Cation Diffusion Research Articles

Zinc binding alters the conformational dynamics and drives the transport cycle of the cation diffusion facilitator YiiP.

YiiP is a secondary transporter that couples Zn2+ transport to the proton motive force. Structural studies of YiiP from prokaryotes and Znt8 from humans have revealed three different Zn2+ sites and a conserved homodimeric architecture. These structures define the inward-facing and outward-facing states that characterize the archetypal alternating access mechanism of transport. To study the effects of Zn2+ binding on the conformational transition, we use cryo-EM together with molecular dynamics simulation to compare structures of YiiP from Shewanella oneidensis in the presence and absence of Zn2+. To enable single-particle cryo-EM, we used a phage-display library to develop a Fab antibody fragment with high affinity for YiiP, thus producing a YiiP/Fab complex. To perform MD simulations, we developed a nonbonded dummy model for Zn2+ and validated its performance with known Zn2+-binding proteins. Using these tools, we find that, in the presence of Zn2+, YiiP adopts an inward-facing conformation consistent with that previously seen in tubular crystals. After removal of Zn2+ with high-affinity chelators, YiiP exhibits enhanced flexibility and adopts a novel conformation that appears to be intermediate between inward-facing and outward-facing states. This conformation involves closure of a hydrophobic gate that has been postulated to control access to the primary transport site. Comparison of several independent cryo-EM maps suggests that the transition from the inward-facing state is controlled by occupancy of a secondary Zn2+ site at the cytoplasmic membrane interface. This work enhances our understanding of individual Zn2+ binding sites and their role in the conformational dynamics that govern the transport cycle.

Global transcriptome analysis of Stenotrophomonas maltophilia in response to growth at human body temperature.

Stenotrophomonas maltophilia is a typical example of an environmental originated opportunistic human pathogen, which can thrive at different habitats including the human body and can cause a wide range of infections. It must cope with heat stress during transition from the environment to the human body as the physiological temperature of the human body (37 °C) is higher than environmental niches (22–30 °C). Interestingly, S. rhizophila a phylogenetic neighbour of S. maltophilia within genus Stenotrophomonas is unable to grow at 37 °C. Thus, it is crucial to understand how S. maltophilia is adapted to human body temperature, which could suggest its evolution as an opportunistic human pathogen. In this study, we have performed comparative transcriptome analysis of S. maltophilia grown at 28 and 37 °C as temperature representative for environmental niches and the human body, respectively. RNA-Seq analysis revealed several interesting findings showing alterations in gene-expression levels at 28 and 37 °C, which can play an important role during infection. We have observed downregulation of genes involved in cellular motility, energy production and metabolism, replication and repair whereas upregulation of VirB/D4 type IV secretion system, aerotaxis, cation diffusion facilitator family transporter and LacI family transcriptional regulators at 37 °C. Microscopy and plate assays corroborated altered expression of genes involved in motility. The results obtained enhance our understanding of the strategies employed by S. maltophilia during adaptation towards the human body.

A Closer Look at Structural Relaxation in Superionic (NH4)4H2(SeO4)3: 1H NMR Studies

Structural relaxation and the role of molecular and proton dynamics in the electrolyte system, (NH4)4H2(SeO4)3 (TeAHSe), are studied at ambient pressure, as a function of temperature and time, by using the solid-state 1H NMR technique. Analysis of 1H NMR spectra collected in the temperature range from 20 to 400 K yielded information about the dynamics of protons in the ordered and disordered crystalline TeAHSe phases. It has been shown that in the low-temperature phase TeAHSe is a proton conductor. In contrast, the electric charge carriers in the superionic phase are protons and NH4+ ions. Therefore, the electrical conductivity in the superionic phase of TeAHSe is a combination of the chemical exchange of protons, proton diffusion within hydrogen bonds, and diffusion of ammonia cations in the bulk of the crystal. We also demonstrate that the enhanced charge transport in the superionic phase of TeAHSe mainly results from the NH4+ cation diffusion process. The unique data from the time evolution of NMR spectra taken at a constant temperature just below the phase transition provide the first direct evidence of ammonium cations involvement in the low-temperature structure recovery (structural relaxation). We proposed a scenario of the process of structural relaxation in the TeAHSe crystal as well as the origin of the phase transformation mechanism to the superionic stage.

