Controllable Gorwth And The Electrochemical Properties Of Polyaniline Nanofibers

Polyaniline(PANI)nanofibers can combine the advantages of PANI,such as lowcost,easy synthesis,adjustable conductivity and good environmental friendship,with the merits of one-dimensional materials,including large ratio of length to diameter,high specific area and high porosity.The study on the preparation of PANI nanofibers is of great significance to the exploration of high-performance electrode material,which can further promote the development in the fields of supercapacitors.As the intrinsic morphology,PANI nanofibers has been investigated in a wide range.However,due to the rapid reaction kinetics and complex polymerization mechanism,the morphology control of PANI nanofibers is still a great challenge.In general,the formation of PANI nanofibers can be divided into the stages of nucleation,growth and overgrowth,and the stages are continuous processes.So as to realize the controllable growth of PANI nanofibers,the nucleation and growth process are separately controlled.Different kinds of approaches are designed for controlling the shapes and structure of seeds,and PANI nanofibers can be controllable obtained after adjusting the growth rate.By optimizing the experimental parameters for the synthesis of PANI nanofibers,the morphology and uniformity of nanofibers are enhanced,the application as high-performance electrode materials in supercapacitors is explored.The main contents were list as follows:1.Formation of PANI nanofibers in the presence of phenylenediamine????,?????????????,?????????????,???????????,As proposed by former researches,the introduction of seeds can improve the seeding process and enhance the controllability of polymerization procedure.Thus,three kinds of phenylenediamine(PDA),including ophenylenediamine(oPDA),m-phenylenediamine/mPDA and para-phenylenediamine(pPDA),are used as seeding center to induce the chemical polymerization of PANI nanofibers.The influences on the polymerization process,morphology,structure and electrochemical properties of final products are investigated.It can be found that oPDA and mPDA can slow down the reaction rate,whereas pPDA accelerates the chemical oxidative process.What is more,the higher content of PDA,the more obvious positive/negative effects.In the presence of different kinds of PDA,PANI nanofibers with diameters of 80�100 nm and length of several micrometers are easy to be prepared.The structure characterization indicates that oPDA and mPDA can change the plane configuration and reduce the chain orientation,whereas pPDA plays an ignorable role in the structure.Under the condition of oPDA with content of 2%,mPDA with content of 2%and pPDA with content of 1%,as-prepared PANI nanofibers exhibit outstanding electrochemical performances with the specific capacitances of 395.1 F/g,408.2 F/g and 389.5 F/g at the current density of 0.5 A/g.2.Formation of PANI nanofibers at the assistance of flowing polymerizationThe structure of seeds can directly influence the structure and property of final product,thus the flowing polymerization is proposed to control the polymerization process,where the seeds are generated under the flowing condition and confined space.By optimizing the flowing rate and aniline monomers,the influences on the morphology,structure and electrochemical properties are studied.The results show that aniline monomers in flowing tubes(An1)and aniline monomers in reaction solution(An2)have apparent influences on the morphology of PANI nanofibers,while flowing rate,An1 and An2 can lead to obvious influences on the crystalline structure and electrochemical properties.Under the conditions of flowing rate of 15 mL/h,An1=0.08 M,An2=0.3 M,PANI nanofibers exhibit the best electrochemical properties with the specific capacitances of 944.4 F/g and 361.9 F/g,at the scan rate of 5 mV/s and current density of 0.5 A/g,respectively.3.Formation of PANI nanofibers by �one-pot� polymerization through adjusting alkaline-acidic conditionThe difference of aniline concentration during flowing polymerization process can affect the uniformity of seeds,whereas the alkaline reaction medium can ensure the uniformity of initially formed seeds.Herein,�one-pot� polymerization is proposed,during which aniline oligomers are firstly created under the alkaline condition and PANI nanofibers are obtained under the acidic condition.The effects of aniline concentrations in alkaline stage(An1)and acidic stage(An2)on the morphology,structure and electrochemical properties of PANI nanofibers are investigated,and the experimental condition which is suitable to the high-performance electrode materials are explored.The results indicate that An1 has prominent effects on the electrical conductivity and electrochemical properties,whereas An2 plays a more important role in controlling the morphology and structure.Under the condition of An1=48mM and An2=0.2 M,the as-prepared PANI nanofibers exhibits the best electrochemical performances with the specific capacitances of 857.2 and 371.5 F/g,respectively,at the scan rate of 5 mV/s and current density of 0.5 A/g.Then ammonia is removed from the reaction medium so as to improve the electrochemical properties of PANI nanofibers.Especially,PANI-2 obtained after ammonia removal for 2 h achieves high specific capacitance of 1025.2 F/g and 419.0 F/g at the scan rate of 5 mV/s and current density of 0.5 A/g,respectively.4.Formation of PANI nanofibers at the aid of sulfonic acid induced selfassemblyThe self-assembly behavior of seeds plays an important role in the formation of PANI nanofibers,thus several kinds of sulfonic acids,such as SSA,pTSA,pASA and CSA,are introduced into the polymerization of PANI nanofibers,and the effects on morphology,structure and properties of PANI nanofibers are investigated.The results reveal that the influence of sulfonic acid on the morphology,chemical structure and crystalline structure is not obvious,whereas the doping with sulfonic acid can effectively boost the electrical conductivity and electrochemical performances.In the presence of 0.2 M CSA,the as-prepared PANI nanofibers shows the most excellent capacitive properties with the specific capacitances of 1379.4 and 569.8 F/g,respectively,at the scan rate of 5 mV/s and current density of 1 A/g.