Polypyrrole redox properties

Two nitrogen-containing electroactive polymers, polypyrrole (PPY) [21] and polyaniline (PAN) [22], have been of particular interest because of their environmental stability, high electrical conductivity and interesting redox properties associated with the chain heteroatoms. More importantly, PAN has been found to exhibit solution processability [23, 24] and partial crystallinity [25,26]. 

The first studies by UV-visible transmission spectroscopy were carried out using an optically transparent electrode (OTE) such as indium oxide [140,141]. Unfortunately an OTE does not allow the nature and the structure of the electrode material to be changed and these play a key role in electrocatalytic processes. Only reflectance spectroscopy is able to investigate in situ, various electrode materials [142], This was effectively checked for the first time with cobalt porphyrin-doped polypyrrole films using the electroreflectance technique [106,143]. This allowed the characterization of the redox properties of the modified PPy electrode and the determination of the redox potential of the Co"VCo" couple. The catalytic effect towards the ORR was also... 

Conducting polymers, for example, polyaniline, polypyrrol, have been extensively investigated taking into account its possible technological applications. From the specific point of view of modified surfaces, it has been shown that, when adsorbed on oxide surfaces such as molybdenum [1], arsenic [2,3], and iron [3] oxides, polyaniUne exerts remarkable effects on their redox properties [4] and/or thermal stabihty of the respective oxides. This chapter presents a brief outline about the achievements on this field of investigation. 

Bedioui, R, C. Bongars, C. Hinnen, C. Bied-Charreton, and J. Devynck (1985). In-situ characterization of redox properties of mes otetrakis (4-carboxyphenyl) porphine cobalt in a polypyrrole film electrode using the electroreflectance technique. Bull. Soc. Chim. Er. 679-682. 

Optimization of Electrical and Redox Properties of Electrogenerated Polypyrroles... 

Momma, T., Kakuda, S., Yarimizu, H., and Osaka, T., Electrochemical redox properties of polypyrrole/Nafion composite film in a solid polymer electrolyte battery, J. Electrochem. Soc., 142, 1766-1769 (1995). 

The redox properties of conducting heterocyclic polymers like polypyrrole are central to many applications of these materials. For this reason the electrochemistry of thin films of these polymers have received a lot of attention. For use in electrically controlled ion binding and delivery, the general idea is that the heterocyclic conducting polymers have cationic backbones and will incorporate counter anions. Upon reduction of the backbone, the anions will be flushed out. Thus, in principle one can develop devices to absorb anions of interest or to release them in response to an electric current. Our work has been spurred by the possibility of delivering drugs with a rate controlled by the current. 

The conjugated polymer complexes composed of polyanilines or polypyrroles are performed to afford the redox systems depending on their structnres and redox properties. As mentioned in the Sect. 3.2, the complexation with copper salts can affect the redox properties of polyanilines to form the reversible redox cycle [17]. The conjugated polymer complex can serve as an oxidation catalyst [18,20,23,24], wherein the coordination of the QD moiety might play an important role in a reversible redox processes of the complexes. Polyanilines or polypyrroles are effectively employed as a redox-active ligand in the Wacker reaction as mentioned in Sect. 3.2. 

Polypyrrole is probably the most common conducting polymer used due to its excellent properties. Pyrrole monomer is commercially available, easily oxidized, water-soluble that conducts to polymers with high electrical conductivity, redox properties and good environmental stability. Over the past three decades polypyrrole has attracted interest for a number of applications including supercapacitor for energy storage and secondary batteries [104], in dye-sensitized solar cells [105]. This polymer has been also used for metal protection [106] and to manufacture patterned arrays of nanoparticles for data storage or biosensors [107]. 

Following the discovery of the unique electronic properties of polypyrrole, numerous polymers of pyrrole have been crafted. A copolymer of pyrrole and pyrrole-3-carboxylic acid is used in a glucose biosensor, and a copolymer of pyrrole and A-methylpyrrole operates as a redox switching device. Self-doping, low-band gap, and photorefractive pyrrole polymers have been synthesized, and some examples are illustrated [1,5]. 

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. 

Scheller et al. reported amperometric pyruvate sensors by potentiostatic co-pol5nmerization of Os(bipy)2pyridineCl-modified pyrrole monomer and thiophene on platinized glassy carbon electrodes on which pyruvate oxidase was adsorbed [78]. This pol5dhiophene based redox pol5uner was reported to have excellent electron transfer properties with significantly improved stability compared with polypyrrole as they are not affected by oxygen [79]. However, notable interference by ascorbate needs to be eliminated. 

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