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.