electrochemical composite formation of thiophene and n-methylpyrrole

Progress in Organic Coatings 59 (2007) 2836

Electrochemical composite formation of thiopoly : Mby ic

k Pace anof Liber 2

Abstract

Electroch d N-7m) was ve thfibers. Carb ylpyrelectrocoate ctronreflectance s tioninvestigated by elpolythiophe than 2007 Else

Keywords: Carbon fiber microelectrodes; Electrochemical composites; Polythiophene; Poly-N-methylpyrrole; Electropolymerization

1. Introduction

Electricmuch attenConductingmaterials ibe controllstructure [1trolled by tsubstrate o

Carbonmaterials, arials such acarbon fibecement. Cations wherfatigue chaapplicationhigh damp

CorresponE-mail ad

cal conductivity, thermal conductivity, and low linear coefficient

0300-9440/$doi:10.1016/jally conducting polymers and their composites attracttion because of their high charge storage ability.polymers possess several advantages as electrode

n batteries. First, the electrochemical properties caned at the molecular level by manipulating monomer] or by doping [2]. Second, surface area can be con-he conditions used for polymerization and/or by thento which the polymer is coated.fibers (CF), which are a new breed of high-strengthre mainly used as reinforcements in composite mate-s CF-reinforced plastics, carboncarbon composites,r reinforced materials, and carbon fiber reinforcedrbon fiber composites are ideally suited to applica-

e strength, stiffness, lower weight, and outstandingracteristics are critical requirements. They also finds where high temperature, chemical inertness, anding are important in addition to having good electri-

ding author. Tel.: +90 212 285 31 53; fax: +90 212 285 63 86.dress: [email protected] (A.S. Sarac).

of thermal expansion [3].There has been much interest in supercapacitors because of

their practical applications as energy storage devices for memorybackup of computers and for electric vehicles [46].

Polypyrrole is one of the most extensively studied conductingpolymers due to the ease of synthesis, good redox properties,stability in the oxidized form, ability to give high electricalconductivity and useful electrical and optical properties [710].Poly-N-methylpyrrole (PNMPy) has attracted attention as a pos-sible alternative to polypyrrole for technological applications inspite of its lower conductivity [11].

Polythiophenes (PTh) have shown considerable promise formaterials applications due to exceptional electrical propertiesand their environmental stability [1114]. On the other hand, thehigh oxidation potential of thiophene compared to the polymercauses some degradation of the polymeric film, which has beenthe subject of a wide variety of studies.

Polythiophene and polypyrrole (PPy) have good electri-cal properties, however, PNMPy exhibits poor environmentalstability, also PTh suffers from brittleness, low elongation,and poor processibility. In order to solve these problems,methods of preparing composites and copolymers, reforming

see front matter 2007 Elsevier B.V. All rights reserved..porgcoat.2007.01.008mers on carbon fiber microelectrodessurface spectroscopy, and electrochem

A. Sezai Sarac a,, Hulya Geyik a, Elif Altura Department of Chemistry, Istanbul Technical University, Polymer Scien

b Materials and Surface Science Institute, UniversityReceived 7 June 2006; received in revised form 31 Decem

emical composite thin film formation (0.60.7m) of thiophene ancarried out by cyclic voltammetry in order to understand and impro

on fiber microelectrodes were coated with polythiophene and N-methd carbon fiber surface mophology was characterized by scanning elepectroscopy for their composition. The effect of monomer concentra

. The impedance behaviour of composite electrodes was characterizedne and poly-N-methylpyrrole exhibits better charge storage propertiesvier B.V. All rights reserved.phene and N-methylpyrroleorphology, characterization

al impedance spectroscopyrlak a, Marina Serantoni b

d Technology, Maslak 34469, Istanbul, Turkeymerick, Limerick, Ireland006; accepted 9 January 2007

methylpyrrole on carbon fiber microelectrodes (diametere surface properties and capacitance behaviour of carbonrole was electrografted onto the thiophene electrode. Themicroscopy and atomic force microscopy and by FTIR-

and scan number on electropolymerization has also beenectrochemical impedance spectroscopy. The composite ofpolythiophene coated carbon fiber microelectrodes.