Cation-Deficient Perovskites for Clean Energy Conversion

ConspectusClean energy conversion technologies can power progress for achieving a sustainable future, while functional materials lie at the core of these technologies. In particular, highly efficient electrocatalysts that are also cost-effective are of utmost concern in the development of several clean energy conversion technologies. These include fuel cells and water electrolyzers. It is well recognized that electrocatalysts are needed to greatly accelerate the kinetics of key electrochemical reactions involved in these energy conversion technologies. Perovskite oxides are being used as key materials that have provided impetus in the development of energy conversion and storage, in view of their flexibility in elemental composition. Over 90% of known elements are able to become incorporated into their metal cation sites, resulting in diversified properties. Several strategies can be used to tailor the intrinsic properties of perovskites, leading to the optimization of their catalytic activity for electrochemical reactions. Cation deficiency has received particular attention as a unique strategy since no other elements or phases are involved, thereby avoiding the unknown effects of foreign elements or phases on performance. In this Account, we present our recent contributions to the study of cation-deficient perovskite oxides in the context of their applications in clean energy conversion. This includes oxygen separation through mixed conducting membranes, which is important for clean combustion, electricity generation through both solid oxide fuel cells using chemical fuels and dye-sensitized solar cells, and hydrogen production from water through both solid oxide electrolysis cells at high temperatures and water electrolyzers at room temperature. The journey begins with a discussion of the defect chemistry and charge compensation mechanisms present in cation-deficient perovskite oxides and then we propose benefits from the cation deficiency strategy that can optimize the materials’ properties in terms of electrical conductivity, phase structure, oxygen vacancy concentration, oxygen ion and cation diffusion properties, and proton transportation. Thus, both the sintering behavior of materials and their catalytic activity is dramatically improved for key reactions such as oxygen reduction, oxygen evolution, hydrogen evolution, and iodine reduction. Accordingly, the remarkable increases in performance of the aforementioned energy conversion systems are achieved through adopting cation-deficient perovskites. At the end of this Account, we conclude with some suggestions on how future research can broaden the applications for cation-deficient perovskites.

Unusual ion transport behaviour of ethylammonium nitrate mixed with lithium nitrate

The diffusivity of ions and ionic conductivity of ethylammonium nitrate (EAN) mixed with lithium nitrate (LiNO3) has been carried out as a function of Li-salt concentration and temperature. An unusual behavior of ion diffusivities and ionic conductivities of the mixtures are observed over a range of Li-salt concentration and temperature. The diffusivities of EA+ and Li+, as measured by pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) diffusometry, are found to be comparable in the lower temperature range. An overall decrease in the ion diffusivity is observed with an increase in the concentration of LiNO3. A lower degree of dissociation of ionic complexes in the presence lower concentration of the Li-salt (less than 6 mol. %) resulted in lower ionic conductivity. In the higher concentration range of Li-salt the Li+ diffusivity is monotonously decreased with an increase in the concentration. In the lower concentration range, the Li+ diffusivity exceeded the diffusivity of EA+ cation demonstrating the release of Li+ from the associates. Being enclosed between glass plates, the diffusivities of EA+ and Li+ showed peculiarities similar to the earlier observed results for neat nitrate ILs: accelerated diffusivity of cations and reversible alteration of diffusivities under the influence of strong static magnetic field.

In situ nanoparticle-induced anti-oxidation mechanisms: Application to FeCrB alloys

In this work, in situ nanoparticles (TiB2 and TiC) can be demonstrated to induce significant improvement in the oxidation resistance of Fe-12 wt.%Cr-3.5 wt.%B alloys. To unravel the roles of nanoparticles in the anti-oxidation of Fe-12 wt.%Cr-3.5 wt.%B alloys, samples with various nanoparticle contents were synthesized to investigate their oxidation resistance. Results show that nanoparticles facilitate the formation of a continuous and dense Cr2O3 protective film and enhance its adhesion with the matrix. Furthermore, the nanoparticle assembly on the surface of borides can inhibit the inward diffusion of oxygen ions and the outward diffusion of cations, thereby effectively controlling the growth of oxide scales.

