Spectroscopic and structural investigations of α‐, β‐, and γ‐AlH₃ phases

Abstract

With its reputation as a high-energy density fuel, aluminum hydride (AlH 3 ) has received renewed attention as a material that is particularly suitable, not only for hydrogen storage but also for rocket propulsion. While the various phases of AlH 3 have been investigated theoretically, there is a shortage of experimental studies corroborating the theoretical findings. In response to this, we present here an investigation of these compounds based primarily on two research areas in which there is the greatest scarcity of information in the literature, namely Raman and infrared (IR) absorption analysis. To the authors' knowledge, this is the first report of experimental far-IR absorption results on these compounds. Two different samples prepared by broadly similar ethereal reactions of AlCl 3 with LiAlH 4 were analyzed. Both Raman and IR absorption measurements indicate that one sample is purely γ -AlH 3 and that the other is a mixture of α-, β-, and γ -AlH 3 phases. X-ray diffraction confirms the spectroscopic findings, most notably for the β-AlH 3 phase, for which optical spectroscopic data are reported here for the first time. Copyright

Aluminum hydride for solid-state hydrogen storage: Structure, synthesis, thermodynamics, kinetics, and regeneration

“…A more recent DTF study by Vajeeston et al [64] demonstrated different frequencies for the vibration modes of α-AlH 3 , which is shown in Table 2 . Manciu et al [65] analyzed the Raman absorption of asprepared α-AlH 3 synthesized by wet chemical method and showed two vibrations at 508 cm −1 and 720 cm −1 ( Table 2 ), which is very similar to those reported by Wong and Miller [61] and by Tkacz et al [66] .…”

Novel methods for synthesizing halide-free alane without the formation of adducts

“…Figures 9b and 9c show the Al-H stretching bands at 1857 and 1725 cm −1 and Al-H bending bands at lower frequencies (874, 740, and 673 cm −1 ) that are attributed to α-AlH 3 . The IR spectra of the washed samples match that of pure α-AlH 3 and correspond well with IR spectroscopic data described in the literature [23,24].…”

New perspectives on potential hydrogen storage materials using high pressure

“…Using X-ray and neutron diffraction as well as spectroscopic techniques, the crystal and electronic structures for four phases (a, a 0 , b and g) have been characterized for AlH 3 (or AlD 3 ). [79][80][81][82][83][84][85][86][87] As the most stable phase, a-AlH 3 has a trigonal structure (space group R% 3c) with corner sharing of the [AlH 6 ] octahedra ( Fig. 1e, 10).…”