Configuration and capacitance properties of polypyrrole/aligned carbon nanotubes synthesized by electropolymerization
XU Ying
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ZHUANG ShuQi
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ZHANG XiaoYan
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HE PinGang
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FANG YuZhi
0
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Department of Chemistry, East China Normal University
,
Shanghai 200062, China
Aligned carbon nanotubes (ACNTs) were modified with polypyrrole (PPy) via electropolymerization. Because of the large specific surface area and excellent electrical conductivity of ACNTs, continuous electropolymerization was able to be carried out, forming a thick PPy coating on the ACNTs. The resulting nanocomposite possessed a core-shell structure with ACNTs as the core, PPy as the shell, and nanoparticles of PPy on the top, and displayed high performance supercapacitance properties.
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Carbon nanotubes (CNTs) were discovered in 1991, and
possess many outstanding physical and chemical properties.
Since then, this interesting nanomaterial has been developed
substantially for science and technology applications.
Generally, CNTs are prepared as a randomly oriented structure
with each nanotube wrapped with others. Recently,
scientists have designed and prepared them with specific
structures, such as aligned CNTs (ACNTs) [1], which have been
employed as a novel electrode nanomaterial to fabricate
bio/chemical sensors [24], and electron field emitters [5].
ACNTs are also promising supercapacitor materials because
their 3D structure offers a large specific surface area,
superior electronic transfer ability through individual nanotubes,
and chemical inertness [69]. However, because ACNTs are
generally directly prepared on substrates without special
protection, the nanotubes are easily cracked. In additional,
they are intrinsically hydrophobic with a low affinity for
aqueous solution. The friability and hydrophobic nature of
ACNTs limits their use as supercapacitors. To improve the
physicochemical and mechanical properties of ACNTs, and
further increase their capacitance, herein, we have modified
the nanotubes by electropolymerization with the conducting
polymer polypyrrole (PPy). Conducting polymers such as
polyaniline [10], polymethyl methacrylate [11],
polythiophene [12] and PPy [1315] have been combined with
traditional CNTs, and such nanocomposite materials display
favorable electronic and mechanical properties including
enhanced capacitance [16,17].
PPy possesses advantages such as easy synthesis, high
electrical conductivity, thermal and chemical stability,
environmental friendliness, low preparation cost and
electropolymerization potential, in addition to the potential to store
energy [18]. However, PPy deposited on common substrates
forms an uncontrolled dense film with high resistance to
ionic and electronic transfer. The highest reported electronic
conductivity of a PPy film is several hundred S/cm [19],
which limits its use as an electrode material, supercapacitor,
and functional component in microelectromechanical
systems. One method to resolve this problem is to use a special
matrix with a high surface area and nanoporosity for
polymerization of PPy, resulting in a large amount of
porous PPy loaded on the matrix surface. CNTs are a good
example of such a matrix, and possess the added advantage
of increasing the electronic conductivity of PPy. To date,
both entangled single- and multi-walled CNTs (i.e.,
SWCNTs and MWCNTs) have been employed as matrices
The Author(s) 2011. This article is published with open access at Springerlink.com
for electropolymerization of PPy, improving the specific
surface area, electric conductivity and mechanical
properties of PPy [2024]. However, there are few reports on the
combination of conducting polymers with ACNTs. Dai and
coworkers [25] first reported the electropolymerization of
conducting polymers including polyaniline and PPy onto
ACNTs for potential application in optoelectronic
nanodevices and sensors. The conducting polymers uniformly
modified the aligned nanotubes during the
electropolymerization process. Windle and coworkers [26] found that
electropolymerizing PPy onto ACNTs increased the specific
capacitance (SC) by about 4 times compared with a pure
PPy film. Wallace et al. [27] fabricated a glucose sensor
using a PPy-coated ACNT electrode.
Herein, PPy-ACNT nanocomposites are formed using an
electrochemical method. The properties of the
nanocomposites are fully investigated, especially the capacitive
behavior. Because the ACNTs possess much lower resistance to
electron transfer than those with structural defects,
individual carbon nanotubes have a high conductivity up to 5000
S/cm, while entangled ones have a conductivity in the order
of 200300 S/cm [2830]. In addition, the 3D ACNTs
possess a much larger surface area than traditional CNTs.
Therefore, it was expected that ACNTs would act as a
suitable matrix for polymerization of PPy, and the resulting
PPy-ACNT nanocomposites would overcome the individual
shortcomings of ACNTs and PPy, facilitating their
application as supercapacitor materials.
ACNTs were prepared on quartz glass substrate by chemical
vapor deposition using iron(II) phthalocyanine as the raw (...truncated)