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<p>When iron is immersed in nitric acid at a concentration of approximately 10&#xa0;M, its corrosion potential spontaneously oscillates due to the alternating processes of dissolution and passivation. In our previous study [<i>J. Electrochem. Soc.</i>, <b>170</b> (2023) 081505], we demonstrated that (1) the corrosion potential oscillation is of the hidden N-shaped negative differential resistance (HN-NDR) type, (2) the anodic partial current associated with iron dissolution exhibits N-NDR behavior due to surface passivation, and (3) the cathodic partial current from nitrate reduction acts as an N-NDR-hiding factor. Although numerical simulations supported these findings, they were based on a simplified model that did not incorporate iron dissolution, and therefore could not fully explain the mechanism of the oscillation. In the present study, we developed a new model to address these limitations. The improved model explicitly includes the concentration of iron ions at the electrode surface, N-NDR behavior arising from surface passivation, and pH-dependent kinetics of passive film formation and breakdown. The local pH at the electrode surface is calculated under the assumption of electroneutrality. Using this model, we successfully reproduced the corrosion potential oscillations and clarified the underlying mechanism.</p> Graphical Abstract <p></p>

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Mechanistic insights into corrosion potential oscillations of iron electrodes in nitric acid via numerical simulation

  • 期刊论文

  • 发表日期：

    2025年8月29日

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  • Ryo Sato,
  • Terumasa Kuge,
  • Shuji Nakanishi,
  • Yoshiharu Mukouyama

摘要

When iron is immersed in nitric acid at a concentration of approximately 10 M, its corrosion potential spontaneously oscillates due to the alternating processes of dissolution and passivation. In our previous study [J. Electrochem. Soc., 170 (2023) 081505], we demonstrated that (1) the corrosion potential oscillation is of the hidden N-shaped negative differential resistance (HN-NDR) type, (2) the anodic partial current associated with iron dissolution exhibits N-NDR behavior due to surface passivation, and (3) the cathodic partial current from nitrate reduction acts as an N-NDR-hiding factor. Although numerical simulations supported these findings, they were based on a simplified model that did not incorporate iron dissolution, and therefore could not fully explain the mechanism of the oscillation. In the present study, we developed a new model to address these limitations. The improved model explicitly includes the concentration of iron ions at the electrode surface, N-NDR behavior arising from surface passivation, and pH-dependent kinetics of passive film formation and breakdown. The local pH at the electrode surface is calculated under the assumption of electroneutrality. Using this model, we successfully reproduced the corrosion potential oscillations and clarified the underlying mechanism.

Graphical Abstract