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Conducting polymer and reduced graphene oxide Langmuir– Blodgett films: a hybrid nanostructure for high performance electrode applications Junfeng Wen Yadong Jiang Yajie Yang Shibin Li Received: 18 November 2013 / Accepted: 14 December 2013 / Published online: 20 December 2013 Ó Springer Science+Business Media New York 2013 Abstract In this work, we prepared a reduced graphene oxide (RGO)/poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid composite with well defined nanostructure. The graphene oxide (GO) was first deposited on substrate through the Langmuir–Blodgett (LB) deposition, which provided a tunable and ordered GO arrangement on sub- strate. Then the GO LB films were reduced to RGO by following thermal treatment, and a ultrathin conducting polymer (CP) PEDOT was directly coated on RGO through a vapor phase polymerization process. The RGO/PEDOT nanocomposite exhibits excellent electrical conductivity about 377.2 S/cm. Electrochemical activity investigation revealed that this nanocomposite exhibits 213 F/g high specific capacitance at a 0.5 A/g current density and shows better capacitance retention rate than pure PEDOT. The detailed study also confirmed that the arrangement of RGO shows distinct influence on the electrical and electro- chemical properties of obtained nanocomposite. Large area RGO/PEDOT nanocomposite with high conductivity and electrochemical activity can be deposited on different substrates. Such high conductivity and electrochemical activity RGO/CP nanocomposite shows promising appli- cation future in organic and flexible electrode materials for sustainable energy storage. 1 Introduction Conducting polymers (CPs) and its nanostructures have been a subject of growing interest due to their promising application on microelectronics, capacitor, sensor, solar cell et al. [14]. It offers a high conductive and optical transparent capability for electrode materials used on electrochemical ultracapacitor and solar cell [5, 6]. The optimized performance of device has been improved due to the construction of CPs and its nanostructure for electrode materials and modified electrode surface [7, 8]. However, Such CPs as poly(3,4-ethylenedioxythiophene) (PEDOT) is brittle and weak in mechanical strengths. This is one of the drawbacks that hinders PEDOT used as organic electrodes [9, 10]. Recently, coupling CPs with carbon nanomaterials, such as graphene, carbon nanotube, has been demonstrated as an effective approach to improve the mechanical strengths and conductive performance of the CPs, and it also shows promising future for device applications [1113]. However, in order to use graphene as an efficient rein- forcing component, it is paramount to incorporate nonag- gregated and noncrumpled graphene sheets with maximum interfacial interactions for efficient load transfer within the polymer matrix [1416]. Due to the surging interest in graphene based materials, GO has regained significant attention as a solution-processable precursor for bulk pro- duction of grapheme used on transparent conductors and ultracapacitors [17, 18]. The reduced graphene oxide (RGO) can be obtained by reducing GO through chemical and thermal treatment [1922]. It has been also demon- strated RGO exhibits high mechanical strength combined with interesting physical properties, including high per- formance of electrical, thermal conductivity and electro- chemical activity [2325]. J. Wen Á Y. Jiang Á Y. Yang (&) Á S. Li State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, People’s Republic of China e-mail: [email protected] 123 J Mater Sci: Mater Electron (2014) 25:1063–1071 DOI 10.1007/s10854-013-1687-z

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Page 1: Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performanceelectrode applications

Junfeng Wen • Yadong Jiang • Yajie Yang •

Shibin Li

Received: 18 November 2013 / Accepted: 14 December 2013 / Published online: 20 December 2013

� Springer Science+Business Media New York 2013

Abstract In this work, we prepared a reduced graphene

oxide (RGO)/poly(3,4-ethylenedioxythiophene) (PEDOT)

hybrid composite with well defined nanostructure. The

graphene oxide (GO) was first deposited on substrate

through the Langmuir–Blodgett (LB) deposition, which

provided a tunable and ordered GO arrangement on sub-

strate. Then the GO LB films were reduced to RGO by

following thermal treatment, and a ultrathin conducting

polymer (CP) PEDOT was directly coated on RGO through

a vapor phase polymerization process. The RGO/PEDOT

nanocomposite exhibits excellent electrical conductivity

about 377.2 S/cm. Electrochemical activity investigation

revealed that this nanocomposite exhibits 213 F/g high

specific capacitance at a 0.5 A/g current density and shows

better capacitance retention rate than pure PEDOT. The

detailed study also confirmed that the arrangement of RGO

shows distinct influence on the electrical and electro-

chemical properties of obtained nanocomposite. Large area

RGO/PEDOT nanocomposite with high conductivity and

electrochemical activity can be deposited on different

substrates. Such high conductivity and electrochemical

activity RGO/CP nanocomposite shows promising appli-

cation future in organic and flexible electrode materials for

sustainable energy storage.

