Formation Of Hydrogen Molecules Research Articles

Co, Ni and Cu-doped Ca2Fe2O5-based oxygen carriers for enhanced chemical looping hydrogen production

Oxygen carrier determines the output characteristics of the chemical looping cycle reaction and is a key factor affecting the chemical looping hydrogen production (CLH) process. In this work, the effect of different dopants (Co, Ni and Cu) on Ca2Fe2O5 brownmillerite-type oxygen carriers and the feasibility of low doping were investigated in an attempt to improve CO conversion and hydrogen yield in the CLH reaction. The redox activity of the transition metal doped oxygen carriers was significantly enhanced. The fuel conversion of CaFeNi was increased to 1.29 times. The average hydrogen yield of CaFeCo was as high as 102.20 mL/g, which was 1.58 times that of CaFe. In addition, density functional theory calculations show that metal-doped Ca2Fe2O5 reduced the energy of oxygen vacancy formation, but they bore a significant energy barrier in the formation of hydrogen molecules. These findings may provide ideas for the modification of oxygen carriers for the CLH process.

Edge sites on platinum electrocatalysts are responsible for discharge in the hydrogen evolution reaction

New insights into the electrochemical functionalities of the edge sites on platinum in the hydrogen evolution reaction and novel nanotechnological strategies to produce edge-rich electrocatalysts are described.

Modeling of hydrogen generation by hexane and its water mixture by radiolysis

The rates of hydrogen molecule formation processes (W) for Н2, СН4, С2Н6, С3Н8, С4Н10, and С5Н12 in hexane were 3, 0.12, 0.56, 0.57, 0.3 and 0.06 × 10−14 molecule/s. Molecular particle yields (G) for Н2, СН4, С2Н6, С3Н8, С4Н10, and С5Н12 in hexane were 3.4, 0.14, 0.6, 0.6, 0.34, and 0.07 molecules/100eV. The rates of molecular hydrogen formation processes (W) and molecular hydrogen yields (G) for 11.5% С6Н14 + 88.5% Н2О systems were 0.50 × 10−14 molecule/s and 1.63 molecules/100eV. These values for 22% С6Н14 + 78% Н2О systems were 1.24 × 10−14 molecules/s and 3.0 molecules/100eV. Also, the values for 50% С6Н14 + 50% Н2О systems were 1.6 × 10−14 molecule/s, and 5.0 molecules/100eV. The values of Gads and Gtot ranged from 4.4 to 22.25 molecules/100eV and 1.8 to 6.5 molecules/100eV. Monte Carlo modeling established the kinetics of the accumulation of radicals and radiolysis products. It was determined that the reactions occurred in spurs involving the hydrated electron eaq, H•, H+, OH•, H2, OH−, and H2O2, and the number of reactions involving these particles was 10.

Self‐Assembled Junctions of 2D Single‐Layer Semiconductors: A Potential Way toward Advanced Photocatalysis

Self‐Assembled Junctions of <scp>2D</scp> Single‐Layer Semiconductors: A Potential Way toward Advanced Photocatalysis

Study of Plasma Electrolysis in Water: Alternative Technologies for Hydrogen Production

