JP3451320B2 - Hydrogen storage alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen storage alloy and a hydrogen storage medium for a hydrogen storage tank.

[0002]

_2. Description of the Related Art Ti ₂ Ni is a cubic E9 ₃ shown in FIG.
It is an alloy having a type structure and reacts with hydrogen to produce hydride T
i ₂ NiH ₃ is formed. This alloy is relatively inexpensive and has a relatively large hydrogen storage capacity of about 2% by weight, but the hydride is chemically stable, and the hydrogen pressure-composition-temperature (PCT) characteristics are shown in FIG. Moreover, even at a high temperature of 180 ° C., only a part of the stored hydrogen is released.
In addition, this hydride has a disproportionation reaction that causes Ti
It has a drawback that it is easily decomposed into H ₂ and TiNi ₃ and loses its ability to release hydrogen. Therefore, Ti ₂ Ni as a hydrogen storage material does not have satisfactory hydrogen release characteristics and durability.

Therefore, Ti or Ni which constitutes the alloy is
Attempts have been made to replace the element with another metal element. However, in this case, as shown schematically in FIG.
The plateau of the T curve, that is, the flat part of the PCT curve where the hydrogen concentration changes at a constant pressure, is inclined by the substitution,
A larger energy is required to take out hydrogen, and for example, a higher temperature is required to take out hydrogen, which is a problem.

[0004]

The main object of the present invention is to:
An object of the present invention is to provide a novel hydrogen storage alloy having excellent hydrogen storage characteristics and hydrogen release characteristics and excellent in durability.

[0005]

Means for Solving the Problems The present inventor has conducted extensive research in view of the problems described above, the alloy having E9 ₃ type structure of cubic crystal represented by Ti ₂ Ni, O, N and C
It has been found that by solid-solving a specific amount of at least one element selected from the above, the hydrogen desorption characteristics of Ti ₂ Ni, the durability, etc. are improved, and a hydrogen storage alloy capable of achieving the above-mentioned object can be obtained. The present invention has been completed.

That is, the present invention provides the following hydrogen storage alloy and hydrogen storage medium. 1. General formula: TiaNibXc (In the formula, X is at least one element selected from N and C, and 3.9 ≦ a ≦ 4.1; 1.9 ≦ b ≦ 2.1;
0 <a hydrogen-absorbing alloy comprising a phase of E9 ₃ type structure of cubic crystal represented by a c ≦ 1). 2. General formula: TiaNibXc (In the formula, X is at least one element selected from N and C, and 3.9 ≦ a ≦ 4.1; 1.9 ≦ b ≦ 2.1;
0 <hydrogen storage alloy containing 50% by volume or more phases of the E9 ₃ type structure of cubic crystal represented by a c ≦ 1). 3 . General formula: In TiaNibXc, 0.3 ≦ c
The hydrogen storage alloy according to the above item 1 or 2 , wherein ≦ 1. 4 . Hydrogen storage tank for hydrogen storage medium comprising a hydrogen storage alloy according to any one of items 1-3.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy of the present invention has a general formula: TiaNibXc (where X is at least one element selected from N and C, and 3.9 ≦ a ≦ 4.1; 1). 9 ≦ b ≦ 2.1;
0 <those including a phase of E9 ₃ type structure of cubic crystal represented by a c ≦ 1).

Such a hydrogen storage alloy has a cubic crystal structure of E9 ₃
It is a non-metal element interstitial alloy in which at least one element selected from oxygen, nitrogen and carbon is solid-solved in Ti ₂ Ni having a type structure, and hydrogen storage characteristics and hydrogen release characteristics are compared with Ti ₂ Ni. Is a great improvement.

In order to exhibit excellent hydrogen storage characteristics and desorption characteristics, the hydrogen storage alloy of the present invention has the above general formula:
(Wherein, X, a, b and c are the same as above) Ti _a Ni _b X _c that phase E9 ₃ type structure of cubic crystal represented by is contained 50% or more by volume in the hydrogen storage alloy preferably , 70 vol% or more, more preferably 90 vol% or more, and most preferably a single phase of the above-mentioned phases. There is no particular limitation on the phases other than the above-mentioned phases, but for example, TiNi, Ti may be used as the sub-phase.
X and the like may be included.

