Preparation and Characterization of a Pseudocapacitor Electrode By

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Journal of Taibah University for Science 10 (2016) 281–285

Preparation and characterization of a pseudocapacitor electrode by

spraying a conducting polymer onto a ﬂexible substrate

a b,∗ a b

Shaker A. Ebrahim , Mohamed E. Harb , Moataz M. Soliman , Mazhar B. Tayel

Department of Materials Science, Institute of Graduate Studies and Research, Alexandria University, P.O. Box 832, Egypt

Department of Electrical Engineering, Faculty of Engineering, Alexandria University, P.O. Box 21544, Egypt

Received 31 March 2015; received in revised form 9 June 2015; accepted 9 July 2015

Available online 31 August 2015

Abstract

In this paper, polyaniline is deposited using a spraying technique onto a ﬂexible current collector for pseudocapacitor applications.

The polyaniline is characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and

optical absorption studies. The energy density of a pseudocapacitor is higher than that of double-layer supercapacitors due to

Faradaic reactions. A high speciﬁc capacitance of 594.92 F/g is obtained at a scan rate of 5 mV/s with a scanning potential window

of (−0.8 to 0.8 V). The results show an increase in the energy density of 82.63 W h/kg at a potential difference of 1 V using a 4 M

potassium hydroxide aqueous electrolyte.

the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Conducting polymer; Polyaniline; Pseudocapacitors; Flexible electrode; Energy density

1. Introduction polymer backbone and, on reduction (“undoping”), they

are released back into solution. Generally, p-dopable

Electronically conducting polymers (ECPs), such as polymers are more stable than n-dopable polymers [5].

polypyrrole (PPy), polyaniline (PANI), polythiophene The doping/undoping process occurs throughout the

(PTh) and poly[3,4-ethylenedioxythiophene] (PEDOT), bulk of the electrodes, offering the opportunity to achieve

can store and release charges through redox pro- high values of speciﬁc capacitance. Among the conduct-

cesses associated with ␲-conjugated polymer chains ing polymers, polyaniline (PANI) has attracted much

[1–5]. When oxidation occurs (also referred to as p- attention because of its low cost, environmental stability,

doping), ions from the electrolyte are transferred to the controllable electrical conductivity, and easy process-

ability [5].

∗ Electrochemical supercapacitors combine the advan-

Corresponding author. Tel.: +20 1020982715.

tages of dielectric capacitors, which can deliver high

E-mail address: [email protected] (M.E. Harb).

power within a very short time, and rechargeable

Peer review under responsibility of Taibah University

batteries, which can store high amounts of energy. Super-

capacitors have found an increasingly important role

in power source applications, such as hybrid electric

vehicles, short-term power sources for mobile electronic

http://dx.doi.org/10.1016/j.jtusci.2015.07.004

CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

282 S.A. Ebrahim et al. / Journal of Taibah University for Science 10 (2016) 281–285

devices, among others. The materials studied for super- The used electrolyte is aqueous potassium hydroxide

capacitors are mainly of three types: carbon, metal oxide, (c = 4 M) [11–15].

and conducting polymer. Due to the Faradaic reaction,

the energy density of a supercapacitor consisting of 2.4. Electrochemical measurements

electro-active materials with several oxidation states or

structures (e.g., transition metal oxides and conduct- The electrochemical performance is analyzed for

ing polymers) is expected to be higher than that of supercapacitor electrodes in a two-electrode system

double-layer capacitors. Conducting polymers offer the via cyclic voltammetry (CV) and electrochemical

advantages ease of synthesis and low cost. In this paper, impedance spectroscopy (EIS) using a Potentio-

PANI is prepared chemically for use as a pseudocapacitor stat/Galvanostat/ZRE Gamry G750 instrument. The

electrode [6]. galvanostatic charge-discharge is performed using a

Gamry Reference 3000 instrument. The cyclic voltam-

metry (CV) response of the electrodes is measured at

2. Experimental work

different scan rates varying from 1 mV/s to 300 mV/s,

and the electrolyte is 4 M potassium hydroxide.

2.1. Materials

Impedance spectroscopy measurements are performed

at a dc bias of 0.1 mA, with a sinusoidal signal of 1 mA

Aniline (C6H5NH2, 99%) was purchased from CDH.

over a frequency range of 1 MHz to 0.05 Hz.

Ammonium persulphate, [(NH4)2S2O8, 98.5%] was

purchased from WINLAB. Hydrochloric acid (HCl,

2.5. Characterization

37%) and camphor sulphonic acid were purchased from

Merck. These materials were used for the preparation

The UV-Visible Thermo (Evolution 600) spectropho-

of polyaniline. Potassium hydroxide (KOH) and sodium

tometer that covers the range of 190 to 900 nm is

hydroxide (NaOH) were obtained from local agents.

used to characterize the optical properties of PANI.

