Diffusions Research Articles

(Invited) From Layered Oxides to Disordered Rocksalt Cathodes: The Role of Electronic Structure, Cation Order, and Structure on the Performance of Dense Cathode Materials

Layered cathode materials are the enabler of today’s Li-ion industry. I will review some of the fundamental relations between electronic structure, cation ordering, and electrochemical performance in layered Li, Na and K-compounds. Diffusion in layered cathodes occurs through a divacancy mechanism which enables the low-energy Li passage through the tetrahedral sites that connect the octahedral positions in the Li layers. This diffusion mechanism provides high rate capability to layered cathodes, but relies on the Li-slab spacing to remain large upon electrochemical cycling. Any migration of transition metals into the Li-layer tends to contract the slab spacing and reduce rate capability. This limits practical layered materials to the NMC chemistry as Ni, Co and Mn4+ are the only ions that have a strong enough octahedral ligand-field stabilization to remain in the transition metal layer upon cycling. This problem is less pronounced for Na-layered oxides as the larger slab spacing makes occupancy of the tetrahedral and octahedral site in the Na-layer much less favorable for transition metals. But layered oxides with large alkali ions such as Na+ and K+ suffer from more sloped voltage profiles with limits their usable energy density.Finally, I will show how the chemical diversity of Li-ion cathodes can be extended to a much broader set of elements by enabling Li-excess disordered rocksalts (DRX). These materials diffuse lithium ions through a statistical network of low-energy migration environments, and have recently been shown to have very high capacity and rate performance.

Boron-doped graphene anode coupled with microporous activated carbon cathode for lithium-ion ultracapacitors

Lithium-ion hybrid capacitors combine the advantages of both high energy of lithium-ion batteries and high-power of ultracapacitors by using one highly reversible battery-type electrode (e.g., graphite, carbon matrix, metal oxides, etc.) and another high surface area supercapacitor-type electrode (e.g., activated carbon) in one unit cell. This work reports the fabrication of a lithium-ion capacitor using boron-doped graphene nanosheets as anode and microporous carbon from activated rice husk as a cathode. The lithium-ion storage characteristics of boron-doped graphene nanomaterials and adsorption properties of microporous carbon leads to the realization of their usage in a lithium-ion capacitor electrode materials. The lithium-ion capacitor full cell with lithiated boron-doped graphene nanomaterial anode and activated rice husk cathode demonstrates energy densities of 162 and 83 W h kg−1 at power densities of 590, 14750 W kg−1, respectively. The mechanistic performance of the LIC full cell below and above the open circuit voltage (OCV) was analysed to understand the diffusion and adsorption control in the achievable energy. The cell cycles till 25,000 cycles with 65 % capacitance retention at 1 A g−1 current density. This study demonstrates a striking balance between the high energy and high power capabilities in a single unit lithium-ion capacitor cell through the utilization of adsorptive as well diffusive ion storage mechanism of the electrode active materials. The full cell is analysed for self discharge and leakage current to realise the practical feasibility of the electrode active materials. Also, the electrochemical impedance spectra reveal the probable reason behind the degradation of cycling performance.

Physicochemical properties of the dissolved organic carbon can lead to different physiological responses of zebrafish (Danio rerio) under neutral and acidic conditions.

Previous studies have suggested that the capacity of natural dissolved organic carbon (DOC) molecules to interact with biological membranes is associated with their aromaticity (SAC340 ); origin (allochthonous versus autochthonous, FI); molecular weight (Abs254/365 ); and relative fluorescence of DOC moieties (PARAFAC analysis). These interactions may be especially important when fish are challenged by acidic waters, which are known to inhibit the active uptake of Na+ and Cl- , while stimulating diffusive ion losses in freshwater fishes. Therefore, zebrafish were acclimated (7 days, pH 7.0) to five natural DOC sources (10 mg C/L), two from the Amazon Basin and three from Canada, together with a "no-added DOC" control. After the acclimation, fish were challenged by exposure to acidic water (pH 4.0) for 3 h. Osmoregulatory parameters were measured at pH 7.0 and 4.0. Acclimation to the five DOC sources did not disturb Na+ , Cl- and ammonia net fluxes, but resulted in differential elevations in Na+ , K+ ATPase and v-type H+ ATPase activities in fish at pH 7.0. However, after transfer to pH.4.0, the control fish exhibited rapid increases in both enzymes. In contrast the DOC- acclimated animals exhibited unchanged (Na+ , K+ ATPase) or differentially increased (v-type H+ ATPase) activities. Na+ , Cl- and ammonia net fluxes remained unchanged in the control fish, but were differentially elevated in most of the DOC treatments at pH 4.0, relative to the same DOC treatments at pH 7.0. Correlations between the osmoregulatory data the DOCs properties highlight that the DOC properties drive different effects on gill physiology.