1 Introduction

Conducting polymers (CPs) and its nanostructures have

been a subject of growing interest due to their promising

application on microelectronics, capacitor, sensor, solar

cell et al. [1–4]. It offers a high conductive and optical

transparent capability for electrode materials used on

electrochemical ultracapacitor and solar cell [5, 6]. The

optimized performance of device has been improved due to

the construction of CPs and its nanostructure for electrode

materials and modified electrode surface [7, 8]. However,

Such CPs as poly(3,4-ethylenedioxythiophene) (PEDOT) is

brittle and weak in mechanical strengths. This is one of the

drawbacks that hinders PEDOT used as organic electrodes

[9, 10]. Recently, coupling CPs with carbon nanomaterials,

such as graphene, carbon nanotube, has been demonstrated

as an effective approach to improve the mechanical

strengths and conductive performance of the CPs, and

it also shows promising future for device applications

[11–13].

However, in order to use graphene as an efficient rein-

forcing component, it is paramount to incorporate nonag-

gregated and noncrumpled graphene sheets with maximum

interfacial interactions for efficient load transfer within the

polymer matrix [14–16]. Due to the surging interest in

graphene based materials, GO has regained significant

attention as a solution-processable precursor for bulk pro-

duction of grapheme used on transparent conductors and

ultracapacitors [17, 18]. The reduced graphene oxide

(RGO) can be obtained by reducing GO through chemical

and thermal treatment [19–22]. It has been also demon-

strated RGO exhibits high mechanical strength combined

with interesting physical properties, including high per-

formance of electrical, thermal conductivity and electro-

chemical activity [23–25].

J. Wen � Y. Jiang � Y. Yang (&) � S. Li

State Key Laboratory of Electronic Thin Films and Integrated

Devices, School of Optoelectronic Information, University of

Electronic Science and Technology of China (UESTC),

Chengdu 610054, People’s Republic of China

e-mail: [email protected]

123

J Mater Sci: Mater Electron (2014) 25:1063–1071

DOI 10.1007/s10854-013-1687-z

Page 2: Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

Nanocomposites based on CPs and RGO indicate

excellent electrochemical and conductive performance

when it is used as electrode materials [26, 27]. However, it

is still a challenge to address tunable arrangement of RGO

to obtain better and effective synergistic effect in nano-

composites. The arrangement feature of carbon sheets in

nanocomposites results in performance, for instance, elec-

trical and electrochemical ability change remarkably.

Moreover, tunable performance can be realized by con-

trolling the loadings of RGO in nanocomposites. So, it is

worthwhile to investigate the influence of RGO arrange-

ment characteristic in the nanocomposite, which provides a

valuable assistance to prepare excellent and tunable per-

formance RGO based nanocomposite [28–30].

In this paper, we demonstrate the preparation of a RGO/

PEDOT nanocomposite by using Langmuir–Blodgett (LB)

and vapor phase polymerization (VPP) methods. This

nanocomposite offers tunable arrangement and loading of

RGO in composite and ultrathin PEDOT coverage on

RGO. Limited work is focused on fabricating RGO based

nanocomposites through LB and VPP deposition and the

influence of defined RGO structure on composite perfor-

mance. In the first step, self-assembly of GO sheets on

substrate was performed using LB technique instead of

regular adsorption and spin-casting. Owing to its flexible

nature, folding and wrinkling of graphene oxide sheets can

be substantially minimized by using LB technique to

deposit the films. It is also a facile transfer way that the

sheets can be transferred easily to any appropriate substrate

for further integration with microelectronic devices. After

the GO LB deposition, the GO sheets is reduced into RGO

through a thermal and water vapor treatment and the

morphology of these RGO sheets can keep a LB sheet

formation with defined structure. After that, the PEDOT is

directly deposited on RGO through following VPP depo-

sition, and VPP deposition ensures close and ultrathin

package of PEDOT on RGO. This RGO/PEDOT nano-

composite combines excellent conductivity and electro-

chemical activity based on carbon RGO and CP, and it

exhibits promising applications in organic and flexible

electrode materials for sustainable energy storage.

