Zero-gap configuration

The problem of ohmic drops has recently been tackled by modifying the cell design. This is a matter of engineering, not of chemistry. The conventional design of divided cell has been replaced with a so-called zero-gap configuration [15], where the... 

Figure 7.2 Cell designs, (a) Conventional alkaline electrolysis (b) advanced alkaline electrolysis (zero gap) (c) SPE configuration (acid electrolysis).

Fig. 12.8. Chlor-alkali cell configurations (a) gap cell (b) zero gap cell (c) SPE cell.

A typical configuration of a SECM system is shown in Fig. 36.6. In this case the solution contains oxidized (Ox) species (denoted mediators) that are reduced on the active part of the microelectrode yielding the reduced (Red) species. The figure also shows a possible reaction of the Red species with the electrode, with the reaction rate If is very large, the approach of the tip to the surface will result in an increase in the reduction reaction (current) on the tip because the regeneration of Ox on the tip will be more efficient in a smaller gap. On tfie otfier fiand, if k is close to zero, the only effect of the tip approach to the surface wifi be the depletion of the Ox species in the gap upon reduction, whose diffusion from the bulk of the solution is now hindered by the probe. These two mechanisms, which result in the positive and negative feedback operation modes, can be used to map the reaction rate k, on the surface. 

Figure 7 Energy-gap red-shift for three different classes of clusters as a function of the number of Si=0 bonds at the surface. Circles SiioH -Om squares Sii4H -Om and triangles Si35H -Om. The red-shift is calculated as the difference between a specific surface configuration and the corresponding fully hydrogenated one (thus the zero in the plot for each class stands for the nonoxidized case m = 0).

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