Review on Electrochemical synthesis of conducting polymers
R.K. Shukla, Divyanshi Srivastava, Vijendra Kumar
Deparment of Physics University of Lucknow, Lucknow, 226007, U.P, India
Email Id: rajeshkumarshukla_100@yahoo.co.in
Abstract
Conductive polymers were widely used in the field of research area because of their unique
properties such as electrical conductivity, mechanical strength, stability etc. The present study
reports the electrochemical synthesis of conducting polymers in the presence of different
doping anions .This study also includes the different aspects such as choice of monomer,
solvents, electrodes and electrolytes for electrochemical synthesis.
Keywords: - Conducting polymers, electrochemical synthesis method, doping anions.
Introduction
Research in electroactive polymers, particularly in aromatic conducting polymers,has
received considerable attention worldwide in the past few years because of their potential
application in the field of microelectronics, optics and optoelectronics [1].
Conducting polymers consists of intresting group. Common class of organic conductive
polymers includes poly(acetylene), poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s,
poly(aniline)s,
poly(flourine)s,
poly(3-alkylthiophene)s,
polytetrathiofulvalenes,
polynapthalenes, poly(p-phenylene sulphide), poly(para- phenylene vinylene)s etc[2]. It can
be prepared via chemical or electrochemical polymerization. Usually Electrochemical
polymerization is preffered, because the Electrochemical synthesis is the most common
method as it is simpler, quick and perfectly controllable [3].This technique involves the direct
formation of conducting polymer films which are suitable in use for electronic devices[4].
Electrochemical polymerization produces thin films with a thickness of few micrometers on
the electrode surface (5), while Chemical oxidation produced fine-grained materials.
Conducting polymers can be reversibly doped and undoped using electrochemical techniques
accompanied by significant changes in conductivity [6]. The electrical conductivity of
conducting polymers changes over several orders of magnitude in response to change in pH,
applied potentials on their environments [7]. However, the yield and quality of the resulting
polymer films are influenced by several factors, such as nature and concentration of monomer
and the counter ion, solvent, cell condition (e.g. electrode and applied potential), temperature
and pH[8,9,10].
Set up
Electrochemical polymerization is performed in a single-compartment cell containing
electrochemical bath which includes a monomer and a supporting electrolyte dissolved in
appropriate solvent.
It also includes three different electrode such as working electrode (cathode), reference
electrode and counter electrode (anode). Film deposited on the counter electrode (anode).
Usually ECP is carried out either Potentiostatically (i.e. constant voltage condition) or
Galvanostatically (i.e. constant current condition) by using a suitable power supply.
Potentiostatic conditions are recommended to obtain thin films while galvanostatic conditions
are recommended to obtain thick films [11].
Fig. Set-up for Electrochemical Polymerization
Choice of monomer
The compound which posses relatively lower anodic oxidation potential and are suspectible
to electrophilic substitution reaction can produce conducting polymer by electrochemical
technique [12]. Conducting polymers is the polymerized form of the monomer. The choice of
monomer depends upon the peak oxidation potential, electrophilic substitution reaction and
maintaining aromatic structure during the process. Table 1 gives peak oxidation potentials of
some of the aromatic compounds. Table 1 shows that the electrochemically polymerizable
monomers reported so far have peak potentials below 2.1V. Low peak potential avoid
complications in the polymerization arising from the oxidative decomposition of the solvent
and the electrolyte [13].
Table1. Electrochemical data for some heterocyclic and aromatic monomers
Monomer
Oxidation potential (V) Vs. SCE
1.pyrrole
2.bipyrrole
3.Terpyrrole
4.Thiophene
5.Biothiophene
6.Terthiophene
7.Azulene
8.Pyrene
9.Carbazole
10.Fluorine
11.Fluoranthene
12.aniline
1.20
0.55
0.26
2.07
1.31
1.05
0.91
1.30
1.82
1.62
1.83
0.71
Electrodes
Generally the electrochemical polymerization is carried out in one-compartment cell by using
three electrodes i.e. reference electrode, working electrode (anode), counter electrode
(cathode). The working electrode is used for electro-deposition of polymer. For this noble
metals or inert materials (such as pt, Au, Glassy carbon, ITO (Indium Tin Oxide) etc.) are
used that should not oxidized concurrently with the aromatic monomer. SCE (Saturated
Calomel Electrode) or Ag/Agcl (saturated KCL) can be used as reference electrode and for
counter electrode Fe, Zn, Al, Stainless Steel etc. are used [3].
