Scalable Synthesis of Freestanding Sandwich-structured Graphene/Polyaniline/Graphene Nanocomposite Paper for Flexible All-Solid-State Supercapacitor

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Abstract We reported a scalable and modular method to prepare a new type of sandwich-structured graphene-based nanohybrid paper and explore its practical application as high-performance electrode in flexible supercapacitor. The freestanding and flexible graphene paper was firstly fabricated by highly reproducible printing technique and bubbling delamination method, by which the area and thickness of the graphene paper can be freely adjusted in a wide range. The as-prepared graphene paper possesses a collection of unique properties of highly electrical conductivity (340 S cm −1 ), light weight (1 mg cm −2 ) and excellent mechanical properties. In order to improve its supercapacitive properties, we have prepared a unique sandwich-structured graphene/polyaniline/graphene paper by in situ electropolymerization of porous polyaniline nanomaterials on graphene paper, followed by wrapping an ultrathin graphene layer on its surface. This unique design strategy not only circumvents the low energy storage capacity resulting from the double-layer capacitor of graphene paper, but also enhances the rate performance and cycling stability of porous polyaniline. The as-obtained all-solid-state symmetric supercapacitor exhibits high energy density, high power density, excellent cycling stability and exceptional mechanical flexibility, demonstrative of its extensive potential applications for flexible energy-related devices and wearable electronics.

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SUBJECT AREAS:

GRAPHENE

BATTERIES

Received
2 November 2014

Accepted
2 March 2015

Published
23 March 2015

Correspondence and

requests for materials

should be addressed to

[S.W. (chmsamuel@](mailto:chmsamuel@mail.hust.edu.cn)

[mail.hust.edu.cn)](mailto:chmsamuel@mail.hust.edu.cn)

## Scalable Synthesis of Freestanding Sandwich-structured Graphene/ Polyaniline/Graphene Nanocomposite Paper for Flexible All-Solid-State Supercapacitor

Fei Xiao 1, Shengxiong Yang 1, Zheye Zhang 1, Hongfang Liu 1, Junwu Xiao 1, Lian Wan 1, Jun Luo 2,
Shuai Wang 1 & Yunqi Liu 3

1Laboratory for Large-Format Battery Materials and System, Ministry of Education Advanced Optoelectronic/Energy Materials and
Interface Chemistry Joint Laboratory School of Chemistry & Chemical Engineering Huazhong University of Science and Technology
Wuhan 430074, P. R. China, 2 National Center for Electron Microscopy, School of Materials Science and Engineering, The State
Key Laboratory of New Ceramics and Fine Processing, Key Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing
100084, P. R. China, 3 Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190, P. R. China.

We reported a scalable and modular method to prepare a new type of sandwich-structured graphene-based
nanohybrid paper and explore its practical application as high-performance electrode in flexible
supercapacitor. The freestanding and flexible graphene paper was firstly fabricated by highly reproducible
printing technique and bubbling delamination method, by which the area and thickness of the graphene
paper can be freely adjusted in a wide range. The as-prepared graphene paper possesses a collection of
unique properties of highly electrical conductivity (340 S cm 21 ), light weight (1 mg cm 22 ) and excellent
mechanical properties. In order to improve its supercapacitive properties, we have prepared a unique
sandwich-structured graphene/polyaniline/graphene paper by in situ electropolymerization of porous
polyaniline nanomaterials on graphene paper, followed by wrapping an ultrathin graphene layer on its
surface. This unique design strategy not only circumvents the low energy storage capacity resulting from the
double-layer capacitor of graphene paper, but also enhances the rate performance and cycling stability of
porous polyaniline. The as-obtained all-solid-state symmetric supercapacitor exhibits high energy density,
high power density, excellent cycling stability and exceptional mechanical flexibility, demonstrative of its
extensive potential applications for flexible energy-related devices and wearable electronics.

ltrathin and flexible energy storage devices are of considerable current interest because of the increasing
demands for modern electronic such as soft electronic equipment, roll-up displays, stretchable integrated
circuits, and portable medical products 1–4 . Supercapacitors (SCs), also known as electrochemical capaci# U
tors or ultracapacitors, are promising energy storage devices that bridge the gap between batteries and conventional capacitors. SCs can provide high specific power (10 kW kg 21 ), long cycle life (3 3 10 5 cycles), and fast
charge/discharge processes (within seconds), and therefore stimulate extensive interests as an alternative or
supplement to batteries in the energy storage field 5–8 . The design of flexible SCs demands flexible electrodes with
favorable mechanical strength and large capacitance. For the development of flexible electrodes in SCs application, two typical strategies are adopted. One is to load active materials on flexible substrates such as carbon
fabrics 9, cellulose 10, nanoporous gold 11 and nickel foam 12,13 . The other is to fabricate freestanding and soft
electrodes. Papers 14, films 15 and clothes 16 made from carbon materials have been demonstrated to be suitable
for this purpose. In comparison with the former method, the freestanding electrodes can significantly simplify cell
packing by eliminating inactive ingredients such as binders and current collectors, and hence improve the overall
performance when the total mass of the device is taken into account, which holds great promising for the
development of ultrathin, lightweight and high-performance SCs.