A.S. Sarac et al. / Progress in Organic Coatings 59 (2007) 2836 29

the monomers of these conducting polymers and blendingwith some commercially available polymer that offers bet-ter mechan[15].

In the pized on caCFME/PThof the meastrograftedto the flexpolymers otheir biocotrograftingflexibility agroup thatAs polythimaterial aouter side(PNMPy coties). Durinwith PNMber, and eleThe compowith cyclicMorphologThe capaciCFMEs watroscopy (E

2. Experim

2.1. Mater

AcetoniHaen Chefrom Riedemethylpyrrpurity of 9320,000 (Cing 320,00electrodes.(diameter =The electrodipping lentape.

2.2. Instru

Polymetonitrile (Aelectrodessition cyclewere measu

2263 potenbines potenpotentiostaA three-ele

electrode, platinum wire as the counter electrode, and Ag/AgClas the reference electrode (in 3.5 M KCl solution) was used.

lms of homopolymers, composites, and copolymers elec-ted onto carbon fiber surfaces were analyzed by FTIRance spectrophotometry (Perkin Elmer, Spectrum One,

Universal ATR attachment with a diamond and ZnSeC70951), SEM (Jed Cheeh from Uness), and AFMO-TopoMetrix Explorer). EIS measurements were alsoed with Parstat 2263 using the supplied Power Sine

re package.

ctropolymerization procedure

ormation of electrochemical composite electrodes

Electrochemical polymerization of thiophene onber base electrodesele

lectrtem

er w

oces50 mn 0

Elec/PTher poerfolectrions.he pntat

emecenele

n th

syngrafe 2.ME

1. ScE.ical and/or chemical properties have been reported

resent study, thiophene (Th) was electropolymer-rbon fiber microelectrode (CFME) and yielding a

electrode. This electrode composed the main parturements as a base electrode. NMPy was then elec-

onto the CFME/PTh under various conditions. Dueibility of the CFME structure, the study of thesen substrates will ease the processing and improvempatibility. Since PTh has a rigid structure, elec-NMPy onto a CFME/PTh electrode will also givend uniformity to the structure because of the methylis bonded to the aromatic ring at the nitrogen.

ophene has a high oxidation potential as a basemicron-sized electrode with PNMPy coating on theof electrode was desired to improve its properties.ating itself has poor physical and mechanical proper-g the electrochemical composite electrode formationPy, the effect of NMPy concentration, scan num-ctrolyte on electropolymerization were investigated.site electrodes surface properties were characterized

voltammetry (CV) and FTIRATR spectroscopy.ical studies were performed with SEM and AFM.tance behavior of these conductive polymer-modifieds investigated with electrochemical impedance spec-IS).

ental

ials

trile (ACN) was used as-received from Riedel-demical without further purification. Pure NaClO4l-de Haen Chemicals was used. Thiophene and N-ole from Lancester and Aldrich Chemicals with a9% were used. High strength (HS) carbon fibersA) (Sigri Carbon, Meitingen, Germany) contain-

0 single filaments in a row were used as workingAll of the electrodes were prepared by using CF7m) attached to a copper wire with Teflon tape.de area is kept constant (3.3 cm2) by adjusting thegth and covering the rest of the fibers with the Teflon

mentation

rizations were performed electrochemically in ace-CN) solution containing 0.2 M NaClO4 for variouswith different monomer concentrations and depo-numbers. Cyclic voltammograms of the polymersred on a Princeton Applied Research (PAR) Parstattiostat, which is a self-contained unit that com-tiostatic circuitry with phase-sensitive detection. Thet connected to a Faraday cage, BAS Cell Stand C3.ctrode system comprised of a CFME as the working

Thin fitrocoareflectwith acrystal(VEECperformsoftwa

3. Ele

3.1. F

3.1.1.carbon

Thethree-eat roommonom

tion prrate ofbetwee

3.1.2.CFME

Aftbeen pbase econditPTh, trepresein Sch

Confor theadditioto 8).

