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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Ca(BH4)2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (2.31 Å) and four longer (2.42 Å) Ca–H bond lengths. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.22 Å. There are two inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted bent 120 degrees geometry to one Ca2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Ca2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zn(BH4)2 by Materials Project

Zn(BH4)2 crystallizes in the tetragonal I4_122 space group. The structure is three-dimensional. Zn2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (1.88 Å) and four longer (2.18 Å) Zn–H bond lengths. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is two shorter (1.22 Å) and two longer (1.24 Å) B–H bond length. There are two inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to one Zn2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Zn2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Ca(BH4)2 crystallizes in the tetragonal P4_2/m space group. The structure is three-dimensional. Ca2+ is bonded in a 10-coordinate geometry to ten H+0.50+ atoms. There are a spread of Ca–H bond distances ranging from 2.29–2.49 Å. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is two shorter (1.22 Å) and two longer (1.23 Å) B–H bond length. There are three inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted bent 120 degrees geometry to one Ca2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to two equivalent Ca2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Ca(BH4)2 crystallizes in the tetragonal P4_2 space group. The structure is three-dimensional. Ca2+ is bonded in a 10-coordinate geometry to ten H+0.50+ atoms. There are a spread of Ca–H bond distances ranging from 2.30–2.49 Å. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is one shorter (1.22 Å) and three longer (1.23 Å) B–H bond length. There are four inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent Ca2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Ca2+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Ca2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Ca(BH4)2 crystallizes in the tetragonal P-4 space group. The structure is three-dimensional. Ca2+ is bonded in a 10-coordinate geometry to ten H+0.50+ atoms. There are a spread of Ca–H bond distances ranging from 2.29–2.49 Å. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is three shorter (1.22 Å) and one longer (1.23 Å) B–H bond length. There are four inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted bent 120 degrees geometry to one Ca2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Ca2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to two equivalent Ca2+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Ca(BH4)2 crystallizes in the orthorhombic Fdd2 space group. The structure is three-dimensional. Ca2+ is bonded in a 12-coordinate geometry to twelve H+0.50+ atoms. There are a spread of Ca–H bond distances ranging from 2.29–2.75 Å. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is one shorter (1.22 Å) and three longer (1.23 Å) B–H bond length. There are four inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent Ca2+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to two equivalent Ca2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(BH4)2 by Materials Project

Mg(BH4)2 crystallizes in the tetragonal I-4m2 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (2.00 Å) and four longer (2.09 Å) Mg–H bond lengths. In the second Mg2+ site, Mg2+ is bonded in a body-centered cubic geometry to eight equivalent H+0.50+ atoms. All Mg–H bond lengths are 2.06 Å. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.23 Å. There are three inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(BH4)2 by Materials Project

Mg(BH4)2 crystallizes in the tetragonal P-4 space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (2.06 Å) and four longer (2.12 Å) Mg–H bond lengths. In the second Mg2+ site, Mg2+ is bonded in a 8-coordinate geometry to eight H+0.50+ atoms. There are four shorter (2.07 Å) and four longer (2.12 Å) Mg–H bond lengths. B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.22 Å. There are four inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted L-shaped geometry to one Mg2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted L-shaped geometry to one Mg2+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in an L-shaped geometry to one Mg2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KNa(BH4)2 by Materials Project

NaK(BH4)2 crystallizes in the trigonal R3 space group. The structure is three-dimensional. K1+ is bonded in a 12-coordinate geometry to twelve H+0.50+ atoms. There are a spread of K–H bond distances ranging from 2.71–2.83 Å. Na1+ is bonded in a 6-coordinate geometry to nine H+0.50+ atoms. There are a spread of Na–H bond distances ranging from 2.35–2.65 Å. There are two inequivalent B3- sites. In the first B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.23 Å. In the second B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.23 Å. There are four inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a 1-coordinate geometry to one K1+, one Na1+, and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to three equivalent Na1+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent K1+, one Na1+, and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to three equivalent K1+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KNa(BH4)2 by Materials Project

NaK(BH4)2 crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. K1+ is bonded in a 12-coordinate geometry to twelve H+0.50+ atoms. There are a spread of K–H bond distances ranging from 2.72–2.92 Å. Na1+ is bonded in a 9-coordinate geometry to nine H+0.50+ atoms. There are three shorter (2.45 Å) and six longer (2.48 Å) Na–H bond lengths. There are two inequivalent B3- sites. In the first B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.23 Å. In the second B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is one shorter (1.22 Å) and three longer (1.23 Å) B–H bond length. There are four inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to three equivalent K1+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a single-bond geometry to three equivalent K1+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent Na1+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent K1+, one Na1+, and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Ca(BH4)2 crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Ca2+ is bonded in a 10-coordinate geometry to ten H+0.50+ atoms. There are a spread of Ca–H bond distances ranging from 2.33–2.52 Å. There are two inequivalent B3- sites. In the first B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. All B–H bond lengths are 1.23 Å. In the second B3- site, B3- is bonded in a tetrahedral geometry to four H+0.50+ atoms. There is two shorter (1.22 Å) and two longer (1.23 Å) B–H bond length. There are eight inequivalent H+0.50+ sites. In the first H+0.50+ site, H+0.50+ is bonded in a distorted L-shaped geometry to one Ca2+ and one B3- atom. In the second H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Ca2+ and one B3- atom. In the third H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to one Ca2+ and one B3- atom. In the fourth H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent Ca2+ and one B3- atom. In the fifth H+0.50+ site, H+0.50+ is bonded in a distorted L-shaped geometry to one Ca2+ and one B3- atom. In the sixth H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom. In the seventh H+0.50+ site, H+0.50+ is bonded in a distorted single-bond geometry to two equivalent Ca2+ and one B3- atom. In the eighth H+0.50+ site, H+0.50+ is bonded in a distorted water-like geometry to one Ca2+ and one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Atomic Layer Deposition for Materials-Based H2 Storage: Mg(BH4)2 as a Case Study

