Electrochemical polymerization applications

Empirical kinetics are useful if they allow us to develop chemical models of interfacial reactions from which we can design experimental conditions of synthesis to obtain thick films of conducting polymers having properties tailored for specific applications. Even when those properties are electrochemical, the coated electrode has to be extracted from the solution of synthesis, rinsed, and then immersed in a new solution in which the electrochemical properties are studied. So only the polymer attached to the electrode after it is rinsed is useful for applications. Only this polymer has to be considered as the final product of the electrochemical reaction of synthesis from the point of view of polymeric applications. 

The historical development of chemically electrodes is briefly outlined. Following recent trends, the manufacturing of modified electrodes is reviewed with emphasis on the more recent methods of electrochemical polymerization and on new ion exchanging materials. Surface derivatized electrodes are not treated in detail. The catalysis of electrochemical reactions is treated from the view of theory and of practical application. Promising experimental results are given in detail. Finally, recent advances of chemically modified electrodes in sensor techniques and in the construction of molecular electronics are given. 

Parent (unsubstituted) PF was first synthesized electrochemically by anodic oxidation of fluorene in 1985 [266] and electrochemical polymerization of various 9-substituted fluorenes was studied in detail later [220,267]. Cyclic voltammogram of fluorene ( r1ed= 1.33 V, Eox = 1.75 V vs. Ag/Ag+ in acetonitrile [267]) with repetitive scanning between 0 and 1.35 V showed the growth of electroactive PF film on the electrode with an onset of the p-doping process at 0.5 V (vs. Ag/Ag+). The unsubstituted PF was an insoluble and infusible material and was only studied as a possible material for modification of electrochemical electrodes. For this reason, it is of little interest for electronic or optical applications, limiting the discussion below to the chemically prepared 9-substituted PFs. 

The mechanism of the polymerization was discussed based on electrochemical measurements. Applications of the electro-oxidative polymerization were also described. 

Comparable to thiophene, pyrrole is a five-membered heterocycle, yet the ring nitrogen results in a molecule with distinctly different behavior and a far greater tendency to polymerize oxidatively. The first report of the synthesis of polypyrrole (PPy) 62 that alluded to its electrically conductive nature was published in 1968 [263]. This early material was obtained via electrochemical polymerization and was carried out in 0.1 N sulfuric acid to produce a black film. Since then, a number of improvements, which have resulted from in-depth solvent and electrolyte studies, have made the electrochemical synthesis of PPy the most widely employed method [264-266]. The properties of electrosynthesized PPy are quite sensitive to the electrochemical environment in which it is obtained. The use of various electrolytes yield materials with pronounced differences in conductivity, film morphology, and overall performance [267-270]. Furthermore, the water solubility of pyrrole allows aqueous electrochemistry [271], which is of prime importance for biological applications [272]. 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

In this paper we report the electrochemical polymerization of the PPy-GOD film on the glassy carbon (GC) electrode in enzyme solution without other supporting electrolytes and the electrochemical behavior of the synthesized PPy-GOD film electrode. Because the GOD enzyme molecules were doped into the polymer, the film electrode showed a different cyclic voltammetric behavior from that of a polypyrrole film doped with small anions. The film electrode has a good catalytic behavior to glucose, which is dependent on the film thickness and pH. The interesting result observed is that the thin PPy-GOD film electrode shows selectivity to some hydrophilic pharmaceutical drugs which may result in a new analytical application of the enzyme electrode. 

Vinylcarbazole polymers and their CT complexes are widely known for their excellent photoconductive properties [115]. The CT processes in this polymer system have been extensively worked out by the conventional absorption spectroscopic techniques, but the application of the XPS technique to them has been rather limited [116]. For poly(Af-vinylcarbazole) (PVK)/perchlorate complex film synthesized via electrochemical polymerization and oxidation, it was shown that the NIs core-level spectrum exhibits a new high BE component shifted by about + 3.0 eV from the neutral carbazole nitrogen at about 400 eV. This new component was attributed to the positively charged carbazole nitrogen associated with CIO4 anion [117],... 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Zhang, L., and Lian, J. 2008. The electrochemical polymerization of o-phenylencdiaminc on 1-tyrosine functionalized glassy carbon electrode and its application. Journal of Solid State Electrochemistry 12, 757-763. 

Another way to functionalize depositions, is to entrap functional molecules in polypyrrole. Incorporation of functional molecules during electrochemical polymerization and the application of so prepared films to sensors have been studied by many workers (27). By means of area-selective deposition much more complicated functional depositions can be prepared on an electrode. The authors have shown that organic dyes (an example of functional molecules) are incorporated in the process of... 

Since the beginning of the electropolymerizations nitrate salts have not found wide application as supporting electrolytes (see Ref. 7 pp. 606-621). The latest results on the nitrate ion influence on electrochemical polymerizations are reported by Bhadani and Prasad, who have published the results of a research on the polymerization of acrylamide both in DMF and in water, employing sodium nitrate as supporting electrolyte. 

In addition to electrochemical polymerization, reactive monomers can be polymerized onto surfaces by using radio frequency (rf) plasma polymerization [194-197]. In this technique an electric discharge through the vapor forms a reactive plasma that chemically modifies the surface. Examples of applications of rf plasma-polymerized surfaces include the formation of (C2F4) films on fiber optic sensors for detection of volatile organics [198] and the formation of alkylamine surfaces on glass fibers by plasma treatment for subsequent chemical modification [199]. 

Similar to the various pCP techniques described previously, the solutions required for chemical or electrochemical polymerization are generally not compatible with the organic semiconductors of OTETs. As a consequence, the application of these procedures is also limited to the fabrication of bottom-contact devices. 

The heterocycles (13) and (14a) (Table 2) find much application in electrochemical polymerization to prepare electroconductive polymers <89TL1655>. The conductive complexes (239), named 2,6-bis(dicyanomethylene)-2,6-dihydrodithieno[3,2-h 2, 3 -d]thiophene, have been described as potential electron acceptors <89BCJ1547>. 

Two major applications have emerged between 1983 and 1993 the first is the use of tellurophene derivatives for the synthesis of electoconducting polymers, and the second is the thermolysis of organotellurium compounds for the production of thin films of cationic tellurides. Semiconductors derived from 3,4-disubstituted tellurophenes have been patented for photosensors <90JAP(K)0241317>. Electrochemical polymerization of benzo[c]tellurophene derivatives provides useful semiconductors <90JAP(K)02263823>, applicable among other uses, for solar cells <88eup273643>. 

Depending on the application type, the main composites result from three synthesis methods, i.e. mixing of the two constituents, and chemical and electrochemical polymerization, and are summarized in Table 5.1. 

Regarding the application in supercapacitor, the flexible PANI nanotube arrays with high and stable specific capacitances were prepared via electrochemical polymerization. The specific capacitances increased with decreasing wall thicknesses (Wang et al., 2012). A three-dimensionally hierarchical porous PPy hydrogel with various mechanical and electrochemical properties are fabricated by controlling the ratio of phytic acid to pyrrole monomer in the synthetic process. The solid-state supercapacitor showed a weight specific capacitance of 380 F g and areal specific capacitance of 6.4 F cm at a mass load of 20 mg cm(Shi et al., 2014). 

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