Surfaces of Other Electrodes

In their electrochemical surface properties, a number of metals (lead, tin, cadmium, and others) resemble mercury, whereas other metals of the platinum group resemble platinum itself. Within each of these groups, trends in the behavior observed coincide qualitatively, sometimes even semiquantitatively. Some of the differences between mercury and other. y- or p-metals are due to their solid state. Among the platinum group metals, palladium is exceptional, since strong bulk absorption of hydrogen is observed here in addition to surface adsorption, an effect that makes it difficult to study the surface itself. 

Surface studies are difficult in the case of many metal electrodes since their regions of ideal or perfect polarizability are very narrow that is, the potentials of anodic dissolution (or oxidation) of the metal and of cathodic hydrogen evolution are close 

TABLE 10.1 Potentials of Zero Charge of Certain Metals in Aqueous Solutions 

A very important characteristic of surface constitution for any metal is the position of its PZC. Table 10.1 reports values for the PZC for a number of metals. We can see that these values vary within rather wide limits. An important difference between platinum group metals and most other metals is the ability of the latter upon anodic polarization to form relatively thick superhcial oxide or salt layers. Owing to their great practical value, these layers are considered in more detail in Section 16.3. For investigations of the structure and of properties of platinum and other electrodes, many nonelectrochemical methods are also widely applied, which is discussed in more detail in Chapter 27. 

The diffuse charge distribution in the semiconductor s surface layer leads to a drastically lower cell capacitance at the semiconductor-electrolyte interface. Typical 

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