TheelectroSchemon CF

Schemeon CFMctrochemical polymerizations were carried out in aode system employing CFME as a working electrodeperature. The concentration of 0.5 M standard Thas chosen during this study. The electropolymeriza-

s was performed in 0.2 M NaClO4 in ACN at a scanV/s for four cycles by CV. The sweep range was

and 1.7 V.

trochemical composite formation of NMPy onbase electrodes

lymerization of PTh the NMPy electrodeposition hasrmed to obtain a thin composite coating. The sameode was used for all of the NMPy electrograftingSince PNMPy has a lower oxidation potential then

otential was in the range of 01.1 V. The schematicion of electrochemical composite formation is shown1.trations of NMPy between 0.008 and 0.5 M were usedctrografting on the CFME/PTh base electrode. Ine effect of cycle number was investigated (from 2

thesis route and possible mechanism of PNMPyting on a CFME/PTh base electrode is shown inFirst, electrooxidation of the thiophene monomer

results in radical cation formation by electron trans-

hematic representation of electrochemical composite preparation

30 A.S. Sarac et al. / Progress in Organic Coatings 59 (2007) 2836

fer from mradical catoligomer fprecoated Cnism.

4. Results

4.1. Cyclicelectropoly

SolutionCFME to pScheme 2. Mechanism of electrochemical composite formation of N-meth

onomer to the electrode. Dimer formation throughion coupling, deprotonation, and neutral dimer andormations follow. NMPy electrografting on the PTh

FME proceeds through the same coupling mecha-

and discussion

voltammetric investigations:merization of Th on CFME

of 0.5 M thiophene was electropolymerized onrepare a homopolymer-coated base electrode which

was used tcycle numbcoatings.

Electrogcan be seeand cathodvalues meataken fromelectrogrowpotentials o0.48 V, respCurrent dewere 0.58yl pyrrole on CFME/PTh base electrode.

o analyze the effect of NMPys concentration anders during electrochemical formation of composite

rowth of thiophene onto CFME have broad peaks asn in Fig. 1. During oxidation and reduction, anodicic peak potentials were determined by taking averagesured from five points on scans. The values werethe fourth oxidation and reduction cycles of theth process. Anodic and cathodic electrogrowth peakf Th homopolymer were determined to be 0.52 andectively. Oxidation potential was found to be 1.43 V.

nsities corresponding to anodic and cathodic peaksand 0.54 mA/cm2, respectively. The current density


Fig. 1. Electrfour cycles onin monomer-f

ratio of anobe 0.93 (Ta

To comthiophenewith 50 mVCFME on(Table 1). Tbutton platwhich is adpolymer elethan a hom

4.2. ElectrN-methylpyelectrochem

4.2.1. EffeSome o

tropolymercan be seen3.3 cm2 fvarying mocycling betfour cycles

For elecpotentials,fourth cycl

Table 1Redox paramCV

[Th]0.1 M on CFM0.5 M on CFM0.5 M on Pt

Mult] = 0.0

idatfor

An ise of

irrefirstPy

ed foasted noic deer, r

08 M. 3 prcon

scan

.08 Mactivtionogrowth of thiophene in 0.2 M NaClO4 in ACN with 50 mV/s forCFME. Inset: scan rate dependence of 0.5 M Th-coated CFME

ree electrolyte between 50 and 300 mV/s.

dic and cathodic peak potentials was calculated toble 1).pare CFMEs and button platinum electrodes, 0.5 Mwas electropolymerized in 0.2 M NaClO4 in ACN

/s for four cycles. Platinum button electrode andset potentials were 1.55 and 1.43 V, respectively

hese results indicate that using CFMEs rather thaninum electrodes decreases the oxidation potentialvantageous for better and easier electron transfer. Thectrodeposited on CFME has a higher current densityopolymer electrografted onto Pt button electrodes.

