Alkaline-earth
hydrides (AH2) are considered as potential hydrogen storage
material. Due to high decomposition temperature and slow sorption
kinetics, these hydrides cannot be used for energy storage applications.
As fluorine is more electronegative than hydrogen, substitution of
hydrogen by fluorine will bring anisotropic bonding interaction, and
hence, it may improve the hydrogen storage properties. Hence, the
structural stability, electronic structure, and chemical bonding of
AH2 and fluorinated AH2 (AH2–x
F
x
) are delineated using
ab initio calculations. From the calculated enthalpy of formation
we have predicted that AH2–x
F
x
are relatively more stable than the corresponding
pure hydrides. The positive and very low value of enthalpy of mixing
for AH2–x
F
x
imply that single-phase of AH2–x
F
x
may form at reasonable temperatures.
The band structure and density of states (DOS) calculations reveal
that AH2–x
F
x
are insulators. Partial DOS, charge density, electron localization
function, and crystal orbital Hamiltonian population analyses conclude
that these compounds are governed mainly by ionic bonding. The calculated
H site energy increases as the fluorination increases and thus fluorination
bring extra stability in the lattice. The present results suggest
that hydrogen closer to fluorine can be removed more easily than that
far away from fluorine. Hence, the fluorination brings disproportionation
in the bonding between the constituents.