Vetter and Schultze

Partial charge transfer during adsorption is difficult to evaluate because separation of the charge transferred to the electrode and that part of the charge transferred across the double layer to give specifically adsorbed ions cannot be done through measurements of the total charge in the external circuit. Vetter and Schultze [102] defined the electrosorption valence as... 

The q-r-E relation was first introduced by Schmidt [3.54] as the charge coverage coefficient, and later described as the electrosorption valency by Vetter and Schultze [3.226, 3.227] ... 

A similar criticism refers to the concept of electrosorption valency introduced by Vetter and Schultze starting from the partial charge concept [34, 35]. 

Eq. (4.26) was probably first derived by SchmidL- Vetter and Schultze introduced the expression electrosorption valency . 

Representative of the work using phase oxide concepts are those of Damjanovic et Vetter and Schultze, and Gilroy.Most... 

Vetter and Schultze have proposed a model for the formation of the anodic layer on Pt which involves features of both the chemisorbed and phase oxide models. They view the formation of the anodic layer as proceeding through the states represented in Figure 10. They propose that the first step involves the following reaction to yield the chemisorbed layer (Figure 10a) ... 

The adsorbed species 0 is not believed to exceed --10% on the basis of the available capacity data. While these workers propose reaction (XX), they also point out that on the basis of the pH dependence alone it is not possible to distinguish between 0 and OH" adsorption. Vetter and Schultze indicate that the species is ionic rather than a covalently bonded species. A clear distinction between ionic vs. covalent bonding is difficult to make on the basis of electrochemical measurements. Even if the adsorption involves an ionic species O " or OH , the compensating charge on the Pt must pass through the external circuit and be equal to that on the adsorbed ionic species except for the small portion compensated by changes in the charge in the outer Helmholtz plane and diffuse layer. 

The principal evidence presented by Vetter and Schultze for the model in Figure 10 and reaction (XX) is the observed relation between capacitance data and coverage as determined from galvanostatic cathodic reduction of the layer. The observed capacitance C was found to depend on coverage 6 as follows ... 

Vetter and Schultze assume that Cox 1/ This follows from the reasoning that capacitance of a parallel plate condenser is Cox = ox/(47t5ox), where Dox is the dielectric constant of the oxide. The effective thickness of the capacitor 8ox is regarded as proportional to the surface coverage 6, Thus Eq. (17) has a form similar to that of Eq. (16). 

At constant potential in H2SO4 solution, Vetter and Schultze found the current associated with the adsorption process to follow the relation... 

Vetter and Schultze proposed that the further stages of growth of the film represented by Figure 10b and c occur through place exchange between adsorbed 0 ions and Pt metal ions under the influence of the potential across the interface. The penetration of into the Pt provides a likely explanation for the aging effects. 

Vetter and Schultze also proposed that the reduction of the oxide occurs pathwise (in a localized way) and therefore with kinetics (Tafel slopes) which are almost independent of thickness or average coverage. 

Gilroy proposed that the reduction of the oxide layer is uniform and typical of that for a desorption process with charge transfer control. This view is contrary to that of Vetter and Schultze and Damjanovic et who... 

GERISCHER In case of chemisorption of ions, the pure electrostatic picture breaks down in explaining the differential capacities. While in electrolytes with solvation of the ions, there is a possibility that the ion approaches closer to the electrode surface under the influence of chemisorptive forces by leaving its solvation shell, it has been shown even there that in most systems the chemisorbed ions are partially discharged [Vetter and Schultze]. This means in my opinion that "chemisorbed ions" can better be described as chemisorbed atoms with a polar bond to the surface. The polari-... 

---