**3.4 Experimental performance**

Generally, experimental set-up for electrochemical synthesis of electroconducting polymers in laboratory conditions is simple. It involves, in majority of cases, standard three-electrode electrochemical cell, although in some cases of galvanostatic polymerization, two electrode cell can be used (Wallace et al., 2009). The polymer obtained by this procedure is deposited directly on the electrode. Novel experimental set-up, enabling electrochemical generation of polyaniline colloids, using flow-through electrochemical cell, was also reported (Aboutanos et al., 1999; Innis et al., 1998). In this novel electrochemical cell, anode was separated from two and cathodes by ion exchange membrane. The anodic and cathodic electrolytes were passed through electrode compartments at specified flow, while polymerization was achieved at constant potential.

The most common experimental techniques used for electrochemical polymerization of aniline are: cyclic voltammetry (potentiodynamic), galvanostatic and potetntiostatic techniques. Polymerization using cyclic voltammetry is characterized by cyclic regular change of the electrode potential and the deposited polymer is, throughout the experiment, changing between its non-conducting and conducting (doped) state, followed by exchange of the electrolyte through polymer (Heinze et al., 2010). At the end of polymerization the obtained polymer is in its non-conducting form, moreover, cyclic voltammetry favors formation of disordered chains and open structure (Heinze et al., 2010) As stated before, relatively high potential is required for electrochemical oxidation of aniline monomer, therefore at first 2 – 10 cycles, the upper potential limit is high, but owing to autocatalytic nature of aniline electropolymerization, the upper potential limit can be decreased to avoid degradation resulted from over oxidation of perningranilin form of polyaniline (Inzelt, 2008). Recently, it was shown that cyclic voltammetry can even be useful for formation of nanostructure polyaniline . It was shown that different sized polyaniline nanofibres were electrochemicaly polymerized, by different scan rates, in the presence of ferrocensulfonic acid (Mu & Yang, 2008).

Electrochemical Polymerization of Aniline 87

that potentiostatic method could be useful in obtaining polyaniline nanowiers (Gupta &

Some of the researches used pulse potentiostatic technique to obtained polyaniline electrochemically (Tang et al., 2000; Tsakova et al., 1993; Zhou et al., 2007). The potentiostatic pulse technique implies application of periodic cathodic and anodic pulses, with important parameters, lower (cathodic) and upper (anodic) limit potentials with additional cathodic and anodic pulses duration, during given time. It was observed (Zhou et al., 2007) that mentioned parameters had strong influence on the morphology of polyaniline,

Owing to its conductivity and redox activity, polyaniline is considered for practical application in various fields. Unfortunately, beside its unique properties, application of polyaniline in biochemical systems is limited as a consequence of the lost of activity at pH above 4 (Karyakin et al., 1994; Malinauskas, 1999; Mu 2011). This problem might be overcome by introduction of so- called pH functional groups into polyaniline chain (Mu, 2011). This could be achieved either by sulfonation (Wei et al., 1996) or by copolymerization, which is more efficient way to alter the properties of parent polymer. Electrochemical polymerization of aniline and aniline derivates with pH functional groups, sulpho, carboxyl or hydroxyl was reported. It was observed that self-doped polyanilines, obtained by electrochemical co-polymerization of aniline with: *o-*aminobenzoic acid, *m*aminobenzoic acid, or *m –* aminobenzensulfonic acid had exhibited redox activity at high

Apart from aniline and aniline derivate, electrolyte solution also contains acid necessary for protonation of nitrogen atom. The obtained co-polymers are often called self-doped polyanilines, since the introduced negatively charged functional groups plays role of an intermolecular dopant which is able to compensate the charge on positively charged nitrogen atoms of the polymer. The presence of intermolecular anion alters properties of "ordinary" polyaniline, and has influence on the polymerization process as well. It was shown that upper switching potential limit had important influence on self-doping, the limit of 0.9 V was proven to be optimal, and while in the case of un- substituted aniline, upper

The problem related to electrochemical activity of self-doped polyaniline is its rapid lost. Recently, it was showed that electrochemical polymerization of aniline and 5-aminosalycylic acid, which nears two acidic functional groups, had lead to co-polymer with satisfactory

Although polyaniline is among the first know electroconductive polymers, the interest in this field of study still exist, since its diverse and unique properties can be useful in various practical applications. Electrochemical polymerization of aniline and aniline derivates were intensively investigated. Various factors such as: electrode material, dopant anions, electrolyte composition, monomer type, pH etc. were proven to exhibit influence in the electropolymerization process and properties of the desired polymer. The electrochemical synthesis of polyaniline, similar to chemical, is practically always performed in strong acidic

Miura, 2007). Modified potentiostatic techniques were also reported.

**3.5 Electrochemical co-polymerization of aniline and aniline derivates** 

thus on its electrochemical activity.

pH (Karyakin et al., 1996).

limit was lower.

