Fabrication Of Polyaniline Encapsulated Electrospun Carbon Nanofibers And Their Supercapacitve Performance

Supercapacitor is a new kind of energy storage device, which has the advantages offast charge/discharge speed, high power density, long durability, and environmentalfriendliness. Electrode material is one of the key factors influencing the supercapacitiveperformance. High performance supercapacitors may be fabricated using the carbonnanofibers/polyaniline (PANI/CNFs) composites by combining the electricaldouble-layer capacitance provided by the CNFs and the pseudocapacitance provided byPANI. In this study, PANI encapsulated electrospun carbon nanofibers were producedby in situ polymerization. SEM, XRD, FT-IR and Raman Spectroscopy were used tostudy the structure of the PANI/CNFs composite fibers. The supercapacitiveperformance of the PANI/CNFs was investigated by cyclic voltammetry(CV),galvanostatic charge-discharge(CD), and electrochemical impedance spectroscopy(EIS)using a electrochemical workstation.The CNFs were produced by electrospinning and carbonozation using PAN as theprecursor. In this part, the concentration of PAN and the protective atmosphere forcarbonization were studied. SEM observation indicates that the CNFs prepared at PANconcentration of3%(wt/v) are uniform and continuous. NH3has etching reactivity onthe CNFs and the surface of the CNFs carbonized in NH3is rough.Two kinds of oxidant were used when preparing the PANI/CNFs compositenanofibers by in situ polymeration of aniline, i.e. APS and FeCl3. When using APS asthe oxidant for preparing the PANI/CNFs nanofibers the effects of anilineconcentration, polymerization time, and the reaction temperature on the formation ofthe PANI encapsulating layers were investigated and the supercapacitive performancewas measured. It is indicated that the optimal supercapacitive performance wasobtained at the aniline concentration of0.03M, polymerization time of6h, andreaction temperature of20oC. The specific capacitance of the PANI/CNFs compositesis515F/g and the energy density reachs57Wh/kg at the current density of2A/g.FeCl3with low redox potential was also used as the oxidant to control the PANI layerthickness, where the dependence of the PANI layer thickness on the polymerizationtime and the supercapacitive performance on the layer thickness were investigated. Theresults indicate that the thickness of the encapsulating PANI layer increases to17.9nmfrom5.7nm when increasing the reaction time to42h from15h. In this stage thesurface of the PANI layer is smooth. The specific capacitance increases first and thendecreases with increasing the thickness of the PANI layer and culminate at13.9nmcorresponding to the highest specific capacitance of378F/g. With further increasingreaction time the surface of the PANI layer becomes rough but improvement of the specific capacitance was observed. Single wall carbon nanotubes were added into thePANI/CNFs nanofibers in order to increase the conductivity. It is indicated that thesupercapacitive performance improves obviously with the internal resistancedecreasing to12Ω, specific capacitance and energy density increasing to564F/g and64Wh/kg at2A/g.New type of CNFs were prepared by carbonizing the PANI/CNFs nanofibers andtheir supercapacitive performance was measured. The measurements indicate that thespecific capacitance, working voltage, and energy density of the new CNFs convertedfrom PANI are205F/g,3V, and63.3Wh/kg, respectively. Comparing with thePANI/CNFs nanofibers and PAN-converted CNFs the PANI-converted CNFs showobviously improved working voltage and energy density.