Pulsed Field Gradient NMR Research Articles

Phospholipid Structural Features Influence Lateral Diffusion

Rapid lateral diffusion of lipids in bilayers is a critical property for function of biological membranes. A systematic study of diffusion as a function of lipid structure in well-defined synthetic bilayers is necessary for the confident interpretation of results on lipid diffusion in natural membranes and cells. Over the past 15 years, a large data set of lipid diffusion rates was accumulated in our lab by pulsed field gradient (PFG) NMR in combination with magic-angle spinning (MAS). The advantage of PFG NMR experiments versus other methods is that NMR reports the diffusion of all matrix lipids, not the diffusion of a low concentration of probe molecules whose behavior does not necessarily reflect that of matrix lipids.

Pore-scale analysis of axial and radial dispersion coefficients of gas flow in macroporous foam monoliths using NMR-based displacement measurements

A micro-scale analysis of mass transport in ceramic foams that are used as catalyst supports in gas phase reactions is of high interest. Although the effects of flow rate and foam parameters on the radial and axial dispersion are known for liquid flows, no pore-scale experimental analysis has been yet reported to correlate the mechanical and diffusional dispersion of gas flows to the geometry of open-cell foams. Here, a spatially resolved Pulsed Field Gradient NMR method is applied to determine dispersion coefficients of thermally polarized gas along axial and transversal directions of open-cell foams. The comparative study of three commercial foam samples with different morphologies shows the effect of open porosity, window size, and flow rate on gas dispersion. Additionally, the influence of mechanical and diffusional dispersion at each flow rate is investigated for individual samples. By observing the transition from diffusional dispersion to mechanically driven dispersion of gas, it is found that diffusional dispersion plays an important role, even at higher flow rates after a transition from Darcy to Darcy-Forchheimer regime occurs. The measured values for dispersion coefficients of methane can be directly used in pseudo-heterogeneous models for the methanation reaction.

Li Coordination of a Novel Asymmetric Anion in Ionic Liquid-in-Li Salt Electrolytes.

We analyze the influence of the asymmetry of the anion on coordination and transport processes in a Li salt/ionic liquid system. The relatively new asymmetric 2,2,2-trifluoromethylsulfonyl-N-cyanamide (TFSAM) anion was investigated in Pyr14TFSAM(1-x)LiTFSAMx over a broad concentration range (up to x = 0.7 Li salt) and was compared to the well-known bis(trifluoromethanesulfonyl)amide (TFSA) anion. In contrast to the TFSA-based system, the system with TFSAM has no phase transition over the whole concentration range. Raman spectroscopy and NMR chemical shifts elucidate the Li coordination in detail. Up to x = 0.3, the asymmetric anion coordinates to Li+ only via the cyano group. With increasing Li salt fraction, the contribution of Li-oxygen coordination increases. This coordination effects influence the transport properties of the system, as examined via pulsed-field-gradient NMR (PFG-NMR). Although the overall diffusivity of both systems is decreasing because of viscosity effects, the relative diffusivity of the Li cation is increasing with x. This suggests a change in the transport mechanism depending on the Li salt fraction. Interestingly, the contribution of structural diffusion at high Li salt concentrations (x ≥ 0.6) seems to be higher in the TFSAM system, influenced by the nonsymmetric coordination, while in the TFSA system, the vehicular transport seems to be still predominant at x ≥ 0.6.

Kinetics of oxygen transfer reactions on the graphene surface. Part II. H2O vs. CO2

This computational chemistry analysis compares the interactions of H2O and CO2 with zigzag graphene edges, and in particular their adsorption and desorption steps. We provide detailed information regarding the geometric and electronic factors that influence both their adsorption and desorption (of H2 and CO) processes. Density functional theory results are compared with experimental information to offer heretofore unavailable insights into key aspects of the rate-limiting steps, inhibition phenomena and nanoscale differences in these two reactions. Thus, for example, the orientation and rotation of the adsorbing H2O molecules are elucidated using intrinsic reaction coordinate calculations and molecular orbital analysis, and these results complement recent pulse field gradient NMR measurements and molecular dynamics calculations. Such mechanistic findings reveal the H2O adsorption process to be a slow rotational phenomenon whereas the low-temperature H2 desorption is geometrically constrained by the presence of contiguous (di)hydrogenated carbon atoms with or without hydroxyl groups. This surface-assisted desorption mechanism is proposed to be responsible for the formation of hexagonal pits during the graphite-H2O reaction. Similar insights were obtained for the graphene-CO2 reaction. Mechanistic schemes are proposed for the desorption products observed in experiments, distinguishing zigzag from armchair sites.

