Metal Dissolution in Combination with Reduction Reactions

14 Metal Dissolution in Combination with Reduction Reactions 

Superimposed metal dissolution and hydrogen evolution with equilibrium potentials Ej (Me/Me +) and Ejq(H2/H+), respectively, leading to the rest or corrosion potential Eg for disappearing current in the external circuit and the corrosion current density i(. Solid curves correspond to the partial current densities of anodic metal dissolution and cathodic hydrogen evolution and to the sum curve of both reactions. 

For open circuit conditions, the net current is zero and the mixed electrode is at the corrosion or rest potential Er. The corrosion current density is  

Defining the polarization n = E - Equation 1.157 may be rearranged as the Butler-Volmer equation for a mixed electrode  

The total current equals the anodic metal dissolution current for high anodic polarizations, and the cathodic hydrogen evolution current for high cathodic polarizations, leading to the semilogarithmic Tafel presentation (Equations 1.160a and b)  

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