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Fabrication And Electrochemical Performance Of Single Crystalline Macroporous Metal Organic Frameworks And Their Derivative Carbon Materials

Posted on:2023-04-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q LiFull Text:PDF
GTID:1521307172453714Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Metal-organic frameworks(MOFs)is a kind of organic-inorganic hybrid material with through-hole pores and highly tunable topology,and their derived carbon materials have received extensive attention in wild fields such as matter separation and transport,energy storage and conversion,and sensing,etc.The pore size of MOFs is usually less than 2 nm,which limits the rapid diffusion.Introducing macroporous(≥50 nm)structures into MOFs can significantly improve the material transfer efficiency.However,macroporous MOFs usually are polycrystalline blocks or amorphous with unavoidable defects,which inhibits the performance of macroporous structure.Fabrication of structurally stable single crystalline macroporous MOFs remains challenging.In this paper,a variety of single crystalline macroporous MOFs were synthesized based on the monodentate ligands method and deprotonation-controlled crystallization process.The methods of fabrication,the mechanism of crystallization and performance of their derived carbon materials for supercapacitors and water electrolysis catalysts was investigated.A method of sodium formate monodentate ligand to control the in-situ crystallization process of metal ions and ligands inside the sacrificial template of PS(polystyrene)spheres was proposed,and the single crystalline macropores of metal carboxylates MOFs HKUST-1were synthesized for the first time.Fabrication by reducing the p H value to inhibit the crystallization of MOFs was proposed.After the metal ions and ligands penetrated into the PS template,the crystallization of MOFs was induced by using a dual-solvents,and the polymetallic(included Zn,Co,Ni,Cu)zeolite imidazolate single crystalline macroporous MOFs was synthesized.The synthesis mechanism of single crystalline macroporous MOFs was analyzed,and the theoretical mechanisms of“deprotonation process regulating MOFs crystallization”and“limited space growth model”were proposed.The hydrolysis process of the monodentate ligands can deprotonate the ligands,triggering the rapid in-situ crystallization of the metal ions and the ligands.While reducing the p H value of the system can inhibit the deprotonation process of the ligands,so that in the system of multiple metal ions,spontaneous crystallization outside the template can be impressed,the metal ions and ligands can be immersed into the interior of the template and induce in-situ crystallization through double-solvents method.The PS spheres template not only shaped the macroporous structure of MOFs,but also can control the directional transport of metal ions and ligands during crystallization by the confinement of its inner space,resulting in the oriented growth of crystal planes.This‘limited space growth model’explained the formation process of the unique tetrahedral structure of macroporous MOFs and provided a theoretical reference for the synthesis of crystalline materials with similar structures.By carbonizing single crystalline macroporous MOFs,ordered macroporous carbon materials with better electrical conductivity were obtained.The single crystalline macroporous HKUST-1 derived IM-HPC has high structural stability,and its macroporous structure improves the material diffusion efficiency.It reaches 214 F g-1,which is 82.9%higher than the traditional HKUST-1-derived MPC and has obvious advantages in rate performance and material durability at high current density.The cobalt-nickel/nitrogen-carbon composite Co Ni@IM-HPC was derived from polymetallic single crystalline macroporous MOFs as a catalyst for hydrogen evolution in water electrolysis.The overpotentials at current densities of10 m A cm-2 in acidic and alkaline environments were 62 and 92 m V respectively,and it also has a good cycle stability.
Keywords/Search Tags:Metal-organic frameworks, Hierarchical porous structures, Ordered macroporous MOFs, MOFs synthesis, Hierarchical porous carbon materials, Supercapacitors, Electrochemical water splitting
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