Open Journal of Organic Polymer Materials, 2015, 5, 89-102
Published Online October 2015 in SciRes. http://www.scirp.org/journal/ojopm
http://dx.doi.org/10.4236/ojopm.2015.54010
How to cite this paper: Branzoi, F. and Branzoi, V. (2015) The Electrochemical Behaviour of PEDOT Film Electrosynthesized
in Presence of Some Dopants. Open Journal of Organic Polymer Materials, 5, 89-102.
http://dx.doi.org/10.4236/ojopm.2015.54010
The Electrochemical Behaviour of PEDOT
Film Electrosynthesized in Presence of Some
Dopants
Florina Branzoi1, Viorel Branzoi2
1Institute of Physical Chemistry “Ilie Murgulescu”, Bucharest, Romania
2University Politehnica of Bucharest, Bucharest, Romania
Email: fbrinzoi@chimfiz.icf.ro
Received 22 June 2015; accepted 27 September 2015; published 30 September 2015
Copyright © 2015 by authors and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/
Abstract
Electropolymerization and characterization of poly(3,4-ethylene dioxythiophene) (PEDOT) doped
with functionalized single-walled carbon nanotubes (SWANTs) polyaminobenzene sulfonic acid
(PABS) and different dopants were studied. It was fabricated by a simple oxidative electropoly-
merization method. The nanocomposite coatings have been prepared by using electrochemical
methods from aqueous solutions, such that the components were deposited onto platinum elec-
trode substrate. The morphology of composite films was analyzed by scanning electron micros-
copy (SEM). The electrochemical and physical properties of the resulting composites were evalu-
ated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier trans-
form infrared spectroscopy (FT-IR) techniques in 0.1 M LiClO4 aqueous solutions. The value of
specific electrochemical capacitance of the composite films is considerably higher than that of the
pure polymers films. The improved properties of the electrodes were obtained by using these
composite films. The dopant substances used were sodium dodecyl sulfate (SDS) and 1,2-Dihy-
droxy-benzene-3,5-disulfonic acid disodium salt hydrate (tiron).
Keywords
Nanocomposite Films, Carbon Nanotubes, Electropolymerization, SEM, EIS, Capacitance
1. Introduction
Conducting polymers are also intriguing molecular structures because of their ability to dramatically change
properties when stimulated by an electric signal. These materials offer exciting prospects for a wide range of
F. Branzoi, V. Branzoi
90
new devices such as membranes, artificial muscles, solar cells, batteries, capacitors, corrosion protection coa t-
ings or sensor applications [1]-[5].
Carbon nanotubes (CNTs), as one of the most interesting carbon materials, have attracted an enormous inter-
est over the recent years, as a result of their unique properties and a broad range of potential applications. Their
very high mechanical resilience, high electrical conductivity, chemical and mechanical properties and large sur-
face areas are particularly relevant for diverse applications such as in nanoelectronics, biosensors, supercapaci-
tors and so on [3]-[7].
Recently, conducting polymers/carbon nanotubes composites have received significant interest because the
incorporation of carbon nanotubes into conducting polymers can lead to new composite materials possessing the
properties of each component with a synergistic effec t that would be useful in particular applications [8]-[13].
Composite materials based on th e coupling of condu cting organic po lymers (CPs) and CNTs h ave shown that
they possess properties of the individua l components with a synergistic effect [14]. In this context, a special at-
tention has been paid to the following CPs: polyaniline (PANI), polypyrrole (PPY), polythiophene (PTh) [15]-
[21]. Among the numerous materials devised, development of the polythiophene derivative, polyethylene-di-
oxythiophene (PEDOT), has shown significant promise for the challenge at hand. Poly(3,4-ethylenedioxy-thio-
phene) (PEDOT) is one of the most successful polythiophene derivatives because of its interesting properties:
high conductivity, unusual electroactivity and relative environmental stability [22] -[26]. PEDOT proved better
aqueous stability and biocompatibility than polypyrrole and polyaniline and th erefore it is considered a promis-
ing polymer appropriate for continuous sensing and even in vivo implantation [27 ]-[29]. It can be produced
electrochemically in a variety of solvents. It has been showed that the electrochemical and physical properties of
polym e rs are greatly infl uenced by the na ture of dopant and electrolyte during the polymeric process [30]-[34].
