Preparation,Structure And Properties Of Porous Carbon Nanosheets For Supercapacitors

In recent years,the new energy storage devices got a rapid development,showing potential application prospects in mobile phones,automotive and other industries.Among them,supercapacitors have drawn much attention because of its long cycle life,high power density.Compared with the coal tar and coal tar pitch,wash oil and methylnaphthalene contain less ingredients and the structure of ingredients are pretty simple,so it can be directly used as building block to construct the porous carbon nanosheets(PNSs)for supercapacitors.In this paper,porous carbon nanosheets for supercapacitors with different structures were prepared from wash oil or methylnaphthalene by using template methods coupled with KOH activation.The structure and morphology of PNSs were characterized by FESEM,TEM and nitrogen adsorption-desorption.The PNSs as the electrode materials were assembled into button-type supercapacitors in aqueous electrolyte,and the energy storage performance was studied by cyclic voltammetry and galvanostatic charge-discharge technology.The conclutions are as follows:Porous carbon nanosheets(PNSs)have been prepared from wash oil by flacked Ca(OH)2 template method coupling with KOH activation.The PNSs made with the mass of wash oil,flacked Ca(OH)2,KOH at 8.0 g,12.0 g,12.0 g at 800 ? is named as PNS8-12-12-800.The specific surface area,microporous specific surface area and average pore size of the PNS8-12-12-800 is 887 m2/g,720 m2/g and 2.09 nm,respectively.In 6 M KOH electrolyte,the PNS8-12-12-800 electrode exhibits a high capacitance of 342.1 F/g and PNS8-12-12-800 supercapacitor renders an energy density of 11.88 Wh/kg at 0.05 A/g.Moreover,PNS8-12-12-800 also shows a high specific capacitance of 219.4 F/g at 20 A/g,exhibiting a high capacity,and a outstanding cycle stability with 94.7 % of the initial capacitance after 7000 cycles at 5 A/g in 6 M KOH electrolyte.Hollow porous carbon nanosheets(PNSs)have been prepared from wash oil with nano-CaCO3 template coupling with KOH by conventional heating method.PNS6-9-12-850 was made with the mass of wash oil,CaCO3,KOH at 6.0 g,9.0 g,12.0 g and the calcination temperature is 850 ?.The as made PNS6-9-12-850 with interconnected microporous and mesoporous possesses average pore size of 7.52 nm and the specific surface area is 1010 m2/g.In 6 M KOH electrolyte,the PNS6-9-12-850 shows a high capacitance(reaching 221.9 F/g at 0.05 A/g)and good rate perfprmance(retention of 79.4 % at 100 A/g).The PNS6-9-12-850 electrode also shows good conductivity(only 0.0013 V voltage drop at 0.2 A/g)and superior cycle stability(remaining 97.1% after 9000 charge-discharge cycles at 5 A/g).Shell porous carbon nanosheets(SPNSs)were synthesized from methylnaphthalene using nano-CaCO3 template method coupling with KOH activation.SPNS6-6-12-900 made with the mass of methylnaphthalene,nano-CaCO3,KOH at 6.0 g,6.0 g,12.0 g at 900 ? possesses pore size range from 1~6 nm and the specific surface area is 1136 m2/g.XPS analysis shows that the SPNS6-6-12-900 contains a certain amount of oxygen-containing functional groups and a small amount of nitrogen-containing functional groups.In 6 M KOH electrolyte,SPNS6-6-12-900 shows a high capacitance of 286.5 F/g and 167.4 F/g in 6 M KOH electrolyte at 0.05 A/g and 100 A/g,respectively.What's more,the capacitance retention of SPNS6-6-12-900 remains at 98.4% after 7000 cycles at 5 A/g in 6 M KOH electrolyte.Thus it can be seen,SPNS6-6-12-900 exhibits excellent charge transfer capability and excellent cycle stability.