U.S. patent application number 14/866387 was filed with the patent office on 2016-01-21 for gas production apparatus.
This patent application is currently assigned to FUJIFILM CORPORATION. The applicant listed for this patent is FUJIFILM CORPORATION, Japan Technological Research Association of Artificial Photosynthetic Chemical Process. Invention is credited to Naotoshi SATO.
Application Number | 20160017506 14/866387 |
Document ID | / |
Family ID | 51623878 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160017506 |
Kind Code |
A1 |
SATO; Naotoshi |
January 21, 2016 |
GAS PRODUCTION APPARATUS
Abstract
A gas production apparatus is provided which include: an element
laminate having a light receiving section on one side and a
conductive substrate on the other, in which laminate a plurality of
elements, each including a semiconductor thin film with pn
junction, are so laminated on each other as to connect in series to
each other; a hydrogen gas generator formed on a surface of a first
element located on the light receiving section side; a first
electrolysis chamber including the hydrogen gas generator; an
oxygen gas generator formed on a back surface of the conductive
substrate; a second electrolysis chamber including the oxygen gas
generator; and an ion-permeable but gas-impermeable diaphragm
provided between the first and second electrolysis chambers.
Inventors: |
SATO; Naotoshi;
(Ashigara-kami-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM CORPORATION
Japan Technological Research Association of Artificial
Photosynthetic Chemical Process |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
FUJIFILM CORPORATION
Tokyo
JP
Japan Technological Research Association of Artificial
Photosynthetic Chemical Process
Tokyo
JP
|
Family ID: |
51623878 |
Appl. No.: |
14/866387 |
Filed: |
September 25, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2014/057583 |
Mar 19, 2014 |
|
|
|
14866387 |
|
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Current U.S.
Class: |
204/252 |
Current CPC
Class: |
Y02E 60/36 20130101;
C25B 9/08 20130101; Y02P 70/50 20151101; Y02P 70/521 20151101; Y02E
10/544 20130101; H01L 31/0687 20130101; C25B 1/10 20130101; Y02P
20/133 20151101; C25B 1/003 20130101; Y02E 60/366 20130101; Y02P
20/134 20151101; C25B 11/04 20130101; H01L 31/0725 20130101 |
International
Class: |
C25B 9/08 20060101
C25B009/08; C25B 1/00 20060101 C25B001/00; C25B 1/10 20060101
C25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2013 |
JP |
2013-068993 |
Claims
1. A gas production apparatus, comprising: an element laminate in
which a plurality of elements, each having a light receiving
portion and including a semiconductor thin film with pn junction,
are so laminated on each other as to connect in series to each
other; a hydrogen gas generator which is formed on a surface of a
first element among the plurality of elements and generates
hydrogen gas, the first element being positioned at one end of the
element laminate; a first electrolysis chamber which includes the
hydrogen gas generator and contains an aqueous electrolytic
solution in contact with the hydrogen gas generator, and the
hydrogen gas generated; an oxygen gas generator that is formed on a
back surface of a conductive substrate, on which the semiconductor
thin film of a second element among the plurality of elements is
formed, and generates oxygen gas, the second element being
positioned at another end of the element laminate; a second
electrolysis chamber which includes the oxygen gas generator and
contains an aqueous electrolytic solution in contact with the
oxygen gas generator, and the oxygen gas generated; and a diaphragm
which is ion-permeable but gas-impermeable, and is provided between
the first electrolysis chamber and the second electrolysis
chamber.
2. The gas production apparatus according to claim 1, wherein the
hydrogen gas generator is provided with a hydrogen generation
surface, and the hydrogen generation surface is formed on a surface
of the semiconductor thin film of the first element.
3. The gas production apparatus according to claim 1, wherein the
first element is composed of a plurality of sub-elements, and the
plurality of sub-elements are disposed on the second element
discretely with respect to the second element.
4. The gas production apparatus according to claim 3, wherein the
plurality of sub-elements each have an element area smaller than
that of the second element.
5. The gas production apparatus according to claim 1, wherein: the
oxygen gas generator is provided with an oxygen generation surface
formed on the back surface of the conductive substrate; and the
oxygen generation surface is inclined upward along a flow direction
of the aqueous electrolytic solution in the second electrolysis
chamber.
6. The gas production apparatus according to claim 1, wherein the
semiconductor thin film includes a CIGS-based compound
semiconductor.
7. The gas production apparatus according to claim 1, wherein the
semiconductor thin film includes a CZTS-based compound
semiconductor.
8. The gas production apparatus according to claim 1, wherein the
semiconductor thin film has an absorption wavelength edge equal to
or greater than 800 nm.
9. The gas production apparatus according to claim 1, further
comprising a hydrogen generation promoter provided on the hydrogen
generation surface of the hydrogen gas generator.
10. The gas production apparatus according to claim 9, wherein the
hydrogen generation promoter is platinum.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of PCT International
Application No. PCT/JP2014/057583 filed on Mar. 19, 2014, which
claims priority under 35 U.S.C. .sctn.119(a) to Japanese Patent
Application No. 2013-068993 filed on Mar. 28, 2013. Each of the
above applications is hereby expressly incorporated by reference,
in its entirety, into the present application.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a gas production apparatus.
Specifically, the present invention relates to a gas production
apparatus that produces hydrogen and oxygen by decomposing water by
receiving light.
[0003] In the prior art, as one of the modes of using solar light
energy as a renewable energy, hydrogen production apparatuses have
been suggested which produce hydrogen used for fuel cells and the
like by using a photoelectric conversion material used for solar
cells and utilizing electrons and holes obtained by photoelectric
conversion for a decomposition reaction of water (for example, see
JP 2012-177160 A and JP 2004-197167 A).
[0004] In both of the hydrogen production apparatuses disclosed in
JP 2012-177160 A and JP 2004-197167 A, a photoelectric conversion
portion or a solar cell, in which two or more pn junctions
generating an electromotive force when solar light is incident
thereon are connected to each other in series, is provided; an
electrolytic solution chamber is disposed at the lower side of the
photoelectric conversion portion or the solar cell that is opposite
to a light receiving surface which receives solar light on the
upper side of the photoelectric conversion portion or the solar
cell; and the inside of an electrolysis chamber is divided by an
ion-conductive partition or diaphragm, and the documents disclose
that by the electric power that is generated in the photoelectric
conversion portion or the solar cell by the received solar light,
water is electrolyzed, and hydrogen is generated.
[0005] According to JP 2012-177160 A, because the hydrogen
production apparatus can also adjust the orientation of the light
receiving surface with respect to the solar light, the amount of
incident light that will be subjected to photoelectric conversion
can be increased, and hydrogen generation efficiency is not
reduced.
[0006] Furthermore, according to and JP 2004-197167 A, because the
hydrogen production apparatus electrolyzes water by using electrode
plates, which are connected to a p-type semiconductor and an n-type
semiconductor of the solar cell, as a positive electrode and a
negative electrode respectively, the efficiency of conversion of
solar energy into hydrogen can be improved.
