WO2016114063A1

WO2016114063A1 - Hydrogen generating electrode

Info

Publication number: WO2016114063A1
Application number: PCT/JP2015/085238
Authority: WO
Inventors: 一成堂免; 東　耕平
Original assignee: 富士フイルム株式会社; 国立大学法人東京大学; 人工光合成化学プロセス技術研究組合
Priority date: 2015-01-13
Filing date: 2015-12-16
Publication date: 2016-07-21
Also published as: JPWO2016114063A1; JP6559710B2

Abstract

The hydrogen generating electrode according to the present invention receives light and generates hydrogen from an electrolytic aqueous solution. The hydrogen generating electrode has an inorganic semiconductor layer having a pn junction, and a mixed layer formed on the inorganic semiconductor layer. The mixed layer has a hydrogen generating catalyst and fine particles having electron transport capability.

Description

Hydrogen generation electrode

The present invention relates to a hydrogen generating electrode that generates light from an aqueous electrolyte solution by receiving light, and more particularly to a hydrogen generating electrode having a large photocurrent density corresponding to the amount of hydrogen generated per unit area.

Conventionally, as one form of utilizing solar energy, which is renewable energy, an electrolysis aqueous solution is obtained by using an electromotive force obtained from this photoelectric conversion material using a photoelectric conversion material used in a solar cell. An apparatus for producing hydrogen by decomposing it has been proposed (see, for example, Non-Patent Document 1).

Non-Patent Document 1 shows an improved Cu ₂ ZnSnS ₄ semiconductor photoelectrode that generates hydrogen from water under sunlight. The semiconductor photoelectrode of Non-Patent Document 1 has a Pt / TiO ₂ / CdS / CZTS (Cu ₂ ZnSnS ₄ ) / Mo / SLG configuration. The TiO ₂ layer is an electron transport layer, and is formed by sputtering to partially cover the CdS layer. Pt is supported on a TiO ₂ layer that partially covers the CdS layer.

In the semiconductor photoelectrode shown in Non-Patent Document 1, a TiO ₂ layer that partially covers the CdS layer is formed by sputtering, but the IE characteristic (current-voltage characteristic) obtained by light irradiation is low. Unfortunately, on the high potential side, there is a problem that the photocurrent density corresponding to the amount of hydrogen generated per unit area is low.

An object of the present invention is to solve the problems based on the above-described prior art and provide a hydrogen generating electrode having a large photocurrent density corresponding to the amount of hydrogen generated per unit area.

In order to achieve the above object, the present invention provides a hydrogen generating electrode that generates light from an aqueous electrolyte solution by receiving light, an inorganic semiconductor layer having a pn junction, a mixed layer formed on the inorganic semiconductor layer, The mixed layer provides a hydrogen generating electrode characterized by having fine particles having an electron transporting capability and a hydrogen generation catalyst.

It is preferable that a hydrogen generation catalyst is supported on the surface of the fine particles. The inorganic semiconductor layer preferably contains any of a CIGS compound semiconductor, a CZTS compound semiconductor, and a CGSe compound semiconductor.
For example, the fine particles having an electron transport ability are composed of TiO ₂ . The mixed layer preferably has a thickness of less than 300 nm. For example, the hydrogen generation catalyst is particulate. The hydrogen generation catalyst is preferably composed of platinum.

According to the present invention, the photocurrent density corresponding to the amount of hydrogen generated per unit area can be increased on the high potential side.

(A) is typical sectional drawing which shows the structure of the hydrogen generating electrode of embodiment of this invention, (b) is a schematic diagram which expands and shows the mixed layer of the hydrogen generating electrode of embodiment of this invention. It is typical sectional drawing which shows the structure of the artificial photosynthesis module using the hydrogen generating electrode of embodiment of this invention. (A) is typical sectional drawing which shows the structure of the hydrogen generating electrode of the comparative example 1 and the comparative example 4, (b) is schematic which shows the structure of the hydrogen generating electrode of the comparative example 2, the comparative example 3, and the comparative example 5. FIG.

Hereinafter, the hydrogen generating electrode of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings. The present invention is not limited to the embodiments of the hydrogen generating electrode described below.
In the following, “to” indicating a numerical range includes numerical values written on both sides. For example, when ε is a numerical value α to a numerical value β, the range of ε is a range including the numerical value α and the numerical value β, and expressed by mathematical symbols, α ≦ ε ≦ β.

FIG. 1A is a schematic cross-sectional view showing a configuration of a hydrogen generating electrode according to an embodiment of the present invention, and FIG. 1B is a schematic diagram showing an enlarged mixed layer of the hydrogen generating electrode according to the embodiment of the present invention. FIG.
The hydrogen generating electrode 10 receives light and generates hydrogen from the electrolyte aqueous solution. The hydrogen generating electrode 10 is formed on the insulating substrate 12 and has a conductive layer 14, an inorganic semiconductor layer 16, and a mixed layer 18.

The insulating substrate 12 supports the hydrogen generating electrode 10 and is made of an electrically insulating material. The insulating substrate 12 is not particularly limited, and for example, a soda lime glass substrate (hereinafter referred to as an SLG substrate) or a ceramic substrate can be used. In addition, the insulating substrate 12 may be a substrate in which an insulating layer is formed on a metal substrate. Here, as the metal substrate, a metal substrate such as an Al substrate or a SUS substrate, or a composite metal substrate such as a composite Al substrate made of a composite material of Al and another metal such as SUS can be used. The composite metal substrate is also a kind of metal substrate, and the metal substrate and the composite metal substrate are collectively referred to simply as a metal substrate. Furthermore, as the insulating substrate 12, a metal substrate with an insulating film having an insulating layer formed by anodizing the surface of an Al substrate or the like can also be used. The insulating substrate 12 may or may not be flexible. In addition to the above, for example, a glass plate such as high strain point glass and non-alkali glass, or a polyimide material can be used as the insulating substrate 12.

