Heterostructured WOx/W2C Nanocatalyst for Li2S Oxidation in Lithium-Sulfur Batteries with High-Areal-Capacity.

Lithium-sulfur (Li-S) batteries show extraordinary promise as a next-generation battery technology due to their high theoretical energy density and the cost efficiency of sulfur. However, the sluggish reaction kinetics, uncontrolled growth of lithium sulfide (Li2S), and substantial Li2S oxidation barrier cause low sulfur utilization and limited cycle life. Moreover, these drawbacks get exacerbated at high current densities and high sulfur loadings. Here, a heterostructured WOx/W2C nanocatalyst synthesized via ultrafast Joule heating is reported, and the resulting heterointerfaces contribute to enhance electrocatalytic activity for Li2S oxidation, as well as controlled Li2S deposition. The densely distributed nanoparticles provide abundant binding sites for uniform deposition of Li2S. The continuous heterointerfaces favor efficient adsorption and promote charge transfer, thereby reducing the activation barrier for the delithiation of Li2S. These attributes enable Li-S cells to deliver high-rate performance and high areal capacity. This study provides insights into efficient catalyst design for Li2S oxidation under practical cell conditions.

Graphene and MOF Assembly: Enhanced Fabrication and Functional Derivative via MOF Amorphization.

The integration of graphene and metal-organic frameworks (MOFs) has numerous implications across various domains, but fabricating such assemblies is often complicated and time-consuming. Herein, a one-step preparation of graphene-MOF assembly is presented by directly impregnating vertical graphene (VG) arrays into the zeolitic imidazolate framework (ZIF) precursors under ambient conditions. This approach can effectively assemble multiple ZIFs, including ZIF-7, ZIF-8, and ZIF-67, resulting in their uniform dispersion on the VG with adjustable sizes and shapes. Hydrogen defects on the VG surface are critical in inducing such high-efficiency ZIF assembly, acting as the reactive sites to interact with the ZIF precursors and facilitate their crystallisation. The versatility of VG-ZIF-67 assembly is further demonstrated by exploring the process of MOF amorphization. Surprisingly, this process leads to an amorphous thin-film coating formed on VG (named VG-IL-amZIF-67), which preserves the short-range molecular bonds of crystalline ZIF-67 while sacrificing the long-range order. Such a unique film-on-graphene architecture maintains the essential characteristics and functionalities of ZIF-67 within a disordered arrangement, making it well-suited for electrocatalysis. In electrochemical oxygen reduction, VG-IL-amZIF-67 exhibits exceptional activity, selectivity, and stability to produce H2O2 in acid media.

Recent Progress on Electrode Design for Efficient Electrochemical Valorisation of CO2 , O2 , and N2.

CO2 reduction, two-electron O2 reduction, and N2 reduction are sustainable technologies to valorise common molecules. Their further development requires working electrode design to promote the multistep electrochemical processes from gas reactants to value-added products at the device level. This review proposes critical features of a desirable electrode based on the fundamental electrochemical processes and the development of scalable devices. A detailed discussion is made to approach such a desirable electrode, addressing the recent progress on critical electrode components, assembly strategies, and reaction interface engineering. Further, we highlight the electrode design tailored to reaction properties (e.g., its thermodynamics and kinetics) for performance optimisation. Finally, the opportunities and remaining challenges are presented, providing a framework for rational electrode design to push these gas reduction reactions towards an improved technology readiness level (TRL).

Benchmark dataset of the effect of grain size on strength in the single-phase FCC CrCoNi medium entropy alloy.

This data article presents the microstructural data as well as the mechanical properties of the CrCoNi medium-entropy alloy (MEA). The data presented in this article are related to the research article entitled "Analysis of strengthening due to grain boundaries and annealing twin boundaries in the CrCoNi medium-entropy alloy", see Ref. Schneider et al., 2019. This article can be referred to for the analysis and interpretation of the data, as well as their comparison to other datasets in literature. Microstructural data available in the present paper are backscattered electron micrographs for sixteen different grain sizes. Also available are pdf reports of grain size analysis (annealing twin boundaries were neglected) and crystallite sizes (including annealing twin boundaries) as well as data describing the number of annealing twin boundaries per grain (n), corresponding Taylor factors (M) and average annealing twin thicknesses (t). Additionally, raw data of stress-strain curves at five different temperatures [77 K, 293 K, 473 K, 673 K and 873 K] are given for all sixteen grain sizes, which may be used for further research, e.g. data mining, machine learning and other analytical methods. Mechanical data such as yield stresses (σ 0.2% ), Hall-Petch parameters (σ 0 and k y ) and critical boundary strengths (τ c ) are provided along with a 1D discrete dislocation dynamics (1-D DDD) simulation results concerning the different boundary strengths.

