WO2016076106A1

WO2016076106A1 - Hydrogen generating electrode

Info

Publication number: WO2016076106A1
Application number: PCT/JP2015/080226
Authority: WO
Inventors: 一成堂免; 尚俊佐藤; 耕嶺岸; 啓熊谷
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: 2014-11-12
Filing date: 2015-10-27
Publication date: 2016-05-19
Also published as: JP6388665B2; JPWO2016076106A1

Abstract

This hydrogen generating electrode generates hydrogen from an aqueous electrolyte solution with use of light. This hydrogen generating electrode comprises: a conductive layer; an inorganic semiconductor layer that is provided on the conductive layer and has a pn junction; a metal layer that is formed on the surface of the inorganic semiconductor layer; and a promoter that is supported by the surface of the metal layer. Light is incident thereon from the promoter side.

Description

Hydrogen generation electrode

The present invention relates to a hydrogen generating electrode that generates hydrogen from an electrolytic aqueous solution by light, and in particular, a hydrogen generating electrode that has a high photocurrent value corresponding to the amount of hydrogen generated and can stably generate hydrogen over a long period of time. About.

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 that decomposes and produces oxygen and hydrogen has been proposed (see, for example, Patent Document 1).

Patent Document 1 describes a photo-water splitting electrode having a structure in which a p-type semiconductor, an n-type semiconductor, and a reaction promoter are stacked in this order on a collecting electrode. By holding the electrode for water splitting in water and irradiating light such as sunlight, hydrogen can be decomposed to produce hydrogen.

JP 2012-46385 A

The photo-water splitting electrode of Patent Document 1 can produce hydrogen by decomposing water upon receiving light such as sunlight, but at present, further increase in the amount of hydrogen generated is desired. . That is, further improvement in the photocurrent value corresponding to the amount of hydrogen generated is required. In addition, when hydrogen is continuously generated, the amount of hydrogen generated may decrease, and it is also required to generate hydrogen stably over a long period of time.

An object of the present invention is to provide a hydrogen generating electrode that solves the problems based on the above-described conventional technology, has a high photocurrent value corresponding to the amount of hydrogen generated, and can stably generate hydrogen over a long period of time. There is to do.

In order to achieve the above object, the present invention provides a hydrogen generating electrode for generating hydrogen from an electrolytic aqueous solution using light, a conductive layer, an inorganic semiconductor layer having a pn junction provided on the conductive layer, The present invention provides a hydrogen generating electrode comprising a metal layer formed on an inorganic semiconductor layer and a promoter supported on the surface of the metal layer, and light is incident from the promoter side. .

The metal layer is preferably composed of a transition metal of group 4 or higher. The metal layer preferably has a single layer structure or a multilayer structure. The metal layer preferably has a thickness of 8 nm or less.
For example, the inorganic semiconductor layer includes a CIGS (Copper indium gallium selenide) compound semiconductor. For example, the inorganic semiconductor layer includes a CZTS (Copper zinc tin sulfide) compound semiconductor. For example, the inorganic semiconductor layer includes a CGSe compound semiconductor. For example, the transition metals of Group 4 or higher are Ti, Zr, Mo, Ta, and W.

According to the present invention, the photocurrent value corresponding to the amount of hydrogen generated is high, and hydrogen can be generated stably over a long period of time.

(A) is typical sectional drawing which shows the structure of the hydrogen generating electrode of embodiment of this invention, (b) is typical sectional drawing which shows the other structure of the hydrogen generating electrode of embodiment of this invention. is there. (A)-(e) is typical sectional drawing which shows the manufacturing method of the hydrogen generating electrode of embodiment of this invention in order of a process.

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 generation electrode according to an embodiment of the present invention, and FIG. 1B is a schematic cross-section showing another configuration of the hydrogen generation electrode according to an embodiment of the present invention. FIG.
The hydrogen generation electrode 10 shown in FIG. 1A is for generating hydrogen from the electrolytic aqueous solution AQ using light L.
In the hydrogen generating electrode 10, a conductive layer 14, a p-type semiconductor layer 16, an n-type semiconductor layer 18, a metal layer 20, and a promoter 22 are stacked in this order on the surface 12 a of the insulating substrate 12. ing. The p-type semiconductor layer 16 and the n-type semiconductor layer 18 constitute an inorganic semiconductor layer 19. Light L is incident from the cocatalyst 22 side.