Electrolytes
Since the electrochemical polymerization reaction proceeds via radical cation intermediates,
nucleophilic character of the solvent and electrolyte imposes certain restrictions on their
choice [12]. The electrolyte used depends upon the choice of solvent and the supporting
electrolyte used. On the basis of nucleophilic character solvent is chose. Aprotic solvents
(viz. Acetonitrile, benzonitrile, etc.) with poor nucleophilic character are preferably used.
And the choice of supporting electrolyte depends upon the solubility, dergree of dissociation
and nucleophilicity criteria [13]. Highly dissociated and poor nucleophilicity produces good
quality films.
Conclusion
While concluding we can include that when compared to oxidative method the
electrochemical method of synthesis is more suitable [14]. The film once obtained by ECP is
then characterized by different characterization methods like SEM, TEM, XRD, UV-Vis,
PL, FTIR, and Resistivity, Conductivity etc. to study its structural and morphological
behaviour. Additionally, this polymer group are used in variety of applications toward
technology like rechargeable batteries, smart windows, electrochromic displays, cleanup,
sensors, corrosion inhibitors (FETs), shielding etc.
References
1. A M Pharhad Hussain and A Kumar, Bull. Mater. Sci., Vol. 26, No. 3, April 2003, pp. 329334, Indian Science Academy.
2. Md. Aminur Rahman, Pankaj Kumar, Deog-Su Park and Yoon- Bo Shim., Sensors, ISSN
1424-8220, 2008 BY MPDI.
3.R.N. Singh, Madhu and R. Awasthi, Banaras Hindu University, India, Intechopen.
4. Naoki Toshima and Susumu Hara s Prog. Polym. Sci. Vol. 20, 155-183, 1995 elsevier sc.
Ltd.
5. A.F. Diaz, K.K. Kanazawa, G.P.Gardini, JCS chem. Commun. (1979) 395.
6. Lee., J.-W.; Park, D.-S.; Shim, Y-B.; Park, S-M. Electrochemical characterization of
poly(1,8- diaminonapthaleneL): a funtionalized Polymer. J. Electrochem. Soc. 1992, 139,
3507-3514.
7. Paul, E.W.; Ricco, A.J.; Wrighton, M.S. Resistance of polyaniline films as a function of
electrochemical potential and the fabrication of polyaniline- based microelectronic devices. J.
Phys. Chem. 1985, 89, 144-1447.
8. Sadki, S.; Schottland, P.; Brodie, N. & Sabouraud, G. (2000). The mechanism of pyrrole
electropolymerization. Chem. Soc. Rev., Vol.29, No.5, pp. 283-293. ISSN 0306-0012
9. Ansari, R. (2006). Polypyrrole conducting electroactive polymers: Synthesis and stability
Studies. E- Journal of Chemistry, Vol.3, No.13, pp. 186-201, ISSN 0973-4945
10.Pina, C.D.; Falletta, E.; Rossi, M. (2011). Conductive materials by metal catalyzed
polymerization. Catal. Today, Vol.160, No.1, pp. 11-27. ISSN 0920-5861
11. A.F.Diaz, J.F. bargon, in: T.A. Skotheim (Ed.), Handbook of Conducting Polymers,
Marcel Dekker, New York, 1986, p. 81.
12. A.F. DIAZ, K.K. Kanazawa, in: J.S. Miller (Ed.), Extended Linear Chain Compounds,
vol. 3, plenum Press, New York, 1982, p. 417.
13. K.Gurunathan, A. Vadivel Murugan, R. Marimuthu, U.P. Mulik, D.P. Amalnerkar Mat.
Chem. and Phy. 61 (1999) 173-191 elsevier.
14. J. Vivekanandan, V. Ponnusamy, A. Mahudeswaran and P.S. Vijayanand Sch. Res. Lib.,
Archives of App. Sc. Research, 2011, 3 (6):147-153.