Hydrogen Migration Research Articles

Halogen-, oxidant- and directing group-free synthesis of donor-acceptor type conjugated polymers.

An intermolecular hydrogen migration from dibutadienylpyridine to dialkynylthiophene catalysed by [Ru(η6-naphthalene)(η4-oxa-bnd)] (oxa-bnd = 9-oxabicyclo[3.3.1]nona-2,6-diene) produces poly(dialkynylthiophene-alt-dibutadienylpyridine). The exact alternating copolymerisation nature is shown by MALDI-TOF MS.

Fragmentation dynamics and absolute dissociative electron attachment cross sections in the low energy electron collision with ethanol.

Dissociative electron attachment (DEA) to ethanol has been probed to study fragmentation dynamics using Time-of-Flight (ToF) mass spectrometric technique. Several fragment ions, namely, H-, O-, OH-, C2H3O- and C2H5O- have been observed. Extra effort has been made to detect low mass ions (here, H-). Absolute DEA cross sections for the formation of O- and OH- have been measured for the first time using relative flow technique (RFT). The threshold energy of different dissociation channels has been calculated using density functional theory (DFT) method. By combining the experimental and theoretical data, we found evidence of hydrogen migration in the production of O and C2H3O- ions.

First principles study of V/Pd interface interactions and their hydrogen absorption properties

Hydrogen permeation through vanadium/palladium (V/Pd) metal composite membranes is an effective and practical method of separating hydrogen from gas mixtures. In order to gain an insight into the relation between the interfacial structure and hydrogen adsorption/diffusion properties of the catalytic Pd layer bonded to the metal membrane, and then improve the ability of the alloy membrane to purify hydrogen, the first principle based on the density functional theory is used to study the hydrogen adsorption/diffusion behavior at the V/Pd metal composite membrane interface. The results show that because the charge density at the V/Pd interface increases with the V/Pd bonding increasing, the dissolution energy of hydrogen atom (H) increases with it approaching to the interface, and it has the highest dissolution energy near the V/Pd interface (0.567 eV). Hydrogen migration energy barrier calculations show that compared with the maximum energy barrier for horizontal diffusion of H along the V/Pd interface (0.64 eV), the H vertical V/Pd interface energy barrier (0.56 eV) is small, thus H tends to migrate vertically V/Pd interface and diffuse from the Pd layer to the V substrate side. As the hydrogen solvation energy of the Pd layer at the V/Pd interface (0.238 eV) is higher than that on the V membrane side (–0.165 eV), H will gather on the V film side of the interface, which is easy to cause hydrogen to be embrittled. Calculations of Pd/Fe doping of the V matrix show that comparing with the undoped energy barrier (0.56 eV), Pd/Fe doping can significantly reduce the maximum energy barrier (0.45 eV/0.54 eV) in the diffusion path of the interface, which is favorable for hydrogen permeation and diffusion. And the doped interface can inhibit the interdiffusion of V layer and catalytic Pd layer to a certain extent, which improves the structural stability of the composite film.

Voltage control of magnetic properties in GdxFe100-x films by hydrogen migration

Voltage control of magnetic properties is a promising path to realize low-power spintronic devices and meets the requirements for quicker information processing speed and ongoing scale reduction. Hydrogen migration induced by voltage gating has been demonstrated to modify the intrinsic magnetic properties of materials by affecting the exchange interaction, electron occupancy, and magnetoelastic effect. Herein, the magnetic properties of a ferrimagnetic Gd29Fe71 film in an all-solid-state multilayer device, which is constructed using a GdOx electrolyte, can be reversibly modulated by voltage-controlled hydrogen migration. Polar MOKE results indicate that hydrogen intercalation/deintercalation can modulate the Gd29Fe71 film's degree of compensation and control the dominant magnetic sublattice. Furthermore, the polarity of the polar MOKE curves can be reversibly switched. As with the increase in hydrogen loading, the compensation point in the Gd29Fe71 film is approached, the density of magnetic domain nucleation sites decreases, and the magnetic domain structures transform from labyrinth domains to uniform large area domains. At the same time, a strong perpendicular magnetic anisotropy is developed. This work shows a possible pathway for reversible control of magnetism in spintronic devices.

