Suppressing diborane production during the hydrogen release of metal borohydrides: The example of alloyed Al(BH 4 ) 3

Harrison, David; Thonhauser, Timo

doi:10.1016/j.ijhydene.2015.12.159

Cited by 9 publications

(8 citation statements)

References 57 publications

(89 reference statements)

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“…Another pathway for MBAs to decompose is through the formation of B 2 H 6 . Previous studies show a strong correlation between χ p , 21 formation enthalpy, 24 and decomposition through B 2 H 6 production for MBs. They also show that this pathway opens up for χ p 1.6, where it becomes-as we will show below-an energetically favorable alternative to direct H 2 formation.…”

Section: B 2 H 6 Production Followed By H 2 Releasementioning

confidence: 86%

“…We find that the kinetic barriers decrease in higher χ p materials, making this pathway viable for χ p 1.6, as suggested previously. 21,24 In particular, for these high-χ p values, this pathway becomes more favorable than direct H 2 release (compare Figs. 8 and 9).…”

Section: B 2 H 6 Production Followed By H 2 Releasementioning

confidence: 94%

“…In high-electronegativity MBs (χ p 1.6), ammoniation raises the material's decomposition temperature relative to the plain MB and it was suggested that this behavior is linked to the creation of a heteropolar dihydrogen bond network between the negatively charged H δ − in [BH 4 ] − and positively charged H δ + in NH 3 . 23 It is also known that the MBs in this category often decompose to release diborane (B 2 H 6 ), 24 but this diborane is not released as a gaseous product in the presence of NH 3 . 25 Instead, it likely acts as an intermediate, reacting with NH 3 to form boron nitrides as well as H 2 .…”

Section: Introductionmentioning

confidence: 99%

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Decomposition mechanisms in metal borohydrides and their ammoniates

Welchman

Thonhauser

2017

J. Mater. Chem. A

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Ammoniation in metal borohydrides (MBs) with the form M (BH 4 ) x has been shown to lower their decomposition temperatures with M of low electronegativity (χ p 1.6), but raise it for high-χ p MBs (χ p 1.6). Although this behavior is just as desired, an understanding of the mechanisms that cause it is still lacking. Using ab initio methods, we elucidate those mechanisms and find that ammoniation always causes thermodynamic destabilization, explaining the observed lower decomposition temperatures for low-χ p MBs. For high-χ p MBs, we find that ammoniation blocks B 2 H 6 formation-the preferred decomposition mechanism in these MBs-and thus kinetically stabilizes those phases. The shift in decomposition pathway that causes the distinct change from destabilization to stabilization around χ p = 1.6 thus coincides with the onset of B 2 H 6 formation in MBs. Furthermore, with our analysis we are also able to explain why these materials release either H 2 or NH 3 gas upon decomposition. We find that NH 3 is much more strongly coordinated with higher-χ p metals and direct H 2 formation/release becomes more favorable in these materials. Our findings are of importance for unraveling the hydrogen release mechanisms in an important new and promising class of hydrogen storage materials, allowing for a guided tuning of their chemistry to further improve their properties.

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Section: B 2 H 6 Production Followed By H 2 Releasementioning

confidence: 86%

Section: B 2 H 6 Production Followed By H 2 Releasementioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Decomposition mechanisms in metal borohydrides and their ammoniates

Welchman

Thonhauser

2017

J. Mater. Chem. A

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“…Decomposition of Al(BH 4 ) 3 was predicted to be a spontaneous process above approximately 400 K, occurring with the release of B 2 H 6 [ 70 ], but the experimentally observed decomposition occurred at room temperature [ 172 , 173 ]. In 2016, Harrison et al proposed reducing diborane production, at least theoretically, by including a second cation, as in Al 1-x Sc x (BH 4 ) 3 [ 182 ].…”

Section: Main-group Borohydridesmentioning

confidence: 99%

“…Yet, LiBH 4 releases B 2 H 6 under several reaction conditions [ 262 ]. Harrison et al mentioned that diborane production did not follow any clear trend but, for threshold values between 1.36 and 1.55 of electronegativity of the corresponding metal in the Pauling scale,

, diborane production is observed [ 182 ].…”

Section: The Boron Problemmentioning

confidence: 99%

Metal Borohydrides beyond Groups I and II: A Review

Suárez‐Alcántara

García

2021

Materials

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This review consists of a compilation of synthesis methods and several properties of borohydrides beyond Groups I and II, i.e., transition metals, main group, lanthanides, and actinides. The reported properties include crystal structure, decomposition temperature, ionic conductivity, photoluminescence, etc., when available. The compiled properties reflect the rich chemistry and possible borohydrides’ application in areas such as hydrogen storage, electronic devices that require an ionic conductor, catalysis, or photoluminescence. At the end of the review, two short but essential sections are included: a compilation of the decomposition temperature of all reported borohydrides versus the Pauling electronegativity of the cations, and a brief discussion of the possible reactions occurring during diborane emission, including some strategies to reduce this inconvenience, particularly for hydrogen storage purposes.

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