Hydrogen Flux Research Articles

The effect of helium reionization on the Ly α forest hydrogen flux statistics

ABSTRACT We assess the impact of quasi-stellar objects (QSOs) on the high-redshift ($z\gt 4$) intergalactic medium using Monte Carlo realizations of QSO populations and the He $\rm \scriptstyle III$ regions they generate, applied to the Sherwood–Relics simulations, allowing for uncertainties in the QSO luminosity function, its evolution, and QSO spectra and ages. While QSO luminosity functions based on optical–infrared selection are unable to reproduce the broadening H $\rm \scriptstyle I$ Ly $\alpha$ optical depth distributions at $z\gt 5$, much broader distributions are found for the higher numbers of QSOs based on X-ray selection, suggesting a large QSO contribution to the ultraviolet background at $z\gt 5$ may offer an alternative to late reionization models to account for the broad H $\rm \scriptstyle I$ Ly $\alpha$ optical depth distributions. Realizations using QSOs based on the higher QSO counts also much better recover the measured pixel flux autocorrelation function at $z\gt 5$. The He $\rm \scriptstyle III$ regions from QSO sources according to both types of luminosity function suppress the pixel flux power spectrum on small scales, $k\gt 0.02\, \mathrm{s\, km^{-1}}$, while enhancing it on larger, both by amounts of up to tens of per cent at $z\gt 4$, with the magnitude increasing with the intergalactic He $\rm \scriptstyle III$ filling factor and the boost in temperature within the He $\rm \scriptstyle III$ regions.

The Effect of Grain Boundary Misorientation on Hydrogen Flux Using a Phase‐Field‐Based Diffusion and Trapping Model

Understanding hydrogen–grain boundary (GB) interactions is critical to the analysis of hydrogen embrittlement in metals. This work presents a mesoscale fully kinetic model to investigate the effect of GB misorientation on hydrogen diffusion and trapping using phase‐field‐based representative volume elements (RVEs). The flux equation consists of three terms: a diffusive term and two terms for high and low angle grain boundary (H/LAGB) trapping. Uptake simulations show that decreasing the grain size results in higher hydrogen content due to increasing the GB density. Permeation simulations show that GBs are high‐flux paths due to their higher enrichment with hydrogen. Since HAGBs have higher enrichment than LAGBs, due to their higher trap‐binding energy, they generally have the highest hydrogen flux. Nevertheless, the flux shows a convoluted behavior as it depends on the local concentration, alignment of GB with external concentration gradient as well as the GB network connectivity. Finally, decreasing the grain size resulted in a larger break‐through time and a larger steady‐state exit flux.

Application of SECM to detect a local electrolyte acidification due to the hydrogen flux desorption from a cathodic charged stainless steel

This work aims to estimate local pH variations of a hydrogen charged sample using Scanning ElectroChemical Microscopy (SECM). For that purpose, the microelectrode is polarized in the cathodic domain, where the proton reduction takes place. An initial calibration suggests that cathodic current of the platinum tip is sensitive to pH variations. Then, this system was applied near the surface of stainless steel previously charged with hydrogen. Coupling this result with the analysis of the uncharged samples at two different pH, it appears that hydrogen desorption induces a local acidification which could explain the increase in dissolution kinetics after hydrogen absorption, which has been reported in many studies.

Measurement of core electron binding energies of silver nanoparticles and their modeling with electron propagator calculations of silver clusters

Silver nanoparticles were synthesized by ionic exchange with zeolites and further reduction with hydrogen flux. Core electron binding energies were determined by X-ray photoelectron spectroscopy at different times of the reduction process. Electron propagator calculations of core electron binding energies were performed including scalar relativistic effects using effective core potentials and zero order regular approximation. Theoretical results were compared to the experiment to get insight into the origin of the experimental signals for carbon, oxygen, silicon, aluminum and silver. Small model molecules and zeolite fragments were used for the calculation of core electron binding energies. It is evidenced that although binding energies tend to converge, fluctuations of more than 1 eV are found for non-symmetric structures in neutral and cationic silver clusters. Detailed analysis shows that these fluctuations originate on the different coordination numbers of ionized silver atoms and charge fluctuations.

