Synthesis Of Cobalt-based MOF And Their Derived Metal Oxides And Performance Study Of Supercapacitors

For the last few decades,due to the frequent occurrence of various natural disasters,the residents of the world have become increasingly conscious of the ecological crisis,and the problem of environmental pollution has become a major event for people all over the world.The use of fossil fuels is the biggest source of responsibility for environmental pollution and harmful gas emissions,and the best way to solve fossil energy problems is to explore new energy sources and develop new energy storage methods.Earlier,the battery has been booming due to its high energy storage capacity,but the low power density makes the existing battery production process can no longer meet the needs of modern society.The advantages of high power density and long cycle life of the novel supercapacitors(SCs)have surpassed batteries and become a new hot research object in the energy storage industry.During the electrode reaction of SCs,the transportation and storage of electrons occur in the electrolyte on or near the electrode material.Therefore,the microstructure of the electrode material is a key factor that affects the performance of the device.The metal-organic framework material has the characteristics of simple synthesis method,high porosity,large specific surface area,neat and ordered internal structure,etc.It has broad application prospect in the field of electrochemical energy storage.For the physical and chemical characteristics of MOF materials with poor conductivity and low thermal stability,they can be further derivatized under certain conditions to obtain many multi-level micro-nano-structure materials with different functions,including metal oxides and metals Sulfides,carbon materials and various composites,etc.These derivatives and MOF itself have huge application prospects in the field of electrochemical energy storage.In this thesis,solvothermal method and high-temperature calcination decomposition method are used,with Co2+as the metal source,doped with Mn2+with multi-stage redox reaction,and using different organic ligands,single-metal cobalt-based metal organic framework materials(Co-MOF-74),bimetallic cobalt/manganese zeolite imidazolate framework material(Co/Mn-ZIF)and tricobalt tetroxide(Co3O4)and cobalt manganese oxide(MnCo2O4.5)calcined at different temperatures The performance of supercapacitors of series materials was studied.It includes the following three parts:1.Through simple solvothermal method,Co(CH3COO)2·4H2O and 2,5-dihydroxyterephthalic acid were reacted to prepare unique micro-nano-scale flower-like Co-MOF-74,and explored different solvent The effect of product morphology.The resulting material showed a specific capacity of 164.2 F g-1 at 0.5 A g-1 in 3 mol L-1 KOH electrolyte.When the current density is fixed to 10 A g-1 and the charge and discharge process is repeated 1500 times,the retention rate of 75%can still be achieved,which is better than many similar reports.When assembled with commercial activated carbon to form a hybrid supercapacitor,the hybrid supercapacitor can reach 64-1 Wh kg-1 and 1080 W kg-1.Adjusting the channel distribution helps to improve the electronic storage of the materialstorage performance.2.Under stirring conditions,add Co(NO3)2·6H2O and MnCl2·4H2O to the 2-methylimidazole solution at the same time to make it grow competitively.The resulting material showed a specific capacity of 926.25 F g-1 at 0.5 A g-1 in 3 mol L-1 KOH electrolyte.After fixing the 10 A g-1 test conditions and repeating the 1500 charge and discharge process,the capacity can still retain 64%,and the performance is in the absolute middle and upstream of similar materials.When assembled into a hybrid supercapacitor,a high energy density of 52.95 Wh kg-1 can be achieved at 1080 W kg-1.The introduction of multi-stage redox reactions can be used as an important experience to improve the conductivity of electrode materials.3.Through high-temperature calcination,Co-MOF-74 and Co/Mn-ZIF were selected as sacrificial templates,and metal oxides were derived under an oxygen atmosphere.Electrochemical tests show that the composites with hollow structure obtained by calcination at 400? have the best electrochemical performance because of their good crystallinity and special hollow structure,which promotes the charge transfer at the catalytic interface and is beneficial to proton transport.