In the above general formula, X is preferably at least one element selected from N and C. A hydrogen storage alloy containing a phase in which X is at least one element selected from N and C in the above general formula is
Especially, the maximum hydrogen storage capacity near room temperature is large, and
It has excellent characteristics in that it has a large hydrogen releasing capacity under a pressure range of about MPa to 0.03 MPa.

The hydrogen storage alloy of the present invention is produced, for example, by mixing the raw materials so that the ratio of each element is the composition ratio of the target alloy, and heating in a non-oxidizing atmosphere to alloy. be able to.

As the raw material, for example, Ti powder and Ni powder can be used as the Ti source and the Ni source, respectively. As the O source, the N source, and the C source, respectively,
Each powder of TiO ₂ , TiN, and TiC can be used, but not limited to these, various Ti compounds containing oxygen, nitrogen, carbon, etc., Ni compounds, etc. can be used as raw materials.

The hydrogen storage alloy of the present invention can be obtained by mixing these raw materials in a desired composition ratio and heating them in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a vacuum atmosphere, an inert gas atmosphere such as He gas, and a reducing atmosphere such as hydrogen gas. The heating temperature is preferably a temperature lower than the melting point of 800 ° C. ~ desired compound at a temperature within this range, as much as possible by heating at a high temperature, the above-mentioned cubic represented by the general formula E9 ₃ type structure It is possible to obtain an alloy close to a single phase containing a large number of phases in a short time. The heating time may be the time for forming the desired alloy, and the specific heating time may be, for example, about 5 hours to 10 days, although it depends on the heating temperature.

In addition to the above-mentioned manufacturing method, the object can be obtained by heating Ti metal powder and Ni metal powder as raw materials in an atmosphere containing oxygen, nitrogen, carbon, etc., for example, in an ammonia atmosphere. It is possible to obtain a hydrogen storage alloy that does.

Unlike Ti ₂ Ni, the hydrogen storage alloy of the present invention does not require activation treatment, and starts hydrogen storage under a hydrogen atmosphere at room temperature and about 3 MPa without special pretreatment. . This means that if the tank is filled with the alloy and hydrogen is filled, it exhibits hydrogen storage performance.
This is an important property in hydrogen storage applications. Also, Ti
₂ Ni is at a temperature of around room temperature gas of hydrogen gas - but never releases hydrogen by solid phase reaction, the hydrogen storage alloy of the present invention, at temperatures near room temperature, that the hydrogen pressure of several atmospheres, Under the hydrogen storage / release conditions required for hydrogen storage materials, it exhibits a plateau region associated with the formation of hydrides, and reversibly stores and releases hydrogen.

The hydrogen storage alloys of the present invention have average mass numbers of 46.4 (Ti ₄ Ni ₂ O) and 46.1 (T, respectively).
i ₄ Ni ₂ N) and 45.8 (Ti ₄ Ni ₂ C), the maximum hydrogen storage amount at 2 MPa is 0.92 wt% (Ti ₄ Ni ₂ O, 0 ° C.), 1 .43
% By weight (Ti ₄ Ni ₂ N, 0 ° C.), and 1.48% by weight
(Ti ₄ Ni ₂ C, 40 ° C.). The maximum hydrogen storage amount can be further increased by increasing the applied hydrogen pressure or lowering the temperature.

According to Westlake's model and a study of hydrogen occupancy positions based on other empirical models, hydrogen is found in these E9
_It can completely occupy the 8a and 96g sites in the type ₃ structure compound. Therefore, the maximum hydrogen storage capacity of these compounds is
Theoretically H / M = 0.93, or 1.96 wt% (Ti
₄ Ni ₂ O), 1.98 wt% (Ti ₄ Ni ₂ N), and 1.99 wt% (Ti ₄ Ni ₂ C).

