Manipulating meso-scale solvent structure from Pd nanoparticle deposits in deep eutectic solvents

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Deep Eutectic Solvents (DESs) possess unique hydrogen bond networks, differing from aqueous electrolytes and ionic liquids.
• DESs exhibit nanoscale structures, presenting both challenges and opportunities for electrochemical applications.
• The properties of DESs are highly sensitive to their composition and temperature.

Purpose of the Study:

• To investigate the near-interface solvent structure of DESs during electrodeposition.
• To understand how solvent structure is affected by applied potential and DES composition.
• To explore the relationship between solvent structure and electrodeposition of Palladium (Pd) nanoparticles.

Main Methods:

• In situ sample-rotated ultra-small angle X-ray scattering (USAXS) to probe nanoscale structure.
• Electrochemical impedance spectroscopy (EIS) to analyze interfacial properties.
• Molecular dynamics (MD) simulations and dipolar orientation analysis for theoretical insights.

Main Results:

• A hierarchical solvent structure was observed on the mesoscale in choline chloride-based DESs.
• This structure intensified within a specific potential range (-0.3 V to -0.9 V vs Ag/AgCl).
• The ethylene glycol system showed a more pronounced structure compared to the urea system, correlating with electrochemical data.

Conclusions:

• The observed solvent structure is tunable by altering the hydrogen bond donor (HBD) in the DES and the applied electrochemical potential.
• Long-range solvent-deposit interactions are significantly influenced by DES composition and potential.
• Understanding these interfacial solvent dynamics is crucial for optimizing DES-based electrochemical processes.