Salt Diffusion Research Articles

Molten salt-assisted controlled synthesis of two-dimensional molybdenum carbide

The present investigation examines the carbothermal reduction synthesis of two-dimensional molybdenum carbide (2D Mo2C) using sodium carbonate (Na2CO3) as a molten salt diffusion promoter and sodium sulfide (Na2S) as a solid-state intercalation agent. Raw molybdenum disulfide (MoS2) powder undergoes carbothermal reduction facilitated by activated carbon and Na2CO3 above 800 °C to produce 2D Mo2C layers intercalated by Na2S. The diffusion of Na2S can be enhanced by the fluidity of molten salt Na2CO3, leading to the expansion of the Mo2C layer spacing to 29 nm under the influence of the temperature field. Na2S intercalation prevents layer shrinkage during cooling while molten Na2CO3 directs 2D growth, yielding 10 nm-thick sheets. The product maintains hexagonal β-Mo2C structure up to 950 °C with microflowers of accordion-shaped nanosheets. Ultrasonication exfoliates the weakly bound Mo2C layers into uniform, freely suspended flakes around 10–100 nm in lateral size. This work demonstrates the tuning of 2D Mo2C morphology in high-temperature reactions by utilizing molten salts. The principal results are the synthesis of micrometer-sized Mo2C sheets with controlled nanoscale thickness and uniform nanosheet dispersions, enabled by molten salt-directed diffusion of intercalated species. The major conclusion drawn is that solid-liquid synergistic diffusion can guide precision synthesis of layered nanomaterials.

Understanding the influence of sodium chloride concentration on ion diffusion in charged polymers

Previous observations made on sulfonated polysulfones equilibrated with solutions of increasing salinity, where salt diffusion coefficients increase concurrently with reductions in water content driven by osmotic de-swelling, are currently unexplained. To further explain the molecular underpinnings of these observations, we characterized the influence of external salt solution concentration on the average salt and ion diffusion properties of two sulfonated polymers: a model cross-linked material (XLAMPS) and a series of sulfonated polysulfones (HQ:BP – XX). Analysis of the average salt and co- and counter-ion diffusion coefficients in these polymers suggest that the increase in charge screening (of electrostatic interactions between anionic sulfonate groups and co-ions) that occurs with increasing salinity affects the salt diffusion coefficients of sulfonated polysulfone in a manner that is different from what would be expected based on changes in water content alone and from what was observed for XLAMPS. Free volume theory describes the influence of these electrostatic effects on salt diffusion using a parameter related to the characteristic free volume element size necessary for diffusion. The results and analysis suggest that charge screening reduces the characteristic free volume element size necessary for diffusion in sulfonated polysulfone, which provides an explanation for the observed increase in average salt diffusion coefficients with increased salinity.

Molecular dynamics simulation of salt diffusion in constituting phosphazene-based polymer electrolyte

A growing demand to visualize polymer models in liquid poses a computational challenge in molecular dynamics (MD) simulation, as this requires emerging models under suitable force fields (FFs) to capture the underlying molecular behaviour accurately. In our present study, we have employed TIP3P potential on water and all atomistic optimized potentials for liquid simulations FFs to study the liquid electrolyte behavior of phosphazene-based polymer by considering its potential use in lithium-ion polymer batteries. We have explored the polymer's local structure, chain packing, wettability, and hydrophobic tendencies against the silicon surface using a combination of a pseudocontinuum model in MD simulation, and surface-sensitive sum frequency generation (SFG) vibrational spectroscopy. The finding yields invaluable insights into the molecular architecture of phosphazene. This approach identifies the importance of hydrophobic interactions with air and hydrophilic units with water molecules in understanding the behavior and properties of phosphazene-based polymers at interfaces, contributing to its advancements in materials science. The MD study uniquely captures traces of the polymer-ion linkage, which is observed to become more pronounced with the increase in polymer weight fraction. The theoretical observation of this linkage's influence on lithium-ion diffusion motion offers valuable insights into the fundamental physics governing the behavior of atoms and molecules within phosphazene-based polymer electrolytes in aqueous environments. Further these predictions are corroborated in the molecular-level depiction at the air-aqueous interface, as evidenced from the OH-oscillator strength variation measured by the SFG spectroscopy.The fundamental findings from this study open new avenues for utilizing MD simulation as a versatile methodology to gain profound insights into intermolecular interactions of polymer. It could be useful in the application of biomedical and energy-related research, such as polymer lithium-ion batteries, fuel cells, and organic solar cells.

