Electron polyaniline

A second type of soHd ionic conductors based around polyether compounds such as poly(ethylene oxide) [25322-68-3] (PEO) has been discovered (24) and characterized. These materials foUow equations 23—31 as opposed to the electronically conducting polyacetylene [26571-64-2] and polyaniline type materials. The polyethers can complex and stabilize lithium ions in organic media. They also dissolve salts such as LiClO to produce conducting soHd solutions. The use of these materials in rechargeable lithium batteries has been proposed (25). 

Polyanilines. Initial preparations of polyaniline (PANI) led to insoluble materials that were difficult to characterize. Use of model compounds and polymers (124,125) allowed for definitive stmctural analysis. Poly( phenylene amineimine) (PPAI) was synthesized directiy to demonstrate that PANI is purely para-linked (126). The synthesis was designed so as to allow linkage through the nitrogen atoms only (eq. 9). Comparison of the properties of PPAI and PANI showed PPAI to be an excellent model both stmcturaHy and electronically. 

Conducting Polymers Electronically conducting polymers (such as polypyrrole, polythiophene, and polyaniline) have attracted considerable attention due to their ability to switch reversibly between the positively charged conductive state and a neutral, essentially insulating, form and to incorporate and expel anionic species (from and to the surrounding solution), upon oxidation or reduction ... 

FIGURE 4-19 Scanning electron micrograph of a polyaniline-coated electrode. 

In situ gravimetry on polyaniline has revealed a complicated dependence of solvent content and transport of the solvent (aqueous or nonaqueous) on pH.187 Two to three water molecules per electron can be inserted during oxidation in strongly acid solutions, while in propylene carbonate, less than one solvent molecule is involved. Propylene carbonate is first ejected from the film during oxidation, then inserted, and finally ejected again in the final stages. 

Nucleation models have also been invoked for the oxidation of polyaniline films.209,213 In both cases, the nucleation of electronically conductive zones was assumed, following Aoki s well-documented model. The possibility that the nucleation of ionically conductive regions could be rate limiting does not appear to have been considered. 

Another convenient way to disperse platinum-based electrocatalysts is to use electron-conducting polymers, such as polyaniline (PAni) or polypyrrole (PPy), which play the role of a three-dimensional electrode.In such a way very dispersed electrocatalysts are obtained, with particle sizes on the order of a few nanometers, leading to a very high activity for the oxidation of methanol (Fig. 10). 

In the case of polyaniline (see Fig. 26.4), the situation is more complicated, since polymerization occurs across the basic nitrogen atom, the electron state of which depends on pH. Thus, doping is possible not only by oxidation but also by a pH change conduction of the material rises by 9 to 10 orders of magnitude between pH 5 and 1 ( 1M aqueous HCl). 

In view of the complexity of the material, it is difficult to unequivocally assign a particular mechanism for electronic conduction in the polymer, although some evidence exists to suggest that it involves three-dimensional variable-range hopping as found for other polymers [213], It has also been suggested that the conductivity of polyaniline is a combination of both ionic and electronic conductivity [207], and is... 

Electronically conducting polymers (ECPs) such as polyaniline (PANI), polypyrrole (PPy) and po 1 y(3.4-cthy 1 cncdi oxyth iophcnc) (PEDOT) have been applied in supercapacitors, due to their excellent electrochemical properties and lower cost than other ECPs. We demonstrated that multi-walled carbon nanotubes (CNTs) prepared by catalytic decomposition of acetylene in a solid solution are very effective conductivity additives in composite materials based on ECPs. In this paper, we show that a successful application of ECPs in supercapacitor technologies could be possible only in an asymmetric configuration, i.e. with electrodes of different nature. 

Polyaniline (PANI) was investigated as electrocatalyst for the oxygen reduction reaction in the acidic and neutral solutions. Galvanostatic discharge tests and cyclic voltammetry of catalytic electrodes based on polyaniline in oxygen-saturated electrolytes indicate that polyaniline catalyzes two-electron reduction of molecular oxygen to H2O2 and HO2". 

As our quantum-chemical calculations show, similar transformation and delocalization of bonds takes place in the conductive forms of some other types of CPs (polyaniline, polypyrolle, etc.). Delocalization of chemical bonds after activation leads to appearance of an electronic conductivity in such types of conducting polymers and creates prerequisites for their application as electrode materials of electrochemical power sources. Such activation can be stimulated by intercalation of ions, applying the potential, and by use of some other low energetic factors. 

Also the case of polyaniline is somewhat different from that of heterocyclic polymers. It has been proposed (MacDiarmid and Maxfield, 1987) that the doping process does not induce changes in the number of electrons associated with the polymer chain but that the high conductivity of the emeraldine salt polymers is related to a highly symmetrical 7r-delocalized structure. 

The benefit of a hybrid phase for the intercalation-deintercalation of mobile species such as Li+ cations is well illustrated by the study of conductive polymers such as polyaniline or polypyrrole intercalated into a V2O5 framework as potential electrode materials in lithium batteries [34]. For PANI/V2O5, an oxidative post-treatment performed under an oxygen atmosphere allowed the authors to compare the conductivity attributed to the polymer, as in absence of reduced cations, there was no electronic hopping between ions, and the conductive state was due only to the... 

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