Hydrogen Atoms Research Articles

Evaluation of hydrogen storage capacity of two-dimensional Sc2N MXene: A DFT study

In this work, the efficiency of hydrogen storage on Sc2N MXenes monolayer is systematically investigated using first-principles calculations. After determining the structural stability of designed monolayer, adsorption sites for the storage of hydrogen atoms (H) and molecules (H2) are identified. The calculated binding energies have indicated that the hydrogen atoms have favorable adsorption at the center or H site of the Sc atoms and hydrogen molecules are found to be the most stable when adsorbed on the top/T site of Sc atoms. The binding energy assessment identified the chemisorption for hydrogen atoms and Kubas-type interactions for H2. To further ascertain the suitability of the Sc2N monolayer for hydrogen storage various analyses including binding energy, partial density of states (PDOS), electron localization function (ELF), Mullikan charge analysis and Hirshfeld charge analysis are conducted. In order to determine the thermal stability of the Sc2N monolayer, desorption temperature with respect to pressure and molecular dynamics study has also been conducted and found the monolayer thermally stable. Desorption isotherms condition with increasing pressure confirms the gravimetric storage uptake. The obtained results have revealed that the hydrogen storage capacity considered monolayer has reached up to 10.8 wt%, which is reasonably high. Hence, the obtained results of hydrogen atom and molecules adsorption have clearly established that Sc2N monolayer is as an exemplary, stable, reliable and efficient medium for hydrogen storage applications.

Restoring the electronic properties of epitaxial graphene on SiC substrate by Ar intercalation

Thermal decomposition of 6H-SiC(0001) under an argon atmosphere is a promising technique to fabricate large-scale epitaxial graphene monolayers for electronic applications. In this manuscript, we report on the intercalation of argon, hydrogen and oxygen atoms underneath a graphene buffer layer (BL) on SiC(0001), involving bond formation between the intercalated agent and Si atoms. Density Functional Theory calculations were performed to investigate the atomic structure, stability and electronic properties of quasi free-standing monolayer graphene and bilayer graphene, accomplished by intercalation. According to our results, as the Ar intercalated atoms saturate the silicon dangling bonds in the upper SiC surface, the BL is completely detached from the substrate and transformed into free-standing graphene. Ar intercalation would be hindered by the concurrent and thermodynamically more spontaneous adsorption of Ar atop the graphene layers, resulting in a pronounced decrease of the process efficiency. High Ar-coverage regimes and low kinetic barriers for Ar intercalation might shift the intercalation/adsorption balance. These factors as well as strategies such as ion implantation could be explored to identify more favorable conditions to experimentally test Ar intercalation as a simple method to achieve control of the electronic properties of the BL and help preserve the unique characteristics of graphene.

Features of the crystal structure and surface of superprotonic conductor caesium hydrogen sulfate phosphate.

The crystal structure of superprotonic conductor caesium hydrogen sulfate phosphate [Cs4(HSO4)3(H2PO4)] have been analyzed using neutron diffraction methods. Additionally, its structure and surface layers have been investigated using atomic force microscopy. From the diffraction data obtained, Fourier syntheses of neutron scattering densities were calculated, and the localization of hydrogen atoms and the parameters of three types of hydrogen bonds in the crystal structure were accurately determined. Correlation of surface characteristics of samples obtained by atomic force microscopy with their crystal structure is shown.

A Type of Chiral C2-Symmetric Arylthiol Catalyst for Highly Enantioselective Anti-Markovnikov Hydroamination.

The development of chiral hydrogen donor catalysts is fundamental in the expansion and innovation of asymmetric organocatalyzed reactions via an enantioselective hydrogen atom transfer (HAT) process. Herein, an unprecedented type of chiral C2-symmetric arylthiol catalysts derived from readily available enantiomeric lactate ester was developed. With these catalysts, an asymmetric anti-Markovnikov alkene hydroamination-cyclization reaction was established, affording a variety of pharmaceutically interesting 3-substituted piperidines with moderate to high enantioselectivity. Results of the designed control experiments and theoretical computation rationalized the origin of stereocontrol and disclosed the spatial effect of the moiety of chiral thiols on the enantioselectivity. We believed the facile synthesis, flexible tunability, and effective enantioselectivity-controlling capability of these catalysts would shed light on the development of versatile chiral HAT catalysts and related asymmetric reactions.

