Hydrogen Sorption Behaviour of Mg-5wt.%La Alloys after the Initial Hydrogen Absorption Process

In our earlier study, it has been shown that trace Na additions can improve the reaction kinetics of Mg-5%La (wt.%) alloys during the first absorption. However, the subsequent hydrogen desorption/absorption process of the Mg-5%La after the first absorption has not been investigated. In this study, we have investigated the hydrogen sorption behaviour of the Mg-5%La alloy after the first absorption in terms of phase evolution, and lattice expansion properties during desorption as function of temperature using in-situ synchrotron Powder X-ray Diffraction (PXRD) and in-situ High Voltage Transmission Electron Microscopy (HVTEM). Two distinct phase evolutions, a continuous phase transformation of LaH3 -> LaH2 + 1/2 H2 (from 250 degrees C) and decomposition of MgH2 -> Mg + H2 (between 440 and 460 degrees C) were identified during the desorption. It is determined that this alloy is cyclable in the absence of Mg12La intermetallic during the subsequent absorption/desorption cycling after the first hydrogen absorption. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.