Kinetics of Minority Carrier Reactions at Semiconductor Electrodes

3 Kinetics of Minority Carrier Reactions at Semiconductor Electrodes 

Electrochemists tend to take for granted the fact that the rate of electton transfer at an electrode varies with applied potential, as expressed by the Butler Volmer or Tafel equations, and this potential dependence is, after all, the basis for most elecU ochemical techniques. In terms of the energy level picture developed above, changing the potential of a metal electrode by some amount, AC/, corresponds to shifting the Fermi level of the metal relative to the electrolyte redox level by a corresponding amount, -qAU. The electrochemical potential of electrons in the metal is given by 

The equilibrium inner potential difference between the metal and the solution is therefore 

Remembering that the Fermi level is equivalent to the electrochemical potential of electrons, it can be seen that changing the potential difference across the metal solution interface changes the relative position of the metal and redox Fermi levels. In effect, the potential change is located across the Helmholtz layer, and the activation energy for cathodic electron transfer is changed by some amount where a is the transfer coefficient. Changing 

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