Definition of the transfer coefficient in electrochemistry (IUPAC Recommendations 2014)

The transfer coefficient alpha is a quantity that is commonly employed in the kinetic investigation of electrode processes. An unambiguous definition of the transfer coefficient, independent of any mechanistic consideration and exclusively based on experimental data, is proposed. The cathodic transfer coefficient alpha(c) is defined as -(RT/F)(dln vertical bar j(c)vertical bar/dE), where j(c) is the cathodic current density corrected for any changes in the reactant concentration on the electrode surface with respect to its bulk value, E is the applied electric potential, and R, T, and F have their usual significance. The anodic transfer coefficient alpha(a) is defined similarly, by simply replacing j(c) with the anodic current density and the minus sign with the plus sign. This recommendation aims at clarifying and improving the definition of the transfer coefficient reported in the 3rd edition of the IUPAC Green Book.