synthesis and characterization of polypyrrole nanotubes/multi-walled carbon nanotubes composites...
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Synthesis and characterization of polypyrrole nanotubes/multi-walled carbon nanotubes composites with superiorelectrochemical performance
Lanlan Yang • Mei Li • Yunqiang Zhang •
Kaihua Yi • Jingyun Ma • Yingkai Liu
Received: 30 October 2013 / Accepted: 14 December 2013 / Published online: 22 December 2013
� Springer Science+Business Media New York 2013
Abstract Novel polypyrrole nanotubes/multi-walled
carbon nanotubes (PPyNTs/MWCNTs) composites have
been successfully synthesized via in situ chemical oxida-
tion polymerization with methyl orange as soft template.
Scanning electron microscopy and transmission electron
microscopy images revealed that MWCNTs intertwined
with the PPyNTs and PPyNTs/MWCNTs composites
formed in water–ethanol solution. The obtained composites
exhibited perfect electrochemical characteristic compared
with PPyNTs and MWCNTs owing to the synergetic effect
and the specific capacitance of the composites was strongly
influenced by the mass ratio of pyrrole to MWCNTs.
According to the galvanostatic charge/discharge analysis,
the specific capacitance of PPyNTs/MWCNTs composites
is up to 352 F g-1 at a current density of 0.2 A g-1 in 1 M
KCl solution, much higher than that of the PPyNTs
(178 F g-1) and MWCNT (46 F g-1), suggesting its
potential application in supercapacitors.
1 Introduction
Carbon nanotubes (CNTs) have recently attracted consid-
erable interest because of their potential applications in
field emitters, nanoelectronic devices, probe tips for scan-
ning probe microscopies and nanotube-based composites
due to their high electrical conductivity, chemical stability,
low mass density, and large surface area [1–3]. Experi-
mentally introducing CNTs into a polymer matrix could
significantly improve not only the mechanical and electri-
cal properties but also the stability of the neat polymer
matrix [4, 5]. Both single-walled carbon nanotubes
(SWCNTs) and multi-walled carbon nanotubes
(MWCNTs) have been used in previous reports [6–8] and
the PPyNTs/MWCNTs composites by the incorporation of
polypyrrole (PPy) with CNTs are expected to yield good
electrochemical performance because PPy has potential
applications owing to its excellent electrical conductivity
and environmental stability [9, 10]. Recently, some of new
methods have been reported for producing composites of
PPy and CNTs such as pulsed laser ablation, electro-
chemical oxidation method [11, 12]. Sw and Je [11] suc-
cessfully prepared the polypyrrole/multi-walled carbon
nanotube (PPy/MWCNTs) nanocomposites with high
loadings by pulsed laser ablation. Han et al. [12] synthe-
sized a series of nanocomposite films of PPy/MWCNTs by
electrochemically and studied the morphology, conductiv-
ity and thermal stability of these composites.
In this paper, a novel facile method was introduced to
synthesis PPyNTs/MWCNTs composites by in situ chemical
oxidation polymerization using ammonium persulfate as
oxidant in the presence of methyl orange (MO). Composites
have been prepared at different mass percentage of poly-
pyrrole to MWCNTs, which influenced the specific capaci-
tance of the samples. The electrochemical performances of
L. Yang � M. Li (&) � Y. Zhang � K. Yi � J. Ma � Y. Liu
School of Materials Science and Engineering, Qilu University of
Technology, Daxue Road, Western University Science Park,
Jinan 250353, People’s Republic of China
e-mail: [email protected]
