Chemistry: electrical current producing apparatus – product – and – Sealed cell having gas prevention or elimation means – Prevention or elimination means is one of the cell...
Reexamination Certificate
2001-09-27
2004-12-28
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Sealed cell having gas prevention or elimation means
Prevention or elimination means is one of the cell...
C429S101000, C429S010000, C429S006000, C429S006000, C148S669000, C148S421000, C420S900000, C420S424000, C420S428000, C420S421000
Reexamination Certificate
active
06835490
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for absorption and release of hydrogen where a hydrogen storage metal alloy is repeatedly subjected to pressurization and depressurization of hydrogen. In more detail, the present invention relates to a hydrogen storage metal alloy having a two-stage plateau- or inclined plateau-property. Particularly, the present invention relates to a method for absorption and release of hydrogen where the amount of released hydrogen increases within practical pressure ranges and temperature ranges, to a hydrogen storage metal alloy suitable for such a method for absorption and release of hydrogen and to a hydrogen fuel battery using the above method for absorption and release of hydrogen.
RELATED ART OF THE INVENTION
At present, there have been worries not only about acid rain due to an increasing NOx (nitrogen oxides) but also about global warming due to an increasing C
0
2
in association with an increase in consumption of fossil fuel such as petroleum and such environmental destruction has become a serious problem. Therefore, our attention has been greatly concentrated on development and practical application of various kinds of clean energy which is friendly to the earth. Part of means for developing such a new energy is a practical application of hydrogen energy. Hydrogen is a constituent element of water inexhaustibly present on the earth and can be not only produced using various kinds of primary energy but also utilized as fluid energy in place of conventionally used petroleum without the risk of destroying the environment because its product of combustion is only water. In addition, unlike electricity, it has excellent characteristics such as its relatively easy storage.
In recent years, therefore, investigation has been actively conducted involving hydrogen storage metal alloys as media for storing and transporting hydrogen and their practical application has been expected. Such hydrogen storage metal alloys are metals/alloys which can absorb and release the hydrogen under an appropriate condition and, by the use of such alloys, it is possible to store the hydrogen not only at lower pressure but also at higher density as compared to the case of the conventional hydrogen cylinders. In addition, the hydrogen volume density thereof is nearly equal to or rather greater than that of liquid or solid hydrogen.
These hydrogen storage metal alloys which have been chiefly investigated are, for example, those alloys which each have a body-centered cubic (hereinafter, referred to as “BCC”) structure, including V, Nb, Ta or Cr—Ti—Mn alloys, Cr—Ti—V alloys, etc. as proposed in Japanese Unexamined Patent Publication (Kokai) No. 10-110225 (JP, A, 10-110225). It has been known that those alloys adsorb and store hydrogen in greater quantities as compared with AB
5
alloys such as LaNi
5
and AB
2
alloys such as TiMn
2
which have been practically used until now. This is because the number of hydrogen absorbing sites in the crystal lattice is great in the BCC structure and the hydrogen absorbing capacity is as large as H/M=ca. 2 wherein H is occluded hydrogen and M is a constituent element for the alloy (about 4.0 wt % in alloys of V, etc. having an atomic weight of around 50), being extremely large.
It has been known that such a BCC alloy having a relatively large hydrogen absorbing capacity conducts a two-step reaction during the course of its absorbing hydrogen to form a hydride, as shown in Reilly and R. H. Wiswall, Inorg. Chem., 9 (1970), 1678). For example, V reacts with hydrogen at ambient temperature and forms two kinds of hydrides depending upon the pressure of hydrogen. At first, at the initial reaction stage wherein hydrogen pressure is low, a very stable hydride is formed as V→VH
0.8
(&agr; phase→&bgr; phase) (hereinafter, referred to as “low-pressure plateau part”) and, at around room temperature, a reverse reaction thereof rarely happens. When further more hydrogen pressure is applied, a hydride is formed as VH
0.8
→VH
2.01
(&bgr; phase→&ggr; phase; referred to as “high-pressure plateau part”). The equilibrium hydrogen pressure of this reaction is appropriate (approximately a few atmospheric pressure at around room temperature). Therefore, such V-containing BCC alloys have been briskly studied as high-capacity hydrogen storage metal alloys.
