Improved Transport Properties Research Articles

Low temperatures improved transport properties of [formula omitted] nanoparticles using co-precipitation technique

Pure ZnO and Mn-doped ZnO nanoparticles with the formula Zn(1−X)Mn(X)O (x = 0 %, 3 %, 6 %, and 9 %) were synthesized through a co-precipitation method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the phase and morphology of the nanoparticles. The x-ray diffraction results confirmed all the prepared samples have a wurtzite crystal structure. The morphological valuations of the produced nanoparticles show that the particles are spherical within a nanometer range. Impedance spectroscopy was used to characterize the impedance in the frequency range of 20 Hz to 2 MHz at temperatures from 140 K to 280 K. Results showed that Mn-doping enhances ac conductivity and decreases the bandgap energy of ZnO. This Mn variation in ZnO at low temperatures and high frequencies has potential applications in optoelectronic devices.

Crowding accelerates the rotation of a bacterial rotor

Understanding the propulsion of a swimmer in a large group of individuals holds the key to unravelling the intriguing dynamics of active matter collective motion. Here, we develop a two-dimensional (2-D) self-assembled rotor, powered by bacterial flagella. At a water–air interface, the average direction of rotation of a rotor is fixed. When the chiral rotor is put into a 2-D bacterial suspension, we examine the average and fluctuation of the angular velocity of the rotor. Remarkably, the average angular velocity of a rotor is found to increase up to 3 times when the density of surrounding bacterial suspension increases and the increase is nonlinear. In a dense suspension of bacteria, the existence of a rotor disrupts vortices in the surrounding active turbulence, and the acceleration of the rotor is independent of the activity level of the surrounding free bacteria. The nonlinear acceleration thus results from hydrodynamic interaction with surrounding crowdedness that can be quantitatively explained by hydrodynamic simulation. The simultaneity between the acceleration of rotor and free bacteria in active turbulence suggests that crowding-induced acceleration may promote the onset of instability. The result will inspire new active-matter-based microfluidic devices with improved transport properties.

(Digital Presentation) The Effect of Coating Quality on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines the impact of the quality of the GDL non-wetting coating on water transport. It is found that there are two distinct regions defined by the coating quality which present fundamentally distinct behaviours, one region characterized by few coating defects with the second marked by significant coating degradation. Simulations consider the influence of heterogeneous wetting and pinning conditions on protruding water droplets in contact with the GDL fibrous matrix. The impact is assessed by examining the breakthrough pressure as a function of protruding droplet volumes. When a non-wetting coating such as PTFE is applied, inherent coating defects determine a mixed-non-wetting (MNW) behaviour of water passing through the pores of the GDL. The MNW behaviour for a quasi-uniform non-wetting coating having less than 25% defects is characterized by a high breakthrough pressure, yielding improved transport properties in the stable displacement regime. The MNW meniscus is critical to establishing a high breakthrough pressure and a small characteristic droplet volume, parameters considered to be important in the design of a GDL that promotes optimal water transport. The coating degrades under normal operating conditions and as a consequence it changes the water transport characteristics of the porous medium. In this range where coating defects are predominant it is found that the water breakthrough pressure changes significantly, rendering poor performance below that of a non-coated wetting GDL. Various degrees of coating degradation are considered and the corresponding Laplace pressure is determined as a function of breakthrough droplet volumes.

Unraveling relationship between complex lifetimes and microscopic diffusion in deep eutectic solvents.

