A study at the molecular level of the mechanism of surface diffusion at electrode–electrolyte interfaces

Using a model for the adsorption of water on electrode surfaces in which only two orientations are considered, it was possible to deduce the exponential dependence between surface diffusion coefficients and potential, which has been experimentally found when measuring the change with time of the roughness factors of columnar structured platinum and gold electrodes in contact with acidic electrolytes. The linear dependence between the logarithm of surface diffusion coefficient and the potential is explained by introducing an empirical coefficient, δ, proportional to the rate of variation of the activation enthalpy for surface diffusion with the potential. An explanation for the change of sign of δ, as well as a semiquantitative estimation of it, can be given using the theoretical description developed here.