U.S. patent application number 11/887937 was filed with the patent office on 2009-02-26 for hydrogen-generating material and hydrogen generator.
Invention is credited to Takeshi Miki, Ryo Nagai, Toshihiro Nakai, Shoji Saibara.
Application Number | 20090049749 11/887937 |
Document ID | / |
Family ID | 37727426 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090049749 |
Kind Code |
A1 |
Miki; Takeshi ; et
al. |
February 26, 2009 |
Hydrogen-Generating Material and Hydrogen Generator
Abstract
A hydrogen generating material of the present invention includes
a metal material that reacts with water to generate hydrogen, and a
heat generating material that reacts with water to generate heat
and is a material other than the metal material. The heat
generating material is unevenly distributed with respect to the
metal material. The hydrogen generating material has a plurality of
regions that differ in content of the heat generating material. The
content of the heat generating material is preferably 30 wt % to 80
wt % in a region with the highest content of the heat generating
material. A hydrogen generator of the present invention includes
the hydrogen generating material and a vessel containing the
hydrogen generating material. The vessel can accommodate another
inner vessel.
Inventors: |
Miki; Takeshi; (Osaka,
JP) ; Nakai; Toshihiro; (Osaka, JP) ; Nagai;
Ryo; (Osaka, JP) ; Saibara; Shoji; (Osaka,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
37727426 |
Appl. No.: |
11/887937 |
Filed: |
August 9, 2006 |
PCT Filed: |
August 9, 2006 |
PCT NO: |
PCT/JP2006/315767 |
371 Date: |
October 5, 2007 |
Current U.S.
Class: |
48/62R |
Current CPC
Class: |
H01M 8/04216 20130101;
Y02E 60/50 20130101; Y02E 60/36 20130101; B01J 2208/025 20130101;
B01J 2219/1923 20130101; Y02B 90/10 20130101; H01M 8/065 20130101;
B01J 16/005 20130101; B01J 2208/00309 20130101; C01B 3/08 20130101;
B01J 2219/00117 20130101; H01M 8/04208 20130101; H01M 2250/30
20130101 |
Class at
Publication: |
48/62.R |
International
Class: |
C10J 3/20 20060101
C10J003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2005 |
JP |
2005-233648 |
Nov 1, 2005 |
JP |
2005-318881 |
May 19, 2006 |
JP |
2006-140690 |
Claims
1. A hydrogen generating material comprising: a metal material that
reacts with water to generate hydrogen; and a heat generating
material that reacts with water to generate heat and is a material
other than the metal material, wherein the heat generating material
is unevenly distributed with respect to the metal material.
2. The hydrogen generating material according to claim 1, having a
plurality of regions that differ in content of the heat generating
material.
3. The hydrogen generating material according to claim 2, wherein
the content of the heat generating material is 30 wt % to 80 wt %
in a region with the highest content of the heat generating
material.
4. The hydrogen generating material according to claim 3, wherein a
proportion of the region with the highest content of the heat
generating material is 3 wt % to 40 wt % of the whole hydrogen
generating material.
5. The hydrogen generating material according to claim 3, having a
region where the content of the heat generating material is 15 wt %
or less.
6. The hydrogen generating material according to claim 1, wherein
the hydrogen generating material is in the form of pellets or
granules.
7. The hydrogen generating material according to claim 1, wherein
the content of the heat generating material present in any one of
locations selected from an end portion, a core portion, and a
surface portion of the hydrogen generating material is higher than
that of the heat generating material present in the other
locations.
8. The hydrogen generating material according to claim 1, wherein a
content of the metal material in the whole hydrogen generating
material is 85 wt % to 99 wt %.
9. The hydrogen generating material according to claim 1, wherein
the metal material is at least one metal selected from the group
consisting of aluminum, silicon, zinc, and magnesium or an alloy
composed mainly of the at least one metal.
10. The hydrogen generating material according to claim 1, wherein
the metal material comprises particles with a particle size of 0.1
.mu.m to 60 .mu.m in a proportion of 80 vol % or more.
11. The hydrogen generating material according to claim 1, wherein
the metal material comprises particles with an average particle
size of 0.1 .mu.m to 30 .mu.m.
12. The hydrogen generating material according to claim 1, wherein
the metal material is in the form of a flake.
13. The hydrogen generating material according to claim 12, wherein
the metal material has a thickness of 0.1 .mu.m to 5 .mu.m.
14. The hydrogen generating material according to claim 1, wherein
the heat generating material is at least one selected from the
group consisting of a calcium oxide, a magnesium oxide, a calcium
chloride, a magnesium chloride, and a calcium sulfate.
15. The hydrogen generating material according to claim 1, further
comprising at least one selected from the group consisting of a
hydrophilic oxide, carbon, and a water absorbing polymer.
16. The hydrogen generating material according to claim 15, wherein
the hydrophilic oxide comprises at least one oxide selected from
the group consisting of alumina, boehmite, silica, magnesia,
zirconia, zeolite, and a zinc oxide.
17. A hydrogen generator comprising: a hydrogen generating
material; and a vessel containing the hydrogen generating material,
wherein the hydrogen generating material comprises a metal material
that reacts with water to generate hydrogen, and a heat generating
material that reacts with water to generate heat and is a material
other than the metal material, and the heat generating material is
unevenly distributed with respect to the metal material.
18. The hydrogen generator according to claim 17, wherein the
hydrogen generating material has a plurality of regions that differ
in content of the heat generating material.
19. The hydrogen generator according to claim 18, wherein the
content of the heat generating material is 30 wt % to 80 wt % in a
region with the highest content of the heat generating
material.
20. The hydrogen generator according to claim 19, wherein a
proportion of the region with the highest content of the heat
generating material is 3 wt % to 40 wt % of the whole hydrogen
generating material.
21. The hydrogen generator according to claim 19, wherein the
hydrogen generating material has a region where the content of the
heat generating material is 15 wt % or less.
22. The hydrogen generator according to claim 17, wherein the
hydrogen generating material is in the form of pellets or
granules.
23. The hydrogen generator according to claim 17, wherein the
content of the heat generating material present in any one of
locations selected from an end portion, a core portion, and a
surface portion of the hydrogen generating material is higher than
that of the heat generating material present in the other
locations.
24. The hydrogen generator according to claim 17, wherein a content
of the metal material in the whole hydrogen generating material is
85 wt % to 99 wt %.
25. The hydrogen generator according to claim 17, wherein the metal
material is at least one metal selected from the group consisting
of aluminum, silicon, zinc, and magnesium or an alloy composed
mainly of the at least one metal.
26. The hydrogen generator according to claim 17, wherein the metal
material comprises particles with a particle size of 0.1 .mu.m to
60 .mu.m in a proportion of 80 vol % or more.
27. The hydrogen generator according to claim 17, wherein the metal
material comprises particles with an average particle size of 0.1
.mu.m to 30 .mu.m.
28. The hydrogen generator according to claim 17, wherein the metal
material is in the form of a flake.
29. The hydrogen generator according to claim 28, wherein the metal
material has a thickness of 0.1 .mu.m to 5 .mu.m.
30. The hydrogen generator according to claim 17, wherein the heat
generating material is at least one selected from the group
consisting of a calcium oxide, a magnesium oxide, a calcium
chloride, a magnesium chloride, and a calcium sulfate.
31. The hydrogen generator according to claim 17, wherein the
hydrogen generating material further comprises at least one
selected from the group consisting of a hydrophilic oxide, carbon,
and a water absorbing polymer.
32. The hydrogen generator according to claim 31, wherein the
hydrophilic oxide comprises at least one oxide selected from the
group consisting of alumina, boehmite, silica, magnesia, zirconia,
zeolite, and a zinc oxide.
33. The hydrogen generator according to claim 17, wherein the
vessel comprises an inlet A for introducing water into the vessel
and an outlet B for discharging hydrogen from the vessel.
34. The hydrogen generator according to claim 17, wherein the heat
generating material is arranged so that water is supplied first to
a region with the highest content of the heat generating material
when water is introduced into the vessel.
35. The hydrogen generator according to claim 17, wherein the
vessel accommodates another inner vessel, and the inner vessel
contains the heat generating material and comprises an inlet C for
introducing water into the inner vessel.
36. The hydrogen generator according to claim 35, wherein the inner
vessel further contains the metal material.
37. The hydrogen generator according to claim 36, wherein a content
of the heat generating material with respect to a total amount of
the heat generating material and the metal material contained in
the inner vessel is higher than that of the heat generating
material in the whole hydrogen generating material present outside
the inner vessel.
38. The hydrogen generator according to claim 37, wherein the
content of the heat generating material in the whole hydrogen
generating material present outside the inner vessel is 1 wt % to
15 wt %.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hydrogen generating
material that reacts with water to produce hydrogen, and a hydrogen
generator using the hydrogen generating material.
