Hydrogen-absorbing alloys

doi:10.1016/S1359-0286(99)00026-1

Current Opinion in Solid State and Materials Science

Volume 4, Issue 3, June 1999, Pages 267-272

https://doi.org/10.1016/S1359-0286(99)00026-1 Get rights and content

Abstract

Improvement of hydrogen capacity in hydrogen-absorbing alloys has been achieved in recent years. Mg-based alloys which were synthesized by ball milling showed lower dehydrogenation temperatures than intermetallic Mg-based alloys. This technique is also effective for preparing a novel Mg-based amorphous alloy, MgNi, and its hydride. Besides conventional intermetallic compounds such as LaNi₅, solid solution alloy, ‘Laves phase related BCC solid solution’ with body-centered-cubic structure showed a hydrogen capacity of 2.2 mass% at room temperature. Alanate, which is not an interstitial hydride, was found to react with gaseous hydrogen reversibly with a catalyst, and its hydrogen capacity was more than 3 mass%.

Introduction

The first report about the hydrogen-absorbing alloy, Mg₂Ni, was published in 1968 [1]. Hydrogen-absorbing alloys have attracted great attention because they are safe and efficient media for transporting hydrogen energy. LaNi₅ was the first, and still the major, hydrogen-absorbing alloy; it absorbs hydrogen at room temperature, and was reported in 1970 [2]. Today, hydrogen-absorbing alloys are commercially used for the electrodes of Ni–hydrogen batteries since 1990 but not yet for energy-carrying media. In 1998, the amount of the alloy produced was worth about several billion yen (several tens of millions of US$).

The alloy used for commercial Ni–hydrogen batteries is basically a LaNi₅-based one. The capacity of the alloy presently used for batteries is not large enough.

Recently the polymer electrolyte fuel cell which is lighter than other fuel cells and works below 373 K was developed especially for efficient and emission-free vehicles. Since the fuel for the fuel cell is hydrogen, on-board storage of hydrogen becomes more realistic. A hydrogen-absorbing alloy is one of the ideal media for hydrogen storage because compactness and safety are key issues for on-board applications. However, the hydrogen capacity of the most popular LaNi₅-based alloys does not exceed 1.4 mass%. The hydrogen capacity of conventional alloys seems to be insufficient for on-board storage of hydrogen.

In two major application fields of hydrogen-absorbing alloys, an increase of hydrogen capacity is strongly desired but the conventional alloys do not reach more than 2 mass% at room temperature.

Hydrogen-absorbing alloys consist of a metal component which forms a stable hydride and a component which does not. The alloys are categorized by the constituting element, which makes stable hydrides. Fig. 1 shows part of the Periodic Table, which shows the elements with the right weights, and form stable hydrides. In order to develop right-weight alloys (in other words, a higher hydrogen capacity according to a weight basis), one of the elements shown should be selected.

In recent years, Mg and Ti have been taken as the most promising elements for hydrogen-absorbing alloys and a remarkable improvement in these alloys has been reported. Alkaline metal hydrides such as NaAlH₄ also attracted attention because they showed a larger hydrogen capacity than conventional alloy hydrides and acceptable kinetics with the existence of a catalyst.

In this review, these three kinds of hydrogen-absorbing alloys will be introduced and discussed.

Section snippets

Mg-based alloy

The typical Mg-based alloy, Mg₂Ni, absorbs hydrogen 3.6 mass% but the hydrogenation temperature is around 600 K [1]. For many applications, the hydrogenation temperature of Mg₂Ni is too high and many efforts have been made to lower the reaction temperature of Mg₂Ni while keeping the hydrogen capacity.

For conventional intermetallic hydrogen-absorbing alloys, substitution is the only and the best method to control reaction temperature [3]. Tsushio and Akiba investigated the substitution of the

Ti-based BCC alloys

For years, the representative of Ti-based alloys was the Laves phase TiMn₂-based one. The hydrogen capacity of the Ti-based Laves phase alloy did not exceed 2 mass%.

Body centered cubic (BCC) metals and alloys intrinsically have a large hydrogen capacity but they have not been used in any application up to now. Even the studies on hydride formation in BCC alloys were fewer than that of intermetallics [29], [30], [31], [32], [33]. Ti-based BCC solid solution alloys which are both single- and

Ti–V–X alloys

Libowitz and Maeland [29] found BCC solid solution alloys that reacted extremely rapidly with hydrogen. They are Ti–V-based alloys such as Ti–V–Fe, Ti–V–Mn, Ti–V–Co, Ti–V–Cr and Ti–V–Ni [30], [31], [32].

Lynch et al. [31] reported hydride formation in the V–Ti–Fe system with BCC structure. They measured pressure–composition–temperature diagrams up to a hydrogen pressure of 7 MPa. This system showed a flat plateau between mono- and di-hydrides.

