Atomic-Scale Three-Dimensional Local Solvation Structures of Ionic Liquids.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Room-temperature ionic liquids (RTILs) offer superior properties for advanced energy devices.
• Understanding solid-liquid interface solvation structures is critical for optimizing device performance.
• Existing experimental techniques lack the resolution to probe these 3D solvation structures at the atomic scale.

Purpose of the Study:

• To develop and demonstrate a novel experimental technique for visualizing the three-dimensional solvation structures of ionic liquids at the atomic scale.
• To investigate and compare the solvation structures of protic and aprotic ionic liquids at the solid-liquid interface.
• To elucidate the relationship between solvation structure and surface charge distribution.

Main Methods:

• Utilized a recently developed ultralow-noise three-dimensional frequency-modulation atomic force microscopy (3D-FM-AFM) technique.
• Supported experimental findings with molecular dynamics (MD) simulations.
• Conducted experiments using both protic and aprotic aqueous solutions on a mica substrate.

Main Results:

• Successfully measured atomic-scale solvation structures of ionic liquids in solution.
• Revealed that aprotic ionic liquids exhibit higher site specificity in their solvation structure compared to protic ones.
• Demonstrated the ability to resolve atomic-scale surface charge distribution on mica, attributed to the absence of a hydrogen-bonding network in aprotic solutions.

Conclusions:

• The developed 3D-FM-AFM technique provides unprecedented atomic-scale insight into ionic liquid solvation structures.
• The distinct solvation behavior of aprotic ionic liquids is crucial for understanding their interfacial properties.
• This methodology represents a breakthrough for studying liquid interfaces and expanding the applications of ionic liquids in energy devices and beyond.