Hydration Environment of Complexes and Their Dynamics in Aqueous Zinc Chloride Solutions

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Aqueous zinc chloride (ZnCl2) solutions are crucial in electrochemistry and battery technology.
• Understanding ion-solvent interactions is key to optimizing electrolyte performance.
• Zinc ions exhibit complex coordination behavior in water, influencing solvent structure and dynamics.

Purpose of the Study:

• To investigate the structure, dynamics, and electrostatics of aqueous ZnCl2 solutions.
• To elucidate the role of chloride ions in modifying zinc ion coordination and water solvation.
• To provide insights into the behavior of electrolytes at a molecular level.

Main Methods:

• Utilized molecular dynamics simulations.
• Employed a machine-learned interatomic potential trained using density functional theory (DFT) at the revPBE-D3 level.
• Analyzed coordination geometries, water dipole moments, and residence/reorientation times.

Main Results:

• Identified the dominant octahedral [Zn(H2O)6]2+ complex in dilute solutions.
• Observed adaptation of coordination geometries (trigonal bipyramidal, tetrahedral) with chloride ion inclusion.
• Quantified 15-30% enhancement in water dipole moments in the first solvation shell.
• Found nonmonotonic dependence of water residence times on chloride content, with minima and maxima observed.
• Reported monotonic decrease in second solvation shell water dynamics with increasing chloride.

Conclusions:

• The coordination environment of zinc ions significantly influences water molecule properties and dynamics.
• Chloride ions play a critical role in modulating the structure and dynamics of zinc solvation shells.
• Simulation results offer a molecular-level understanding of electrolyte behavior relevant to electrochemical applications.