Hydrogen Kinetics Research Articles

Aeronomy of the atmosphere of ultra-hot Jupiter Kelt9B taking into account the kinetics of hydrogen atom levels

Ultra-hot Jupiter Kelt9b impels to reconsider existing models of the upper atmospheres of hot exoplanets, which were previously developed using the example of G or M star systems such as HD209458b and GJ436b. The unique conditions of interaction between the radiation of an A-class star and the atmosphere necessitate kinetic modeling of excited levels of elements, primarily the hydrogen atom. For Kelt9b, the absorption was measures for several Balmer lines and lines of a number of heavy elements, the quantitative interpretation of which is an urgent task. In this work, for the first time, 3D modeling of the atmosphere of a planet with a close location of the Roche lobe has been implemented, taking into account the aeronomy and kinetics of excited hydrogen.

Modeling of Hydrogen Combustion from a 0D/1D Analysis to Complete 3D-CFD Engine Simulations

Hydrogen and its unique properties pose major challenges to the development of innovative combustion engines, while it represents a viable alternative when it is based on renewable energy sources. The present paper deals with the holistic approach of hydrogen combustion modeling from a 0D/1D reactor evaluation with Cantera up to complete engine simulations in the 3D-CFD tool QuickSim. The obtained results are referenced to the current literature and calibrated with experimental data. In particular, the engine simulations are validated against measurements of a single-cylinder research engine, which was specifically adapted for lean hydrogen operation and equipped with port fuel injection and a passive pre-chamber system. Special attention is hereby given to the influence of different engine loads and varying lambda operation. The focus of this work is the complementary numerical investigation of the hydrogen flame speed and its self-ignition resistance under the consideration of various reaction mechanisms. A detailed transfer from laminar propagation under laboratory conditions to turbulent flame development within the single-cylinder engine is hereby carried out. It is found that the relatively simple reaction kinetics of hydrogen can lead to acceptable results for all mechanisms, but there are particular effects with regard to the engine behavior. The laminar flame speed and induction time vary greatly with the inner cylinder conditions and significantly affect the entire engine’s operation. The 3D-CFD environment offers the opportunity to analyze the interactions between mixture formation and combustion progress, which are indispensable to evaluate advanced operating strategies and optimize the performance and efficiency, as well as the reliability, of the engine.

Improved Hydrogen Storage Thermodynamics and Kinetics of As-Milled Ce-Mg-Ni-Based Alloys by Adding Ni

Improved Hydrogen Storage Thermodynamics and Kinetics of As-Milled Ce-Mg-Ni-Based Alloys by Adding Ni

Rare-Earth Metal-Based Materials for Hydrogen Storage: Progress, Challenges, and Future Perspectives.

Rare-earth-metal-based materials have emerged as frontrunners in the quest for high-performance hydrogen storage solutions, offering a paradigm shift in clean energy technologies. This comprehensive review delves into the cutting-edge advancements, challenges, and future prospects of these materials, providing a roadmap for their development and implementation. By elucidating the fundamental principles, synthesis methods, characterization techniques, and performance enhancement strategies, we unveil the immense potential of rare-earth metals in revolutionizing hydrogen storage. The unique electronic structure and hydrogen affinity of these elements enable diverse storage mechanisms, including chemisorption, physisorption, and hydride formation. Through rational design, nanostructuring, surface modification, and catalytic doping, the hydrogen storage capacity, kinetics, and thermodynamics of rare-earth-metal-based materials can be significantly enhanced. However, challenges such as cost, scalability, and long-term stability need to be addressed for their widespread adoption. This review not only presents a critical analysis of the state-of-the-art but also highlights the opportunities for multidisciplinary research and innovation. By harnessing the synergies between materials science, nanotechnology, and computational modeling, rare-earth-metal-based hydrogen storage materials are poised to accelerate the transition towards a sustainable hydrogen economy, ushering in a new era of clean energy solutions.

