Poly redox cycle

During continuous redox cycling, the first cycle usually differs from the following ones. This effect is referred as break-in. In poly(vinylferrocene), PVF, films this has been related to the incorporation of solvent and ions into the film, decreasing its resistivity [132]. This effect has been observed for several polyelectrolyte and polymer-modified electrodes, for example, polyaniline [155]. 

Fig. 7.2 The redox cycling of poly(pyrrole) involving intercalation and expulsion of (a) the anion or (b) the cation from the electrolyte to effect charge balance.

Our published studies [18, 19] of poly(thionine) redox switching showed that, in acetic acid buffer, the leuco (reduced) form (L) is oxidized, losing two electrons and two protons, to generate the oxidised form (7 ). Furthermore, acetic acid is coordinated only to the 7-form so that reduction causes 7 to lose an acetic acid molecule. However, reduction of 7 to L follows a different path than the reverse of the oxidation path. Water transfer is also involved in the redox cycle. We can (in simplified form) write the overall redox switching process as ... 

Fig. 13.6. Cube representing the poly(thionine) redox mechanism. Shaded (white) circles at the corners of the cube indicate species that are (are not) accessed in the redox cycle.

Fig. 13.9. EQCM data obtained during the "break-in" of a poly(vinylferrocene) film (T = 23.7 nmol cm 2). Frames a and b, respectively, correspond to the current- and mass change-potential curves for the first two redox cycles in aqueous 0.1 mol dm-- NaCI04 immediately following deposition from CH.CI ,. In frame a, the current (electron flux) was converted to the equivalent mass flux of counter ions, for subsequent correlation with the total (observed) gravimetric response of frame b. Potential scan rate 5mVs l. The star symbol denotes the first anodic scan responses. (Adapted from Ref. [37] with permission.)...

Fig. 13.16. Redox cycling of a broken-in poly(vinylferrocene) film on short time scales. Reconfiguration is assumed faster than (de-)soivation in the lower cube.

Redox cycling of poly(thionine) films in aqueous acetic acid solution involves not only electron transfer (coupled with proton transfer to maintain electroneutrality), but also film solvation and acetic acid coordination... 

Redox cycling of poly(vinylferrocene) films involves not only coupled electron/anion transfer, but also solvation and polymer configuration changes. The situation is further complicated by both reversible and irreversible elements of solvation and configuration changes, commonly referred to as break-in", immediately following deposition. Here, a dou-... 

The use of the ETSM to study polymeric systems, especially redox and conducting polymers, is a rapidly growing area of research. It has been used to elucidate die mechanisms of film formation, ion and solvent transport phenmnena, and compositional changes that occur in these films upon redox cycling. Among the redox polymer systems that have been studied are poly(vinylferrocene)... 

NQOl is a homodimer with a flavodoxin fold (5). This enzyme does not stabilize the semiquinone state. The obligate two-electron transfer mechanism prevents the generation of quinone radicals and redox cycling, which would result in oxidative stress. The NADPH and quinone substrates occupy the same site, consistent with the observed ping-pong bi-bi mechanism. NQOl is inhibited by many (poly)aromatic compounds including the anticoagulant dicoumarol and the phytoalexin resveratrol (5). 

Fig. 18 Current, beam deflection, and frequency change responses (panels (a-c), respectively) of a poly(l-hydroxyphenazine) film to a redox cycle under cyclic voltammetric conditions. Electrodes glassy carbon (probe beam experiment) and Au (area = 0.36 cm ) on 5-MHz AT-cut quartz crystals (QCM experiment). Solution 1 mol dm HCIO4. Potential scan rate 50 mV s (Reproduced from Ref. [122] with permission from Elsevier.)...

Borjas, R., and D.A. Buttry. 1991. EQCM studies of film growth, redox cycling, and charge trapping of n-doped and p-doped poly(thiophene). Chem Mater 3 872. 

