A Kramers reaction rate theory for electrochemical ion transfer reactions

A simple model for electrochemical ion transfer reactions, based on an extended Anderson-Newns model [W. Schmickler, Chem. Phys. Lett. 237 (1995) 152], is treated within the framework of the multidimensional Kramers theory to calculate ion transfer rates. It is shown that for univalent ion transfer, the rate constant may be substantially influenced by a partial charge transfer during the rate-determining step of the adsorption process, even though the activation barrier is mainly determined by the separation from the metal surface. In the limit of strongly overdamped solvent dynamics, however, the energetically favourable adiabatic electron exchange with the electrode is suppressed and the effective reaction coordinate is again one-dimensional, and given by the separation from the surface.