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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

X-ray Crystal Structure of Thorium Tetrahydroborate, Th(BH 4 ) 4 , and Computational Studies of An(BH 4 ) 4 (An = Th, U)

Here the crystal structure of Th(BH 4 ) 4 is described. Two of the four BH 4 – ions are terminal and tridentate (κ 3 ), whereas the other two bridge between neighboring Th IV centers in a κ 2 ,κ 2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH 4 – groups by 14 Th–H bonds. The six boron atoms describe a distorted octahedron in which the κ 3 -BH 4 – ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An(BH 4 ) 4 (An = Th, U) were also investigated by DFT. The geometries of [An(BH 4 ) 6 ] 2– , [An3(BH 4 ) 16 ] 4– , and [An 5 (BH 4 ) 26 ] 6– fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th(BH 4 ) 6 ] 2– units are predicted to feature 16-coordinate Th IV centers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mg(BH 4 ) 2 -Based Hybrid Metal–Organic Borohydride System Exhibiting Enhanced Chemical Stability in Melt

The formation of a chemically stable and thermally cyclable Mg(BH 4 ) 2 melt is proven to be possible through the utilization of an organic borohydride salt additive. While extensive exploration of additives for lowering the melting point and modifying the chemical stability of Mg(BH 4 ) 2 has been reported, this is the first study to use the organic borohydride salt, tetramethylammonium borohydride (TMAB), to modify the melting behavior of Mg(BH 4 ) 2 . Here, examination of a 5:1 molar mixture of Mg(BH 4 ) 2 and TMAB revealed a reversible melt between 180 and 195 °C, which was reproduced for five thermal cycles. The mixture melt exhibited an enhanced chemical stability compared to melts of the individual Mg(BH 4 ) 2 and TMAB species. It was observed that between room temperature and 250 °C (over 50 °C above the melting point), the mixture releases <0.1 wt % mass, consisting primarily of H 2 . The mixture also exhibits greatly reduced evolution of volatile boron containing compounds compared to either Mg(BH 4 ) 2 or TMAB. The use of TMAB to chemically stabilize a Mg(BH 4 ) 2 -rich melt demonstrated in this work represents an exciting pathway to modification of Mg(BH 4 ) 2 relevant to both hydrogen-storage and magnesium battery fields.

08 HYDROGEN↗
DOE OSTI2022

First-Principles Elucidation of Initial Dehydrogenation Pathways in Mg(BH 4 ) 2

Complex borohydrides such as Mg(BH 4 ) 2 offer one of highest capacities to chemically store hydrogen for onboard applications; however, it suffers greatly from kinetic constraints that prevent realization of full capacity and reversibility. Understanding these kinetic limitations solely from experiments is extremely challenging due to the unusual complexity of various competing elemental reaction steps involved during the de/rehydrogenation reaction. This work aims to map out the energetics associated with initial dehydrogenation of Mg(BH 4 ) 2 from first-principles simulations and to identify the preferred reaction pathways. Our calculations suggest the rate-limiting step during BH 4 – –B 3 H 8 – conversion is the formation of the B 2 H 7 – intermediate. We further emphasize and clarify that the B 3 H 8 – and H – intermediates, formed during initial Mg(BH 4 ) 2 decomposition, appear as molecular species that are embedded in the Mg–BH 4 –Mg matrix as evidenced in the nuclear magnetic resonance measurements and not as bulk MgH 2 and Mg(B 3 H 8 ) 2 as previously assumed in theoretical predictions of the thermodynamics.

08 HYDROGEN↗
DOE OSTI2025

Unusual products arising from the tandem dehydrogenation of Mg(BH 4 ) 2 and pyrrolidine

The dehydrogenation of Mg(BH 4 ) 2 in the presence of O-Lewis base donors has been widely explored but there have been very few studies of dehydrogenation of the borohydride in the presence of N-Lewis bases. Mg(BH 4 ) 2 has been found to react with pyrrolidine at room temperature to form BH 3 -pyrrolidine adduct. Upon heating, further dehydrogenation reactions occur to form bis(pyrrolidino)borane, tris(pyrrolidino)borane and other B–N intermediates. Reacting Mg(BH 4 ) 2 and pyrrolidine in a 1 : 6 molar ratio exclusively yields tris(pyrrolidino)borane which is in accordance with predicted stoichiometric factors. The formation of these products contrasts with the routine production of higher boranes and/or intractable polymers from the dehydrogenation of Mg(BH 4 ) 2 in the presence O-Lewis bases. The amount of H 2 released in these reactions was determined both by the Parr autoclave pressure readings and the eudiometer measurements. Both measurements align with the values predicted by the stoichiometric factors associated by the proposed pathway.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Li(BH)6 by Materials Project

