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Issue 3, 2013
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Diborane release and structure distortion in borohydrides

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Hydrogen desorption from borohydrides is often accompanied by the release of diborane. The amount of diborane released as a byproduct during the decomposition of borohydrides scales inversely with the borohydride stability, which in turn depends on the electronegativity of the corresponding cation. We present a model based on the difference between the symmetric and asymmetric assembly of B2H6 units at the surface. The origin of this reaction is the degree of distortion of the BH4 anions in the bulk, hitherto depending on the degree of ionization of the cation. A practical measure of the distortion is the range in which the stretching vibration modes appear, which is the difference in the energy of the stretching vibrations of hydrogen atoms with maximum different bonding lengths (Badger's rule). We propose from this relation that the diborane released from the surface of the relatively unstable LiZn2(BH4)5 is formed from a recombination of BH2δ+ and BH4δ units. Ultra high vacuum mass spectroscopy measurements support the presented model and clarify the decomposition of stable borohydrides, such as LiBH4. The sublimation of borohydrides in UHV competes with their decomposition.

Graphical abstract: Diborane release and structure distortion in borohydrides

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Publication details

The article was received on 19 Jul 2012, accepted on 21 Sep 2012 and first published on 24 Sep 2012

Article type: Paper
DOI: 10.1039/C2DT31608K
Citation: Dalton Trans., 2013,42, 719-725
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    Diborane release and structure distortion in borohydrides

    E. Callini, A. Borgschulte, A. J. Ramirez-Cuesta and A. Züttel, Dalton Trans., 2013, 42, 719
    DOI: 10.1039/C2DT31608K

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