Carbon-based nanomaterials have attracted enormous scientific
and technological interest for their potential applications in energy
storage and conversion such as ultracapacitors, batteries, fuel cells
and solar cells. Among the large family of carbon materials, graphene, consisting of a single-layer of sp 2 -hybridized carbon atoms,
has been paid the most intensive attention because of its excellent
electrical conductivity, superior mechanical flexibility, high theoretical surface area and relatively inert electrochemistry 17–19 . More
importantly, recent reports by several groups including us have
shown that graphene nanosheets can be assembled into freestanding
and flexible 3D graphene foam 20, or paper-like structure via vacuum
filtering 21,22, self-assembly 23–25, pressing graphene aerogel 26 or hydrogel 27 and drying on petri dish 28 . However, for the preparation of
graphene paper, these methods either have complicated procedure
of manufacturing or cannot produce graphene paper with large area,
which greatly limit its large-scale production. On the other hand, the
double-layer capacitance originated form pristine graphene material
is much lower than the pseudocapacitance of conductive polymers or
transition metal oxides. Therefore, it is still a great challenge to
develop a novel and facile method to fabricate freestanding and
flexible graphene paper with high conductivity, good capacitive performance and favorable mechanical strength that can be scaled up for
widespread commercialization.

In this work, we present a facile method to prepare a new type of
sandwich-structured graphene/polyaniline/graphene nanohybrid
paper with desirable properties of high conductivity, good chemical
stability and excellent mechanical robustness. Large-scale graphene
paper used in this study was fabricated by a novel printing technique
and subsequent CO2 bubbling delamination method. In order to
increase the energy storage capacity of graphene paper, polyaniline
(PANI) nanofibers were in situ electropolymerized on it 29 . Utilizing
both Faradaic and non-Faradaic processes to store charge, the PANI
nanofibers modified graphene (graphene/PANI) hybrid paper electrode could achieve high energy and power densities without sacrificing the cycling stability and affordability. More importantly, our
results have showed that the following dip coating of an ultrathin
graphene layer on the surface of the porous PANI nanofibers leads to
the formation of a graphene/PANI/graphene nanohybrid paper with
a unique sandwich structure, which further increases the specific

capacitance and improves the cycling stability of the paper electrodes. The freestanding graphene/PANI/graphene nanocomposite
paper was used as binder-free electrode to fabricate all-solid-state
symmetric SC with polymer gel as electrolyte. The resultant flexible
and light-weight SC exhibited high energy density, high power density and excellent cycling stability. Particularly, its volumetric energy
density outperforms many previously reported solid-state SCs, such
as polypyrrole-coated paper symmetric SC 10, carbon/MnO2 fiber
symmetric SC 30, H-TiO2@MnO2//H-TiO2@C asymmetric SC 31 and
WO3-x/MoO3-x asymmetric SC 32 . It is worth noting that the proposed modular approach for the fabrication of freestanding sandwich-structured graphene nanohybrid paper is not just restricted to
the graphene/polyaniline/graphene system, but also contributes to
the design of hybrid nanoarchitectures with tailored compositions
and functions. These substantially demonstrate the extensive potential applications the proposed graphene nanohybrid paper for flexible energy-related device and wearable electronics.

Results
Fig. 1a schematically describes the procedure for preparing graphene-based nanohybrid paper. The graphene oxide (GO) paper
was firstly fabricated by spreading GO solution on a piece of standard
commercial A4 paper via a facile and scalable printing technique
(Fig. 1b). The area of GO paper can be freely adjusted by choosing
different sized cellulose paper substrate, which provides the possibility to produce large-area graphene paper. Moreover, the thickness of
GO paper can also be tailored in a wide range by using different
volume and concentration of GO dispersion. Aftrer that, the resultant GO paper was chemically reduced using hydroiodic acid (HI)
solution and simultaneously peeled off from A4 paper via a bubbling
delamination method to form a freestanding reduced GO (RGO)
paper. As demonstrated in Fig. 1c and 1d, when the A4 paper coated
GO film was soaked in acids such as HCl, H2SO4 and CH3COOH, a
lot of bubbles generated and provided a gentle force to delaminate
GO film from the commercial A4 paper. These bubbles produced
from the chemical reaction between the additions of the A4 paper
and HCl are identified to be CO2 bubbles (Fig. S1). If the acid has
reducing property, GO paper would be peeled off and reduced simultaneously. During the bubbling delaminating process, the CO2 bub

Figure 1 | (a) Schematic image illustrating the formation of a freestanding RGO paper. (b) Fabrication process of GO film by the printing method.
(c, d) Peeling GO film from the printing paper with the bubbling delamination method in 1 M HCl (since HI is dark colored, we used HCl instead to
illustrate this process). (e) Photograph of large-scale RGO paper. (f) Photograph of RGO paper with excellent flexibility. (g) Photograph of RGO, PANI/
RGO and RGO/PANI/RGO paper

Figure 2 | Top view and cross-sectional view SEM images of RGO paper
(a, b), PANI/RGO paper (c, d) and RGO/PANI/RGO paper (e, f).

