Synthesis Of Quinoline Pitch And Its Capacitance Performance Of Porous Carbon

With the continuous consumption of fossil energy and the increasingly serious environmental pollution it brings,there is a strong demand to develop green and sustainable energy such as wind,solar and nuclear energy,but the storage of these energy sources is a key to their full development.Supercapacitors and other chemical energy storage devices have solved this problem.Supercapacitors(SCs)are widely used in memory backup power systems,industrial power supplies and energy management systems due to their high power density and almost infinite cycle times.Porous carbon materials are often used as electrode materials for SCs,and nitrogen-containing porous carbons(NPC)are more popular than pure carbon materials because of their superior electrochemical properties.In this paper,a high-purity quinoline pitch was synthesized by self-boosting method using nitrogen-containing monomer quinoline as raw material and aluminum trichloride as catalyst.The basic properties were measured such as softening point,coking value,group composition and ash.And then,the chemical structures were analyzed by FTIR,UV-vis,GC-MS,GPC and XPS.Meanwhile,the carbonization behavior and the microstructures of coke were studied by TG/DTG,XRD,Raman and PLM.Finally,the nitrogen-containing porous carbon was prepared by KOH and Zn Cl2 activation.The carbon skeleton structures,pore structures,morphology and surface properties were characterized by XRD,Raman,XPS,N2 adsorption measuring instrument,SEM and TEM.In addition,the capacitance performance was examined through the three-electrode test system in a 6M KOH solution.The results indicated that:(1)The synthesized quinoline pitch was composed of nitrogen-containing aromatic hydrocarbons of different molecular weights,and the number average molecular weight was about 255,the ash content was low(<1%),the coking value was high(58.43%),and the nitrogen content was up to 8.22 wt%.As a result,the quinoline pitch is a kind of high quality nitrogen carbon material precursor.(2)During the carbonization process,the quinoline pitch appeared three obvious weight loss peaks at 170 °C,240 °C and 420 °C.The pyrolysis activation energy Ea decreased first and then increased with the increasing of conversion rate α,and then decreased and increased again.As the carbonization temperature increased,the turbostratic structure of coke gradually changed into the graphite-like structure,and the degree of defects of carbon network in the microcrystals became larger.The optical structure of coke was mainly leaflet texture.(3)The KOH activation effect was much better than Zn Cl2.When the alkali carbon ratio was 3 and the activation temperature was 700 °C,the prepared NPC had a graded pore structure,mainly micropores and mesopores,and the surface nitrogen content and the specific surface area were 3.69 wt% and 2562 m2/g,respectively.The specific capacitance was 452 F/g at a current density of 0.5 A/g,and it still had a specific capacitance of 260 F/g at a high current density of 50 A/g.Its capacitance came from pesudocapacitor and electric double layer capacitance,in which the electric double layer capacitor accounted for the main part.There is a 91% capacitance retention after 10000 cycle at a current density of 1A/g.