The Driving-Force Dependence of Electrochemical Rate Parameters: Origins of Anodic-Cathodic Asymmetries for Metal Aquo Redox Couples.

The consequences of differences in the intramolecular force constants and the ionic entropies between the oxidized and reduced states of aquo redox couples upon their electrochemical kinetics are examined as a function of the driving force. A generalized harmonic oscillator model is utilized that involves estimating the activation barrier from the individual force constants in the oxidized and reduced states rather than employing average reduced values. Noticeable asymmetry in the anodic and cathodic Tafel plots is predicted for redox couples having large ca. twofold differences in force constants, the plots being markedly more curved at anodic over-potentials.