Doped polypyrrole

Figure 13. (a) Substituted polypyrrole, (b) self-doped polypyrrole, (c) heteroaromatic polymer showing the monomer unit, (d) composite polypyrrole-polyelectrolyte, and (e) hybrid material. (Polyaniline macroion photo supplied by Gomez-Romero and M. Lira.)... 

From an analysis of data for polypyrrole, Albery and Mount concluded that the high-frequency semicircle was indeed due to the electron-transfer resistance.203 We have confirmed this using a polystyrene sulfonate-doped polypyrrole with known ion and electron-transport resistances.145 The charge-transfer resistance was found to decrease exponentially with increasing potential, in parallel with the decreasing electronic resistance. The slope of 60 mV/decade indicates a Nemstian response at low doping levels. 

As expected, the impedance responses obtained in practice do not fully match that of the model of Fig. 9.13. However, as shown by the typical case of Fig. 9.14 which illustrates the response obtained for a 5 mol% ClO -doped polypyrrole electrode in contact with a LiC104-propylene carbonate solution (Panero et al, 1989), the trend is still reasonably close enough to the idealised one to allow (possibly with the help of fitting programmes) the determination of the relevant kinetics parameters, such as the charge transfer resistance, the double-layer capacitance and the diffusion coefficient. 

Fig. 9.14 The ac impedance response of a Q04-doped polypyrrole electrode over a frequency range extending from 0.006 Hz to 6.5 kHz.

Another problem still to be solved in polymer batteries is the self-discharge of the polymer electrode in common electrolyte media. Effectively, the majority of the polymer electrodes show a poor charge retention in organic electrolytes. In situ spectroscopic measurements (Scrosati et al., 1987) have clearly demonstrated the occurrence of spontaneous undoping processes. A typical example is illustrated in Fig. 9.17 which is related to the change of the absorbance of doped polypyrrole upon contact with the electrolyte. 

The tetraphenylborate ion-doped polypyrrole electrode was sensitive to zinc ions [464, 465], and its sensitivity was dependent on the polymer macrostructure. 

There is no doubt that doped polypyrrole is very much more stable than is polyacetylene, but reports are variable of exactly how stable it is. Street 393) reported that the polymer loses less than 20% of its initial conductivity after one year in air at ambient temperature and Diaz and Kanazawa 589) claimed that the polymer is stable at 100-200 °C, depending on the counter-ion the latter authors also reported that polypyrrole is undoped reversibly by ammonia treatment. Munstedt 590) found that the conductivity of doped polypyrrole was unchanged after 200 days at 80 °C in... 

A polypyrrole-electrolyte-polypyrrole battery has been described 611) but the n-doped polypyrrole is unstable. This can be avoided by using a polypyrrole-polyanion anode, where the charge and discharge depend upon small cations moving into and out of the electrode612). A polythiophene-polythiophene battery has also been described 135). Polyaniline has been studied as a potential battery cathode, for use with an aqueous electrolyte 613,6I4). 

Perhaps the original hope for these polymers was that they would act simultaneously as immobilisation matrix and mediator, facilitating electron transfer between the enzyme and electrode and eliminating the need for either O2 or an additional redox mediator. This did not appear to be the case for polypyrrole, and in fact while a copolymer of pyrrole and a ferrocene modified pyrrole did achieve the mediation (43), the response suggested that far from enhancing the charge transport, the polypyrrole acted as an inert diffusion barrier. Since these early reports, other mediator doped polypyrroles have been reported (44t45) and curiosity about the actual role of polypyrrole or any other electrochemically deposited polymer, has lead to many studies more concerned with the kinetics of the enzyme linked reactions and the film transport properties, than with the achievement of a real biosensor. 

Kapui et al. prepared a novel type of polypyrrole films [168]. The film was impregnated by spherical styrene-methacrylic acid block copolymer micelles with a hydrophobic core of 18 nm and a hydrophilic corona of 100 nm. The properties of the micelle-doped polypyrrole films were investigated by cyclic voltammetry and SECM. It was found that the self-assembled block copolymer micelles in polypyrrole behave as polyanions and the charge compensation by cations has been identified during electrochemical switching of the polymer films. 

Relevant Facts. Microscopic examination of the surface of ionically doped polypyrrol shows a fractal surface. The real surface area can be probed by using organic compounds (e.g., jMiitrophenol) of various sizes and finding, by UV-visible measurements of the change in solution concentration caused... 

First report on a conducting polymer, viz oxidised iodine doped polypyrrole by D.E. Weiss et al., a polyactetylene derivative Development of Thermoplastic Vulcanizates, a new class of thermoplastic elastomers by Gessler, Fisher, Coran and Patel. 

Shimizu et al. used simple rhodium-aqua ions (Rh3+) immobilized onto polymer-modified electrodes to perform the electrochemical reduction of NAD+ [114]. Rh3+ was loaded onto polymeric anion doped-polypyrrole membranes coated on the surface. Electrochemical reduction of NAD+ with immobilized Rh3+ was performed at —0.85 V, where Rh3+ was reduced to Rh+. NADH was produced without detectable formation of NAD-dimers. 