Turbulent Ice–Ocean Boundary Layers in the Well-Mixed Regime: Insights from Direct Numerical Simulations

Abstract The meltwater mixing line (MML) model provides a theoretical prediction of near-ice water mass properties that is useful to compare with observations. If oceanographic measurements reported in a temperature–salinity diagram overlap with the MML prediction, then it is usually concluded that the local dynamics are dominated by the turbulent mixing of an ambient water mass with near-ice meltwater. While the MML model is consistent with numerous observations, it is built on an assumption that is difficult to test with field measurements, especially near the ice boundary, namely, that the effective (turbulent and molecular) salt and temperature diffusivities are equal. In this paper, this assumption is tested via direct numerical simulations of a canonical model for externally forced ice–ocean boundary layers in a uniform ambient. We focus on the well-mixed regime by considering an ambient temperature close to freezing and run the simulations until a statistical steady state is reached. The results validate the assumption of equal effective diffusivities across most of the boundary layer. Importantly, the validity of the MML model implies a linear correlation between the mean salinity and temperature profiles normal to the interface that can be leveraged to construct a reduced ice–ocean boundary layer model based on a single scalar variable called thermal driving. We demonstrate that the bulk dynamics predicted by the reduced thermal driving model are in good agreement with the bulk dynamics predicted by the full temperature–salinity model. Then, we show how the results from the thermal driving model can be used to estimate the interfacial heat and salt fluxes and the melt rate. Significance Statement We investigate the turbulent dynamics and thermodynamical properties of water masses below ice shelves using new data from high-resolution simulations. This is important because there are currently too few observations of ice–ocean boundary layer dynamics to construct reliable models of ice-shelf melting as a function of ocean conditions. Our results demonstrate that the turbulent diffusivities of salt and temperature are approximately equal in the well-mixed regime. This implies a linear correlation between the mean temperature and salinity profiles, consistent with the meltwater mixing line prediction that is often used to interpret polar observations. We take advantage of this correlation to propose a reduced model of ice–ocean boundary layers that can predict ice-shelf melt rates at relatively low computational cost.

Enhancement of pork marinating efficiency through pulsed electric field pretreatment: Integration of parameter optimization, kinetic modeling and quality characteristics

Marination is an important part of meat processing, the disadvantage is that the process of marinating is slow and prone to losing nutrients. In this study, pork tenderloins were pretreated with pulsed electric field (PEF) before being immersed in the marinade at 4 °C. The aim was to investigate the effect of PEF pretreatment (PEFP) on the marination process, specifically mass transfer and the quality of the pork. Additionally, the response surface method (RSM) was employed to explore the optimal conditions for PEFP. Results showed that under the best condition (2 kV/cm, 141.2 Hz and 2.3% duty cycle), the NaCl content of pork cured for 6 h reached 3.31%, which could effectively shorten the marinating time of pork (up to 40%). After marinating for 6 h with PEFP, the weight, moisture, and salt changes increased significantly. The effective diffusion coefficient (De) was raised to 1.71 × 10−10 (PEFP) from 1.36 × 10−10 (control) and the kinetic model of mass transfer over time has good linear correlation. The scanning electron microscopy (SEM) results indicate that PEFP altered the muscle fibre structure of pork to some extent, resulting in loosely arranged muscle fibre bundles. The total bacterial colony count results showed that PEFP had a good sterilization effect on microorganisms in pork. Furthermore, PEFP does not alter the colour or pH of marinated pork while improving its tenderness. These results showed that PEFP could effectively promote salt diffusion to shorten marinating time and improve meat tenderness.

Coordination and diffusion in glyoxal-based electrolytes for potassium-ion batteries.