bles generated from the cellulose paper substrate prompt the graphene film peeling off the paper in a self-releasing way, which enable
us to produce ultrathin freestanding graphene paper with a thickness
of 800 nm (Fig. S2) or thick graphene paper with a thickness more
than 100 mm. Electrochemical delamination methods have previously been used to transfer graphene grown on Cu 33 or Pt 34 foil by
H2 bubbles at the interface of the graphene and metal substrates.
Compared with these reported method, our strategy to delaminate
printed graphene film from paper substrate by CO2 bubbles is more
facile, effective and scalable. The obtained RGO paper exhibits highly
electrical conductivity of 340 S cm 21, light weight of 1 mg cm 22 and
excellent mechanical flexibility, which allows it to be rolled up,
twisted or bent to any curvature (Fig. 1e and 1f). Furthermore, the
reproducibility of the proposed method for the fabrication of graphene paper has also been evaluated. The electrical conductivity (S
cm 21 ) and mass thickness (mg cm 22 ) of ten graphene papers display
the relative standard deviation (RSD) less than 5.0% (Fig. S3), confirming that this method is highly reproducible. These features
enable it a robust substrate for the further electropolymerization of
PANI nanofibers on it. Then, PANI layer with dark green color was
uniformly coated on the RGO paper, which was denoted by PANI/
RGO. The weight ratio of RGO and PNAI in PANI/RGO paper has
been measured to be 352. After dip-coating and reduction, the PANI/
RGO paper was completely covered by a layer of RGO film, as shown
in Fig. 1g, and the sandwich-structured RGO/PANI/RGO paper was
obtained. The RGO film that coated on the surface of PANI/RGO is
ultrathin, so that its weight is negligible. The weight ratio of RGO and
PNAI in RGO/PANI/RGO paper is the same to that in PANI/RGO.
The resultant conductive, light-weight and flexible paper-like nanocomposite will facilitate industrial application of SCs, especially the
spiral wound SCs.

Fig. 2 shows SEM images of different nanohybrid papers. RGO
paper exhibits wrinkle-like morphology on its surface (Fig. 2a) and
well-layered structure with a uniform thickness of 5 mm throughout
its cross-section (Fig. 2b). After in situ electropolymerizing, PANI
nanofibers with a diameter of about 70 nm are tangled and twisted to
form 3D porous networks on RGO paper (Fig. 2c), which effectively
facilitates ions transport between the electrode surface and electrolyte The SEM image of a cross section of the PANI/RGO paper

reveals that the porous PANI layers are loaded on both sides of
RGO paper (Fig. 2d). The as-obtained PANI/RGO paper was then
wrapped by an ultrathin RGO layer via dipping in GO solution and
reduced by HI. As shown in Fig. 2e, the surface of PANI/RGO paper
has been entirely covered by RGO nanosheets, and the PANI nanofibers are sandwiched between RGO layers to form freestanding
RGO/PANI/RGO nanohybrid paper (Fig. 2f).

The deconvoluted C1s XPS spectra of the GO and RGO papers are
shown in Fig. 3a and 3b, which suggest that GO paper is highly
functionalized with oxygenated groups, such as epoxy/hydroxyl
groups (C–O,,286.5 eV), carbonyl group (C 5 O,,288.3 eV)
and carboxyl group (O 2 C 5 O,,290.3 eV). After reduced by
HI, the C/O ratio increases from 2.5 to 6.6, demonstrative of the
elimination of a large fraction of oxygenated groups on GO
nanosheets by chemical reduction. Fig. 3c exhibits the XRD patterns
of GO and RGO paper. The GO paper exhibits one peak centered at
10.5u, corresponding to the (002) reflection of stacked GO sheets
with a layer-to-layer distance (d-spacing) of 8.42 A ˚ . Compared with
GO paper, the XRD peak of RGO paper shift to 24.1u with the
decrease of d-spacing to 3.69 A ˚, further confirming the removal of
the oxygen-containing groups on GO nanosheets. The FTIR spectrum of the GO paper shows a broad absorption band centered at
2995, 3637 cm 21 attributed to O–H stretching vibrations of
adsorbed water molecules and structural OH groups, and two
absorption band centered at 1645 cm 21 and 1242 cm 21 ascribed to
carboxyl and epoxy stretching vibrations 35 . After being soaked in HI
solution for a few minutes, GO paper was then effectively reduced to
RGO paper, which was demonstrated by decreased dramatically
absorption peak of oxygen functional group. For PANI/RGO paper,
the FT-IR spectrum is dominated by that of the PANI (Fig. 3d), the
C 5 C stretching vibrations of quinoid and benzenoid rings, the C-N
stretching vibration and C 5 N stretching vibration appear at 1574,
1489, 1303 and 1142 cm 21 respectively, which are in good agreement
with previous spectroscopic characterizations of PANI 36,37 .