Exploring low-temperature oxidation chemistry of 2- and 3-pentanone

The low-temperature oxidation chemistry of 2- and 3-pentanone was investigated over a wide range of conditions using a jet-stirred reactor (JSR) and a rapid compression machine (RCM). The JSR oxidation experiment was performed at the pressure of 93.3 kPa over a temperature range of 600-1000 K. Detailed speciation information was obtained using synchrotron vacuum ultraviolet photoionization mass spectrometry. Ignition delay times (IDTs) of 2- and 3-pentanone were measured in an RCM from 640 to 820 K at pressures of 15 and 25 bar and an equivalence ratio of 1.0. The two C5 ketones showed NTC behavior and two-stage ignition phenomena. Mole fraction time histories of intermediate species during the two-stage ignition process of both ketones were obtained using a fast-sampling system coupled with gas chromatography. There are distinct differences between 2- and 3-pentanone in species concentration profiles and IDTs. A kinetic mechanism for the low-temperature oxidation of 2- and 3-pentanone was developed, which can satisfactorily predict all available measurements. The reaction path analyses indicate that the intramolecular hydrogen migration reaction of ROO radicals tends to produce resonance-stabilized QOOH radical structures. The secondary oxygen addition reaction of resonance-stabilized QOOH radicals thus is the most important source of OH radicals in the low-temperature oxidation of ketone fuels. The intramolecular hydrogen migration reactions are slowed down in the presence of the carbonyl functional group, which makes the low-temperature reactivity of the two C5 ketones lower than that of n-pentane. The position of the carbonyl functional group affects the species pools during the oxidation of the two ketones to a great extent. Larger production of CH4, C3H6, CH3COCH3, and C2H5CHO were observed in 2-pentanone oxidation, while the production of CH3CHO was favored during 3-pentanone oxidation both in the JSR and RCM experiments. The different lengths of the carbon chain on both sides of the carbonyl group in 2- and 3-pentanone resulted in the difference in the species distribution.

Direct bond fission and hydrogen migration as the trigger forces in the pyrolysis of n-pentyl nitrate at low pressure

Nitrates are a potential class of substances as cetane improvers of diesel fuel and are critical raw materials for some military explosives. Thus, an in-depth investigation of the thermal decomposition mechanism of nitrates is important for further improving their effects. Herein, a combination of experimental and computational studies was performed for the pyrolysis of n-pentyl nitrate in the temperature range of 400‒900 K. Using synchrotron radiation vacuum ultraviolet photoionization, some intermediates and products, such as ethylene, formaldehyde, propene, ethenol, pentanal, NO2, and HONO, were identified according to their photoionization efficiency curves. Quantum chemical calculations at the CBS-QB3 level were conducted to elucidate the overall reaction mechanism of n-pentyl nitrate pyrolysis. Along the direct bond fission of n-pentyl nitrate, primary products, C5H11O• radical and NO2, and butyl radical and CH2ONO2, can further dissociate into many products, in which formaldehyde is the most dominant. In addition, two hydrogen-atom migration channels followed by decomposition are verified for the decomposition of n-pentyl nitrate according to the observation of trans-HONO, pentanal, and 1-pentene. These evidences highlight that both bond fission and hydrogen migration play comparable roles as potential driving forces in the pyrolysis of n-pentyl nitrate at low pressure. This thermal decomposition mechanism of n-pentyl nitrate provides some useful clues for developing combustion models of long chain nitrates in future.

Ethanol Oxidation on Gold Nanowire Containing Oxygen Impurities: A Study by Ab Initio Molecular Dynamics Simulations

Linear atomic chain (LAC) gold nanowires (Au-NWs) containing oxygen impurities are materials that could be used as supports to stimulate chemical reactions. Its peculiar structural characteristics, such as abnormal Au-Au bonds, make it interesting to explore the chemical reactions of this material at a theoretical level. This work investigated the chemical reaction of ethanol supported on Au-NW containing two oxygen impurities. Using <em>ab initio</em> molecular dynamics simulations, it was shown that the presence of oxygen impurity in the LAC conditions the minimum energy paths (MEP) that ethanol will follow in its chemical transformation. When the structure of the LAC contains two oxygen impurities, the formation of acetaldehyde and acetic acid as reaction products were observed. Specifically, the presence of two oxygen impurities in the LAC favors the migration of hydrogens of the -CH<sub>2</sub>- and -OH groups of ethanol towards the LAC. In addition, it was observed that the formation of the C-O bond was favored, which implies an additional reaction intermediate that leads to a total of two different reaction paths in ethanol oxidation.

