Journal of Electroanalytical Chemistry 724 (2014) 21–28

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Journal of Electroanalytical Chemistry

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Polyaniline based electrodes for electrochemical supercapacitor:Synergistic effect of silver, activated carbon and polyaniline

http://dx.doi.org/10.1016/j.jelechem.2014.04.0061572-6657/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author.E-mail addresses: jinhyeok@chonnam.ac.kr (J.H. Kim), patilps_2000@yahoo.com

(P.S. Patil).1 Co-corresponding author.

Dipali S. Patil a, S.A. Pawar a, R.S. Devan b, S.S. Mali d, M.G. Gang c, Y.R. Ma b, C.K. Hong d,J.H. Kim c,1, P.S. Patil a,⇑a Department of Physics, Shivaji University, Kolhapur 416004, Indiab Department of Physics, National Dong Hwa University, Hualien 97401, Taiwanc Department of Materials Science and Engineering, Chonnam National University, Gwangju 500-757, South Koread School of Applied Chemical Engineering, Chonnam National University, Gwangju 500-757, South Korea

a r t i c l e i n f o a b s t r a c t

Article history:Received 4 January 2014Received in revised form 9 April 2014Accepted 11 April 2014Available online 24 April 2014

Keywords:PolyanilineActivated carbonSilverSupercapacitor

The composite thin films of Silver–activated carbon/polyaniline (Ag–AC/PANI) have been deposited onstainless steel substrates by a facile dip coating technique. The formation of Ag–AC/PANI electrode is ana-lyzed by Fourier transform infrared, Fourier transform-Raman and X-ray photoelectron spectroscopytechniques. Field Emission Scanning Electron Microscopy revealed the presence of Ag nanoparticles onthe porous spongy background of PANI. The highest specific capacitance of 567 Fg�1at 5 mV s�1 andenergy density of 86.30 W h kg�1 at 1 mA cm�2 is observed for the Ag–AC/PANI indicating positive syn-ergistic effect of silver, activated carbon and PANI. In which silver nanoparticles help in improving theelectronic conductivity and activated carbon enhances the electrochemical stability of the PANIelectrodes.

� 2014 Elsevier B.V. All rights reserved.

1. Introduction

Supercapacitors, also known as electrochemical capacitors orultracapacitors have attracted much attention because of theirpulse power supply, long cycle life, simple principle and highdynamic of charge propagation [1,2]. According to the charge stor-age mechanism supercapacitors can be divided into two subclass-es: 1. Electrical double layer capacitor (EDLC) in which thecapacitance arises from the charge separation at the electrode–electrolyte interface and 2. Pseudocapacitors in which the pseud-ocapacitance arises from faradaic reaction occurring at the elec-trode–electrolyte interface. They can store much more energythan conventional capacitors and offer higher power density thanbatteries. Batteries are widely used for energy storage in industrialand consumer electronics devices because of their high energydensity but are limited in their power density. When a battery ischarged or discharged, the redox reactions change the molecularor crystalline structure of the electrode materials, which oftenaffects their stability so batteries generally must be replaced afterseveral thousand charge–discharge cycles. Unlike batteries, in

pseudocapacitors ions simply cling to the atomic structure of anelectrode. This faradaic energy storage with only fast redox reac-tions makes charging and discharging much faster than batteries[3]. When high power is required in battery operated devices (i.e.in pulse applications), the combination of the supercapacitor con-nected in parallel to the battery gives the advantages of both,enhancing the performance of the battery and extending its life,exploiting the batteries to its maximum potential. The main threecategories of electrode materials for electrochemical capacitors arecarbon materials such as carbon nanotubes, Activated carbons(AC), transition metal oxides like MnO2, RuO2 and electronicallyconducting polymers (CP) viz., Polyaniline (PANI), polypyrrole [4–10]. Among the above, the conducting polymers offer the advanta-ges of lower cost in comparison with metal oxides and high chargedensity in contrast to carbon materials.

