Structure of the Complex Metal Hydride BaReH9

Abstract

Our interest in materials for hydrogen storage applications has prompted us to investigate the structure of complex metal hydrides.' The ideal storage material would have a very high hydrogen density. Of the known complex metal hydrides, dipotassium nonahydridorhenate, KzReH? has a hydrogen density of 103 g of WL, approximately 1.5 times that of liquid hydrogen. It also has a 3:l hydrogen to metal atom ratio, one of the highest known. The [ReH& anion has tricapped trigonal prismatic symmetry (D3h).3 In the revised synthesis of this hydride? the disodium salt is first synthesized and then converted to the dipotassium salt by way of the barium salt. This intermediate, BaReH9, has no reported characterizations, however the hydrogen-to-metal ratio is 4.5:1, making it the metal hydride with the highest known hydrogen to metal ratio. With the higher hydrogen-to-metal ratio, the hydrogen density might also be expected to be increased. For this reason, we have undertaken an investigation of this compound.Barium nonahydridorhenate was prepared according to the published procedure from the disodium salt.4 The conversion gave average yields of approximately 95%; overall yields of approximateIy 40% were obtained based on the initial perrhenate. The dried white powder slowly turned gray and eventually black when exposed to air for periods of several weeks. X-ray powder diffraction and IR measurements of the colored powder after prolonged exposures showed the presence of the hydride with an additional strong peak at 1450 cm-' but no perrhenate absorptions. The frequency of the new absorption corresponds to the frequency normally attributed to carbonate impurities.2 The decomposition of this salt therefore appears to proceed via a pathway different from that of the alkali metal salts.4bAn IR spectrum of the dried white powder, in KBr pellets, was measured on a Perkin-Elmer 883 spectrophotometer. An

Structural and thermodynamic properties of metallic hydrides used for energy storage☆

“…However, this value can vary in very large proportions depending on the compounds and the largest reported value reaches 4.5 H/M for BaReH 9 [3]. The stability of the formed hydride is determined by its hydrogen equilibrium pressure at a given temperature.…”

Cohesion ofBaReH9andBaMnH9Singh1, Gupta2, Gupta3 2007Phys. Rev. B161120View full textAdd to dashboardCite

“…This follows a previous electronic structure calculation by Orgaz and Gupta,8 done using the X-ray crystal structure of Ref. 4 and the Xα method. The present calculations were done using a general potential self-consistent method, with calculated H positions, and allow us to present a more accurate electronic structure and detailed analysis of the bonding.…”

“…The crystal structure (spacegroup P 6 3 /mmc), which was determined using X-ray diffraction by Stetson and co-workers, 4 is depicted in Fig. 1.…”

Metallization and Superconductivity in the Hydrogen-Rich Ionic Salt BaReH9

“…1). [20][21] The hydrogen density in BaReH 9 (134 g/L) is approximately twice that of liquid hydrogen at ambient pressure, indicating that hydrogen atom is chemically precompressed. [20][21][22][23][24] Markopoulous et al 23 examined theoretically the high pressure behavior of BaReH 9 and predicted that metallization occurs at 115 GPa assuming the crystal structure of BaReH 9 remains in the ambient pressure structure.…”