Significantly decreased stability of MgH2 in the Mg-In-C alloy system: Long-period-stacking-ordering as a new way how to improve performance of hydrogen storage alloys?

Hydrogen storage (HS) performance of Mg-In-CB alloys (CB amorphous carbon) is studied. Indium concentration covers primary solid solution (Mg), two phase area (Mg) + beta 1 and also alloys containing ordered beta structures. Seven Mg-In-CB alloys are prepared by ball-milling in hydrogen atmosphere. Kinetic curves and PCT isotherms are measured in the temperature interval from 200 degrees C to 375 degrees C. Hydrogen sorption experiments are done by the Sieverts method under the hydrogen gas pressure ranging from 0.1 MPa to 2.5 MPa. X-ray diffraction spectroscopy is used for structure investigation. Alloy with 13" structure shows reversible amorphization during temperature cycling between about 100 degrees C and 350 degrees C. It is found that hydrogen sorption capacity varies between about 6 wt % H-2 for (Mg) and 0.6 wt % H-2 for beta" structure. Hydride decomposition enthalpy calculated from desorption PCT experiments decreases to 54 +/- 3 kJ x (mol H-2)(-1) and 57 +/- 3 kJ x (mol H-2)(-1) for ordered alloys in the interval from 69 to 71 wt % In, and even down to 51.5 kJ x (mol H-2)(-1) for amorphous beta" structure. Activation energy of desorption kinetics is also lowered in the ordered structure. (C) 2019 Elsevier Ltd. All rights reserved.