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<p>The electrode redox potential, which varies substantially with the electrolyte, governs both the direction and thermodynamic driving force of electrochemical reactions. However, a comprehensive understanding and effective control of redox potential shifts remain unestablished. Here we report the pronounced effect of coordination-shell ions on the redox potential of metal electrodes. Cooperative interactions between the metal ion and surrounding anions and cations with large differences in hardness/softness amplify the redox potential shift, as corroborated by liquid Madelung potential. Specifically, in the Zn/Zn<sup>2+</sup> system, the addition of soft anions paired with hard cations destabilizes the Zn<sup>2+</sup> solution structure and upshifts the redox potential, whereas hard anions with soft cations stabilize the structure and induce a downshift. Following this principle, a potential gap exceeding 0.6 V was achieved—a remarkably large but reasonable value for a divalent system. This ion hardness/softness-based strategy also demonstrates practical benefits in Zn plating/stripping tests, where electrolytes with upshifted redox potentials enable an average Coulombic efficiency exceeding 99.9%.</p><p></p>

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Metal electrode potential diverges with ion additions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月26日

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  • Qiu Zhang,
  • Seongjae Ko,
  • Taisei Sakata,
  • Shin-ichi Nishimura,
  • Norio Takenaka,
  • Atsushi Kitada,
  • Chunsheng Wang,
  • Atsuo Yamada

摘要

The electrode redox potential, which varies substantially with the electrolyte, governs both the direction and thermodynamic driving force of electrochemical reactions. However, a comprehensive understanding and effective control of redox potential shifts remain unestablished. Here we report the pronounced effect of coordination-shell ions on the redox potential of metal electrodes. Cooperative interactions between the metal ion and surrounding anions and cations with large differences in hardness/softness amplify the redox potential shift, as corroborated by liquid Madelung potential. Specifically, in the Zn/Zn2+ system, the addition of soft anions paired with hard cations destabilizes the Zn2+ solution structure and upshifts the redox potential, whereas hard anions with soft cations stabilize the structure and induce a downshift. Following this principle, a potential gap exceeding 0.6 V was achieved—a remarkably large but reasonable value for a divalent system. This ion hardness/softness-based strategy also demonstrates practical benefits in Zn plating/stripping tests, where electrolytes with upshifted redox potentials enable an average Coulombic efficiency exceeding 99.9%.