The combination of CNTs with CPs offers an attractive route to reinforce the polymer as well as to introduce
electronic properties based on morphological modification or electronic interaction between the two components
[10]-[13] [18]-[26]. However, it is difficu lt to process CNTs and insoluble in most solv ents. In order to broaden
their applications it is necessary to tailor their solubility properties. For this cause, in this study SWCNTs-sin-
gle-walled carbon nanotubes covalently functionalized with polyaminobenzene sulfonic acid were used. The
SWCNTs graft copolymer has excellen t solubility in water and some organic solvents and it also exhibits an or-
der of magnitude increase in electrical conductivity. It was also demonstrated that SWCNTs-PABS (single
walled carbon nanotubes functionalized with polyaminobenzene sulfonic acid) showed an improved sensor per-
formance compared to unfunctionalized SWCNTs, because polyaminobenzene sulfonic acid is a conductive or-
ganic compound in its own right. Additionally, the presence of numerous functional groups in SWCNTs-PABS
means that there is potential for covalent immobilization of various big molecules , es pecially biomolecules.
This study is a continuation of previous work on the synthesis and analysis of the composite films doped with
some functionalized single -walled carbon nanotubes that have been deposited on the platinum substrate by elec-
trochemical polarization metho d.
In this study the electrochemical synthesis of nanocomposite films from conducting polymers-poly(3,4-eth-
ylene dioxythiophene) and functionalized single-walled carbon nanotubes with polyaminobenzene sulfonic acid
(PEDOT-FSWCNTs) and different dopants (sodium dodecyl sulfate and 1,2-Dihydroxy-benzene-3,5-disulfonic
acid disodium salt hydrate) is described. The electrochemical characterization of these nanocomposites was by
cyclic voltammetry, electrochemical impedance spectroscopy, and the surface morphology analysis was by scan-
ning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) techniques.
2. Experimental
The electrochemical synthesis and measurements were carried out by using a single-compartment cell with the
conventional three electrode set up at room temperature. The cell was connected to a VoltaLab potentiostat cou-
pled to a PC running Voltamaster software. A saturated calomel electrode (SCE) was employed as the reference
electrode and a platinum gauze as an auxiliary electrode. The working electrode was a platinum disk with a sur-
face area 0.5 cm2. All chemicals were reagent grade and used as received without further purification. In this
paper were used 3,4-ethylenedioxy thiophene (EDOT) (99.5% Aldrich), LiClO4 (Merck), sodium dodecyl sul-
fate (SDS) (98% Fluka), tiron (Fluka) and single-walled carbon nanotubes functionalized with polyaminoben-
zene sulfonic acid (FSWCNTs) were the commercial product from Sigma-Aldrich with the following charac ter-
F. Branzoi, V. Branzoi
91
istics: 80% - 90% carbon basis, D × L 2 - 10 nm × 0.5 - 2 μm, bundle dimensions. All the solutions were pre-
pared with double distilled water.
2.1. Preparation of Modified Electrode
Before each electrochemical measurement the surface of the working electrode was mechanically polished with
0.3 and 0.05 μm alumina powders and rinsed in double distilled water and ethanol. The prepared electrodes were
dried and used for modification.
Nanocomposite films of CPs/FSWCNTs have been prepared by electrochemical polymerization from a solu-
tion containing the functionalized carbon nanotubes (FSWCNTs) and the corresponding monomer (PEDOT).
FSWCNTs were used in this paper namely: single wall carbon nanotubes (SWCNTs) functionalized with poly-
aminobe nz ene sulfoni c ac id (see Scheme 1).
In first stage consisted of preparing the FSWCNTs aqueous suspension (10 mg/L) by using sonication (1
hour). Furthermore, the synthesis solution was obtained by dissolving the monomer and the corresponding sup-
porting electrolyte in the FSWCNTs aqueous suspension. The behavior of the negatively charged FSWCNTs in
solution was that of the only supporting electrolyte and dopant for the PEDOT depositions. Therefore, during
the electropolymerization process, the FSWCNTs are encased in polymers in the form of counter ions or
dopants.
Thus, PEDOT/SWCNTs composite films were obtained from an aqueous solution containing 0.025 mol/L of
2,3-dioxythiophene + 0.1 M of LiClO4 + 10 mg/L of FSWCNTs by cyclic voltammetry in the potential scanning
range of 0 mV to +1250 mV at a scan rate of 10 mV/s and for a cycles number of 20.