Ionic conductivity and hydrogen permeability of microporous polysulfone membranes grafted by acrylic acid

Energy losses and purity of product gases in alkaline water electrolysis strongly depend on properties of a separator positioned between the electrodes. This paper reports on heterogeneous separators based on microporous polysulfone membranes modified by graft co-polymerization of acrylic acid. After neutralization with KOH, the pores of the modified membranes were filled with potassium polyacrylate, a superabsorbent material forming hydrogel upon intake of an aqueous electrolyte. Under electrolysis conditions of 50 °C and atmospheric pressure, increasing amount of hydrogel in pores suppresses hydrogen permeability without apparent reduction of ionic conductivity. We have identified the product of ionic resistance and hydrogen flux as a suitable parameter to compare performance of separators of various thickness. In terms of this parameter, present separators surpass the performance of Zirfon™ Perl UTP 500 tested under the identical conditions. Ex-situ aging test in 30 wt% KOH at 60 °C has revealed preservation of high wettability for up to 1340 h.

Ejection of molten tin in the presence of a hydrogen plasma

One of the significant obstacles left if the development of a fusion power plant is the development of Plasma Facing Components (PFCs) that can withstand the large heat and particle flux incident on the first wall and divertor region. As solid PFCs struggle with microstructure growth, sputtering and melting, liquid metals have been a popular potential replacement. Liquid metal's use as a PFC has been increasing due to its ability to self-repair damage as well as pump lost fuel and waste particles to create a low recycling edge. Currently, tin, lithium and lithium eutectics are the commonly considered liquid metals for use as a fusion PFC. It is therefore important to research the Plasma Material Interaction (PMI) between a hydrogen plasma and the liquid metal PFC candidates. This work, conducted at the Center for Plasma Material Interaction (CPMI), investigated how a molten tin surface reacts when exposed to a hydrogen plasma, building off observations by ASML of particles being ejected from a molten tin surface in the presence of a hydrogen plasma. With the ejection of tin affecting ASML's systems as well, since ejected tin can travel around their systems and cause contamination of equipment or wafers that can be destructive to the lithography process. So, for this work, molten tin was exposed to a hydrogen plasma, of varying electron densities and temperatures, and any ejected particles were collected on a witness plate to determine the particle sizes, angular distribution and mass flux. This work found the ejected tin particles range in size from 10′s ofnms to 10′s of microns and that the mass flux of tin from the molten surface is in the 10′s of mgm2*s, increasing with increased atomic hydrogen flux to the molten tin surface. Showing macroscopic amounts of molten tin are ejected in the presence of a hydrogen plasma, therefore showing tin may not be a suitable fusion PFC material.

Comparative analysis of hydrogen production from ammonia decomposition in membrane and packed bed reactors using diluted NH3 streams

Ammonia decomposition is a key technology for its use as a hydrogen carrier and in the recovery of H2 from waste streams containing ammonia. The coupling of the catalytic decomposition of ammonia with an H2 permeoselective membrane improves the process by mitigating thermodynamic constraints and producing a flux of high-purity hydrogen, not requiring further separation/purification. In this study, we compare the behaviour of an eggshell catalyst 1.3 wt % Ru/Al2O3 catalyst in a packed bed reactor (PBR) and a packed bed membrane reactor (PBMR) using an ultrathin Pd membrane (3.4 μm). Tests were made at 11 bar(a) with a weight hourly space velocity of NH3 in the 0.560–1.68 Lꞏg−1ꞏh−1 range and temperatures of 350–400 °C, e.g. milder conditions than the conventional ammonia cracking catalysts. Under optimised conditions (0.56 Lꞏg−1ꞏh−1, 400 °C, sweep gas flow 0.55 L min−1), the PBMR shows excellent performance, achieving NH3 conversion, H2 productivity and recovery factor of 99%, 47 mmolH2·gRu−1·min−1, and 94.9%, respectively. PBMR increases by ∼50% the conversion rate compared to PBR. Without a sweep gas, PBMR performances are lower, even still higher than in PBR. For the first time, superior or comparable performance was demonstrated compared to similar systems using pure ammonia in terms of conversion, hydrogen recovery, H2 productivity, and Ru utilisation. These results can be further enhanced with vacuum systems to convert diluted ammonia streams into high-purity hydrogen for small-scale distributed systems and can be extended to other reactions.

