Hydrogen Storage Characteristics Of Mg Research Articles

Effects of volatilization of lithium on hydrogen storage characteristics of Mg–Ni–Li alloy

Abstract

Enhanced low temperature hydrogen desorption properties and mechanism of Mg(BH4)2 composited with 2D MXene

Mg(BH4)2 occupies a large hydrogen storage capacity of 14.7 wt%, and has been widely recognized to be one of the potential candidates for hydrogen storage. In this work, 2D MXene Ti3C2 was introduced into Mg(BH4)2 by a facile ball-milling method in order to improve its dehydrogenation properties. After milling with Ti3C2, Mg(BH4)2–Ti3C2 composites exhibit a novel “layered cake” structure. Mg(BH4)2 with greatly reduced particle sizes are found to disperse uniformly on Ti3C2 layered structure. The initial dehydrogenation temperature of Mg(BH4)2 has been decreased to 124.6 °C with Ti3C2 additive and the hydrogen liberation process can be fully accomplished below 400 °C. Besides, more than 10.8 wt% H2 is able to be liberated from Mg(BH4)2–40Ti3C2 composite at 330 °C within 15 min, while pristine Mg(BH4)2 merely releases 5.3 wt% hydrogen. Moreover, the improved dehydrogenation kinetics can be retained during the subsequent second and third cycles. Detailed investigations reveal that not only Ti3C2 keeps Mg(BH4)2 particles from aggregation during de/rehydrogenation, but also the metallic Ti formed in-situ serves as the active sites to catalyze the decomposition of Mg(BH4)2 by destabilizing the B–H covalent bonds. This synergistic effect of size reduction and catalysis actually contributes to the greatly advanced hydrogen storage characteristics of Mg(BH4)2.

Enhancement of the Hydrogen-Storage Characteristics of Mg by Adding Mg2Ni and Ni to MgH2 via High Energy Ball Milling in Hydrogen Atmosphere

In this work, Mg2Ni and Ni were added to MgH2 in order to improve the hydrogen-storage properties of Mg. A 94 wt% MgH2+5 wt% Mg2Ni+1wt% Ni (named 94MgH2+5Mg2Ni+1Ni) sample was prepared by milling in a hydrogen atmosphere in a planetary ball mill for 5 h. The Mg2Ni was hydrided during milling in a hydrogen atmosphere. The 94MgH2+5Mg2Ni+1Ni had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed for 60 min) of near 5 wt%. At n=1, the sample released 0.18 wt% for 2 min, 2.14 wt% for 5 min, 4.65 wt% for 10 min, and 5.46 wt% for 60 min at 648 K. The reactive mechanical grinding of MgH2 with Mg2Ni and Ni is believed to facilitate nucleation (by creating defects, which serve as active sites for nucleation, on the surfaces and inside the Mg particles), increase reactivity with hydrogen (by making clean surfaces), and decrease the diffusion distances of hydrogen atoms (by reducing the particle size of Mg). (Received April 10, 2017; Accepted July 28, 2017)

Hydrogen Storage Characteristics of Mg, Mg-5TaF<SUB>5</SUB>, and Mg-5NbF<SUB>5</SUB> Prepared via Grinding in a Hydrogen Atmosphere

Hydrogen Storage Characteristics of Mg, Mg-5TaF<SUB>5</SUB>, and Mg-5NbF<SUB>5</SUB> Prepared via Grinding in a Hydrogen Atmosphere

Enhancement of Hydrogen Storage Characteristics of Mg by Addition of Nickel and Niobium (V) Fluoride via Mechanical Alloying

A specimen with a composition of 80 wt% Mg+14 wt% Ni+6 wt% NbF5 (termed Mg-Ni-NbF5) was prepared by mechanical alloying. Its hydrogen absorption and release characteristics were then examined. Mg2NiH4 was formed by a reaction of Mg with nickel and hydrogen during mechanical alloying and hydrogen absorption-release cycling. The particles after hydrogen absorption-release cycling became smaller than those after mechanical alloying owing to the expansion and contraction of the particles upon cycling. The cycled Mg-Ni-NbF5 had a fairly high hydrogen absorption rate and a large hydrogen storage capacity, with an effective hydrogen storage capacity close to 5.6 wt% at 593 K. The cycled Mg-Ni-NbF5 absorbed 5.58 wt% H in 12 bar H2 and released 4.81 wt% H in 1.0 bar H2 at 573 K for 60 min. At 593 K, the cycled specimen absorbed 4.53 wt% H for 5 min, 5.27 wt% H for 10 min, 5.50 wt% H for 25 min, and 5.58 wt% H for 60 min in 12 bar H2, and released 1.28 wt% H for 5 min, 2.26 wt% H for 10 min, 4.13 wt% H for 30 min, and 4.81 wt% H for 60 min in 1.0 bar H2.

