Diffusion at Au(100)/Cd2+ interface during electrodeposition

The kinetics of thin alloy film formation and growth within the underpotential range of Cd electrodeposition on Au(100) have been studied at room temperature in 50 mM H2SO4+1 mM CdSO4 solution. Calculations of the diffusion coefficients of Cd in the Au electrode surface, together with in situ atomic force microscopy (EC-AFM) observation and polarization experiments, have shown that the overall alloying process at the Au(100)/Cd2+ interface consists of two processes: one very fast, which occurs within 2 ML and is characterized by D≈10−16 cm2 s−1; and another one, much slower, which is characterized by D≈10−18 cm2 s−1, suggesting a solid state diffusion process. The concentration distribution of Cd in the Au electrode surface was obtained. Based on this new kinetic approach to the alloying process at the metal/electrolyte interface, a mechanism was proposed for the surface alloying process that occurs in the underpotential region.