Surface coverage current flow

In classical kinetic theory the activity of a catalyst is explained by the reduction in the energy barrier of the intermediate, formed on the surface of the catalyst. The rate constant of the formation of that complex is written as k = k0 cxp(-AG/RT). Photocatalysts can also be used in order to selectively promote one of many possible parallel reactions. One example of photocatalysis is the photochemical synthesis in which a semiconductor surface mediates the photoinduced electron transfer. The surface of the semiconductor is restored to the initial state, provided it resists decomposition. Nanoparticles have been successfully used as photocatalysts, and the selectivity of these reactions can be further influenced by the applied electrical potential. Absorption chemistry and the current flow play an important role as well. The kinetics of photocatalysis are dominated by the Langmuir-Hinshelwood adsorption curve [4], where the surface coverage PHY = KC/( 1 + PC) (K is the adsorption coefficient and C the initial reactant concentration). Diffusion and mass transfer to and from the photocatalyst are important and are influenced by the substrate surface preparation. 

When the surface activity is stronger, the surface coverage is high throughout the values of Aq calculated (curve 2). The peak becomes dull and there is no big difference between the surface coverages in the forward and reverse scans. Nevertheless, by and large, the results of numerical calculation in Figure 7.5 indicate that the properties of the electrochemical instability under the current flow are essentially the same as those in the thermodynamic equilibrium. 

Term II represents the desorption of the adsorbed species from the reactive surface and decreases the surface coverage. Term III is the forward electrochemical ionization reaction responsible for current flow. From inspection of Eq. (4.62), in the case of an adsorption-limited reaction, the kinetic limiting current density should be the maximum possible adsorption rate where the surface coverage 6 becomes zero, or... 

Fig. 5.6. Reactive sputter process for depositing the compound film AB. (a) Balance of reactive gas flow Qtot, which is partially gettered at the target (Qt) and at the substrate (Qc) and partially pumped by the vacuum pump (Qp). The fraction of the target surface At that is covered by the compound AB is 6>t. The fraction of the collecting area Ac covered is Gc. j is the sputter current density, (b) Definition of particle fluxes that alter the target and collecting area coverage fractions 6>t and 6>c (see text), (modified from [70])...

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