Lithium Ion Disorder and Conduction Mechanism in LiCe(BH₄)₃Cl

We investigate the diffusion mechanism of Li ions in LiCe­(BH₄)₃Cl, which exhibits fast Li ion conduction. It was previously shown that eight Li ions partially occupy the 12<i>d</i> Wyckoff sites in the <i>I</i>4̅3<i>m</i> structure and the Li ion diffusion takes place via jumping through the three-dimensional network of the 12<i>d</i> sites. In this study, we employ first-principles nudged elastic band simulation to elucidate the diffusion mechanism and discover that the Li ion does not directly jump to the neighboring 12<i>d</i> site, but instead passes through the closest 6<i>b</i> site. Moreover, the 6<i>b</i> site turns out to be another stable Li ion site, not just a transient point during a jump event. The occupation of the 6<i>b</i> site and the Li ion diffusion mechanism were assured by first-principles molecular dynamics simulations. The partial occupancy of the 12<i>d</i> site and 6<i>b</i> site at 500 K is approximately 1/2 and 1/3, respectively. The experimental diffraction data can be consistently interpreted. The peculiar crystal structure of LiCe­(BH₄)₃Cl allowing efficient and fast Li ion diffusion is again highlighted together with the role of [BH₄]⁻ ion in thermodynamically stabilizing LiCe­(BH₄)₃Cl

Discovery of Fluidic LiBH₄ on Scaffold Surfaces and Its Application for Fast Co-confinement of LiBH₄–Ca(BH₄)₂ into Mesopores

Generation of fluidic LiBH₄ molecules, <i>f</i>-LiBH₄, was demonstrated by NMR spectroscopy of LiBH₄ bulk powder mixed with silica scaffold surface materials under minor heat treatment. In the presence of the fumed silica or mesoporous MCM-41 and SBA-15, LiBH₄ shows increased translational mobility at relatively low temperature (ca. 95 °C) and becomes liquid-like by evidence from ¹H–¹¹B <i>J</i>-coupling in ¹H and ¹¹B MAS NMR or substantial line narrowing of ⁷Li static NMR. This high diffusional mobility of LiBH₄ at the molecular level has never been seen for bulk LiBH₄, and the property is attributed to the interfacial interaction with the mesoporous scaffold surfaces. While <i>f</i>-LiBH₄ facilitates the confinement of LiBH₄ itself into various scaffold materials, LiBH₄ migrates along the SBA-15 surface to reach other metal borohydride particles, Ca­(BH₄)₂ in this case, and promotes the formation of similarly fluidic LiBH₄–Ca­(BH₄)₂ composite (LC solid solution) for coconfinement into mesopores. <i>In situ</i> variable temperature (VT) NMR spectroscopy detects the co-infiltration process of eutectic LiBH₄–Ca­(BH₄)₂ composite (LC) into mesopores of SBA-15. The infiltration rates measured for LiBH₄ bulk powder or LC composite showed dependence on pore sizes (MCM-41 vs SBA-15) and heat treatment conditions (static vs MAS)

Hydrogen Back-Pressure Effects on the Dehydrogenation Reactions of Ca(BH₄)₂

The dehydrogenation reactions of Ca­(BH₄)₂ are investigated under different isobaric conditions using in situ synchrotron radiation powder X-ray diffraction and nuclear magnetic resonance measurements. Ca­(BH₄)₂ dissociates in multiple steps, and several intermediate phases, such as an amorphous phase(s), CaB₂H_<i>x</i>, and CaB₁₂H₁₂, are observed during dehydrogenation. Among the intermediate phases, it is known that CaB₂H_<i>x</i> is fully reversible, while the more stable CaB₁₂H₁₂ with an icosahedral structure hinders reversible reactions. Here, we try to control the dehydrogenation reaction pathway of Ca­(BH₄)₂ by applying different hydrogen back-pressures. The decomposition reaction of Ca­(BH₄)₂ in the absence of a catalyst was found to be sensitive to the H₂ back-pressure. At <i>p</i>(H₂) = 1 bar, Ca­(BH₄)₂ decomposes via two competitive dehydrogenation reaction routes to form CaB₂H_<i>x</i> or CaB₁₂H₁₂. At <i>p</i>(H₂) = 10 bar, the overall dehydrogenation reaction remains unchanged. However, the formation of CaB₂H_<i>x</i> is reduced, and amorphous elemental boron is observed as a final dehydrogenation product. At <i>p</i>(H₂) = 20 bar, the elemental boron formation is significantly increased, and the formation of the CaB₂H_<i>x</i> phase is suppressed. Possible routes to form CaH₂ and elemental boron are discussed