M. Li � J. Ma � Y. Liu
Shandong Provincial Key Laboratory of Processing and Testing
Technology of Glass and Functional Ceramics, Jinan 250353,
People’s Republic of China
M. Li � J. Ma � Y. Liu
Key Laboratory of Amorphous and Polycrystalline Materials,
Qilu University of Technology, Jinan 250353, People’s Republic
of China
123
J Mater Sci: Mater Electron (2014) 25:1047–1052
DOI 10.1007/s10854-013-1685-1
PPyNTs/MWCNTs composites were investigated in detail
and the specific capacitance of the composites is as high as
352 F g-1 at a current density of 0.2 A g-1.
2 Experimental
2.1 Preparation of the PPyNTs/MWCNTs composites
The MWCNTs were sonicated with a concentrated solution
of H2SO4/HNO3 (3/1 volume ratio) for 8 h to make the
nanotubes smaller and generate –COOH groups with the
strong oxidative interaction of HNO3 and activated C on
the surface of the MWCNTs [13–16]. PPyNTs/MWCNTs
composites were synthesized via in situ chemical oxidative
polymerization directed by modified MO as self-degrad-
able templates. Typically, 0.098 g MO was dissolved in
150 mL mixture solution of deionized water (125 mL) and
ethanol (25 mL). Some red flocculent precipitate appeared
immediately once 0.6 mL HCl was injected into the solu-
tion. After mechanical agitation for 5 min. Py and
MWCNTs were added into the above mixture dropwisely.
And then the solution (1.64 g of ammonium peroxodisul-
fate (APS) dissolved in 50 mL distilled water) was slowly
added into the mixture. The polymerization reaction sys-
tem was carried out below 5 �C for 24 h with constant
mechanical stirring. The resultant black precipitate was
filtrated and washed with deionized water/ethanol (10 mL/
10 mL) six times until filtrate was colorless and neutral.
The finally products were dried under a vacuum atmo-
sphere at 60 �C for 24 h.
Changing the mass ratio of the Py to MWCNTs with
5:2, 5:1, 9:1, 10:1 and 11:1 and repeating the above pro-
cess, five composites samples were obtained.
2.2 Characterization
The morphology of the product was directly observed with
scanning electron microscopy (SEM) (FEIco-Holland,
JSM-6700F) and transmission electron microscopy (TEM)
(JEOL, JEM-1011). An X-ray diffraction (XRD) pattern
was taken with a Bruker D8 ADVANCE XRD instrument
at a 10 min-1 scanning speed from 20� to 80�. Fourier
transform infrared spectroscopy (FTIR) spectra of the
samples were obtained with a Shimadzu FTIR-8400s
spectrophotometer in the range of 4,000–500 cm-1 and the
sample was impressed into KBr pellets.
2.3 Electrochemical measurements
The electrochemical performances of the samples were
evaluated by the use of PARSTAT2263 electrochemical
workstation under computer control at room
temperature. Cyclic voltammetry (CV), galvanostatic
charge–discharge and electrochemical impedance spec-
troscopy (EIS) were measured in a conventional three-
electrode electrochemical cell with Platinum foil and
saturated calomel electrode (SCE). The working elec-
trodes were prepared by mixing the as-prepared sam-
ples, poly (tetrafluoroethylene) (PTFE) and carbon
black at the mass ratio of 8:1:1, the mixtures were
coated onto a 1 cm 9 1 cm nickel foam current col-
lector, and dried at 60 �C for 8 h.
3 Results and discussion
3.1 Characteristics of the PPyNTs/MWCNTs
composites
The nanostructure of the as-prepared PPyNTs/MWCNTs
composites with 1:1 mass ratio of Py to MWCNTs, was
investigated by SEM and TEM. Figure 1a and b are the
SEM images of MWCNTs and PPyNTs, and the inset
images are the TEM images of them, respectively. The
SEM images (Fig. 1c) clearly illustrated the microscopic
structure of PPyNTs/MWCNTs composites and the TEM
image revealed the slender MWCNTs intertwined on the
wide PPy nanotubes randomly. The possible mechanism
scheme is presented in Fig. 1d and the upper part is the
cross-section diagram and the lower part is the front view
of the interaction among the MO template, PPyNTs and
MWCNTs. Firstly, the MO tubular micelles formed in the
solution and Py molecules were absorbed in the MO
micelles inside and the PPyNTs formed gradually during
the polymerization. Then, the acid groups on the surface of
MWCNTs were attracted to the PPyNTs surface due to the
hydrogen bonds formation between –COOH groups of
modified MWCNTs and –NH groups of the PPy [17].