2.2. Characterization of the Modified Electrodes
The electrochemical properties of the composite films were evaluated by cyclic voltammetry (CV), electro-
chemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR) and scanning electron
microscopy (SEM). The electrochemical characterization of the PEDOT/FSWCNTs was carried out in 0.1 M
LiClO4 cycling aqueous solutions for comparison and because the dopant anion of the polymeric films is the
same with the anion of the cycling solution. Twenty consecutive potential scans were performed for modified
electrodes and they were cycled in the potential range of 0 mV to +1250 mV with a scan rate of 50 mV/s. The
impedance measurements were carried using a VoltaLab 40 potentiostat/galvanostat in the frequency range of
100 kHz to 1 mHz with an AC wave of 5 mV (peak-to-peak) overlaid on a DC bias potential and the impedance
data were obtained at a rate of 10 points per decade change in frequency.
3. Results and Discussions
In the first stage, the PEDOT/Pt coating has been also electrodeposited onto electrode surface (platinum) by
electrochemical polymerization from an aqueous solutions containing 0.025 mol/L 2,3-dioxythiophene and 0.1
M LiClO4 as supporting electrolyte (see Figure 1 inset). The obtained the PEDOT/Pt film was presented in pre-
vious wor k.
Composite films of poly(3,4 -ethylenedioxythiophene) and functionalized, single-walled carbon nanotubes
with polyaminobenzene sulfonic acid (PEDOT-SWCNTs/PABS) were fabricated by a simple oxidative electro-
polymerization method. These films were electrodeposited on a platinum working electrode using a classical
system with three electrodes.
The PEDOT/SWCNTs-polyaminobenzene sulfonic acid film was obtained on the platinum substrate in a
Scheme 1. Chemical structure of single walled carbon nanotube functionalized with polyaminoben-
zene sulfonic acid (SWCNTs-PABS).
F. Branzoi, V. Branzoi
92
synthesis solution of 0.025 mol/L 2,3-dioxythiophene + 10 mg/L carbon nanotubes polyaminobenzene sulfonic
acid. The obtained cyclovoltammograms are given in Figure 1 and have the same shapes with those obtained for
PEDOT/Pt modified electrode cycled in the same conditions, but in this case the anodic peaks are much higher
than those for PEDOT film. The current is increasing upon continuous cycling, being indicative for a conductive
film formation. This fact can be explained taking into account that, FSWCNTs (in our case SWCNTs-PABS) are
negatively charged and they can act as doped anions and consequently, the conductivity of PEDOT/FSWCNTs
composite film increases.
The PEDOT/SWCNTs-PABS composites presents higher currents (7.62 mA/cm 2) than PEDOT films (4.96
mA/c m 2), which translates into larger capacitance. Also, the PEDOT/FSWCNTs having more a poros structure
for ion transportand a higher and potential-independent electronic conductivity through the adsorbed SWCNTs
film, can explain the difference in current between PEDOT and PEDOT/FSWCNTs. The presented facts indi-
cate a faster kinetics in the composite, which can be attributed to the higher electronic conductivity of the
FSWCNTs network. Therefore the redox processes that take place in nanocomposite film are more complex and
more intense than the ones in the pure PEDOT film.
The PEDOT/ SWCNTs-PABS/dopant films were obtained on the platinum substrate in a synthesis solution of
0.025 mol/L 2,3-dioxythiophene + 10 mg/L SWCNTs-PABS + 0.01 mol/L dopant substance in 0.1 M LiClO4 by
cyclic voltammetry in the scanning potential range of 0 to +1250 mV at a scan rate of 10 mV/s and for 10 cycles.
The dopant substances used were SDS (Sodium dodecyl sulfate) and tiron (1,2-Dihydroxybenzene-3,5-disul-fo-
nic acid disodium salt hydrate).
In the presence of dopant (SDS and tiron, see Figure 2 and Figure 3 ), it is observed that the current response
of doped PEDOT films increases with addition of the dopant. Moreover, the current increases with continuous
cycling in the potential range as seen in Figure 2 and Figure 3. The comparison of repetitive cyclic voltammo-
grams of PEDOT and PEDOT/SWCNTs-PABS/dopant composite film, respectively, clearly showed differences.
furthermore, the current intensities are lower in case of pure PEDOT than with respect to nanocomposite/dopant
and they decrease upon continuous cycling as it can be seen from voltammograms in Figure 2 and Figure 3.
