Pulsed field gradient stimulated echo methods for improved NMR diffusion measurements in heterogeneous systems

Cotts, R. M.; Hoch, M.; Sun, Tao; Markert, J. T.

doi:10.1016/0022-2364(89)90189-3

Cited by 410 publications

(484 citation statements)

References 9 publications

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“…Saddle coils (10 mm inner diameter for 1 H, 5 mm for 19 F and 13 C) were used for radiofrequency excitation and detection, with the working electrode positioned in the detection area, with the B 1 field and electrode orientated as indicated in the SI. The 13-interval pulse sequence 50 with bipolar pulsed field gradients was used for diffusion measurements to minimise the effects of any magnetic field gradients inherent to the sample. The maximum g used was 17 T⋅m -1 , and the effective gradient pulse duration, δ, (as defined in Figure 1b) was 0.5 ms.…”

Section: Methodsmentioning

confidence: 99%

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

et al. 2017

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Ionic transport inside porous carbon electrodes underpins the storage of energy in supercapacitors and the rate at which they can charge and discharge, yet few studies have elucidated the materials properties that influence ion dynamics. Here we use in situ pulsed field gradient NMR spectroscopy to measure ionic diffusion in supercapacitors directly. We find that confinement in the nanoporous electrode structures decreases the effective self-diffusion coefficients of ions by over two orders of magnitude compared to neat electrolyte, and in-pore diffusion is modulated by changes in ion populations at the electrode-electrolyte interface during charging.Electrolyte concentration and carbon pore size distributions also affect in-pore diffusion and the movement of ions in and out of the nanopores. In light of our findings we propose that controlling the charging mechanism may allow the tuning of the energy and power performances of supercapacitors for a range of different applications.As renewable energy and green technologies such as electric vehicles become prevalent, we must develop new ways to store and release energy on a range of timescales. Rechargeable batteries are ideal for timescales of minutes or hours (electric cars, portable electronic devices, grid storage etc.), while supercapacitors are more promising for second or sub-second timescales and are increasingly being used for transport applications where rapid charging and discharging are required. The superior power handling and cycle lifetime of supercapacitors comes at the expense of energy density, with recent materials-driven research aiming to address this issue by fine-tuning the nanoporous structure of the carbon electrodes, 1,2 and by using ionic liquid electrolytes that are stable at higher voltages. 3,4 Both approaches have afforded some increases in energy density, though not without sacrificing power density. The delicate balance between energy and power density must be understood if supercapacitors are to be used in a wide range of applications.Fundamental studies based on spectroscopic, 5-14 and theoretical, 15-18 methods have recently revealed the complex nature of charging in supercapacitors. Prior to charging, the electrode pores contain a large number of electrolyte ions, 15,19,20 and as a result charge storage is generally more complex than simple counter-ion adsorption (counter-ions are defined as having charge opposite to the electrode in which they are located). [5][6][7]15 A range of different charging mechanisms can operate

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Section: Methodsmentioning

confidence: 99%

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

et al. 2017

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“…Here the NMR pulse sequence used was a complex bipolar stimulated echo pulsed-field gradient (BPStE-PFG) originally designed by Cotts [28]. Cotts sequence was an adapted form of a Stejskal-Tanner pulse sequence which eliminates background magnetic fields and has been used here at Leeds in previous studies [8].…”

Section: Nmr Diffusionmentioning

confidence: 99%

Pulsed-Field Gradient NMR Self Diffusion and Ionic Conductivity Measurements for Liquid Electrolytes Containing LiBF4 and Propylene Carbonate

Richardson

Voice

Ward

2014

Electrochimica Acta

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Page 1 of 42A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 AbstractLiquid electrolytes have been prepared using lithium tetrafluoroborate (LiBF 4 ) and propylene carbonate (PC). Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) measurements were taken for the cation, anion and solvent molecules using lithium ( 7 Li), fluorine ( 19 F) and hydrogen ( 1 H) nuclei, respectively. It was found that lithium diffusion was slow compared to the much larger fluorinated BF 4 anion likely resulting from a large solvation shell of the lithium. Ionic conductivity and viscosity have also been measured for a range of salt concentrations and temperatures. By comparing the measured conductivity with a ideal predicted conductivity derived from the Nernst-Einstein equation and self diffusion coefficients the degree of ionic association of the anion and cation was determined and was observed to increase with salt concentration and temperature. Using the measured viscosity and self diffusion coefficients the effective radius of each of the species was determined for various salt concentrations.

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“…Instead, we used a modified stimulated echo sequence (PGSTE-bp) incorporating alternating bi-polar diffusion-encoding gradient pulses which cancel out the effect of the background gradients on the diffusion measurement (19,20). The sequence is illustrated in Fig.…”

Section: Echo (Pgse) Technique Unsuitable For Measuring D(t)mentioning

confidence: 99%

The Narrow Pulse Approximation and Long Length Scale Determination in Xenon Gas Diffusion NMR Studies of Model Porous Media

Mair

Sen

Hürlimann

et al. 2002

Journal of Magnetic Resonance

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We report a systematic study of xenon gas diffusion NMR in simple model porous media: random packs of mono-sized glass beads, and focus on three specific areas peculiar to gas-phase diffusion. These topics are: (i) diffusion of spins on the order of the pore dimensions during the application of the diffusion encoding gradient pulses in a PGSE experiment (breakdown of the 'narrow pulse approximation' and imperfect background gradient cancellation), (ii) the ability to derive long-length scale structural information, and (iii) effects of finite sample size. We find that the time-dependent diffusion coefficient, D(t), of the imbibed xenon gas at short diffusion times in small beads is significantly affected by the gas pressure. In particular, as expected, we find smaller deviations between measured D(t) and theoretical predictions as the gas pressure is increased, resulting from reduced diffusion during the application of the gradient pulse. The deviations are then completely removed when water D(t) is observed in the same samples. The use of gas also allows us to probe D(t) over a wide range of length scales, and observe the long-time asymptotic limit which is proportional to the inverse tortuosity of the sample, as well as the diffusion distance where this limit takes effect (~ 1 -1.5 bead diameters). The Pade′ approximation can be used as a reference for expected xenon D(t) data between the short and long time limits, allowing us to explore deviations from the expected behaviour at intermediate times as a result of finite sample size effects. Finally, the application of the Pade′ interpolation between the long and short time asymptotic limits yields a fitted length scale (the "Pade′ length"), which is found to be ~ 0.13b for all bead packs, where b is the bead diameter.

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Pulsed field gradient stimulated echo methods for improved NMR diffusion measurements in heterogeneous systems

Cited by 410 publications

References 9 publications

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

Pulsed-Field Gradient NMR Self Diffusion and Ionic Conductivity Measurements for Liquid Electrolytes Containing LiBF4 and Propylene Carbonate

The Narrow Pulse Approximation and Long Length Scale Determination in Xenon Gas Diffusion NMR Studies of Model Porous Media

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