BACKGROUND ART
[0002] With the recent widespread use of cordless equipment such as
a personal computer or portable telephone, batteries used as a
power source of cordless equipment are increasingly required to
have a smaller size and higher capacity. At present, a lithium ion
secondary battery that can achieve a small size, light weight, and
high energy density is being put to practical use and growing in
demand as a portable power source. However, the lithium ion
secondary battery has a problem of not being able to ensure a
sufficient continuous available time for some cordless
equipment.
[0003] To solve this problem, e.g., fuel cells such as a polymer
electrolyte fuel cell (PEFC) are being developed. The fuel cells
can be used continuously as long as a fuel and oxygen are supplied.
The PEFC uses a polymer electrolyte membrane as an electrolyte,
oxygen in the air as a positive active material, and a fuel as a
negative active material, and has attracted considerable attention
because it is a battery that can have a higher energy density than
the lithium ion secondary battery.
[0004] Although there are several candidates for fuels used for the
PEFC, the individual fuels have technical problems. A direct
methanol fuel cell (DMFC), in which methanol is used as a fuel and
allowed to react directly at the electrode, is miniaturized easily
and expected to be a future portable power source. In the DMFC,
however, the voltage is reduced due to crossover in which methanol
at the negative electrode passes through the solid electrolyte and
reaches the positive electrode, and thus a high energy density
cannot be achieved. On the other hand, when hydrogen is used as a
fuel, a fuel cell with a high-pressure tank holding hydrogen or a
hydrogen-storing alloy tank is employed to some extent. However,
the fuel cell using such a tank is not suitable for a portable
power source, since both the volume and the weight of the fuel cell
are increased, and the energy density is reduced. Moreover, when a
hydrocarbon fuel is used, there is a cell with a reformer for
reforming the fuel to extract hydrogen. However, this type of cell
requires supply of heat to the reformer, thermal insulation of the
reformer, and the like. Therefore, the cell is not suitable for a
portable power source either.
[0005] Under these circumstances, a fuel cell has been proposed
that produces hydrogen by the chemical reaction of water and a
hydrogen generating substance such as aluminum, magnesium, silicon,
or zinc at a low temperature of 100.degree. C. or less, and uses
the hydrogen thus produced as a fuel (see, e.g., Patent Documents 1
to 3). Moreover, an apparatus is known in which a small container
including iron powder is placed in a large container including iron
powder, and heat is generated by introducing air into the large
container, while hydrogen is produced by adding water to the small
container (see, e.g., Patent Document 4).
[0006] Patent Document 1: U.S. Pat. No. 6,506,360
[0007] Patent Document 2: JP 2566248 B2
[0008] Patent Document 3: JP 2004-231466 A
[0009] Patent Document 4: JP 2005-317443 A
[0010] In the methods of Patent Documents 1 to 3, however, the
equivalent amount of a basic substance (e.g., a calcium oxide or
sodium hydroxide) corresponding to the amount of the hydrogen
generating substance needs to be added. The energy density
decreases as the proportion of the substance other than the
hydrogen generating substance increases, leading to a reduction in
the amount of hydrogen generated. In particular, the method of
Patent Document 3 uses heat generated by the reaction of a calcium
oxide and water for the reaction of the hydrogen generating
substance. It has been clear that although the hydrogen production
reaction proceeds successfully if the calcium oxide content is 15
wt % or more, no hydrogen is produced if the calcium oxide content
is less than 15 wt %.
[0011] The method of Patent Document 4 can produce hydrogen without
the addition of a basic substance, as used in Patent Document 3.
However, the temperature of the system is increased to 200.degree.
C. to 400.degree. C. because the heat of reaction is large.
Moreover, it is difficult to reduce the weight of the apparatus.
Therefore, this apparatus is not suitable for a portable power
source.
[0012] The present inventors studied the generation of hydrogen
using a hydrogen generating material that was obtained by mixing a
heat generating material such as a calcium oxide and a hydrogen
generating substance uniformly. The results showed that the time it
takes to start generating hydrogen and the time it takes for the
hydrogen generation rate to reach a maximum differ significantly
depending on the weight ratio of the hydrogen generating substance
to the heat generating material. Specifically, it became evident
that if the content of the heat generating material is 30 wt % or
more with respect to the total volume of the hydrogen generating
substance and the heat generating material, both the time before
starting the generation of hydrogen and the time required for
maximizing the hydrogen generation rate can be reduced
considerably, compared to the content of the heat generating
material of less than 30 wt %. This may be because the amount of
heat generated by the reaction of the heat generating material and
water is increased, thereby accelerating the reaction of the
hydrogen generating substance and water.
[0013] However, when the content of the heat generating material in
the hydrogen generating material is increased, the proportion of
the hydrogen generating substance (hydrogen source) is reduced,
resulting in a low energy density. Accordingly, the amount of
hydrogen generated is reduced. On the other hand, when the content
of the heat generating material is reduced, it takes time before
hydrogen starts to be generated. In addition, the reaction product
is deposited on the surface of the hydrogen generating substance as
the reaction proceeds, and may interfere with the hydrogen
production reaction. Therefore, even if the proportion of the
hydrogen generating substance is high, the reaction efficiency is
not necessarily improved. Thus, the studies revealed that there are
still some problems to be solved.
DISCLOSURE OF INVENTION
[0014] A hydrogen generating material of the present invention
includes a metal material that reacts with water to generate
hydrogen, and a heat generating material that reacts with water to
generate heat and is a material other than the metal material. The
heat generating material is unevenly distributed with respect to
the metal material.
[0015] A hydrogen generator of the present invention includes a
hydrogen generating material and a vessel containing the hydrogen
generating material. The hydrogen generating material includes a
metal material that reacts with water to generate hydrogen, and a
heat generating material that reacts with water to generate heat
and is a material other than the metal material. The heat
generating material is unevenly distributed with respect to the
metal material.
[0016] In the hydrogen generating material of the present
invention, the heat generating material is unevenly distributed
with respect to the metal material, namely, the content of the heat
generating material is higher in some regions than in others of the
hydrogen generating material. Thus, heat generated by the reaction
of the heat generating material in those regions and water can be
utilized effectively for the reaction of the metal material and
water, so that the hydrogen production reaction can start easily in
a short time. Therefore, the amount of the heat generating material
can be reduced in the whole hydrogen generating material. In other
words, the hydrogen generating material of the present invention
can increase the content of the metal material that serves as a
hydrogen source, and thus allows hydrogen to be produced
efficiently.
[0017] The hydrogen generator of the present invention can produce
hydrogen efficiently by using the above hydrogen generating
material.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic cross-sectional view showing an
example of a hydrogen generator of the present invention.
[0019] FIG. 2 is a schematic cross-sectional view showing an
example of a fuel cell that is to be combined with a hydrogen
generator of the present invention.
[0020] FIG. 3 is a schematic cross-sectional view showing another
example of a hydrogen generator of the present invention.
[0021] FIG. 4 is a schematic cross-sectional view showing yet
another example of a hydrogen generator of the present
invention.
[0022] FIG. 5 is a graph showing (a) a change in surface
temperature of a vessel over time and (b) a change in hydrogen
generation rate over time in a hydrogen generator of Working
Example 1.
[0023] FIG. 6 is a graph showing (a) a change in surface
temperature of a vessel over time and (b) a change in hydrogen
generation rate over time in a hydrogen generator of Comparative
Example 1.
[0024] FIG. 7 is a graph showing (a) a change in surface
temperature of an outer vessel over time and (b) a change in
hydrogen generation rate over time in a hydrogen generator of
Working Example 6.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] Hereinafter, a hydrogen generating material and a hydrogen
generator using the hydrogen generating material of the present
invention will be described.
Embodiment 1
[0026] A hydrogen generating material of an example of the present
invention reacts with water to produce hydrogen. This hydrogen
generating material includes a metal material that reacts with
water to generate hydrogen, and a heat generating material that
reacts with water to generate heat and is a material other than the
metal material. In the hydrogen generating material of the present
invention, the heat generating material is unevenly distributed
with respect to the metal material.
[0027] The hydrogen generating material with the above
configuration allows hydrogen to be produced efficiently, even if
the amount of the heat generating material included in the hydrogen
generating material is reduced.
[0028] The reaction of the hydrogen generating material and water
is not particularly limited by a reaction mechanism or the like as
long as the reaction can produce hydrogen. In an example of this
reaction, first, an exothermic reaction of the heat generating
material and water occurs in a region with a higher content of the
heat generating material. Then, heat generated by the exothermic
reaction causes the metal material present in the region where the
exothermic reaction has occurred or its vicinity to start reacting
with water. Since this reaction of the metal material and water
also is an exothermic reaction, once the reaction has started,
hydrogen can continue to be produced, even if the amount of heat
supplied from the reaction of the heat generating material and
water is reduced. Thus, the hydrogen production reaction can
proceed gradually from the region with a higher content of the heat
generating material to the other regions, and finally can occur
throughout the hydrogen generating material.
