Slow Diffusion Research Articles

Elucidating the diffusion and interaction mechanisms of Zn2+ and H+ in MnO2 for aqueous zinc-ion batteries: A DFT study

MnO2 is a promising cathode material for aqueous zinc-ion batteries (AZIBs) with potential applications in large-scale energy storage systems. However, its practical use is hindered by poor cyclic stability and slow diffusion kinetics. Despite considerable efforts, success has been limited due to an unclear understanding of the intrinsic properties of Zn2⁺ and proton (H⁺) insertion into MnO2. This study investigates the predominant phases of MnO2—α, β, δ, and γ—and elucidates their reaction mechanisms using first-principles computational methods based on density functional theory (DFT). Our research reveals that H⁺ ions exhibit a higher initial insertion voltage compared to Zn2⁺ ions, but their diffusion in MnO2 is significantly impeded by strong interactions with oxygen. Additionally, H⁺ insertion partially obstructs Zn2⁺ ion migration. Furthermore, the insertion of Zn2⁺/H⁺ and the adsorption of H⁺ on the MnO2 surface are intricately linked to the dissolution process of manganese. This work significantly enhances our fundamental understanding of MnO2 as a cathode material for AZIBs.

Construction of pyrrolo[3,2-b]pyrrolyl-linked covalent organic polymers to promote continuous overall H2O2 production

Sacrificial agent-free, solar-driven photocatalytic oxygen reduction holds promise for hydrogen peroxide production. However, the rapid recombination of electron–hole pairs in catalysts and the slow diffusion rate of oxygen on the catalyst surfaces significantly hinder the efficiency of hydrogen peroxide production. To address these issues, we developed a novel class of pyrrolo[3,2-b]pyrrolyl-linked covalent organic polymers (COPs) combined with microreactor technology to enhance hydrogen peroxide synthesis. These structurally well-defined polymers feature photoactive pyrrolo[3,2-b]pyrrolyl units were assembled from aldehyde, aniline, and 2,3-butanedione through a one-pot three-component reaction. Integrating pyrrolo[3,2-b]pyrrolyl moieties into the COPs creates donor–acceptor structures that facilitate the separation of photogenerated electrons and holes. Among them, COP-2 achieved the highest H2O2 yield of 5446 μmol g−1 h−1. Furthermore, we designed a coiled tube photomicroreactor to improve mass transfer efficiency in the gas–liquid–solid triphase system, boosting the H2O2 yield to 20285 μmol g−1h−1 without the need for a sacrificial agent. This study offers new insights into integrating polymer photocatalysts with microflow technology, underscoring the potential for future green and continuous H2O2 production.

Efficient Preparation of Metal-Ion Intercalated Vanadium-Based Cathodes for High-Performance Aqueous Zinc-Ion Batteries: Na2V6O16·3H2O as an Example.

The inherent challenges associated with aqueous zinc ion batteries (AZIBs), such as low energy density and slow diffusion kinetics, pose significant obstacles to their widespread adoption as energy storage systems. These limitations mainly stem from the nongreen and complex preparation process of high-quality cathode materials. In this study, we propose an approach utilizing microwave-assisted ball milling to expedite the fabrication of vanadium-based intercalated nanomaterials, aiming at solving the problem of prolonged reaction at high temperatures, which is unavoidable in the preparation of anode materials. Na2V6O16 (NVO) nanorods were synthesized in just 40 min under aqueous solvent conditions. These nanorods exhibit remarkable electrochemical properties, including a high specific capacity of 564 mA h g-1 at 0.1 A g-1 and an excellent cycle life, maintaining 164.2 mA h g-1 after 5000 cycles at 5 A g-1. Additionally, the incorporation of Na+ into the electrolyte effectively mitigates the stripping of Na+ and the deposition of Zn dendrimers from NVO, further contributing to enhanced cycling stability. The findings of this study offer a promising approach to the rapid and efficient synthesis of high-quality ZIB cathode materials.

Polymer-Interface-Tissue Model to Estimate Leachable Release from Medical Devices.

