Hydrogen desorption properties of MgH2-Ni-Ni2Si composites prepared by mechanochemical method

To improve hydrogen desorbability of Mg, some composites were prepared from MgH2, Ni and Ni2Si mixed powders by the mechanochemical method. The MgH2-Ni(2 mol%)-Ni2Si(1 mol%) composite was slower in hydrogen desorption rate at 250 degrees C than the MgH2-Ni(2 mol%) composite, while the hydrogen desorption rate at 220 degrees C for the former was faster than that for the latter. The XRD pattern of the MgH2-Ni(2 mol%) composite showed that after hydrogen desorption at 400 degrees C small diffraction peaks assigned to Mg2Ni were observed with peaks assigned to Mg. They shifted to smaller angles after hydrogen absorption at 250 degrees C and come back to the original positions after hydrogen desorption at 250 degrees C, suggesting reversible hydrogen absorption/desorption of Mg2Ni. In contrast, Ni2Si was not changed over the whole processes. These results indicated that Ni2Si worked as a catalyst for hydrogen desorption, leading to the improvement of desorbability at 220 degrees C. (C) 2013 Elsevier B.V. All rights reserved.