PANI is one of the most promising materials which is frequentlyused as electrode material for supercapacitor due to its propertiessuch as easy synthesis, controllable electric conductivity, chemicalstability and three oxidation states (Leucoemeraldine, Emeraldineand Pernigraniline) which contribute to its high specific capaci-tance [11–15]. The oxidation and reduction processes are accompa-nied by doping (intercalation) and dedoping (deintercalation) ofcounter-anions respectively. Since these processes are reversible,charge storage in PANI is facilitated to yield a pseudocapacitance(C/) behavior. Additionally, separation of charges takes place at

22 D.S. Patil et al. / Journal of Electroanalytical Chemistry 724 (2014) 21–28

the PANI electrolyte interface and this gives rise to the existenceof double layer capacitance (Cdl) Thus, the total capacitance,Ct = Cdl + C/ [10]. However the Ag–AC/PANI nanocomposite filmsinvestigated in this study exhibit porous and spongy morphology.Thus an electrolyte penetrates into the nanocomposites to manifest3-D electrode–electrolyte interface to augment C/. The excellentelectrode required for the supercapacitor consists of good elec-tronic conductivity, electrochemical stability and high surface area.The main drawback of using PANI as supercapacitor electrode ismainly concerned with their low cycle life because during the dop-ing/dedoping process (insertion/deinsertion of counter ions) under-goes swelling and shrinkage leading to mechanical degradation ofthe electrodes [16,17]. To overcome this problem, research hasfocused on synthesizing PANI/carbon based materials (such as AC,Carbon nanotubes, and Graphene) and PANI/ Metal oxides (suchas RuO2, and MnO2) composite electrodes [18–22]. The electronicconductivity of green protonated emeraldine form of PANI is lowerthan that of metals [23]. So, one of the challenging issues in devel-opment of high performance supercapacitor is to improve its elec-tronic conductivity of the PANI electrode which is reversiblycontrolled both by the charge transfer doping and by protonation.Extensive research work has been focused on enhancing electronicconduction of the electrodes by using metal doping [24–27].

We have reported on Mn doped PANI and Ag doped PANI elec-trodes for supercapacitor with specific capacitances of �474 Fg�1

and 512 Fg�1 respectively [28,29]. The enhanced electron transferin the Ag/PANI system is attributed to the charge hopping throughthe metallic conductor Ag nanoparticles that mediate the effectivecharge migration through the PANI. However, there have been alimited number of studies on the effect of metal incorporationbetween carbon materials and CP on the electrochemical proper-ties of carbon materials/CP nanocomposites [30–33] .

Therefore in the present investigation, firstly AC/PANI compositewas prepared by using in situ chemical oxidative polymerization ofthe corresponding aniline monomer and silver nanoparticles incorpo-rated into AC/PANI composite. The structural and morphologicalproperties of PANI, Ag–PANI, AC/PANI and Ag–AC/PANI are investi-gated. The effect of Ag nanoparticles on electrochemical performancesuch as specific capacitance, current density and electrochemicalstability of the AC/PANI composite electrode is discussed.

Fig. 1. FT-IR transmittance spectra of the (a) AC, (b) PANI, (c) Ag–PANI, (d) AC/PANIand (e) Ag–AC/PANI samples recorded in the wavenumber range of 900–1900 cm�1.

2. Experimental details

Ag–AC/PANI films were chemically synthesized by adoptingtwo step processes: initially the AC/PANI composite was preparedby using an in situ polymerization method. Briefly, the anilinemonomer was first mixed with AC in 1 M HCl by ultrasonicationto form a homogeneous suspension. Ammonium persulphate(APS) was dissolved separately in 1.0 M HCl. Then APS was addedto this mixture to obtain the homogeneous composite of AC/PANI.Afterward, optimized quantity (1.2 wt.%) of silver nitrate (AgNO3)was dissolved in the AC/PANI solution. When AgNO3 added intothe solution then protonation takes place and PANI gets oxidizedand metallic silver was produced with nitric acid as a byproduct.To obtain the uniform distribution of Ag ions in the AC/PANIsolution, the mixture was ultrasonicated for 30 min. Uniformdepositions of Ag–AC/PANI films were obtained on stainless steelsubstrates by dip coating technique. The solution was kept underconstant stirring for proper dispersion of Ag in AC/PANI throughoutthe film deposition process. The size of stainless steel samples was2 cm � 1 cm approximately. The thickness of the films was mea-sured by using Ambios XP-1 surface profiler which is about880 nm. The mass of active material (�0.3 mg) was calculated fromweight difference between the weight of substrate beforedeposition and weight of the substrate after deposition. PANI film

was prepared by without addition of AC and AgNO3 whereas Ag–PANI and AC/PANI films were prepared by without addition of ACand AgNO3 respectively.

