Preparation Of Porous Carbon Materials By Thermal Pyrolysis Of Lignin And Its Application In Supercapacitors

Lignin as a natural nature of the polymer has received widespread attention.In this paper,porous carbon material was prepared by direct pyrolysis and catalytic pyrolysis using lignin as raw material.The pyrolysis characteristics of the porous carbon material were analyzed by SEM,particle size,organic element,TG and FTIR.Among them,direct thermal cracking discusses the effect of different temperatures on the pyrolysis characteristics,and catalytic thermal cracking discusses the effects of different carbon-to-alkali ratios on the pyrolysis characteristics.Then carbon materials obtained by different pyrolysis methods were used in the electrode material of supercapacitor to discuss their electrochemical properties.The results show that the pyrolysis process of lignin is divided into three stages:free water removal,volatile analysis and deep pyrolysis.Lignin pyrolysis process is relatively complicated,can be seen as a continuous chemical bond breaking and recombination process,at lower temperatures,lignin aromatic ring branch of the functional groups broken,generating aliphatic substances,as the temperature rise High,the benzene ring also began to break,the structure of the macromolecule pyrolysis for small molecules,further recombination of free radicals at high temperatures.The morphology of the carbon pore material obtained by direct pyrolysis of lignin is spherical or hemispherical,with a large number of pores on the surface,and the surface is rough with undulating structure.Particle size distribution,and with increasing temperature particle size becomes smaller.The morphology of the carbon pore material obtained by catalytic pyrolysis is spherical or hemispherical,the morphology of which is mostly hemispherical,and the surface is rough and has an undulating structure with a large number of pore structures on the surface.However,with the increase of the ratio of carbon to base,the undulating structure becomes less and less obvious.The distribution is basically the same,the average particle size is about 66 microns.Compared with the direct pyrolysis of sodium hydroxide catalytic cracking carbon material is conducive to the smaller particle size,particle size and the amount of sodium hydroxide has nothing to do.The supercapacitor assembled with KOH as electrolyte was obtained by direct thermal cracking of carbonaceous material at different temperatures.The carbonaceous material at 700?had the best electrical properties.Charge and discharge process reversible stability.At different current densities,the specific capacitance decreased from 40.8F/g to 38F/g,down about 5%.500 cycles at 1A/g super-large current,good cycle performance.The supercapacitor assembled with different electrolyte,which is obtained by direct thermal cracking at 700?,is superior to KOH as electrolyte in the super-electricity with Na₂SO₄ as electrolyte.Although both charge and discharge processes are reversible and stable,and the cycling performance is good,the specific capacitance of Na₂SO₄ solution decreases from 7.8F/g to 5F/g with a decrease of about 36%under different current densities.Its specific capacitance is significantly lower than KOH as electrolyte over-electric ratio capacitance,and the decline in the proportion of serious.Carbon materials with different carbon-to-alkali ratios were 1:1 with carbon-to-alkali ratio of 1:1.Charge and discharge process reversible stability.At different current densities,the specific capacitance decreased from 71 F/g to 62 F/g,and the specific capacitance of single electrode reached 284 F/g,down about 13%.500 cycles at 1A/g super-large current,good cycle performance.