During the first po tential scan, the polymerization potential of PEDOT/SWCNTs-PABS /dopant on Pt is around
1.05 V, while the onset of polymerization shifts significantly on following scans to more positive potentials and
stabilizes at 1.15 V. The choice of the electrochemical synthesis method has an influence on the morphology,
appearance and adhesion of the polymer. Generally, all PEDOT composite films obtained by alternating polari-
zation were uniform, smooth and adherent to the surface of Pt electrode than the ones obtained at constant cur-
rent or potential.
The electrochemical behaviour of the PEDOT, PEDOT/SWCNTs-PABS films deposited electrochemically
from aqueous solution in the absence and presence of dopant (SDS and tiron) was characterized further using
cyclic voltammetry. The electrochemical characteristics of obtained PEDOT/Pt film was study in the cycling
solutions, an aqueous solution of 0.1 M LiClO4 (see Figure 4 inset) and it was presented in previous work.
(a) (b)
Figure 1. Polymerization cyclovoltammograms of 2,3-dioxythiophene + SWCNTs-PABS in 0.1 M LiClO4 aqueous solution.
Inset electropolymerization PEDOT/Pt.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-2
0
2
4
6
8
i(mA/cm2)
E( V)
PEDOT
cycle 1
cycle 2
cycle 5
cycle 10
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-2
0
2
4
6
8
10
12
i(mA /cm2)
E(V)
PEDOT+CNTS-PABS
cycle
1
cycle 2
cycle 3
cycle 5
cycle 10
F. Branzoi, V. Branzoi
93
(a) (b)
Figure 2. Polymerization cyclovoltammograms of (a) PEDOT/SWCNTs-PABS/SDS and (b) PEDOT/ C NT-PABS/tiron in
0.1 M LiClO4 aqueous solution.
(a) (b)
Figure 3. Comparative polymerization cyclovoltammograms of PEDOT + SWCNTs-PABS + dopant in 0.1 M LiClO4
aqueous solution, 1st Cycle (a) and 10th Cycle (b).
(a) (b)
Figure 4. Cyclic voltammogra ms of PEDOT/ SWCNTs-PABS film in cycling solution (monomer free) of 0.1 M LiClO4. In-
set PEDOT/Pt film.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-2
0
2
4
6
8
10
i(mA/cm2)
E(V)
PEDOT- CNTS/PABS- SDS
cycle1
cycle2
cycle3
cycle5
cycle10
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-2
0
2
4
6
8
10
12
i(mA/cm
2)
E(V)
PEDOT- CNTS/PABS-TIRON
cycle1
cycle2
cycle3
cycle5
cycle10
F. Branzoi, V. Branzoi
94
Figure 4 reports the cyclic voltammograms of PEDOT/CNT-PABS recorded in aqueous solution of 0.1 M
LiClO4 in wide potential range to explore all possible electrochemical properties of this film in aqueous electr o-
lyte. The modified electrode type PEDOT/CNT-PABS/Pt was cycled on the potential range from 0 up to 1250
mV with a sweep rate of 50 mV/s and for a cycles number of 20, see Figure 4. These films can be cycled re-
peatedly between the conducting (oxidized) and insulating (neutral) state without significant decomposition of
the material, which is consistent with th e results reported in the liter ature [35]. For the cyclic volta mmograms to
exhibit better capacitive features (e.g. a rectangular shape), the potential ranges should be chosen to avoid the
polymer becoming undoped and thus insulating, at very negative potentials and overoxidized at too positive po-
tentials. As can be seen, the curves of these composite films have nearly rectangular shape, which is typical of
the pure capacitive behaviour of the tested object [36]-[40].
The electrochemical characteristics of obtained PEDOT/CNT-PABS/dopant films were study in the same
working conditions (see Figure 5 and Figure 6). However, the current of film obtained by potentiodynamic
method in presence of dopant is nearly 2 times more than of the film gained in absence of dopant. Analyzing in
(a) (b)
Figure 5. Cyclic voltammogr ams of PEDOT/ SWCNTs–PAB S/SDS a nd PEDOT/SWCNTs-PABS/tiron film in cycling solu-
tion (monomer free) of 0.1 M LiClO4.
