A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite and its application for electrochemical supercapacitor

Article abstract of DOI:10.1016/j.electacta.2010.04.067

A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite [MnO₂/P(An-co-oAs)] was successfully synthesized by a delamination/reassembling process using P(An-co-oAs) ionomer and layered manganese oxide in aqueous solution. This nanocomposite obtained was then characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), electron microscopy (SEM), and thermogravimetric (TG) analysis. X-ray diffraction and electron microscope analysis showed that the MnO ₂/P(An-co-oAs) nanocomposite had a lamellar structure with increasing interlayer spacing. The MnO₂/P(An-co-oAs) nanocomposite exhibited substantially improved conductivity, which was near 100 times greater than that of its pristine MnO₂ (3.5 × 10^-7 S cm^-1). The specific capacitance of the MnO₂/P(An-co-oAs) nanocomposite reached 262 F g^-1 in 1 M Na₂SO₄ at a current density of 1 A g^-1, which was significantly higher than that of either of its two pristine materials [MnO₂ (182 F g^-1) or P(An-co-oAs) (127 F g^-1)] owing to the synergic effect between the two pristine components. The fabrication mechanism of the nanocomposite was also proposed and discussed in this paper.

Full text of DOI:10.1016/j.electacta.2010.04.067

Electrochimica Acta 55 (2010) 5414–5419
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite
and its application for electrochemical supercapacitor
Xiao-feng Yang, Geng-chao Wang∗, Rui-yu Wang, Xing-wei Li
Key Laboratory for Ultrafine Materials of Ministry of Education, Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering,
East China University of Science & Technology, Shanghai 200237, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel layered manganese oxide/poly(aniline-co-o-anisidine) nanocomposite [MnO2/P(An-co-oAs)]
was successfully synthesized by a delamination/reassembling process using P(An-co-oAs) ionomer and
layered manganese oxide in aqueous solution. This nanocomposite obtained was then characterized
by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), electron microscopy (SEM), and
thermogravimetric (TG) analysis. X-ray diffraction and electron microscope analysis showed that the
MnO2/P(An-co-oAs) nanocomposite had a lamellar structure with increasing interlayer spacing. The
MnO2/P(An-co-oAs) nanocomposite exhibited substantially improved conductivity, which was near
100 times greater than that of its pristine MnO2 (3.5 × 10−7 S cm−1). The specific capacitance of the
MnO2/P(An-co-oAs) nanocomposite reached 262 F g−1 in 1 M Na2SO4 at a current density of 1 A g−1, which
was significantly higher than that of either of its two pristine materials [MnO2 (182 F g−1) or P(An-co-
oAs) (127 F g−1)] owing to the synergic effect between the two pristine components. The fabrication
mechanism of the nanocomposite was also proposed and discussed in this paper.
Received 20 January 2010
Received in revised form 13 April 2010
Accepted 18 April 2010
Available online 24 April 2010
Keywords:
Layered manganese oxide
Conducting polymer
Delamination/reassembling
Supercapacitor
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
formation of conducting polymers-intercalated inorganics com-
posites has been proved to be able to improve both the conductivity
Supercapacitors, as important energy storage devices, have
attracted great interest due to their high power density, excel-
lent reversibility and cycleability [1,2]. Considerable studies have
been focused on the development of new electrode materials
with improved performance. The electrode materials for super-
capacitors have been classified into three categories: high-surface
carbons, transition metal oxides, and conducting polymers [3–7].
Among them, manganese oxide (MnO2) is one of the most attrac-
tive candidates for supercapacitor electrode materials because of its
low cost, natural abundance and good environmental compatibility
[8–15].
and cyclability of layered inorganics due to the synergies of
the inorganic and organic components [27–30]. However, lay-
ered MnO2 has a higher charge density in the interlayer than
other layered materials [31], which makes the preparation of
conducting polymers-intercalated layered MnO2 nanocomposites
via the conventional intercalation reaction very difficult. Several
new approaches, such as the exchange reaction [32], the inor-
ganic/organic interface reaction method [33], the electrochemical
route [34], and the surfactant-assisted delamination/reassembling
method [35], have been recently developed to synthesize conduct-
ing polymers-intercalated layered MnO2 nanocomposites.
