Transition Metal Doped Porous Carbon Nanomaterials For Electrocatalysis And Zn-air Battery

As global environmental and energy issues become more prominent,there is an urgent need to develop environmentally friendly and energy-intensive energy storage and conversion devices such as solar cells,lithium-ion batteries,metal-air batteries and fuel cells to maintain sTab.le economic growth.However,the currently synthesized materials have hindered their large-scale commercial application due to shortcomings such as difficulty in preparation,high price,and poor sTab.ility.Therefore,it is of great practical significance to explore a practical and simple method for preparing high-performance electrode materials and applied in the above equipment for solving the current energy crisis has a very good role.In recent years,one-dimensional nanomaterials prepared based on electrospinning technology have high chemical activity and specific surface area and low bulk density because of their unique structure.In addition,nanomaterials prepared by electrospinning technology can significantly reduce cost and improve efficiency compared with conventional materials,and thus can be widely used in energy fields such as batteries and catalysis.Metal-Organic Frameworks（MOFs）are a class of regular porous materials that are self-assembled from the"center"of metal ions and the"skeleton"of organic ligands.Compared with traditional porous materials,MOFs exhibit more unique advantages as a new class of porous materials,such as ultra-high specific surface area,adjusTab.le regular pore structure and rich metal/ligand combination.In addition,MOFs can also be used as a matrix material or precursor to prepare a series of derivative materials,including introducing an electrocatalytically active component into the pore structure of the framework,and obtaining a carbon-based catalyst or metal compound by high temperature treatment.These MOF derivatives may evolve more excellent morphologies and chemistries,such as carbon nanotubes and graphene,while preserving the pore structure and chemical composition of MOFs,thereby further expanding the application of MOFs in energy.The research content of this thesis is mainly through the combination of electrospinning technology and Zeolitic Imidazole Frameworks（ZIFs）MOFs materials,and further preparation of various morphologies and components by various post-treatment methods.One dimensional MOFs nanomaterials.By changing the metal content in the precursor,the doping amount of the metal in the finally obtained one-dimensional carbon nanocomposite was adjusted and the electrocatalytic performance was investigated.The specific research progress and results of this thesis are as follows:1.Fe/N-doped porous carbon nanofibers（Fe₃C@FeN@CNF）inlaid with Fe₃C/Fe nanoparticles are used as bifunctional electrocatalysts.The composite nanofibers coated with ZIF-8 and iron precursor were prepared by direct electrospinning,and Fe₃C@FeN@CNF was prepared by pyrolysis process.During the pyrolysis process,ZIF-8 is converted to nitrogen-doped porous carbon（NC）,the iron precursor is converted into randomly distributed graphitized layer-coated Fe₃C/Fe nanoparticles,and the surrounding N is coordinated to form Fe-Nx.Active site.Fe₃C@FeN@CNF exhibits high electrocatalytic activity and sTab.ility in oxygen reduction and oxygen evolution due to its unique one-dimensional porous structure and synergy between chemical components,even with commercial Pt/C catalysts.Comparable.The method of the present study is equally applicable to the preparation of other high performance metal doped MOF-based derivatized electrocatalysts.2.Preparation of Fe₃C/Co/N doped multi-structure carbon nanotubes（CNCo-5@Fe）.Firstly,PAN/M（Ac）₂（M=Zn,Co）nanofibers were prepared by electrospinning technology,which can be used as a carrier for providing metal elements or as a template for bimetallic organic framework（BMZIF）nanometers.The crystal grows on the surface of the fiber.Secondly,by immersing the electrospun fiber in a solution of2-methylimidazole,the metal ion in the fiber is reacted with 2-methylimidazole to synthesize a bimetallic organic framework（BMZIF）nanocrystal on the surface of the fiber,and then pass N,BMZIF-n nanotubes were prepared by etching with N-dimethylformamide（DMF）.Again,the BMZIF-n nanotubes were mixed with Fe-Phen（a complex of FeSO₄ and phenanthroline）to adsorb Fe-Phen on the surface of the nanotubes,and the dried BMZIF-n@Fe-Phen was prepared by freeze-drying technique.Finally,the Fe₃C/Co/N doped multi-structure carbon nanotubes（CNCo-5@Fe）were obtained by pyrolysis in a nitrogen atmosphere.Electrochemical test results show that the mesoporous tubular structure of CNCo-5@Fe exhibits better electrocatalytic activity,sTab.ility and methanol tolerance in alkaline medium,and even better than Pt/C catalyst.The high performance of the above CNCo-5@Fe can be attributed to the synergistic effect of the following factors,including a large number of uniformly distributed active sites（Fe₃C,Fe-Nx and Co-Nx）in the catalyst to improve the reactivity and large specific surface area energy.The active site is sufficiently contacted with the electrolyte,the degree of high graphitization can improve the conductivity of the material,and the one-dimensional tubular structure can improve the transport efficiency of the reactants and products.Therefore,the design introduced in this study hopes to provide guidance for the design and synthesis of other MOFs materials and their derivatives,not only in the field of energy storage,but also open up new opportunities in other frontier fields.