Dealloying and selective dissolution are serious corrosion processes, but also employed in technology. We studied the surface structure of Cu0.83Pd0.17(001) and Cu3Au(001) during electrochemical selective Cu dissolution below the critical potential in-situ in 0.1 M H2SO4 (pH=1) electrolyte. In both cases we observe the formation of an epitaxial layer of nano-scale islands of the noble component of the original alloy (Au or Pd). These islands form a metallic passivation layer suppressing massive dissolution of Cu. The Au islands developed {111} facets. By re-deposition of Cu ions from the electrolyte solution onto Pd islands, an epitaxial Cu layer is formed. (c) 2007 Elsevier B.V. All rights reserved.