Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes
Introduction
Supercapacitors occupy important position among various power systems due to their advantages over the second batteries and conventional capacitors, and potential applications in a series of electronic devices and electrical vehicles [1]. It is well known that carbon nanotubes (CNTs) possess high surface area, tunable surface function, high electrical conductivity and environmental stability, thereby are widely used as the electrode materials for electric double-layer capacitors. On the other hand, the controllable structures and outstanding properties (e.g., high doping level and quick electrochemical switching) of electronically conducting polymers (ECPs) [2], [3], [4], [5] endow them the possibility for the application as prospective materials in pseudocapacitors. Recently, much effort was devoted to the combination of ECP with CNT to improve the electrochemical performance of the materials [6], [7], [8], [9], [10], [11]. However, some drawbacks of CNTs, including insolubility, poor dispersibility and bad compatibility, hinder their uniform incorporation with ECP matrixes [12], [13], [14], [15]. Accordingly, extensive attention has been focused on the enhancement of the interaction between CNT and ECP [16], [17], [18], [19], [20], [21]. The most common method is to treat CNTs with strong inorganic acids, such as HNO3, H2SO4 or the mixture of HNO3/H2SO4 to generate carboxylic group capped CNTs before their direct association with ECPs [22]. The control of morphology of ECPs on CNTs is another challenging issue. The utilization of organometallic-functionzied CNTs as morphology-guiding agent is a possible strategy to tune the growth of ECPs on CNTs. Unfortunately, scarce investigation has been conducted along this line.
In the present study, a microwave hydrothermal strategy has been employed to functionalize acid-treated CNTs with a thorn-like organometallic, the methyl orange–iron (III) chloride (MO–FeCl3) complex. This complex can serve as both morphology-guiding agent and oxidant, thereby polypyrrole nanoparticles can be attached directionally on CNTs by the polymerization of pyrrole in the absence of extra oxidants. Fig. 1 illustrates the chemical structure of MO [23], [24] and the possible mechanism for the synthesis of CNT/MO–FeCl3 and the resulting polypyrrole/carbon nanotube (PPy/CNT) composite. To the best of our knowledge, the preparation of such organometallic-functionized CNTs (CNT/MO–FeCl3) and the corresponding PPy/CNT composite has not been reported by far. This investigation offers a new prospect for the preparation of 1D nanostructured polymer perpendicular-modified CNTs. The resulted PPy/CNT composite has been characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy, infrared spectroscopy and X-ray diffraction, and its application as electrode for supercapacitors has also been estimated by electrochemical investigation.
Section snippets
Synthesis of CNT/MO–FeCl3 composites
Pyrrole from Aldrich (99%) was distilled prior to use and stored at −5 °C in a nitrogen atmosphere. CNTs from Shenzhen Nanotech Port Co. Ltd. (China) were purified by refluxing in concentrated nitric acid. All other reagents including methyl orange (MO, (CH3)2NC6H4-NNC6H4SO3Na) were of analytical grade and used as received. Typically, purified CNTs (0.07 g) and methyl orange (MO, 0.4312 g) were dispersed in 240 mL deionized water and sonicated for 30 min so that the MO was uniformly adsorbed on the
Morphology and structure analysis
Typical TEM images of functionalized CNTs prepared by both the microwave hydrothermal route and the conventional solution method, and the resulted PPy/CNT composite are displayed in Fig. 2. Obviously, the CNT surface treated by the microwave hydrothermal technique were very rough (Fig. 2a), as distinct from the smooth surface of the raw CNTs. As can be seen from the TEM picture of a single CNT (Fig. 2b), lots of thorns were covered densely on the surface of the CNT. However, for CNTs
Conclusions
A thorn-like MO–FeCl3 complex was successfully grown on CNTs by the microwave hydrothermal technique. Further, PPy/CNT composite with controllable morphology was obtained with the aid of the MO–FeCl3 complex. The electrochemical performance indicated that the prepared composites had a specific capacitance of 304 F g−1. Through a series of chemical characterizations, it was clear that the growth of granular-like PPy was closely related to the shape and size of the oxidative compounds on CNTs. If
Acknowledgments
This work was supported by the Natural Basic Research Program of China (973 Program; No. 2007CB209703) and the Natural Sciences Foundation of Xinjiang Uygur Autonomous Region (No. 200821123).
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2016, Synthetic MetalsCitation Excerpt :For both types of colloids, the electrochemical activity was reduced at higher PVP concentration. This electrochemical behaviour of PPy colloid is much more attractive as compared with the literature work, where some of the PPy did not show significant redox peaks during cyclic voltammetry tests [28,43]. Since the CV test was carried out directly using PPy colloid as the electrolyte solution, the appearance of sharp redox peaks (corresponding to a much higher current signal) in the CV curve of nanotubular PPy may be due to (1) good interaction of PPy with the electrolyte environment which gives a significant current signal [44] and (2) the aqueous colloidal form of PPy induced its limited coating on the working electrode surface, thus the CV curve shows predominantly pseudocapacitance nature instead of double layer capacitance usually related with rectangular shape CV curve [45].