Effect of Sn2+on Anodic Dissolution of Ni in Perchloric Acid

The effect of Sn 2+ on the anodic dissolution of nickel was investigated in deaerated 0.2 M HClO 4 solution containing Sn 2+ at room temperature. It has been found that the addition of 10 −3 M Sn 2+ inhibits completely the anodic dissolution of Ni. In contrast, tin itself is not passivated in 0.2 M HClO 4 irrespective of the addition of 10 −3 M Sn 2+ . Besides, the anodic dissolution of Ni is not inhibited by the surface coating with Sn (IV) colloid which mainly consistis of hydrous or amorphous nano-crystalline SnO 2 . X-ray photoelectron spectroscopy (XPS) analysis used to supplement our recent X-ray absorption spectroscopy (XAS) results has indicated that the inhibition effect of Sn 2+ on anodic dissolution of Ni is associated with the underpotential deposition (UPD) of Sn on Ni. The metallic bond between Sn and Ni in the Sn-UPD layer on Ni is a prerequisite to the formation of Sn residue adhered to the Ni substrate at the more noble potential that brings the inhibition effect on anodic dissolution of Ni. Moreover, the difference between inhibition effects of Sn 2+ and Pb 2+ on anodic dissolution of Ni was discussed on the basis of the difference between Sn- and Pb-UPD on Ni.