Structural characterization and hydrogen storage properties of MgH2-Mg2CoH5 nanocomposites

Mixtures of XMg-Co containing different amounts of Mg (X = 2, 3 and 7) were reactive milled under hydrogen atmosphere. 2Mg-Co only formed the Mg2CoH5 complex hydride, while the mixtures 3Mg-Co and 7Mg-Co formed different contents of Mg2CoH5 and MgH2. Their structural features and hydrogen storage properties were analyzed by different techniques. In-situ synchrotron X-ray diffraction, combined with thermal analysis techniques, (differential scanning calorimetry, thermal gravimetric analysis and quadrupole mass spectrometer) was carried out to observe the behavior of the MgH2-Mg2CoH5 mixtures during the first H-desorption. It was found that the presence of the Mg2CoH5 complex hydride has a beneficial effect on the first H-desorption of the MgH2. Additionally, after first desorption, conventional hydrogenation under high pressure and high temperature of 3Mg-Co and 7Mg-Co samples led to the formation of the Mg6Co2H11 complex hydride. The presence of Mg6Co2H11 considerably impaired the desorption properties of the nanocomposites.