The hydrogen generating electrode 10 is disposed, for example, in a container 30 that is configured to transmit light L. An electrolytic aqueous solution AQ is placed in the container 30 so that the hydrogen generating electrode 10 is completely immersed. For example, a configuration of a three-electrode system in which the hydrogen generation electrode 10 is a working electrode, an Ag / AgCl electrode is used as a reference electrode (not shown), a platinum wire is used as a counter electrode (not shown), and these are connected to a potentiostat. And In this state, by controlling the potential of the hydrogen generating electrode 10 with respect to the reference electrode and irradiating light L from the cocatalyst 22 side, the electrolytic aqueous solution AQ is decomposed to generate hydrogen. Note that a system for generating hydrogen using the hydrogen generating electrode 10 is not particularly limited. For example, it may be connected to an oxygen generating electrode, soaked together in the electrolytic aqueous solution AQ, and irradiated with light L from the cocatalyst 22 side to generate hydrogen.

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.

Next, each part of the hydrogen generating electrode 10 will be described.
The insulating substrate 12 supports the hydrogen generating electrode 10 and is configured to have electrical insulation. 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 (Steel Use Stainless) substrate, or a composite made of a composite material of Al and another metal such as SUS, or a composite metal substrate such as an Al substrate. Is available. 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. In addition, when using the thing containing a CIGS compound semiconductor for the p-type semiconductor layer 16, when there exists what supplies an alkali ion (for example, sodium (Na) ion: Na ^<+> ) to the insulated substrate 12 side, photoelectric Since conversion efficiency improves, it is preferable to provide an alkali supply layer for supplying alkali ions to the surface 12a 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 19. Although it will not specifically limit if the conductive layer 14 has electroconductivity, For example, it is comprised with 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 19 generates an electromotive force. In the inorganic semiconductor layer 19, a pn junction is formed at the interface between the p-type semiconductor layer 16 and the n-type semiconductor layer 18. A p-type semiconductor layer 16 is formed on the conductive layer 14.
The inorganic semiconductor layer 19 is a layer that absorbs the light L that has passed through the n-type semiconductor layer 18 and generates holes on the p side and electrons on the n side. The p-type semiconductor layer 16 has a photoelectric conversion function. In the p-type semiconductor layer 16, holes generated as carriers at the pn junction are moved from the p-type semiconductor layer 16 to the conductive layer 14 side, and electrons generated as carriers at the pn junction are transferred from the n-type semiconductor layer 18 to the metal layer 20 side. Move to. The film thickness of the p-type semiconductor layer 16 is preferably 0.5 to 3.0 μm, particularly preferably 1.0 to 2.0 μm.

The p-type semiconductor layer 16 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 composed of not only Cu (In, Ga) Se ₂ (CIGS) but also CuInSe ₂ (CIS), CuGaSe ₂ (CGS), or the like.
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 18 forms a pn junction at the interface with the p-type semiconductor layer 16 as described above. The n-type semiconductor layer 18 allows the light L to pass therethrough so that the incident light L reaches the p-type semiconductor layer 16.
The n-type semiconductor layer 18 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 18 is preferably 10 nm to 2 μm, more preferably 15 to 200 nm. For the formation of the n-type semiconductor layer 18, for example, a chemical bath deposition method (hereinafter referred to as CBD method) is used.
For example, a window layer may be provided on the n-type semiconductor layer 18. This window layer is composed of, for example, a ZnO layer having a thickness of about 10 nm.

The metal layer 20 is formed on the inorganic semiconductor layer 19, that is, on the surface 18 a of the n-type semiconductor layer 18.
The metal layer 20 is preferably composed of a transition metal of group 4 or higher. Examples of the group 4 or higher transition metal include Ti, Zr, Mo, Ta, and W.
Note that if the thickness t of the metal layer 20 is too thick, the amount of light incident on the inorganic semiconductor layer 19 becomes small, which is not preferable. Therefore, the metal layer 20 preferably has a thickness t of 8 nm or less, more preferably 6 nm or less. The lower limit of the metal layer 20 is a thickness that can exhibit the above-described function and can be manufactured.
The metal layer 20 can be formed by, for example, a sputtering method, a vacuum evaporation method, an electron beam evaporation method, or the like.