Plasma electrolysis has been studied as an alternative method for generating hydrogen. A plasma reactor is used in this electrolysis to produce glowing plasma and the reactive interface fluid layer has an asymmetrical spiral-rod electrodes configuration. Plasma electrolysis was carried out in 2 positions at the surface of the solution and at a depth of 5 mm. On the surface, it is divided into 4 regions of I-V characteristics, namely the conventional electrolysis area, the plasma formation region, the gas formation area that covers the anode, and the glowing plasma region. While at a depth of 5 mm, the formation of plasma with a voltage of 500 V takes 120 seconds to heat the solution with a conventional electrolysis mechanism around the anode. Glowing plasma at a depth of 5 mm resembles the shape of a ball with a larger diameter as the addition of stress and the addition of the concentration of NaCl solution. The mechanism for the formation of hydrogen molecules occurs in the reactive interfacial fluid layer. The plasma ball will increase with a greater voltage. The enlargement of the glowing plasma with increasing operating voltage shows that voltage is a very important factor in the generation of plasma in water. The diameter of the glowing plasma sphere produced for electrolysis at the surface of the solution and at a depth of 5 mm in the solution always increases with increasing voltage. Furthermore, the greater the molarity of the NaCl solution in water, the larger the glowing plasmasphere. The production of hydrogen increases as the voltage increases, this is indicated by the increase in spectrum intensity Hδ and H2. HIGHLIGHTS A unique coronavirus epidemic that has swept throughout the globe is examined and analysed COVID-19 outbreaks in various places are analysed using machine learning models, which are visualised using charts, tables, graphs and predictions depending on the available data For prediction models, the time series forecasting package (PROPHET) is utilised as part of machine learning GRAPHICAL ABSTRACT

Quantum Tunnelling Driven H2 Formation on Graphene.

It is commonly believed that it is unfavorable for adsorbed H atoms on carbonaceous surfaces to form H2 without the help of incident H atoms. Using ring-polymer instanton theory to describe multidimensional tunnelling effects, combined with ab initio electronic structure calculations, we find that these quantum-mechanical simulations reveal a qualitatively different picture. Recombination of adsorbed H atoms, which was believed to be irrelevant at low temperature due to high barriers, is enabled by deep tunnelling, with reaction rates enhanced by tens of orders of magnitude. Furthermore, we identify a new path for H recombination that proceeds via multidimensional tunnelling but would have been predicted to be unfeasible by a simple one-dimensional description of the reaction. The results suggest that hydrogen molecule formation at low temperatures are rather fast processes that should not be ignored in experimental settings and natural environments with graphene, graphite, and other planar carbon segments.

General-purpose neural network interatomic potential for the α -iron and hydrogen binary system: Toward atomic-scale understanding of hydrogen embrittlement

To understand the physics of hydrogen embrittlement at the atomic scale, a general-purpose neural network interatomic potential (NNIP) for the $\ensuremath{\alpha}$-iron and hydrogen binary system is presented. It is trained using an extensive reference database produced by density functional theory (DFT) calculations. The NNIP can properly describe the interactions of hydrogen with various defects in $\ensuremath{\alpha}$-iron, such as vacancies, surfaces, grain boundaries, and dislocations; in addition to the basic properties of $\ensuremath{\alpha}$-iron itself, the NNIP also handles the defect properties in $\ensuremath{\alpha}$-iron, hydrogen behavior in $\ensuremath{\alpha}$-iron, and hydrogen-hydrogen interactions in $\ensuremath{\alpha}$-iron and in vacuum, including the hydrogen molecule formation and dissociation at the $\ensuremath{\alpha}$-iron surface. These are superb challenges for the existing empirical interatomic potentials, like the embedded-atom method based potentials, for the $\ensuremath{\alpha}$-iron and hydrogen binary system. In this study, the NNIP was applied to several key phenomena necessary for understanding hydrogen embrittlement, such as hydrogen charging and discharging to $\ensuremath{\alpha}$-iron, hydrogen transportation in defective $\ensuremath{\alpha}$-iron, hydrogen trapping and desorption at the defects, and hydrogen-assisted cracking at the grain boundary. Unlike the existing interatomic potentials, the NNIP simulations quantitatively described the atomistic details of hydrogen behavior in the defective $\ensuremath{\alpha}$-iron system with DFT accuracy.