Modeling of hydrogen separation through Pd membrane with vacuum pressure using Taguchi and machine learning methods

The performance of hydrogen purification using palladium (Pd) membrane is analyzed by Taguchi and machine learning (ML) methods. Three system factors are considered: the feed gas mixture composition (i.e., H2, CO2, and H2O), retentate-side total pressure, and vacuum pressure. The Taguchi method designs the experimental cases based on the constructed orthogonal array. In addition, the hydrogen flux is investigated by the analyses of variance (ANOVA) and artificial neural networks (ANN) methods. The results show that the effects of the considered factors on the hydrogen permeation performance can be ranked as feed gas mixture composition > retentate-side total pressure > vacuum pressure. Both the retentate-side pressure and vacuum pressure present a positive effect on hydrogen flux. The average relative error of hydrogen flux between the experimental results and predictions by ANN is 2.1%, which proves that the ANN method is an effective technique for predicting the hydrogen flux through the Pd membrane. The ML classification test is then performed for hydrogen purity by three machine learning methods: decision tree (DT), support vector machine (SVM), and ensemble method. Among the various classification models, the Quadratic SVM model exhibits a relatively high average training accuracy but shows overfitting. However, the bagged model of the ensemble method can achieve an impressive training accuracy of 91.4% and a prediction accuracy of 85.7%.

Measurements of atomic hydrogen recombination coefficients and the reduction of Al2O3 using a heat flux sensor

The knowledge of atomic hydrogen recombination coefficient (γ) is essential for plasma simulations to calculate accurate atomic hydrogen fluxes. However, γ is a complex material property, and it is affected by the experimental conditions under which it is measured. Therefore, values of γ can differ even by a few orders of magnitude for the same material. In this paper, we demonstrate measurements of hydrogen recombination coefficients at room temperature using an in-house-built catalytic sensor for two selected materials: aluminum Al-5083 (alimex) and stainless steel 316 l, under the load of low-temperature H2 plasma with an admixture of H2O or N2 gases. The plasma settings were carefully chosen to mimic properties of the so-called extreme ultraviolet-generated plasma.1 The measured γ values agree well with literature data obtained for similar plasma conditions and show a correlation with ion energy. Additionally, we show a novel application of the sensor for indirect measurements of the reduction of oxidized surfaces as a function of ion dose. In these experiments, a correlation between reduction time and background water pressure is observed.

Investigation of Hydrogen Flux Influence on InGaP Layer and Device Uniformity

In this study, we conduct a comprehensive examination of the influence of hydrogen (H2) carrier gas flux on the uniformity of epitaxial layers, specifically focusing on the InGaP single layer and the full structure of the InGaP/GaAs heterojunction bipolar transistor (HBT). The results show that an elevated flux of H2 carrier gas markedly facilitates the stabilization of layer uniformity. Optimal uniformity in epitaxial wafers is achievable at a suitable carrier gas flux. Furthermore, this study reveals a significant correlation between the uniformity of the InGaP single layer and the overall uniformity of HBT structures, indicating a consequential interdependence.

Hydrogen transport through Mo2C/PdCu composite membranes

First-principle calculations have been adopted to systematically investigate the adsorption and dissociation of H2 on Mo2C (100) and (001) surfaces, as well as the fluxes of hydrogen dissociative adsorption on the Mo2C surfaces and the hydrogen across the Mo2C(100)/PdCu(110) and Mo2C(001)/PdCu(110) interfaces. It is observed that the adsorption and dissociation of H2 as well as the hydrogen flux on the Mo2C (100) surfaces are energetically more favorable than on the Mo2C (001) surfaces. Calculations also reveal that the hydrogen flux across the Mo2C(100)/PdCu(110) and Mo2C(001)/PdCu(110) interfaces is one and six order of magnitude greater than the hydrogen desorption flux on the permeation side of PdCu, respectively. In other words, the hydrogen diffusion in BCC PdCu bulk and hydrogen desorption are the dominant steps of hydrogen transport through Mo2C/PdCu composite membranes, rather than the hydrogen diffusion across the Mo2C/PdCu interfaces. The calculational findings are consistent with the similar experimental observations in the literature, and provide a profound understanding regarding the hydrogen transport across Mo2C-coated PdCu membrane.

