Open Journal of Applied Sciences, 2012, 2, 70-77
doi:10.4236/ojapps.2012.22009 Published Online June 2012 (http://www.SciRP.org/journal/ojapps)
Synthesis and Characterisations of TiO2 Coated
Multiwalled Carbon Nanotubes/Graphene/Polyaniline
Nanocomposite for Supercapacitor Applications
Debasis Ghosh1, Soumen Giri1, Swinderjeetsingh Kalra2, Chapal Kumar Das1*
1Materials Science Centre, Indian Institute of Technology Kharagpur, Kharagpur, India
2Department of Chemistry, Dayanand Anglo-Vedic (D.A.-V.) College, Kanpur, India
Received March 27, 2012; revised April 26, 2012; accepted May 5, 2012
ABSTRACT
Nowadays with ever increasing demand of energy, developing of alternative power sources is an important issue all
over the world. In this respect we have prepared nanocomposites based on metal oxide (titanium oxide) coated multi-
walled carbon nanotubes (MWCNTs)/polyaniline (PANI) with graphene and without graphene and studied their elec-
trochemical performance. The formation of the polymer in the nanocomposites was confirmed by the Fourier Transform
Infrared Spectroscopy (FTIR) study. The morphological characterisations were carried out by the Field Emission Scan-
ning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). To characterize the prepared
nanocomposites electrode, a cyclic voltammetry test for measuring specific capacitance, and an impedance test were
conducted. The highest value of specific capacitance obtained for the TiO2 coated MWCNTs/PANI nanocomposite was
443.57 F/g at 2 mV/s scan rate. Upon addition of graphene nanosheet to the TiO2 coated MWCNTs in a weight ratio of
(9:1) the specific capacitance value increased to 666.3 F/g at the same scan rate, also resulting in an increase in energy
density and power density.
Keywords: Supercapacitors; Polyaniline; Nanocomposites; Graphene Nanosheet
1. Introduction
Supercapacitors, also known as electrochemical capaci-
tors or ultracapacitors are of interest in terms of their
high energy density and high power density as well as
pollution free long term energy supply source. Conven-
tional capacitor has the property of high power density
but suffers from low energy density, whereas, conven-
tional battery has got the property of high energy density
but low power density. Supercapacitors form a bridge
between the two by combining the high energy density
and high power delivery status. Supercapacitors store
energy either by the formation of electrical double layer
at the electrode electrolyte interface, typically known as
Electric Double Layer Capacitor (EDLC) or by the
pseudocapacitance mechanism or by both. The charge
storage mechanism in EDLC is non-faradaic i.e. no elec-
tron transfer reaction occurs and the process is directly
electrostatic [1]. EDLC increases the rate of response but
suffers from comparatively less amount of charge storage.
In case of redox supercapacitor, the active species un-
dergoes fast and reversible oxidation and reduction. The
pseudocapacitance, which ar due to electron transfer ises
redox process, causes typically 10 times greater charge
storage comparable to that of EDLC. Typically, designing
of a supercapacitor requires three essential components,
the electrodes, the electrolyte and the separator. The su-
percapacitor electrode plays the role of charge stor-
age/delivery and determines energy density and power
density [2]. For the supercapacitor electrode materials,
carbon materials, conducting polymer and metal oxides
are mostly used [3]. Carbon materials such as activated
carbon, nano porous carbon materials were used previ-
ously but now these are replaced mostly by CNT and
graphene. The charge storage mechanism in pristine
CNT is due to electrical double layer formation and it has
got very good absorption characteristic due to the acces-
sible mesopores formed by the entangled individual
CNTs [4]. However the specific capacitance of pristine
CNT is low and due to their bundle structure, their effect-
tive surface area decreases. This results in their restricted
use in many devices. Graphene is an outstanding material
for supercapacitor electrode owing to its very high sur-
face area (2675 m2/g), high thermal conductivity, ex-
treme electrical conductivity and very high mechanical
strength. Use of metal oxide as electrode materials such
*Corresponding author.

