Research On Preparation And Capacitance Performances Of Metal-organic Framework Materials And Their Derivatives

The demand for clean,efficient and sustainable energy continues to rapidly increase due to the rapid development of economies,the excessive consumption of fossil fuels and the increasing deterioration of environment.Among electrochemical energy storage technologies,supercapacitor has a wide application prospect on account of its remarkable characteristics,including higher power density,fast charge/discharge ability,long life and environmental friendiness.It is very important to prepare electrode materials with abundant porosity and high electrochemical activity.Metal-organic frameworks?MOFs?are a category of porous crystalline material composed of organic ligand and metal center.Due to the characteristics of adjustable apertures,diverse structures and large accessible surface areas,MOFs have attracted widespread attention in a large number of fields,including energy storage,catalysis,adsorption and sensor.For supercapacitor,MOFs are used as versatile sacrificial templates for the preparation of various porous carbons,metal compounds and their composite materials,showing satisfactory electrochemical performance.In addition,because of massive redox centers and high porosity,the original MOFs also exhibit favorable electrochemical performance.In this thesis,a series of MOFs and their derivatives have been prepared by simple solvothermal method,chemical precipitation method or hydrothermal method and are used as electrode materials to research their electrochemical performance.The main contents of thesis are as follows:?1?Bi-MOF materials have been prepared using one-pot solvothermal method.The composition and morphology of Bi-MOF materials are adjusted via altering the molar ratio between Bi³⁺and trimesic acid.When the molar ratio between Bi³⁺and trimesic acid is adjusted to 2:1,three-dimensional hierarchical Bi-MOF microsphere?labeled as BM-2?composed of numerous interconnected thin nanosheets are obtained.This material possesses large specific surface area(69.5 m² g^-1)and suitable pore size distribution?6.43nm?,which shortens the diffusion pathway of electrolyte ions and offers massive reaction electroactive sites.The results show that BM-2 based electrode delivers a high specific capacitance of 896.1 F g^-1 at 0.50 A g^-1,remarkable rate capability(85.7%retention at 5.0 A g^-1)and favorable cycling stability(71.2%capacitance retention at 2.0 A g^-1 after 2000cycles),which are superior to other contrastive materials.?2?ZIF-8 precursor is prepared by chemical precipitation method using zinc nitrate and di-methylimidazole as raw materials.Then,it is directly in situ selenized to form zinc-nickel selenide,followed by adding nickel nitrate for hydrothermal reaction to obtain a novel Zn-Ni-Se/Ni?OH?₂ hierarchical microflower material composed of corrugated nanosheets.The loosely packed structure provides ample channels for ion transport and improves the structural stability of materials.Compared with Zn-Ni-Se and Ni?OH?₂ based electrodes,the resultant Zn-Ni-Se/Ni?OH?₂ based electrode exhibits markedly enhanced electrochemical properties with a specific capacitance of 1632.8 F g^-1 at 2.0 A g^-1 and superior cycling stability(85.4%of the initial retention after 2000 cycles at 6.0 A g^-1),indicating that the combination of multiple components can promote the electrochemical performance of materials.?3?A series of Ni/Ga-MOF materials have been prepared with one-pot hydrothermal method via adjusting the molar ratio between gallium nitrate and nickel nitrate.According to the results of FE-SEM analysis,the different molar ratios of gallium nitrate and nickel nitrate have obvious influence on the morphology of Ni/Ga-MOF materials.Compared to NM material with thicker lamellar structure and GM material with bulk structure,as-prepared NGM-2 material exhibits an ultrathin tremella-like morphology,which is prone to expose more electroactive sites.The results show that the specific capacitance of Ni/Ga-MOF based electrodes increases firstly and decreases later during the molar ratio of Ni:Ga changing from 10:0 to 0:10.When the molar ratio of Ni:Ga is 3:7,as-obtained NGM-2based electrode shows the highest specific capacitance of 1108.8 F g^-1 at a current density of0.50 A g^-1,superior rate capability(approximately 83.4%of initial capacitance at a current density of 7.0 A g^-1)and favorable cycling stability(77.5%of the initial retention after 2000cycles at 2.0 A g^-1),which are superior to other contrastive materials.?4?Based on the 3D structure of Ni foam,CoMn-LDH/CoMoS_x nanocomposites have been prepared in situ by chemical precipitation and hydrothermal method.For comparison,CoMn-LDH and CoMoS_x nanomaterials with single component are prepared.According to the results of FE-SEM analysis,the loose porous CoMoS_x nanoparticles grow uniformly on the surface of CoMn-LDH nanosheets.This unique structure effectively avoids the aggregation of CoMoS_x nanoparticles and increases the reactive sites.Compared with CoMn-LDH and CoMoS_x based electrodes,as-prepared CoMn-LDH/CoMoS_x based electrode exhibits markedly enhanced electrochemical properties with a specific capacitance of 1786.3 F g^-1 at 2.0 A g^-1,excellent rate capability(approximately 88.1%of initial capacitance at 10.0 A g^-1)and and superior cycling stability(85.2%of the initial retention after 2000 cycles at 6.0 A g^-1),which is attributed to the synergistic effect of CoMn-LDH and CoMoS_x materials and the unique structure of nanocomposites.In summary,a series of MOFs and their derivatives have been synthesized by simple preparation method in this thesis.The electrochemical tests show that Bi-MOF microsphere,Zn-Ni-Se/Ni?OH?₂ microflower,tremella-like Ni/Ga-MOF materials and CoMn-LDH/CoMoS_x nanocomposites show excellent capacitive behavior,demonstrating that as-prepared MOFs and their derivatives are a class of promising materlais for supercapacitor.