Electrical Propagation of Condensed and Diffuse Ions Along Actin Filaments.

In this article, we elucidate the roles of divalent ion condensation and highly polarized immobile water molecules on the propagation of ionic calcium waves along actin filaments. We introduced a novel electrical triple layer model and used a non-linear Debye-Huckel theory with a non-linear, dissipative, electrical transmission line model to characterize the physicochemical properties of each monomer in the filament. This characterization is carried out in terms of an electric circuit model containing monomeric flow resistances and ionic capacitances in both the condensed and diffuse layers. We considered resting and excited states of a neuron using representative mono and divalent electrolyte mixtures. Additionally, we used 0.05V and 0.15V voltage inputs to study ionic wavesalong actin filaments in voltage clamp experiments. Our results reveal that the physicochemical properties characterizing the condensed and diffuse layers lead to different electrical conductive mediums depending on the ionic species and the neuron state. This region specific propagation mechanism provides a more realistic avenue of delivery by way of cytoskeleton filaments for larger charged cationic species. A new direct path for transporting divalent ions might be crucial for many electrical processes found in localized neuron elements such as at mitochondria and dendritic spines.

Lanthanide Stabilized All-Inorganic CsPbI2Br Perovskite Solar Cells with Superior Thermal Resistance

The stability of perovskite solar cells, especially at high temperature (85 °C) conditions, is one of the most critical aspects to advance practical application. All-inorganic perovskites, by substituting the volatile organic compounds with cesium, have exhibited a promising thermal resistance and energy conversion potentials. However, the thermal stability of the all-inorganic perovskite solar cells is strongly related to the phase transition of the perovskite as well as the thermal resistance of each charge transport and collection layer. Herein, we incorporated Eu(Ac)3 into the perovskite precursor to fabricate photoactive γ-CsPbI2Br. The Eu3+ ions can associate with the negatively charged halide plumbates in the solution and accumulate at the grain boundaries in the as-achieved thin films, effectively reducing the nonradiative recombination centers and stabilizing the γ-CsPbI2Br with moderate grain size. A champion efficiency above 12% in an inverted device architecture can be achieved. In the presence of Eu3+ ions, the phase transition of the γ-CsPbI2Br to nonperovskite is significantly mitigated and can be reversibly restored via thermal repairing. Moreover, we thermally treat the electron transport [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) layer prior to the device completion to induce nanomorphology reorientation and replace the reactive Ag electrode by inert Cu to prevent electrode corrosion by diffusive halide ions from the perovskite. As a result, the thermal (at 85 °C, time to 80% of the initial efficiency or t80 ≈ 200 h) and moisture (relative humidity or RH = 40%, t80 > 500 h) stability of the all-inorganic CsPbI2Br solar cells can be remarkably enhanced.

High-Performance and High-Voltage Supercapacitors Based on N-Doped Mesoporous Activated Carbon Derived from Dragon Fruit Peels.

