Diffusion Channels Research Articles

Features of Hydrogen-Enriched Methane–Air Flames Propagating in Hele-Shaw Channels

Mixtures of hydrogen with common hydrocarbon fuels are considered viable for reducing carbon footprint in modern industry, power production, and transportation. The addition of hydrogen alters the kinetics and thermophysical properties of the mixtures, as well as the composition and properties of combustion products, requiring detailed research into the features of flame propagation in hydrogen-enriched hydrocarbon–air mixtures. Of particular interest are also the safety aspects of such fuels. In this paper, experimental results are presented on the premixed laminar flame propagation in channels formed by two closely spaced plates (Hele-Shaw cell), with the internal straight walls forming a diverging (diffuser) channel with the opening angles between 5 and 25 degrees. Methane–hydrogen–air mixtures with the hydrogen relative contents of 0%, 25%, and 50% and global equivalence ratio of unity were ignited by a spark near the closed narrow end of the channel. Experiments were performed with the gap width of 3.5 mm; video recordings were processed in order to determine the quantitative features of the flame front propagation (leading and trailing point coordinate, coordinates of the cusps, cell sizes and shapes). The main features of flame propagation (fast initial expansion, development of cellular flame, self-induced longitudinal oscillations) are obtained and compared to clarify the effect of hydrogen contents in the fuel and channel geometry (gap width, opening angle).

Enabling High-Voltage and Long Lifespan Sodium Batteries via Single-Crystal Layer-Structured Oxide Cathode Material.

Manganese-based layer-structured transition metal oxides are considered promising cathode materials for future sodium batteries owing to their high energy density potential and industrial feasibility. The grain-related anisotropy and electrode/electrolyte side reactions, however, constrain their energy density and cycling lifespan, particularly at high voltages. Large-sized single-crystal O3-typed Na[Ni0.3Mn0.5Cu0.1Ti0.1]O2 was thus designed and successfully synthesized toward high-voltage and long-lifespan sodium batteries. The grain-boundary-free single-crystal structure and unidirectional Na+ diffusion channels enable a faster Na+ diffusion rate and high electronic conductivity. Meanwhile, the large-area exposed (003) crystal plane can not only exhibit a higher energy barrier for electrode-electrolyte side reactions but also alleviate the interlayer sliding and structural collapse during charge-discharge processes. The lattice oxygen in contact with the electrolyte was stabilized, and the TMO6 octahedral structure integrity was maintained as well. A high specific capacity of 160.1 mAh g-1 at a current density of 0.1 C was demonstrated. Coupled with hard carbon as the anode, the full cell can also demonstrate an excellent capacity and cycling stability, achieving a high specific capacity of 141.1 mAh g-1 at 0.1 C. After 100 cycles at 2 C, the capacity retention rate is 97.3%.

In situ growth of 3D nano-array architecture Bi2S3/nickel foam assembled by interwoven nanosheets electrodes for hybrid supercapacitor

Transition metal sulfides have been regarded as significant candidates of battery-type electrode materials for high-performance hybrid supercapatteries (HSC). Bi2S3/nickel foam (NF) integrated electrodes are fabricated by adjusting the molar ratio of thiourea to bismuth nitrate and the hydrothermal reaction temperature by a simple template-free hydrothermal method via in-situ growth of Bi2S3 on nickel foam. The optimal Bi2S3/NF-8-120 electrode presents unique three-dimensional (3D) nano-array architecture assembled by interwoven nanosheets, which could provide abundant accessible channels for electrolyte ion diffusion. The Bi2S3/NF-8-120, as binder-free electrode, exhibits an ultrahigh specific capacity (652 mAh/g at 1 A/g), prominent rate capability (372 mAh/g at 32 A/g), and excellent cycle stability (90.1% retention after 1000 cycles). The HSC delivered an energy density of 115.6 Wh/kg at a power density of 550 W/kg and 105.9 Wh/kg at 16500 W/kg. Moreover, the HSC exhibits excellent cycling stability with a specific capacitance retention of 96.4% after 1000 cycles, indicating applicable potential of the Bi2S3/NF-8-120 electrode for HSCs.

