Transition from Vehicular to Structural Ionic Transport in Electrified Alkali Aqueous Solutions

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding ion solvation and dynamics under electric fields is vital for natural and technological processes.
• Traditional simulation methods face accuracy-convergence trade-offs.
• Electrified ionic solutions are key to electrochemical applications.

Purpose of the Study:

• To investigate solvation structures and ionic transport mechanisms of electrified alkali cationic solutions.
• To extend the perturbed neural network potential molecular dynamics (PNNP MD) approach for accurate simulations.
• To elucidate the field-dependent behavior of Li+, Na+, and Cs+ in aqueous solutions.

Main Methods:

• Utilized perturbed neural network potential molecular dynamics (PNNP MD).
• Simulated ionic current density under varying static electric fields.
• Analyzed solvation structures and coordination numbers for alkali cations.

Main Results:

• Obtained ionic conductivities for Li+, Na+, and Cs+ in agreement with experimental data.
• Discovered distinct ion migration mechanisms: vehicular for Li+, structural for Cs+.
• Identified Na+ as a 'Goldilocks' ion exhibiting a field-induced transition from vehicular to structural transport.

Conclusions:

• Ion-solvent interactions significantly influence transport mechanisms under electric fields.
• The conductance mechanism of ions with moderate interactions can be tuned by external fields.
• PNNP MD provides accurate insights into ion solvation and dynamics in electrified solutions.