Aqueous mixtures of deep eutectic solvents (DESs) have emerged as a subject of interest in recent years for their tailored physicochemical properties. However, a comprehensive understanding of water's multifaceted influence on the microscopic dynamics, including its impact on improved transport properties of the DES, remains elusive. Additionally, the diffusion mechanisms within DESs manifest heterogeneous behavior, intricately tied to the formation and dissociation kinetics of complexes and hydrogen bonds. Therefore, it is imperative to explore the intricate interplay between bond kinetics, diffusion mechanism, and dynamical heterogeneity. This work employs water as an agent to explore their relationships by studying various relaxation phenomena in a DES based on acetamide and lithium perchlorate over a wide range of water concentrations. Notably, acetamide exhibits Fickian yet non-Gaussian diffusion across all water concentrations with Fickian (τf) and Gaussian (τg) timescales following a power-law relationship, τg∝τfγ, γ ∼ 1.4. The strength of coupling between bond kinetics and different diffusion timescales is estimated through various power-law relationships. Notably, acetamide-water hydrogen bond lifetime is linked to diffusive timescales through a single power-law over the entire water concentration studied. However, the relationship between diffusive timescales and the lifetime of acetamide-lithium complexes shows a sharp transition in behavior at 20 wt. % water, reflecting a change from vehicular diffusion below this concentration to structural diffusion above it. Our findings emphasize the critical importance of understanding bond dynamics within DESs, as they closely correlate with and regulate the molecular diffusion processes within these systems.

Understanding the electronic structure and transport properties of A-site SrTiO3-δ ceramics with enhanced configuration entropy

Since SrTiO3 is attractive due to its versatile electronic properties ranging from dielectric to semiconducting behavior, the effect of systematic co-substitution of various A-site cations on the electronic structure and transport properties of oxygen-deficient SrTiO3-δ bulk ceramics was analyzed. The materials were synthesized by reverse co-precipitation method and densified by spark plasma sintering (SPS) in a vacuum, followed by a post-thermal treatment in a reducing atmosphere (5 % H2/Ar). The phase purity was confirmed by X-ray diffraction (XRD), different microstructures were revealed by scanning electron microscopy (SEM), and characterization in terms of electrical conductivity (σel) and Seebeck coefficient (S) were performed. The largest power factor was obtained with Sr0.25Ca0.25Na0.25La0.25TiO3-δ by maintaining electrical conductivity while increasing the Seebeck coefficient. Density Functional Theory (DFT) calculations were applied to obtain information on band structures, the projected density of states (PDOS), and electron density differences (EDD). Band structures indicated that oxygen deficiency essentially changed the conductive nature of the studied materials by shifting the Fermi level to the conductive zone, while PDOS plots define the role of each element located at the A site. The electronic structure is affected to the greatest extent in the cases when Nd and Pr are present at the A-site. However, the obtained experimental and computational (DFT) results could not completely match and explain all phenomena since understanding the effect of different cations at A-site on oxygen vacancy formation seems to be a challenging task, and therefore, some hypotheses are proposed. This work attempts to understand the role of a particular cation at A-site on the electronic band structure and its relevance to the formation of oxygen vacancies, thereby providing valuable insights for future high-entropy perovskite titanates with improved transport properties.

Thermoelectric potential: role of bismuth in CuSb1−xBixSe2 for improved transport properties

Thermoelectric potential: role of bismuth in CuSb1−xBixSe2 for improved transport properties

(Digital Presentation) The Effect of Coating Quality on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines the impact of the quality of the GDL non-wetting coating on water transport. It is found that there are two distinct regions defined by the coating quality which present fundamentally distinct behaviours, one region characterized by few coating defects with the second marked by significant coating degradation. Simulations consider the influence of heterogeneous wetting and pinning conditions on protruding water droplets in contact with the GDL fibrous matrix. The mixed-non-wetting behaviour for a uniform non-wetting coating having less than 25% defects is characterized by a high breakthrough pressure, yielding improved transport properties in the stable displacement regime. The coating degrades under normal operating conditions and it changes the water transport characteristics unfavorably through a significant decrease in breakthrough pressure, and an up to six-fold increase in droplet volume. Various degrees of coating degradation are considered and the corresponding Laplace pressure is determined as a function of droplet volumes at breakthrough.

