US20160017506A1

US20160017506A1 - Gas production apparatus

Info

Publication number: US20160017506A1
Application number: US14/866,387
Authority: US
Inventors: Naotoshi Sato
Original assignee: Fujifilm Corp; Japan Technological Research Association of Artificial Photosynthetic Chemical Process
Current assignee: Fujifilm Corp; Japan Technological Research Association of Artificial Photosynthetic Chemical Process
Priority date: 2013-03-28
Filing date: 2015-09-25
Publication date: 2016-01-21
Also published as: CN105102683B; JP2014189883A; CN105102683A; JP5993768B2; AU2014246142B2; AU2014246142A1; WO2014156899A1

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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. §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

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.
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).
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.
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.
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

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.
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.
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.
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.
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.
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.
Preferably, the plurality of sub-elements each have an element area smaller than that of the second element.
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.
It is preferable that the semiconductor thin film includes a CIGS-based compound semiconductor.
It is also preferable that the semiconductor thin film includes a CZTS-based compound semiconductor.
Preferably, the semiconductor thin film has an absorption wavelength edge equal to or greater than 800 nm.
The gas production apparatus preferably further comprises a hydrogen generation promoter provided on the hydrogen generation surface of the hydrogen gas generator.
Preferably, the hydrogen generation promoter is platinum.
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

FIG. 1 is a cross-sectional view schematically showing an example of a gas production apparatus according to an embodiment of the present invention.

FIG. 2 is a top view of the gas production apparatus shown in FIG. 1.

