Coupled partial ion-transfer steps in the anodic dissolution of metals

A new model is proposed for the anodic dissolution of metals. It is assumed (i) that the rate-determining process is the transfer of metal ions throug h the double layer, (ii) that ion-transfer proceeds in two steps via an ads orbed, partially solvated ionic intermediate, and (iii) that the surface co ncentration of the intermediate species affects the potential distribution across the double layer, hence also the ionic transfer rate. It is shown th at the model can explain the current-potential characteristics and the elec trical impedance of anodically dissolving metals. The low-frequency loop of the electrical impedance is shown to arise from relaxation of the double l ayer during transfer of an ion. (C) 1999 The Electrochemical Society. S0013 -4651(98)09-010-7. All rights reserved.