The ability to predict clinically relevant exposure to potentially hazardous compounds that can leach from polymeric components can help reduce testing needed to evaluate the biocompatibility of medical devices. In this manuscript, we compare two physics-based exposure models: 1) a simple, one-component model that assumes the only barrier to leaching is the migration of the compound through the polymer matrix and 2) a more clinically relevant, two-component model that also considers partitioning across the polymer-tissue interface and migration in the tissue away from the interface. Using data from the literature, the variation of the model parameters with key material properties were established, enabling the models to be applied to a wide range of combinations of leachable compound, polymer matrix and tissue type. Exposure predictions based on the models suggest that the models are indistinguishable over much of the range of clinically relevant scenarios. However, for systems with low partitioning and/or slow tissue diffusion, the two-component model predicted up to three orders of magnitude less mass release over the same time period. Thus, despite the added complexity, in some scenarios it can be beneficial to use the two-component model to provide more clinically relevant estimates of exposure to leachable substances from implanted devices.

Efficient Computation of Radiative Heat Recovery from Porous Ceramic Monoliths for Efficient Solar Thermochemical Fuel Production

Solar thermochemical hydrogen (STCH) produced by heat-driven water-splitting is a promising route for producing green hydrogen and other zero-emission synfuels. However, the efficiency of STCH must be dramatically increased for it to make an impact on decarbonization efforts. We have previously presented a novel Reactor Train System (RTS) for significantly increasing the efficiency of STCH by employing heat recovery from the redox material and efficient gas exchange processes. In this paper we present a higher-fidelity model for the RTS that accommodates the slow heat diffusion through the STCH redox material. For this purpose, a novel method is introduced for transient modelling of radiative heat in participating media. This method, called GREENER: Generalized Radiation Exchange Factors and Net Radiation, combines the accuracy of Monte Carlo Ray Tracing with the low computational cost of the P1 or Rosseland diffusion approximations. Along with STCH, GREENER has application for modelling volumetric solar receivers, high temperature heat recovery systems like heat exchangers and regenerators, and packed bed reactors. Using the GREENER method, the RTS counterflow radiative heat exchanger is shown to achieve heat recovery effectiveness greater than 70%. The performance of non-uniform porous redox morphologies is evaluated, and high-performing configurations are identified.

Embolism propagation does not rely on pressure only: time-based shifts in xylem vulnerability curves of angiosperms determine the accuracy of the flow-centrifuge method.

Centrifuges provide a fast approach to quantify embolism resistance of xylem in vulnerability curves (VCs). Since embolism formation is assumingly driven by pressure only, spin time is not standardised for flow centrifuge experiments. Here, we explore to what extent embolism resistance could be spin-time dependent, and hypothesise that changes in hydraulic conductivity (Kh) would shift VCs towards higher water potential (Ψ) values over time. We quantified time-based shifts in flow-centrifuge VCs and their parameter estimations for six angiosperm species by measuring Kh over 15minutes of spinning at a particular speed, before a higher speed was applied to the same sample. We compared various VCs per sample based on cumulative spin time, and modelled the relationship between Kh, Ψ, and spin-time. Time-based changes of Kh showed considerable increases and decreases at low and high centrifuge speeds, respectively, which generally shifted VCs towards more positive Ψ values. Values corresponding to 50% loss of hydraulic conductivity (P50) became less negative by up to 0.72MPa in Acer pseudoplatanus, and on average by 8.5% for all six species compared to VCs that did not consider spin-time. By employing an asymptotic exponential model, we estimated time-stable Kh, which improved the statistical significance of VCs in 5 of the 6 species studied. This model also revealed the instability of VCs at short spin times with embolism formation in flow-centrifuges following a saturating exponential growth curve. Although pressure remains the major determinant of embolism formation, spin-time should be considered in flow-centrifuge VCs because not considering the time-dependent stability of Kh overestimates embolism resistance. This spin-time artefact is species-specific, and likely based on relatively slow gas diffusion that is associated with embolism propagation. The accuracy of VCs is improved by determining time-stable Kh values for each centrifuge speed, without considerably extending the experimental time to construct VCs.

