Electrochemical Characterization of Dissolved Oxides in Molten FLiNaK

• Published in: Journal of the Electrochemical Society Vol. 172; no. 8; pp. 86502 - 86510
• Main Authors: Shaheen, Nora A., Hoyt, Nathaniel C.
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.07.2025
• Subjects: Lithium Oxide; Molten Salts; oxygen; peroxide; Square wave voltammetry
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1945-7111/adf469

Molten fluoride salts have long been the subject of investigation given their application in a variety of industrial processes. Oxides are a common exogeneous impurity within these systems, and can lead to many operational and regulatory concerns. In recent studies, the electro-oxidation of dissolved metallic oxides has been attributed to a single step oxygen evolution reaction despite voltametric evidence suggesting otherwise. Here, we first use square wave voltammetry to confirm that the oxidation of dissolved oxides in fluorides proceeds via a two-electron transfer reaction and then demonstrate that the presence of a peroxide-mediated redox reaction better explains the electrochemical data. Numerical simulations were then used to support the determination of improved diffusion coefficients to enable electroanalytical measurements of the oxide concentration across at a variety of temperatures. A linear Arrhenius relationship was observed when the experimental data was corrected for ohmic resistance effects. Concentration measurements using the corrected square wave voltammetry data demonstrated high accuracy across a large range of concentrations, while the uncorrected data showed plateauing and high errors. In total, this work serves to rectify previously misconstrued electrochemical data of oxides in molten salts and demonstrate how accurate, in situ concentration measurements can be achieved in real-world systems.