Real-time and highly responsive hydrogen mapping in pure Fe using TiO2 thin films

A hydrogen visualization method with high responsivity and chemical stability under atmospheric corrosion is necessary to inhibit hydrogen embrittlement, which can occur with hydrogen uptake of structural materials. In this study, a highly responsive hydrogen mapping technique for steels was successfully established using a TiO2 thin film and Pd intermediate layer. The color of the TiO2 film on the hydrogen-detection side changes during hydrogen charging on the hydrogen-entry side of the Fe specimen, indicating that the color changes were attributed to the hydrogen uptake of the Fe surface and subsequent introduction of hydrogen atoms to the TiO2 film. Considering the responsivity and visibility, the optimal thickness of the TiO2 film was determined to be 20 nm. As TiO2 is a chemically stable material, the proposed mapping technique can be used to monitor the hydrogen absorbed into metallic materials under outdoor conditions.

Delayed fracture behavior of ultra-high-strength mooring chain steel evaluated by potentiostatic hydrogen-charging combined with SSRT

The influence of hydrogen charging potentials on the hydrogen embrittlement susceptibility of R6 ultra-high strength mooring chain steel was investigated via constant potential hydrogen charging slow strain rate tensile tests combined with thermal desorption analysis. The results reveal that hydrogen charging leads to a 38.94% decrease in elongation, while the impact on tensile strength is relatively minor. Furthermore, the specimens experienced intergranular cracking at the critical potential of −1150 mV, with the size of the brittle region increasing as the negative charging potential becomes more negative. And, hydrogen atoms can cause local embrittlement of materials and increase KAM value.

Zn-Mediated Fragmentation of N-Alkoxyphthalimides Enabling the Synthesis of gem-Difluoroalkenes.

Zn-mediated generation of alkoxyl radicals from N-alkoxyphthalimides emerged as an efficient approach for forming diverse and valuable alkyl radicals through β-scission or a hydrogen atom transfer process. The alkyl radical species can be further trapped by α-trifluoromethyl alkenes to construct a series of gem-difluoroalkenes.

Computational exploration of two-dimensional vacancy-free boridene sheet and its derivatives: high stabilities and the promise for hydrogen evolution reaction

The recent synthesis of a two-dimensional (2D) MBene sheet, referred to as the boridene sheet (Mo4B6Tz), has ignited considerable interest in exploring 2D transition metal borides. Boridene has an ordered arrangement of metal vacancies, which are pivotal to its stability. Employing first-principles calculations, we explored the stable phases, electronic properties and catalytic abilities of boridene with different vacancy concentrations (Vm). Our results demonstrate that Vm significantly influences the cohesive energies of boridene sheets. Phonon spectrum and ab initio molecular dynamics simulations reveal the high stability of the vacancy-free boridene Mo6B6T6 (T = O, -OH), underscoring their potential for experimental realization. Substituting Mo atoms with Nb, Ta, or W enhances the structural stability of boridene sheets, leading to the identification of four stable variants: Nb6B6F6, Ta6B6F6, Ta6B6O6, and W6B6O6. These boridene sheets exhibit metallic behavior, with five structures displaying near-zero Gibbs free energy for hydrogen atom adsorption, indicating their potential as catalysts for the hydrogen evolution reaction. The uncovering of vacancy-free boridenes and their 2D derivatives greatly broadens the scope of the MBene family.

Assessing the global natural orbital functional approximation on model systems with strong correlation.

In the past decade, natural orbital functional (NOF) approximations have emerged as prominent tools for characterizing electron correlation. Despite their effectiveness, these approaches, which rely on natural orbitals and their associated occupation numbers, often require hybridization with other methods to fully account for all correlation effects. Recently, a global NOF (GNOF) has been proposed [Piris, Phys. Rev. Lett. 127, 233001 (2021)] to comprehensively address both dynamic and static correlations. This study evaluates the performance of GNOF on strongly correlated model systems, including comparisons with highly accurate Full Configuration Interaction calculations for hydrogen atom clusters in one, two, and three dimensions. Additionally, the investigation extends to a BeH2 reaction, involving the insertion of a beryllium atom into a hydrogen molecule along a C2v pathway. According to the results obtained using GNOF, consistent behavior is observed across various correlation regions, encompassing a range of occupations and orbital schemes. Furthermore, distinctive features are identified when varying the dimensionality of the system.