Infrared (IR) spectroscopy was used to confirm the formation ofPANI in which the powdered material collected from the depositedfilm was characterized by infrared spectrometer (Perkin–Elmer,model 783, USA). Raman studies were conducted using Brukermake FT-Raman spectrometer. The Raman spectra were recordedby a laser radiation at an excitation wavelength of 1064 nm. X-ray photoelectron spectra were recorded by using XPS, VG Multilab2000, Thermo VG Scientific, UK, for phase evaluation. The surfacemorphology of the films was examined by analyzing the Fieldemission scanning electron microscope (FE-SEM), JEOL JSM JSM-6500F equipped with an energy dispersive X-ray spectrometer(EDS). The electrochemical measurements were performed in anelectrolyte of 1.0 M H2SO4 in a conventional three electrodearrangement comprising graphite counter electrode and saturatedcalomel electrode (SCE) serving as the reference electrode, usingscanning potentiostat (model-CHI-400A) CH Instrument, USA.The charge–discharge and electrochemical impedance spectros-copy (EIS) experiment is carried out in the three electrode cell con-sisting of platinum as counter electrode and SCE as reference usingWonatech WMPG 1000-potentiostat- Galvanostat.

3. Results and discussion

All the samples were subjected to the structural, optical, mor-phological and electrochemical characterization.

Fig. 1(a–e) shows the FTIR spectra of the powders collectedfrom AC, PANI, Ag–PANI, AC/PANI and Ag–AC/PANI samples over900–1900 cm�1. The FTIR spectrum for AC is as shown inFig. 1(a) there are four peaks at 1612, 1163, 1120 and 1021 cm�1.The PANI (Fig. 1(b)) spectrum consists of four distinct peaks; at1560, 1492, 1304 and 1131 cm�1. The bands are assigned to theN@Q@N stretching, NABAN stretching (where Q & B denotes thequinoid & Benzenoid), NAH bending and AN@ vibration respec-tively, which are similar to those obtained by Li et al. [34].

The samples Ag–PANI, AC/PANI and Ag–AC/PANI exhibit all thepeaks corresponding to PANI. The intensity of peaks for Ag-PANIand Ag–AC/PANI decreases as compared to PANI sample due tothe presence of Ag nanoparticles in the polymer matrix which isconsistent with the observation of Khanna et al. [35].The peaks

D.S. Patil et al. / Journal of Electroanalytical Chemistry 724 (2014) 21–28 23

corresponding to 1560, 1492, 1304 and 1131 cm�1 for PANIshowed shift toward the higher wavenumber 1586, 1498, 1305and 1140 cm�1 for AC/PANI and Ag–AC/PANI sample respectively.This shift in wavenumber observed due to the presence of acti-vated carbon in PANI. The peak at 1021 cm�1 for activated carbonalso reflects in AC/PANI and Ag–AC/PANI which confirms the for-mation of AC/PANI composite.

To get more insight about the bending and stretching vibra-tions, the films were characterized for their FT-Raman spectra.The Raman spectra were recorded by laser radiation at an excita-tion wavelength of 1064 nm. FT-Raman spectra of all samples(PANI, Ag/PANI, AC/PANI and Ag–AC/PANI) recorded in the wave-number range of 800–1800 cm�1 as shown in Fig. 2. The character-istic bands at 1590, 1505, 1359 and 1175 cm�1 to CAC stretching ofquinoid units, CAC stretching of the benzene ring, CAN+ stretchingand CAN stretching respectively for pure PANI (Fig. 2(a)). Theassignments of peaks reveal that the synthesized product is PANI.Similar bands were also observed for all samples Fig. 2(b–d). Itwas observed that the intensity of all four peaks goes on increasingfrom PANI sample to Ag–AC/PANI sample. This increase in peakintensity indicates an Ag and AC particle plays an electrocatalyticrole in PANI. The highest peak intensity observed for the Ag–AC/PANI sample than the other samples due to combining electrocat-alytic role of AC and Ag in PANI.

