The inhibiting effect of organic substances at polycrystalline and amalgam electrodes

The influence of the nature of the electrode on the inhibiting effect of organic substances at fixed surface coverage was considered. The relations between the surface coverage by molecules of aliphatic alcohols and carbonic acids and the rates of reactions of the ionic transfers (ITR) Cd(II)/Cd, Zn(II)/Zn, Pb(II)/Pb as well as that of the electronic transfer Eu(III)/Eu(II) were obtained by a coulostatic method on renewable amalgam and solid electrodes. In the case of ITR, a significant decrease of the inhibiting effect was found with the transition from amalgam to polycrystalline electrodes, which was not observed in the case of the recharge reaction. Analysis of the possible reasons for the observed effects, including the influence of the solid surface inhomogeneity and new phase formation on the results of relaxation measurements as well as changes of the double layer structure, was carried out. It was shown that the first two factors did not contribute significant distortions to the values of the adsorption and kinetic parameters obtained by the coulostatic method on solid electrodes renewed by cutting. The basic reason for the effect may be the change in orientation of the adsorbate and related ion-dipole interaction between the activated complex and organic molecules in the surface layer. Simulations for the energy of the electrostatic interaction carried out within the framework of a 'fixed grid' model show good correlation between the experimental and simulated dependences. (C) 2003 Elsevier Science B.V. All rights reserved.