Glyoxal-based electrolytes have been identified as promising for potassium-ion batteries (PIBs). Here we investigate the properties of electrolytes containing bis(fluorosulfonyl)imide (KFSI) in 1,1,2,2-tetra-ethoxy-ethane (tetra-ethyl-glyoxal, TEG) using density functional theory (DFT) calculations, Raman spectroscopy, and impedance spectroscopy. The coordination and configuration of the complexes possible to arise from coordination of the K+ ions by FSI and TEG were investigated both from an energetic point of view as well as qualitatively determined via comparing experimental and artificial Raman spectra. Overall, the K+ coordination depends heavily on the electrolyte composition with contributions both from FSI and TEG. Energetically the coordination by both the trans FSI anion conformer and the TEG solvent with four z-chain conformation is preferrable. From the spectroscopy we find that at lower concentrations, the predominant coordination is by TEG, whereas at higher concentrations, K+ is coordinated mostly by FSI. Concerning the diffusion of ions, investigated by impedance spectroscopy, show that the diffusion of the potassium salt is faster as compared to lithium and sodium salts in comparable electrolytes.

Three-Dimensional Modeling of Polygonal Ridges in Salt Playas.

In this work, we investigate the formation of the curious polygonal salt ridges that tessellate salt playas worldwide using suitable three-dimensional modeling and simulation of the dynamical processes that are responsible for their formation. We employ the principles of fracture mechanics under cyclic wetting and drying, fluid and mass transport in fracture channels, and processes of crystallization and self-organization to finally replicate the almost Voronoidal pattern of salt ridge mosaics observed in playas. The model is generic and applicable to playas having different salt compositions, as the effect of the salt diffusion coefficient and critical salinity for crystallization are factored in. The final pattern of polygonal salt ridges obtained by simulation visually resembles the geometry of the salt ridges reported in the literature. A single equation describing the time of first crystallization of salt in terms of evaporation suction pressure P, diffusion coefficient D of salt, and relative salinity Δc with respect to critical salinity at saturation, has been proposed. The saturation of crystal growth rate is shown to be a dynamic equilibrium between advection and diffusion processes. We show that the stable polygonal geometry of the salt playas is an effort toward the total minimization of system energy.

Construction of PPS based carbon fiber photothermal foam for crude oil absorption and seawater desalination

Efficient and clean solar energy conversion through photothermal materials has garnered significant attention, finding applications across energy, environmental protection, and healthcare sectors. This project focused on developing waste PPS-based carbon fiber (PCF) foam, emphasizing the high-value utilization of waste fibers in solar photothermal oil-absorption and photothermal evaporation applications. With exceptional light-absorption capabilities exceeding 97 %, the PCF@PDMS foam demonstrated superior photothermal conversion efficiency alongside impressive mechanical properties, facilitating effective absorption of highly viscous crude oil. Through PVA/CNF hydrophilic modification, internal water supply channels were integrated into the mPCF@PDMS foam, optimizing the evaporation surface area by retaining hydrophobic regions. This design not only enhanced thermal insulation but also significantly increased the evaporation rate to 2.00 kg·m−2·h−1 with an efficiency of 89.89 % under 1.0 sun irradiation. The presence of hydrophobic regions endowed the evaporator with self-floating ability, enhancing its practicality. During simulations of seawater desalination, the prepared evaporator exhibited remarkable salt crystallization resistance attributed to the strong water supply capacity and Marangoni effect induced during saltwater evaporation, facilitating salt diffusion and water evaporation. Overall, the foams developed in this project hold substantial application potential in the realm of photothermal technology.

Modeling high‐intensity ultrasound to enhance shrimp (Penaeus vannamei) brining without compromising crucial purchase attributes

