Dual-alkali Activation Methods For The Preparation Of Porous Carbons For Supercapacitors

Coal tar, anthracene oil and petroleum asphalt may function as good carbon sources for the preparation of high-performance carbon materials due to that there are many polycyclic aromatic hydrocarbons in them. In this paper, coal tar,anthracene oil and petroleum asphalt were employed as carbon sources for the preparation of porous carbons(PCs) with different morphologies and structures,respectivey by using calcium hydroxide(Ca(OH)2) as template coupled with potassium hydroxide(KOH). The as-made PCs were characterized by N2adsorption/desorption, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectrum. The electrochemical properties of PCs were investigated by cyclic voltammetry,galvanostatic charge/discharge and electrochemical impedance spectroscopy. The main conclusions are as follows.(1) Porous carbon nanosheets(PCNs) were synthesized from coal tar by using Ca(OH)2 as template coupled with KOH activation. Under optimal conditions,PCN6-9-12 made with the mass of coal tar, Ca(OH)2, KOH at 6 g, 9 g, 12 g in argon atmosphere possesses the average pore size of 1.69 nm with the specific surface area of 2236 m2/g. In 6 M KOH electrolyte, the specific capacitance of PCN6-9-12 at the current density of 0.05 A/g reaches 259 F/g with the energy density of 8.99 Wh/kg.When the current density is increased to 20 A/g, the specific capacitance of PCN6-9-12 remains at 210 F/g with a capacitance retention of 81.1%, and the energy density of PCN6-9-12 supercapacitors remains at 6.34 Wh/kg. The capacitance retention of PCN6-9-12 remains 90.3% after 5000 cycles at 2 A/g.(2) By using anthracene oil as carbon source, curly porous carbons(CPCs) were prepared. Under optimal conditions, CPC made with the mass of anthracene oil,Ca(OH)2, KOH at 6 g, 9 g, 12 g at 850 oC in argon atmosphere is named as CPC6-9-12-850. With the increase of Ca(OH)2 mass from 6 g to 12 g in the reactants, the specific surface area, average pore size and total pore volume of CPCs passes through a maximum, of which that of CPC6-9-12-850 reaches 2838 m2/g, 2.15 nm and1.53cm3/g, respectively. As the current density increases from 0.05 A/g to 20 A/g, the specific capacitance of CPC6-9-12-850 drops from 289 F/g to 229 F/g with a capacitance retention of 80.6%. The CPC6-9-12-850 electrode shows good cycle stability with capacitance retention of 92.8% at 5 A/g after 10000 cycles.(3) By using petroleum asphalt as carbon source, bubble-like porous carbons(BPCs) were prepared. Under optimal conditions, BPC3.6-9-18 made with the mass of petroleum asphalt, Ca(OH)2, KOH at 3.6 g, 9 g, 18 g in argon atmosphere. The specific surface area, average pore size and total pore volume of BPC3.6-9-18 is 3516m2/g, 2.22 nm and 1.95cm3/g, respectively. In 6 M KOH electrolyte, BPC3.6-9-18 shows the highest specific capacitance of 320 F/g at 0.05 A/g. When the current density increases to 40 A/g, the specific capacitance of BPC3.6-9-18 remains at 264 F/g with a capacitance retention of 82.5%. The capacitance retention of BPC3.6-9-18 electrode remains 95.8% after 10000 cycles at 5 A/g, showing excellent rate performance.