Preparation And Electrochemical Performance Of Porous Nano Carbons For Supercapacitor

Supercapacitor has the characteristics of high power density, long cycle life, wide operation temperature range, etc. Supercapacitor has wide applications in the fields of transportation, communication, etc. Its overall performance is mainly determined by the electrode materials and the type of electrolyte. Porous nano-cage carbon(PNC), mesoporous nano carbon(MNC) and shell-like porous graphene(SPG) were prepared and investigated as electrode materials of supercapacitor in this paper. The structure and surface morphology of porous carbons(PCs) were characterized and analyzed by nitrogen adsorption-desorption, scanning electron microscopy, X-ray diffraction, etc. The electrochemical performance of carbon-based electrodes was evaluated by using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The main conclusions are as follows:PNCs were prepared rapidly from metal-organic framework(MOF-5) by KOH activation under 600 W of microwave power at 20 min of activation time. The average pore size and the total volume increases from 1.94 nm to 4.88 nm and from 0.39 cm3/g to 1.52 cm3/g with the increase of the mass ratio of MOF-5/KOH, respectively. The specific surface area of PNCs rises from 798 m2/g to 1595 m2/g, then drops to 1247 m2/g. The specific capacitance retention of PNC13.5-4.5 electrode remains at 83% in 6 M KOH electrolyte when the current density increases from 0.05 A/g to 20 A/g, showing excellent rate performance. The PNC14.4-3.6 exhibits an extremely high energy density of 64.88 Wh/kg in BMIMPF6 ionic liquid electrolyte. Several kinds of MNCs were prepared via adding coal tar pitch(CTP) as additional carbon source to the reactants of MOF-5 and KOH by conventional heating under vaccum conditions on the basis of the above results. The average pore size and the total volume of MNCs increase from 2.82 nm to 5.02 nm and from 0.7 cm3/g to 1.08 cm3/g as the mass of CTP from 0 g up to 4 g, repectively, with the specific surface area of MNCs decreasing from 1219 m2/g to 860 m2/g. But, it shows the opposite results when the mass of CTP continuously increases. In 6 M KOH electrolyte, the specific capacitance of MNC4-8-6 decreases from 242 F/g to 194 F/g with an 80.2% retention when the current density increases from 0.05 A/g to 20 A/g, showing good rate performance.SPGs were synthesized from CTP using nano-ZnO as directed template to form core coupled with KOH activation by conventional heating. The average pore size, specific surface area and the total volume of SPG4.2-16.8-6 reach 2.57 nm, 1862 m2/g and 1.19 cm3/g, respectively. While for SPG4.2-16.8-6-AP, it is 1.82 nm, 1985 m2/g and 0.9 cm3/g. When the current density increases from 0.05 A/g to 20 A/g, the specific capacitance of SPG4.2-16.8-6 drops from 230 F/g to 178 F/g with 77.4% retention, showing good rate performance too. The SPG4.2-16.8-6 electrode shows high cycle stability with capacitance retention of 97.7% at 1 A/g after 1000 charge-discharge cycles.