Preparation And Electrochemical Performance Of Biomass Shell-based Activated Carbon

In order to meet the challenges caused by population growth and excessive consumption of fossil fuels,it is extremely urgent to develop green,efficient and sustainable energy storage and conversion equipment.Supercapacitors（SCs）have the advantages of high-power density and cycle stability,while the shortcoming of low energy density limits their large-scale applications.This thesis aims at the disadvantages of relatively low high-value utilization of biomass waste and limited specific capacitance of carbon materials were studied.The physicochemical components of seven kinds of biomass shells and their relationship with the morphology,structure and specific surface area of activated carbon were studied.Specific work contents are as follows:（1）Seven kinds of biomass shells were choosing as precursors to prepare activated carbons.The elemental composition,main ingredients and content,types of surface functional groups,thermal decomposition of the precursors were systematically analyzed.Biomass-based ACs activated carbon were prepared by KOH one-step activation method.The micromorphology,specific surface area,and pore structure of ACs were compared and analyzed.The results showed that all biomass shells possess a carbon content of more than 45%and are rich in cellulose,hemicellulose and lignin,showing that they are lignocellulosic biomass with high carbon content,and have the potential to be developed as high-quality activated carbon materials.However,the contents of cellulose,hemicellulose,and lignin varied greatly in different kinds of shells.When the content of cellulose and hemicellulose is similar,and the lignin content is relatively high,it is easier to obtain activated carbon with developed pore structure and large specific surface area.Hazelnut shell-based AC has the highest specific surface area and developed pore structure among these biomass shells,which is expected to be used to construct high-performance electrode materials for SCs through further condition optimization and modification.（2）Hazelnut shell andγ-polyglutamic acid were chose as carbon source and nitrogen source,respectively.Nitrogen-doped 2D activated porous carbon nanosheets（PCNs）were prepared through chemical crosslinking and KOH activation processes.PCNs with high specific surface area(2393 m² g^-1)and high microporosity was obtained by optimizing activation temperature and composite ratio of carbon and nitrogen.The results show that the activated carbon prepared in the conditions of activation temperature of 800℃and recombination ratio of 1 displayed the best electrochemical performance.At the current density of 0.5A g^-1,the specific capacitance could reach to 321 F g^-1 and the capacitance retention rate was more than 93%at the current density of 5 A g^-1 for 13,000 cycles).（3）Hazelnut shell AC/polypyrrole composite was prepared by chemical oxidation polymerization using hazelnut shell AC as carbon skeleton and polypyrrole as nitrogen source.N-doped porous AC was prepared by KOH activation.The preparation conditions,including activation temperature,recombination ratio and activation ratio,were optimized to obtain the layered porous activated carbon with high specific capacity(the specific capacitance of 324 F g^-1 at the current density of 0.5A g^-1).The assembled symmetrical SC with activated carbon electrode has an energy density of 11.4 W h kg^-1.