Preparation Of "Brick-and-mortar" 3D Porous Carbon And Its Energy Storage Properties

Porous carbons derived from metal-organic frameworks(MOFs)have attracted increasing attention as promising electrode materials for high-performance supercapacitors due to their versatile porous structure,moderate specific surface area,and multi-intersecting open channel system.Unfortunately,the partial breakdown of the frameworks could not be avoided during the carbonization process,resulting in the decreased conductivity of as-prepared porous carbons,thus limiting the rate performance for supercapacitors.In this thesis,the "brick-and-mortar" sandwich porous carbon building was prepared by solvothermal method.The microstructures and surface chemistry of the materials were characterized by X-ray diffraction,scanning and transition electron microscopy,Raman spectra and X-ray photoelectron spectroscopy.Cyclic voltammetry,galvanostatic charge-discharge method and electrochemical impedance method were further employed to investigate the electrochemical performance.The electrochemical energy storage mechanism and model were proposed.The research contents were illustrated in detail as follow:Firstly,the porous carbon materials were prepared by using graphene oxide,MOF-5 and graphene/MOF-5 as precursors,respectively.Furthermore,the effects of precursors on the structure and electrochemical properties of porous carbon materials were investigated.The results showed that graphene sheets not only improve the conductivity but also act as structural and conductive scaffolds to support porous carbon film,maintaining stable mesopore channels for ion transport and short paths for electron transfer.Thus,the as-obtained porous carbon(C-GMOF)displayed high specific capacitance and excellent rate performance.Even at 5 V/s,it showed high specific capacitance of 140 F/g.Secondly,the microstructure and electrochemical properties of the porous carbon materials were influenced by the content of graphene,the concentration of MOF-5 precursor and carbonization temperature.The results illustrated that the surface area and conductivity of porous carbon materials,which would influence the electrochemical performance of the material,were affected by the content of graphene.The electrochemical performance first increased and then decreased after reaching an optimum performance with the increase of the content of graphene and the concentration of MOF-5 precursor.With the increase of carbonization temperature,the conductivity is improved.But further increase of carbonization temperature would lead to the partial collapse of the pore structure.Thus the material showed an optimum capacity with the carbonization temperature 800 ?.Finally,the as-assembled symmetric supercapacitors were fabricated by using the optimized porous carbon materials,which delivered high power density,energy density and outstanding cycling stability.The assembled C-GMOF symmetric supercapacitors achieved high energy density of 10.6 Wh/kg at power density of 11.9 kW/kg and excellent cycling stability with 94%retention of its initial capacitance after 10,000 cycles.