Polarization Behavior

Metallic surfaces can be polarized by the application of an external voltage or by the spontaneous production of a voltage away from equilibrium. This deviation from equilibrium potential is called polarization. The magnitude of polarization is usually described as an overvoltage (h) which is a measure of polarization with respect to the equilibrium potential (Eeq) of an electrode.

This polarization is said to be either anodic, when the anodic processes on the electrode are accelerated by changing the specimen potential in the positive (noble) direction or cathodic when the cathodic processes are accelerated by moving the potential in the negative (active) direction. There are three distinct types of polarization in any electrochemical cell, the total polarization across an electrochemical cell being the summation of the individual elements:

E(applied) - Eeq = htotal = hact +hconc +iR

where:

hact is the activation overpotential, a complex function describing the charge transfer kinetics of the electrochemical processes. hact is predominant at small polarization currents or voltages.

hconc is the concentration overpotential, a function describing the mass transport limitations associated with electrochemical processes. hact is predominant at large polarization currents or voltages.

iR is often called the ohmic drop. iR follows Ohm's law and describes the polarization that occurs when a current passes through an electrolyte or through any other interface such as surface film, connectors ...