ochemical composite formation ofrrole on CFME/PTh base electrode andical characterization

ct of NMPy concentration

Fig. 2.([NMPy

The ox0.73 Vtions.decrea

Theon theent NMobservto be fshowea drastHowevfor 0.0

Fig0.08 Mferentwith 0electroseparaf the cyclic voltammograms obtained from elec-ization of 0.08 M on CFME/PTh base electrodes

in Fig. 2. The films were grown on CFMEs (areaor approximately 1000 single fibers) in solutions ofnomer concentrations from 0.008 to 0.5 M of NMPyween 0 and 1.1 V (Ag/AgCl scan rate 50 mV s1) for.trogrowth processes the current densities, anodicand cathodic potentials were measured from the

es and redox parameters are summarized in Table 2.

eters of electrogrowth of Th on CFME and on Pt obtained from

Ec (V) Ea (V) Eonset (V) Ia/IcE 0.60 0.58 1.45 0.53E 0.52 0.48 1.43 0.93

1.1 0.80 1.55 0.88

with scan rThe inve

tropolymercompositesthe 0.08 Mare presentobtained fo

Table 2The effect oelectrogrowth

ConcentrationM (NMPy)0.0080.0200.0400.0800.500

a These datisweep experiment for the electropolymerization of NMPy8 M) on CFME/PTh base electrode in 0.2 M NaClO4 in ACN.

ion potentials of the monomers were 0.86, 0.76, andthe fourth cycle with increasing NMPy concentra-ncrease in the concentration of NMPy resulted in athe onset potential of the composite electrodes.

versible oxidation of the monomer appears clearlycycle followed by a nucleation loop for five differ-

concentrations. A regular and reversible growth wasr all composites. Polymer deposition rates appeared

r with increasing NMPy concentration. The resultssignificant differences inEa, but theEc values showedcrease with increasing the monomer concentration.

eversibility of electrogrowth of composites was betterNMPy concentration exhibiting a Ia/Ic value of 0.98.

esents the redox behaviour of composite films with acentration of NMPy in monomer-free solutions at dif-rates. The current intensity of the composite obtained

NMPy increases with the scan rate suggesting thee film coats the CFME/Th base electrode. However,

of anodic and cathodic peak potential (E) increasesate which is due to a decrease in reversibility.stigation of NMPy concentration effect during elec-

ization indicates that the current intensity of allis higher than PTh itself and between compositesconcentration of NMPy is the highest. The results

ed in Fig. 4 which indicate that a linear behaviour isr the composite obtained at 0.08 M NMPy, i.e. the

f NMPy concentration on redox parameters during polymer

, Eaa (V) Eca (V) Eonset E Ia/Ic

0.60 0.30 0.86 0.30 0.960.60 0.21 0.82 0.39 0.950.63 0.19 0.77 0.44 0.890.67 0.28 0.76 0.39 0.980.68 0.17 0.73 0.51 0.88

a were taken from fifth cycles.


Fig. 3. Cyclic voltammogram of 0.08 M PNMPy coated on CFME/Th baseelectrode in monomer-free solution of 0.2 M NaClO4 in ACN at a scan rateof: (a) 50 mV/s; (b) 100 mV/s; (c) 150 mV/s; (d) 200 mV/s; (e) 250 mV/s; (f)300 mV/s.

electron transfer rate is faster and also the composite showedthin layer behavior. The regression coefficient of the compos-ite is higher for 0.008 M NMPy (R: 0.997) compared to otherconcentrati

4.3. FTIR

4.3.1. EffeThe elec

respective astructure wand practiccopolymermicron lev

Fig. 4. Comparison of composite current values under different scan rates inmonomer-free electrolyte.

