What does cathodic protection primarily do?

Cathodic protection primarily aims to protect metals from corrosion. This is achieved by making the metal a cathode in an electrochemical cell, which prevent corrosion by either using sacrificial anodes or impressed current systems. The function of cathodic protection is to either provide a source of electrons to the protected metal or to shift its electrochemical potential to a level where corrosion is significantly reduced or inhibited.

While one of the choices mentions shifting the potential in the positive direction, this is not the primary purpose of cathodic protection. Instead, cathodic protection works to make the protected metal more negative relative to the surrounding environment, thereby reducing the likelihood of corrosion. The use of sacrificial anodes and impressed current systems are methods employed within the broader context of cathodic protection, but they are not the defining characteristic or primary goal of the method itself.

Therefore, the correct answer encapsulates the main objective of cathodic protection: to prevent corrosion of metals.