Inhibition effect of underpotential deposition of metallic cations on aqueous corrosion of metals

Abstract

Abstract The experimental results reported so far for the inhibition effect of underpotential deposition (UPD) of metallic cations on aqueous corrosion of metals are criticized and discussed based on the prerequisite for UPD. The inhibition effect of Pb2+, Cd2+, Zn2+ or Mn2+ on hydrogen evolution or hydrogen absorption on Armco iron or various steels is classified into three potential regions: bulk deposition, UPD and adsorption of metallic cations without discharging. Moreover, the inhibition effect of Pb2+, Tl+ or Sn2+ on anodic dissolution of pure Fe, Ni or Ni-base alloys in acidic solutions is ascribed to the UPD of these metallic cations. Particularly, in situ X-ray absorption spectroscopy (XAS) for Pb-UPD on Ni has indicated that the electro-deposited Pb species on the Ni surface is metallic to form partly surface alloy and the metallic Pb blocks the active dissolution sites of Ni to inhibit the anodic dissolution. In contrast, in situ XAS for Sn-UPD on Ni has indicated that the electro-deposited Sn species is not only bonded with Ni atoms but also bonded with oxygen atoms and that the anodic dissolution of Ni is inhibited by the oxygenated Sn species on Ni.