1. The overpotential, or overvoltage, is the difference between the electrode potential and the equilibrium potential defined asEeq=E° ± [(RT)/F]ln{([A]eqa[B]eqb.)/[C]eqc[D]eqd.}, whereE° is the standard potential corresponding to the overall reaction and [A]eq, [B]eq, [C]eq, [D]eqare the equilibrium activities of the reactants and products. The overpotential is thus different from the “driving force” of the reaction defined as the opposite of the standard free energy of the reaction: ΔG° = ±F(E−E°), referred to the standard state of the reactant and product system.
2. Bockris, J. O. M. R., Amylya, K. N., and Gamboa-Aldeco, M. E.Modern Electrochemistry: Fundamentals of Electronics,2nded.Kluwer Academic/Plenum Publishers:New York, 2001; Vol.2A, pp1275−1287.
3. Recent developments in understanding factors of electrocatalysis
4. Homogeneous redox catalysis of electrochemical reaction
5. Or any other two dimensionless parameters obtained from the combination of these two. Beyond the choice of the two parameters, the important point is that their number is two.