JP7320775B2 - Hydrogen generating electrode and method for producing hydrogen generating electrode - Google Patents
Hydrogen generating electrode and method for producing hydrogen generating electrode Download PDFInfo
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- JP7320775B2 JP7320775B2 JP2019079377A JP2019079377A JP7320775B2 JP 7320775 B2 JP7320775 B2 JP 7320775B2 JP 2019079377 A JP2019079377 A JP 2019079377A JP 2019079377 A JP2019079377 A JP 2019079377A JP 7320775 B2 JP7320775 B2 JP 7320775B2
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- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 81
- 239000001257 hydrogen Substances 0.000 title claims description 81
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 81
- 238000004519 manufacturing process Methods 0.000 title claims description 21
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- 238000000034 method Methods 0.000 claims description 46
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- 239000003426 co-catalyst Substances 0.000 claims description 21
- 229910052783 alkali metal Inorganic materials 0.000 claims description 20
- 150000001340 alkali metals Chemical class 0.000 claims description 20
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- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 2
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- SIXIBASSFIFHDK-UHFFFAOYSA-N indium(3+);trisulfide Chemical compound [S-2].[S-2].[S-2].[In+3].[In+3] SIXIBASSFIFHDK-UHFFFAOYSA-N 0.000 description 2
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Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/133—Renewable energy sources, e.g. sunlight
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- Electrodes For Compound Or Non-Metal Manufacture (AREA)
Description
本発明は、光によって水から水素を発生させる水素発生用電極、及び、水素発生用電極の製造方法に関する。 TECHNICAL FIELD The present invention relates to a hydrogen generating electrode that generates hydrogen from water with light, and a method for producing a hydrogen generating electrode.
太陽エネルギーを利用する光エネルギー変換システムの実用化は、地球温暖化の抑制、枯渇しつつある化石資源依存からの脱却を目指す観点から、近年、その重要性が増している。中でも、太陽エネルギーを用いて水を分解し水素を製造する技術は、現行の石油精製、アンモニア、メタノールの原料供給技術としてのみならず、燃料電池をベースとした将来の水素エネルギー社会における水素供給技術として、有望視されている。 In recent years, the importance of practical application of a light energy conversion system using solar energy has increased from the viewpoint of curbing global warming and breaking away from dependence on fossil resources, which are being depleted. Above all, the technology that uses solar energy to split water and produce hydrogen is not only a raw material supply technology for the current petroleum refining, ammonia, and methanol, but also a hydrogen supply technology for the future hydrogen energy society based on fuel cells. As such, it is viewed as promising.
上述の太陽エネルギーを用いて水を分解する方法の重要な要素として、光水分解用電極がある。光水分解用電極として、水素発生用電極、すなわち光を用いて水から水素を発生させる電極について、すでに多くの報告がなされている。
例えば、特許文献１には、集電層上に、ｐ型半導体、ｎ型半導体、反応助触媒が、この順で積層された構造の光水分解用電極が記載され、特許文献１で用いられるｐ型半導体はＣｕ、Ｇａ及びカルコゲン元素からなる化合物であることが記載されている。この光水分解用電極を水中に保持し、太陽光等の光を照射することにより、水を分解して水素を製造することができる。
特許文献２には、Ｃｕ、Ｇａ、Ｉｎ、Ｚｎ、及びＳまたはＳｅからなる特定の組成を有する複合金属化合物が集電導電体層上に積層された光触媒電極が記載されている。この光触媒電極は優れた光電気化学特性を有し、光触媒電極に疑似太陽光を照射することにより、水を分解して水素を製造することができる。
非特許文献１には、Ｐｔ／ＣｄＳ／ＣＩＧＳ（Ｃｕ－Ｇａ－Ｉｎ－Ｓｅ）から成る光カソードが記載され、この光カソードを用いた疑似太陽光照射による光電気化学特性および水分解による水素生成の結果が示されている。非特許文献１に示された光電気化学特性において、電流密度は比較的大きいもののオンセット電位は０．７ＶｖｓＲＨＥ付近である。
非特許文献２には、ＣＧＩＺＳ（Ｃｕ－Ｇａ－Ｉｎ－Ｚｎ－Ｓ）光触媒に関する粒子転写電極のカソード特性が記載されており、貴側オンセットなどの優れた特性が示されている。
An important element of the above-described method of decomposing water using solar energy is a photo-water decomposition electrode. As a photowater-splitting electrode, many reports have already been made on a hydrogen generating electrode, that is, an electrode that generates hydrogen from water using light.
