Proton transport properties in an ionic liquid having a hydroxyl group

Area of Science:

• Ionic liquids
• Proton transport
• Materials science

Background:

• Hydroxyl groups in ionic liquids can influence proton conductivity.
• Understanding these effects is crucial for developing advanced electrolytes.

Purpose of the Study:

• To synthesize and characterize a hydroxyl-functionalized ionic liquid, choline bis(trifluoromethylsulfonyl)amide ([N(111(2OH))][N(Tf)(2)]).
• To investigate the impact of hydroxyl groups on proton transport in mixtures with an acid source, 1,1,1-Trifluoro-N-(trifluoromethylsulfonyl)methanesulfoneamide (HN(Tf)(2)).

Main Methods:

• Synthesis of [N(111(2OH))][N(Tf)(2)] and its mixtures with HN(Tf)(2) at various molar ratios.
• Thermal property analysis, viscosity measurements, and ionic conductivity testing.
• Pulsed Field Gradient Nuclear Magnetic Resonance (PFG-NMR) for proton diffusion studies.

Main Results:

• [N(111(2OH))][N(Tf)(2)] exhibits a melting point of 27 °C and thermal stability above 400 °C.
• Mixture viscosity increases with higher acid molar fraction, while ionic conductivity decreases monotonically.
• PFG-NMR revealed a larger self-diffusion coefficient for protons from the hydroxyl group and acid, suggesting fast intermolecular proton transfer.

Conclusions:

• The presence of a hydroxyl group in the ionic liquid affects proton transport properties.
• A strong correlation exists between ionic conductivity and viscosity in these mixtures.
• Fast intermolecular proton transfer occurs between the hydroxyl group and the acid source.