D. GHOSH ET AL. 71
as RuO2, MnO2, SnO2, NiO [5-8] have been studied in
detail. The combination of CNT or graphene with the
metal oxide also has been investigated in the recent years.
A. L. M. Reddy and S Ramaprabhu obtained specific ca-
pacitance of 138 and 93 F/g for RuO2/MWNT and SnO2/
MWNT nanocomposite electrodes respectively [9]. For
the graphene metal oxide nanocomposites, Cheng et al.
obtained a specific capacitance of 328 F/g for MnO2/
graphene at 1mA charging current [10], whereas, Wang
et al reported high specific capacitance of 855 F/g for
Ni(OH)2/graphene nanocomposites at 5mV/s scan rate
and 367 F/g for RuO2/graphene at 2 mV/s scan rate [11].
Conducting polymers such as, polypyrrole, polyaniline
(PANI), polythiophene are used as another part of elec-
trode material. Among the various conducting polymers,
PANI has been studied extensively due to its low cost,
easy synthesis procedure, redox reversibility as well as
good environmental stability and moderated electrical
conductivity [1,12]. Graphene or CNT combines with the
conducting polymer and stores energy by the electronic
and ionic charge separation as well as by the faradaic
charge transfer across the electrode electrolyte interface
[1,13-16]. CNT and graphene have free surface pi-elec-
trons. The surface pi-electrons can interact strongly with
PANI through the quinoid ring and thereby facilitate the
functionalization of CNT and graphene. LI. Fang et al.
found a specific capacitance of 305.3 F/g for CNT/PANI
composite with a 50 nm thick coating of PANI over CNT.
Similarly, L. B. Kong et al. obtained the highest specific
capacitance value of 224 F/g for the MWCNTs/PANI
nanocomposite materials containing MWCNTs of 0.8
wt% [17]. In case of graphene based PANI composites A.
V. Murugan reported highest specific capacitance of 408
F/g for (1:1) weight of PANI and graphene [18]. TiO2 is
a non-toxic, low cost transition metal oxide and available
in abundance. Various composite materials for superca-
pacitor applications containing TiO2 have been investi-
gated in detail. Reddy et al. obtained a specific capaci-
tance of 166 F/g for TiO2/MWCNTs nanocrystalline com-
posite by chemical reduction method [9]. C. Bian et al.
studied the fibriform polyaniline/nano-TiO2 composite
containing 80% conducting polyaniline by mass which
showed maximum specific capacitance of 330 F/g at a
constant current density of 1.5 A/g [19]. Further, A. K.
Mishra and S. Ramaphrabu found a maximum specific
capacitance of 265 F/g for TiO2 decorated functionalised
graphene [20]. However in our present work, we have
prepared three nanocomposites based on MWCNTs/PANI,
TiO2-MWCNTs/PANI and graphene/TiO2-MWCNTs/PANI,
where the composition of graphene: TiO2-MWCNTs is
9:1 by weight. The samples have been prepared by in situ
oxidative polymerisation method and their efficiency as
supercapacitor electrode material has been studied exten-
sively.
2. Experimental
2.1. Apparatus and Reagents
MWCNTs were obtained from Iljin Nano Technology,
Korea, (95% purity and 20 - 40nm diameter). Graphene
was obtained from Sinocarbon Materials Technology Co.
Ltd. China. Ammonium persulphate (APS), Cetyltrime-
thylammoniumbromide (CTAB) were supplied by Loba-
Chemie Pvt. Ltd. Mumbai (India). Aniline was obtained
from E. Merck Ltd. (India). Titanium(IV) n-butoxide and
iso-propanol were purchased from Sigma Aldrich. All
the chemicals were used without any further purification.