A micro thermal conductivity detector with diffusion channels suppressing the effect of forced convection

A micro thermal conductivity detector with diffusion channels suppressing the effect of forced convection

Heterostructure Design of Amorphous Vanadium Oxides@Carbon/Graphene Nanoplates Boosts Improved Capacity, Cycling Stability and High Rate Performance for Zn2+ Storage

AbstractAs a promising power supplier, flexible aqueous zinc ion batteries (AZIBs) have drawn great attention and been demonstrated potential applications in portable electronic devices, yet their capacity, stability, and rate performance are severely limited by cathode materials. Herein, a spontaneous encapsulation and in situ phase transformation strategy is proposed for the construction of heterostructured amorphous vanadium oxide@carbon/graphene (A‐VOx@C/G) nanoplates as highly stable and efficient cathode materials for Zn2+ storage. In this design, A‐VOx provides abundant active sites with rapid ion diffusion channels and robust tolerance against ion insertion/extraction, while N‐doped carbon encapsulation and interlaced graphene network ensure efficient electron transfer. The mechanisms respectively for phase transformation during electrochemical amorphization and charge storage during cycling are investigated in detail. The as‐prepared A‐VOx@C/G achieves an outstanding electrochemical performance with 429 mAh g−1 at 0.5 A g−1, 73% retained at 20 A g−1 (315 mAh g−1), and excellent stability over 2000 cycles at 20 A g−1 (91% retention). Moreover, quasi‐solid‐state AZIBs assembled from A‐VOx@C/G cathode exhibit high flexibility and can sustain large mechanical deformation without performance degradation. It is believed that this study provides a guideline toward designing high‐performance cathode materials for AZIBs through structure optimization.

Recent Advances in Selective Chemical Etching of Nanomaterials for High‐Performance Electrodes in Electrocatalysis and Energy Storage

AbstractTo move beyond an energy economy dominated by fossil fuel utilization, high‐performance electrochemical cells must be designed for energy storage and conversion. Selective etching is a promising, cost‐effective solution‐processing method for the large‐scale top‐down production of nanomaterials for high‐performance electrodes. This review outlines general methodologies and mechanisms by which selective etching can be applied to create nanomaterials, including various template‐assisted, facet‐selective, and electrochemical methods, as well as in‐depth case studies of state‐of‐the‐art research involving selectively etched nanomaterials for electrocatalytic and energy storage applications. In addition, the standard design strategies by which the electrochemical performance of selectively etched nanomaterials is enhanced, including increased surface area, morphology, diffusion channels, heterojunction interfaces, and facet reactivity, are discussed. This review provides a foundation of knowledge for researchers seeking the rational design of nanomaterials for electrode application through selective etching.

Harmonizing Wide Voltage Window and High Energy Density toward Asymmetric All-Solid-State Supercapacitor.

All-solid-state supercapacitors are known for their safety, stability, and excellent cycling performance. However, their limited voltage window results in lower energy density, restricting their widespread application in practical scenarios. Therefore, in this work, CC/MoO3@Ti3C2Tx negative electrode and Mo1Al1-MnO2/CC positive electrode materials are synthesized and prepared by electrochemical deposition co-coating and one-step hydrothermal methods, respectively, and assembled into an asymmetric supercapacitor (ASC) device based on the two electrode materials. The study reveals that the surface capacitances of the positive and negative electrodes are 1685.5 mF cm-2 and 1134.98mFcm-2 correspondingly, with potential windows of both as high as 1.1V. Surprisingly, the potential window of the all-solid-state supercapacitor assembled based on the two electrodes reaches 2.2V, and the energy density reaches 0.44m W h cm-2, which is much higher than the performance indicators based on similar electrodes. The resulting excellent performance parameters are mainly attributed to the efficient synergy between the pseudo-capacitance effect of the MoO3 film and the high electrical conductivity of the Ti3C2Tx sheets, as well as the great improvement of the intrinsic electron mobility and ion diffusion channel stability of MnO2 by Mo and Al bimetallic doping.

Suppressed P3-O3' Phase Transition and Enhanced Na+ Diffusion Kinetics of O3-Type Layered Oxide Cathode via Multivariate Doping.

