Electropolymerization electrodes

MWCNTs were functionalized with iron phthalocyanines (FePc) to improve the sensitivity towards hydrogen peroxide. A highly sensitive glucose sensor with an FePc-MWCNT electrode based on the immobilization of GOx on poly(o-amino-phenol) (POAP)-electropolymerized electrode surface [219]. A hemin-modified MWCNT electrode to be used as a novel 02 sensor was obtained by adsorption of hemin at MWCNTs and the electrochemical properties of the electrode were characterized by cyclic voltammetry [220]. 

M thiocyanate solution. The lifetime of these electropolymerized electrodes (at least 2 months) is a significant improvement over that of PVC-based electrodes that use cobalt porphyrins (28, 29). The latter electrodes were selective toward thiocyanate, but the slopes of the calibration curves deteriorated substantially in less than one month. The improved lifetimes of the poly[Co(o-NH2)TPP] electrodes may be attributed to the covalent fixation of the ionophore to the polymeric matrix ... 

Volf, R., T.V. Shishkanova, P. Matejka, M. Hamplava, and V. Krai (1999). Potentio-metric anion response of poly(5,15-bis(2-ammophenyl)porphyrin) electropolymerized electrodes. Anal. Chim. Acta 381,197-205. 

The enzyme can be immobilized on the electrode by several techniques (53). The simplest method, first used in 1962, is to trap an enzyme solution between the electrode surface and a semipermeable membrane. Another technique is to immobilize the enzyme in a polymer gel such as polyacrylamide which is coated on the electrode surface. Very thin-membrane films can be obtained by electropolymerization techniques (49,54,55) using polypyrrole, polyindole, or polyphenylenediamine films, among others. These thin films (qv) offer the advantage of improved diffusion of substrate and product that... 

Entrapment of biochemically reactive molecules into conductive polymer substrates is being used to develop electrochemical biosensors (212). This has proven especially useful for the incorporation of enzymes that retain their specific chemical reactivity. Electropolymerization of pyrrole in an aqueous solution containing glucose oxidase (GO) leads to a polypyrrole in which the GO enzyme is co-deposited with the polymer. These polymer-entrapped GO electrodes have been used as glucose sensors. A direct relationship is seen between the electrode response and the glucose concentration in the solution which was analyzed with a typical measurement taking between 20 to 40 s. 

Flavin adenine dinucleotide (FAD) has been electropolymerized using cyclic voltammetry. Cyclic voltammograms of poly (FAD) modified electrode were demonstrated dramatic anodic current increasing when the electrolyte solution contained NADH compare with the absence of pyridine nucleotide. 

When polypyrrole was electrogenerated from dry acetonitrile electrolytes, a black polymer grew and adhered to the electrode. After a few seconds of electropolymerization, a black cloud was observed around the electrode. The film obtained had poor electrochemical and physical properties. Increasing the water content to 2% (w/w) gives, at 800 mV, films with improved properties. The black cloud around the electrode disappears. 

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... 

Fig. 2. Experimental (a) and simulated (b) voltammograms characterizing the beginning of the electropolymerization of V-phenylcarbazole (CH3NO2, Pt-electrode)...

Despite the vast quantity of data on the chemistry of electropolymerization, relatively little is known about the processes involved in the deposition of polymers on the electrode, i.e. the heterogeneous phase transition. Research — voltammetric... 

Galvanostatic, potentiostatic as well as potentiodynamic techniques can be used to electropolymerize suitable monomeric species and form the corresponding film on the electrode. Provided that the maximum formation potentials for all three techniques are the same, the resulting porperties of the films will be broadly similar. The potentiodynamic experiment in particular provides useful information on the growth rate of conducting polymers. The increase in current with each cycle of a multisweep CV is a direct measure of the increase in the surface of the redoxactive polymer and, hence, a suitable measure of relative growth rates (Fig. 5). 

Electropolymerization is also an attractive method for the preparation of modified electrodes. In this case it is necessary that the forming film is conductive or permeable for supporting electrolyte and substrates. Film formation of nonelectroactive polymers can proceed until diffusion of electroactive species to the electrode surface becomes negligible. Thus, a variety of nonconducting thin films have been obtained by electrochemical oxidation of aromatic phenols and amines Some of these polymers have ligand properties and can be made electroactive by subsequent inincorporation of transition metal ions... 

