Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions: I . pH and Carbonate Ion Effects in Film Formation and Dissolution

Abstract

The effects of carbonate ions on the electrolytic oxidation and reduction processes that take place at zinc electrodes in aqueous alkaline solutions have been studied by cyclic voltammetry; the behavior is compared with that in sulfate and chloride solutions at the same pH. A reaction which corresponds in the first anodic peak false(A1false) of the cyclic voltammograms for zinc in carbonate solutions is found to be first order with respect to hydroxide ions in the pH range 12.0–13.5. It has a diffusion‐controlled current component. A second anodic peak false(A2false) is only observed in carbonate solutions, but the diffusing species associated with the processes at peaks A1 and A2 is found to be the same, as indicated by the identity of slopes of inormalp vs. r1/2 plots in rotating disk electrode experiments. It is suggested that this behavior can be explained in terms of a residual current passing through a porous oxide/hydroxide film that is already formed in the A1 process. The breakdown of the passive films in Cl− or SO42− solutions, and the resistivity of the passive film formed in CO32− solutions, is examined and discussed.

Electrochemical Behaviors of Zn Anode in Carbonate-based Aqueous Solutions

“…1(a) is in good agreement with that reported by Conway et al 9 The anodic current peak A 1 at around ¹1.2 V vs. Hg/HgO corresponds to dissolution of Zn and a flatter peak A 2 observed at around ¹1.0 to ¹0.8 V vs. Hg/HgO is the formation of The Electrochemical Society of Japan http://dx.doi.org/10.5796/electrochemistry.83.864…”

“…[9][10][11] As shown in Fig. 1(b), two strong anodic current peaks were observed when the concentration of K 2 CO 3 was higher than 4.0 M, while the extent of anodic oxidation of Zn in 0.5-3.0 M K 2 CO 3 aqueous solutions were quite small.…”

“…3,6 There are few papers found that deals with the electrochemistry of Zn in carbonate aqueous electrolyte solutions. [9][10][11] Among them, redox behavior of Zn in concentrated carbonate system have not been reported. In this paper, Zn electrode behaviors in carbonate-based aqueous solutions (the aqueous solutions of K 2 CO 3 and concentrated K 2 CO 3 containing KOH) were examined.…”

Corrosion Inhibition of Zinc by Aqueous Vanadate Species

“…Although identification of these species is complex, these presumably arise from the reduction of two distinct Zn 2+ surface species. [26][27][28] Identical scans in which the only change was the removal of the 5000 s hold displayed only the peak at ∼-1.4 V SCE . Therefore, it is assumed that the peak at ∼-1.2 V SCE arose from a Zn 2+ surface species generated during the holding period.…”

“…The stability of the hydrozincite layer on the vanadate short-pretreated Zn (Figure 4c) versus the layer's instability in the absence of vanadate provides possible insight into the mechanism of corrosion inhibition provided by vanadate, as the formation of hydrozincite is known to provide corrosion inhibition on Zn under atmospheric exposure. 18,26,33,34 The differences in the spectra of the short pretreated and immersed in NaCl sample versus the sample that was simply immersed in the NaCl+NaVO 3 are also of note. The strong, wide band between 650 and 1030 cm −1 , present in Figure 4d but absent in Figure 4c, indicates the presence of polymerized vanadate [35][36][37] on the sample immersed in NaCl+NaVO 3 .…”