Discussion
As described above, it will be of great interest to study the electrochemical performance of these nanohybird paper electrodes. The
electrochemical measurements were conducted in a three-electrode
configuration in 1 M H2SO4 aqueous solution. As shown in Fig. 4a,
the CV curve of RGO paper exhibits a nearly rectangular and symmetric shape, indicative of perfect electrical double-layer capacitance
behavior and fast charging/discharging process characteristic. For
PANI/RGO and RGO/PANI/RGO papers, two couples of redox
peaks (C1/A1, C2/A2) are observed. The pair of redox peaks C1/
A1 is due to the redox transitions between the semiconducting-state
form (leucoemeraldine form) and a conducting state (polaronic
emeraldine form), and the pair of redox peaks C2/A2 is associated
with the faradaic transformation of emeraldine-pernigraniline 38 .
Evidently, in comparison with that of PANI/RGO, RGO/PANI/
RGO paper electrode exhibits larger CV area, indicating a higher
specific capacitance of RGO/PANI/RGO paper 39 .

Fig. 4b shows the galvanostatic (GV) charge/discharge curves of
the as-prepared RGO/PANI/RGO paper electrode at different current densities. During the charging and discharging steps, the charge
curve of RGO/PANI/RGO paper is almost symmetric to its corresponding discharge counterpart with a slight curvature, which is similar to that of PANI/RGO paper. However, the ‘‘IR drop’’ of RGO/
PANI/RGO paper electrode is much lower than that of PANI/RGO
paper electrode, as shown in Fig. 4c, which reflects the lower internal
resistance of RGO/PANI/RGO paper electrode with respect to that of
PANI/RGO paper electrode. As a matter of fact, the PANI-based
electrode material usually has large internal resistance as it is fully
charged or discharged because of its poor electrical conductivity.
However, in this work, the electrical conductivity of PANI/RGO
paper electrode has been dramatically increased by further coating

Figure 3 | Deconvoluted C1s XPS spectra of (a) GO paper and (b) RGO paper. (c) XRD patterns of GO and RGO papers. (d) FTIR spectra of GO, RGO
and PANI/RGO papers.

of an ultrathin RGO film on the PANI/RGO paper to form sandwichstructured RGO/PANI/RGO paper, which enhances the electrical
conductivity by the large-scale p–p conjugation between PANI and
RGO, and thus facilitates the charge transfer, resulting in a lower
internal resistance and less wasted energy. The specific capacitances
(Cs) of RGO, PANI/RGO and RGO/PANI/RGO paper electrodes
calculated from their charg/discharge curves are illustrated in
Fig. 4d. At a current density of 1 A g 21, the Cs of RGO, PANI/
RGO and RGO/PANI/RGO paper are 55 F g 21, 522 F g 21 and
581 F g 21, respectively. RGO/PANI/RGO paper not only exhibits
the highest specific capacitance values but also maintains them well
at high current density compared to other electrodes. Its specific
capacitance is preserved 64.4% (from 581 to 374 F g 21 ) as the current
density increases from 1 to 10 A g 21, which is superior to many other
graphene nanohybrid electrodes such as graphene/CNT 40, graphene/
MnO241,42 and graphene/PANI43,44. More importantly, we have

shown that the power densities of RGO/PANI/RGO paper are also
higher than those of PANI/RGO paper at a variety of current density
of 1, 2, 5, 8 and 10 A g 21 (Fig. 4e). Therefore, it can be ensured that
increasing the electrode thickness by extra RGO does not scarify the
power density of RGO/PANI/RGO paper electrode.

The significant improved supercapacitive performances of RGO/
PANI/RGO paper electrode in terms of high specific capacitance and
good rate capability can be recognized as: i) RGO paper possesses
highly electrical conductivity and mechanical strength, which acts as
an ideal current collector for high-performance supercapacitor; ii)
After in situ electropolymerization of PANI nanofibers on ROG
paper, the PANI/RGO exhibits a better electrochemical capacitive
characteristic and superior reversible redox reaction due to the incremental pseudocapacitive contribution the overall capacitance. iii)
Although PANI exhibits poor electrical conductivity, this drawback
can be overcome by further coating an ultrathin RGO layer on it. The
strong p–p interactions between the highly conductive RGO layer
and the PANI chains in the RGO/PANI/RGO could provide a good
conducting network which facilitates the redox reaction of PANI

component and increases the pseudocapacitance of the nanohybrid
paper electrode.

The Nyquist plots of RGO, PANI/RGO and RGO/PANI/RGO
paper electrodes have been demonstrated in Fig. 4f with an expanded
view of the high-frequency region and an equivalent circuit in the
inset. All plots feature the most vertical line in a low-frequency
region, indicating a nearly ideal capacitive behavior. The x-intercept
of the Nyquist plots represents the equivalent series resistance (ESR)
for supercapacitor electrodes and the charge transport resistance.
The charge transfer resistance of PANI/RGO paper (23.8 V) is larger
than that of RGO paper (9.7 V) because of the lower conductivity of
PANI. When PANI/RGO paper has been covered by a layer of highly
conductive RGO, the ESR of the sandwich-structured RGO/PANI/
RGO paper reduces to 12.7 V, reflecting the higher conductivity
achieved in RGO/PANI/RGO system. These are consisted with the
results obtained by GV charge–discharge measurements.