2.2. Preparation of Nanocomposites
Titanium oxide (TiO2) coated MWCNTs have been syn-
thesised by following a sol-gel process, already reported
by Siu-Ming Yuen et al. [21]. In brief, MWCNTs were
dispersed in iso-propanol and it was followed by addition
of Titanium(IV) n-butoxide and distilled water in a weight
ratio of MWCNT:titanium(IV) n-butoxide:iso-propanol:
water (1:0.3:50:25). The whole reaction mixture was kept
at room temperature for 48 hours and then the isopropa-
nol was evaporated by heat treatment to obtain TiO2
coated MWCNTs. Nanocomposites based on unmodified
MWCNTs/PANI and TiO2 modified MWCNTs/PANI
were prepared by insitu oxidative polymerisation of ani-
line, reported elsewhere. 60 mg MWCNTs were dispersed
in water by using cetyltrimethyl ammonium bromide
(CTAB) as dispersing agent by ultrasonication for 30
minutes using ultrasonic processor, Sonapros PR-250. To
that suspension, 0.6 ml aniline monomer was added and
sonicated for further 10 minutes. Subsequently, ammo-
nium persulphate (APS) solution containing 2.04 gm
APS was added and the sonication was continued for
another 20 minutes. Then the whole suspension was kept
at 0˚C - 5˚C for 12 hours, filtered and washed with water
ethanol solution to remove the unreacted monomer and
the residue was dried to get MWCNTs/PANI nanocom-
posites. The same procedure was followed for the TiO2-
MWCNTs/PANI and graphene/TiO2-MWCNT/PANI com-
posites preparation. For preparation of the graphene/TiO2-
MWCNTs/PANI nanocomposites, the weight ratio ini-
tially taken for the graphene to TiO2-MWCNTs was (9:1).
2.3. Fabrication of Electrode
For fabrication of the electrode for electrochemical char-
acterisations the nanocomposites were dispersed in 1%
nafion solution via sonication. The nafion solution was
prepared by mixing 10 µl nafion in 1ml dehydrated
ethanol. The well dispersed samples were casted onto the
glassy carbon (GC) electrode surface (diameter –3 mm)
and completely dried in air. Here the GC electrode acted
as working electrode.

D. GHOSH ET AL.
72
3. Results and Discussion
3.1. Fourier Transform Infrared Spectroscopy
(FTIR) Study
FTIR of the MWCNTs and graphene based nanocompo-
sites was performed using a NEXUS 870 FTIR (Thermo
Nicolet) to investigate the formation of PANI in presence
of TiO2 coated MWCNTs and TiO2 coated CNT/graphene
nanocomposites and the plot is shown in Figure 1. The
peak at 1575 cm–1 indicates the C=C stretching fre-
quency of the quinoid ring of the PANI unit, whereas the
peak at 1464 cm–1 indicates the C=C stretching of the
benzenoid ring [22] that shifts to 1485 cm–1 for the gra-
phene/TiO2-MWCNTs/PANI. The peaks at 1299 cm–1
and 801 cm–1 denote the C-N stretching and C-C or C-H
stretching of benzenoid unit. The peak at 3433 cm–1 can
be attributed to the N-H stretching frequency [23]. For
the TiO2 coated MWCNTs/graphene/PANI composite
the peak gets broadened near 3435 cm–1 probably due to
some moisture absorption thereby O-H stretching fre-
quency contributing to some extent. The peaks at 2855
cm–1 and 2923 cm–1 are associated with the symmetric
and asymmetric vibrations of C-H bond [23,24]. All
these FTIR data indicate the formation of PANI for both
the composites. The peak at 608 cm–1 indicates the Ti-O
stretching frequency of the TiO2 unit thus confirming the
formation of TiO2 over MWCNT [25].
