Preparation And Electro-chemical Properties Of Hierarchical Porous And Partly Graphitized Active Carbon

Electric supercapacitor?ESs?,as one of the most promising energy-storage devices,are attracting widely interest due to their long cycle life,short charge-discharge time,high power density and environmentally friendly and so on.Furthermore,the materials for the electrode are more remarkable.Now,we pay attention to the widespread materials-active carbons,which are prepared in different ways,and applied them in supercapacitor.The active carbon materials?ACs?derived from fallen leaves?FLs?are prepared by the activations of mixed KOH and K₂CO₃.Characterizations reveal that the use of single activator KOH creates the most of micropores in three dimensional and K₂CO₃ produces the mesopores/macropores mostly in shallow.When combining KOH with K₂CO₃,the pore size of ACs is enlarged.The surface areas and hierarchical pore structures are related to the mass ratio of two activators.The electrochemical properties are monitored with the cyclic voltametry,charging-discharging and electrical impedance spectra.The prepared sample displays high specific capacitance of up to 242 F/g?0.3 A/g,6 M KOH?in a two-electrode system.Their good cycling stability with nearly no capacitance decrease is obtained after2000 cycles.Otherwise,the optimized active condition is that the mass rate is C:KOH:K₂CO₃=1:1:2,the active temperature is 700^oC and obtain 1 h.Partly graphitized active carbon materials are obtained by the catalysts of boron and nitrogen with renewable fallen leaves as carbon source.The experiment shows that the active carbon is graphitized with single addition of boron,the specific capacitance decreases due to the decrease of active sites.The co-injected nitrogen can remedy the loss of active sites,which plays a complementary role to increase the specific capacitance to 254F/g at the current density of 0.5 A/g without addition of conductive agent-carbon black?CB?.The energy density and the power density of reach to 48.6 Wh/kg and 3600 W/kg at the potential window of 1.5 V.The control experiments explain the roles of CB in supercapacitor.It is clear that CB improves the conductivity,but blocks the pores of partly graphitized active carbons.