Prediction of the optimal hydrogen storage in high entropy alloys

Hydrogen is the most abundant element in nature, characterized by its vast resources, recyclability, and environmentally friendly. Also, it can exist in various forms, such as gas, liquid, or solid, to meet different storage needs. In solid-state storage, the hydrogen storage alloys have received widespread attention due to hydrogen is stored in the form of hydrides. In recent years, high entropy alloys (HEAs), as a new type of novel alloy design concept have attracted a lot of attention in many fields including hydrogen storage due to their unique structures and excellent properties. Moreover, the freedom of element selection leads to various types of HEAs, further enhancing the potential for their application in hydrogen storage. This article focuses on the hydrogen storage performance of HEAs and provides a comprehensive overview of the hydrogen storage mechanism, thermodynamics, and kinetics. Additionally, we summarize and compare the hydrogen storage capacities of previously published HEAs and introduce two empirical parameters, valence electron concentration (VEC) and atomic size difference (δ), and their relationship with hydrogen storage capacity. By applying the K-means clustering algorithm, we conclude that the optimal hydrogen storage capacity of HEAs occurs when 4 <VEC < 6 and 5.3 % <δ < 7.5 %. This finding offers valuable guidance for the future design of efficient hydrogen storage HEAs.

Autoignition of methane and methane/hydrogen blends in CO2 bath gas

Combustion in large dilutions of carbon dioxide (CO2) has the potential to enable fossil fuel combustion with 100 % inherent carbon capture by simplifying the post-combustion carbon capture process into the facile separation of CO2 and water. Emerging technologies that employ CO2 as a bath gas, exemplified by the Allam-Fetvedt cycle, are gaining widespread international attention, evidenced by ongoing plant developments in both the United Kingdom and the United States. This study presents new ignition delay time datasets (IDTs) for the combustion of methane and methane/hydrogen blends at 20 and 40 bar. The chemical kinetics governing these distinct conditions are investigated by utilizing two distinct chemical kinetic mechanisms, namely UoS sCO2 2.0 and NUIGMech1.1. Ignition delay datasets of methane/hydrogen blends are presented alongside a detailed discussion of the effect CO2, in contrast to N2, on the combustion mechanism. The differences in kinetics of pure methane and pure hydrogen are also discussed with regards to key reactions and the radical pool. This study aims to elucidate the intricate interplay of factors shaping ignition dynamics in CO2– enriched environments.

Synchronously upgrading of hydrogen storage thermodynamic, kinetics and cycling properties of MgH2 via VTiMn catalyst

To effectively enhance the hydrogen storage performance of MgH2, the multimetallic catalyst VTiMn was triumphantly synthesized by mechanical alloying, and the MgH2-10 wt% VTiMn composite was further fabricated. The results revealed that VTiMn significantly improved the thermodynamic, kinetics and cycle properties of MgH2. Compared with pure MgH2, VTiMn promotes its plateau pressure to increase by 0.16 MPa and the initial desorption temperature to decrease by 47 K, showing obvious thermodynamic instability. Meanwhile, the MgH2-VTiMn composite can adsorb 5.5 wt% H2 within 72 s and release within 1200 s at 523 K. The activation energies of hydrogen absorption and desorption are 30.1 and 90.5 kJ/mol, respectively. After 130 cycles at 598 K, 83 % hydrogen capacity retention can still be achieved. Characterisation indicated that the composite formed a core–shell structure with MgH2 coated on the VTiMn surface. Part of the Mn element in VTiMn diffused into the Mg matrix, accompanied by the precipitation of nanoscale α-Mn particles at high temperature. The improved absorption kinetics can be attributed to the accelerated H atoms diffusion by the microcracks in VTiMn and the phase boundaries provided by the nano-precipitated phase, while the desorption kinetics benefits from the promotion of Mg nucleation and growth by α-Mn. Due to the effect of temperature, the rate-determining steps of the hydrogen absorption and desorption process of the composite at 598 K change from H atoms diffusion and Mg nucleation growth to H atoms surface penetration, respectively. These findings will facilitate a more comprehensive understanding of multimetallic catalysts.