Fig. 5 shows the spectra between 700 and 4000 cm1 ofCFME/PTh homopolymer and CFME/PTh/PNMPy compos-ite electrodes with an increase in NMPy concentration. The

/PTh 1tic

1200n).of pcreaing0 cming ocon

posce o

Fig. 5. ATRconcentrationons.

characterization

ct of NMPy concentrationtrografted composite structure and doping with thenion of the supporting electrolyte into the compositeas studied by FTIRATR. This technique is preciseal and is a good tool for structural characterization ofs having thicknesses ranging from the nanometer toel.

CFME(aroma1332positiopeakswas instretchat 142stretchNMPythe compresenFTIR analysis for the effect of NMPy concentration on composite formation. Thiovaries as: (a) [NMPy] = 0.008 M; (b) thiophene homopolymer; (c) [NMPy] = 0.08 Melectrode shows significant bands at 1418 cmstretching of C C bond) and a broad peak atcm1 (deformation in plane of CH bond at

These are known to be characteristic vibrationalolythiophene [16]. When the NMPy concentrationsed, characteristic peaks of PPy asymmetric ringmode at 1515 cm1 [17] and the symmetric mode1 appear. A peak at about 1300 cm1 shows NCf NMPy as well. The peak intensities increased withcentration confirming the inclusion of NMPy intoite structure. Since ClO4 absorbs at 1075 cm1 the

f a strong absorption band at this wave number in allphene concentration was held constant at 0.5 M Th and NMPy; (d) [NMPy] = 0.5 M.


Fig. 6. IR ana t four cycles and the cycle number was changed for 0.5 M Th/0.08 MNMPy compo

compositewith this an

4.3.2. EffeFTIRA

ferent cyclof NMPy wof NMPy,characterisLarraz et awith characbe seen ne1433 cm1of NMPy wtwo cycles.

4.4. Morph

4.4.1. ConThe mor

tigated comfor sample50 mV/s anmonomer c

tion and costructure. FCFME/PThhave an effhomogenouthe inclusioposites forwas aboutcentrationThe structucentrationslysis of the cycle number effect. Thiophene cycle number was held constant asite to: (a) eight cycles; (b) four cycles; (c) two cycles.

electrodes indicates that these composites are dopedion.

ct of NMPys cycle numberTR spectra of electrochemical composites with dif-e numbers are shown in Fig. 6. Characteristic peaks

ere between 1200 and 1600 cm1. For two cyclesindistinct peaks can be seen. The intensity of thetic peaks increased linearly with the cycle numbers.l. [18] attributed the bands at 1460 cm1 to NMPyteristic peaks of CN, C C, and C CN, which canar to 1416 cm1 for four cycles of NMPy and atfor eight cycles. No significant characteristic peaksere observed for the electrografting of NMPy forological investigation

centration effect of NMPy (by SEM)phology of PNMPy coated base electrodes was inves-paratively by scanning electron microscopy (SEM)

s obtained potentiodynamically with a scan rate ofd compared with samples obtained for changes ofoncentration, cycle number, and of composite forma-polymer formation in order to understand the surfaceig. 7 shows electrochemically deposited samples onbase electrodes. NMPy concentration was found to

ect on the film morphology. PTh has very smooth ands structure, however, small grains were formed withn of NMPy. The increase in radius of polymer com-0.04 and 0.08 M NMPy composites (on CFME/PTh)0.6 and 0.7m, respectively. As the monomer con-of NMPy increases, the grains get bigger (Fig. 7b).re of NMPy is more cauliflower-like for higher con-.

Fig. 7. (a) SEM image of 0.04 M NMPy coated on CFME/PTh (radius thick-ness increase: 0.6m); (b) SEM image of 0.08 M NMPy coated on CFME/PTh(radius thickness increase: 0.7m).


Fig. 8. (a) SEwith two cyclewith eight cyc

4.4.2. CycFig. 8 sh

During thewas used othe NMPysteps. As eincreases th

4.4.3. MorFig. 9

ing monom20 mV/s. Tis very sim[20] wherefrom V-sha45 nm

As showtration of NThis indica


Fig. 10. Nyquist plots of 0.02, 0.04 and 0.08 M NMPy coated on CFME/PThbase electrode and 0.5 M Th homopolymer on CFME in 0.2 M NaClO4 in ACNat 50 mV/s.