Fig. 5 shows the cycling performance of RGO/PANI/RGO paper
with controlled PANI/RGO paper. The RGO/PANI/RGO paper
retains 85% of its initial capacitance after 10000 cycles, which outperforms that of PANI/RGO paper (57%). As active electrode materials for supercapacitors, the conducting polymers often suffer from
poor cyclic stability because of the cyclic mechanical stress caused by
material swelling and shrinking. However, the coating of mechanically stronger graphene nanosheet on the surface of network PANI
nanofibesr can enhance the restraint of shrinkage and swelling of
PANI chains during numerous charge/discharge cycles. In addition,
the graphene layer on PANI/RGO paper can also mechanically stabilize the PANI nanomaterials and keep them bound together during
the cycling tests to avoid PANI material loss from electrode surfaces,
which effectively improve the cycling performance of the resultant
nanohybrid electrode.

To make flexible SCs entirely wearable, the electrolyte needs to be
fully encapsulated in the devices without any leakage. Taking this
into account, the use of solid gel electrolytes is more suitable than
liquid electrolytes of H SO for further applications of flexible SCs 45

Figure 4 | (a) CV curves of RGO/PANI/RGO, PANI/RGO and RGO paper electrodes at a scan rate of 10 mV s 21 in 1 M H2SO4 electrolyte. (b) GV charge/
discharge curves of RGO/PANI/RGO paper at different current densities. (c) GV charge/discharge curves of RGO/PANI/RGO, PANI/RGO and
RGO paper electrodes at the current density of 1 A g 21 . (d) Specific capacitances of RGO/PANI/RGO, PANI/RGO and RGO paper electrodes versus
discharge current densities. (e) Power densities of RGO/PANI/RGO and PANI/RGO paper electrodes versus discharge current densities. (f) Nyquist plots
of RGO/PANI/RGO, PANI/RGO and RGO paper electrodes.

CV curves of the solid-state device show a rectangular shape and two
pairs of redox peaks at different scan rates from 5 to 100 mV s 21
(Fig. 6a), indicating a pseudocapacitive behavior. Moreover, the symmetrical GV charge/discharge curves reveal the good capacitive performance as well (Fig. 6b). The Nyquist plots of the solid-state SC
device demonstrated in Fig 6c feature almost vertical line in a low

frequency region, indicating a nearly ideal capacitive behavior.
Furthermore, the charge-transfer resistance (Rct) of the solid-state
SC is about 4.5 V, which reveals the low resistance of the redox
reaction of the solid-state SC device. The as-prepared device maintains its 88% areal capacitance (107 mF cm 22 ) as discharge current
density increases from 0 2 to 2 mA cm 22 (Fig 6d) Even when the

current density increases to 10 mA cm 22, it still maintains 62% areal
capacitance.

The Ragone plots for the electrode materials are shown in Fig. 6e.
For the electrode materials among the current density measurement
range, it has a volumetric energy density of 5.4 mWh cm 23 (10.79 wh
kg 21 ), which outperforms many previously reported solid-state SCs,
such as polypyrrole-coated paper symmetric SC (1 mWh cm 23 ) 10,
carbon/MnO2 fiber symmetric SC (0.22 mWh cm 23 ) 30, H-TiO2@
MnO2//H-TiO2@C asymmetric SC (0.3 mWh cm 23 ) 31, and
WO3-x/MoO3-x asymmetric SC (1.9 mWh cm 23 ) 32 . Three solid-state
SC (10 mm 3 25 mm) units connected in series can light a red lightemitting diode (LED) at 2.4 V, as shown in Fig. 6f.

In summary, we reported a facile and scalable method to prepare
freestanding sandwich-structured graphene/PANI/graphene nanocomposite paper and demonstrated its practical application in flexible all-solid-state SCs. The graphene/PANI/graphene nanohybrid
Figure 5 | Cycle performance of RGO/PANI/RGO and PANI/RGO paper paper exhibited three unique features: i) the constituent graphene
electrodes at 10 A g 21 over 10000 cycles. paper fabricated by the simple and scalable printing method and

Figure 6 | (a) CV curves, (b) GV charge–discharge curves, (c) Nyquist plot and (d) areal capacitance versus discharge current for the solid-state device.
(e) Ragone plot of energy density versus power density for different solid-state device. (f) Photograph of a red LED lit by in-series solid-state SCs with
three units

subsequent HI treatment possessed high conductivity, light weight,
mechanical robustness and chemical stability, which functions itself
as an ideal current collector for SC architecture as well as the substrate for the further loading of active electrode materials on it. ii)
PANI nanofibers synthesized by a green in situ electropolymerization method have effectively improved the electrochemical performance of the nanohybrid paper. iii) dip-coating of an ultrathin
graphene layer on the surface of the porous PANI nanofibers has
endowed the sandwich-structured graphene/PANI/graphene nanohybrid paper electrode with enhanced specific capacitance and
increased cycling stability. The resultant flexible symmetric SC based
on the graphene/PANI/graphene nanohybrid paper and polymer gel
electrolyte exhibits high energy density, high power density and
excellent cycling stability, which makes it promising for the future
applications in flexible energy-related device and modern wearable/
portable electronics. It is worth noting that this modular approach
for the fabrication of freestanding sandwich-structured graphene
nanohybrid paper is not just restricted to the graphene/PANI/graphene system, but also contributes to the design of hybrid nanoarchitectures with tailored compositions and functions, which provides
new insights on designing high-performance paper electrode for
flexible energy-related device and modern wearable/portable
electronics.

