Synthesis and Electrochemical Properties of Polypyrrole Conducting Polymer in Sheath like Nanotube Arrays Structured ove
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Synthesis and Electrochemical Properties of Polypyrrole Conducting Polymer in Sheath like Nanotube Arrays Structured over TiO2 for Supercapacitor Energy Storage Devices Navjot K. Sidhu1,2, A.C.Rastogi1,2 1
Electrical and Computer Engineering Department, Center for Autonomous Solar Power (CASP), Binghamton University, State University of New York, Binghamton, NY 13902, U.S.A. 2
ABSTRACT The vertical TiO2 nanotube arrays constituting the core of 3-D nanoscale electrode architecture were synthesized over Ti sheet by anodization. Such formed TiO2 nanotubes are electrically conducting and amorphous as confirmed by XRD studies. Nanotube morphology is affected by water content and in the present study, close-packed 3-4 μm long TiO2 nanotube arrays of 45-50 nm diameter are formed with 2% water as revealed by the transmission and scanning electron microscopy. The redox active polypyrrole sheath is created by ultra-short pulsed current electropolymerization. Electrochemical properties of the 3-D nanoscaled TiO2 nanotube corepolypyrrole sheath electrodes relevant to the energy storage were investigated using cyclic voltammetry (CV) plots, electrochemical impedance spectroscopy (EIS), Charge discharge (CD) tests. High areal capacitance density of 48 mF cm-2 and low charge transfer resistance 12 cm-2 with least ion diffusion limitation are realized at optimized polypyrrole sheath thickness. The Raman spectra studies reveal anion at specific chain locations involve in the redox process. INTRODUCTION Electrochemical energy storage in supercapacitor devices is emerging as prominent technology for high power applications in modern portable electronics for which material systems based on conducting polymers are being actively investigated [1]. Among others, polypyrrole which exhibits pseudocapacitance due to charge transfer reactions is widely studied [2]. However, the focus has been on 2-dimensional (2-D) random micro or macroporous structural forms aimed to achieve high surface area for accessible ions. The strategy in this work is to develop electrodes in the 3-D nanoscale architecture for accelerate ion kinetics and more pervasive ion access. Accordingly, we synthesized vertically aligned TiO2 nanotube ordered arrays as core and created conjugated polypyrrole conducting polymer nanotube sheaths for improved electrochemical energy storage. EXPERIMENT Fabrication of TiO2 Core and PPy- shell structure TiO2 nanotubes forming the core for Ppy is fabricated by anodization of Ti foil in the presence of fluoride ions. Experiment is carried out in two electrode geometry having platinum electrode as a counter and a reference electrode Ag/AgCl in ethylene glycol organic electrolyte. 0.25 wt % ammonium fluoride is added and potential of 30V is applied for 7 hours. Anodization is initiated by adding 2% vol. of water and with minimum water content, nanotube array without rippled
edges were prevented. Figure 1(a) shows organized nanotube structure. Diameter of nanotubes lies in the range of 45-50 nm. Ethanol cleaning for 30 minutes has be
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