Electrochemical Behaviour and Chemical Species of Sm(II) in AlCl3 -NaCl with Different Lewis Acidity

Abstract

AlCl₃ -NaCl was utilized as an electrolyte in this work due to its low melting point and Lewis acidity, in which samarium exists in two oxidation states, Sm(III) and Sm(II), resulting in unique electrochemical behaviours. Sm metal dissolves in AlCl₃ -NaCl melt to form SmCl₂ , which is verified by electrochemical and spectroscopic techniques. As the Lewis acidity of the melt increases, the diffusion coefficient of Sm(II) gradually increases, and the activation energy of diffusion decreases. Moreover, an additional co-reduction peak of Sm³⁺ and AlCl₄ ^- is observed to be more positive than that of Al(0)/Al(III) in Lewis basic melt, which may be tightly correlated with the variation of Sm(II) coordination in AlCl₃ -NaCl melt and ligand variation from Cl^- to AlCl₄ ^- and Al₂ Cl₇ ^- as the Lewis acidity of the AlCl₃ -NaCl melt increases, according to the in situ electronic absorption spectra of Sm in this melt.

Keywords: Lewis acidity melt; coordination modes; electrochemistry; in situ electron absorption spectroscopy; lanthanides.