Synergistic dosing effect of TiC/FeCr nanocatalysts on the hydrogenation/dehydrogenation kinetics of nanocrystalline MgH2 powders

Abstract

Nanocrystalline MgH2 powders were synthesized by reactive ball milling of elemental Mg powders milled for 200 h under a high hydrogen gas pressure of 50 bar. The end-product obtained after 200 h of milling was contaminated (∼2.3 wt.%) with the materials (Fe–12Cr stainless steel). In order to improve the hydrogenation/dehydrogenation kinetics of metal hydride powders, the as-synthesized MgH2 was doped with previously prepared TiC nanopowders, which contaminated with 2.4 wt.%, and then ball milled under hydrogen gas atmosphere for 50 h. The results related to the morphological examinations of the fabricated nanocomposite powders beyond the micro-and nano-levels showed excellent distributions of 5TiC/5Fe–12Cr dispersoids embedded into the fine host matrix of MgH2 powders. The as-fabricated nanocomposite MgH2/5TiC/5Fe–12Cr powders possessed superior hydrogenation/dehydrogenation characteristics, suggested by a low value of the activation energy (97.74 kJ/mol), and the short time required for achieving a complete absorption (6.6 min) and desorption (8.4 min) of 5.5 wt.% H2 at moderate temperature of 275 °C under a hydrogen gas pressure ranged from 0 bar to 8 bar. Under these temperature and hydrogen gas pressure, this new nanocomposite system possessed excellent absorption/desorption cyclability of 530 complete cycles, achieved in a cyclic-life-time of 515 h. The effects of ball milling time, grain sizes, as well as TiC- and Fe–12Cr concentrations on the hydrogenation/dehydrogenation processes and cyclability were investigated and discussed.