Preparation And Electrochemical Performance Of Coal Tar Pitch-base Porous Carbon For Supercapacitor

As a new energy storage device, supercapacitor is widely used in the field oftransportation, communication, etc. It has become a hot topic in the electric vehiclepower system in recent years. Its overall performance is mainly determined by theelectrode materials and electrolyte. Porous carbon (PC) is an ideal electrode materialwith large specific surface area and developed pore structure. Coal tar pitch is theby-product in dry distillation process of coal. The high carbon content, low ashcontent, widely accessible and low price of coal tar pitch enable it as the carbonsource of supercapacitor,s electrode materials.Microporous carbons (MPCs) and hierarchical porous carbons (HPCs) wereprepared from coal tar pitch by KOH activation or γ-Fe2O3template. Pore structureand surface morphology of PCs were characterized by using N2adsorption/desorption,X-ray diffraction (XRD), XPS, Boehm titration, field emission scanning electronmicroscopy (FESEM), and transmission electron microscopy (TEM) techniques. Theobtained MPCs or HPCs are used as the electrode materials of supercapacitor, ofwhich the electrochemical performance were investigated by the cyclicvoltammograms, electrochemical impedance spectroscopy, and constant currentcharge/discharge techniques in different electrolyte. The main conclusions are asfollows:(1) The PCs with high specific surface area were prepared from coal tar pitch withKOH as activation agent by microwave or conventional heating. At the mass ratio ofKOH/coal pitch of14/7, the MPC14/7Mmade by microwave heating has a surface area(SBET) of1786m2/g, a total pore volume (Vt) of0.87g/cm3, and the average pore size(Dap) of1.94nm, the proportion of microporous specific surface area and pore volumewere57.4%and54.0%, respectively. The SBETof MPC14/7Cmade by conventionalheating reaches1760m2/g, with a Vtof0.84cm3/g, and a Dapof1.91nm. And almostall PCs made by conventional heating were microporous structure.The specific capacitance of MPC14/7Cis281F/g in6M KOH with the energydensity of9.7Wh/kg at the current density of0.05A/g. The capacitance retention ofMPC14/7Cis88.3%with the increase of current density from0.05to2A/g. Theretention of the capacitance and energy density of MPC14/7Mis99.3%and98.6%after1000cycles charge/discharge, showing very good electrochemical stability. (2) The MPC14/7Mwas selected as the activation material, and the specificcapacitance is up to269F/g in6M KOH electrolyte at the current density of0.05A/g,and the energy density of MPC14/7Mcapacitor reaches18.1Wh/kg in1M Et4NBF4/PCorganic electrolyte at the operating voltage of2.7V. The specific capacitance is165F/g when the operating voltage increases to1.6V in0.5M K2SO4electrolytewith theenergy density of14.3Wh/kg. The MPC14/7Melectrode shows the maximumcapacitance in6M KOH, the highest energy density in1M Et4NBF4/PC and modestcapacitance and energy density in0.5M K2SO4electrolyte.(3) The HPCs were prepared by using γ-Fe2O3as template by microwave orconventional heating. The XRD analysis results show that the γ-Fe2O3works astemplate and catalytic activation in the preparation process of HPCs. With theincreasing mass of γ-Fe2O3template, the specific surface area of HPCs increases from761to1330m2/g, the Dapis from1.78to4.05nm. HPC7-14-0Cmade without theaddition of KOH shows the greatest Dapof6.61nm. Compared with conventionalheating, HPCs made by microwave heating shows larger Dap, smaller SBETand Vt.The specific capacitance of HPC4.2-16.8-6Cis194F/g in6M KOH electrolyte at thecurrent density of0.1A/g, showing92.5%capacitance retention when the currentdensity increases to3.5A/g with a good rate performance. The specific capacitance isstill as high as186F/g after1000cycles. The energy density of HPC4.2-16.8-6Cis up to20.3Wh/kg in1M Et4NBF4/PC electrolyte. The retention of energy density ofHPC4.2-16.8-6Mcapacitor is the highest. And the energy density remains at12.6Wh/kgat119.7W/kg while it drops to2.2Wh/kg at2067.3W/kg.