scholarly journals Sorption of molecular hydrogen on the graphene-like matrix doped by N- and B-atoms

2021 ◽  
Vol 12 (2) ◽  
pp. 112-123
Author(s):  
M. T. Kartel ◽  
◽  
V. V. Lobanov ◽  
E. M. Demyanenko ◽  
Wang Bo ◽  
...  
Keyword(s):  
Molecular Hydrogen ◽  
Hydrogen Desorption ◽  
Dissociative Adsorption ◽  
Complete Analysis ◽  
Hydrogen Chemisorption ◽  
Dissociative Chemisorption ◽  
Hydrogen Atoms ◽  
Hydrogen Molecules ◽  
H2 Molecule ◽  
Energy Of Formation

The regularities of interaction of hydrogen molecules with graphene-like planes, where two carbon atoms are replaced by nitrogen or boron atoms, have been studied by the methods of quantum chemistry (DFT, B3LYP, 6-31G**). To take into account the dispersion contributions to the energy of formation of intermolecular complexes that occur during the formation of adsorption supramolecular structures, Grimme’ dispersion correction is used - D3. To study the effect of the size of a graphene-like cluster on the energy of molecular hydrogen chemisorption, polyaromatic molecules (PAM) are used of pyrene, coronene and that consisting of 54 carbon atoms, as well as their nitrogen- and boron-containing analogues where N- and B-atoms are placed in a para-position relative to each other, in the so-called piperazine configuration. The insertion of a heteroatom changes the structure of the transition state and the mechanism of chemisorption. An analysis of the results of quantum chemical calculations showed the highest exothermic dissociative adsorption of the H2 molecule on B-containing graphene-like ones. For N-containing PAM, the exothermicity of the mentioned reaction is somewhat lower, for it a possibility of desorption of atomic hydrogen desorption the surface of the latter with subsequent recombination in the gas phase has been also shown. At the same time, for models of pure graphene-like layer, the data obtained indicate the impossibility of chemisorption of molecular hydrogen. Without a complete analysis of the results for all the possible locations of the pair of hydrogen atoms (formed due to dissociation of the H2 molecule) bound by nitrogen-containing polyaromatic molecules, it can be noted that the dissociative chemisorption of the H2 molecule, regardless of the nature of heteroatom in the PAM, is thermodynamically more probable at the periphery of the model molecules than that in their centers.

The action of X-rays on ferrous and ferric salts in aqueous solutions

1952 ◽  
Vol 211 (1106) ◽  
pp. 375-398 ◽  
Keyword(s):  
Molecular Hydrogen ◽  
Ph Dependence ◽  
Oh Radicals ◽  
Specific Rate ◽  
X Rays ◽  
Ferrous Ions ◽  
Hydrogen Atoms ◽  
Hydrogen Molecules ◽  
Specific Rate Constant ◽  
Theoretical Considerations

The action of X-rays on the ferrous-ferric system has been studied under a variety of conditions. The H atoms and OH radicals formed primarily by the action of the radiation on the water react according to Fe 3+ + H → Fe 2+ + H + and Fe 2+ + OH → Fe 3+ + OH - . Experiments carried out in the presence of molecular hydrogen, where the latter reaction competes with the reaction H 2 + OH → H 2 O + H, permit us to deduce that the specific rate constant of the reaction between OH radicals and ferrous ions is about five times greater than that of the corresponding reaction with hydrogen molecules. The study of the pH dependence of the reaction has led to the assumption that molecular hydrogen ions, H + 2(hydr.) , intervene in this process undergoing the reaction Fe 2+ + H + 2(hydr.) → Fe 3+ + H 2 , and that these ions exist in the equilibrium: H + H + (hydr.) ⇌ H + 2(hydr.) . Experimental evidence and some theoretical considerations which have led to the assumption of H + 2 in aqueous systems have been discussed in detail. In the presence of molecular oxygen the hydrogen atoms react according to H + O 2 → HO 2 , followed by reactions of the latter radical (cf. Haber & Weiss 1934). A comparison of the experimentally determined yields under different conditions with the absolute (chemical) yields as derived from the proposed mechanism has led to the estimation of the energy ( W H 2 O ) required for the production of a radical pair (H + OH) by the action of X-rays on water. This has been found to be W H 2 O = 19⋅4 ± 0⋅4 eV.