XPS N 1s spectra of PANI and Ag–AC/PANI samples are pre-sented in Fig. 3(a and b). Usually, XPS spectra of PANI can be decon-voluted into three distinct curves, related to the quinoid imine, thebenzenoid amine and positively charged nitrogen. Fig. 3 (a and b)shows the major two peaks related to quinoid imine and benzenoidamine are observed at 399.34 (±0.01) eV and 400.53 (±0.53) eV forPANI whereas 399.18 (±0.02) eV and 400.09 (±0.14) eV for Ag–AC/PANI respectively. There is small variation observed for bindingenergies (BE) between PANI and Ag–AC/PANI due to the influenceof AC and Ag in PANI.

The Ag (3d) spectrum of Ag–AC/PANI film is as shown inFig. 3(c), which precisely determines the double peak features ofthe Ag (3d5/2) and Ag (3d3/2). The Ag (3d5/2), and Ag (3d3/2) peaksare located at the binding energies of 366.62 (±0.23) and372.76 eV (±0.01), respectively. These values of BE are slightlylower than the previous reported values of Ag metal in literature,about 368.24 eV for Ag (3d5/2) and 374.25 eV for Ag (3d3/2) [36].Silver is a metal having anomalous properties in BE shifts when

Fig. 2. FT-Raman spectra of the (a) PANI, (b) Ag–PANI, (c) AC/PANI and (d) Ag–AC/PANI samples recorded in the wavenumber range of 800–1800 cm�1.

being oxidized, i.e. the Ag 3d peaks shift to lower BE values. Hence,the shift toward higher BE observed for our sample indicate the sil-ver oxidation after bonding with PANI chain [37].

For comparison, the BEs of all samples summarized in Table 1which predicted the PANI phase form in all samples. The slight dif-ference in BE observed for AC/PANI, Ag–PANI and Ag–AC/PANIcompared with pure PANI due to influence of AC and Ag particles.Ag (3d) spectrum reveals the presence of Ag in Ag–PANI and Ag–AC/PANI sample.

Fig. 4(a–d) shows surface morphologies of PANI, Ag–PANI, AC/PANI and Ag–AC/PANI samples, at �50000 magnifications. PANIand AC/PANI samples revealed spongy morphology. Whereas thepresence of Ag particles on the background of spongy PANI isobserved for Ag–PANI and Ag–AC/PANI samples. The particles arespherical and granular in nature and seem to be nanosized, whichis in agreement with the previous result reported by Afzal et al.[38]. The presence of Ag nanoparticles on spongy PANI providesthe least resistance path to electron. Hence the fast electrons trans-port between the current collectors and the active materialsenhance the current density and hence the specific capacitance [39].

In order to confirm the particle size of Ag sample was character-ized by HRTEM which is as shown in Fig. 5 (image A and B). ThePANI with Ag nanoparticles can be clearly seen. It is apparent thatthe average diameter of Ag nanoparticles varies from 70 to 160 nm.

The selected area electron diffraction (SAED) patterns of Ag–PANI sample as shown in Fig. 5 (image C and D). The appearanceof bright spot in the centre of electron diffraction pattern(Fig. 5(C)) confirms that the corresponding region is amorphousnature which is due to PANI. However in some regions, the electrondiffraction pattern consisted of both the bright spot in the centreand many diffraction spots which revealed both amorphous andcrystalline nature of sample. This crystalline nature of sample isdue to the presence of Ag nanoparticles on the spongy PANI.

Electrochemical impedance spectroscopy (EIS) measurementscan provide useful information about the redox reaction resistanceand equivalent series resistance. In this study, impedance mea-surements were carried out over the frequency range from 0.1 to1 � 105 Hz. Fig. 6(a–d) presents the typical Nyquist plots of PANI,Ag–PANI, AC/PANI and Ag–AC/PANI electrodes in 1 M H2SO4

electrolyte respectively.The Nyquist plot consists of a semicircle in the high frequency

(HF) region and a straight line in the low frequency (LF) region.The HF intercept with the real axis is equal to the solution resis-tance (Rsol) and the diameter of the semicircle is equal to the elec-trode resistance which arises from the charge transfer resistance(Rct) in PANI film.

