Comparative Investigations on Hydrogen Absorption–Desorption Properties of Sm–Mg–Ni Compounds: The Effect of [SmNi5]/[SmMgNi4] Unit Ratio

To understand the effect of [RNi5]/[RMgNi4] unit ratio on hydrogen storage properties of layered R–Mg–Ni compounds, the hydrogen absorption–desorption characteristics of Sm–Mg–Ni compounds have been investigated comparatively in this work. As the [SmNi5]/[SmMgNi4] unit ratio increases, the parameters of [SmNi5] and [SmMgNi4] units in layered Sm2MgNi9, Sm3MgNi14, and Sm4MgNi19 compounds decrease gradually, leading to the elevation of equilibrium pressure, enlargement of slope, and reduction of hysteresis of their P–C isotherms as well as the decline of enthalpy change for hydrogen absorption–desorption. The hydrogen capacities of the layered Sm–Mg–Ni compounds at 298 K are higher than those of SmMgNi4 and SmNi5, and the cycle stability can be improved by the increase of [SmNi5]/[SmMgNi4] unit ratio.