163 research outputs found
Thermodynamics of the O₂/O²⁻ redox couple in molten (LiCl+KCl+Li₂O) systems
Activity coefficients of oxide ion were determined by the measurements of the standard formal potential of O₂/O²⁻ with a boron-doped diamond (BDD) electrode in molten (LiCl + KCl): LiCl:KCl = {58.5:41.5 (eutectic), 65:35, 70:30, 75:25} mol% at T = (673 to 803) K. The activity coefficient decreases with the increase of the LiCl content in the melt: (18.7 ± 1.5, 7.7 ± 1.0, 4.1 ± 0.4, and 1.6 ± 0.1), respectively, at T = 773 K in each melt. The result is explained by the attractive force between Li⁺ and O²⁻ which is stronger than that between K⁺ and O²⁻
Oxygen Electrode Reaction in a LiCl–KCl Eutectic Melt
Oxygen electrode reaction was investigated on a boron-doped diamond electrode in a LiCl–KCl eutectic melt. The standard formal potential of O₂/O²⁻ decreases with the elevation of temperature. The potential at 773 K is 2.424 ± 0.003 V vs Li⁺/ Li. The standard formal free energy change increases with the temperature elevation, calculated to be -456.4 ± 0.5 kJ mol⁻¹ at 773 K. The standard formal entropy and enthalpy changes are determined to be -151 ± 3 J K⁻¹ mol⁻¹ and -573.5 ± 0.1 kJ mol⁻¹, respectively, at 773 K
Dissolution Behavior of Lithium Oxide in Molten LiCl−KCl Systems
The solubility of lithium oxide was measured in molten LiCl−KCl containing (58.5, 75, 90, and 100) mol % LiCl in the temperature range of (673 to 923) K. The melt with a higher content of LiCl has a higher solubility of Li₂O. The pure LiCl has the highest solubility of Li₂O, (12.0 ± 0.2) mol % at 923 K. The estimated standard formal potential of O₂/O²⁻ increases linearly as the temperature decreases and as the mole fraction of LiCl increases
Stability of a boron-doped diamond electrode in molten chloride systems
Stability of a boron-doped diamond as an oxygen evolution electrode material was evaluated at 773 K in molten LiCl–KCl (58.5:41.5 mol%), LiCl–KCl (75:25 mol%), LiCl–CaCl₂ (64:36 mol%), LiCl–NaCl–CaCl₂ (52.3:13.5:34.2 mol%). In molten LiCl–KCl systems, the BDD is stable at 773 K regardless of the concentration of oxide ion and the composition of the melt. In molten LiCl–CaCl₂ and LiCl–NaCl–CaCl₂, the BDD electrode is less stable than in molten LiCl–KCl systems
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
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