Investigation of hydrogen storage properties on the Mg-La-Ni alloy compounded with C@Pr2O3 composite catalyst

To explore the effect of C@Pr2O3 on the hydrogen storage performance of Mg-La-Ni alloy. In experiment, a nanostructured composite catalyst C@Pr2O3 was prepared using chemical blowing carbonization. The microstructures of the catalyst and alloy powder were characterized using techniques such as transmission electron microscope, high-resolution transmission electron microscopy, scanning electron microscope, and selective region electron diffraction. Hydrogen storage properties of the alloy were evaluated using Pressure-composition-temperature equipment, and it was observed that the addition of the catalyst significantly enhanced the hydrogen kinetics of the alloys. At 320 ℃, the two-minute hydrogen saturation ratio of Mg96NiLa3 +5 wt% C@Pr2O3 was 80.65 %, Mg96NiLa3 +7 wt% C@Pr2O3 releases 3 wt% H2 at 340 °C for 6 min. This can be attributed to the addition of nanoscale C and catalyst Pr2O3, which improved the hydrogen kinetics of the alloys. The dehydrogenation activation of Mg96NiLa3 +5 wt%C@Pr2O3 is 85.2 kJ/mol, enhancing the rate of hydrogen release while simultaneously reducing the activation energy required for dehydrogenation of the alloy. The enthalpy of hydrogen absorption of Mg96NiLa3 +5 wt% C@Pr2O3 was 72 KJ/mol. However, the thermodynamic properties of the alloy were still not satisfied with the requirements of practical application.

Kinetics of hydrogen constrained graphene growth on Cu substrate

Kinetics of hydrogen constrained graphene growth on Cu substrate

Enhanced hydrogen kinetics of Mg–Ni–La alloys via slight Y element additive

Alloying represents an effective approach for addressing challenges related to over stable thermodynamics and slow kinetics in magnesium alloys. The incorporation of Y dopant served to enhance the quantity of grain boundaries and phase boundaries, thereby addressing the issue of high dehydrogenation temperature observed in Mg85–Ni10–La5, which can be decreased to 273.3 °C after the addition of 0.5 wt% Y additive. In addition, the initial hydrogenation rate of Mg85–Ni10–La4.5-Y0.5 reached up to 3.42 wt% H2 at 260 °C and the apparent activation energy for dehydriding was decreased from 115.31 to 86.05 kJ/mol. Theoretical calculations suggested that the hydrogen adsorption energy of Mg85–Ni10–La4.5-Y0.5 was dramatically lower than that of Mg85–Ni10–La5, improving hydrogenation properties. The consistency between theoretical calculations and experimental outcomes provided a valuable reference for the selection of suitable magnesium-based hydrogen storage materials.

A parametric study on hydrogen storage in AB5 hydride alloys: Heat and mass transfer, thermodynamics, and design

The design of heat exchangers plays an important role in the performance of solid-state hydrogen storage devices. In this study, three different designs of hydrogen storage devices were investigated, incorporating phase change material (PCM), specifically, RT25HC into their walls in various shapes. A mathematical model, validated using previous experimental data, was employed to calculate heat and mass transfer and determine the reaction time period. The calculations were conducted using ANSYS Fluent, with a constant hydrogen supply pressure of 10 bars and a temperature of 295 K. The absorption properties of the storage reactor were investigated through various parameters such as liquid fraction, hydrogen concentration, and natural convection heat transfer coefficients. Results showed that the geometric structure and PCM distribution significantly impacted the performance of the hydrogen storage devices. Design 1, with a centralized PCM distribution, demonstrated moderate heat transfer rates and a longer reaction time. Design 2, featuring a more distributed PCM layout, improved heat transfer rates and reduced hydrogen kinetics time by 40%. Design 3, which optimized the geometric structure with advanced PCM shapes, achieved the highest heat transfer rates and improved hydrogen kinetics time by 50%. This design also enabled the storage of thermal energy at a high density, ranging from 10.2 J/g to approximately 190.5 J/g. The study provides critical information on the design of efficient solid hydrogen storage processes. The findings suggest significant potential for improved performance in industrial applications such as electric vehicles and domestic energy supply. The high efficiency of the large-scale reactor is due to its well-designed system, which effectively converts chemical energy into thermal energy. Optimizing the reactor geometry and PCM distribution is crucial for achieving superior hydrogen storage and retrieval performance.