SUMMARY OF THE INVENTION
[0007] In both of the hydrogen production apparatuses disclosed in
JP 2012-177160 A and JP 2004-197167 A, in the electrolysis chamber
that is on the side opposite to the light receiving surface of the
photoelectric conversion portion or the solar cell, that is, in the
electrolysis chamber that is on the back surface side of the
photoelectric conversion portion or the solar cell, hydrogen and
oxygen are generated as a result of electrolysis of water.
Therefore, if the generated gas such as hydrogen or oxygen adheres
to a gas generation surface of the gas generating electrode of the
photoelectric conversion portion or the electrode plate of the
solar cell and stays between the gas generation surface and an
aqueous solution such as an electrolytic solution, a contact area
between the gas generation surface and the aqueous solution is
reduced, and this leads to a problem in that the efficiency of
generating gas such as hydrogen and oxygen is reduced.
[0008] Although the hydrogen production apparatuses disclosed in JP
2012-177160 A and JP 2004-197167 A show high gas generation
efficiency particularly at the initial gas generation stage, with
the passage of time, the amount of gas staying between the gas
generation surface and the aqueous solution such as an electrolytic
solution increases. As a result, because a contact area between the
gas generation surface and the aqueous solution is reduced, the
efficiency of generating gas such as hydrogen and oxygen greatly
decreases, and this leads to a problem in that gas cannot be stably
generated.
[0009] An object of the present invention is to solve the
aforementioned problems of the prior art and to provide a gas
production apparatus which can maintain high gas generation
efficiency at the initial gas generation stage and even after the
passage of time, and can stably produces hydrogen gas and oxygen
gas as high-purity gases completely separated from each other.
[0010] In order to achieve the above object, the present invention
provides a gas production apparatus comprising: an element laminate
in which a plurality of elements, each having a light receiving
portion and including a semiconductor thin film with pn junction,
are so laminated on each other as to connect in series to each
other; a hydrogen gas generator which is formed on a surface of a
first element among the plurality of elements and generates
hydrogen gas, the first element being positioned at one end of the
element laminate; a first electrolysis chamber which includes the
hydrogen gas generator and contains an aqueous electrolytic
solution in contact with the hydrogen gas generator, and the
hydrogen gas generated; an oxygen gas generator that is formed on a
back surface of a conductive substrate, on which the semiconductor
thin film of a second element among the plurality of elements is
formed, and generates oxygen gas, the second element being
positioned at another end of the element laminate; a second
electrolysis chamber which includes the oxygen gas generator and
contains an aqueous electrolytic solution in contact with the
oxygen gas generator, and the oxygen gas generated; and a diaphragm
which is ion-permeable but gas-impermeable, and is provided between
the first electrolysis chamber and the second electrolysis
chamber.
[0011] The hydrogen gas generator is preferably provided with a
hydrogen generation surface which is formed on a surface of the
semiconductor thin film of the first element.
[0012] The first element is preferably composed of a plurality of
sub-elements which are disposed on the second element discretely
with respect to the second element.
[0013] Preferably, the plurality of sub-elements each have an
element area smaller than that of the second element.
[0014] The oxygen gas generator is preferably provided with an
oxygen generation surface which is formed on the back surface of
the conductive substrate and inclined upward along a flow direction
of the aqueous electrolytic solution in the second electrolysis
chamber.
[0015] It is preferable that the semiconductor thin film includes a
CIGS-based compound semiconductor.
[0016] It is also preferable that the semiconductor thin film
includes a CZTS-based compound semiconductor.
[0017] Preferably, the semiconductor thin film has an absorption
wavelength edge equal to or greater than 800 nm.
[0018] The gas production apparatus preferably further comprises a
hydrogen generation promoter provided on the hydrogen generation
surface of the hydrogen gas generator.
[0019] Preferably, the hydrogen generation promoter is
platinum.
[0020] According to the present invention, it is possible to
maintain high gas generation efficiency at the initial gas
generation stage and even after the passage of time and to stably
produce hydrogen gas and oxygen gas as high-purity gases completely
separated from each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a cross-sectional view schematically showing an
example of a gas production apparatus according to an embodiment of
the present invention.
[0022] FIG. 2 is a top view of the gas production apparatus shown
in FIG. 1.
[0023] FIG. 3 is a flow chart showing an example of a process of
manufacturing the gas production apparatus shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Hereinafter, the gas production apparatus according to the
present invention will be specifically described based on a
preferred embodiment shown in the attached drawings.
[0025] The present invention is an apparatus producing hydrogen and
oxygen by using, as an electrode for decomposing water, a
semiconductor thin film having a pn junction and used in a solar
cell or the like. With a single element constituted with, for
example, a pn junction-semiconductor thin film, a conductive film,
and a support substrate, the ability to photolyze water is
insufficient, and an electromotive force equal to or higher than a
starting voltage of electrolysis of water is not obtained.
Therefore, in the apparatus of the present invention, a plurality
of elements are connected to each other in series in order that the
electromotive force may be increased, and the total electromotive
force of the elements may become equal to or higher than the
starting voltage of electrolysis of water. Furthermore, in the
apparatus of the present invention, through a photolysis reaction
of water, hydrogen is generated from the side of a light receiving
surface of the elements, oxygen is generated from the side of a
surface opposite to the light receiving surface, and thus the
hydrogen and oxygen generated by the decomposition of water are
separately collected. In this way, the apparatus produces hydrogen
and oxygen at a high purity. As the method for connecting the
elements to each other, a method is preferably used in which the
element that will be laminated on an element having a large element
area is constituted with a plurality of sub-elements having a small
element area, and the sub-elements are discretely laminated on the
element having a large element area.
[0026] First, characteristics of the gas production apparatus
according to the invention will be described in comparison with the
gas production apparatus of the prior art.
[0027] As described above, in the prior art, all of the surfaces
(gas generation surfaces) of the electrodes for electrolysis that
generate gas are disposed on the back surface side of the
photoelectric conversion portion that is opposite to the light
receiving surface receiving solar light. In contrast, the present
invention is characterized in that the hydrogen generation surface
and the light receiving surface receiving solar light are disposed
on the same side. In this way, if the hydrogen generation surface
is disposed on the side of the light receiving surface, desired
effects, such as being able to maintain high gas generation
efficiency regardless of the passage of time and being able to
stably produce hydrogen gas and oxygen gas, are obtained.
[0028] FIG. 1 is a cross-sectional view schematically showing an
example of a gas production apparatus according to an embodiment of
the present invention, and FIG. 2 is a top view of the gas
production apparatus shown in FIG. 1.
[0029] First, as shown in the drawings, a gas production apparatus
10 has an element laminate 12 in which a plurality of elements, in
each of which a semiconductor thin film having a pn junction is
formed, are vertically laminated on each other in series; a
hydrogen gas generation portion 14a which is disposed at an open
end of the element positioned at the upper end of the element
laminate 12; an oxygen gas generation portion 14b which is disposed
at an open end of the element positioned at the lower end of the
element laminate 12; a container 18 constituting an electrolysis
chamber 16 which contains an aqueous electrolytic solution AQ in
contact with the two gas generation portions 14a and 14b, and
hydrogen gas and oxygen gas that are generated in the gas
generation portions 14a and 14b respectively; and a diaphragm 20
which partitions the electrolysis chamber 16 into two electrolysis
chambers 16a and 16b including the gas generation portions 14a and
14b respectively.
