JPS6140292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to TiFe, which can store a large amount of hydrogen at a predetermined temperature and hydrogen gas pressure, and can easily release hydrogen by slight heating or depressurization of hydrogen gas, or both. The present invention relates to hydrogen storage materials.

Hydrogen is expected to form the core of secondary energy in future clean energy systems;
Among these, hydrogen storage and transportation forms include high-pressure gas, liquid hydrogen, and solidification using metal hydrides. Among these methods, methods using metal hydrides are attracting attention because of their safety and ease of handling. The reasons for this are: (1) the hydrogen storage density per unit volume is more than 1000 times that of gaseous hydrogen;
It is comparable to that of liquid hydrogen. (2) Hydrogen storage does not require a high-pressure container, so there are no problems with pressure resistance or hydrogen embrittlement. (3) Metal hydrides are thermodynamically stable. (4) The dissociation pressure of metal hydrides is almost constant, and hydrogen gas at a constant pressure can be obtained by determining the dissociation temperature. Examples include.

Therefore, a wide range of applications are being considered, including hydrogen storage containers using metal hydrides, fuel cells, fuel cylinders for internal combustion engines, as well as hydrogen purification equipment, air conditioners, compressors, and refrigerators. It has many advantages over conventional ones in terms of improved performance, simplification of the device, and improved characteristics.

As described above, solidification of hydrogen using metal hydrides is attracting attention as a form of hydrogen storage and transportation, but in order to be put to practical use as a hydrogen storage material, (1) it must be easy to activate; (2) A large amount of hydrogen that can be reversibly absorbed and released, (3) A small amount of residual hydrogen (the amount of hydrogen that remains in the alloy without being released even when the pressure is lowered), (4) Hydrogen absorption and The hysteresis of the release equilibrium pressure curve is small; (5) the production equilibrium pressure and dissociation equilibrium pressure of metal hydrides near room temperature are several atmospheres; (6) the hydrogen absorption and release rate is fast; (7) ) less deterioration of alloy performance due to repeated absorption and release of hydrogen; (8) low cost;
Various hydrogen storage materials have been proposed. . Among these, the TiFe alloy disclosed in US Pat. No. 3,516,232 is currently the closest to practical application in terms of hydrogen storage properties and alloy cost. However, this alloy has a strong surface film formed by oxide, nitride, or impurities in hydrogen gas, making it difficult to activate the alloy.
For activation, for example, the alloy must be heated to 250 to 450°C in tens of atmospheres of hydrogen after being crushed, and the equilibrium pressure for metal hydride formation near room temperature is quite high; It has drawbacks such as the presence of large hysteresis in the equilibrium pressure curves during absorption and release. Therefore,
As an alloy that facilitates the activation of TiFe and lowers the equilibrium pressure for metal hydride formation, iron-titanium-calcium (TiFeCa) is created by adding a small amount of calcium to the TiFe alloy and reducing the atomic ratio of Fe to Ti. There are elemental alloys (patent application 57-56682
(described in issue). This prior art alloy is
TiFe ₁ ― _x ― _y Ca _x (0<x≦0.02, 0<y≦0.10)
Activation is easier than with TiFe alloys, and after alloy pulverization, it is possible to absorb hydrogen under several tens of atmospheres of hydrogen at room temperature, and the equilibrium pressure near room temperature is about several atmospheres. However, the waiting time until hydrogen is pressurized and hydrogen begins to be absorbed is still long.
In addition, there is a large hysteresis between the equilibrium pressure curves at the time of hydrogen absorption and release. In the case of absorption, a pressure considerably higher than the hydrogen pressure obtained at the time of release is required, so extra energy is required for pressurization, and the equilibrium pressure of the alloy and the reaction during hydrogenation and dehydrogenation are When applied to heat pumps and the like that utilize heat, it causes a significant decrease in efficiency, and there are still problems from the perspective of practical application.

The purpose of the present invention is to simplify the activation of the TiFeCa ternary alloy (described in Japanese Patent Application No. 57-56682), which is a drawback of the aforementioned TiFeCa ternary alloy (described in Japanese Patent Application No. 57-56682), and at the same time improve the hysteresis characteristics, thereby making it more practical for hydrogen storage. The purpose is to provide materials. That is, the present inventors achieved the above-mentioned
TiFeCa ternary alloy and Ti atomic ratio
The present invention was completed by discovering that the quaternary alloy TiFeCaMm to which Mitsushi metal is added in an amount of 0.20 or less is extremely practical as a hydrogen storage material.

The present invention provides a hydrogen storage material that reacts with hydrogen to form a metal hydride, wherein the hydrogen storage material has the general formula TiFe _a Ca _b Mm _c (where Mm represents Mitsushi Metal,
a, b and c are each when Ti is set to 1
The atomic ratio of Fe, Ca and Mm is 0.88≦a<
1,0<b≦0.02, 0<c≦0.20).

