Interfacial interactions and structures of protic ionic liquids on a graphite surface: A first-principles study and...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Protic ionic liquids (PILs) are emerging as electrolytes for energy storage devices like batteries and supercapacitors.
• Understanding the interface between PILs and electrode materials is crucial but remains underexplored compared to aprotic ionic liquids (AILs).

Purpose of the Study:

• To systematically investigate the adsorption mechanisms of various PILs on graphite surfaces.
• To compare the interfacial behavior of PILs with their corresponding AILs.
• To elucidate the factors governing PIL adsorption and interfacial structure on graphite.

Main Methods:

• First-principles calculations were employed to model adsorption.
• Three groups of PILs (pyrrolidinium-based, imidazolium-based, ammonium-based) were studied.
• Corresponding AILs were included for comparative analysis.

Main Results:

• Adsorption is governed by electrostatic, van der Waals, and aromatic interactions (π-π stacking, C-H/N-Hπ).
• PILs exhibit different interfacial interactions and structures on graphite compared to AILs, primarily due to anion-substrate interactions.
• Proton transfer observed in gas-phase PILs (imidazolium/ammonium cations with nitrate anions) is reduced or eliminated at the graphite interface.

Conclusions:

• Anion-substrate interactions are key to the distinct interfacial behavior of PILs on graphite.
• The graphite interface modulates proton transfer phenomena in certain PILs.
• These findings provide insights into designing PIL-based electrolytes for enhanced energy storage performance.