The thickness of the insulating substrate 12 is not particularly limited, and may be, for example, about 20 to 20000 μm, preferably 100 to 10,000 μm, and more preferably 1000 to 5000 μm. When the p-type semiconductor layer 20 includes a CIGS (Cu (In _1-x Ga _x ) Se ₂ ) compound semiconductor, alkali ions (for example, sodium (Na) ions are formed on the insulating substrate 12 side. : Na ⁺ ) improves the photoelectric conversion efficiency. Therefore, it is preferable to provide an alkali supply layer for supplying alkali ions on the surface 12 a of the insulating substrate 12. In the case of the SLG substrate, the alkali supply layer is not necessary.

The conductive layer 14 is formed on the surface 12 a of the insulating substrate 12 and applies a voltage to the inorganic semiconductor layer 16. Although it will not specifically limit if the conductive layer 14 has electroconductivity, For example, it is comprised by metals, such as Mo, Cr, and W, or what combined these. The conductive layer 14 may have a single layer structure or a laminated structure such as a two-layer structure. Among these, the conductive layer 14 is preferably composed of Mo. The thickness of the conductive layer 14 is generally about 800 nm, but the thickness of the conductive layer 14 is preferably 400 nm to 1 μm.

The inorganic semiconductor layer 16 generates an electromotive force. The inorganic semiconductor layer 16 includes a p-type semiconductor layer 20 and an n-type semiconductor layer 22, and the p-type semiconductor layer 20 forms a pn junction at the interface with the n-type semiconductor layer 22. A p-type semiconductor layer 20 is formed on the conductive layer 14.
The inorganic semiconductor layer 16 is a layer that absorbs light that has passed through the n-type semiconductor layer 22 and generates holes on the p side and electrons on the n side. The p-type semiconductor layer 20 has a photoelectric conversion function. In the p-type semiconductor layer 20, holes generated at the pn junction are moved from the p-type semiconductor layer 20 to the conductive layer 14 side, and electrons generated at the pn junction are moved from the n-type semiconductor layer 22 to the transparent electrode layer 50 side. . The thickness of the p-type semiconductor layer 20 is preferably 0.5 to 3.0 μm, and particularly preferably 1.0 to 2.0 μm.

The p-type semiconductor layer 20 is preferably composed of, for example, a CIGS compound semiconductor having a chalcopyrite crystal structure or a CZTS compound semiconductor such as Cu ₂ ZnSnS ₄ . The CIGS compound semiconductor layer may be made of not only Cu (In, Ga) Se ₂ (CIGS) but also CuInSe ₂ (CIS), CuGaSe ₂ (CGSe), or the like. The p-type semiconductor layer 20 may be composed of a CGSe compound semiconductor.
As CIGS layer forming methods, 1) multi-source vapor deposition, 2) selenization, 3) sputtering, 4) hybrid sputtering, and 5) mechanochemical process are known.
Examples of other CIGS layer forming methods include screen printing, proximity sublimation, MOCVD (Metal Organic Chemical Vapor Deposition), and spray (wet film formation). For example, a fine particle film containing a group 11 element, a group 13 element, and a group 16 element is formed on a substrate by a screen printing method (wet film forming method) or a spray method (wet film forming method), and a thermal decomposition treatment ( At this time, a crystal having a desired composition can be obtained by performing a thermal decomposition treatment in a group 16 element atmosphere) (JP-A-9-74065, JP-A-9-74213, etc.).

The n-type semiconductor layer 22 forms a pn junction at the interface with the p-type semiconductor layer 20 as described above. The n-type semiconductor layer 22 transmits light so that incident light reaches the p-type semiconductor layer 20.
The n-type semiconductor layer 22 includes, for example, 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), and other metal sulfides containing at least one metal element selected from the group consisting of Cd, Zn, Sn, and In Is formed. The film thickness of the n-type semiconductor layer 22 is preferably 10 nm to 2 μm, more preferably 15 to 200 nm. The n-type semiconductor layer 22 is formed by, for example, a chemical bath deposition method (hereinafter referred to as CBD method).

In the hydrogen generating electrode 10 shown in FIG. 1A, a mixed layer 18 is formed on the inorganic semiconductor layer 16, that is, on a surface 22a of an n-type semiconductor layer 22 described later.
As shown in FIG. 1B, the mixed layer 18 includes fine particles 24 having an electron transport ability and hydrogen generation catalyst particles 26. In the mixed layer 18, the fine particles 24 and the hydrogen generation catalyst particles 26 are mixed, but the fine particles 24 are bonded and stacked, and the hydrogen generation catalyst particles 26 are supported on the surfaces of the fine particles 24. The hydrogen generation catalyst particles 26 are preferably carried on the interface between the n-type semiconductor layer 22 and the mixed layer 18, the inside of the mixed layer 18, and the surface of the fine particles 24. Thereby, the area which the hydrogen production | generation catalyst particle 26 contacts with water can be increased, and the generation amount of hydrogen can be increased.