Heterogeneous Photocatalytic C(sp2)‒H Activation of Formatefor Hydrocarboxylation of Alkenes.

Light-driven carboxylation offers a promising approach for synthesizing valuable fine chemicals under mild conditions. Here we disclose a heterogeneous photocatalytic strategy of C(sp2)‒H activation of formate for hydrocarboxylation of alkenes over zinc indium sulfide (ZnIn2S4) under visible light. This protocol functions well with a variety of substituted styrenes with good to excellent yields; it also works for unactivated alkenes albeit with lower yields. Mechanistic studies confirm the existence of CO2•- as a key intermediate. It was found that C(sp2)‒H activation of formate is induced by S• species on the surface of ZnIn2S4 via hydrogen atom transfer (HAT) instead of a photogenerated hole oxidation mechanism. Moreover, both cleavage of the C(sp2)‒H of HCOO- and formation of a benzylic anion were found to be involved in the rate-determining step for the hydrocarboxylation of styrene.

Metal-organic frameworks derived low-cost Cu-doped Co3O4 for efficient reduction of ultra-low nitrate concentrations to ammonia

The electrochemical reduction of nitrate to ammonia represents a potential approach for the valorization of waste, offering the dual benefit of mitigating various environmental concerns and concurrently yielding the valuable product of ammonia. However, on the way to its further application, the lacking of low-cost and efficient electrocatalysts under low nitrate concentrations is still one pressing issue because of the intense hydrogen evolution reaction (HER) competition and many by-products. Herein, metal–organic frameworks (MOF) derived low-cost Cu-Co3O4/NF exhibits excellent electrocatalytic activity in the low nitrate concentrations (2 mmol/L), attaining the ammonia yield rate of 0.076 mmol h−1 cm−2 and 92.4 % Faradic efficiency at −0.53 V vs. RHE. The combined results of In-situ FTIR and theoretical calculation reveal the atomic hydrogen reduction pathway, decrease in free energy of intermediate reactions and inhibition of HER of Cu-Co3O4/NF. This work introduces one economical, efficient and simple strategy and further demonstrates the superior effect of MOF derivatives in fascinating low nitrate concentration reduction to ammonia.

Hydrogen‐Bond‐Mediated Formation of C−N or C=N Bond during Photocatalytic Reductive Coupling Reaction over CdS Nanosheets

AbstractReductive amination of carbonyl compounds and nitro compounds represents a straightforward way to attain imines or secondary amines, but it is difficult to control the product selectivity. Herein, we report the selective formation of C−N or C=N bond readily manipulated through a solvent‐induced hydrogen bond bridge, facilitating the swift photocatalytic reductive coupling process. The reductive‐coupling of nitro compounds with carbonyl compounds using formic acid and sodium formate as the hydrogen donors over CdS nanosheets selectively generates imines with C=N bonds in acetonitrile solvent; while taking methanol as solvent, the C=N bonds are readily hydrogenated to the C−N bonds via hydrogen‐bonding activation. Experimental and theoretical study reveals that the building of the hydrogen‐bond bridge between the hydroxyl groups in methanol and the N atoms of the C=N motifs in imines facilitates the transfer of hydrogen atoms from CdS surface to the N atoms in imines upon illumination, resulting in the rapid hydrogenation of the C=N bonds to give rise to the secondary amines with C−N bonds. Our method provides a simple way to control product selectivity by altering the solvents in photocatalytic organic transformations.

