Preparationg Of MOF-derived Multi-leve Nanaomaterials Based On Etching Method And Application Of Supercapacitors

With the rapidly developing of science and technology,the quality and styles of human are greatly enhanced,accompanying the amount of energy demand are also increased,which pose serious environmental pollution issues and restrict the sustainable development of human society.The developing of clean and pollution-free renewable energy?solar,wind,water,biomass,etc.?to replace the fossils is considered to be the fundamental way to solve the energy and pollution crisis.However,due to the uneven distribution in space and in-time,renewable energy the large-scale application of clean energy is limited.Therefore,the research and development of fast and high-density energy storage devices present important research and application value.Super-capacitors?SCs?are a new type of energy storage device between traditional capacitors and rechargeable batteries.Compared with traditional capacitors,it display the following advantage:large capacity,high energy density,wide operating temperature range and extremely long service life.Compared with the battery,it possess the features of high power density and environment-friendly.It is well known that the electrode material is the key element for a supercapacitor.The transition metal-based nanomaterials are recognized as a powerful electrode materials to assemble high-energy-density supercapacitor devices because of their advantages of high theoretical capacitance.Metal-organic frameworks?MOFs?,a kinds of uniform porous three-dimensional network,construct by multi-dentate N/O-based organic ligands and inorganic metal ions or ion clusters via coordination bonds.Due to the advantages of diverse morphologies and structures,rich pore structures,highly dispersed metal centers,high order,and orientation,MOFs are an excellent precursor material for preparing electrode materials.In this paper,through an etching strategy,the organic ligands in MOFs are replaced by inorganic anions with strong coordination ability,a series of electrode materials with high active sites,high specific surface area and controllable morphology are obtained.The main research contents are as follows:1.In this chapter,using a layered Ni-MOF as precursor,a metaborate pillar-structure hierarchical?-Ni?OH?₂ material is successfully prepared through a controlled etching strategy.Firstly,the layered Ni-MOF precursor is prepared under solvothermal conditions,and then the metaborate pillar-structure hierarchical?-Ni?OH?₂ material is obtained by optimizing the amount of etching agent?Na₂B₄O₇·10H₂O?.Its unique pillar-structure hierarchical structure inherits the porous struture of their MOF parent and a large specific surface area(463 m² g^-1)is obtained,which provides abundant holes and channels for the rapid diffusion of the electrolyte and rich active sites for electrochemical reactions.Meanwhile,the unique pillar-supported?-Ni?OH?₂structure is robust to avoid the phase transfer reaction from?-Ni?OH?₂ to?-Ni?OH?₂during the charge/discharge process in strong alkaline electrolyte,which can provide deeply and durably faraday reaction.Unique pillar-supported?-Ni?OH?₂ structure as electrode material shows high specific capacity of 244.4 mAh g^-1(1760 F g^-1)at 1 A g^-1,excellent rate performance?53%?when the current density up to 10 A g^-1,and good cycle stability(capacity retention 61.1%after 10,000 cycles at 5 A g^-1).2.In this chapter,using a leaf-shape Ni-MOF as a precursor,an anion and cation co-doped hollow porous leaf-shape structure electrode material is successfully prepared by a controlled etching strategy under normal temperature conditions.Firstly,the leaf-shaped Ni-MOF precursor is prepared under normal temperature.And then,nickel element is introduced through the LDH?metal hydroxide?coating process.Finally,the anion and cation co-doped hollow porous leaf-shape nanosheets?Ni-Co/V?was formed through a NaVO₃ etching process which.The optimized Ni-Co/V-12-2nanosheet not only possesses cationic and anion double doping structure,but also presents hierarchical 3D hollow structure.This unique phase and structure can promote the diffusion of electrolyte and shorten the ion diffusion distance.Therefore,the prepared Ni-Co/V-12-2 nanosheets display high specific capacitance(1274 F g^-1 at1 A g^-1),excellent rate performance(maintaining 92.6%from 1 A g^-1 to 10 A g^-1),and excellent cycle life?93.14%after 5000 cycles?.In this chapter,using nickel foam?NF?is used as the substrate Co-MOF array is grown in the surface NF under liquid phase conditions to obtain Co-MOF@NF.Then,NiCo-LDH@NF is obtained by the LDH coating process.Finally,through a sodium metavanadate etching process,the ultra-thin nanomaterial grown on foamed nickel?NCV@NF?is obtained at room temperature..The obtained ultra-thin nanosheet materials are mutually branched to provide diffusion channel for electrons/ions.The structure and performance of NCV@NF-1,NCV@NF-5,NCV@NF-8,NCV@NF-10,NCV@NF-12 is analyzed and compared.The result demonstrate that the NCV@NF-10 electrode material present the best electrochemical performance.NCV@NF-10 electrode material shows a specific capacity of 1618 mAh cm^-2 at 1 mA cm^-2.When the current density increases to 30 mA cm^-2,the capacity retention rate can reach 77.13%,behaves an excellent rate performance.