2 Experimental

2.1 Materials

Graphite flakes used for GO preparation, 3,4-ethylenedi-

oxythiophene (EDOT) (under the respective trade name

Clevios M) and Iron(III) chloride used for PEDOT VPP

deposition were purchased from Sigma-Aldrich. GO was

synthesized from natural graphite flakes was prepared

through Hummer’s method. Stable dispersion of GO in a

solution mixture of methanol/DI water (4:1) was subjected

to ultrasonication for 30 min followed by centrifugation at

2,500 rpm, and this GO solution was used as LB film

deposition.

2.2 Preparation of RGO LB films/PEDOT

nanocomposite

Single GO sheets deposition was carried out in KSV-5000

LB system. The trough was carefully cleaned with chlo-

roform and then filled with DI water. GO solution was

dropwise spread onto the water surface using a glass syr-

inge. Surface pressure was monitored using a tensiometer

attached to a Wilhelmy plate. The film was compressed by

barriers at a speed of 1 mm/min. The GO monolayer was

transferred to substrates at various points during the com-

pression by vertically dipping the substrate into the trough

and slowly pulling it up (1 mm/min). The substrate was

first processed with a hydrophilic treatment in order to

deposit uniform single layer GO. After the GO LB depo-

sition, the single GO layer covered substrate was treated in

a water vapor oven at 190 �C for 4 h GO reduction. Then

the RGO layer covered substrate was fixed in oCVD

reactor for a PEDOT VPP deposition. The reactor pressure

was held at *10 mTorr, and the substrate temperature was

maintained at 120 �C. The EDOT was heated to 150 �C

and introduced into the reactor at a flow rate of *3 sccm

for slow reaction. Iron(III) chloride was evaporated from a

heated crucible between 130 and 150 �C. The different

thickness of PEDOT can be obtained by varying the time of

polymerization. The schematic preparation of RGO/PE-

DOT nanocomposite is shown in Fig. 1.

2.3 Characterization

The surface pressure–area (p–A) isotherm recorded by

computer and the morphology analysis of GO sheets at air–

water interface was characterized by the Brewster Angle

Microscopy (BAM 300). Surface morphology of LB film

was investigated by atomic force microscopy (AFM,

Model SP 3800, SII, Japan) with a tapping mode. Mor-

phological properties were investigated with scanning

electron microscopy (SEM), using a Hitachi made (SEM)

scanning electron microscopy (Model S-2400). Elemental

composition analysis was carried out by X-ray photoelec-

tron spectrum (XPS) with a Scienta ESCA200 spectrometer

at the pressure of 3 9 10-10 mbar and monochromatized

Al Ka radiation (hm = 1,486 eV). FT-IR spectrum was

characterized with a WGH-30 analysis instrument (Tianjin,

China).

The current–voltage (I–V) curves of RGO and RGO/

PEDOT was obtained by using a keithley semiconducting

testing system with model 4200. Electrochemical

1064 J Mater Sci: Mater Electron (2014) 25:1063–1071

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performance was characterized by using a CHI600 elec-

trochemistry workstation. Cyclic voltammetry (CV), gal-

vanostatic charge–discharge were performed with 1 mol/L

H2SO4 aqueous electrolyte using a platinum sheet as

counter electrode, and Ag/AgCl as the reference electrode.

To investigate the conductive performance, A GO, RGO

and RGO/PEDOT-FET device was fabricated with source

and drain electrodes on Si/SiO2 substrate with gold back

gate. The length and width of the channel of the FET

device are 60 and 50 lm respectively. The electrodes

(source and drain) were made by thermally coated gold of

20 nm thickness. All the measurements were performed at

ambient temperature.

3 Results and discussion

Figure 2 shows surface pressure–area (p–A) isothermal of

GO at air–water interface. Due to the geometrically simi-

larity of GO with air–water interface, GO can float on a

water surface without surfactants or stabilizing, which

makes it ideally accommodate the flat sheets. It can be seen

from the Fig. 2 that GO sheets arrange compactly at air–

water interface with continuous compression. This compact

arrangement of GO sheets can be constructed on different

substrate through vertical or horizontal deposition. By

controlling the surface pressure, surface coverage of the

graphene oxide sheets was manipulated to realize a uniform

deposition with compact and incompact arrangement.