(a) (b)
Figure 6. Comparative cyclic voltammograms of PEDOT/SWCNTs-PABS/dopant films in cycling solution (monomer free)
of 0.1 M LiClO4, 1st Cycle (a) and 20th Cycle (b).
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-6
-3
0
3
6
9
12
i(mA/cm
2
)
E( V)
PEDOT-CNTS/PABS-SDS
Cycle1
Cycle2
Cycle3
Cycle5
Cy cle10
Cy cle20
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-6
-3
0
3
6
9
12
15
i(mA /cm
2
)
E( V)
PEDOT-CNTS/PABS-TIRON
cy cle1
cy cle2
cy cle3
cy cle5
cycle10
cycle20
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-10
-5
0
5
10
15
20
i(mA/cm2)
E( V)
Cy cle 1
PEDOT
PEDOT-CNTS/PABS
PEDOT-CNTS/PA BS/SDS
PEDOT-CNTS/PABS/TIRON
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-6
-4
-2
0
2
4
6
8
10
i(mA/cm
2
)
E( V)
Cy cle 10
PEDOT
PEDOT-CNTS/PABS
PEDOT-CNTS/PA BS/SDS
PEDOT-CNTS/PABS/TIRON
F. Branzoi, V. Branzoi
95
comparison the obtained results it can be observed that, in all the cases the PEDOT/CNT-polyaminobenzene
sulfonic acid/dopant composite film reveals current much higher than PEDOT film.
The comparison of repetitive cyclic voltammograms between the behaviour of the presented types of elec-
trode shows some differences. By comparing the cyclic voltammograms for PEDOT/PT, PEDOT/CNTs-PABS/
Pt and PEDOT/CNTs-PABS/dopant/Pt films it can be seen that the shape of voltammograms is similar, but the
composites presents higher currents than the pure polymeric ones, which can be translated into larger capaci-
tance of the composites. The explanation of this is that the PEDOT chains becoming neutral and the negative
charge of immobile functionalized FCNTSF being balanced by the cations with small size from the supporting
electrolyte solution, these large CNT anions are immobile and hence expert a permanent electrostatic repulsion
to the electron on the polymer chain. The shape of the cyclic voltammograms curve in all the cases is close to rec-
tangular (see Figures 4-6). The best electrochemical behavior is presented by PEDOT/CNTs-PABS/dopant/Pt.
The surface morphology, formation mechanism and electrochemical nature of PEDOT-FSWCNTs films were
investigated using scanning electron microscopy (SEM), cyclic voltammetry (CV) and alternating current (AC)
impedance spectroscopy (EIS). Cyclic voltammetry and electrochemical impedance spectroscopy revealed that
the PEDOT-SWCNTs/PABS electrode had higher electrocatalytic activity for the redox reaction and a smaller
charge transfer resistance than the PEDOT electrodes.
Further, the composite films were studied by EIS at open circuit potential, in an aqueous solution of 0.1 M
LiClO4 at 25˚C. The resulting Nyquist plots and Bode plots for PEDOT/SWCNTs-PABS and PEDOT/SWCNTs-
PABS/dopant systems are shown in Figure 7 and Figure 8. The impedance plot is composed of a semicircle
(a) (b)
(c) (d)
Figure 7. The Nyquist diagrams for modi fied electrodes. (a) PE DOT/Pt; (b) PEDOT/SWCNTs-PABS/Pt; (c) PEDOT/SWCNTs-
PABS/SDS/Pt and (d) PEDOT/SWCN Ts-PABS/tiron/Pt at open circuit potential in an aqueous solution of 0.1 M LiClO4.
F. Branzoi, V. Branzoi
96
at high frequencies and a capacitive slope at low and middle frequencies (see Figure 7 and Figure 8). The
semicircle appeared at high frequencies is considered to owe to the charge transfer resistance, which originates
from the interface structure between the porous electrode surface and the electrolyte [36]-[39]. At low frequen-
cies, the impedance plot becomes a near vertical line. The Nyquist plots for PEDOT, PEDOT/SWCNTs-PABS
and PEDOT/ = SWCNTs-PABS/dopant composite films are featured by a vertical trend at low frequencies, in-
dicating a capacitive behaviour according to the equivalent circuit theory [37]-[40]. Bode diagrams point out
also the capacitive behaviour in concordance with Nyquist plots (see in comparison Figures 7(a)-(d) and Fig-
ures 8(a)-(d)).