Alternatively, the mixed layer 18 may be formed using core-shell particles having a core of fine particles 24 and a shell of hydrogen-producing catalyst particles 26. Further, a hydrogen generation catalyst may be supported in the form of a film on the surface of the laminate of the fine particles 24. Further, in the hydrogen generating electrode 10 shown in FIG. 1 (a), the hydrogen generating catalyst particles 26 are supported on the surfaces of the fine particles 24. However, the hydrogen generating catalyst is not limited to the particulate form, and is in the form of a piece. Alternatively, a membrane-like hydrogen generation catalyst may be supported on the surface of the fine particles 24.
The thickness t of the mixed layer 18 is preferably 300 nm or less. If it is 300 nm or less, the photocurrent density corresponding to the amount of hydrogen generated per unit area can be reliably increased.

The fine particles 24 of the mixed layer 18 have an electron transport capability and do not change in quality when immersed in an aqueous electrolyte solution. As will be described later, the fine particles 24 can move carriers between the fine particles 24. In this case, electrons can move, the surface area increases, and when the hydrogen generation catalyst particles 26 are supported, water is added. The number of reaction sites for reduction is not particularly limited as long as the conditions satisfy that the number of reaction sites increases and the electron transport ability is satisfied. For example, the fine particles 24 are made of, for example, TiO ₂ . The size of the fine particles 24 is, for example, about 5 to 10 nm.

The hydrogen generation catalyst particles 26 of the mixed layer 18 include, for example, simple substances composed of Pt, Pd, Ni, Au, Ag, Ru, Cu, Co, Rh, Ir, Mn, etc. oxides, for example, can be formed of NiOx and RuO _2. The size of the hydrogen generation catalyst particles 26 is not particularly limited, but is about 0.5 nm to 5 nm, for example, because the hydrogen generation catalyst particles 26 attach to the surface of the fine particles 24.
In addition, the loading method of the hydrogen production | generation catalyst particle 26 is not specifically limited, For example, a photo-deposition method and a sputtering method can be used.

In the mixed layer 18 shown in FIG. 1B, for example, a dispersion liquid in which the fine particles 24 are dispersed is applied to the surface 22 a of the n-type semiconductor layer 22. Then, it is dried. Thereby, a layer composed of the fine particles 24 is formed. Then, for example, it is immersed in an aqueous solution containing chloroplatinic acid, and Pt particles (platinum particles) are supported on the surfaces of the fine particles 24 as the hydrogen generation catalyst particles 26 by a photo-deposition method. In this way, the mixed layer 18 can be formed.
The mixed layer 18 can be formed using, for example, particles in which the hydrogen generation catalyst particles 26 are previously supported on the surfaces of the fine particles 24. Moreover, the mixed layer 18 can also be formed using a sol-gel method.

In the hydrogen generating electrode 10, by providing the above-described mixed layer 18 on the inorganic semiconductor layer 16 having a pn junction, the photocurrent density can be increased on the high potential side, thereby increasing the amount of hydrogen generation. Can do.
In the present invention, the mixed layer 18 provided on the inorganic semiconductor layer 16 having a pn junction is not a dense film structure formed by, for example, sputtering, but a laminated structure in which fine particles 24 having an electron transporting ability are bonded to each other. The surface area of the fine particles 24 is increased by supporting the hydrogen-producing catalyst particles 26 on the surface. As a result, the area where the hydrogen generation catalyst particles 26 supported on the fine particles 24 are in contact with the electrolytic aqueous solution containing water is increased as compared with the case of the above-described dense film configuration and the structure without the electron transport layer. It is estimated that the photocurrent density corresponding to the amount of hydrogen generated per unit area can be increased on the high potential side.
In addition, when satisfying the condition of water decomposition starting voltage of electrolytic aqueous solution + 0.6V> photovoltaic power between hydrogen generation region and oxygen generating region> water decomposition starting voltage of electrolytic aqueous solution, The effect of increasing the photocurrent density corresponding to the amount of hydrogen generated is further increased.

The hydrogen generation electrode 10 described above can be used in an artificial photosynthesis module that decomposes an electrolytic aqueous solution into hydrogen and oxygen by light.
Hereinafter, an artificial photosynthesis module using the hydrogen generation electrode 10 shown in FIGS. 1A and 1B will be described.
FIG. 2 is a schematic cross-sectional view showing the configuration of the artificial photosynthesis module using the hydrogen generating electrode of the embodiment of the present invention.
In the artificial photosynthesis module 30 shown in FIG. 2, the same components as those of the hydrogen generating electrode 10 shown in FIGS. 1A and 1B are denoted by the same reference numerals, and detailed description thereof is omitted.

In the artificial photosynthesis module 30, a hydrogen electrolysis chamber 36 and an oxygen electrolysis chamber 38 are arranged side by side with a partition wall 34 in a container 32. An electrolytic aqueous solution AQ is supplied into the container 32. In order to supply the electrolytic aqueous solution AQ into the container 32, piping, a pump, and the like are necessary, but these are not shown.
The container 32 constitutes the outer shell of the artificial photosynthesis module 30, and if the electrolytic aqueous solution AQ can be held inside without leaking and the light L from the outside can be transmitted inside, the structure Is not particularly limited.