Designing the mesopore-dominated activated carbon electrodes has witnessed a significant breakthrough in enhancing the electrolyte breakdown voltage and energy density of supercapacitors. Herein, we designed N-doped mesoporous-dominated hierarchical activated carbon (N-dfAC) from the dragon fruit peel, an abundant biomass precursor, under the synergetic effect of KOH as the activating agent and melamine as the dopant. The electrode with the optimum N-doping content (3.4 at. %) exhibits the highest specific capacitance of 427 F g–1 at 5 mA cm–2 and cyclic stability of 123% capacitance retention until 50000 charge–discharge cycles at 500 mA cm–2 in aqueous 6 M KOH electrolytes. We designed a 4 V symmetric coin cell supercapacitor cell, which exhibits a remarkable specific energy and specific power of 112 W h kg–1 and 3214 W kg–1, respectively, in organic electrolytes. The cell also exhibits a significantly higher cycle life (109% capacitance retention) after 5000 GCD cycles at the working voltage of ≥3.5 V than commercial YP-50 AC (∼60% capacitance retention). The larger Debye length of the diffuse ion layer permitted by the mesopores can explain the higher voltage window, and the polar N-doped species in the dfAC enhance capacitance and ion transport. The results endow a new path to design high-capacity and high-working voltage EDLCs from eco-friendly and sustainable biomass materials by properly tuning their pore structures.

UO2 Spheres Produce by External Gelation Process

UO2 kernels, a key component of fuel elements for high temperature gas cooled reactors, have usually been prepared by sol-gel methods. Sol-gel processes have a number of advantages, such as simple processes and facilities, and higher sphericity and density. In this study, to produce 900 μm-sized UO2 particles using an external gelation process, contact length extension of the NH3 gas of the broth droplets pass and the improvement of the gelation device capable of spraying 14 MNH4OH solution are used to form 3,000 μm-sized liquid droplets. To produce high-sphericity and high-density UO2 particles, HMTA, which promotes the gelation reaction in the uranium broth solution, is added to diffuse ammonium ions from the outside of the gelation solution during the aging process and generate ammonium ions from the inside of the ADU gel particles. Sufficient gelation inside of ADU gel particles is achieved, and the density of the UO2 spheres that undergo the subsequent treatment is 10.78 g/cm3; the sphericity is analyzed and found to be 0.948, indicating good experimental results.

Mesoporous structure favorable for high voltage and high energy supercapacitor based on green tea waste-derived activated carbon

Designing high voltage, high energy, and activated carbon-based supercapacitors has been a long-time wish for meeting various electronic module requirements. This paper focuses on the approach of synthesizing the hierarchical porous activated carbon with dominant mesopores using eco-friendly green tea waste. The desirable ample pore space achieved by changing the weight ratio of KOH activating agent renders more ionic accessibility and space charge distribution. This feature leads to the achievement of 4 V double layer supercapacitor with a remarkable specific energy of 142 Wh kg−1 and specific power of 3192 W kg−1, respectively using an acetonitrile organic electrolyte. The fabricated cell also exhibits a superior 104% capacitance retention after 25 000 charge-discharge cycles at the working potential of ≥3 V. Besides, the hierarchical porous activated carbon soaked in an aqueous KOH electrolyte shows a high specific capacitance of 397 F g−1 at 5 mA cm−2, high rate capability of 100 mA cm−2, and excellent cycle life of 116% capacitance retention after 50 000 cycles tested at 200 mA cm−2. The larger Debye length of the diffuse ion layer permitted by the mesopores is proposed to explain the higher voltage window as against low voltage of micropore dominated commercial activated carbon. The present research may pave the way toward the design of high-energy supercapacitors through recycling tea waste.

Waste-to-resources: Green preparation of magnetic biogas residues-based biochar for effective heavy metal removals

The agricultural wastes disposal and polluted water purification are always the key issues of environmental restoration. In this work, a magnetic biogas residue-based biochar (mBR-C) by direct pyrolysis and sonochemical method was prepared from biogas residue (BR). Response design methodology based on Box-Behnken design was used for the preparation parameters optimization. The characterization results identified that mBR-C had well-developed pore structure and surface area, which was beneficial to diffuse and capture heavy metal ions. Traces of toxic heavy metal in mBR-C was leached (˂0.04 mg/L) through TCLP method, indicating the environmental safety of the magnetic biochar. Meanwhile, the mBR-C exhibited excellent solid-liquid separation efficiency because of its strong magnetism. The series of adsorption experiments indicated that mBR-C could capture Cu2+ and Pb2+ rapidly, and the maximum adsorption capacity for Cu2+ and Pb2+ was 75.76 and 181.82 mg/g, respectively, which was higher than some other biochars previously reported. mBR-C was further applied in the synthetic wastewater treatment, which could effectively purify at least 600 mL (150 BV) to meet emission standards. After several column adsorption-desorption cycles, the adsorption capacity could still reach 85%, implying that mBR-C has good reusability and stability. Overall, the mBR-C can be used as an eco-friendly, desirable, economic and recyclable biosorbent in heavy metal polluted water treatment, providing a new idea for a combination of biogas residue recycle and wastewater treatment.

