Electrochemical Characterization of ZnCl ₂ in NaCl–KCl and LiCl–KCl for Application to Zn Electrorefining from Zn–Ni Alloys

Electrorefining (ER) in molten chlorides is a promising route for purifying reactive metals and actinide surrogates, but reliable potential control requires stable reference electrodes (REs) and well-characterized transport properties. Here, the electrochemistry of ZnCl2 is investigated in NaCl–KCl at 973 K and LiCl–KCl at 773 K as a basis for potential-controlled ER of Zn from Zn–Ni alloys. Diffusion coefficients and standard potentials of the Zn2+/Zn couple were determined using cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP), and open-circuit potential (OCP) measurements, with solution resistance obtained from electrochemical impedance spectroscopy (EIS) and the number of electrons confirmed by square-wave voltammetry (SWV). ER runs in NaCl–KCl without a RE produced high-purity Zn but low yield and cathodic Faradaic efficiency due to volatilization of Zn and ZnCl2 at 973 K. Switching to LiCl–KCl and integrating a saturated Ni/NiCl2 (15 mol %) RE enabled potential-controlled ER at 773 K. Runs with lower Ni content in the Zn–Ni alloy composition increased cathodic Faradaic efficiency to ∼99% and Zn recovery to ∼73%, while avoiding Ni co-deposition. These results demonstrate that combining buffered REs with lower-temperature chloride salts enables efficient, selective ER of Zn and provides a framework for future surrogate and actinide systems.