Research On The Preparation And Property Of Biochar And Their Composites Used In Supercapacitor Electrode

The increasing demand of clean,efficient and safe energy in recent years brings more requests on energy storage devices.Supercapacitor is important in energy storage because of high power density and good cycle stability.Some synthesis and raw materials are costly and complex in obtaining the specific structure of supercapacitor electrode.Biomass is a cheap,green and renewable material.The use of biomass is good for the sustainable development of our society.In this dissertation,we take advantage of the specific structure of biomass and use it to prepare supercapacitor electrode by carbonization and activation.In particular,we explore the strategy to synthesize biomass/metal composites for electrochemical materials.The first chapter introduces the classification and energy storage mechanism of supercapacitor,the application of biomass in supercapacitor electrode and the importance of this project.In the second chapter,we report the synthesis of super high aspect ratio one dimensional hierarchically porous carbon with plant metaplexis.The diameter of the pipe is about 4?m,the shell of the pipe is about 0.2?m,and the length of the pipe is from 4 cm to 7 cm.The specific surface area of the activated material is 1394 m²g^-1,and the pore volume is 0.79 vm³g^-1.The main size of the pore is micropores while macropores and mesopores exist in the product.The specific capacitance of the material is 256.5 F g^-1thanks to the high specific surface area.The hierarchically porous structure reduce the resistance of electrolyte ion diffusion,and the super high aspect ratio reduces the charge transfer resistance.The excellent structure leads to a very low equivalent series resistance of 0.103?.In the third chapter,inspired by the capability of the hyperaccumulators to enrich heavy metal ions,we grow Egeria densa with cobalt salt solution to obtain metal excessive loaded biomass.The cobalt ions loaded in Egeria densa were reduced to cobalt nanospheres after activation,and the 100 nm diameter nanospheres dispersed in the hierarchical porous carbon skeletons uniformly.The well dispersed cobalt nanospheres exhibit obvious pseudocapacitance.The specific capacitance is 1017 F g^-1.The superior conductivity and hierarchical porous carbon skeletons lead to low impedance.Energy density of the assembled asymmetric supercapacior is55 W h kg^-1while the power density is 495 W kg^-1,and the energy density maintains 27 W h kg^-1while the power density increases to 9.27 kW kg^-1.Egeria densa is of high reproducibility and green,and the cobalt solution used for plant growth is reusable,which meets the requirements of green chemistry.The material exhibits potential application as supercapacitor electrode material,and the experiment provides new strategy for biomass/metal composite synthesis.In the fourth chapter,inspired by the preparation of Chinese food tofu,we added different metal salt into the boiling soybean milk to obtain the corresponding tofu.All metal salt tofu were successfully prepared by optimizing the experimental conditions.Metal ions were well loaded in the corresponding tofu with uniform dispersion,and keep the good dispersion after activation and became metal nanospheres.After analyzing the effect of different metal on tofu in the high temperature activation,we prepared bimetal tofu with certain ratio.Iron in the material creates plenty of pores and the cobalt provides pseudocapacitance.The synergy effect of the two metals creates a superior performance on electrochemistry.The specific capacitance of the product is381 F g^-1.The Cobalt increases the graphite degrees of the carbon during activation,which brings about better conductivity,while the iron decreases the resistance of electrolyte ion diffusion by creating more pores.The material exhibits low resistance,excellent coulomb efficiency and rate capacity on the joint efforts of both metals.The energy density only decreases 34%while the power density increases 10 times.This work involves cheap and green raw material as well as simple synthesis.The product shows potential application in electrochemitry.The experiment provides new strategy for biomass/metal composite synthesis in electrochemistry.The last chapter is the summary and outlook of the three research systems in this dissertation.