Dehydrogenation of Alkali Metal Aluminum Hydrides MAlH4 (M = Li, Na, K, and Cs): Insight from First-Principles Calculations

• Published in: Batteries (Basel) Vol. 9; no. 3; p. 179
• Main Authors: Zhou, Rui, Mo, Xiaohua, Huang, Yong, Hu, Chunyan, Zuo, Xiaoli, Ma, Yu, Wei, Qi, Jiang, Weiqing
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.03.2023
• Subjects: alkali metal aluminum hydrides; Aluminum; Aluminum hydrides; cation electronegativity; Cations; Cesium; Decomposition; Dehydrogenation; dehydrogenation performance; Density functional theory; Electronegativity; electronic structure; Energy; Energy of dissociation; First principles; first-principles calculations; Free energy; Heat of formation; Hydrogen; Hydrogen storage; Hydrogen storage materials; Investigations; Ionic interactions; Lithium aluminum hydrides; Mathematical analysis; Metal hydrides; Optimization; Sodium; Thermal stability
• ISSN: 2313-0105; 2313-0105
• DOI: 10.3390/batteries9030179

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, MAlH4 (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 (Ed-H2) of MAlH4 (M = Li, Na, K, and Cs) correlates with the Pauling electronegativity of cation M (χP); that is, the Ed-H2 (average value) decreases, i.e., 1.211 eV (LiAlH4) < 1.281 eV (NaAlH4) < 1.291 eV (KAlH4) < 1.361 eV (CsAlH4), with the increasing χP 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 MAlH4 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.