The interfacial structure of super-concentration LiNO₃ aqueous electrolyte studied by second harmonic generation

Area of Science:

• Electrochemistry
• Surface Science
• Spectroscopy

Background:

• Aqueous electrolytes are crucial for electrochemical devices.
• Understanding interfacial structure is key to improving electrochemical performance.
• Super-concentration electrolytes offer potential advantages but require detailed interfacial studies.

Purpose of the Study:

• To investigate the interfacial structure of super-concentration LiNO3 aqueous electrolytes.
• To elucidate the mechanism behind the broadened electrochemical stability window (ESW).

Main Methods:

• Non-resonant second harmonic generation (SHG) spectroscopy.
• Heterodyne-detected SHG spectra.
• Cyclic voltammetry at a Pt electrode.

Main Results:

• At the air/LiNO3 interface, increased LiNO3 concentration led to changes in SHG intensity and phase, indicating a thickened interfacial water layer with minimal nitrate adsorption.
• At the Pt/LiNO3 interface, increasing LiNO3 concentration reduced adsorbed hydrogen atoms and free water molecules at the cathodic potential limit.
• These interfacial changes correlate with an expanded electrochemical stability window.

Conclusions:

• The interfacial water layer structure and adsorption behavior significantly influence electrolyte properties.
• Reduced adsorbed hydrogen and free water at the electrode interface contribute to the broadened ESW in super-concentration LiNO3 electrolytes.
• SHG spectroscopy is a powerful tool for probing interfacial structures in concentrated electrolytes.