Polarization in electrochemistry refers to effects counteracting and lowering the efficiency of electrochemical processes. The mechanism is typically depletion of reagents causing concentration gradients in boundary layers or the formation of compounds partly passivating the electrode surfaces and having the effect (depending on conditions) of decreasing the ouput voltage of batteries, increasing the voltage required by electrolysis cells or lowering currents. It is a type of kinetic deviation from equilibrium conditions. It is usually distinguished from overpotential

Overpotential

Overpotential is an electrochemical term which refers to the potential difference between a half-reaction's thermodynamically determined reduction potential and the potential at which the redox event is experimentally observed. The term is directly related to a cell's voltage efficiency...

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As an electrochemical phenomenon it is of importance for corrosion typically lowering corrosion rates. However, polarisation in corrosion protection systems could increase corrosion.