MHONGOOSE: A MeerKAT nearby galaxy survey

The MHONGOOSE (MeerKAT Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen ( gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low column densities. The column density sensitivity (3sigma over 16 ranges from $ $ cm$^ $ at $90''$ resolution to $ $ cm$^ $ at the highest resolution of $7''$. The mass sensitivity ($3 over 50 is $ at a distance of 10 Mpc (the median distance of the sample galaxies). The velocity resolution of the data is 1.4 One of the main science goals of the survey is the detection of cold accreting gas in the outskirts of the sample galaxies. The sample was selected to cover a range in masses from $10^7$ to almost in order to optimally sample possible accretion scenarios and environments. The distance to the sample galaxies ranges from 3 to 23 Mpc. In this paper, we present the sample selection, survey design, and observation and reduction procedures. We compared the integrated fluxes based on the MeerKAT data with those derived from single-dish measurement and find good agreement, indicating that our MeerKAT observations are recovering all flux. We present moment maps of the entire sample based on the first ten percent of the survey data, and find that a comparison of the zeroth- and second-moment values shows a clear separation in the physical properties of the between areas with star formation and areas without related to the formation of a cold neutral medium. Finally, we give an overview of the companion and satellite galaxies in the 30 fields, five of which have not previously been cataloged. We find a clear relation between the number of companion galaxies and the mass of the main target galaxy.

Strong damped Lyman-α absorption in young star-forming galaxies at redshifts 9 to 11.

Primordial neutral atomic gas, mostly composed of hydrogen, is the raw material for star formation in galaxies. However, there are few direct constraints on the amount of neutral atomic hydrogen (Hi) in galaxies at early cosmic times. We analyzed James Webb Space Telescope (JWST) near-infrared spectroscopy of distant galaxies, at redshifts ≳8. From a sample of 12 galaxies, we identified three that show strong damped Lyman-α absorption due to Hi in their local surroundings. The galaxies are located at spectroscopic redshifts of 8.8, 10.2, and 11.4, corresponding to 400 to 600 million years after the Big Bang. They have Hi column densities ≳1022 cm-2, which is an order of magnitude higher than expected for a fully neutral intergalactic medium, and constitute a gas-rich population of young star-forming galaxies.

Super-X and Conventional divertor configurations in MAST-U ohmic L-mode; a comparison facilitated by interpretative modelling

Abstract Measurements are presented, alongside corresponding interpretative SOLPS-ITER simulations, of the first MAST-U experiments comparing ohmically heated L-mode fuelling scans in Conventional divertor (CD) and Super-X divertor (SXD) configurations. In experiment, at comparable outer mid-plane separatrix electron density, $n_{e,\rm{sep,OMP}}$, the maximum lower outer target heat load was found to be a factor 16$\pm7$ lower in SXD compared to CD. In simulation, a factor 26.8 reduction was found (slightly higher than the experimental range), suggesting an additional reduction in SXD compared to the factor 9.3 expected from geometric considerations alone. According to the simulations, this additional reduction in the SXD is due to a net radial transport of the energy remaining downstream of the $T_e=5$ eV location. This energy is carried out of the critical (highest heat load) flux tube by deuterium atoms, demonstrating the importance of a longer legged divertor which provides space for this to occur. Importantly, in both simulation and experiment, the SXD has minimal impact on the upstream $n_e$ and $T_e$ profiles. Spectral inferences of detachment front movement in SXD compare well between simulation and experiment. In regions of high magnetic field gradient, the parallel movement of the front towards the X-point becomes less sensitive to increasing $n_{e,\rm{sep,OMP}}$, in qualitative agreement with simplified models and previous predictive simulations. Additional aspects, regarding the target ion flux rollover, upstream separatrix temperature and drift effects, are also presented and discussed.

Markovnikov Hydrochlorination of Unactivated Alkenes with FeCl3 via a HAT/XAT Sequence.

Hydrochlorination of alkenes is a practical strategy for accessing organic chlorides. Herein, we report the hydrochlorination of unactivated alkenes via a hydrogen atom transfer/halogen atom transfer process using earth-abundant and biocompatible FeCl3 as a chlorine source under extraordinarily mild reaction conditions. The protocol is easy to operate with notable features such as excellent chemoselectivity, remarkable efficiency, a broad substrate scope, and good functional group tolerance. Importantly, the synthetic utility is highlighted by scaled-up reactions, late-stage derivatizations of products, and the modification of sulfonamides.

