Comparative kinetic study of Cd diffusion into Au(100) and Ag(100) during electrodeposition

Abstract

The kinetics of thin alloy film formation and growth during Cd electrodeposition on Au(100) and Ag(100) has been studied at room temperature in 50 mM H₂SO₄ + 1 mM CdSO₄ solution within the Cd underpotential range from − 0.3 to − 0.45 V. Electrochemical experiments and atomic force microscopy studies have shown that the overall alloying process at the Cd²⁺/Au(100) and Cd²⁺/Ag(100) interfaces consisted of two processes: one very fast, which occurred within a few atomic layers and is characterized by a diffusion coefficient, D≈10⁻¹⁶ cm² s⁻¹, and another much slower, which is characterized by D≈10⁻¹⁹ cm² s⁻¹, suggesting a solid state diffusion process. Based on a new kinetic approach to the alloying process at the metal/electrolyte interface in the underpotential region, the differences in kinetic parameters are discussed.