Journal of Electroanalytical Chemistry 717-718 (2014) 110–118

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Journal of Electroanalytical Chemistry

journal homepage: www.elsevier .com/locate / je lechem

Galvanodynamic synthesis of polyaniline: A flexible methodfor the deposition of electroactive materials

1572-6657/$ - see front matter � 2014 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.jelechem.2014.01.018

⇑ Corresponding author. Tel.: +1 (904)297 8050; fax: +1 (904)2975050.E-mail address: eftekhari@nias.us (A. Eftekhari).

Ali Eftekhari a,⇑, Parvaneh Jafarkhani b,c

a National Institute of Arts & Sciences, 411 Walnut Street, Green Cove Springs, FL 32043-3443, United Statesb NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singaporec Department of Materials Science and Engineering, National University of Singapore, Singapore 117576, Singapore

a r t i c l e i n f o

Article history:Received 23 October 2013Received in revised form 12 December 2013Accepted 10 January 2014Available online 22 January 2014

Keywords:ElectrodepositionElectroactive materialsElectropolymerizationConducting polymersPolyaniline

a b s t r a c t

Galvanodynamic synthesis is introduced as a new flexible electrochemical method for the preparation ofelectroactive materials, as utilized for electropolymerization of aniline in the present seminal work. It isindeed a missing method in the four possible electrochemical methods namely potentiodynamic, poten-tiostatic, galvanostatic, and finally galvanodynamic. This explicit comparative study shows the flexibilityof this method in controlling the physical and electrochemical properties of the polyaniline film. Electro-chemical polymerization was performed by scanning the current in a given range. Different approachesfor this purpose were also introduced as the synthesis can be performed under different conditionsthrough linear scanning, cyclic scanning, and repetitive cyclic scanning. Effects of various controllableparameters, such as scan rate, the current range, and the scan direction were also examined. In compar-ison with other electrochemical methods, galvanodynamic synthesis has higher flexibility to alter con-trollable parameters in favor of a specific application. For instance, synthesis of polyaniline to displaycharacteristic redox peaks suitable for battery performance or strong capacitive behavior ideal forsupercapacitors.

� 2014 Elsevier B.V. All rights reserved.

1. Introduction

Since the first report of electropolymerization by Diaz et al. [1],this is one of the dominant approaches for the synthesis ofconductive polymers. Different electrochemical techniques suchas potentiodynamic [2–10], potentiostatic [11–19], and galvano-static [20–29] have been successfully employed for electropoly-merization of monomers. The first one is based on cyclicvoltammetry, which is a common electrochemical technique. Inthis method, electropolymerization is performed by scanning thepotential in a given potential range covering the potential requiredfor the monomer oxidation and the polymer growth. The secondone is performed by applying a constant potential to polymerizethe monomer. The third one is based on applying a constantcurrent. In general, all three methods are based on applying the re-quired current or potential to initiate the electropolymerizationprocess. However, the results are quite different, and it is indeedan important factor for the investigation of conductive polymers(and mechanism of polymerization), and more importantlyprovides unique opportunities for the preparation of desirable con-ductive polymers [30–43].

In these electrochemical methods, the applied current or poten-tial can be constant or under scanning condition. This reminds thatanother method is missed in this variety, as the current can also bescanned. Similar to the case of potentiodynamic polymerization, itis named galvanodynamic polymerization. The latter method couldbe also employed for the electrochemical synthesis of conductivepolymers, but to our knowledge, there is no report utilizing thismethod. This can be attributed to the fact that galvanodynamicmethod, i.e., voltammetry under galvanostatic condition, is not acommon electrochemical technique. However, it is very simpleand can be performed by almost all modern electrochemicalinstruments.

