Proton conduction in hydronium solvate ionic liquids affected by ligand shape

Area of Science:

• Materials Science
• Electrochemistry
• Physical Chemistry

Background:

• Ionic liquids (ILs) are tunable solvents with applications in energy storage.
• Proton conduction in ILs is crucial for fuel cell technology.
• Hydronium solvate ILs offer a promising pathway for proton transport.

Purpose of the Study:

• To investigate how different polyether ligands affect proton conduction in hydronium solvate ILs.
• To compare the proton mobility in ILs with cyclic versus acyclic ligands.
• To elucidate the mechanism of proton transport in these systems.

Main Methods:

• Synthesis of hydronium solvate ionic liquids with various polyether ligands (18-crown-6, dicyclohexano-18-crown-6, benzo-18-crown-6, pentaethylene glycol dimethyl ether).
• Pulsed-field gradient spin echo nuclear magnetic resonance (PFGSE-NMR) to measure proton diffusion.
• Density functional theory (DFT) calculations to model ligand-ion interactions.

Main Results:

• Proton mobility was higher with acyclic ligands (G5) compared to cyclic ligands (18C6, Dh18C6, B18C6).
• Protons moved faster in ILs with acyclic ligands than with cyclic ones.
• Coordination of cyclic ether ligands to hydronium ions was identified as essential for fast proton conduction.

Conclusions:

• Ligand structure significantly impacts proton conduction in hydronium solvate ILs.
• Acyclic polyether ligands facilitate faster proton transport.
• These findings are relevant for developing advanced electrolyte systems for fuel cells and artificial ion channels.