O3-NaNi1/3Fe1/3Mn1/3O2 has attracted much attention as a cathode for sodium-ion batteries, because of its low cost and high sodium-ion storage capacity. However, its slow Na+ diffusion kinetics and harmful P3-O3' phase transition with severe bulk strain at high voltage leads to poor rate capability and fast capacity fading. Herein, we propose a multivariate doping strategy with Cu, Mg, and Ti ions to solve the above problems of the O3-NaNi1/3Fe1/3Mn1/3O2 cathode. The O3-Na(Ni1/3Fe1/3Mn1/3)0.9Cu0.03Mg0.02Ti0.05O2 (NFMCMT) cathode exhibits enlarged Na+ diffusion channels and a strengthened layered structure, which improves the Na+ diffusion kinetics, suppresses the harmful P3-O3' phase transition at high voltages, and inhibits the intragranular fatigue cracks, leading to enhanced rate capability and cycling performance. As a result, the NFMCMT exhibits outstanding performance in the 2-4.1 V voltage window, delivers a discharge capacity of 151.2 mAh g-1 with the 81.5% capacity retention for 100 cycles at 0.1 C, and 83.1% capacity retention for 300 cycles at 5 C. Especially in the rate performance, the NFMCMT delivers a 115.6 mAh g-1 and 100.1 mAh g-1 discharge capacity even at 5 and 10 C. This work provides an effective multivariate doping strategy for development of high-performance layered oxide cathodes for sodium-ion batteries.

Molecular Dynamics Simulations of HEMA-Based Hydrogels for Ophthalmological Applications.

The structural and dynamic properties of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(N-vinylpyrrolidone-co-2-hydroxyethyl methacrylate) [P(VP-co-HEMA)], dry and as hydrogels, were studied by molecular dynamics simulations. The P(VP-co-HEMA) chains differed in the number of VP mers, distributed randomly or in blocks. In all considered configurations, HEMA and VP side chains proved relatively rigid and stable. Water concentration had a significant impact on their dynamic behavior. Oxygen atoms of hydroxyl and carbonyl groups of HEMA and carbonyl groups of VP are preferred sites of hydrogen bonding with water molecules. The copolymer swelling results in diffusion channels, larger in systems with high water content. In low-hydrated materials, water shows subdiffusion, while normal diffusion predominates in the high-hydrated ones. The VP side chains in copolymers with HEMA do not enhance the mobility of water.

Highly Stable Aqueous Zn‐Ion Batteries Achieved by Suppressing the Active Component Loss in Vanadium‐Based Cathode

AbstractAqueous zinc–ion batteries (AZIBs) hold significant promise for large‐scale energy storage due to their inherent safety and environmental benefits. However, their practical application is often limited by rapid capacity loss from the dissolution of active cathode materials. Here, an effective strategy is proposed to suppress the active component loss by doping high‐valence Sn4+ in V3O7·H2O (Sn–V3O7·H2O) cathode material to achieve highly stable AZIBs. An impressive capacity retention of 89.3% over 6000 cycles at 5.0 A g−1 and a high specific capacity of 408 mAh g−1 at 0.1 A g−1 are attained. The Sn4+ doping thermodynamically lowers the formation energy of Sn–V3O7·H2O and increases the dissolution energy of VO2+ ions, thereby reinforcing the structural stability and suppressing the vanadium dissolution. Besides, Sn4+ doping enhances electrical conductivity and broadens Zn2+ diffusion channels, significantly accelerating Zn2+ intercalation and deintercalation kinetics. The experimental results are integrated with mechanism analysis and density functional theory calculation to elucidate the dissolution dynamics of V‐based cathodes, and employ X‐ray absorption spectroscopy to reveal the local electronic structures and chemical valences of vanadium during charge/discharge processes, thereby providing comprehensive insights into high‐performance cathode materials for AZIBs.

Vertically Aligned Ultrathin CoNi-LDH@NiS@MXCF Core-Shell Heterostructure for Flexible Supercapacitor Electrodes and Oxygen Evolution Reaction.

