Preparation Of Heteroatom Doped Porous Carbon From Biomass For Supercapacitors

The performance of supercapacitors is mainly determined by the electrode.The porous carbon material is an ideal candidate for the electrode material due to its high specific surface area and developed pores.Porous carbon can be prepared from a wide range of biomass by thermochemical transformation and activation process.Though this method is simple and economical,at present there is still bottleneck of insufficient energy density.Doping boron,nitrogen,oxygen,phosphorus and other heteroatoms into the porous carbons has been proved to be an effective way to improve the electrochemical properties.Based on this,this paper selected different kinds of biomass as precursors,and the prepared porous was doped with heteroatoms through different methods.Furthermore,their capacitive behaviors was investigated:?1?One-dimensional biomass ramie fiber was selected as the precursor,zinc chloride was selected as the activator,boric acid and urea were used to introduce boron and nitrogen.Experimental results show that compared with single element doping,co-doping method significantly improves boron doping,thus improving the conductivity and wettability of carbon materials,resulting in higher specific capacitance and better dual capacitance characteristics of corresponding electrodes,even the specific surface area is not outstanding(600⁹00 m²g^-1).Under the three-electrode system,the specific capacitance of double-doped porous carbon in the 6 M KOH electrolyte reaches 279 F g^-1.In the symmetrical electrode supercapacitor system,the energy density reaches 6.5 wh kg^-1 at 480 W kg^-1.?2?Soybean dreg,a nitrogen-rich agricultural waste,was used as the precursor.The porous carbon materials containing a large number of N/O functional groups were obtained by water heat treatment associated with KOH activation.The corresponding electrode is endowed with excellent electrochemical properties by the fine structure of hierarchical porous structure,wide specific surface area and the heteratomic functional groups which came from itself.When the activator agent and hydrochar reach the most optimal ratio?3:1?,the porous carbon electrode in the 6M KOH electrolyte with A current density of 1A g^-1 can reach 321.3F g^-1 and have A good rate performance,which can still have A specific capacitance of 191 F g^-1 under the large current of 30 A g^-1.In addition,a symmetrical supercapacitor system was fabricated based on the as-prepared porous carbon,with an energy density of 9 Wh kg^-1 in the 6M KOH electrolyte and a specific capacitance retention rate of 90.8%after 5000 cycles at 5 A g^-1,showing excellent cyclic stability.Furthermore,the energy density was successfully expanded to 25.9 wh kg^-1,by the application of 1M Na₂SO₄ electrolyte.