[0029] Therefore, except for the region with a higher content of
the heat generating material, the hydrogen generating material may
include either no or a small amount of heat generating material.
Consequently, the amount of the heat generating material can be
reduced in the whole hydrogen generating material. Since the
hydrogen generating material has the region with a higher content
of the heat generating material, a large amount of heat is
generated locally as soon as water is supplied to the region, and
the heat induces the reaction of the metal material and water.
Accordingly, both the time before starting the generation of
hydrogen and the time required for maximizing the hydrogen
generation rate also can be reduced.
[0030] In the hydrogen generating material of the present
invention, the metal material and the heat generating material can
be combined in various ways as long as the heat generating material
is unevenly distributed. For example, (1) the hydrogen generating
material may be a mixture of the metal material and the heat
generating material, and the content of the heat generating
material is higher in some regions than in others; (2) the hydrogen
generating material may include a mixture of the metal material and
the heat generating material, and there are some regions where only
the metal material or the heat generating material is present; or
(3) the hydrogen generating material may include a region
consisting of the metal material and a region consisting of the
heat generating material.
[0031] The shape of the hydrogen generating material is not
particularly limited. For example, (i) the hydrogen generating
material may include the metal material and the heat generating
material respectively in the form of particles, granules, or
pellets; (ii) the hydrogen generating material may include
secondary particles composed of a particulate metal material and a
particulate heat generating material; or iii) the hydrogen
generating material may be molded into pellets or granules, each of
which includes the metal material and the heat generating material.
In particular, the pellet or granular hydrogen generating material
is more preferred because of its excellent portability. When the
hydrogen generating material is formed into pellets by compression
molding, the packing density is improved, and the energy density is
increased. On the other hand, when the hydrogen generating material
is granulated into granules, the particle size is controlled
easily. For example, if the particle size of the hydrogen
generating material is 5 .mu.m to 300 .mu.m, the time before
starting the generation of hydrogen can be reduced.
[0032] It is preferable that the content of the heat generating
material present in any one of locations selected from the end
portion, the core portion, and the surface portion of the hydrogen
generating material is higher than that of the heat generating
material present in the other locations.
[0033] For example, when the hydrogen generating material is formed
into pellets or granules, the end portion of the hydrogen
generating material indicates a part of the surface or its vicinity
of a pellet or granule, and the surface portion of the hydrogen
generating material indicates a part of the surface of the pellet
or granule. When the hydrogen generating material including a
particulate metal material and a particulate heat generating
material is placed in a container, the end portion of the hydrogen
generating material indicates a region that is in contact with or
in the vicinity of a part of the inside surface of the container,
and the surface portion of the hydrogen generating material
indicates a region that is in contact with a part of the inside
surface of the container. If the end or surface portion of the
hydrogen generating material has a higher content of the heat
generating material, water can be supplied first to those
locations, and then quickly brought into contact with the heat
generating material during the process of producing hydrogen (which
will be described later), thereby allowing the hydrogen production
reaction to start in a short time.
[0034] On the other hand, the core portion of the hydrogen
generating material in the form of pellets or granules indicates a
center or a portion around the center of a pellet or granule. When
the hydrogen generating material including the particulate metal
material and the particulate heat generating material is placed in
a container, the core portion indicates a center or a region around
the center of the container. If the core portion of the hydrogen
generating material has a higher content of the heat generating
material, it takes some time for water to reach the core portion
during the process of producing hydrogen (which will be described
later). Therefore, compared to the hydrogen generating material
with a higher content of the heat generating material in the end or
surface portion, the hydrogen production reaction takes longer to
start. However, heat generated in the core portion of the hydrogen
generating material is not likely to be dissipated to the outside
and is accumulated inside the material, so that the temperature of
the metal material can be increased more efficiently. Thus, the
reaction of the metal material and water can be maintained more
stably.
[0035] To produce a pellet hydrogen generating material, the
process of injecting the hydrogen generating material into a die
may be divided into a plurality of steps so that a portion with a
high content of the heat generating material is formed. To produce
a granular hydrogen generating material, the hydrogen generating
material may be granulated while injecting the material at several
different times. In this manner, the proportion of the heat
generating material can be changed between the surface portion and
the core portion of each granule.
[0036] The content of the metal material in the hydrogen generating
material of the present invention is preferably 85 wt % to 99 wt %,
and more preferably 90 wt % to 97 wt %. By controlling the content
of the metal material within these ranges, a large amount of
hydrogen can be produced. This content is a weight percentage of
the metal material when the total weight of the metal material and
the heat generating material in the whole hydrogen generating
material is expressed as 100.
[0037] The metal material of the present invention is not
particularly limited as long as it can react with water to generate
hydrogen by heating. The metal material is preferably at least one
metal selected from aluminum, silicon, zinc, and magnesium or an
alloy thereof. The alloy may have any composition, but preferably
includes the element selected from the above group of metals as the
main component. The content of the element is preferably 80 wt % or
more, and more preferably 85 wt % or more. If the content of the
element is low, the amount of hydrogen generated by the reaction of
the metal material and water is reduced.
[0038] The metal material can react with water to generate hydrogen
by heating at room temperature or higher. However, since a stable
oxide film is formed on the surface of the metal material, it is
impossible or difficult to generate hydrogen if the temperature is
low, or the metal material is in the form of a bulk such as a plate
or block. On the other hand, the metal material can be handled
easily in the air due to the presence of the oxide film.
[0039] For example, the reaction of aluminum, which is one of the
metal material, and water may be expressed as any one of the
following formulas (1) to (3).
2Al+6H.sub.2O.fwdarw.Al.sub.2O.sub.3.3H.sub.2O+3H.sub.2 (1)
2Al+4H.sub.2O.fwdarw.Al.sub.2O.sub.3.H.sub.2O+3H.sub.2 (2)
2Al+3H.sub.2O.fwdarw.Al.sub.2O.sub.3+3H.sub.2 (3)
[0040] Although the metal material is not particularly limited by
its particle size, the particle size may be 100 .mu.m or less, and
preferably 50 .mu.m or less because the smaller the particle size
is, the better the rate of reaction becomes. In the particle size
distribution of the metal material, particles with a particles size
of 0.1 .mu.m to 60 .mu.m are present preferably in a proportion of
80 vol % or more, and more preferably in a proportion of 90 vol %
or more of the whole metal material. It is most preferable that all
the metal material particles have a particle size within the above
range. The average particle size of the metal material is
preferably 0.1 .mu.m to 30 .mu.m, and more preferably 0.1 .mu.m to
20 .mu.m. The metal material with these particle sizes can be
obtained easily by classification using a sieve.
[0041] The reaction of the metal material in the bulk state and
water does not proceed easily. However, when the particle size of
the metal material is small (e.g., 100 .mu.m or less), the effect
of suppressing the reaction due to the oxide film is reduced, so
that the reactivity with water can be improved by further heating.
Thus, the hydrogen production reaction can be sustained. On the
other hand, if the average particle size of the metal material is
less than 0.1 .mu.m, it is difficult to handle the metal material
in the air because the ignitability is enhanced. Moreover, since
the bulk density of the hydrogen generating material is reduced,
the packing density is reduced, and thus the energy density is
likely to be low. Therefore, it is desirable that the average
partide size of the metal material is 0.1 .mu.m or more. In other
words, the metal material having the above particle size
distribution and average particle size is less affected by the
oxide film and can generate hydrogen efficiently.
[0042] In this specification, the average particle size means a
value of 50% diameter of an accumulated volume percentage, i.e.,
d.sub.50. Also, the particle size distribution and the average
particle size are measured by a laser diffraction scattering
method. According to this method, specifically, the measuring
object is dispersed in a liquid phase such as water and irradiated
with a laser beam to detect scattering intensity distribution, and
the particle size distribution is measured using the scattering
intensity distribution. The measuring device for the laser
diffraction scattering method may be, e.g., "MICROTRAC HRA"
manufactured by Nikkiso Co., Ltd.
[0043] The metal material is preferably flake particles, and more
preferably the flake particles having, e.g., a major axis of
several tens of micrometers and a thickness of 0.1 .mu.m to 5
.mu.m. By reducing the thickness of the metal material, it is
considered that the effect of the formation of the oxide film is
reduced, and the reaction with water proceeds easily to the
particle core.
[0044] To make it easier for the metal material to react with
water, it is preferable not to form an aggregate that consists of
the metal material and has a size of 1 mm or more. The formation of
such an aggregate can be suppressed, e.g., by mixing and stirring
the metal material and the heat generating material or by coating
the metal material with the heat generating material in the
manufacturing process of the hydrogen generating material.
[0045] The heat generating material may be any substance as long as
it causes an exothermic reaction with water at room temperature.
For example, a substance that reacts with water to form a hydroxide
or hydrate, or a substance that reacts with water to generate
hydrogen can be used. In this specification, the room temperature
means a temperature in the range of 20.degree. C. to 30.degree. C.