AbstractTraditional brining methods, such as immersion, are time‐consuming and affect the quality of the food product. Thus, high‐intensity ultrasound (HIUS) has been studied as a brining‐assisted non‐thermal technology. However, this approach to shrimp and the assessment of the individual and combined effects of HIUS parameters, for example, time (t), power (P), and salt concentration (SC), is a knowledge gap. This study aimed to model HIUS‐brining for improving salt diffusion and water properties while maintaining relevant purchase attributes closer to fresh shrimp (Penaeus vannamei) quality. Our findings suggest HIUS improves salt diffusion, decreasing Aw and enhancing water‐holding capacity (WHC). Instead, the increased P reduced hardness and enhanced whiteness. HIUS‐brining (22.02 min/267.89 W/6.68%) maximized Na+ (2.58%) and WHC (86.31%), minimized Aw (.92), and retained hardness (71.07 N) and whiteness (55.14) close to freshness. Therefore, it is possible to employ HIUS in the shrimp brine to improve salt diffusion without damaging physicochemical attributes.Practical applicationsDespite traditional methods for seafood brining being considered effective, they are time‐consuming, taking hours to reach the desirable moisture value. High‐intensity ultrasound (HIUS) is an emerging non‐thermal technology recently explored as a brining technology for animal‐origin food, such as meat. The cavitation induced by HIUS generates gas microbubbles. The implosion increases local temperature and pressure and generates microjets, facilitating the mass transfer (sponge effect) and salt diffusion in the muscle tissues. However, the cavitation mechanism also releases free radicals, resulting in physicochemical alterations during processing, such as damage to color and texture. The present research contributes to providing a better understanding of the application and optimization of HIUS to accelerate the shrimp brining process. The findings herein are promising for the industrial utilization of sonication to obtain brined products without damaging the quality attributes of shrimp.

Comprehensive analysis of the Spartina alterniflora WD40 gene family reveals the regulatory role of SaTTG1 in plant development.

The WD40 gene family, prevalent in eukaryotes, assumes diverse roles in cellular processes. Spartina alterniflora, a halophyte with exceptional salt tolerance, flood tolerance, reproduction, and diffusion ability, offers great potential for industrial applications and crop breeding analysis. The exploration of growth and development-related genes in this species offers immense potential for enhancing crop yield and environmental adaptability, particularly in industrialized plantations. However, the understanding of their role in regulating plant growth and development remains limited. In this study, we conducted a comprehensive analysis of WD40 genes in S. alterniflora at the whole-genome level, delving into their characteristics such as physicochemical properties, phylogenetic relationships, gene architecture, and expression patterns. Additionally, we cloned the TTG1 gene, a gene in plant growth and development across diverse species. We identified a total of 582 WD40 proteins in the S. alterniflora genome, exhibiting an uneven distribution across chromosomes. Through phylogenetic analysis, we categorized the 582 SaWD40 proteins into 12 distinct clades. Examining the duplication patterns of SaWD40 genes, we observed a predominant role of segmental duplication in their expansion. A substantial proportion of SaWD40 gene duplication pairs underwent purifying selection through evolution. To explore the functional aspects, we selected SaTTG1, a homolog of Arabidopsis TTG1, for overexpression in Arabidopsis. Subcellular localization analysis revealed that the SaTTG1 protein localized in the nucleus and plasma membrane, exhibiting transcriptional activation in yeast cells. The overexpression of SaTTG1 in Arabidopsis resulted in early flowering and increased seed size. These outcomes significantly contribute to our understanding of WD40 gene functions in halophyte species. The findings not only serve as a valuable foundation for further investigations into WD40 genes in halophyte but also offer insights into the molecular mechanisms governing plant development, offering potential avenues in molecular breeding.

Temperature effects on ion migration and energy consumption during brackish water electrodialysis desalination

Electrodialysis (ED) is a well-established brackish water (BW) desalination technology based on the selective electro-transfer mechanism of ions for meeting freshwater demands in scarce water regions. While the influence laws of water temperature difference caused by changing seasons on the performance of BWED need to be clarified further. This study examined the effect of temperature on the desalination efficiency and energy consumption of BWED by controlling the water temperature with a constant temperature tank. Results showed that higher temperature significantly increased the current density and salt flux of BWED, but also caused a decrease and then an increase in energy consumption. The apparent activation energy of BWED system in low temperature range is about 40 % higher than that in high temperature range, indicating that higher temperature is contributed to reduce the ion transport resistance. While higher temperature increased ion diffusivity and membrane pore size, with a corresponding rise in LCD of ∼0.41 mA/cm2 and an increase in desalination ratio of ∼7.75 % for increment of every 10 °C, thus enhanced reverse salt diffusion. The running parameters of BWED system should be regularly regulated with the seasonal temperature based on the trade-off between desalination efficiency and energy consumption to ensure an efficient operation.