Tuning Transition Metal‐Containing Molecular Magnets by On‐Surface Polymerization

AbstractPorphyrins are promising multifunctional units particularly interesting for the realization of molecular nanodevices. Their structural variety allows to create precursors suitable for the on‐surface polymerization of porphyrin blocks. The corresponding increased stability and improved transport properties of the formed polymerized molecular nanostructures make them practically worthwhile. For the case of 2D porphyrin materials, the effect of polymerization on the magnetic properties of transition metal ions has not been reported yet. Therefore, details on the properties of an extended covalent nickel tetraphenylporphyrin network formed via Ullmann coupling on the Cu(111) surface are reported. By using photoelectron and absorption spectroscopies together with density functional theory calculations, it is systematically evolving how the functional properties of the Ni centers are changed within a polymerized molecular structure in comparison to single‐molecule nickel tetraphenylporphyrin derivatives that build the 2D molecular network. A model that explains the differences in the electronic and magnetic properties observed for the Ni centers in both structures based on the additional rigidity characteristic of the molecular layer after polymerization is drawn.

Dual-optimization of transport properties enabled by high-pressure treatments for CuInTe2 thermoelectric materials

CuInTe2 is the focus of much research interest in I-III-VI2 diamondoid compounds due to its potentially high thermoelectric performance. However, its unmatched transport behaviors among electrical and thermal properties seriously impede enhanced thermoelectric performance. In this work, we demonstrate that high pressure can dual-optimize the electrical and thermal transport properties, leading to enhanced thermoelectric performance in CuInTe2 with cationic defects. The results indicate that the carrier concentration level is increased while greatly enhancing carrier mobility owing to the influence of high pressure on the band and electronic structures, realizing an excellent power factor of 1406 μWm−1K−2. Furthermore, high-pressure treatments and cationic defects can introduce multiple defect structures with various sizes, strongly scattering full-frequency phonons to reduce lattice thermal conductivity. With these great merits enabled by high pressure, the thermoelectric performance of CuInTe2 with cationic defects is improved and a maximum zT of 1.12 is obtained at 773 K, fully verifying the advantages of high-pressure treatments in terms of improving transport properties.

Al-doped Bi2Se3 nanoparticulate semiconductors with controlled resonance states for enhanced thermoelectric efficiency

The generally lower thermoelectric figure of merit (zT < 0.1) of eco-friendly Bi2Se3 semiconductors constrains the waste energy conversion efficiency in the resulting devices compared to a relatively toxic Bi2Te3. We strategically introduce an aluminium (Al) dopant to create resonance states near the Fermi level and obtain Al–Bi2Se3 nanoparticulate semiconductors with enhanced zT. As an electron feeder, these resonance states significantly improve transport properties within the Al–Bi2Se3 semiconductors. The theoretical calculation shows the creation of the resonance states by hybridizing the dopant's s-orbitals with the host's p-orbitals near the Fermi level. The Al–Bi2Se3 semiconductors effectively moderate electron concentration and the Seebeck-dependent effective mass, resulting in an ultrahigh zT of 0.57 over a broad temperature range of 300–473 K. The nanoparticle size (20 nm) efficiently impedes the propagation of lattice vibration, leading to an ultralow total thermal conductivity of 0.399 Wm−1/K. In contrast to conventional doping approaches, our strategic resonance doping is pivotal to enhancing the thermoelectric performance of the Bi2Se3 semiconductors and providing a pathway for synthesizing other semiconductor materials.

Evaluating Strategies to Enhance Li Transference in Salt-in-Ionic Liquid Electrolytes: Mixed Anions, Coordinating Cations, and High Salt Concentration.

The increased safety of salt-in-ionic liquid electrolytes compared with established carbonate-based systems has promoted intense research in this field, but low conductivities, slow lithium transport, and unfavorable lithium anion correlations still prevent a mass market application. In particular, strong Li-anion correlations lead to dominant vehicular Li transport with the same drift direction for anions and lithium in the electric field. Here, three different strategies and their mutual interplay are evaluated, which could reduce Li-anion coordination, i.e., high salt concentration, a mixed-anion composition, as well as an ether functionalization of the organic cation. To this end, two series of highly concentrated IL-based electrolytes, based on either ethylmethylimidazolium (EMIM) or the ether-functionalized 1-methoxyethyl-1-methylpyrrolidinium (Pyr12O1) organic cation, and employing mixed bis(fluorosulfonyl)imide/bis(trifluoromethylsulfonyl)imide (FSI/TFSI) anions are investigated. Measurements of conductivities, diffusion coefficients, and electrophoretic mobilities reveal no beneficial effect due to the increased heterogeneity of the FSI/TFSI-based electrolyte matrix, generally showing improved transport properties with increasing FSI share. However, a combination of both the ether-functionalized cation and high FSI content is proven successful, as lithium mobilities are positive, and vehicular transport is overcome by structural Li transport. Our study demonstrates the decisive role of synergy of the different approaches: While the single effect of a high salt concentration, weakly lithium-coordinating anions, or organic cations with lithium-affine functional groups is too weak to prevent vehicular transport, their joint effect can overcome vehicular Li transport, leading to improved Li conduction in ionic liquids.

