Refining anodic and cathodic dissolution mechanisms: combined AESEC-EIS applied to Al-Zn pure phase in alkaline solution

Abstract

In this work, the use of atomic emission spectroelectrochemistry (AESEC) coupled to electrochemical impedance spectroscopy (EIS) is presented as a method of revealing dissolution mechanisms. To illustrate the method, the dissolution kinetics of Al cations from an Al-Zn pure phase (Zn-68 wt.% Al) was investigated in an alkaline solution. In the cathodic potential domain, a nearly direct formation of dissolved Al 3+ was observed, while in the anodic potential domain the Al dissolution occurred by migration across a ZnO/Zn(OH) 2 film. It was demonstrated that this methodology can be applied to a nonstationary system during a potentiostatic experiment for a lower Al content phase (Zn-22 wt.% Al). The nature of the charge transfer mechanisms depended on the applied potential and could be identified by comparing the direct current and alternating current faradaic yield using AESEC-EIS.

Recent insights in corrosion science from atomic spectroelectrochemistry

“…In contrast to Mg and Zn, Al and Al alloys displayed a negative difference effect due to chemical dissolution. [ 58–60,66,67,90 ] The dissolution current of Al in NaOH solution was found to be an order of magnitude higher than the corrosion current estimated by Tafel extrapolation. [ 58,66 ]…”

“…Apart from conventional alloys, most multi‐principal element alloys studied using ASEC are found to dissolve incongruently. [ 85–91 ] Evolution of dissolution rate of each alloying element from alloys is found to depend on applied potential, exposure duration, pH, and so on. For example, both pH and exposure duration influenced the dissolution ratios of $$\frac{{{{{\upsilon}}_{Zn}}}}{{{{{\upsilon}}_{Al}}}}$$ in Al‐Zn alloys, [ 72 ] $$\frac{{{{{\upsilon}}_{Mg}}}}{{{{{\upsilon}}_{Si}}}}$$ in Mg 2 Si.…”

“…Han et al [ 90 ] investigated Al 0.5 Zn alloys using the EIS‐ASEC approach at different potential domains in 0.1 NaOH solution. Three potential domains were selected based on ASEC‐PDP results, included (1) cathodic region displaying selective (non‐faradaic) dissolution of Al, (2) intermediate region displaying selective dissolution of Zn as a consequence of oxidation of Zn(0) enriched layer, and (3) anodic region characterized by the nearly congruent (faradaic) dissolution of the alloy.…”

“…EIS‐ASEC analysis of Al 0.7 Zn revealed the unique frequency dependency of the dissolution behavior of both elements in the same electrolyte. [ 90 ] By comparing the DC and AC yields, the authors presented a detailed analysis of oxide formation, dissolution, and diffusion processes occurring at the alloy‐electrolyte interface.…”

“…In contrast to Mg and Zn, Al and Al alloys displayed a negative difference effect due to chemical dissolution. [58][59][60]66,67,90] The dissolution current of Al in NaOH solution was found to be an order of magnitude higher than the corrosion current estimated by Tafel extrapolation. [58,66] The dissolution current density of several passive metals and alloys displaying spontaneous passivity was found to be relatively lower than the corrosion current density estimated from PDP curves.…”