Since the main theme of the present paper is to introduce a newmethod for the synthesis of conductive polymers, the results werereported in a comparative manner to reveal the role of controllablefactors. In a systematic research, voltammetric behavior and mor-phology of each polyaniline film is reported, as they are commonproperties of electroactive materials including conductive poly-mers. On the other hand, this introduces an opportunity for designof co-electrodeposition leading to the formation of polymer-based(nano)composite films, which is indeed an active area of both fun-damental and applied research [44].

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2. Experimental

All electrochemical experiments including galvanodynamicsynthesis were performed using an Autolab PGSTAT30 potentio-stat/galvanostat connected to a computer running its correspond-ing software. The electrochemical polymerization of aniline wascarried out from a typical electrolyte solution of 0.1 M aniline in0.5 M H2SO4. The current scan rate was typically 200 lA cm�2 s�1,unless otherwise noted for the investigation of the influence ofscan rate. The working electrode was a Pt plate prepared from athick platinum foil (with thickness 0.5 mm) to facilitate theSEM investigations. One side of the foil was insulated to guaranteethe common one-dimensional electrochemistry. A conventionalthree-electrode cell containing a Pt rod as the counter electrodeand an Ag/AgCl in 3 M KCl as the reference electrode was employedfor the electrochemical measurements. Different polyaniline filmswere synthesized by this method according to the experimentalconditions specified in the text. After the electropolymerizationprocess, the polyaniline films were thoroughly washed with doubledistilled water and dried at 60 �C.

The cyclic voltammetric measurements were also carried outwith the same apparatus in the supporting electrolyte of 0.5 MH2SO4, and the potential scan rate was typically 100 mV s�1. SEMimages were taken by a Philips XL30 scanning electron microscope.

(c)

(d)

Fig. 1. (a) Cyclic galvanodynamic polymerization of aniline with the current scanrate of 200 lA cm�2 s�1, and (b) cyclic voltammetric behavior of the resultingpolyaniline film in the supporting electrolyte of 0.5 M H2SO4 recorded with thepotential scan rate of 100 mV s�1. (c and d) SEM images of the polyaniline film.

3. Results and discussion

Fig. 1a shows a galvanodynamic synthesis of polyaniline per-formed in the course of a complete cycle with the upper limit of1.25 mA cm�2. Similar to the conventional galvanostatic synthesisof conductive polymers, the potential can be representative of theelectropolymerization process. For the current densities lower than0.5 mA cm�2, the potential is low to initiate the electropolymeriza-tion process. It is in agreement with the galvanostatic synthesis ofconductive polymers, as no electropolymerization occurs at lowcurrent densities. For the typical case of polyaniline, galvanostaticpolymerization just occurs at current densities higher than0.5 mA cm�2, which is in full agreement with the results obtainedhere for galvanodynamic polymerization.

By scanning the current from 0 to 0.5 mA cm�2, the potentialmonotonically increases to reach the value of 0.8 V vs. Ag/AgCl,which is sufficient to induce the electropolymerization of aniline.After reaching this value, the potential is approximately constantfor higher values of the current density (e.g., up to 1.25 mA cm�2).In the latter regime, the electropolymerization of aniline occurs butit is different across the current scanning. During the reverse scan,the electropolymerization proceeds in the same manner, but forthe current densities lower than 0.5 mA cm�2, the first regime isnot similar to that observed during the forward scan. This can beattributed to the fact that electropolymerization of aniline on pre-viously deposited polyaniline (i.e. continuing the polymer growth)is easier than that on the bare substrate surface. Thus, electropoly-merization occurs even at low current densities in the course ofreverse scan.

