Effects of Ni-loading contents on dehydrogenation kinetics and reversibility of Mg2FeH6

Effects of Ni precursors on the formation of Mg–Fe–Ni intermetallic hydrides, kinetics, and reversibility

“…In the case of S2, the 1 st rehydrogenated sample reveals the diffractions of MgH 2 , Fe, Fe-Ni alloy, and MgO as well as Mg 2 Fe (1−x) Ni x H 6 , shown as a new diffraction peak locating between those of Mg 2 FeH 6 and Mg 2 NiH 4 . 23,25 The formations of MgH 2 , Mg 2 FeH 6 , and Mg 2 NiH 4 in S1 conrm rehydrogenation of Mg, MgH 2 + Fe, and Mg 2 Ni, respectively (reverse reactions of eqn ( 6) and ( 7) as well as eqn ( 5)). Besides, it was reported that Mg 2 NiH 4 was able to be synthesized by hydrogenating the mixture of coarsegrained Mg and Ni(Fe) nanoparticles and most of Ni(Fe) transformed to a-Fe when the reaction completed (eqn ( 8)).…”

“…5) can be explained by the reaction between Fe-Ni alloy and MgH 2 to form Mg 2 NiH 4 . In the case of the 1 st rehydrogenated S2, hydrogenations of Mg into MgH 2 (reverse reaction of eqn ( 6)) and Mg 2 Ni + Mg 2 FeH 6 into Mg 2 Fe (1−x) Ni x H 6 (eqn (9)) 23,25 are observed. Signicantly enhanced diffraction of Fe-Ni alloy and irreversibility of Mg 2 NiH 4 upon the 1 st hydrogenation of S2 suggest the increase of solid solution of Fe and Ni as well as no reaction between MgH 2 and Fe-Ni alloy (eqn ( 8)).…”

“…The samples were prepared by (i) milling MgH 2 with the plain steel containing TM impurities (e.g., 316L stainless steel and g-Fe(Ni) nanoparticles) 8,18,19 and (ii) compositing TMs in metallic form or compounds with Mg + Fe, MgH 2 + Fe, or Mg 2 FeH 6 . [20][21][22][23][24][25] These processes increased Mg 2 FeH 6 yield with the improved kinetic properties and reversibility. Immediate reaction between MgH 2 and 316L SS via either reactive ball milling under hydrogen pressure or ball milling under Ar atmosphere and annealing under hydrogen pressure resulted in partial substitution of Fe with Cr and Ni to form Mg 2 (Fe, Cr, Ni)H x .…”

“…From our previous work, Mg 2 Fe 0.75 Ni 0.25 H 6 formed during dehydrogenation of 20 wt% Ni-doped Mg 2 FeH 6 showed excellent reversible hydrogen capacities with respect to as-prepared Mg 2 FeH 6 , for example, hydrogen reproduction during the 2 nd cycle increased from 78 to 85%. 23 Besides, Ni-substituted contents in Mg 2 FeH 6 was optimized by varying Mg 2 FeH 6 : Mg 2 NiH 4 mole ratios to obtain Mg 2 Fe (1− x ) Ni x H 6 with the best kinetics. 25 It was found that dehydrogenation kinetics and reversibility were enhanced with Ni-substituted contents, and the most stable composition upon cycling was x ∼ 0.5 (Mg 2 Fe 0.5 Ni 0 .…”

Improved H-Storage Performance of Novel Mg-Based Nanocomposites Prepared by High-Energy Ball Milling: A Review

“…These catalytic species play an important role in the hydrogenation/dehydrogenation process and usually provide active sites for the nucleation reaction. Doping nanocrystalline Mg 2 FeH 6 by Ni promotes the reaction of Ni with MgH 2 and Fe, resulting in the formation of Mg 2 NiH 4 and FeNi 3 phases, respectively [122]. The Mg 2 FeH 6 -20Ni alloy possesses a two-step dehydrogenation sequence, in contrast to the single-step reaction of the as-prepared material.…”