Preparation Of Metal-organic Framework Derivatives And Its Application In Supercapacitors

Supercapacitors(also known as electrochemical capacitors)as a new type of energy storage devices,with high power density,high charge-discharge efficiency and good cycle stability,plays an irreplaceable role in urban transportation,high-speed emu trains,cranes,electronic and electrical equipment,wind and solar power generation,military aerospace and other areas requiring high power output.However,the low energy density compared with batteries has been an important factor restricting the further development of supercapacitors.According to the energy density(E)calculation formula:E=1/2CV² for the supercapacitors,improving the specific capacitance(C)of the electrode and broadening the potential window(V)of the device can increase the energy density of the supercapacitor effectively.As the core component of the supercapacitors,the electrode material has a crucial influence on the improving specific capacitance and widening potential window.In this work,metal organic frameworks(MOFs)with 3D pore structure,cyclical mesh skeleton structure and 3D space outspread were used as precursors to synthesis corresponding derivatives that used as electrode materials for supercapacitors by high temperature controllable calcination process.By regulating the components and structures of derivatives,the mechanism and characteristics of energy storage in the field of supercapacitors are studied to improve the energy density by increasing their specific capacitance and potential window.This work provides experimental basis for the development of a supercapacitor assembled by MOFs derivatives.The main research contents and results of this work are as follows:1.Preparation of carbon-doped Co₃O₄/Fe₂O₃ metal oxide with positive and negative electrode response and study on the performances of supercapacitorsCo₃O₄ and Fe₂O₃is a typical positive electrode and negative electrode material of the supercapacitor,respectively.The Co₃O₄/Fe₂O₃ metal oxide by controllable calcination Co₃[Fe(CN)₆]₂·10H₂O in air is prepared in this work.Because of the particularity of component,the material can be used as positive and negative electrode for supercapacitor simultaneously,and the carbon doping can improve the electrical conductivity of the electrode effectively.When used as positive electrode Co₃O₄ is the active component,and it‘s specific capacitance can achieve 312 A g^-1at the current density of 1 A g^-1;When used as negative electrode,Fe₂O₃ is the active component,and it‘s specific capacitance can achieve 267 F g^-1 at the current density of 1 A g^-1.In addition,the energy storage mechanism and capacitance contribution distribution of Co₃O₄/Fe₂O₃ as positive electrode and negative electrode are discussed respectively.The results show that the capacitance value of Co₃O₄ is largely controlled by the surface capacitance contribution,while Fe₂O₃ is largely controlled by the diffusion process under the same sweep speed.Finally,the obtained Co₃O₄/Fe₂O₃ mixed metal oxides were used as positive and negative electrodes respectively,with KOH as electrolyte to assemble a 1.5 V aqueous supercapacitor,and the energy density is 35.15 Wh kg^-1 at the power density of 1125 W kg^-1.2.Preparation of electrode materials with charge matching and research on high energy density supercapacitors.In this work,two kinds of metal-organic framework(MOF)derivatives,concave surface Ni O/Co₃O₄ microcubes and Fe₂O₃ microleaves are prepared via contrllable thermal treatment.The concave surface Ni O/Co₃O₄ microcubes exhibited a specific capacitance of 430 F g^-1 at 0?0.5 V,and the Fe₂O₃ microleaves exhibited a specific capacitance of 328 F g^-1 at-0.9?0 V.By calculation,it is found that their charges is matching,and when the mass ratio of the positive and negative electrodes is 1:1.37,the same positive and negative charge can be provided,and assembled into electrochemical capacitors,which deliver a relatively high specific energy density of 46 Wh kg^-1 at 690W kg^-1.In addition,a solar-charging power system consisting of the electrochemical capacitors and monocrystalline silicon plates is fabricated and a motor fan or 25 LEDs is powered for 5 and 30 min,respectively.This work not only adds two novel materials to the growing categories of MOF-derived advanced materials,but also successfully achieves an efficient solar-supercapacitors system for the first time based on all MOF derivatives,which has a certain reference for developing efficient solar-charge systems.3.Preparation of wide-potential window layered potassium manganate positive electrode material and research on high energy density supercapacitors.Zeolitic imidazolate framework-67(ZIF-67)was used as a precursor to prepare nanoporous carbon,and K_0.5Mn₂O₄ nanosheets were subsequently grown on the nanoporous carbon surface through a facile in situ redox process(denoted as C@K_0.5Mn₂O₄).The electrode potential window of C@K_0.5Mn₂O₄ was extended to 0?1.2 V,and the as-prepared C@K_0.5Mn₂O₄ and nanoporous carbon were used as the positive and negative electrode to assemble a 2.4 V aqueous supercapacitors,which is higher than that of most reported aqueous supercapacitors.Benefitting from the wide voltage wiondow that the as-asscembled supecapacitors exhibited a large energy density of 60 Wh kg^-1 at a power density of 1200 W kg^-1 and excellent rate performance(41 Wh kg^-1 even at a specific power density of 12.3 W kg^-1)as well as good cycling stability(92.6%capacitance retention over 10000 cycles at 10 A g^-1).This work successfully assembled a high energy density supercapacitor with a 2.4v high voltage window,which is of great significance to further practical application of the supercapacitor.4.Preparation of high specific capacitance cobalt sulfide positive electrode material and research on high energy density supercapacitors.Co₃O₄(HCON)and porous carbon nanoctahedron(NC)were prepared by controlled calcination of the precursor ZIF-67 in air and nitrogen atmosphere,respectively,and further hydrothermal reaction vulcanized Co₃O₄ to obtain Co S(HCSN)nanoctahedron.A series of electrochemical tests showed that the electrochemical performance of HCSN was better than that of HCON,and then,the reasons for the electrochemical performance improvement after sulfuration were analyzed from physicochemical properties,energy storage mechanism and conductivity.Finally,an aqueous supercapacitors with 1.6 V voltage windows was assembled by using the NC as negative electrode,HCSN as positive electrode and KOH as electrolyte.Due to the high specific capacitance of HCSN,the energy density of HCSN//NC devices is up to 80 Wh kg^-1.This work proves that increasing the specific capacitance of a single electrode can effectively improve the overall energy density of the supercapacitor,which provides an experimental basis for the further development of the high energy density supercapacitor.