Finite element modeling of hydrogen migration and hydride precipitation in Zr alloys

The Finite Element software, ABAQUS® together with subroutine codes written in FORTRAN is used to fully couple the mass diffusion – displacement analysis of hydrogen redistribution and hydride precipitation in a stress gradient. Since the redistribution of hydrogen in solid solution is driven by gradients in H concentration, stress, and temperature, two different precipitation models were investigated in specimens subjected to such gradients, and the results validated against available experimental data and analytical solutions where applicable. Simulation results obtained with the new Hydride Nucleation Growth and Dissolution (HNGD) model that considers growth in the hysteresis region show closer agreement with experimental observations, signifying that the previous hydride precipitation model may be underestimating the amount of hydride precipitation.

The effect of clay on initial and residual saturation of hydrogen in clay-rich sandstone formation: Implications for underground hydrogen storage

Understanding wettability in rock-brine-hydrogen systems is essential for dependable predictions of capillary/residual trapping in clay-rich sandstone formations. Despite being the most used technique, wettability assessment based on contact angle measurements is confronted with inherent uncertainties that limit its reliability. In contrast, core flooding techniques provide a more direct and realistic picture of wettability and its time evolution. Nuclear Magnetic Resonance (NMR) allows us to evaluate the initial and residual hydrogen saturations and distribution along the core specimen. It is a fast, reliable, and effective way of inferring the impact of wettability on hydrogen migration, and residual trapping in prospective geo-storage rock formations. Recent publications have reported the evaluation of wettability in a brine-hydrogen-rock system where the rock is a clean sandstone (no clays). Here we evaluate the impact of the presence of clays in a sandstone, which has not been reported yet. NMR monitoring was employed to characterize the initial and residual hydrogen saturations in the Bandera Grey (BG) sandstone. To investigate the impact of clay minerals on hydrogen saturation, same rock sample was characterized in its natural state, and after heating it to 700 °C for 12 h in an air environment to burn off clay minerals, During the NMR core flooding experiments, ten pore volumes (PVs) were injected/withdrawn during the drainage/imbibition cycles at a fluid injection rate of 2 mL/min under room temperature and 1000 psi confining pressure. Due to the hydrophilicity of quartz and clay, the tested BG sandstone (clay-rich sandstone) shows a significant residual/trapped saturation (∼3.5% can be reproduce); therefore, clay-rich sandstone may not be ideal for hydrogen storage unless cushion gas is used.The results show that initial and residual hydrogen saturations were slightly changed after firing (from 16% to 18% for initial and from 14% to 13% for residual). This also suggests that the wettability of the BG sandstone-brine-hydrogen system is slightly impacted by clay content and type. We also observed that clay firing at 700 °C has little effect on the porosity and gas permeability of the BG sandstone. Moreover, X-ray powder diffraction (XRD) results showed that quartz content increases from 68.1% to 76.2%, Kaolinite transformed into illite and clinochlore disappeared. The disappearance of chlorite after firing suggests that it is transformed into another clay type.

Focal adhesion kinase signaling is necessary for the hydrogen sulfide-enhanced proliferation, migration and invasion of HTR8/SVneo human trophoblasts