Li(BH)4(BH)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight boranediylradical molecules and four Li(BH)4 clusters. In each Li(BH)4 cluster, Li is bonded in a 5-coordinate geometry to four H atoms. There are a spread of Li–H bond distances ranging from 1.94–2.26 Å. There are four inequivalent B sites. In the first B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the second B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the third B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the fourth B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. There are four inequivalent H sites. In the first H site, H is bonded in a bent 120 degrees geometry to one Li and one B atom. In the second H site, H is bonded in a distorted L-shaped geometry to one Li and one B atom. In the third H site, H is bonded in an L-shaped geometry to one Li and one B atom. In the fourth H site, H is bonded in a water-like geometry to one Li and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li2(BH)11 by Materials Project

(Li(BH)3)2(BH)5 crystallizes in the monoclinic C2 space group. The structure is one-dimensional and consists of ten boranediylradical molecules and two Li(BH)3 ribbons oriented in the (1, 0, 0) direction. In each Li(BH)3 ribbon, there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a distorted see-saw-like geometry to four H+0.64+ atoms. There is two shorter (1.88 Å) and two longer (2.11 Å) Li–H bond length. In the second Li1+ site, Li1+ is bonded in a distorted see-saw-like geometry to four H+0.64+ atoms. There is two shorter (1.88 Å) and two longer (2.11 Å) Li–H bond length. There are three inequivalent B+0.82- sites. In the first B+0.82- site, B+0.82- is bonded in a distorted single-bond geometry to one H+0.64+ atom. The B–H bond length is 1.21 Å. In the second B+0.82- site, B+0.82- is bonded in a distorted single-bond geometry to one H+0.64+ atom. The B–H bond length is 1.21 Å. In the third B+0.82- site, B+0.82- is bonded in a distorted single-bond geometry to one H+0.64+ atom. The B–H bond length is 1.21 Å. There are three inequivalent H+0.64+ sites. In the first H+0.64+ site, H+0.64+ is bonded in a T-shaped geometry to two Li1+ and one B+0.82- atom. In the second H+0.64+ site, H+0.64+ is bonded in a water-like geometry to one Li1+ and one B+0.82- atom. In the third H+0.64+ site, H+0.64+ is bonded in a water-like geometry to one Li1+ and one B+0.82- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Kinetic and modeling studies of the mechanism of the dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2

Since its discovery over 15 years ago, the reversible dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 has remained one of the more intriguing hydrogen-cycling systems. While the mechanism of this reaction has been the subject of a good deal of speculation and computational studies, prior to this work it had not been probed through kinetic studies. Previous reports of the dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 have not included kinetic studies. The present studies have shown that the dehydrogenation of Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 is suppressed by hydrogen pressure indicating that the rate-limiting step in this process involves hydrogen elimination. Computational modeling of kinetic data obtained from monitoring the hydrogen elimination from Mg(BH 4 ) 2 to Mg(B 3 H 8 ) 2 under static vacuum over a range of temperatures supports that the dehydrogenation occurs through a reversible three-step process in which the elimination of hydrogen from the [B 3 H 10 ] − intermediate is rate limiting. A mechanism involving the low energy transfer of neighboring BH3 groups is proposed to account for the formation of [B 3 H 8 ] − at relatively low temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

A New Record Census of Dwarf AGN and a Bimodal $M_{\rm BH}$-$M_{\star}$ Scaling Relation with DESI DR1

Using the first spectroscopic data release from the Dark Energy Spectroscopic Instrument (DESI DR1), we search for AGN signatures in 1,678,787 low-redshift ($0.001 \le z \le 0.45$) line-emitting galaxies. Based on the [NII]-BPT emission-line ratio diagnostic, we identify AGN in 314,245/1,211,573 (25.9%) high-mass ($\log (M_{\star}/M_{\odot}) > 9.5$) and 9648/467,214 (2.1%) dwarf ($\log (M_{\star}/M_{\odot}) \le 9.5$) galaxies. Among these AGN, 17,949 are broad-line candidates (BL-AGN) with broad H$α$ emission, enabling black hole (BH) mass estimates using single-epoch virial methods. We find that the AGN fraction in line-emitting galaxies increases monotonically with stellar mass, rising from $\sim$1.4% at the low-mass end to $\sim$93.3% at the high-mass end. Using the large BL-AGN sample, we extend the $M_{\rm BH} - M_{\star}$ scaling relation down to $\log (M_{\star}/M_{\odot}) \approx 7.8$ and $\log (M_{\rm BH}/M_{\odot}) \approx 4.4$. In the context of high-redshift overmassive BHs, our results suggest that galaxies and their central BHs may follow two distinct evolutionary pathways across cosmic time. With this paper, we release the EmFit value-added catalog, containing emission-line flux and width measurements for $\sim$7.4 million galaxies, the largest catalog with emission-line decomposition into narrow, broad, and outflow components to date. This work significantly expands upon the early DESI results and provides a statistical sample for probing the galaxy$-$BH connection in the low-mass galaxy regime.