scholarly journals A First-Principles Study of Hydrogen Desorption from High Entropy Alloy TiZrVMoNb Hydride Surface

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 553
Author(s):  
Jinjing Zhang ◽  
Jutao Hu ◽  
Haiyan Xiao ◽  
Huahai Shen ◽  
Lei Xie ◽  
...  
Keyword(s):  
Density Functional ◽  
Underlying Mechanism ◽  
Hydrogen Desorption ◽  
High Entropy Alloy ◽  
Hydrogen Atoms ◽  
Desorption Process ◽  
High Entropy ◽  
The Density Functional Theory ◽  
Hydride Hydrogen ◽  
Atomic States

The desorption behaviors of hydrogen from high entropy alloy TiZrVMoNb hydride surface have been investigated using the density functional theory. The (110) surface has been determined to be the most preferable surface for hydrogen desorption from TiZrVMoNb hydride. Due to the high lattice distortion and heterogeneous chemical environment in HEA hydride, hydrogen desorption from the HEA hydride surface is found to be complex. A comparison of molecular and atomic hydrogen desorption reveals that hydrogen prefers to desorb in atomic states from TiZrVMoNb hydride (110) surface rather than molecular states during the hydrogen desorption process. To combine as H2 molecules, the hydrogen atoms need to overcome attractive interaction from TiZrVMoNb hydride (110) surface. These results suggest that the hydrogen desorption on TiZrVMoNb hydride (110) surface is a chemical process. The presented results provide fundamental insights into the underlying mechanism for hydrogen desorption from HEA hydride surface and may open up more possibilities for designing HEAs with excellent hydrogen desorption ability.

Investigation of the Hydrogen Transport Processes in Crystalline Silicon of n-Type Conductivity

2007 ◽  
Vol 131-133 ◽  
pp. 425-430 ◽  
Author(s):  
Anis M. Saad ◽  
Oleg Velichko ◽  
Yu P. Shaman ◽  
Adam Barcz ◽  
Andrzej Misiuk ◽  
...  
Keyword(s):  
Hydrogen Concentration ◽  
Room Temperature ◽  
Crystalline Silicon ◽  
Transport Processes ◽  
Concentration Profiles ◽  
Hydrogen Transport ◽  
Hydrogen Atoms ◽  
Near Surface ◽  
Type Conductivity ◽  
Hydrogen Molecules

The silicon substrates were hydrogenated at approximately room temperature and hydrogen concentration profiles vs. depth have been measured by SIMS. Czochralski grown (CZ) wafers, both n- and p-type conductivity, were used in the experiments under consideration. For analysis of hydrogen transport processes and quasichemical reactions the model of hydrogen atoms diffusion and quasichemical reactions is proposed and the set of equations is obtained. The developed model takes into account the formation of bound hydrogen in the near surface region, hydrogen transport as a result of diffusion of hydrogen molecules 2 H , diffusion of metastable complexes * 2 H and diffusion of nonequilibrium hydrogen atoms. Interaction of 2 H with oxygen atoms and formation of immobile complexes “oxygen atom - hydrogen molecule” (O - H2 ) is also taken into account to explain the hydrogen concentration profiles in the substrates of n-type conductivity. The computer simulation based on the proposed equations has shown a good agreement of the calculated hydrogen profiles with the experimental data and has allowed receiving a value of the hydrogen molecules diffusivity at room temperature.

Gas Source Silicon Molecular Beam Epitaxy

1991 ◽  
Vol 220 ◽  
Author(s):  
H. Hirayama ◽  
M. Hiroi ◽  
K. Koyama ◽  
T. Tatsumi ◽  
M. Sato
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Molecular Beam ◽  
Hydrogen Desorption ◽  
Dissociative Adsorption ◽  
Molecular Beam Epitaxial ◽  
Gas Source ◽  
Surface Migration ◽  
Micron Size ◽  
Silicon Hydrides

