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To enhance the hydrogen storage performance of Mg-Ni system alloys, multi-elemental alloys incorporating Y element, namely Mg _2-x Y _x Ni _0.9 Co _0.1 (x = 0, 0.1, 0.2, 0.3), were synthesized through ball milling and sintering. The microstructures of Mg _2-x Y _x Ni _0.9 Co _0.1 (x = 0, 0.1, 0.2, 0.3) alloys were characterized using XRD and SEM/EDS techniques, and the hydrogen storage properties of Mg _2 Ni _0.9 Co _0.1 and Mg _1.7 Y _0.3 Ni _0.9 Co _0.1 alloys were evaluated via the Sieverts method. At a sintering temperature of 500 °C, the Y element existed in the form of Y/Y _2 O _3 phases and displayed no reactivity with other alloy constituents. The addition of Y enhanced the activation performance of Mg-Ni system alloys, because it takes 2 times for Mg _1.7 Y _0.3 Ni _0.9 Co _0.1 alloy to complete activation, while Mg _2 Ni _0.9 Co _0.1 needs 3, albeit causing a slight reduction from 3.6 wt% to 3.2 wt% in the hydrogen storage capacity when Y replaced Mg. The enthalpy of hydrogen desorption of Mg _1.7 Y _0.3 Ni _0.9 Co _0.1 alloy was 57.4 kJ mol ^−1 H _2 , which was significantly lower than that of Mg _2 Ni _0.9 Co _0.1 (68.0 kJ mol ^−1 H _2 ) and Mg _2 Ni alloy (64.4 kJ mol ^−1 H _2 ), indicating improved thermodynamic properties. Moreover, the apparent activation energy of Mg _2 Ni _0.9 Co _0.1 (71.48 kJ mol ^−1 H _2 ) was lower than that of Mg _1.7 Y _0.3 Ni _0.9 Co _0.1 (83.62 kJ mol ^−1 H _2 ), implying that the addition of Y reduced the kinetic properties.