Polythiophenes present a multitude of color contrasts. These polymers, with a functional group terminal to a flexible alkyl chain at the 3-position of the ring, are used for many specialized applications. One such candidate of this class is poly(3-[12-(/7-methoxyphenoxy)dodecyl]thiophene [poly(12-MPDDT)], synthesized by Ribeiro et al., which exhibited a deposition charge of ca. 65 mCcm" presented greater stability over a large number of redox cycles (> 1000), a chromatic contrast of 40 % at 725 nm, a Coulombic efficiency of 80 % and good optical memory in the neutral state (E = 0.0 V) [15]. 

Reynolds et al. subsequently expanded their studies on poly pyrrole-co-(3-(pyrrol-l-yl)propanesulfonate) in order to investigate charge and mass transport during electrochemical redox cycling [30]. Chemical analysis of the copolymers prepared from a 1 1 feed ratio of monomers provided the composition shown in Figure... 

Poly(vinylbenzyl mercaptan) has been described by several authors. The synthesis always follows the same path chloromethylation of polystyrene followed by reaction with thiourea and hydrolysis of the isothiuronium salt 1,53,55,63-65). The redox properties of a polymer obtained from chloromethylated styrene-divinylbenzene copolymers have been evaluated (3). Redox capacities givrai for mercaptyl resins were determined to be 2. W>-5.27 milliequivalents of iodine reduced per gram of (dry) resin in aqueous potassium iodide. The oxidized form of the resin could be easily reduced with 10% aqueous bisulfite fmr a complete redox cycle. Recently polyvinylbenzyl mercaptan resins were prepared directly by treating chloromethylat polystyrene with KSH in dimethyl formamide (66). 

Poly(isothianaphthene) films on semitransparent gold electrodes can retain about 75% of their initial optical density after 6 x 10 cycles [180]. The conditions of the electrosynthesis are important for the electrochromic properties under many repeated redox cycles [181]. A comparison of different materials brought the result that 3-methylPT is a better material for electrochromic applications than... 

The inner structure of polyelectrolyte multilayer films has been studied by neutron and X-ray reflectivity experiments by intercalating deuterated PSS into a nondeut-erated PSS/PAH assembly [94, 99]. An important lesson from these experiments is that polyelectrolytes in PEMs do not present well-defined layers but are rather interpenetrated or fussy systems. As a consequence, polyelectrolyte chains deposited in an adsorption step are intertwined with those deposited in the three or four previous adsorption cycles. When polyelectrolyte mobility is increased by immersion in NaCl 0.8 M, the interpenetration increases with time as the system evolves towards a fully mixed state in order to maximize its entropy ]100]. From the point of view of redox PEMs, polyelectrolyte interpenetration is advantageous in the sense that two layers of a redox polyelectrolyte can be in electrochemical contact even if they are separated by one or more layers of an electroinactive poly ion. For example, electrical connectivity between a layer of a redox polymer and the electrode is maintained even when separated by up to 2.5 insulating bUayers [67, 101-103]. 

ZnO displays similar redox and alloying chemistry to the tin oxides on Li insertion [353]. Therefore, it may be an interesting network modifier for tin oxides. Also, ZnSnOs was proposed as a new anode material for lithium-ion batteries [354]. It was prepared as the amorphous product by pyrolysis of ZnSn(OH)6. The reversible capacity of the ZnSn03 electrode was found to be more than 0.8 Ah/g. Zhao and Cao [356] studied antimony-zinc alloy as a potential material for such batteries. Also, zinc-graphite composite was investigated [357] as a candidate for an electrode in lithium-ion batteries. Zinc parhcles were deposited mainly onto graphite surfaces. Also, zinc-polyaniline batteries were developed [358]. The authors examined the parameters that affect the life cycle of such batteries. They found that Zn passivahon is the main factor of the life cycle of zinc-polyaniline batteries. In recent times [359], zinc-poly(anihne-co-o-aminophenol) rechargeable battery was also studied. Other types of batteries based on zinc were of some interest [360]. 

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