3.2. XRD Analysis
The modification of MWCNTs surface by TiO2 was con-
firmed by the XRD analysis using a Rigaku difractome-
ter with a Cu Kα radiation (λ = 1.54056 cm–1). Figure 2
shows the XRD pattern of pure MWCNTs, TiO2 coated
MWCNTs and graphene/TiO2-MWCNTs/PANI nano-
composite. For pure MWCNTs, the strong and sharp
Figure 1. FTIR of TiO2-MWCNTs/PANI and graphene/TiO2-
MWCNTs/PANI.
diffraction peak at 26˚ corresponds to (022) reflections of
MWCNTs. In case of TiO2 coated MWCNTs, additional
peaks appear at scattering angles 25.36˚, 37.95˚, 48.12˚,
53.98˚, 55.12˚ and 62.75˚ corresponding to the reflec-
tions from (101), (004), (200), (105), (211), (204) crys-
talline plane respectively [26]. This indicates the crystal-
line nature of the TiO2 coated MWCNTs. However in
case of the composite, the corresponding peak at 25.24˚,
which is a characteristic peak of pure PANI is absent
which means that most of the PANI is deposited on the
surface of the TiO2 coated MWCNTs [19]. This is an
advantage as it shortens the diffusion path of the electro-
lyte and provides a larger electrochemical surface.
3.3. Morphological Characterizations
The surface morphologies of the as prepared nanocom-
posites were analysed by FESEM using Carl Zeiss-SU-
PRATM 40 with an accelerating voltage of 5 kV. The
samples were first gold coated to make the surface well
conducting. Figures 3(a)-(c) represent the FESEM im-
ages of pristine MWCNTs, graphene and neat PANI. The
FESEM image gives the evidence of smooth surface of
the pristine MWCNTs and graphene. The FESEM im-
ages of the TiO2-MWCNTs/PANI and graphene/TiO2-
MWCNTs/PANI nanocomposites are shown in Figures
3(d) and (e) which show a uniform coating of the PANI
over the as prepared TiO2 modified MWCNTs surface
which makes the surface rough. For further analysis,
transmission electron microscopy (TEM) was carried out
by using TECNAI G2-20S-TWIN inorder to inspect the
extent of dispersion of the in situ formed PANI in the
nanocomposites. For the TEM analysis the samples were
well dispersed in acetone and a drop was placed on a
copper grid and dried in air. Samples subjected to both
FESEM and TEM analyses were prepared at room tem-
Figure 2. XRD pattern of MWCNTS, TiO2 coated MWCNTs
and graphene/TiO2-MWCNTs/PANI.

D. GHOSH ET AL.
73
3.4. Electrochemical Characterizations
perature. Figures 4(a)-(c) represent the TEM images of
neat MWCNTs, neat graphene and neat PANI. The TEM
image of TiO2 coated MWCNTs is shown in Figure 4(d).
The presence of TiO2 makes the MWCNTs surface rough.
Figure 4(e) represents the TEM image of graphene/TiO2-
MWCNTs/PANI. From the picture, it is clear that PANI
is uniformly coated onto the TiO2-MWCNTs and Graphene
surface and forms a sandwiched structure in the nano-
composite.
Electrochemical characterisations such as Cyclic Volt-
ammetry (CV) and Electrochemical Impedance Spec-
troscopy (EIS) of the prepared nanocomposites were car-
ried out by GAMRY Ref 3000 instrument by using a
three electrode system where platinum and saturated
calomel electrode (SCE) were used as counter and refer-
ence electrodes respectively. For the electrochemical
characterizations potential window was chosen from
Figure 3. FESEM image of (a) neat MWCNTs; (b) Graphene; (c) Neat PANI; (d) TiO2-MWCNTs/PANI and (e) Graphene/
TiO2-MWCNTs/PANI.
Figure 4. TEM image of (a) MWCNTs; (b) Graphene; (c) Pure PANI; (d) TiO2 coated MWCNTs and (e) Graphene/ TiO2-
MWCNTs/PANI (SAED image is shown in inset).

D. GHOSH ET AL.
74
–0.7 V to +0.7 V) under which the nanocom(posites
Specific capacitance:
showed excellent electrochemical behaviour and the elec-
trolyte used was 1 M KCl. The specific capacitance (Cs
in F/g) of the nanocomposites from the CV measurement
are calculated by using the following equation [27].