A Fourier Transform Infrared PerkinElmer (Spectrum

2.2. Polyaniline preparation

BX) Spectrophotometer is used to cover the spectral

−1

range from 400 to 4000 cm . An XRD machine (X-Ray

Aniline (0.2 M) is added to 0.2 M HCl and then kept

7000 Shimadzu-Japan) equipped with a Cu-K␣ radiation

for 1 h at room temperature. Ammonium persulphate λ

source ( = 0.15418 nm) operating at 30 kV and 30 mA

(APS) in 20 mL of distilled water is then slowly added ◦ −1

is operated at a scanning rate of 4 min over 2θ values

to the suspension under stirring. The molar ratio of ani- ◦ ◦

between 5 and 90 to characterize the structural proper-

line, hydrochloric acid and APS is 1:1:1. The reaction is

ties. Scanning electron microscopy (SEM) is performed

conducted by the in situ polymerization method in an ice

using a JEOL JSM 6360LA instrument operated at an

bath for 1 h and then left at rest to polymerize for 24 h at

acceleration voltage of 20 kV. A Raman Microscope Sen-

room temperature. The prepared mixture is ﬁltered and

terra Bruker, Germany, at a wavelength 532 nm is used

then rinsed with distilled water. PANI is simultaneously

◦ to characterize the chemical bonding structure.

dedoped by 25 mL of 8 M sodium hydroxide at 90 C

for 5 h. The emeraldine salt is dried in air and then at

◦ 3. Results and discussion

60 C for 24 h. PANI is doped with camphor sulphonic

acid (CSA) and then dissolved in chloroform [7–10].

Fig. 1 shows the UV–vis spectrum of PANI doped

with CSA in chloroform. Two electronic transitions are

2.3. Preparation of ﬂexible PANI electrode observed at 357 nm and 787 nm. The characteristic band

at 357 nm can be attributed to the ␲–␲ transition on

A ﬂexible plastic sheet is coated with gold using a the polymer chain. The characteristic band at 787 nm is

thermal vacuum evaporator. Camphor sulphonic acid attributed to a polaron due to CSA doping and corre-

doped PANI dissolved in chloroform is sprayed on sponds to localization of electrons [14,16].

the active area (1 cm 1 cm) of the gold-coated plas- Fig. 2 shows the FTIR spectrum of a chemically syn-

tic sheet using an air compressor and a spray gun. The thesized polyaniline in its undoped state. PANI shows

◦

samples are left in an oven at 70 C to dry for 12 h vibration bands at 1588, 1495, 1322, 1164, 848 and

−1 −1

prior to performing the electrochemical measurement. 622 cm . The 1588 cm vibration band is due to the

Electrochemical measurements are performed using two C C double bond of the quinoid rings, whereas the

−1

electrodes measurements in an electrochemical cell. 1495 cm vibration band arises due to the vibration

S.A. Ebrahim et al. / Journal of Taibah University for Science 10 (2016) 281–285 283

Fig. 3. XRD pattern of undoped polyaniline.

Fig. 1. UV–vis absorption spectrum of PANI doped with Camphor

sulfonic acid dissolved in chloroform.

Fig. 4. Raman spectrum of undoped polyaniline.

Fig. 5 shows the SEM images of the PANI doped with

CSA sprayed onto a substrate of gold-coated ﬂexible

plastic substrate at different magniﬁcations. The SEM

images of CSA doped polyaniline consist of smooth ﬁbre

Fig. 2. FTIR spectra of undoped PANI. shapes. From the images, the low magniﬁcation (1500 )

image conﬁrms the interconnected ﬁbrous network of

of the C C double bond associated with the benzenoid the polyaniline electrode. These ﬁbres are relatively

−1

ring. The origin of the 1322 cm is related to various smooth and are randomly distributed on the substrate

stretching and bending vibrations associated with a C N with many pores with a diameter and length ranging

−1

single bond. The vibration band at 1164 cm is due to from 1 to 10 ␮m, as observed from the high magniﬁ-

the presence of C N double bonds. The vibration band at cation (10,000×) image. It can be inferred that the ﬁbre

−1

848 cm is attributed to C H vibration [10,14,16–20]. network of polyaniline is porous and has a large surface

Fig. 3 shows the XRD pattern of undoped polyaniline. area.