Synthesis and hydrogen storage characteristics of Mg–B–H compounds by a gas–solid reaction

Magnesium borohydride [Mg(BH4)2] is an attractive complex hydride for hydrogen storage. In this study, attempts to synthesize Mg(BH4)2 were carried out by a solid–gas reaction through MgH2 and B2H6 in the absence of a liquid medium. The source of B2H6 was obtained by heating a mixture of NaBH4 and ZnCl2. The profile of pressure versus temperature indicated that the absorption kinetics of B2H6 by MgH2 were slow. Structural analysis confirmed the formation of Mg–B–H compounds. The reaction products presented two-step hydrogen release during heating. A small amount of hydrogen could be released from the as-synthesized Mg–B–H compounds at a low temperature of 215 °C. The slow reaction kinetics were significantly affected by the surface conditions of the MgH2 powders.

Hydrogen-storage characteristics of Mg–14Ni–6Fe2O3–2CNT prepared by reactive mechanical grinding

In order to improve the reaction kinetics of Mg with H2, CNT (carbon nanotube) was added to Mg together with Ni and Fe2O3 by reactive mechanical grinding. The content of additives was about 20wt% with that of Fe2O3 6wt%. These contents of additives and Fe2O3 were known optimum ones to improve the hydriding and dehydriding rates of Mg. Samples with compositions of 80wt% Mg–14wt% Ni–6wt% Fe2O3 (named as Mg–14Ni–6Fe2O3), and 78wt% Mg–14wt% Ni–6wt% Fe2O3–2wt% CNT (named as Mg–14Ni–6Fe2O3–2CNT) were prepared. The hydriding and dehydriding properties of these samples were then examined, and the effects of Ni, Fe2O3, and CNT additions on the hydriding and dehydriding rates of Mg-based alloys were discussed.

Direct synthesis and hydrogen storage characteristics of Mg–B–H compounds

This paper reports a comparative study of synthesizing Mg(BH 4) 2 by mechanically milling Mg + B, MgH 2 + B and MgB 2 powders following hydrogenation under hydrogen atmosphere. It has been shown that the milled Mg + B and MgH 2 + B powders consisted of magnesium hydride and boron, while the milled MgB 2 powder remained unchanged during the milling process. TEM, Raman spectra and TPD measurements confirmed the formation of amorphous Mg–B–H compounds in the milled Mg + B and MgH 2 + B powders, which could be Mg(B x H y ) n moieties. The total hydrogen desorption amounts after 3 h were 3.7 wt.% and 3.9 wt.% for the milled Mg + B and MgH 2 + B powders respectively, whereas the milled MgB 2 showed little apparent hydrogen desorption. After a hydrogenation process was carried out, the further hydrogenated MgB 2 powder was found to contain the amorphous Mg–B–H compounds and could release 0.25 wt.% hydrogen.

Electrochemical hydrogen storage characteristics of Mg–Pd–Ni ternary alloys

Mg 1− x Pd x Ni ( x = 0.03, 0.05, 0.06, 0.07, 0.08, 0.10, 0.20) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. The XRD studies showed that Mg 6Pd and Mg–Pd phases form in the high-Pd-containing alloys. The discharge capacities of the alloys increased sharply up to 15 h milling. Further increase up to 25 h did not cause change in the discharge capacities considerably. Among the Mg 1− x Pd x Ni ternary alloys, Mg 0.93Pd 0.07Ni alloy was observed to exhibit the best charge/discharge cyclic performance. The hydrogen storage capacity of the high-Pd-containing alloys (Mg 1− x Pd x Ni; x > 0.07) deteriorated as Pd content of the alloy increased. This observation was attributed to the Mg–Pd phase formations. According to the EIS experiments as Pd atomic ratio increased up to 0.07 the charge transfer resistances of the alloys decreased. Further increase in Pd atomic ratio, however, brought about the increase in the charge transfer resistances.

Improvement of hydrogen storage characteristics of Mg by planetary ball milling under H 2 with metallic element(s) and/or Fe 2O 3

Among samples of Mg–Ni, Mg–Ni–5Fe 2O 3, and Mg–Ni–5Fe, Mg–Ni–5Fe had the highest hydriding and dehydriding rates. For the as-milled Mg–Ni–5Fe alloy and the hydrided Mg–Ni–5Fe alloy after activation, the weight percentages of the constituent phases were calculated using the FullProf program. The creation of defects and the diminution of Mg particle size through reactive mechanical grinding and hydriding–dehydriding cycling, and the formation of the Mg 2Ni phase are considered to increase the hydriding and dehydriding rates. Mg–14Ni–2Fe–2Ti–2Mo had higher hydriding and dehydriding rates than did any of the other samples (Mg–Ni, Mg–Ni–5Fe 2O 3, Mg–Ni–5Fe, and Mg–14Ni–6Fe 2O 3) prepared in this work.