2
d
V
IVV
1
21
V
s
Cm
VV



(1)
where, I(V) is the instantaneous current in CV,
under the I-V curve, ν is the
scan rate (V/s), (V2 – V1) is the potential window and m is
However, the better activity of the TiO2-MWCNTs/PANI

2
V
1
d
V
IVV
 is the area
the mass of the electroactive material. Figure 5(a) repre-
sents the CV plots of MWCNTs/PANI, TiO2-MWCNTs/
PANI and graphene/TiO2-MWCNTs/PANI composites at
10 mV/s scan rate which showed specific capacitance
respectively, 114 F/g, 158.09 F/g, and 269.46 F/g. The
highest specific capacitance value obtained for the
TiO2-MWCNTs/PANI composite was 443.57 F/g at 2
mV/s scan rate. Upon addition of graphene at a weight
percentage of (9:1) to that of TiO2 coated MWCNTs, the
specific capacitance value increases tremendously. The
highest specific capacitance obtained for the nanocom-
posite, graphene/TiO2-MWCNTs/PANI was 666.3 F/g at
2 mV/s scan rate. For MWCNTs/PANI composite the
combination of MWCNTs and PANI shows superior
performance than the individual component (already re-
ported) possibly due to the combination of easy electro-
lyte accessibility and a reduction in diffusion distance.
is due to the better synergism between the PANI and the
TiO2modified MWCNTs surface. TiO2 is an n-type semi-
conductor and the surface charge is more than the other
region due to the effective contribution of the positively
charged depletion region [28]. Incorporation of graphene
causes an increase in the surface area on which PANI can
grow. This improves the area of contact with the electro-
lyte and an improved conductivity in the redox pseudo-
capacitive composite structure results in an increased su-
percapacitance. The CV plot of graphene/TiO2-MWCNTs/
PANI at various scan rates are given in Figure 5(b). The
non-rectangular nature of the CV curve and presence of
peaks at low scan rate indicate deviation from ideal be-
haviour and the considerable contribution of pseudoca-
pacitance to the total specific capacitance. The pseudo-
capacitance can arise due to both TiO2 and PANI. Figure
5(c) represents the variation of specific capacitance with
scan rate for the two composites. The energy density and
power density of the composites are calculated by using
the following equations [29]
Energy density 2 12 s ECV (2)
Power density PET
where Cs
(3)
is the specific capacitance in F/g, V is the oper-
ating voltage range in Volt and T is the discharge time.
The highest value of energy density for TiO2-MWCNTs/
PANI and graphene/TiO2-MWCNTs/PANI was respect-
tively 120.75 Wh/kg and 181.3 Wh/kg at 2 mV/s scan
rate whereas highest power density was respectively
3152 W/kg and 5142.85 W/kg at 200 mV/s scan rate.
Figure 5. Comparison of CV plot of MWCNTs/PANI, TiO2-MWCNTs/PANI and graphene/TiO2-MWCNTs/PANI at 10 mV/s
scan rate (a), CV plot of graphene/TiO2-MWCNTs/PANI nanocomposites at 2 mV/s, 10 mV/s, 50 mV/s, 100 mV/s and 200
mV/s scan rate (b), and Variation of specific capacitance of TiO2-MWCNTs/PANI and graphene/TiO2-MWCNTs/PANI with
scan rate (c).

D. GHOSH ET AL. 75
Various values of specific capacitance, energy density
nd power d
composites may be due to the constant phase element
a ensity obtained at different scan rates are
pedance Spectroscopy
ar-
ge
(CPE) which arises due to (1) rough surface of the elec-
end for TiO2-
given in Tables 1 and 2.
