Effect of Y Content on the Hydrogen Storage Properties of Ball-Milled Mg-Y-Ni Alloy

Abstract

Metal hydride hydrogen storage is currently the fastest growing and most promising method of hydrogen storage. In this paper, the microstructure and gaseous hydrogen storage properties of the ball-milled Mg-Y-Ni alloy were characterized thoroughly by varying the content of rare earth element Y. The Mg2.4-xY x Ni (x = 0.05, 0.1, 0.15, 0.2) alloys were first melted by vacuum high-frequency induction melting furnace. Subsequently the alloy ingots were mechanically crushed and mechanically ball milled for the same time. The phase structure and surface morphology of the ball-milled samples were also characterized, investigated and analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM). The results showed that the main phase of the alloy is the Mg2Ni phase, followed by the Ni3Y phase and a small amount of the Mg phase and MgNi2 phase. And the diffraction peaks of the Ni3Y phase are obviously enhanced with the increase of Y content, demonstrating that the exchange of Y for Mg promotes the formation of the Ni3Y phase, but the intermetallic compound Ni3Y phase was consistently present as a chemically inert material regardless of hydrogen absorption/desorption. Based on the hydrogen storage properties, the gestation period of the alloys with different Y contents showed a trend of decreasing and then increasing. For alloys with different Y contents, the Y0.1 alloy demands the shortest time for the initial activation of hydrogen absorption. And when the temperature is 573 K, the maximum values of hydrogen absorption/desorption saturation rate of Y0.1 alloy have reached 80.17% and 96.02%, respectively. In contrast to the kinetic properties, there is no significant difference in the enthalpy and entropy changes for different Y contents, indicating that the addition of rare earth element Y has minimal effect on the thermodynamic properties of the alloy.

Keywords: Mg-Y-Ni alloys, Mechanical ball milling, Activation performance, Kinetic and thermodynamic properties