Fast grain‐boundary diffusion paths in ionic solids: Space‐charge layers versus interfacial core

AbstractThe accelerated diffusion of ions along grain boundaries in ionic solids may occur along two possible paths: (a) the interface core (IC), as known for metals; and (b) space‐charge layers (SCLs), located adjacent to the core, in which the point defects responsible for diffusion are accumulated. In this study, we examined whether it is possible, on the basis of diffusion profiles, to discriminate between IC and SCL diffusion paths. Taking cation diffusion along grain boundaries in MO2 oxides as our example system, we used finite‐element‐method (FEM) calculations to obtain cation diffusion profiles for various combinations of fast grain‐boundary diffusion along the two possible diffusion paths. Three characteristics of the grain‐boundary feature in diffusion profiles were investigated: the quantitative description of this grain‐boundary “tail”, its dependence on diffusion time, and its dependence on temperature (activation enthalpy). For all calculated diffusion profiles, with varying ratios of IC to SCL diffusion, no criterion was found that allowed the dominant diffusion path to be identified. Consideration of the activation enthalpies, however, may provide an indication of the dominant path: If the activation energy for grain‐boundary diffusion approaches or equals the activation enthalpy for bulk diffusion, one may conclude that SCL diffusion dominates.

Modifying Li+ and Anion Diffusivities in Polyacetal Electrolytes: A Pulsed-Field-Gradient NMR Study of Ion Self-Diffusion

Polyacetal electrolytes have been demonstrated as promising alternatives to liquid electrolytes and poly(ethylene oxide) (PEO) for rechargeable lithium-ion batteries; however, the relationship between polymer structure and ion motion is difficult to characterize. Here, we study structure–property trends in ion diffusion with respect to polymer composition for a systematic series of five polyacetals with varying ratios of ethylene oxide (EO) to methylene oxide (MO) units, denoted as P(xEO-yMO), and PEO. We first use 7Li and 19F pulsed-field-gradient NMR spectroscopy to measure cation and anion self-diffusion, respectively, in polymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixtures. At 90 °C, we observe modest changes in Li+ diffusivity across all polymer compositions, while anion (TFSI–) self-diffusion coefficients decrease significantly with increasing MO content. At a given reduced temperature (T – Tg), all polyacetal electrolytes exhibit faster Li+ self-diffusion than PEO. Intriguingly, P(EO-MO) and P(EO-2MO) also show slower TFSI– anion self-diffusion than PEO at a given reduced temperature. Molecular dynamics simulations reveal that shorter distances between acetal oxygen atoms (O–CH2–O) compared to ether oxygens (O–CH2–CH2–O) promote more diverse, often asymmetric, Li+ coordination environments. Raman spectra reveal that anion-rich ion clusters in P(EO-MO) and P(EO-2MO) lead to decreased anion diffusivity, which along with increased cation diffusivity, support the viability of polyacetals as high-performance polymer electrolytes.

Influence of the PuO2 content on the sintering behaviour of UO2-PuO2 freeze-granulated powders under reducing conditions

The sintering behaviour of freeze-granulated UO2-PuO2 powders containing 33 and 15 mol% Pu/(U + Pu) was investigated under reducing conditions up to 1700 °C. For both compositions, the “grain size versus relative density” trajectory was constructed. All the experimental points form a single trajectory meaning that a relative density/grain size pair obtained after sintering seems independent of the thermal path (heating rate, soak time, soak temperature) and of the Pu content. Exploiting the “grain size versus relative density trajectory” enabled also to propose that densification was controlled by grain boundary diffusion and grain growth by the grain boundaries whatever the Pu content. An activation energy around 510 kJ/mol was obtained for densification, which was close to the value reported for the grain boundary diffusion of plutonium cations in U1-xPuxO2 polycrystals. Whatever the Pu/(U + Pu) content, the sintered microstructure of 98 % dense samples possesses a homogeneous distribution of plutonium and uranium cations.