Transport properties of concrete containing lithium slag

Lithium Slag (LS), also known as Delithiated Beta Spodumene (DBS), is a by-product of lithium extraction from spodumene ore that contains active silicon dioxide and aluminium oxide making it a potential supplementary cementitious material (SCM) for concrete. This study investigated the transport properties of concrete at 28, 90, and 180 days by incorporating LS as an SCM with cement replacement levels of 20%, 40%, and 60%. The findings reveal that 20% to 40% LS enhanced compressive strength, and reduced permeable voids, water penetration, sorptivity, and porosity, leading to improved transport properties. As LS reacts slowly, 40% LS resulted in 18.34% higher compressive strength at 180 days compared to that of the control mix. Therefore, VPV, water penetration depth, and sorptivity co-efficient of concrete with 40% LS were found 15.96%, 24.79% and 38.46%, respectively, lower than the control mix. In addition, porosity analysis confirmed that with the increase of LS in concrete, porosity decreased over time. Moreover, SEM analysis demonstrated the development of CaCO3 crystals at 40% LS, further reducing porosity. However, beyond 60% cement replacement by LS, a decline in concrete properties was observed due to unreacted LS particles. Therefore, this research underscores the potential use of LS to enhance durability of concrete.

Numerical minimization of neoclassical poloidal viscosity for supersonic equilibria in tokamak geometry

Extensive experimental evidence has shown that the presence of poloidal flow in tokamaks can dramatically improve transport properties. However, theory indicates that poloidal flows are damped by poloidal viscosity, thus necessitating external drivers, such as neutral beam injection or radio frequency heating. In this work, ideal magnetohydrodynamic equilibria are calculated via the FORTRAN code FLOW [Guazzotto et al., Phys. Plasmas 11, 604 (2004)] and a postprocessor is used to estimate the neoclassical poloidal viscosity. The equilibrium inputs, which correspond to intuitive physical quantities, are then numerically optimized to reduce a viscosity figure of merit. We present supersonic equilibria in tokamak geometry with minimized neoclassical poloidal viscosities for various velocity free function inputs, plasma aspect ratios, and collisionality regimes. Benchmarks are made against an analytic theory as well as a classical expression of poloidal viscosity. Numerical confirmation of the analytic theory is obtained in the high aspect ratio and high collisionality limit. Good agreement is also seen near the plasma core and edge, with discrepancies arising in the intermediate region. Outside of these limits, rotation input function profiles are found that provide ∼order of magnitude improvements over the analytic theory, with additional progress being made toward predictions for tokamak-relevant equilibria.