Enhancement for hydrogen transport properties by tailoring lattice matching in V-Pd-Fe ternary alloy membrane

V-based alloy membranes have huge potential for hydrogen separation and purification due to their higher hydrogen permeability, but suffer from hydrogen embrittlement. To address this matter, Pd and Fe have been chosen as alloying additions in V-based membranes to inhibit hydrogen embrittlement and maintain high hydrogen permeation performance based on the lattice-matching strategy. The phase structure, composition, microstructure and hydrogen permeation properties of V-Pd-Fe ternary alloy are investigated systematically, and the V-Fe and V-Pd binary alloys are presented for comparison. The results show that the prepared V-Pd-Fe ternary can match almost perfectly with pure V in lattice constants. Attributing to the lattice-matching strategy, the V-Pd-Fe ternary alloy exhibits more excellent hydrogen permeable properties than that of V-Fe and V-Pd binary alloys. The reduction of hydrogen embrittlement is ascribed to the lower hydrogen solubility that induced by the lattice distortion and electronegativity of Fe and Pd. Meanwhile, the manipulated lattice constant that parallel to pure V maintains high hydrogen permeation performance. Additionally, the designed ternary V87.8Pd8Fe4.2 alloy exhibits exceptional long-term hydrogen permeation stability at 573 and 623 K, and hydrogen flux gradually decreases at 673 and 723 K is observed due to the interdiffusion between Pd film and V87.8Pd8Fe4.2 substrate and defects in the Pd coating. This study offers new scenario and method for optimized hydrogen permeable properties and restrains hydrogen embrittlement in the alloy membrane.

Critical heat flux of liquid hydrogen, liquid methane, and liquid oxygen: a review of available data and predictive tools

Available experimental data dealing with critical heat flux (CHF) of liquid hydrogen (LH2), liquid methane (LCH4), and liquid oxygen (LO2) in pool and flow boiling are compiled. The compiled data are compared with widely used correlations. Experimental pool boiling CHF data for the aforementioned cryogens are scarce. Based on only 25 data points found in five independent sources, the correlation of Sun and Lienhard (1970) is recommended for predicting the pool CHF of LH2. Only two experiments with useful CHF data for the pool boiling of LCH4 could be found. Four different correlations including the correlation of Lurie and Noyes (1964) can predict the pool boiling CHF of LCH4 within a factor of two for more than 70% of the data. Furthermore, based on the 19 data points taken from only two available sources, the correlation of Sun and Lienhard (1970) is recommended for the prediction of pool CHF of LO2. Flow boiling CHF data for LH2 could be found in seven experimental studies, five of them from the same source. Based on the 91 data points, it is suggested that the correlation of Katto and Ohno (1984) be used to predict the flow CHF of LH2. No useful data could be found for flow boiling CHF of LCH4 or LO2. The available databases for flow boiling of LCH4 and LO2 are generally deficient in all boiling regimes. This deficiency is particularly serious with respect to flow boiling.

In-situ hydrogenated V2O5 thin films: Study of the structural dynamics and their behavior as Li-ion batteries cathode

This investigation focuses on a one-step preparation method to produce hydrogenated V2O5 thin films by controlling the atmosphere of the DC reactive magnetron sputtering process. An increasing hydrogen flux during the film deposition promotes the formation of defects such as oxygen vacancies and hydroxyl sites in the oxide matrix. The hydrogenated samples were tested as cathodes in Li-ion batteries and exhibited lower charge capacities but superior stability to cycling compared to pristine V2O5 film. These results pave the way to prepare hydrogenated transition metal oxide thin films by a simple route without further thermal procedures and affordable conditions.