Ionicity of deep eutectic solvents by Walden plot and pulsed field gradient nuclear magnetic resonance (PFG-NMR).

Deep eutectic solvents (DESs) have attracted considerable attention due to their unique properties. Owing to similar structures and properties, DESs are also called "quasi-ionic liquids" or "ionic liquid analogous". However, for a deeper understanding and application of DESs, a comprehensive investigation on the ionicity of DESs is crucial. In this work, the effects of the structure and components of typical DESs on the ionicity were investigated. Moreover, the ionicity was discussed by using Walden plot, and the validity of applying it to DESs was verified using pulsed field gradient nuclear magnetic resonance (PFG-NMR). We found that the lack of free charged species and high viscosities make it difficult to achieve optimal conductivities for DESs, and thus most of them exhibit "poor ionic" nature. Fortunately, with an in-depth understanding of its microstructure and physicochemical properties, the properties of DESs can be finely tailored by selecting or even designing suitable parent compounds for functional applications. In particular, the ionicity of Li-based DESs was investigated for their potential application as electrolytes in Li-ion batteries.

Obtaining Hydrodynamic Radii of Intrinsically Disordered Protein Ensembles by Pulsed Field Gradient NMR Measurements.

In the disordered state, a protein exhibits a high degree of structural freedom, in both space and time. For an ensemble of disordered or unfolded proteins, this means that the ensemble comprises a high diversity of structures, ranging from compact collapsed states to fully extended polypeptide chains. In addition, each chain is highly dynamic and undergoes conformational changes and local dynamics on both fast and slow timescales. The size properties of disordered proteins are thus best described as ensemble averages. A straightforward measure of the size is the hydrodynamic radius, RH, of the ensemble. Since the disordered state is conformationally fluid, the observed RH does not refer to a particular shape or fold. Instead, it should be interpreted as a measure for the average compaction of the structural ensemble. In addition to characterizing the disordered ensemble itself, RH can be used to, with good precision, monitor changes in the ensemble size properties upon functional interactions of the disordered protein, e.g., dimerization, ligand binding, and folding pathways. Here, we present a step-by-step protocol for diffusion measurements using pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy. We describe how to calibrate the magnetic field gradient and offer different schemes for sample preparation. Finally, we describe how to obtain RH directly from the diffusion coefficient as well as from using an internal standard as a reference.

Tailored crystalline order of nascent polyethylene from metallocene supported on confined polystyrene

Building the desirable superstructure of polyethylene is one of the important topics for developing high value-added products, which brings potential benefits for society and sustainable development. Crystalline order is the ubiquitous superstructure for enhancing mechanical properties of polymeric materials. In this work, polystyrene copolymers (c-PS) are incorporated into pores of silica through the wet-impregnation procedure of styrene and p-chloromethyl styrene followed by the in-situ free-radical copolymerization. Metallocene catalyst is further immobilized on supported silica. This incorporated c-PS is proved to be coated on the surface of silica pore walls rather than blocking the interparticle channels. The swelling behavior of c-PS inside the pores are performed by pulsed field gradient NMR (PFG-NMR) and thermoporosimetry (TPM-DSC), where a swelling behavior is shown in the toluene owing to the matched solubility parameters between the c-PS and toluene. According to the swelling behavior of c-PS confined in the pores, a compartmentalization is created hindering the formation of chain overlaps and increasing the crystallinity order of nascent polymers. As a result, the nascent polyethylene with a high crystallinity (i.e., bulk crystallinity Xc,DSC = 72.9 % and linear crystallinity Xc,WAXD = 90.5 %) is synthesized. There is a considerable activity (i.e., 3.8 × 106 g PE·(molZr·h)−1) at 70 °C. Finally, the particle morphology of the nascent polyethylene is investigated based on the swelling behavior of c-PS.