Enhanced defect-water hydrogen evolution method for efficient solar utilization: Photo-thermal chemical coupling on oxygen vacancy

Oxygen vacancy (VO) was identified as an effective method for the improvement of materials in the area of photocatalysis and electrocatalysis. Besides, VO was confirmed to participate in the decomposition of water, the direct thermal application of reductive photo-induced VO has been considered an adaptive method for solar utilization. Here, the generation and consumption of VOs was detected on titanium dioxide surface, base mechanism and produced hydrogen was further obtained. The photochemical activity boosted upon transition metal doping, and the water splitting performance rise to 12.97-fold result from the increased amount of photo-induced VOs. Furthermore, the reaction pathway density functional theory calculations exhibited the difficulty during hydrogen molecule formation, guiding the metal particles loading to improve the VOs reactivity. A maximum hydrogen yield was achieved on Ni/Cu-TiO2 equal to 27.01 μmol/g-cat, which was approximately 36.0 times the behave of bare titanium dioxide. These conclusions demonstrate the obvious impact of quantity and quality of photo-induced VOs in VO-based reactions, and contribute to a new approach for solar functional material engineering.

First-principles study of hydrogen trapping behavior in face centered cubic metals (M=Ni, Cu and Al) with monovacancy

Using ab initio density functional approach, we analyze the trapping behavior of Hydrogen atom in a series fcc structure metals (M = Ni, Cu and Al). From the calculations we found that the potential trapping sites in all these three metals is strongly correlated with the electron charges distribution and the swelling of the nH-Vac cluster is largely determined by the transferring charges of the metal atoms around the vacancy. According to our results, in both intrinsic metals and the metal with monovacancy the hydrogen atoms are always prone to be trapped at the interstitial site with large pre-existed charges and the growth of nH-Vac cluster greatly depends on the charges supplying by the surrounding metal atoms. By our calculations the deficit charges supplying by the nearby metal atoms always accompany a strain energy increment which forbid the nH-Vac swelling. This mechanism is identified in all these three fcc metals. We also found that the formation of hydrogen molecule at the center of the vacancy can only be identified in Aluminum no matter the trapping sites around the vacancy are fully occupied or not. But in Ni and Cu with the same fcc structure H2 molecule are not popular.

Relationship between the Behavior of Hydrogen and Hydrogen Bubble Nucleation in Vanadium

Hydrogen plays a significant role in the microstructure evolution and macroscopic deformation of materials, causing swelling and surface blistering to reduce service life. In the present work, the atomistic mechanisms of hydrogen bubble nucleation in vanadium were studied by first-principles calculations. The interstitial hydrogen atoms cannot form significant bound states with other hydrogen atoms in bulk vanadium, which explains the absence of hydrogen self-clustering from the experiments. To find the possible origin of hydrogen bubble in vanadium, we explored the minimum sizes of a vacancy cluster in vanadium for the formation of hydrogen molecule. We show that a freestanding hydrogen molecule can form and remain relatively stable in the center of a 54-hydrogen atom saturated 27-vacancy cluster.

Calculating the ground state energy of hydrogen molecules and helium hydride ions using Bohr’s quantum theory

Molecular composition and chemical bonding have always been the fundamental basics in computing chemistry. As the helium hydride ion has been proven to be widespread in the Universe, it has once again ignited interest in this substance. To understand its composition, such as getting the ground state energy and chemical bonds length of the helium hydride ion, one needs to solve the Schrödinger equation based on quantum mechanics and the variational method. However, such methods are not intuitive for non-related field researchers. In this paper, Bohr’s semi-classical quantum model is first used to explain the formation of the bonds’ length, and to calculate the ground state energy of hydrogen molecules. Then, such methods are extended to the helium hydride ion. Our model gives a comparably accurate result compared with the results from variational methods. Furthermore, the physical picture of this method is straightforward, and is suitable for intuitively explaining the formation of hydrogen molecules and helium hydride ions.

Predictive model of hydrogen trapping and bubbling in nanovoids in bcc metals.

