal Co and Co-N/C are the main active sites of ORR.So the bifunctional activity of the catalyst is due to the synergy of different active sites inside it.The electrocatalytic performance test in alkaline electrolyte shows that the Co-COFs/CNT-700 catalyst has excellent ORR performance,with the initial potential（E₀）and half-wave potential(E_1/2)reaching 0.926 V and 0.848 V,and the ORR performance is close to commercial use 0.971 V and0.858 V of 20%Pt/C;At the same time,The OER performance test found that the overpotential of the Co-COFs/CNT-700 catalyst at a current density of E_j=10 was as low as 470m V,which is slightly higher than the 440 m V of Ir O₂.The voltage difference of bifunctional activityΔE(E_j=10-E_1/2)is as low as 874 m V,showing good ORR and OER bifunctional activity.The performance characterization of the assembled Zinc-air battery shows that the highest power density of the Co-COFs/CNT-700 catalyst can be as high as 114 m W·cm^-2,and its cycle stability was better than that of the 20%Pt/C+Ir O₂ catalyst.2.By introducing the second metal Fe and Co to form a bimetallic synergistic effect,the bifunctional activity is further improved.Based on carboxylated multi-walled carbon nanotubes,tetraaminocobalt phthalocyanine and amino iron phthalocyanine are grown on the surface of carbon nanotubes through Schiff base reaction to form a covalent iron covalent organic polymer（CoFe-COP）layer.Then pyrolyze to obtain CoFe-COP/CNT-700 catalyst.Analysis by Raman and XPS found that there are active sites such as pyridine nitrogen,graphitic nitrogen and CoFe-N-C in the catalyst,which are beneficial to the improvement of the catalyst’s ORR and OER performance.The addition of Fe will not only change the electronic structure of the catalyst surface,but also can form a positive synergistic catalytic effect with metal Co.Characterization test results show that the CoFe-COP/CNT-700 catalyst has active sites for metal Co and Fe,Co/Fe-N/C,pyridine nitrogen and graphite nitrogen.The introduction of a covalent organic framework structure effectively prevents the aggregation of metal atoms with exposing more active sites.CoFe-COP wrapped on the surface of carbon nanotubes can form nitrogen-doped carbon materials during high-temperature pyrolysis and the introduction of nitrogen can effectively improve the stability and methanol resistance of the catalyst.CoFe-COP/CNT-700 catalyst exhibits excellent ORR and OER performance comparable to 20%Pt/C and Ir O₂ catalysts.The voltage differenceΔE of the bifunctional activity is as low as 822 m V.The actual application performance of the Zinc-air battery shows that the peak power of the CoFe-COP/CNT-700 catalyst still reaches 117m W·cm^-2,and it has a round-trip efficiency of more than 52.1%in the 65 h cycle charge and discharge test.3.The two catalysts prepared in the thesis have ORR and OER activities close to 20%Pt/C and Ir O₂ catalysts.In the practical application of Zinc-air batteries,it also shows dual-functional activity close to commercial 20%Pt/C and Ir O₂ catalysts,and its cycle stability has been significantly improved and improved,and it has a good application prospect in Zinc-air batteries.It provides a reference for the preparation of non-precious gold metal bifunctional catalysts.