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For the next-generation high temperature microreactors, yttrium dihydride (YH2) is an attractive solid state neutron moderator. Despite a number of recent investigations, the mechanism of hydrogen transport remains poorly understood. Experimental evaluations of diffusivity are inconclusive with large variations in diffusivities and activation energies. In this work, we perform ab initio molecular dynamics (AIMD) simulations on YH2 for temperatures spanning 300 K to 1200 K. Our main finding is that YH2 shows a superionic-like behavior with hydrogen atoms hopping from one native site to another above a characteristic temperature of 800 K. This correlated motion results in quasi-one-dimensional string-like displacements that enable the hydrogen atoms to diffuse rapidly. We confirm that the octahedral sites are mostly unoccupied, although channeling through them is the most favored pathway between lattice hops above 800 K. At the highest temperature of 1200 K, the string relaxation time is merely of the order of a few picoseconds, which indicates a liquid-like diffusive behavior. Based on the formation of spontaneous thermal vacancies, an order-disorder crossover temperature Tα 800 K is established for YH2 with an activation energy of 0.83 eV for hydrogen diffusion in the superionic-like state.

Exploration of molybdenum complexes as homogeneous hydrogenation catalysts has garnered significant attention, but hydrogenation of unactivated olefins under mild conditions are scarce. Here, we report the synthesis of a molybdenum complex, [Cp*Mo(Ph 2 PC 6 H 4 S−CH = CH 2 )(Py)] + ( 2 ), which exhibits intriguing reactivity toward C 2 H 2 and H 2 under ambient pressure. This vinylthioether complex showcases efficient catalytic activity in the hydrogenation of various aromatic and aliphatic alkenes, demonstrating a broad substrate scope without the need for any additives. The catalytic pathway involves an uncommon oxidative addition of H 2 to the cationic Mo(II) center, resulting in a Mo(IV) dihydride intermediate. Moreover, complex 2 also shows catalytic activity toward C 2 H 2 , leading to the production of polyacetylene and the extension of the vinylthioether ligand into a pendant triene chain. Exploration of molybdenum complexes as homogeneous hydrogenation catalysts has garnered significant attention, but hydrogenation of unactivated olefins under mild conditions are scarce. Here, the authors report the synthesis of a cationic Mo(II) complex, which exhibits intriguing reactivity toward C 2 H 2 and H 2 under ambient pressure.

The first examples of tetrasubstituted conjugated bis‐guanidinate (CBG) supported monomeric and thermally stable gallium dihalides [LGaX2], (X=Cl (Ga−Cl), I (Ga−I)) and dihydride (Ga−H) [LGaH2] (where L=(ArHN)(ArN)−C=N−C=(NAr)(NHAr); Ar=2,6‐Et2−C6H3) compounds are reported. The reaction of in situ generated LLi with 1.0 equiv. GaX3 (X=Cl, I) afforded compounds Ga−Cl and Ga−I. The reaction between Ga−Cl and Li[HBEt3] in benzene yielded the dihydride compound Ga−H. All reported compounds (Ga−Cl, Ga−I, and Ga−H) were characterized by NMR, HRMS, and single‐crystal X‐ray diffraction studies. Ga−H was probed for the hydroboration of carbodiimides (CDI), isocyanates, and isothiocyanates with HBpin. Compound Ga−H was also found effective for the catalytic hydroboration of imines, nitriles, alkynes, esters, and formates, affording the corresponding products in quantitative yields. Stoichiometric reactions with a CDI were performed to establish the catalytic cycle. The bis‐guanidinate stabilized, structurally characterized gallium dihalides (Ga−Cl, Ga−I) and dihydride (Ga−H) compounds are reported. Gallium hydride (Ga−H) is an effective catalyst for the chemoselective reduction of heteroallenes with HBpin. Moreover, Ga−H is a potent catalyst for the hydroboration of imines, nitriles, alkynes, esters, and formates, yielding the corresponding hydroborated products.