The interplay between hydrogen and nanovoids, despite long being recognized as a central factor in hydrogen-induced damage in structural materials, remains poorly understood. Here, focusing on tungsten as a model body-centred cubic system, we explicitly demonstrate sequential adsorption of hydrogen adatoms on Wigner-Seitz squares of nanovoids with distinct energy levels. Interaction between hydrogen adatoms on nanovoid surfaces is shown to be dominated by pairwise power-law repulsion. We establish a predictive model for quantitative determination of the configurations and energetics of hydrogen adatoms in nanovoids. This model, combined with the equation of states of hydrogen gas, enables the prediction of hydrogen molecule formation in nanovoids. Multiscale simulations, performed based on our model, show good agreement with recent thermal desorption experiments. This work clarifies fundamental physics and provides a full-scale predictive model for hydrogen trapping and bubbling in nanovoids, offering long-sought mechanistic insights that are crucial for understanding hydrogen-induced damage in structural materials.

Formation of globular clusters induced by external ultraviolet radiation – II. Three-dimensional radiation hydrodynamics simulations

We explore the possibility of the formation of globular clusters under ultraviolet (UV) background radiation. One-dimensional spherical symmetric radiation hydrodynamics (RHD) simulations by Hasegawa et al. have demonstrated that the collapse of low-mass (10^6-10^7 solar masses) gas clouds exposed to intense UV radiation can lead to the formation of compact star clusters like globular clusters (GCs) if gas clouds contract with supersonic infall velocities. However, three-dimensional effects, such as the anisotropy of background radiation and the inhomogeneity in gas clouds, have not been studied so far. In this paper, we perform three-dimensional RHD simulations in a semi-cosmological context, and reconsider the formation of compact star clusters in strong UV radiation fields. As a result, we find that although anisotropic radiation fields bring an elongated shadow of neutral gas, almost spherical compact star clusters can be procreated from a "supersonic infall" cloud, since photo-dissociating radiation suppresses the formation of hydrogen molecules in the shadowed regions and the regions are compressed by UV heated ambient gas. The properties of resultant star clusters match those of GCs. On the other hand, in weak UV radiation fields, dark matter-dominated star clusters with low stellar density form due to the self-shielding effect as well as the positive feedback by ionizing photons. Thus, we conclude that the "supersonic infall" under a strong UV background is a potential mechanism to form GCs.

Vacuum ultraviolet photolysis of hydrogenated amorphous carbons

Context. Hydrogenated amorphous carbon (a-C:H) has been proposed as one of the carbonaceous solids detected in the interstellar medium. Energetic processing of the a-C:H particles leads to the dissociation of the C-H bonds and the formation of hydrogen molecules and small hydrocarbons. Photo-produced H2 molecules in the bulk of the dust particles can diffuse out to the gas phase and contribute to the total H2 abundance.

Effect of beryllium bonds on the keto–enol tautomerism of formamide derivatives: a subtle basicity–acidity balance

The effects of the association of BeH2 to formamide derivatives have been investigated through the use of G4 high-level ab initio calculations. The association takes place preferentially at the carbonyl group of the amide in the keto tautomer and to the imino group in the enol form. In both cases, the complexes formed are stabilized through the formation of beryllium and dihydrogen bonds. The relative stability of these complexes is the result of a subtle balance between the changes induced by the formation of the beryllium bond on the intrinsic basicity and acidity of the amide. One of the main consequences of this balance is the significant stabilization of the enol tautomer due to the concomitant increase in the basicity of the imino group with respect to the carbonyl group and the significant acidity enhancement of the OH group, which leads to the formation of very strong BeH···HO dihydrogen bonds in the enol complexes. For the Cl-, Br- and NO2-formamide derivatives, this dihydrogen bond is so strong that a spontaneous formation of hydrogen molecule takes place. The formation of the beryllium bond not only stabilizes the enol forms, but also leads to a significant decrease in the activation barriers involved in the enolization process.