The grain-scale signature of isotopic diffusion in ice

Abstract. Diffusion limits the survival of climate signals on the water stable isotopes in ice sheets. Diffusive smoothing acts not only on annual signals near the surface, but also on long-timescale signals at depth as they shorten to decimetres or centimetres. Short-circuiting of the slow diffusion in crystal grains by fast diffusion along liquid veins can explain the “excess diffusion” found on some ice-core isotopic records. But experimental evidence is lacking as to whether this mechanism operates as theorised; theories of the short-circuiting also under-explore the role of diffusion along grain boundaries. The non-uniform patterns of isotopic deviation δ across crystal grains induced by short-circuiting offer a testable prediction of these theories. Here, we extend the modelling for grain boundaries (and veins) and calculate these patterns for different grain-boundary diffusivities and thicknesses, temperatures, and vein-water flow velocities. Two isotopic patterns are shown to prevail in ice of millimetre grain size: (i) an axisymmetric “pole” pattern with excursions in δ centred on triple junctions, in the case of thin, low-diffusivity grain boundaries, and (ii) a “spoke” pattern with excursions around triple junctions showing the impression of grain boundaries, when these are thick and highly diffusive. The excursions have widths ∼ 10 %–50 % of the grain radius and variations in δ ∼ 10−2 to 10−1 times the bulk isotopic signal for oxygen and deuterium, which set the minimum measurement capability needed to detect the patterns. We examine how the predicted patterns vary with depth through a signal wavelength to suggest an experimental procedure, based on laser ablation mapping, of testing ice-core samples for these signatures of isotopic short-circuiting. Because our model accounts for veins and grain boundaries, its predicted enhancement factor (quantifying the level of excess diffusion) characterises the bulk-ice isotopic diffusivity more comprehensively than past studies.

Application of Decentralized Wastewater Treatment Technology in Rural Domestic Wastewater Treatment

The management of domestic wastewater in rural areas has always been challenging due to characteristics such as the wide distribution and dispersion of rural households. There are numerous domestic sewage discharge methods used in rural areas, and it is difficult to treat the sewage. To address this problem, decentralized wastewater treatment systems (DWTSs) have been installed around the globe to reuse and recycle wastewater for non-potable uses such as firefighting, toilet flushing, and landscape irrigation. This study compares the currently implemented treatment processes by investigating them from the point of view of their performance and their advantages and disadvantages to provide new ideas for the development of rural wastewater treatment technologies. According to conventional treatment technologies including activated sludge (OD, A/O, A/A/O, SBR), biofilm (biofilter, MBBR, biological contact oxidation, biofluidized bed) and biogas digesters, natural biological treatment technologies including artificial wetlands (surface flow, vertical flow, horizontal submerged flow artificial wetlands), soil percolation systems (slow, fast, subsurface percolation and surface diffusion) and stabilization pond technology and combined treatment technologies are categorized and further described.

Cosmic-Ray Feedback on Bistable Interstellar Medium Turbulence

While cosmic rays (E ≳ 1 GeV) are well coupled to a galaxy’s interstellar medium (ISM) at scales of L > 100 pc, adjusting stratification and driving outflows, their impact on small scales is less clear. Based on calculations of the cosmic-ray diffusion coefficient from observations of the grammage in the Milky Way, cosmic rays have little time to dynamically impact the ISM on those small scales. Using numerical simulations, we explore how more complex cosmic-ray transport could allow cosmic rays to couple to the ISM on small scales. We create a two-zone model of cosmic-ray transport, with the cosmic-ray diffusion coefficient set at the estimated Milky Way value in cold gas but smaller in warm gas. We compare this model to simulations with a constant diffusion coefficient. Quicker diffusion through cold gas allows more cold gas to form compared to a simulation with a constant, small diffusion coefficient. However, slower diffusion in warm gas allows cosmic rays to take energy from the turbulent cascade anisotropically. This cosmic-ray energization comes at the expense of turbulent energy which would otherwise be lost during radiative cooling. Finally, we show our two-zone model is capable of matching observational estimates of the grammage for some transport paths through the simulation.

