Electrode polarization

A change in the electrode potential when a d.c current is passed through the electrode is called electrode polarization. The value of electrode potential is dependent on the difference in the potential between the potential of the polarized electrode and that of the electrode in equilibrium with the electrolytic solution. Polarization is also defined as the deviation of the electrode potential from equilibrium due to an electric current passing through the galvanic cell. Among cathodic and anodic polarization, cathodic polarization is common. There are mainly three types of electrode polarization. They are concentration polarization, resistance polarization and activation polarization. Concentration polarization is due to the concentration gradients developed when the current is passing. A good agitation in the electrolyte reduces the concentration polarization. Temperature, electrode surface area, ionic strength etc. also affects concentration polarization. Resistance polarization is the potential drop occurs either due to high resistivity of the electrolyte or due to insulation effect of the film on the electrode surface formed by the reaction products.