A multilayer core-shell heterostructure with CoNi-LDH as the core and NiS nanosheets as the shell is deposited on MXene-coated carbon nanofibers by electrospinning and electrochemical deposition. This unique structure not only combines highly conductive and hydrophilic one-dimensional carbon nanofibers but also exposes abundant two-dimensional reactive sites and multiple ion diffusion channels to maximize material utilization, enhance electron transfer kinetics, accelerate Faraday reaction, high capacitance and strong stability. The CNNS@MXCF electrode exhibits outstanding electrochemical characteristics, including a capacity of 1441.8 F g-1 at a current density of 1 A g-1 and excellent cycling stability. The CNNS@MXCF//VN@MXCF device shows a high energy density of 84.4 Wh kg-1 at 0.8 kW kg-1 power density, with nearly 92% capacitance retention after 10,000 cycles (30 A g-1). In addition, the oxygen evolution reaction (OER) shows a small overpotential of 128 mV, confirming the versatility and large potential of the materials and strategy.

Probing a solid electrolyte interphase layer with sub-nanometer pores using redox mediators

The solid electrolyte interphase (SEI) layer is crucial for lithium-ion batteries and has a significant impact on the electrochemical performance of negative electrodes, particularly for conversion-type materials with large volume changes and metallic lithium anode. However, the SEI layer has not yet been well understood. In this work, we used redox mediators of various sizes to probe the SEI layer that formed in carbonate-based electrolytes. The SEI layer has diffusion channels that allow the mediators smaller than benzoquinone (5.7 Å) to pass, suggesting that lithium ions have to partially de-solvate to pass through. Additionally, due to partial desolvation, the diffusion coefficient in the diffusion channels was higher than that in the bulk electrolytes. Both lithium salts and solvents influenced the size and areal density of channels. Herein, we aim to enhance comprehension of SEI structure and provide a method to study porous SEI layers using mediators, which can be extended to other electrochemical systems.

In-situ growth of series-connected CoNi2S4 hollow nanocages strung by carbon nanotubes for high-performance hybrid supercapacitors

For supercapacitors (SCs), there is an urgent need to develop positive materials with excellent electrochemical performance. In this work, in-situ growth of series-connected CoNi2S4 hollow nanocages derived from zeolitic imidazolate framework-67 (ZIF-67) and strung by carboxylated carbon nanotubes (C-CNTs) were successfully synthesized through a two-step ordered ion etching/exchange procedure. The special connection structure and synergistic effect between CoNi2S4 nanocages and C-CNTs greatly improve the electrochemical performance of the hybrid (CoNi2S4/C-CNTs), in which porous CoNi2S4 hollow nanocages offer electrochemical active sites and fast ion diffusion channels, while C-CNTs provide electron transport paths. The optimized hybrid, CoNi2S4/C-CNTs20, exhibits excellent electrochemical performance with a high specific capacity (1314.6C g−1 at 1 A g−1) and an impressive rate capability (72.1 % retention at 20 A g−1). Furthermore, the hybrid supercapacitor (HSC) using CoNi2S4/C-CNTs20 and active rice husk carbon (ARHC) as the positive and negative electrodes, respectively, demonstrates an outstanding energy density of 47.9 Wh kg−1 at a power density of 800 W kg−1 and remarkable cycling stability of 90 % at 5 A g−1 after 8500 cycles. Our work will open up a brand-new strategy to oriented design electrode materials for various energy storage devices.

Perovskiet-like BaZrO3 nanocatalyst with rich oxygen vacancies on boosting hydrogen storage property of MgH2