Size effects and stochastic behavior of nanoindentation pop in.

A statistical model for pop in initiated at preexisting dislocations during nanoindentation is developed to explain size-dependent pop-in stresses. To verify theoretical predictions of this model, experiments were performed on single-crystal Mo, utilizing indenter radii that vary by over 3 orders of magnitude. The stress where plastic deformation begins ranges from the theoretical strength in small volumes, to 1 order of magnitude lower in larger volumes. An intermediate regime shows wide variability in the stress to initiate plastic deformation. Our theory accurately reproduces the experimental cumulative probability distributions, and predicts a scaling behavior that matches experimental behavior.

Softening caused by profuse shear banding in a bulk metallic glass.

By controlling the specimen aspect ratio and strain rate, compressive strains as high as 80% were obtained in an otherwise brittle metallic glass. Physical and mechanical properties were measured after deformation, and a systematic strain-induced softening was observed which contrasts sharply with the hardening typically observed in crystalline metals. If the deformed glass is treated as a composite of hard amorphous grains surrounded by soft shear-band boundaries, analogous to nanocrystalline materials that exhibit inverse Hall-Petch behavior, the correct functional form for the dependence of hardness on shear-band spacing is obtained. Deformation-induced softening leads naturally to shear localization and brittle fracture.

Influence of indenter tip geometry on elastic deformation during nanoindentation.

Nanoindentation with a Berkovich indenter is commonly used to investigate the mechanical behavior of small volumes of materials. To date, most investigators have made the simplifying assumption that the tip is spherical. In reality, indenter tips are much more complex. Here, we develop a new method to describe the tip shape using the experimentally determined area function of the indenter at small depths (0-100 nm). Our analysis accurately predicts the elastic load-displacement curve and allows the theoretical strength of a material to be determined from pop-in data. Application of our new method to single crystal Cr3Si shows that the predicted theoretical strengths are within 12% of the ideal strength G/2pi, where G is the shear modulus.

Theoretical strength and the onset of plasticity in bulk metallic glasses investigated by nanoindentation with a spherical indenter.

The mechanical behavior of bulk metallic glasses (BMGs) was investigated by nanoindentation with a spherical indenter. The transition from perfectly elastic behavior to plastic deformation was clearly observed as a pop-in event (sudden displacement excursion) on the load-displacement curves. Hertzian stress analysis was used to describe fully the load-displacement behavior during elastic deformation and to determine the theoretical shear strengths of the BMGs.

Forces on biological cells due to applied alternating (AC) electric fields. II. Electro-rotation.

Measurements are presented of angular velocities of rotation of mammalian cells of K562 (human) and SP2 (mouse) in external alternating electric fields over a frequency range of 0.5 kHz to 12 MHz. Electro-rotation of the cells was observed for the case of "two cells in contact' using two parallel, cylindrical electrodes; only one cell was located on the electrode. A theoretical analysis is also presented which shows that the cell rotation arises from a torque produced by the interaction between the primary electric dipole moment induced in the spinning cell and the secondary electric fields, generated by the primary dipole induced in the adjacent cell. These secondary fields are out of phase with the applied electric field. The results show that (a) only the cell not located on the electrode rotates, (b) maximal electro-rotation occurs at two different excitation field frequency domains for the frequency range employed here, (c) the spin speed of the rotating cell at each frequency domain is much less than the excitation frequency, (d) the rotation direction of the cell depends on the angle (theta) between the external electric field and the line joining the centres of the two cells and (e) for a given angle theta, the rotation direction is the same for both excitation frequency domains. The experimental measurements allowed us to estimate the conductivities of the cytoplasms and membrane capacitances of the cells of K562 and SP2. The conductivities of the cytoplasms of the cells of K562 and SP2 were estimated to be 0.2 and 0.3 Sm-(1), respectively, whereas the membrane capacitances of these cells were found to be 2.7 +/- 0.8 and 9.8 +/- 0.6 mFm-(2), respectively.

Forces on biological cells due to applied alternating (AC) electric fields. I. Dielectrophoresis.