Here, the electrolytic aqueous solution AQ is, for example, a liquid mainly composed of H ₂ O, and may be distilled water, or an aqueous solution containing water as a solvent and containing a solute. In the case of water, for example, it may be an electrolytic solution that is an aqueous solution containing an electrolyte, or may be cooling water used in a cooling tower or the like. In the case of the electrolytic solution, for example, an aqueous solution containing an electrolyte, such as a strong alkali (KOH), a polymer electrolyte (Nafion (registered trademark)), an electrolytic solution containing 0.1 M H ₂ SO ₄ , 0.1 M sodium sulfate. Electrolytic solution, 0.1M potassium phosphate buffer, etc.

The partition wall 34 is for isolating the hydrogen gas generated in the hydrogen electrolysis chamber 36 and the oxygen gas generated in the oxygen electrolysis chamber 38 so as not to be mixed. Therefore, the configuration of the partition wall 34 is not particularly limited as long as it has the above-described isolation function.
The partition wall 34 is composed of hydroxide ions (pH is increased) increased due to generation of hydrogen in the hydrogen electrolysis chamber 36 and hydrogen ions (pH is decreased) increased due to oxygen generation in the oxygen electrolysis chamber 38. The container 32 may be separated from the hydrogen electrolysis chamber 36 and the oxygen electrolysis chamber 38 in order to allow hydroxide ions and hydrogen ions to pass therethrough. In this case, the partition wall 34 is made of, for example, a material having ion permeability and gas non-permeability. Specifically, for example, an ion exchange membrane, a ceramic filter, porous glass, or the like is used. The thickness of the partition wall 34 is not particularly limited, and is preferably 10 to 1000 μm.

In the artificial photosynthesis module 30, for example, two photoelectric conversion units 40, a hydrogen gas generation unit 42, and an oxygen gas generation unit 44 are formed on the planar insulating substrate 12, and these are electrically connected in the direction M. Connected in series.
The photoelectric conversion unit 40 and the hydrogen gas generation unit 42 are disposed in the hydrogen electrolysis chamber 36, and the photoelectric conversion unit 40 and the oxygen gas generation unit 44 are disposed in the oxygen electrolysis chamber 38.

The photoelectric conversion unit 40 receives light and generates power to supply power for generating hydrogen gas in the hydrogen gas generation unit 42 and power for generating oxygen gas in the oxygen gas generation unit 44 It is.
The photoelectric conversion unit 40 is configured by laminating a conductive layer 14, a p-type semiconductor layer 20, an n-type semiconductor layer 22, a transparent electrode layer 50, and a protective film 52 in order from the insulating substrate 12 side, and is used for a solar cell. It has the same structure as the photoelectric conversion element.
In the photoelectric conversion unit 40, the p-type semiconductor layer 20 and the n-type semiconductor layer 22 constitute the inorganic semiconductor layer 16 as described above, and a pn junction is formed at the interface between the p-type semiconductor layer 20 and the n-type semiconductor layer 22. Yes.

The inorganic semiconductor layer 16 is a layer that absorbs incident light L and generates holes on the p side and electrons on the n side. The p-type semiconductor layer 20 has a photoelectric conversion function. In the p-type semiconductor layer 20, holes generated at the pn junction are moved from the p-type semiconductor layer 20 to the conductive layer 14 side, and electrons generated at the pn junction are moved from the n-type semiconductor layer 22 to the transparent electrode layer 50 side. . The thickness of the p-type semiconductor layer 20 is preferably 0.5 to 3.0 μm, and particularly preferably 1.0 to 2.0 μm.

The two photoelectric conversion units 40 are connected in series in the direction M. However, the number is not limited as long as an electromotive force capable of generating hydrogen gas and oxygen gas can be obtained. Two or more may be sufficient. Since a higher voltage can be obtained by connecting a plurality of photoelectric conversion units in series, it is preferable to connect the plurality of photoelectric conversion units in series.
Between the photoelectric conversion units 40, an opening groove P2 that penetrates the n-type semiconductor layer 22 and the p-type semiconductor layer 20 and reaches the surface of the conductive layer 14 is formed at a position different from the formation position of the separation groove P1 in the direction M. A partition wall 34 is provided in the opening groove P2.

In the artificial photosynthesis module 30, when the light L is incident on the photoelectric conversion unit 40 from the protective film 52 side, the light L passes through the protective film 52, each transparent electrode layer 50, and each n-type semiconductor layer 22, An electromotive force is generated in each p-type semiconductor layer 20, and for example, a current (movement of holes) from the transparent electrode layer 50 toward the conductive layer 14 is generated. Therefore, in the artificial photosynthesis module 30, the hydrogen gas generation unit 42 becomes a negative electrode (electrolysis cathode), and the oxygen gas generation unit 44 becomes a positive electrode (electrolysis anode).
Note that the type (polarity) of the produced gas in the artificial photosynthesis module 30 varies as appropriate according to the configuration of the photoelectric conversion unit, the configuration of the artificial photosynthesis module 30, and the like.

The protective film 52 is insoluble in a weakly acidic solution and a weakly alkaline solution, and also has light transmission properties, water shielding properties, and insulating properties.
Specifically, the protective film 52 has translucency and protects the photoelectric conversion unit 40. Specifically, the protective film 52 is a portion other than the hydrogen gas generation region in the hydrogen electrolysis chamber 36, and the oxygen gas in the oxygen electrolysis chamber 38. It is provided so as to cover a portion other than the generation region. Specifically, the protective film 52 covers the entire surface of the transparent electrode layer 50 and the side surface of the hydrogen generation electrode 10.
Protective film 52, for _example, a _{_{_{_{SiO 2, SnO 2, Nb 2}}}} O 5, Ta 2 O 5, Al 2 O 3 and _Ga 2 _{O 3} or the like. The thickness of the protective film 52 is not particularly limited, and is preferably 100 to 1000 nm.

