Study On Process And Properties Of Preparation Of Porous Carbon And Composite Carbon Nanofibers Prepared Based On Corn-straw

With the increasing global problem of non-renewable energy depletion and environmental pollution,the search for clean,efficient and sustainable new energy,as well as new technologies related to energy conversion and storage,has widely attracted attention by researchers all over the world.Supercapacitors are energy storage devices that can be safely charged or discharged in transitory time,have a long cycle life and high power density.In recent years,supercapacitors have been used in the fields of hybrid electric vehicles,mobile electronic devices,and distributed sensor networks.Therefore,the research of supercapacitors as storage device for neo envirmental-friendly energy is a requirement of social development.Supercapacitors plays a vital role in protecting the environment and reducing energy consumption in the future,and has high theoretical and practical application value.China is a big agricultural country with abundant reserves of biomass waste like corn-straw.Transforming it into new energy storage materials can not only alleviate the energy crisis,but also reduce the environmental pollution caused by burning straw.In this work,corn-straws were used as the basic raw materials,and different treatment methods were used to obtain carbon materials with different morphologies.The microstructure and electrochemical properties of the carbon materials were investigated,feasibility as a supercapacitor electrode material studied.The main research contents are as follows:(1)Porous carbon electrode materials were prepared by KOH activation method using corn-straw as raw material.The optimal activation conditions were selected by electrochemical performance comparison:the mass ratio of activator to corn-straws was 2:1,and the activation temperature was 800°C.comparing the electrochemical properties of porous carbon were obtained by KOH activation method,mixed salt method and modified Hummers method.The experimental results show that the corn-straw based porous carbon prepared by KOH activation method has the highest specific capacitance.The activated carbon material prepared under this condition has a high specific surface area of 1067.11 m~2/g,has a large pore,mesoporous and microporous structure,and has a large amount of oxygen-containing functional groups on the surface.Capacitor performance is characterized by obvious electric double layer characteristics.The specific capacitance reaches 239 F/g at 1 A/g current density,and the specific capacitance retention rate is 97.12%after constant current charge and discharge 5000 cycles with current density of 1A/g.It not only solves the environmental pollution problem caused by burning straw,but also enhance the corn-straw’s comprehensive and high-value utilization.(2)Nanofiber mats were prepared by electrospinning using pretreated corn-straw carbon doped polyacrylonitrile(PAN).The pre-oxidized nanofiber mat was activated by KOH solution,then carbonized to obtain activated carbon nanofiber.The optimal activation conditions were as follows:the mass ratio of PAN/corn-straw carbon was 8:2,activated by 10%KOH solution,the mass ratio of solute KOH to nanofiber mat was 1:3,and the carbonization temperature was800°C.The specific capacitance was 265.4 F/g at a current density of 1 A/g.The retention rate was 95.91%after 5,000 cycles of constant current charge and discharge with a current density of 2 A/g.Its specific surface area reaches 1491.96 m~2/g,and it has microporous,mesoporous and macroporous pore structure.As a new energy material,it has excellent developing potential and research value.(3)The nanofiber mat was prepared by electrospinning using pretreated corn-straw carbon doped polyacrylonitrile(PAN).The pre-oxidized nanofiber mat was activated by solid KOH,then carbonized to produce hierarchical porous carbon(HPC).The optimal activation process conditions were as follows:the mass ratio of solid KOH to nanofiber mat was 2:1,and the carbonization temperature was 800°C.The specific capacitance is 332 F/g at a current density of 1 A/g.The retention rate was 94.18%after 5,000 cycles of constant current charging and discharging at a current density of 2 A/g.Its specific surface area reaches 2192.73 m~2/g,and it has microporous,mesoporous and macroporous pore structure,which is an excellent choice for electrode materials of supercapacitors.(4)Innovative development of a new activation method for the preparation of activated carbon nanofibers-enzymatic hydrolysis method,this method has mild reaction conditions and is completely green and non-polluting to the environment.The nanofiber mat was prepared by electrospinning using polyacrylonitrile(PAN)and corn-straw carbon as carbon sources,doping withβ-cyclodextrin.The intermediate temperatureα-amylase hydrolyzes the nanofiber mat,and then carbonizes at 800°C for 2 h to obtain activated carbon nanofibers.The optimum process conditions are:enzymatic hydrolysis temperature 75°C,enzyme concentration 58.82U/m L,hydrolysis time 90 min,β-cyclodextrin doping amount 20 wt%.The activated carbon nanofibers prepared by the enzymatic hydrolysis method under the optimal process conditions have a good fiber structure,a high degree of graphitization,a rich pore structure,and a specific surface area of 268.09 m~2/g.At the same time,we studied its electrochemical performance.The actived carbon nanofibers have a specific capacitance of 213 F/g at a current density of 0.5 A/g,and it has a small electrolyte diffusion resistance.The retention rate was 94.31%after 5,000cycles of constant current charging and discharging with a current density of 2 A/g,showing good practical application prospects.