Enhancing Ion Mobility in Solids with Physics-Informed and AI-Driven Descriptors

The field of sustainable energy storage and conversion has witnessed increasing interest in ionic conductors due to their potential applications in electrochemical devices such as electrodes and solid electrolytes. In this study, we employed a combination of density functional theory investigations and artificial intelligence techniques to develop a robust descriptor for ion mobility [1,2]. Our descriptor incorporates factors like structural distortions, electronegativity, ionic radii, and oxidation states. By investigating various charge carrier chemistries and the anion and cation chemistries of the host lattice, we discovered that migration barriers are interconnected through linear scaling relations. Building upon this descriptor, we conducted a comprehensive study that employed both theoretical and experimental approaches to identify cathode materials with enhanced mobility for Mg-ions. Our focus was on oxide spinels, and we employed periodic density functional theory calculations to analyze the migration of Mg2+ ions and evaluate the electronic, geometrical, and stability properties of different transition metals within the spinel structures. Our findings reveal that electronegative transition metals, such as Rh, facilitate high mobility of Mg-ions and promote favorable cathode functionality within oxide spinel frameworks [3]. Based on these insights, we identified MgRh2O4 as a promising candidate and proceeded to prepare and characterize it structurally. This study opens up new possibilities for utilizing functional cathode materials with improved transport properties in battery-related applications. [1] M. Sotoudeh and A. Groß JACS Au 2022, 2, 463–471.[2] M. Sotoudeh, M. Dillenz, A. Groß, Adv. Energy Sustainability Res. 2021, 2, 2100113. [3] M. Sotoudeh, M. Dillenz, J. Döhn, J. Hansen, S. Dsoke, A. Groß, Chem. Mater. 2023, 35, 4786–4797.

Impact of fluorination on Li+ solvation and dynamics in ionic liquid-hydrofluoroether locally concentrated electrolytes

The thermal, physical, structural, and transport properties of ionic liquid (IL) electrolytes based on n-methyl-n-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide [PYR14][TFSI] and Li-salts of lithium (nonafluorobutane)(trifluoromethanesulfonyl)imide [Li][IM14] and [Li][TFSI] (0 ≤ xLi ≤ 0.3), with addition of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) (0 ≤ xTTE ≤ 0.45) were studied. While [IM14] increases glass transition, TTE improves conductivity over a wider liquidus range. Li+ is solvated primarily by [TFSI] with some contribution by [IM14]. However, both 7Li- 19F HOESY NMR and spatial distribution functions (SDFs) derived from molecular dynamics (MD) indicate short contacts between the fluorines of TTE and Li+. This is a result of tighter anion-solvated Li+ without aggregation of the Li+ solvates, consistent with Raman measurements, thus confirming the existence of fluorous domains in the bulk which leads to improved fluidity and a Li+ diffusivity of 1.26 × 10−12 m2/s at 0 °C (xLi = 0.20) with a Li+ transference of 0.16. Improved transport properties translated to a higher capacity of the TTE/IL electrolyte in a Li||LiFePO4 half-cell with 95mAh/g at 0.1C, compared to the IL electrolyte without TTE (60 mAh/g). This study demonstrates the tunability of solvation and transport properties in IL electrolytes by asymmetric fluorinated anions and hydrofluoroether co-solvents for low temperature Li-ion batteries.

A comprehensive study on transport behaviour and physicochemical characteristics of PU/based 3-phase mixed matrix membranes: Effect of [HNMP][HSO4] ionic liquid and ZnO nanoparticles

The gas separation industry has witnessed a significant focus on mixed matrix membranes (MMMs) due to their exceptional potential, surpassing the performance of conventional polymeric membranes. This study aimed to develop and evaluate MMMs using polyurethane (PU) as the polymer matrix and zinc oxide (ZnO) and ionic liquids (ILs) as fillers. PU/ZnO, PU/IL, and PU/ZnO/IL MMMs were prepared utilizing the dry-phase inversion method, and their efficacy in separating CO2, CH4, and N2 gases was investigated under various conditions. A comprehensive characterization protocol using FTIR, FESEM, TGA, AFM, and tensile testing was employed for their thorough characterization. The membranes’ transport properties were assessed at different pressures and filler concentrations. Results showed that IL incorporation increased gas permeability by enhancing solubility, diffusion, ionic interactions, swelling, and accessible volume. Incorporating ZnO and IL particles in the PU matrix simultaneously improved transport properties, particularly selectivity. Robeson’s diagram analysis shows that the PU/0.5%ZnO/2%IL MMM performed best. Furthermore, molecular simulation methods, including Monte Carlo and molecular dynamics simulations, assessed adsorption isotherms and physicochemical properties such as free volume, density, and X-ray diffraction. Simulation outcomes were highly reliable with experimental results, affirming the results’ efficiency and validation. Overall, this study demonstrated the efficiency of using ZnO and IL in the MMMs, highlighting their potential in gas separation applications.