Probing Electrocatalytic Synergy in Graphene/MoS2/Nickel Networks for Water Splitting through a Combined Experimental and Theoretical Lens.

The development of low-cost and active electrocatalysts signifies an important effort toward accelerating economical water electrolysis and overcoming the sluggish hydrogen or oxygen evolution reaction (HER or OER) kinetics. Herein, we report a scalable and rapid synthesis of inexpensive Ni and MoS2 electrocatalysts on N-doped graphene/carbon cloth substrate to address these challenges. Mesoporous N-doped graphene is synthesized by using electrochemical polymerization of polyaniline (PANI), followed by a rapid one-step photothermal pyrolysis process. The N-doped graphene/carbon cloth substrate improves the interconnection between the electrocatalyst and substrate. Consequently, Ni species deposited on an N-doped graphene OER electrocatalyst shows a low Tafel slope value of 35 mV/decade at an overpotential of 130 mV at 10 mA/cm2 current density in 1 M KOH electrolytes. In addition, Ni-doped MoS2 on N-doped graphene HER electrocatalyst shows Tafel slopes of 37 and 42 mV/decade and overpotentials of 159 and 175 mV, respectively, in acidic and alkaline electrolytes at 10 mA/cm2 current density. Both these values are lower than recently reported nonplatinum-group-metal-based OER and HER electrocatalysts. These excellent electrochemical performances are due to the high electrochemical surface area, a porous structure that improves the charge transfer between electrode and electrolytes, and the synergistic effect between the substrate and electrocatalyst. Raman spectroscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations demonstrate that the Ni hydroxide species and Ni-doped MoS2 edge sites serve as active sites for OER and HER, respectively. Finally, we also evaluate the performance of the HER electrocatalyst in commercial alkaline electrolyzers.

Improving oxygen resistance of hydrogen storage alloys with graphite or nickel coating

A series of graphite- and Ni-coated hydrogen storage alloys were prepared with simple ball-mill method, and their hydrogen storage behaviors were characterized and compared with bare alloys. The results showed that the oxygen resistance of the graphite-coated materials increased, while the hydrogen storage kinetics decreased significantly. For the Ni-coated materials, oxygen resistance was noticeably improved and excellent oxygen resistance was achieved with sufficient Ni loading, while the hydrogen storage capacity and kinetics were also maintained or even improved. Our results show that the elemental coating method is an effective method to improve the oxygen resistance of hydrogen storage alloys, which brings about new insights into the design of these materials.

The Influence of Acetone on the Kinetics of Water Electrolysis Examined at Polycrystalline Pt Electrode in Alkaline Solution

This study investigated the impact of acetone on the electrochemical behavior of polycrystalline platinum electrodes in 0.1 M NaOH solution, with respect to the kinetics of hydrogen and oxygen evolution reactions (HER and OER) and indirectly to the underpotential deposition of hydrogen (UPDH). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to analyze these processes for acetone concentrations ranging from 1.0 × 10−6 to 1.0 × 10−3 M. The addition of (CH3)2C=O enhanced the catalytic efficiency of alkaline water splitting, which was believed to be a result of a significant reduction in the surface tension phenomenon (due to mutual interaction of acetone and water molecules), thus considerably facilitating hydrogen bubble detachment from the Pt electrode. Key findings in this work are described with respect to facilitation of both the HER and the OER reactions’ kinetics by the presence of acetone (also undergoing Pt electroreduction over the potential range for UPDH) in the working solution, without an electrode surface poisoning effect. The latter implies significant opportunities for traces of organic additives into alkaline electrolyte to improve the industrial alkaline water electrolysis process.