Influence of slip velocity at the core of a diffuse soft particle and ion partition effects on mobility.

Nonlinear effects on the electrophoresis of a soft particle, consisting of a rigid hydrophobic core coated with a diffuse polymer layer (PEL) suspended in an electrolyte medium, are studied. The impact of the ion partitioning effect arising due to the Born energy difference between the PEL and the electrolyte is approximated based on the equilibrium Boltzmann equation, with which the ion distribution and hence, the charge density is modified. The equations describing the electrokinetic transport comprising the Darcy-Brinkman extended Navier-Stokes equations which includes the ion partitioning effect coupled with the modified Nernst-Planck equations and Poisson equations for electric field are solved numerically. The present numerical model for the soft particle compares well with the existing theoretical solutions and experimental results in the limiting cases. A deviation from existing simplified models based on the Boltzmann distribution of ions occurs when the Debye layer polarization, relaxation and the electroosmosis induced by the PEL immobile charge become significant. The hydrophobicity of the inner core strongly influences the nonlinear electrokinetic effects by modifying the Debye layer, electroosmotic flow in the PEL and surface conduction. The results indicate that the ion partitioning can significantly increase the electrophoretic mobility of the soft particle by attenuating the shielding effect. When the Debye layer is in the order of the particle size the hydrophobicity of the core surface and the ion partitioning effect manifest the surface conduction, which implies that the Boltzmann distribution of ions is no longer valid. The core hydrophobicity and ion partitioning effect have influence on the condensation of the PEL immobile charge, which creates a significant impact on the mobility.

MOF-derived NiCo2S4@C as a separator modification material for high-performance lithium-sulfur batteries

Functional separator, which serves as a barrier layer in lithium-sulfur (Li–S) battery, can effectively restrict the shuttle effect of polysulfide (PS). Herein, functional separators, modified with NiCo2S4@C which is derived from an annealing conversion of metal-organic framework (MOF) precursors, are prepared. For the modified separators, it is extremely advantageous to diffuse lithium ions and absorb PS. Owing to the presence of three-dimensional (3D) conductive network, moreover, the adsorbed PS can further be utilized during charging and discharging, resulting in high specific capacity and superior cycling life. When it is tested at a relatively high current density of 1.0 C, the Li–S battery assembled with a NiCo2S4@C-modified separator exhibits an initial capacity of 880 mA h g−1. After 200 testing cycles, furthermore, it can still provide a capacity of 700 mA h g−1, and its capacity decay rate is only 0.102% per cycle.

Recent Development of Closed-form Approximate (Log-)Transition Probability Density Functions of Diffusion Processes

Transition probability density function (TPDF) or log-TPDF of a diffusion is quite useful in many ways. For example, it can be employed not only to estimate a diffusion by the maximum likelihood estimation but also to simulate data from a diffusion or to price an asset when the underlying process follows a diffusion. However, unfortunately, the true TPDF of a diffusion is unknown with a few exceptions in general. Starting from Ait-Sahalia (2002)'s pioneering work on approximate but explicit TPDF of a univariate time-homogeneous diffusion to Choi (2019a)'s recent work on closed-form approximate TPDF of a multivariate time-inhomogeneous jump diffusion, several researchers have subsequently established the way to approximate the TPDFs or log-TPDFs of more general diffusion models. This article explains how people have resolved problems to generalize the method from Ait-Sahalia(2002)'s paper to Choi(2013, 2015)'s multivariate time-inhomogeneous diffusions. Due to space constraints, explanations of detailed theories or assumptions for their proof are reduced to the minimum and we show important results, with tacit facts not described in the original papers. In addition, we also introduce papers derived from and related to those key studies.

