Preparation of LaMgNi4-xCox alloys and hydrogen storage properties

The LaMgNi4-xCox (x=0, 0.3, 0.5) compounds were prepared by the method of levitation melting and a subsequent heat treatment at 1073 K for 10 h. XRD analysis shows that the obtained LaMgNi4-xCox alloys consist of a single phase with the structure of cubic SnMgCu4(AuBe5 type). The hydrogen absorption/desorption properties of LaMgNi4 were investigated by PCI measurement at various temperatures (T=373, 398, 423 K) and the results show that the maximum absorbed hydrogen capacity reaches 1.45% (5.79H/M) under a hydrogen pressure of 4.3 MPa at 373 K. The XRD patterns during absorbing procedure at 373 K indicate the phase structure changing from cubic (alpha-LaMgNi4) to orthorhombic (beta-LaMgNi4H3.41) and after hydrogenation finally back to cubic (gamma-LaMgNi4H4.87), and a partial desorption was also observed under this condition. With increasing temperature, a slight decrease of the absorbed hydrogen content was observed and the number of plateaus reduces from two to one, but the hydrogen absorption kinetics improves. The electrochemical properties of the LaMgNi4-xCox were measured by simulated battery test, which shows that the discharge capacity of the alloys significantly improves with the increase of Co content.