Improvement in the Hydrogenation and Dehydrogenation Features of Mg by Milling in Hydrogen with Vanadium Chloride

Abstract

VCl3 (vanadium (III) chloride) was selected as an additive to Mg to increase the hydrogenation and dehydrogenation rates and the hydrogen storage capacity of Mg. Instead of MgH2, Mg was used as a starting material since Mg is cheaper than MgH2. Samples with a composition of 95 wt% Mg + 5 wt% VCl3 (named Mg-5VCl3) were prepared by milling in hydrogen atmosphere (reactive milling). In the first cycle (n=1), Mg-5VCl3 absorbed 5.38 wt% H for 5 min and 5.95 wt% H for 60 min at 573 K in 12 bar hydrogen. The activation of Mg-5VCl3 was completed after three hydrogenation-dehydrogenation cycles. During milling in hydrogen, β-MgH2 and γ-MgH2 were produced. The formed β-MgH2 and γ-MgH2 are considered to have made the effects of reactive milling stronger as β-MgH2 and γ-MgH2 themselves were being pulverized. The introduced defects and the interfaces between the Mg and the phases formed during the reactive milling and during hydrogenation-dehydrogenation cycling are believed to serve as heterogeneous active nucleation sites for MgH2 and Mg-H solid solution. The phases generated during hydrogenation-dehydrognation cycling are also believed to prevent the particles from coalescing during hydrogenation-dehydrognation cycling.

Improvement in Hydriding and Dehydriding Features of Mg–TaF5–VCl3 Alloy by Adding Ni and x wt% MgH2 (x = 1, 5, and 10) Together with TaF5 and VCl3

“…The reactive mechanical milling of Mg with Ni, TaF 5 , and VCl 3 is thought to increase the hydriding and dehydriding rates by forming defects [35][36][37][38] (leading to easier nucleation) [39][40][41], making new clean surfaces (leading to an increase in the reactivity of Mg particles with hydrogen) [30,42], and decreasing the particle size of Mg (leading to a decrease in the diffusion distances of hydrogen atoms) [9,10,[36][37][38]43]. Especially, the added Ni is believed to form the Mg 2 Ni phase, which has higher hydriding and dehydriding rates than Mg at the same conditions [36,44], contributing greatly to the increases in the reaction rates.…”

“…To increase the hydrogen uptake and release rates of magnesium, magnesium (Mg), or magnesium hydride (MgH 2 ) was alloyed [2][3][4][5][6][7][8][9][10] with Ni and Y [11], V [12], and Nb [13]. In addition, Mg or MgH 2 was mixed with compounds such as LaNi 5 [14], FeTi and FeTiMn [15], Nb 2 O 5 [16], and La 2 O 3 [17].…”

Fast Hydrogen Sorption Kinetics in Mg-VCl3 Produced by Cryogenic Ball-Milling

“…Other V-containing compounds have improved the hydriding/dehydriding of Mg/MgH 2 [ 15 , 21 , 22 , 23 ]. In particular, the addition of VCl 3 [ 24 , 25 , 26 ] resulted in quick sorption kinetics [ 27 , 28 , 29 ]. A survey on the Web of Science on the topics Mg or MgH 2 , VCl 3 , and hydrogen storage produced only 12 published papers.…”

“…Of them, three used VCl 3 as a co-catalyst; and in the other three, the MgH 2 was mixed with other hydrogen storage materials. Of the papers on MgH 2 -VCl 3 [ 24 , 25 , 26 , 27 , 28 , 29 ], the information on kinetics or thermodynamics is incomplete, as we detail in the discussion section. In comparison, a survey in the same database of MgH 2 , Nb 2 O 5 , and hydrogen storage produced 272 papers.…”

“…On the other hand, the reported amount of VCl 3 added to MgH 2 spans from 5 wt.% to 23.9 wt.% (i.e., up to 5 mol%) [ 25 , 26 , 29 , 30 , 31 ]. In the present work, we explored the use of a relatively high amount of VCl 3 , but in between the amounts reported [ 25 , 26 , 29 , 30 , 31 ]: 15 wt.% (or 2.65 mol%).…”