Influence of the substitution of La for Mg on the microstructure and hydrogen storage characteristics of Mg 20− xLa xNi 10 ( x = 0–6) alloys

In order to enhance the glass forming ability of the Mg 2Ni-type hydrogen storage alloy, the Mg in the alloy was partially substituted by La. The alloys Mg 20− x La x Ni 10 ( x = 0, 2, 4, 6) were prepared by casting and rapid quenching. The structures and morphologies of the as-cast and the quenched alloys were studied by XRD, SEM and HRTEM. It was found that no amorphous phase was formed in the as-quenched La-free alloy. But the as-quenched alloys containing La held a major amorphous phase, confirming that the substitution of La for Mg significantly enhances the glass forming ability of the alloys. When La content x ≤ 2, the major phase in the as-cast alloys is Mg 2Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La,Mg)Ni 3 + LaMg 3 phase. Thermal stability of the as-quenched alloys was studied by DSC, showing that La content engenders a negligible influence on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and the quenched alloys were measured by an automatically controlled Sieverts apparatus. The results showed that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly rise with increasing La content. For La content x = 2, the as-quenched alloy displays an optimal hydrogen desorption kinetics at 200 °C. The electrochemical measurement showed that the discharge capacities of the as-cast alloys rose with the increase of La content, but those of the as-quenched alloys obtained the maximum values with the variation of La content. The cycle stability of the as-cast and the quenched alloys significantly improved with increasing La content.

Enhancement of the hydrogen storage characteristics of Mg by reactive mechanical grinding with Ni, Fe and Ti

Mg-10wt%Ni-5wt%Fe-5wt%Ti powder was prepared by reactive mechanical grinding using a planetary ball mill. The Mg-10wt%Ni-5wt%Fe-5wt%Ti powder exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after two hydriding–dehydriding cycles. After the reactive mechanical grinding, the particle size of the powder was reduced, as compared with those of the starting materials. The hydrogen storage properties were measured at temperatures of 473 K, 573 K and 623 K. The activated Mg-10wt%Ni-5wt%Fe-5wt%Ti powder absorbed 5.31 wt% and 5.51 wt% of hydrogen for 5 min and 1 h, respectively, at 573 K under 12 bar H 2. It desorbed 5.18 wt% of hydrogen at 573 K under 1.0 bar H 2 for 1 h. The initial hydrogen absorption rate increased when passing from 473 K to 573 K, but decreased at 623 K. The hydrogen desorption rate increased rapidly with increasing temperature from 473 K to 623 K. The hydrogen storage capacity was about 6.72 wt% at 573 K.

Dependence of hydrogen storage characteristics of Mg–TiFe 0.92Mn 0.08 composite on amount of TiFe 0.92Mn 0.08

We investigated the hydrogen storage characteristics of Mg– x wt.%TiFe 0.92Mn 0.08 ( x = 20 , 35, and 50) composites prepared by wet mechanical milling. TiFe 0.92− x Mn 0.08 and α -Fe phases were formed in these composites by the decomposition of TiFe 0.92Mn 0.08 after activation. The kinetics of the hydrogen absorption at low temperature was improved by increasing the amount of TiFe 0.92Mn 0.08. These improvements appear to be attributable to the TiFe 0.92− x Mn 0.08 phase, which plays an important role as a pathway for the diffusion of hydrogen into the Mg matrix. In contrast, the hydrogen desorption temperature decreased as the amount of α -Fe originating from TiFe 0.92Mn 0.08 increased. The Mg–50 wt.%TiFe 0.92Mn 0.08 composite started to desorb hydrogen at the same temperature as Mg–50 wt.%Fe composite prepared under the same milling conditions although the former had much better hydrogen absorption characteristics than the latter at low temperature. We consider that the presence of α -Fe probably contributes to the improvement in the hydrogen desorption characteristics.

Effects of mechanical alloying on the hydrogen storage characteristics of Mg- xwt% Ni ( x = 0, 5, 10, 25 and 55) mixtures

Magnesium is alloyed mechanically with nickel in a planetary mill. Magnesium without nickel is also treated under the same conditions. The hydriding and dehydriding properties of these materials are investigated. The Mg 2Ni phase develops in the mechanically alloyed Mg- xwt% Ni ( x = 0, 5, 10, 25 and 55) mixtures along with hydriding-dehydriding cycles. The principal effects of mechanical alloying and hydriding-dehydriding cycling are the augmentation in the active nucleation sites and the decrease in the effective particle size. The effects of mechanical alloying and hydriding-dehydriding cycling on the hydriding and dehydriding reactions of Mg in the mixtures are most important in Mg-25wt % Ni under our experimental conditions.