Phase evolution, hydrogen storage thermodynamics and kinetics of ternary Mg90Ce5Sm5 alloy

Greatly stable thermodynamics and sluggish kinetics impede the practical application of Mg-based hydrogen storage alloys. The modifications of composition and structure are important strategies in turning these hydrogen storage properties. In this study, Mg-based Mg90Ce5Sm5 ternary alloy fabricated by vacuum induction melting was investigated to explore the performance and the reaction mechanism as hydrogen storage material by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and pressure-composition isotherms (PCI) measurements. The results indicate that the Mg-based Mg90Ce5Sm5 ternary alloy consists of two solid solution phases, including the major phases (Ce, Sm)(5)Mg-41 and the minor phases (Ce, Sm)Mg-12. After hydrogen absorption, these phases transform into the MgH2 and (Ce, Sm)H-2.(23) phase, while after hydrogen desorption, the MgH2 transforms into the Mg phase, but the (Ce, Sm)H-2.(23) phases are not changed. The alloy has a reversible hydrogen capacity of about 5.5 wt% H-2 and exhibits well isothermal hydrogen absorption kinetics. Activation energy of 106 kl/mol was obtained from the hydrogen desorption data between 573 and 633 K, which also exhibits the enhanced kinetics compared with the pure MgH2 sample, as a result of bimetallic synergy catalysis function of (Ce, Sm)H-2. 23 phases. The rate of hydrogen desorption is controlled by the release and recombination of H-2 from the Mg surface. Furthermore, the changes of enthalpy and entropy of hydrogen absorption/desorption were calculated to be -80.0 kl/mol H-2, -137.5 J/K/mol H-2 and 81.2 kl/mol H-2, 139.2 J/K/mol H-2, respectively. (C) 2020 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.