Compliance with imposed hydrogen concentration limits in the lithium loop of the DEMO-Oriented Neutron Source (DONES) requires the installation of an yttrium-based hydrogen trap. To determine an appropriate H-trap design, it is essential to have access to a numerical tool capable of simulating hydrogen transport in the DONES lithium loop connected to an yttrium pebble-bed. In the past, a simplified model was created that allows such calculations when hydrogen concentrations in the lithium are low. However, in certain DONES operating phases, the concentration in the lithium is high and in a range where yttrium dihydride (YH 2 ) formation is likely. Due to the anticipated great impact of YH 2 formation on the H-trap performance a new model is developed that includes the mechanism of hydride formation. It is based on a mathematical reproduction of complete pressure-composition isotherms of the Li–H and Y–H systems. Thus, the conditions that trigger YH 2 formation are determined and the variation of hydrogen solubility in different yttrium hydride phases is deduced. An approximate concentration-dependent relationship of hydrogen diffusivity in yttrium is derived and incorporated into the model. Simulations are performed to analyze the dynamics of the concentration decrease during purification of the lithium circuit prior to the experimental DONES phase by varying design parameters of the trap. It is found that hydride formation greatly increases the hydrogen gettering capacity of the H-trap and limits the maximum concentration in the lithium. Indeed, YH 2 formation may be purposefully triggered to exploit its beneficial properties for DONES. Simulations of the hydrogen purification process during the experimental phase of DONES show that the H-trap must be replaced at least every 28 days to meet tritium limits. This work sets the conditions for the required pebble-bed mass of the H-trap at a given temperature to comply with the DONES safety requirements. Finally, the model is validated by numerical reproduction of experimental results.

Aluminum hydrides are versatile compounds utilized as reducing agents, precursors of aluminum complexes, and as catalysts for polymerization reactions. However, their photophysical properties have been overlooked, although several luminescent aluminum complexes have been utilized conventionally for emitting layers in modern light-emitting devices. Herein, we report the synthesis and photophysical properties of a luminescent β-diketiminate dihydride complex through the reaction between lithium aluminum hydride and the corresponding ligand. The obtained compound exhibits crystallization-induced emission (CIE) properties at room temperature and long-lifetime phosphorescence at 80 K. Our experimental and theoretical investigations suggest that low-energy molecular vibration could play an important role in the realization of the CIE property.

The effect of Al addition on the structure, microstructure and hydrogen storage properties of the ternary TiVNb alloy was investigated from small amounts to equimolar composition. Alx(TiVNb)1−x (x = 0.05, 0.175 and 0.25) alloys are bcc single-phase materials with decreasing lattice parameters with increasing Al content. Al addition progressively decreases the hydrogen storage capacity but also destabilizes fcc dihydride formation for alloys with x ≤ 0.10. Among the different compositions, the most promising alloy was found to be that with x = 0.05 Al content that exhibited high initial storage capacity (2.96 wt.%), a less stable hydride (ΔH = −52 kJ/mol H2 and ΔS = −141 J/K∙mol H2), better desorption properties (desorption onset temperature around 100 °C) and enhanced reversible capacity during cycling (2.83 wt.%) compared to the ternary TiVNb. In situ and ex situ synchrotron X-ray powder diffraction, together with thermal desorption experiments, showed improved desorption properties with Al addition, together with a two-step reaction with hydrogen. These findings highlight the use of small quantities of lightweight Al in refractory multi-principal element alloys as a promising approach for enhancing the solid-state hydrogen storage performance of bcc-type alloys.