Impedance spectroscopy of (TlGaSe2)1−x(TlInSe2)x solid solutions in radio frequency range

The processes of charge transport on alternating current in [Formula: see text] solid solutions have been studied. It has been established that in weak alternating electric fields, there is a hopping mechanism of charge transfer over localized states in the vicinity of the Fermi level. A quantitative assessment of parameters was made in the framework of the effective medium theory and the Mott approximation. The use of impedance spectroscopy methods in [Formula: see text] solid solutions in the frequency range of 25–106 Hz, at temperatures of 180, 240 and 300 K charge transfer processes has been investigated. It was found that at 300 K in the low-frequency region, there are additional contributions to the conductivity, which, apparently, is associated with diffuse ion transfer near the boundary of the solid electrolyte and the electrode. Impedance locus curves, at low frequencies and at a temperature of 300 K, are characteristic of Warburg diffuse impedance.

A Review of ex vivo Elemental Mapping Methods to Directly Image Changes in the Homeostasis of Diffusible Ions (Na+, K+, Mg2 +, Ca2 +, Cl-) Within Brain Tissue.

Diffusible ions (Na+, K+, Mg2+, Ca2+, Cl–) are vital for healthy function of all cells, especially brain cells. Unfortunately, the diffusible nature of these ions renders them difficult to study with traditional microscopy in situ within ex vivo brain tissue sections. This mini-review examines the recent progress in the field, using direct elemental mapping techniques to study ion homeostasis during normal brain physiology and pathophysiology, through measurement of ion distribution and concentration in ex vivo brain tissue sections. The mini-review examines the advantages and limitations of specific techniques: proton induced X-ray emission (PIXE), X-ray fluorescence microscopy (XFM), secondary ion mass spectrometry (SIMS), laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the sample preparation requirements to study diffusible ions with these methods.

A highly efficient method to fabricate normally-off AlGaN/GaN HEMTs with low gate leakage via Mg diffusion

A method to achieve p-type doping gate by Mg diffusion is proposed to fabricate normally-off AlGaN/GaN high electron mobility transistors (HEMTs). The fabrication is completed via first slight etching to introduce defects into the gate region and then rapid annealing to diffuse Mg ions into the AlGaN barrier, thereby forming a p-type doping layer and positively shifted threshold voltage. In addition, the MgO layer formed by thermal oxidation could effectively passivate the surface traps that were caused in the previous etching procedure. The as-fabricated HEMTs demonstrate a low gate leakage of 2 × 10−7 mA/mm and a VTH of 1.4 V. This technique offers a simplified and highly effective method to fabricate high performance GaN power devices.

Analysis of Al and Cu salt infiltration into a poly 2-vinylpyridine (P2vP) polymer layer for area selective deposition applications

This work is motivated by the desire to develop a semiconductor device patterning technology based on precursor infiltration into block copolymer materials. Developing an understanding of the preferential infiltration of metal precursors into one of the polymer blocks is of critical importance to advance this patterning approach. In this study, metal salts were used as a means to diffuse metal ions into a poly 2-vinylpyridine (P2vP) polymer brush layer (~4 nm thick) which was deposited by spin coating on a silicon substrate. Thin P2vP films infused with aluminum nitrate and copper nitrate by a wet chemical process were analyzed with angle resolved hard x-ray photoelectron spectroscopy (AR HAXPES). From these photoemission measurements, significant information about the chemical compositional profile of the infiltrated films was obtained. The large sampling depth of HAXPES measurements (20–30 nm) enabled details of the chemical composition of the thin film to be characterized and subsequent angle-resolved HAXPES measurements offered a robust analysis of the interfaces and discrete layers that are present in the films. These measurements displayed evidence of bonding interactions between the elements in the polymer film and the infiltrated salts assisting in the development of an understanding of the infiltration process which needs to be optimized for device fabrication applications. Aluminum nitrate presented more evidence of infiltration into P2vP, while copper nitrate was more predominated at the surfaces into the P2vP.

Calculation of salt-dependent free energy of binding of β-lactoglobulin homodimer formation and mechanism of dimer formation using molecular dynamics simulation and three-dimensional reference interaction site model (3D-RISM): diffuse salt ions and non-polar interactions between the monomers favor the dimer formation.

