First principle study of hydrogen storage in doubly substituted Mg based hydrides

•The doubly substituted MgH2 with TM and Al or Li decreases the heat of formation.•The desorption temperature is lowered.•The gravimetric storage capacity is maintained around 7.6 wt%.•Decreasing the ionic bonding Mg–H improves the dehydrogenation performance of MgH2.

Ab-initio calculations are carried out to analyze the improvement of hydrogen storage properties, in Mg-based hydrides, through a double substitution (Mg14TMAlH32 and Mg14TMLiH32 TM = Ti, Sc, Zn). The calculations are performed using the all-electron full-potential local-orbital minimum-basis scheme (FPLO9.00-34). Our results indicate a decrease of the heat of formation and desorption temperature, while preserving the gravimetric storage capacity around 7.6 wt%, these outcomes are probably due to the second substitution, Al or Li, which are characterized by their light weights. Discussions of the charge exchange and the density of states are done, to offer more possible explanations of our results.