Conductivity polymer film electrodes

Figure 11.40 Electrochemical cell for a separate investigation of the reactions on an iron electrode and on a conducting polymer film electrode. WEI, working iron/steel electrode WE2, polythiophene covered platinum electrode CE, counter electrode RE, reference electrode and P, potentiostat.

Fig. 11 Schematic of the electrode-electrolyte interface for a conductive polymer film electrode (after Ref. [47]).

Mizutani, F., S.I. Lijima, Y. Tanabe, and K. Tsuda (1985). Conducting polymer film electrodes with immobilized catalytic sites. J. Chem. Soc., Chem. Commun. 1728-1729. 

Oguro, K., Kawami, Y. and Takenaka, H. (1992). Bending of an ion-conducting polymer film-electrode composite by an electric stimulus at low voltage. Journal of Micromachine Society 5, 1, pp. 27-30. 

Nemat-Nasser S, Wu Y (2003) Comparative experimental study of ionic polymer-metal composites with different backbone ionomeis and in various cation forms. J Appl Phys 93 5255-5267 Nemat-Nasser S, Zamani S (2006) Modeling of electrochemomechanical response of ionic polymer-metal composites with various solvents. J Appl Phys 100 064310 Oguro K, Kawami Y, Takenaka H (1992) Bending of an ion-conducting polymer film-electrode composite by an electric stimulus at low voltage. J Micromach Soc 5 27-30 Palmre V, Lust E, Janes A et al (2011) Electroactive polymer actuators with carbon aerogel electrodes. J Mater Chem 21 2577-2583... 

Table 20.8 Summary of Voltammetry Studies on Conducting Polymer Film Electrodes...

A. Galal, Z. Wang, A. E. Karagozler, H. Zimmer, H. B. Mark, Jr., and P. B. Bishop, A potentiometric halide ion sensor based on conducting polymer film electrode, II. Effect of electrode conditioning and technical specifications. Anal. Chim. Acta 299(2) 145 (1994). 

G. Inzelt, Charge transport in conducting polymer film electrodes, Chem. Biochem. Eng. Q., 2007,21,1, pp. 1-14. 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

It is now 20 years since the first report on the electrochemistry of an electrode coated with a conducting polymer film.1 The thousands of subsequent papers have revealed a complex mosaic of behaviors arising from the multiple redox potentials and the large changes in conductivity and ion-exchange properties that accompany their electrochemistry. 

The electrochemistry of conducting polymers has been the subject of several reviews2-8 and has been included in articles on chemically modified electrodes.9-14 The primary purpose of this chapter is to review fundamental aspects of the electrochemistry of conducting polymer films. Applications, the diversity of materials available, and synthetic methods are not covered in any detail. No attempt has been made at a comprehensive coverage of the relevant literature and the materials that have been studied. Specific examples have been selected to illustrate general principles, and so it can often be assumed that other materials will behave similarly. 

A number of approaches are available to improve the morphology and homogeneity of electrochemically deposited conducting polymer films. Priming of the electrode surface with a monolayer of adsorbed or covalently bonded monomer leads to more compact deposits of polyaniline,87,88 poly thiophene,80 and polypyrrole.89,90 Electrode rotation has been shown to inhibit the deposition of powdery overlayers during poly(3-methylthiophene) deposition.81... 

The electrochemistry of a polymer-modified electrode is determined by a combination of thermodynamics and the kinetics of charge-transfer and transport processes. Thermodynamic aspects are highlighted by cyclic voltammetry, while kinetic aspects are best studied by other methods. These methods will be introduced here, with the emphasis on how they are used to measure the rates of electron and ion transport in conducting polymer films. Charge transport in electroactive films in general has recently been reviewed elsewhere.9,11... 

Figure 16. General transmission-line model for a conducting polymer-coated electrode. CF is the faradaic pseudo-capacitance of the polymer film, while Rt and Rt are its electronic and ionic resistance, respectively. R, is the uncompensated solution resistance.

The kinetics of charge transfer between metallic electrodes and conducting polymer films have proved to be difficult to investigate, and little reliable data exist. Charge-transfer limitations have been claimed in cyclic voltammetry, and Butler-Volmer kinetics have been used in a number of... 

In our tests, we used pasted mixtures of carbon-carbon electrode components with KOH solution having a density of 1,26 g em"3. Positive and negative electrodes were pasted onto the conductive polymer film, separated by ionoconductive separator, made out of special paper, pressed between external collectors of nickel-plated copper with pressure of 8 kgf-ern 2. 

It usually takes place close to the melting temperature of the polymer when the pores collapse turning the porous ionically conductive polymer film into a nonporous insulating layer between the electrodes. At this temperature there is a significant increase in cell impedance and passage of current through the cell is restricted. This prevents further electrochemical activity in the cell, thereby shutting the cell down before an explosion can occur. 

A conducting polymer film on a transparent ITO electrode was obtained by oxidative polymerization of 6-0-(2-azulenecarbonyl)-(3-D-glucopyranose-l,2,3,4-tetraacetate 37. A negative couplet (kmax 367 and 404 nm) in the CD spectrum was attributed to a twisted biazulene subunit with R configuration. Electrochemical oxidation resulted in the disappearance of the CD absorption, while reduction to the neutral form reestablished the CD band. The modulation of the chirality can be explained by interconversion between a neutral, twisted form of the polyazulene and a more planar, conducting form. 

Hillman et al. measured the quartz crystal impedance to determine changes in rigidity, swelling and ionic exchange in conducting polymer films [57, 58] and have also used dynamic quartz crystal impedance of modified electrodes during film growth and redox conversion [57] by qualitative analysis of the acoustic admittance-frequency peak width. 

If the chronoamperometric response of a - polymer-modified electrode is measured alone - in contact with inert - supporting electrolyte - Cottrell-type response can be obtained usually for thick films only, because at short times (f < 0.1-1 ms) the potential is not established while, at longer times (t > 10-100 ms), the finite diffusion conditions will prevail and / exponentially decreases with time. Another complication that may arise is the dependence of D on the potential in the case of - conducting polymer films [vi]. 

Polymer film electrodes are prepared either by evaporation technique or by -> electropolymerization. Redox polymers that are usually synthesized chemically are dissolved in a suitable solvent, placed as a droplet on the surface of a metal (or dip-coating, spin-coating techniques are applied) and the solvent is subsequently left to evaporate. The electrode can be used in other solvents in which the polymer is insoluble. Conducting polymer layers are usually developed by electropolymerization directly on the surface of the metal. 

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