Moreover, large area LB deposition can also be realized on

GO sheets with tunable arrangement on different substrates.

To keep the original morphology of GO, we choose

thermal treatment at a water vapor environment as

efficiently reduction process to obtain RGO. Figure 3

shows AFM images of single layer GO and RGO sheets

deposited on Si substrate. The thermal treatment does not

lead to distinct morphology change of as-prepared GO, and

the obtained RGO sheets can keep ordered and compact

formation from GO LB films. Figure 3b (indicated by

black arrow) shows high surface pressure results in occa-

sional wrinkles and overlaps. It also can be seen that, due to

assemble from abundant GO sheets, large numbers of

interspace exists in RGO LB sheets although deposited at

very high surface pressure, and this hampers formation of

complete single GO layer with large area. However, as a

nanocomposites preparation method, this discontinuous

RGO sheets affords convenient template for CP inserting

and covering on RGO and this RGO/CP nanocomposite

Fig. 1 Schematic RGO/PEDOT preparation based on LB and VPP deposition, and digital camera images of RGO LB films and RGO LB films/

PEDOT deposited on Si substrate

Fig. 2 Surface pressure–area (p–A) isothermal of GO at air–water

interface with continuous compress, and arrangement evolution

images of GO monitored by BAM

J Mater Sci: Mater Electron (2014) 25:1063–1071 1065

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Page 4: Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

would represent excellent synergistic effect for improving

electrical and electrochemical performance. As above-

mentioned in this paper, we investigate the influence of this

tunable RGO sheets arrangement on obtained nanocom-

posites performance and prepare the RGO/CP nanocom-

posites with tunable performance.

Vapor phase polymerization process is able to form

chemically well defined and ultrathin polymeric films

directly on the well-defined surface or template, which

results in the formation of a well defined nanofilm struc-

ture. As shown in Fig. 3b, after the VPP depositon of

PEDOT, a dinstinct change of film morphology and

thickness is observed in RGO LB films. The RGO LB

sheets is covered with lots of protuberances PEDOT layers,

and these protuberances become more obvious in RGO/

PEDOT nanocomposites obtained from lower surface

pressure. The thickness of PEDOT layer deposited on RGO

can be adjusted by controlling the VPP deposition time and

a ultrathin PEDOT layer can be obtained in a short depo-

sition time. The thickness of PEDOT films in Fig. 3b is

about 40–50 nm. As shown in Fig. 1, a color change of

RGO films is observed after VPP deposition of PEDOT and

RGO/PEDOT films shows deep blue color due to the doped

state of PEDOT.

The FT-IR spectra of GO LB films, RGO LB films, and

PEDOT/RGO is shown in Fig. 4. The featureless FT-IR

spectrum of RGO indicates that the thermal reduction of

GO at the water vapor environment is relatively complete

with few oxygen-containing groups. From the FT-IR

spectrum of RGO/PEDOT, the vibrational bands at about

1,519 and 1,342 cm-1 are attributed to the C=C and C–C

stretching vibrations of the quininoid structure of the thi-

ophene ring, respectively. The bands at 1,200, 1,142, and

1,088 cm-1 are ascribed to the C–O–C bond stretching in

the ethylene dioxy (alkylenedioxy) group. Additionally, the

C–S bond in the thiophene ring is evidenced by the

Fig. 3 a AFM images of GO

LB films and after thermal

treatment, b RGO LB films

deposited at different surface

pressure and SEM images after

VPP deposition of PEDOT

1066 J Mater Sci: Mater Electron (2014) 25:1063–1071

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presence of bands at about 981 and 836 cm-1. The series

of bands suggests that the PEDOT is deposited on RGO

through a chemical VPP deposition. Figure 5 shows the

presence of sulfur spin-split doublet of RGO/PEDOT at

around 164.4 eV (S 2p3/2) and 167.5 eV (S 2p1/2).The

higher binding energy doublet at around 174.2 and

175.5 eV is ascribed to sulfur spin-split coupling from

PEDOT/Cl- due to the incorporation of counterion Cl-

into PEDOT. As shown in Fig. 1, the result is accordance

with the color change after the VPP deposition of PEDOT,

indicating the formation of doped PEDOT.

