High-pressure phases induce H-vacancy diffusion kinetics in TM-doped MgH<inf>2</inf>: Ab initio study for hydrogen storage improvement

Abstract

© 2019 Hydrogen Energy Publications LLC The improvement of the hydrogen storage mechanism in TM-doped MgH2 by structural high-pressure effects has been found using ab initio calculation. Phase transition, formation enthalpy and H-vacancy mechanism of α-, β-, and γ-MgH2 with 3.125% of Ni, Pd and Pd dopants are analyzed under the pressure conditions of 0, 5 and 10 GPa. It is found that the enthalpy of β- and γ-phases based on the α-phase decreases in TM-doped systems, especially for the heavier atomic size of dopants (Pt > Pd > Ni). As a result, the γ-phase has become structural stable at ambient pressure. The occupation enthalpy of TM substitutions in β and γ phases is easier than that in the α phase, which indicates ability of mixing impurities. High pressure induces the occupation of H-vacancy in all compounds. The activation energy curves of MgH2 with Ni, Pd and Pt dopants are also analyzed, and the minimal barriers are significantly dominated in the γ phase.