3.5. Electrochemical Im
Electrochemical Impedance Spectroscopy (EIS) was c
ried out by using GAMRY ref.3000 using an ac volta
amplitude 5 mV between the frequency range 0.1 Hz to1
MHz. EIS is a very important and useful technique to
formulate a hypothesis when the EIS experimental data is
fitted with an suitable equivalent circuit model. Thus it is
a convenient tool to obtain many a electrochemical in-
formation such as, electrolyte resistance, charge transfer
resistance, double layer capacitance etc. [30]. The Ny-
quist plots of the nanocomposites for analysis the EIS
data are shown in Figure 6(a). The equivalent circuit to
which the EIS data was fitted is shown in Figure 6(b).
For an ideal capacitor the impedance plot should be a
vertical line and parallel to the imaginary impedance axis.
However our as prepared nanocomposites show devia-
tion from ideality. The non-ideal behaviour of the nano-
Table 1. Various values of specific capacitance (F/g), energy d
WCNTs/PANI nanocomposites at different scan rate.
trode, (2) different thickness of coating, (3) non-uniform
distribution of current due to edge effect and (4) distribu-
tion of reaction rate at surface due to distribution of ac-
tive sites with different activation energies. CPE corre-
sponds to the capacitance and follow the equation, ZCPE =
Z(jw)–n, where n is the CPE constant and ranges from
zero to one. Generally for supercapacitor, n varies from
0.5 to 1. n = 0 indicates the resistor, n = 1 indicates the
ideal capacitor and n = 0.5 indicates the Warburg behav-
iour. It can be seen that all the nanocomposites show a
semicircle loop at higher frequency region indicating
charge transfer resistance. In the lower frequency region
the imaginary part of the impedance sharply increases
indicating capacitive behaviour of the nanocomposites.
The graphene/TiO2-MWCNTs/PANI nanocomposite shows
much higher impedance in the lower frequency region
compared to that of other two nanocomposites. The in-
formation obtained from the EIS after fitting it to an
equivalent circuit model is shown in Table 3.
sity (Wh/kg) and Power density (W/kg) obtaine
M
Scan rate 2 mV/s 10 mV/s 50 mV/s 100 mV/s 200 mV/s
Specific capacitance 443.57 158 45.59 33.82 22.5
Energy density 120.75 43.03 12.41 9.2 6.2
Power density 621 1106.53 7 1595 2365.3152
Tus valuespecific capacita), energy de(Wh/kg) and pnsity (W/kgined for gra-
hene/TiO2-MWCNTs/PANI nanocomposites at different scan rate.
able 2. Vario of snce (F/gnsity ower de) obta
p
Scan rate 2 mV/s 10 mV/s 50 mV/s 100 mV/s 200 mV/s
Specific capacitance 666.3 269.464 80.27 50 33.89
Energy density 181.3 73.35 21.85 14 10
Power density 932 1866 2809.4 3600 5142.85
(a) (b)
Figure 6. EIS plot of M WCNTa), equivalent circ uit mode
to which the EIS data are fits/PANI, TiO2-MWCNTs/PANI and graphe ne/TiO2-MWCNTs/PANI ( ted (b). l

D. GHOSH ET AL.
76
Table 3. Fitting data for equivalent electrical circuit elements of MWCNTs/PANI, TiO2-MWCNTs/PANI and graphene/
TiO2-MWCNTs/PANI nanocomposites.
lution
s) CPE, Y0, (S × sn)Freq. power
(0 < n ≤ 1)
Chargen transfer
resistance(Rct)
Warburg (W)
resistance (S × s1/2)
So
resistance (R
ohms) (ohms) (ohms)
MWCNT/PANI 1.538 456.6e–6 0.681 24.60 185.5e–3
TiO2-MWCNT/PANI 1.–6
NT/PANI
159 248.1e
–6
0.729 13.47 486.9e
–3
–-3
graphene/ TiO2-MWC1.123 78.12e0.857 23.64 79.13e
4
TiO2-MWCNTs/PANI and grap
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