Tailoring properties of borohydrides for hydrogen storage: A review

Abstract

Hydrogen is recognized as a possible future energy carrier, which can be produced from renewable energy and water. A major challenge in a future ‘hydrogen economy’ is the development of safe, compact, robust, and efficient means of hydrogen storage, in particular for mobile applications. The present review focuses on light metal boron based hydrides, for which the general interest has expanded significantly during the past few years. Synthesis methods, physical, chemical and structural properties of novel boron based hydrides are reviewed along with new approaches for improving kinetic and thermodynamic properties: (i) anion substitution, (ii) reactive hydride composites and (iii) nanoconfinement of hydrides and chemical reactions. The light metal borohydrides reveal a fascinating structural chemistry and have the potential for storing large amounts of hydrogen. A combination of the different approaches may provide a new route to a wide range of interesting energy storage materials in the future.

Thermodynamics of Metal Hydrides: Tailoring Reaction Enthalpies of Hydrogen Storage Materials

“…The decomposition temperature of the bialkali metal borohydrides like LiK(BH 4 ) 2 is approximately the average of the decomposition temperature of the mono alkali borohydrides (Rude et al, 2011). Investigations of Li et al and Seballos et al (Seballos et al, 2009) confirmed that this correlation between desorption enthalpy / observed T d holds true for many double cation MM'(BH 4 ) n systems, see Fig.…”

“…However, no clear indicative experimental results for F --substitution in borohydrides are found yet. In contrast to the F the heavier and larger halides Cl, Br, I are found to readily substitute in some borohydrides for the BH 4 --ion and form solid solutions or stoichiometric compounds and are so far reported to stabilize the hydride phase leading to an increase of the desorption enthalpy |H| (Rude et al, 2011). Fig.…”

“…Decomposition temperatures, T dec for metal borohydrides plotted as a function of the electronegativity of the metal, M'. (Rude et al, 2011) 3.2 Thermodynamic tuning using multicomponent systems: reactive additives and reactive hydride composites In 1967 Reilly and Wiswall (Reilly & Wiswall, 1967) found another promising approach to tailor reaction enthalpies of hydrides (MH x ) by mixing them with suitable reactants (A):…”

A thermodynamic assessment of LiBH4

“…For these reasons, several attempts have been recently carried out in order to promote hydrogen desorption and absorption processes. Because electronic structure calculations indicate that a charge transfer from the metal cations M n þ to the [BH 4 ] anions is a key feature determining the thermodynamic stability of M(BH 4 ) n , cation and anion substitutions in LiBH 4 have been investigated [3][4][5][6][7]. Moreover, a destablization of LiBH 4 via reaction with a second hydride system has been suggested, in order to reduce the Gibbs Free Energy (GFE) difference between hydrogenated and de-hydrogenated species [2,8].…”

“…Moreover, a destablization of LiBH 4 via reaction with a second hydride system has been suggested, in order to reduce the Gibbs Free Energy (GFE) difference between hydrogenated and de-hydrogenated species [2,8]. As an example, LiBH 4 -MgH 2 reactive hydride composite has been deeply studied [5,9]. Even if the mechanisms of dehydrogenation reactions have not been clarified yet, the addition of a small amount of a promoter (e.g.…”