Examples of the substance that reacts with water to form a
hydroxide or hydrate include oxides of alkali metals (such as a
lithium oxide), oxides of alkaline-earth metals (such as a calcium
oxide and magnesium oxide), chlorides of alkaline-earth metals
(such as a calcium chloride and magnesium chloride), and sulfuric
acid compounds of alkaline-earth metals (such as a calcium
sulfate). Examples of the substance that reacts with water to
generate hydrogen include alkali metals (such as lithium and
sodium) and alkali metal hydrides (such as a sodium borohydride,
potassium borohydride and lithium hydride). These substances may be
used individually or in combination of two or more. If the heat
generating material is a basic substance, it is dissolved in water
to form a high concentration alkaline aqueous solution. This
alkaline aqueous solution dissolves the oxide film formed on the
surface of the hydrogen generating substance, so that the
reactivity with water can be improved significantly. The
dissolution of the oxide film may be a starting point of the
reaction of the metal material and water. In particular, if the
heat generating material is an alkaline-earth metal oxide, it has
the advantages of being easy to handle as well as being a basic
substance.
[0046] There is also a substance that causes an exothermic reaction
with a substance other than water at room temperature. For example,
a substance such as iron powder that reacts with oxygen to generate
heat has been known. However, if the hydrogen generating material
includes the substance reacting with oxygen and the metal material
as a hydrogen source, the oxygen required for the exothermic
reaction may decrease the purity of hydrogen generated from the
metal material or oxidize the metal material, thus reducing the
amount of hydrogen generated. In the present invention, therefore,
it is preferable to use the heat generating material selected from
the above oxides or the like of alkaline-earth metals that react
with water to generate heat. For the same reason, it is also
preferable to use the heat generating material that does not
generate any gas other than hydrogen during the reaction.
[0047] Although the heat generating material is not particularly
limited by its particle size, the particle size may be 0.1 .mu.m to
200 .mu.m, preferably 0.1 .mu.m to 60 .mu.m, and more preferably
0.1 .mu.m to 20 .mu.m. The smaller the particle size is, the better
the rate of reaction becomes. If the particle size of the heat
generating material is less than 0.1 .mu.m, it is difficult to
handle the heat generating material. Moreover, the packing density
of the hydrogen generating material is reduced, and thus the energy
density is likely to be low. Therefore, it is preferable that the
particle size of the heat generating material is controlled within
the above ranges.
[0048] The hydrogen generating material further may include at
least one selected from a hydrophilic oxide, carbon, and a water
absorbing polymer (referred to as additives in the following). By
using the additives with the metal material, the reaction of the
metal material and water can be accelerated to produce hydrogen
efficiently. This is because the additives may serve to improve
contact between the hydrogen generating material and water or to
prevent deposition of the reaction product formed by the reaction
of the hydrogen generating material and water on the surface of the
unreacted metal material. When the hydrogen generating material is
formed into pellets, it is also expected that the additives may
assist water in penetrating into the pellets. Examples of the
hydrophilic oxide include alumina, boehmite, silica, magnesia,
zirconia, zeolite, and a zinc oxide. The hydrogen generating
material may include at least one selected from these oxides.
Examples of the carbon include carbon black such as acetylene black
or Ketjen black, graphite, easily-graphitizable carbon,
hardly-graphitizable carbon, and activated carbon. Examples of the
water absorbing polymer include cellulose such as carboxymethyl
cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, and
polyacrylic acid. These additives may be used individually or in
combination of two or more.
[0049] The hydrogen generating material of the present invention
preferably includes at least one selected from an aluminum powder
and aluminum alloy powder as the metal material. More preferably,
the hydrogen generating material further includes alumina or
boehmite as the hydrophilic oxide.
Embodiment 2
[0050] A hydrogen generating material of another example of the
present invention reacts with water to produce hydrogen. This
hydrogen generating material includes a hydrogen generating
material A and a hydrogen generating material B independently. The
hydrogen generating material A includes a metal material that
reacts with water to generate hydrogen, and a heat generating
material that reacts with water to generate heat and is a material
other than the metal material. The hydrogen generating material B
has a lower content of the heat generating material than the
hydrogen generating material A.
[0051] The reaction of the hydrogen generating material and water
is not particularly limited by a reaction mechanism or the like as
long as the reaction can produce hydrogen. In an example of this
reaction, first, an exothermic reaction of the heat generating
material and water occurs in the hydrogen generating material A.
Then, heat generated by the exothermic reaction causes the metal
material included in the hydrogen generating material A to start
reacting with water. Next, the heat of reaction in the hydrogen
generating material A is transferred to the hydrogen generating
material B adjacent to the hydrogen generating material A. This
heat transfer provides a starting point from which the hydrogen
production reaction starts in the hydrogen generating material
B.
[0052] The hydrogen generating material B may include either no
heat generating material or a significantly lower content of the
heat generating material than the hydrogen generating material A.
Therefore, the amount of the heat generating material can be
reduced in the whole hydrogen generating material, compared to when
the heat generating material is uniformly distributed. Thus, the
proportion of the metal material can be increased, resulting in a
larger amount of hydrogen generated. Alternatively, even if the
amount of the heat generating material is not reduced, both the
time before starting the generation of hydrogen and the time
required for maximizing the hydrogen generation rate can be
reduced. In either case, the hydrogen generation efficiency can be
improved.
[0053] The hydrogen generating material of this embodiment can use
the same materials and sizes as those of the metal material and the
heat generating material in Embodiment 1, and also can use the
additives as described in Embodiment 1.
[0054] In this embodiment, it is desirable that the hydrogen
generating material A is located in the surface or the corner of
the whole hydrogen generating material. With this arrangement,
water can be supplied first to the hydrogen generating material A,
and then quickly brought into contact with the heat generating
material included in the hydrogen generating material A, thereby
allowing the hydrogen production reaction to start in a short time.
If the hydrogen generating material A is surrounded by the hydrogen
generating material B, and preferably is located in the center of
the whole hydrogen generating material, the reaction of the metal
material and water can be maintained more stably. When water is
supplied to the hydrogen generating material, it takes some time
for water to reach the hydrogen generating material A. However,
heat generated in the hydrogen generating material A is not likely
to be dissipated to the outside and is accumulated inside the
hydrogen generating material, so that the temperature of the metal
material can be increased more efficiently.
[0055] When the hydrogen generating material of the present
invention has a plurality of regions that differ in content of the
heat generating material, the content of the heat generating
material is preferably 30 wt % to 80 wt %, and more preferably 35
wt % to 65 wt % in the region with the highest content of the heat
generating material. In the case of this embodiment, it is
preferable that the content of the heat generating material in the
hydrogen generating material A is within the above ranges. This can
further reduce the time it takes to start generating hydrogen as a
result of the reaction of the heat generating material.
[0056] It is preferable that the proportion of the region with the
highest content of the heat generating material in the whole
hydrogen generating material, i.e., the ratio of the hydrogen
generating material in the region with the highest content of the
heat generating material to the whole hydrogen generating material
is 3 wt % to 40 wt %. In the case of this embodiment, it is
preferable that the content of the hydrogen generating material A
in the whole hydrogen generating material is within the above
range. Thus, hydrogen can be produced efficiently.
[0057] The hydrogen generating material B may include only the
metal material. However, it is preferable that the hydrogen
generating material B includes the heat generating material to
accelerate the reaction of the metal material and water. In such a
case, if the content of the heat generating material in the
hydrogen generating material B is too high, it may be difficult to
obtain the effect of reducing the amount of the heat generating
material in the whole hydrogen generating material. Therefore, the
content of the heat generating material is lower in the hydrogen
generating material B than in the hydrogen generating material A.
Specifically, the content of the heat generating material in the
hydrogen generating material B is 1 wt % to 15 wt %.
[0058] At least one of the hydrogen generating materials A and B is
preferably granular in shape. The granular hydrogen generating
material may be formed simply by granulating the material into
granules. Therefore, the particle size can be controlled easily.
For example, if the particle size of the hydrogen generating
material is 5 .mu.m to 300 .mu.m, the time before starting the
generation of hydrogen can be reduced.
Embodiment 3
[0059] In the present invention, the hydrogen generating material
reacts with water to produce hydrogen. An example of the method for
producing hydrogen will be described below. There is no particular
limitation to the process of preparing the hydrogen generating
material. For example, the hydrogen generating material that is
formed into pellets and has a higher content of the heat generating
material in its end portion may be placed in a reaction vessel. In
another process, a metal material powder and a heat generating
material powder may be put into a reaction vessel separately, and
then mixed as needed. At this time, the amount of each powder or
the timing of putting each powder into the reaction vessel may be
adjusted so that the content of the heat generating material is
higher in a portion of the hydrogen generating material in the
reaction vessel. Alternatively, a plurality of types of hydrogen
generating materials with different contents of the heat generating
material may be prepared by mixing the metal material and the heat
generating material beforehand, and each of the hydrogen generating
materials may be put into a reaction vessel separately. The process
of supplying water to the hydrogen generating material thus
prepared is not particularly limited as long as the hydrogen
generating material can react with water. Thus, the location inside
the reaction vessel where water is supplied, the supply rate of
water, or the like can be selected appropriately. In this process,
the supplied water reacts with the heat generating material in the
hydrogen generating material, and heat liberated from this reaction
causes the metal material to start reacting with water. Moreover,
the heat generated by the reaction of the heat generating material
or the heat generated by the reaction of the metal material and
water can provide a starting point from which a reaction of another
metal material and water starts, and thus the hydrogen production
reaction continues to proceed.