Objective: Hydrogen sulfide (H2S) has been elucidated that it promotes migration and invasion in human placenta trophoblasts. However, the signaling pathway underlying H2S-based regulation of trophoblasts remains unknown. Hence, we investigated the potential effect of sodium hydrosulfide (NaHS), an exogenous H2S donor, on extravillous trophoblasts. Methods: The Cell Counting Kit-8 was used to detect the proliferative activity of trophoblasts and to screen the optimal concentration of NaHS. The migration and invasion of HTR8/SVneo cells were measured by Transwell assays. Gene expression was determined by quantitative real-time PCR analysis. Protein expression was determined by western blot. Results: We found that NaHS could promote the proliferation, migration, and invasion of HTR8/SVneo cells. The phosphorylation of focal adhesion kinase (FAK), Src, and extracellular signal-regulated kinase (ERK) were activated by NaHS. Moreover, NaHS also upregulated the expression of matrix metalloproteinase-2(MMP-2) and MMP-9, downregulated the expression of E-cadherin in HTR8/SVneo cells. The application of NaHS could increase the expression of cystathionine-β-synthase. Conclusion: Both FAK–Src signaling and the upstream signaling cascade of ERK activation play a significant important role in NaHS-induced proliferation, migration, and invasion via upregulating activity of MMP-2, MMP-9, and downregulating E-cadherin in HTR8/SVneo cells. These novel findings may provide a strong foundation for the clinical application of H2S donor drugs.

On the electrocatalytically active sites in graphene-based vanadium redox flow batteries

There is too much controversy and too little interdisciplinary analysis of the role of carbon electrodes in a wide range of electrochemical and electrocatalytic processes. Here we focus on vanadium redox flow batteries (VRFB), which play a central role in the transition to renewable energy sources in the electricity sector of the global economy. We used density functional theory (DFT) to determine the relationship between chemically and electrocatalytically active sites on the positive electrode and the effects of chemical surface modification that introduces a variety of oxygen functional groups. Carefully selected aromatic (Ar) model clusters were analyzed to assess the extent of the electron density accumulation on and around the free carbon sites at graphene edges. The results reveal trends that help to resolve the controversies surrounding the role of phenolic or carboxyl groups in the redox mechanism. We conclude, in agreement with other chemical and electrocatalytic reactions that involve oxygen transfer (e.g., CO2 gasification or oxygen reduction reaction), that carbene-type edge carbon atoms are responsible for VO2+ adsorption and reduction of V5+ to V4+ in VO2+. The presence of Ar-OH and Ar-COOH groups can actually inhibit the redox process as a consequence of hydrogen and/or oxygen migration to the adjacent active sites. The presence of ArO groups, while affecting the electron density at the active sites, is confirmed to have a positive effect of stabilizing the free zigzag carbon sites in a triplet ground state.

CFD modeling of liquid-metal heat pipe and hydrogen inactivation simulation

The use of hydrogen window is a potential way for liquid metal heat pipes (LMHPs) to avoid hydrogen inactivation when operated in a hydrogen-containing atmosphere. To reveal the effects of hydrogen permeation on heat transfer in LMHPs in a visual way, we develop a comprehensive CFD model in this work for the first time, and experimental tests are also carried out for model validation. The experimental results show that the top end of an LMHP reduces to below 400 ℃ after hydrogen inactivation, when the heating temperature of the evaporator is maintained at 950 ℃. It takes about 150 min for the LMHP to recover performance by flushing its hydrogen window with nitrogen controlled at 50 mL/min. The CFD model is demonstrated reliable by comparing the predicted heat output and temperature distribution with the experimental results in steady state. The CFD model is capable of reproducing the liquid up-throwing phenomenon, and revealing the impact of hydrogen-buffer formation on heat transfer. In addition, the hydrogen migration along with the returning condensate leads to the formation of a gas blanket covering the inner surface in the condenser, which has a negative effect on the heat transfer as well.

Modifying Interface of Carbon Support-Stimulated Hydrogen Spillover for Selective Hydrogenation

Hydrogen spillover on heterogeneous catalysts offers a new opportunity to improve catalytic hydrogenation. Due to the slow migration of hydrogen under mild conditions, hydrogen spillover-improved hydrogenation is still unsatisfactory on carbon material-supported metal nanoparticles. Herein, the modifying interface of carbon support-stimulated hydrogen spillover for hydrogenation has been successfully identified on the dual-active sites of Pt nanoparticles and modified carbon black (Pt/C–H2O2). The oxygen-containing-group-modified carbon black, which was achieved by a commonly used H2O2 treatment, not only triggered the efficient hydrogen migration along the carbon supports but also enhanced the adsorption of polar substrates, thus affording simultaneously enhanced catalytic activity and selectivity as well as stability. For probe reaction of 6-chloroquinoline hydrogenation to 6-chloro-1,2,3,4-tetrahydroquinoline, Pt/C–H2O2 catalysts yielded a 6.1 times higher catalytic activity with a high selectivity >99.5% than that on Pt/C with selectivity <96.0%. This work is anticipated to provide a facile and effective methodology for fabricating highly performed hydrogenation heterogeneous catalysts.

