Redox polymer electrodes

Anson FC, Ni CL, Saveant JM. 1985. Electrocatalysis at redox polymer electrodes with separation of the catalytic and charge propagation roles. Reduction of dioxygen to hydrogen peroxide as catalyzed by cobalt(II) tetrakis(4-A-methylpyridyl)porphyrin. J Am Chem Soc 107 3442. 

Kato T, Liu JK, Yamamoto K, Osborne PG, Niwa O. 1996. Detection of basal acetylcholine release in the microdialysis of rat frontal cortex by high- performance liquid chromatography using a horseradish peroxidase-osmium redox polymer electrode with pre-enzyme reactor. J Chromatogr B 682 162-166. 

Redox polymer Electrode material Enzyme used Substrate Applied potential Reference... 

Andrieux, C.P, Dumas-Bouchiat, J.M., and Saveant, J.-M. 1982. Catalysis of electrochemical reactions at redox polymer electrodes Kinetic model for stationary voltammetric techniques. Journal of Electroanaytical Chemistry 131, 1-35. 

Denny, R.A., and Sangaranarayan, M.V. 1998. Dynamics of electron hopping in redox polymer electrodes using kinetic Ising model. Jourrtal of Solid State Electrochemistry 2, 67-72. 

Andrieux, C. P., Dumas-Bouchiat, J. M., Saveant, J. M., Catalysis of Electrochemical Reactions at Redox Polymer Electrodes. Kinetic Model for Stationary Voltammetric Techniques , J. Elec-troanal. Chem. 131 (1982) 1-35. 

At present analysis of diffusion and kinetics in these redox polymer electrodes is at an early stage, although there have been some preliminary attempts to understand the behavior of the systems. It is clear that more work on basic models for such electrodes, taking into account diffusion and enzyme kinetics is required. 

The main drawback of redox polymer electrodes, both in fundamental studies and in chemical analysis, stems from the difficulty in controlhng the concentration and spatial organization of redox sites within the film (4). The main use of redox polymer modified electrodes has been in fundamental studies of electron transfer mechanisms. These electrodes are also used as electrochemical sensor devices, but on a much more limited scale (117). Many of these limitations are overcome by the use of ion-exchange polymers, as outlined below. 

Andrieux CP, Dumasbouchiat JM, Saveant JM. Catalysis of electrochemical reactions at redox polymer electrodes kinetic model for stationary voltammetric techniques. 

Akhoury A, Bromberg L, Hatton TA (2013) Interplay of electron hopping and bounded diffusion during charge transport in redox polymer electrodes. J Phys Chem B 117 333-342... 

Much work has been done on exploration and development of redox polymers that can rapidly and efftciendy shutde electrons. In several instances an enzyme has been attached to the electrode using a long-chain polymer having a dense array of electron relays. The polymer which penetrates and binds the enzyme is also bound to the electrode. 

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. 

Pseudocapacitance is used to describe electrical storage devices that have capacitor-like characteristics but that are based on redox (reduction and oxidation) reactions. Examples of pseudocapacitance are the overlapping redox reactions observed with metal oxides (e.g., RuO,) and the p- and n-dopings of polymer electrodes that occur at different voltages (e.g. polythiophene). Devices based on these charge storage mechanisms are included in electrochemical capacitors because of their energy and power profiles. 

FIGURE 6-8 Composition of an electron-relaying redox polymer used for wiring enzymes to electrode transducer. (Reproduced with permission from reference 14.)... 

Intensive research on the electrocatalytic properties of polymer-modified electrodes has been going on for many years Until recently, most known coatings were redox polymers. Combining redox polymers with conducting polymers should, in principle, further improve the electrocatalytic activity of such systems, as the conducting polymers are, in addition, electron carriers and reservoirs. One possibility of intercalating electroactive redox centres in the conducting polymer is to incorporate redoxactive anions — which act as dopants — into the polymer. Most research has been done on PPy, doped with inter alia Co 96) RyQ- 297) (--q. and Fe-phthalocyanines 298,299) Co-porphyrines Evidently, in these... 

Theories neglect that catalysts usually have limited turnover numbers due to destructive side reactions. This may not be so obvious in analytical experiments but it has severe consequences for large scale applications. A simple calculation can illustrate this problem if a redox polymer with a monomer molecular weight of 400 Da and a density of 1 g cm " is considered with all redox centers addressable from the electrode and accessible to the substrate with a turnover number of 1000, then, to react 1 nunol of substrate at a 1 cm electrode surface, at least 5 pmol of active catalyst centers corresponding to 2 mg of polymer, or a dry film thickness of 20 pm are required. This is 20 times more than the calculated optimum film thickness for rather favorable conditions... 

The application of two successive redox polymer layers at an electrode surface gives rise to rectifying properties because the electron transport between the electrode and the outer layer has to be mediated by the inner redox polymer Among several conbeivable situations, the one where the inner layer possesses two reversible redox potentials (e.g. a Ru"(bipy)j polymer) and the outer layer has one redox transition with a potential between the former ones (e.g. polyvinylferrocene) is most interesting gjj electrode device has two opposite-sign rectifying... 

Fig. 5. Schematic representation of a Pt electrode coated with succesive layers of redox polymers A and B a bilayer transistor electrode. Arrows indicate directions in which communication of the electrode and the outer layer is possible (from ref. ).

The redox processes responsible for the switching of the bridging redox polymer can also be brought about by redox processes induced by molecular species in solution Alternatively, the switching processes can be designed so that a solution component is essential for, or mediates the redox process. The array electrode can then be used as a sensor for those solution constituents. 

Pishko MV, Katakis I, Lindquist SE, Ye L, Gregg BA, Heller A. 1990. Direct electron exchange between graphite electrodes and an adsorbed complex of glucose oxidase and an osmium-containing redox polymer. Angew Chem 102 109-111. 

Andrieux CP, Saveant J-M. 1992. Catalysis at redox polymer coated electrodes. In Murray RW, editor. Molecular Design of Electrode Surfaces. New York Wiley, p. 207. 

An alternative strategy for co-immobilization of mediator and GOx is based on adsorption of enzyme, cross-linked, as was described for the laccase-based biocatalytic cathodes [30, 37 42], to an osmium-based redox polymer film, on carbon electrodes [1-3, 54],... 

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