A Holistic Approach for Elucidating Local Structure, Dynamics, and Speciation in Molten Salts with High Structural...

Area of Science:

• Materials Science
• Physical Chemistry
• Spectroscopy

Background:

• Molten salts (MS) are crucial in various industrial applications, often containing minority components as corrosion products.
• Understanding ion solvation, exchange, and speciation in these complex environments is vital for process control and material integrity.
• Conventional methods struggle to accurately characterize ions in highly disordered coordination environments within molten salts.

Purpose of the Study:

• To develop and validate a multimodal approach for examining ion solvation, exchange, and speciation in molten salts.
• To accurately quantify populations of different ion coordination states, even in disordered environments.
• To elucidate the relationship between ion speciation, temperature, and melt composition in molten salt systems.

Main Methods:

• Combined extended X-ray absorption fine structure (EXAFS) spectroscopy and optical spectroscopy.
• Integrated *ab initio* molecular dynamics (AIMD) simulations for calculating coordination state spectra.
• Employed linear combination fitting of computed EXAFS spectra to experimental data for quantitative analysis.

Main Results:

• Successfully quantified heterogeneous distributions of Ni(II) coordination states in ZnCl2+KCl melts.
• Demonstrated that Ni(II) speciation is sensitive to temperature and variations in melt composition.
• Linked observed speciation patterns to differences in chloride exchange dynamics at varying conditions.

Conclusions:

• The multimodal approach accurately characterizes ion coordination states in complex molten salt systems.
• Ion speciation in molten salts is dynamically controlled by temperature and composition-dependent exchange processes.
• This research provides critical insights for controlling ion solubility and transport in molten salts.