Dehydrogenation Reaction Pathway of the LiBH₄–MgH₂ Composite under Various Pressure Conditions

This paper investigates dehydrogenation reaction behavior of the LiBH₄–MgH₂ composite at 450 °C under various hydrogen and argon back-pressure conditions. While the individual decompositions of LiBH₄ and MgH₂ simultaneously occur under 0.1 MPa H₂, the dehydrogenation of MgH₂ into Mg first takes place and subsequent reaction between LiBH₄ and Mg into LiH and MgB₂ after an incubation period under 0.5 MPa H₂. Under 1 MPa H₂, enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H₂ is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H₂. The formation of Li₂B₁₂H₁₂ as an intermediate product during dehydrogenation seems to be responsible for the incubation period. The degradation in hydrogen capacity during hydrogen sorption cycles is not prevented with the dehydrogenation under 1 MPa H₂, which effectively suppresses the formation of Li₂B₁₂H₁₂. The overall dehydrogenation behavior under argon pressure conditions is similar to that at hydrogen pressure conditions, except that under 2 MPa Ar

An improvement of legislative base of market of insurance services is in Ukraine

У статті окреслено необхідність реформування діючого законодавства України в сфері функціонування страхового ринку, запропоновані основні заходи щодо покращення його стану.In the article outlined necessity of reformation of current legislation of Ukraine for the sphere of functioning of insurance market, basic measures are offered on the improvement of his state

In Situ NMR Study on the Interaction between LiBH₄–Ca(BH₄)₂ and Mesoporous Scaffolds

We discuss the use of nuclear magnetic resonance (NMR) spectroscopy to investigate the physical state of the eutectic composition of LiBH₄–Ca­(BH₄)₂ (LC) infiltrated into mesoporous scaffolds and the interface effect of various scaffolds. Eutectic melting and the melt infiltration of mixed borohydrides were observed through in situ NMR. In situ and ex situ NMR results for LC mixed with mesoporous scaffolds indicate that LiBH₄ and Ca­(BH₄)₂ exist as an amorphous mixture inside of the pores after infiltration. Surprisingly, the confinement of the eutectic LC mixture within the mesopores is initiated below the melting temperature, which indicates a certain interaction between the borohydrides and the mesoporous scaffolds. The confined borohydrides remain inside of the pores after cooling. These phenomena were not observed in microporous or nonporous materials, and this observation highlights the importance of the pore structure of the scaffolds. Such surface interactions may be associated with a faster dehydrogenation of the nanoconfined borohydrides

Trends in Syntheses, Structures, and Properties for Three Series of Ammine Rare-Earth Metal Borohydrides, M(BH₄)₃·<i>n</i>NH₃ (M = Y, Gd, and Dy)

Fourteen solvent- and halide-free ammine rare-earth metal borohydrides M­(BH₄)₃·<i>n</i>NH₃, M = Y, Gd, Dy, <i>n</i> = 7, 6, 5, 4, 2, and 1, have been synthesized by a new approach, and their structures as well as chemical and physical properties are characterized. Extensive series of coordination complexes with systematic variation in the number of ligands are presented, as prepared by combined mechanochemistry, solvent-based methods, solid–gas reactions, and thermal treatment. This new synthesis approach may have a significant impact within inorganic coordination chemistry. Halide-free metal borohydrides have been synthesized by solvent-based metathesis reactions of LiBH₄ and MCl₃ (3:1), followed by reactions of M­(BH₄)₃ with an excess of NH₃ gas, yielding M­(BH₄)₃·7NH₃ (M = Y, Gd, and Dy). Crystal structure models for M­(BH₄)₃·<i>n</i>NH₃ are derived from a combination of powder X-ray diffraction (PXD), ¹¹B magic-angle spinning NMR, and density functional theory (DFT) calculations. The structures vary from two-dimensional layers (<i>n</i> = 1), one-dimensional chains (<i>n</i> = 2), molecular compounds (<i>n</i> = 4 and 5), to contain complex ions (<i>n</i> = 6 and 7). NH₃ coordinates to the metal in all compounds, while BH₄^– has a flexible coordination, i.e., either as a terminal or bridging ligand or as a counterion. M­(BH₄)₃·7NH₃ releases ammonia stepwise by thermal treatment producing M­(BH₄)₃·<i>n</i>NH₃ (6, 5, and 4), whereas hydrogen is released for <i>n</i> ≤ 4. Detailed analysis of the dihydrogen bonds reveals new insight about the hydrogen elimination mechanism, which contradicts current hypotheses. Overall, the present work provides new general knowledge toward rational materials design and preparation along with limitations of PXD and DFT for analysis of structures with a significant degree of dynamics in the structures

