ИСТИНА

It is typical of alloy electrodes that their surface composition substantially differs from the volume composition. The phenomenon of spontaneous enrichment of the alloy surface with individual components (surface segregation) is interesting for both theory and practice because determines in many aspects the electrocatalytic and corrosion properties of alloys, plays the important role in solving certain problems of modern technology (microelectronics, nanotechnology), etc. The electrochemical measurements on mechanically renewable electrodes of alloys in the potential region of their ideal polarizability are a promising method for studying the surface segregation at the electrochemical interface. The mechanical renewal of the electrode surface in situ makes it possible to create the well reproducible initial state in which the surface and volume compositions of the alloy coincide. This state is used as the starting point for studying the processes that induce changes in the surface composition and lead to formation of the equilibrium electrode/solution interface. Earlier, this method allowed us to study the kinetics and the mechanism of surface segregation of individual components of binary alloys depending on their phase diagram (eutectic alloys, solid solutions or solid solutions with limited solubility of components), the electrode potential, the electrolyte composition, etc. In this study, for the eutectic system Ag-Bi (1 at.% Bi), the effect of surface segregation of bismuth atoms on the kinetics of the model reaction of reduction of S2O82- anions is considered. For this purpose, the impedance measurements were carried out on alloy electrodes and also on electrodes of individual components at different potentials and in different moments after the surface renewal. The detailed analysis of Nyquist diagrams made it possible to calculate the dependences of the charge transfer resistance of the reaction (Rct) on the potential and the time from the moment of the alloy surface renewal in electrolyte solution. It is shown that Rct is very sensitive to the increase in the content of bismuth atoms in the surface layer (surface segregation) observed with the increase in the time of alloy electrode contact with solution. Based on the data obtained, we put forward the model interpretation of the evolution of kinetic parameters of the reaction of electroreduction of S2O82- anions which attributes this effect to the surface relaxation of the renewable alloy electrode in the course of formation of its equilibrium boundary with the electrolyte solution. The results of studying the surface segregation of bismuth on the Ag-Bi alloy electrode/electrolyte interface are compared with the data obtained by Auger electron spectroscopy for the interface of the same alloy with vacuum. The study was carried out with the financial support by the Russian Foundation for Basic Research (grant no. 12-03-01027-a).