Polypyrrole, additives

A similar catalytic activity with a monomeric porphyrin of iridium has been observed when adsorbed on a graphite electrode.381-383 It is believed that the active catalyst on the surface is a dimeric species formed by electrochemical oxidation at the beginning of the cathodic scan, since cofacial bisporphyrins of iridium are known to be efficient electrocatalysts for the tetraelectronic reduction of 02. In addition, some polymeric porphyrin coatings on electrode surfaces have been also reported to be active electroactive catalysts for H20 production, especially with adequately thick films or with a polypyrrole matrix.384-387... 

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. 

The work of Christensen and Hamnett (1991) provided the first positive evidence for bipolarons and showed, for the first time, that the oxidation of polypyrrole was accompanied by a dramatic decrease in the film thickness, linking this with the generation of these carriers. Taken in addition to all the work discussed above their work provided some of the final pieces in a workable theory of the conduction mechanism in polypyrrole. 

Electrochemical communication between electrode-bound enzyme and an electrode was confirmed by such electrochemical characterizations as differential pulse voltammetxy. As shown in Fig. 11, reversible electron transfer of molecularly interfaced FDH was confirmed by differential pulse voltammetry. The electrochemical characteristics of the polypyrrole interfaced FDH electrode were compared with those of the FDH electrode. The important difference between the electrochemical activities of these two electrodes is as follows by the employment of a conductive PP interface, the redox potential of FDH shifted slightly as compared to the redox potential of PQQ, which prosthetic group of FDH and the electrode shuttling between the prosthetic group of FDH and the electrode through the PP interface. In addition, the anodic and cathodic peak shapes and peak currents of PP/FDH/Pt electrode were identical, which suggests reversibility of the electron transport process. 

A microsensor system for simultaneous amperometric determination of H2O2 and 02 consists of two working electrodes, one Pt counterelectrode and one WO3 reference electrode. The working electrodes are GCE covered with HRP immobilized in an elec-trodeposited membrane of polypyrrole the working electrode for 02 has in addition a layer of immobilized superoxide dismutase. Operation with this system is at pH 5.1, setting both working electrodes at —60 mV. Other operating modes are also possible. ... 

Polypyrrole/poly(ethylene-co-vinyl acetate) conducting composites with improved mechanical properties were prepared by a similar method [167], In addition, polyaniline/polystyrene [168] and polyaniline/poly(alkyl methacrylate) [169] composites have been synthesised. A solution of persulphate in aqueous HC1 was added to an o/w HIPE of polymer and aniline in an organic solvent, dispersed in aqueous SDS solution, causing aniline polymerisation. Films were processed by hot- or cold-pressing. 

Solid-state ion sensors with conducting polymers as sensing membranes have also proved useful in some applications. Of particular importance are the pH sensors based on polyaniline that can be also applied in non-aqueous solutions. Polypyrrole-based sensors for nitrate also show great promise for water analysis. However, in addition to these two excellent examples, a large number of functionalized conducting polymers have been synthesized already, and these materials may offer unique possibilities for fabrication of durable, miniaturized ion sensors. 

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. 

Additional improvements can be achieved through the use of multilayers (based on different overlaid films). Such combination of the properties of different films has been documented with bilayers of Nation/CA (14) and Nafion/collagen (29). The former allows selective measurements of the neurotransmitter dopamine in the presence of the slightly larger epinephrine and the anionic ascorbic acid (Figure 5). In addition to bilayers, mixed (composite) films, such as PVP/CA (75) or polypyrrole/Eastman Kodak AQ (30) layers can offer additional permselectivity advantages, such composites exhibit properties superior to those of their individual components. Also promising are sensor arrays, based on electrodes coated with... 

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