Proton Hopping and Long-Range Transport in the Protic Liquid [Im][TFSI], Probed by Pulsed-Field Gradient NMR and Quasi-Elastic Neutron Scattering

Published

July 1, 2012

Author(s)

Megan L. Hoarfrost, Madhu Sudan Tyagi, Rachel A. Segalman, Jeffrey A. Reimer

Abstract

Protic ionic liquids are promising candidates for a wide variety of electrochemical applications owing to their high proton conductivity, good thermal and electrochemical stability, and negligible volatility. Proton hopping leads to enhanced conductivity in the protic ionic liquid imidazolium bis(trifluoromethylsulfonyl)imide ([Im][TFSI] with an excess of neutral imidzzole. In this work, proton dynamics in [Im][TFSI] are studied in order to provide insight into the proton hopping conductivity mechanism. Proton hopping is shown to be characterized by a deviation from a linear Γ vs q₂ relationship in quasi-elastic neutron scattering (QENS) experiments, opening the door for future QENS studies of proton hopping in ionic liquids and ionic liquid composite materials. In addition, proton hopping is found to be encompassed in the lower energy of two translational processes identified by QENS. This low energy process contributes most to long-range diffusion. NMR diffusion measurements show that proton hopping decreases with increasing temperature, but significant proton hopping persists even at the maximum experimental temperature of 120 °C. This, in combination with minimal ion aggregation, leads to high proton conductivity and a high H⁺ transference number over a wide temperature range.

Citation

Journal of Physical Chemistry B

Volume

116

Issue

28

Pub Type

Journals

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Keywords

Quasi-elastic Neutron Scattering, NMR, Ionic Liquids, Proton Hopping

Citation

Hoarfrost, M. , Tyagi, M. , Segalman, R. and Reimer, J. (2012), Proton Hopping and Long-Range Transport in the Protic Liquid [Im][TFSI], Probed by Pulsed-Field Gradient NMR and Quasi-Elastic Neutron Scattering, Journal of Physical Chemistry B, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=911167 (Accessed May 2, 2025)