**4. Conclusion** 

redox activity (Mu, 2011).

Galvanostatic polymerization, owing to current control, enables reaction to proceed at constant rate. Galvanostatic synthesis permits estimation of the polymer mass deposited on the electrode (Kankare, 1998). On the other hand, galvanostatic polymerization leads to formation of polyaniline in its conductive form.

Electrochemical polymerization of aniline on graphite electrode from hydrochloride acid electrolyte, obtained by cyclic voltammetry (numbers on the figure refers to cycle number) given in Fig. 4., while in the insert of the Fig.4, hronopotnetiometric curve of galvanostatic polymerization from the same electrolyte is shown (Gvozdenović et al., 2011; Jugović, PhD thesis, 2009; Jugović et al., 2009)

Electrochemical polymerization of aniline proceeds together with insertion of chloride anions (dopant) from the electrolyte, according to:

$$\text{(PANN)}\_{\text{n}} + \text{nyCl}^{\cdot} \rightarrow \text{[PANN}\* \text{ (Cl}\text{)}\text{]}\_{\text{n}} + \text{nyer}$$

Where *y* refers to doping degree, ration between the number of charges in the polymer and the number of monomer units (Kankare, 1998).

As seen on cyclic voltammograms in Fig.4., doping of chloride ions started at potential of ∼ - 0.1 V (SCE), the first well defined anodic peak, situated at potential of 0.2 V (SCE) indicate transition of leucoemeraldine form of polyaniline to emeraldine salt, followed by the changes of *y* between 0 and 0.5.

Fig. 4. Cyclic voltammograms of electrochemical polymerization of aniline on graphite electrode from aqueous solution of 1.0 mol dm-3 HCl and 0.25 mol dm-3 aniline, at scan rate of 20 mV s-1. Insert: Chronopotentiometric curves of aniline polymerization at constant current density of 2.0 mA cm-2.

Second anodic peak, occurred at potenial of ∼ 0.5 V (SCE) denotes formation of fully doped perningraniline salt (*y* = 1).

The potentiostatic technique of electrochemical polymerization is characterized by pronounced changes in the current i.e. polymerization rate, and similarly to galvanostatic polymerization obtained polymer is in its doped form (Heinze et al., 2010). It was observed

Galvanostatic polymerization, owing to current control, enables reaction to proceed at constant rate. Galvanostatic synthesis permits estimation of the polymer mass deposited on the electrode (Kankare, 1998). On the other hand, galvanostatic polymerization leads to

Electrochemical polymerization of aniline on graphite electrode from hydrochloride acid electrolyte, obtained by cyclic voltammetry (numbers on the figure refers to cycle number) given in Fig. 4., while in the insert of the Fig.4, hronopotnetiometric curve of galvanostatic polymerization from the same electrolyte is shown (Gvozdenović et al., 2011; Jugović, PhD

Electrochemical polymerization of aniline proceeds together with insertion of chloride

(PANI)n + n*y*Cl- → [PANI*y*+ (Cl-)]n + n*y*e-Where *y* refers to doping degree, ration between the number of charges in the polymer and

As seen on cyclic voltammograms in Fig.4., doping of chloride ions started at potential of ∼ - 0.1 V (SCE), the first well defined anodic peak, situated at potential of 0.2 V (SCE) indicate transition of leucoemeraldine form of polyaniline to emeraldine salt, followed by the

Fig. 4. Cyclic voltammograms of electrochemical polymerization of aniline on graphite electrode from aqueous solution of 1.0 mol dm-3 HCl and 0.25 mol dm-3 aniline, at scan rate of 20 mV s-1. Insert: Chronopotentiometric curves of aniline polymerization at constant

Second anodic peak, occurred at potenial of ∼ 0.5 V (SCE) denotes formation of fully doped

The potentiostatic technique of electrochemical polymerization is characterized by pronounced changes in the current i.e. polymerization rate, and similarly to galvanostatic polymerization obtained polymer is in its doped form (Heinze et al., 2010). It was observed

formation of polyaniline in its conductive form.

anions (dopant) from the electrolyte, according to:

the number of monomer units (Kankare, 1998).

thesis, 2009; Jugović et al., 2009)

changes of *y* between 0 and 0.5.

current density of 2.0 mA cm-2.

perningraniline salt (*y* = 1).

that potentiostatic method could be useful in obtaining polyaniline nanowiers (Gupta & Miura, 2007). Modified potentiostatic techniques were also reported.

Some of the researches used pulse potentiostatic technique to obtained polyaniline electrochemically (Tang et al., 2000; Tsakova et al., 1993; Zhou et al., 2007). The potentiostatic pulse technique implies application of periodic cathodic and anodic pulses, with important parameters, lower (cathodic) and upper (anodic) limit potentials with additional cathodic and anodic pulses duration, during given time. It was observed (Zhou et al., 2007) that mentioned parameters had strong influence on the morphology of polyaniline, thus on its electrochemical activity.