The method for forming the protective film 52 is not particularly limited, and can be formed by RF (high frequency) sputtering, DC (direct current) reactive sputtering, MOCVD, or the like.
The protective film 52 can be made of, for example, an insulating epoxy resin, an insulating silicone resin, an insulating fluororesin, or the like. In this case, the thickness of the protective film 52 is not particularly limited and is preferably 2 to 1000 μm.

The hydrogen gas generation unit 42 is basically composed of the hydrogen generation electrode 10 described above, and its side surface is covered with a protective film 52. In the hydrogen gas generator 42, the functional layer 19 is formed on the surface 22 a of the n-type semiconductor layer 22, and the mixed layer 18 is formed on the surface 19 a of the functional layer 19. For this reason, in the hydrogen gas generation unit 42, the detailed description of the configuration of the hydrogen generation electrode 10 is omitted. The hydrogen generating electrode 10 is immersed in the electrolytic aqueous solution AQ and is in contact with the electrolytic aqueous solution AQ. The protective film 52 on the side surface of the hydrogen generation electrode 10 prevents a short circuit due to contact with the electrolytic aqueous solution AQ.
In the mixed layer 18, electrons are supplied to hydrogen ions (protons) H ⁺ ionized from water molecules to generate hydrogen molecules, that is, hydrogen gas (2H ⁺ + 2e ⁻ −> H ₂ ). In the hydrogen gas generator 42, the mixed layer 18 constitutes a hydrogen gas generation region.

The functional layer 19 prevents moisture from entering the inorganic semiconductor layer 16 and suppresses bubble formation inside the inorganic semiconductor layer 16. The functional layer 19 is required to have transparency, water resistance, water shielding, and conductivity. The functional layer 19 improves the durability of the hydrogen generating electrode 10.

The functional layer 19 is preferably made of, for example, a metal or a conductive oxide (overvoltage is 0.5 V or less) or a composite thereof. More specifically, the functional layer 19 is made of transparent conductive material such as ITO (Indium Tin Oxide), ZnO doped with Al, B, Ga, and In, or IMO (In ₂ O ₃ doped with Mo). A membrane can be used. The functional layer 19 may have a single layer structure or a laminated structure such as a two-layer structure. Further, the thickness of the functional layer 19 is not particularly limited, and is preferably 10 to 1000 nm, and more preferably 50 to 500 nm.
The method for forming the functional layer 19 is not particularly limited, and can be formed by a vapor deposition method such as an electron beam evaporation method, a sputtering method, a CVD method, or a coating method. The functional layer 19 is not necessarily provided also in the hydrogen gas generation unit 42.

The oxygen gas generation unit 44 includes a region 60 that is an extension of the conductive layer 14 of the right photoelectric conversion unit 40, and this region 60 serves as an oxygen gas generation region.
Specifically, the region 60 of the extended portion of the conductive layer 14 of the photoelectric conversion unit 40 takes out electrons from the hydroxide ions OH ⁻ ionized from the water molecules and generates oxygen molecules, that is, oxygen gas (2OH ⁻ −). _{_{> H 2 O + O 2/}} 2 + 2e -) and oxygen gas generator 44, the surface 60a serves as a gas generation region.
A promoter (not shown) for generating oxygen may be formed on the surface 60a of the region 60 of the conductive layer 14, and in this case, the promoter is formed in an island shape so as to be scattered, for example. Also good.
The co-catalyst for oxygen generation is composed of, for example, IrO ₂ , CoO _x or the like. Further, the size of the oxygen-generating cocatalyst is not particularly limited, and is preferably 0.5 nm to 1 μm. In addition, the formation method of the co-catalyst for oxygen generation is not particularly limited, and can be formed by a coating baking method, a dipping method, an impregnation method, a sputtering method, a vapor deposition method, or the like.

As described above, the photoelectric conversion unit 40 functions as a photoelectric conversion element, and includes the p-type semiconductor layer 20 and the n-type semiconductor layer 22. Since the p-type semiconductor layer 20 and the n-type semiconductor layer 22 are as described above, detailed description thereof is omitted.
Note that the absorption wavelength of the inorganic semiconductor forming the p-type semiconductor layer 20 is not particularly limited as long as it is a wavelength region where photoelectric conversion is possible. As an absorption wavelength, it is only necessary to include a wavelength region such as sunlight, in particular, a visible wavelength region to an infrared wavelength region, but the absorption wavelength end includes 800 nm or more, that is, the infrared wavelength region. Is preferred. The reason is that as much solar energy as possible can be used. On the other hand, the longer absorption wavelength end corresponds to the reduction of the band gap, which can be expected to reduce the electromotive force for assisting water decomposition. Therefore, it can be expected that the number of connections for connecting the photoelectric conversion units 40 in series is increased, so that the longer the absorption edge, the better.

The transparent electrode layer 50 has translucency, takes light into the p-type semiconductor layer 20, and pairs with the conductive layer 14 to move holes and electrons generated in the p-type semiconductor layer 20 ( It functions as an electrode through which current flows, and functions as a transparent conductive film for connecting two photoelectric conversion units 40 in series.
The transparent electrode layer 50 is made of, for example, ZnO doped with Al, B, Ga, In or the like, or ITO. The transparent electrode layer 50 may have a single layer structure or a laminated structure such as a two-layer structure. The thickness of the transparent electrode is not particularly limited and is preferably 0.3 to 1 μm.
In addition, the formation method of a transparent electrode is not specifically limited, It can form by vapor phase film-forming methods, such as an electron beam vapor deposition method, a sputtering method, and CVD method, or the apply | coating method.

