Controlled Synthesis Of Anion-Doped MOFs-Derived Nanomaterials And Their Supercapacitor Performance Study

It is well known that energy is the cornerstone of economic and social.Due to the shortcomings of non-renewable,limited reserves and high pollution,the traditional fossil energy can not meet the increasing energy demand of modern society.Therefore,the development of clean and renewable new energy technologies has become a worldwide consensus.However,the electric energy obtained by new energy technology commonly present intermittent and random,which cannot be directly connected to the grid.Meanwhile,the mobile electric energy storage device also faces challenges such as safety,cycle life and charging speed.Therefore,it is urgent to develop a safe and efficient energy storage device to promote the development of new energy technology.Supercapacitors are considered as one of the most promising energy storage technologies because of their long cycle life,fast charging speed and high security.Electrode material is the key to determine supercapacitor performance.How to design electrode materials with improved the active specific surface area,rapid ion mass transfer channel,and rich pore space to alleviate the volume effect in charging/discharging process has become a key research direction in recent years.Metal organic framework（MOFs）is an ideal precursor material for supercapacitor electrode due to its diverse composition and morphology,high specific surface area,design porous structure and suitable stability.In this paper,a series of MOFs derived cobalt-nickel based cathode materials are constructed by controllable mixed anionic etching strategy.These electrode materials effectively inherit the high specific surface area and rich pore structure of the precursor for enhanced specific surface area and electrolyte diffusion rate,and the doped anionic doping was used to improve the electronic structure of the materials,which is benefit for the achievement of significant performance enhancement.The main research contents include:1.Preparation of sub-nano sulfides functionalized layered double hydroxides and their supercapacitor performance study:Here,using ZIF-67 as precursor,the VO₃^-doped Co/Ni-LDH hollow nanocage is constructed by LDH coating and then OH^-and VO₃^-mixed etching strategy.Furthermore,through a VO₃^-induced S^2-anion-exchange process,（Ni/Co）_1-xS sub-nanoparticle functionalized VO₃^-doped Co/Ni-LDH hollow nanocages（S-CNV-LDH）are successfully prepared.The hierarchical hollow nanocage structure constructed by the（Ni/Co）_1-xS sub-nanoparticle-functionalized S-CNV-LDH nanoplates can provide rich channels,abundant heterojunction interfaces and enhanced conductivity for a fast and deep mass-transfer process.Therefore,the optimized S-CNV-LDH nanocages present a high specific capacitance of 1345 F g^-1 at 1 A g^-1 and an excellent rate capability of 84.6%at 10 A g^-1.Furthermore,an S-CNV-LDH//AC device is fabricated and a high energy density of 42.51 W h kg^-1 is achieved at 0.8 k W kg^-1.2.Preparation of Multi-shell amorphous Co/Ni-（PO4）x（OH）y hollow nanocages and their supercapacitor performance study:The multishell layer structure has stronger cyclic stability than the hollow structure because of the mutual support between the shell layers.Influenced by the above controlled etching process,Co/Ni-based hydroxide phosphate（CNHP）hollow polyhedrons with multiple-shell are synthesized by a cobalt-nickel layered double hydroxide（Co/Ni-LDH）coating and step-by-step phosphate etching strategy,using ZIF-67 dodecahedron as templates.Through rational controlling the LDH coating and Na₃PO₄ etching time,double shells Co/Ni-（PO₄）_x（OH）_yhollow polyhedron（DS-CNHP）and triple shells Co/Ni-（PO₄）_x（OH）_y hollow polyhedron（TS-CNHP）are successfully constructed.The as-obtained TS-CNHP presents a high specific capacitance of 1506 F g^-1 at 1 A g^-1.Furthermore,a hybrid TS-CNHP//AC supercapacitor device is fabricated,and a high energy density of 34.4 Wh·kg^-1 is achieved at the power density of 0.375 k W kg^-1.3.Preparation of double shell Co/Ni（CO3）（OH）microspheres and their supercapacitor performance study:In order to simplify the synthesis steps of multishell materials,cobalt-nickel-based hydroxide carbonate（CNHC）microspheres with a double-shell structure were synthesized by a one-step etching method.During the etching process,the metal ions released by the hydrolysis of MOFs will react with CO₃^2-and OH^-at the interface to form a self-supported shell layer by basic carbonate nanosheets.With the continuous etching,the cavity between the inner MOF core and outer shell layer is gradually larger,then a new self-supported inner shell basic carbonate nanosheets will be formed on the interface of MOF core,which produces the target double shells structure constructed by self-supported Co/Ni（CO₃）_x（OH）_y nanosheets.The unique structure can provide abundant channels and a large number of accessible active centers for enhanced electrochemical reaction kinetics.The optimized CNHC-12h electrode demonstrates a high specific capacitance of 1233.6 F g^-1 at 1 A g^-1 and outstanding ratio performance of maintaining 80%initial capacitance when the current density is expanded ten times.In addition,the as-fabricated CNHC-12h//AC device delivers a high energy density of 41.8Wh kg^-1 at 0.8 k W kg^-1 and can operate the thermometer normally for 20 min with 5 s charging time.4.Preparation of porous Co/Ni（PO4）（OH）microspheres and their supercapacitor performance study:Using Co Ni MOFs as substrates,the MOFs-derived Co Ni（PO₄）（OH）microspheres with extremely large specific surface area are constructed by a KOH and Na₃PO₄ simultaneous etching process.The organic ligand in MOFs will be in situ substituted by PO₄^3-and OH^-,which may well maintain the high surface area of MOFs parents,and the immigration and emigration of etching anions and released organic anions will provide rich channels for fast electrolyte diffusion.The optimized CNHP 2-3 electrode demonstrates a high specific capacitance of 1845.3 F g^-1 at 1 A g^-1and excellent ratio performance of keeping 85%initial capacitance when the current density is expanded ten times.In addition,an CNHP 2-3//AC device is fabricated and a high energy density of 50.9 Wh kg^-1 is achieved at 0.8 k W kg^-1.In this thesis,a series of anion-doped MOFs-derived micro and nano materials are synthesized by the anion-mixed etching strategy.The competitive etching of anions can regulate the pore and electronic structure of the products,which provides a path for the design and preparation of high performance supercapacitor electrode materials.