Radiation Hydrodynamic Simulations of Massive Stars in Gas-rich Environments: Accretion of AGN Stars Suppressed by Thermal Feedback

Massive stars may form in or be captured into active galactic nuclei (AGN) disks. Recent 1D studies employing stellar-evolution codes have demonstrated the potential for rapid growth of such stars through accretion up to a few hundred solar masses. We perform 3D radiation hydrodynamic simulations of moderately massive stars’ envelopes in order to determine the rate and critical radius R crit of their accretion process in an isotropic gas-rich environment in the absence of luminosity-driven mass loss. We find that in the “fast-diffusion” regime where characteristic radiative diffusion speed c/τ is faster than the gas sound speed c s , the accretion rate is suppressed by feedback from gravitational and radiative advection energy flux, in addition to the stellar luminosity. Alternatively, in the “slow-diffusion” regime where c/τ < c s , due to adiabatic accretion, the stellar envelope expands quickly to become hydrostatic and further net accretion occurs on thermal timescales in the absence of self-gravity. When the radiation entropy of the medium is less than that of the star, however, this hydrostatic envelope can become more massive than the star itself. Within this subregime, the self-gravity of the envelope excites runaway growth. Applying our results to realistic environments, moderately massive stars (≲100M ⊙) embedded in AGN disks typically accrete in the fast-diffusion regime, leading to a reduction of steady-state accretion rate 1–2 orders of magnitudes lower than expected by previous 1D calculations and R crit smaller than the disk scale height, except in the opacity window at temperature T ∼ 2000 K. Accretion in slow diffusion regime occurs in regions with very high density ρ ≳ 10−9 g cm−3, and needs to be treated with caution in 1D long-term calculations.

Stock price delay and the cross-section of expected returns: A story of night and day

We examine how individual stock price reacts to intraday and overnight market information. By examining stock betas, we document a stark gap between day beta and night beta and nontrivial asynchronous beta, which captures the slow diffusion of information. We provide evidence that this information delay can predict future stock returns over a one-month period. Long-short portfolios sorted on the gap between day beta and night beta and asynchronous beta generate raw returns of 0.8% and 0.39% and risk-adjusted alphas of 0.77% and 0.28% per month. These results are robust to alternative asset pricing models and when controlling for firm characteristics, such as size, book-to-market ratios, liquidity, investor recognition and limits-to-arbitrage characteristics. We also explore the heterogeneity of the information delay premium and find that the predictive power of information delay for future return is stronger among small, value firms, less visible firms, illiquid firms and firms with higher limit-to-arbitrage. We also provide evidence that our measure of price delay indeed offers incremental information for cross-section return prediction after we explicitly control for the conventional measure of Hou and Moskowitz (2005)’s price delay.

Influence of 3D Structural Design on the Electrochemical Performance of Aluminum Metal as Negative Electrode for Li-Ion Batteries.

Aluminum (Al) is one of the most promising active materials for producing next-generation negative electrodes for lithium (Li)-ion batteries. It features low density, high specific capacity, and low working potential, making it ideal for producing energy-dense cells. However, this material loses its electrochemical activity within 100 cycles, making it practically unusable. Several claims in the literature support the idea that a dual degradation mechanism is at play. First, the slow diffusion of Li in the Al matrix causes the electrochemical reactions to be partly irreversible, making the initial capacity of the cell drop. Second, the stress caused by cycling make the active material pulverize and lose activity. Recent work shows that shortening the diffusion path of Li by 3D structuring is an effective way to mitigate the first capacity loss mechanism, while alloying Al with other elements effectively mitigates the second one. In this work, we demonstrate that the benefits of 3D structuring and alloying are cumulative and that a mesh made of an Al-magnesium alloy performs better than both a pure Al foil and a foil of an Al-Mg alloy.

Low-crystalline 1T/2H-MoSe2 heterostructure as the high-rate and ultra-long-lifespan cathode materials for magnesium ion batteries

