Essentially, Cathodic Protection (CP) is the intentional application of a direct electrical current in the opposition to naturally occurring electrochemical corrosion of metal.  Cathodic Protection is now a generally accepted and economical practive for reducing  or eliminating the corrosion of metals, particularly steel.

Steel structures as varied as underground storage tanks, ships' hulls, oil well casings, hot water heaters, gas pipelines, concrete reinforcing, steel bridges and offshore drilling rigs are successfully protected by cathodic protection.

In order to mitigate the corrosion reactions, the steel component must be made cathodic, so that reaction

½O₂  + H₂O + 2e^- → 2OH^-      

will occur and NOT

Fe → Fe²⁺ + 2e^-

Correspondingly, an anodic reaction must occur on the surface of the anode which is provided for the Cathodic Protection (CP) system.

In Impressed Current CP systems, the anode is generally a conductive material which is not consumed. Typically an anode consists of a titanium substrate coated with a noble metal or metal oxide catalyst. In this case the anode reaction becomes the formation of oxygen from water:

 2H₂O →  O₂  + 4H⁺  + 4e^-