In recent years, birnessite-type layered manganese oxide has
attracted increasing attention due to its novel structure and unique
properties [16–21]. However, layered manganese oxide has poor
electrical conductivity [22] and structural instability during the
charge/discharge cycles [23,24]. Conducting polymers such as
polyaniline have also been regarded as one of the most promising
materials due to their excellent conductivity, ease of prepara-
tion, and great electrochemical activity, but exhibit much lower
electrochemical energy density and poor cyclability [25,26]. The
The delamination/reassembling process is an effective method
to synthesize polymer-intercalated layered MnO2 nanocompos-
ites. Some polymer-intercalated layered MnO2 nanocomposites
have been prepared using this method [36–38]. However, it is
difficult to synthesize conducting polymers-intercalated layered
MnO2 composites directly through this method because of the
low charge density and poor water-solubility of conducting poly-
mers. Although, Yang et al. [26,35] synthesized polyaniline and
polypyrrole-intercalated layered manganese oxide nanocompos-
ites by a delamination/reassembling method, they did not achieve
this in water system and used surfactant and organic solvent (NMP).
To our knowledge, no one has reported a successful synthesis of the
layered conducting polymers/MnO2 nanocomposite using delami-
nation/reassembling process in aqueous solution.
∗
Corresponding author. Tel.: +86 21 64253527.
E-mail address: gengchaow@ecust.edu.cn (G.-c. Wang).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.04.067

X.-f. Yang et al. / Electrochimica Acta 55 (2010) 5414–5419
5415
to give P(An-co-oAs) ionomer to MnO2 mass ratio of 0.5. After
being stirred for 48 h at room temperature, the reaction mixture
was filtered and washed with excess water and DMAc until the
filtrate became clear. The MnO2/P(An-co-oAs) nanocomposite was
obtained after air-drying.
2.5. Instrumentation
Scheme 1. Chemical structure of P(An-co-oAs) ionomer.
Fourier transform infrared spectra (FTIR) were recorded from
KBr sample pellets using a Nicolet 5700 spectrometer with a res-
olution of 2 cm−1. X-ray diffraction (XRD) patterns of the samples
were generated by a Rigaku D/Max 2550 VB/PC X-ray diffractome-
ter using Cu K␣ radiation. The diffraction data were recorded at 2ꢀ
angles varying between 3◦ and 50◦. Scanning electron microscopy
(SEM) images were taken with a JEOL JSM-6360 instrument.
Transmission electron microscopy (TEM) images were obtained
using a JEOL JEM-2100 microscope at an accelerating voltage of
200 kV. Thermogravimetric analysis (TGA) was preformed on a
TGA/SDTA/851e thermogravimetric analyzer from room tempera-
ture to 800 ◦C at a heating rate of 10 ◦C min−1 under air atomsphere.
The Mn content of sample was determined by ICP spectrometry
(Thermo Elemental IRIS 1000) after dissolving the sample in a
mixed solution of HCl and H2O2. The zeta potential of the sam-
ples was measured using a Malvem Zetasizer 3000HS analyzer. The
ionic strength of a dilute suspension was maintained at 10−3 M
using KCl. In conductivity tests, samples were molded into pel-
lets of about 13 mm diameters. The pellet surface was coated with
thin silver paint to reduce specimen-electrode contact resistance
and then placed between two stainless steel electrodes. A VC9808
digital multimeter was used to measure the resistance. The con-
ductivity can be calculated based on the thickness, surface area and
resistance.
To synthesize a conducting polymer/MnO2 nanocomposite in
an aqueous system, the water-soluble poly(aniline-co-o-anisidine)
(P(An-co-oAs)) ionomer was first prepared, which is an promis-
ing polymer due to its high conductivity in combination with
excellent water-solubility. Then, a layered MnO2/P(An-co-oAs)
nanocomposite was fabricated based on the electrostatic interac-
tion between positively charged P(An-co-oAs) ionomers and the
negatively charged MnO2 nanosheets in aqueous solution. The lay-
ered composite shows the improved electrical conductivity and
electrochemical properties compared with pristine MnO2, and has
the potential for an electrode material of supercapacitors.