Alkali Ions Pre‐Intercalated Layered MnO2 Nanosheet for Zinc‐Ions Storage

AbstractRecently, rechargeable zinc‐ion batteries in mild acidic electrolytes have attracted considerable research interest as a result of their high sustainability, safety, and low cost. However, the use of conventional Zn‐ion storage materials is hindered by insufficient specific capacity, sluggish reaction kinetics, or poor cycle life. Here, these limitations are addressed by pre‐intercalating alkali ions and water crystals into layered δ‐MnO2 (birnessite) to prepare K0.27MnO2·0.54H2O (KMO) and Na0.55Mn2O4·1.5H2O with ultrathin nanosheet morphology via a rapid molten salt method. In these materials, alkali ions and water crystals act as pillars to stabilize the layered structures, which can enable rapid diffusion of cations in the KMO structure, resulting in high power capability (90 mAh g−1 at 10 C) and good cycling stability. Furthermore, electrochemical quartz crystal microbalance measurements shed light on the charge storage mechanism of KMO in an aqueous Zn‐ion battery which, combined together with in‐operando X‐ray diffraction techniques, suggests that the charge storage process is dominated by the (de)intercalation of H3O+ with further dissolution–precipitation of Zn4(OH)6(SO4)·5H2O solid product on the KMO surface during cycling.

Characterization of a Novel Family IV Esterase Containing a Predicted CzcO Domain and a Family V Esterase with Broad Substrate Specificity from an Oil-Polluted Mud Flat Metagenomic Library

Two novel esterase genes, est2L and est4L, were identified from a previously constructed metagenomic library derived from an oil-polluted mud flat sample. The encoded Est2L and Est4L were composed of 839 and 267 amino acids, respectively, without signal peptides. Est2L was a unique fusion type of protein composed of two domains: a domain of the CzcO superfamily, associated with a cationic diffusion promoter with CzcD, and a domain of the acetylesterase superfamily, belonging to family IV with conserved motifs, such as HGG, GXSAG, and GXPP. Est2L was the first fused esterase with a CzcO domain. Est4L belonged to family V with GXS, GXSMGG, and PTL motifs. Native Est2L and Est4L were found to be in dimeric and tetrameric forms, respectively. Est2L and Est4L showed the highest activities at 60 °C and 50 °C, respectively, and at a pH of 10.0. Est2L preferred short length substrates, especially p-nitrophenyl (pNP)-acetate, with moderate butyrylcholinesterase activity, whereas Est4L showed the highest activity with pNP-decanoate and had broad specificity. Significant effects were not observed in Est2L from Co2+ and Zn2+, although Est2L contains the domain CzcD. Est2L and Est4L showed high stabilities in 30% methanol and 1% Triton X-100. These enzymes could be used for a variety of applications, such as detergent and mining processing under alkaline conditions.

Characterization of the gene family encoding metal tolerance proteins in Triticum urartu: Phylogenetic, transcriptional, and functional analyses.

Homeostasis of microelements in organisms is vital for normal metabolism. In plants, the cation diffusion facilitator (CDF) protein family, also known as metal tolerance proteins (MTPs), play critical roles in maintaining trace metal homeostasis. However, little is known about these proteins in wheat. In this study, we characterized the MTP family of Triticum urartu, the donor of 'A' genome of Triticum aestivum, and analysed their phylogenetic relationships, sequence signatures, spatial expression patterns in the diploid wheat, and their transport activity when heterologously expressed. Nine MTPs were identified in the T. urartu genome database, and were classified and designated based on their sequence similarity to Arabidopsis thaliana (Arabidopsis) and Oryza sativa MTPs. Phylogenetic and sequence analyses indicated that the triticum urartu metal tolerance protein (TuMTP)s comprise three Zn-CDFs, two Fe/Zn-CDFs, and four Mn-CDFs; and can be further classified into six subgroups. Among the TuMTPs, there are no MTP2-5 and MTP9-10 counterparts but two MTP1/8/11 orthologs in relation to AtMTPs. It was also shown that members of the same cluster share similar sequence characteristic, i.e. number of introns, predicted transmembrane domains, and motifs. When expressed in yeast, TuMTP1 and TuMTP1.1 conferred tolerance to Zn and Co but not to other metal ions; while TuMTP8, TuMTP8.1, TuMTP11, and TuMTP11.1 conferred tolerance to Mn. When expressed in Arabidopsis, TuMTP1 localized to the tonoplast and significantly enhanced Zn and Co tolerance. TuMTPs showed diverse tissue-specific expression patterns. Taken together, the closely clustered TuMTPs share structural features and metal specificity but play diverse roles in the homeostasis of microelements in plant cells.