Methods
Fabrication of RGO/PANI/RGO Composite Paper. First, well dispersed GO solution
(5mg mL 21 ) was dropped onto a piece of commercial printing paper surface. Then, the
rod was rolled back and forth to make the GO solution covered uniformly on the paper.
After subsequent air-drying, a uniform GO paper are obtained. The GO paper was
reduced by means of soaking in the HI solution (45 wt%) for 10 minutes at room
temperature, during this process, bubbles generated from the cellulose papers prompt
the thin film peeling off the paper in a self-releasing way. Subsequently, the RGO paper
was rinsed with a saturated sodium bicarbonate solution, water and methanol and dried
by vacuum drying at 80uC. RGO paper was then coated by a layer of uniform porous
nanofiber network of PANI via in situ electropolymerization. In the typical procedure,
the PANI nanofibers were synthesized by a two-step method on a conventional threeelectrode system in a 1 M HCl electrolyte containing 0.3 M aniline monomer. The first
step of the nucleation of PANI was performed at a constant potential of 0.8 V for 1 min
at room temperature. In the second step, the nanowires were grown under a constant
current condition with current density of 2 mA cm 22 46 . After that, the PANI layer was
covered with an ultrathin GO film through dip-coating method. The resultant GO/
PANI/RGO paper was also soaked in the HI solution for a few minutes at room
temperature, and the RGO/PANI/RGO paper was obtained.

Characterization. Scanning electron microscopy (SEM) images were taken on a
FESEM instrument (SIRION 200, FEI, Nederland). X-ray photoelectron
spectroscopy (XPS) measurements were performed on VG ESCALAB 250
spectrometer with monochromatic Al Ka (1486.71 eV) X-ray radiation (15 kV and
10 mA) and hemispherical electron energy analyzer. Xray powder diffraction (XRD)
patterns were recorded using a diffractometer (X’ Pert PRO, Panalytical B.V.,
Netherlands) equipped with a Cu Ka radiation source (l 5 1.5406 A ˚ ). Fourier
transform infrared (FTIR) spectra were obtained on Bruker VERTEX 70 FTIR
spectrophotometer (Germany).

Electrochemical Tests. The electrochemical characteristics were evaluated by cyclic
voltammetry, galvanostatic charge/discharge and electrochemical impedance
spectroscopy using a CHI 660E electrochemical workstation (Shanghai CH
Instruments Co., China). A conventional three-electrode system was adopted. The
working electrode was RGO/PANI/RGO paper, and the counter and reference
electrodes were platinum plate and saturated calomel electrode (SCE), respectively.
The aqueous electrolyte is 1 M H2SO4. In the case of all-solid-state SCs, two piece of
RGO/PANI/RGO paper were immersed into a hot clear solution of PVA/H2SO4
electrolyte for 5 minutes, then taken out and assembled together with a piece of filter
paper sandwiched in between the two electrodes. Finally, the device was solidified for
4 h at room temperature. The weight being used in the calculation of capacitance is
referring to the weight of the entire device. The gel electrolyte was fabricated by
mixing 6 g H2SO4 and 6 g PVA in 60 mL deionized water and heated up to 85uC for
1 h under vigorous stirring. CV measurements were conducted in a voltage range of
0–0.8 V with voltage sweep rates from 5 to 100 mV s 21 . Galvanostatic charge/
discharge measurements were carried out at different current density from 1 to 10 A
g 21 . EIS tests were performed from 10 mHz to 100 kHz with an amplitude of 5 mV
referring to open circuit potential 47 .

