Stability and Reversibility of LiBH₄

Abstract

LiBH4 is a complex hydride and exhibits a high gravimetric hydrogen density of 18.5 wt %. Therefore it is a promising hydrogen storage material for mobile applications. The stability of LiBH4 was investigated by pcT (pressure, concentration, and temperature) measurements under constant hydrogen flows and extrapolated to equilibrium. According to the van 't Hoff equation the following thermodynamic parameters are determined for the desorption: enthalpy of reaction DeltarH = 74 kJ mol-1 H2 and entropy of reaction DeltarS = 115 J K-1 mol-1 H2. LiBH4 decomposes to LiH + B + 3/2H2 and can theoretically release 13.9 wt % hydrogen for this reaction. It is shown that the reaction can be reversed at a temperature of 600 degrees C and at a pressure of 155 bar. The formation of LiBH4 was confirmed by XRD (X-ray diffraction). In the rehydrided material 8.3 wt % hydrogen was desorbed in a TPD (temperature-programmed desorption) measurement compared to 10.9 wt % desorbed in the first dehydrogenation.

In situ X-ray Raman spectroscopy study of the hydrogen sorption properties of lithium borohydride nanocomposites

“…3B. Based on this deconvolution result there is about 10% boron present, a majority of (480%) Li 2 B 12 H 12 and a little amount (B5%) of LiBH 4 . This result seems to suggest that with 1 bar of hydrogen, partial re-hydrogenation to LiBH 4 can be achieved for these nanoconfined LiBH 4 -C samples.…”

“…Comparing the B K-edge XRS of the LiBH 4 -C deh (red) with the bulk LiBH 4 Note that for reactions (3a) and (3b), LiC x represents intercalated lithium and does not imply the formation of Li-C bonds.…”

“…S5). The slope of the first peak in the B K-edge of LiBH 4 -C deh is strongly linked to the content of boron powder and the height of the XRS peak is connected to the Li 2 4 to carbon via reaction eqn (3a). The Li K-edge XRS could as well be informative on this aspect, since whenever boron is present also LiH or Li in some form should be present.…”

“…Among these options, storing hydrogen as metal hydrides is interesting from the view point of safety, energy density and volume density. As the gravimetric density of the material is an important consideration, many studies have focused on hydrides of light-weight elements or alloys such as MgH 2 , LiBH 4 , NaBH 4 , NaAlH 4 and Mg(BH 4 ) 2 . Especially, the alkali-metal borohydrides have been widely investigated for reversible hydrogen storage due to their high hydrogen content: 1,2 for example LiBH 4 contains 18.5 wt% hydrogen.…”

“…Unfortunately, LiBH 4 and many other complex hydrides undergo multiple desorption steps with often amorphous and sometimes volatile intermediates that cannot be characterized using standard techniques such as X-ray diffraction (XRD). Transmission electron microscopy (TEM) is also ineffective due to the weak scattering of electrons by the light elements Li, Na and B. Additionally, confinement of LiBH 4 in nanoporous carbon materials, which was shown to be a promising strategy to improve hydrogen release and uptake in these complex hydrides, 8,10,11 often leads to nanocomposites that are amorphous after preparation.…”