Hydrogen Energetics Research Articles

Electron excitation of a surface by atoms from hydrogen plasma in the presence of ultraviolet radiation

The dependence describing the probability of the electron excitation of a crystal by the energy of a chemical reaction on the energy of electron transitions is derived. It is found that the probability of electron chemoexcitation grows exponentially when the energy of electron transitions falls in the solid state. The efficiency of the nonadiabatic chemo-electronic conversion of energy in structures of hydrogen energetics based on Schottky diodes is calculated.

Mechanism of Polymer Collapse in Miscible Good Solvents.

We propose a physical mechanism for co-nonsolvency of a stimulus-responsive polymer in water/methanol mixed solution based on results obtained with molecular simulations. Even though the phenomenon is well known, the mechanism behind co-nonsolvency is still under debate. Herein, we study co-nonsolvency of poly(N-isopropylacrylamide) (PNiPAM) in methanol aqueous solutions, the most widely studied and experimentally well-characterized system. Our results show that at low alcohol content of the solution methanol preferentially binds to the PNiPAM globule and drives polymer collapse. The energetics of electrostatic, hydrogen bonding, or bridging-type interactions with the globule is found to play no role. Instead, preferential methanol binding results in a significant increase in the globule's configurational entropy, stabilizing methanol-enriched globular structures over wet globular structures in neat water. This mechanism drives the reduction of the lower critical solution temperature with increasing methanol content in the co-nonsolvency regime and eventually leads to polymer collapse. The globule-to-coil re-entrance at high methanol concentrations is instead driven by changes in solvent-excluded volume of the coil and globular states imparted by a decrease in solvent density with increasing methanol content of the solution: with increasing proportion of larger solvent particles (methanol), the entropic (cavity formation) cost of redistributing solvent molecules upon polymer re-entrance becomes smaller. This effect provides a natural explanation for the experimentally observed dependence of the re-entrance transition on chain molecular weight.

Interaction of hydrogen with impurities in group IVB metals

The energetics of hydrogen bonding with Group IVB metals and the interaction of hydrogen with impurities of 3d-transition and simple metals (Al, Ga, Si, Ge) have been investigated using the projector-augmented-wave (PAW) method within the framework of the density functional theory (DFT). It has been found that the solubility of hydrogen in Ti, Zr, and Hf increases upon their alloying with metals located in the middle of the 3d period. The relationship between the interaction energy of hydrogen with impurities, the lattice distortions, and the electronic structure of the studied systems has been analyzed. It has been shown that impurities do not affect the preferred hydrogen sorption positions in titanium but can change these positions in zirconium and hafnium. The influence of impurities and hydrogen on the electronic structure of metals has been examined. The obtained results have demonstrated that, in the studied metals, the interactions of hydrogen with impurities of 3d-transition and simple metals are determined by different mechanisms: the attraction of hydrogen by transition metal impurities is caused by the size effect, whereas the repulsion of hydrogen by simple metals can be associated with the electronic factors.

ВОДОРОДНАЯ ЭНЕРГЕТИКА И СОВРЕМЕННЫЙ ТРАНСПОРТ

World experience of practical introduction of hydrogen energetics in sphere of automobile technologies is analyzed. Possibility of stage-by-stage development of researches in the field of hydrogen transport energetics of Russia is discussed

Influence of energy-environmental factors on the competitiveness of hydrogen as a motor fuel (in transport energy installations)

It is described in the paper that for maintaining eco-safe motor transport systems evolution, the development of criteria, based on which it would be possible to evaluate the perfection and technical condition of automobiles is necessary. On the basis of experimental data handling, obtained while testing automobiles of a various make, based on the analysis and coordination of numerous research results, the authors have confirmed that benzopyrene is a reliable indicator of prioritized carcinogenic hydrocarbon emission level and can be used as an indicator of total carcinogenicity () of automobile exhaust gases. Formulas for the calculation are given. The changes in specific cost expenditures () when using hydrogen, as an additional energy carrier were calculated. An assessment of the total energy expenditure and atmospheric emissions when using different fuel technologies in motor transport was made. It is proved that adding hydrogen to the diluted air-fuel mixture in the ICE is economically sound. The expediency of wind-power potential at the self-supporting motorway filling stations was found. It is emphasized that with the full implementation of the mentioned technologies, an increase in socio-economical attractiveness of the hydrogen energetics transport component is expected.