Chemical Degradation of the La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.8Sm0.2O2−δ Interface during Sintering and Cell Operation

A complete cell consisting of NiO-Ce0.8Sm0.2O3−δ//Ce0.8Sm0.2O3−δ//(La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ elaborated by a co-tape casting and co-sintering process and tested in operating fuel cell conditions exhibited a strong degradation in performance over time. Study of the cathode–electrolyte interface after cell testing showed, on one hand, the diffusion of lanthanum from (La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ into Sm-doped ceria leading to a La- and Sm-doped ceria phase. On the other hand, Ce and Sm diffused into the perovskite phase of the cathode. The grain boundaries appear to be the preferred pathways of the cation diffusion. Furthermore, a strontium enrichment was clearly observed both in the (La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ layer and at the interface with electrolyte. X-ray photoelectron spectroscopy (XPS) indicates that this Sr-rich phase corresponded to SrCO3. These different phenomena led to a chemical degradation of materials and interfaces, explaining the decrease in electrochemical performance.

The Cd-induced morphological and photosynthetic disruption is related to the reduced Fe status and increased oxidative injuries in sugar beet

Cadmium (Cd) toxicity is a form of soil contamination that causes losses in plant growth and yield. Understanding the effects of Cd-induced changes in physiological and cellular processes will help scientists develop better scientific strategies for sugar beet plant improvement. Cd toxicity triggered a substantial decrease in morphological parameters and total soluble protein in sugar beets, as well as membrane damage and cell death. Furthermore, the SPAD score and photosynthetic OJIP parameters in leaves were severely affected due to Cd stress. This was correlated with the decreased FCR activity and BvIRT1 expression in roots, suggesting the adverse effect of Cd in Fe acquisition in sugar beet. Our findings also revealed that BvHMA3 and BvNRAMP3 were upregulated in Cd-exposed roots, indicating that these genes might be involved in Cd uptake in sugar beet. In silico analysis of BvHMA3 and BvNRAMP3 proteins showed close partnerships with several Arabidopsis genes mainly linked to metal tolerance protein, cation diffusion facilitator, vacuolar metal transporter, and vacuolar Fe transporter. Subsequently, Cd-exposed sugar beet showed severe sensitivity to oxidative damages resulted in elevated H2O2 and O2.- without possessed efficient antioxidant defense. Finally, growth retardation in Cd-exposed sugar beets is linked to photosynthetic inefficiency caused by low Fe levels and oxidative stress in cells. These results may be used to improve Cd-sensitive sugar beet plants by breeding or transgenic programs.

Hydrogel-Mediated Mineralization Generates Oriented Crystalline Films Comprising Granular-Rhombohedral Heterogeneous Structures.

Gel-mediated crystallization is a common system to produce self-organized materials, which is fundamental to the development of bottom-up approaches to functional complex materials. Mineralization in hydrogel matrices nevertheless remains empirical in the generation of crystallization products with tailored heterogeneous structures. We demonstrate that the employment of the hydrogels with proper cationic diffusivity can trigger the consecutive growth of oriented, granular-rhombohedral heterogeneous structures. The controllable morphogenesis leads to continuous calcitic CaCO3 films comprising spatial heterogeneity, where epitaxial match assumedly favors the successive deposition of both granular and rhombohedral layers. The scenario of consecutive growth is disclosed, where the thickness of the granular layers can become a valuable indicator to reflect the retardancy degree of crystallization. The evaluation of the physicochemical properties of the hydrogels finally establishes a direct correlation between the cationic diffusivity of the hydrogels and the appearance of the heterogeneous structures. The current work therefore sheds light on the implementation of rational morphogenetic approaches to crystalline materials with tailored complex architectures.