The capacitances of the electrode materials were calculated, according to the equation:
( )
12π.
im
C fZ= −
(f = frequency; Zim = imaginary impedance), from the slope of the linear correlation between the imaginary im-
pedance and the reciprocal of the frequency at low frequencies.
From these Figures 7-9 and Table 1, one can observe higher capacitance the one order of magnitude value
for PEDOT/FSWCNTs and dopant film in respect with PEDOT pure polymeric films. The embedded FSWCNTs
that provide interconnected pathways for electrons through the FSWCNTs and ions through the pore network or
the direct interaction between the delocalised electrons on polymer chains and the FSWCNTs contribute to the
higher capacitance of the composite films. We can conclude that the capacitance of PEDOT/ FSWCNTs is lar-
ger than that of the pure polymeric PEDOT films because the mesoporous structure of FSWCNTs makes the
dopping ions center into/eject from PEDOT/FSWCNTs composite films more easily. The combined resistance
(a) (b)
(c) (d)
Figure 8. The Bode diagrams for modified (a) PEDOT/Pt; (b) PEDOT/SWCNTs-PABS/Pt; (c) PE DOT/SWCNTs-PABS/
SDS/Pt and (d) PEDOT/SWCNTs-PABS/tiron/Pt at open circuit potential in an aqueous solution of 0.1 M LiClO4.
-3 -2 -10 1 2 3 4 5
1.0
1.5
2.0
2.5
3.0
3.5
log Z
log Frequency
PEDOT/Pt
-3 -2 -10123456
1,2
1,4
1,6
1,8
2,0
2,2
2,4
log Z
log Frequency
Phase [degree]
PEDOT-CNTS/PABS
-2 0 2 4 6
-80
-70
-60
-50
-40
-30
-20
-10
0
10
-3 -2 -10123456
1,2
1,4
1,6
1,8
2,0
2,2
2,4
Phase [degree]
log Z
log Frequency
PEDOT-CNTS/PABS-SDS
-2 0 2 4 6
-70
-60
-50
-40
-30
-20
-10
0
10
-3 -2 -10123456
1,2
1,4
1,6
1,8
2,0
2,2
2,4
2,6
log Z
Phase [degree]
log Frequency [Hz]
PEDOT-CNTS/PABS-TIRON
-3 -2 -10123456
-70
-60
-50
-40
-30
-20
-10
0
10
F. Branzoi, V. Branzoi
97
Figure 9. Capa citance evaluation for PEDOT, PEDOT/CNT -PABS and PEDOT/
CNT-PABS/dopant modified electrodes.
Table 1. Real impedance and capacitance values of pure PEDOT film and PEDO/FSWCNTs (polyaminobenzene sulfonic
acid) nanocomposite film with different dopants obtained by co-polymerization using the cyclic voltammetry (CV) at 0.01
Hz.
Polymeric film Slope values obtained from graph-Z= f (1/2πf) C [F/cm2] Zr (Ώcm2) at 0.01 Hz
PEDOT 103 0.009 357
PEDOT/CNT-PABS 14 0.0714 64
PEDOT/CNT-PABS/SDS 13.5 0.0741 101
PEDOT/CNT-PABS/tiron 14 0.0714 144
of the electrolyte and the film including electronic a s well as ionic contributions is indicated by the real imped-
ance at low frequencies where the capacitive behaviour predominates. The values of the real impedance at 0.01
Hz are given also in Table 1 . It can be seen that the PEDOT/FSWCNTs films were significantly lower in resis-
tance than PEDOT films. In comparison with the PEDOT film, it can be observed that PEDOT/FSWCNTs of-
fered much higher overall conductivity. As mentioned before, the real impedance of an electrode material, in
general, decreases as the material’s porosity increases due to improved ionic accessibility [40]-[49].
