Transfer coefficient (alpha) is used to define kinetics of electro-chemical reaction. We can see this coefficient in butler volmer and tafel equation. This alpha says about fraction of the interfacial potential at an electrode and electrolyte interface.
The value of α depends on the symmetry of the activation barrier called the transfer coefficient. α defines the fraction of the potential energy affecting the reduction rate in the electrode reaction. Thus, an increase in the amount of hydrogen reduction on the electrode surface results in a decrease in charge transfer resistance.
How to calculate the value of α (alpha) in Equation 6.4.8 for a quasi-reversible reactions? [From BARD A J, FAULKNER L R. Electrochemical methods: fundamentals and applications, 2nd Edition [M]. New York: John Wiley & Sons, 2001, p.238]