As shown in Fig 6a, current versus voltage (I–V) char-

acteristics of GO LB films deposited at different surface

pressure is studied. The linear I–V curves of all GO LB

films confirm the good ohmic contact between GO LB film

and electrodes. It has been proven that the electrical per-

formance of GO LB films dependences weakly on depo-

sition surface pressure, which is ascribed to the poor

conductivity of GO sheets.

After the thermal treatment, the reduced GO resembles

graphene but with some residual oxygen and structural

defects presents a conductivity that is comparable to that of

doped conductive polymers25. The tunable electrical per-

formance of RGO is also an useful property for the

application in organic electronics. To evaluate the electri-

cal performance of RGO LB films, the GO LB films are

Fig. 4 FT-IR spectrum of GO LB films, RGO LB films, and PEDOT/

RGO nanocomposites

Fig. 5 XPS core-level spectra of RGO-PEDOT

Fig. 6 Current–voltage (I–V) curves of a GO LB films, b RGO LB

films and c variation of RGO/PEDOT constructed from GO films

deposited at 15 mN/m

J Mater Sci: Mater Electron (2014) 25:1063–1071 1067

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Page 6: Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

reduced into RGO by a thermal treatment, and the I–V

curves of this RGO LB films is shown in Fig. 6b. A dra-

matically enhancement of conductivity, more than 2 orders

of magnitude, is observed after the thermal treatment of

GO. This result indicates the successful thermal reduction

of GO to RGO in LB films and it is also confirmed by FT-

IR analysis. Whereas, unlike GO, the deposition surface

pressure shows relative strong influence on electrical per-

formance of RGO LB films, and the RGO obtained from

high deposition surface exhibits better conductive perfor-

mance. It is well known that RGO LB films obtained from

higher surface pressure addresses more compact and con-

tinuous arrangement of RGO sheets, resulting in uniform

and compact conducting channel for effective carries

transfer. Moreover, due to the functional group is removed,

the individual RGO sheet exhibits better conductivity than

GO. The slight change in conducting channel caused by

deposition surface pressure results in remarkable change of

conducting performance in RGO LB films. Figure 6c

shows the change of conductive performance after VPP

deposition of PEDOT on RGO LB films. The coverage of

PEDOT on RGO and insertion in interspace of adjacent

RGO sheets lead to complete coverage of nanocomposites

on substrate. It can be seen that, in our experiment, the

RGO LB films exhibits slight lower conductivity than pure

PEDOT obtained through VPP deposition and the obtained

GO/PEDOT exhibits slight decrease in conductivity.

Table 1 shows electrical conductivity of PEDOT, RGO

and PEDOT/RGO. A 20 layers RGO LB films exhibits

electrical conductivity about 326.7 S/cm, and PEDOT

deposited from VPP process with same thickness has a

conductivity about 382.5 S/cm. It can be seen that the RGO

shows comparable conductive performance to that of

doped CP due to some residual oxygen and structural

defects in carbon sheets. This alike conductive perfor-

mance ensure lower contact resistance and better syner-

gistic effect between PEDOT and RGO in nanocomposites.

After VPP deposition of PEDOT on RGO, a slight elec-

trical conductivity decrease of PEDOT/RGO is presented,

and this conductive performance mostly comes from CP

due to the latter formed continuous PEDOT layer. It can be

seen that, compared with pure PEDOT and RGO LB films,

a expected synergistic effect obtained in RGO/PEDOT

nanocomposites, and this nanocomposites exhibits high

conductivity about 377.2 S/cm.

As a electrochemical capacitor electrode applications,

the brittle and weak mechanical strength of PEDOT hin-

ders it is used as organic electrodes, for instance, electro-

chemical electrode for supercapacitors. The direct

Table 1 Electrical conductivity of PEDOT, RGO LB films and PE-

DOT/RGO

Conductivity(S/cm) PEDOT RGO (20 layers) RGO/PEDOT

382.5 326.7 377.2

Fig. 7 Cycle voltammetry curves of a RGO/PEDOT, GO/PEDOT

and VPP PEDOT at a 60 mv/s scanning voltage speed, b RGO/

PEDOT at different scanning voltage speed and c GO/PEDOT at

different scanning voltage speed

1068 J Mater Sci: Mater Electron (2014) 25:1063–1071

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deposition of ultrathin PEDOT layer onto RGO LB films

produces nanocomposites with good mechanical strength

as well as an enhancement of specific surface area.