DFT study of the CaNi5Hx compounds (0.0⩽x⩽1.0)

Abstract Density functional theory based electronic structure calculations which included crystal structure optimizations were performed for CaNi 5 H x ( x = 0.0, 0.25, 0.5, 1.0) compounds. Only hydrides with one H atom per unit cell were considered in the present work. Site preference of hydrogen atoms and energetics of hydride formation were investigated. It was found that hydrogen atoms prefer, in notation of space group P6/mmm , 12n sites and that 3f sites are the second most preferred sites what is compatible with previous neutron diffraction studies. Enthalpy of formation of α solid solution and for α → β reaction were calculated and compared with available experimental data and fair agreement was found between calculated and experimental values of enthalpies of formation.

International Society for Computational Biology Honors David Eisenberg with 2013 Accomplishment by a Senior Scientist Award

International Society for Computational Biology Honors David Eisenberg with 2013 Accomplishment by a Senior Scientist Award

Peculiarities of aluminium interaction with Ga85In15 eutectics as evidenced by X-ray synchrotron diagnostics

A set of X-ray synchrotron techniques, viz., diffraction, EXAFS/XANES spectroscopy and microtomography, is applied to elucidate microstructural changes in a technical aluminium alloy treated with GaIn eutectics. Such a treatment gives rise simultaneously to a prominent enbrittlement of the material and its activation towards reaction with water with the hydrogen evolution. The latter fact makes the activated aluminium a promising energy carrier for the small-scale hydrogen energetics. It is demonstrated that both phenomena are caused by the fast diffusion of the eutectics along intergrain boundaries and microcracks throughout the bulk of polycrystalline Al. The diffusion is promoted by the formation of (Al-Ga-In) solid solution in near-surface regions of Al crystalline grains. The progressive loss of activity of aluminium treated with GaIn eutectics upon a prolonged storage in humid air is due to the decomposition of the eutectics accompanied by the segregation of indium metal and partial gallium oxidation.

Supracrystalline analogues of carbon nanomaterials for the hydrogen storage

It is shown that, in contrast to the known two-dimensional carbon nanoallotropes graphene and graphane their supracrystalline analogues have a greater specific surface area and, consequently, a greater sorption capacity. It allows to recommend them as promising hydrogen storage for the hydrogen energetics.

Complexation of Np(v) with oxalate at 283–343 K: spectroscopic and microcalorimetric studies

Thermodynamic parameters including the equilibrium constants and enthalpy of complexation of Np(V) with oxalate at variable temperatures (T = 283-343 K, ionic strength = 1.05 mol kg(-1) NaClO(4)) were determined by spectrophotometric and microcalorimetric titrations. The results show that the complexation of Np(V) with oxalate is moderately strong and becomes weaker at higher temperatures. The complexation is exothermic and driven by both enthalpy (negative) and entropy (positive) in the temperature range from 283 K to 343 K. As the temperature is increased, both the enthalpy and entropy of complexation increase (ΔH becomes less negative and ΔS becomes more positive), having opposing effects on the complexation. Because the increase in the enthalpy (ΔH) exceeds that of the entropy term (TΔS), the complexation of Np(V) with oxalate becomes weaker at higher temperatures. The effect of temperature on the complexation is discussed in terms of the energetics of ion solvation and hydrogen bonding involved in the complexation.