1. Lu, X. M. & Xia, Y. N. Electronic Materials: Buckling Down for Flexible
Electronics Nat Nanotechnol 1 163 164 (2006)

2. Pushparaj, V. L. et al. Flexible Energy Storage Devices Based on Nanocomposite
Paper. Proc. Natl. Acad. Sci. 104, 13574–13577 (2007).
3. Nishide, H. & Oyaizu, K. Toward Flexible Batteries. Science 319, 737–738 (2008).
4. Miller, J. R. Valuing Reversible Energy Storage. Science 335, 1312–1313 (2012).
5. Conway, B. E. Kluwer Academic/Plenum: New York 1999.
6. Arico, A. S., Bruce, P., Scrosati, B., Tarascon, J. M. & Schalkwijk, W. V.
Nanostructured Materials for Advanced Energy Conversion and Storage Devices.
Nat. Mater. 4, 366–377 (2005).
7. Miller, J. R. & Simon, P. Electrochemical Capacitors for Energy Management.
Science 321, 651–652 (2008).
8. Simon, P. & Gogotsi, Y. Materials for Electrochemical Capacitors. Nat. Mater. 7,
845–854 (2008).
9. Lu, X. H. et al. Stabilized TiN Nanowire Arrays for High Performance and Flexible
Supercapacitors. Nano Lett. 12, 5376–5381 (2012).
10. Yuan, L. Y., Yao, B., Hu, B., Huo, K. F., Chen, W. & Zhou, J. Polypyrrole-Coated
Paper for Flexible Solid-State Energy Storage. Energy Environ. Sci. 6, 470–476
(2013).
11. Lang, X. Y., Hirata, A., Fujita, T. & Chen, M. W. Nanoporous Metal/Oxide Hybrid
Electrodes for Electrochemical Supercapacitors. Nat. Nanotechnol. 6, 232–236
(2011).
12. Zhou, C., Zhang, Y. W., Li, Y. Y. & Liu, J. P. Construction of High Capacitance 3D
CoO@ Polypyrrole Nanowire Array Electrode for Aqueous Asymmetric
Supercapacitor. Nano Lett. 13, 2078–2085 (2013).
13. Zhang, Z. Y., Xiao, F., Qian, L. H., Xiao, J. W., Wang, S. & Liu, Y. Q. Facile
Synthesis of 3D MnO2-Graphene and Carbon Nanotube-Graphene Composite
Networks for High Performance, Flexible, All-Solid-State Asymmetric
Supercapacitors. Adv. Energy Mater. 1400064 (2014)
14. Cong, H. P., Ren, X. C., Wang, P. & Yu, S. H. Flexible Graphene-Polyaniline
Composite Paper for High Performance Supercapacitor. Energy Environ. Sci. 6,
1185–1191 (2013).
15. Yang, X. W., Cheng, C., Wang, Y., Qiu, L. & Li, D. Liquid-Mediated Dense
Integration of Graphene Materials for Compact Capacitive Energy Storage.
Science 341, 534–537 (2013).
16. Bao, L. H. & Li, X. D. Towards Textile Energy Storage from Cotton T-Shirts. Adv.
Mater. 24, 3246–3252 (2012).
17. Novoselov, K. S. et al. Electric Field Effect in Atomically Thin Carbon Films.
Science 306, 666–669 (2004).
18. Huang, Y., Liang, J. J. & Chen, Y. S. An Overview of the Applications of GrapheneBased Materials in Supercapacitors. Small 8, 1805–1834 (2012).
19. Zhang, Z. Y., Xiao, F., Guo, Y. L., Wang, S. & Liu, Y. Q. One-Pot Self-Assembled
Three-Dimensional TiO2-Graphene Hydrogel with Improved Adsorption
Capacities and Photocatalytic and Electrochemical Activities. ACS Appl. Mater.
Interfaces 5, 2227–2233 (2013).
20. Chabi, S., Peng, C., Yang, Z., Xia, Y. & Zhu, Y. Three dimensional (3D) flexible
graphene foam/polypyrrole composite: towards highly efficient supercapacitors.
RSC Adv. 5, 3999–4008 (2015)
21. Zhang, L. L. et al. Highly Conductive and Porous Activated Reduced Graphene
Oxide Films for High Power Supercapacitors. Nano Lett. 12, 1806–1812 (2012).
22. Weng, Z., Su, Y., Wang, D. W., Li, F., Du, J. H. & Cheng, H. M. Graphene-Cellulose
Paper Flexible Supercapacitors. Adv. Energy Mater. 1, 917–922 (2011).
23. Chen, C. M. et al. Self-Assembled Free-Standing Graphite Oxide Membrane. Adv.
Mater. 21, 3007–3011 (2009).
24. Xiao, F., Song, J., Gao, H., Zan, X., Xu, R. & Duan, H. W. Coating Graphene Paper
with 2D-Assembly of Electrocatalytic Nanoparticles: A Modular Approach
Toward High Performance Flexible Electrodes. ACS Nano 6, 100–110 (2012).
25. Xiao, F., Li, Y., Zan, X., Liao, K., Xu, R. & Duan, H. W. Growth of Metal-Metal
Oxide Nanostructures on Freestanding Graphene Paper for Flexible Biosensors.
Adv. Funct. Mater. 22, 2487–2494 (2012).
26. Liu, F., Song, S., Xue, D. & Zhang, H. Folded Structured Graphene Paper for High
Performance Electrode Materials. Adv. Mater. 24, 1089–1094 (2012).
27. Xu, Y. X., Lin, Z. Y., Huang, X. Q., Liu, Y., Huang, Y. & Duan, X. F. Flexible SolidState Supercapacitors Based on Three-Dimensional Graphene Hydrogel Films.
ACS Nano 7, 4042–4049 (2013).
28. Moon, I. K., Lee, J., Ruoff, R. S. & Lee, H. Reduced Graphene Oxide by Chemical
Graphitization. Nat. Commun. 1, 73 (2010).
29. Yuan, L. Y. et al. Paper-Based Supercapacitors for Self-Powered Nanosystems.
Angew. Chem. Int. Ed. 124, 5018–5022 (2012).
30. Xiao, X. et al. Fiber-Based All-Solid-State Flexible Supercapacitors for SelfPowered Systems. ACS Nano 6, 9200–9206 (2012).
31. Lu, X. H. et al. H-TiO2@MnO2//H-TiO2@C Core-Shell Nanowires for High
Performance and Flexible Asymmetric Supercapacitors. Adv. Mater. 25, 267–272
(2013).
32. Xiao, X. et al. WO3-x/MoO3-x Core/Shell Nanowires on Carbon Fabric as an
Anode for All-Solid-State Asymmetric Supercapacitors. Adv. Energy Mater. 2,
1328–1332 (2012).
33. Wang, Y. et al. Electrochemical Delamination of CVD-Grown Graphene Film:
Toward the Recyclable Use of Copper Catalyst. ACS Nano 5, 9927–9933 (2011).
34. Gao, L. B. et al. Repeated Growth and Bubbling Transfer of Graphene with
Millimetre-Size Single-Crystal Grains Using Platinum. Nat. Commun. 3, 699
(2012).
35. Si, Y. & Samulski, E. T. Synthesis of Water Soluble Graphene. Nano Lett. 8,
1679 1682 (2008)

