A new reversible Mg3Ag–H2 system for hydrogen storage

• Mg3Ag compound with high-purity was prepared by hydrogen metallurgy.
• Mg3Ag is first employed for reversible hydrogen storage with altered thermodynamics.
• The enhanced cyclic stability is due to the prevention of MgH2 sintering by MgAg.

For the first time, the compound Mg3Ag was employed as a medium for hydrogen storage. It has been demonstrated that the hydriding/dehydriding process of Mg3Ag is reversible through the reaction Mg3Ag + 2H2 ↔ 2MgH2 + MgAg with obtaining altered thermodynamics. An enhanced cycling stability is also achieved by the capacity retention of 95% after 30 cycles, much higher than 70% for the pure Mg sample, which can be explained that the agglomeration and sintering of the resulting MgH2 are efficiently prevented by the formation of hard and brittle MgAg phase upon multi-cycling.