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

To understand the effect of [RNi 5 ]/[RMgNi 4 ] 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 [SmNi 5 ]/[SmMgNi 4 ] unit ratio increases, the parameters of [SmNi 5 ] and [SmMgNi 4 ] units in layered Sm 2 MgNi 9, Sm 3 MgNi 14, and Sm 4 MgNi 19 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 SmMgNi 4 and SmNi 5, and the cycle stability can be improved by the increase of [SmNi 5 ]/[SmMgNi 4 ] unit ratio.