The hydrogen storage alloy of the present invention is made of Ti ₂ N
The hydrogen dissociation pressure is 2-3 orders of magnitude higher than i, and the slope of the plateau is flat.

Therefore, the effective hydrogen storage amount in the pressure range of 0.01 to 1 MPa is less than 0.2% by weight of Ti ₂ Ni at 20 ° C., whereas the effective hydrogen storage amount is less than 0.2% by weight of Ti ₄ Ni ₂ N and Ti. _Four
For Ni ₂ C, 1.11 wt% (0 ° C.) and 1.
It is as very large as 06% by weight (60 ° C), and a remarkable improvement is recognized. In the case of metal element substitution, since such a dramatic change in dissociation pressure and flatness of the plateau cannot be achieved at the same time, the excellent effect of the hydrogen storage alloy of the present invention is due to the addition of an interstitial non-metal element. it is conceivable that.

The hydrogen storage alloy of the present invention can be used for various known uses as a hydrogen storage alloy by utilizing such excellent properties.

For example, the hydrogen storage alloy of the present invention can reversibly generate hydrogen by a gas-solid state reaction under a temperature near room temperature, a hydrogen pressure of 10 atm or less, which is required for hydrogen storage materials. Can store and release. Therefore, the hydrogen storage alloy of the present invention, water can be used as a heat refrigerant, is used to safely store gaseous hydrogen at a temperature near room temperature, and to take out stored hydrogen as needed, hydrogen storage tank hydrogen storage It is highly useful as a medium.

When the hydrogen storage alloy of the present invention is used for the above-mentioned use as a hydrogen storage medium, the value of c in the above general formula is preferably 0.3 ≦ c ≦ 1. It is more preferable that 0.5 ≦ c ≦ 1 and more preferable that 0.7 ≦ c ≦ 1.

[0023]

EFFECTS OF THE INVENTION The hydrogen storage alloy of the present invention has excellent hydrogen storage characteristics and hydrogen desorption characteristics, and has good durability. In particular, the hydrogen storage alloy of the present invention can safely store gaseous hydrogen at temperatures near room temperature and take out stored hydrogen, and is very useful as a hydrogen storage medium for hydrogen storage tanks.

[0024]

EXAMPLES The present invention will be described in more detail with reference to examples. Example 1 TiO ₂ , T as oxygen, nitrogen and carbon sources, respectively
iN and TiC powders are used, and further, Ti source and Ni are used.
Using Ti and Ni powders as sources, Ti _57.1 N
Each raw material powder was mixed so as to have a composition of i _28.6 X _14.3 (X = O, N or C), and powder-molded in vacuum to produce pellets (diameter 13 mm, thickness 1 mm).

Next, the obtained pellets were melted by Ar arc and then held in a high vacuum at 900 ° C. for 72 hours to obtain a hydrogen storage alloy.

Powder X for each of the obtained hydrogen storage alloys
The line diffraction result is shown in FIG. As apparent from FIG. 4, each of the hydrogen storage alloy is one that comprises a phase of E9 ₃ type structure similar cubic and Ti ₂ Ni.

Further, when the concentration of the non-metal light element in the Ti ₂ Ni type alloy phase of each sample was examined by using an electron microscope equipped with an elemental analysis device, it was found to be 14 atom%, and the concentration of oxygen, nitrogen and carbon was It was found that whichever the addition was made, it was possible to form a solid solution up to 14 atomic%, and the composition was represented by Ti ₄ Ni ₂ X (X = O, N or C). Oxygen, nitrogen, and occupies the position of the carbon were both centers of 16c becomes irregular Ti octahedra in E9 ₃ type structure. Ti ₄ Ni ₂ X (X = O, N
Or the presence ratio of the phases of cubic E9 ₃ type structure represented by C) is 98% in the oxygen-containing alloy, 90 in the nitrogen-containing alloy
% And 50% for carbon-containing alloys. Both sub-phases were TiNi and TiX (X = O, N or C) phases.