For the PANi pattern, three characteristic peaks appear Fig. 6 shows cyclic voltammetry (using two probes

◦ ◦ ◦

at 10 , 23 and 32 corresponding to (011), (020) and connection) of polyaniline electrodes deposited onto a

(200) amine salt crystals, respectively. The amorphous gold coated ﬂexible current collector at a scan rate of

nature of the sample is conﬁrmed by the XRD spectrum, 5–300 mV/s with a scanning potential window of (−0.8

◦

which shows a broad band at 23 and low intensity peaks to 0.8 V). The CV curve area is gradually enlarged with

related to poorly crystallized PANI [21,22]. the increase of the voltage scan rate. This result indicates

Fig. 4 shows the Raman spectrum of PANI. The spec- pseudo capacitive behaviour. The oxidation and reduc-

trum of neat PANI shows bands at 1160, 1217, 1485 tion peaks appeared at 0.6 V and −0.2 V. The calculated

−1

and 1588 cm corresponding to the C H bending of speciﬁc capacitance is 594.92 F/g at scan rate of 5 mV/s,

+•

the quinoid ring, C N stretching of the bipolaron and the weight of active material is 8 mg. The calcu-

structure, N H bending of the bipolaronic structure lated speciﬁc capacitance provides an increased energy

and C C stretching of the benzenoid ring, respectively density of 82.63 W h/kg at potential difference of 1 V [10,16–21]. [10–12].

284 S.A. Ebrahim et al. / Journal of Taibah University for Science 10 (2016) 281–285

Fig. 5. SEM images of PANI doped with CSA ﬁlm at different magniﬁcations: (a) 1500 and (b) 10,000.

Fig. 6. Cyclic voltammetry of a supercapacitor based on PANI (PE-

Gold substrate) electrodes.

Fig. 7. Nyquist plot of supercapacitor with PANI electrodes.

Fig. 7 shows the Nyquist plot, which is a plot of the

determines the rate of the charge and discharge and,

imaginary component (Z ) of the impedance against the

consequently, the power capability of the supercapaci-

real component (Z ), and the frequency response of the

◦

tor. The slope of the 45 portion of the curve is called

PANI electrode/electrolyte system. The pseudocapacitor

the

Nyquist plot shows a straight line in the low-frequency Warburg resistance and is a result of the frequency

dependence of ion diffusion/transport in the electrolyte region and a semicircle in the high-frequency region.

[10–13,23].

The semicircle corresponds to charge transfer resistance

Rp. The value of charge transfer resistance is found to be Fig. 8 shows the galvanostatic charge/discharge

120.2 . The intersection of the curve at the X-axis rep- curves of PANI at constant currents of 0.1 mA and

resents the internal or equivalent series resistance (ESR). mA. The curve for 10 mA is highly linear and almost

typically

ESR is the sum of the electrolyte resistance, the intrin- triangular. In addition, the discharge curve is

nearly

sic resistance of the active electrode material, and the symmetric with its corresponding charge counter-

parts, indicating that the electrode has good capacitive

contact resistance at the interface between active mate-

characteristics.

rial and the current collector. The value of equivalent The curve for 0.1 mA charging occurs in

nearly series resistance is found to be 3.7 . This resistance 21.7 s and discharges in 3.6 s.

S.A. Ebrahim et al. / Journal of Taibah University for Science 10 (2016) 281–285 285

[9] J. Stejskal, Polyaniline preparation of a conducting polymer, Pure

Appl. Chem. 74 (2002) 857–867.

[10] H. Wang, Q. Hao, X. Yang, L. Lu, X. Wang, A nanostruc-

tured graphene/polyaniline hybrid material for supercapacitors,

Nanoscale 2 (2010) 2164–2170.

[11] H. Gómez, M.K. Ram, F. Alvi, P. Villalba, E. Stefanakos, A.

Kumar, Graphene-conducting polymer nanocomposite as novel

electrode for supercapacitors, J. Power Sources 196 (2011)

4102–4108.

[12] B.C. Kim, J.S. Kwon, J.M. Ko, J.H. Park, C.O. Too, G.G. Wal-

lace, Preparation and enhanced stability of ﬂexible supercapacitor

Fig. 8. Charge and discharge curves at a constant current of 0.1 mA

prepared from Naﬁon/polyaniline nanoﬁber, Synth. Metals 160 and 10 mA.

(2010) 94–98.

[13] Y. Zhang, H. Feng, X. Wu, L. Wang, A. Zhang, H. Dong, T. Xia,

4. Conclusions

X. Li, L. Zhang, Progress of electrochemical capacitor electrode

materials, Int. J. Hydrogen Energy 4 (2009) 4889–4899.