There are several important phenomena in chemistry, biology, and physics where molecules (or parts of a molecule) having charges of the same sign come closer together and become stable. DNA condensation, RNA folding, colloid-colloid interactions are some of the examples of this kind. In the current work, we have investigated how β-lactoglobulin, a protein found in milk, in spite of carrying +13 charge, favors the homodimer formation in the presence of salt. We have focussed on calculating the protein-protein binding free energy in the presence of salt and identifying the thermodynamic and microscopic mechanism of the process. Estimation of binding free energy of this salt-dependent process is done by combining molecular dynamics simulation with statistical mechanical theory of three-dimensional reference interaction site model (3D-RISM). Binding free energy is evaluated from the chemical potential of the solutes as opposed to potential of mean force calculation, which gives only a constrained free energy. Our calculated values semi-quantitatively match with the experimental results. By examining the different components of binding free energy, we have found that the role of salt ions (especially of Cl-) is to shift the equilibrium towards the dimer. Non-polar (Lennard-Jones) interactions between the monomers is also favorable to the binding free energy. However, water slightly disfavors the dimer formation. For the microscopic mechanism, heterogeneous of both Na+ and Cl- near the charged residues at the binding interface and change of this charge distribution on dimer formation contribute to the stability. A fine-tuning of enthalpic and entropic effects of salt ions is found to operate at different salt concentrations. Both thermodynamic and microscopic mechanism of dimer formation gives detailed insight into the complex electrostatics of charged protein-protein binding.

Дослідження впливу технологічних параметрів процесу вакуумного азотування алюмінієвих сплавів на властивості дифузійних іонноазотованих шарів

Дослідження впливу технологічних параметрів процесу вакуумного азотування алюмінієвих сплавів на властивості дифузійних іонноазотованих шарів

Diffusion coefficients of trivalent rare earth/actinide ions in acid and alkaline aqueous solutions

Leaching is one of the key process of rare earth (RE) element recovery. This paper was set out to validate the effectiveness of acid/alkali in RE leaching by measuring the limiting ionic conductivity (λo), self-diffusion coefficient (Di) and overall diffusion coefficient (DAB) to obtain a clear insight on the transport properties of ions and salts in aqueous solution. The calculation diffusivity of Di which is diffuse individual ions in pure water and DAB diffuse in chemical reagents were determined using Nernst-Haskell equation, applicable for 25°C. The results of Di were found to be consistent with experimental data from the literature where most of calculation and experiment data are less than 5% error. The final outcome had managed to confirm that NaOH is best reagent for most RE element leaching, which suits the common practice of the industry.

Revealing the Elemental Distribution within Latent Fingermarks Using Synchrotron Sourced X-ray Fluorescence Microscopy.

Fingermarks are an important form of crime-scene trace evidence; however, their usefulness may be hampered by a variation in response or a lack of robustness in detection methods. Understanding the chemical composition and distribution within fingermarks may help explain variation in latent fingermark detection with existing methods and identify new strategies to increase detection capabilities. The majority of research in the literature describes investigation of organic components of fingermark residue, leaving the elemental distribution less well understood. The relative scarcity of information regarding the elemental distribution within fingermarks is in part due to previous unavailability of direct, micron resolution elemental mapping techniques. This capability is now provided at third generation synchrotron light sources, where X-ray fluorescence microscopy (XFM) provides micron or submicron spatial resolution and direct detection with sub-μM detection limits. XFM has been applied in this study to reveal the distribution of inorganic components within fingermark residue, including endogenous trace metals (Fe, Cu, Zn), diffusible ions (Cl-, K+, Ca2+), and exogeneous metals (Ni, Ti, Bi). This study incorporated a multimodal approach using XFM and infrared microspectroscopy analyses to demonstrate colocalization of endogenous metals within the hydrophilic organic components of fingermark residue. Additional experiments were then undertaken to investigate how sources of exogenous metals (e.g., coins and cosmetics) may be transferred to, and distributed within, latent fingermarks. Lastly, this study reports a preliminary assessment of how environmental factors such as exposure to aqueous environments may affect elemental distribution within fingermarks. Taken together, the results of this study advance our current understanding of fingermark composition and its spatial distribution of chemical components and may help explain detection variation observed during detection of fingermarks using standard forensic protocols.