Differentiating Diffusivity in Different Channels of ZSM‐5 Zeolite by Pulsed Field Gradient (PFG) NMR

AbstractDifferentiating the diffusivity in straight channel and sinusoidal channel of ZSM‐5 zeolite is a prerequisite for catalyst optimization for the required product distribution with specific orientation. Herein, the intracrystalline diffusivities of n‐butane and iso‐butane in power ZSM‐5 zeolite were investigated by pulse field gradient (PFG) NMR, respectively. Different diffusion behaviors of the selected isomers were revealed. The effective self‐diffusion coefficient of n‐butane is about three orders of magnitude higher than that of iso‐butane. For the selected isomers, the opposite loading‐dependence were presented in self‐diffusion coefficients. Moreover, an equation containing diffusion tensors in different directions in orthogonal coordinate was successfully applied to fit the diffusion coefficients of n‐butane in straight and sinusoidal channel of ZSM‐5, respectively. The diffusivity of n‐butane in straight channel is nearly one order of magnitude faster than that in sinusoidal channel, predicting its dominant diffusion path.

NMR Investigation into the Influence of Surface Interactions on Liquid Diffusion in a Mesoporous Catalyst Support

Pulsed field gradient NMR diffusion measurements provide a non-invasive measure of the mass transport (self-diffusion) characteristics of liquids confined to porous catalyst materials. Here we explore the ability of this technique to probe the diffusive behaviour of a series of short-chain primary alcohols within a mesoporous catalyst support material; through the comparison of our results with highly surface-sensitive NMR relaxation data, we show that the evaluation of bulk-pore diffusion dynamics may provide a simple and indirect method to access and explore surface interaction phenomena occurring at the catalyst-liquid interface.

Demulsification of crude oil emulsions tracked by pulsed field gradient NMR. Part II: Influence of chemical demulsifiers in external AC electric field

Crude oil emulsions can reach stability levels that pose severe challenges for the processing industry. Certain conventional methods are used to deal with these challenges, such as chemical demulsification. In this article, two chemicals were mixed with crude oil emulsions to study their separation capabilities in the presence and absence of external AC fields. Experiments were conducted at 65 ⁰C to lower crude oil viscosity, which in turn affects separation efficiency. Effects from the chemical and electrical constituents on the crude oil emulsion was tracked by a pulsed field gradient NMR method, developed in a previous study. The NMR measured emulsified water content for 2 h, continuously, as a function of sample height. Given the water content, droplet sedimentation and free water layer kinetics could be quantified. Droplet size distributions from the top half oil phase were obtained at the beginning and end of each experiment, with the intent of mapping coalescence and sedimentation development of droplets. However, tracking droplet size evolution proved challenging due to rapid changes within the emulsion. The main focus with the NMR technique was therefore on sedimentation and free water layer kinetics. A synergy was observed between the two chemicals and low AC fields. The two chemicals showed varied degrees of separation efficiency, where limited amounts of water was resolved by chemical 1 without electric field, though it improved separation past the limit of electrical treatment when used in combination with AC field. Above a given electric field, sedimentation by electrocoalscence dominates, and the effect of chemical demulsifier is marginal. Chemical 2 achieved promising results as a lone separation method, while further enhancing separation in collaboration with AC fields.

Polymer Electrolytes for LIBs Based on Perfluorinated Sulfocationic Nepem-117 Membrane and Aprotic Solvents.

