Electroactive polymer films

Since model compounds reveal well-defined cyclic voltammograms for the Cr(CNR)g and Ni(CNR)g complexes (21) the origin of the electroinactivity of the polymers is not obvious. A possible explanation (12) is that the ohmic resistance across the interface between the electrode and polymer, due to the absence of ions within the polymer, renders the potentially electroactive groups electrochemically inert, assuming the absence of an electronic conduction path. It is also important to consider that the nature of the electrode surface may influence the type of polymer film obtained. A recent observation which bears on these points is that when one starts with the chromium polymer in the [Cr(CN-[P])6] + state, an electroactive polymer film may be obtained on a glassy carbon electrode. This will constitute the subject of a future paper. 

The above mechanistic aspect of electron transport in electroactive polymer films has been an active and chemically rich research topic (13-18) in polymer coated electrodes. We have called (19) the process "redox conduction", since it is a non-ohmic form of electrical conductivity that is intrinsically different from that in metals or semiconductors. Some of the special characteristics of redox conductivity are non-linear current-voltage relations and a narrow band of conductivity centered around electrode potentials that yield the necessary mixture of oxidized and reduced states of the redox sites in the polymer (mixed valent form). Electron hopping in redox conductivity is obviously also peculiar to polymers whose sites comprise spatially localized electronic states. 

In the area of ion sensing, cation recognition by electrodes containing functionalized redox-active polymers has been an area of considerable interest. Fabre and co-workers have reported the development of a boronate-functionalized polypyrrole as a fluoride anion-responsive electroactive polymer film. The electropolymerizable polypyrrole precursor (11) (Fig. 11) was synthesized by the hydroboration reaction of l-(phenylsulfonyl)-3-vinylpyrrole with diisopinocampheylborane followed by treatment with pinacol and the deprotection of the pyrrole ring.33 The same methodology was utilized for the production of several electropolymerizable aromatic compounds (of pyrrole (12) (Fig. 11), thiophene (13 and 14) (Fig. 11), and aniline) bearing boronic acid and boronate substituents as precursors of fluoride- and/or chloride-responsive conjugated polymer.34... 

In the last 30 years considerable progress has been made in the development of tailor-made electrode surfaces by chemical modification [4-12] of electrodes surfaces with electroactive polymer films. A comprehensive description of electroactive polymer-modified electrodes can be found in the book edited by M. Lyons [13]. 

Scrosati, B., in Solid State Electrochemistry (Ed. P.G. Bruce), Cambridge University Press, Cambridge, 1995, Chapter 9 for latest status, see Electrochim. Acta 1999, 44, 1845-2163 (a special issue for electroactive polymer films). 

Visualizing Ion and Solvent Transfer Processes in Electroactive Polymer Films... 

The modification of electrode surfaces with electroactive polymer films provides a means to control interfacial characteristics. With such a capability, one can envisage numerous possible applications, in areas as diverse as electronic devices, sensors, electrocatalysis, energy conversion and storage, electronic displays, and reference electrode systems [1, 2]. With these applications in view, a wide variety of electroactive polymeric materials have been investigated. These include both redox polymers (by which we imply polymers with discrete redox entities distributed along the polymer spine) and conducting polymers (by which we imply polymers with delocalised charge centres on the polymer spine). 

Visualizing Ion and solvent transfer processes In electroactive polymer films Ch. 13... 

Our goal is to develop a method for visualizing extremely complicated electroactive polymer film redox switching mechanisms. To exemplify the problem and our proposed solution, we discuss the mechanisms of two... 

The electrochemical quartz crystal microbalance is a versatile technique for studying several aspects of electroactive polymer film dynamics. For rigid films, it is a sensitive probe of mobile species (ion and solvent) population changes within the film in response to redox switching. For non-rigid films, it can be used to determine film shear moduli. In the former case, one simply follows changes in crystal resonant frequency. In the latter case, the frequency dependence of resonator admittance in the... 

We conclude that the scheme of cubes is well suited to explaining and visualizing a range of electroactive polymer film characteristics, notably those associated with break-in", overpotential, electrode history and experimental time scale phenomena. This approach should be of particular value when using non-electrochemical population probes in conjunction with electrochemical control functions. 