After galvanodynamic synthesis of polyaniline according to thesimple manner followed above, it is necessary to examine theelectrochemical behavior of this polyaniline film. Fig. 1b shows acharacteristic voltammetric behavior of polyaniline having threeredox couples. In fact, the polyaniline film synthesized by galvano-dynamic method displays an ideal electrochemical behavior aswell as those synthesized by other electrochemical techniques.Since, in galvanostatic synthesis of conductive polymers, theapplied current density strongly affects the film morphology, it isappropriate to examine this feature for the system under investiga-tion. SEM images of the polyaniline film prepared in Fig. 1a

illustrate a smooth but wrinkled surface (Fig. 1c and d). This is ofparticular interest, as this morphological structure is not common

(a)

(b)

(c)

(d)

Fig. 2. (a) Cyclic galvanodynamic polymerization of aniline performed in the courseof 5 successive cycles (the current scan rate of 200 lA cm�2 s�1). (b) Electrochem-ical behavior and (c and d) morphological structure of the polyaniline synthesized.

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in electrochemical synthesis of polyaniline. In other words, galva-nodynamic polymerization may result in the formation of novelmorphological structures.

Although galvanodynamic polymerization is highly effectiveand can be successfully performed just during a single cycle as re-ported above (Fig. 1), it is useful to investigate galvanodynamicpolymerization performing in the course of successive cycles.Fig. 2a depicts galvanodynamic polymerization of aniline during5 successive cycles. Obviously, for subsequent cycles (2nd and soforth), a similar pattern can be observed during both forward andreverse scans. This means that, as quoted before, the electropoly-merization easily proceeds after the formation of first layers ofthe polyaniline film on the substrate surface. On the other hand,the potential slightly decreases by increasing the cycle number.

Similar voltammetric behavior (as reported in Fig. 1b) is obser-vable for the polyaniline film prepared by 5 successive cycles.Interestingly, the charge under the CV illustrated in Fig. 2b isapproximately 5 times higher than that calculated in Fig. 1b. Thisprovides a strong evidence for the fact that the electropolymer-ization was successful in the course of all subsequent cycles(2nd and so forth) as well as the first cycle. The morphologicalstructure of the polyaniline film prepared during 5 cycles(Fig. 2c and d) is almost similar to that of the polyaniline filmprepared during just one cycle (Fig. 1c and d), as the generalsmooth morphology with wrinkled structure is clearly observable.However, a different morphology consisting of circular particles isalso detectable.

Since this is an interesting feature, it is useful to continue thegalvanodynamic synthesis during more cycles. According toFig. 3a, galvanodynamic polymerization of polyaniline is quitesimilar to the previous ones (Figs. 1a and 2a), and the potentialgradually decreases by increasing the cycle number. Surprisingly,for the last cycles, the potential reaches a noticeably low value,but it seems that the electropolymerization occurs even at suchlow potentials under galvanodynamic condition. Efficiency of theelectropolymerization at such low potentials can be provedaccording to the capacity of the electroactive film. The typical CVof the polyaniline film prepared during 20 cycles (Fig. 3b) indicatesthat its charge is approximately 4 times higher than that of thepolyaniline film prepared during 5 cycles (Fig. 2b) and 20 timeshigher than that of the polyaniline film prepared by 1 cycle(Fig. 1b). In other words, electropolymerization under galvanody-namic condition is efficient, independent of the film thickness.

Morphological investigation of the latter polyaniline films canreveal the mixed morphological structures observed for thepolyaniline film prepared during 5 cycles (Fig. 2c and d). Fig. 3cand d shows that the dominant morphological structure of thepolyaniline film prepared during 20 cycles is the circular particlespartially observed in Fig. 2c and d. In fact, successive cycling undergalvanodynamic condition is in favor of the formation of such par-ticle-based morphology rather than the wrinkled morphologicalstructure generated during the first cycle. And, in a regular manner,this particle-based morphology is dominant for the polyanilinefilms prepared during more cycles.