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

Hereinafter, the gas production apparatus according to the present invention will be specifically described based on a preferred embodiment shown in the attached drawings.
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.
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.
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.
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.
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 14 a 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 14 b 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 14 a and 14 b, and hydrogen gas and oxygen gas that are generated in the gas generation portions 14 a and 14 b respectively; and a diaphragm 20 which partitions the electrolysis chamber 16 into two electrolysis chambers 16 a and 16 b including the gas generation portions 14 a and 14 b respectively.
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.
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 14 a and 14 b respectively.
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.
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 24 a. The nine small-sized pn junction elements (hereafter also referred to as “sub-elements”) 24 a 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 (24 a), 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.
The transparent conductive film 32 functions as a lower electrode in the pn junction element 24 (24 a) 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 (24 a). Since the transparent protective film 34 constitutes an upper electrode of the pn junction element 24 (24 a), a transparent conductive protective film is used as the transparent protective film 34.
Accordingly, it can be said that the pn junction element 24 (24 a) 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.
Incidentally, the sub-elements 24 a 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 24 a are not disposed, the transparent conductive film 32 is so exposed in the electrolysis chamber 16 a 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 (24 a), 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 16 a and comes into contact with the aqueous electrolytic solution AQ, and therefore a short circuit occurs.
Accordingly, it is preferable to cover the surface of the transparent conductive film 32 in portions exposed in the electrolysis chamber 16 a, and the lateral faces of the pn junction element 24 (24 a) as well, with a transparent insulating film 37.
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).
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).
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 14 a (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 14 b (anode electrode for electrolysis) generating oxygen.
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.
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.
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.
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.
The transparent conductive film 32 is composed of, for example, a transparent conductive film such as an IMO (Mo-added In₂O₃) 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.
The transparent protective film 34 is composed of, for example, a transparent conductive film such as an ITO (Sn-added In₂O₃) 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.
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 μm, and preferably 100 μm to 1,500 μm.
The back surface of the conductive plate 26 of the pn junction element 22 becomes the gas generation portion 14 b (anode electrode for electrolysis) generating oxygen, and generates oxygen molecules, that is, oxygen (oxygen gas) by withdrawing electrons from hydroxide ions OH⁻ ionized from water molecules in the aqueous electrolytic solution AQ (2OH⁻→H₂O+O₂/2+2e⁻), that is to say, functions as an oxygen gas generation surface.
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 40 b together with the aqueous electrolytic solution AQ with efficiency. In the example as illustrated, a supply port 38 b of the aqueous electrolytic solution AQ is on the right side in the drawing, and the discharge port 40 b 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.
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 40 b 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.
In order to accelerate the generation of oxygen by the photolysis reaction of water, an oxygen generation promoter such as IrO₂, CoO_xor 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.
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.
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.
Favorable examples of the chalcogen compound (compound containing S, Se, or Te) include:
a II-VI compound such as ZnS, ZnSe, ZnTe, CdS, CdSe or CdTe;
a group I-III-VI₂compound such as CuInSe₂, CuGaSe₂, Cu(In, Ga)Se₂, CuInS₂, CuGaSe₂or Cu(In, Ga) (S, Se)₂; and
a group I-III₃-VI₅compound such as Culn₃Se₅, CuGa₃Se₅or Cu(ln, Ga)₃Se₅.
Favorable examples of the compound semiconductors of a chalcopyrite-type structure and of a defect stannite-type structure include:
a group I-III-VI₂compound such as CuInSe₂, CuGaSe₂, Cu(In, Ga)Se₂, CuInS₂, CuGaSe₂or Cu(In, Ga) (S, Se)₂; and
a group I-III₃-VI₅compound such as CuIn₃Se₅, CuGa₃Se₅or Cu(In, Ga)₃Se₅.
In the above description, (In, Ga) and (S, Se) represent (In_1-xGa_x) and (Si_1-ySe_y) respectively (here, x=0 to 1, y=0 to 1).
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)Se₂but also with a known material used in the CIGS-based material such as CuInSe₂(CIS).
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.
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).
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.
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.
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.
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 μm, 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”).
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.
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.
The transparent conductive film 32 is constituted with IMO (Mo-added In₂O₃), 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 μm to 2 μm, and more preferably 0.3 μm to 1 μm.
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.
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.
In addition, the transparent protective film 34 serves as the gas generation portion 14 a (cathode electrode for electrolysis) generating hydrogen and generates hydrogen molecules, that is, hydrogen (hydrogen gas) by supplying electrons to hydrogen ions (protons) H⁺ ionized from water molecules (2H⁺+2e⁻→H₂). The surface of the transparent protective film 34 functions as a hydrogen gas generation surface.
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 In₂O₃). 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.
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.
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 14 a generating hydrogen, and the region thereof constitutes a hydrogen gas generation region.
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.
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.
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.
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.
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.
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 14 a generating hydrogen, and the region thereof constitutes a hydrogen gas generation region.
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 16 a, 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 24 a constituting the pn junction element 24.
The transparent insulating film 37 is constituted with, for example, SiO₂, SnO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, Ga₂O₃or the like. The thickness of the transparent insulating film 37 is not particularly limited, and is preferably 100 nm to 1,000 nm.
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.
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 24 a 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 24 a, 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.
Therefore, it is preferable that the total light receiving areas of the pn junction elements 22 and 24 are balanced according to their ability.
The element laminate 12 is constituted as above.
The element laminate 12 can be manufactured by the following manufacturing method, but the present invention is not limited thereto.
FIG. 3 is a flowchart showing an example of a process of manufacturing the gas production apparatus shown in FIGS. 1 and 2.
First, in Step S100, as the conductive plate 26, for example, a Mo substrate is prepared.
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.
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.
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.
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.
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.
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.
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 24 a) that are discretely disposed.
Then, in Step S116, on the group of structures A formed as above, as the transparent insulating film 37, for example, a SiO₂film 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 (SiO₂film) 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 24 a (structures A) as the pn junction element 24.
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 24 a) (structures A), as the hydrogen generation promoter 36, for example, a Pt promoter is supported by a known method such as a photodeposition method.
In this way, the element laminate 12 can be manufactured.
The container 18 houses the element laminate 12 and constitutes the electrolysis chamber 16 composed of the electrolysis chamber 16 a 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 24 a on the upper side constituting the gas generation portion 14 a, contains (retains) hydrogen as the gas generated from the gas generation portion 14 a, and is provided on the upper side of the element laminate 12, and the electrolysis chamber 16 b 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 14 b, contains (retains) oxygen as the gas generated from the gas generation portion 14 b, and is provided on the lower side of the element laminate 12.
As shown in FIG. 2, the electrolysis chamber 16 a on the upper side and the electrolysis chamber 16 b 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 16 a and 16 b communicate with each other.
A plurality of (three in the example illustrated in the drawings) supply ports 38 a for supplying the aqueous electrolytic solution AQ into the electrolysis chamber 16 a are provided in an upper part of a lateral face on the right side in FIG. 1 of the electrolysis chamber 16 a 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 40 a for discharging the aqueous electrolytic solution AQ in the electrolysis chamber 16 a and a plurality of (three in the example illustrated in the drawings) collection ports 42 for collecting hydrogen generated in the electrolysis chamber 16 a are both provided in an upper part of a lateral face on the left side in FIG. 1 of the electrolysis chamber 16 a in the container (on the upper left side of the apparatus).
A plurality of (two in the example illustrated in the drawings) supply ports 38 b for supplying the aqueous electrolytic solution AQ into the electrolysis chamber 16 b are provided in a lower part of a lateral face on the right side in FIG. 1 of the electrolysis chamber 16 b 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 40 b for discharging the aqueous electrolytic solution AQ in the electrolysis chamber 16 b together with oxygen generated in the electrolysis chamber 16 b are provided in a lower part of a lateral face on the left side in FIG. 1 of the electrolysis chamber 16 b in the container 18 (on the lower left side of the apparatus). The oxygen discharged from the discharge ports 40 b together with the aqueous electrolytic solution AQ is collected by a collection portion not shown in the drawings.
Both the supply ports 38 a and the discharge ports 40 a 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 24 a) from staying on the surface of the transparent protective film 34, can be generated in the electrolysis chamber 16 a. 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 38 a and the discharge ports 40 a is the same as the position of the surface of the aqueous electrolytic solution AQ in the electrolysis chamber 16 a.
In contrast, both the supply ports 38 b and the discharge ports 40 b are placed in the position of the back surface of the conductive plate 26 that constitutes the ceiling of the electrolysis chamber 16 b and is inclined upward toward the downstream side.
In the electrolysis chamber 16 a, hydrogen is retained above the surface of the aqueous electrolytic solution AQ. Therefore, the ceiling of the electrolysis chamber 16 a 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 38 a and the discharge ports 40 a.
The number of the supply port 38 a, the discharge port 40 a, 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 38 a, the discharge ports 40 a, 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 24 a).
The number of the supply ports 38 b and the discharge ports 40 b 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 38 b and the discharge ports 40 b in a position ensuring a water flow on the back surface of the conductive plate 26 of the pn junction element 22.
In order that the hydrogen generated in the electrolysis chamber 16 a and the oxygen generated in the electrolysis chamber 16 b 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 16 a (with increased pH) and the hydrogen ions increased as a result of the generation of oxygen in the electrolysis chamber 16 b (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 16 a and the electrolysis chamber 16 b. The diaphragm 20 is a membrane permeable to ions but impermeable to gas.
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 16 a on the upper side and the electrolysis chamber 16 b 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 16 a, which comes into contact with the pn junction element 24 on the upper side, from the region of the electrolysis chamber 16 b, 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.
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 μm to 1,000 μm.
The gas production apparatus of the present invention is basically constituted as above.
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

