Electrode, coating/covering

Catalysis at multilayered electrode coatings is then addressed. Besides the rate of the catalytic reaction within the film and the diffusion of the substrate and products between the bulk of the bathing solution and the film-solution interface, the current response depends on two additional factors permeation of the substrate through the film, and transport of electrons through the film. Analysis of the first of these factors also involves a discussion of the inhibition of the electrode electron transfer that the presence of a film on the electrode surface may cause, whether the electrode is covered by a monolayer or by a thicker film. This discussion also addresses the important case where inhibition is due to deposition onto the electrode surface of one of the reaction products. 

If the surface of a metal or carbon electrode is covered with a layer of some functional material, the electrode often shows characteristics that are completely different from those of the bare electrode. Electrodes of this sort are generally called modified electrodes [9] and various types have been developed. Some have a mono-molecular layer that is prepared by chemical bonding (chemical modification). Some have a polymer coat that is prepared either by dipping the bare electrode in a solution of the polymer, by evaporating the solvent (ethanol, acetone, etc.) of the polymer solution placed on the electrode surface, or by electrolytic polymerization of the monomer in solution. The polymers of the polymer-modified electrodes are either conducting polymers, redox polymers, or ion-exchange polymers, and can perform various functions. The applications of modified electrodes are really limit-... 

Such a dilemma can be overcome by using semiconductor electrodes coated with sparsely scattered, extremely small (nanometer-sized) metal dots,42 45) such as shown schematically in Fig. 4.9 with n-Si used as a semiconductor. The naked Si surface is covered with naturally grown thin Si02 layer and passivated. The photocurrent flows through the metal dots. The photocurrent can be stable in aqueous redox electrolyte because the Si surface is covered and protected by coating with metal dots and Si02. 

Su and his coworkers reported a simple way to make GOx enzyme-decorated diamond film electrode (Su et al. 2004). The enzyme containing solution was prepared in phosphate buffer containing bovine serum album. The mixture was added with glutaraldehyde, afterward. The resulting enzyme solution was rapidly coated onto the cleaned diamond film electrode with NaOH solution at room temperature by a syringe. The electrode was covered and incubated for 1 h at room temperature. After thoroughly washing with water, it was stored in dark at 4°C for use. 

The real problem area with CdS concerns its ability to photo-oxidize water to O2. Earlier reportsthat forms of CdS loaded with Pt and RUO2 were effective photocatalysts for the cyclic cleavage of water have not been reproduced and there are serious doubts about their validity. However, some Support for this work has been obtained with CdS electrodes coated with RUO2 and covered with polypyrrole, but the experimental evidence showing O2 formation is inadequate for such an important conclusion. Other workers have failed to observe O2 formation with catalyst-loaded CdS and, in fact, irradiation of CdS in aerated solution results in rapid consumption of O2. In... 

A new set of electrodes were described that consisted of a graphite electrode covered with an optically active polyamino acid, such as poly-L-valine With this electrode a product with an ee of 43% from the reduction of 4-methylcoumarin was obtained while a more effective result, an ee of 54%, in the oxidation of cyclohexyl phenyl sulfide on a Pt electrode coated with poly-L-valine was obtained... 

Dubois et al. (21,22) have showed that the electrochemical oxidation of phenol euid its derivatives, on metal surfaces, produced hydrophobic, adherent, euid insulating polymer films of uniform thickness. Both Yacynych and Mark (17). and Helneman et al. (13) showed the oxidation of 1,2-diaminobenzene to be irreversible, and with successive cyclic voltammetric scans formed an insulating polymer film completely covering the electrode surface. Heineman et al. ( 22) further showed that 1,2-diaminobenzene forms a polymeric film over a pH range of 4 to 10, and that platinum electrodes coated with the poly(1,2-diaminobenzene) provided a nearly Nernstian response to pH. Cheek et al. (J[6) studied the pH response of platinum and vitreous carbon with polymer films of either 1,2-diaminobenzene or phenol. These polymer films are selective enough to allow the permeation of protons, while limiting access to larger molecules, which could be potential interferents. 

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