Two Step Reaction with Adsorbed Intermediate

Let us consider two examples which are of importance for the discussion of the mechanism of the hydrogen electrode in acid electrolytes  

Adsorbed hydrogen atoms formed by the Volmer reaction [7] combine to H2 molecules on the surface in the Tafel [8] reaction. In the second mechanism, the Volmer reaction occurs simultaneously with the Hey-rovsky [9] reaction  

Hydrogen molecules are formed by discharge of ions on H atoms. 

Under equilibrium conditions, ( M s)rev is determined by Eq. II, 12 for both mechanisms. It will vary with the electrode material because of / o,e ( )- The chemical potential of H atoms is the same for different electrode materials  

The activity is a function of the coverage 0 of the electrode surface with H atoms. The coverage will depend upon the nature of the electrode material because of /Zo,h- The standard free energy dGo,H of hydrogen adsorption is related to /Zo,h- 

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