Charge transfer in ultrafast isomerization of acetylene ions

First-principle calculations are employed to investigate the ultrafast isomerization of the acetylene cation and dication. We use the time-dependent density functional theory together with the Ehrenfest dynamics to track the coupled electron-nuclear dynamics. For both the acetylene cation and the dication, we observe nonadiabatic behaviors during the isomerization. We find that the charge transfer not only alters the electronic structure through nonadiabatic transitions, but also plays a key role in the subsequent hydrogen migration. We show that nonadiabatic transitions affect the structural modification of the excited potential energy surface, and also facilitate the ultrafast isomerization through the creation of a channel of increased negative charge that facilitates the proton movement. For the acetylene cation, we find a timescale for hydrogen isomerization of $66\ifmmode\pm\else\textpm\fi{}4$ fs, which is consistent with previous pump-probe experiments and on-the-fly calculations. For the dication, we find nonadiabatic transitions occur before the isomerization and identify a similar channel for the proton. Moreover, we find the formation of vinylidene-like structures is always accompanied by a characteristic charge separation on the carbon skeleton. These heuristics will be useful in identifying tautomers and motivating the ultrafast charge-transfer detection methods for future experiments.

Ionization and ultrafast hydrogen migration of methylamine in few-cycle intense near-infrared laser fields

Double ionization and ultrafast hydrogen migration of methylamine induced by a few-cycle intense near-infrared laser pulse are investigated by the coincidence momentum imaging method. By reference to the results obtained by DFT calculations, the peak profiles in the kinetic energy release distributions have been assigned to the singlet and triplet decomposition channels of CH3NH22+. The anisotropy in the angular distribution of the ejection direction of the fragment ions is interpreted based on the symmetries of the (7a’) HOMO orbital. By the pump–probe measurements, it is revealed that the ultrafast hydrogen migration in CH3NH2+ proceeds within ∼ 30 fs.

Revealing hydrogen migration effect on ammonia synthesis activity over ceria-supported Ru catalysts

Catalytic reactions involving hydrogen over reducible oxide-supported metal catalysts are inseparable from the hydrogen storage capacity and hydrogen migration, which are mainly dependent on the interaction between reducible oxides and active metals. In this work, we report that the hydrogen migration rate of Ru/CeO2 could be tuned by changing cerium nitrate solvents for the preparation of ceria. There are more kinds of oxygen species and a large amount of Ce3+ concentration, defects and Ru−O−Ce interfacial sites for Ru catalyst supported on ceria obtained by ethanol-precipitated synthesis, resulting in a reduction in the amount of the exposed Ru species and proportion of Ru metal. In such a case, the migration and desorption of hydrogen species as well as nitrogen activation would be inhibited. Conversely, there are a higher ratio of Ru metal and a great deal of the Ru exposure for Ru catalyst supported on ceria obtained by water-precipitated synthesis, facilitating the migration and desorption of hydrogen species, as well as nitrogen activation. As a result, the water-precipitated synthesized ceria-supported Ru catalyst has 4.9-fold higher in catalytic activity than Ru catalyst supported on the ethanol-precipitated synthesized ceria. This work provides insight into the design of Ru catalysts used ammonia synthesis by controlling hydrogen spillover and migration between Ru species and CeO2.