Diffusion of tritiated water, 137Cs+, and 125I− in compacted Ca-montmorillonite: Experimental and modeling approaches

Mechanistic understanding and predictive modeling of radionuclide diffusion in Na- and Ca-montmorillonite are essential to evaluate the long-term evolution of the bentonite barrier and their impact on radionuclide migration during geological disposal of radioactive wastes. Thus, the diffusion behavior of 137Cs+, 125I−, and tritiated water (HTO) in compacted Ca-montmorillonite was investigated as a function of porewater salinity and dry density via both experiments and models. The effective diffusion coefficient (De) followed in the order of 137Cs+ > HTO > 125I−. The De of 137Cs+ decreased with increasing salinity, whereas the dependence of De of 125I− on salinity was uncertain. The cation excess and anion exclusion effects for Ca-montmorillonite were lower than those for Na-montmorillonite. The integrated sorption and diffusion (ISD) model, assuming the homogeneous pore structure and the electrical double layer (EDL) theory for 2:1 electrolyte (CaCl2), could account for the observed trends for De in Ca-montmorillonite. The lower dependence of De on the porewater salinity in Ca-montmorillonite was caused by the reduction of the EDL thickness for divalent cations (Ca2+) in comparison with that for monovalent cations (Na+). The multipore model could improve the fit for De of 125I− at low salinity due to the reduction of interlayer pore volumes and anion exclusion effect, however, the disparity at higher densities was considerably larger. From these results, cation diffusion for compacted Ca-montmorillonite could be mainly explained by the electrostatic interactions in the homogeneous pore model; in contrast, anion diffusion was sensitive to both electrostatic interactions and heterogeneous pore structures. The proposed ISD model is an effective tool to evaluate the radionuclide diffusion and sorption behavior in both compacted Ca-montmorillonite and Na-montmorillonite.

Ion Transport and Electrochemical Properties of Fluorine-Free Lithium-Ion Battery Electrolytes Derived from Biomass

Unlike conventional electrolytes, ionic liquid (IL)-based electrolytes offer higher thermal stability, acceptable ionic conductivity, and a higher electrochemical stability window (ESW), which are indispensable for the proper functioning of Li-ion batteries. In this study, fluorine-free electrolytes are prepared by mixing the lithium furan-2-carboxylate [Li(FuA)] salt with the tetra(n-butyl)phosphonium furan-2-carboxylate [(P4444)(FuA)] IL in different molar ratios. The anion of these electrolytes is produced from biomass and agricultural waste on a large scale and, therefore, this study is a step ahead toward the development of renewable electrolytes for batteries. The electrolytes are found to have Tonset higher than 568 K and acceptable ionic conductivities in a wide temperature range. The pulsed field gradient nuclear magnetic resonance (PFG-NMR) analysis has confirmed that the (FuA)− anion diffuses faster than the (P4444)+ cation in the neat (P4444)(FuA) IL; however, the anion diffusion becomes slower than cation diffusion by doping Li salt. The Li+ ion interacts strongly with the carboxylate functionality in the (FuA)− anion and diffuses slower than other ions over the whole studied temperature range. The interaction of the Li+ ion with the carboxylate group is also confirmed by 7Li NMR and Fourier transform infrared (FTIR) spectroscopy. The transference number of the Li+ ion is increased with increasing Li salt concentration. Linear sweep voltammetry (LSV) suggests lithium underpotential deposition and bulk reduction at temperatures above 313 K.

