Anodically electropolymerized polypyrrole

Oxide, flouride, and polymeric films, as well as certain others, are used as protective coatings for HTSC materials (for example, see [505]). The electrodeposition of conducting polymers such as polypyrrole [433,491, 493, 506], polythiophene and its derivatives [493, 507], and polyaniline [478] is the most effective process. Anodic electropolymerization in acetonitrile solutions proceeds without any degradation of the HTSC substrate and ensures continuous and uniform coatings. Apparently, this method is promising not only for the fabrication of compositions with special properties based on HTSC [50, 28,295] as mentioned above, but also for the creation of junctions with special characteristics [507]. 

Poly(l-vinylimidazole)i2-[Os-(4,4 -dimethyl-2,2-bipyridyl)2Cl2] and poly(vi-nylpyridine)-[Os-(Ai,Ai -methylated-2,2 -biimidazole)3] were reported for their efficient capability of mediating electrons transfer between bacterial cells to electrodes. With S. oneidensis, the osmium redox polymer modified anode showed a 4-fold increase in current generation and a significant decrease in the start-up time for electrocatalysis. Using an anode modified with electropolymerized polypyrrole, a dramatie improvement in energy output was noticed in the MFCs. MFCs with a polypyrrole/ anthraquinone-2,6-disulfonic disodium salt (PPy/AQDS)-modified anode... 

Kudoh, Y, et al. 1996. Covering anodized aluminum with electropolymerized polypyrrole via manganese oxide layer and application to solid electrolytic capacitor. / Power Source 60 157. 

Rectifying bilayer electrodes with sequential bilayer structures are prepared from any pair of 3-butylPT/polypyrrole and 3-bromoPT/polypyrrole by anodic electropolymerization on platinum electrodes [130]. 

In 1979, Diaz et al. produced the first flexible, stable polypyrrole (PPy) film with high conductivity (1(X) Scm ). The substance was polymerized on a Pt-electrode by anodic oxidation in acetonitrile. The then known chemical methods of synthesis " usually produced low conductivity powders from the monomers. By contrast, electropolymerization in organic solvents formed smooth and manageable films of good conductivity. Thus, this technique soon gained general currency, stimulating further electropolymerization experiments with other monomers. In 1982, Tourillon... 

A molecularly imprinted polypyrrole film coating a quartz resonator of a QCM transducer was used for determination of sodium dodecyl sulphate (SDS) [147], Preparation of this film involved galvanostatic polymerization of pyrrole, in the presence of SDS, on the platinum-film-sputtered electrode of a quartz resonator. Typically, a 1-mA current was passed for 1 min through the solution, which was 0.1 mM in pyrrole, 1 mM in SDS and 0.1 M in the TRIS buffer (pH = 9.0). A carbon rod and the Pt-film electrode was used as the cathode and anode, respectively. The SDS template was then removed by rinsing the MlP-film coated Pt electrode with water. The chemosensor response was measured in a differential flow mode, at a flow rate of 1.2 mL min-1, with the TRIS buffer (pH = 9.0) as the reference solution. This response was affected by electropolymerization parameters, such as solution pH, electropolymerization time and monomer concentration. Apparently, electropolymerization of pyrrole at pH = 9.0 resulted in an MIP film featuring high sensitivity of 283.78 Hz per log(conc.) and a very wide linear concentration range of 10 pM to 0.1 mM SDS. 

It has been mentioned already that polypyrrole (25) and polythiophene (26) play an important role as electrical conductors and polymeric anodes in battery cells [2,47,226]. Since the charging and discharging of the conjugated polymer is accompanied by the incorporation and removal of counterions it is clear that the material can also act as a carrier of chemically different anions which influence the physical, chemical and physiological properties of the material [292]. With regard to the full structural elucidation of the polymers it must be added, however, that the electropolymerization process of pyrrole and thiophene does not provide a clean coupling of the heterocycles in the 2,5-positions. Instead, the 3- and 4-position can also be involved giving rise to further fusion processes under formation of complex polycyclic structures [47]. 

Pyrrole electropolymerization on noninert metallic substrates has been specially optimized for aluminum [33,34] and stainless steel [35,36]. In the case of aluminum electrodes, highly conductive polypyrrole films are obtained from solutions of t-butylammonium p-toluenesulfonate in acetonitrile [37]. Their conductivities range between 10 and 350 S cm", as a function of the electrical and chemical variables of synthesis. On stainless steel, highly conductive polypyrrole films can be obtained by means of square waves of potential [36]. In this case, charging of the electrical double layers, oxidation of pyrrole molecules, and formation of a porous oxide layer occur during the application of the anodic step and promote the polymerization process. The application of the cathodic potential seems to avoid corrosion... 

The possibility of electrochemical oxidation of the ion beam-produced carbonaceous layer at the surface of the conducting polymers (polyaniline, polypyrrole, polythiophene) was also demonstrated [99,100,112]. In this case the anodic oxidation and dissolution of the implanted layer result in regeneration of the electrode surface, accompanied by a substantial increase of the electrochemical activity [99,100,112]. On the other hand, an increase of the surface resistance of the conducting polymers by several orders of magnitude upon implantation with low doses (<10 ions cm [99]), originating in the destruction of the initial rr-electron system, leads to passivation of the polymer electrodes with respect to further electropolymerization [112] and galvanic deposition of metals [99,1(K)]. In particular, this offers the possibility of metal pattern formation with a resolution of several micrometers at the surface of the conducting polymers [99,1(K)]. 

Among all of the methods of synthesis to produce polypyrrole, the electrochemical procedure is one of the most useful procedures to obtain polypyrroles with high conductivities. The general details are similar to other conducting polymers such as poly(p-phenylene) or polythiophene. The experimental requirements are not difficult, because it is possible to work in aqueous solution at ambient pressure and temperature. The main problem is related to the difficulty in producing large amounts of polypyrrole due to the limitations imposed by the size of the anode. Second, even the most simple electrochemical process of pynole electropolymerization involves different experimental variables in order to optimize polymer properties. These variables can be chemical, such as solvent, monomer concentration, and salt concentration, or physical, such as temperature, nature and shape of the electrodes, cell geometry, or electrical conditions. Commonly, all of these variables are interdependent. 

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