Surface segregation of cadmium atoms at the interface of mechanically renewable Ag–Cd alloy electrode with surface-inactive electrolyte solution

Abstract

The surface segregation of cadmium atoms at the interface of mechanically renewed electrodes of the Ag–Cd alloy (containing 1 at % Cd; the region of cadmium solid solutions in silver) with a surface-inactive electrolyte solution is studied in the potential range of ideal polarizability by means of impedance spectroscopy and cyclic voltammetry. It is shown that method of mechanic renewal makes it possible to obtain well reproducible data on the kinetics of electrode surface enrichment with atoms of cadmium which is the surface-active component of this alloy. As follows from the analysis of dependences of the electric double layer (EDL) capacitance on the potential (C vs. E curves) pertaining to different times after the electrode renewal, these dependences can be well described in terms of the model of capacitors connected in series (“the common dense layer”). Using this model, the dependences of the alloy surface coverage with cadmium atoms on the time of exposure of the freshly renewed electrode surface to the electrolyte solution are calculated. The mechanism of surface segregation of cadmium atoms is proposed. It allows the kinetics of relaxation processes that occur in the alloy surface layer to be consistently interpreted. The electrochemical data are supplemented and compared with the results of analysis of the surface composition and the data of the profile analysis over the depth of the same alloy at its interface with vacuum, performed by means of Auger electron spectroscopy.