[0030] The element laminate 12 is for generating hydrogen and
oxygen through a photolysis reaction of water by receiving light
such as solar light through a light receiving surface, and has a
plurality of (two in the example illustrated in the drawings) pn
junction elements 22 and 24 that are vertically laminated on each
other in the drawing. Hereinafter, as a typical example, the number
of the pn junction elements connected to each other in series is
described as two. However, as long as the total electromotive force
of a plurality of pn junction elements is equal to or higher than
the starting voltage of the electrolysis of water, the number of
the pn junction elements is not limited to two as in the example
illustrated in the drawings. It goes without saying that the number
of the pn junction elements may be arbitrarily set.
[0031] The pn junction elements 22 and 24 are photoelectric
conversion elements with a laminated structure having the same
constitution as that of a solar battery cell used as a solar cell.
The pn junction elements 22 and 24 are for generating electrons and
holes through photoelectric conversion by receiving light such as
solar light through the light receiving surfaces, and sending the
generated electrons and holes to the gas generation portions 14a
and 14b respectively.
[0032] The pn junction element 22 on the substrate side of the
element laminate 12, that is, on the lower side in the drawing is
an oxygen generation element generating oxygen and has a conductive
plate 26, a photoelectric conversion layer 28, and a buffer layer
30 that are laminated on each other in this order from the lower
side toward the upper side in the drawing. The pn junction element
22 has a transparent conductive film 32, which becomes an upper
electrode, on the buffer layer 30.
[0033] The pn junction element 24 on the light receiving surface
side of the element laminate 12, that is, on the upper side in the
drawing is a hydrogen generation element generating hydrogen. The
pn junction element 24 is an assembly of a plurality of (nine in
the example illustrated in the drawings) small-sized pn junction
elements 24a. The nine small-sized pn junction elements (hereafter
also referred to as "sub-elements") 24a are disposed on the pn
junction element 22, specifically, on the transparent conductive
film 32 discretely, that is, in the form of scattered islands. In
the pn junction element 24 (24a), the transparent conductive film
32, the photoelectric conversion layer 28, the buffer layer 30, and
a transparent protective film 34 are laminated on each other in
this order from the pn junction element 22 on the lower side toward
the upper side in the drawing. On the transparent protective film
34, a promoter 36 for generating hydrogen is formed in the form of
scattered islands.
[0034] The transparent conductive film 32 functions as a lower
electrode in the pn junction element 24 (24a) and functions as an
upper electrode in the pn junction element 22. Therefore, it can be
said that the transparent conductive film 32 functions as an
electrode common to both the pn junction elements 22 and 24 (24a).
Since the transparent protective film 34 constitutes an upper
electrode of the pn junction element 24 (24a), a transparent
conductive protective film is used as the transparent protective
film 34.
[0035] Accordingly, it can be said that the pn junction element 24
(24a) is constituted with the transparent conductive film 32, the
photoelectric conversion layer 28, the buffer layer 30, the
transparent protective film 34, and the hydrogen generation
promoter 36.
[0036] Incidentally, the sub-elements 24a are discretely disposed
in the form of scattered islands on the transparent conductive film
32, so that, in a position in which the sub-elements 24a are not
disposed, the transparent conductive film 32 is so exposed in the
electrolysis chamber 16a as to come into contact with the aqueous
electrolytic solution AQ to thereby short-circuit. Furthermore, the
lateral faces of the pn junction element 24 (24a), that is, the
lateral faces of the photoelectric conversion layer 28, the buffer
layer 30 and the transparent protective film 34 as laminated are
also exposed in the electrolysis chamber 16a and comes into contact
with the aqueous electrolytic solution AQ, and therefore a short
circuit occurs.
[0037] Accordingly, it is preferable to cover the surface of the
transparent conductive film 32 in portions exposed in the
electrolysis chamber 16a, and the lateral faces of the pn junction
element 24 (24a) as well, with a transparent insulating film
37.
[0038] In the element laminate 12, light is incident on the pn
junction element 24 from the transparent protective film 34 side
and passes through the transparent protective film 34 and the
buffer layer 30. As a result, an electromotive force is generated
in the photoelectric conversion layer 28, and for example, the
migration of a charge (electrons) to the transparent protective
film 34 from the transparent conductive film 32 occurs. In other
words, an electric current flowing to the transparent conductive
film 32 from the transparent protective film 34 is generated (the
migration of holes occurs).
[0039] On the other hand, light incident on the pn junction element
22 from the transparent insulating film 37 side passes through the
transparent insulating film 37, the transparent conductive film 32,
and the buffer layer 30. As a result, an electromotive force is
generated in the photoelectric conversion layer 28, and for
example, the migration of a charge (electrons) to the transparent
conductive film 32 from the conductive plate 26 occurs. In other
words, an electric current flowing to the conductive plate 26 from
the transparent conductive film 32 is generated (the migration of
holes occurs).
[0040] Therefore, in the element laminate 12, the transparent
protective film 34 of the pn junction element 24 on the upper side
becomes the gas generation portion 14a (cathode electrode for
electrolysis) generating hydrogen, and the conductive plate 26 of
the pn junction element 22 on the lower side becomes the gas
generation portion 14b (anode electrode for electrolysis)
generating oxygen.
[0041] The conductive plate 26 is composed of, for example, Mo, and
functions as a substrate supporting the element laminate 12 and as
an oxygen generation surface generating oxygen.
[0042] The photoelectric conversion layer 28 is composed of, for
example, a CIGS (Copper indium gallium (di)selenide)-based compound
semiconductor film or a CZTS (Copper zinc tin sulfide)-based
compound semiconductor film. In the pn junction element 22 on the
lower side, the photoelectric conversion layer 28 is formed on the
conductive plate 26, and in the pn junction element 24 on the upper
side, the photoelectric conversion layer 28 is formed on the
transparent conductive film 32.
[0043] The buffer layer 30 is composed of, for example, a CdS thin
film and is formed on the surface of the photoelectric conversion
layer 28. At the interface between the buffer layer 30 and the
photoelectric conversion layer 28, pn junction is formed.
Consequently, it can be said that the photoelectric conversion
layer 28 is a thin film of a p-type semiconductor, and the buffer
layer 30 is a thin film of an n-type semiconductor.
[0044] The photoelectric conversion layer 28 and the buffer layer
30 are used in both the pn junction element 22 on the lower side
and the pn junction element 24 on the upper side, and at least one
of the photoelectric conversion layer 28 and the buffer layer 30
may be the same for both the pn junction elements 22 and 24 or may
vary between the pn junction elements 22 and 24.
[0045] The transparent conductive film 32 is composed of, for
example, a transparent conductive film such as an IMO (Mo-added
In.sub.2O.sub.3) film and is formed on the buffer layer 30. Herein,
in the pn junction element 22 on the lower side, the transparent
conductive film 32 functions as an upper electrode. Accordingly,
the transparent conductive film 32 is a conductive film which
functions as a light receiving surface on the pn junction composed
of the buffer layer 30 and the photoelectric conversion layer 28 in
the pn junction element 22, and also functions as a lower electrode
of the pn junction element 24 on the upper side. That is, the
transparent conductive film 32 functions as a conductive film which
connects the pn junction element 22 on the lower side to the pn
junction element 24 on the upper side in series.