Diffusivities in water or aqueous solutions of sodium chloride with dissolved hydrogen and methane by dynamic light scattering

Knowledge of diffusion in water or aqueous solutions of sodium chloride with dissolved hydrogen and methane is important for geological hydrogen storage. This study examines the accessibility of diffusivities in the corresponding mixtures through dynamic light scattering at macroscopic thermodynamic equilibrium and provides corresponding data for hydrogen-storage-relevant temperatures T up to 393 K and pressures up to 20 MPa. The thermal and mutual diffusivities are simultaneously accessible in mixtures of water and hydrogen. Moreover, for water with dissolved mixtures of hydrogen and methane, the thermal diffusivity and an apparent diffusivity related to the diffusion of the gas mixture can be accessed. In aqueous solutions of sodium chloride at T > 300 K, a strong molecular association leading to a quasi-static light-scattering pattern in the liquid sample was observed, which hindered the determination of the molecular gas diffusivities. However, the salt diffusion coefficient was accessible for all T values.

Visualization of salt diffusion in beef curing process using Smartphone-Assisted ratiometric fluorescent sensor

Herein, a smartphone-assisted fluorescent sensor was proposed for real-time fluorescence imaging and monitoring of salt diffusion in beef curing process. The glutathione modified carbon quantum dots @ curcumin (CQDs@CCM) probe with dual-emissive properties was prepared using natural biomass materials. In the probe, the CQDs with blue fluorescence was quenched by CCM due to the inner filter effect (IFE). When the probe was exposed to highly saturated sodium salt, CCM formed a complex with sodium ions, interrupting the IFE behavior and resulting in the fluorescence recovery of CQDs. Significantly, the innovative application of CCM in curing scenarios effectively circumvents the interference of other metal ions. To our knowledge, this is the first report to apply smartphone-assisted fluorescent sensor to salt imaging of cured beef. Notably, the finite element analysis was performed to simulate the diffusion of salt in beef using COMSOL, and the simulation showed similar results to fluorescence analysis, indicating the established visualizing method and the simulated model can provide effective information for beef marination process. This study provide technical support for precise control of the beef curing degree and offer new insights into the fluorescence imaging in food flavor monitoring.

Effect of titanium oxide/reduced graphene (TiO2/rGO) addition onto water flux and reverse salt diffusion thin-film nanocomposite forward osmosis membranes

Thin-film nanocomposite (TFN) forward osmosis (FO) membranes have attracted significant attention due to their potential for solving global water scarcity problems. In this study, we investigate the impact of titanium oxide (TiO2) and titanium oxide/reduced graphene (TiO2/rGO) additions on the performance of TFN-FO membranes, specifically focusing on water flux and reverse salt diffusion. Membranes with varying concentrations of TiO2 and TiO2/rGO were fabricated as interfacial polymerizing M-phenylenediamine (MPD) and benzenetricarbonyl tricholoride (TMC) monomers with TiO2 and its reduced graphene composites (TiO2/rGO). The TMC solution was supplemented with TiO2 and its reduced graphene composites (TiO2/rGO) to enhance FO performance and reverse solute flux. All MPD/TMC polyamide membranes are characterized using various techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements. The results demonstrate that incorporating TiO2/rGO into the membrane thin layer improves water flux and reduces reverse salt diffusion. In contrast to the TFC membrane (10.24 L m−2h−1 and 6.53 g/m2 h), higher water flux and higher reverse solute flux were detected in the case of TiO2and TiO2/rGO-merged TFC skin membranes (18.81 and 24.52 L m−2h−1 and 2.74 and 2.15 g/m2 h, respectively). The effects of TiO2 and TiO2/rGO stacking on the skin membrane and the performance of TiO2 and TiO2/rGO skin membranes have been thoroughly studied. Additionally, being investigated is the impact of draw solution concentration.Graphical

Facile preparation of anatase coated nanofiber mats for multifaceted water treatment