Magnesium hydride (MgH2) as a promising solid hydrogen syorage material has been extensively researched. but the higher separating temperature and sluggish kinetics hinder its large-scale practical application. To solve this problem, a BaZrO3 nanocatalyst with abundant oxygen vancies is manuscripted, exerts significant improvement to the hydrogen storage performance of MgH2. Impressively, the onset dehydrogenation temperature of MgH2-10 wt% BaZrO3-Ov composite is reduced markedly from 390 °C(for pure MgH2) to 260 °C. Additionally, the composite can discharge 4.22 wt% H2 with 10 min at 275 °C and a total dehydrogenation amouut of 5.88 wt% is achieved at 300 °C. For hydrogen absorption, the composite can rapidly recharge hydrogen at a low temperature of 150 °C and approximately 5.08 wt% H2 can be absorbed at 275 °C within 10 min. The dehydrogenation activation energy of BaZrO3-Ov-added MgH2 is as low as 92.61 kJ mol−1 compared to pure MgH2 (164.78 kJ mol−1). Meantime, the composite presents unexceptionable reversible kinetic performance with a retention rate of 97.35 % after 10 cycles. The excellent catalytic effects can be attributed to the in-situ generation of ZrO2-Ov, BaO-Ov and ZrH2 from BaZrO3-Ov during the first de-/rehydrogenation cycle, which function as nanosized active sites on MgH2 matrix to accelerate electron transfer and provide abundant hydrogen diffusion channels. Density functional theory calculations results verify that the Mg–H length and dehydrogenation energy barrier are ameliorated through BaZrO3-Ov. This work provides a unique perspective on modification MgH2 by perovskiet-like BaZrO3-Ov nanocatalyst.

Effects of layered walnut NiS@NTA on hydrogen storage performance of MgH2

To investigate the effects of NiS concentration in NiS/C composites on catalytic performance and hydrogen storage performance of MgH2 particles, we synthesized nitrilotriacetic acid (NTA) chelating agent–derived composites with various NiS proportions via a hydrothermal process, labeled as NiS@NTAx (x = 0.065, 0.078, 0.091, 0.107, and 0.119, respectively). The composites exhibited a layered walnut morphology. After ball milling 5 wt% NiS@NTAx with MgH2, the resulting MgH2–5 wt%NiS@NTA0.078 composite (NiS: 83.5 wt% and C: 16.5 wt%) demonstrated the excellent performance, which could absorb 3.0 wt% of H2 at 353 K and released 3.5 wt% of H2 at 573 K within 60 min, and the intital dehydrogenation temperature was decreased to 508 K.. Undergoing 20 hydrogen absorption/desorption cycles, the composite maintained hydrogenation/dehydrogenation capacity retention rates of 97.4 % and 96.4 % with activation energies of 24.1 and 67.3kJ/mol, respectively. The in situ formation of MgS and Mg2Ni catalysts promoted electron transfer during Mg and MgH2 transformation. Moreover, as a prominent transition metal, Ni Ni element reacts with the hydrogen absorption and desorption of Mg to form Mg2Ni/Mg2NiH4, which is like a “hydrogen pump” and provides additional hydrogen diffusion channels due to more interfaces. MgS additionally functioned as a catalyst in the reaction system, improving overall reaction kinetics. Carbon additives reduced particle agglomeration, stabilized the particle size, and moderately improved hydrogen diffusion during hydrogen absorption/desorption cycles. The in situ adjustment of NiS concentration in NiS/C samples and its impacts on MgH2 hydrogenation/dehydrogenation offer insights for designing high-performance sulfide catalysts.

Ordered and Expanded Li Ion Channels for Dendrite‐Free and Fast Kinetics Lithium–Sulfur Battery

AbstractThe uncontrolled polysulfide shuttling and lithium dendrite growth greatly impede the practical implementation of Li–S batteries. These issues can be alleviated by constructing an artificial layer that immobilizes soluble polysulfides and regulates Li+ flux. Here, a layer‐expanded lithium montmorillonite is fabricated through molecular intercalation to serve as a dual regulator for Li–S batteries. The lithiophilic montmorillonite, with its ordered and expanded Li+ diffusion channels, exhibits a high transference number, and promotes homogeneous Li deposition. Additionally, its moderate adsorption of polysulfides, combined with favorable Li diffusion behavior, enhanced the redox kinetics of sulfur species. This unique structure enables a prolonged lifespan of 1000 cycles at 0.5C with a low capacity decay of 0.04% per cycle for practical Li–S batteries.