[0060] It is preferable that water is supplied first to the portion
of the hydrogen generating material having a higher content of the
heat generating material so that the supplied water can react
efficiently with the heat generating material and the metal
material. In this manner, if the amount of heat required for the
hydrogen production reaction to start is generated first, the
subsequent reaction can proceed efficiently. For example, in the
case of Embodiment 2, water may be supplied first to the hydrogen
generating material A placed in the reaction vessel.
Embodiment 4
[0061] An example of a hydrogen generator of the present invention
will be described in detail with reference to the drawings. FIG. 1
is a schematic cross-sectional view of a hydrogen generator
including a vessel that contains a hydrogen generating material.
The hydrogen generating material includes a metal material that
reacts with water to generate hydrogen, and a heat generating
material that reacts with water to generate heat and is a material
other than the metal material. The heat generating material and the
metal material are arranged in the vessel so that the heat
generating material is unevenly distributed with respect to the
metal material. The hydrogen generator of FIG. 1 is in the form of
a cartridge. In FIG. 1, a cartridge 1 includes a vessel 6 with an
inlet 7 through which water is supplied and an outlet 8 through
which hydrogen is discharged. A hydrogen generating material 2
including two types of hydrogen generating materials 2a, 2b is
placed in the vessel 6. The hydrogen generating materials 2a and 2b
correspond to the hydrogen generating materials A and B in
Embodiment 2, respectively.
[0062] The cartridge 1 with the above configuration can produce
hydrogen efficiently, even if the amount of the heat generating
material included in the hydrogen generating material 2 is reduced.
The cartridge 1 is suitable particularly for carrying out the
production method of hydrogen in Embodiment 3.
[0063] The hydrogen generating materials 2a, 2b may include the
same materials as the metal material and the heat generating
material used in Embodiment 2. Moreover, a partitioning material 5
may be arranged between the hydrogen generating materials 2a, 2b to
prevent mixing of the two materials. The partitioning material 5
may be any material that does not interfere with the reaction of
the hydrogen generating materials 2a, 2b and water nor the transfer
of heat generated in the hydrogen generating material 2a to the
hydrogen generating material 2b. For example, aluminum foil,
stainless steel foil, or copper foil can be used.
[0064] The size and shape of the vessel 6 are not particularly
limited. However, since the vessel 6 is used as a reactor in which
the reaction of the hydrogen generating material and water takes
place, it is desirable that the vessel 6 can be hermetically
sealed, except for the water inlet 7 and the hydrogen outlet 8, to
prevent leakage of the supplied water and the generated hydrogen to
the outside. A material suitable for the vessel 6 is substantially
impermeable to water and hydrogen and has heat resistance (high
enough not to cause any failure, even if the vessel is heated,
e.g., at about 120.degree. C.). Examples of the material include
metals such as aluminum, titanium and nickel, resins such as
polyethylene, polypropylene and polycarbonate, ceramics such as
alumina, silica and titania, and heat-resistance glass. The
structure of the inlet 7 is not particularly limited as long as
water can be supplied from the outside. For example, the inlet 7
may be either an opening formed in the vessel 6 or a pipe connected
to the vessel 6. It is preferable that the inlet 7 is connected to
a pump capable of controlling the water supply, since the amount of
hydrogen generated can be controlled by adjusting the water
supply.
[0065] The structure of the outlet 8 is not particularly limited as
long as hydrogen is discharged to the outside. For example, the
outlet 8 may be either an opening formed in the vessel 6 or a pipe
connected to the vessel 6. The outlet 8 also may be provided with a
filter to prevent the contents of the vessel 6 from getting out.
The filter is not particularly limited as long as it transmits gas
and substantially rejects liquid and solid. For example, a porous
gas-liquid separation film made of polytetrafluoroethylene (PTFE)
or porous film made of polypropylene can be used.
[0066] As shown in FIG. 1, a water absorbing member 9 may be
arranged at the end of each of the inlet 7 and the outlet 8 inside
the vessel 6. Apart of the supplied water is held by the water
absorbing member 9, and the remaining water wets the hydrogen
generating material, thereby allowing the hydrogen production
reaction to start. The generated hydrogen can be fed to the
negative electrode of a fuel cell through the outlet 8. Although
the water absorbing member 9 is not necessarily required, the water
held by the water absorbing member 9 is supplied in accordance with
the water consumption in the hydrogen production reaction, so that
fluctuations in the hydrogen generation rate over time can be
suppressed to some extent. Thus, it is desirable to use the water
absorbing member 9. The water absorbing member 9 is not
particularly limited as long as it can absorb and hold water, and
may be absorbent cotton or nonwoven fabric in general.
Embodiment 5
[0067] An example of a fuel cell that is to be combined with a
hydrogen generator of the present invention will be described with
reference to the drawings. FIG. 2 is a schematic cross-sectional
view showing an example of a fuel cell. A fuel cell 10 includes a
membrane electrode assembly that includes a positive electrode 12
for reducing oxygen, a negative electrode 11 for oxidizing
hydrogen, and a solid electrolyte 13 located between the positive
electrode 12 and the negative electrode 11, and a hydrogen
generator (not shown) for supplying hydrogen to the negative
electrode 11. As the hydrogen generator, e.g., the hydrogen
generator in Embodiment 4 can be used.
[0068] Each member of the fuel cell 10 is not particularly limited
as long as they can be used generally for a fuel cell.
[0069] The positive electrode 12 may be, e.g., a conductive
material that supports a catalyst. Examples of the catalyst include
platinum fine particles and fine particles of an alloy of platinum
and at least one metal selected from iron, nickel, cobalt, tin,
ruthenium, and gold. As the conductive material, e.g., a carbon
material can be used mainly, such as carbon black, activated
carbon, carbon nanotube and carbon nanohorn. In general, a catalyst
supporting carbon can be used in which the catalyst is dispersed
and supported on the surface of the conductive material. Moreover,
the positive electrode 12 has a positive terminal 18.
[0070] The negative electrode 11 may be, e.g., a conductive
material that supports a catalyst. Examples of the catalyst include
platinum fine particles and fine particles of an alloy of platinum
and at least one metal selected from ruthenium, indium, iridium,
tin, iron, titanium, gold, silver, chromium, silicon, zinc,
manganese, molybdenum, tungsten, rhenium, aluminum, lead,
palladium, and osmium. As the conductive material, the same
materials as those for the positive electrode can be used.
Moreover, the negative electrode 11 has a negative terminal 17.
[0071] The solid electrolyte 13 is located between the positive
electrode 12 and the negative electrode 11 and made of a material
that does not have electron conductivity, but can transport
protons. Examples of the material include a polyperfluorosulfonic
acid resin film, a sulfonated polyethersulfonic acid resin film, a
sulfonated polyimide resin film, a sulfuric acid-doped
polybenzimidazole film, phosphoric acid-doped SiO.sub.2 known as a
solid electrolyte, a hybrid of a polymer and phosphoric acid-doped
SiO.sub.2, and a gel electrolyte obtained by impregnating a polymer
and an oxide with an acid solution.
[0072] In the membrane electrode assembly, a diffusion layer 14 is
arranged on the outside of each of the positive electrode 12 and
the negative electrode 11. The diffusion layer 14 may be, e.g., a
porous carbon material.
[0073] A positive separator 16 for supplying air (oxygen) is
located on the side of the positive electrode 12, and a negative
separator 15 for supplying hydrogen is located on the side of the
negative electrode 11 in the membrane electrode assembly. The
negative separator 15 communicates with the hydrogen generator that
provides hydrogen.
[0074] By combining the fuel cell 10 with the hydrogen generator of
the present invention, hydrogen is supplied efficiently from the
metal material hydrogen source), and therefore the fuel cell 10
using this hydrogen as a fuel can generate electric power
efficiently. Moreover, since the hydrogen production reaction in
the hydrogen generator involves water, the hydrogen gas generated
includes a moderate amount of moisture and can be used preferably
for the fuel cell using hydrogen as a fuel.
Embodiment 6
[0075] FIG. 3 is a schematic cross-sectional view showing another
example of a hydrogen generator of the present invention. The
hydrogen generator of FIG. 3 is in the form of a cartridge
different from Embodiment 4.
[0076] A cartridge 20 of this embodiment includes an outer vessel
21, an inner vessel 22 and a hydrogen generating material 23 that
are contained in the outer vessel 21, and a hydrogen generating
material 24 that is contained in the inner vessel 22. The inner
vessel 22 is surrounded by the hydrogen generating material 23.