A simple predictive three-step chemical model for gaseous stoichiometric hydrogen–oxygen detonation quenching

Two types of three-step chain-branching kinetics for gaseous hydrogen–oxygen detonation quenching are proposed. The reaction rates dependency on density and pressure, as well as the change in molecular weight are included and fitted to results of detailed chemistry not only along the Hugoniot curve but also behind transverse waves. The trend of induction and reaction times and reduced activation energy of zero-dimensional constant pressure combustion process as well as the induction, reaction lengths, and peak thermicity of the ZND model are focused on in the calibration procedure. One model (3SM-I) is designed to model the ideal detonation whereas the other (3SM-N) focuses on the Dn−κ curve during calibration, i.e. the detonation velocity-mean front curvature curves, aiming to capture the non-idealities. The predictive ability using the proposed models is evaluated in a detonation transmission configuration, a layer of ▪ mixture being confined by N2, in determining the critical height, reactive layer height at which detonation transmission is not possible. Both approaches get closer to the critical height from detailed chemistry. With the present set of model parameters, 3SM-I is better than 3SM-N for prediction of critical height. Moreover, borrowing analytical ignition criteria and wave hierarchy approach, the comparison of various chemical models that are able to recover the critical height suggests that the slope of the Dn−κ curve, linked with the chemical response to losses, is the first key parameter for the critical height determination. In addition, the dynamics of the extinction near criticality such as appearance of transverse detonation and quenching distance from 3SM-I are in very good agreement with that of detailed chemistry due to better estimation of the chemical features along the Hugoniot curve and behind transverse waves. The present study provides a guideline to get simplified chemical models from detailed chemistry for predictive simulations.Novelty and significance statementThe novelty of research is two-fold. The first is to provide general guideline to get simplified models from detailed chemistry for the simulation of detonation extinction with improved predictive ability. The tested configuration was that of a stoichiometric hydrogen–oxygen mixture semi-confined by nitrogen. The evolution of the induction, reaction times, and the maximum thermicity were used as fitting targets for our 3-step model. Furthermore, they were evaluated not only at the post-shock states along the Hugoniot curve, but also behind the transverse waves, keystones of the cellular structure. Second, borrowing analytical ignition criteria and wave hierarchy approach, the comparison of different chemical models that were able to recover the critical height suggested that the slope of the normal velocity–curvature curve was the first key parameter for the critical height determination. Moreover, the dynamics of extinction near criticality, and quenching distance depended on the reaction rate dependency on density and pressure.

First-principles calculation to investigate phase transition and associated changes in electronic, excitonic, and optical behavior of RbMgH3 perovskite polymorphs

Motivated by recent experimental and theoretical research on the ability to store and release hydrogen from a hydride perovskite with a large ionic character called RbMgH3, we conducted a study using density functional theory (DFT) to investigate the optoelectronic behavior of RbMgH3 in both Cubic and Hexagonal structures, as well as its phase transition.Our findings reveal that RbMgH3 exhibits an indirect band gap of 2.41 eV in the Hexagonal phase and a direct band gap of 2.15 eV in the Cubic phase. Additionally, we calculated the Gibbs energy to predict the occurrence of the phase transition. It was determined that RbMgH3 undergoes a structural transformation from Cubic to Hexagonal at a pressure of 1.78 GPa. This transition has the potential to enhance the storage kinetics of hydrogen, making RbMgH3 suitable for various applications.

Ethynyl Radical Hydrogen Abstraction Energetics and Kinetics Utilizing High-Level Theory.

The ethynyl radical, C2H, is found in a variety of different environments ranging from interstellar space and planetary atmospheres to playing an important role in the combustion of various alkynes under fuel-rich conditions. Hydrogen-atom abstraction reactions are common for the ethynyl radical in these contrasting environments. In this study, the C2H + HX → C2H2 + X, where HX = HNCO, trans-HONO, cis-HONO, C2H4, and CH3OH, reactions have been investigated at rigorously high levels of theory, including CCSD(T)-F12a/cc-pVTZ-F12. For the stationary points thus located, much higher levels of theory have been used, with basis sets as large as aug-cc-pV5Z and methods up to CCSDT(Q), and core correlation was also included. These molecules were chosen because they can be found in either interstellar or combustion environments. Various additive energy corrections have been included to converge the relative enthalpies of the stationary points to subchemical accuracy (≤0.5 kcal mol-1). Barriers predicted here (2.19 kcal mol-1 for the HNCO reaction and 0.47 kcal mol-1 for C2H4) are significantly lower than previous predictions. Reliable kinetics were acquired over a wide range of temperatures (50-5000 K), which may be useful for future experimental studies of these reactions.

