Factor groups electrochemical

The various possible electrode reactions at the cathode and at the anode in electrolytic cells have been shown in Table 6.2. It has been pointed before that the outcome of an electrolytic process can be made on the basis of knowledge of electrode potentials and of overvoltages. The selection of the ion discharged depends on the following factors (i) the position of the metal or group in the electrochemical series (ii) the concentration and (iii) the nature of the electrode. Examples provided hereunder deliberate on these aspects. 

It is intriguing that analysis of the volcano curve predicts that the apex of the curve occurs at AH(H2)ads = 0 (formally, AG = 0) [26]. This value corresponds to the condition D(M-H) = 1/2D(H-H), that is, forming an M-H bond has the same energetic probability as forming an H2 molecule. This condition is that expressed qualitatively by the Sabatier principle of catalysis and corresponds to the situation of maximum electrocatalytic activity. Interestingly, the experimental picture shows that the group of precious transition metals lies dose to the apex of the curve, with Pt in a dominant position. It is a fact that Pt is the best catalyst for electrochemical H2 evolution however, its use is made impractical by its cost. On the other hand, Pt is the best electrocatalyst on the basis of electronic factors only, other conditions being the same. 

We have previously commented on the fact that Ex j2 -values might be influenced by adsorption properties, e.g., of a long alkyl group (Fig. 7). While this factor would be expected to be most pronounced for slow electrochemical reactions, it should be taken into account whenever correlations involving substrates with widely differing adsorption properties are discussed. 

Such controlling factors are matched by complementary properties of the solid surface, i.e., the hydrophobic or hydrophilic surface character, porosity and topology, charge, hydration, and the presence and composition of surface groups. Particularly for electrochemical surfaces intrinsic catalytic reactivity of the surface groups formed spontaneously or by po-tentiostatic control also follow. Both in the context of electrochemical protein reactivity, and in the broader areas of proteins at surfaces, surface control and modification to structural and functional compatibility with the proteins are key issues. The use of electrochemical promoters, illustrated below, is one such example [32-34]. 

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