Microstructure and properties study of Mg2-xYxNi0.9Co0.1 (x = 0, 0.1, 0.2, 0.3) hydrogen storage alloys

Abstract 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.