[0046] The transparent protective film 34 is composed of, for
example, a transparent conductive film such as an ITO (Sn-added
In.sub.2O.sub.3) film, and is formed on the buffer layer 30 in the
pn junction element 24 on the upper side. Herein, the transparent
protective film 34 functions as an upper electrode of the pn
junction element 24 on the upper side. Accordingly, the transparent
protective film 34 functions as the light receiving surface on the
pn junction composed of the buffer layer 30 and the photoelectric
conversion layer 28 and also functions as the hydrogen generation
surface generating hydrogen.
[0047] The conductive plate 26 is constituted with, for example, a
metal such as Mo, Al, Cu, Cr, W, Ni, Ta, Fe or Co, or a combination
of these metals. The conductive plate 26 may have a single layer
structure or a laminated structure such as a double layer
structure. The back surface of the conductive plate 26 becomes an
oxygen gas generation surface generating oxygen and comes into
direct contact with an aqueous electrolytic solution. Therefore,
the conductive plate 26 is preferably of a metal that is not easily
oxidized. Particularly, the conductive plate 26 is preferably
constituted with Mo. The film thickness of the conductive plate 26
is generally about 1,000 .mu.m, and preferably 100 .mu.m to 1,500
.mu.m.
[0048] The back surface of the conductive plate 26 of the pn
junction element 22 becomes the gas generation portion 14b (anode
electrode for electrolysis) generating oxygen, and generates oxygen
molecules, that is, oxygen (oxygen gas) by withdrawing electrons
from hydroxide ions OH.sup.- ionized from water molecules in the
aqueous electrolytic solution AQ
(2OH.sup.-.fwdarw.H.sub.2O+O.sub.2/2+2e.sup.-), that is to say,
functions as an oxygen gas generation surface.
[0049] Accordingly, the back surface of the conductive plate 26 is
preferably inclined toward the downstream side from the upstream
side along the stream of the aqueous electrolytic solution AQ such
that the generated oxygen does not stay on the back surface. The
direction of the inclination is not particularly limited. When the
back surface of the conductive plate 26 is inclined downward toward
the downstream side, the oxygen generated on the back surface is
highly effectively removed. When it is inclined upward toward the
downstream side, it is possible to cause the oxygen gas, which
floats from the aqueous electrolytic solution AQ and is
concentrated on the back surface of the conductive plate 26, to
flow to a discharge port 40b together with the aqueous electrolytic
solution AQ with efficiency. In the example as illustrated, a
supply port 38b of the aqueous electrolytic solution AQ is on the
right side in the drawing, and the discharge port 40b for
discharging the generated oxygen together with the aqueous
electrolytic solution AQ is on the left side in the drawing.
Consequently, in order to rapidly discharge the generated oxygen,
it is better for the back surface of the conductive plate 26 to be
inclined upward toward the left side in the drawing from the right
side in the drawing.
[0050] If the back surface of the conductive plate 26 is inclined
as above, it is possible to rapidly move the generated oxygen from
the back surface of the conductive plate 26 that serves as the
oxygen generation surface, without causing the oxygen to stay on
the back surface, and to discharge the oxygen from the discharge
port 40b together with the aqueous electrolytic solution AQ.
Therefore, it is possible to bring the back surface of the
conductive plate 26 into contact with the aqueous electrolytic
solution AQ at all times, and to generate oxygen with excellent
efficiency by causing a photolysis reaction of water on the entire
back surface of the conductive plate 26.
[0051] In order to accelerate the generation of oxygen by the
photolysis reaction of water, an oxygen generation promoter such as
IrO.sub.2, CoO.sub.x or the like may be formed in the form of
scattered islands on the back surface of the conductive plate 26
which becomes the oxygen gas generation surface.
[0052] At the interface between the buffer layer 30 and the
photoelectric conversion layer 28, the photoelectric conversion
layer 28 forms the pn junction of which the photoelectric
conversion layer 28 side is of a P-type and the buffer layer 30
side is of an N-type. The photoelectric conversion layer 28 absorbs
the light reaching it after passing through the transparent
insulating film 37, the transparent conductive film 32 and the
buffer layer 30, generates holes on the p-side and electrons on the
n-side, and has a function of photoelectric conversion. In the
photoelectric conversion layer 28, the holes generated in the pn
junction are migrated toward the conductive plate 26 from the
photoelectric conversion layer 28, and the electrons generated in
the pn junction are migrated toward the transparent conductive film
32 from the buffer layer 30. The film thickness of the
photoelectric conversion layer 28 is preferably 200 nm to 3,000 nm,
and particularly preferably 500 nm to 2,000 nm.
[0053] The photoelectric conversion layer 28 is preferably a
compound semiconductor-based photoelectric conversion semiconductor
layer. The main component of the photoelectric conversion layer 28
is not particularly limited (the main component referring to a
component comprising not less than 20% by mass of the layer). In
view of obtaining high photoelectric conversion efficiency, a
chalcogen compound semiconductor, a compound semiconductor having a
chalcopyrite structure, and a compound semiconductor having a
defect stannite-type structure can be suitably used as the main
component.
[0054] Favorable examples of the chalcogen compound (compound
containing S, Se, or Te) include:
[0055] a II-VI compound such as ZnS, ZnSe, ZnTe, CdS, CdSe or
CdTe;
[0056] a group I-III-VI.sub.2 compound such as CuInSe.sub.2,
CuGaSe.sub.2, Cu(In, Ga)Se.sub.2, CuInS.sub.2, CuGaSe.sub.2 or
Cu(In, Ga) (S, Se).sub.2; and
[0057] a group I-III.sub.3-VI.sub.5 compound such as
Culn.sub.3Se.sub.5, CuGa.sub.3Se.sub.5 or Cu(ln,
Ga).sub.3Se.sub.5.
[0058] Favorable examples of the compound semiconductors of a
chalcopyrite-type structure and of a defect stannite-type structure
include:
[0059] a group I-III-VI.sub.2 compound such as CuInSe.sub.2,
CuGaSe.sub.2, Cu(In, Ga)Se.sub.2, CuInS.sub.2, CuGaSe.sub.2 or
Cu(In, Ga) (S, Se).sub.2; and
[0060] a group I-III.sub.3-VI.sub.5 compound such as
CuIn.sub.3Se.sub.5, CuGa.sub.3Se.sub.5 or Cu(In,
Ga).sub.3Se.sub.5.
[0061] In the above description, (In, Ga) and (S, Se) represent
(In.sub.1-xGa.sub.x) and (Si.sub.1-ySe.sub.y) respectively (here,
x=0 to 1, y=0 to 1).
[0062] The photoelectric conversion layer 28 is preferably
constituted with, for example, a CIGS-based compound semiconductor
having a chalcopyrite crystal structure or a CZTS-based compound
semiconductor, among others. That is, the photoelectric conversion
layer 28 is preferably constituted with a CIGS layer. The CIGS
layer may be constituted not only with Cu(In, Ga)Se.sub.2 but also
with a known material used in the CIGS-based material such as
CuInSe.sub.2(CIS).
