Electrophoretic NMR

Scheler, Ulrich

doi:10.1002/9780470034590.emrstm0154.pub2

Cited by 5 publications

(6 citation statements)

References 39 publications

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“…The discrepancy between the dc conductivity and the conductivity estimated from the Nernst–Einstein equation is generally attributed to the nonideal behavior of the electrolyte. Hence, the concept of the ionicity, defined as the inverse Haven ratio H R –1 , was introduced to account for an overall degree of correlation between all species. − Using electrophoretic NMR, ion-specific information about the correlations is available, and the effective charge ε c of an ion species was introduced as defined by eq . ,− …”

Section: Results and Discussionmentioning

confidence: 99%

“…Electrophoretic NMR (eNMR) is a unique technique for the investigation of the migration behavior of ions and neutral molecules in an electric field. The eNMR experiment is similar to a diffusion NMR experiment based on pulsed field gradients, but with the additional application of electric field pulses causing a coherent displacement of the investigated nuclei and a phase modulation of their signal. , This phase modulation is directly proportional to the drift velocity of the investigated species, and the resulting mobility is a transport parameter accounting for ion–ion correlations. Furthermore, the observation of the drift velocity of neutral molecules via eNMR can yield valuable information about their coordination to ions and the resulting correlated migration. , …”

Section: Introductionmentioning

confidence: 99%

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Chelating Additives Reversing the Lithium Migration Direction in Ionic Liquid Electrolytes

Ackermann

Schönhoff

2020

J. Phys. Chem. C

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Binary electrolytes of Li salt in ionic liquid (IL) are interesting systems for battery application. Typical for these systems is a strong Li-anion coordination causing vehicular Li+ transport in negatively charged Li-anion clusters and negative Li+ transference numbers. We investigate the influence of the additives tetrahydrofuran, monoglyme and triglyme on the Li+ migration behavior in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (EMImTFSA) based mixtures via electrophoretic NMR. When adding coordinating additives, we partly observe a reversal of the lithium migration direction and an electrophoretic drift of the neutral molecule. Using the same O:Li ratio, this effect is strongly depending on the chelating ability of the respective additive. Strongly coordinating additives form a chelate with the Li ion and render its drift velocity and its transference number positive, while the nonchelating additive tetrahydrofuran has a weaker effect on the Li drift. By choice of a suitable additive, it is therefore possible to decompose negatively charged lithium-anion clusters while maintaining ionic liquid-like properties. These findings provide a mechanistic explanation for the beneficial effect of additives on Li+ transport in IL-based battery cells.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Chelating Additives Reversing the Lithium Migration Direction in Ionic Liquid Electrolytes

Ackermann

Schönhoff

2020

J. Phys. Chem. C

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“…In this experiment, the electric field is generated (PL Scientific, Stockholm) by applying 0–200 V across two blackened electrodes touching the solution at the top and bottom of the sample. Gradient and electric field strengths were calibrated by reference to known standards (diffusion, water; electrophoretic mobility, tetramethylammonium bromide) …”

Section: Methodsmentioning

confidence: 99%

“…Gradient and electric field strengths were calibrated by reference to known standards (diffusion, water; electrophoretic mobility, tetramethylammonium bromide). 38 ■ RESULTS AND DISCUSSION Polymer-Only Solutions. Figure 1 presents the selfdiffusion coefficients of the family of polymers used in this study as functions of concentration and degree of modification in aqueous solution, D 2 O.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Electrophoretic NMR Characterization of Charged Side Chain Cationic Polyelectrolytes and Their Interaction with the Anionic Surfactant, Sodium Dodecyl Sulfate

et al. 2019

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Oppositely charged polymers and surfactants show a complex phase behavior with large regions of solubility and insolubility dependent on the concentrations of the species present. Here, a series of quaternized hydroxyethyl cellulose (cationic) polymers have been characterized by pulsed-gradient spin−echo NMR (PGSE-NMR) and electrophoretic NMR (eNMR) in simple aqueous (D 2 O) solutions and in combination with the oppositely charged (anionic) surfactant, sodium dodecyl sulfate (SDS). Analysis of the effective charge on the polymer derived from both the eNMR and PGSE-NMR results yields a readily interpretable insight into the polymer behavior; the effective charge on the polymer at infinite dilution shows a linear relationship with the degree of modification. On addition of low concentrations of SDS, typically C surf < 5 mM, the surfactant interacts with the charged polymers, leading to substantial changes in the dynamics of the system (polymer diffusion, viscosity). At these levels of surfactant addition, there is no macroscopic phase separation. Further, with the absence of an interaction with the parent, the uncharged polymer strongly suggests that the SDS only interacts with the charged moieties present on the functionalized side groups and not the polymer backbone. Ultimately, the charge on the soluble polymer/ surfactant complex was found to depend linearly on the level of surfactant binding across a series of polymers with differing levels of modification with the charge becoming effectively zero at the macroscopic phase separation boundary.

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“…Theoretical background and practical implementations of the technique can be found in a number of seminal works. [6][7][8][9][10][11] Ion mobilities in several electrolyte solute ions have been determined from linear fits of v i vs. E data. [12][13][14][15][16][17][18][19][20][21] The relationships between the electrophoretic mobilities, u +¿ ¿ and u −¿¿ , and the three electrochemically determined transport coefficients remains to be established.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Interpretation of Ion Velocities in Concentrated Electrolytes Measured by Electrophoretic NMR

Timachova

Newman

Balsara

2019

J. Electrochem. Soc.

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Electrophoretic NMR (eNMR) is emerging as a powerful technique for characterizing ion transport in electrolyte systems. We show that the standard approach for analyzing eNMR data is valid only for dilute electrolytes and provide a theoretical framework for interpreting eNMR results for all binary electrolyte systems with univalent salts. We derive relationships between the velocities of the ion species and the solvent in terms of the electrochemical Stefan-Maxwell diffusion coefficients and provide modified expressions for correctly calculating the transference number and conductivity from eNMR data in concentrated electrolytes. Our approach suggests that it is necessary to measure not just the displacement of ion species during the application of current in an eNMR experiment but also the displacement of the uncharged solvent in order to correctly calculate ion mobilities and the transference number.

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Electrophoretic NMR

Cited by 5 publications

References 39 publications

Chelating Additives Reversing the Lithium Migration Direction in Ionic Liquid Electrolytes

Chelating Additives Reversing the Lithium Migration Direction in Ionic Liquid Electrolytes

Electrophoretic NMR Characterization of Charged Side Chain Cationic Polyelectrolytes and Their Interaction with the Anionic Surfactant, Sodium Dodecyl Sulfate

Theoretical Interpretation of Ion Velocities in Concentrated Electrolytes Measured by Electrophoretic NMR

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