Mechanisms of hydrides' nucleation and the effect of hydrogen pressure induced driving force on de-/ hydrogenation kinetics of Mg-based nanocrystalline alloys

摘要

Aiming to gain insight on the hydrogen storage properties of Mg-based alloys, partial hydrogenation and hydrogen pressure related de-/hydrogenation kinetics of Mg-Ni-La alloys have been investigated. The results indicate that the phase boundaries, such as Mg/Mg2Ni and Mg/Mg17La2, distributed within the eutectics can act as preferential nucleation sites for b-MgH2 and apparently promote the hydrogenation process. For bulk alloy, it is observed that the hydrogenation region gradually grows from the fine Mg-Ni-La eutectic to primary Mg region with the extension of reaction time. After high-energy ball milling, the nanocrystalline powders with crystallite size of 12-20 nm exhibit ameliorated hydrogen absorption/desorption performance, which can absorb 2.58 wt H2 at 368 K within 50 min and begin to desorb hydrogen from -508 K. On the other side, variation of hydrogen pressure induced driving force significantly affects the reaction kinetics. As the hydrogenation/dehydrogenation driving forces increase, the hydrogen absorption/desorption kinetics is markedly accelerated. The dehydrogenation mechanisms have also been revealed by fitting different theoretical kinetics models, which demonstrate that the rate-limiting steps change obviously with the variation of driving forces. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.