For example, 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 laminated in this order on a current collecting layer, and is used in Patent Document 1. The p-type semiconductor is described as being a compound consisting of Cu, Ga and chalcogen elements. By holding this photo-water splitting electrode in water and irradiating it with light such as sunlight, water can be split and hydrogen can be produced.
Patent Document 2 describes a photocatalyst electrode in which a composite metal compound having a specific composition consisting of Cu, Ga, In, Zn, and S or Se is laminated on a collector conductor layer. This photocatalyst electrode has excellent photoelectrochemical properties, and by irradiating the photocatalyst electrode with simulated sunlight, it is possible to decompose water and produce hydrogen.
Non-Patent Document 1 describes a photocathode composed of Pt/CdS/CIGS (Cu—Ga—In—Se), and photoelectrochemical properties and hydrogen generation by water decomposition by simulated sunlight irradiation using this photocathode. results are shown. In the photoelectrochemical characteristics shown in Non-Patent Document 1, the current density is relatively large, but the onset potential is around 0.7 V vs RHE.
Non-Patent Document 2 describes the cathodic properties of particle transfer electrodes for CGIZS (Cu--Ga--In--Zn--S) photocatalysts, showing excellent properties such as noble-side onset.
上述の通り、太陽エネルギーを利用する光エネルギー変換システムの実用化に対して、太陽エネルギーにより水を分解して水素を製造する光水分解用電極を用いる技術は、優れた解決策であると考えられている。その際に、光水分解用電極を有する光電気化学セルとして、水素発生用の光カソード（水素発生用電極）と酸素発生用の光アノードの２つの光水分解用電極を組み合わせる２電極システムが典型的なものである。この２電極システムにおいては、各電極の電流電位曲線が、より高い電流密度で交わることが、高い太陽エネルギー変換効率に直結する。そのためには、各電極の電流密度がより大きいことに加えて、電流密度の立ち上がり電位（オンセット電位）が、水素発生用の光カソードではより貴側であり、酸素発生用の光アノードではより卑側にあることが望まれる。すなわち、より具体的には、水素発生用の光カソードと酸素発生用の光アノードとが交わることが想定される０．６～１．０ＶｖｓＲＨＥの電位において、より大きな電流密度を示す水素発生用の光カソード及び酸素発生用の光アノ―ドが求められている。これまでに開発されてきた水素発生用の光カソードに着目すると、その報告例は多いが、１．０ＶｖｓＲＨＥ前後の貴側オンセット電位を示す水素発生用の光カソードはほとんど報告されておらず、また、０．６～１．０ＶｖｓＲＨＥの電位において大きな電流密度を示すものが非常に少ないというのが実情である。
すなわち、太陽光などの光を用いて水から水素を発生させる、水素発生用の光カソードとして、より高い電流密度とより貴側のオンセット電位となる光電気化学特性を示す水素発生用電極の開発が望まれている。
As mentioned above, we believe that the technology that uses photo-water splitting electrodes that produce hydrogen by splitting water using solar energy is an excellent solution to the practical use of photo-energy conversion systems that utilize solar energy. It is At that time, as a photoelectrochemical cell having a photowater-splitting electrode, a two-electrode system combining two photowater-splitting electrodes, a photocathode for hydrogen generation (electrode for hydrogen generation) and a photoanode for oxygen generation, is used. Typical. In this two-electrode system, the intersection of the current-potential curves of each electrode at higher current densities directly leads to high solar energy conversion efficiency. To this end, in addition to the higher current density of each electrode, the rising potential of the current density (onset potential) is more noble in the photocathode for hydrogen evolution and more noble in the photoanode for oxygen evolution. It is desirable to be on the low side. That is, more specifically, at a potential of 0.6 to 1.0 V vs RHE at which the photocathode for hydrogen generation and the photoanode for oxygen generation are assumed to intersect, the hydrogen generation photocathode showing a larger current density There is a need for a photocathode and a photoanode for oxygen evolution. Focusing on the photocathode for hydrogen generation that has been developed so far, there are many reported examples, but there are few reports for photocathode for hydrogen generation showing a noble side onset potential around 1.0 V vs RHE. Moreover, the actual situation is that very few materials exhibit a large current density at a potential of 0.6 to 1.0 V vs RHE.