Pucha, Ragadeepika [Utah U.; Arizona U., Astron. D↗
DOE OSTI2020

Materials Data on K(BH)5 by Materials Project

K2(BH)9BH crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional and consists of four boranediylradical molecules and one K2(BH)9 framework. In the K2(BH)9 framework, there are two inequivalent K sites. In the first K site, K is bonded in a 8-coordinate geometry to eight H atoms. There are a spread of K–H bond distances ranging from 2.67–3.05 Å. In the second K site, K is bonded in a 8-coordinate geometry to eight H atoms. There are a spread of K–H bond distances ranging from 2.79–3.07 Å. There are nine inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the second B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the third B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the fourth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the fifth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the sixth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the seventh B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the eighth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the ninth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. There are nine inequivalent H sites. In the first H site, H is bonded in a distorted bent 120 degrees geometry to one K and one B atom. In the second H site, H is bonded in a single-bond geometry to two K and one B atom. In the third H site, H is bonded in a distorted single-bond geometry to two equivalent K and one B atom. In the fourth H site, H is bonded in a distorted single-bond geometry to two K and one B atom. In the fifth H site, H is bonded in a single-bond geometry to two equivalent K and one B atom. In the sixth H site, H is bonded in a distorted single-bond geometry to two equivalent K and one B atom. In the seventh H site, H is bonded in a distorted single-bond geometry to two K and one B atom. In the eighth H site, H is bonded in a distorted single-bond geometry to one K and one B atom. In the ninth H site, H is bonded in a single-bond geometry to two K and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(BH)5 by Materials Project

Na2(BH)9BH crystallizes in the monoclinic P2_1/c space group. The structure is one-dimensional and consists of four boranediylradical molecules and two Na2(BH)9 ribbons oriented in the (1, 0, 0) direction. In each Na2(BH)9 ribbon, there are two inequivalent Na sites. In the first Na site, Na is bonded in a 3-coordinate geometry to six H atoms. There are a spread of Na–H bond distances ranging from 2.09–2.61 Å. In the second Na site, Na is bonded in a 7-coordinate geometry to seven H atoms. There are a spread of Na–H bond distances ranging from 2.40–2.70 Å. There are nine inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the second B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the third B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the fourth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the fifth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.19 Å. In the sixth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the seventh B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the eighth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the ninth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. There are nine inequivalent H sites. In the first H site, H is bonded in a 3-coordinate geometry to two Na and one B atom. In the second H site, H is bonded in a distorted single-bond geometry to two equivalent Na and one B atom. In the third H site, H is bonded in a 2-coordinate geometry to two Na and one B atom. In the fourth H site, H is bonded in a linear geometry to one Na and one B atom. In the fifth H site, H is bonded in a linear geometry to one Na and one B atom. In the sixth H site, H is bonded in a distorted water-like geometry to one Na and one B atom. In the seventh H site, H is bonded in a distorted single-bond geometry to two Na and one B atom. In the eighth H site, H is bonded in a single-bond geometry to one Na and one B atom. In the ninth H site, H is bonded in a distorted single-bond geometry to one Na and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rb(BH)5 by Materials Project