Figure 8 Thickness dependence of total shielding efficiency (SET) of highly conducting polymers (A) stretched heavily iodine doped Tsukamoto polyacetylene, (B) camphor sulfonic acid doped polyaniline cast from m-cresol solvent, (C) PFg doped polypyrrole.

The preferred route to stable conducting polymers is to engineer stability into the monomer unit. Thus, although both neutral and doped polyenes are unstable toward molecular oxygen, doped polypyrrole and... 

Finally, the oxidation of D-glucose at Pt-based electrocatalysts incorporated in polypyrrole [55,56] or in polyaniline [57] was also considered. The first work [55] was carried out in Pt-doped polypyrrole films in a neutral medium (phosphate buffer) in view of biosensor applications. Then the use of Pt-Pd catalysts dispersed in PPy led to higher current densities of glucose oxidation than on pure metal dispersed in PPy. This may be related to the decrease of catalytic poisoning (by adsorbed CO as shown by infrared reflectance spectroscopy [58]), due to the presence of Pd. 

Pandey, P. C. Singh, G. Srivastava, P. K. Electrochemical synthesis of tetraphenylborate doped polypyrrole and its applications in designing a novel zinc and potassium ion sensor. Electroanalysis. 2002, 14, 427-432... 

Balamurugan, A., and Chen, S.-M. 2007. Silicomolybdate doped polypyrrole film modified glassy carbon electrode for electrocatalytic reduction of Cr(VI). Journal of Solid State Electrochemistry 11, 1679-1687. 

To enhance the response of the polypyrrole sensor towards DMMP, acid dopants were added to the polypyrrole structure. The rational for doping polypyrrole was to introduce secondary doping sites for DMMP in the structure. Secondary doping... 

Fig. 26 Sensor response of doped polypyrrole for (a) HCl, (b) NDSA, and (c) ASQA dopants...

Polypyrrole is one of a series of heterocyclic polymers which has attracted much attention due to its characteristic electric and electronic properties. However, there are some problems relating to the physical and material properties associated with its structure. The fundamental structural formulae shown in Fig. 16.5 have been generally proposed for the structures of dedoped and doped polypyrroles, where the aromatic form corresponds to the dedoped state and the quinoid form corresponds to the doped state [9-11]. However, the actual structure appears to be more complicated. At present the exact structure is not known because the polymer is amorphous and insoluble. Consequently, various structures have been proposed for polypyrrole [10]. 

From these calculated results, and the experimental findings that the observed N NMR chemical shift for peak y appears towards a high frequency with respect to that for peak /3, and the fact that the intensity of peak y for doped polypyrrole is larger than that for dedoped polypyrrole, it can be concluded that the major peak y, at —129 ppm, is assigned to the nitrogen... 

I Kapui, RE Gyurcsanyi, G Nagy, K Toth, M Area, E Area. Investigation of styrene-methacrylic acid block copolymer micelle doped polypyrrole films by scanning electrochemical microscopy. J Phys Chem B 102 9934-9939, 1998. 

In the light of the structural data now available, Kohiman el al. [223] have investigated the metallic state of PPy-PFe (and of sulphonate-doped polypyrrole) and compared it with the behaviour of other conducting... 

Highly doped polypyrrole films exhibit shielding levels above 40 dB Irom 300 MHz to 2 GHz [23a,b]. In the case of highly conducting polyaniline, these performances vary between 50 and 150 dB for thiek-nesses lower than 80 pm [23c] as shown in Figure 8.1. 

Figure 8.1. Thickness dependence of total Shielding Efficiency (SE,) of highly conducting polymers measured at 6.5 GHz (from [23c]) sample A stretched heavily iodine doped Tsukamoto polyacetylene (dotted line is obtained by using calculation of Se, with approximated values of a absorption coefficient and n) sample B unstretched heavily iodine doped Tsukamoto polyacetylene sample C camphor sulphonic acid doped polyaniline in m-cresol solvent sample D PFe doped polypyrrole sample E TSO doped polypyrrole Inset comparison of (microwave conductivity), c, and tan 6, Reprinted from ref. 23c with permission. Copyright American Institute of Physics.

Moreover, the metallic nature already observed in the case of polyacetylene [58,59] has been found in other polymers such as camphor sulphonic acid (CSA) doped polyaniline [60] or polypyrrole [61]. In these materials, a negative dielectric constant [53], and a cross-over from the metallic to the non-metallic state between 20 and 50 K has been revealed in the case of polyaniline [62]. Polyorthotoluidine fibres doped with CSA in m cresol exhibit similar behaviour [63-65], PFg doped polypyrrole also exhibits such behaviour and the Drude model has been used for a description of dielectric constant evolution up to the infrared range [66], This model has also been applied to polyaniline [67],... 

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