Preparation And Energy Storage Properties Of Polyaniline / Polypyrrole Coaxial Composite Nanofiber

Supercapacitor with high power density, fast charge and discharge, long cycle life,which can be used in the power electric vehicles, portable equipment and data memory storage devices, has great potential applications. As the supercapacitor electrode materials, owing to the low price, ease of synthesis, good electrochemical properties, excellent chemical stability, polyaniline(PANi) and polypyrrole(PPy) have attracted wide attention. PANi stands out for ease of synthesis, unique doping/dedoping mechanism, controllable structure, whereas, it is only applied in acid electrolyte. PPy with excellent electrical, electrochemical properties and can be used in the neutral or alkaline electrolyte, but has some shortcoming, the poor stability, high cost of monomer. The study of the composite conducting materials with excellent performance is an important direction for supercapacitor electrode materials research. In this paper, we used a simple in-situ chemical oxidation polymerization to prepare a core-shell polyaniline/polypyrrole coaxial composite nanofiber. In the preparation of PANi nanofibers, we focused on the effect of co-solvent in interfacial polymerization on PANi nanofibers. Furthermore we disscussed the application of polyaniline nanofibers and polyaniline / polypyrrole composite nanofibers as electrode materials for supercapacitor.Our main results are listed as following:(1) The influence of co-solvent on the reaction process : We use chloroform solution containing the aniline monomer as organic phase and hydrochloric acid solution containing oxidant as aqueous phase.The aqueous phase is added a certain amount of an organic solvent as co-solvent. The monomer and oxidant reacted at the interface.By monitoring the reaction process, we studied the impact of co-solvent on reaction process in interfacial polymerization. The reaction rate of cosolvent system, is slower than the system of ammonium persulfate as the oxidant without co-solvent system and faster than ferric chloride as the oxidant without co-solvent system. And in the following order: dimethylsulfoxide, methanol, ethanol, acetone, dimethylcarbinol, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, reaction rate of co-solvent system gradually slowed down. Thus the co-solvent can effectively slow down the rate of reaction of interfacial polymerization and has an important influence on the reaction process in interfacial polymerization. The interfacial tension test showed, interfacial tension gradually reduced in the order of dimethylsulfoxide, methanol, ethanol, acetone, methylcarbinol, dimethylacetamide, dimethylformamide, N- methylpyrrolidone, which was consistent with the order of the reaction rate. Moreover, FE-SE showed the PANi of all the system are nanofibrous.(2) The influence of co-solvent on the chemical structure and electrochemical performance: In the first co-solvent system(methanol, ethanol, acetone, dimethylcarbinol), from methanol to dimethylcarbinol, the PANi nanofibers have better performance with longer length, higher conductivity, better crystallinity, higher thermal stability, higher capacitance. The second co-solvent system(dimethylacetamide, dimethylformamide) prepared PANi nanofibers with poor conductivity, bad crystallinity, poor thermal stability and unsatisfactory electrochemical properties.The third cosolvent(dimethylsulfoxide, N- methylpyrrolidone), PANi prepared in dimethylsulfoxide co-solvent exhibited best performance while the performance of the PANi nanofibers from Nmethylpyrrolidone co-solvent systems is not ideal.(3) PANi/PPy coxial composite nanofiber: An efficient approach was presented to prepare composite nanofibers by in situ chemical polymerization of pyrrole in the presence of PANi nanofiber with best performance in co-solvent interfacial polymerization as a template.The morphologies and structures of composite nanofibers were studied by TEM, FTIR, Raman, XRD and TGA, and more attention were paid to their electrochemical properties as supercapacitor electrode materials. The results showd that the composite nanofibers had higher capatiance than pure PANi and PPy.When the PANi nanofiber is synthesized by the dimethylacrbino and dimethylsulfoxide co-solvent system, the PANi/PPy has best electrochemical.