Studies On Preparation And Supercapacitive Behaviors Of Porous Carbon Obtained From Metal Framework

Electrochemical double layer capacitors （EDLCs）, are a new type of energystorage and conversion devices, which combine with many kinds of advantages fromtraditional capacitor and batteries/fuel cells. Due to possessing the advantages of highpower density, fast charge-discharge rate, and long cycle life, and so on, the deviceshave been applied to various fields such as telecommunication devices, portableelectronic devices, standby power systems and electric hybrid vehicles. It is wellknown that the key factor about the development of supercapacitors depends upon thedevelopment of the electrode material with high performance. Theoretically, the mostsuitable electrode materials for supercapacitors are the porous carbons which possesshigh specific surface areas. Therefore, in this study, the porous carbon materials withdifferent pore structure were prepared by using the metal organic frameworkcompound MOF-5as the carbon precursor or template. The preparation processes ofporous carbon materials were discussed, and the corresponding modification ofmaterials were also performed. The main results are as follows:Porous carbons （PCs） were prepared directly from a porous metal-organicframework （MOF-5） at different carbonized temperatures under Ar atmosphere. Theeffects of carbonized temperature on the morphology and performance wereinvestigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, N2adsorption-desorption, cyclic voltammetry （CV）, galvanostatic charge-discharge andso on. The results showed that PCs were porous carbon material with mainlymesoporous and partially graphitized structure. The optimal carbonized temperaturewas900℃and the sample （PC-900） had narrow pore size distribution （2-10nm） andthe specific surface area closed to1000m2g^-1. The specific capacitance of thePC-900supercapacitor was as high as60.4F g^-1at a current density of1A g^-1in6mol L-1KOH electrolyte and the loss of specific capacitance was nearly neglectable.after5000cycles.Porous carbon was directly prepared from pyrolysis of MOF-5at a carbonizationtemperature of900oC. The as-prepared sample was activated in concentrated nitricacid solution in order to gain highly activated porous carbon （APC-900）. Oxygenousfunctions on the surface of APC-900and PC-900were studied by fourier transforminfrared spectrometer （FI-IR） and the electrochemical performance of PC-900andAPC-900was investigated by electrochemical tests. The results showed that APC-900 had lower specific surface area and lower average pore size, and more oxygenousfunctions on the suface. Besides, APC-900had an excellent electrochemicalperformance. Its specific capacitance was as high as312.8F g^-1at a scan rate of1mVs^-1, but the specific capacitance of PC-900was only207.8F g^-1.The PC-F porous carbon were prepared by polymerizing and then carbonizingcarbon precursor of furfuryl alcohol accommodated in a porous metal-organicframework （MOF-5） template at a carbonization temperature of900oC. In order toimprove the surface structure and electrochemical performance of PC-F, theas-prepared PC-F was activated in16mol L-1HNO3to gain the highly activatedAPC-F. The physicical and electrochemical performances of PC-F and APC-F werecharacterized. It was found that the oxygen-enriched functional groups on the surfaceof the porous carbon material have obviously increased after HNO3activation andAPC-F showed an excellent electrochemical performance. The specific capacitance ofAPC-F reached317.2F g^-1at the scan rate of1mV s^-1.The APC-F was used as the electrode material of supercapacitor. The effects ofdifferent aqueous electrolyte on the electrochemical performance of supercapacitorwere discussed. It has been found that the supercapacitor in6mol L-1KOHelectrolyte exhibited the best electrochemical preporties. The specific capacitance upto77.0F g^-1was obtained at the current density of1A g^-1.