It is observed that the electrode resistance of PANI (48.29 X)decreases significantly to 14.18 X for AC/PANI electrode due tothe conducting properties of AC. After incorporation of Ag the con-ductivity of the electrode is increased and therefore the diameter(10.98 X) of semicircle for Ag–PANI and Ag–AC/PANI electrodereduced. When AgNO3 added into the PANI suspension then pro-tonation takes place and PANI gets oxidized and metallic silver isproduced with nitric acid as a byproduct. On reaction of metallicsilver with PANI it produces a complex structure. The nitrogenatoms of PANI act as donor atoms during complexation. The elec-tron density on the nitrogen atoms of PANI decreases upon forma-tion of the Ag complex making the nitrogen atoms electrondeficient. This enhances conductivity in the resultant complex ofAg may help to enhance the specific capacitance [29].

The all electrodes exhibit a nearly straight line of a limiting dif-fusion process, which is a characteristic feature of pure capacitivebehavior.

To identify the oxidation and reduction potentials and the effectof AC and Ag on the electrochemical performance of PANI, Cyclicvoltammogram (CV) of all samples have been recorded over �0.2

392 394 396 398 400 402 404 406 408 410

400.53 eV

Inte

nsit

y (A

.U.)

Binding Energy (eV)

399.34 eV

N 1s(a)

392 394 396 398 400 402 404 406 408 410

400.09 eV

Inte

nsit

y (A

.U.)

Binding Energy (eV)

(b)N 1s

399.18 eV

360 362 364 366 368 370 372 374 376 378 380

372.76 eV

366.62 eV

Binding Energy (eV)

Inte

nsit

y (A

.U.)

Ag (3d3/2)

Ag (3d5/2)(c)

Fig. 3. N1s XPS core level spectra of (a) PANI, (b) Ag–AC/PANI and (c) Ag (3d) XPS spectrum of Ag–AC/PANI.

Table 1Summary of binding energies of various PANI based electrodes.

Sample code N1s core level spectrum Ag (3d) spectrum

Quinoid imine BE (eV) Benzenoid amine BE (eV) Ag (3d5/2) BE (eV) Ag (3d3/2) BE (eV)

PANI 399.34 400.53 – –Ag–PANI 399.25 399.94 366.91 372.77AC/PANI 399.26 400.27 – –Ag–AC/PANI 399.18 400.09 366.62 372.76

24 D.S. Patil et al. / Journal of Electroanalytical Chemistry 724 (2014) 21–28

to 0.8 V versus SCE at 5 mV s�1 in 1.0 M H2SO4 (Fig. 7(a–d)).Fig. 7(a) shows a CV for PANI.

The oxidization peak corresponding to the leucoemeraldine toemeraldine salt at about 0.22 V and the reduction peaks corre-sponding to the leucoemeraldine and emeraldine base are foundto be at 0.06 V and 0.64 V respectively were observed in pure PANIsample. The small peaks between 0.3 V and 0.55 V potential areattributed to transformation of PANI charge carriers consisting ofpolaron (radical cation) and bipolaron (dication) forms delocalizedon PANI chains. All these peaks are observed in Ag–PANI, AC/PANIand Ag–AC/PANI. The reaction between the Leucoemeraldine base(LB), emeraldine salt (ES) and emeraldine base (EB) is as follows:

PANIþ nSO2�4 � ðPANI2nþÞðSO2�

4 Þ þ 2e�

ðLB; yellowÞ ðES; greenÞ

ES�EBþ nSO2�4 þ 2nHþ

ðgreenÞ ðblueÞ

Similar reactions were represented by Wang et al. for PANI elec-trode in KCl-doped poly (2-acrylamido-2-methylpropanesulfonic

acid) gel electrolyte [40]. From this it was observed that the redoxreaction takes place at the electrode–electrolyte interface whichleads to the pseudocapacitance behavior.

One additional dominant anodic peak observed at about 0.25 Vversus SCE for Ag–PANI and Ag–AC/PANI. This is recognized due tothe oxidation of silver which further proves the presence of Ag inthe PANI [41,42].

Also, another minute cathodic peak observed near to the leuco-emeraldine reduction peak which is due to the reduction of the Agnanoparticles. Comparable results obtained by Gao et al. wherethey prepared Ag/PANI composite by simple chemical route andstudied its electrochemical behavior in 0.1 M N2 saturated H2SO4

solution [43]. The electrochemical reactions can be rationalizedas follows:

Ag0n�Agþn þ e�

At 0.45 V leading peak observed for Ag–AC/PANI because of thecontribution of high surface area of AC and electronic conductivityof Ag into the PANI provides large reaction sites. The highest cur-rent density was observed for the Ag–AC/PANI.