[0063] The method for forming the photoelectric conversion layer 28
is not particularly limited. For example, as the method for forming
the CIGS layer containing Cu, In, Ga, or S, 1) a multi-source vapor
deposition method, 2) a selenization method, 3) a sputtering
method, 4) a hybrid sputtering method, and 5) a mechanochemical
processing method are known.
[0064] Examples of other methods for forming the CIGS layer include
a screen printing method, a close-spaced sublimation method, an
MOCVD method, a spraying method (wet film formation method), and
the like. For example, by a screen printing method (wet film
formation method), a spraying method (wet film formation method) or
the like, a fine particle film containing elements of group Ib,
group IIIb, and group VIb is formed on a substrate and subjected to
thermal decomposition processing (optionally performed in a group
VIb element atmosphere), and in this way, a crystal having a
desired composition can be obtained (JP 9-74065 A, JP 9-74213 A,
and the like).
[0065] As described above, in the present invention, the
photoelectric conversion layer 28 is preferably constituted with a
CIGS-based compound semiconductor having a chalcopyrite crystal
structure or a CZTS-based compound semiconductor, for example.
However, the present invention is not limited thereto, and any
photoelectric conversion element may be used as long as it makes it
possible to form a pn junction composed of an inorganic
semiconductor and generate hydrogen and oxygen by causing a
photolysis reaction of water. For example, a photoelectric
conversion element utilized in a solar battery cell constituting a
solar battery is preferably used. Examples of such a photoelectric
conversion element include a thin film silicon-based thin film-type
photoelectric conversion element, a CdTe-based thin film-type
photoelectric conversion element, a dye-sensitized thin film-type
photoelectric conversion element, and an organic thin film-type
photoelectric conversion element, in addition to a CIGS-based thin
film-type photoelectric conversion element, a CIS-based thin
film-type photoelectric conversion element, and a CZTS-based thin
film-type photoelectric conversion element.
[0066] The absorption wavelength of the inorganic semiconductor
forming the photoelectric conversion layer 28 is not particularly
limited as long as the absorption wavelength is within a wavelength
range allowing photoelectric conversion. The wavelength range may
be any range including wavelength regions of solar light and the
like, particularly, from a visible wavelength region to an infrared
wavelength region. The absorption wavelength edge of the inorganic
semiconductor is preferably equal to or greater than 800 nm, that
is to say, a wavelength range including up to an infrared
wavelength region is preferred. This is because more than half of
the solar light energy reaching the ground is included in an
ultraviolet-visible region at wavelengths of not more than 800 nm,
and effective use of such solar energy makes it significant to
produce hydrogen energy by the inventive apparatus as an
alternative to fossil fuels.
[0067] The buffer layer 30 is so formed as to constitute a pn
junction layer together with the photoelectric conversion layer 28,
that is, to form a pn junction at the interface between the
photoelectric conversion layer 28 and the buffer layer 30, to
protect the photoelectric conversion layer 28 at the time of
forming the transparent conductive film 32, and to transmit the
light incident on the transparent conductive film 32 to the
photoelectric conversion layer 28.
[0068] The buffer layer 30 preferably contains a metal sulfide
containing at least one metal element selected from the group
consisting of Cd, Zn, Sn and In, with specific examples including
CdS, ZnS, Zn(S, O) and/or Zn(S, O, OH), SnS, Sn(S, O) and/or Sn(S,
O, OH), InS, In(S, O) and/or In(S, O, OH). The film thickness of
the buffer layer 30 is preferably 10 nm to 2 .mu.m, and more
preferably 15 nm to 200 nm. The buffer layer 30 is formed by, for
example, a chemical bath deposition process (hereafter referred to
as "CBD process").
[0069] A window layer may be disposed between the buffer layer 30
and the transparent conductive film 32. The window layer is
constituted with, for example, a ZnO layer having a thickness of
about 10 nm.
[0070] The transparent conductive film 32 has light transmitting
properties. In the pn junction element 22 on the lower side, the
transparent conductive film 32 brings light into the photoelectric
conversion layer 28, and functions as an upper electrode that is
paired with the conductive plate 26 as a lower electrode and moves
the holes and electrons generated in the photoelectric conversion
layer 28 (to causes an electric current to flow). Furthermore, the
transparent conductive film 32 functions as a lower electrode of
the pn junction element 24 on the upper side and also functions as
a transparent conductive film for directly connecting the pn
junction element 22 on the lower side to the pn junction element 24
on the upper side such that the pn junction elements 22 and 24 are
connected to each other in series.
[0071] The transparent conductive film 32 is constituted with IMO
(Mo-added In.sub.2O.sub.3), ZnO doped with Al, B, Ga, In or the
like, or ITO (indium tin oxide), for example. The transparent
conductive film 32 may have a single layer structure or a laminated
structure such as a double layer structure. The thickness of the
transparent conductive film 32 is not particularly limited, and is
preferably 0.1 .mu.m to 2 .mu.m, and more preferably 0.3 .mu.m to 1
.mu.m.
[0072] The method for forming the transparent conductive film 32 is
not particularly limited. The transparent conductive film can be
formed by a vapor phase film formation method such as an electron
beam vapor deposition method, a sputtering method and a CVD method
or by a coating method.
[0073] The transparent protective film 34 is formed on the upper
surface of the buffer layer 30 in the pn junction element 24 on the
upper side and has light transmitting properties. The transparent
protective film 34 brings light into the photoelectric conversion
layer 28, functions as an upper electrode that is paired with the
transparent conductive film 32 as a lower electrode and moves the
holes and electrons generated in the photoelectric conversion layer
28 (to causes an electric current to flow), and functions as a
transparent conductive film which protects the buffer layer 30 and
the photoelectric conversion layer 28.
[0074] In addition, the transparent protective film 34 serves as
the gas generation portion 14a (cathode electrode for electrolysis)
generating hydrogen and generates hydrogen molecules, that is,
hydrogen (hydrogen gas) by supplying electrons to hydrogen ions
(protons) H.sup.+ ionized from water molecules
(2H.sup.++2e.sup.-.fwdarw.H.sub.2). The surface of the transparent
protective film 34 functions as a hydrogen gas generation
surface.
[0075] As the transparent protective film 34, it is possible to use
the same transparent conductive film as the transparent conductive
film 32, such as ITO (indium tin oxide), ZnO doped with Al, B, Ga,
In or the like, or IMO (Mo-added In.sub.2O.sub.3). The transparent
protective film 34 may have a single layer structure or a laminated
structure such as a double layer structure, as the transparent
conductive film 32. The thickness of the transparent protective
film 34 is not particularly limited, and is preferably 10 nm to 200
nm, and more preferably 30 nm to 100 nm.
[0076] The method for forming the transparent protective film 34 is
not particularly limited, as is the case with the transparent
conductive film 32. The transparent protective film 34 can be
formed by a vapor phase film formation method such as an electron
beam vapor deposition method, a sputtering method and a CVD method
or by a coating method.