Sustainable integration of coal mine overburden as a substitute for natural sand in concrete to enhance its mechanical and durability properties

The viability of coal mine overburden (CMOB) as a sustainable substitute for natural sand (NS) in concrete production is investigated in this study, with a specific focus on the critical aspects of strength and durability. The reliability of select nondestructive testing (NDT) methods for evaluating the mechanical and durability properties of CMOB-incorporated concrete is rigorously validated. It is revealed that concrete strength and durability are significantly enhanced by the replacement of NS with CMOB up to 60%. Optimal mechanical strength, minimal void content, improved transport properties, and excellent chloride resistance are attained at this replacement ratio. Replacing 60% of NS with CMOB results in a substantial enhancement, with strength properties increasing by 10–35% and durability properties by 10–75%, compared to the control concrete made solely with NS. Furthermore, analytical models for estimating durability properties based on measurable strength characteristics are introduced, offering a practical quality assurance tool for construction projects. This research marks a significant step towards sustainable construction practices by validating NDT methods for evaluation of CMOB-incorporated concrete.

Lithium disilicate as an alternative silicate battery material. A theoretical study

Advanced atomistic simulations are used to study the ion transport in the Na- and K-doped lithium disilicate Li2Si2O5 which is considered as a potential battery material for solid state alkali batteries. In order to evaluate the ease with which Li2Si2O5 can store Na and K ions, the Na and K incorporation mechanisms into Li2Si2O5 are studied by using lattice statics simulations. Our calculations revealed that the defect formation energies for K and Na doping of Li2Si2O5 amount to 0.49 eV/dopant and 0.96 eV/dopant, respectively. The Li ion diffusion in Li2Si2O5 is significantly enhanced upon Na and K doping. The activation energies of Li ion diffusion in all samples are in the range of 0.5–0.6 eV, while for conduction 0.4–0.5 eV. At higher dopant concentrations, K doping increases the Li ion diffusion/conduction, reaching their improved transport properties at x = 0.14 with low activation energy for diffusion and conduction. At a low dopant concentration of x = 0.02, Na doping also improves the Li ion diffusion/conduction. Our results demonstrate the potential of the doped lithoum disilicate Li2Si2O5 as an effective material for alkali ion batteries and strongly suggest experimental verification.

Improved thermoelectric power factor of multilayered poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and Cu2Se thin films

Cu2Se is a promising thermoelectric material due to its superionic behavior with superior transport properties. Here we report a facile method of spin coating for the fabrication of multilayers of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and Cu2Se thermoelectric materials for mid-temperature range applications. The synthesis of multilayered thin films with a unique organic-inorganic hybrid framework could be used in flexible thermoelectric devices. The detailed investigation of PEDOT:PSS and Cu2Se multilayered thin films reveals interaction between organic and inorganic material as inferred by AFM and FTIR. The electronic transport properties were investigated for all specimens, with the highest PF of 20.1 µW/m. K2 at 450 K was achieved from the bilayer stacking of Cu2Se and PEDOT:PSS, which is about 82 % higher as compared to that of pure PEDOT:PSS at the same temperature. These improved transport properties are the combined effect of energy filtering and interface effects. The proposed strategy opens up an avenue for research on chalcogenide based composite materials with an organic framework for flexible thermoelectric device applications.

An effective strategy to boost hydrogen separation performance through stable mixed proton‐electron conducting membrane

AbstractHydrogen separation and purification are key to widespread application of hydrogen energy. Hydrogen permeable membranes based on lanthanum tungstate (LWO) attract attention due to favorable mechanical strength and chemical stability. However, industrial application of LWO‐based membranes has remained challenging because of modest hydrogen permeances. Here we report a novel graded porous supported symmetric (GPSS) LWO‐based membrane with improved transport properties, gas exchange dynamics, and operational stability, boosting stable hydrogen flux by several times over previously reported state‐of‐the‐art membranes.