Polymer electrolytes have been obtained by using Nepem-117 membranes in a Li+ form intercalated by polar aprotic solvents, such as dimethylformamide, dimethyl sulfoxide (DMSO), and dimethylacetamide (DMA), and solvent mixtures, such as ethylene carbonate-propylene carbonate (EC-PC), EC-DMA, EC-PC-DMA, and EC-PC-DMA-tetrahydrofuran. The obtained electrolytes have been characterized by IR impedance and 7Li pulsed field gradient NMR spectroscopy. Ion mobility was observed to increase with higher degrees of solvation of the membranes. A method is demonstrated to determine the solvent uptake corresponding to the percolation threshold. With comparable solvent uptake, materials containing a solvent with a higher permittivity and a lower viscosity have higher values of ionic conductivity. The membranes containing the three-component mixture of EC-PC-DMA show the highest ionic conductivity values (8.1 and 2.1 mS/cm at 25 and -20 °C, respectively). Such values exceed the conductivity of electrolytes on the basis of the Nafion membranes solvated with aprotic solvents.

Rapid and Tunable Assisted-Microwave Preparation of Glass and Glass-Ceramic Thiophosphate "Li7P3S11" Li-Ion Conductors.

Glass and glass-ceramic samples of metastable lithium thiophosphates with compositions of 70Li2S-30P2S5 and Li7P3S11 were controllably prepared by using a rapid assisted-microwave procedure in under 30 min. The rapid preparation times and weak coupling of the evacuated silica ampules with microwave radiation ensure minimal reactivity of the reactants and the container. The microwave-prepared samples display comparable conductivity values with more conventionally prepared (melt quenched) glass and glass-ceramic samples, on the order of 0.1 and 1 mS cm-1 at room temperature, respectively. Rietveld analysis of synchrotron X-ray diffraction data acquired with an internal standard quantitatively yields phase amounts of the glassy and amorphous components, establishing the tunable nature of the microwave preparation. X-ray photoelectron spectroscopy and Raman spectroscopy confirm the composition and the appropriate ratios of isolated and corner-sharing tetrahedra in these semicrystalline systems. Solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy resolves the seven crystallographic Li sites in the crystalline compound into three main environments. The diffusion behavior of these Li environments as obtained from pulsed-field gradient NMR methods can be separated into one slow and one fast component. The rapid and tunable approach to the preparation of high quality "Li7P3S11" samples presented here coupled with detailed structural and compositional analysis opens the door to new and promising metastable solid electrolytes.

Synthesis of highly active ETS-10-based titanosilicate for heterogeneously catalyzed transesterification of triglycerides.

In this contribution, the preparation of hierarchically structured ETS-10-based catalysts exhibiting notably higher activity in the conversion of triolein with methanol compared to microporous titanosilicate is presented. Triolein, together with its unsaturated analog trilinolein, represent the most prevalent triglycerides in oils. The introduction of mesopores by post-synthetic treatment with hydrogen peroxide and a subsequent calcination step results in the generation of an additional active surface with Brønsted basic sites becoming accessible for triolein and enhancing the rate of transesterification. The resulting catalyst exhibits a comparable triolein conversion (≈73%) after 4 h of reaction to CaO (≈76%), which is reportedly known to be highly active in the transesterification of triglycerides. In addition, while CaO showed a maximum conversion of 83% after 24 h, the ETS-10-based catalyst reached 100% after 8 h, revealing its higher stability compared to CaO. The following characteristics of the catalysts were experimentally addressed – crystal structure (X-ray diffraction, transmission electron microscopy), crystal shape and size (scanning electron microscopy, laser diffraction), textural properties (N2 sorption, Hg porosimetry), presence of hydroxyl groups and active sites (temperature-programmed desorption of NH3 and CO2, 29Si magic angle spinning nuclear magnetic resonance (NMR)), mesopore accessibility and diffusion coefficient of adsorbed triolein (pulsed field gradient NMR), pore interconnectivity (variable temperature and exchange spectroscopy experiments using hyperpolarized 129Xe NMR) and oxidation state of Ti atoms (electron paramagnetic resonance). The obtained results enabled the detailed understanding of the impact of the post-synthetic treatment applied to the ETS-10 titanosilicate with respect to the catalytic activity in the heterogeneously catalyzed transesterification of triglycerides.

Protein Translational Diffusion and Intermolecular Interactions of Globular and Intrinsically Unstructured Proteins.

