Electrode potential and cell potential

A galvanic cell is composed of two half cells, each consisting of electronic (metal plates) and electrolytic (solution of ions) conductors in contact. At the surface of separation of the solid metal and the solution there exists a difference of electrical potential. This potential difference established due to the electrode half reaction occurring at the electrode surface is the electrode potential.

A potential is associated with each half reaction, be it oxidation or reduction. The potential associated with an oxidation reaction is the oxidation potential, while that associated with a reduction gives the reduction potential. The overall cell potential — also called the electromotive force (emf) — is made of the contributions from each of the electrodes. In other words, the cell potential is the algebraic sum of the electrode potentials:

where $E_{oxi}$ is the oxidation potential of the anode (-) and $E_{red}$ is the reduction potential of the cathode (+). …