The Study On Preparation And Properties Of Biomass-based Porous Carbon Doped With Heteroatoms

Today’s rapid consumption of fossil energy has led people to turn their attention to the development of clean energy.It is very important to develop and design an efficient and environmentally friendly energy storage device to rationally use the energy in nature.Electrochemical energy storage system is one of the important ways to store and utilize electric energy efficiently.Among them,supercapacitors have developed rapidly in recent years,and their performance is between traditional capacitors and secondary batteries,it not only ensures high power density output but also high energy density,and at the same time has a fast charge/discharge rate,long cycling stability,long service life,low environmental pollution and many other advantages,it is an energy storage device with extremely promising application prospects.Electrode materials are an important part of supercapacitors.Among different types of electrode materials,porous carbon materials have been widely studied because of their low cost,rich pore structure,high specific surface area,and strong practicability.The development and utilization of biomass porous carbon can explore new materials for long-term sustainable energy storage,enhance the cost competitiveness of the energy supply market,reduce environmental impacts,and meet the urgent needs for green and sustainable development strategies.The purpose of this paper is to prepare heteroatom-doped porous carbon electrode materials using biomass with abundant resources and low cost,and optimize the structure of the material to obtain high specific surface area,high porosity,good stability and excellent electrochemical performance practical capacitor.The details are as follows:1.Heteroatom-doped porous carbon material has been synthesized by direct pyrolysis with pig nails followed by chemical activation using K₂CO₃ as activator,and the influence of the synthesis temperature on the micromorphology,composition and electrochemical properties of the sample was discussed.The experimental results show that the pig nail has the characteristics of heteroatom self-doping.Without adding any chemical reagents,the product already contains a small amount of heteroatoms such as N and O.In different samples,the specific surface area of KPNC-700 is 2056 m² g^-1,and the total pore volume is 1.05 cm³ g^-1.The rich pore structure provides more transmission paths for the migration of electrolyte ions and reduces the diffusion resistance of ions.The abundant nitrogen and oxygen functional groups in the material not only help to enhance the wettability of the electrode material in the electrolyte,but also help to enhance the specific capacitance.Therefore,in the three-electrode system,the specific capacitance of KPNC-700 is as high as 333.5 F g^-1.By repeating galvanostatic charge/discharge test for 2000 cycles,the specific capacitance can still maintain 97.6%of the initial value.It has excellent electrochemical performance and excellent cycle stability.2.Using corn starch as the carbon precursor,urea as the nitrogen source,and K₂CO₃ as the activator,a heteroatom-doped porous carbon material was prepared by a one-step high-temperature pyrolysis method,and the influence of the Ratio of activator to raw material on the micromorphology,composition and electrochemical properties of the sample was discussed.The experimental results show that the content of nitrogen atoms in corn starch is very small.Therefore,adding urea not only provides a large number of nitrogen atoms for the material to increase the active sites of the reaction,but also the released gas can create a part of the pores for the material,and it can be used for subsequent pickling creates more porosity.In different samples,NPC-1 has the highest specific surface area of 2388 m² g^-1,the largest total pore volume,1.31 cm³ g^-1,N atom doping amount of 4.72%,O atom doping amount of 18.46%,and these advantages cooperate with each other and work together to provide more sites for the Faraday reaction.Therefore,in the three-electrode system,the specific capacitance of NPC-1 is as high as 292.7 F g^-1.By repeating galvanostatic charge/discharge test for2000 cycles,the specific capacitance can still maintain 89.7%of the initial value.It has excellent electrochemical performance and excellent cycle stability.In summary,this thesis uses two kinds of biomass,pig nails and corn starch,as raw materials,and the relatively mild weak alkaline reagent K₂CO₃as the activator.Two different preparation methods（in-situ doping and post-doping）are used to synthesize porous carbon materials,and through a series of characterization and testing methods,the feasibility of its application in the field of supercapacitor energy storage has been proved.It not only broadens the multiple selectivity of biomass,but also reduces the environmental pollution of biomass waste,and provides new ideas for the development of supercapacitors.