2. Experimental
2.1. Materials
Aniline and o-anisidine (analytical grade, Shanghai Chem-
ical Reagent Co.) were distilled under vacuum prior to use.
Ammonium persulfate (APS, Shanghai Chemical Reagent Co.) was
purified by recrystallization from ethanol and deionized water
(1/1). Manganese nitrate, sodium hydroxide, tetramethylammo-
nium hydroxide (TMAOH), dimethylacetamide (DMAc) and other
reagents were received as analytical grade and used without further
purification.
Electrochemical tests were performed at room temperature
using a CHI760C electrochemical analyzer. A three-electrode cell
was used with a working electrode, a platinum counter electrode,
and a standard calomel electrode (SCE) as reference electrode. The
working electrode was prepared by mixing 75 wt% active material,
20 wt% acetylene black and 5 wt% poly(vinylidene fluoride) (PVDF)
in N-methyl-2-pyrrolidone (NMP) and then pressed on a 1 × 1 cm2
of stainless-steel sheet (1.2 × 107 Pa). The electrode was heated at
100 ◦C for 8 h to evaporate solvent. The mass of active material on
2.2. Preparation of delaminated MnO2
The sodium-type layered manganese oxide (Na–MnO2) was
synthesized as reported in the literature [16]. A solution of 0.6 M
NaOH and 2 M H2O2 was poured quickly into 0.3 M Mn(NO3)2
solution. The mixture was stirred vigorously for 30 min. The wet
precipitate then went through a hydrothermal treatment at 150 ◦C
for 16 h in 2 M NaOH solution. The resulting Na–MnO2 was treated
with 0.1 M HCl solution for 3 days at room temperature to produce
proton-type birnessite manganese oxide (H-MnO2). The H-MnO2
has a chemical formula of H0.23Na0.02Mn1.01O2·0.66H2O. H-MnO2
(0.4 g) obtained was suspended in a 0.25 M aqueous solution of
TMAOH (125 mL) for 10 days at room temperature. The suspension
was centrifuged at a speed of 12,000 rpm for 30 min and washed
three times with 300 mL deionized water each time to obtain the
delaminated MnO2 nanosheets.
working electrode ranged between 0.7 mg cm−2 and 1.0 mg cm−2
The electrolyte was 1 M Na2SO4 aqueous solution.
.
3. Results and discussion
3.1. Characterization of nanocomposite
Fig. 1 shows the XRD patterns of P(An-co-oAs) ionomer,
H-MnO2, delaminated MnO2 slurry, and MnO2/P(An-co-oAs)
nanocomposite. For P(An-co-oAs) ionomer (Fig. 1a), a notice-
able amorphous-like halo in the 2ꢀ range of 20–30◦ is due to
its non-crystalline structure. H-MnO2 has three main diffraction
peaks at 12.3◦ (d001 = 0.72 nm), 24.7◦ (d002 = 0.36 nm) and 38.6◦
(d003 = 0.23 nm) of 2ꢀ, corresponding to 0 0 1, 0 0 2 and 0 0 3 crys-
tal plane, respectively, which indicates that the H-MnO2 has the
typical monoclinic layered structure of a birnessite with interlayer
spacing of 0.72 nm (Fig. 1b). The peak observed at 36.5◦, proba-
bly resulted from the presence of a minor amount of ␥-Mn3O4
(hausmannite) impurities. Similar peaks were also observed from
previous reports [26,35].
2.3. Synthesis of P(An-co-oAs) ionomer
The deprotonated aniline/o-anisidine copolymer [P(An-co-oAs)]
was synthesized following the procedure described in the litera-
ture [32] and the water-soluble P(An-co-oAs) ionomer (Scheme 1)
was prepared following the procedures reported by Cheung et al.
[39]. The freshly made deprotonated P(An-co-oAs) was dissolved in
DMAc solution (7 mg mL−1). 1 M HCl was dropped into the filtered
solution prepared above until the pH reached 5.0. The solution was
then further filtered through a 0.22 ␮m filter before use.
