The microstructures and thermodynamic properties of MmNi_5-xAl_x hydrogen storage alloys are studied in this article. The structure was assessed with XRD and SEM. Pressure-composition isotherms for hydrogen absorption/desorption at 0, 25 and 50 °C were used for assessment of thermodynamic properties. XRD results show that the samples consist of single-phase CeNi₅–type. The alloys exhibit second phases, porosities, and cracks. Al microsegregation is the main reason for the second phase formation. With increasing Al, the microsegregation and the amount of second phases are increased. The hydrogen storage capacities of MmNi_5-xAl_x (x = 0.2, 0.3, 0.4 at %) alloys are 1.40, 1.37 and 1.34 wt%, respectively. The equilibrium pressures and hysteresis (1.14, 0.96 and 0.72 for 0.2, 0.3 and 0.4 Al, respectively) for all three compositions decrease with increasing Al, that proves the formation of more stable hydrides. Furthermore, the enthalpy of hydride formation decrease to -20.770, -23.565, -26.306 kJ mol^-1 H2 for the MmNi_5-xAl_x (x = 0.2, 0.3, 0.4 at %) alloys, respectively. This shows the improvement of thermodynamic stability and properties.

本文研究了MmNi _5-x Al _x储氢合金的显微组织和热力学性能。用XRD和SEM评估结构。0、25 和 50 °C 下氢吸收/解吸的压力组成等温线用于评估热力学性质。XRD 结果表明样品由单相CeNi ₅型组成。合金表现出第二相、孔隙率和裂纹。Al 微偏析是第二相形成的主要原因。随着Al的增加，微观偏析和第二相的数量增加。MmNi _5-x Al _x的储氢能力(x = 0.2, 0.3, 0.4 at %) 合金分别为 1.40、1.37 和 1.34 wt%。所有三种成分的平衡压力和滞后（0.2、0.3 和 0.4 Al 分别为 1.14、0.96 和 0.72）随着 Al 的增加而降低，这证明形成了更稳定的氢化物。此外，对于 MmNi _5-x Al _x (x = 0.2, 0.3, 0.4 at %) 合金，氢化物形成焓分别降低至 -20.770、-23.565、-26.306 kJ mol ^-1 H2 。这显示了热力学稳定性和性能的改进。