Charge transfer coefficient, and symmetry factor (symbols α and β, respectively) are two related parameters used in description of the kinetics of electrochemical reactions.
[1] According to an IUPAC definition,[2] for a reaction with a single rate-determining step, the charge transfer coefficient for a cathodic reaction (the cathodic transfer coefficient, αc) is defined as: The anodic transfer coefficient (αa) is defined by analogy:[3] where: The charge transfer coefficient signifies the fraction of the interfacial potential at an electrode-electrolyte interface that helps in lowering the free energy barrier for the electrochemical reaction.
It is charge transfer coefficient that signifies this part that is utilized in activating the ion to the top of the free energy barrier.
In operating batteries and fuel cells, charge transfer coefficient is the parameter that signifies the fraction of overpotential that affects the current density.
This parameter has had a mysterious significance in electrochemical kinetics for over three quarters of the previous century[citation needed].