CV curves of all the electrodes recorded at a different potentialscan rates are as shown in inset of Fig. 7(a–d). As scan rateincreases area under the curve increases and the anodic shift in

Fig. 4. Field Emission Scanning Electron Micrographs of the (a) PANI, (b) Ag–PANI, (c) AC/PANI and (d) Ag–AC/PANI samples at �50,000 magnifications.

Fig. 5. Transmission Electron Microscopy images of Ag–PANI (A and B). Selected electron diffraction pattern of Ag–PANI (C and D) sample.

D.S. Patil et al. / Journal of Electroanalytical Chemistry 724 (2014) 21–28 25

Fig. 6. Nyquist plot for (a) PANI, (b) Ag–PANI, (c) AC/PANI and (d) Ag–AC/PANIsamples in 1 M H2SO4 electrolyte.

26 D.S. Patil et al. / Journal of Electroanalytical Chemistry 724 (2014) 21–28

the oxidation peaks and the cathodic shift in the reduction peaksare observed due to the resistance of electrode. The anodic peakof the couple is better resolved, especially at higher scan rates. Thismay be compared with the linear variation of peak current withthe square root of the scan rate.

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8-0.6

-0.3

0.0

0.3

0.6

0.9

1.2(a)

-0.2 0.0 0.2 0.4 0.6 0.8

-4

-2

0

2

4

6 5 mVSec -1

10 mVSec -1

20 mVSec -1

40 mVSec -1

60 mVSec -1

80 mVSec -1

100 mVSec-1

Cur

rent

den

sity

/ m

Acm

-2

Voltage Vs SCE / Volts

Voltage Vs SCE (Volts)

Cur

rent

den

sity

(mA

cm-2

)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8

-1

0

1

2

3

4 (c)

-0.2 0.0 0.2 0.4 0.6 0.8-12

-8

-4

0

4

8

12

16

Voltage Vs SCE / Volts

5 mVSec-1

10 mVSec-1

20 mVSec-1

40 mVSec-1

60 mVSec-1

80 mVSec-1

100 mVSec-1

Cur

rent

Den

sity

/ m

Acm

-2

Voltage Vs SCE (Volts)

Cur

rent

Den

sity

(mA

cm-2

)

Fig. 7. Cyclic voltammograms of the (a) PANI, (b) Ag–PANI, (c) AC/PANI and (d) Ag–AC/PAfigure is with different scan rate.

The specific capacitance of each film was calculated from CVcurves by using following equation [44]:

Cs ¼R

idV2m� DV � S

where Cs is the specific capacitance,R

idV is the integrated area ofthe CV curve, m is mass of active material, DV is the potentialrange, S is the scan rate.

The specific capacitance about 285, 512, 534 and 567 Fg�1

observed for PANI, Ag–PANI, AC/PANI and Ag–AC/PANI samplesrespectively. The maximum capacitance (567 Fg�1) for Ag–AC/PANI sample is observed because of the contribution of both typesof capacitances viz., electric double layer capacitance of AC andpseudocapacitive behavior of PANI.

The variation of specific capacitance with respect to scan ratesis as shown in Fig. 8. Generally, the specific capacitance decreaseswith the increase of potential scan rate. It is accepted that at a lowscan rate, the presence of inner active sites, which undergo theredox transitions completely, can lead to produce specific capaci-tance to that at high scan rate because of the diffusion effect of pro-ton within the electrode [45]. The small change of the specificcapacitance for Ag–AC/PANI electrodes with respect to scan ratesuggests that the good rate capability of the electrode.