The hydrogenation characteristics of each hydrogen storage alloy were investigated equilibrium using a Sibelts type apparatus.

Among the sub-phases, TiX was not observed to react with hydrogen. For TiNi, PC at the same temperature
T characteristics were measured, and for each sample, PCT of TiNi phase
By correcting the contribution to the characteristics, Ti ₄ Ni ₂ X
The PCT curve of the (X = O, N or C) phase was determined.

The PCT curve of the TiNi phase is shown in FIG.
The PCT curve of the i ₄ Ni ₂ X (X = O, N or C) phase is shown in FIG.
~ Shown in FIG.

Further, the hydrogen storage alloy of the present invention and Ti₂Ni
To compare the characteristics of Ti_FourNi ₂N, Ti_FourNi₂C
And Ti₂The PCT curve for Ni is shown in FIG. T
i₂PCT characteristics of Ni should be determined based on gas-solid reaction.
Therefore, Ti in FIG.₂Ni's PCT song
The wire is nickel hydroxide on the positive electrode in 6N-KOH aqueous solution.
Object, negative electrode Ti₂Electrochemical method using Ni alloy
Therefore, it is obtained.

[0032] As seen from FIG. 9, the hydrogen storage alloy of the present invention is different from the Ti ₂ Ni, hydrogen dissociation pressure increases 2-3 digits, for plateau slope, as compared to Ti ₂ Ni, flat In particular, it was confirmed that it has excellent hydrogen storage / release characteristics at a temperature around room temperature.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a crystal structure of a hydrogen storage alloy of the present invention.

FIG. 2 is a graph showing PCT characteristics of Ti ₂ Ni.

FIG. 3 is a graph schematically showing the PCT characteristics of a substitutional alloy.

FIG. 4 is a drawing showing powder X-ray diffraction results for the hydrogen storage alloy of the present invention and Ti ₂ Ni.

FIG. 5 is a graph showing PCT characteristics of TiNi.

FIG. 6 is a graph showing the PCT characteristics of Ti ₄ Ni ₂ O.

FIG. 7 is a graph showing the PCT characteristics of Ti ₄ Ni ₂ N.

FIG. 8 is a graph showing PCT characteristics of Ti ₄ Ni ₂ C.

FIG. 9 is a graph showing PCT characteristics of Ti ₄ Ni ₂ N, Ti ₄ Ni ₂ C and Ti ₂ Ni.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Satoshi Kiyobayashi 1-831 Midorigaoka, Ikeda-shi, Osaka Inside Institute of Industrial Science and Technology, Institute of Industrial Technology (72) Inventor Nobuhiko Takeichi 1-8, Midorigaoka, Ikeda-shi, Osaka No. 31 Inside Institute of Industrial Science and Technology, Institute of Industrial Technology (56) References JP-A-9-274912 (JP, A) JP-A-60-221961 (JP, A) International Publication 95/017531 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 14/00 C01B 3/00 C01B 31/30 C01G 53/00 F17C 11/00

Claims (4)

(57) [Claims] 1. A general formula: TiaNibXc (where X is at least one element selected from N and C, and 3.9 ≦ a ≦ 4.1; 1.9 ≦ b ≦ 2.1;
0 <a hydrogen-absorbing alloy comprising a phase of E9 ₃ type structure of cubic crystal represented by a c ≦ 1). 2. A general formula: TiaNibXc (wherein X is at least one element selected from N and C, and 3.9 ≦ a ≦ 4.1; 1.9 ≦ b ≦ 2.1;
0 <c ≦ 1 a is) in cubic E9 ₃ -type structure phase 50 vol% or more including hydrogen-absorbing alloys represented. 3. In the general formula: TiaNibXc, 0.
The hydrogen storage alloy according to claim 1 or 2 , wherein 3 ≦ c ≦ 1. 4. A hydrogen storage medium for a hydrogen storage tank, which comprises the hydrogen storage alloy according to any one of claims 1 to 3 .