Trends in Syntheses, Structures, and Properties for Three Series of Ammine Rare-Earth Metal Borohydrides, M(BH₄)₃·<i>n</i>NH₃ (M = Y, Gd, and Dy)

Fourteen solvent- and halide-free ammine rare-earth metal borohydrides M­(BH₄)₃·<i>n</i>NH₃, M = Y, Gd, Dy, <i>n</i> = 7, 6, 5, 4, 2, and 1, have been synthesized by a new approach, and their structures as well as chemical and physical properties are characterized. Extensive series of coordination complexes with systematic variation in the number of ligands are presented, as prepared by combined mechanochemistry, solvent-based methods, solid–gas reactions, and thermal treatment. This new synthesis approach may have a significant impact within inorganic coordination chemistry. Halide-free metal borohydrides have been synthesized by solvent-based metathesis reactions of LiBH₄ and MCl₃ (3:1), followed by reactions of M­(BH₄)₃ with an excess of NH₃ gas, yielding M­(BH₄)₃·7NH₃ (M = Y, Gd, and Dy). Crystal structure models for M­(BH₄)₃·<i>n</i>NH₃ are derived from a combination of powder X-ray diffraction (PXD), ¹¹B magic-angle spinning NMR, and density functional theory (DFT) calculations. The structures vary from two-dimensional layers (<i>n</i> = 1), one-dimensional chains (<i>n</i> = 2), molecular compounds (<i>n</i> = 4 and 5), to contain complex ions (<i>n</i> = 6 and 7). NH₃ coordinates to the metal in all compounds, while BH₄^– has a flexible coordination, i.e., either as a terminal or bridging ligand or as a counterion. M­(BH₄)₃·7NH₃ releases ammonia stepwise by thermal treatment producing M­(BH₄)₃·<i>n</i>NH₃ (6, 5, and 4), whereas hydrogen is released for <i>n</i> ≤ 4. Detailed analysis of the dihydrogen bonds reveals new insight about the hydrogen elimination mechanism, which contradicts current hypotheses. Overall, the present work provides new general knowledge toward rational materials design and preparation along with limitations of PXD and DFT for analysis of structures with a significant degree of dynamics in the structures

Trends in Syntheses, Structures, and Properties for Three Series of Ammine Rare-Earth Metal Borohydrides, M(BH₄)₃·<i>n</i>NH₃ (M = Y, Gd, and Dy)

Fourteen solvent- and halide-free ammine rare-earth metal borohydrides M­(BH₄)₃·<i>n</i>NH₃, M = Y, Gd, Dy, <i>n</i> = 7, 6, 5, 4, 2, and 1, have been synthesized by a new approach, and their structures as well as chemical and physical properties are characterized. Extensive series of coordination complexes with systematic variation in the number of ligands are presented, as prepared by combined mechanochemistry, solvent-based methods, solid–gas reactions, and thermal treatment. This new synthesis approach may have a significant impact within inorganic coordination chemistry. Halide-free metal borohydrides have been synthesized by solvent-based metathesis reactions of LiBH₄ and MCl₃ (3:1), followed by reactions of M­(BH₄)₃ with an excess of NH₃ gas, yielding M­(BH₄)₃·7NH₃ (M = Y, Gd, and Dy). Crystal structure models for M­(BH₄)₃·<i>n</i>NH₃ are derived from a combination of powder X-ray diffraction (PXD), ¹¹B magic-angle spinning NMR, and density functional theory (DFT) calculations. The structures vary from two-dimensional layers (<i>n</i> = 1), one-dimensional chains (<i>n</i> = 2), molecular compounds (<i>n</i> = 4 and 5), to contain complex ions (<i>n</i> = 6 and 7). NH₃ coordinates to the metal in all compounds, while BH₄^– has a flexible coordination, i.e., either as a terminal or bridging ligand or as a counterion. M­(BH₄)₃·7NH₃ releases ammonia stepwise by thermal treatment producing M­(BH₄)₃·<i>n</i>NH₃ (6, 5, and 4), whereas hydrogen is released for <i>n</i> ≤ 4. Detailed analysis of the dihydrogen bonds reveals new insight about the hydrogen elimination mechanism, which contradicts current hypotheses. Overall, the present work provides new general knowledge toward rational materials design and preparation along with limitations of PXD and DFT for analysis of structures with a significant degree of dynamics in the structures