Preparation And Capacitance Performance Research Of Biomass-based Porous Actived Carbon Materials

Supercapacitors?SCs?have attracted tremendous attention as a class of efficient energy storage devices because they can offer high power density and excellent cycling stability,along with the potential to form a device with an energy density close to traditional batteries.The electrode material is one of key factors that affect the electrochemical properties of the supercapacitor,which mainly containing the following three types:carbon materials,transition metal compounds and conducting polymers.Among them,porous carbon materials,especially activated carbons?ACs?,are the most widely used electrode material of supercapacitor for their chemical stability,less weight,low cost,good electric conductivity and environment-friendly advantage.The developed micro/mesporous channels and ultrahigh specific surface area of ACs do not only accelerate the kinetic process of ion migration but also provide abundant surface active sites that are essential to high specific capacitance and outstanding cycleability of supercapacitors.Herein,the biomass waste has been used as low-cost precursor to produce porous carbon for supercapacitor.The biomass waste was carbonized at mild conditions followed by chemical activation or direct carbonization.The morphology,structure and electrochemical properties of the materials are characterized in detail.The main research contents and results are as follows:1.Nitrogen-doped porous activated carbons have been fabricated through ZnCl₂activation method directly with the waste tea-leaves as carbon precursor.The resulting activated carbon TPACs-2 exhibits 3.0 wt%nitrogen content and a specific surface area of 1143.9 m²g^-1.As an electrode material for supercapacitor,TPACs-2 possesses a large specific capacitance of 296 F g^-11 at a current density of 0.5 A g^-11 in 2 M KOH aqueous electrolyte in three-electrode systems.Furthermore,the symmetric supercapacitor fabricated with TPACs-2 electrodes delivers a high energy density of13.5 Wh kg^-11 at a power density of 221 W kg^-11 and superior cycle stability with only9%loss after 5000 cycles,operating in the wide voltage range of 0-1.8 V in 0.5 M Na₂ SO₄ aqueous electrolyte.2.The porous activated carbons have been fabricated through pre-carbonation and subsequent ZnCl₂-activation carbonization with the seed melon pericarp as carbon precursor.The obtained SMACs-2 material has a high specific surface area of2248.79 m²g^-1and a pore volume up to 1.75 cm³g^-1.As an electrode material for supercapacitor,SMACs-2 exhibits a high specific capacitance of 340 F g^-11 at a current density of 0.5 A g^-11 in three-electrode systems with 2 M KOH as aqueous electrolyte.A symmetric supercapacitor used SMACs-2 as electrodes exhibits energies density of13.5 Wh kg^-11 at a power density of 230 W kg^-11 operated in the voltage range of 0-1.8V in 0.5 M Na₂SO₄ aqueous electrolyte and shows good electrochemical performance.3.Nitrogen-doped porous activated carbons?N-PHACs?have been successfully synthesized using pomegranate husk as carbon precursor via ZnCl₂-activation carbonization and subsequent urea-assisted hydrothermal nitrogen-doping method.The obtained N-PHACs possesses high specific surface area(up to 1754.8 m²g^-1),pore volume(1.05 cm³ g^-1),and nitrogen-doping content?4.51 wt%?.Besides,as an electrode material for supercapacitor,the N-PHACs-based material showed a high specific capacitance of 254 F g^-1at a current density of 0.5 A g^-1in 2 M KOH aqueous electrolyte in three-electrode systems.The assembled N-PHACs-based symmetric capacitor with a wide operating voltage range of 0-1.8 V exhibits a maximum enery density of 15.3 Wh kg^-1at a power density of 225 W kg^-1and superiorcycle stability?only 6%loss after 5000 cycles?in 0.5 M Na₂SO₄ aqueous electrolyte.