Preparation Of High Specific Surface Area Nitrogen-doped Bio Porous Carbon By One-step Carbonization For Supercapacitors

With the development of society,people have more and more demand for energy storage devices.The energy density and power density of supercapacitor(SC)are between traditional capacitors and batteries.It shows good safety performance and has been widely used in some fields.Porous carbon is applied on SC because it is easy to obtain and cheaper.However,its lower specific capacitance and energy density limited the application.Improving the energy density of porous carbon is still one of the research hotspots.Conventional preparation of porous carbon usually requires carbonization first and then activation again,it is cumbersome and requires heating for two times,which consume more energy.Under such a background,this paper studies how to obtain porous carbon with excellent electrochemical performance by a simple preparation method.Nitrogen doping is an effective means to improve the electrochemical performance of porous carbon.In this paper,chitin was used as both carbon source and nitrogen source.In order to simplify the preparation process,chitin was fully mixed with KOH activator by ball milling,and then carbonized and activated in one step.Nitrogen-doped porous carbon with the highest specific surface area of 1735.84 m2 g-1 and the maximum nitrogen content of 7.12%was prepared.The 6 mol L-1 KOH solution was used as the electrolyte,and the three-electrode electrochemical test showed that the sample Ct-C-600 had the highest specific capacitance(218.4 F g-1).Using Ct-C-600 as the active material,6 mol L-1 KOH solution as the electrolyte,assembled into a symmetric SC.the SC with the two-electrode electrochemically testing,the maximum voltage window can reach 1.4 V,and the highest energy density reaches 15.8 wh kg-1.The highest power density reached 3500 W kg-1,and after 4000 cycles,the initial specific capacitance was maintained at around 70%,which verified the practicality of Ct-C-600 as an electrode material.Factors affecting electrochemical performance were analyzed by performing a series of characterizations.Since the degree of uniform mixing of the KOH activator and the chitin by the ball milling method is limited,the prepared nitrogen-doped porous carbon has a limited specific surface area.Chitin is relatively difficult to dissolve and hard to be modified.In order to prepare porous carbon with higher specific surface area,chitosan as the derivative of chitin was modified,so that it could form a homogeneous colloid with the KOH solution.One-step preparation of nitrogen-doped porous carbon with high specific surface area and large pore volume was carried out by taking modified chitosan as the carbon and nitrogen source and KOH as the activator.The prepared sample of CS-C-1 with a chitosan/KOH mass ratio of 1:1 had a specific surface area of 2952.9 m2 g"1 and a pore volume of 2.32 cm3 g-1.With 6 moll L-1 KOH solution as the electrolyte,the specific capacitance of the product reached 325.6 F g-1(0.5 A g-1),and the performance did not degrade after 5000 cycles.The results indicate the potential of CS-C-1 as a promising electrode material for supercapacitors.[EMIm]CF3SO3 ionic liquid as electrolyte,CS-C-1 as active material,assembling symmetric SC.The voltage window reached 3.5 V,and the highest energy density was obtained at 69.0 Wh kg-1.the maximum power density obtained was 6775 W kg-1,which proves that ionic liquid has a good application prospect in SC.