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

摘要

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.