To meet the requirements for vehicular solid-state hydrogen (H2) storage, novel materials such as metal borohydrides have increasingly been investigated, in particular, magnesium borohydride (Mg(BH4)2). While these materials have a high H2 capacity (> 14 wt%), poor hydrogenation-dehydrogenation cyclability and material degradation, (e.g., loss of boron), need to be overcome. Prior research has indicated that nano-encapsulation and chemical additives can address these challenges. Therefore, we pursued these two strategies simultaneously with atomic layer deposition (ALD) on Mg(BH4)2. We investigated the use of metal-oxides (e.g., Al2O3, TiO2, CeO2), Pt- group metals (e.g., Pd, Ru) as well as pulsing only one precursor molecule (e.g., Al(CH3)3, BBr3, TiCl4), and assessed these modified Mg(BH4)2 in terms of their H2 storage properties. This presentation will also present the benefits and limitations of using vapor-phase techniques to modify the properties of Mg(BH4)2.

atomic layer deposition↗
DOE OSTI2021

Al2O3 Atomic Layer Deposition on Nanostructured γ-Mg(BH4)2 for H2 Storage

In the context of the growing hydrogen (H 2 ) economy, the demand for H 2 storage materials is high, and metal borohydrides are of particular interest. Magnesium borohydride, Mg(BH 4 ) 2 , has one of the highest hydrogen capacities of all known metal hydrides (14.9 wt % H) but suffers from high operating temperatures, slow kinetics for (de)hydrogenation, and the loss of capacity upon cycling. Strategies to address these challenges include nanoencapsulation and the use of chemical additives. This work is the first to utilize these two strategies simultaneously by using atomic layer deposition (ALD). For this new approach to modify borohydrides, we chose the well-studied Al 2 O 3 ALD process using trimethylaluminum and water. Although there has been limited use of aluminum-based additives for Mg(BH 4 ) 2 , we demonstrate that the low-temperature H 2 capacity was doubled, desorption kinetics were increased by a factor of 3, and 100 cycles of Al 2 O 3 suppressed the release of diborane compared to the uncoated Mg(BH4)2. We identified that the use of trimethylaluminum and water in the ALD process affected the decomposition pathway and that the Al 2 O 3 film growth is dominated by infiltration due to the high porosity of the ..gamma..-phase Mg(BH 4 ) 2 . From these results, the potential of ALD as a method to functionalize solid-state H 2 storage materials is inferred, and recommendations for future ALD processes are presented.

08 HYDROGEN↗
DOE OSTI2020

Materials Data on Ca(BH4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2024

Ca-dimers, solvent layering, and dominant electrochemically active species in Ca(BH4)2 in THF

Abstract Divalent ions (Mg, Ca, and Zn) are being considered as competitive, safe, and earth-abundant alternatives to Li-ion electrochemistry, but present challenges for stable cycling due to undesirable interfacial phenomena. We explore the formation of electroactive species in the electrolyte Ca(BH 4 ) 2 ∣THF using molecular dynamics coupled with a continuum model of bulk and interfacial speciation. Free-energy analysis and unsupervised learning indicate a majority population of neutral Ca dimers and monomers with diverse molecular conformations and an order of magnitude lower concentration of the primary electroactive charged species – the monocation, $${\rm{CaBH}}_{4}^{+}$$ CaBH 4 + – produced via disproportionation of neutral complexes. Dense layering of THF molecules within ~1 nm of the electrode surface strongly modulates local electrolyte species populations. A dramatic increase in monocation population in this interfacial zone is induced at negative bias. We see no evidence for electrochemical activity of fully-solvated Ca 2+ . The consequences for performance are discussed in light of this molecular-scale insight.

