Nanostructure of the deep eutectic solvent/platinum electrode interface as a function of potential and water content

Area of Science:

• Electrochemistry
• Materials Science
• Surface Science

Background:

• Deep Eutectic Solvents (DESs) are emerging as versatile alternatives to traditional solvents.
• Understanding the interfacial behavior of DESs at electrode surfaces is crucial for their electrochemical applications.
• The influence of water and applied potential on DES interfacial nanostructure remains an active area of research.

Purpose of the Study:

• To investigate the interfacial nanostructure of three common DESs (ChCl:Urea, ChCl:EG, ChCl:Gly) at a Pt(111) electrode.
• To determine the effect of varying water content (up to 50 wt%) and applied potential on DES interfacial properties.
• To compare the behavior of DESs with that of ionic liquids regarding water content.

Main Methods:

• Contact mode atomic force microscopy (AFM) force-distance curves were employed to probe interfacial nanostructure.
• Cyclic voltammetry was used to further characterize the interfacial behavior of specific DES-water mixtures.
• Experiments were conducted at an open circuit potential (OCP) and applied potentials of ±0.25 V.

Main Results:

• Water addition increased interfacial nanostructure in DESs up to ~40 wt%, after which it decreased, contrasting with ionic liquids.
• Pure DESs showed one interfacial layer at OCP, increasing to 3-6 layers with 40-50 wt% water.
• Applied potential increased near-surface layers for pure DESs, while for water-containing DESs, it caused a short-range exponential decay, indicative of salt solution-like behavior.

Conclusions:

• The interfacial nanostructure of DESs is highly sensitive to water content and applied potential.
• DESs exhibit distinct interfacial responses to water compared to ionic liquids.
• The findings suggest that DES-water mixtures can form interfacial structures analogous to electrolyte solutions under specific electrochemical conditions.