A promoter 22 is formed on the surface 20 a of the metal layer 20. The co-catalyst 22 may be formed on one surface, or may be formed in an island shape so as to be scattered, for example.
The co-catalyst 22 is composed of, for example, a simple substance composed of Pt, Pd, Ni, Au, Ag, Ru, Cu, Co, Rh, Ir, Mn, etc., and an alloy thereof, and an oxide thereof, for example, NiOx. And RuO ₂ . The size of the co-catalyst 22 is not particularly limited and is preferably 0.5 nm to 1 μm and the height is preferably about several nm. The method for forming the co-catalyst 22 is not particularly limited, and can be formed by a coating and baking method, a photo-deposition method, a vacuum deposition method, a sputtering method, an impregnation method, or the like.

The metal layer 20 imparts conductivity to the surface layer of the n-type semiconductor layer 18 formed of, for example, CdS while allowing the light L to enter the inorganic semiconductor layer 19. Carriers generated in the inorganic semiconductor layer 19 and electrons in the hydrogen generating electrode 10 in FIG. 1A can easily move to the promoter 22 side by the metal layer 20.
When the metal layer 20 is not present, the generated carriers in the surface layer portion of the n-type semiconductor layer 18 that is not in contact with the cocatalyst 22 are difficult to move in a direction parallel to the surface 18a (hereinafter simply referred to as a lateral direction), and are close in the lateral direction It is difficult for carriers (electrons) to move to the co-catalyst 22 that performs. On the other hand, by providing the metal layer 20, carriers (electrons) that have flowed into the metal layer 20 can easily move to the close promoter 22. Thereby, among the generated electrons, the amount of electrons moving to the promoter 22 can be increased, and the photocurrent value corresponding to the amount of hydrogen generated can be increased.
In addition, the cocatalyst 22 is made of metal or the like, and the metal layer 20 can be more stably bonded to the cocatalyst 22 than the n-type semiconductor layer 18, and adhesion can be improved. As a result, the hydrogen generating electrode 10 can generate stable hydrogen, and as a result, hydrogen can be stably generated over a long period of time.

In the hydrogen generating electrode 10 shown in FIG. 1A, the metal layer 20 has a single layer structure, but is not limited to this, and may have a multilayer structure. Specifically, a metal layer 24 having a two-layer structure may be used as shown in the hydrogen generating electrode 10a shown in FIG. The metal layer 24 includes a first metal layer 26 provided on the n-type semiconductor layer 18 side, and a second metal layer 28 provided thereon. The metal layer 24 has the same function as the metal layer 20 described above.
In the hydrogen generation electrode 10a shown in FIG. 1B, 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.

When the metal layer 24 has a multilayer structure, the total thickness t of the first metal layer 26 and the second metal layer 28 is preferably 8 nm or less in consideration of the amount of incident light L, more preferably 6 nm or less. If the total thickness t of the metal layer 24 is too thick, the amount of incident light on the inorganic semiconductor layer 19 becomes small like the metal layer 20 described above, which is not preferable. The metal layer 24 can also be formed by, for example, a sputtering method, a vacuum evaporation method, an electron beam evaporation method, or the like.
The first metal layer 26 and the second metal layer 28 are also preferably composed of a transition metal of group 4 or more, like the metal layer 20 described above. The transition metal of Group 4 or higher is, for example, Ti, Zr, Mo, Ta, or W.
By forming the first metal layer 26 on the surface 18a of the n-type semiconductor layer 18 with Ti and the second metal layer 28 with Mo, the amount of hydrogen generation and long-term stability of hydrogen generation can be obtained. Therefore, it is preferable.

Next, a method for manufacturing the hydrogen generating electrode 10 will be described.
2 (a) to 2 (e) are schematic cross-sectional views showing a method of manufacturing a hydrogen generating electrode according to an embodiment of the present invention in the order of steps.
First, for example, a soda lime glass substrate to be the insulating substrate 12 is prepared.
Next, as shown in FIG. 2A, for example, a Mo film or the like to be the conductive layer 14 is formed on the surface 12a of the insulating substrate 12 by sputtering.