Sturm H, Geuss M, Schulz E (1999) Scanning force microscopy investigations on electroactive polymer films. In Kosta AA (ed) Tenth International Symposium on Electrets (ISE10). IEEE, Piscataway, p 465... 

In the case of a large - pseudocapacitance, e.g., an - electroactive polymer film on the surface, the currenttime decay reflect the - diffusion rate of the -> charge carriers through the surface layer, thus shorter times the decay of the current should conform to the Cottrell equation. At long times, when (Dt)1/2 > L, where L is the film thickness, the concentration within surface film impacts on the film-solution boundary, the chronoam-perometric current will be less than that predicted by the Cottrell equation, and a finite diffusion relationship... 

It has been shown that electroactive polymer films on electrodes can mediate electron transfer for metal deposition (9-11). Haushalter and Krause (5) have described the treatment of PMDA-ODA films with highly reactive Zintl complexes (e.g., Sn9 4, SnTe4 4) to yield an intercalated material able to reduce ions of platinum, palladium and silver at the film surface. Mazur et al., (12) reported the deposition of conductive Ag, Cu, and Au metal interlayers within a PMDA-ODA film by electrochemical reduction. 

One of the more important aspects of complexes of the type cw-[Os(bipy)2(L2)] + (L = vinylpyridine) is then-use as derivatives to form electroactive polymer films. Thus polypyridine films containing redox-active Os centers can be generated by electropolymerization of the coordinated vinylpyridine ligands of the parent complex from homogeneous solution. Importantly, these polypyridyl films contain redox-active Os fragments at each unit. 

Electrocatalysis is a type of electrosynthesis that uses surface modified electrodes, or mediators/electrocatalysts to facilitate the redox reaction. Meyer reported the design and synthesis of a chemically modified electrode that consists of a thin polymer film with covalently attached redox sites,designed to facilitate rapid electron transport for electrocatalysis. Complexes of Fe, Ru, Os, Re, and Co were synthesized in such a way that when electrochemically reduced, they reacted to form smooth electroactive polymer films that adhered well to the working electrode to form a chemically modified electrode designed for electrocatalysis. 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 4, number 11). After oxidative dimerization the TMS ether can be mildly hydrolyzed (H and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 4, numbers 9, 12, and 13). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [60]. Dibenzo-crown ethers are converted by anodic oxidation to electroactive polymers. Films of these polytriphenylenes exhibit unusual doping properties 62-64]. 

Under current investigation are the synthesis and properties of multimetallic thin films containing Ru, Os1, and Re1 in a wide variety of coordination environments. Judicious choice of such materials may lead to creation of an electroactive polymer film which would exhibit a bandlike spectrum of reversible, metal-centered redox processes extending from ca. -0.6 to +1.5 V. 

These results indicate that the structure of electroactive polymer films and the oxidation state of the metal center can be obtained at relatively low coverages, and this should have important implications in trying to identify the structure of reactive intermediates in electrocatalytic reactions at chemically modified electrodes. 

Osmium and ruthenium polypyridine complexes initially received much attention from Dwyer and coworkers because the M(II), M(III), and M(IV) oxidation states are substitution inert.Interest in them has been renewed because of their photochemical reactions and the role they play in the study of reactions of coordinated ligands " and of mixed valence ions and in the preparation of electroactive polymer films. The aqua complexes " also have important potential applications in the selective oxidation of organic molecules and water. We found that trifluoromethanesulfonato (triflato) complexes are convenient synthetic intermediates in the preparation of aqua and oxo species, " and we describe the syntheses of the cii-bis(2,2 -bipyridine) complexes here. 

PEC catalysis using polymeric assistance is considered to be a natural outgrowth of polymer assisted electrochemical and photochemical catalysis. Early experiments, mostly combining electroactive polymer films with small band gap semiconductors have demonstrated the feasibility of using such systems in the PEC decomposition of water. Both gaseous H2 and O2 have been separately generated from polymer coated photoelectrodes H2 from poly-Mv2+ films on p-Si and O2 from polypyrrole films on n-CdS. 

Peerce, P. J., Bard, A. J. (1980). Polymer films on electrodes m. Digital simulation model for cyclic voltammetry of electroactive polymer film and electrochemistry of poly(vinylferrocene) on platinum. J Electroanal Chem 114, 89-115. 

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