Interpretation and Significance of Heats of Activation for Electrochemical Reactions Exhibiting Anomalous Tafel Slopes

Abstract

Heats of activation for electrochemical reactions studied over a wide range of temperatures are considered in relation to the temperature dependence of the Tafel slope factor b. Experimentally, b is found to have anomalous temperature dependence, i.e., other than the classical form , for hydrogen evolution at Hg, Cd, Pb, Ni, and Pt and the consequences of this behavior in calculation of heats of activation are evaluated. Curvature of the electrochemical Arrhenius plots is shown to arise for certain of the cases treated and is discussed in relation to the problem of detection of proton tunneling at low temperatures. Other difficulties associated with temperature dependence of coverage by atomic H and temperature‐dependent structure changes in the solvent are considered.