Pressure-induced phase of NaAlH4: A potential candidate for hydrogen storage?

Abstract

The electronic structure and structural stability of the technologically interesting material NaAlH4 are studied using an ab initio projected augmented plane-wave method for different possible structure modifications. We predict that α-NaAlH4 converts to β-NaAlH4 at 6.43 GPa with a 4 % volume contraction. Both modifications have nonmetallic character with finite energy gaps, the calculated band gap for β-NaAlH4 being almost half of that for the α phase. β-NaAlH4 stores hydrogen more volume efficient than the α phase and would if stabilized at ambient conditions be an interesting candidate for further studies with regard to hydrogen absorption/desorption efficiency.

Structural study of ball-milled sodium alanate under high pressure

“…They reported two possible phase transformations: one at ∼3 GPa which was less obvious as a structural transformation, and a second at ∼12 GPa to the orthorhombic structure. Our previous X-ray measurements on commercially available NaAlH 4 showed the phase transformation to ␤-NaAlH 4 phase with orthorhombic structure which is in agreement with the predicted structure by Vajeeston et al [12] followed by amorphisation at ∼13.6 GPa [14].…”

“…Enhanced desorption kinetics were clearly demonstrated for NaAlH 4 doped with Ti and/or Zr catalyst [9][10][11]. Ab initio calculations by projected augmented plane wave method indicate that NaAlH 4 undergoes a phase transformation from tetragonal structure with space group I4 1 /a, i.e., SrMgH 4 -type structure to the ␤-orthorhombic (Cmc2 1 ) structure at 6.43 GPa with a 45% volume contraction [12]. It was also suggested that the ␤-NaAlH 4 stores more hydrogen volumetrically than the ␣-phase and would, if stabilized at ambient conditions, be an interesting candidate for further studies with regard to hydrogen absorption/desorption efficiency.…”

The Crystal Structure and Surface Energy of NaAlH4: A Comparison of DFT Methodologies

“…A number of results taken from the literature are also shown in these tables for comparison. Vajeeston et al 3 and Ke and Tanaka 4 used the PAW method of VASP with the PBE and PW91 functionals, respectively, to optimize the structure of NaAlH 4 . Opalka and Anton 5 similarly used the PW91 functional with VASP but did not report coordinates for the hydrogen degrees of freedom.…”

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Typically, in these studies some flavor of density functional theory (DFT) 20-22 is used to calculate properties of the bulk solid or of the surface of the solid material. A wide range of DFT methodologies and implementations are currently in regular use for these predictive studies, with little attention being paid to any strengths or weaknesses of particular methods.…”

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

“…(b) There occurs a high-pressure phase transition. Highpressure phases were theoretically predicted for NaAlH 4 (above 64.3 kbar [36]), experimentally found for the lithium analogue LiAlH 4 (tetragonal above 70 kbar and 373-673 K, and orthorhombic above 70 kbar and 773 K [37]). The latter showed a downward shift of the ν 3 [AlH 4 ] − stretching band.…”