Measurements are presented of dielectrophoretic forces for SP2 (mouse) and K562 (human) cells in external alternating electric fields over a frequency range of 10 kHz to 2 MHz. Using a spherical shell model of the cell, the dielectrophoretic force is derived from the interaction between the induced electric dipole moment in the cell and the external electric field. The frequency dependence of the force has its origin in the dispersion with frequency of the impedances of the cell membrane, the cytoplasm and the external medium (a Maxwell-Wagner dispersion). The predicted tri-phasic form of the variation of the dielectrophoretic force is in good agreement with the experimental results presented. Using the theoretical model, the experimental measurements also provided an estimation of 0.18 +/- 0.03 S m-1 and 0.12 +/- 0.04 S m-1 for the conductivities of the cytoplasm of cells of SP2 and K562, respectively, and 6.0 +/- 2.0 mF m-2 and 2.0 +/- 1.0 mF m-2 for the capacitances of the plasma membrane of these cells.

Ion distributions in plane and cylindrical chambers.

The ion chamber equations of Thomson include both ion recombination and space-charge terms. Neglecting the space-charge term, an exact solution is obtained for the ion densities across a plane ionization chamber. The method is extended to the cylindrical chamber, and examples are given of the expected ion distributions in both geometries. Current-voltage relationships are derived for both chambers and compared with those of other workers. If the space-charge term is retained, the ion chamber equations for both geometries are not soluble in closed form. The cylindrical chamber is considered and a computer solution is obtained for the ion distributions and current. Comparison with the nonspace-charge solution shows that while there is only a small difference in the current-voltage relationship, a significant difference can occur in the ion concentrations.

Water and ions in muscles and model systems.

THE NUCLEAR MAGNETIC REASONANCE (NMR) RELAXATION TIMES OF PROTONS IN TOAD MUSCLE WATER HAVE BEEN MEASURED AT THREE FREQUENCIES: 2.3, 8.9, and 30 MHz. The results are analyzed in terms of a distribution of correlation times, and it is found that only a few percent of the observed protons have mobilities more than two orders of magnitude smaller than normal. Sodium and chloride ion chemical potentials in some hydrated materials with similar proton NMR characteristics to toad muscle have been found to be heightened, but not sufficiently to account for the distribution of sodium ions in muscle.

A nuclear magnetic resonance study of hydrated systems using the frequency dependence of the relaxation processes.

A practical method is described for determining some characteristics of the spectrum of proton mobilities in a hydrated system from the frequency dependence of the nuclear magnetic resonance (NMR) relaxation processes. The technique is applied to water in association with agarose and gelatin. The results for agarose are consistent with the hypothesis that a fraction of the protons is distributed over states of reduced mobility and exchanges rapidly with the remaining fraction which is attributed to water in the normal state. No variation in the characteristics of the modified fraction could be detected for water concentrations in the range 1.2-50 g H(2)O/g agarose. Within the modified fraction, higher mobilities are more common than low mobilities; at 1.2 g H(2)O/g agarose, not more than 10% of the proton population has mobilities more than 100 times smaller than normal. The modified proton fraction is tentatively identified with agarose hydroxyl protons and possibly water molecules bound to the polymer. Proton states with mobilities intermediate between water and ice have also been detected in hydrated gelatin. As in agarose, higher mobilities are the most common. In contrast to agarose, the characteristics of the modified proton states are markedly dependent on water concentration. They are tentatively attributed to gelatin protons coupled for spinlattice relaxation with those of the bulk phase by exchange and spin diffusion.

The electrical characteristics of fixed charge membranes: solution of the field equations.

A theoretical analysis is made of the electrical characteristics of a membrane containing two fixed charge regions, of opposite sign, in contact. Profiles of ion concentrations, electrostatic potential, space charge density, as well as the voltage-current characteristics were obtained by numerical integration of the field equations on a computer. Comparison with the predictions of an earlier analysis of this system (Coster, 1965) shows that the latter is valid to a good approximation for membranes > 70 A in thickness. In particular the form of the electrical characteristics, including the punch-through effect, have been verified by the computer analysis. The range of useful validity of the earlier analysis, the use of Boltzmann statistics when currents are present, and variation of membrane capacitance with applied potential, are discussed in the light of the results obtained.

A thermodynamic analysis of fluxes and flux-ratios in bioligical membranes.

Flux and flux-ratio equations are derived on the basis of the phenomenological equations of irreversible thermodynamics. Deviations of flux-ratios from that given by the often quoted Ussing (1949) relation are predicted, even in the absence of active transport, by considering the dependence of coupled fluxes on the membrane potential. The treatment is extended to include the interpretation of fluxes measured with tracers. Estimation of the numerical values of the resistance coefficients show that the voltage dependence of the entrainment terms can adequately account for the departures from the Ussing relation and the discrepancies between isotopically and electrically measured membrane conductances.