Electrochemical-potential advantage

ORR catalysis by Fe or Co porphyrins in Nation [Shi and Anson, 1990 Anson et al., 1985 Buttry and Anson, 1984], polyp5rrolidone [Wan et al., 1984], a surfactant [Shi et al., 1995] or lipid films [CoUman and Boulatov, 2002] on electrode surfaces has been studied. The major advantages of diluting a metalloporphyrin in an inert film include the abUity to study the catalytic properties of isolated molecules and the potentially higher surface loading of the catalyst without mass transport Umit-ations. StabUity of catalysts may also improve upon incorporating them into a polymer. However, this setup requires that the catalyst have a reasonable mobUity in the matrix, and/or that a mobile electron carrier be incorporated in the film [Andrieux and Saveant, 1992]. The latter limits the accessible electrochemical potentials to that of the electron carrier. 

The possibilities afforded by SAM-controlled electrochemical metal deposition were already demonstrated some time ago by Sondag-Huethorst et al. [36] who used patterned SAMs as templates to deposit metal structures with line widths below 100 nm. While this initial work illustrated the potential of SAM-controlled deposition on the nanometer scale further activities towards technological exploitation have been surprisingly moderate and mostly concerned with basic studies on metal deposition on uniform, alkane thiol-based SAMs [37-40] that have been extended in more recent years to aromatic thiols [41-43]. A major reason for the slow development of this area is that electrochemical metal deposition with, in principle, the advantage of better control via the electrochemical potential compared to none-lectrochemical methods such as electroless metal deposition or evaporation, is quite critical in conjunction with SAMs. Relying on their ability to act as barriers for charge transfer and particle diffusion, the minimization of defects in and control of the structural quality of SAMs are key to their performance and set the limits for their nanotechnological applications. 

The operation of molecular devices in wet systems can yield performances unobtainable in dry systems. For example, molecular devices in wet systems can provide characteristic electron transfer control. While wet systems have a disadvantage in performance speed because of the slow mobility of ions, they have a notable advantage in fine and precise control of the direction and kinetics of electron transfer, even at room temperature. This characteristic can lead to a low noise level, because electron transfer is governed by the absolute electrochemical potentials of a series of molecules coexisting in the system. 

Exchange of species between a solution and a polymer film is an established means of probing solution composition. The quartz crystal microbalance can monitor such exchange processes with high sensitivity. When combined with selectivity via electrochemical control and appropriate choice of polymer, the EQCM becomes an attractive sensor. In order that the potential advantages of the EQCM can be realised, certain criteria must be met. 

Sodium is selected as the solid state transported reactant in PEVD. This is because not only is Na" a component in the PEVD product phase Na COj, but also the mobile ionic species in the solid electrolyte (Na "-[3"-alumina) and in the auxiliary phase of the sensor. Thus, PEVD can take advantage of the solid electrochemical cell (substrate) of the sensor to transport one reactant (sodium) across the substrate under an electrochemical potential gradient. This gradient... 

The electrosynthesis of HTSCs began to develop somewhat later than most other approaches and at first could compete with the conventional methods only in specific applications. However, in the last two to three years, interest has grown in certain versions of HTSC electrosynthesis. The main limitation of electrosynthetic methods lies in the need to use conductive substrates or materials covered with thin conductive layers. The most significant potential advantage of all electrochemical methods consists in the possibility of accurately controlling the amount of the resulting product by on-line coulometry, the error of which does not exceed a few percent of the charge consumed in the formation of a monolayer. 

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