Thermodynamical stability of calcium borohydrideCa(BH4)2

Abstract

We have prepared pure Ca͑BH 4 ͒ 2 without any solvent adducts and determined its structural parameters by powder x-ray diffraction measurement. The crystal structure of Ca͑BH 4 ͒ 2 is found to be orthorhombic with space group Fddd ͑No. 70͒. Using this structural information, the first-principles calculations have been performed to investigate the fundamental properties of Ca͑BH 4 ͒ 2 . The interaction between Ca atoms and BH 4 complexes has an ionic character while the internal bonding of BH 4 is essentially covalent. It is confirmed that Ca͑BH 4 ͒ 2 obeys the linear relationship between the heat of formation and the Pauling electronegativity of the cation, which has been proposed in a previous study ͓Nakamori et al., Phys. Rev. B 74, 045126 ͑2006͔͒.

Structure and dynamics of ammonium borohydride

“…10 NH 4 BH 4 was synthesized from NH 4 F and NaBH 4 (Sigma-Aldrich) in liquid ammonia, using Parry et al's 6 procedure. As we report elsewhere, we found the initial reaction product to be NH 3 solvates, which decompose by 250 K into NH 4 BH 4 and NH 3 . The resulting NH 4 BH 4 powder could be stored indefinitely at liquid nitrogen temperature.…”

“…Extensive experimental and theoretical structural studies have been carried out in an effort to understand and tailor their hydrogen desorption and adsorption dynamics. [2][3][4][5] Several research directions are being explored, but there is no definite solution to the high temperature hydrogen desorption and irreversibility problems associated with these compounds. Ammonium borohydride, NH 4 BH 4 , has the highest gravimetric hydrogen density, 24.523 wt%, yet although it was first synthesized more than 50 years ago, 6 its structure and properties are only now being fully explored.…”

Synthesis and Characterization of NaBD3H, A Potential Structural Probe for Hydrogen Storage Materials

“…Moreover, promising compounds such as Ca(BH 4 ) 2 undergo several phase transitions with increasing temperature, and the structural characterization of all phases remains to be completed. [2][3][4] In particular, the accurate determination of boron hydrogen bond length in solids is experimentally difficult.…”

First-principles study on thermodynamical stability of metal borohydrides: Aluminum borohydride Al(BH4)3

“…We have also determined the structural parameters experimentally for Ca(BH 4 ) 2 and its fundamental properties have been predicted theoretically. 13 Aluminum borohydirde Al(BH 4 ) 3 is liquid at ambient temperatures with the melting point of 209 K. The structures of the solid phase have been investigated by x-ray diffraction measurements. 14 Cooling liquid Al(BH 4 ) 3 , the orthorhombic β phase was initially grown and then the transition to the monoclinic α phase occurred at a temperatures in the range 180-195 K. In this study, we predict the thermodynamical stability of Al(BH 4 ) 3 and reexamine the correlation between the stability of borohydrides and the cation electronegativity.…”