Hydride Formation Research Articles

The formation of a lithium-iridium complex hydride toward ammonia synthesis.

Noble metal elements are focal catalytic candidates for many chemical processes, but have received little attention in the field of nitrogen fixation except ruthenium and osmium. Iridium (Ir), as a representative, has been shown to be catalytically inactive for ammonia synthesis because of its weak nitrogen adsorption and severe competitive adsorption of H over N that strongly inhibits the activation of N2 molecules. Here we show that, upon compositing with lithium hydride (LiH), iridium can catalyze ammonia formation at much enhanced reaction rates. The catalytic performance of the LiH-Ir composite can be further improved by dispersion on a MgO support with a high specific surface area. At 400 °C and 10 bar, the MgO-supported LiH-Ir (LiH-Ir/MgO) catalyst shows a ca. 100-fold increase in activity compared to the bulk LiH-Ir composite and the MgO-supported Ir metal catalyst (Ir/MgO). The formation of a lithium-iridium complex hydride phase was identified and characterized, and this phase may be responsible for the activation and hydrogenation of N2 to NH3.

Formation of distinct iron hydrides via mechanistic divergence in directed C-H Bond activation of aryl ketones, esters and amides.

Directing groups play an important role in controlling the selectivity of C-H bond activation. Here we demonstrate that for iron, the nature of the directing group (e.g., ketone, ester, or amide) influences the C-H activation process. In this study the C-H bond activation step either occurs with or without the assistance of the directing group resulting in distinct cis- and trans-isomers of the corresponding iron hydride.

RESEARCH INTO THE EFFECT OF ETCHING PROCESS OF POROUS TITANIUM CURRENT COLLECTORS IN HYDROCHLORIC ACID ON THE PERFORMANCE OF WATER ELECTROLYZERS WITH A PROTON EXCHANGE MEMBRANE

Based on the modern methods of SEM, voltammetry, and gravimetric analysis, samples of current collectors used in electrolyzers with a solid polymer electrolyte, made of porous titanium with various degrees of etching in concentrated hydrochloric acid, were studied. A gravimetric study of the etching process of samples of various sizes from porous titanium showed that throughout the process there is a loss of mass of the sample, with the exception of two short intervals, presumably due to the formation of hydrides (60-80 sec) and oxides (4-5 min), and the samples of smaller volumes were more sensitive to weight loss and weight growth. The use of the SEM method made it possible to reveal that etching over different time intervals changes the structure of porous titanium, reducing the average particle size and increasing their porosity .In this case, the surface inhomogeneity increases due to the formation of cavities in titanium and deterioration of the contact of the current collector surface with the catalytic layer. The consequence of this is the difference in the current-voltage characteristics of electrolysis cells with different duration of etching of the current collectors: there is a decrease in the productivity of electrolysis with an increase in the duration of etching of the current collectors by ~8% for etching more than 1 minute and ~18% for etching more than 4 minutes as compared to the simultaneous immersion of the sample in acid to clean the surface.

Electrocatalytic hydrogen evolution reaction by a Ni(N2O2) complex based on 2,2′-bipyridine

A Ni complex containing a N2O2 ligand is active for the hydrogen evolution reaction. Mechanistic studies suggest the formation of hydrogen-bonded adducts facilitates hydride formation and near barrierless hydride protonation.

Stability of Subnanometer MoS Wires under a Realistic Environment.

The interaction of small molecules with low-dimensional structures plays a major role in many important practical processes such as metal hydride formation, energy storage systems, and catalysis. In this work, we carried out first-principles density functional theory calculations of hydrogen and oxygen adsorption as well as their diffusion on subnanometer MoS nanowires. The nanowires are robust against adsorption of hydrogen. On the other hand, interaction with oxygen shows that the nanowires can oxidize with a small barrier (0.20 eV). In addition, our findings indicate that the interaction with hydrogen or oxygen does not modify the metallic character of the nanowire. The calculations also show that the singlet state is the most stable for 2O adsorbed on the MoS nanowire. Such results open the path for understanding the behavior of MoS nanowires under a realistic environment.

