Study On Preparation And Properties Of Carbon-based Electrode Materials Based On Metal-organic Frameworks

As one of the new energy storage devices, electrochemical capacitors have attractedgreat attention in many fields, due to its high power density, long cycling life,environmental-friendly and low maintenance cost. Electrode materials are the cores of theelectrochemical capacitors. Therefore, it is increasingly important to develop new electrodematerials for improving performance of electrochemical capacitors in the field of new energy.This thesis aims to prepare new electrode materials with low cost and high power density.Using metal-organic frameworks as precursors, various carbon-based electrode materialshave been prepared by different methods. Their morphologies and electrochemical capacitivebehaviors were investigated by various material characterization techniques andelectrochemical methods. The main points of this thesis are summarized as follows:(1) Nitrogen-doped mesoporous carbons (NMCs) have been synthesized by directcarbonization of zeolitic imidazolate frameworks-8(ZIF-8) nanopolyhedrons without anytemplate or pore-forming agent. The morphology and structure of NMCs were investigatedby scanning electron microscopy (SEM), transmission electron microscopy (TEM), Ramanspectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface areaand pore size analyzer. The electrochemical capacitive behavior of NMCs was investigatedby cyclic voltammetry (CV) and choronopotentionetry in1M H2SO4aqueous solution.Results show that the specific surface area of NMCs is up to2737m2g-1. The average size ofNMCs is ca.200nm. The pore volume of mesoporous (2~50nm) is about74.1%of the totalpore volume. NMCs have high specific capacitance (307F g-1at1A g-1) and excellent powerproperty (only25.4%decrease and the linearly denpendent coefficient (R) is as high as0.9998with the increase of scan rate from10to1000mV s-1). In addition, NMCs alsopossess good long-term cycle stability (the specific capacitance remains96.9%of the initialvalue after5000cycles even at a high loading current density of10A g-1).(2) Slice γ-MnO2/NMCs-11compound (MCs) have been prepared via in situ synthesisof slice γ-MnO2on the surface of NMCs-11based on C-KMnO4reaction. The morphologyand structure of MCs were investigated by SEM, TEM, XRD and surface area and pore sizeanalyzer. The electrochemical capacitive behavior of MCs was investigated by CV andchoronopotentionetry in0.1M Na2SO4aqueous solution. Results show that slice γ-MnO2grows radially on the surface of NMCs-11. The average size of MCs is in the range of600~700nm. The specific surface area of MCs is121.70m2g-1and the average pore size isca.7.64nm. MCs have high specific capacitance (270.8F g-1at0.1A g-1) and excellent power property (the specific capacitance retention is67.3%and the linearly denpendentcoefficient (R) is0.9942with the increase of scan rate from1to20mV s-1). In addition, thespecific capacitance remains56.7%of the initial value after800cycles at the scan rate of20mV s-1.(3) Nitrogen-doped bamboo-like carbon tubes (NBCs) have been prepared by directcarbonization of Zn-Fe-ZIFs under a high temperature nitrogen atmosphere. The morphologyand structure of NBCs were investigated by SEM, TEM, XRD and surface area and pore sizeanalyzer. The electrochemical capacitive behavior of NBCs was investigated by CV andchoronopotentionetry in1M H2SO4aqueous solution. Results show that NBCs isbamboo-liked multi-walled carbon tubes with both open ends. The average diameter of NBCsis in the range of30~100nm with wall thickness of ca.17nm. The specific surface area ofNBCs is up to605m2g-1, its total pore volume is0.64cm3g-1and its pore size distribution ismainly concentrated in the range from3.7to45nm. NBCs have excellent power property(the specific capacitance retention is80.5%and the linearly denpendent coefficient (R) is ashigh as0.9972with the increase of scan rate from5to100mV s-1). And NBCs also have highspecific capacitance (296F g-1at1A g-1). In addition, NBCs have excellent long-term cyclestability (only6.3%decrease after2000cycles even at a high loading current density of5Ag-1).