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23Na NMR T1 relaxation measurements as a probe for diffusion and dynamics of sodium ions in salt–glycerol mixtures

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journal contribution
posted on 12.07.2021, 09:00 by C D’Agostino, SJ Davis, AP Abbott
Mixtures of sodium salts with oxygen-containing molecules are useful from the perspective of applications such as sodium ion batteries because they fill the gap between deep eutectic solvents and molten salt hydrates. In a previous work, the physical properties (such as diffusion coefficients, conductivity, viscosity, and glass transition temperature) of four salts, namely, Na2B4O7 · 10H2O, NaOAc · 3H2O, NaBr, and NaOAc, were measured with glycerol. Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) was also used to measure self-diffusion coefficients of 1H-bearing species. However, the technique was not able to measure diffusion of sodium ions due to the very fast NMR relaxation rate of such species, resulting in loss of the PFG NMR signal. In the current work, this study is expanded using 23Na T1 relaxation measurements which, under certain assumptions, can be translated into diffusion coefficients. Analysis of the physical properties is then correlated with self-diffusion coefficient measurements to elucidate information about structure and ionic mobility. It is shown that NaOAc · 3H2O, NaBr, and NaOAc fit models for ionic conductivity and diffusion, which are consistent with ionic liquids where charge transport is limited by ionic mobility rather than the number of charge carriers. The waters of hydration of NaOAc · 3H2O do not appear to form a separate phase but are instead strongly coordinated to the cation. In contrast, Na2B4O7 · 10H2O appears to form a water-rich phase with enhanced sodium mobility.

History

Citation

J. Chem. Phys. 154, 224501 (2021); https://doi.org/10.1063/5.0051672

Author affiliation

School of Chemistry

Version

AM (Accepted Manuscript)

Published in

Journal of Chemical Physics

Volume

154

Issue

22

Pagination

224501

Publisher

AIP Publishing

issn

0021-9606

eissn

1089-7690

Acceptance date

01/05/2021

Copyright date

2021

Available date

12/07/2021

Language

en

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