A model for low temperature electrochemical proton transfer: Temperature and isotope effects on kinetic parameters

Simple framework is suggested for low temperature proton transfer reactions at electrodes. Temperature and potential dependence of the electrode current and apparent transfer coefficient, αobs, are calculated. The results are in accordance with experimental observations [M. Cappadonia, S. Krause, and U. Stimming, Electrochim. Acta, 42, 841 (1997)], including the tendency for αobs extrapolated to T=0 K to approach negative values. This behavior of αobs results in a weak and rather inverse dependence of activation energy on overpotential and a strong potential dependence of the “entropic” factor. The observed isotope effect is basically accounted for by the change of the mass of the tunneling hydrogen isotope and the corresponding changes in the isotope-dependent characteristic frequencies of the medium.