Alkaline Zinc Passivation Mechanism is Controlled by Hydroxide Concentration

Reed M. Wittman; Robert L. Sacci; Thomas A. Zawodzinski

doi:10.1149/1945-7111/adc6c7

Alkaline Zinc Passivation Mechanism is Controlled by Hydroxide Concentration

Reed M. Wittman, Robert L. Sacci, Thomas A. Zawodzinski

Energy Storage & Conversion

Research output: Contribution to journal › Article › peer-review

Abstract

We studied Zn passivation and oxide growth in Zincate (Zn(OH)₄²⁻) in 4 and 8 M KOH solutions using an electrochemical quartz crystal microbalance (EQCM), building on our initial work at 1 M KOH where passivation was kinetically controlled. A porous passivating oxide spontaneously forms on Zn electrodes when KOH is above 4 M and saturated with zincate. However, passivation does not occur when bulk zincate concentration is decreased, resulting in continual Zn dissolution. EQCM data suggests that the passivation mechanism is strongly affected by pOH. Mass transport and kinetic processes in the 4 M KOH electrolytes couple and govern Zn passivation. At 8 M, KOH concentration shifts passivation to mass transport control. We explain this by the increased solubility of Zn(OH)₃⁻ with increasing pOH. The variation in the mechanism of passivation implications for how passivation is handled in Zn-alkaline batteries. The importance of controlling the mass transport increases with increased pOH, suggesting that electrode design, additives, and potential flow should be optimized. At lower pOHs, kinetics and mass transport must be balanced to manage passivation effectively. Additionally, the changing nature of the native oxide layer on the surface has implications for the evenness of deposition and dissolution on the Zn electrode.

Original language	English
Article number	040514
Journal	Journal of the Electrochemical Society
Volume	172
Issue number	4
DOIs	https://doi.org/10.1149/1945-7111/adc6c7
State	Published - Apr 1 2025

Funding

EQCM equipment and measurements were supported by laboratory directed research initiative at Oak Ridge National Laboratory. This manuscript has been partially authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The DOE Office of Electricity for Grid Reliability supported R.M.W. and T.A.Z. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly-owned subsidiary of Honeywell International, Inc., for the US DOE\u2019s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the US DOE or the United States Government. EQCM equipment and measurements were supported by laboratory directed research initiative at Oak Ridge National Laboratory. This manuscript has been partially authored by UT-Battelle, LLC under Contract No. DE-AC05\u201300OR22725 with the U.S. Department of Energy. The DOE Office of Electricity for Grid Reliability supported R.M.W. and T.A.Z. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly-owned subsidiary of Honeywell International, Inc., for the US DOE\u2019s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the US DOE or the United States Government.

Keywords

alkaline zinc
electrochemical quartz crystal microbalance
metal anodes
zinc battery
zinc corrosion
zinc electrodeposition
zinc passivation

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10.1149/1945-7111/adc6c7

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title = "Alkaline Zinc Passivation Mechanism is Controlled by Hydroxide Concentration",

abstract = "We studied Zn passivation and oxide growth in Zincate (Zn(OH)42−) in 4 and 8 M KOH solutions using an electrochemical quartz crystal microbalance (EQCM), building on our initial work at 1 M KOH where passivation was kinetically controlled. A porous passivating oxide spontaneously forms on Zn electrodes when KOH is above 4 M and saturated with zincate. However, passivation does not occur when bulk zincate concentration is decreased, resulting in continual Zn dissolution. EQCM data suggests that the passivation mechanism is strongly affected by pOH. Mass transport and kinetic processes in the 4 M KOH electrolytes couple and govern Zn passivation. At 8 M, KOH concentration shifts passivation to mass transport control. We explain this by the increased solubility of Zn(OH)3− with increasing pOH. The variation in the mechanism of passivation implications for how passivation is handled in Zn-alkaline batteries. The importance of controlling the mass transport increases with increased pOH, suggesting that electrode design, additives, and potential flow should be optimized. At lower pOHs, kinetics and mass transport must be balanced to manage passivation effectively. Additionally, the changing nature of the native oxide layer on the surface has implications for the evenness of deposition and dissolution on the Zn electrode.",

keywords = "alkaline zinc, electrochemical quartz crystal microbalance, metal anodes, zinc battery, zinc corrosion, zinc electrodeposition, zinc passivation",

author = "Wittman, {Reed M.} and Sacci, {Robert L.} and Zawodzinski, {Thomas A.}",

note = "Publisher Copyright: {\textcopyright} 2025 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.",

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doi = "10.1149/1945-7111/adc6c7",

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AU - Sacci, Robert L.

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N2 - We studied Zn passivation and oxide growth in Zincate (Zn(OH)42−) in 4 and 8 M KOH solutions using an electrochemical quartz crystal microbalance (EQCM), building on our initial work at 1 M KOH where passivation was kinetically controlled. A porous passivating oxide spontaneously forms on Zn electrodes when KOH is above 4 M and saturated with zincate. However, passivation does not occur when bulk zincate concentration is decreased, resulting in continual Zn dissolution. EQCM data suggests that the passivation mechanism is strongly affected by pOH. Mass transport and kinetic processes in the 4 M KOH electrolytes couple and govern Zn passivation. At 8 M, KOH concentration shifts passivation to mass transport control. We explain this by the increased solubility of Zn(OH)3− with increasing pOH. The variation in the mechanism of passivation implications for how passivation is handled in Zn-alkaline batteries. The importance of controlling the mass transport increases with increased pOH, suggesting that electrode design, additives, and potential flow should be optimized. At lower pOHs, kinetics and mass transport must be balanced to manage passivation effectively. Additionally, the changing nature of the native oxide layer on the surface has implications for the evenness of deposition and dissolution on the Zn electrode.

AB - We studied Zn passivation and oxide growth in Zincate (Zn(OH)42−) in 4 and 8 M KOH solutions using an electrochemical quartz crystal microbalance (EQCM), building on our initial work at 1 M KOH where passivation was kinetically controlled. A porous passivating oxide spontaneously forms on Zn electrodes when KOH is above 4 M and saturated with zincate. However, passivation does not occur when bulk zincate concentration is decreased, resulting in continual Zn dissolution. EQCM data suggests that the passivation mechanism is strongly affected by pOH. Mass transport and kinetic processes in the 4 M KOH electrolytes couple and govern Zn passivation. At 8 M, KOH concentration shifts passivation to mass transport control. We explain this by the increased solubility of Zn(OH)3− with increasing pOH. The variation in the mechanism of passivation implications for how passivation is handled in Zn-alkaline batteries. The importance of controlling the mass transport increases with increased pOH, suggesting that electrode design, additives, and potential flow should be optimized. At lower pOHs, kinetics and mass transport must be balanced to manage passivation effectively. Additionally, the changing nature of the native oxide layer on the surface has implications for the evenness of deposition and dissolution on the Zn electrode.

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KW - metal anodes

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Alkaline Zinc Passivation Mechanism is Controlled by Hydroxide Concentration

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