Molecular Resolution Nanostructure and Dynamics of the Deep Eutectic Solvent-Graphite Interface as a Function of
Justin S Freeman1, Mesfin Haile Mamme2,3, Jon Ustarroz2,4
1School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, 6009, Australia.
Small (Weinheim an Der Bergstrasse, Germany)
|January 10, 2023
Summary
Deep eutectic solvents (DESs) show promise for electrochemical applications. This study reveals their ordered nanostructures at solid-liquid interfaces, offering insights for designing advanced DES-based devices.
Area of Science:
- Electrochemistry
- Materials Science
- Physical Chemistry
Background:
- Deep eutectic solvents (DESs) are gaining interest for electrochemical applications due to their cost-effectiveness, renewability, and non-toxicity compared to conventional electrolytes.
- Understanding the molecular-scale nanostructures at the solid-liquid interface is crucial for optimizing DES performance in electrochemical systems.
- However, these interfacial nanostructures and their dynamics under applied potential remain largely unexplored.
Purpose of the Study:
- To investigate the molecular-scale lateral nanostructures of deep eutectic solvents at the solid-liquid interface.
- To reveal the arrangement and orientation of DES components within the Stern and near-surface layers as a function of applied potential.
- To understand the dynamic response of the interfacial layers upon changes in electrical potential.
Main Methods:
- Utilized in situ amplitude modulated atomic force microscopy (AM-AFM) to probe the solid-liquid interface with high resolution.
- Employed molecular dynamics (MD) simulations to complement experimental observations and provide molecular-level insights.
- Studied the archetypal 1:2 choline chloride:urea (reline) DES at a highly oriented pyrolytic graphite (HOPG) surface under varying potentials.
Main Results:
- Revealed highly ordered lateral nanostructures at the solid-liquid interface of reline with unprecedented molecular resolution.
- Identified and located choline, chloride, and urea molecules within the Stern layer on the graphite surface, including their orientations.
- Observed dynamic restructuring of the Stern layer upon potential switching, with equilibrium taking several minutes to establish.
Conclusions:
- The study provides valuable molecular-level insights into the nanostructure and dynamics of DESs at solid-liquid interfaces.
- Demonstrated the ability of AM-AFM and MD simulations to resolve interfacial structures of DESs.
- Findings are critical for the rational design and application of DESs in various electrochemical technologies.