Vinyl substituted bipyridine complexes of ruthenium 9 and osmium 10 can be electropolymerized directly onto electrode surfaces The polymerization is initiated and controlled by stepping or cycling the electrode potential between positive and negative values and it is more successful when the number of vinyl groups in the complexes is increased, as in 77 A series of new vinyl substituted terpyridinyl ligands have recently been synthesized whose iron, cobalt and ruthenium complexes 72 are also susceptible to electropolymerization... 

The permanent inclusion of solution constituents during the electropolymerization of pyrrole was also used to prepare modified electrodes with cobalt phthalocya-nine and glucose oxidase 122423) examples. Another technique of perhaps... 

Some progress has also been achieved in the use of chiral polymer films at electrodes. Conductive polythiophenes containing optically active substituents in the 3-positions were prepared by electropolymerization of suitable monomers without apparent lc s of optical activity The polymer of exhibits distinct... 

Fig. 2. Curve A Eleotropolymerization of ImH H2(o-NH2)TPP in 0.1M Et NClO /CH CN by sweeping potential at 200mV/s on Pt electrode. Numbers represent scan number. Curve B Cyclic voltammogram of an electropolymerized film of poly-[H2(o-NH2)TPP] on a Pt electrode, in 0.1M Et NClO /CH CN at 200 mV/s. Integration of the charge under the wave shows that coverage is 3.5X10 9 mol/cm of the porphyrin sites. Curve C Rotated disk electrode voltammetry of the Os(lII,Il) reaction for 0.2 mM...

Dloxygen reduction electrocatalysis by metal macrocycles adsorbed on or bound to electrodes has been an Important area of Investigation (23 ) and has achieved a substantial molecular sophistication in terms of structured design of the macrocyclic catalysts (2A). Since there have been few other electrochemical studies of polymeric porphyrin films, we elected to inspect the dloxygen electrocatalytic efficacy of films of electropolymerized cobalt tetraphenylporphyrins. All the films exhibited some activity, to differing extents, with films of the cobalt tetra(o-aminophenylporphyrin) being the most active (2-4). Curiously, this compound, both as a monomer In solution and as an electropolymerized film, also exhibited two electrochemical waves... 

The [Co(terpy)2]+ ion (terpy = 2,2 6, 2"-terpyridine) has been found to catalyze the reduction of C02 when the divalent precursor is immobilized on electrode surfaces. The vinyl-substituted terpy analog was electropolymerized to give a film that reduced the overpotential for C02 reduction in DMF and MeCN by more than 1V.104 The activity of this surface-confined species was superior to that of the complexes in solution.105 Similarly, in water, the [Co(terpy)2]2+ ion immobilized and reduced in situ within a Nafion film also catalyzes the reduction of C02106 and H+ ions.107... 

Polymeric films of [(//5-C s Me5)M(L)Cl]+complexes (M = Ir, Rh L = pyrrole-substituted bpy or phen) have been coated on an electrode by oxidative electropolymerization. The buildup of hydrido complexes in films is well known 27,28,30 the high electrocatalytic activity of these molecular electrode materials towards dihydrogen evolution in organic and aqueous electrolytes is also well known.25,31 For example, H2 is evolved at —0.55 V vs. SCE at a poly [(j75-C5Me5)-Rh(bpy)Cl]+ film in pH 1 aqueous solution.31... 

Asymmetric ECH with [Rh(L)2(Cl)2]+ complexes containing chiral polypyridyl ligands has been attempted, in homogeneous media (L = (7)-(12)) and at carbon electrodes coated with polymer films prepared by electropolymerization of [Rh(13)2(Cl)2]+ -61 62 The latter catalytic system gave the best results in terms of turnover number (up to 4,750) and enantiomeric excess, (ee) when applied to the hydrogenation of acetophenone (ee 18%) and 2-butanone (ee 10%).62 Polymeric materials derived from the complexes [RhI(bpy)(COD)]+ 36 and [Pd(bpy)2]2+33have also been applied to the ECH reaction. 

Complex (21), a Con-cyclam analogue, is very active for the reduction of N02 and NH2OH intermediates and catalyzes the complex electrochemical conversion of N03 to NH3 325 Gold electrodes modified with cobalt-cyclam incorporated in Nafion films,324 or by electropolymerization of the pyrrole-substituted cobalt cyclam (22)326 have shown catalytic activity for the reduction of nitrate in strongly basic media. 

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