Performance assessment of a novel porous catalytic reactor with a hydrogen-selective membrane for enhanced methane dry reforming process – CFD investigation

This manuscript offers a thorough examination of the efficiency of a reactor-assisted membrane system for the production of syngas through a process of methane dry reforming (DRM). The proposed strategy aims to bring attention to the optimization of the DRM and reverse water gas shift (RWGS) reactions, towards achieving increased conversions of methane and carbon dioxide, as well as increased purity in syngas production. This goal will be accomplished by integrating a selectively permeable membrane within the central region of the tubular catalytic porous bed reactor. The primary objective of the current research is to quantitatively assess the impact of operational parameters on both the hydrogen flux and concentration distribution of the various components residing in the reactor. This study highlights the impact of inlet feed pressure on hydrogen flux. It is found that an elevation in the inlet feed pressure from 1 to 4 bar yields an average increase in hydrogen flux from 2.60 to 4.21 kg/(m2.h), particularly when the inlet feed pressure is set at 2 bar. However, a subsequent increase to attain a pressure of 4 bar results in a decline in hydrogen flux to a rate of 2.78 kg/(m2.h). Moreover, increasing the inlet feed temperature from 900 to 1100 K leads to a substantial augmentation in the average hydrogen flux, from 7.08 to 8.56 kg/(m2.h), while maintaining a reactor wall temperature of 1000 K. As another finding, a molar ratio of CH4/CO2 of 1 leads to the greatest mean hydrogen flux of 4.73 kg/(m2.h) across the membrane interface. The current research work could provide useful tips/guidelines for efficient reactor design and optimization; it also enhances comprehension of reactor-assisted membrane systems in the context of syngas production.

Energy spectra of energetic neutral hydrogen backscattered and sputtered from the lunar regolith by the solar wind

Context. The solar wind impinging on the lunar surface results in the emission of energetic neutral atoms. This particle population is one of the sources of the lunar exosphere. Aims. We present a semi-empirical model to describe the energy spectra of the neutral emitted atoms. Methods. We used data from the Advanced Small Analyzer for Neutrals (ASAN) on board the Yutu-2 rover of the Chang’E-4 mission to calculate high-resolution average energy spectra of the energetic neutral hydrogen flux from the surface. We then constructed a semi-empirical model to describe these spectra. Results. Excellent agreement between the model and the observed energetic neutral hydrogen data was achieved. The model is also suitable for describing heavier neutral species emitted from the surface. Conclusions. A semi-analytical model describing the energy spectrum of energetic neutral atoms emitted from the lunar surface has been developed and validated by data obtained from the lunar surface.

Low-temperature hydrogen production and consumption in partially-hydrated peridotites in Oman: implications for stimulated geological hydrogen production

The Samail Ophiolite in Oman, the largest exposed body of ultramafic rocks at the Earth’s surface, produces a continuous flux of hydrogen through low-temperature water/rock reactions. In turn, the scale of the subsurface microbial biosphere is sufficient to consume much of this hydrogen, except where H2 is delivered to surface seeps via faults. By integrating data from recent investigations into the alteration history of the peridotites, groundwater dynamics, and the serpentinite-hosted microbial communities, we identify feasible subsurface conditions for a pilot demonstration of stimulated geological hydrogen production. A simple technoeconomic analysis shows that the stimulation methods to be used must increase the rate of net hydrogen production at least 10,000-fold compared to the estimated natural rate to economically produce hydrogen from engineered water/rock reactions in the peridotite formations. It may be possible to meet this challenge within the upper 1–2 km, given the projected availability of reactive Fe(II)-bearing phases and the lower drilling costs associated with shallower operations. Achieving ≥10,000-fold increases in the H2 production rate will require a combination of stimuli. It will likely be necessary to increase the density of fracturing in the reaction volume by at least two orders of magnitude. Then, the H2-production rates must also be increased by another two orders of magnitude by increasing the water/rock ratio and modifying the chemistry of the injected fluids to optimize formation of Fe(III)-bearing secondary phases. These fluid modifications must be designed to simultaneously minimize microbial consumption of H2 within the stimulation volume. In contrast, preserving the high potentials for biological H2 consumption in the shallow groundwaters replete with oxidants such as nitrate, sulfate and dissolved inorganic carbon will reduce the potential for any inadvertent leaks of hydrogen to the atmosphere, where it acts as an indirect greenhouse gas.

