Preparation And Electrocatalytic Properties Of Transition Metal-based Catalysts Derived From MOFs

An effective way to solve the problems of air pollution and global warming caused by the consumption of fossil fuels is to explore and develop clean and renewable energy.Electrochemical energy conversion and storage devices such as electrolytic water and metal-air batteries have been widely studied due to their excellent conversion efficiency,high energy capacity,and low environmental impact.These energy conversion technologies are based on key electrochemical reaction processes,including oxygen evolution reaction,hydrogen evolution reaction and oxygen reduction reaction.Currently,most reactions use noble metal（Pt,Ru/Ir）-based materials as catalysts,whose high price and scarcity significantly inhibit their large-scale integration with commercial renewable energy technologies.Metal organic frameworks have been proven to be promising self sacrificial templates and precursors for the preparation of various metal oxides and transition metal phosphides due to their high specific surface area,large pore volume,and extraordinary tunability in structure.Compared with other catalytic materials,Metal organic framework derived non noble metal matrix composite show unique advantages in morphology,multi pore and other aspects,and can easily be functionalized with other heterogeneous elements and metal/metal oxides.These characteristics make them show great advantages in the field of electrocatalysis.In this perspective,this thesis focuses on the design,preparation and catalytic properties of transition metal based composite catalysts derived from metal organic frameworks（Fe,Co,Ni）.The concrete contents of the study are as follows:1.Ethylenediaminetetraacetic dianhydride modified Co-BDC-NH₂ MOF chelated nickel ions and derivatized for electrocatalytic oxygen evolution reactionCo-MOF-EDTA was prepared by covalence of ethylenediaminetetraacetic dianhydride with strong metal chelating group to MOF using Co-BDC-NH₂ as precursor,Co-MOF-EDTA material was used to chelate the metal nickel ions in water to obtain Co-MOF-EDTA-Ni.Ni O/Ni Co₂O₄@NC heterojunction composites were obtained after calcination under nitrogen atmosphere,and used as catalysts for electrocatalytic oxygen evolution reaction.The experimental results show that Ni O/Ni Co₂O₄@NC exhibits good oxygen evolution reaction activity in 1 M potassium hydroxide,and its overpotential is only 305 m V at a current density of 10 m A cm^-2,and the Tafel slope is small and the stability is good.The Ni O/Ni Co₂O₄@NC heterojunction composite fully utilizes the advantages of Ni O and spinel Ni Co₂O₄ structure,which is conducive to electron transport and further enhances the activity of the catalyst surface.2.Ethylenediaminetetraacetic dianhydride covalently modified MIL-101-NH₂（Fe）MOF as an efficient adsorbent to recover waste heavy metal ions and derivate into an efficient bifunctional electrocatalystMetal-organic framework materials have enormous potential in the field of environmental adsorption due to their large surface area,high porosity,and functionalizability.Using ethylenediaminetetraacetic dianhydride with strong metal chelating ability to covalently attached to MIL-101-NH₂（Fe）,significantly improves the removal rate of heavy metal ions in wastewater.Meanwhile,the recovered waste metal ions are transformed into high-performance Fe Ni₃/Ni Fe₂O₄@NC dual-functional oxygen evolution reaction and oxygen reduction reaction catalysts.Density functional theory calculations reveal that the synergistic effect of the Fe Ni₃/Ni Fe₂O₄@NC heterostructure can enhance conductivity,optimize the free energy of*to OH*during oxygen evolution reaction reaction,and promote catalytic reactivity.This work not only improved the removal rate of heavy metal ions but also obtained high-performance bifunctiona catalysts,providing a new approach for the secondary recovery and utilization of heavy metal ions in wastewater and the preparation of low-cost catalysts.3.Preparation of cytosine-terephthalic acid double-ligand MOF and study on the electrocatalytic performance of its derivatives for water crackingUsing the"synergistic"strategy of cytosine and terephthalic acid,a double-ligand Co-MOF was prepared.Taking advantage of the fact that cytosine molecules contain more nitrogen,N and P co-doped Co P@NC electrocatalysts were successfully obtained after phosphating derivatization.The experimental results indicate that the Co P@NC catalyst exhibits excellent performance in both oxygen evolution reaction and hydrogen evolution reaction.In 1 M KOH electrolyte,at a current density of 10 m A cm^-2,the corresponding overpotential for oxygen evolution reaction and hydrogen evolution reaction are 290 m V and190 m V,respectively.The Tafel slopes are 77.2 m V dec^-1 and 44.1 m V dec^-1,respectively,and it exhibits good cycling stability and durability.The excellent electrocatalytic performance is attributed to the co-doping of N and P,which increases the active sites thereby improving the catalytic activity.This doping can also promote the electron transfer speed in the electrolyte,thus making the reaction faster and maintaining a good electrochemical stability.