Hydrogen embrittlement and failure mechanisms of multi-principal element alloys: A review

• Hydrogen embrittlement (HE) of multi-principal element alloys is reviewed. • HE behavior between traditional alloys and high-entropy alloys is compared. • Further research directions on HE of high-entropy alloys are identified. • Strategy for the improvement of strength and HE-resistance are suggested. Multi-principal element alloys exhibit excellent physical, chemical and mechanical properties, and they are used as novel structural materials for potential applications in nuclear energy, hydrogen energy, and petrochemical fields. However, exposing components made of the alloys to service conditions related to the mentioned applications may induce hydrogen embrittlement (HE) as one of the typical failure mechanisms. In this review, we report and summarize the progress in understanding HE in multi-principal element alloys, with a particular focus on high-entropy alloys (HEAs). The review focuses on four aspects: (1) hydrogen migration behavior (hydrogen dissolution, hydrogen diffusion, and hydrogen traps); (2) factors affecting HE (hydrogen concentration, alloy elements and microstructure); (3) tensile mechanical properties in the presence of hydrogen and micro-damage HE mechanisms; (4) the design concept for preventing hydrogen-induced mechanical degradation. The differences in the HE behavior and failure mechanisms between HEAs and traditional alloys are compared and discussed. Moreover, specific research directions for further investigation of fundamental HE issues and a strategy for a simultaneous improvement in strength and HE resistance are identified.

The Role of Carbon in the Formation of Intrinsic Point Defects and Hydrogen Migration in α‐Al2O3‐Based Tritium Permeation Barriers

The impurity effect is one of the major concerns for α‐Al2O3‐based tritium permeation barriers (TPBs). The effect of carbon, a common impurity element in α‐Al2O3, on the formation of intrinsic point defects and hydrogen migration behaviors is investigated by first‐principles calculations. It is found that carbon has a significant influence on the existing form, charge state, and relative stability in α‐Al2O3. In view of the hydrogen migration, carbon is not beneficial for the hydrogen permeation resistance in α‐Al2O3‐based TPBs because carbon can remarkably reduce the hydrogen migration barrier in α‐Al2O3.

Key role of plastic strain gradient in hydrogen transport in polycrystalline materials

Hydrogen transport by moving dislocations is one of the key mechanisms for hydrogen embrittlement, which is considered responsible for local hydrogen accumulation at preferential crack initiation sites. Although numerous experiments corroborate this mechanism, there are few theoretical models for it available. In the present work, a novel hydrogen transport model is developed within the coupled framework of crystal plasticity and hydrogen balance. The hydrogen transport flux in the present model is divided into two parts: the first-order hydrogen transport flux driven by plastic strain and the second-order hydrogen transport flux driven by plastic strain gradient. With the calibrated parameters by fitting experimental results, the first-order hydrogen transport flux is negligible even for nickel with a low hydrogen diffusivity. In polycrystals, due to the intrinsic plastic heterogeneity induced by grain orientation mismatch, the second-order hydrogen transport flux results in significant dynamic hydrogen segregation at grain boundaries during deformation, which is expected to drive the hydrogen-induced intergranular cracking as observed in experiments. This dynamic segregation behavior is related to the evolution rate of geometrically necessary dislocations, depending on the grain boundary characters. The roles of grain refinement in hydrogen transport are clarified with the present model. This study shows the vital role of plastic strain gradient induced by grain boundary constraint in hydrogen transport, which is essential in understanding hydrogen migration and accumulation in deformed polycrystalline metals.

Precise equilibrium structures of 1H- and 2H-1,2,3-triazoles (C2H3N3) by millimeter-wave spectroscopy.

The 1H- and 2H-1,2,3-triazoles are isomeric five-membered ring, aromatic heterocycles that may undergo chemical equilibration by virtue of intramolecular hydrogen migration (tautomerization). Using millimeter-wave spectroscopy in the 130-375GHz frequency range, we measured the spectroscopic constants for thirteen 1H-1,2,3-triazole and sixteen 2H-1,2,3-triazole isotopologues. Herein, we provide highly accurate and highly precise semi-experimental equilibrium (re SE) structures for the two tautomers based on the spectroscopic constants of each set of isotopologues, together with vibration-rotation interaction and electron-mass distribution corrections calculated using coupled-cluster singles, doubles, and perturbative triples calculations [CCSD(T)/cc-pCVTZ]. The resultant structures are compared with a "best theoretical estimate" (BTE), which has recently been shown to be in exceptional agreement with the semi-experimental equilibrium structures of other aromatic molecules. Bond distances of the 1H tautomer are determined to <0.0008 Å and bond angles to <0.2°. For the 2H tautomer, bond angles are also determined to <0.2°, but bond distances are less precise (2σ ≤ 0.0015). Agreement between BTE and re SE values is discussed.