Preparation And Supercapacitive Storage Properties Of Biomass Derived Porous Carbon Materials

Developing and utilizing green and clean renewable resources,such as wind and solar energy,is an effective way to solve future energy and environmental issues.At present,the conversion of large-scale renewable energy into electricity mainly uses energy conversion technologies,such as solar cells and mechanical generators,etc..However,direct introduction into the grid will cause changes in voltage and frequency,due to unsteady characteristics of renewable energy generation.Therefore,exploring stable,efficient,high-performance and low-cost energy storage technology is a great strategic significance for China's energy structure adjustment and the future development of the smart grid and city.Among them,supercapacitors(SCs)as a new type of energy storage device have received tremendous attention,mainly due to its high-impact characteristics,such as high safety,high efficiency,and high stability.Meanwhile,the development of flexible SCs can meet the needs of flexible and portable electronic devices in the future.As known,utilizing green and renewable waste biomass resources to prepared biomass-derived porous carbon and porous carbon fibers with high specific surface area and controllable pore structure is one of the important research topics in the field of biomass resources and SCs energy storage.In recent years,garbage classification has attracted more and more attention.Among them,many kinds of waste biomass resource materials are common waste resources.In this work,porous carbon,hierarchically porous carbon,heteroatoms co-doped hierarchically porous carbon,and graphitized porous carbon fiber have been prepared and derived from waste biomass,such as liquid(Waste fruit grain orange),solid(Peanut meal,etc.),the flexible cotton fiber and so on.And the supercapacitive storage properties of these materials are measured as the electrode for SCs.This strategy provides a new way for the development of high performance and high stability supercapacitive energy storage materials and high-value utilization of waste biomass resources.This work mainly focuses on research work from the following aspects:1)The fruit grain orange with the expired deadline(FGO)from Huiyuan(?)derived porous carbon was prepared by a low-cost and facile hydrothermal process and chemical activation car-bonization(KOH).Then,the effects of KOH dosage on the physicochemical properties were investigated.When the mass ratio of KOH to hydrothermal carbon material is 4,the specific surface area of fruit grain orange derived porous carbon material(HPC-4)can reach up to 2149 m2·g-1 with rich microporous structure.The supercapacitive storage properties of HPC-4 were tested.The largest specific capacitance of HPC-4 is 452.7 F·g-1 at 1 A·g-1.The assembled HPC-4//HPC-4 all-solid-state symmetrical SCs displays energy density of 14.1 W h kg-1(140 W kg-1)and excellent stability(capacitance retention rate can reach 90%after 6000 GCD cycles).And the assembled HPC-4//HPC-4 all-solid-state symmetrical SCs can light red LED,indicating its potential for SCs application,which provides a basis for high-value utilization of liquid biomass resources and high-performance porous carbon material for SCs.2)To obtain hierarchically porous carbon materials with more mesoporous and macroporous structures,peanut meal as solid waste derived hierarchically porous carbon materials(N-P-S-HPC)were firstly prepared by one-step carbonization method using ZnC12 and Mg(NO3)2 6H2O as dual-template.The influence of carbonization temperature and the mass ratio of the dual-template to peanut meal were investigated.The results show that the carbonization temperature is 800? and the mass ratio of the dual-template to peanut meal is 2,N-P-S-HPC exhibits the specific surface area of 2090 m2·g-1 and abundant pore structure(micropore,mesoporous and macroporous).Meanwhile,N-P-S-HPC can well inherit the heteroatoms(N,P and S elements)of peanut meal,and the contents of N,P and S elements are 11.2 atomic%,0.82 atomic%,and 0.64 atomic%,respectively.N-P-S-HPC shows excellent capacitive performance.The specific capacitance of N-P-S-HPC is 525 F·g-1 at 1 A·g-1,in which the pseudo-capacitance contribution rate of heteroatoms N,P and S co-doping can reach up to 23%(Trasatti analysis method),higher than that of commercial activated carbon(specific capacitance:230 F·g-1,pseudo-capacitance contribution:8%).The assembled N-P-S-HPC//N-P-S-HPC symmetrical SCs exhibits a high energy density of 24.9 Wh·kg-1(400 W·kg-1)and excellent cycle stability(after 6000 CV cycles at 300 mV·s-1,the capacitance retention of 90%).Furthermore,fruit grain orange derived hierarchically porous carbon(FGO-HPC)was prepared by a one-step carbonization method using ZnCl2 and Mg(NO3)2 6H2O as dual-template which displays ultrahigh specific surface area.Among them,the specific surface area of mesoporous and macroporous for FGO-HPC is 592.9 m2·g-1,which is better than HPC-4(237 m2·g-1,Chapter 2).Furthermore,a variety of biomass-derived hierarchically porous carbon materials were prepared by the same method,which displays excellent pore structure,high specific surface area,and outstanding specific capacitance,indicating that the one-step carbonization method with dual-template is universality.3)Considering that some biomass contains fewer heteroatoms co-doping,a rich N and S co-doped succulent leaves derived hierarchically porous carbon sheets(N-S-HPSC)was prepared by a facile one-step carbonization method with thiourea as S source and N source.The results show that N-S-HPSC exhibits a rich N(9.5 atomic%)and S(2.21 atomic%)co-doping and large specific surface area of 2136.2 m2·g-1 with abundant pores structure(micropores,mesopores,and macropores).The capacitive performances were tested for SCs.The specific capacitance of N-S-HPSC is 455.3 F·g-1 at 1 A·g-1.The voltage window of the assembled N-S-HPSC//N-S-HPSC symmetric SCs using 1 M Na2SO4 electrolyte can be widened to 1.8 V.Meanwhile,the assembled N-S-HPSC//N-S-HPSC symmetric SCs displays high energy density of 19.89 Wh·kg-1(450 W·kg-1)and excellent cyclic stability,which indicates that the thiourea in the process(one-step carbonization with two-template)can improve the amount of N and S co-doping and the supercapacitive storage performances.4)To utilize the unique structure of biomass resources(cotton fibers),ZIF-67@ZIF-8 composite structure was in situ grown on the surface of flexible waste cosmetic cotton fiber substrate.And the partially graphitized N-doped porous carbon fiber material(N-PC@GCF)was firstly prepared.And the electrochemical properties were tested.The results show that N-PC@GCF inherits the excellent flexibility of cotton fiber,improves the specific surface area,and increases the content of N element doping and partial graphitization structure.The specific capacitance of N-PC@GCF is 427 F·g-1(0.5 A·g-1),which is much higher than waste cosmetic cotton fiber derived carbon fiber(30.1 F·g-1).The assembled N-PC@GCF//N-PC@GCF symmetrical flexible SCs exhibit a high energy density of 30 Wh·kg-1(1440 W·kg-1),excellent stability and flexibility.Besides,it can be used to light the red LED,which indicates that cotton derived flexible porous carbon fiber material is of significance and potential practical value for flexible supercapacitive energy storage.