Complex aluminum hydrides with high hydrogen capacity are among the most promising solid-state hydrogen storage materials. The present study determines the thermal stability, hydrogen dissociation energy, and electronic structures of alkali metal aluminum hydrides, MAlH
4 (M = Li, Na, K, and Cs),
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Complex aluminum hydrides with high hydrogen capacity are among the most promising solid-state hydrogen storage materials. The present study determines the thermal stability, hydrogen dissociation energy, and electronic structures of alkali metal aluminum hydrides, MAlH
4 (M = Li, Na, K, and Cs), using first-principles density functional theory calculations in an attempt to gain insight into the dehydrogenation mechanism of these hydrides. The results show that the hydrogen dissociation energy (E
d-H
2) of MAlH
4 (M = Li, Na, K, and Cs) correlates with the Pauling electronegativity of cation M (χ
P); that is, the E
d-H
2 (average value) decreases, i.e., 1.211 eV (LiAlH
4) < 1.281 eV (NaAlH
4) < 1.291 eV (KAlH
4) < 1.361 eV (CsAlH
4), with the increasing χ
P value, i.e., 0.98 (Li) > 0.93 (Na) > 0.82 (K) > 0.79 (Cs). The main reason for this finding is that alkali alanate MAlH
4 at higher cation electronegativity is thermally less stable and held by weaker Al-H covalent and H-H ionic interactions. Our work contributes to the design of alkali metal aluminum hydrides with a favorable dehydrogenation, which is useful for on-board hydrogen storage.
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