Finally, the PPyNTs/MWCNTs composites were obtained
which retained the cavities of both the PPyNTs and
MWCNTs and these cavities may be favourable to improve
the specific capacitance of the composites which would be
further expressed in the followed discussion.
The X-ray diffraction (XRD) patterns of the original
MWCNTs, PPyNTs and their composites were displayed in
Fig. 1e, the broad reflection centered at 2h value of 10� and
27� was the characteristic of the doped amorphous PPyNTs
[18]. The peaks centered at 26.08�, 42.84�, 53.50� and
78.02� could be assigned to the (002) (100) (004) and (110)
reflections of graphite from the MWCNTs, respectively
[19]. For the composites, the broad peak also shifts from
2h = 27� to 26.5� and the peaks at 53.50� and 78.02� were
much weaker than the MWCNTs implying that the PPyNTs
and MWCNTs have been connected with each other. The
FTIR absorption spectra of the PPyNTs and PPyNTs/
1048 J Mater Sci: Mater Electron (2014) 25:1047–1052
123
MWCNTs composites were shown in Fig. 1f. For PPyNTs,
the characteristic polypyrrole ring peaks are located at
1,535 and 1,444 cm-1, which are due to the asymmetric
and symmetric ring-stretching modes, respectively [20].
The peaks at 1,163, 1,035 and 893 cm-1 are attributed to
the =C–H group in-plane vibrations and out-plane vibra-
tions. Compared with the PPyNTs, it is clearly observed for
the composites that most of the marked peaks are obviously
blue shifted when the MWCNTs was incorporated with the
PPyNTs. The reason may be related to the hydrogen bonds
between –COOH groups of modified MWCNTs and –NH
groups of the PPy and the strong p–p stacking between PPy
conjugate backbone and graphitic sidewall of MWCNTs
[7].
Fig. 1 a–c SEM images of MWCNTs, PPyNTs and PPyNTs/MWCNTs composites, respectively. The inset of SEM images is TEM images of
MWCNTs, PPyNTs and PPyNTs/MWCNT composites. d–f scheme of synthesis mechanism, XRD and FTIR spectra of composites, respectively
J Mater Sci: Mater Electron (2014) 25:1047–1052 1049
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3.2 Electrochemical performance
The electrochemical property of the PPyNTs/MWCNTs
composites was characterized in potassium chloride media
(1 M KCl) by means of a three-electrode cell system.
Figure 2a, is the galvanostatic charge–discharge curves of
MWCNTs, PPyNTs and PPyNTs/MWCNTs (9:1) com-
posites electrodes at current densities of 0.2 A g-1, and the
specific capacitances are 352, 178 and 46 F g-1 for
PPyNTs/MWCNTs, PPyNTs and MWCNTs, respectively.
