The polarization and corrosion characterization of zinc and modified zinc in concentrated alkali metal hydroxide electrolyte: The effect of a zinc oxide/hydroxide surface.

摘要

The polarization and corrosion of Zn in concentrated 9N KOH is important for characterizing the Zn anode in primary, secondary and reserve batteries. Currently, Zn is alloyed with Hg to decrease corrosion and increase discharge. The exact role of Hg and other metal additions to Zn on the polarization and corrosion behavior is not well understood. This study investigates the polarization and corrosion behavior of Zn modified by immersion pretreatment in dilute aqueous metal ion solutions of HgCl{dollar}sb2{dollar}, Pb(C{dollar}sb2{dollar}H{dollar}sb3{dollar}O{dollar}sb2{dollar}){dollar}sb2{dollar}, PbCl{dollar}sb2{dollar}, InCl{dollar}sb3{dollar} and TlCl. These metals are reportedly beneficial additions to the Zn anode. Further, the effect of alkali metal cation on the anodic and cathodic reactions were studied in deaerated concentrated alkali metal hydroxide electrolytes, LiOH (1-5N), NaOh (1-9N) and KOH (1-9N).; The initial electrochemical behavior of Zn is controlled by a thin air-formed heterogeneous Zn oxide/hydroxide surface. The hydroxide surface is anodically active associated with the preferred adsorption of OH{dollar}sp-{dollar} ion on Zn(OH){dollar}sb2{dollar}. Anodic polarization decreases from LiOH {dollar}>{dollar} NaOH {dollar}>{dollar} KOH, in agreement with the electrolyte activity and the decrease in cation hydration. The anodic dissolution mechanism is independent of the electrolyte; however, the heterogeneous surface results in nonuniform dissolution. The oxide surface is cathodically active. The thin air-formed surface is not dissolved or reduced during cathodic polarization. At low cathodic overpotential, hydrogen evolution occurs by water reduction with charge transfer assisted by the alkali metal cation. At high overpotential hydrogen evolution is consistent with alkali metal cation penetration mechanism.; Zinc pretreatment in HgCl{dollar}sb2{dollar} solution fluxes the heterogeneous air-formed surface film to form a uniform Hg-containing Zn(OH){dollar}sb2{dollar} after immersion in 9N KOH. The Hg-modified Zn(OH){dollar}sb2{dollar} surface film increases cathodic polarization and depolarizes anodic dissolution. The Hg contained in the Zn(OH){dollar}sb2{dollar} surface film is less than 1 atomic percent.; The metal ion treatments, Pb(C{dollar}sb2{dollar}H{dollar}sb3{dollar}O{dollar}sb2)sb2{dollar}, PbCl{dollar}sb2{dollar}, InCl{dollar}sb3{dollar} and TlCl, alter the electrochemical behavior of Zn through metal deposition on and stabilization of the air-formed Zn oxide/hydroxide surface. Both the anodic and cathodic reactions are polarized more following metal ion pretreatment.