Next, as illustrated in FIG. 2B, for example, a CIGS film is formed as the p-type semiconductor layer 16 on the conductive layer 14. This CIGS film is formed by any of the film forming methods described above.
Next, as shown in FIG. 2C, for example, a CdS layer that becomes the n-type semiconductor layer 18 is formed on the surface 16 a of the p-type semiconductor layer 16 by the CBD method. Thereby, the inorganic semiconductor layer 19 is formed.
Next, as shown in FIG. 2D, a single-layer metal layer 20 is formed on the surface 18a of the n-type semiconductor layer 18 by using, for example, a sputtering method.
Next, as shown in FIG. 2 (e), a Pt promoter is supported on the surface 20a of the metal layer 20 as a hydrogen generating promoter 22 using, for example, a photo-deposition method. Thereby, the hydrogen generating electrode 10 is formed.

The method for manufacturing the hydrogen generating electrode 10a shown in FIG. 1B with the metal layer 24 having a multilayer structure differs from the method for forming the hydrogen generating electrode 10 shown in FIG. Except for this point, the steps are the same as those in the method for manufacturing the hydrogen generating electrode 10 shown in FIGS. 2A to 2C and 2E, and thus detailed description thereof is omitted.
In the method for manufacturing the hydrogen generating electrode 10a shown in FIG. 1B, when the metal layer 24 is formed, first, the first metal layer 26 is formed on the surface 18a of the n-type semiconductor layer 18 by using, for example, sputtering. Form. Next, the second metal layer 28 is formed on the first metal layer 26 by using, for example, a sputtering method. The promoter 22 is formed on the surface 28a of the second metal layer 28 of the metal layer 24 as described above.
The hydrogen generation electrode 10a shown in FIG. 1B also uses, for example, the hydrogen generation electrode 10a as a working electrode, an Ag / AgCl electrode as a reference electrode (not shown), and a platinum wire as a counter electrode (not shown). By adopting a three-electrode system configuration in which these are connected to a potentiostat, hydrogen can be generated in the same manner as the hydrogen generation electrode 10 shown in FIG. Furthermore, for example, it can be connected to an oxygen generating electrode, immersed in the electrolytic aqueous solution AQ together with the hydrogen generating electrode 10a, and irradiated with light L from the cocatalyst 22 side to generate hydrogen.

As described above, the metal layer 20 is provided in the hydrogen generation electrode 10 shown in FIG. 1A, and the metal layer 24 is provided in the hydrogen generation electrode 10a shown in FIG. Electrons generated in the semiconductor layer 19 can be easily moved to the cocatalyst 22 side. Thereby, among the electrons generated as carriers, the amount of electrons moving to the promoter 22 can be increased, and the photocurrent value corresponding to the amount of hydrogen generated can be increased. Furthermore, since the metal layers 20 and 24 can improve the adhesion to the co-catalyst 22 as described above, stable hydrogen generation is possible, and hydrogen can be stably generated over a long period of time.
Further, both the hydrogen generating electrode 10 shown in FIG. 1A and the hydrogen generating electrode 10a shown in FIG. 1B can be used in an artificial photosynthesis module that decomposes the electrolytic aqueous solution AQ into hydrogen and oxygen by light L. .

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 3 and Comparative Examples 1 and 2 shown below were produced.
ABPE (Applied bias photon-to-current efficiency) (%) was measured for the hydrogen generating electrodes of Examples 1 to 3 and Comparative Examples 1 and 2, and the maximum value was obtained. The results are shown in Table 1 below. ABPE (%) was measured with a three-electrode system using a potentiostat by irradiating pseudo-sunlight onto a hydrogen generating electrode. The measurement conditions of ABPE (%) are shown below.

Light source: Solar simulator (AM1.5G) XES-70S1 manufactured by Mitsunaga Electric Mfg. Co., Ltd.
Electrolyte: 0.5M Na ₂ SO ₄ + 0.25M Na ₂ HPO ₄ + 0.25M NaH ₂ PO ₄ pH 7.0
Electrochemical measuring device: Potentiostat Hokuto Denko HZ-7000
Reference electrode: Ag / AgCl electrode Counter electrode: Platinum wire Working electrode: Hydrogen generation electrode

Stability was determined for the hydrogen generating electrodes of Examples 1 to 3 and Comparative Examples 1 and 2. The results are shown in Table 1 below.
Stability is a value represented by the ratio between the photocurrent value at the start of driving and the photocurrent value after one hour of driving, assuming that the holding potential is 0.3 V _RHE . The ratio is obtained by the photocurrent value after 1 hour of driving / the photocurrent value at the start of driving. In addition, hydrogen can be generated more stably as the ratio value is larger.
The hydrogen generation electrodes of Examples 1 to 3 and Comparative Examples 1 and 2 were further evaluated comprehensively according to the following judgment criteria in consideration of ABPE (%) and stability. The results are shown in Table 1 below.
The evaluation criteria were “A” when the ABPE (%) value was not less than Comparative Example 1 and the above-mentioned ratio was not less than 0.5, and “B” otherwise. That is, a value of ABPE (%) less than Comparative Example 1 or a ratio of less than 0.5 is determined as “B”.
Hereinafter, the hydrogen generating electrodes of Examples 1 to 3 and Comparative Examples 1 and 2 will be described.