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

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.
The results are shown in Table 1.
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 24 a)).
Transparent conductive film: IMO (Mo-added In₂O₃), a thickness of 1,000 nm
P-type semiconductor thin film: CIGS, a thickness of 500 nm
N-type semiconductor thin film: CdS, a thickness of 50 nm
Protective film: ITO (Sn-added In₂O₃), a thickness of 50 nm
Promoter: Pt
2. Constitution of oxygen generation element (pn junction element 22).
Conductive plate: Mo, a thickness of 1 mm
P-type semiconductor thin film: CIGS, a thickness of 2,000 nm
N-type semiconductor thin film: CdS, a thickness of 50 nm
3. Form of conductive plate.
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.
Size: 15 cm×20 cm
5. Form of hydrogen generation element.
Size: 3 cm to 5 cm for each side
Number of elements: nine (two or more)
Disposition of elements: the respective elements are discretely disposed.

6. Others

Diaphragm: Nafion (substance permeable to ions but impermeable to gas)
Aqueous electrolytic solution: 0.1M Na₂SO₄solution (pH 9.5)
Promoter: Pt particles (size: up to 20 nm in diameter)
Material for container (module): glass
Light source for irradiation: irradiation with simulated solar light of AM 1.5.

Comparative Example 1

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.
The results are shown in Table 1.

Comparative Example 2

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×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.
The results are shown in Table 1.
The evaluation was performed as below.
As the amount of gas generated (initial stage), the amount of gas generated immediately after the start of light irradiation was measured.
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.
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/min·m², 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/min·m². Based on such determination criteria, the evaluation was made. Herein, the standard value of 50 ml/min·m²is a numerical value converted based on a solar light conversion efficiency of 1%.

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 · m²	55 ml/min · m²	A
Comp.	0 ml/min · m ²	0 ml/min · m²	B
Example 1
Comp.	55 ml/min · m²	30 ml/min · m²	B
Example 2

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/min·m², and the amount of hydrogen gas generated after 24 hours was 55 ml/min·m². 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.
In Comparative Example 1, the amount of hydrogen gas generated immediately after the start of light irradiation was 0 ml/min·m², and the generation of gas could not be detected. Furthermore, the amount of hydrogen gas generated was still 0 ml/min·m²even after 24 hours, and the generation of gas could not be detected.
In Comparative Example 2, the amount of hydrogen gas generated immediately after the start of light irradiation was 55 ml/min·m². 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/min·m². 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.
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.
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.
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.
The above results clearly show the effects of the present invention.

Claims

What is claimed is:

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.