The delaminated MnO2 slurry gave only an amorphous halo
in its XRD pattern (Fig. 1c). The halo can be explained from the
scatter of the MnO2 nanosheets, which is similar to the case pre-
viously reported [16]. This indicates that the TMAOH delaminated
the stacked H-MnO2 sheets into individual primary plates.
2.4. Preparation of MnO2/P(An-co-oAs) nanocomposite
A specific volume of P(An-co-oAs) ionomer solution (2 mg mL−1
was added to 50 mL of the above colloidal solution of birnessite
)

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X.-f. Yang et al. / Electrochimica Acta 55 (2010) 5414–5419
Fig. 1. X-ray diffraction patterns of (a) P(An-co-oAs) ionomer, (b) H-MnO2, (c)
delaminated MnO2 slurry, and (d) MnO2/P(An-co-oAs) nanocomposite.
Fig. 3. FTIR spectra of (a) H-MnO2, (b) delaminated MnO2, (c) MnO2/P(An-co-oAs)
nanocomposite, and (d) P(An-co-oAs) ionomer.
The MnO2/P(An-co-oAs) nanocomposite showed a new phase
with an interlayer spacing of 0.74 nm (Fig. 1d). Compared with H-
MnO2, the diffraction peak corresponding to 0 0 1 plane became
broader and weaker. This phenomenon suggested that the delam-
inated MnO2 sheets were reassembled to construct layered MnO2,
and the decrease of structural regularity probably resulted from the
inserting of some P(An-co-oAs) ionomer moleculars.
The SEM and TEM images of the delaminated MnO2 nanosheets
are shown in Fig. 2a and b, respectively. From the SEM image
of the delaminated MnO2, as shown in Fig. 2a, one can observe
the uniformly distributed patterns of flake with 1–2 ␮m in lateral
dimension. The TEM micrograph of delaminated MnO2 nanosheets
shows that the objects have very homogeneous contrast, which
reflects their ultrathin nature and uniform thickness (Fig. 2b).
Fig. 2c shows the SEM image of the MnO2/P(An-co-oAs)
nanocomposite. It is apparent that the MnO2/P(An-co-oAs)
nanocomposite has plate-like texture, reflecting layered
microstructure. In the TEM micrograph of MnO2/P(An-co-oAs)
nanocomposite (Fig. 2d), one can find that dark MnO2 stripes were
surrounded by lightish P(An-co-oAs) ionomers, which indicates
that the P(An-co-oAs) ionomers partly deposit on the surface
of the restacking MnO2. Further, the interlayer distance of the
nanocomposite was determined by measuring the line width in
the magnified image shown in the lower-right corner of Fig. 2d.
The interlayer distance measured using this method is about
1.65 nm. It can be interpreted that some P(An-co-oAs) ionomers
with ordered structure are intercalated into the interlayer of the
MnO2, leading to the increasing of interlayer spacing.
The FTIR spectra of H-MnO2, delaminated MnO2, MnO2/P(An-
co-oAs) nanocomposite, and P(An-co-oAs) ionomer are shown in
Fig. 3. In all FTIR spectra of the samples, the absorption at ca.
1630 cm−1 can be observed, which corresponds to the deformation
vibration of surface or interlayer water molecules. For the H-MnO2
and dried delaminated MnO2, the band in 420–520 cm−1 range is
assigned to Mn–O stretching vibration [40]. Moreover, the delami-
nated MnO2 sheets still showed two sharp bands at 1485 cm−1 and
952 cm−1, which can be ascribed to the adsorption of TMA+ ions
(Fig. 3b) [36]. The characteristic absorption bands of P(An-co-oAs)
ionomer (Fig. 3d) appear at 1587 cm−1 and 1485 cm−1 are assigned
to C C stretching vibrations of the quinoid and benzenoid rings,
Fig. 2. (a) SEM and (b) TEM image of delaminated MnO2. (c) SEM and (d) TEM image of MnO2/P(An-co-oAs) nanocomposite. The insert of (d) magnified image of red square
view.