36. Li, Y., Zhao, X., Xu, Q., Zhang, Q. & Chen, D. Facile Preparation and Enhanced
Capacitance of the Polyaniline/Sodium Alginate Nanofiber Network for
Supercapacitors. Langmuir 27, 6458–6463 (2011).
37. Gao, Y. et al. Silver/Polyaniline Composite Nanotubes: One Step Synthesis and
Electrocatalytic Activity for Neurotransmitter Dopamine. J. Phys. Chem. C 113,
15175–15181 (2009).
38. Wang, Y. G., Li, H. Q. & Xia, Y. Y. Ordered Whiskerlike Polyaniline Grown on the
Surface of Mesoporous Carbon and Its Electrochemical Capacitance
Performance. Adv. Mater. 18, 2619–2623 (2006).
39. Gao, Z. et al. A New Partially Reduced Graphene Oxide Nanosheet/Polyaniline
Nanowafer Hybrid as Supercapacitor Electrode Material. Energy Fuels 27,
568–575 (2012).
40. Fan, Z. J. et al. Three-Dimensional Carbon Nanotube/Graphene Sandwich and Its
Application as Electrode in Supercapacitors. Adv. Mater. 22, 3723–3728 (2010).
41. Yu, G. H. et al. Solution-Processed Graphene/MnO2 Nanostructured Textiles for
High Performance Electrochemical Capacitors. Nano Lett. 11, 2905–2911 (2011).
42. Yu, G. H. et al. Enhancing the Supercapacitor Performance of Graphene/MnO2
Nanostructured Electrodes by Conductive Wrapping. Nano Lett. 11, 4438–4442
(2011).
43. Wu, Q., Xu, Y. X., Yao, Z., Liu, A. & Shi, G. Q. Supercapacitors Based on Flexible
Graphene/Polyaniline Nanofiber Composite Films. ACS Nano 4, 1963–1970
(2010).
44. Wang, D. W. et al. Fabrication of Graphene/Polyaniline Composite Paper via In
Situ Anodic Electropolymerization for High Performance Flexible Electrode. ACS
Nano 3, 1745–1752 (2009).
45. Bae, J., Song, M. K., Park, Y. J., Kim, J. M., Liu, M. & Wang, Z. L. Fiber
Supercapacitors Made of Nanowire-Fiber Hybrid Structures for Wearable/
Flexible Energy Storage. Angew. Chem. Int. Ed. 50, 1683–1687 (2011).
46. Cheng, Q., Tang, J., Ma, J., Zhang, H., Shinya, N. & Qin, L. C. Polyaniline-Coated
Electro-etched Carbon Fiber Cloth Electrodes for Supercapacitors. J. Phys. Chem.
C 115, 23584–23590 (2011).

47. Li, S. et al. Vertically Aligned Carbon Nanotubes Grown on Graphene Paper as
Electrodes in Lithium-Ion Batteries and Dye-Sensitized Solar Cells. Adv. Energy
Mater. 1, 486–490 (2011).

Acknowledgments
This research was financially supported by the National Natural Science Foundation of
China (Project No. 51173055 and No. 21305048), and the Shenzhen strategic emerging
industry development special fund project (No. JCYJ2013040114474419 0).

Author contributions
F.X., S.X., S.W., H.F. and Y.Q. proposed, planned, and designed the project. F.X., S.X., Z.Z.,
L.W., J.W. and J.L. performed the material preparation, characterizations, and catalytic
tests. All authors contributed to writing the manuscript.

Additional information
[Supplementary information accompanies this paper at http://www.nature.com/](http://www.nature.com/scientificreports)
[scientificreports](http://www.nature.com/scientificreports)

Competing financial interests: The authors declare no competing financial interests.

How to cite this article: Xiao, F. et al. Scalable Synthesis of Freestanding
Sandwich-structured Graphene/Polyaniline/Graphene Nanocomposite Paper for Flexible
All-Solid-State Supercapacitor. Sci. Rep. 5, 9359; DOI:10.1038/srep09359 (2015).

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