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<p>In this study, the electrochemical behavior of Eu(II)/Eu(III) redox couple in LiF-NaF-KF (46.5–11.5–42&#xa0;mol%) (FLiNaK) molten salt was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), and chronopotentiometry (CP) on inert tungsten electrode at 923&#xa0;K. The results showed that the Eu(II)/Eu(III) couple was a one-electron exchanged system, corresponding to the reduction of Eu(III) to Eu(II) and the oxidation of Eu(II) to Eu(III), and both processes were reversible and diffusion-controlled. Then, the concentration ratio of Eu(II)/Eu(III) was determined by combining SWV and X-ray photoelectron spectroscopy (XPS) techniques, and the results showed that Eu(III) was decomposed into Eu(II) during heat treatment and Eu(III) and Eu(II) would coexist in molten FLiNaK. Therefore, Eu(II)/Eu(III) was chosen as a redox indicator with its concentration ratio to assess the redox properties of molten salt. Then, the regulation of [Eu(II)]/[Eu(III)] ratio was studied by introducing Li and CeF<sub>4</sub>. The addition of Li as a reducing agent increases the [Eu(II)]/[Eu(III)] ratio, while the addition of CeF<sub>4</sub> as an oxidizing agent decreases the [Eu(II)]/[Eu(III)] ratio. Moreover, the influence mechanism of O<sup>2−</sup> on the [Eu(II)]/[Eu(III)] ratio was also investigated by Raman spectroscopy and X-ray diffraction (XRD). The results showed that the [Eu(II)]/[Eu(III)] ratio decreased with the increasing amount of O<sup>2−</sup> added to the molten salt. This is related to the change of free F<sup>−</sup> concentration and coordination environment in molten salt caused by the formation of EuOF(s), which promotes the transformation of Eu(II) into Eu(III) with a relatively strong coordination ability with F<sup>−</sup>.</p>

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Electrochemical behavior and regulation of Eu(II)/Eu(III) redox couple in molten fluorides

  • 期刊论文

  • 发表日期：

    2025年11月17日

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  • Yingjie Li,
  • Yan Luo,
  • Lei Wang,
  • Xu Li,
  • Qingnuan Li,
  • Hao Peng,
  • Qiang Dou

摘要

In this study, the electrochemical behavior of Eu(II)/Eu(III) redox couple in LiF-NaF-KF (46.5–11.5–42 mol%) (FLiNaK) molten salt was studied by cyclic voltammetry (CV), square wave voltammetry (SWV), and chronopotentiometry (CP) on inert tungsten electrode at 923 K. The results showed that the Eu(II)/Eu(III) couple was a one-electron exchanged system, corresponding to the reduction of Eu(III) to Eu(II) and the oxidation of Eu(II) to Eu(III), and both processes were reversible and diffusion-controlled. Then, the concentration ratio of Eu(II)/Eu(III) was determined by combining SWV and X-ray photoelectron spectroscopy (XPS) techniques, and the results showed that Eu(III) was decomposed into Eu(II) during heat treatment and Eu(III) and Eu(II) would coexist in molten FLiNaK. Therefore, Eu(II)/Eu(III) was chosen as a redox indicator with its concentration ratio to assess the redox properties of molten salt. Then, the regulation of [Eu(II)]/[Eu(III)] ratio was studied by introducing Li and CeF4. The addition of Li as a reducing agent increases the [Eu(II)]/[Eu(III)] ratio, while the addition of CeF4 as an oxidizing agent decreases the [Eu(II)]/[Eu(III)] ratio. Moreover, the influence mechanism of O2− on the [Eu(II)]/[Eu(III)] ratio was also investigated by Raman spectroscopy and X-ray diffraction (XRD). The results showed that the [Eu(II)]/[Eu(III)] ratio decreased with the increasing amount of O2− added to the molten salt. This is related to the change of free F− concentration and coordination environment in molten salt caused by the formation of EuOF(s), which promotes the transformation of Eu(II) into Eu(III) with a relatively strong coordination ability with F−.