Polarization curve of electrode reactions

Polarization in the cathodic direction accelerates the cathodic reaction and is called cathodic polarization polarization in the anodic direction accelerates the anodic reaction and is called anodic polarization. In Fig. 7-4 the polarization curve is cathodic at potentials more negative and is anodic at potentials more positive than the equilibrium potential E. In electrode reaction kinetics the magnitude of polarization (the potential change in polarization) is called the overvoltage or overpotential and conventionally expressed by symbol ii, which is negative in cathodic polarization and positive in anodic polarization. 

For ordinary electrode reactions, as is described in Sec. 7.2.2, the kinetics is linear (a linear afiinity versus reaction rate relationship and a linear potential versus current relationship) in the vicinity of equilibrium potential. q and 

In the range of electrode potential in which the kinetics is exponential, the overvoltage ti is a linear function of the logarithm of reaction current, logi, as shown in Eqn. 7-19 and in Fig. 7-5  

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