[0077] The hydrogen generating materials 23 and 24 correspond to
the hydrogen generating materials B and A in Embodiment 2,
respectively. The outer vessel 21 includes a first inlet 25 for
introducing water into the vessel and a first outlet 27 for
discharging hydrogen from the vessel. The inner vessel 22 includes
a second inlet 26 for introducing water into the vessel and a
second outlet 28 for discharging hydrogen from the vessel. A water
absorbing member 29 is arranged at the end of each of the first
inlet 25 and the first outlet 27 inside the outer vessel 21.
Similarly, a water absorbing member 30 is arranged at the end of
each of the second inlet 26 and the second outlet 28 inside the
inner vessel 22.
[0078] The hydrogen generating material 24 may include only the
heat generating material without the metal material. In such a
case, the second outlet 28 can be eliminated because no hydrogen is
generated. Moreover, the hydrogen generating material 23 may
include only the metal material. The cartridge 20 with the above
configuration can produce hydrogen efficiently, even if the amount
of the heat generating material is reduced. The reason for this
will be described below.
[0079] In an example of the hydrogen production reaction in the
cartridge 20 of this embodiment, first, an exothermic reaction of
externally supplied water and the heat generating material included
in the hydrogen generating material 24 occurs in the inner vessel
22. Then, heat generated in the inner vessel 22 is transferred to
the hydrogen generating material 23 in the outer vessel 21. This
heat transfer provides a starting point from which the reaction of
water supplied to the outer vessel 21 and the hydrogen generating
material 23 starts to produce hydrogen.
[0080] When the amount of heat generated in the inner vessel 22 is
sufficiently large, hydrogen can be produced without including the
heat generating material in the hydrogen generating material 23.
Therefore, the amount of the heat generating material used in the
entire cartridge 20 can be reduced. Even if the amount of the heat
generating material is not reduced, both the time before starting
the generation of hydrogen and the time required for maximizing the
hydrogen generation rate can be reduced by making the content of
the heat generating material higher in the hydrogen generating
material 24 than in the hydrogen generating material 23, as
described above.
[0081] In the cartridge 20 of this embodiment, the inner vessel 22
is surrounded by the hydrogen generating material 23. Therefore,
the heat generated in the inner vessel 22 is transferred easily to
the hydrogen generating material 23, so that the temperature of the
metal material can be increased more efficiently. It is preferable
that the inner vessel 22 is located substantially in the center of
the outer vessel 21 and surrounded by the hydrogen generating
material 23. It is more preferable that all the outside surfaces of
the inner vessel 22 except the second inlet 26 and the second
outlet 28 come into contact with the hydrogen generating material
23. This configuration can transfer the heat generated in the inner
vessel 22 more efficiently to the hydrogen generating material
23.
[0082] In the cartridge 20 of this embodiment, the ratio of the
weight of the hydrogen generating material 24 to the total weight
of the hydrogen generating materials 23, 24 is preferably 3 wt % to
40 wt %, and more preferably 5 wt % to 15 wt %. By controlling the
weight ratio of the hydrogen generating material 24 within these
ranges, the balance between the hydrogen generation efficiency and
the amount of hydrogen generated is improved.
[0083] The size and shape of the outer vessel 21 are not
particularly limited. For example, the outer vessel 21 includes a
lid and a main body. Since the outer vessel 21 is used as a reactor
in which the hydrogen production reaction of the hydrogen
generating material 23 and water takes place, it is desirable that
the outer vessel 21 can be hermetically sealed to prevent leakage
of the supplied water to the outside as well as escape of the
generated hydrogen from the vessel other than the first outlet 27.
A material suitable for the outer vessel 21 is substantially
impermeable to water and hydrogen and also has heat resistance
(high enough not to cause any failure, even if the vessel is
heated, e.g., at about 120.degree. C.). Examples of the material
include metals such as aluminum, titanium and nickel, resins such
as polyethylene, polypropylene and polycarbonate, ceramics such as
alumina, silica and titania, and heat-resistance glass. In
particular, when the outer vessel 21 is made of at least one
material selected from polyethylene, polypropylene, and
polycarbonate, it can exhibit high thermal insulation performance
and sufficient heat resistance.
[0084] The size and shape of the inner vessel 22 are not
particularly limited. For example, the inner vessel 22 includes a
lid and a main body. Since the inner vessel 22 is used as a reactor
in which the reaction of the hydrogen generating material 24 and
water takes place, it is desirable that the inner vessel 22 can be
hermetically sealed to prevent leakage of the supplied water to the
outside as well as escape of the generated hydrogen from the vessel
other than the second outlet 28. A material suitable for the inner
vessel 22 has heat resistance (high enough not to cause any
failure, even if the vessel is heated, e.g., at about 120.degree.
C.), and more preferably has high heat conductivity. Examples of
the material include resins such as polyethylene, polypropylene and
polycarbonate, ceramics such as alumina, silica and titania,
heat-resistance glass, and metals. In particular, it is preferable
to use at least one metal selected from aluminum, titanium, nickel,
and iron.
[0085] In this embodiment, the first inlet 25, the first outlet 27,
the second inlet 26, and the second outlet 28 are independent of
each other. However, the present invention is not limited thereto.
For example, if the first inlet 25 and the second inlet 26 are
connected in part, it is not necessary to supply water separately
to the outer vessel 21 and the inner vessel 22. When hydrogen is
generated by the reaction of the hydrogen generating material 24,
the first outlet 27 and the second outlet 28 may be connected in
part, so that the hydrogen that comes out of the outer and inner
vessels 21, 22 can be collected together.
[0086] Moreover, the first inlet 25 may be eliminated, and the
inside of the inner vessel 22 may communicate with the inside of
the outer vessel 21 through the second outlet 28. Accordingly,
water supplied to the inner vessel 22 further can reach the
hydrogen generating material 23 in the outer vessel 21. In such a
case, the outer vessel 21 may have only the second inlet 26 and the
first outlet 27, thus simplifying the structure. With this
configuration, water that is supplied from the second inlet 26
first reacts with the hydrogen generating material 24 in the inner
vessel 22 to generate heat, which can induce the hydrogen
production reaction of the hydrogen generating material 23.
Moreover, hydrogen generated in the inner vessel 22 also can be
transferred to the outer vessel 21 through the second outlet 28
along with the water supplied to the inner vessel 22. Therefore,
the hydrogen generated in the inner vessel 22 and the hydrogen
derived from the reaction of the hydrogen generating material 23
can be drawn together from the first outlet 27.
[0087] However, when many impurities such as basic mists are
contained in the hydrogen that is discharged from the second outlet
28, it is desirable that the first outlet 27 and the second outlet
28 are independent of each other so that the hydrogen generated in
the inner vessel 22 is not mixed with the hydrogen derived from the
reaction of the hydrogen generating material 23. The use of
hydrogen containing the basic mists, e.g., as a fuel of a fuel cell
may degrade the solid electrolyte membrane. In this case, the basic
mists include a base for accepting protons and are produced, e.g.,
when the heat generating material is a basic substance.
[0088] The cartridge of this embodiment as shown in FIG. 3 can
provide hydrogen generated by the reaction of water and the
hydrogen generating material 23 that has a lower content of the
heat generating material, namely, hydrogen containing a smaller
amount of the basic mists or the like as a fuel of a fuel cell.
Therefore, it is possible to avoid the problem of degradation of
the solid electrolyte membrane. When the inlets 25, 26 are used
independently for the respective outer and inner vessels 21, 22, a
reactant other than water (e.g., oxygen) also can be supplied to
the inner vessel 22, and thus the heat generating material in the
inner vessel 22 may be a metal powder such as iron powder that
reacts with oxygen to generate heat.
Embodiment 7
[0089] FIG. 4 is a schematic cross-sectional view showing yet
another example of a hydrogen generator of the present invention.
The hydrogen generator of FIG. 4 is in the form of a cartridge
different from Embodiment 6.
[0090] A cartridge 40 of this embodiment includes an outer vessel
21, an inner vessel 22 and a hydrogen generating material 23 that
are contained in the outer vessel 21, a hydrogen generating
material 24 that is contained in the inner vessel 22, and a heat
insulator 41. The inner vessel 22 is located with its one side
coming into contact with the inside surface of one side of the
outer vessel 21. The heat insulator 41 is located around the
periphery of the outer vessel 21.
[0091] The material and shape of the heat insulator 41 are not
particularly limited. For example, a porous heat insulating
material such as styrofoam or polyurethane foam, or a sheet of a
heat insulating material with a vacuum insulation structure can be
used appropriately. The other configurations are similar to those
of the cartridge 20 in Embodiment 6. In FIG. 4, the same components
as those in FIG. 3 are denoted by the same reference numeral, and
the explanation will not be repeated.
