It is divided into two parts Metal ion concentration cell: This type of corrosion is possible when two similar electrodes come in contact similar electrolytic solution with dissimilar concentration. If more difference in concentration of electrolytic is there then this corrosion reaction is possible Electrode which is present in dilute solution will behave like anode undergoes corrosion with oxidation reaction. Electrode which is present in dilute solution behaves like anode as it undergoes oxidation reaction & another electrode which is present in concentrated solution acts as cathode due to reduction reaction.

Oxygen concentration cell: Single electrode if it is placed in its electrolytic solution, it results in the formation of O2 Concentration cell. Part of electrode which is present in its electrolytic solution act as an anode & part which is above water level acts as cathode as oxygen concentration above water is more & protected from corrosion.