Moreover, RGO/PEDOT nanocomposits can present

hybrid capacitance performance based on carbon and CP,

and high conductive performance of RGO/PEDOT can also

make sure device with low equivalent series resistance

(ESR) for fast charge/discharge. Therefore, the electro-

chemical capacitive properties of the RGO/PEDOT mate-

rials are investigated by using cycle voltammetry, charge/

discharge techniques and electrochemical impedance

spectra (EIS).

Figure 7a shows the cyclic voltammograms (CVs) of

RGO/PEDOT, GO/PEDOT and VPP PEDOT electrode at a

constant scanning voltage speed. RGO/PEDOT curve

shows almost rectangular shape, suggesting the good

capacitive properties of RGO/PEDOT. This good capaci-

tive behavior is contributed to the successive redox reac-

tions of PEDOT along with the transport of counterions

into and out of the polymer. However, a distorted rectan-

gular CV is obtained from the VPP PEDOT electrode,

indicating an uncompensated resistance in the system.

Figure 7b, c show cycle voltammetry curves of GO/PE-

DOT and RGO/PEDOT at different scanning voltage

speed. It can be observed the redox current of RGO-PE-

DOT increases with the increase of scan rate, indicating a

good rate capability. In the present study, due to the

comparable conductivity of RGO and PEDOT, the RGO/

PEDOT composite may represent good conductive syner-

gistic effect and low contact resistance, leading to the

observed good capacitive behavior. Compared with RGO-

PEDOT, the increase of redox current is relative slight in

GO-PEDOT electrode (in Fig. 7c), which may ascribe to

the poor conductive performance of this nanocomposite.

Figure 8 shows the charge/discharge curves of RGO/

PEDOT and GO/PEDOT respectively. The curves of RGO/

PEDOT almost exhibit equilateral triangle shape because

the potential of charge/discharge is a linear response to

time, indicating a good reversibility during the charge/

discharge processes (Fig. 8a). As expected from the CV

results, the GO/PEDOT nanocomposite performed rela-

tively poor charge/discharge performance. The charging

and discharging cycle deviates markedly from the ideal

triangular shape of a capacitor, and the discharge time is

short and unstable (Fig. 8c). The inset nyquist plot in

Fig. 8a, c demonstrate the EIS performance of PEDOT/

RGO and PEDOT/GO electrodes. It can be seen that the

PEDOT/RGO presents distinct semicircle performance in

low frequency and exhibits better capacitance performance

than PEDOT/GO. This indicates that a low resistance

interface is formed between the PEDOT and RGO and this

interface is also suitable for solution ions fast adsorption

and desorption. Moreover, compared with PEDOT/GO, the

PEDOT/RGO electrode also presents lower equivalent

resistance during the charge/discharge process due to the

high conductive nature. In addition, as shown in Fig. 8b, d,

Fig. 8 Charge/discharge curves

of a RGO/PEDOT electrode at

different scanning current

b RGO/PEDOT obtained from

different deposition surface

pressure at a 1.0 A/g scanning

current, c GO/PEDOT electrode

at different scanning current,

d GO/PEDOT obtained from

different deposition surface

pressure at a 1.0 A/g scanning

current, and the insets in (a) and

(c) shows nyquist plot of

different electrode

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PEDOT/RGO nanocomposites obtained from GO LB films

deposited at higher surface pressure shows larger specific

capacitance. We conclude that, with the increase of film

deposition pressure, more GO sheets are deposited on

substrate, which leads to more RGO is formed in RGO/

PEDOT nanocomposites successively. Therefor, larger

specific surface area afforded by RGO is presented to

solution ion and directly results in the enhancement of

specific capacitance of electrode materials.

The specific capacitances obtained from these data are

tabulated in Table 2, it can be seen that both RGO/PEDOT

and GO/PEDOT containing carbon sheets exhibit larger

specific capacitance than pure PEDOT. The surface pres-

sure of the deposition of GO LB film influences obviously

on specific capacitance of nanocomposites. The RGO/PE-

DOT deposited at a surface pressure about 20 mN/m shows

high specific capacitance about 213 F/g at a current density

of 0.5 A/g.

