Polyvinylferrocene PVF

The chemical stability and electrochemical reversibility of PVF films makes them potentially useful in a variety of applications. These include electrocatalysis of organic reductions [20] and oxidations [21], sensors [22], secondary batteries [23], electrochemical diodes [24] and non-aqueous reference electrodes [25]. These same characteristics also make PVF attractive as a model system for mechanistic studies. Classical electrochemical methods, such as voltammetry [26-28] chronoamperometry [26], chronopotentiometry [27], and electrochemical impedance [29], and in situ methods, such as spectroelectrochemistry [30], the SECM [26] and the EQCM [31-38] have been employed to this end. Of particular relevance here are the insights they have provided on anion exchange [31, 32], permselectivity [32, 33] and the kinetics of ion and solvent transfer [34- 

One general observation from these studies, upon which our present studies shed light, is that mobile species movement can be markedly dependent upon film history [37, 38]. 

Thin films of PVF exposed to non-swelling solvents are anticipated to behave as rigidly coupled masses, so that the Sauerbrey equation (equation (13.1)) accurately describes the EQCM responses. However, experimental conditions may not always conform to this situation. For example, an early EQCM study of PVF electroprecipitation yielded film mass data that were not consistent with coulometric assay of the film [39] non-rigidity of PVF films in the CH2C12 deposition solution was suggested. Also, Oyama et al. have studied thermoresponsive N-isopropylacrylamide-vinylferrocene copolymers [40] and found them to exhibit potential dependent viscoelastic characteristics. In the light of these observations, we use the crystal impedance technique (illustrated schematically in Fig. 13.1) to guide our study of PVF films. 

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Ferrocene-based Linear Polymers. The first derivative that was studied from the electrochemical point of view was polyvinylferrocene (PVF). As illustrated in Figure 25, it displays a single oxidation process, which in some solvents is affected by problems of adsorption of the oxidation product (though not of the ideal Langmuir isotherm type discussed in Chapter 2, Section 1.6). 

Figure 13.8 Curve A Cyclic voltammogram of polyvinylferrocene (PVF) on gold in 0.1 M KPF6. Scan rate 10 mV s1. Curve B EQCM frequency curve obtained simultaneously with Curve A. [From Ref. 84.]...

Adsorption. Adsorption can be reversible or irreversible. This method has been used particularly for the preparation of polymer-modified electrodes. A solution of polymer is either painted on the electrode and the solvent evaporated, or the electrode is immersed in a solution of the polymer. Relevant examples are polymers that let charge pass through the film polyvinylpyridine (PVP), polyvinylferrocene (PVF), porphyrins, and phthalocyanines. Direct deposition in the gas phase or sputtering are also possible. 

The direct formation of polymer films on electrode surfaces from their monomeric constituents is an attractive method for the preparation of PMEs. One such method is the polymerization of vinyl monomers from the gas phase using a radiofrequency plasma discharge. However note that polyvinylferrocene (PVF) films formed by plasma polymerization have been found to be cross-linked to a greater degree than electrodeposited PVF films, thus limiting penetration of electrolyte ions. ... 

Polyvinylferrocene (PVF) has been shown to be stable and reversible when deposited as uniform spin-coated films. In our laboratory and others, the oxidation process in PVF is nearly Nernstian in character. In a previous section, it was shown that a Nernstian response would be expected for ion insertion in inorganic or polymeric systems which obey a lattice gas model. In the present section, however, attention is on the behaviour of an electroactive film at a fixed injected species composition, as the concentration of... 

Polyvinylferrocene has been studied as a model system in our laboratory [83] and others [51-52, 64, 84-85]. Electrodeposited PVF has inferior stability as compared with spin coated material and the latter has been observed to behave reversibly over many cycles and for many days [83]. 

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