A pseudocapacitor is fabricated using polyaniline that [14] D.S. Dhawale, D.P. Dubal, V.S. Jamadade, R.R. Salunkhe,

is sprayed onto a gold-coated plastic sheet as a ﬂex- C.D. Lokhande, Fuzzy nanoﬁbrous network of polyaniline elec-

trode for supercapacitor application, Synth. Metals 160 (2010)

ible electrode. By using the spraying method, PANI

519–522.

is adhered and uniformly distributed along the surface

[15] K.S. Ryu, K.M. Kim, Y.J. Park, N.G. Park, M.G. Kang, S.H.

of the current collector. The electrochemical proper-

Chang, Redox supercapacitor using polyaniline doped with Li

ties of PANI reveal a superior capacitive performance. salt as electrode, Solid State Ionics 152 (2002) 861–866.

The fabricated pseudocapacitor provides an increased [16] Z. Luo, L. Zhua, Y. Huang, H. Tang, Effects of graphene reduction

degree on capacitive performances of graphene/PANI composites,

speciﬁc capacitance of 594.92 F/g and an increased

Synth. Metals 175 (2013) 88–96.

energy density of 82.63 W h/kg. The power density of

[17] B. Rajagopalan, S.H. Hur, J.S. Chung, Surfactant-treated

the pseudocapacitor is 82.63 kW/kg at a discharge time

graphene covered polyaniline nanowires for supercapacitor elec-

of 3.6 s. trode, Nanoscale Res. Lett. 10 (2015) 183–192.

[18] W. Wu, D. Pan, Y. Li, G. Zhao, L. Jing, S. Chen, Facile fabrication

References of polyaniline nanotubes using the self-assembly behavior based

on the hydrogen bonding: a mechanistic study and application

in high-performance electrochemical supercapacitor electrode,

[1] C. Arbizzani, M. Mastragostino, Polymer based redox supercap-

Electrochim. Acta 152 (2015) 126–134.

acitors, Electrochim. Acta 41 (1996) 21–26.

[19] L. Zu, X. Cui, Y. Jiang, Z. Hu, H. Lian, Y. Liu, Y. Jin, Y. Li, X.

[2] A. Laforguea, P. Simona, J.F. Fauvarquea, J.F. Sarraub, P. Laille,

Wang, Preparation and electrochemical characterization of meso-

Hybrid supercapacitors based on activated carbons and conduct-

porous polyaniline-silica nanocomposites as an electrode material

ing polymers, J. Electrochem. Soc. 148 (2001) 1130–1134.

for pseudocapacitors, Materials 8 (2015) 1369–1383.

[3] M. Mastragostino, C. Arbizzani, F. Soavi, Polymer based super-

[20] Z. Gao, F. Wang, J. Chang, D. Wu, X. Wang, F. Xu, S. Gao,

capacitors, J. Power Sources 97 (2001) 812–815.

K. Jiang, Chemically grafted graphene-polyaniline composite

[4] C. Arbizzani, M. Mastragostino, F. Soavi, New trends in electro-

for application in supercapacitor, Electrochim. Acta 133 (2014)

chemical supercapacitors, J. Power Sources 100 (2001) 164–170.

325–334.

[5] F. Béguin, E. Frackowiak, Supercapacitors Materials Systems and

[21] F.P. Du, J.J. Wang, C.Y. Tang, C.P. Tsui, X.L. Xie, K.F. Yung,

Applications, ﬁrst ed., Wiley-VCH, Germany, 2013, pp. 207–

Enhanced electrochemical capacitance of polyaniline/graphene

233.

hybrid nanosheets with graphene as templates, Composites 53

[6] B.E. Conway, Transition from supercapacitor to battery behav-

(2013) 376–381.

ior in electrochemical energy storage, J. Electrochem. Soc. 138

[22] G.Y. Zhao, H.L. Li, Preparation of polyaniline nanowire arrayed

(1991) 1539–1548.

electrodes for electrochemical supercapacitors, Microporous

[7] C. Bian, A. Yu, Dedoped polyaniline nanoﬁbres with micropores

Mesoporous Mater. 110 (2008) 590–594.

for high rate aqueous electrochemical capacitor, Synth. Metals

[23] R. Bolagam, R. Boddula, P. Srinivasan, Synthesis of highly

160 (2010) 1579–1583.

crystalline polyaniline with the use of (Cyclohexylamino)-1-

[8] G.A. Snooka, P. Kao, A.S. Best, Conducting polymer based super-

propanesulfonic acid for supercapacitor, J. Appl. Electrochem.

capacitor devices and electrodes, J. Power Sources 196 (2011)

45 (2015) 51–56. 1–12.