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

Materials Data on Li2MgB4(H17N3)2 by Materials Project

(Li(BH4)2)2Mg(NH3)6 crystallizes in the tetragonal P4_32_12 space group. The structure is one-dimensional and consists of four Mg(NH3)6 clusters and two Li(BH4)2 ribbons oriented in the (0, 0, 1) direction. In each Mg(NH3)6 cluster, Mg2+ is bonded in an octahedral geometry to six N3- atoms. There are a spread of Mg–N bond distances ranging from 2.22–2.28 Å. There are three inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+ and three H+0.76+ atoms. There is one shorter (1.02 Å) and two longer (1.03 Å) N–H bond length. In the second N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+ and three H+0.76+ atoms. There is one shorter (1.02 Å) and two longer (1.03 Å) N–H bond length. In the third N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+ and three H+0.76+ atoms. There is two shorter (1.02 Å) and one longer (1.03 Å) N–H bond length. There are nine inequivalent H+0.76+ sites. In the first H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the second H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the third H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the fourth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the fifth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the sixth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the seventh H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the eighth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In the ninth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one N3- atom. In each Li(BH4)2 ribbon, Li1+ is bonded in a 8-coordinate geometry to eight H+0.76+ atoms. There are a spread of Li–H bond distances ranging from 1.94–2.28 Å. There are two inequivalent B3- sites. In the first B3- site, B3- is bonded in a tetrahedral geometry to four H+0.76+ atoms. All B–H bond lengths are 1.23 Å. In the second B3- site, B3- is bonded in a tetrahedral geometry to four H+0.76+ atoms. All B–H bond lengths are 1.23 Å. There are eight inequivalent H+0.76+ sites. In the first H+0.76+ site, H+0.76+ is bonded in a water-like geometry to one Li1+ and one B3- atom. In the second H+0.76+ site, H+0.76+ is bonded in a water-like geometry to one Li1+ and one B3- atom. In the third H+0.76+ site, H+0.76+ is bonded in a distorted single-bond geometry to two equivalent Li1+ and one B3- atom. In the fourth H+0.76+ site, H+0.76+ is bonded in a water-like geometry to one Li1+ and one B3- atom. In the fifth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one B3- atom. In the sixth H+0.76+ site, H+0.76+ is bonded in a water-like geometry to one Li1+ and one B3- atom. In the seventh H+0.76+ site, H+0.76+ is bonded in a distorted single-bond geometry to two equivalent Li1+ and one B3- atom. In the eighth H+0.76+ site, H+0.76+ is bonded in a single-bond geometry to one B3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Melting of Magnesium Borohydride under High Hydrogen Pressure: Thermodynamic Stability and Effects of Nanoconfinement

The thermodynamic stability and melting point of magnesium borohydride were probed under hydrogen pressures up to 1000 bar (100 MPa) and temperatures up to 400 °C. At 400 °C, Mg(BH4)2 was found to be chemically stable between 700 and 1000 bar H2, whereas under 350 bar H2 or lower pressures, the bulk material partially decomposed into MgH2 and MgB12H12. The melting point of solvent-free Mg(BH4)2 was estimated to be 367-375 °C, which was above previously reported values by 40-90 °C. Our results indicated that a high hydrogen backpressure is needed to prevent the decomposition of Mg(BH4)2 before measuring the melting point and that molten Mg(BH4)2 can exist as a stable liquid phase between 367 and 400 °C under hydrogen overpressures of 700 bar or above. The occurrence of a pure molten Mg(BH4)2 phase enabled efficient melt-infiltration of Mg(BH4)2 into the pores of porous templated carbons (CMK-3 and CMK-8) and graphene aerogels. Both transmission electron microscopy and small-angle X-ray scattering confirmed efficient incorporation of the borohydride into the carbon pores. The Mg(BH4)2@carbon samples exhibited comparable hydrogen capacities to bulk Mg(BH4)2 upon desorption up to 390 °C based on the mass of the active component; the onset of hydrogen release was reduced by 15-25 °C compared to the bulk. Importantly, melt-infiltration under hydrogen pressure was shown to be an efficient way to introduce metal borohydrides into the pores of carbon-based materials, helping to prevent particle agglomeration and formation of stable closo-polyborate byproducts.

White, James L.↗
DOE OSTI2021

Thermal conversion of unsolvated Mg(B3H8)2 to BH4- in the presence of MgH2

In the search for energy storage materials, metal octahydrotriborates, M(B3H8)n, n=1,2, are promising candidates but their synthesis suffers from residual solvents which tend to interact and greatly alter their decomposition mechanism. Therefore, we studied the thermal conversion of unsolvated Mg(B3H8)2 to BH4 -: as synthesized, and in the presence of MgH2. The conversion of our unsolvated Mg(B3H8)2 starts at ~100°C and yields ~22 wt% of BH4 - along with the formation of (closo-hydro)borates and volatile boranes. This loss of boron (B) is a sign of poor cyclability of the system. However, the addition of MgH2 to unsolvated Mg(B3H8)2 drastically increases the thermal conversion to 85-88wt% of BH4 - while simultaneously decreasing the amounts of B-losses. Our results strongly indicate that the presence of activated MgH2 substantially decreases the formation of (closohydro) borates and provides the necessary H2 for the B3H8-to-BH4 conversion. This is the first report of a metal octahydrotriborate system to selectively convert to BH4 - under moderate conditions of temperature (200°C) in less than 1h, making the MgB3H8-MgH2 system very promising for energy storage applications.

Gigante, Angelina↗