A candidate LiBH4 for hydrogen storage: Crystal structures and reaction mechanisms of intermediate phases

Abstract

First-principles calculation and x-ray diffraction simulation methods have been used to explore crystal structures and reaction mechanisms of the intermediate phases involved in dehydriding of LiBH 4 . LiBH 4 was found to dehydride via two sequential steps: first dehydriding through LiBH, followed by the dehydriding of LiBH through LiB. The first step, which releases 13.1 wt. % hydrogen, was calculated to have an activation barrier of 2.33 eV per formula unit and was endothermic by 1.28 eV per formula unit, while the second step was endothermic by 0.23 eV per formula unit. On the other hand, if LiBH 4 and LiBH each donated one electron, possibly to the catalyst doped on their surfaces, it was found that the barrier for the first step was reduced to 1.50 eV. This implies that the development of the catalyst to induce charge migration from the bulk to the surface is essential to make LiBH 4 usable as a hydrogen storage material in a moderate temperature range, which is also important to stabilize the low-temperature structure of Pnma ͑no. 62͒ LiBH on dehydrogenation. Consequently, the high 13.1 wt. % hydrogen available from the dehydriding of LiBH 4 and LiBH and their phase stability on Pnma when specific catalysts were used suggest that LiBH 4 has good potential to be developed as the hydrogen storage medium capable of releasing the Department of Energy target of 6.5 wt. % for a hydrogen fuel cell car in a moderate temperature range. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2042632͔There is great interest in small and lightweight hydrogen storage materials. 1,2 Hydrogen fuel, which can be produced from renewable energy sources, contains a much larger chemical energy per mass ͑142 MJ kg −1 ͒ than any hydrocarbon fuel, thus making a hydrogen fuel cell an attractive alternative to the internal combustion engine for transportation. A hydrogen fuel cell car needs to store at least 4 kg hydrogen to cover the same range as a gasoline-powered car. 1 On the other hand, to store this hydrogen at room temperature and atmospheric pressure requires such a large volume that corresponds to a balloon with a 4.5 m diameter, which is hardly a practical volume for a small vehicle. To reduce this problem, one could consider using liquid hydrogen for hydrogen storage since it has a high mass density 1 ͑70.8 kg m −3 ͒. However, to liquefy hydrogen requires expensive processes due to its low condensation temperature 1 ͑−252°C at 1 bar͒. An additional problem is that heat transfer through the available modern containers can result in a loss of up to 40% of the energy content in hydrogen. 3 Currently, in this respect, there is much interest in storing hydrogen on advanced carbons and lightweight metals. Dillon et al. 4 reported that 6 -8 wt. % hydrogen was stored in singlewalled nanotubes ͑SWNTs͒. However, controversial results 5,6 have been reported concerning the true hydrogen storage capacity on advanced carbons. Hirscher and his coworkers 5 argued against Dillon's report by showing that titanium hydrides in the SWNT stor...

Reversibility of Al/Ti Modified LiBH4

“…13 For a complete substitution of Li by M, it has been found both theoretically and experimentally that a correlation exists between the Pauling electronegativity of the cation (M) and the thermodynamical stability of the borohydride. 39,40 This correlation does not apply when there is no or only partial substitution. Indeed, Au et al 41 and Yang et al 42 have screened a batch of additives, and if one classifies them with respect to their Pauling electronegativities, the sequence obtained does not match with their effectiveness in destabilizing the hydride.…”

Ionic conductivity and the formation of cubic CaH2 in the LiBH4–Ca(BH4)2 composite

“…All above-mentioned crystalline solid electrolytes have considerably lower Li + conductivities, with the exception of Li 10 GeP 2 S 12 which has a Li + conductivity of 12 m/S/cm at 27°C [13]. Lithium borohydride has been investigated extensively in recent years, both as a hydrogen storage material [18][19][20][21][22][23] and as a crystalline solid electrolyte material for lithium batteries [24][25][26]. It is lightweight (0.666 g/cm 3 ) and has been shown to be electrochemically stable up to 5 V [27].…”

Reactivity of LiBH4: In Situ Synchrotron Radiation Powder X-ray Diffraction Study

“…12 Furthermore, several new structures and compositions of lithium tetrahydridoboranates were proposed from theoretical calculations. [13][14][15] In order to release more hydrogen reversibly at lower temperatures, further knowledge of the mechanism of gas release is needed. Alter-natively, a catalyst can be added or a new reaction pathway can be obtained from a suitable reactive hydride composite.…”