[0077] As described above, the transparent protective film 34
functions as an electrode for generating hydrogen, and the surface
thereof functions as a hydrogen gas generation surface.
Accordingly, the transparent protective film 34 functions as the
gas generation portion 14a generating hydrogen, and the region
thereof constitutes a hydrogen gas generation region.
[0078] On the surface of the transparent protective film 34, the
hydrogen generation promoter 36 for accelerating the generation of
hydrogen is formed in the form of scattered islands.
[0079] Examples of the hydrogen generation promoter 36 include a
component composed solely of Pt (platinum), Pd (palladium), Ni
(nickel), Au (gold), Ag (silver), Ru (ruthenium), Cu (copper), Co
(cobalt), Rh (rhodium), Ir (iridium), or Mn (manganese), an alloy
as a combination of these, and an oxide thereof. The size of the
hydrogen generation promoter 36 is not particularly limited, and is
preferably 1 nm to 100 nm.
[0080] The method for forming the hydrogen generation promoter 36
is not particularly limited, and the hydrogen generation promoter
36 can be formed by a photodeposition method, a sputtering method,
an impregnation method, or the like.
[0081] As in the example illustrated, it is preferable that the
hydrogen generation promoter 36 is provided on the upper surface of
the transparent protective film 34. However, when hydrogen can be
sufficiently generated, the hydrogen generation promoter 36 may be
not provided.
[0082] In the example illustrated, the hydrogen generation promoter
36 is formed and scattered on the upper surface of the transparent
protective film 34 formed on the upper surface of the buffer layer
30. However, the present invention is not limited thereto. The
transparent protective film 34 may not be provided, and the
hydrogen generation promoter 36 may be directly formed and
scattered on the upper surface of the buffer layer 30.
[0083] In this case, the buffer layer 30 functions as an N-type
semiconductor and as an electrode for generating hydrogen, and the
surface thereof functions as a hydrogen gas generation surface.
Therefore, the buffer layer 30 functions as the gas generation
portion 14a generating hydrogen, and the region thereof constitutes
a hydrogen gas generation region.
[0084] The transparent insulating film 37 has light transmitting
properties. For protecting the pn junction elements 22 and 24,
specifically, for protecting the portion outside the hydrogen gas
generation regions in the electrolysis chamber 16a, the transparent
insulating film 37 is so provided as to cover the portion outside
the gas generation regions. Specifically, the transparent
insulating film 37 covers the portion of the surface of the
transparent conductive film 32 that does not have the pn junction
element 24 on the upper side formed therein and, accordingly,
serves as the light receiving surface of the pn junction element 22
on the lower side, and all the lateral faces of the individual
sub-elements 24a constituting the pn junction element 24.
[0085] The transparent insulating film 37 is constituted with, for
example, SiO.sub.2, SnO.sub.2, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5,
Al.sub.2O.sub.3, Ga.sub.2O.sub.3 or the like. The thickness of the
transparent insulating film 37 is not particularly limited, and is
preferably 100 nm to 1,000 nm.
[0086] The method for forming the transparent insulating film 37 is
not particularly limited. The transparent insulating film 37 can be
formed by an RF sputtering method, a DC reactive sputtering method,
an MOCVD method or the like.
[0087] The region of the transparent conductive film 32, in which
the transparent insulating film 37 is formed while the pn junction
element 24 on the upper side is not formed, serves as the light
receiving surface of the pn junction element 22 on the lower side.
In contrast, in each of the sub-elements 24a of the pn junction
element 24 on the upper side, the buffer layer 30 or the
transparent protective film 34 of the relevant sub-element serves
as the light receiving surface. Consequently, in order to generate
hydrogen and oxygen with excellent efficiency by a photolysis
reaction of water, according to the ability of the pn junction
elements 22 and 24, for example, according to the electromotive
force or the amount of electrons or holes generated, a
predetermined balance needs to be achieved between the total light
receiving area of the pn junction element 24 on the upper side,
that is, the total area of the light receiving surfaces of all the
sub-elements 24a, and the total light receiving area of the pn
junction element 22 on the lower side, that is, the total area of
the region of the transparent conductive film 32 in which the pn
junction element 24 on the upper side is not formed. For example,
when the pn junction elements 22 and 24 are equal in ability, they
are preferably also equal in total light receiving area.
[0088] Therefore, it is preferable that the total light receiving
areas of the pn junction elements 22 and 24 are balanced according
to their ability.
[0089] The element laminate 12 is constituted as above.
[0090] The element laminate 12 can be manufactured by the following
manufacturing method, but the present invention is not limited
thereto.
[0091] FIG. 3 is a flowchart showing an example of a process of
manufacturing the gas production apparatus shown in FIGS. 1 and
2.
[0092] First, in Step S100, as the conductive plate 26, for
example, a Mo substrate is prepared.
[0093] Thereafter, in Step S102, on one surface of the conductive
plate 26, as the photoelectric conversion layer 28, for example, a
CIGS-based compound semiconductor film (P-type semiconductor layer)
is formed by a known method such as a selenization/sulfuration
method or a multi-source simultaneous vapor deposition method.
[0094] Then, in Step S104, on the photoelectric conversion layer 28
formed as above, as the buffer layer 30, for example, a CdS film
(N-type semiconductor layer) is formed by a known method such as a
CBD (chemical bath deposition) process.
[0095] Subsequently, in Step S106, on the buffer layer 30 formed as
above, as the transparent conductive film 32, for example, an ITO
film which becomes a transparent conductive layer is formed by a
known method such as an MOCVD method or an RF sputtering
method.
[0096] Thereafter, in Step S108, on the transparent conductive film
32 formed as above, as the photoelectric conversion layer 28, for
example, a CIGS-based compound semiconductor film (P-type
semiconductor layer) is formed in the same manner as in Step
S102.
[0097] Then, in Step S110, on the photoelectric conversion layer 28
formed as above, as the buffer layer 30, for example, a CdS film
(N-type semiconductor layer) is formed in the same manner as in
Step S104.
[0098] Subsequently, in Step S112, on the buffer layer 30 formed as
above, as the transparent protective film 34, for example, a ZnO
film which becomes a protective layer is formed by a known method
such as an MOCVD method or an RF sputtering method.
[0099] After that, in Step S114, a structure A (pn junction element
24 on the upper side) composed of the photoelectric conversion
layer 28 (CIGS-based compound semiconductor film), the buffer layer
30 (CdS film), and the transparent protective film 34 (ZnO film)
formed as above is cut by a mechanical scribing method, thereby
forming a group of structures A (a group of sub-elements 24a) that
are discretely disposed.
[0100] Then, in Step S116, on the group of structures A formed as
above, as the transparent insulating film 37, for example, a
SiO.sub.2 film which becomes a transparent insulating layer is
formed by a known method such as an MOCVD method, an RF sputtering
method, or a DC reactive sputtering method. Subsequently, by a
known method such as a CMP method, the transparent insulating film
37 (SiO.sub.2 film) formed on the upper surface portion of the
structures A is selectively scraped off such that the transparent
protective film 34 (ZnO film), which becomes a protective layer, is
exposed only on the upper surface portion of the sub-elements 24a
(structures A) as the pn junction element 24.