Figu r e 10 shows the SEM images of the PEDOT and composite film. In Figure 10(a) a nodular accumulating
structure is evidenced. The size of the nodules ranged a few hundred nanometers in diameter and they aggregate
to form gobbets. In Figure 10(b), the effect of dopant on the morphology of PEDOT film can be observed: la-
mellar structure with almost vertical orientation to the substrate. It is evident that dopant changes the morphol-
ogy of PEDOT film into a more porous structure with higher interface area. This is in agreement with the SEM
results presented below that illustrated a smaller porosity in the PEDOT film than in the case of the composite
film (see Figure 10(c)). The SEM images showed that the nanocomposite films, PEDOT/CNT-PABS were
more porous than PEDOT films (see Figure 10(c)).
Fourier transform infrared (FT-IR see Figure 11) spectra were carried with a Bruker optics spectrometer at
room temperature. A ll spectra in this paper were obtained at a resolution 4 cm1 in the region 4000 - 500 cm1.
FT-IR spectrometer is a powerful instrument that can be used to determine type of bonding for to obtain a new
composite. The characteristic bands in the FT-IR spectrum for PEDOT and nanocomposite are the following: a
very weak and a medium band at 3000 - 4000 cm1 is assigned to the C-H and OH stretching modes; vibration at
1551, 1482, 1353 and 931 cm1 for PEDOT + nano co mpo zit and 1521 , 1416, 1201 and 904 cm1 for PEDOT are
attributed to the stretching modes of C=C, C-C, and C-S in the thiophene ring [50]-[53]. The bands at 1212 and
1056 cm1 are assigned to the stretching modes of the ethylenedioxy (alkylenedioxy) group and the band around
1039 and 916 cm1 is due to the ethylenedioxy ring deformation mode. The spectrum shows several bands of
which the band at 834 cm1 for nanocompozit and 813 cm1 for PEDOT is assigned to the symmetric C-S-C
F. Branzoi, V. Branzoi
98
(a) (b)
(c)
Figure 10. SEM images of the film surface of (a) PEDOT; (b) PEDOT/SDS a nd (c) PEDOT/CNT-PABS doped film forma-
tion by cyclic voltammetry (0 to 1250 mV at a scan rate of 10 mV/s).
deformation. The band at 1054 cm1 (nanocompozit) and 1418 cm1 (PEDOT) is assigned to the symmetric
C-O-C ether bond. A difference that can be observed is the intensity ratio of bands the spectrum (1500 - 600
cm1) of nanocompozit film than PEDOT band, exhibits a clear difference in intensity [54]-[57]. This may sug-
gest that the dopant promotes and stabilizes the structure of the film (nanocomposite).
4. Conclusions
Nanocomposite films type PEDOT/FSWCNTs-polyaminobenzene sulfonic acid with different dopants was syn-
thesized by cyclic voltammetry technique from a synthesis solution.
The electrochemical activity of PEDOT/FSWCNTs/dopant/Pt modified electrode in 0.1 M LiClO4 cycling
solution is much higher than that of PEDOT/Pt modified electrode in the same cycling solution. Electroch emi-
cally synthesiszed composite film of conducting polymer PEDOT and FSWCNTs have in common a porous
structure at micro- and nano-meter scales.
Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and FT-IR spectroscopy demon-
strated that these composite films had similar electrochemical response rates to pure polymeric films but a lower
resistance and much improved mechanical integrity.
F. Branzoi, V. Branzoi
99
Figure 11. FT-IR spectra of PEDOT and nanocompozit.
The best electrochemical behavior is presented by PEDOT/CNTs-PABS/dopant/Pt.
Nearly rectangular shaped cyclic voltammograms are obtained for all composite films suggesting that the
charge and the discharge reversibly occur at the electrode/electrolyte interface.
The Nyquist plots for both PEDOT and composite films PEDOT/FSWCNTs are featured by a vertical trend at
low frequencies, indicating a capacitive behaviour according to the equivalent circuit theory.
The PEDOT/FSWCNTs-polyaminobenzene sulfonic acid composite films have high specific capacitance,
very quick charging/discharging ability and very low charge transfer resistance.
The SEM mic rograph of t he c ompos ite shows a porous morphology that wrapped on t he surfa ce of FSWCNTs.
The PEDOT/FSWCNTs composite was a very promising electrode material for application in supercapacitor.
Acknowledgements
Financial support from PN-II-ID-PCE-2008-2 contract number 596 , code ID_716 (The National University Re-
search Council) is gratefully acknowledged.
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