HYDROGEN ACCUMULATOR IN AUTONOMOUS ENERGY DEVICES

The purpose of the research. One of the main difficulties into solving the issues of energy supply for autonomous consumers with heat and electricity in agricultural production is the inconsistency of supply schedules and energy consumption. The uneven nature of the operating modes of wind and solar power plants requires the creation of an energy storage system. In this connection, the task of creating autonomous power plants that use hydrogen and thermal energy storage systems arises. Results. A fundamentally new type of porous gas-reinforced materials − gazars, which are the basis of hydrogen batteries − have been investigated. They have unique properties that are very valuable for structural materials: strength and lightness, as well as a number of special properties. Consider the existing methods of hydrogen storage − in the form of hydrides, in liquid and compressed states, which have significant disadvantages for their use in energy devices. Thus, hydride batteries have a number of attractive aspects: comparative safety, soft storage mode and hydrogen yield. However, they have a low capacity and require expensive metals: La, Ni, Ti and rare earth metals, the reserves of which in the earth's crust are limited. The structure and properties of gas-reinforced metals, which have a monolithic matrix and a cellular structure of the porous space, have been investigated to determine the functional capabilities and prospective areas of their use. The dependence of the porosity on the relative size of the pores for various options for their placement in the sample was established. It is shown that in order to accelerate the processes of saturation and discharge of battery gases and to increase their capacity, battery cells with closed unidirectional cylindrical pores should be used. Hydrogen saturation is conducted when one of the ends of the battery is heated and the rest of the surface is cooled with a temperature difference of 573…773 K. Conclusions. Research in laboratory conditions showed that batteries based on porous metals, having a monolithic matrix and a cellular structure of the porous space, have advantages compared to the well-known ones: hydride, balloon, cryogenic. This is a relatively high hydrogen capacity; relative cheapness; possibility of multiple use; the possibility of using batteries as elements of power structures, as well as the use of unpurified technical hydrogen.

Phase transformations and microstructure evolutions during depressurization of hydrogenated Fe–Mn–Si–Cr alloy

Hydride formation and associated phase transformations have been extensively studied in pure Fe. However, the understanding of hydrogenation in Fe-based alloy systems is still lacking. Such an investigation is particularly important in the case of austenitic (face-centered cubic) steels given that hydrogen has been reported to alter the austenite phase stability. In the current work, we investigate the phase transformations associated with depressurization of non-hydrogenated and hydrogenated Fe–Mn–Si–Cr alloy (FMS) (Fe-28.84Mn-7.04Cr-6.14Si, in mass %) using in-situ x-ray diffraction technique. Additionally, we study the change in microstructure using electron backscatter diffraction (EBSD) and electron channeling contrast imagining (ECCI).

Energy conditions for the formation of magnesium hydride

In the present article we consider a novel approach to analyze the processes and kinetics of transformation of magnesium to hydride. Here approach consists to take into account the contributions of mechanics factors such as the work of external forces, the energy of elastic deformation and the energy required to form a unit volume nucleate of new phase. Request for a stable state of either a mechanical system or thermodynamic conditions governing a phase transformation, is to determine a minimum value to the total energy of the system. Analyzing the stability conditions needed when forming a metal hydride nucleus at constant temperature and pressure needs to consider the following: - the volumetric effects at the phase transformation, - the ratio of elastic moduli of metal to hydride phase, - the work spent at the formation of a unit volume of hydride. Under these considerations, it was shown that the most energetically favorable is forming an ellipsoidal hydride nucleus. Moreover, the larger difference in semi-axes, the more stable ellipsoid nucleus. Then, calculations of the stress-strain level states on both sides of the metal/hydride interface have been carried out. It was shown that the near-boundary range during the phase transformation is the place where accumulate inhomogeneous and intense stresses, which can contribute to two parallel processes. Firstly, increase of hydrogen concentration could appear in the distorted area. Secondly, a local accumulation of incoherent boundaries in between the two phases will develop stresses exceeding by more twice the shear yield stress. The presence of these compression zones could give rise new defects such as dislocations, micro-cracks. Consequently this should lead to decrease in magnitude of the powder of material.

Formation of vacancy-type defects and hydride introduced by irradiation in pure titanium

The effect of hydrogen ion irradiation on the formation of hydride and vacancy-type defects in pure titanium was investigated by X-ray diffraction (XRD), Doppler broadening spectrum (DBS), and coincidence Doppler broadening spectrum (CDB) based on slow positron beam. The XRD results showed that γ-TiH was observed in single hydrogen ion-irradiated and hydrogen + deuterium (H + D) sequentially irradiated specimens but not in the single deuterium plasma-implanted sample. This finding indicates that the vacancy-type defects caused by H ion irradiation greatly promoted the formation of γ-TiH. The DBS results showed that for the single D plasma-implanted sample, the damage peak was closer to the surface region and lower compared to the other two samples containing γ-TiH, indicating that vacancy generated by lattice distortion didn't diffuse to the depth of the matrix, and the concentration of that was smaller, which was not conducive to the deuteride formation. For the H + D sequentially irradiated sample, the number of hydrogen-vacancy complexes (HmVn) further increased compared with the single H ion-irradiated sample. Thus, the effective volume of vacancy defects was reduced, which led to the decrease in the S parameter.