The study of intermolecular interactions of proteins has been an important problem for many years. This paper presents an approach to analyze different levels of protein interactions in solutions through a set of the second- and higher-order virial coefficients. The proposed approach is based on the diversified analysis of protein translational collective diffusion and self-diffusion obtained by dynamic light scattering and the pulsed-field gradient NMR (PFG NMR) spectroscopy experimental data. The experimental results were analyzed within the theoretical approach based on Vink's frictional formalism of nonequilibrium thermodynamics and the standard Derjaguin-Landau-Verwey-Overbeekb (DLVO) theory of interactions of colloid particles in electrolyte solutions. The second- and higher-order virial coefficients were obtained to estimate the pairwise and many-body intermolecular interactions in the solutions of globular α-chymotrypsin and intrinsically unstructured αS-casein. The second virial coefficients were calculated from the model of the protein-protein potential of mean force. The description of protein-protein interactions includes a set of interaction potentials: the attractive charge-dipole, dipole-dipole, the dispersion Hamaker, the mean force osmotic-attraction, and the repulsive charge-charge ones. It has been found that the major contribution to the intermolecular αS-casein interactions is made by the repulsive charge-charge potential, whereas for the case of α-chymotrypsin, the contributions from other types of interaction are of importance. It was determined that the model was well suited to describe the interactions of both globular and intrinsically disordered proteins. The suggested combination of Vink's approach and the DLVO theory is novel and holds much promise to make a profound analysis of the processes in systems containing various types of protein molecules.

NMR 1D-Imaging of Water Infiltration into Porous Bitumen-Salt Matrices: The Effect of Salt Solubility

We investigate water infiltration in porous matrices made of bitumen and salts with different solubilities. Dispersion, inside bitumen, of either SrSO4 or MgSO4 at 40% mass fraction was achieved, as a way to model materials used in the context of nuclear waste conditioning. Pulsed field gradient nuclear magnetic resonance (PFG-NMR) and environmental scanning electron microscopy (ESEM) measurements allow us to characterize the evolution of the porous structure as a consequence of water infiltration (due to a leaching phenomenon) for durations up to 1.5 year. PFG-NMR enables performing 1D-imaging of water at different times to monitor its slow seeping inside the material. Profiles observed at the maximum time interval (1.5 year) demonstrate that different leaching behaviors exist depending on whether the salts dispersed inside bitumen are of the soluble or insoluble type. NMR relaxation and diffusion measurements were also taken. Remarkably, when performed in combination with 1D-imaging, such measurements yield information on the surface-to-volume ratio of the water-filled porous network, at different times, as a function of depth. In the case of the matrix-containing insoluble salts, relaxation measurements lead to discrimination between two different water populations differing by their T2 or T1 values. These values are described in the framework of surface-driven relaxation. A two-step model of leaching is proposed that globally accounts for the different observations (NMR 1D-imaging, relaxation/diffusion, as well as ESEM). The present work gives insight into the leaching behavior of porous bitumen-salt matrices and could be used as an input for modeling their evolution on longer timescales.

Quantitative Tortuosity Measurements of Carbonate Rocks Using Pulsed Field Gradient NMR

Tortuosity is an important physical characteristic of porous materials; for example, it is a critical parameter determining the effective diffusion coefficient dictating mixing between miscible fluids in porous rock structures as is relevant to enhanced gas recovery processes. Accurate measurement of tortuosity remains challenging, resulting in various definitions dictated largely by the measurement protocol applied. Here, we focus primarily on ‘diffusive’ tortuosity (τd), which is defined as the ratio of the bulk fluid diffusion coefficient to the restricted diffusion coefficient applicable to the porous media under study. Specifically, we consider carbonate rock cores ranging in permeability from 2 to 5300 mD and adapt pulsed field gradient (PFG) NMR methodology such that accurate measurements of tortuosity are obtained over a sufficiently representative length scale of the porous media. To this end, we deploy supercritical methane as a probe molecule exploiting both its high mobility and proton density. Tortuosity measurements are shown to be independent of both pressure and diffusion observation time, conclusively proving that our measurements are in the asymptotic regime in which all of the pore space is adequately sampled by the diffusing methane molecules. The resultant ‘diffusive’ tortuosity measurements (which ranged from 3.1 to 5.6) are then compared against independent electrical conductivity measurements of tortuosity using a two-electrode impedance technique applied to the carbonate samples saturated with brine solution. Agreement between the ‘diffusive tortuosity,’ as measured by PFG NMR, and ‘electrical’ tortuosity was remarkably good (within 10%), given the very different measurements techniques used, for most of the carbonate rock samples considered.

