Strain tuned dehydrogenation thermodynamics of magnesium based hydride: A first principle study

[Display omitted] •The effects of strain on dehydrogenation thermodynamics of MgH2 are studied.•The metastable tetragonal and even orthorhombic MgH2 phase form upon strain.•The dehydrogenation enthalpy of MgH2 decreases substantially with increasing strain.•Triaxial tensile strain prefers to improve dehydrogenation thermodynamics of MgH2.•Strain tuned dehydrogenation thermodynamics are explained by electronic structures. To improve the dehydrogenation thermodynamics of magnesium based hydride, i.e. MgH2, it is essential to weaken its structural stability. From density functional theory calculations, we show that the crystal structure and dehydrogenation thermodynamics of MgH2 are sensitive to the applied lattice strain. The metastable tetragonal and even orthorhombic MgH2 phase form upon strain. Meanwhile, the hydrogen desorption enthalpy decreases substantially with increasing strain. Especially, the triaxial tensile strain is more conductive to improve the dehydrogenation thermodynamics of MgH2, which can be attributed to the narrower energy gap of MgH2 induced by triaxial tensile strain relative to uniaxial and biaxial tensile ones. These results prompt a new insight to tune the dehydrogenation thermodynamics of metal hydrides by introducing proper lattice strain.