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5417
Table 1
Zeta potentials for delaminated MnO2 sheets and P(An-co-oAs) ionomer as a func-
tion of pH value.
pH value
Zeta potential/mV
Delaminated MnO2
P(An-co-oAs) ionomer
3
5
7
9
−10.3
−15.5
−35.2
−38.2
25.4
54.3
−42.3
−45.5
oAs) ionomer showed opposite signs when the pH equaled 5, at
which point the difference of these zeta potentials also maximized.
This indicates that the delaminated MnO2 sheets and P(An-co-
oAs) ionomers are good sources for fabricating MnO2/P(An-co-oAs)
composite at pH 5 via an electrostatic assembly process.
A formation mechanism of MnO2/P(An-co-oAs) nanocompos-
ite involving a delamination/reassembling process is illustrated in
Scheme 2. The starting Na–MnO2 with a layered structure con-
tains one layer of water and Na+ ions between the MnO2 sheets.
The absorbed Na+ exchanges with HCl to yield the H-MnO2. When
the H-MnO2 is soaked in TMAOH solution, the TMA+ intercalation
and water washing lead to the delamination of MnO2 sheets. As
showed by the zeta potentials above, the electrostatic interaction
will cause the positive P(An-co-oAs) ionomers to assemble on the
surface of negative delaminated MnO2 sheets. Additionally, some
delaminated MnO2 sheets combine with H+ and reassemble to lay-
ered MnO2 in period of air-drying, since H+ ions possesses higher
charge density than that of P(An-co-oAs) ionomers.
Fig. 4. TG curves of (a) Na–MnO2, (b) MnO2/P(An-co-oAs) nanocomposite, and (c)
P(An-co-oAs) ionomer.
respectivily. In the spectrum of MnO2/P(An-co-oAs) nanocompos-
ite (Fig. 3c), both absorption bands of P(An-co-oAs) (1573 cm−1
,
1481 cm−1) and MnO2 (420–520 cm−1) appear, confirming the
presence of the two pristine components in nanocomposite. The
sharp bands at 1485 cm−1 and 952 cm−1 in the spectrum of
nanocomposite disappear, which indicates that most of the TMA+
ions were replaced by P(An-co-oAs) ionomers. It is also found that
the C O stretching mode for the quinoid and benzenoid rings
in the composite shifted to lower wavenumbers (from 1587 and
1485 cm−1 to 1573 and 1481 cm−1, respectively). This is because
the P(An-co-oAs) chains change from curly chains to outstretched
chains by the electrostatic interaction, leading to the enhancement
of the conjugation degree of the P(An-co-oAs) chains [41].
3.3. Electrical conductivity
The room temperature conductivity of H-MnO2 is
Fig. 4 depicts TG curves of Na–MnO2, MnO2/P(An-co-oAs)
nanocomposite, and P(An-co-oAs) ionomer. The TG curve of
Na–MnO2 shows two weight losses (Fig. 4a). A weight loss of 10%
before 200 ◦C resulted from the dissipation of adsorbed and inter-
layer water. A small weight loss (1.3%) occurred between 730 and
790 ◦C might be caused by the evolution of oxygen due to a par-
tial reduction of Mn (IV) to Mn (III) form [36]. In the TG curve of
MnO2/P(An-co-oAs) nanocomposite (Fig. 4b), a weight loss of 5.1%
before 140 ◦C was due to the removal of the interlayer water. A
weight loss (16.1%) happened from 140 cm−1 to 330 ◦C could be
attributed to the removal of acid dopant anions (Cl−) and the dis-
sipation of TMA+ ions in the interlayer. Further weight loss (11.2%)
observed in the range of 330 cm−1 and 610 ◦C was contributed by
the decomposition of skeletal P(An-co-oAs) chain outside inter-
layer. It is also found that a weight loss over 610 ◦C is notable, which
can be associated with the decomposition of skeletal P(An-co-
oAs) chain in interlayer. This indicates that the thermal stability of
P(An-co-oAs) in MnO2/P(An-co-oAs) nanocomposite has increased
compared to pure P(An-co-oAs) ionomer (Fig. 4c). TG analytical
results further support the conclusion that some P(An-co-oAs)
ionomers insert into the MnO2 interlayer.