Intracrystalline Transport Barriers Affecting the Self-Diffusion of CH4 in Zeolites |Na12|-A and |Na12-xKx|-A.

Carbon dioxide must be removed from biogas or natural gas to obtain compressed or liquefied methane, and adsorption-driven isolation of CO2 could be improved by developing new adsorbents. Zeolite adsorbents can select CO2 over CH4, and the adsorption of CH4 on zeolite |Na12-xKx|-A is significantly lower for samples with a high K+ content, i.e., x > 2. Nevertheless, we show, using 1H NMR experiments, that these zeolites adsorb CH4 after long equilibration times. Pulsed-field gradient NMR experiments indicated that in large crystals of zeolites |Na12-xKx|-A, the long-time diffusion coefficients of CH4 did not vary with x, and the upper limit of the mean-square displacement was about 1.5 μm, irrespective of the diffusion time. Also for zeolite |Na12|-A samples of three different particle sizes (∼0.44, ∼2.9, and ∼10.6 μm), the upper limit of the mean-square displacement of CH4 was 1.5 μm and largely independent of the diffusion time. This similarity provided further evidence for an intracrystalline diffusion restriction for CH4 within the medium- and large-sized zeolite A crystals and possibly of clustering and close contact among the small zeolite A crystals. The upper limit of the long-time diffusion coefficient of adsorbed CH4 was (at 1 atm and 298 K) about 10-10 m2/s irrespective of the size of the zeolite particle or the studied content of K+ in zeolites |Na12-xKx|-A and |Na12|-A. The T1 relaxation time for adsorbed CH4 on zeolites |Na12-xKx|-A with x > 2 was smaller than for those with x < 2, indicating that the short-time diffusion of CH4 was hindered.

Relationship between ethane and ethylene diffusion inside ZIF-11 crystals confined in polymers to form mixed-matrix membranes

Self-diffusivities of ethane were measured by multinuclear pulsed field gradient (PFG) NMR inside zeolitic imidazolate framework-11 (ZIF-11) crystals dispersed in several selected polymers to form mixed-matrix membranes (MMMs). These diffusivities were compared with the corresponding intracrystalline self-diffusivities in ZIF-11 crystal beds. It was observed that the confinement of ZIF-11 crystals in ZIF-11/Torlon MMM can lead to a decrease in the ethane intracrystalline self-diffusivity. Such diffusivity decrease was observed at different temperatures used in this work. PFG NMR measurements of the temperature dependence of the intracrystalline self-diffusivity of ethylene in the same ZIF-11/Torlon MMM revealed similar diffusivity decrease as well as an increase in the diffusion activation energy in comparison to those in unconfined ZIF-11 crystals in a crystal bed. These observations for ethane and ethylene were attributed to the reduction of the flexibility of the ZIF-11 framework due to the confinement in Torlon leading to a smaller effective aperture size of ZIF-11 crystals. Surprisingly, the intra-ZIF diffusion selectivity for ethane and ethylene was not changed appreciably by the confinement of ZIF-11 crystals in Torlon in comparison to the selectivity in a bed of ZIF-11 crystals. No ZIF-11 confinement effects leading to a reduction in the intracrystalline self-diffusivity of ethane and ethylene were observed for the other two studied MMM systems: ZIF-11/Matrimid and ZIF-11/6FDA-DAM. The absence of the confinement effect in the latter MMMs can be related to the lower values of the polymer bulk modulus in these MMMs in comparison to that in ZIF-11/Torlon MMM. In addition, there may be a contribution from possible differences in the ZIF-11/polymer adhesion in different MMM types.