Rb2(BH)9BH crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of four boranediylradical molecules and one Rb2(BH)9 sheet oriented in the (-1, 0, 2) direction. In the Rb2(BH)9 sheet, there are two inequivalent Rb sites. In the first Rb site, Rb is bonded in a 6-coordinate geometry to six H atoms. There are a spread of Rb–H bond distances ranging from 2.52–3.12 Å. In the second Rb site, Rb is bonded in a distorted pentagonal pyramidal geometry to six H atoms. There are a spread of Rb–H bond distances ranging from 2.71–3.11 Å. There are nine inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the second B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the third B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the fourth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the fifth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the sixth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the seventh B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the eighth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the ninth B site, B is bonded in a distorted single-bond geometry to one H atom. The B–H bond length is 1.20 Å. There are nine inequivalent H sites. In the first H site, H is bonded in a distorted single-bond geometry to one Rb and one B atom. In the second H site, H is bonded in a distorted single-bond geometry to one Rb and one B atom. In the third H site, H is bonded in a distorted single-bond geometry to two Rb and one B atom. In the fourth H site, H is bonded in a distorted single-bond geometry to two Rb and one B atom. In the fifth H site, H is bonded in a distorted single-bond geometry to two equivalent Rb and one B atom. In the sixth H site, H is bonded in a distorted bent 120 degrees geometry to one Rb and one B atom. In the seventh H site, H is bonded in a distorted bent 150 degrees geometry to one Rb and one B atom. In the eighth H site, H is bonded in a distorted bent 120 degrees geometry to one Rb and one B atom. In the ninth H site, H is bonded in a distorted single-bond geometry to one Rb and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(BH)6 by Materials Project

Na(BH)5BH crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four boranediylradical molecules and two Na(BH)5 clusters. In each Na(BH)5 cluster, Na is bonded in a 6-coordinate geometry to six H atoms. There are a spread of Na–H bond distances ranging from 2.28–2.54 Å. There are five inequivalent B sites. In the first B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the second B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. In the third B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the fourth B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.20 Å. In the fifth B site, B is bonded in a single-bond geometry to one H atom. The B–H bond length is 1.21 Å. There are five inequivalent H sites. In the first H site, H is bonded in a water-like geometry to one Na and one B atom. In the second H site, H is bonded in a water-like geometry to one Na and one B atom. In the third H site, H is bonded in a distorted water-like geometry to one Na and one B atom. In the fourth H site, H is bonded in a distorted single-bond geometry to two equivalent Na and one B atom. In the fifth H site, H is bonded in a water-like geometry to one Na and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li2(BH)7 by Materials Project

(Li(BH)3)2BH crystallizes in the monoclinic C2 space group. The structure is one-dimensional and consists of two boranediylradical molecules and two Li(BH)3 ribbons oriented in the (1, 0, 0) direction. In each Li(BH)3 ribbon, there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a 2-coordinate geometry to four H1+ atoms. There are two shorter (2.00 Å) and two longer (2.29 Å) Li–H bond lengths. In the second Li1+ site, Li1+ is bonded in a 2-coordinate geometry to four H1+ atoms. There are two shorter (2.21 Å) and two longer (2.26 Å) Li–H bond lengths. There are three inequivalent B+1.29- sites. In the first B+1.29- site, B+1.29- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.21 Å. In the second B+1.29- site, B+1.29- is bonded in a single-bond geometry to one H1+ atom. The B–H bond length is 1.21 Å. In the third B+1.29- site, B+1.29- is bonded in a distorted single-bond geometry to one H1+ atom. The B–H bond length is 1.21 Å. There are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted L-shaped geometry to one Li1+ and one B+1.29- atom. In the second H1+ site, H1+ is bonded in a 3-coordinate geometry to two Li1+ and one B+1.29- atom. In the third H1+ site, H1+ is bonded in a water-like geometry to one Li1+ and one B+1.29- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pr(H 3 BNMe 2 BH 3 ) 3 and Pr(thd) 3 as Volatile Carriers for Actinium-225. Deposition of Actinium-Doped Praseodymium Boride Thin Films for Potential Use in Brachytherapy

Here we show that the praseodymium N,N-dimethylaminodiboranate complex Pr(H 3 BNMe 2 BH 3 ) 3 and the 2,2,6,6-tetramethylheptane-3,5-dionate complex Pr(thd) 3 can serve as volatile carriers for 225 Ac. The actinium coordination complexes Ac(H 3 BNMe 2 BH 3 ) 3 and Ac(thd) 3 are the likely species subliming with the carrier material. A sample of 225 Ac-doped Pr(H 3 BNMe 2 BH 3 ) 3 was used to deposit amorphous 225 Ac-doped praseodymium boride films on glass and Si(100) at 300 °C. Furthermore, the α emission spectra of the refractory films are well-resolved, suggesting that they could be used as radioactive implants for brachytherapy and related treatments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Analysis of Intermediates and Products from the Dehydrogenation of Mg(BH 4 ) 2

