The Preparation And Superelectric Properties Of Anionic Biopolymer-based Hierarchical Carbon

Supercapacitor has the characteristic of long cycle life span,high power density,short charging/discharging time,and environment-friendly,which has been widely studied by researchers around the world.Porous carbon has the advantages of large specific surface area,abundant raw materials,high conductivity and good thermal/chemical stability.As electrode material of supercapacitor,it has attracted many scientists'interest.In this thesis,heteroatom doped porous carbon materials based on the"egg-box"model were prepared by in-situ pyrolysis combined with chemical activation and applied to supercapacitors.The surface of porous carbon is modified by O,N and S heteroatom to introduce pseudo-capacitance.In-situ template can manufacture uniform mesopores,and potassium hydroxide can activate to manufacture abundant micropores,so as to synthesize high-performance micro/mesoporous hierarchical porous carbon.N/O co-doped pectin-based hierarchical porous carbon was synthesized by in-situ calcium carbonate template combined with potassium hydroxide activation method using pectin as carbon source,calcium acetate as calcium source,urea as nitrogen source.The effects of activation temperature,the addition of template source,the removing of template and the addition of urea on the structure and supercapacitor performance of porous carbon were studied.The results that the specific surface area of NHPC-700 activated at 700?can reach 2928 m² g^-1.The addition of urea introduced many nitrogen atoms,and prodeced a large number of micropores and mesopores.The addition of calcium acetate manufactures many mesopores by in-situ derived calcium carbonate,and there mesopores provides active sites for potassium hydroxide to improve the activation efficiency.In a three-electrode system,the specific capacitance of NHPC-700 is as high as 338 F g^-1 in 6 M KOH.In a two-electrode system,the energy density of NHPC-700 can reach 22.4 Wh kg^-1 at the power density of 880 W kg^-1 in 1M Na₂SO₄.In order to further optimize the supercapacitor performance of porous carbon,the doping of S and N was completed at the same time.N/O/S co-doped hierarchical porous carbon was synthesized by in-situ Mg O template combined with activation method of potassium hydroxide using sodium alginate as carbon source,magnesium acetate as magnesium source.Adding thiourea and increasing the concentration of template source increased the specific surface area of porous carbon.The specific surface area of PCNS-2Mg is 1480.1 m² g^-1,and the specific capacitance at the current density of 1 A g^-1 is 327 F g^-1.The pore size distribution of porous carbon without"egg box"is too dispersed.N/O/S co-doped porous carbon derived from sodium alginate was synthesized by in-situ hard template method combined with potassium hydroxide activation using sodium alginate as carbon source,calcium acetate and zinc acetate as calcium sources and zinc sources,thiourea as sulfur sources and nitrogen sources,respectively.The structure of porous carbon was optimized by changing the type/concentration of template source and adding thiourea.The type of template source did not affect the mesoporous size of porous carbon without the addition of thiourea,and the mesoporous were concentrated at 25 nm.However,the mesoporous size of porous carbon decreased with the addition of thiourea.The mesoporous size of PCNS-Ca was concentrated at about 13 nm,while that of PCNS-Zn was concentrated at about 6 nm.The addition of thiourea can not only introduce sulfur and nitrogen atoms,but also increase the specific surface area.PCNS-Zn shows the most excellent electrochemical performance.The specific capacitance of PCNS-Zn is as high as 350 F g^-1 at 1 A g^-1 in a three-electrode system,and the capacitance retention rate from 1 A g^-1 to 50 A g^-1 is 82%.After 5000cycles,the capacitance retention rate of PCNS-Zn is still as high as 90.4%.The supercapacitor performance of samples with zinc acetate as the template source is higher than that of the samples with magnesium acetate as the template source,which highlights the advantage of the preparation of hierarchical porous carbon based on the "egg box" structure.