EARLY STRUCTURE FORMATION FROM PRIMORDIAL DENSITY FLUCTUATIONS WITH A BLUE, TILTED POWER SPECTRUM

While observations of large-scale structure and the cosmic microwave background (CMB) provide strong constraints on the amplitude of the primordial power spectrum (PPS) on scales larger than 10~Mpc, the amplitude of the power spectrum on sub-galactic length scales is much more poorly constrained. We study early structure formation in a cosmological model with a blue-tilted PPS. We assume that the standard scale-invariant PPS is modified at small length scales as $P(k) \sim k^{m_{\rm s}}$ with $m_{\rm s} > 1$. We run a series of cosmological hydrodynamic simulations to examine the dependence of the formation epoch and the characteristic mass of primordial stars on the tilt of the PPS. In models with $m_{\rm s} > 1$, star-forming gas clouds are formed at $z > 100$, when formation of hydrogen molecules is inefficient because the intense CMB radiation destroys chemical intermediates. Without efficient coolant, the gas clouds gravitationally contract while keeping a high temperature. The protostars formed in such "hot" clouds grow very rapidly by accretion to become extremely massive stars that may leave massive black holes with a few hundred solar-masses at $z > 100$. The shape of the PPS critically affects the properties and the formation epoch of the first generation of stars. Future experiments of the CMB polarization and the spectrum distortion may provide important information on the nature of the first stars and their formation epoch, and hence on the shape of the small-scale power spectrum.

Effect of trimethylsilane pressure on hot-wire chemical vapor deposition chemistry using vacuum ultraviolet laser ionization mass spectrometry

In this study, the authors investigated the effect of sample pressure on the reaction chemistry of trimethylsilane (TriMS) in the hot-wire chemical vapor deposition (CVD) process. The secondary gas-phase reaction products were examined in a reactor with varying TriMS pressures. The reaction products were analyzed using a laser ionization source with a vacuum ultraviolet wavelength of 118 nm, coupled with mass spectrometry. By increasing TriMS pressure, methane formation was observed. To our knowledge, this is the first successful use of either open-chain alkylsilanes or four-membered-ring (di)silacyclobutane molecules as an independent precursor gas in the hot-wire CVD reactor to achieve methane formation. Our results showed that methane was formed mainly from the radical chain reactions with minor contributions from molecular elimination. The increase in the sample pressure also led to the formation of other small hydrocarbon molecules including acetylene, ethene, propyne, and propene. The formation of hydrogen molecules was enhanced when the sample pressure was increased. In addition, the change in the sample pressure had a direct effect on the radical recombination and disproportionation reactions. This is reflected in the different behavior assumed by the main products from these two types of reactions, i.e., tetramethylsilane, hexamethyldisilane from the former, and three methyl-substituted disilacyclobutanes from the latter. The trapping of free radicals resulting from the in-situ produced ethene and propene molecules is responsible for the observed difference.

Effects of implementing PSI-light on hydrogen production via biophotolysis in Chlamydomonas reinhardtii mutant strains

A new strategy in hydrogen production via biophotolysis developed previously was implemented in mutant strains of Chlamydomonas reinhardtii. Implementing PSI-light successfully demonstrated improved hydrogen production in the wild type strain of C. reinhardtii in a previous study, however, the results also showed rapid attenuation of hydrogen production even under PSI-light due to inhibited hydrogenase activity caused by oxygen, which was simultaneously produced through the water splitting reactions of PSII under light. In order to further decrease oxygen generation under PSI-light during the hydrogen production phase, use of some mutant strains of C. reinhardtii, that are known to show limited oxygen generation, were investigated.Continuous supply of PSI-light after a short anaerobic adaptation under dark conditions achieved significantly prolonged hydrogen production up to ≈ 18 h in a chlorophyll b deficient mutant (cbn 1–48) and a very high light tolerant mutant (VHLR-S4) yielding chlorophyll content based H2 production of 220 and 176 dm3 kg−1 (equivalent to dry cell weight based H2 production of 4.24 and 8.73 dm3 kg−1), respectively. In addition, by iterating light and dark every 1.5 h with PSI-light, hydrogen production was successfully extended to 27 h yielding chlorophyll content based H2 production of 366 dm3 kg−1 (equivalent to dry cell weight based H2 production of 8.81 dm3 kg−1) in cbn 1-48. Further, greater energy conversion efficiency from light to the formation of hydrogen molecules was achieved with the combination of PSI-light and some mutant strains compared to alternate methods of biophotolysis.

