| In this work,LiBr hydrate solvent was selected and used to dissolve biomass including wood powders,pulp and chitin,which was also served as the reaction medium for hydrothermal carbonization treatment.The impacts of the preparation conditions on the yield and morphology of carbon spheres were carefully studied to prepare carbon spheres with spherical morphology.Subsequently,porous carbon spheres with high specific surface area could be prepared by high-temperature carbonization and chemical activation,which could be further used as the electrode material for supercapacitor.In the LiBr hydrate,lithium cation could coordinate with oxygen atoms from molecules of water,and bromide anion could combine with the H in the hydroxyl groups of cellulose,hemicellulose and acetylglucosamine to form hydrogen bonds.Meanwhile,lithium cation could interact with the O interaction of the hydroxyl group,thus decomposed the intermolecular and intramolecular hydrogen bonds and destroyed the crystalline matrix,leading to the final dissolution of cellulose,hemicellulose and acetylglucosamine.It was determined through experiments that the optimal operation conditions for preparing carbon spheres were 170℃,reaction time 5 h,HCl concentration 5 wt.%and LiBr concentration 65 wt.%.The average particle size of the prepared carbon spheres was 603 nm with a yield of 22.4%.Compared to raw materials,carbon spheres had uniform spherical morphology,abundant multifunctional groups and excellent thermal stability.The LiBr hydrate could still achieve a yield of 18.3%after five cycles with the addition of 3.8 g LiBr on each cycle.In addition,levulinic acid and 5-hydroxymethyl furfural were detected in the organic liquid phase reaction products,indicating the great potential of biomass valorisation with this innovative process.The porous carbon spheres were further prepared after high-temperature carbonization and chemical activation,which all had the typical porous structure.The ID/IG value of the products increased after activation,indicating the low degree of graphitization.Taking the best sample of porous carbon spheres prepared from wood powders and chitin as representative,the mass ratios of KOH to raw materials were 3:1 and 4:1,respectively.The maximum specific surface area of the products were 2415 m2/g and 3428 m2/g,respectively.The average pore sizes were 2.46 nm and 2.58 nm,respectively.Meanwhile,porous carbon spheres prepared from chitin had nitrogendoped effect.The products were tested with three-electrodes in the KOH solution of 6 mol/L.When the current density was 1 A/g,they showed high specific capacitances of 258 F/g and 335 F/g,respectively;When assembled into two-electrodes double layer capacitor in the KOH solution of 6 mol/L,they showed high energy densities of 13.75 Wh/kg and 17.08 Wh/kg at the power density of 250 W/kg,respectively.After 5000 cycles,they could maintain 95.5%and 98.9%of the initial specific capacitance respectively. |