[0101] Finally, in Step S118, only on the transparent protective
film 34 exposed on the upper surface portion of the pn junction
element 24 (sub-elements 24a) (structures A), as the hydrogen
generation promoter 36, for example, a Pt promoter is supported by
a known method such as a photodeposition method.
[0102] In this way, the element laminate 12 can be
manufactured.
[0103] The container 18 houses the element laminate 12 and
constitutes the electrolysis chamber 16 composed of the
electrolysis chamber 16a on the upper side, which contains
(retains) the aqueous electrolytic solution AQ in contact with the
upper surface of the transparent protective film 34 of the pn
junction element 24a on the upper side constituting the gas
generation portion 14a, contains (retains) hydrogen as the gas
generated from the gas generation portion 14a, and is provided on
the upper side of the element laminate 12, and the electrolysis
chamber 16b on the lower side, which contains (retains) the aqueous
electrolytic solution AQ in contact with the back surface of the
conductive plate 26 of the pn junction element 22 at the lower end
constituting the gas generation portion 14b, contains (retains)
oxygen as the gas generated from the gas generation portion 14b,
and is provided on the lower side of the element laminate 12.
[0104] As shown in FIG. 2, the electrolysis chamber 16a on the
upper side and the electrolysis chamber 16b on the lower side
communicate with each other in a region that surrounds the outer
periphery of the element laminate 12 along the inner surface of the
container 18, and a diaphragm 20 is disposed in the region in which
the electrolysis chambers 16a and 16b communicate with each
other.
[0105] A plurality of (three in the example illustrated in the
drawings) supply ports 38a for supplying the aqueous electrolytic
solution AQ into the electrolysis chamber 16a are provided in an
upper part of a lateral face on the right side in FIG. 1 of the
electrolysis chamber 16a in the container 18 (on the upper right
side of the apparatus). Furthermore, a plurality of (four in the
example illustrated in the drawings) discharge ports 40a for
discharging the aqueous electrolytic solution AQ in the
electrolysis chamber 16a and a plurality of (three in the example
illustrated in the drawings) collection ports 42 for collecting
hydrogen generated in the electrolysis chamber 16a are both
provided in an upper part of a lateral face on the left side in
FIG. 1 of the electrolysis chamber 16a in the container (on the
upper left side of the apparatus).
[0106] A plurality of (two in the example illustrated in the
drawings) supply ports 38b for supplying the aqueous electrolytic
solution AQ into the electrolysis chamber 16b are provided in a
lower part of a lateral face on the right side in FIG. 1 of the
electrolysis chamber 16b in the container 18 (on the lower right
side of the apparatus). Furthermore, a plurality of (two in the
example illustrated in the drawings) discharge ports 40b for
discharging the aqueous electrolytic solution AQ in the
electrolysis chamber 16b together with oxygen generated in the
electrolysis chamber 16b are provided in a lower part of a lateral
face on the left side in FIG. 1 of the electrolysis chamber 16b in
the container 18 (on the lower left side of the apparatus). The
oxygen discharged from the discharge ports 40b together with the
aqueous electrolytic solution AQ is collected by a collection
portion not shown in the drawings.
[0107] Both the supply ports 38a and the discharge ports 40a are
provided in a position slightly above the position of the
transparent protective film 34, such that a water flow, which
prevents the hydrogen generated by the transparent protective film
34 of the pn junction element 24 (a group of the sub-elements 24a)
from staying on the surface of the transparent protective film 34,
can be generated in the electrolysis chamber 16a. Therefore, it is
possible to bring the surface of the transparent protective film 34
into contact with the aqueous electrolytic solution AQ at all
times, and to generate hydrogen with excellent efficiency. It goes
without saying that the position of the supply ports 38a and the
discharge ports 40a is the same as the position of the surface of
the aqueous electrolytic solution AQ in the electrolysis chamber
16a.
[0108] In contrast, both the supply ports 38b and the discharge
ports 40b are placed in the position of the back surface of the
conductive plate 26 that constitutes the ceiling of the
electrolysis chamber 16b and is inclined upward toward the
downstream side.
[0109] In the electrolysis chamber 16a, hydrogen is retained above
the surface of the aqueous electrolytic solution AQ. Therefore, the
ceiling of the electrolysis chamber 16a is constituted such that it
is inclined upward toward the downstream side, as the back surface
of the conductive plate 26, and is separated from the surface of
the aqueous electrolytic solution AQ. Furthermore, in order to
collect the retained hydrogen with excellent efficiency, the
collection ports 42 are provided in a position slightly above the
position of the surface of the aqueous electrolytic solution AQ,
that is, a position slightly above the position of the supply ports
38a and the discharge ports 40a.
[0110] The number of the supply port 38a, the discharge port 40a,
and the collection port 42 is not particularly limited, and may be
arbitrarily set as long as a water flow, which prevents the
hydrogen from staying on the hydrogen gas generation surface, can
be generated. However, it is preferable to provide a required
number of the supply ports 38a, the discharge ports 40a, and the
collection ports 42 in a position ensuring a water flow on the
surface of the pn junction element 24 (a group of the sub-elements
24a).
[0111] The number of the supply ports 38b and the discharge ports
40b is not particularly limited either, and may be arbitrarily set
as long as a water flow, which prevents the oxygen from staying on
the oxygen gas generation surface, can be generated. However, it is
preferable to provide a required number of the supply ports 38b and
the discharge ports 40b in a position ensuring a water flow on the
back surface of the conductive plate 26 of the pn junction element
22.
[0112] In order that the hydrogen generated in the electrolysis
chamber 16a and the oxygen generated in the electrolysis chamber
16b may be separately collected at high purity, and that the
hydroxide ions increased as a result of the generation of hydrogen
in the electrolysis chamber 16a (with increased pH) and the
hydrogen ions increased as a result of the generation of oxygen in
the electrolysis chamber 16b (with reduced pH) may permeate the
diaphragm 20 to cause neutralization, the diaphragm 20 separates
the electrolysis chamber 16 in the container 18 into the
electrolysis chamber 16a and the electrolysis chamber 16b. The
diaphragm 20 is a membrane permeable to ions but impermeable to
gas.
[0113] As described above, the diaphragm 20 is disposed in a region
surrounding the outer periphery of the element laminate 12 along
the inner surface of the container 18, in which region the
electrolysis chamber 16a on the upper side and the electrolysis
chamber 16b on the lower side communicate with each other. The
diaphragm 20 is attached to the inner wall surface of the container
18 and the outer wall surface of the element laminate 12 in a state
of coming into close contact with these without a void. As a
result, the diaphragm 20 can separate the region of the
electrolysis chamber 16a, which comes into contact with the pn
junction element 24 on the upper side, from the region of the
electrolysis chamber 16b, which comes into contact with the pn
junction element 22, such that the permeation of gas does not occur
while the permeation of ions occur.
[0114] The diaphragm 20 is constituted with, for example, an ion
exchange membrane, a ceramic filter, or Vycor glass. The thickness
of the diaphragm 20 is not particularly limited, and is preferably
10 .mu.m to 1,000 .mu.m.
[0115] The gas production apparatus of the present invention is
basically constituted as above.
