The Structural And Hydriding-dehydriding Kinetics Of Mg-Al-Ni Hydrogen Storage Alloy

Hydrogen storage alloy was a kind of material, the bulk hydrogen atoms can storage in the crystal gaps of the alloy, which has reversible nature of hydrogen absorption and desorption. The remarkable superiority with light and safe caused a great deal of concern. The Mg-based hydrogen storage alloys have many advantages, such as large hydrogen capacity, low density, high storage capacity, low price, and so on. So it is considered as one of the most promising hydrogen storage materials. As a represented alloy of Mg-based hydrogen storage materials, Mg2Ni has the better absorption and desorption behaviors at low temperature and hydrogen pressure. The substitution of Al for partial Mg atoms in the Mg2Ni can be used to improve hydrogen properties of the alloy.In this paper, the alloys are prepared from Mg, Al and Ni powders (purity above 99.9%) by mechanical milling under argon atmosphere using a SPEX-8000 mixer-mill. XRD, SEM, XPS, synchrotron radiation EXAFS, PCT measurement and hydrogen absorption and desorption kinetics were used to analyze the properties of the different milling time alloys. In this paper, we investigated the relationship between the change in the structure of alloy and hydrogen storage capacity of alloy, and the evolution of crystal structure and chemical state of Mg1.9Al0.1Ni alloy during hydrogen absorption/desorption cycling. The H/D kinetic curves indicated that the hydrogen storage capacity increased with the increased cycles in the beginning and the samples were activated after 10 cycles have the better hydrogen storage capacity. Meanwhile, the local structure of Mg1.9Al0.1Ni alloys were investigated by extended X-ray absorption fine structure (EXAFS). The bondlength, coordination numbers and the degree of disorder were obtained using WinXAS software. The EXAFS results indicate the Ni-Ni bondlength has no obviously change with the cycles increasing, whereas the Ni-Mg bondlength increases, and the Ni-Mg bondlength is longer obviously than before 10 cycles whereas it has no obviously change after 10 cycles.