Next, a method for manufacturing the artificial photosynthesis module 30 will be described.
In addition, the manufacturing method of the artificial photosynthesis module 30 is not limited to the manufacturing method shown below.
First, for example, a soda lime glass substrate to be the insulating substrate 12 is prepared.
Next, for example, a Mo film or the like that becomes the conductive layer 14 is formed on the surface of the insulating substrate 12 by sputtering.
Next, for example, by using a laser scribing method, a predetermined position of the Mo film is scribed to form a separation groove P <b> 1 extending in the width direction of the insulating substrate 12. Thereby, the conductive layers 14 separated from each other by the separation groove P1 are formed.

Next, for example, a CIGS film is formed as the p-type semiconductor layer 20 so as to cover the conductive layer 14 and fill the isolation trench P1. This CIGS film is formed by any of the film forming methods described above.
Next, for example, a CdS layer to be the n-type semiconductor layer 22 is formed on the p-type semiconductor layer 20 by the CBD method.
Next, in the direction M, it extends in the width direction of the insulating substrate 12 at a position different from the formation position of the separation groove P1, and reaches the surface 14a of the conductive layer 14 from the n-type semiconductor layer 22 through the p-type semiconductor layer 20. Two opening grooves P2 are formed. In this case, a laser scribe method or a mechanical scribe method can be used as the scribe method.

Next, for example, Al, B, Ga, Sb, or the like that becomes the transparent electrode layer 50 is added so as to extend in the width direction of the insulating substrate 12 and fill the opening groove P2 on the n-type semiconductor layer 22. A ZnO: Al layer is formed by sputtering or coating.
Next, the ZnO: Al layer in the opening groove P2 is removed so as to leave a part, and two slightly narrow opening grooves P2 reaching the surface of the conductive layer 14 are formed again. Thereby, three laminated bodies (not shown) are formed. One becomes the hydrogen generating electrode 10 and the remaining two become the photoelectric conversion unit 40. As the scribe method, a laser scribe method or a mechanical scribe method can be used.

Next, an SiO ₂ film, for example, serving as the protective film 52 is formed by RF sputtering on the outer surface and side surfaces of the multilayer body and the surface of the conductive layer 14 at the bottom surface of the two opening grooves P2.
Next, a groove is formed again at a position corresponding to the opening groove P2 between the two laminated bodies, and a partition wall 34 is provided in the groove.
Next, the ZnO: Al layer of the photoelectric conversion unit 40 is peeled off using a laser scribe method or a mechanical scribe method, and an amorphous ITO layer, for example, is formed as the functional layer 19 on the exposed surface 22a of the n-type semiconductor layer 22. It is formed by a sputtering method using a patterning mask.
Next, for example, a dispersion liquid in which the fine particles 24 are dispersed is applied to the surface 22 a of the n-type semiconductor layer 22. Then, it is dried. Thereby, a layer composed of the fine particles 24 is formed. Then, a mask other than the formation layer of the fine particles 24 is used as a mask, and immersed in an aqueous solution containing, for example, chloroplatinic acid, and the hydrogen generating catalyst particles 26 are supported on the surfaces of the fine particles 24 by a photo-deposition method. Thereby, the hydrogen generation electrode 10 is formed, and the hydrogen gas generation part 42 is formed.

Next, the deposit on the area | region 60 of the extension part of the conductive layer 14 of the photoelectric conversion unit 40 is removed using a laser scribe method or a mechanical scribe method, and the area | region 60 is exposed. Thereby, the oxygen gas production | generation part 44 is formed.
A container 32 having substantially the same size as the insulating substrate 12 is prepared, and the insulating substrate 12 on which the photoelectric conversion unit 40, the hydrogen gas generation unit 42, and the oxygen gas generation unit 44 are formed is stored in the container 32. As a result, a hydrogen electrolysis chamber 36 and an oxygen electrolysis chamber 38 are formed by the partition wall 34. In this way, the artificial photosynthesis module 30 can be manufactured.

Also in the artificial photosynthesis module 30, like the hydrogen generation electrode 10 described above, the hydrogen gas generation unit 42 has a high photocurrent density corresponding to the amount of hydrogen generated per unit area on the high potential side. Thereby, the artificial photosynthesis module 30 with excellent performance can be obtained.

The present invention is basically configured as described above. The hydrogen generating electrode of the present invention has been described in detail above. However, the present invention is not limited to the above embodiment, and various improvements or modifications may be made without departing from the spirit of the present invention. is there.

Hereinafter, the effect of the hydrogen generating electrode of the present invention will be described in detail.
In this example, in order to confirm the effect of the present invention, hydrogen generating electrodes of Examples 1 to 4 and Comparative Examples 1 to 5 shown below were produced. Of the configurations of the hydrogen generating electrodes of Examples 1 to 4 and Comparative Examples 1 to 5, the composition of the inorganic semiconductor layer, the thickness of the mixed layer, and the thickness of the TiO ₂ layer are shown in Table 1 below. In Table 1 below, “-” shown in the column of the thickness of the mixed layer and the column of the thickness of the TiO ₂ layer indicates that there is no layer.
The hydrogen generation electrodes of Examples 1 to 4 and Comparative Examples 1 to 5 were subjected to IE (current-voltage) measurement, and the reduction current density (relative value) was obtained. The results are shown in Table 1 below. It is known that the reduction current density (relative value) is a parameter proportional to the amount of hydrogen produced.
In the IE measurement, a hydrogen generating electrode is used as a working electrode, Ag / AgCl is used as a reference electrode, Pt wire is used as a counter electrode, and these are immersed in an aqueous solution of 0.5M Na ₂ SO _{4 and} correspond to AM1.5G. The simulated sunlight was irradiated.
Hereinafter, the hydrogen generating electrodes of Examples 1 to 4 and Comparative Examples 1 to 5 will be described.

