Electrocatalysis volcano” Curve

Volcano curves lay down the grounds for a predictive tool in electrocatalysis. 

A complete theory of electrocatalysis leading to volcano curves has been developed only for the process of hydrogen evolution and can be found in a seminal paper by Parsons in 1958 [26]. The approach has shown that a volcano curve results irrespective of the nature of the rate-determining step, although the slope of the branches of the volcano may depend on the details of the reaction mechanism. 

Hydrogen evolution is the only reaction for which a complete theory of electrocatalysis has been developed [33]. The reason is that the reaction proceeds through a limited number of steps with possibly only one type of intermediate. The theory predicts that the electrocatalytic activity depends on the heat of adsorption of the intermediate on the electrode surface in a way giving rise to the well known volcano curve. The prediction has been verified experimentally [54] (Fig. 2) and the volcano curve remains the main predictive basis on which the catalytic activity is discussed [41, 55],... 

If correlations do exist for simple metals, predictions are much more difficult for composite materials. On the other hand, cathode activation has two aims (i) to replace active but expensive materials with cheaper ones, and (ii) to enhance the activity of cheaper materials so as to approach or even surpass that of the more expensive catalysts. In the case of pure metals there is little hope to find a new material satisfying the above requirements since in the volcano curve each metal has a fixed position which cannot be changed. Therefore, activation of pure metals can only be achieved by modifying its structure so as to enhance the surface area (which has nothing to do with electrocatalysis in a strict sense), and possibly to influence the mechanism and the energetic state of the intermediate in the wanted direction. This includes the preparation of rough surfaces but also of dispersed catalysts. Examples will be discussed later. 

Fig. 23 Sketch of a volcano curve in electrocatalysis involving adsorption of B as an intermediate (Eq. 33) resulting from Eqs (38) and (41). (Reprinted with permission from Ref. 57, Copyright 2003 by John Wiley Sons Ltd).

Figure 9.1 Volcano curve for the electrocatalysis of the HER at various metals in terms of dependence of log % values on metal-to-H bond energy. ...

Electrocatalysis, Fundamentals - Electron Transfer Process Current-Potential Relationship Volcano Plots, Fig. 3 Schematics of a volcano curve in electrocatalysis with adsorption of B being the rate-determining step... 

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