Preparation and Selected Properties of an Improved Composite of the Electrophoretically Deposited Single-Wall Carbon Nanotubes, Electrochemically Coated with a C60-Pd and Polybithiophene Mi

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• 作者：Piotr Pieta ; Ganesh M. Venukadasula ; Francis D’ ; Souza ; Wlodzimierz Kutner
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：August 6, 2009
• 年：2009
• 卷：113
• 期：31
• 页码：14046-14058
• 全文大小：675K
• 年卷期：v.113,no.31(August 6, 2009)
• ISSN：1932-7455

文摘

An improved carbon nanotube conducting composite material for electrochemical capacitors has been devised and tested. It was prepared by electrophoretic deposition of a film of noncovalently surface modified with 1-pyrenebutyric acid HiPCO single-wall carbon nanotubes (pyr-SWCNTs), which were then electrochemically coated, under multiscan cyclic voltammetry (CV) conditions, with a mixed film of the fullerene-palladium (C₆₀-Pd) polymer and the polybithiophene (PBT) polymer. Both the electrophoretic deposition of pyr-SWCNTs and electrochemical polymerization of (C₆₀-Pd)-PBT was in situ monitored by piezoelectric microgravimetry (PM) with the use of an electrochemical quartz crystal microbalance (EQCM). Atomic force microscopy imaging of the film revealed that pyr-SWCNTs formed tangles of pyr-SWCNTs bundles surrounded by globular clusters of (C₆₀-Pd)-PBT. X-ray photoelectron spectroscopy provided information on the mole ratio of BT/C₆₀/Pd ≈ 1:2:4 indicating that, most likely, the C₆₀-Pd and PBT polymers are not interconnected in the composite film. The electrochemical and visco-elastic properties of the pyr-SWCNTs/(C₆₀-Pd)-PBT film were investigated and compared to those of the (C₆₀-Pd)-PBT film by simultaneously performed CV and PM measurements in a blank acetonitrile solution of tetra-n-butylammonium perchlorate. Both films revealed two potential windows of electrochemical activity, that is, one at potentials more negative than −0.40 V versus Ag/AgCl due to fullerene electroactivity and the other at potentials more positive than 0.40 V due to PBT electroactivity. Advantageously, both cathodic and anodic currents for the pyr-SWCNTs/(C₆₀-Pd)-PBT film were much higher than those for the (C₆₀-Pd)-PBT film due to the more developed electrode area in the presence of pyr-SWCNTs and, hence, higher capacitance. The highest value of specific capacitance (C_s), determined from the CV measurements, for the negative potential range was 100, 75, and 50 F g⁻¹ while for the positive potential range it was 200, 180, and 50 F g⁻¹ for the film of pyr-SWCNTs/(C₆₀-Pd)-PBT, (C₆₀-Pd)-PBT, and pyr-SWCNTs, respectively. From the electrochemical impedance spectroscopy measurements, it followed that both for the potential range of 0 to −1.10 V and 0 to 1.0 V, the Warburg-type region was linear and its slope was 45° at high and intermediate frequencies indicating control of the charge transport rate by the rate of the semi-infinite diffusion of counterions within the film. At low frequencies, control of this transport rate by the finite diffusion rate dominated, as characterized by sharp upturns in the -Z″ versus Z′ curves. A modified Randles equivalent circuit was used to determine impedance parameters for the pyr-SWCNTs/(C₆₀-Pd)-PBT film-coated electrode. Constant-current 90 mA charging and discharging at different voltage limits for the pyr-SWCNTs/(C₆₀-Pd)-PBT film-coated Au disk electrode was reversible and pseudolinear for the voltage range not exceeding 1.60 V.