Nomura and Akiba [33] reported on hydrogen and the

Laves phase related BCC solid solution

Iba and Akiba reported that Ti-based AB₂ alloys consisted of BCC and Laves phases and every phase contributed to hydrogenation [39], [40], [41]. In particular, the BCC phase absorbed hydrogen in a favorable manner like the intermetallic compounds and showed the same hydrogenation pressure (equilibrium pressure) as other component phases [42]. The BCC solid solution phase that appears with the Laves phases is a promising candidate for a hydrogen-absorbing alloy. Therefore, they name this type of

Alkali metal aluminum hydride

Bogdanovic reported a new reversible hydrogen storage material, NaAlH₄ and its related inorganic salt-type hydrides with Ti catalyst [*45]. For this kind of ionic hydride it has been considered that the gas–solid reaction is irreversible. The reason is that the alkali metal hydride has ionic compounds of H⁻ which differ remarkably to the interstitial hydride (or the hydride of a conventional hydrogen-absorbing alloy). However, he showed that the reaction is reversible and the hydrogen capacity

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In this work, the hydrogen storage behavior of Ti₂CrV + X wt.% Zr₃Fe, where X = 2, 4, 6, 8 and 10 was investigated. The synthesis of all samples was carried out through arc-melting, followed by comprehensive characterization using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The pure-Ti₂CrV as-cast sample presented a single-phase microstructure. However, the addition of the Zr₃Fe led to a remarkable transformation, resulting in the appearance of a Zr-rich secondary phase. It was found that the first hydrogenation is improved with the addition of at least 6 wt% of Zr₃Fe, avoiding any preheating of the sample. These samples achieved their maximum capacity in approximately 10 min at room temperature. The maximum capacity recorded was 4.2 wt% H for the sample with X = 6 wt% Zr₃Fe, while for X = 8 and 10 wt% Zr₃Fe, the capacity recorded was 4.1 wt% and 4.0 wt%, respectively.
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Hydrogen-absorbing alloys

Abstract

Introduction

Section snippets

Mg-based alloy

Ti-based BCC alloys

Ti–V–X alloys

Laves phase related BCC solid solution

Alkali metal aluminum hydride

The reaction of hydrogen with alloys of magnesium and nickel and the formation of Mg2NiH4

Inorg. Chem.

Reversible room-temperature absorption of large quantities of hydrogen by intermetallic compounds

Philips Res. Repts.

Hydrogen desorption properties of the quaternary alloy system Mg2−xM1xNi1−yM2y

J. Alloys Comp.

Hydrogenation properties of Mg-based Laves phase alloys

J. Alloys Comp.

Hydrogen properties of Mg1−xM1xCu2 (M1=La and Nd) with larger interstitial sites than MgCu2

J. Alloys Comp.

Hydrogenation properties of MgNi0.86M10.03 (M1=Cr, Fe, Co, Mn) alloys

J. Alloys Comp.

Hydrogen absorption in nanocrystalline Mg2Ni formed by mechanical alloying

J. Alloys Comp.

Catalytic effect of Pd on hydrogen absorption in mechanically alloyed Mg2Ni, LaNi5 and FeTi

J. Alloys Comp.

Nanocrystalline metal hydrides

J. Alloys Comp.

Hydrogen absorption of Mg-based composite prepared by mechanical milling: Factors affecting its characteristics

J. Alloys Comp.

Characterization and hydriding properties of Mg–graphite composites prepared by mechanical grinding as new hydrogen storage materials

J. Alloys Comp.

Mg composites for hydrogen storage. The dependence of hydriding properties on composition

J. Alloys Comp.

Mechanically milled Mg composites for hydrogen storage: The relationship between morphology and kinetics

J. Alloys Comp.

Phase components and hydriding properties of the sintered Mg–x wt.% LaNi5 (x=20–50)

J. Alloys Comp.

Structural and hydriding properties of amorphous MgNi with interstitial dissolved carbon

J. Alloys Comp.

Structural characterization and reversible hydrogen absorption properties of Mg2Ni rich nanocomposite materials synthesized by mechanical alloying

J Alloys Comp

Ball milling of Mg2Ni under hydrogen

J. Alloys Comp.

Effect of processing parameters on Mg-based hydrogen storage materials prepared by mechanical alloying

Notable hydriding properties of a nanostructured composite material of Mg2Ni–H system synthesized by reactive mechanical grinding

Acta Mater.

Structural and hydriding properties of Mg–Ni–H system with nano- and/or amorphous structures

Acta Mater.

Effect of nanometer-scale structure on hydriding properties of Mg–Ni alloys: Review

Intermetallics

Structural and hydriding properties of (Mg1−xAlx)Ni–H(D) with amorphous or CsCl-type cubic structure (x=0–0.5)

Acta Mater.

The reaction of hydrogen with alloys of magnesium and nickel and the formation of Mg₂NiH₄

Hydrogen desorption properties of the quaternary alloy system Mg_2−xM1_xNi_1−yM2_y

Hydrogen properties of Mg_1−xM1_xCu₂ (M1=La and Nd) with larger interstitial sites than MgCu₂

Hydrogenation properties of MgNi_0.86M1_0.03 (M1=Cr, Fe, Co, Mn) alloys

Hydrogen absorption in nanocrystalline Mg₂Ni formed by mechanical alloying

Catalytic effect of Pd on hydrogen absorption in mechanically alloyed Mg₂Ni, LaNi₅ and FeTi

Phase components and hydriding properties of the sintered Mg–x wt.% LaNi₅ (x=20–50)

Structural characterization and reversible hydrogen absorption properties of Mg₂Ni rich nanocomposite materials synthesized by mechanical alloying

Ball milling of Mg₂Ni under hydrogen

Notable hydriding properties of a nanostructured composite material of Mg₂Ni–H system synthesized by reactive mechanical grinding

Structural and hydriding properties of (Mg_1−xAl_x)Ni–H(D) with amorphous or CsCl-type cubic structure (x=0–0.5)