Preparation And Supercapacitor Electrochemical Properties Of Porous Carbon Based Materials

Supercapacitors called electrochemical capacitors have been attracted much attention because of their high power density,long cycle life?>100000 cycles?and simple principle.Electrode material is the key part of supercapacitors.In recent years,many scholars have studied and applied biomass carbon material to supercapacitors,due to it have the earth-abundant,renewable,low cost and other advantages.Herein,three different biomass materials were selected as the carbon sources,the porous carbon materials with different morphologies and high specific surfaces have been prepared by KOH activation.Their electrochemical performances used as supercapacitors have been studied.1.Nitrogen-doped porous carbon materials have been prepared using cycas leaves as the carbon source and urea as the nitrogen source by carbonization.The effects of urea doping with different content on the properties and structure of the materials were studied.The results show that CU2-700 synthesized at the ratio of 2:1 for urea to precursor displays a high specific surface area(2628 m²?g^-1)and the largest total pore volume(1.39 cm³?g^-1).Its specific capacitance is 373 F?g^-1 at 0.5 A?g^-1 in 6 M KOH electrolyte.In addition,a symmetric supercapacitor fabricated by CU2-700 possesses the specific capacitance of 260F?g^-1 at 0.5 A?g^-1,an energy density of 9.13 Wh?kg^-11 at a power density of 125 W?kg^-1 and capacitance retention rate of 85.0%(after 10000 cycles at 5 A?g^-1)in 6?M KOH electrolyte.2.Litchi shell-based carbon material has been prepared by using Litchi shell as the carbon source and KOH as activator by carbonization.The effects of KOH radio on the properties and structure of the materials were studied.The research indicates the LZK4-700 holds a high specific surface area of 1725 m²?g^-1 and pore volume of 0.69cm³?g^-11 as the ratio of KOH to precursor is 4.In 6 M KOH electrolyte,the as-prepared LZK4-700-based electrode materials exhibit the specific capacitance is 345 F?g^-1 at 0.5A?g^-11 and a long-term cycling stability(capacitance retention of 90.2%after 10000 cycles at 20 A?g^-1).Furthermore,a symmetric supercapacitor fabricated by LZK4-700 can deliver the maximum energy density of 9.03 Wh?kg^-1 and the maximum power density of 5000W?kg^-1,and present an outstanding capacitance retention rate of 94.6%over 10000 cycles at 5 A?g^-1.3.Pomelo peel using as the carbon source,Pomelo peel-derived carbon materials have been prepared by KOH activation.The effects of activation temperature and the ratio of activator to precursor have been discussed.The results demonstrate that the prepared carbon material appears porous with honeycomb shape when the ratio of KOH to precursor is 2 and activation temperature is 800°C.Meanwhile,YZP2-800 as an electrode has the best electrochemical performance in prepared pomelo peel-derived carbon materials.Moreover,the assembled symmetric supercapacitor in two-electrode system shows an excellent specific capacitance of 271 F?g^-1,its energy density is 9.41 Wh?kg^-1 and the power density is 125 W?kg^-1 at current density of 0.5 A?g^-1.Under the constant current density of 5 A?g^-1,the capacitance retention rate is 95.5%after the 10000 cycles.