Hydrogen energetics and charge transfer in the Ni/LaNbO4 interface from DFT calculations

Calculations based on density functional theory have been used to simulate interface structures between the tetragonal and monoclinic phases of LaNbO4 (LN) and Ni. Schottky barrier heights were calculated using the interface electronic structure; they were 3.0 and 1.8eV for p- and n-type barriers. The hydrogen interstitials were found to be significantly higher stable in the LN part of the interface than in bulk LN. Also, the potential energy curve of hydrogen diffusion from Ni into LN exhibited a deep well of around 2eV, located in the gap region between two components. The stability of H atom in the gap region and interfacial layers of LN is explained by metal-induced gap states and indicates that there will be an accumulation of hydrogen in this area. It was shown that hydrogen is ionized when enters from Ni to the LN interfacial layer, approaching to the O atoms and that the electron lost from hydrogen resides in the interface states, located in the band gap of LN.

Energetics of small hydrogen–vacancy clusters in bcc iron

Hydrogen may be trapped in voids in iron, leading to undesirable material properties. In this paper, the energetics of small hydrogen–vacancy clusters in body centered cubic iron are investigated. Results from two interatomic potentials are compared. We use molecular dynamics and Monte Carlo methods to find the minimum energy configurations of voids of up to ten vacancies containing up to 50 hydrogen atoms with ratios of hydrogen to vacancy of 10 or less. The formation energies and binding energies of defects to these clusters are calculated. Our results indicate that the hydrogen stabilizes bubbles by causing vacancies to be more tightly bound to clusters, while neighboring irons are less tightly bound. Hydrogen itself becomes less well bound to clusters as the inventory increases. The more physically relevant potential indicates a maximum supported ratio of hydrogen atoms to vacancies of about 4.

Energetics of hydrogen in GeO2, Ge, and their interfaces

The energetics of interstitial hydrogen in GeO2, Ge, and their interfaces are calculated using a hybrid density functional. We find that interstitial atomic hydrogen unexpectedly behaves as a donor in GeO2, like H in ZnO but unlike H in SiO2. At Ge:GeO2 interfaces, the donor electron can transfer to the lower lying Ge conduction band, which stabilises the O-H bond/donor complex. This reduces the probability of passivating Ge dangling bond (Pb) centers at Ge:GeO2 interfaces.

Structure and energetics of hydrogen chemisorbed on a single graphene layer to produce graphane

Chemisorption of hydrogen on graphene is studied using atomistic simulations with the second generation of reactive empirical bond order Brenner inter-atomic potential. The lowest energy adsorption sites and the most important metastable sites are determined. The H concentration is varied from a single H atom, to clusters of H atoms up to full coverage. We found that when two or more H atoms are present, the most stable configurations of H chemisorption on a single graphene layer are ortho hydrogen pairs adsorbed on one side or on both sides of the graphene sheet. The latter has the highest hydrogen binding energy. The next stable configuration is the ortho– para pair combination, and then para hydrogen pairs. The structural changes of graphene caused by chemisorbed hydrogen are discussed and are compared with existing experimental data and other theoretical calculations. The obtained results will be useful for nanoengineering of graphene by hydrogenation and for hydrogen storage.

THE ENERGETICS OF MOLECULAR GAS IN NGC 891 FROM H2AND FAR-INFRARED SPECTROSCOPY

We have studied the molecular hydrogen energetics of the edge-on spiral galaxy NGC\,891, using a 34-position map in the lowest three pure rotational H$_2$ lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1), and S(2) lines are bright with an extinction corrected total luminosity of $\sim2.8 \times 10^{7}$ L$_{\odot}$, or 0.09\% of the total-infrared luminosity of NGC\,891. The H$_2$ line ratios are nearly constant along the plane of the galaxy -- we do not observe the previously reported strong drop-off in the S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find no evidence for the very massive cold CO-free molecular clouds invoked to explain the past observations. The H$_2$ level excitation temperatures increase monotonically indicating more than one component to the emitting gas. More than 99\% of the mass is in the lowest excitation (T$_{ex}$ $\sim$125 K) ``warm'' component. In the inner galaxy, the warm H$_2$ emitting gas is $\sim$15\% of the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction is twice as high. This large mass of warm gas is heated by a combination of the far-UV photons from stars in photo-dissociation regions (PDRs) and the dissipation of turbulent kinetic energy. Including the observed far-infrared [OI] and [CII] fine-structure line emission and far-infrared continuum emission in a self-consistent manner to constrain the PDR models, we find essentially all of the S(0) and most (70\%) of the S(1) line arises from low excitation PDRs, while most (80\%) of the S(2) and the remainder of the S(1) line emission arises from low velocity microturbulent dissipation.