Chromite Pellet Prereduction by Methane‐Containing Gas: Influence Factors and Consolidation Mechanism

Prereduction process of chromite is an effective method for saving energy and reducing emissions during ferrochrome alloy production. This study investigates the factors affecting the reduction and strength levels of chromite pellets reduced in a CH4–H2 atmosphere. Thermodynamic calculations indicate that carbon from methane pyrolysis is highly active, and chromium oxide can be converted to metal chromium and carbide at lower temperature of 1100 °C. The experimental results show that extending the reduction time can increase the pellet metallization rate without sacrificing strength at 1100 °C in 10% CH4. As the reaction progressed, the carbon from methane cracking diffused into the pellet through the metallic iron, creating observable diffusion channels. Continuous methane input further facilitates this mechanism, leading to iron carbide precipitation and ultimately compromising the pellet strength. The consolidation mechanism of pellets in CH4–H2 = 10:90 atmosphere is analyzed using X‐ray diffraction, scanning electron microscopy‐energy dispersive X‐ray spectroscopy, and chemical analysis. The consolidation process of the pellets can be divided into four stages—namely, liquid phase formation, phase transition, strengthening, and carbonization stages.

The role of Nb in enhancing the corrosion resistance of U-Nb alloy to hydrogen

The corrosion resistance of uranium to hydrogen has been significantly enhanced by niobium addition while its mechanism remains unknown. To better understanding the underlying effect of niobium addition, behaviours of hydrogen in α-U, dilute U-Nb alloy and concentrated U-Nb alloy have been systematically explored by ab-initio calculations and experimental observations. Our findings suggest that Nb atoms play distinct roles in the dilute and concentrated single-phase U-Nb alloys, shifting from hydrogen traps to rapid hydrogen diffusion channels. Moreover, the dominant mechanisms enhancing hydrogen corrosion resistance differ between dilute and concentrated U-Nb alloys.

Electrochemistry and Cycling Dependent Structural Analysis of High and Low Mn Based Disordered Rocksalt Cathodes for Lithium-Ion Batteries

Cobalt-free cation-disordered rocksalt (DRX) materials have recently emerged as a class of next-generation high-capacity cathodes for lithium-ion batteries which can incorporate earth abundant, low-cost elements such as Mn and Ti. One of the reasons for their enhanced performance is due to the presence of percolating lithium rich clusters which enable facile lithium transport. Structural phenomena such as cation short-range ordering and phase transformations in DRX materials at small length scales are known to dramatically impact local Li clusters and hence the Li diffusion channels, Li transport, and hence electrochemical properties of DRX cathodes. Recently, Mn-rich DRX materials (Mn/Ti ratio >1) have shown to phase transform upon extended cycling, resulting in improved capacity and rate performance in these materials. Therefore, it is crucial to understand the nature of the DRX structure as a function of cycling to maximize the performance in DRX materials. Interestingly, these phase changes are not observed in DRX with a low Mn content (Mn/Ti ratio <1). Keeping this in mind, the goal of this research is to understand the structural changes during electrochemical cycling and investigate the differences in electrochemical properties (Li ion transport, rate capability, cycling) in high and low Mn DRX cathodes. In addition to the electrochemical characterization, a suite of material characterization techniques such as X-ray diffraction, X-ray absorption Spectroscopy, and pair distribution function analysis, are used to perform in depth cycling dependent structural analysis and compared between the high Mn and low Mn DRX compositions. Overall, this study and poster presentation will discuss key scientific insights related to the cycling induced phase transformation and electrochemical performance of Mn-Ti based DRX cathodes. Based on these results, further investigations into synthetic manipulation of the DRX structure can be performed to utilize the full potential of the newly formed phase upon cycling.

Synthesis and Characterisation of iron doped manganese oxides for thermal energy storage

Iron-doped manganese oxides were synthesized using a co-precipitation method and thermodynamically characterized to demonstrate their potential as a thermochemical energy storage medium. Thermochemical energy storage, via chemical bonds that employ reversible redox reactions, is a promising approach to tackle solar thermal energy storage. Hysteresis loops observed confirm that the pore network consisted of mesopores that were not filled with pore condensate, and the narrow loop indicates a narrow size distribution. Barrett-Joyner-Halenda (BJH) studies of all the synthesized materials showed that they have a high mesoporous and specific area, essential for supplying reduced diffusion channels over the Mn oxides, Good conductivity through electron transfer, with the presence of active sites allow the study thermochemical approaches. The BJH studies showed the material MnOFe2 (2.5:1) to have a higher pore area, which is effective in the adsorption process of the material.