(Example 1)
The hydrogen generation electrode of Example 1 has the same configuration as the hydrogen generation electrode 10 shown in FIG.
In the hydrogen generating electrode of Example 1, first, Mo was formed to a thickness of about 500 nm on a soda lime glass substrate by sputtering, and a Mo electrode was formed as the conductive layer 14. Next, a CuGaSe ₂ (CGSe) thin film was formed as the p-type semiconductor layer 20 on the Mo electrode. In this CuGaSe ₂ (CGSe) thin film, granular raw materials of high-purity copper (purity 99.9999%), high-purity Ga (purity 99.999%), and high-purity Se (purity 99.999%) were used as an evaporation source. . A chromel-alumel thermocouple was used as a substrate temperature monitor. After the main vacuum chamber is evacuated to 10 ⁻⁸ Torr (1.3 × 10 ⁻⁵ Pa), the deposition rate from each evaporation source is controlled, and the film thickness is about 100 ° C. under the film forming conditions with the maximum substrate temperature of 530 ° C. A 1.2 μm CGSe thin film was formed.
Subsequently, a CdS thin film having a thickness of about 90 nm was formed by a solution growth method. This CdS thin film is an n-type semiconductor layer 22 that functions as a buffer layer.
Next, a solaronix TiO ₂ nanoparticle dispersion (HT-L / SC) is applied to the surface 22a of the n-type semiconductor layer 22 by spin coating, and dried at a temperature of 120 ° C. for 30 minutes. 10 nm TiO ₂ nanoparticles were laminated to a thickness of 150 nm. On the other hand, it was immersed in an aqueous solution containing chloroplatinic acid, and the Pt promoter was supported on the surfaces of the fine particles 24 as the hydrogen generation catalyst particles 26 by the photo-deposition method. In this way, a mixed layer 18 having a thickness of 150 nm was formed.

(Example 2)
The hydrogen generation electrode of Example 2 has the same configuration as the hydrogen generation electrode of Example 1, that is, the same configuration as the hydrogen generation electrode 10 shown in FIG. Example 2 is different from Example 1 in that the p-type semiconductor layer 20 is replaced with a CuGaSe ₂ (CGSe) thin film, except that a CIGS thin film is formed as described later. Since it is the same as an electrode, the detailed description is abbreviate | omitted.
In Example 2, high-purity copper (Cu) and indium (In) (purity 99.9999%), high-purity gallium (Ga) (purity 99.999%), high-purity selenium (Se) ( A granular raw material having a purity of 99.999% was used. A chromel-alumel thermocouple was used as a substrate temperature monitor. After the main vacuum chamber was evacuated to 10 ⁻⁶ Torr (1.3 × 10 ⁻³ Pa), the deposition rate from each evaporation source was controlled, and the film thickness was about 530 ° C. under the film forming conditions. A 1.2 μm CIGS thin film was formed.

(Example 3)
The hydrogen generation electrode of Example 3 has the same configuration as the hydrogen generation electrode of Example 1, that is, the same configuration as the hydrogen generation electrode 10 shown in FIG. Since Example 3 is the same as the hydrogen generation electrode of Example 1 except that a mixed layer 18 having a thickness of 300 nm is formed as compared with Example 1, detailed description thereof is omitted.
Example 4
The hydrogen generation electrode of Example 4 has the same configuration as the hydrogen generation electrode of Example 1, that is, the same configuration as the hydrogen generation electrode 10 shown in FIG. Since Example 3 is the same as the hydrogen generation electrode of Example 1 except that a mixed layer 18 having a thickness of 50 nm is formed as compared with Example 1, detailed description thereof is omitted.

(Comparative Example 1)
The configuration of the hydrogen generating electrode of Comparative Example 1 is the same as that of the hydrogen generating electrode 100 shown in FIG. In the hydrogen generating electrode 100, the same components as those of the hydrogen generating electrode 10 shown in FIG. 1A are denoted by the same reference numerals, and detailed description thereof is omitted. The comparative example 1 is different in that the mixed layer 18 is not provided and the hydrogen generation catalyst particles 102 are formed on the surface 22a of the n-type semiconductor layer 22, and the other configuration is the hydrogen generating electrode 10 shown in FIG. Is the same.
Similarly to Example 1, the hydrogen generation catalyst particles 102 are formed by dipping in an aqueous solution containing chloroplatinic acid and by a photo-deposition method.

(Comparative Example 2)
The configuration of the hydrogen generating electrode of Comparative Example 2 is the same as that of the hydrogen generating electrode 100a shown in FIG. In the hydrogen generation electrode 100a, the same components as those of the hydrogen generation electrode 10 shown in FIG. 1A are denoted by the same reference numerals, and detailed description thereof is omitted. The comparative example 2 is different in that the TiO ₂ layer 104 is formed on the surface 22a of the n-type semiconductor layer 22 and the hydrogen generation catalyst particles 102 are formed on the surface of the TiO ₂ layer. This is the same as the hydrogen generating electrode 10 shown in FIG.
The TiO ₂ layer 104 is formed by sputtering to a thickness of 5 nm. Similarly to Example 1, the hydrogen generation catalyst particles 102 are formed by dipping in an aqueous solution containing chloroplatinic acid and by a photo-deposition method.

