Electrodes, layer coatings

Chronocoulometry, 62 Clark electrode, 190 Coated wire electrodes, 160 Cobalt, 82, 85 Cobalt phthalocyanine, 121 Collection efficiency, 113, 135 Collection experiments, 113 Combination electrode, 148 Compact layer, 19 Composite electrodes, 47, 114, 133 Computer control, 80, 106 Concentration profile, 7, 9, 11, 29, 36, 87, 132... 

The next step was to alternate the deposition of Cd and Te. As Te is more noble than Cd, various amounts of Te were first deposited and then exposed to a Cd ion solution at underpotential. Figure 8 is a graph of the Cd coverages observed to form on a Cu electrode initially coated with various amounts of Te. The slope of the graph is 0.95 (the Cd/Te ratio), which is consistent with the Cd reacting 1 1 with the Te. Similar results were observed for deposits formed on Pt and Au electrodes. The graph indicates that the Cd reacted at underpotential quantitatively with the Te, even when multiple atomic layers of Te were present. 

The most common cause of trouble when working with optically transparent electrodes (OTEs) is scratches in the thin film of conductor. Since the electrode is coated with a thin layer of semiconductor, a scratch can in effect cut right through the conductive layer, thus causing an insulatory channel. The two parts of the semiconductor on either side of the scratch are therefore prevented from communicating with each other, and so the portion of the electrode beyond the scratch is rendered useless. 

In electrochemical systems, metal meshes have been widely used as the backing layers for catalyst layers (or electrodes) [26-29] and as separators [30]. In fuel cells where an aqueous electrolyte is employed, metal screens or sheets have been used as the diffusion layers with catalyst layers coated on them [31]. In direct liquid fuel cells, such as the direct methanol fuel cell (DMFC), there has been research with metal meshes as DLs in order to replace the typical CFPs and CCs because they are considered unsuitable for the transport and release of carbon dioxide gas from the anode side of the cell [32]. 

The peculiar electrochemical behaviour of electrode surfaces coated with a layer of phosphatidylcholine (PC) adds a new dimension to the practical applications of this type of sensor as it enables development of electrochemical processes within a lipid layer. Redox-active amphiphiles readily... 

The dye-sensitised solar cell (DSSC) is constructed as a sandwich of two conducting glass electrodes filled with a redox electrolyte. One of the electrodes is coated, using a colloidal preparation of monodispersed TiOj particles, to a depth of a few microns. The layer is heat treated to rednce resistivity and then soaked in a solution of the dye until a monomolecnlar dispersion of the dye on the TiO is obtained. The dye-coated electrode (photoanode) is then placed next to a connter electrode covered with a conducting oxide layer that has been platinised , in order to catalyse the reduction of the mediator. The gap between the two electrodes is filled with an electrolyte containing the mediator, an iodide/triodide conple in acetonitrile. The structure is shown schematically in Fignre 4.29. 

One problem for the coated system is that the film is peeled off after prolonged irradiation. In order to have a more adhesive film, the surface of n-Si was modified with N-(3-trimethoxysilyIpropyl)pyrrole (22). Pyrrole was then electrodeposited on this modified electrode as shown in Eq. (24) 85). The durability of the coated poly(pyrrole) was improved by such a treatment of n-Si surface. The n-Si electrode coated only with poly(pyrrole) gave a declined photocurrent from 6.5 to 1.8 mA cm-2 in less than 18 h, while the poly(pyrrole) coated n-Si treated at first with 22 as Eq. (24) gave a stable photocurrent of 7.6 mA cm-2 for 25 h. When an n-Si electrode was coated with Pt layer before the deposition of poly(pyrrole), the stability of the semiconductor was improved remarkably (ca. 19 days)85b). A power conversion efficiency of 5.5% was obtained with iodide/iodine redox electrolytes. 

Electrophoretic Deposition consists in application of a DC electric field between two electrodes immersed in a suitable colloidal suspension, thus causing migration of the suspended phase toward one of the electrodes and the deposition of a coating at that electrode. This technique is usually applied when it is desired ro deposit a uniform layer (coating) of a material on an irregularly shaped form. For example, deposition of rubber or synthetic polymers on various articles may be done by this method (Refs 5,... 

Electrodes classified in the second group of electrode systems are those in which the metal electrode is coated with a layer of a sparingly soluble salt of the electroactive species and the metal ion of the metal electrode, such that the potentiometric response is indicative of the concentration of the inactive anion species. Thus the silver/silver-chloride electrode system, which is representative of this class of electrodes, gives a potential response that is directly related to the logarithm of the chloride ion activity (see also Chapter 1, section 1.5), even though it is not the electroactive species ... 

Another method to monitor DNA damage in films employed a cationic electroactive probe that binds better to ds-DNA than to damaged DNA. Co(bpy)3+ was used to probe films of (PDDA/ds-DNA)2 grown layer-by-layer on PG electrodes first coated with a layer of PSS.[46] After incubation of (PDDA/ds-DNA)2 films with styrene oxide, electrodes were rinsed, placed into 20 pM Co(bpy)i+, and the Com/Con reduction peak at 0.04 V vs. SCE from the DNA-bound complex was monitored by SWV. Peak current decreased with increasing time of reaction with... 

The spatial and temporal response of a nematic phase to a distorting force, such as an electric (or magnetic) field is determined in part by three elastic constants, kii, k22 and associated with splay, twist and bend deformations, respectively, see Figure 2.9. The elastic constants describe the restoring forces on a molecule within the nematic phase on removal of some external force which had distorted the nematic medium from its equilibrium, i.e. lowest energy conformation. The configuration of the nematic director within an LCD in the absence of an applied field is determined by the interaction of very thin layers of molecules with an orientation layer coating the surface of the substrates above the electrodes. The direction imposed on the director at the surface is then... 

Figure 6.29 shows, as an example, the effect of surface modification on the sta-bihty of sihcon electrode in an aqueous solution. The bare sihcon surface is quickly passivated in aqueous solution under illumination. Coating the electrode with a layer of either ferrocene or polypyrrole gives an improvement in the stabihty. The stability is further improved by a two-layer coating of ferrocene/polypyrrole as shown in Fig. 6.29. 

Techniques such as potentiometry, polarography, and microcalorimetry have been chosen in exploiting the benefits of immobilized enzymes (see Chapter 4). Enzymes incorporated into membranes form part of enzyme electrodes. The surface of an ion-sensitive electrode is coated with a layer of porous gel in which an enzyme has been polymerized. When the electrode is immersed in a solution of the appropriate substrate, the action of the enzyme produces ions to which the electrode is sensitive. For example, an oxygen electrode coated with a layer containing glucose oxidase can be used to determine glucose by the amount of oxygen consumed m the reaction, and urea can be estimated by the combination of a selective ammonium ion-sensitive electrode and a urease membrane. 

An alternative strategy to achieve electrode selectivity is through control of the vertical distribution of the active layer. Coating of the photoanode preferentially with... 

Hori el al. prepared porous silver coated SPEs with an AEM (Selemion AMV). The silver electrode layer became more porous... 

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