3.5 × 10−7 S cm−1, which shows an insulator property while P(An-
co-oAs) ionomer presents a conductivity of 1.06 × 10−2 S cm−1
.
Under the same condition, the MnO2/P(An-co-oAs) nanocomposite
possesses a conductivity of 1.77 × 10−5 S cm−1. One can easily
find from above values that the conductivity of nanocomposite is
enhanced by near 100 times from that of H-MnO2.
3.4. Electrochemical properties
The cyclic voltammograms of Na–MnO2, P(An-co-oAs) and
MnO2/P(An-co-oAs) nanocomposite electrode in 1 M Na2SO4 at a
scan rate of 20 mV s−1 are depicted in Fig. 5. P(An-co-oAs) and
MnO2/P(An-co-oAs) nanocomposite electrodes exhibit symmetric
3.2. Fabrication mechanism of nanocomposite
The zeta potentials of delaminated MnO2 sheets and P(An-co-
oAs) ionomer as a function of pH value are listed in Table 1. The zeta
potentials of delaminated MnO2 in 3–9 pH range were always nega-
tive and the absolute value of zeta potentials increased with the pH
value, which indicates that the MnO2 sheets absorbed more nega-
tive charges at the higher pH value. For the P(An-co-oAs) ionomer,
the zeta potentials were positive at acidic condition and negative
in neutral or basic solution. This is because the P(An-co-oAs) was
partly protonated at acidic condition (see Scheme 1). It is also found
that the zeta potentials of the delaminated MnO2 and the P(An-co-
Fig. 5. Cyclic voltammograms of (a) P(An-co-oAs), (b) Na–MnO2, and (c)
MnO2/P(An-co-oAs) nanocomposite electrode measured in 1 M Na2SO4 at a scan
rate of 20 mV s−1
.

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X.-f. Yang et al. / Electrochimica Acta 55 (2010) 5414–5419
Scheme 2. Schematic illustration of formation for MnO2/P(An-co-oAs) nanocomposite.
Fig. 6. Cyclic voltammograms for MnO2/P(An-co-oAs) nanocomposite electrode
measured in 1 M Na2SO4 at different scan rates.
Fig. 7. Charge–discharge curves of (a) P(An-co-oAs), (b) Na–MnO2, and (c)
MnO2/P(An-co-oAs) nanocomposite electrode measured in 1 M Na2SO4 at a current
density of 1 A g−1
.
rectangular graphs, indicating the ideal capacitive behaviors. For
the Na–MnO2, the ideal capacitive behavior is poor, and the pseudo-
capacitance behavior dominates, which may be attributed to redox
reactions of interfacial oxycations in various oxidation states [42].
Moreover, the enclosed area of MnO2/P(An-co-oAs) nanocompos-
ite is larger than that of either of Na–MnO2 and P(An-co-oAs)
electrode, indicating that the nanocomposite has higher specific
capacitance. The higher specific capacitance of the MnO2/P(An-
co-oAs) nanocomposite can be explained as follows. First, the
P(An-co-oAs) in nanocomposite configures into ordered structure
and agglomerates in nanometer size, which reduces the paths of
ion diffusion in P(An-co-oAs) phase and enhances utilization of
electrode materials [25], Second, the existence of electrical con-
ductive P(An-co-oAs) phase facilitates electron transport to the
MnO2 phase with low conductivity [43]. In the nanocomposite, the
large surface area of MnO2 nanosheets embed with the P(An-co-
oAs) likewise contribute to the high capacitance [44]. All the three
aspects mentioned above lead to a high specific capacity.
