Why do two different metals with junctions at the same temperature produce no net current?

When two different metals are placed in contact, electrons flow between them until their Fermi levels align, creating a contact potential at the junction.12

In a closed circuit consisting of two different metals, two such junctions are formed. When both junctions are at the same temperature, the contact potentials at each junction are equal in magnitude but opposite in direction. Consequently, these potentials cancel each other out, resulting in no net electromotive force and no flow of electric current.12

A net current only flows when a temperature difference is maintained between the two junctions. This temperature gradient disrupts the balance because the metals typically possess different temperature dependencies for their Fermi levels, leading to the generation of a thermal electromotive force known as the Seebeck effect.12