Kinetics of surface segregation of bismuth atoms at the interface of a mechanically renewable Ag-Bi alloy electrode with a surface-inactive electrolyte solution

Abstract

The time effects observed on mechanically renewed electrodes of eutectic-type Ag-Bi alloys in NaF solutions in the potential range of ideal polarizability are studied by the impedance method and cyclic voltammetry. The changes in the electric double layer (EDL) capacitance observed with the increase in the time of the electrode-solution contact from the moment of electrode renewal indicate that the process of surface enrichment with Bi atoms occurs. The analysis of obtained data leads to a conclusion that the surface segregation of Bi proceeds by the mechanism of surface diffusion, which provides the anomalously high diffusion rates as compared with the processes of volume diffusion in the solid phase. The results of studies of the surface segregation of bismuth on the Ag-Bi alloy/electrolyte interface are compared with the Auger-spectroscopic data for the interface of the same alloy with vacuum. Assumptions are put forward and substantiated that allow the differences in the kinetics of surface segregation processes observed on different interfaces to be consistently interpreted.