Access to and availability of freshwater is increasingly important as the World’s population grows and pollution threatens freshwater resources providing an underlying impetus to explore efficient and environmentally friendly water treatment technologies targeting seawater, industrial wastewater and domestic sewage. By embedding SiO2 in blow spun polyacrylonitrile (PAN) fibers that after peroxidation form a flexible nonwoven mat (SiO2@PNMs) and subsequent carbonization of the PAN and hydrolysis of TiO2 onto the SiO2 nanoparticles (TiO2/SiO2@CNMs), a multifunctional solar evaporator within the fields of photothermal conversion, catalytic degradation, desalination and disinfection is obtained. The sunlight light absorption is above 90 % and due to disruption of inter-water hydrogen bonds and the ability to evaporate through the sides of the nonwoven mat, the evaporation rate of 1.71 kg m-2h−1 exceeds the theoretically considered maximum at an energy conversion efficiency of 92.1 %. The evaporation rate remains stable through a 40-day cycle and the evaporation rate is unaffected by addition of NaCl in concentrations up to 20 % due to salt diffusion and pumping through the porous nonwoven structure demonstrating. anti-salt, anti-fouling and self-cleaning ability. In addition to the solar-driven water evaporation process, the photocatalytic properties of the anatase TiO2 crystals combined with the conducting effect of the carbon fibers trap photogenerated electrons and retard electron-hole complexation to maintain the release of reactive oxygen species to decompose organic dyes and inactivate bacteria in the water source. This multifunctional nanofiber mats provide a simple and sustainable avenue for the production of fresh water, and has potential application in desalination of seawater and purification of printing and dyeing wastewater.

Cost-Effective 3D-Printed Bionic Hydrogel Evaporator for Stable Solar Desalination.

Solar desalination using hydrogel evaporators is an eco-friendly, highly efficient means with natural sunlight for sustainable freshwater production. However, it remains challenging to develop a cost-effective and scalable method to prepare salt-resistant hydrogel evaporators for stable desalination. Here, inspired by tree transpiration and hierarchical porous structure, a 3D-printed bionic hydrogel evaporator (3DP-BHE) is designed for long-term solar desalination. Commercialized activated carbon (AC) is introduced into biomass starch skeleton as a solar light absorber to build 3DP-BHE in a cost-effective fashion ($10.14m-2 of total materials cost). The bionic tree leaf layer for 94.01% light absorption and timely vapor diffusion. The bionic tree trunk layer with 3D printed bimodal porous structure for water transfer, thermal isolation, and salt ions convection and diffusion. With the unique bionic structure, the 3DP-BHE achieves a stable evaporation rate of 2.13kgm-2h-1 at ≈90.5% energy efficiency under one sun (1kWm-2). During the 7-day desalination of 10wt.% brine, a steady evaporation rate of 1.98kgm-2h-1 is maintained with a record-high cost-effectiveness (195.3gh-1$-1) manner. This 3DP-BHE will open significant opportunities for affordable solar desalination systems on multiple scales, from individual households to off-grid communities.

Colloidal diffusiophoresis in crossed electrolyte gradients: Experimental demonstration of an “action-at-a-distance” effect predicted by the Nernst-Planck equations

In an externally imposed electrolyte (salt) concentration gradient, charged colloids drift at speeds of order one micrometre per second. This phenomenon is known as diffusiophoresis. In systems with multiple salts and “crossed” salt gradients, a nonlocal component of the electric field associated with a circulating (solenoidal) ion current can arise. This is in addition to the conventional local component that depends only on the local salt gradients. Here we report experimental observations verifying the existence of this nonlocal contribution. To our knowledge this is the first observation of nonlocal diffusiophoresis. The current develops quasi-instantaneously on the timescale of salt diffusion. Therefore, in systems with multiple salts and crossed salt gradients, one can expect a nonlocal contribution to diffusiophoresis which is dependent on the geometry of the system as a whole and appears as a kind of instantaneous “action-at-a-distance” effect. The interpretation is aided by a magnetostatic analogy. Our experiments are facilitated by a judicious particle-dependent choice of salt (potassium acetate) for which the two local contributions to diffusiophoresis almost cancel, effectively eliminating conventional diffusiophoresis. This enables us to clearly identify the novel, nonlocal effect and may be useful in other contexts, for example, in sorting particle mixtures. Published by the American Physical Society 2024

Cucurbit[6]uril builds a water channel for improving the water/salt selectivity of polybenzimidazole