Mechanism of hydrogen-induced defects and cracking in Ti and Ti–Mo alloy

Mechanism of Hydrogen-induced defects and cracking in Ti and Ti–Mo alloy was systematically analyzed from the perspective of microstructure. Results show that more hydrogen atoms can be dissolved in Ti–Mo alloy due to the existence of β phase, and the precipitation amount of hydride is reduced under the same hydrogen charging conditions. The analysis of positron annihilation results show that the solid solution of Mo element reduces the hydrogen induced defect concentration in the alloy and inhibit the combination of hydrogen and defects. At the same time, Mo atom can affect the electronic structure of Titanium hydrides, and then reduce the bonding between titanium atoms and hydrogen atoms, thereby reducing the formation of brittle titanium hydride. The reduction of hydride and hydrogen induced defect concentration significantly decrease the hardening rate of Ti–Mo alloy, thereby effectively reducing the hydrogen embrittlement sensitivity of titanium and inhibiting its hydrogen absorption cracking tendency.

Diffusion and redistribution of hydrogen atoms in the vicinity of localized deformation zones

The presence of hydrogen atoms in the lattice of polycrystalline metals can lead to hydrogen embrittlement. The diffusion of hydrogen atoms and formation of hydrides depend on several parameters such as the microstructure of the metal alloy, the presence of stress risers, and the applied loading condition. In this study, a non-local crystal plasticity finite element model is coupled with hydrogen diffusion equations to study the effects of such parameters on the stress-assisted diffusion of hydrogen atoms in zirconium polycrystals. The concentrations of hydrogen atoms in the lattice and dislocation trap sites under different scenarios are studied to deconvolute the effects of texture, microstructure, and applied strain on hydrogen diffusion. It is shown that the concentration of hydrogen in the lattice peaks in the vicinity of grain boundaries and most importantly, at the triple-junction points. It is further shown that in localized deformation zones, such as twin or notch tips where dislocations concentrate, the effects of trapped hydrogen content can be significant.

Stress corrosion cracking of TC4 ELI alloy with different microstructure in 3.5% NaCl solution

Stress corrosion cracking (SCC) of TC4 ELI alloy was investigated by slow strain rate test (SSRT) with an in site electrochemical experiment in 3.5% NaCl solution. Results indicated that both lamellar microstructure (LM) and equiaxed microstructure (EM) of TC4 ELI alloy possessed a certain stress corrosion sensitivity at the strain rate from 6 × 10 −5 s −1 to 4 × 10 −4 s −1 , which attained maximum at 1 × 10 −4 s −1 . Meanwhile, the LM of TC4 ELI alloy exhibited significantly higher stress corrosion sensitivity than the EM, it could be ascribed to the higher α phase content and present of triangular grain boundaries, which promoted an active anodic reaction and facilitated the formation of hydrides. Finally, partial cleavage plane was found in TC4 ELI alloy with LM after fracture at the strain rate 1 × 10 −4 s −1 . The SCC mechanism could be explained by the interaction of anodic dissolution along with hydrogen-induced cracking. • The stress corrosion susceptibility of titanium alloy was strongly affected by strain rate, both LM and LM of TC4 ELI alloy possessed a certain stress corrosion sensitivity within the range from 6 × 10 −5 s −1 to 4 × 10 −4 s −1 , and obtain maximum at the strain rate 1 × 10 −4 s −1 . • The LM of TC4 ELI alloy exhibited significantly higher stress corrosion sensitivity than the EM, it could be ascribed to the higher α phase content and present of triangular grain boundaries, which promoted an active anodic reaction and facilitated the formation of hydrides. • Partial cleavage plane was found in TC4 ELI alloy with LM after fracture at the strain rate 1 × 10 −4 s −1 , the SCC mechanism could be explained by the combined effect of anodic dissolution and hydrogen induced cracking.

Comparing B-H Bond Activation in NiIIX(NNN)-Catalyzed Nitrile Dihydroboration (X = Anionic N-, C-, O-, S-, or P-donor).