(Example 1)
The hydrogen generation electrode of Example 1 has the same configuration as the hydrogen generation electrode 10a shown in FIG. The configuration of each part is as follows. The hydrogen generating electrode of Example 1 was insulated by connecting the conductive wire to the conductive layer and then covering the exposed portion with an epoxy resin.
<Configuration of hydrogen generating electrode>
Insulating substrate: soda lime glass, 1 mm thick conductive layer: Mo, 500 nm thick inorganic semiconductor layer p type semiconductor layer: CIGS, 1500 nm thick n type semiconductor layer: CdS, 50 nm thick metal layer Mo film, 3 nm thick (promoter side)
Ti film, 3nm thickness (n-type semiconductor layer side)
Cocatalyst: Pt (photodeposition method)

(Example 2)
The hydrogen generating electrode of Example 2 has the same configuration as the hydrogen generating electrode 10 shown in FIG. Since the hydrogen generating electrode of Example 2 has the same configuration as that of Example 1 except that the metal layer is a single-layer film of Mo film having a thickness of 3 nm as compared with Example 1, the detailed description thereof is as follows. Omitted.

(Example 3)
The hydrogen generating electrode of Example 3 has the same configuration as the hydrogen generating electrode 10 shown in FIG. Since the hydrogen generating electrode of Example 3 has the same configuration as that of Example 1 except that the metal layer is a single-layer Ti film having a thickness of 3 nm as compared with Example 1, the detailed description thereof is as follows. Omitted.

(Comparative Example 1)
Compared to Example 1, Comparative Example 1 has the same configuration as that of Example 1 except that the metal layer is not formed, and thus detailed description thereof is omitted. In Comparative Example 1, since there is no metal layer, “-” is written in the column “Configuration of metal layer” and the column “Metal layer thickness” in Table 1 below.

(Comparative Example 2)
Since Comparative Example 2 has the same configuration as that of Example 1 except that a crystalline ITO film having a thickness of 5 nm is formed instead of the metal layer as compared with Example 1, detailed description thereof is omitted. . In Comparative Example 2, since a crystalline ITO film was formed, “Crystal ITO” was described in the column “Metal Layer Configuration” in Table 1 below.
In Examples 2 and 3 and Comparative Examples 1 and 2, the method for producing the hydrogen generating electrode, the method for measuring ABPE (%), and the method for calculating the stability are the same as those in Example 1, and therefore detailed description thereof will be given. Is omitted.

In each of Examples 1 to 3, the maximum value (%) of ABPE was high and the stability was good. By making the metal layer into a two-layer structure of Mo film and Ti film as in Example 1, a high value with good balance was obtained in both the maximum value (%) and stability of ABPE.
On the other hand, the metal layer is not formed in Comparative Example 1, the maximum value (%) of ABPE is smaller than that of Examples 1 to 3, and the stability is poor. In Comparative Example 2, instead of the metal layer, a crystalline ITO film having the same thickness as that of Example 1 was formed, but the maximum value (%) of ABPE was as low as that of Comparative Example 1, Moreover, the stability is worse than that of Comparative Example 1.

(Example 4: Pt / Mo / Ti / CdS / ZnSe: Cu (In, Ga) Preparation and Evaluation of Se ₂ electrode)
Using soda lime glass (Float glass, manufactured by Koshi Optical Co., Ltd.) coated with Mo by sputtering (as a substrate material), i) formation of ZnSe: Cu (In, Ga) Se ₂ thin film by multi-source deposition method, ii) CdS layer formation by chemical bath deposition (hereinafter abbreviated as CBD) method, iii) Mo / Ti layer formation by sputtering method, and iv) Pt loading by vacuum deposition method. Then, a Pt / Mo / Ti / CdS / ZnSe: Cu (In, Ga) Se ₂ electrode was produced. Hereinafter, each process will be described in detail.