Effect of Co content on electrochemical hydrogen kinetics properties of single-phase BCC-type MgAlTiCoxNi high entropy alloys used as a negative electrode in basic and acidic electrolyte

In this report, the effect of Co content on the electrochemical hydrogen storage reaction kinetic of MgAlTiCoxNi (x = 1, 1.5 and 2) High Entropy Alloys (HEAs) as negative electrodes under basic (6 M KOH) and acidic (1 M H2SO4) electrolyte was studied. Empirical thermodynamic parameters were used to predict the formation of HEAs. The alloys were obtained after 8 h of high-energy ball-milling. The structural analysis showed the formation of a BCC structure and a reduction of the unit lattice with increasing Co content. At high temperatures, the structure changes from BCC-type to B2-type. The morphology and surface area of the MgAlTiCoNi, MgAlTiCo1.5Ni, and MgAlTiCo2Ni alloy powders are very similar. Electrochemical measurements show that alloys exposed to acidic solutions as negative electrodes exhibit higher discharge capacity and better electrochemical hydrogen storage kinetics properties. The increase in Co content in the alloys in both basic and acidic solutions reduced the discharge capacity. Furthermore, a high Co content in the electrodes exposed to an acidic electrolyte reduces the anticorrosion properties of the alloy. The MgAlTiCoNi HEA electrode achieved the best electrochemical performance with a discharge capacity of 465 mAh/g in an acidic electrolyte after a short galvanic charge (60 min). The concentration of Co in the HEAs revealed a direct relationship with the hydrogen diffusion rate, while the lattice parameter is associated with the discharge capacity.

Effect of excess air ratio and ignition timing on the combustion and emission characteristics of the ammonia-hydrogen Wankel rotary engine

As a hydrogen carrier, ammonia can suppress knock and enhance thermal efficiency of the hydrogen-fueled Wankel rotary engine (WRE), and achieve zero carbon emissions. This research established a three-dimensional fluid dynamics model coupled with detailed reaction kinetics of ammonia and hydrogen and verified it based on experiments. Incorporating 10% volume fraction of ammonia into the hydrogen-fueled WRE eliminates knock and decreases the excess air ratio (λ) from 1.8 to 1.4, effectively improving the indicated mean effective pressure (IMEP). The results indicate that when λ exceeds 1.4, flame propagation accelerates with higher concentration of the mixture. This enhances peak in-cylinder pressure and heat release rate, but it results higher NOx emissions. As λ varies from 1.8 to 1.4, NOx emission levels rise by 47.4%. At λ ≤ 1.2, the rapid flame propagation leads to short combustion duration, diminishing the power output. At this stage, the NO formation is dominated by H radicals, and the NOx production reaches its minimum value at λ of 1.0. In summary, the ammonia-hydrogen WRE achieves optimal performance at λ of 1.4 and ignition timing of −5 °CA after top dead center, the indicated thermal efficiency reaches 36.9% and the IMEP achieves 0.683 MPa.

Enhanced reversible hydrogen storage in LiBH4-Mg(BH4)2 composite with V2C-Mxene

Solid-state borohydride was one of the promising solid-state hydrogen storage materials, but the reversibility and kinetics of hydrogen de/absorption in borohydrides still need improvement. In this study, a new strategy of repeated ball milling and melting was first used to produce LiBH4-Mg(BH4)2 nanocomposites (LMBH) effectively loaded on V2C Mxene as the matrix. The LMBH-20V2C composite released 8.1 wt% of hydrogen at 350 °C while un-doped LMBH only released 4.3 wt% under the same conditions. Two-step dehydrogenation with lower activation energies (118.2 and 125.2 kJ/mol) were found in LMBH-V2C composites. More than 5 wt% reversible hydrogen capacity was discovered in LMBH-V2C samples, which was 138 % more than that of un-doped LMBH. The nano-sized LMBH-V2C composite retained unaggregated, and VH2.01 species was formed during cycling as an active “hydrogen pump”. The outstanding hydrogen storage performance of LMBH-V2C composites could be attributed to the combination of nano-sizing and catalysis from V2C Mxene.