Study On The Preparation Of High Surface Area Activated Carbon Using Coconut Shell And Its Application In Super Capacitor

In this paper, the high surface area activated carbon was prepared using coconutshell charcoal as raw material and KOH as activation, the influence of the differentactivating parameters on the structures and performance of the activated carbon wasinvestigated. Different methods like multiple activation, vacuum assisted method andsecondary activation method were used to adjust the pore structure of the activatedcarbon. The as-prepared activated carbon was fabricated to super capacitor to study theinfluence of the activation process conditions and pore structure adjustment methods onthe capacity of the activated carbon and the charge-discharge performance of the supercapacitor. The results indicate that:The most important process parameter is the mass ratio between KOH and coconutshell charcoal during the preparation of activated carbon. The activation reaction needsadequate activation time at a certain activation temperature, at the same time, theheating rate and the protective gas flow should be appropriate. In order to obtain highspecific surface area as well as high yield for the activation carbon, the size of thecarbonized material should be appropriate. The optimal conditions are that the particlesize of carbonized material is80to180μm, the mass ratio between KOH and carbon is4:1to5:1, the activation temperature is750℃to800℃, the activation time is1h to1.5h, the heating rate is10℃/min and the protective gas flow is800mL/min.It is meaningful to study the methods used to adjust the pore structure of theactivated carbon that would make the activated carbon more useful and suit to therequirement of practical application. During the dissolved mixing of carbonizedmaterial and activator, a vacuum assisted method can effectively tune the pore structureof the activated carbon, the as-synthesized activated carbon has a specific surface areaof2366m2/g, a pore volume of1.356cm3/g and a mesopore ratio of25.37%.Comparedto that without vacuum assistance, the pore volume and the mesopore ratio is increased0.382cm3/g and22.19%, respectively. When the vacuum assistance is combined withsecondary activation method, it can magnify the balanced effect of secondary activationmethods to the activated carbon with different specific surface area,which couldincrease the specific surface area of the activated carbon from2281m2/g to2488m2/gand the mesopore ratio from12.89%to32.19%. In comparison, the use of ZnCl2\KOHcombined activator would increase the content of mesopore, at the same time it deducesthe specific surface area of the activated carbon. When the percent of ZnCl2is20in thecombined activator, the mesopore ratio increased13.21%and it is very little that thespecific surface area reduce from2333m2/g to2316m2/g.The activated carbon should have high specific surface area and percent ofmesopore, when it is used in super capacitor. The method used to expend the pore of the activated carbon is beneficial to transfer electrolyte ion in the pore and improve thecapacity of the capacitor. The as-prepared activated carbon with a specific surface areaof2413m2/g and a mesopore ratio of4.03%was fabricated to super capacitor, and thecapacity of the activated carbon is241F/g. The increase of mesopore ratio will influencethe capacity of the activated carbon and it will replace the specific surface area andbecome the most important factor that influence the capacity of the activated carbonwhen the mesopore ratio is more than20%. After adjusting the pore structure, theactivated carbon with a specific surface area of2488m2/g and a mesopore ratio of32.19%and has a capacity of294F/g.