ABSTRACT
Whenever only one electrode reaction takes place on a metal surface in a given solution, that system is called a single electrode. This is the case for copper immersed into de-aerated and slightly acidic copper sulfate solution:
Cu + 2 = Cu 2+ e (4.1)
The open circuit potential (ocp) is the potential set up spontaneously by an electrode in the absence of an external current. For a single electrode, the open circuit potential is equal to the equilibrium potential, E .rev
If the potential of an electrode differs from the open circuit potential, an electric current is crossing the electrode-electrolyte interface. The overpotential η is defined as the difference between the electrode potential and the equilibrium potential of an electrode reaction:
η = – revE E (4.2)
A positive overpotential indicates that an anodic current is crossing the interface; a negative one means that the current is cathodic.