Two-dimensional layered-like materials are attracted extensive attention to be the potential cathode materials for magnesium ion batteries because of the wide layer distances and high capacities. Whereas such strong interaction between bivalent Mg2+ and layered cathode materials is prone to cause the slow diffusion kinetics, and irreversible electrochemical reaction, finally bringing about the low specific capacity and inferior rate capability. Meanwhile, limited by the inherent crystal structure of MoSe2 and unsuitable electrolyte, the magnesium storage properties are not ideal. Herein, the low-crystalline 1T/2H-MoSe2 heterostructure (LC-MoSe2) is synthesized via one-step hydrothermal method. Such low-crystalline feature of LC-MoSe2 and MgCl+ in the electrolyte significantly decrease the Mg2+ diffusion barrier, and largely promote the Mg2+ diffusion kinetics. The rich heterogeneous interfaces in the 1T/2H-MoSe2 boost the electron/ion transfer kinetics and endow plentiful active sites for the Mg2+ storage. As expected, the LC-MoSe2 exhibits a high discharge capacity (257.4 mAh g−1/0.5 A g−1/200 cycles) and stable long-span cyclic life of 2000/1000 loops even at 2/5 A g−1, distinctly transcending those of relatively high-crystalline MoSe2 (HC-MoSe2). Such electrode can also surprisingly cycle at an ultra-high rate of 10 A g−1. Meanwhile, the charge transfer/ion diffusion kinetics along with charge storage mechanism of LC-MoSe2 are carried out by various kinetics strategies from experimental and theoretical aspects. The reaction mechanism has also been discussed by some ex-situ characterization techniques. The remarkable Mg2+ storage properties of LC-MoSe2 cathode materials provide new ideas for the long-run development of MIBs.

High-Entropy Materials for Application: Electricity, Magnetism, and Optics.

High-entropy materials (HEMs) have recently emerged as a prominent research focus in materials science, gaining considerable attention because of their complex composition and exceptional properties. These materials typically comprise five or more elements mixed approximately in equal atomic ratios. The resultant high-entropy effects, lattice distortions, slow diffusion, and cocktail effects contribute to their unique physical, chemical, and optical properties. This study reviews the electrical, magnetic, and optical properties of HEMs and explores their potential applications. Additionally, it discusses the theoretical calculation methods and preparation techniques for HEMs, thereby offering insights and prospects for their future development.

Edge‐Enriched MoS2 as a High‐Performance Cathode for Aqueous Zn‐Ion Batteries

AbstractRechargeable aqueous zinc ion batteries (AZIBs) with the advantages in low cost, high safety, and environmental friendliness have broad application prospects in the field of energy storage. However, the slow diffusion kinetics of multivalent Zn2+ in materials make it hard to find a suitable cathode. Herein, HNO3 etched MoS2 with edge‐enriched feature is proved to be a promising cathode for high‐performance AZIBs. The highly exposed edges with superior electrochemical activity can not only offer more reactive sites for zinc storage but also facilitate electrolyte accessibility and shortens the ion transport pathway, thus accelerating reaction kinetics. As a result, the edge‐enriched MoS2 cathode exhibited higher specific capacity of 187 mAh g−1 at 0.1 A g−1 and outstanding cycling performance (89 % capacity retention after 700 cycles at 1 A g−1).

Composite edible film mimicking cell wall based on arabinoxylan, β-glucan and nanocellulose: Microstructural, physico-chemical properties, and preservation effect

To achieve sustainable environmental development, various biodegradable films have been designed to replace plastic films. The cell walls of the wheat bran aleurone layers primarily comprise alternately overlapping arabinoxylan (AX), β-glucan (BG) and small quantities of cellulose and ferulic acid. The differences in their composition can affect their mechanical strength and hydration. Therefore, multilayer films of AX, BG, cellulose nanofibers (CNFs), and free ferulic acid were prepared to simulate the cell walls of wheat aleurone layers, and the effect of different CNF contents on cell walls characteristics was investigated. The microstructure, physical properties, and hydration characteristics of multilayer films were studied using scanning electron microscopy, time-domain nuclear magnetic resonance, and thermogravimetric analysis. The AX/BG/8%CNF multilayer films possessed excellent thermal stability and mechanical properties along with slow moisture diffusion and flowability. When the CNF content within the films was 8%, the polymer composite structure hindered the diffusion of moisture. Inspired by the biological effects of wheat grain cell walls, cellulose multilayer films were used for blueberries preservation, and the decay rate, weight loss index, and respiration rate of blueberries were found to decrease significantly.