The recent report of near-ambient superconductivity in the nitrogen-doped lutetium hydride has attracted considerable attention. Subsequent follow-up studies confirmed the pressure-induced color changes in both N-free and N-doped LuH 2 but failed to reproduce superconductivity. It remains a puzzle why the samples in the original report exhibited pronounced resistance anomaly reminiscent of the superconducting transition. Here, we show that percolation of metallic grains with high conductivity through the insulating surfaces in cold-pressed LuH 2 samples can occasionally produce sharp resistance drops, which even display magnetic field and/or current dependences but stay far from zero resistance. The insulating surface of LuH 2 grain should be attributed to the modification of hydrogen stoichiometry or the contamination by oxygen/nitrogen, resulting in an increase of resistance by over six orders of magnitude. Such an effect is more significant than that discovered recently in LaH 3± x , which may indicate that LuH 2 can be a potential superionic conductor. Our results call for caution in asserting the resistivity drops as superconductivity and invalidate the background subtraction in analyzing the corresponding resistance data.

We are reporting the synthesis, the physicochemical, and the hydrogen sorption properties of a novel bcc high entropy alloy Ti0.30V0.25Cr0.10Zr0.10Nb0.25. At room temperature, the alloy rapidly absorbs hydrogen reaching a capacity of 2.0 H/M (3.0 wt.%) and forming a dihydride with fcc structure, as confirmed by both synchrotron X-ray diffraction and neutron diffraction. The absorption Pressure–Composition Isotherms corroborated with synchrotron X-ray diffraction prove that the reaction with hydrogen occurs within two steps, i.e., bcc alloy → bcc monohydride → fcc dihydride. The thermodynamic parameters calculated for the second step transformation evidence the formation of a stable dihydride with ΔHabs = −75 kJ/molH2. The phase transition during hydrogen/deuterium desorption was investigated by in situ synchrotron X-ray and neutron diffraction confirming a reversible reaction with hydrogen. Furthermore, the cycling properties show a decrease of the capacity over the first cycles followed by a stabilization at 2.44 wt.%, whereas the absorption kinetics improve after the first cycle reaching full capacity after only 30 s at room temperature.

For the next-generation high temperature microreactors, yttrium dihydride (YH 2 ) is an attractive solid state neutron moderator. Despite a number of recent investigations, the mechanism of hydrogen transport remains poorly understood. Experimental evaluations of diffusivity are inconclusive with large variations in diffusivities and activation energies. In this work, we perform ab initio molecular dynamics (AIMD) simulations on YH 2 for temperatures spanning 300 K to 1200 K. Our main finding is that YH 2 shows a superionic-like behavior with hydrogen atoms hopping from one native site to another above a characteristic temperature of 800 K. This correlated motion results in quasi-one-dimensional string-like displacements that enable the hydrogen atoms to diffuse rapidly. We confirm that the octahedral sites are mostly unoccupied, although channeling through them is the most favored pathway between lattice hops above 800 K. At the highest temperature of 1200 K, the string relaxation time is merely of the order of a few picoseconds, which indicates a liquid-like diffusive behavior. Based on the formation of spontaneous thermal vacancies, an order-disorder crossover temperature T α ~ 800 K is established for YH 2 with an activation energy of 0.83 eV for hydrogen diffusion in the superionic-like state.

The evolution of the phase contents and kinetic characteristics of hydrogen desorption processes by composites based on the eutectic alloy Mg89Ni11, including those with additives of graphene-like material (GLM), obtained by reactive ball-milling in hydrogen, were studied using the in situ high-temperature X-ray diffraction technique, volumetric measurements on a Sieverts setup, and approximation of the registered kinetic curves by Avrami−Erofeev equation. It was shown that at the initial stage of desorption processes at 300–360°C and 0–1 atm. H 2 , the decomposition of the magnesium dihydride phase makes the main contribution to the amount of hydrogen released from the composites. The addition of GLM has a positive effect on the kinetics of hydrogen desorption processes, concurring with that of the heat-conducting phase Mg 2 NiH ≤0.3 , which is also present in the composite. It was found that the apparent activation energy for the hydrogen desorption by composites is within a range of 125–140 kJ/mol H 2 . The correlation of the obtained values with the results of both experimental studies and quantum-chemical calculations obtained in the study of other magnesium systems is discussed.