Hydrogen-Induced Reversible Phase Transformations and Hydrogen Storage Properties of Mg-Ag-Al Ternary Alloys

Overly stable thermodynamics and sluggish kinetics hinder the practical applications of Mg-based hydrogen storage alloys. Compositional and structural modifications are important strategies in tuning these hydrogen storage properties. In this study, Mg-based Mg-Ag-Al ternary alloys were investigated to explore their performance as hydrogen storage alloys. Mg80Ag15Al5 exhibits a reaction pathway that differs from that in pure Mg, in which the intermediate phase, consisting of a new ternary solid solution MgAg(Al), reacts with MgH2 during dehydriding and contributes to an increase in the dehydriding equilibrium pressure (0.22 MPa at 300 degrees C) and to a reversible hydrogen storage capacity of 1.7 wt %. Adjusting the composition to Mg85Ag5Al10 results in a reversible hydrogen storage capacity of approximately 3.8 wt % and an elevated equilibrium pressure (0.26 MPa at 300 degrees C). These Mg-Ag-Al ternary alloys also show enhanced hydrogen sorption kinetics relative to that of Mg, and the apparent activation energies for hydrogenation and dehydrogenation of the Mg85Ag5Al10 sample are lowered to 74.5 kJ mol(-1) and 124.8 kJ mol(-1), respectively. This work demonstrates the possibility of exploring new hydrogen storage alloys via creating different reaction pathways for hydrogen-induced reversible phase transformations.