Structure and Energetics of Half-monolayer Hydrogen on W(110)

Structure and Energetics of Half-monolayer Hydrogen on W(110)

First-principles energetics of hydrogen traps in α-Fe: Point defects

We performed a series of density functional theory (DFT) calculations to quantify the binding energy of hydrogen to a number of point defects in body-centered cubic Fe, e.g. vacancies, interstitial carbon and substitutional solutes. We found the following: (i) Vacancies are the strongest H trap, with a binding energy of 0.57 eV. (ii) The binding energy of H to C is 0.09 eV. (iii) Most substitutional solutes (except Si, Cr, Mn, Co, and Mo) trap H with positive binding energies up to 0.25 eV. The maximum H binding energy for Si, Cr, Mn, Co and Mo is essentially zero, meaning they do not interact with H. (iv) The H–substitutional solute binding energies are roughly correlated with the solute atom’s electronegativity and size. (v) The presence of a solute atom near a vacancy does not affect hydrogen binding to the vacancy provided the solute atom is not significantly larger than Fe.

First-principles study of H on the reconstructed W(100) surface

The first-principles calculations were used to study the hydrogen energetics on the (100) tungsten $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})R45\ifmmode^\circ\else\textdegree\fi{}$ surface. Two equilibrium sites for H at the surface are identified, with a low migration barrier from the energetically clearly higher long bridge site to the short bridge site. At low coverages, the majority of H surface diffusion events take place via the short bridge sites. The energetics for H penetration from the surface to the solute site in the bulk was defined, showing that the bulk H diffusion via neighboring tetrahedral sites takes place at depths beyond the second subsurface layer.

Dissecting the paradoxical effects of hydrogen bond mutations in the ketosteroid isomerase oxyanion hole

The catalytic importance of enzyme active-site interactions is frequently assessed by mutating specific residues and measuring the resulting rate reductions. This approach has been used in bacterial ketosteroid isomerase to probe the energetic importance of active-site hydrogen bonds donated to the dienolate reaction intermediate. The conservative Tyr16Phe mutation impairs catalysis by 10(5)-fold, far larger than the effects of hydrogen bond mutations in other enzymes. However, the less-conservative Tyr16Ser mutation, which also perturbs the Tyr16 hydrogen bond, results in a less-severe 10(2)-fold rate reduction. To understand the paradoxical effects of these mutations and clarify the energetic importance of the Tyr16 hydrogen bond, we have determined the 1.6-A resolution x-ray structure of the intermediate analogue, equilenin, bound to the Tyr16Ser mutant and measured the rate effects of mutating Tyr16 to Ser, Thr, Ala, and Gly. The nearly identical 200-fold rate reductions of these mutations, together with the 6.4-A distance observed between the Ser16 hydroxyl and equilenin oxygens in the x-ray structure, strongly suggest that the more moderate rate effect of this mutant is not due to maintenance of a hydrogen bond from Ser at position 16. These results, additional spectroscopic observations, and prior structural studies suggest that the Tyr16Phe mutation results in unfavorable interactions with the dienolate intermediate beyond loss of a hydrogen bond, thereby exaggerating the apparent energetic benefit of the Tyr16 hydrogen bond relative to the solution reaction. These results underscore the complex energetics of hydrogen bonding interactions and site-directed mutagenesis experiments.

Фотоэнергетика и водородная энергетика: возможности и достижения

Фотоэнергетика и водородная энергетика: возможности и достижения