[0092] In the cartridge 40 of this embodiment, the inner vessel 22
is located in contact with the outer vessel 21. Therefore, heat
generated in the inner vessel 22 is transferred quickly to the
entire outer vessel 21, and the temperature of the whole hydrogen
generating material 23 can be increased more efficiently. The
larger the contact area between the inner vessel 22 and the outer
vessel 21 is, the more efficiently the heat is transferred. In this
case, both the outer vessel 21 and the inner vessel 22 are
preferably made of a high heat-conductive material such as metal,
and the materials for the two vessels may be either the same or
different. Since the heat insulator 41 is located around the
periphery of the outer vessel 21, the heat transferred to the outer
vessel 21 is not likely to be dissipated to the outside and can be
accumulated inside the vessel.
[0093] Hereinafter, the present invention will be described in
detail by way of examples. The present invention is not limited to
the following examples.
WORKING EXAMPLE 1
[0094] A hydrogen generating material A (a content of the heat
generating material: 50 wt %) was prepared by mixing 0.5 g of
aluminum powder (with an average particle size of 3 .mu.m) and 0.5
g of calcium oxide powder (with an average particle size of 40
.mu.m) in a mortar. A hydrogen generating material B (a content of
the heat generating material: 5 wt %) was prepared by mixing 3.8 g
of the aluminum powder and 0.2 g of the calcium oxide powder in a
mortar.
[0095] Next, 0.05 g of absorbent cotton (water absorbing member)
was placed in an aluminum can (8 mm length, 34 mm width, 50 mm
height). Then, 1 g of the hydrogen generating material A and 4 g of
the hydrogen generating material B were filled into the aluminum
can in a slanting position, as shown in FIG. 1. As a partitioning
material, aluminum foil was arranged between the hydrogen
generating materials A and B. Moreover, 0.05 g of absorbent cotton
(water absorbing member) was put on the hydrogen generating
material B. The proportions of the hydrogen generating material A
and the aluminum powder in the whole hydrogen generating material
were 20 wt % and 86 wt %, respectively.
[0096] Subsequently, the aluminum can was covered with an aluminum
plate that had a water inlet pipe made of aluminum and used for
introducing water and a hydrogen outlet pipe made of aluminum and
used for discharging hydrogen. The end of the water inlet pipe was
located near the hydrogen generating material A, thus providing a
hydrogen generator as shown in FIG. 1.
[0097] Next, the water inlet pipe was connected to a pump for
supplying water to the hydrogen generating materials A, B. The pump
fed water into the aluminum can at 0.17 ml/min. Thus, the water
first reacted with the heat generating material (calcium oxide
powder) included in the hydrogen generating material A, and then
the heat of reaction caused the aluminum powder included in the
hydrogen generating materials A, B to start reacting with water to
generate hydrogen. At a temperature of 25.degree. C., water was
supplied until no hydrogen was generated, and hydrogen that flowed
through the hydrogen outlet pipe was collected while measuring the
surface temperature of the aluminum can. A water-displacement
method was used to collect the hydrogen.
[0098] The volume of the collected hydrogen was measured as an
amount of hydrogen generated. Using a theoretical amount of
hydrogen generated (1360 ml) per 1 g of aluminum at 25.degree. C.
and 1 atm as a reference, the ratio of the weight of the aluminum
used to the theoretical amount of hydrogen generated was determined
as a reaction rate of the aluminum. Moreover, the hydrogen
generation rate was calculated from a change in the amount of
hydrogen generated over time, thereby determining the time it took
for the hydrogen generation rate to reach a maximum.
[0099] During the test, the temperature (surface temperature) of
the aluminum can, i.e., the reaction temperature of the hydrogen
generating material was increased to a maximum of 95.degree. C. On
the other hand, hydrogen was generated continuously at a
substantially constant generation rate. It was also confirmed that
when the supply of water was stopped, the hydrogen generation was
stopped after several minutes.
WORKING EXAMPLE 2
[0100] A hydrogen generator was produced in the same manner as
Working Example 1 except that a hydrogen generating material A (a
content of the heat generating material: 35 wt %) was prepared by
mixing 0.65 g of the aluminum powder and 0.35 g of the calcium
oxide powder in a mortar, and a hydrogen generating material B (a
content of the heat generating material: 8.75 wt %) was prepared by
mixing 3.65 g of the aluminum powder and 0.35 g of the calcium
oxide powder in a mortar. The proportions of the hydrogen
generating material A and the aluminum powder in the whole hydrogen
generating material were 20 wt % and 86 wt %, respectively.
Moreover, hydrogen was generated in the same manner as Working
Example 1.
WORKING EXAMPLE 3
[0101] A hydrogen generator was produced in the same manner as
Working Example 1 except that a hydrogen generating material A (a
content of the heat generating material: 30 wt %) was prepared by
mixing 0.7 g of the aluminum powder and 0.3 g of the calcium oxide
powder in a mortar, and a hydrogen generating material B (a content
of the heat generating material: 10 wt %) was prepared by mixing
3.6 g of the aluminum powder and 0.4 g of the calcium oxide powder
in a mortar. The proportions of the hydrogen generating material A
and the aluminum powder in the whole hydrogen generating material
were 20 wt % and 86 wt %, respectively. Moreover, hydrogen was
generated in the same manner as Working Example 1. Working Example
4
[0102] A hydrogen generator was produced in the same manner as
Working Example 1 except that a hydrogen generating material B (a
content of the heat generating material: 5 wt %) was prepared by
mixing 3.55 g of the aluminum powder, 0.2 g of the calcium oxide
powder, and 0.25 g of alumina (with an average particle size of 1
.mu.m) in a mortar. The proportions of the hydrogen generating
material A and the aluminum powder in the whole hydrogen generating
material were 20 wt % and 81 wt %, respectively. Moreover, hydrogen
was generated in the same manner as Working Example 1.
COMPARATIVE EXAMPLE 1
[0103] A hydrogen generator was produced in the same manner as
Working Example 1 except that a hydrogen generating material (a
content of the heat generating material: 14 wt %) was prepared by
mixing 4.3 g of the aluminum powder and 0.7 g of the calcium oxide
powder in a mortar, and this hydrogen generating material was
filled uniformly into the aluminum can. Moreover, hydrogen was
generated in the same manner as Working Example 1. Table 1 shows
the configurations of the hydrogen generating materials in Working
Examples 1 to 4 and Comparative Example 1. With respect to each of
the hydrogen generating materials, Table 2 shows the reaction rate
of aluminum in the hydrogen production reaction and the time
required for maximizing the hydrogen generation rate. FIGS. 5 and 6
are graphs showing (a) a change in the surface temperature of the
aluminum can (vessel) over time and (b) a change in the hydrogen
generation rate over time in the hydrogen generators of Working
Example 1 and Comparative Example 1, respectively.
TABLE-US-00001 TABLE 1 Content of heat generating material (wt %)
Proportion of Al in Proportion of Al Hydrogen Hydrogen Proportion
of hydrogen the whole hydrogen Average particle particles with a
generating generating generating material A generating material
size of Al powder particle size of 60 material A material B (wt %)
(wt %) (.mu.m) .mu.m or less (wt %) Working 50 5 20 86 3 100
Example 1 Working 35 8.75 20 86 3 100 Example 2 Working 30 10 20 86
3 100 Example 3 Working 50 5 20 81 3 100 Example 4 Comparative --
-- -- 86 3 100 Example 1
TABLE-US-00002 TABLE 2 Reaction rate Time required for of aluminum
maximizing the hydrogen (%) generation rate (min) Working Example 1
65 1 Working Example 2 64 2 Working Example 3 64 3 Working Example
4 68 1 Comparative Example 1 64 40
[0104] In Working Examples 1 to 4, hydrogen was generated at a
reaction rate of more than 60%, and the time required for
maximizing the hydrogen generation rate was as short as 3 minutes
or less. Therefore, the reaction reached a steady state in a short
time from the beginning of water supply, and hydrogen was drawn
stably. In Comparative Example 1, in which the aluminum powder and
the heat generating material were mixed uniformly, although the
generation of hydrogen was observed like Working Examples 1 to 4,
the time required for maximizing the hydrogen generation rate was
long, i.e., 40 minutes. Thus, it took a long time before the
reaction reached a steady state and hydrogen was drawn stably.
[0105] As shown in FIGS. 5 and 6, the suiface temperature of the
aluminum can was raised in a short time in Working Example 1,
compared to Comparative Example 1. This is because water is
supplied first to the hydrogen generating material A having a
higher content of the heat generating material, so that a
sufficient amount of heat for starting the reaction of the metal
material (aluminum powder) and water is applied to the aluminum
powder. Thus, the hydrogen production reaction may be
accelerated.