ABSTRACTGas source silicon molecular beam epitaxial (Si-MBE) growth is microscopically governed by a disociative adsorption of silicon hydrides, such as Si2H6 source gas molecules on Si surface. The dissociative adsorption generates SiH species on the surface. From this hydride phase, hydrogen desorbs thermaly. The temperature dependence of the growth rate indicated that the hydrogen desorption from the SiH is the rate limiting step. In HBO2 Knudsen cell doping, B adsorbates block the surface migration. Such a blocking effect can be avoided by B2H6 gas dopant, because of the similar incorpration mechanism of B2H6 to that of Si2H6. However, in PH3 gas doping, a crystal quality degradation was observed at a high doping range due to the preferentially high sticking coefficient of PH3 and the resulting surface dangling bond termination. The selective epitaxial growth of a B doped layer using Si2H6 and B2H6 was applied to a novel structured base fabrication for super self-aligned selectively grown base transistor (SSSBT). A successful achievement of the SSSBT fabrication indicates the high potentiality of gas source Si-MBE to the sub-micron size ultra-high speed bipolar large scale integrated (LSI) circuits.

scholarly journals Conversion of HI Molecule to H2 Molecule

2015 ◽  
Vol 5 ◽  
pp. 82-86
Author(s):  
Arjun Kumar Gautam
Keyword(s):  
Historical Development ◽  
Molecular Hydrogen ◽  
Interstellar Dust ◽  
Formation Rate ◽  
Theoretical Models ◽  
Molecular Gas ◽  
Astronomical Data ◽  
Interstellar Dust Grains ◽  
H2 Formation ◽  
H2 Molecule

In this article I review the historical development and conversion of atomic to molecular hydrogen in astronomy. I discuss how the discoveries of HI and H2 in the interstellar medium were followed by studies of the relative abundance of atomic and molecular gas. Understanding this led to increasingly sophisticated theoretical models for H2 formation on the surface of interstellar dust grains. In certain situations, astronomical data can be used to constrain the formation rate of H2 molecules. Finally, I use the reasonably well-determined chemistry of HI and H2 to determine the overall timescale of star formation. The Himalayan Physics Vol. 5, No. 5, Nov. 2014 Page: 82-86

Rate constants for dissociative chemisorption of hydrogen molecules on copper clusters

2006 ◽  
Vol 73 (15) ◽  
Author(s):  
R. C. Forrey ◽  
G. H. Guvelioglu ◽  
P. Ma ◽  
X. He ◽  
H. Cheng
Keyword(s):  
Rate Constants ◽  
Dissociative Chemisorption ◽  
Copper Clusters ◽  
Hydrogen Molecules

Nano-Columnar Mg Thin Films Created by Plasma Sputter Deposition for Improved Hydrogen Kinetics and Storage Properties

2004 ◽  
Vol 837 ◽  
Author(s):  
M. W. Zandbergen ◽  
S. W. H. Eijt ◽  
W. J. Legerstee ◽  
H. Schut ◽  
V. L. Svetchnikov
Keyword(s):  
Thin Films ◽  
Hydrogen Storage ◽  
Hydrogen Permeation ◽  
Hydrogen Desorption ◽  
Sputter Deposition ◽  
Hydrogen Molecules ◽  
Concomitant Reduction ◽  
And Storage ◽  
Determining Factor ◽  
Storage Properties

ABSTRACTThe hydrogen storage properties of nanostructured Mg and MgH2 thin films were studied as created by Ar and Ar+H2 plasma sputter deposition. Columnar structures with typical widths of ∼120 nm are observed with their long columnar axis extending throughout the thickness of the films. Applying substrate bias voltages during deposition results in narrower columns. A concomitant reduction in hydrogen desorption temperature from 400 °C to 360 °C is observed. Capping the Mg films with a ∼100 nm thin Pd layer leads to significantly reduced hydrogen desorption temperatures of ∼200 °C induced by the catalytic activity of the Pd cap layer. Also, hydrogen permeation of the films is strongly improved. The rate-determining factor is found to be the dissociation of the hydrogen molecules. Optimum hydrogen loading conditions of the Pd/Mg films were obtained just above ∼200 °C at hydrogen pressures of 0.25–1.0 MPa, resulting in hydrogen storage capacities in the range of 4–7 wt%.

