Adsorption and desorption of ad-atoms

Curve 1 shows the situation for an uncharged surface and no potential difference between electrode and electrolyte, A(p = = 0. (p is the local Galvani potential. 

The situation with A(p 0 but without partial discharge is shown in curve 3. An electrical energy zF (p has to be subtracted from the chemical energy. In the transition state 

With partial discharge, the situation is shown in curve 2. In the transition state the electrical energy is still zFAcp. In the ad-atom position the potential is the fraction x d 2ad with x d = 0 at the pre-electrode position and x d = 1 at the metal surface. 

With the activation energies the following rate equations can be derived. For adsorption (a cathodic process with the charge transfer coefficient aj 

For desorption (an anodic process with the charge transfer coefficient aj 

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