Influences on homogeneous chemical reactions in the diffuse double layer

Abstract

Summary An approximate theoretical treatment of the various influences on homogeneous chemical reactions in the diffuse double layer is given and compared with experimental results. The dissociation and recombination of carboxylic acids prior to the charge transfer step of the hydrogen evolution at a mercury electrode is taken as an example. On the basis of a modified Gouy-Chapman-theory the profiles of the various double-layer parameters across the effective diffuse double layer are computed and the profile of the dissociation field effect is then obtained with Onsager's theory. The double-layer effects on the recombination rate are also discussed. Good agreement between the experimentally accessible global effect of the double-layer effects and the overall theoretical result developed, is achieved. Under the conditions assumed, the dissociation field effect proves to be the dominant double-layer influence on the reaction type considered. Finally, decrease of dissociation for thermodynamic reasons caused by the polarization of the solvent is discussed. It is shown that these restrictions remain very marginal for the reaction type treated under the assumed conditions, although they might be of more importance for other cases.