Surface Properties and Gas Adsorption

2003 ◽  
Author(s):  
Toshiaki Enoki ◽  
Morinobu Endo ◽  
Masatsugu Suzuki
Keyword(s):  
Alkali Metal ◽  
Activated Charcoal ◽  
Low Temperatures ◽  
Gas Adsorption ◽  
Hydrogen Adsorption ◽  
Hydrogen Chemisorption ◽  
Guest Molecules ◽  
Hydrogen Molecules ◽  
General Aspects ◽  
Stage 1

It is well known that alkali metal binary GICs adsorb gaseous species (H2, N2, Ar, CH4, etc.) physisorptively at low temperatures, where physisorbed gaseous molecules are accommodated in the interstitials of the alkali metal lattice within the graphitic galleries (Lagrange and Hérold, 1975; Lagrange et al., 1972, 1976; Watanabe et al., 1971, 1972, 1973). The capacity for hydrogen adsorption, which is estimated at 144 cm3/g in KC24, for example, is large and comparable to the capacity in other adsorbers such as zeolite or activated charcoal. Interestingly, the physisorption phenomenon in alkali metal GICs has different features from that in conventional adsorbents such as zeolite or activated charcoal; that is, guest molecules in alkali metal GICs are not simply bonded to the adsorbents through weak van der Waals forces without any change in the electronic structures. Here we discuss the gas physisorption phenomenon in alkali metal GICs from general aspects, in relation to their specific features. Then in subsequent sections, we will give details of actual cases. Hydrogen is a typical gaseous molecule adsorbed in alkali metal GICs. Hydrogen physisorption takes place at low temperatures below about 200 K, where hydrogen molecules are accommodated in the graphitic galleries and are not dissociated into atomic hydrogen species. When the temperature is increased to over 200 K, the alkali metal GICs work as catalysts to hydrogen, resulting in the occurrence of hydrogen chemisorption. Hydrogen physisorption will be discussed in Section 8.1.2, hydrogen chemisorption and related issues have been discussed partly in Sections 2.2.1 and 5.4.1 from the viewpoints of structure and electronic properties, and will be discussed again in Section 8.1.2. Figure 8.1 represents the composition dependence of the amount of physisorption of hydrogen molecules in KCm at 77 K (Lagrange and Hérold, 1975). The composition of 1/m = 1/8 corresponds to the stage-1 compound and the composition 1/m = 1/24 to the stage-2 compound; intermediate compositions between 1/8 and 1/24 are considered to have a mixed structure of stage-1 and stage-2 compounds. The stage-1 compound does not adsorb hydrogen at all.

scholarly journals Effect of Size on Hydrogen Adsorption on the Surface of Deposited Gold Nanoparticles

Nanomaterials ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 344 ◽  
Author(s):  
Andrey Gatin ◽  
Maxim Grishin ◽  
Nadezhda Dokhlikova ◽  
Sergey Ozerin ◽  
Sergey Sarvadii ◽  
...  
Keyword(s):  
Experimental Study ◽  
Gold Nanoparticles ◽  
Scanning Tunneling Microscopy ◽  
Molecular Hydrogen ◽  
Hydrogen Adsorption ◽  
Pyrolytic Graphite ◽  
Scanning Tunneling ◽  
Hydrogen Chemisorption ◽  
Tunneling Microscopy ◽  
Average Size

An experimental study of molecular hydrogen adsorption on single gold nanoparticles of various sizes deposited on the surface of highly oriented pyrolytic graphite (HOPG) was carried out by means of scanning tunneling microscopy and spectroscopy. The effect of size on the HOPG/Au system was established. Hydrogen was dissociatively chemisorbed on the surface of gold nanoparticles with an average size of 5–6 nanometers. An increase in the size of nanoparticles to 10 nm or more led to hydrogen chemisorption being inhibited and unable to be detected.

Dissociative chemisorption of hydrogen molecules on defective graphene-supported aluminium clusters: a computational study

2018 ◽  
Vol 20 (41) ◽  
pp. 26506-26512 ◽  
Author(s):  
Deepak Kumar ◽  
Thillai Govindaraja ◽  
Sailaja Krishnamurty ◽  
Selvaraj Kaliaperumal ◽  
Sourav Pal
Keyword(s):  
Density Functional Theory ◽  
Chemical Bonding ◽  
Density Functional ◽  
Computational Study ◽  
Dissociative Chemisorption ◽  
Functional Theory ◽  
Hydrogen Molecules ◽  
Defective Graphene

Using periodic density functional theory-based calculations, in the present study, we address the chemical bonding between aluminium clusters (Aln, n = 4–8 and 13) and monovacant defective graphene.

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