FIG. 1
is a conceptional chart of a PCT curve of a single substance V having a two-stage plateau comprised of the aforementioned low-plateau and high-plateau parts. The flat region at the hydrogen pressure of 10
−1
Pa in
FIG. 1
is a low-pressure plateau part and the flat region at the hydrogen pressure of 10
6
Pa is a high-pressure plateau part. The inclined region between the low-pressure plateau part and the high-pressure plateau part is a region complying with Sieverts's law. Besides V, an example of the metal having such a two-stage plateau is Nb (low-pressure phase: NbH, high-pressure phase: NbH
2
). In addition, Ti shows a two-stage plateau by a transformation of &agr;→&bgr;→&ggr; although it operates at elevated temperature. An intermetallic compound having a two-stage plateau includes FeTi which works at near 40° C. Further, alloys such as (Zr, Ti)V
2
show an inclined plateau and those alloys are also used as hydrogen storage metal alloys.
Examples of the prior art techniques presumably based upon the idea of developing a high-capacity hydrogen storage metal alloy relying on the above-mentioned two-stage plateau and inclined plateau characteristics are as follows:
(a) spinodal decomposition tissues are expressed in a body-centered cubic structure Ti alloy (the above JP, A, 10-110225);
(b) a Ti—Cr—V alloy is admixed with Cu and/or rareearth elements (the above JP, B2, 4-77061);
(c) a Ti alloy melt is rapidly cooled to form a BCC mono phase at room temperature (Japanese Unexamined Patent Publication (Kokai) No. 10-158755 (JP, A, 10-158755)); and
(d) a BCC alloy comprised as main elements of Ti—Cr is adjusted for its lattice constant (Japanese Unexamined Patent Publication (Kokai) No. 07-252560 (JP, A, 07-252560)).
Among the above-mentioned methods for absorbing and releasing hydrogen, those where temperature for absorption and desorption of hydrogen is mentioned are JP, A, 10-110225 and JP, A, 07-252560, both which disclose the methods where hydrogen is absorbed and released at a constant temperature, provided that, in the latter JP, A, 07-252560, the activating pretreatment is carried out by means of a two-stage treatment comprising a low temperature in the former stage and a high temperature in the latter stage while the temperature for hydrogen absorption and desorption is constant (20° C.). In Japanese Patent Publication No. 59/38293 (JP, B2, 59/38293), hydrogen is absorbed with a hexagonal Ti—Cr—V type alloy which is not a BCC alloy and a method of heating at 100° C. or higher (lines 32 to 39, column 4) is for absorbing and releasing hydrogen at a constant temperature as well.
However, in the hydrogen storage metal alloy having the above-mentioned two-stage plateau characteristic such as V-containing BCC alloy which has been often investigated as the high-capacity hydrogen storage metal alloy, the hydrogen-absorbing reaction at the low-pressure plateau region proceeds only to the side of the reaction with hydrogen at room temperature. Therefore, it has not been carried out in the prior art that the hydrogen occluded is taken out in such a low-pressure plateau region and used as an effective hydrogen.
Thus, in the above-mentioned JP, A, 10-110225 and JP, B2, 4-77061, such a low-pressure plateau region is not referred to. In the latter patent, since there is a teaching that the production of TiH
2
(high-pressure plateau region compound) is to be avoided, only the hydrogen-absorbing reaction between the low-pressure plateau region and the high-pressure plateau region is utilized.
It is said that, in general, the amount of hydrogen taken out from a body-centered cubic structure type hydrogen storage metal alloy such as pure V an
Kuriiwa Takahiro
Okada Masuo
Bell Bruce F.
Hayes & Soloway P.C.
Tohoku Techno Arch Co., Ltd.
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