Study On Preparation Of Multimetallic Layered Double Hydroxides And Their Supercapacitive Properties

In recent decades,the excessive use of traditional energy(such as fossil fuels,coal,etc.)has caused climate change and environmental pollution.These effects have raised people’s awareness of environmental protection and promoted the development of green energy.Among them,electrochemical energy devices such as rechargeable batteries,supercapacitors and electrocatalytic hydrogen production technology are outstanding.As an important power storage device,supercapacitors(SCs)have the advantages of high power density,long cycle stability and safety compared with other energy storage devices,and have great potential applications.The performance of energy storage devices of supercapacitors mostly depends on the electrode materials.Layered double hydroxides(LDHs)are considered to be excellent electrode materials for supercapacitors because of their structural stability and high theoretical specific capacitance during charge and discharge.On the other hand,Metal-organic framework(MOF)is a kind of important functional materials with highly porous structure.The LDHs materials prepared with MOF as precursors and self-sacrificing templates can inherit the special morphology and high porosity of MOF,which provides a new way to obtain supercapacitor electrode materials with excellent electrochemical supercapacitance performance.In this thesis,the electrode materials of morphology-controllable LDHs were prepared for electrochemical supercapacitor by ion exchange using MOF as precursor and self-sacrificing template,and the corresponding electrochemical capacitance performance is investigated.The specific work is as follows:(1)Zinc-Cobalt-Nickel layered double hydroxide(ZCN-LDH)was prepared by ion exchange using the Zinc-Cobalt zeolite imidazole framework(ZnCo-ZIF)dodecahedral cube as the precursor and the self-sacrificing template,and were investigated for the supercapacitor performance.The morphology,structure,element composition,valence and porosity of the samples were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffractometry(XRD),X-ray photoelectron spectroscopy(XPS)and automatic micropore physical adsorption analyzer.In addition,the electrochemical performance of ZCN-LDH in 3 M KOH electrolyte were investigated by cyclic voltammetry,galvanostatic charge-discharge method,electrochemical impedance spectroscopy and cyclic stability tests.The results show that the prepared ZCN-LDH electrode material has a layered structure with a specific surface area of about 239.0 m2 g-1.The capacitance of ZCN-LDH is 1475.6 F g-1 at the current density of 1 A g-1 and maintains a rate performance of 69.5%at 20 A g-1.After 10000 cycles of charge and discharge process,the capacitance retention is 85.3%.The asymmetric supercapacitor device assembled with ZCN-LDH electrode as positive electrode and activated carbon electrode as negative electrode exhibits an energy density of 77.0 Wh kg-1 at a power density of 807 W kg-1,which can maintain a capacity of 90.1%after 5000 cycles.(2)Nickel-manganese-layered double hydroxide(NiMn-LDH)was prepared by ion exchange under alkaline hydrothermal conditions taking nickel-manganese metal-organic framework(NiMn-MOF)as the precursor and self-sacrificing template,and were investigated for the supercapacitor performance.The morphology,structure,element composition and valence of the prepared samples were studied by SEM,XRD,XPS and BET.In addition,the electrochemical performance of NiMn-LDH in 3 M KOH electrolyte was tested by cyclic voltammetry,galvanostatic charge-discharge method,electrochemical impedance spectroscopy and cyclic stability test.The results show that NiMn-LDH has a high specific capacitance of 1382.2 F g-1 at the current density of 1 A g’1.After 5000 cycles of charge and discharge process,the capacitance retention is 91.2%.The asymmetric supercapacitor device assembled with NiMn-LDH electrode as positive electrode and activated carbon electrode as negative electrode displays an energy density of 70.8 Wh kg-1 at a power density of 750.6 W kg-1,and can maintain the energy density of 47.9 Wh Kg-1 even at a high power density of 7493.2 W kg-1,implying the excellent rate performance.