[0106] Comparing Working Examples 1 to 3 shows that the time
required for maximizing the hydrogen generation rate depends on the
content of the heat generating material in the hydrogen generating
material A. This is because the heat of reaction is increased with
an increase in the heat generating material, and the reaction of
the aluminum powder and water may be accelerated further. In
contrast, the reaction rate of aluminum does not depend on the
content of the heat generating material in the hydrogen generating
material A and is substantially the same. Accordingly, it is
considered that the particle size or shape of the aluminum powder
may have a greater effect on the reaction rate than the content of
the heat generating material.
[0107] Due to the addition of alumina, the proportion of the metal
material in the hydrogen generating material is lower in Working
Example 4 than in Working Example 1. However, since the alumina
accelerates the hydrogen production reaction, the reaction rate is
higher than that of Working Example 1, and the time required for
maximizing the hydrogen generation rate is the same as that of
Working Example 1. This is because the bond (binding) of the metal
material and the reaction product may be suppressed by adding the
alumina.
WORKING EXAMPLE 5
[0108] 10 parts by weight of platinum supporting carbon that
supports 50 wt % of platinum, 80 parts by weight of a
polyperfluorosulfonic acid resin solution ("NAFION" manufactured by
Sigma-Aldrich, Inc.), and 10 parts by weight of water were stirred
sufficiently and dispersed uniformly to form an electrode paste.
The electrode paste was applied on a PTFE film and then dried,
resulting in a positive electrode.
[0109] Nest, a negative electrode was prepared in the same manner
as the positive electrode except that platinum-ruthenium alloy
supporting carbon that supports 54 wt % of alloy of platinum and
ruthenium (the molar ratio of Pt to Ru was 2:3) was used instead of
the platinum supporting carbon of the positive electrode.
[0110] As a solid electrolyte, a polyperfluorosulfonic acid resin
film ("NAFION 112" manufactured by DuPont. Co.) was prepared. Next,
the solid electrolyte was located between the surface of the
positive electrode coated with the electrode paste and the surface
of the negative electrode coated with the electrode paste, which
then were joined together by hot pressing. Subsequently, the PTFE
films were removed from the positive and negative electrodes, and a
carbon paper was arranged as a diffusion layer on the surface of
each electrode from which the PTFE film had been removed, thus
providing a membrane electrode assembly. Moreover, the positive
electrode had a positive terminal, and the negative electrode had a
negative terminal.
[0111] A separator for supplying air (oxygen) was located on the
side of the positive electrode, and a separator for supplying
hydrogen was located on the side of the negative electrode in the
membrane electrode assembly. Thus, a fuel cell was provided, as
shown in FIG. 2. This fuel cell was combined with the hydrogen
generator of Working Example 1, and hydrogen produced by the
hydrogen generator was fed to the negative electrode of the fuel
cell through the hydrogen outlet pipe. Consequently, a high output
of 200 mW/cm.sup.2 was obtained at 25.degree. C. The hydrogen
generator including the hydrogen generating material of the present
invention was small in size, suitable for carrying, and also useful
for a fuel source of a fuel cell.
WORKING EXAMPLE 6
[0112] 0.01 g of absorbent cotton (water absorbing member) was
placed in an aluminum can (5 mm length, 18 mm width, 20 mm height)
that served as an inner vessel. Then, 0.8 g of hydrogen generating
material, which was the same as the hydrogen generating material A
in Working Example 1, was filled into the inner vessel, and 0.01 g
of absorbent cotton (water absorbing member) was put on the
hydrogen generating material A. Subsequently, the inner vessel was
sealed with an aluminum lid that had a water inlet pipe (second
inlet) made of aluminum and used for introducing water and a
hydrogen outlet pipe (second outlet) made of aluminum and used for
discharging hydrogen.
[0113] A hydrogen generating material B was prepared by mixing 4.0
g of aluminum powder (with an average particle size of 3 .mu.m) and
0.3 g of calcium oxide powder (with an average particle size of 40
.mu.m) in a mortar. Next, as shown in FIG. 3, 0.05 g of absorbent
cotton (water absorbing member) was placed in an aluminum can (8 mm
length, 34 mm width, 50 mm height) that served as an outer vessel.
Then, both the hydrogen generating material B and the inner vessel
were placed in the outer vessel so that the inner vessel was
surrounded by the hydrogen generating material B and located in the
center of the outer vessel. Moreover, 0.05 g of absorbent cotton
(water absorbing member) was put on the hydrogen generating
material B. Finally, the outer vessel was sealed with an aluminum
lid that had a water inlet pipe (first inlet) made of aluminum and
used for introducing water and a hydrogen outlet pipe (first
outlet) made of aluminum and used for discharging hydrogen. Thus, a
hydrogen generator was provided.
[0114] Next, 1 ml of water was supplied from the second inlet to
the inner vessel by using a syringe, so that the water reacted with
the heat generating material (calcium oxide powder) included in the
hydrogen generating material A to generate heat. Moreover, while
water was supplied from the first inlet to the outer vessel at a
rate of 0.17 ml/min by using a pump, the heat generated in the
inner vessel caused the metal material (aluminum powder) included
in the hydrogen generating material B to react with the water to
generate hydrogen. The hydrogen thus generated was taken out of the
vessel through the first outlet and collected by a
water-displacement method. Subsequently, the reaction rate of
aluminum and the time required for maximizing the hydrogen
generation rate were determined in the same manner as Working
Example 1. During the test, the temperature (surface temperature)
of the outer vessel was increased to a maximum of 95.degree. C. On
the other hand, hydrogen was generated continuously at a
substantially constant generation rate. It was also confirmed that
when the supply of water was stopped, the hydrogen generation was
stopped after several minutes.
[0115] A cold trap was arranged between the hydrogen outlet pipe
(first outlet) of the outer vessel and the water-displacement
device to collect basic mists. The basic mists generated were
cooled and collected in the liquid state by the cold trap, and then
the liquid was subjected to neutralization titration. Thus, the
number of moles of the basic mists, i.e., OH.sup.- in the water
vapor containing OH.sup.- ions was calculated. In the
neutralization titration, a hydrochloric acid standard solution
(concentration: 1.0.times.10.sup.-3 mol/l) was used as an acid, and
phenolphthalein was used as an indicator.
COMPARATIVE EXAMPLE 2
[0116] In the hydrogen generation test with the hydrogen generator
of Comparative Example 1, basic mists included in a hydrogen gas
were collected, and the amount of the basic mists was measured in
the same manner of Working Example 6.
[0117] Table 3 shows the configurations of the hydrogen generating
materials in Working Example 6 and Comparative Example 2. With
respect to each of the hydrogen generating materials, Table 4 shows
the reaction rate of aluminum in the hydrogen production reaction,
the time required for maximizing the hydrogen generation rate, and
the number of moles of the basic mists (OH.sup.- ions)
collected.
TABLE-US-00003 TABLE 3 Content of heat generating material (wt %)
Proportion of Al in Proportion of Al Hydrogen Hydrogen Proportion
of hydrogen the whole hydrogen Average particle particles with a
generating generating generating material A generating material
size of Al powder particle size of 60 material A material B (wt %)
(wt %) (.mu.m) .mu.m or less (wt %) Working 50 7 16 86 3 100
Example 6 Comparative -- -- -- 86 3 100 Example 2
TABLE-US-00004 TABLE 4 Time required for maximizing Number of
Reaction rate the hydrogen moles of of aluminum generation rate
basic mists (%) (min) (.mu.mol) Working Example 6 65 3 6
Comparative Example 2 64 40 15
[0118] FIG. 7 is a graph showing (a) a change in the surface
temperature of the outer vessel over time and (b) a change in the
hydrogen generation rate over time in the hydrogen generator of
Working Example 6.
[0119] In the hydrogen generator of Working Example 6, as shown in
Table 4 and FIG. 7, hydrogen was generated at a reaction rate of
more than 60%, the reaction reached a steady state in a short time
from the beginning of water supply, and hydrogen was drawn stably,
as with the hydrogen generators of Working Examples 1 to 4.
[0120] The hydrogen generator of Working Example 6 can collect only
hydrogen derived from the reaction of the hydrogen generating
material (hydrogen generating material B) having a lower content of
the heat generating material (calcium oxide) that is a basic
substance. Therefore, the amount of the basic mists in the hydrogen
gas can be reduced, compared to the hydrogen gas generated in the
hydrogen generator of Comparative Example 1. In the hydrogen
generator of Working Example 6, the hydrogen generating material
having a high content of the basic substance is placed in a
separate vessel, so that scattering of the basic mists can be
reduced.
[0121] The invention may be embodied in other forms without
departing from the spirit or essential characteristics thereof. The
embodiments disclosed in this application are to be considered in
all respects as illustrative and not limiting. The scope of the
invention is indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are intended to be
embraced therein.
INDUSTRIAL APPLICABILITY
[0122] As described above, the hydrogen generating material of the
present invention can increase the content of the metal material
that serves as a hydrogen source, and thus allows hydrogen to be
produced efficiently. Therefore, the hydrogen generating material
can be used widely as a fuel source of a fuel cell, particularly
for the fuel cell of small portable equipment.
* * * * *