[0116] The gas production apparatus of the present invention has
been specifically described, but the present invention is not
limited to the aforementioned examples. It goes without saying that
the present invention can be improved or modified in various ways
without departing from the gist and scope of the present
invention.
EXAMPLES
[0117] Hereinafter, the gas production apparatus of the present
invention will be specifically described based on the following
Examples, to which the present invention is not limited.
Example 1
[0118] First, as Example 1, the gas production apparatus 10 shown
in FIG. 1 that was constituted as below was prepared, the
electrolysis chamber 16 was filled with an aqueous electrolytic
solution, the apparatus was irradiated with light, and the amount
of the generated hydrogen gas and oxygen gas was evaluated.
[0119] The results are shown in Table 1.
[0120] The element laminate 12 of the gas production apparatus 10
of Example 1 was prepared according to the preparation flow shown
in the flowchart of FIG. 3.
1. Constitution of hydrogen generation element (pn junction element
24 (sub-elements 24a)).
[0121] Transparent conductive film: IMO (Mo-added In.sub.2O.sub.3),
a thickness of 1,000 nm
[0122] P-type semiconductor thin film: CIGS, a thickness of 500
nm
[0123] N-type semiconductor thin film: CdS, a thickness of 50
nm
[0124] Protective film: ITO (Sn-added In.sub.2O.sub.3), a thickness
of 50 nm
[0125] Promoter: Pt
2. Constitution of oxygen generation element (pn junction element
22).
[0126] Conductive plate: Mo, a thickness of 1 mm
[0127] P-type semiconductor thin film: CIGS, a thickness of 2,000
nm
[0128] N-type semiconductor thin film: CdS, a thickness of 50
nm
3. Form of conductive plate.
[0129] Shape on oxygen gas generation side: processed to be
inclined toward the flow direction of oxygen gas (no oxygen gas
bubbles staying)
4. Form of oxygen generation element.
[0130] Size: 15 cm.times.20 cm
5. Form of hydrogen generation element.
[0131] Size: 3 cm to 5 cm for each side
[0132] Number of elements: nine (two or more)
[0133] Disposition of elements: the respective elements are
discretely disposed.
6. Others
[0134] Diaphragm: Nafion (substance permeable to ions but
impermeable to gas)
[0135] Aqueous electrolytic solution: 0.1M Na.sub.2SO.sub.4
solution (pH 9.5)
[0136] Promoter: Pt particles (size: up to 20 nm in diameter)
[0137] Material for container (module): glass
[0138] Light source for irradiation: irradiation with simulated
solar light of AM 1.5.
Comparative Example 1
[0139] As Comparative Example 1, a gas production apparatus of the
same constitution as that of Example 1 was prepared except that the
hydrogen generation portion and the oxygen generation portion were
formed in the same element. The prepared gas production apparatus
was irradiated with light in the same manner as in Example 1, and
the amount of the generated gas was evaluated.
[0140] The results are shown in Table 1.
Comparative Example 2
[0141] Next, as Comparative Example 2, a gas production apparatus
of the same constitution as that of Example 1 was prepared except
that the hydrogen generation element and the oxygen generation
element have the same size (15 cm.times.20 cm), and the apparatus
was constituted with one hydrogen generation element and one oxygen
generation element. The prepared gas production apparatus was
irradiated with light in the same manner as in Example 1, and the
amount of the generated gas was evaluated.
[0142] The results are shown in Table 1.
[0143] The evaluation was performed as below.
[0144] As the amount of gas generated (initial stage), the amount
of gas generated immediately after the start of light irradiation
was measured.
[0145] As the amount of gas generated (after a passage of time),
the amount of gas generated 24 hours after the start of light
irradiation was measured.
[0146] In Table 1, "A" of the column of comprehensive determination
indicates a case in which both the amount of hydrogen gas generated
(initial stage) and the amount of hydrogen gas generated (after a
passage of time) exceeded 50 ml/minm.sup.2, while "B" of the column
of comprehensive determination indicates a case in which either or
both of the amount of hydrogen gas generated (initial stage) and
the amount of hydrogen gas generated (after a passage of time) were
less than 50 ml/minm.sup.2. Based on such determination criteria,
the evaluation was made. Herein, the standard value of 50
ml/minm.sup.2 is a numerical value converted based on a solar light
conversion efficiency of 1%.
TABLE-US-00001 TABLE 1 Amount of hydrogen Amount of hydrogen gas
generated (after gas generated a passage of Comprehensive (initial
stage) time) determination Example 1 65 ml/min m.sup.2 55 ml/min
m.sup.2 A Comp. 0 ml/min m.sup.2 0 ml/min m.sup.2 B Example 1 Comp.
55 ml/min m.sup.2 30 ml/min m.sup.2 B Example 2
[0147] As shown in Table 1, in Example 1 of the present invention,
the amount of hydrogen gas generated immediately after the start of
light irradiation was 65 ml/minm.sup.2, and the amount of hydrogen
gas generated after 24 hours was 55 ml/minm.sup.2. Because the
generated hydrogen gas bubbles adhered to part of the hydrogen
generation portion on the light receiving surface side, the contact
area between the hydrogen generation portion and the solution was
reduced due to the bubbles, and as a result, the gas generation
efficiency was reduced, and the amount of gas generated after 24
hours was reduced compared to the initial stage. However, by
discretely disposing the hydrogen generation elements, a turbulent
flow occurred in the water introduced into the apparatus, and in
this way, most of the bubbles could be removed.
[0148] In Comparative Example 1, the amount of hydrogen gas
generated immediately after the start of light irradiation was 0
ml/minm.sup.2, and the generation of gas could not be detected.
Furthermore, the amount of hydrogen gas generated was still 0
ml/minm.sup.2 even after 24 hours, and the generation of gas could
not be detected.
[0149] In Comparative Example 2, the amount of hydrogen gas
generated immediately after the start of light irradiation was 55
ml/minm.sup.2. Because the element for generating hydrogen gas
covered the entirety of the element for generating oxygen gas, the
amount of light reaching the element for generating oxygen gas was
reduced, and accordingly, the total gas generation ability of the
system was reduced. Furthermore, the amount of hydrogen gas
generated after 24 hours was 30 ml/minm.sup.2. Because the
generated hydrogen gas bubbles covered the entire light receiving
surface, light was scattered due to the bubbles, and accordingly,
the amount of incident light was reduced, and the gas generation
efficiency was markedly reduced.
[0150] As is evident from the above results, in Example 1 of the
present invention, a large amount of gas was generated immediately
after the start of light irradiation, and the amount of gas
generated could be maintained at a high level even after a passage
of time. Therefore, it is understood that gas could be stably
generated.
[0151] In contrast, it is understood that, in Comparative Example
1, a potential (electromotive force) necessary for decomposing
water into hydrogen and oxygen could not be obtained.
[0152] Moreover, it is understood that, in Comparative Example 2,
although a large amount of gas was generated immediately after the
start of light irradiation, the amount of gas generated was
markedly reduced after a passage of time, and gas could not be
stably generated. The above results show the superiority of Example
1 of the present invention.
[0153] The above results clearly show the effects of the present
invention.
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