The Fabrication Of Pitch-based Porous Carbon Material And Their Applications In Energy Storage

Porous carbon(PC)is a common carbon material with large specific surface area and its adjustable pore size.So it has extensive applications in energy storage.Coal tar pitch(CTP)is the by-product from coal tar distillation.The high carbon content and low price of coal tar pitch enable it as the carbon source of porous carbon materials.In this paper,we refined CTP by the solvent-centrifugal method to control the content of quinoline insoluble(QI)and ash in it.And then use the refined CTP as precursor to prepare the co-doped porous carbon,studies its performance by use it as electrode material of supercapacitor,lithium sulfur batteries and fuel cell.Pore structure and surface morphology of PC were characterized by using N2 adsorption/desorption,X-ray diffraction(XRD),XPS,Scanning electron microscopy(SEM),and transmission electron microscopy(TEM)techniques.The electrochemical performance was investigated by the cyclic voltammograms(CV),electrochemical impedance spectroscopy(EIS),and constant current charge/discharge techniques.The main conclusions are as follows:(1)By the characterization and analysis of CTP refined by toluene and tetrahydrofuran,the results show that it is difficult for tetrahydrofuran to effective separation of QI and ash,because of its excellent solubility for CTP.To the toluene,separation effect increased by the increasing of solvent proportion,but the production rate is reduced.While solvent ratio is 3:1,and centrifugal time is 10 minutes,and speed of centrifugal is under 4000 rpm,the content of QI and ash in purified pitch is below 0.1 % and its yield is more than 60 %,which satisfied requirement of raw materials and the desired goals achieved.(2)Nitrogen and sulfur-doped graphene-like porous carbon(N,S-PGC)for supercapacitors were synthesized by ammonium sulfate-assisted chemical blowing from CTP.The N,S-PGC with mass proportion of CTP and(NH4)2SO4 being 5:1 and co-carbonization at 1000 ℃possess a surface area(SBET)of 1119.4 m2/g,which has activated by KOH(a-N,S-PGC)was 2326.3 m2/g.As the supercapacitors of electrode material,the as-made N,S-PGC shows a high capacitance of 208.6 F/g in 6 M KOH electrolyte at a current density of 0.5 A/g,the capacitance of a-N,S-PGC was 368 F/g at a current density of 0.5 A/g.Its excellent cycle stability with 95.22 % and 97.44 % capacitance retention after 10000 cycles,respectively.We also tested the electrochemical performance of the co-doped carbon materials as lithium sulfur batteries and fuel cell electrode materials,respectively.And the results show that a-N,S-PGC possessed the better rate performance and cycle stability.It exhibits high initial discharge capacity of 958 mAh/g at 0.1 C(1 C = 1675 mA/g,based on sulfur content)and high rate capability of 424 mAh/g at 1 C,as well as excellent long term cycling stability at a current rate of 0.1 C with capacity of 674 mAh/g for over 150 cycles.The a-N,S-PGC possessed excellent oxygen reduction activities,long-term durability and tolerance to methanol crossover than the commercial Pt/C reference electrocatalyst.(3)Nitrogen and phosphorus co-doped graphene-like porous carbon(N,P-PGC)for supercapacitors was directly prepared by co-carbonization of coal tar pitch(CTP)and(NH4PO3)n.The material was activated by generated H3PO4.And N,P-PGC with mass proportion of CTP and(NH4PO3)n being 5:1 and co-carbonization at 900 ℃ exhibits a high capacitance of 219 F/g in 6 M KOH electrolyte at current density of 0.5 A/g and excellent cycle stability with 95.6 % capacitance retention after 10000 cycles.We also tested the electrochemical performance of the co-doped carbon materials as lithium sulfur batteries and fuel cell electrode materials,respectively.And the results show that N,P-PGC possessed the better rate performance and cycle stability.It exhibits high initial discharge capacity of 885 mAh/g at 0.1 C(1 C = 1675 mA/g,based on sulfur content)and high rate capability of 298 mAh/g at 1 C,as well as excellent long term cycling stability at a current rate of 0.1 C with capacity of 406 mAh/g for over 150 cycles.N,P-PGC possessed excellent oxygen reduction activities,long-term durability and tolerance to methanol crossover than the commercial Pt/C reference electrocatalyst.