Mg2(Co1/3Fe1/3Ni1/3), Mg2(Cu1/3Fe1/3Ni1/3), Mg2(Co1/3Cu1/3Fe1/3), Mg2(Co1/3Cu1/3Ni1/3), and Mg2(Co1/4Cu1/4Fe1/4Ni1/4) Materials for Hydrogen Storage

Hydrogen is a promising energy vector; however, its storage in solid-state materials is still an unresolved problem. Hydrogen storage on Mg-based materials is an ongoing research area. Here, five materials, Mg2(Co1/3Fe1/3Ni1/3), Mg2(Cu1/3Fe1/3Ni1/3), Mg2(Co1/3Cu1/3Fe1/3), Mg2(Co1/3Cu1/3Ni1/3), and Mg2(Co1/4Cu1/4Fe1/4Ni1/4), are reported for hydrogen storage. The hydriding and dehydriding reactions in these materials proceed via two steps. The first step is associated with the Mg/MgH2 equilibrium, while the second step is related to the simultaneous formation of mixtures of hydrided Mg-intermetallics. All of the studied materials demonstrate easy hydriding in mild conditions (15 bar, 300 °C). Mg2(Co1/3Fe1/3Ni1/3) can be considered the best material among the studied series, with a hydrogen storage capacity of 3.8 wt. % and a dehydriding onset temperature of 243 °C. The presence of Cu modified the equilibrium pressure of the second hydriding step and induced partial dehydriding at 250 °C in pressure-composition isothermal testing. The presence of Fe favored the hydrogen uptake in the first hydriding reaction, from 0.5 wt. % at the material without Fe to 1.1–2.2 wt. % in the Fe materials. The elements Co, Co, Cu, and Fe demonstrated synergistic effects on hydriding/dehydriding reactions.