Quantifying Uncertainty in Sustainable Biomass and Production of Biotic Carbon in Enceladus' Notional Methanogenic Biosphere

AbstractBeneath Enceladus' ice crust lies an ocean which might host habitable conditions. Here, the scale and productivity of a notional Enceladean methanogenic biosphere are computed as a function of the core‐to‐ocean flux of hydrogen and the ratio between abiotic and biotic methane in Enceladus' space plume. Habitats with an ocean‐top pH range of 8–9 have up to 40%–60% probability of being energy‐limited. Those at pH > 9 are increasingly uninhabitable, and those <8.5 are increasingly likely to host exponential growth, possibly leading to compositional inconsistencies between the ocean and Cassini gas observations. In those cases, energy‐based habitability models cannot infer an inhabited Enceladus consistent with both Earth life and Cassini measurements without including additional microbial growth limiters such as nutrient limitation, toxicity, or spatial constraints. If methanogens are isolated to a 350 K seafloor habitat and consume 10 mol s−1 of H2, the most probable biomass is 103, 103.7 kg C with ocean‐top pH 8,9, respectively. Biomass production consistent with space plume fluxes is 104–106 kgC yr−1—milligrams of cellular carbon per kilogram of H2O ejected—but requires that >50% of the space plume methane is biotic. Alternative scenarios are presented, and biomass is generally lower when habitat temperature is higher. Ocean biomass density cannot yet be reliably estimated owing to uncertainties in the scale and physicochemical properties of Enceladus' putative habitats. Evaluating abiotic to biotic ratios in plume methane and organic material could help identify false negative results from life detection missions and constrain the scale of an underlying biosphere.

The behavior of helium bubble evolution under neutron irradiation in different tungsten surfaces

Tungsten, as a kind of material for the plasma-facing wall in fusion reactor and tokamak, is subjected to irradiation by the high-energy neutron and the high fluxes of hydrogen and helium plasmas. Especially, in the presence of helium (He) bubbles, neutron irradiation can significantly exacerbate the deterioration of the material's mechanical properties. However, due to experimental limitations, the evolution of He bubbles in tungsten irradiated by neutrons and the underlying mechanisms remain unclear. Here, molecular dynamics (MD) simulation is used to investigate the behavior of He bubbles in tungsten with different crystal surfaces irradiated by neutrons. We observed the complete evolutionary process of the He bubble, i.e. standing, expanding, and bursting. During this process, high-energy neutron transfers energy to atoms within the He bubble through cascade collision, leading to a rapid increase in energy and pressure of the He bubble, and then the rapid expansion of the He bubble makes the pressure rapidly released, ultimately leading to the rupture of the helium bubble. Furthermore, we also explore the evolution of the He bubble under varying conditions (such as temperature, neutron energy, and He/vacancy ratio) within the same crystal surface. We found that at lower temperatures and neutron energy with a higher He/vacancy ratio, it tends to form pinhole-like channels to release helium atoms, resulting in the He bubble bursting. On the contrary, it tends to form a hill-like expansion to spurt helium atoms out, leading to the bubble bursting. Additionally, it was found that the direction and time of He bubble rupture varied under different crystal surfaces. He bubbles under the (112) surface burst the slowest with excellent corrosion resistance. These findings provide new insights into the behavior of irradiation resistance of fusion reactor materials under extreme conditions and offer significant guidance for the improvement and selection of optimal materials for plasma-facing walls.

Hydrogen Flux Inhibition of Pd-Ru Membranes under Exposure to NH3.

The hydrogen flux inhibition of Pd-Ru membranes under exposure to 1-10% NH3 at 673-773 K was investigated. The Pd-Ru membranes were characterized by XRD, SEM, XPS, and hydrogen permeation tests. The results show that when exposed to 1-10% NH3 at 723 K for 6 h, the hydrogen flux of Pd-Ru membranes sharply decreases by 15-33%, and the decline in hydrogen flux becomes more significant with increasing temperatures. After the removal of 1-10% NH3, 100% recovery of hydrogen flux is observed. XPS results show that nitrogenous species appear on the membrane surface after NH3 exposure, and the hydrogen flux inhibition may be related to the competitive adsorption of nitrogenous species. By comparing the hydrogen flux of Pd-Ru membranes exposed to 10% NH3 with 10% N2, it is indicated that the rapid decrease in hydrogen flux is due to the concentration polarization and competitive adsorption of nitrogenous species. The competitive adsorption effect is attenuated, while the concentration polarization effect becomes more pronounced with increasing temperature.