After extensive investigation of repetitive cyclic galvanodynam-ic synthesis of polyaniline, the scanning range of the currentdensity is an important controllable parameter, which should beinvestigated. To examine this feature, a single cyclic galvanody-namic polymerization was performed in a wider range of currentdensity (Fig. 4a). Although, its difference with the previous case(as reported in Figs. 1–3) is just a gradual increase of the potentialfor higher values of current density, a significant difference isobserved in the course of reverse scan (towards lower currentdensities). During the reverse scan, the potential significantly in-creases to reach a constant value of 1.8 V vs. Ag/AgCl. This indicatesthat the electropolymerization occurs at an extremely high

potential even when lower current densities are applied. Theelectrochemical behavior of this polyaniline film is slightly differ-ent from that prepared in a narrower current range (Fig. 1), as

(a)

(b)

(c)

(d)

Fig. 3. (a) Long cyclic galvanodynamic polymerization of aniline during 20successive cycles (the current scan rate of 200 lA cm�2 s�1). (b) Electrochemicalbehavior and (c and d) morphological structure of the polyaniline synthesized.

(a)

(b)

(c)

(d)

Fig. 4. (a) Cyclic galvanodynamic synthesis of polyaniline in a wider range of thecurrent density. (b) Electrochemical behavior and (c and d) morphological structureof the polyaniline film.

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the capacitive background of the CV is enormously high and thepeaks are less visible. The morphology of this polyaniline filmcontains the smooth structure (Fig. 4c and d), which was also ob-served above for the polyaniline film prepared at a narrower range

of the current density (Fig. 1c and d), but the surface is no longerwrinkled. Instead, the circular particles formed during subsequentcycles (as illustrated in Fig. 3c and d) appear on the main polyan-iline film with smooth structure.

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(b)

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Fig. 5. (a) Cyclic galvanodynamic synthesis of polyaniline in an extremely widerrange of the current density. (b) Electrochemical behavior and (c and d) morpho-logical structure of the polyaniline film.

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By performing the galvanodynamic polymerization at an extre-mely wide range of the current densities, the potential reaches theaforementioned limit of 1.8 V vs. Ag/AgCl even during the forwardscan (Fig. 5a). In this case, the potential during the reverse scan isalmost constant at the mentioned limit. But the rate of extremedecrease of the potential for the current densities lower than0.5 mA cm�2 is similar to that detected for the case reported inFig. 4a, and the values of the potential at the current densitiesapproaching zero are also approximately the same for the lattertwo cases. This indicates that the nature of the polyaniline filmsynthesized at this particular limit is constant, independent ofthe highest current density applied.

However, the morphology of the polyaniline experienced highercurrent densities (Fig. 5c–e) is completely different from that illus-trated in Fig. 4. By taking into account the similarities of the twolatter cases, one can deduce that this enormously rough morphol-ogy corresponds to the expansion of the aforementioned circularparticles appearing on the base smooth structure. This is basedon the hypothesis obtained by comparison of two different casesreported in Figs. 1 and 4 that increasing the upper limit of thecurrent density in the galvanodynamic polymerization results inthe formation of circular particles (which may also be producedby further cycling), and this phenomenon should be regularlystrengthened by increasing the value of the current density. Never-theless, it seems that formation of such particle-based morphologyis accompanied by a type of irregularity (Fig. 5c and d); whereas,the number of such circular particles increases upon cycling(Fig. 3d).

Since the galvanodynamic polymerization was performed incyclic mode, the current density is scanned in both directions.Thus, it is necessary to investigate the influence of first scan’sdirection, as it can play a critical role in the polymerization initia-tion, which strongly affects the entire process. Fig. 6a indicates acyclic voltammetric polymerization, i.e. identical to that ofFig. 5a, but the experiment is started from the upper limit of thecurrent density. These two similar cases are significantly differentowing to the starting point. In the latter case, the potential in-creases by decreasing the current density to reach the aforemen-tioned limit. Of course, it is indeed an apparent effect, and it isbetter to express this phenomenon as: the potential increases byprogress of the experiment time. In other words, the system re-quires a certain time to reach that potential limit, independent ofthe scan direction.