The thermodynamic properties of key compounds, Mg(B 3 H 8 ) 2 , MgB 2 H 6 , MgB 10 H 10 , Mg(B 11 H 14 ) 2 , Mg 3 (B 3 H 6 ) 2 , and MgB 12 H 12 , proposed to be formed in the release of hydrogen from magnesium borohydride Mg(BH 4 ) 2 and uptake of hydrogen by MgB 2 , have been investigated using solid–state density functional theory (DFT) calculations. Further, more accurate treatment of cell–size effects to the entropies were also investigated, in order to improve the accuracy of the thermodynamic properties of complex borohydrides. We find that the zero–point energy corrections can lower the electronic energies of reaction by 20–30 kJ/(mol H 2 ) for these intermediates, while adding the thermal and entropy contributions results in the total decrease up to ~50 kJ/(mol H 2 ). Although our treatment lowers the calculated formation energy of Mg(B 3 H 8 ) 2 , it is still too high to explain the experimental observation of B 3 H 8 – . We discuss possible reasons for this disparity and propose that the formation of B 3 H 8 – and H – in a disordered amorphous phase has a large energy difference compared to the phase–separated Mg(B 3 H 8 ) 2 and MgH 2 considered in calculations. Comparison of the experimental and NMR chemical shifts calculated within a DFT approach for known species Mg(BH 4 ) 2 , Mg(B 3 H 8 ) 2 , Mg(B 11 H 14 ) 2 , MgB 10 H 10 and MgB 12 H 12 provides validation for predicting the chemical shifts of the other compounds which are yet to be confirmed experimentally. These include MgB 2 H 6 and the proposed tri–anion species Mg 3 (B 3 H 6 ) 2 that both have favorable thermodynamics for reversible hydrogen storage in Mg(BH 4 ) 2 without the formation of MgH 2 as a co–product which could phase–separate and inhibit rehydrogenation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Effect of Salt Concentration on the Interfacial Solvation Structure and Early Stage of Solid–Electrolyte Interphase Formation in Ca(BH 4 ) 2 /THF for Ca Batteries

The Ca 2+ solvation structure at the electrolyte/electrode interface is of central importance to understand electroreduction stability and solid–electrolyte interphase (SEI) formation for the novel multivalent Ca battery systems. Here, using an exemplar electrolyte, the concentration-dependent solvation structure of Ca(BH 4 ) 2 -tetrahydrofuran on a gold model electrode has been investigated with various electrolyte concentrations via electrochemical quartz crystal microbalance with dissipation (EQCM-D) and X-ray photoelectron spectroscopy (XPS). For the first time, in situ EQCM-D results prove that the prevalent species adsorbed at the interface is CaBH 4 + across all concentrations. As the salt concentration increases, the number of BH 4 – anions associated with Ca 2+ increases, and much larger solvated complexes such as CaBH 4 + ·4THF or Ca(BH 4 ) 3 – ·4THF form at the interface at high concentrations prior to Ca plating. Different interfacial chemistries lead to the formation of SEIs with different components demonstrated by XPS. High electrolyte concentrations reduce the solvent decomposition and promote the formation of thick, uniform, and inorganic-rich (i.e., CaO) SEI layers, which contribute to improved Ca plating efficiency and current density in electrochemical measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Crystallographic characterization of (C 5 H 4 SiMe 3 ) 3 U(BH 4 )

New syntheses have been developed for the synthesis of (borohydrido-κ 3 H)tris­[η 5 -(tri­methyl­sil­yl)cyclo­penta­dien­yl]uranium(IV), [U(BH 4 )(C 8 H 13 Si) 3 ] or Cp' 3 U(BH 4 ) (Cp' = C 5 H 4 SiMe 3 ) and its structure has been determined by single-crystal X-ray crystallography. This compound crystallized in the space group P1¯ and the structure features three η 5 -coordinated Cp' rings and a κ 3 -coordinated (BH 4 ) – ligand.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of Glymes on the Distribution of Mg(B 10 H 10 ) and Mg(B 12 H 12 ) from the Thermolysis of Mg(BH 4 ) 2

We examined the effects of concentrations and identities of various glymes, from monoglyme up to tetraglyme, on H 2 release from the thermolysis of Mg(BH 4 ) 2 at 160–200 °C for 8 h. 11 B NMR analysis shows major products of Mg(B 10 H 10 ) and Mg(B 12 H 12 ); however, their relative ratio is highly dependent both on the identity and concentration of the glyme to Mg(BH 4 ) 2 . Selective formation of Mg(B 10 H 10 ) was observed with an equivalent of monoglyme and 0.25 equivalent of tetraglyme. However, thermolysis of Mg(BH 4 ) 2 in the presence of stoichiometric or greater equivalent of glymes can lead to unselective formation of Mg(B 10 H 10 ) and Mg(B 12 H 12 ) products or inhibition of H 2 release.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