Expression of overpotentials

For an electrode reaction out of equilibrium, the galvanic potential deviates from the equilibrium potential by the overpotential  

For the aluminum-air couple, applying Equation (12.30) along with the mixed potential theory yields the following correlation at the anode  

Expressions of three overpotentials involved in the model computations are obtained by combining Equations (12.31) and (12.32)  

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