Developing three-dimensional hydrophobic photocatalysts to enhance mass transfer for promoting hydrogen peroxide production

Photocatalytic oxygen reduction reaction (ORR) is a promising approach for hydrogen peroxide (H2O2) production to alternative conventional anthraquinone process. However, the slow O2 diffusion and low-efficiency water oxidation reaction (WOR, limitation of protons) pathways have restricted the H2O2 production efficiency of organic photocatalysts. Therefore, a promising strategy to develop photocatalysts with three-dimensional (3D) architectures possessing high O2 diffusion, high-efficiency WOR pathway, and quick H2O2 desorption is desirable. Herein, a hydrophobic two-dimensional porous organic polymer (2D-POP) based on tetraphenylethylene (TPE) was synthesized as the building block. 3D-POPs (TPE-2 and TPE-3) were subsequently developed through the Friedel-Crafts alkylation reaction to regulate the O2 adsorption and optical properties. The 3D architectures allow O2 to diffuse into the interlayers, leading to efficient extraction of O2 from air, thus an excellent H2O2 production rate of 2.57 mmol g−1 h−1has been achieved by TPE-2 in air and without sacrificial agents, which only decreases by 4% compared to that in O2 due to a suitable specific surface area, good photoelectric properties, and excellent mass transfer of O2, H+, and H2O2. Furthermore, the H2O2 production rate of TPE-2 reaches 2.67 mmol g−1 h−1 in a triphasic system in air, which is higher than that in a traditional diphasic system, and the concentration of H2O2 reaches 1.80 mmol L−1 h−1. Additionally, by adding external Fe2+ or Fe3+ to make the utmost of photogenerated H2O2 and trigger the in-situ Fenton reaction for the formation of ·OH, TPE-2 exhibits extraordinary photodegradation efficiency toward representative organic pollutants, reaching > 99% removal within 60 min for bisphenol A and 2,4-dichlorophenoxyacetic acid with high concentrations (200 ppm).

Hydrodynamic solar-driven interfacial evaporation - Gone with the flow

Evaporation has been one of the most classic desalination processes on the Earth. When we try to use the power of water flow itself, the evaporation process can perform even better. Here, we report a hydrodynamic solar-driven interfacial evaporation process which water evaporation rate can achieve 6.58 kg·m-2·h-1 (over 100 times higher than natural evaporation). A waterwheel-structure solar interfacial evaporator was designed and assembled by printed filter papers. The evaporator can both rapidly distribute solution on the evaporation interface and be hydraulically driven to rotate continuously to improve the evaporation rate by water flow. The hydrodynamic solar-driven interfacial evaporation process successfully overcomes the problem of slow diffusion of water vapor, but also realizes the day-and-night operation of process and the self-cleaning of salt fouling. Apart from the application in solar desalination, the developed evaporator has great potentials in vapor production and salt recovery for industrial use.

LBE corrosion behavior of helium pre-irradiated martensitic steel

In the design of the spallation target of CiADS, T91 steel was selected for the most critical component, the beam window. A Si-modified martensitic steel (SIMP) has been currently developed, which has better corrosion resistance and is planning to replace T91 as a material of beam window in the future. In order to assess the effect of irradiation damage on the microstructure evolution and corrosion behavior of the SIMP, the pre-irradiated samples with irradiation doses from 5 × 1015 to 3 × 1017 He/cm2 exposed in static lead-bismuth eutectic (LBE) with saturated oxygen at 350 °C for 4000 h were investigated. Results show that pre-irradiation neither change the double-layer structure of the oxide layer nor significantly affect the corrosion rate. This may be due to the slow diffusion of elements at low temperatures, and the low irradiation dose not reaching the threshold for triggering accelerated corrosion.

Light-Driven Reverse Water Gas Shift Reaction with 1000-H Stability on High-Entropy Alloy Catalysts.

Highly stable and active catalysts are of significant importance and a longstanding challenge for a number of industrial chemical transformations. Here, motivated by the principle of the high entropy-stabilized structure, high-entropy alloy-loaded porous TiO2 as an efficient and sintering-resistant catalyst for the light-driven reverse water gas‒shift reaction without external heating is synthesized. The optimized CoNiCuPdRu/TiO2 catalyst exhibits a long-term stability of 1000h (1.23molgmetal -1h-1 CO production rate, >99% high selectivity). In situ characterizations confirm that the slow diffusion effect of high-entropy alloys endows the catalyst with excellent structural stability. The CO adsorption measurements and theoretical calculations consolidate that the hydrogen surface coverage weakens CO adsorption on the catalyst surface. Two major problems of catalyst deactivation - sintering and poisoning, are handled in one case, which synergistically enable unparalleled stability. This work provides new guidance for the rational design of ultradurable harsh-condition operation catalysts for industrial catalysis.