The composition of Mitsushi metal used in the present invention is Ce
Approximately 50%, La approximately 30%, Nd approximately 15%, remainder other rare earth elements and impurity elements (Fe0.86%, others)
(manufactured by Santoku Metal Co., Ltd.).

The reasons for limiting the ranges of subscripts a, b, and c in the above formula are as follows. That is, as described in Japanese Patent Application No. 57-56682, the hydrogen absorption/desorption equilibrium pressure gradually decreases as the value of a becomes smaller, but when it becomes smaller than 0.88, it becomes close to room temperature after metal hydride formation. The amount of residual hydrogen (the amount of hydrogen remaining in the alloy without being released) increases gradually when hydrogen is released, and the amount of hydrogen stored that can be absorbed and released decreases.
The hydrogen storage properties are the best in the range of 0.88≦a<1. Furthermore, as b increases, the formation of metal hydrides becomes easier; however, when b exceeds approximately 0.02, the amount of decomposed hydrogen at room temperature after metal hydride formation gradually decreases, and the amount of residual hydrogen increases; b≦
The hydrogen storage properties in the range of 0.02 are the best. On the other hand, as c increases, the formation of metal hydrides becomes easier, that is, the waiting time until the start of hydrogen absorption in hydrogen gas after alloy pulverization becomes shorter, and the equilibrium pressure curve between hydrogen absorption and release increases. The hysteresis difference will gradually become smaller, but even if it exceeds 0.20, the effect of improving hysteresis will not be noticeable, and the amount of absorbed hydrogen will decrease, the plateau part of the equilibrium curve will become unclear, and Mitsushi Metal is relatively expensive. For these reasons, hysteresis improvement in the range of 0<c≦0.20 is most effective.

The present invention will be described in more detail below based on Examples.

Examples Alloys according to the invention TiFe _0.90 Ca _0.008 Mm _0.01 and TiFe _0.88 Ca _0.01 Mm _0.10 and TiFe _0.90 Ca _0.01
(control alloy) were melted by arc melting in Ar, and ground into 50 to 200 meshes in air.
Each alloy was placed in a thermobalance device capable of controlling temperature and pressure in a high-pressure hydrogen gas atmosphere, and the amount of hydrogen absorbed or released by the alloy was determined from weight changes accompanying the hydrogen absorption and release reactions of the alloy.

Figure 1 shows an example of the temporal change in the amount of hydrogen absorbed by the alloy, which was determined from the weight change when a constant pressure of 4 MPa of hydrogen was applied at 20°C after the alloy was crushed.
This result shows that while the TiFe _0.90 Ca _0.01 alloy starts absorbing hydrogen after a waiting time of about 1.5 hours,
Mm of 0.01 and 0.10 respectively for Ti atomic ratio
TiFe _0.90 Ca _0.008 Mm _0.01 and
The TiFe _0.88 Ca _0.01 Mm _0.10 alloy begins to absorb hydrogen after a waiting time of approximately 1 hour and 0.7 hour, respectively, and as the amount of Mm added increases, the waiting time until the absorption starts becomes shorter, and the initial It became clear that the amount of absorbed hydrogen increased. FIG. 2 shows the equilibrium pressure curves during hydrogen absorption and release at 60° C. for the alloy used in FIG. 1 after repeated hydrogen release and absorption five times.
As is clear from this result, TiFe _0.90 Ca _0.1
It can be seen that the hysteresis formed by both equilibrium curves during hydrogen absorption and desorption of the alloy gradually decreases as the amount of Mm added increases.

With such a quaternary alloy according to the present invention,
This has the effect of shortening the waiting time until hydrogen absorption starts after alloy pulverization and improving hysteresis in the equilibrium pressure curve.

[Brief explanation of the drawing]

FIG. 1 shows an alloy according to the invention and
FIG. 2 is a diagram showing the initial hydrogen absorption rate for the TiFe _0.90 Ca _0.01 alloy. FIG. 2 is a diagram showing the equilibrium pressure curve during hydrogen absorption and desorption of the alloy of FIG. 1 at 60°C.

Claims (1)

[Claims] 1. A hydrogen storage material that reacts with hydrogen to form a metal hydride, the hydrogen storage material having the general formula TiFe _a Ca _b Mm _c (where Mm represents Mitsushi Metal,
a, b and c are each when Ti is set to 1
The atomic ratio of Fe, Ca and Mm is 0.88≦a<
1,0<b≦0.02, 0<c≦0.20) A quaternary titanium-iron-calcium-mitsumetal hydrogen storage material.