Ca-Mg-Ni containing alloys, method for preparing the same and use thereof for gas phase hydrogen storage

Abstract

Disclosed are new Ca, Mg and Ni-containing alloys of the general formula:

(Ca_cMg_dM_e)_b(Ni_1-zT_z)_a

where: M is at least one metal selected from the group consisting of Y, Ce, La, Pr, Nd, Th, Nd, Ti, V, Zr, Ta, Hf, Sr, Ba and Misch metals; T is at least one element selected from the group consisting of Al, Zn, Cu, Fe, Co, Mn, Cr, Mo, W, Si, Ga, Ge, In, Sn, Ag, C and B; a is an integer equal to 2 or 5; z is a number ranging from 0 to 0.5; and when a is equal to 2, then 0.9≦b≦1.1; and when a is equal to 5, then either 1.75≦b≦2.25 or 0.75≦b≦1.31.

These alloys which are of the AB₂, A₂B₅ or AB₅ types, may be single phase or multiphase and are useful for reversibly absorbing hydrogen from a gas phase. Also disclosed is a method for preparing the above alloys.

Description

FIELD OF THE INVENTION [0001] The present invention is directed to Ca, Mg and Ni-containing alloys. It is also directed to a method for preparing these alloys and to their use for reversibly absorbing hydrogen from a gas phase. BACKGROUND OF THE INVENTION [0002] The use of hydrogen gas as a fuel for PEM fuel cells has received considerable attention in recent years because PEM fuel cells using pure hydrogen can provide high efficiency and ultra clean power. Unfortunately, widespread use of hydrogen energy is not currently feasible because of economic and technological barriers. One of the important barriers is the lack of cost effective, safe hydrogen storage method. [0003] Hydrogen gas is very light. It can be compressed under high pressure and stored in pressurized vessels. It can also be liquefied and stored in liquid form. Hydrogen also reacts with metal or non-metals to form hydrides. Some metal hydrides called “low temperature metal hydrides” are reversible at ambient temperat...

AI Technical Summary

Benefits of technology

[0043] The invention also relates to a method for preparing the above mentioned alloys, comprising the steps of: milling a mixture of elemental powders and / or pre-alloyed combination of elemental powders of Ca, Mg, M, Ni and T annealing and / or sintering the milled mixture at a temperature higher than 600° C. In another embodiment, the temperature is higher than 800° C.

Problems solved by technology

Unfortunately, widespread use of hydrogen energy is not currently feasible because of economic and technological barriers.

One of the important barriers is the lack of cost effective, safe hydrogen storage method.

The most serious shortcomings of the reversible metal hydrides and more particularly the low temperature metal hydrides are their low gravimetric storage density and the high cost.

However, the high cost of conventional low temperature metal hydrides results in too expensive storage devices.

Amongst the known hydrogen storage materials, conventional lanthanum or mischmetal-based alloys of the AB5 type like LaNi5 alloys are inherently expensive because they make use of a rare earth metal.

However, hydrogen can not be extracted at temperatures below 100° C. under normal pressure.

However, this hydride can only desorbs partially (half of the amount absorbed) at 400° K and 1 bar.

According to these authors, the low reversibility of this alloy limits practical applications.

That phase is known for not absorbing hydrogen and consequently the properties deteriorate.

Since Ca and Mg have very high evaporation rate, it is very hard to produce a stoichiometric Ca—Mg—Ni alloy in large quantity.

Homogenization by long annealing treatments is required but adds costs to the alloys.

In practice, this means that the use of this technology would be expensive.

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