The CV of this polyaniline film (Fig. 6b) is very similar to thatreported in Fig. 5b, and their charges are approximately the same.Nevertheless, a completely different morphology is observable forthe latter polyaniline film in comparison with the former one. Onceagain, wrinkled structure with nanoscale smoothness is appeared(Fig. 6c and d). However, this morphology is very complicated asanother morphological structure is also detectable (Fig. 6d). Itseems that tiny patches are formed upon the polyaniline film.

To shed light on the role of the scanning direction, the polyan-iline film was also prepared by one scan only. Fig. 7a shows a lineargalvanodynamic synthesis of polyaniline started from the currentdensity of 5.0–0.0 mA cm�2. This is exactly half of the synthesisperformed in Fig. 6a. It is obvious that the curve illustrated inFig. 7a is identical to the second scan (in the forward direction)of Fig. 6a. This indicates that the forward scan is independent ofa previous reverse scan, and the forward scan in the presenceand absence of such initial reverse scan is the same (compareFigs. 6a and 7a). The cyclic voltammogram of this polyanilineexhibits almost a capacitive behavior (Fig. 7b), indicating a notice-able difference in the material properties of this polyaniline film ascompared with that reported in Fig. 6.

This is of practical importance, as polyaniline is a promisingmaterial for the preparation of (nano)composites for supercapacitors

[45–47]. Polyaniline is used as a soft matrix and additives such ascarbon nanomaterials induce capacitive behavior. The presentexperimental results show the possibility of maximizing the

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(b)

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Fig. 6. (a) Reverse cyclic galvanodynamic synthesis of polyaniline in an extremelywider range of the current density. (b) Electrochemical behavior and (c and d)morphological structure of the polyaniline film.

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Fig. 7. (a) Linear cyclic galvanodynamic synthesis of polyaniline in an extremelywider range of the current density. (b) Electrochemical behavior and (c and d)morphological structure of the polyaniline film.

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capacitive behavior of polyaniline in favor of supercapacitors. In gal-vanostatic synthesis of manganese oxide, we recently reported thepossibility of controlling the electrochemical behavior of the electro-active material in favor of battery or supercapacitor [48,49].

SEM images of this polyaniline film (Fig. 7c and d) indicate thatthe morphological structure detected for the polyaniline film pre-pared by cyclic galvanodynamic polymerization (Fig. 6) is merely

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Fig. 8. (a) Galvanodynamic polymerization with a low scan rate of 100 lA cm�2 s�1.(b) Electrochemical behavior and (c and d) morphological structure of thepolyaniline film.

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due to the polymerization pathway in the reverse scan (in thiscase, the positive direction), as the morphological structure ap-peared during the first scan (the case of Fig. 7) is completely differ-ent. A smooth structure (probably with the same origin of the tinypatches detected in Fig. 6d) is the dominant morphology; whilehuge spherical particle (probably with the same origin of the afore-mentioned circular particles) are formed upon it.

Since the current density is scanned in the course of galvanody-namic polymerization, the current scan rate also plays an impor-tant role in the electropolymerization process. Fig. 8a depicts aslow galvanodynamic polymerization conducted with a low cur-rent density, i.e. half of that applied for the cases reported above.The first regime defined for the case of Fig. 1 is shorter in this case,and the second regime starts at current densities significantly low-er than 0.5 mA cm�2. Obviously, the polymerization is initiated atthe required current density, and independent of its scan rate.

However, the reverse scan is somewhat altered, as the potentialis not constant and its threshold has a lower value (Fig. 8a). In thesubsequent cycles, the gradual decrease of the potential (as ob-served for the cases reported in Figs. 2b and 3b) is no longer obser-vable; and since sufficient time is available, the system constantlyremains at high potentials. The cyclic voltammetric behavior ofthis polyaniline film (Fig. 8a) is similar to that reported in Fig. 5b,but the morphology is significantly different (Fig. 8c and d).

