Understanding Electrochemical Interactions of Iodide and Chloride Species in LiCl-KCl Molten Salt

Iodine is produced through nuclear fission reactions in nuclear reactors. Understanding the electrochemistry of iodine species is crucial for reprocessing used nuclear fuels via molten salt electrolysis, deploying next-generation molten salt nuclear reactors, and developing iodide-based molten salt batteries. Cyclic voltammetry (CV) was conducted in LiCl-KCl eutectic molten salts at 450, 500, and 550 °C, both with and without the addition of KI as an iodine source. Based on the CV results, the diffusivities of iodide and triiodide species, as well as the activation energies for diffusion, were determined. Additionally, formal potentials of various iodide and interhalogen complexes were derived, allowing for the calculation of the stability constants for halide exchange reactions. The diffusivities of iodide ranged from 0.14 to 6.9 × 10−7 cm2/s, while those of triiodide were roughly an order of magnitude lower. Increasing the KI content from 1 wt% to 5 wt% reduced the diffusion coefficient, whereas increasing temperature, as expected, boosted diffusivity. The activation energy for iodide diffusion in LiCl-KCl increased from 46.5 kJ/mol to 112 kJ/mol as KI concentration rose from 1 wt% to 5 wt%.