Passivation phenomenon and variable properties of ytterbium in different Lewis acid AlCl3-NaCl melts

To further explore the application of the low-temperature molten salt in processing heavy rare earths, the properties of ytterbium in AlCl 3 -NaCl melts have been investigated. In this melt, YbCl 2 powder products are prepared by electrolysis based on the dissolution reaction of Yb metal. The properties of Yb(II) in AlCl 3 -NaCl melts have also been studied in detail. In-situ UV–VIS absorption spectroscopy demonstrates that the coordination of Yb(II) changes in AlCl 3 -NaCl melts with different Lewis acidity, leading to variations in its diffusion ability. In addition, the conversion of Yb(II)/Yb(III) shows typical soluble-soluble reversible electrochemical behavior in strongly acidic AlCl 3 -NaCl. However, the electrochemical behavior of Yb(II) on inert electrodes becomes complicated when the amount of AlCl 3 in AlCl 3 -NaCl melts less than 52 mol%. This change is attributed to the formation of a YbCl 3 passivation film on the inert electrode during the electro-oxidation of Yb(II). Soaking the passivated electrode in the melt can alleviate the passivation. Understanding the electrochemical and spectroscopic properties of ytterbium in AlCl 3 -NaCl melts paves the way for its subsequent applications.