Alternatively, galvanodynamic polymerization with a fast cur-rent scan rate also confirmed the above-mentioned hypothesis.According to Fig. 9a, the first regime is wider to meet the requiredtime for the phenomenon occurring at this regime. The second re-gime is no longer stable and there is a significant increase of thepotential. In addition, the potential decrease in the course ofcycling is more significant for this fast galvanodynamic polymeri-zation, at least during the first cycles. Fig. 9b displays that thecyclic voltammograms of this polyaniline film is weaker in com-parison with those prepared by slower scans, as can be judgedfrom its weaker peaks. The morphology is indicative of the forma-tion of nanoparticles covered by a smooth but wrinkled layer(Fig. 9c and d).

Further increase of the current scan rate results in similareffects, which are stronger (Fig. 10a and b). In addition to theelectrochemical behavior, the morphological structure of the poly-aniline films is also strongly changed by varying the current scanrate. According to the SEM images of the polyaniline film preparedat an extremely high scan rate of 1000 lA cm�2 s�1 (Fig. 10c and d),it seems that the morphology of this polyaniline film has beenmade from the spherical particles detected during the galvanody-namic polymerization at lower scan rate of 200 lA cm�2 s�1. Butthere is a tendency towards horizontal growth rather than verticalgrowth, as such spherical particles are closely packed in the lattercase (Fig. 10c and d). In this case, a highly dense polymer withsmooth structure is formed. In general, these results indicate thatthe influence of the current scan rate on galvanodynamic polymer-ization is systematic, and the results can be correlated to the scanrates applied.

The powerfulness of an electrochemical method for controllingthe materials properties is the flexibility of controllable parame-ters. The main controllable parameter in potentiostatic synthesisis the applied potential, which is not very flexible, as electropoly-merization can be induced only within a narrow potential window.Time is not a helpful controllable parameter, as the polymerizationprogress is constant and longer synthesis just results in thicker filmwithout changing the material properties. The controllable param-eter in potentiodynamic synthesis is the potential scale rate, whichshould be kept within the common ranges to satisfy conventionalelectrochemistry. Potential window cannot be highly altered, asthe complete oxidation/reduction should be performed to maintainthe polymer structure.

Galvanostatic synthesis is more flexible, but limited to a rangeof current densities in which the electropolymerization occursbut does not result in over-oxidation. As presented above,

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Fig. 9. (a) Galvanodynamic polymerization with a high scan rate of500 lA cm�2 s�1. (b) Electrochemical behavior and (c and d) morphologicalstructure of the polyaniline film.

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Fig. 10. (a) Galvanodynamic polymerization with an extremely high scan rate of1000 lA cm�2 s�1. (b) Electrochemical behavior and (c and d) morphologicalstructure of the polyaniline film.

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galvanodynamic synthesis has several controllable parameters,which can be fairly altered to control the material properties. (i)The range of current densities can be widely changed while

reserving the current density needed to induce the electrodeposit-ion. (ii) The scan rate of current density can be changed and reservethe electrodeposition time by changing the number of cycles too.

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(iii) The direction of synthesis or even designing a special synthesisby incomplete cycles in different directions.

4. Conclusion

Galvanodynamic polymerization was introduced as a flexibleelectrochemical technique for the synthesis of polyaniline, owingto several controllable parameters, which have strong influenceson the electroactive material synthesized. In this method, the cur-rent density is scanned in a given range. It is also possible to makethe synthesis in the course of a complete cycle, or even during sev-eral successive cycles. Both the electrochemical properties andmorphological structure of the electroactive material are stronglycontrolled by the experimental conditions involved during the gal-vanodynamic synthesis. It is easily possible to prepare electroac-tive materials with different properties by adjusting variouscontrollable parameters involved such as the current range, scanrate, number of cycles, and the scan direction. This is just a begin-ning to introduce this possibility and opportunity and furtherapplication of this method for various systems can reveal furtherfeatures.

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