One of the key steps in many metal complex-catalyzed hydroboration reactions is B-H bond activation, which results in metal hydride formation. Anionic ligands that include multiple lone pairs of electrons, in cooperation with a metal center, have notable potential in redox-neutral B-H bond activation through metal-ligand cooperation. Herein, using an easily prepared NpyridineNimineNpyrrolide ligand (L2)-, a series of divalent NiIIX(NNN) complexes were synthesized, with X = bromide (2), phenoxide (3), thiophenoxide (4), 2,5-dimethylpyrrolide (5), diphenylphosphide (6), and phenyl (7). The complexes were characterized using 1H and 13C NMR spectroscopy, mass spectrometry, and X-ray crystallography and employed as precatalysts for nitrile dihydroboration. Superior activity of the phenoxy derivative (3) [vs thiophenoxy (4) or phenyl (7)] suggests that B-H bond activation occurs at the Ni-X (vs ligand Ni-Npyrrolide) bond. Furthermore, stoichiometric treatment of 2-7 with a nitrile showed no reaction, whereas stoichiometric reactions of 2-7 with pinacolborane (HBpin) gave the same Ni-H complex for 2, 3, and 5. Considering that only 2, 3, and 5 successfully catalyzed nitrile dihydroboration, we suggest that the catalytic cycle involves a conventional inner sphere pathway initiated by substrate insertion into Ni-H.

Detection of zirconium hydrides in transmission electron micrographs using deep neural networks

Zirconium alloys are commonly employed in nuclear power applications. Under typical operating conditions, hydrogen ingress can lead to the formation of brittle Zr hydrides in the alloy. To study this behavior, transmission electron microscopy (TEM) is routinely used to image hydrides in Zr-alloys. However, the analysis of these TEM micrographs is a complex time-consuming task. Here, we employed a mask region-based convolutional neural network (Mask R-CNN) to automate an essential part of the analysis process: the identification and annotation of hydrides. In addition, although training a neural network usually requires large training datasets (in the order of thousands of images), the proposed framework was developed using a limited training dataset with the recourse of transfer learning. This work shows that the Mask R-CNN is capable of correctly and quickly labeling thermo-mechanically cycled hydrides in TEM images of pressure tube material.

Microstructure and Hydrogen Permeability of Nb-Ni-Ti-Zr-Co High Entropy Alloys.

Hydrogen separation membranes are one of the most promising technologies for hydrogen purification. The development of high-entropy alloys (HEAs) for hydrogen separation membranes is driven by a "cocktail effect" of elements with different hydrogen affinities to prevent hydride formation and retain high permeability due to the single-phase BCC structure. In this paper, equimolar and non-equimolar Nb-Ni-Ti-Zr-Co high entropy alloys were fabricated by arc melting. The microstructure and phase composition of the alloys were analyzed by scanning electron microscopy and X-ray diffraction, respectively. The hydrogen permeation experiments were performed at 300-500 °C and a hydrogen pressure of 4 bar. In order to estimate the effect of composition and lattice structure on hydrogen location and diffusivity in Nb-Ni-Ti-Zr-Co alloy, ab initio calculations of hydrogen binding energy were performed using virtual crystal approximation. It was found that Nb-enriched and near equimolar BCC phases were formed in Nb20Ni20Ti20Zr20Co20 HEA while Nb-enriched BCC and B2-Ni(Ti, Zr) were formed in Nb40Ni25Ti18Zr12Co5 alloy. Hydrogen permeability tests showed that Nb20Ni20Ti20Zr20Co20 HEA shows lower activation energy and higher permeability at lower temperatures as well as higher resistance to hydrogen embrittlement compared to Nb40Ni25Ti18Zr12Co5 alloy. The effect of composition, microstructure and hydrogen binding energies on permeability of the fabricated alloys was discussed.

Nitrile modulated-Ni(0) phosphines in trans-selective phenylpropenoids isomerization: An allylic route by a regular η1-N(end-on) or an alkyl route via a flipped-nitrile?

Acetonitrile has been widely viewed as a weakly coordinating solvent in metal-catalyzed reactions. Evidence is presented herein that it worked as an actor ligand in nickel-catalyzed stereoselective isomerizations of eugenol, methyl eugenol, estragole, and allylphenol, with trans-isomerized products of ≥95%. Nickel(0)(nitrile)phosphines were generated in situ from Ni(II) salt in the presence of phosphines, Zn, and nitrile with Ni/phosphines/Zn/nitrile mole ratio as low as 1:2:1:1. The isomerization of eugenol gave trans-isoeugenol of >97% in 30 min at r.t. with Ni turnover frequency (TOF) up to 1,116 h−1 and the activation energy of 61 kJ·mol−1. High selectivity of trans-isoeugenol was retained in continuous and multi-gram trials. Density functional theory (DFT)/PBE0-D3 calculations rationalized the possible formation of nickel hydride (i.e., Ni(H)(η1-CH2CN)(phosphine) complex) from η1-N(end-on)-Ni complex. This nitrile modulated-Ni(0) complex indicated the complex followed an alkyl-type isomerization, instead of a conventional allylic-type one.

