Polymer-electrolyte systems, redox

In this section, we review recent developments of redox capacitors with conducting polymer electrodes and EDLC with SPE or gel electrolyte systems. 

An ionically conductive polymer is applied to the lithium battery, the fuel cell, etc. These polymer electrolytes have a fairly high ionic conductivity. However, general electrochemical measurement could not be performed in such polymer electrolytes. Electrochemical measmement in such polymer electrolytes has been possible only by special electrode systems described earlier. The reason is that the diffusion of ions or redox molecules and the rate of electron transfer are slow in these polymer electrolytes. 

Most polymer electrolytes behave rather well from the point of view of electronic insulation as the polymer matrices are intrinsically non-conducting. Complications have already been alluded to in the case of other polymer electrolytes [101]. In addition, certain polymer electrolytes have been prepared which have been deliberately designed to conduct both electronic and ionic species. Examples include materials with an electronically conducting backbone to which ionically conducting side chains are attached [109] and those based on redox systems [110]. In these cases, the cationic transference number is further attenuated, since... 

It is important for the system analysis that redox sites are confined to the polymer matrix, i.e., electrochemical potentials of ox and red in the electrolyte, fired and filx are not defined/ Therefore the equilibrium potential across the polymer/electrolyte interface is defined by the ion-(in particular X ) partitioning equilibria, Eqn. 5. The electrode potential ( measured with the reference electrode in the electrolyte) of the electrode coated with the electroactive polymer film can thus be formulated as... 

Due to the presence of interactions, the apparent redox potential of a redox couple inside a polyelectrolyte film can differ from that of the isolated redox couple in solution (i.e. the standard formal redox potential) [121]. In other words, the free energy required to oxidize a mole of redox sites in the film differs from that needed in solution. One particular case is when these interations have an origin in the presence of immobile electrostatically charged groups in the polymer phase. Under such conditions, there is a potential difference between this phase and the solution (reference electrode in the electrolyte), knovm as the Donnan or membrane potential that contributes to the apparent potential of the redox couple. The presence of the Donnan potential in redox polyelectrolyte systems was demonstrated for the first time by Anson [24, 122]. Considering only this contribution to peak position, we can vwite ... 

In this chapter, we describe three different systems with which to construct electro- and photo-functional molecular assemblies on electrode surfaces. The first is the bottom-up fabrication of redox-conducting metal complex oligomers on an electrode surface and their characteristic redox conduction behavior, distinct from conventional redox polymers.11-13 The second is a photoelectric conversion system using a porphyrin and redoxconducting metal complex.14 The third is the use of a cyanobacterial photosystem I with molecular wires for a biophotosensor and photoelectrode.15 16 These systems will be the precursors of new types of molecular devices working in electrolyte solution. 

Polyelectrolytes and soluble polymers containing triarylamine monomers have been applied successfully for the indirect electrochemical oxidation of benzylic alcohols to the benzaldehydes. With the triarylamine polyelectrolyte systems, no additional supporting electrolyte was necessary [91]. Polymer-coated electrodes containing triarylamine redox centers have also been generated either by coating of the electrode with poly(4-vinyltri-arylamine) films [92], or by electrochemical polymerization of 4-vinyl- or 4-(l-hydroxy-ethyl) triarylamines [93], or pyrrol- or aniline-linked triarylamines [94], Triarylamine radical cations are also suitable to induce pericyclic reactions via olefin radical cations in the form of an electron-transfer chain reaction. These include radical cation cycloadditions [95], dioxetane [96] and endoperoxide formation [97], and cycloreversion reactions [98]. 

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