Research On Modification And Electrochemical Performance Of Coal Based Activated Carbon

Supercapacitor is a new energy storage device which between conventionalcapacitor and battery, it has wide application prospect and huge economic value.Activated carbon is the first choice electrode materials for supercapacitor, its structureand properties play a key role to supercapacitor performance. However, energy densityof activated carbons for supercapacitors is lower. In order to improve theelectrochemical performance of activated carbons, activated carbons prepared fromIndonesian lignite by KOH as activation agent were modified by copper nitrate,manganese nitrate and ammonia solution, respectively. The specific surface area andpore size distribution of activated carbons before and after modification were studied bynitrogen adsorption at77K, the crystallite structure, surface morphology and functionalgroups of activated carbons were characterized by SEM,XRD and FTIR spectroscopy,respectively. Moreover, the electrochemical performance of activated carbon electrodeswere characterized by constant current charge-discharge, cyclic voltammograms andalternating current impedance. The pore structures and electrochemical performance ofactivated carbons modified by ammonia solution under atmospheric pressure and highpressure were investigated. Finally, activated carbons prepared from Indonesian ligniteand modified Indonesian lignite （by ammonia solution） were studied.The results indicated that the activated carbons could be loaded on a certainamount of metal oxide that were modified by copper nitrate, and manganese nitrate.Thespecific surface area and total pore volume of modified activated carbons weredecreased slightly, but the rate of mesopores increased, and improved the surfacewettability. The specific capacitance of modified activated carbons as electrodematerials is increased, specific capacitance from the original275F·g^-1were improved to323F·g^-1,341F·g^-1, respectively. The electrochemical performance such as alternatingcurrent impedance could be also improved.The results by investigating the activated carbon modified by ammonia solutionunder atmospheric pressure and high pressure are shown as following. Nitrogenfunctional groups were introduced on the carbon surface, but the specific surface areahad a little increase and the rate of mesopores had little decrease. Compared with ammonia solution modification under atmospheric pressure, more nitrogen functionalgroups were loaded on the surface of activated carbons under high pressuremodification, moreover, the electrochemical performance turned to be more excellent,the specific capacitance can reached to348F·g^-1.The residual specific capacitance ismore than98.9%after1000-cycles under the current density of42.5mA·g^-1.The content of N element and nitrogen functional groups of activated carbonsprepared by modified Indonesian lignite were more than that of the original activatedcarbons. Specific surface area and pore volume of modified carbons showed larger thanthe original carbon, but there is no obvious distinction on the rate of mespores.Theelectrochemical performance of modified carbons could be improved. The specificcapacitance of modified carbons could be as high as371F·g^-1, which is21%higher thanthat of unmodified carbons. Cyclic voltammetry curves of modified carbon electrodesshowed obvious redox peaks, which proved pseudocapacitances were generated in theprocess.