Influence of the Incorporation of Nd in ZnO Films Grown by the HFCVD Technique to Enhance Photoluminiscence Due to Defects

In this work, optical–structural and morphological behavior when Nd is incorporated into ZnO is studied. ZnO and Nd-doped ZnO (ZnO-Nd) films were deposited at 900 °C on Silicon n-type substrates (100) by using the Hot Filament Chemical Vapor Deposition (HFCVD) technique. For this, pellets were made by from powders of ZnO(s) and a mixture of ZnO(s):Nd(OH)3(s). The weight percent of the mixture ZnO:Nd(OH)3 in the pellet is 1:3. The gaseous precursor generation was carried out by chemical decomposition of the pellets using atomic hydrogen which was produced by a tungsten filament at 2000 °C. For the ZnO film, diffraction planes (100), (002), (101), (102), (110), and (103) were found by XRD. For the ZnO-Nd film, its planes are displaced, indicating the incorporation of Nd into the ZnO. EDS was used to confirm the Nd in the ZnO-Nd film with an atomic concentration (at%) of Nd = 10.79. An improvement in photoluminescence is observed for the ZnO-Nd film; this improvement is attributed to an increase in oxygen vacancies due to the presence of Nd. The important thing about this study is that by the HFCVD method, ZnO-Nd films can be obtained easily and with very short times; in addition, some oxide compounds can be obtained individually as initial precursors, which reduces the cost compared to other techniques. Something interesting is that the incorporation of Nd into ZnO by this method has not yet been studied, and depending on the method used, the PL of ZnO with Nd can increase or decrease, and by the HFCVD method the PL of the ZnO film, when Nd is incorporated, increases more than 15 times compared to the ZnO film.

High-Resolution Crossed-Beam Dynamics Studies of the D + Para-H2 → HD + H Reaction at 1.21 eV.

Understanding kinetic isotope effects is important in the study of the reaction dynamics of elementary chemical reactions, particularly those involving hydrogen atoms and molecules. As one of the isotopic variants of the hydrogen exchange reaction, the D + para-H2 reaction has attracted much attention. However, experimental studies of this reaction have been limited primarily due to its strong experimental background noise. In this study, by using the velocity map ion imaging method and the near-threshold ionization technique, together with improvements on the vacuum condition in the vicinity of the collision zone, background noise was reduced significantly, and quantum state-resolved differential cross sections (DCSs) for the D + para-H2 reaction at a collision energy of 1.21 eV were acquired in a crossed molecular beams experiment. Interestingly, clear rotational state-dependent angular distributions were noticed in the quantum state-resolved DCSs. The most intense peak's positions for HD (v', j') products shift to different scattering directions as the product's ro-vibrational quantum number increases. Two different microscopic reaction mechanisms are found to be involved in this reaction for HD products in different vibrational states. The results show a direct correlation between the scattering angle and the product's rotational quantum number, revealing that the contributions of impact parameters are strongly influenced by the corresponding centrifugal barrier.

Achieving Negatively Charged Pt Single Atoms on Amorphous Ni(OH)2 Nanosheets with Promoted Hydrogen Absorption in Hydrogen Evolution

HighlightsPt–Ni bonded Pt single-atom (SA) catalyst, rather than classic Pt–O bonded SA catalyst, was successfully constructed.The electronic states of Pt SA catalyst were deeply regulated and negatively charged Ptδ− was realized.Pt–Ni bonded Pt SA catalyst-enhanced absorbability for activated hydrogen atoms and promoted hydrogen absorption.

Two-in-One Role of Benzophenone in Photoinduced C(sp3)-H Monofluoralkenylation: Hydrogen-Atom Transfer and Single-Electron Transfer.

A new protocol for monofluoralkenylation of C(sp3)-H bonds with gem-difluoroalkenes was reported. In this protocol, benzophenone serves as a photocatalyst with dual roles of hydrogen-atom transfer and single-electron transfer. The excited state of benzophenone abstracts a hydrogen atom from a C(sp3)-H bond to generate a corresponding carbon radical, which subsequently undergoes a radical addition/SET/β-F elimination process rather than radical-radical cross-coupling of previous work. This reaction shows high regioselectivity for the α-carbon atoms of ethers, thioethers, and amines, enabling the preparation of monofluoroalkenes.