Polybenzimidazole (PBI) has garnered significant interest in desalination due to its exceptional chemical stability and mechanical strength, but suffers from poor water permeability. In this work, different contents of hydroxylated Cucurbit [6]uril (CB [6] were added to PBI to build a “water transport channel”. The effects of CB [6] addition on the chemical structure and surface morphology were analyzed by FTIR, SEM, and Zeta potential, respectively. Based on the solution-diffusion model, the effect of CB [6] on the water/salt transport properties of PBI membranes was thoroughly investigated. The results show that appropriate CB [6] doping can enhance water sorption of PBI through the special “outer hydrophilic and inner hydrophobic cavity” structure, and boost water diffusion with the channeling effect of the hydrophobic CB [6] cavity. While the complexation between the carbonyl group in CB [6] and Na+ ions slightly increased salt sorption, the specific cavity structure of CB [6] can significantly decrease salt diffusion by blocking salt ions and increasing transport path tortuosity. The cavity effect of CB [6] was further confirmed by hybridizing CB [6] with biphenylsulfonyl-substituted PBI when the cavity can be occupied. Therefore, the introduction of CB [6] improves the water/salt diffusion selectivity and then the permeability selectivity of PBI. Notably, the PBI@CB [6] membrane with a 0.25 wt% CB [6] loading exhibited a 40-fold increase in water permeability coefficient compared to pure PBI, while experiencing only a slight decrease in salt permeability coefficient, water/salt selectivity almost exceeding the empirical upper bound line of polymers. This work provides a theoretical foundation for the development of high-performance desalination membranes based on macrocyclic molecules such as CB [6].

Study of restricted diffusion of lithium salts in diglyme confined in mesoporous carbons as a model for cathodes in lithium-air batteries.

The Li+ ion mobility through the porous cathode is a critical aspect in the development of commercial Li-air batteries. The bulk transport properties of lithium salts in organic solvents are not reliable parameters for the design of this type of battery since confinement could significantly modify the transport properties, especially when pore diameters are below 10 nm. In this work, we studied the effect of the carbon mesostructure and surface charge on the diffusion of LiTf and LiTFSI salts dissolved in diglyme, typical electrolytes for lithium-air batteries. Interdiffusion coefficients of the salts were determined using a conductimetric method. NMR spectroscopy and relaxometry were used to explore the effect of the carbon structure and the surface charge density on the interaction between the electrolytes and the pore wall. We showed that carbon micro/mesoporous structure plays a critical role in the transport properties of the electrolyte, producing a decrease of up to 2-3 orders of magnitude in the salt interdiffusion coefficients when going from bulk solutions to pores below 4 nm in diameter. It was observed that for pores 25 nm in diameter, the reduction in the diffusion coefficient can be mainly ascribed to the porosity of the sample, giving tortuosity factors around 1. However, for smaller pore sizes (1-10 nm diameter) bigger tortuosity coefficients were observed and were related to strong ion-pore wall interactions. Moreover, it was noticed that the ratio between the diffusion coefficients of the two studied salts dissolved in diglyme, is different in bulk and under confinement, demonstrating that the interactions of the ions with the charged pore wall probably compete with the cation-anion interactions, affecting salt association under confinement.

An MPM-Based Phase-Field Simulation of Plating and Stripping of Lithium with a Solid Electrolyte Interphase

A methodology for performing phase-field simulations of plating and stripping in the presence of a solid electrolyte interphase (SEI) is presented and applied to a lithium metal electrode. Material point method (MPM) simulations are performed assuming a homogeneous SEI layer and are compared with experiment. Results are consistent with experiment for two electrolytes and confirm the dominance of the SEI layer in determining cell impedance. Notably, in some instances, the SEI potential drop greatly affected activation overpotential, differing from the applied potential. To accurately depict stripping current vs potential for SEI-free systems, the model considered non-ideal electrolyte effects: concentration-dependent salt activity coefficient, salt diffusion coefficient, and electrolyte conductivity. Conversely, systems with SEI layers displayed minimal non-ideal concentration-related electrolyte effects due to impedance originating primarily from the SEI. In plating scenarios, low SEI salt concentration negated the need for non-ideal SEI effects. However, for stripping, non-ideal salt-concentration dependent SEI effects were crucial in reproducing experimental behavior, owing to high salt concentration at the electrode/SEI interface.