(Comparative Example 3)
The configuration of the hydrogen generating electrode of Comparative Example 3 is the same as that of the hydrogen generating electrode 100a shown in FIG. In the hydrogen generation electrode 100a, the same components as those of the hydrogen generation electrode 10 shown in FIG. 1A are denoted by the same reference numerals, and detailed description thereof is omitted. The comparative example 2 is different in that the TiO ₂ layer 104 is formed on the surface 22a of the n-type semiconductor layer 22 and the hydrogen generation catalyst particles 102 are formed on the surface of the TiO ₂ layer. This is the same as the hydrogen generating electrode 10 shown in FIG.
The TiO ₂ layer 104 is formed to a thickness of 10 nm by sputtering. Similarly to Example 1, the hydrogen generation catalyst particles 102 are formed by dipping in an aqueous solution containing chloroplatinic acid and by a photo-deposition method.

(Comparative Example 4)
The configuration of the hydrogen generating electrode of Comparative Example 4 is the same as that of the hydrogen generating electrode 100 shown in FIG. In the hydrogen generating electrode 100, the same components as those of the hydrogen generating electrode 10 shown in FIG. 1A are denoted by the same reference numerals, and detailed description thereof is omitted. In Comparative Example 4, the mixed layer 18 is not provided, and the hydrogen generation catalyst particles 102 are formed on the surface 22a of the n-type semiconductor layer 22. The p-type semiconductor layer 20 is a CIGS thin film instead of the CuGaSe ₂ (CGSe) thin film. The other structure is the same as that of the hydrogen generating electrode 10 shown in FIG.
The CIGS thin film was produced in the same manner as the CIGS thin film of Example 2 described above. Similarly to Example 1, the hydrogen generation catalyst particles 102 are formed by dipping in an aqueous solution containing chloroplatinic acid and by a photo-deposition method.

(Comparative Example 5)
The configuration of the hydrogen generating electrode of Comparative Example 5 is the same as that of the hydrogen generating electrode 100a shown in FIG. In the hydrogen generation electrode 100a, the same components as those of the hydrogen generation electrode 10 shown in FIG. 1A are denoted by the same reference numerals, and detailed description thereof is omitted. In Comparative Example 5, a CIGS thin film is formed as the p-type semiconductor layer 20 instead of the CuGaSe ₂ (CGSe) thin film, and the TiO ₂ layer 104 is formed on the surface 22a of the n-type semiconductor layer 22. The difference is that the hydrogen generation catalyst particles 102 are formed on the surface of the TiO ₂ layer, and the other configuration is the same as that of the hydrogen generation electrode 10 shown in FIG.
The CIGS thin film was produced in the same manner as the CIGS thin film of Example 2 described above. The TiO ₂ layer 104 is formed by sputtering to a thickness of 5 nm. Similarly to Example 1, the hydrogen generation catalyst particles 102 are formed by dipping in an aqueous solution containing chloroplatinic acid and by a photo-deposition method.

As shown in Table 1, all of Examples 1 to 4 have a high reduction current density (relative value) proportional to the amount of hydrogen generation, regardless of the composition of the p-type semiconductor layer.
On the other hand, all of Comparative Examples 1 to 4 have a low reduction current density (relative value). In Comparative Examples 2, 3, and 5, a TiO ₂ layer is formed. However, since the formation method is a sputtering method, the reduction current density (relative to Comparative Example 1 and Comparative Example 4 in which no TiO ₂ layer is provided). Value) is high, but lower than Examples 1-4.

10, 100, 100a Hydrogen generating electrode 12 Insulating substrate 14 Conductive layer 16 Inorganic semiconductor layer 18 Promoter 20 p-type semiconductor layer 22 n-type semiconductor layer 30 Artificial photosynthetic module 32 Container 34 Partition 36 Hydrogen electrolysis chamber 38 Oxygen electrolysis chamber 40 Photoelectric conversion unit 42 Hydrogen gas generator 44 Oxygen gas generator

Claims

A hydrogen generating electrode that receives light to generate hydrogen from an aqueous electrolyte solution,
an inorganic semiconductor layer having a pn junction;
A mixed layer formed on the inorganic semiconductor layer,
The mixed layer includes a fine particle having an electron transporting ability and a hydrogen generation catalyst.
The hydrogen generating electrode according to claim 1, wherein the hydrogen generating catalyst is supported on the surface of the fine particles.
The hydrogen generating electrode according to claim 1, wherein the inorganic semiconductor layer includes any one of a CIGS compound semiconductor, a CZTS compound semiconductor, and a CGSe compound semiconductor.
The hydrogen generating electrode according to any one of claims 1 to 3, wherein the fine particles having an electron transporting capability are composed of TiO 2 .
The hydrogen generating electrode according to any one of claims 1 to 4, wherein the mixed layer has a thickness of less than 300 nm.
The hydrogen generating electrode according to any one of claims 1 to 5, wherein the hydrogen generating catalyst is in the form of particles.
The hydrogen generating electrode according to any one of claims 1 to 6, wherein the hydrogen generating catalyst is made of platinum.