Temperature dependence of the transfer coefficient in electron and atom group transfer processes

Abstract

The Tafel “ b-coefficient” for several different electrochemical processes appears to be almost independent of the temperature over wide ranges, indicative of a transfer coefficient which increases approximately linearly with increasing temperature. It is shown here that the transfer coefficient calculated on the basis of electron and atom group transfer theory does in fact rise with increasing temperature. If the effect is ascribed solely to vibrational frequency dispersion of the external solvent and quantum mechanical freezing of solvent modes at the lower temperatures, it is much smaller than the observed effects. Large vibrational frequency shifts in local modes, eg corresponding to adsorption of reaction intermediates, can, however, lead to effects comparable in magnitude with those observed. A transfer coefficient which increases significantly with increasing temperature can also arise from solvent dielectric spatial dispersion or local structural extension which becomes increasingly important with decreasing temperature.