Preparation Of Porphyrin-Based Conjugated Microporous Polymeric Carbonbased Catalysts And Their Cathodic Oxygen Reduction Performance

The cathodic oxygen reduction reaction（ORR）is one of the fundamental reactions for building fuel cells,and the development of high-performance and high-activity ORR catalysts is of great significance for next-generation fuel cells.Pt-based catalysts have excellent electrocatalytic activity and are currently the most used commercial ORR catalysts.However,Pt reserves are limited,it is a non-renewable resource and is susceptible to the influence of methanol and CO during the reaction process.The development of non-Pt-based catalysts with excellent performance has become an important research direction in this field.Carbon-based materials have the advantages of abundant sources,high porosity,durability,etc.They can be doped with heteroatoms in various ways to optimize their catalytic performance,making them an important constituent of non-Pt-based catalysts,which have received considerable attention.For carbon-based catalyst systems,differences in the type of carbon source and preparation methods usually lead to the preparation of catalysts with widely varying structures,chemical compositions,and heteroatom aggregation patterns,thus limiting their application in ORR.From a materials design perspective,the development of new,highly efficient carbon-based catalysts with adjustable structure and chemical composition and sample preparation methods is the way forward for ORR.Conjugated microporous polymers（CMPs）are an important branch of porous organic polymers with the advantages of a three-dimensional network structure extended by aπ-conjugated system,diverse synthetic routes,and adjustable structural and chemical composition.As an excellent carbon source for ORR catalysts,the rigid block units in their porous structure can avoid the collapse of the porous structure during high-temperature pyrolysis.In addition,the chemical composition of CMPs can be modified by changing the chemical composition of the block units,thus enabling the functional modification of heteroatoms in ORR catalysts.Based on the above analysis,in this thesis,hollow tubular and spherical CMPs were prepared by Sonogashira-Hagihara cross-coupling reaction using nitrogen-containing porphyrin molecules as the block units,and ORR catalysts with tubular and hollow spherical shapes were prepared using them as the carbon source.The main studies include.（1）N-CMP was prepared by Sonogashira-Hagihara cross-coupling reaction using m-tetra-（4-chlorophenyl）porphyrin and 1,3,5-triethynylbenzene as monomers,toluene and triethylamine as solvents and Pd（0）/Cu I as catalysts.N-CMP was used as the carbon source and Fe Cl₃ as the iron source,and the N-doped（N-CMP-x）and Fe,N co-doped（Fe/N-CMP-1000）carbon-based catalysts were prepared by pyrolysis under nitrogen atmosphere.The structural and chemical compositions of the catalysts were characterized by SEM and TEM,Raman,X-ray photoelectron spectroscopy,and isothermal adsorption and desorption of nitrogen.The results revealed that both N-CMP-x and Fe/N-CMP-1000 have hollow tubular morphology and porous structures.The ORR performance of the samples was tested using cyclic voltammetry and linear scanning voltammetry.The results showed that the synergistic effect of N and Fe atoms improved the ORR performance of the catalysts.Compared to commercial Pt/C catalysts,Fe/N-CMP-1000 has a higher onset potential（0.95 V）,half-wave potential（0.85 V）,and ultimate current density value(5.34 m A cm^-2),as well as good durability and methanol resistance.（2）Based on the study in the previous chapter,CMPs with hollow spherical structures（CMP-NP）were prepared using SiO₂ as a template,and m-tetra（4-chlorophenyl）porphyrin and 1,3,5-triethynylbenzene as monomers.The hollow spherical ORR catalysts（CMP-NP-x）were prepared by pyrolysis using CMP-NP as the carbon source.CMP-NP-x has a high specific surface area of(868-1118 m²g^-1).Of the CMP-NP-x samples,CMP-NP-900 had the highest specific surface area and N content,exhibiting the highest onset potential（0.930 V）and half-wave potential（0.852 V）.In addition,the hollow spherical CMPs-based catalysts exhibited superior ORR performance compared to the tubular carbon catalysts prepared under the same conditions.