i) Formation of ZnSe: Cu (In, Ga) Se ₂ thin film by multi-source deposition method Raw materials Ga, In, Cu, Se, Zn {Ga shot (6N: manufactured by Furuuchi Chemical Co., Ltd.), In shot (6N: Flutuchi) Chemical shot), Cu shot (6N: manufactured by Furuuchi Chemical Co., Ltd.), Se shot (6N: manufactured by Asahi Metal Co., Ltd.), and Zn shot (6N: manufactured by Asahi Metal Co., Ltd.)} are individually pyrolyzed boron nitride (Pyrolitic Boron Nitride). : PBN) Put in a crucible made of PBN), and heat and evaporate the raw materials independently in a vacuum vessel maintained at a pressure of <10 ⁻⁵ Pa, at an appropriate temperature (first 5 minutes at 350 ° C., other 35 minutes at 450 ° C.) By depositing on a controlled substrate material, a ZnSe: Cu (In, Ga) Se ₂ thin film (p-type semiconductor layer, 1500 nm thickness) was obtained. The feed rate of the raw material was controlled by measuring the deposition rate of each raw material using a quartz vibrator film thickness meter (manufactured by ULVAC, CRTM-6000) and controlling the temperature of each crucible. The deposition rate of each raw material was Cu: 0.042 nm / s, Ga: 0.014 nm / s, In: 0.048 nm / s, Zn: 0.35 to 0.40 nm / s, Se: 1 nm / s.

ii) Formation of CdS layer by CBD method Cd source cadmium acetate dihydrate (Kanto Chemical Co., 98.0%) and S source thiourea (Kanto Chemical Co., 98.0%) were used. In an oil bath, 50 ml of distilled water, 50 ml of ammonia water (special grade, 28% by mass, manufactured by Wako Pure Chemical Industries, Ltd.) and 0.666 g of cadmium acetate dihydrate were placed in a glass beaker to obtain a CBD solution. In the obtained CBD solution, the ZnSe: Cu (In, Ga) Se ₂ thin film prepared by the multi-source vapor deposition method is immersed, and then 2.855 g of thiourea is quickly added. A CdS layer (n-type semiconductor layer, 50 nm thick) was formed by placing in a water bath and treating for 14 minutes.

iii) Formation of Mo / Ti layer by sputtering method Mo film, 3 nm thickness (promoter side)
Ti film, 3nm thickness (n-type semiconductor layer side)

iv) Supporting Pt by vacuum vapor deposition Pt was vapor-deposited by 2 to 3 nm using a vacuum vapor deposition apparatus (ULVAC KIKOH, VWR-400M).

Using the electrode prepared above, the ABPE (%) was measured and the stability was evaluated in the same manner as in Example 1. The result was equal to or higher than that in Example 1.

DESCRIPTION OF SYMBOLS 10 Hydrogen generating electrode 12 Insulating substrate 14 Conductive layer 16 P-type semiconductor layer 18 N-type semiconductor layer 19

Inorganic semiconductor layer

20, 24 Metal layer 22 Promoter 24 First metal layer 26 Second metal layer 30 Container AQ Electrolysis aqueous solution

Claims

A hydrogen generating electrode for generating hydrogen from an aqueous electrolytic solution using light,
A conductive layer;
An inorganic semiconductor layer having a pn junction provided on the conductive layer;
A metal layer formed on the inorganic semiconductor layer;
A promoter supported on the surface of the metal layer,
The hydrogen generating electrode, wherein the light is incident from the promoter side.
The hydrogen generating electrode according to claim 1, wherein the metal layer is composed of a transition metal of group 4 or higher.
The hydrogen generating electrode according to claim 1 or 2, wherein the metal layer has a single layer structure or a multilayer structure.
The hydrogen generating electrode according to any one of claims 1 to 3, wherein the metal layer has a thickness of 8 nm or less.
The hydrogen generating electrode according to any one of claims 1 to 4, wherein the inorganic semiconductor layer includes a CIGS compound semiconductor.
The hydrogen generating electrode according to any one of claims 1 to 4, wherein the inorganic semiconductor layer contains a CZTS compound semiconductor.
The hydrogen generating electrode according to any one of claims 1 to 4, wherein the inorganic semiconductor layer includes a CGSe compound semiconductor.