The cyclic voltammograms for MnO2/P(An-co-oAs) nanocom-
posite at different scan rates are presented in Fig. 6. It can be found
that the cyclic voltammograms are symmetric rectangular graphs
at low scan rates, showing almost ideal capacitive behavior. As the
scan rate increases, the polarization intensifies, and the CV profile
deviates gradually from rectangularity. In general, the effective dif-
fusion of ions is greatly restrained at higher scan rate, and the ions in
the electrolyte only reach the outer surface of MnO2/P(An-co-oAs)
nanocomposite electrode [45,46], leading to a poor capacitive char-
acteristic. On the contrary, slow diffusion of ions into the interlayer
of electrode lead to the complete insertion process and deinsertion
process.
a current density of 1 A g−1. For Na–MnO2 and P(An-co-oAs), the
charge curves are dissymmetric to the corresponding discharge
counterparts in whole potential region and the slope of curves has
remarkable fluctuation. Whereas, the charge–discharge curve of
MnO2/P(An-co-oAs) nanocomposite is almost symmetric and the
slope of curve is potential independent, which further proves that
MnO2/P(An-co-oAs) nanocomposite electrode has ideal capacitive
behavior. The specific capacitances can be calculated as follows:
I/m
C =
ꢁV/t
where C (F g−1) is specific capacitance, I (A) is charge–discharge
current, ꢁV is 0.9 V, and m (g) is mass of active material, and t (s)
is discharging time.
The specific capacitances of Na–MnO2, P(An-co-oAs), and
MnO2/P(An-co-oAs) nanocomposite are 182 F g−1, 127 F g−1 and
262 F g−1, respectively. This indicates that the specific capacitance
of nanocomposite is higher than either of the two pristine compo-
nents, which is attributed to the structural change and increased
conductivity of composite as shown aforementioned.
The specific capacitance of MnO2/P(An-co-oAs) nanocomposite
is 315 F g−1, 262 F g−1, and 193 F g−1 at current density of 0.5 A g−1
,
1 A g−1, and 2 A g−1 (Fig. 8), respectively. These data shows that the
capacitance still retain about 61% of its original value when the cur-
rent density increases as much as 4 times. The high capacitance
retention of the nanocomposite indicates a higher rate capabil-
ity, which results from the existence of conducting P(An-co-oAs)
ionomer.
The charge–discharge cycling stability of Na–MnO2, P(An-co-
oAs) and MnO2/P(An-co-oAs) nanocomposite are presented in
Fig. 9. It is found that the specific capacitance of pure P(An-co-oAs)
Fig. 7 shows the charge–discharge behavior of Na–MnO2, P(An-
co-oAs), and MnO2/P(An-co-oAs) nanocomposite in 1 M Na2SO4 at

X.-f. Yang et al. / Electrochimica Acta 55 (2010) 5414–5419
5419
nanocomposite as a electrode material in supercapacitor shows
that this nanocomposite exhibits high specific capacitance of 262 F
g
−1 and good cycling stability of 90% retention of the initial specific
capacitance after 1000 cycles.
Acknowledgements
We greatly appreciate the financial supports of National Natu-
ral Science Foundation of China (50773020), Shanghai Municipal
Science and Technology Commission (0852nm02000), Shanghai
Leading Academic Discipline Project (B502) and Shanghai Key Lab-
oratory Project (08DZ2230500).
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electrode decreases rapidly after 300 cycles due to its structural
variety in cycle process, reflecting its poor cyclability. However,
the specific capacitance of MnO2/P(An-co-oAs) nanocomposite has
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to Na–MnO2. The high cycling stability of the MnO2/P(An-co-oAs)
nanocomposite can be explained as follows. In the nanocompos-
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structural change is therefore restricted during electrochemical
cycles, the layered MnO2/P(An-co-oAs) nanocomposite shows the
improved electrochemical performance compared to its pristine
MnO2 and P(An-co-oAs).
4. Conclusions
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In this paper, we successfully synthesized the layered
MnO2/P(An-co-oAs) nanocomposite by delamination/reassembl-
ing process in aqueous solution. The data of zeta potentials indicate
that the optimal fabrication condition of the MnO2/P(An-co-oAs)
nanocomposite is when the pH equals 5. At this condition, the
nanocomposite exhibits layered structure with enlarged inter-
layer spacing. The electrochemical behavior of MnO2/P(An-co-oAs)