Charge Transport in Nonstoichiometric 2-Fluoropyridinium Triflate Protic Ionic Liquids

Pyridinium triflate protic ionic liquids have been demonstrated to be highly dissociated, and nonstoichiometric compositions have been used in protic energy devices such as the all-organic proton battery. Herein, we use a combination of pulsed field gradient NMR spectroscopy and electrochemical impedance spectroscopy to investigate the charge transport properties of the nonstoichiometric protic ionic liquid 2-fluoropyridinium triflate and the variation with acid doping level. While all diffusion coefficients decreased with the amount of acid doping, the room temperature conductivity increased due to the concurrent increase in charge carrier concentration. The maximum room temperature conductivity was 7.33 mS/cm, obtained when 14% of the pyridine was protonated with triflic acid, while higher acid doping levels lead to liquid/solid mixtures with low conductivity. PEDOT supercapacitor cells with this electrolyte demonstrated very high capacitance (83.9 F/g) and charge storage capacity (23.3 mAh/g). In addition we predict that using a lower acid doping level than previously will result in superior electrolyte performance in proton batteries due to improvements in conductivity, processability and electrochemical stability. (Less)

Measurements of Transport Properties of Lithium Salt in Block Copolymer Electrolyte

High charging rate of batteries is an important technical challenge to improve performance of electric vehicles. The battery charging is a function of the redox reactions at the electrode surfaces and transport of ions in the electrolyte. Limiting current density in a battery, the maximum current density at steady state, determines the charging rate. It is a function of the transference number and the diffusion coefficient. The measurement of the transference number and the diffusion coefficient of solid electrolytes has been restricted because of the complexity of experiments. Pulsed-field gradient nuclear magnetic resonance is a powerful method to measure the self-diffusion coefficients of the ions, which can be used to calculate the salt diffusion coefficient and the transference number, but it is only valid for dilute solutions.1, 2 Accurate measurement of the transport parameters for concentrated electrolyte has been conducted combining restricted diffusion, concentration cell and constant current experiments.3 The limitations of this approach are inherently large error from the independent measurements and long experiment time. In this study, the diffusion coefficient and transference number of lithium salt in polystyrene-poly(ethylene oxide) (SEO) electrolyte has been measured by spectroscopic and electrochemical methods with a simple experimental setup. A one-dimensional numerical diffusion model was used to determine the salt diffusion coefficient as a function of concentration. A non-monotonic concentration dependence was observed, initially decreasing with increasing salt concentration, then increasing after a minimum at 1.3 M. The transference number was obtained by measuring the concentration change near the electrodes after an applied current. This concentration change can be determined using calibrated cell potential measurements or custom spectroelectroscopic measurements. A steady-state current experiment was also conducted for comparison. This is a conventional measurement of the transference number in dilute limit.4 Deviations between these two measurements are an indication of non-ideality that can be the result of interactions between the ions and the EO segments and/or the existence of ion pairs and multiplets, which are expected in concentrated systems. The spectroelectroscopic experiment would provide more accurate measurement of the transport properties for concentrated solid electrolyte with reduced errors and practical information for the improvement of battery performance. References Pesko, D. M.; Timachova, K.; Bhattacharya, R.; Smith, M. C.; Villaluenga, I.; Newman, J.; Balsara, N. P., Negative Transference Numbers in Poly(ethylene oxide)-Based Electrolytes. 2017; Vol. 164, pp E3569-E3575.Timachova, K.; Watanabe, H.; Balsara, N. P. Macromolecules 2015, 48, (21), 7882-7888.Ma, Y. P.; Doyle, M.; Fuller, T. F.; Doeff, M. M.; Dejonghe, L. C.; Newman, J. Journal of the Electrochemical Society 1995, 142, (6), 1859-1868.Bruce, P. G.; Vincent, C. A. Journal of electroanalytical chemistry and interfacial electrochemistry 1987, 225, (1-2), 1-17.