The specific capacitance of the PPyNTs/MWCNTs com-
posites is much higher than that of PPyNTs and MWCNTs
under the same current density which is unambiguous in
the specific capacitance curves (Fig. 2b). By further
increasing the current density to 0.5, 1, 3 A g-1, the specific
capacitances are still as high as 311, 285 and 237 A g-1 for
the composites sample. Figure 2c is the specific capacitance
curves of PPyNTs/MWCNTs composites with different
Fig. 2 a, b Galvanostatic charge–discharge and the specific capac-
itance at different charge/discharge current density for the MWCNTs,
PPyNTs, PPyNTs/MWCNTs composites, respectively. c The specific
capacitance at different charge/discharge current density of the
composites with different mass ratio. d CV of PPyNTs, MWCNTs
and PPyNTs/MWCNTs. e EIS of PPyNTs, MWCNTs and PPyNTs/
MWCNTs. f Equivalent electrical circuit used in EIS fitting data
1050 J Mater Sci: Mater Electron (2014) 25:1047–1052
123
mass ratio of the pyrrole and MWCNTs (A, B, C, D, E
correspond to the mass ratio of 11:1, 10:1, 5:2, 5:1, 9:1). The
specific capacitance increased at the beginning and then
decreased with the increase of Py. The value of specific
capacitance reached its maximum when the mass ratio of Py
to MWCNTs was 9:1 at different current density from 0.2 to
5 A g-1. It can be ascribed to the synergetic effect between
MWCNTs and PPyNTs which worked best when the mass
ratio of Py to MWCNTs was 9:1. The connection density of
the MWCNTs with PPyNTs and the cavities existed in both
MWCNTs and PPyNTs affected the specific capacitance of
the composites. Figure 2d depicted the cyclic voltammetry
(CV) behavior of the MWCNTs, PPyNTs, and PPyNTs/
MWCNTs composites at scan rate of 5 mv s-1. Compared
with the CV curves of pure PPyNTs and MWCNTs, the CV
curve of the composites takes on rectangular shape and
symmetric current–potential characteristics, meaning the
ideal capacitive behavior.
To further confirm the advantages of the PPyNTs/
MWCNTs composites over PPyNTs and MWCNTs as
supercapacitor electrode materials, the electrochemical
properties of composites, PPyNTs and MWCNTs were
fully evaluated by electrochemical impedance spectros-
copy (EIS). As shown in Fig. 2e, for the PPyNTs/
MWCNTs composites, the impedance plot featured a ver-
tical trend at low frequencies, indicating perfect capacitive
behavior according to the equivalent circuit theory [21].
The Fig. 2f showed the equivalent circuit for the fitting of
the EIS data, the Rs is obtained from x-intercept of the
Nyquist plot, and the Rct is the charge transfer resistance
which can be estimated by the diameter of semicircles at
the high frequency region [22]. As shown in the Fig. 2e,
the Rct for MWCNTs, PPyNTs and PPyNTs/MWCNTs
composites changed little and the composites appeared a
higher slope of the straight line than that of PPyNTs and
MWCNTs, indicating that the PPyNTs/MWCNTs com-
posites may possess excellent capacitance performance. It
may be explained by the synergetic effect of MWCNTs and
PPyNTs, which was aroused by the hydrogen bonds, the
hollow structure and the strong p–p stacking between
PPyNTs and MWCNTs. MWCNTs acted as ‘‘bridge’’
which connected the PPyNTs together and improved the
electrochemical property of the composites.
The electrochemical stability of the PPyNTs, MWCNTs
and PPyNTs/MWCNTs composites were investigated in
the same condition of the charge–discharge test (Fig. 3). In
the case of MWCNTs electrode, the specific capacitance
keeps 97 % at the current density of 1 A g-1, higher than
that of composites and PPyNTs electrode, however, the
capacitance was much lower than that of PPyNTs/
MWCNTs composites and PPy electrode. The capacitance
retention rate of PPyNTs/MWCNTs still reaches about
94 %, higher than that of PPyNTs (56 %) at the current
density of 1 A g-1 after 1,000 cycles. Therefore, the
PPyNTs/MWCNTs composites have potential applications
at the electrode material for supercapacitors.
4 Conclusions
In summary, we have successfully synthesized PPyNTs/
MWCNTs composites by an in situ chemical oxidation
polymerization using MWCNTs and Py as the starting
materials. The obtained composites exhibited ideal electro-
chemical performance and its specific capacitance was as
high as 352 F g-1 at a current density of 0.2 A g-1 owing to
synergistic effect. This facile and effective approach for the
synthesis of MWCNTs/conducting polymer composites
further extends the applications of MWCNTs and should be
very promising for the fabrication of inexpensive, high-
performance electrochemical supercapacitors.
Acknowledgments This study was supported by the College Sci-
entific Plan Fund of Shandong Education Department (J10LD23) and
the Doctoral Startup Foundation of Qilu university of technology
(12042826).
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