4.5. Electrochemical impedance spectroscopy (EIS)

Electrocto monitorelectrodes.capacitive lbon fiber/pfast chargewith NMPyresults shoture increaangle (seesupercapacsure the chNMPy onpresents theing monomof electrod

Fig. 11. BodeCFME/PTh b

Fig. 12. Nyquon CFME/Pth

Bode phase plots of 0.08 M NMPy coated on CFME/PTh base electrodefour, and eight cycles in 0.2 M NaClO4 in ACN at 50 mV/s.

a lower charge storage ability and divergence from thetive line.hemical impedance spectroscopy was performedthe electrochemical behavior of the composite

All composites show a slight deviation from theine (y-axis), indicating fast charge transfer at the car-olymer and polymer/solution interfaces, as well astransport in the polymer bulk. Composite electrodesand CFME/PTh base electrodes were compared and

wed that inclusion of NMPy to the electrode struc-ses the charge storage from 68 to 80 Bode phaseFig. 10), which is very close to 90 as observed initors. Due to that increase a second step to mea-arge storage from increasing the concentration of

CFME/PTh base electrode was performed. Fig. 11results due to NMPys cauliflower structure increas-er concentration, which destroys the homogeneity

e and therefore decreases the electron transfer result-

Fig. 13.for two,

ing incapaciphase plots of 0.008, 0.02, 0.04, 0.08 and 0.5 M NMPy coated onase electrode in 0.2 M NaClO4 in ACN at 50 mV/s.

The effwith three sFigs. 12 anabout a sligposite film.thinner comcapacitor)a phase ang

5. Conclu

The effelectrolytepolythiophcompositesurface chatroscopy, aist plots of 0.08 M NMPy coated with two, four, and eight cyclesbase electrode in 0.2 M NaClO4 in ACN at 50 mV/s.ect of NMPy cycle numbers ranging from 2 to 8teps on CFME/PTh base electrode was investigated.d 13 indicate that the thicker composite film bringsht decrease in the capacitive behaviour of the com-That result supports the Bode plot (Fig. 13) since theposite film presents a phase angle of 80 (near ideal

and the thick film with eight cycles of NMPy showsle of 70 (smaller).

sion

ect of NMPy concentration, scan number, andon electropolymerization of N-methylpyrrole on

ene coated CFME was investigated. The obtainedelectrode surface properties were characterized byracterization techniques, i.e. CV, FTIRATR spec-nd morphological techniques such as SEM and


AFM. The capacitance behaviour of these conductive polymer-modified carbon fiber microelectrodes is investigated with EIS.

Conducting polymer nano-composite coatings on micron-sized carbon fiber electrode materials can be used inmicron-sized battery applications. These studies indicate thatthe electrochemical properties (especially capacitance) can becontrolled at the molecular level by manipulating compositestructure and content, with the thin composite film exhibitingnear ideal capacitor behavior.

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Electrochemical composite formation of thiophene and N-methylpyrrole polymers on carbon fiber microelectrodes: Morphology, characterization by surface spectroscopy, and electrochemical impedance spectroscopyIntroductionExperimentalMaterialsInstrumentation

Electropolymerization procedureFormation of electrochemical composite electrodesElectrochemical polymerization of thiophene on carbon fiber base electrodesElectrochemical composite formation of NMPy on CFME/PTh base electrodes

Results and discussionCyclic voltammetric investigations: electropolymerization of Th on CFMEElectrochemical composite formation of N-methylpyrrole on CFME/PTh base electrode and electrochemical characterizationEffect of NMPy concentration

FTIR characterizationEffect of NMPy concentrationEffect of NMPys cycle number

Morphological investigationConcentration effect of NMPy (by SEM)Cycle number effect of NMPy by SEMMorphological investigation by AFM

Electrochemical impedance spectroscopy (EIS)

ConclusionReferences