Strain effect on structural and dehydrogenation properties of MgH2 hydride from first-principles calculations

The structure, stability, dehydrogenation thermodynamic and kinetic properties of MgH2 hydride under different biaxial strain conditions were investigated by using first-principles calculations based on the density functional theory (DFT). The results show that either biaxial tensile or compressive strain is likely to cause the structural deformation of MgH2 crystal, and its lattice distortion becomes severe with increasing magnitude of strain. Due to the contribution of strain energy, the biaxial strain not only weakens the structural stability of MgH2, but also lowers its hydrogen desorption enthalpy and dehydrogenation temperature. Furthermore, the diffusion activation energy of hydrogen atom in MgH2 host is also decreased, which results in a remarkable improvement of dehydrogenation properties. Noticeably, the effect of tensile strain in improving dehydrogenation thermodynamics is relatively superior to that of compressive one, while the role of the latter in enhancing dehydrogenation kinetics is relatively stronger than that of the former. Further analysis of electronic structures suggests the strain-induced changes in structural and dehydrogenation properties of MgH2 are closely associated with the value of total densities of states at the Fermi level as well as the bonding electrons number below Fermi level. These results provide an insight for developing better MgH2-based nanocomposite hydrogen storage materials by introducing suitable interface misfit strain.