Electrochemical evaluation of Fe2+ ions in MgCl2−NaCl−KCl melt

A comprehensive electrochemical assessment of Fe²⁺ behavior in a MgCl₂−NaCl−KCl melt was reported, involving cyclic voltammetry (CV), square wave voltammetry (SWV), and chronoamperometry (CA) analyses. Reduction of Fe²⁺ in MgCl₂−NaCl−KCl was observed to occur in a single step involving two electrons, exhibiting quasi-reversible behavior. The diffusion coefficient of Fe²⁺ (5.75×10⁻⁵ cm²/s) in this system was experimentally determined at 973 K, with an associated diffusion activation energy of 25.06 kJ/mol in the range of 973−1048 K, and an estimated standard rate constant for Fe²⁺/Fe of around 1×10⁻³ cm/s. The nucleation of Fe on the tungsten electrode in the MgCl₂−NaCl−KCl molten salt is insensitive to temperature and overpotential. It is found that the nucleation mode is related to the concentration of Fe²⁺ surrounding the electrode and evolves from an instantaneous to a progressive process, accompanied by a deterioration of magnesium electrolysis due to Fe impurities.