The cyclic stability of PANI, Ag–PANI, AC/PANI and Ag–AC/PANIwere recorded up to the 2000 cycles. The specific capacitance of allthe samples changed along with the number of cycles as shown inFig. 9(a and d). It indicates that the 31% 18%, 14% and 13% loss

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8

-1

0

1

2

3(d)

-0.2 0.0 0.2 0.4 0.6 0.8

-12

-8

-4

0

4

8

12

16 5 mVs-2

10 mVs-2

20 mVs-2

40 mVs-2

60 mVs-2

80 mVs-2

100 mVs-2

Cur

rent

Den

sity

/ m

Acm

-2

Voltage Vs SCE / Volts

Voltage Vs SCE (Volts)

Cur

rent

Den

sity

(m

Acm

-2)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8-1.0

-0.5

0.0

0.5

1.0

1.5(b)

-0.2 0.0 0.2 0.4 0.6 0.8

-9

-6

-3

0

3

6

9

12

Voltage Vs SCE / Volts

Cur

rent

den

sity

/ m

Acm

-2

Voltage Vs SCE (Volts)

Cur

rent

den

sity

(mA

cm-2

)

5 mVSec-1

10 mVSec-1

20 mVSec-1

40 mVSec-1

60 mVSec-1

80 mVSec-1

100 mVSec-1

NI at 5 mV s�1 scan rate within a potential window of �0.2 to 0.8 V versus SCE. Inset

Fig. 8. Variation of specific capacitance with respect to scan rate (a) PANI, (b) Ag–PANI, (c) AC/PANI and (d) Ag–AC/PANI.

Fig. 9. Variation of specific capacitance measured at 30 mV s�1 with respect tocycle numbers (a) PANI, (b) Ag–PANI, (c) AC/PANI and (d) Ag–AC/PANI.

Fig. 10. Galvanostatic charge/discharge characteristics of (a) PANI, (b) Ag–PANI, (c)AC/PANI and (d) Ag–AC/PANI at 1 mA cm�2 current density.

D.S. Patil et al. / Journal of Electroanalytical Chemistry 724 (2014) 21–28 27

observed for PANI, Ag–PANI, AC/PANI and Ag–AC/PANI sampleswith respect to its specific capacitance after 2000 cycles respec-tively. This improvement in stability is observed due to the chem-ical linkage between organic and inorganic material and alsocontribution of AC into the PANI matrix.

Fig. 10(a–d) show the Galvanostatic charge/discharge plots ofall samples at 1 mA cm�2 in the potential range between �0.2and 0.8 V using 1 M H2SO4 as electrolyte. From this it was observedthat the shape of curve for all the samples is triangular in naturewhich leads to the ideal capacitive behavior of the material withalmost symmetric charge/discharge curve. Moreover, the smalldeviation to linearity is typical of a pseudocapacitive contribution,which showed that the capacitance of the electrodes mainly origi-nated from pseudocapacitance.

The specific energy (SE) of films was calculated using the fol-lowing equation:

SE ¼ ItDVm

where I is the applied current density, t is discharge time, DV isthe potential range and m is mass of active material. The specificenergy 32.96, 59.17, 78.49 and 86.30 W h kg�1 observed for PANI,

Ag–PANI, AC/PANI and Ag–AC/PANI respectively at current densityof 1 mA cm�2. These parameters reveal that Ag–AC/PANI samplefeatures good performance as supercapacitor material.

4. Conclusions

In the present work, we demonstrate the electrochemical per-formance of Ag–AC/PANI electrode prepared by simple and costeffective chemical route. For electrochemical supercapacitor spe-cific capacitance, energy density and electrochemical stability arethe important parameters. It is found that the specific capacitance(567 Fg�1), energy density (86.30 W h kg�1) and electrochemicalstability (87% after 2000 cycles) values are better for Ag–AC/PANIelectrodes. This is due to enhancement of electrical and mechanicalproperties by synergistic effect through the interaction of the ACand Ag with the PANI matrix. This improved electrochemical per-formance of Ag–AC/PANI electrode material is of particular interestand may be used to develop high performance supercapacitor.

Acknowledgements

One of the authors DSP wishes to acknowledge the Departmentof Science and Technology (DST) New Delhi (INDIA) for financialsupport through Women Scientist Scheme-A (WOS-A) project.SAP wishes to acknowledge DST for financial support throughDST-PURSE scheme.

PSP wish to acknowledge the CSIR, New Delhi for financialassistance through major research project (Sanction No. 03/(1240)/12/EMR-II). This work is partially supported by the HumanResource Development of the Korea Institute of Energy technologyEvaluation and Planning (KETEP) grant funded by the Korea Gov-ernment Ministry of knowledge Economy (No. 20124010203180).

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