The bonding of H in Zr under strain

Accurate computer simulation is important for understanding the role of irradiation-induced defects in zirconium alloys found in nuclear reactors. Of particular interest is the distribution and trapping of hydrogen, and the formation of zirconium hydride. These simulations require an accurate representation of Zr-H bonding in order to predict the behaviour of H around atomic-scale defects, dislocation lines, and dislocation loops. Here we explore the bonding of H in Zr under strain, how well it is represented by state-of-the-art Embedded Atom Method (EAM) potentials, and what physics is needed for an accurate representation in a Linear Combination of Atomic Orbitals (LCAO) Density Functional Theory (DFT) framework. For H in dilute solution under hydrostatic strain in the range -10% to +10%, solution energies and Zr-H bond lengths computed using EAM potentials are found to be in poor agreement with plane-wave DFT results. We note that the bond lengths are in a poor agreement even in equilibrium. LCAO basis sets are used to explore the importance of electron distribution around H atoms, and the transfer of electrons between H and Zr. The electron distribution around H atoms is found to be important to the explanation of the difference between octahedral and tetrahedral interstitial sites for H, with H in a tetrahedral site having very similar bonding to H in zirconium hydrides. The interatomic electron transfer has a smaller impact but is needed for maximum accuracy.

A Promising Energy Storage System Based on High-Capacity Metal Hydrides

In this paper, based on the study of hydrogen accumulation in the electrodes of nickel–cadmium batteries, a high-capacity hydrogen storage system (HSS) is proposed. It has been experimentally proven that hydrogen accumulates in the electrodes of nickel–cadmium batteries in large quantities over the course of their operation. It has been shown that hydrogen accumulates in metal–ceramic matrices of sintered oxide–nickel electrodes in the form of metal hydrides. The gravimetric capacity of the nickel matrix is 20.3 wt% and the volumetric capacity is 406 kg m−3. The obtained gravimetric capacities for metal–ceramic matrices exceed almost four times the criteria for onboard hydrogen storage systems established by the US Department of Energy (DOE), as well as previously obtained results for any reversible hydrogen accumulation materials. In addition, in our previous papers, it was proved that if we use thermal runaway for the desorption of hydrogen from metal hydrides then the kinetic and thermodynamic criteria established by the US DOE may be significantly exceeded. Thus, within the framework of the proposed HSS, using the electrochemical method of hydrogen accumulation and the thermal runaway process, one can not only achieve all of the criteria established by the US DOE for HSS but also significantly exceed them.

Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry.

Electrochemical mass spectrometry (EC-MS) is combined with chronoamperometry to quantify H coverage associated with the surface hydride phase on Cu(111) in 0.1 mol/L H2SO4. A two-step potential pulse program is used to examine anion desorption and hydride formation, and the inverse, by tracking the 2 atomic mass unit (amu) signal for H2 production in comparison to the charge passed. On the negative potential step, the reduction current is partitioned between anion desorption, hydride formation, and the hydrogen evolution reaction (HER). For modest overpotentials, variations in partial processes are evident as inflections in the chronoamperometry and EC-MS signal. On the return step to positive potentials, hydride decomposition by H recombination to H2 occurs in parallel with sulfate adsorption. The challenge associated with the inherent diffusional delay in the EC-MS response is mitigated by total H2 collection and steady-state analysis facilitated by the thin-layer EC-MS cell geometry as demonstrated for the HER on a non-hydride forming Ag electrode. Analysis of the respective transients and steady-state response on Cu(111) reveals a saturated hydride fractional coverage of 0.67 at negative potentials with an upper bound charge of 106 μC/cm2 (average electrosorption valency of ≈1.76) associated with adsorption of the () mixed sulfate-water adlayer at positive potentials.

Influence of the Current Regime during Electrodeposition in a Cr(III)-Containing Fe-Cr-Ni Electrolyte on the Near-Surface pH, Alloy Composition, and Microcrack Behavior

This study shows the electrodeposition of Fe-Cr-Ni alloys using the advantages of a stepped direct-current deposition in a Cr(III)-containing electrolyte, and its influence on the pH value. The resulting coatings are uniform and free of microcracks, with a Cr content around 30% and thicknesses above 10 µm. The influence of the current mode (direct current, stepped direct current, pulsed current) on pH development is investigated and correlated with the arising microstructure and alloy composition. Considering the current flow, it can be stated that pauses interrupt high overvoltage and restrain the pH increase at the cathode. The associated formation of chromium hydrides and their deposition onto the chromium layer, leading to cracking, is thus reduced. In this work, direct evidence for this theory and a suggestion for near-surface pH measurement during electrodeposition are presented.