Effect of Y content on the hydrogen storage properties of ball-milled Mg2.4-xYxNi (x=0.05, 0.1, 0.15, 0.2) alloys

Metal hydride hydrogen storage is currently the fastest growing and most promising method of hydrogen storage. In this paper, the Mg2.4-xYxNi (x = 0.05, 0.1, 0.15, 0.2) alloys were first melted by vacuum high-frequency in-duction melting furnace. Subsequently the alloy ingots were mechanically crushed and mechanically ball milled for the same time. And the microstructure and gaseous hydrogen storage properties of the ball-milled alloy were characterized thoroughly by varying the content of rare earth element Y. 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 hydrogen storage alloys with different Y contents can be fully activated after one hydrogen absorption/desorption cycle, and 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 Mg2.3Y0.1Ni alloy demands the shortest time for the initial activation of hydrogen absorption. And when the temperature is 573 K, the time taken to absorb 90% of the hydrogen capacity was 8 min, 6 min, 8 min and 12 min, and the time taken to release 90% of the hydrogen capacity was 4.6 min, 3.4 min, 5 min and 6 min for alloys with different Y contents, respectively. And the maximum values of hydrogen absorption/desorption saturation rate of Mg2.3Y0.1Ni alloy have reached 80.17% and 96.02%, respectively. The activation energy of hydrogen release of the alloys decreases from 123.9 kJ/mol to 113.1 kJ/mol. 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.