The Electrochemical Behavior of Oxide Ion in a LiCl–NaCl–CaCl₂ Eutectic Melt

The solubility of lithium oxide was determined to be 5.2 mol% in a LiCl–NaCl–CaCl₂ eutectic melt (52.3:13.5:34.2 mol%, melting point 713 K) at 773 K. The electrochemical window of the melt, 3.4 V, was determined by cyclic voltammetry at 773 K. The reaction at the anode limit was confirmed as Cl₂ gas evolution. The reaction at the cathode limit was found to be a liquid Li–Na–Ca alloy formation identified by X-ray photoelectron spectroscopy and inductively coupled plasma analyses of the deposits. Oxygen gas evolution occurred without dissolution of anode material according to the reaction, O²⁻ → 1/2O₂ + 2e⁻, when a boron-doped diamond electrode was anodically polarized at more positive potentials than 3.0 V vs Li⁺, Na⁺, Ca²⁺/Li–Na–Ca in a LiCl–NaCl–CaCl₂ melt containing Li₂O at 773 K