Rate performance of electrode films is a vital factor for

the practical application in electrochemical capacitor. As

shown in Fig. 9, the rate performance of RGO/PEDOT and

PEDOT is evaluated by charging/discharging at different

current densities. For RGO/PEDOT, the specific capaci-

tance maintained 87 % capacitance after 2,000 cycles at

scan current density 0.5 A/g. The results indicate a good

cycling ability of the composite materials. The RGO LB

sheets provided a robust support for the CPs. Therefore, the

mechanical strength of the composites is enhanced, and the

swelling and shrinking of ultrathin CPs during the long-

term cycling is avoided. Compared with pure PEDOT, the

composite RGO/PEDOT is more stable and suitable for

high performance electrochemical electrode materials. The

GO/PEDOT electrode also presents good capacitance

retention performance, and it can keep more than 80 % of

initial capacitance after 2,000 cycles (the data is not

shown). However, the higher equivalent resistance in this

composite restricts it as high performance electrochemical

electrode materials due to the higher ESR and worse EIS

performance during fast charge/discharge process.

Moreover, it also can be seen that the surface pressure

for GO LB film deposition is crucial to rate performance of

RGO/PEDOT nanocomposites. Nanocomposites obtained

from GO LB films deposited at higher surface pressure

shows better capacitance retention performance. It is well

known that more GO sheets deposit on substrates at higher

surface pressure and loading analysis in nanocomposites

confirm that RGO loadings increase from 5 to 12 % with

the increase of surface pressure from 5 to 20 mN/m. More

RGO loading formed in nanocomposites realizes a distinct

increase of specific area. In addition, the good conductive

performance of RGO/PEDOT also produces good capaci-

tive performance. With the decrease of surface pressure,

less RGO is formed in RGO/PEDOT nanocomposite. The

RGO/PEDOT constructed on GO LB films deposited at

5 mN/m exhibits poor capacitive retention characteristic

like pure PEDOT, and it can only maintained 78 %

capacitance after 500 cycles. So, It is crucial to address the

uniform and high density arrangement of RGO LB sheets

in PEDOT/RGO nanocomposites, which could ensure the

optimized large specific capacitance and prevent PEDOT

from aggregating and swelling simultaneously. With the

controlling of RGO loadings in PEDOT/RGO, this nano-

composite exhibits tunable electrical and electrochemical

performance for high performance electrode materials.

4 Conclusions

LB deposition provides facile way to deposit large area GO

LB films on different substrate with tunable arrangement.

The direct coating of ultrathin CP layer on RGO sheets is

achieved by using a VPP method. The combination of LB

and VPP methods provides a simple and efficient way to

prepare RGO-PEDOT nanocomposites. The electrical

properties reveals a good electrical synergistic effect

achiever after the VPP deposition of PEDOT on RGO. The

Table 2 Specific capacitances of GO/PEDOT, RGO/PEDOT

obtained from different deposition pressure and VPP PEDOT at a

0.5 A/g current density

Samples Specific capacitance (F/g)

5 mN/

m

10 mN/

m

15 mN/

m

18 mN/

m

22 mN/

m

GO/PEDOT 83 92 117 133 136

RGO/PEDOT 105 122 147 213 209

PEDOT (VPP

deposition)

76 9 9 9 9

Fig. 9 Capacitance retention performance RGO-PEDOT and PE-

DOT (at 0.5 A/g scan current density)

1070 J Mater Sci: Mater Electron (2014) 25:1063–1071

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Page 9: Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

electrical properties of subsequent RGO depend on the

surface pressure of the deposition of GO LB film. The

superior capacitive performance of the RGO-PEDOT com-

posites is demonstrated by the test of electrochemical

properties. The specific capacitance of sample RGO/PEDOT

is as high as 213 F/g at a current density of 0.5 A/g. The

capacitive retention of RGO/PEDOT electrode was 87 %

after 2,000 cycles, which is much better than that of pure

PEDOT. Tunable arrangement of RGO in nanocomposites

obtained by LB deposition resulted in good and variable

capacitive performance of the RGO/CP composites.

Acknowledgments The work was supported by the National Sci-

ence Foundation of China (NSFC) (No.61101029 and No.61204098),

A Plan for Supporting the New Century Talents (No. NCET-12-

0091).

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