Modeling of hydrogen isotope exchange from porous graphite

A 3D Kinetic Monte Carlo (KMC) model has been used to study the hydrogen isotope exchange from porous graphite at a single granule length scale (micrometers). The present KMC model is part of a previously reported multi-scale model developed by the authors [1]. SDTrimSP [2,3] simulations have been carried out and the results have been used to get some of the input parameters for the KMC where the diffusive–reactive aspect of H and D are studied. These SDTrimSP calculations show that the incident energetic ion beams lead to the development of inter-connected pores in the graphite sample. In the presence of these connected pores hydrogen molecule formation is not a local process. It takes place throughout the implantation zone and not only at the end of the ion range. For samples having less internal porosity mixing is very low. Therefore the internal structure of graphite, which affects the diffusion coefficient [4–7] and consequently molecule formation and atomic re-emission [8,9], plays the most crucial role for the H, D mixing. A new mechanism based on the KMC and SDTrimSP simulation is proposed to explain the experimental data.

Radiation-stimulated hydrogen transfer in metals and alloys

Investigations of atom and molecule emission from the surface and the surface layers of solids into vacuum under different impacts have been carried out for many decades (methods and statement of some of them are reviewed in [1–9]). But only during recent 30–40 years, due to scientific and technical achievements in obtaining and diagnostics of vacuum, it has become possible to develop methods and equipment for obtaining information on the qualitative and quantitative content of various gas impurities in compact and porous solids (e.g., hydrogen, oxygen, nitrogen, water vapor, hydrocarbon gas, CO2, CO, etc.), which are adsorbed on the surface and dissolved in the surface layer and bulk. These impurities release from heated or irradiated (by ions or electrons) materials in the form of atoms and molecules, and are detected by mass-spectrometry. In particular, it was revealed that using radiation exposure, controlling the hydrogen concentration in bulk solids, it is possible to create nonequilibrium thermodynamic systems that cannot be synthesized by traditional methods [10–12]. These problems have become urgent in recent years to researchers in different scientific areas [10, 14–16] because this allows one to achieve deep, controlled restructuring of metals and alloys on their different structure levels [10, 13]. Actively absorbing the irradiation energy, the electronic subsystem of MeHx alloys transits to excited state. Since the frequency of collective oscillations of the hydrogen subsystem is outside the phonon spectrum of the metal crystalline lattice, its relaxation is hindered. Exposed to the electron beam in the subthreshold range, hydrogen atoms begin to actively migrate through the bulk crystal and go outside. This evidences manifestation of collective properties by the internal hydrogen metal atmosphere and is represented in a number of nonlinear effects, in particular, in the dependences of the release rate, diffusion coefficients, energy of hydrogen (deuterium) atoms on the density and energy of the exciting electron beam, or X-ray quanta. It was found that the hydrogen subsystem, preserving for a long time the supplied energy on the time scale of electronic relaxation in metals, is able to stimulate processes of rapid diffusion, nonequilibrium hydrogen escape under irradiation [11, 13]. The goal of the present work: Based on investigation of hydrogen (deuterium) release from metals under ionizing radiation in the subthreshold range, to determine the optimal conditions of dehydrogenization and consider the model of hydrogen release from metals, investigate the possibility of release of nuclear reaction products, in particular, protons and alpha particles, and also to study the mechanism of energy transfer from hydrogen to nuclear subsystem. Contrary to the known models of electron-stimulated desorption (ESD) [1, 2], which normally use electron energies from 0.5 to several keV, in the present work we consider not only the processes of hydrogen molecule formation and detachment from metal surfaces, but also processes stimulating