1995 Volume 44 Issue 4 Pages 247-256
The ionic electrode potential is defined by the real potential of potential-determining ion in the electrode. i.e. the real free energy for the ion transfer from the point at the outer potential of aqueous solution to the point inside the eletrode. Provided that the electrode has both electronic and ionic energy levels, the ionic and the electronic electrode potentials are in the same scale with different zero levels, and hence either can be applied to ion transfer electrodes. However, only the ionic potential can be applicable to the electrodes that have no electronic energy level in the range of practical interest, such as ionic solid electrodes and electronically nonconductive polymer membrane electrodes. The equilibrium electrode potential of oxide-covered metal electrodes corresponds either to the oxide fomation potential of the metal electrode with ion transfer equilibrium at the metal/oxide interface, or to the flat band potential of the oxide electrode with electron transfer equilibrium at the metal/oxide interface. Two-layered oxide film on metal electrodes, consisting of lower and higher valence oxides, involves an irreversible potential difference in the inner layer of lower valence oxide.