Sintering mechanisms of partially stabilized zirconia (TZ3Y) with ZnO and Co3O4 as sintering additives

In this work, the sintering mechanisms of 3 mol% yttria-stabilized zirconia (TZ3Y) and TZ3Y containing 0.3 wt% of ZnO or Co3O4 were analyzed by determining the apparent activation energy of sintering from dilatometry data and observing the evolution of microstructure. Dilatometry test was performed at a heating rate ranging from 5 to 20 °C/min from room temperature up to 1500 °C. The main mechanism of each sintering additive for the studied samples was revealed from the variation of the sintering activation energy as a function of the relative density and scanning electron microscopy images. The mechanism for the ZnO additive was the formation of a liquid phase at the beginning of the sintering process, while the Co3O4 additive acted via solid-state sintering by increasing cation diffusivity.

Influence of Alkyl Chain Length on Thermal Properties, Structure, and Self-Diffusion Coefficients of Alkyltriethylammonium-Based Ionic Liquids.

The application of ionic liquids (ILs) has grown enormously, from their use as simple solvents, catalysts, media in separation science, or electrolytes to that as task-specific, tunable molecular machines with appropriate properties. A thorough understanding of these properties and structure–property relationships is needed to fully exploit their potential, open new directions in IL-based research and, finally, properly implement the appropriate applications. In this work, we investigated the structure–properties relationships of a series of alkyltriethylammonium bis(trifluoromethanesulfonyl)imide [TEA-R][TFSI] ionic liquids in relation to their thermal behavior, structure organization, and self-diffusion coefficients in the bulk state using DSC, FT-IR, SAXS, and NMR diffusometry techniques. The phase transition temperatures were determined, indicating alkyl chain dependency. Fourier-transformed infrared spectroscopy studies revealed the structuration of the ionic liquids along with alkyl chain elongation. SAXS experiments clearly demonstrated the existence of polar/non-polar domains. The alkyl chain length influenced the expansion of the non-polar domains, leading to the expansion between cation heads in polar regions of the structured IL. 1H NMR self-diffusion coefficients indicated that alkyl chain elongation generally caused the lowering of the self-diffusion coefficients. Moreover, we show that the diffusion of anions and cations of ILs is similar, even though they vary in their size.

(Invited) Fast Ion Dynamics in Solids As Probed By NMR: Disorder, Dimensionality and Correlation Effects

NMR offers plenty of tools to analyze ionic jump processes in crystalline and amorphous solids at atomic scale. Both high-resolution and time-domain 1H(2H), 6,7Li, 19F, 23Na NMR helps shedding light on the origins of rapid self-diffusion in materials being relevant for energy storage.It is well accepted that in materials with strong site preferences, such as LiAlO2, the Li+ ions are subjected to extremely slow exchange processes. The loss of this site preference, as it is the case in glasses and some nanocrystalline phases, may, however, lead to rapid cation diffusion. Examples that benefit from this effect include cation-mixed, high-entropy fluorides ((Ba,Ca)F2) and LiTi2(PS4)3. In general, in non-equilibrium phases site disorder, polyhedra distortions, strain and the various types of local defects will affect both the migration activation energy and the corresponding Arrhenius pre-factor. Whereas in (Me,Ca)F2 (Me = Ba, Pb) cation mixing influences F anion dynamics, in Li6PS5X (X = Br, Cl, I) the potential landscape can be manipulated by anion site disorder and the introduction of extrinsic defects. In some cases, this leads to rather flat landscapes enabling the ions to have access to concerted displacement processes, as is seen in LLZO-type garnets. On the other hand, in the mixed conductor Li4+x Ti5O12 cation-cation repulsions immediately lead to a boost in Li+ diffusivity at the early stages of chemical lithiation. For Na-bearing closo-borates, the influence of rotational anion dynamics is usually considered to explain long-range cation transport. Recent examples of our group also include Li- and Na-conducting MOFs, for which, as in the case of the closo-borates and the famous Na-β''-alumina, transitions from correlated to uncorrelated motion are observed at sufficiently high temperature.Finally, rapid diffusion is also expected for materials that are able to guide the ions along (macroscopic) pathways with confined dimensions, as we have recently observed for layer-structured fluorides such as RbSn2F5 or MeSnF4 with their buried interfaces.