That is, as a photocathode for hydrogen generation, which generates hydrogen from water using light such as sunlight, a hydrogen generation electrode that exhibits photoelectrochemical characteristics such as a higher current density and a more noble onset potential. Development is desired.
本発明は、かかる現状に鑑み、高い電流密度とより貴側のオンセット電位となる光電気化学特性を示す水素発生用電極及び水素発生用電極の製造方法を提供することを目的とする。 An object of the present invention is to provide a hydrogen generating electrode exhibiting photoelectrochemical characteristics such as a high current density and a more noble onset potential, and a method for producing the hydrogen generating electrode.
前記の課題を解決するために本発明者らが検討した結果、集電層上に、ｐ型半導体層及びｎ型半導体層をこの順に有し、ｎ型半導体層上に助触媒を担持し、ｐ型半導体層が、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有し、必要に応じてＺｎ及びＳｅの少なくとも一方を含有するｐ型半導体を含む水素発生用電極が、光によって水から水素を発生させる水素発生用電極として高い電流密度とより貴側のオンセット電位となる光電気化学特性を示すことを見出し、本発明を完成した。即ち本発明は以下の構成を有するものである。 As a result of studies by the present inventors in order to solve the above problems, a p-type semiconductor layer and an n-type semiconductor layer are provided in this order on the current collecting layer, a promoter is supported on the n-type semiconductor layer, The p-type semiconductor layer contains Cu, S, at least one of Ga and In, and an alkali metal as essential components, and optionally contains a p-type semiconductor containing at least one of Zn and Se. As an electrode for generating hydrogen from water by light, the present inventors have found that the electrode exhibits photoelectrochemical characteristics such as a high current density and a more noble onset potential as an electrode for generating hydrogen from water, and completed the present invention. That is, the present invention has the following configurations.
［１］光によって水から水素を発生させる水素発生用電極であって、集電層上に、ｐ型半導体層及びｎ型半導体層をこの順に有し、前記ｎ型半導体層上に助触媒を担持し、前記ｐ型半導体層が、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有し、必要に応じてＺｎ及びＳｅの少なくとも一方を含有するｐ型半導体を含むことを特徴とする水素発生用電極。 [1] A hydrogen generating electrode for generating hydrogen from water by light, having a p-type semiconductor layer and an n-type semiconductor layer in this order on a current collecting layer, and a promoter on the n-type semiconductor layer. A p-type semiconductor supported, wherein the p-type semiconductor layer contains Cu, S, at least one of Ga and In, and an alkali metal as essential components, and optionally at least one of Zn and Se. An electrode for hydrogen generation, comprising:
［２］前記アルカリ金属が、Ｌｉ及びＮａから選択される少なくとも一種であることを特徴とする上記［１］に記載の水素発生用電極。 [2] The electrode for hydrogen generation according to [1] above, wherein the alkali metal is at least one selected from Li and Na.
［３］前記ｎ型半導体層が、Ｃｄ、Ｚｎ、Ｉｎ、Ｇａ、Ｔｉ、Ｚｒ及びＳｎから選択される少なくとも一種の金属の、硫化物、酸化物又は水酸化物を含むことを特徴とする上記［１］又は［２］に記載の水素発生用電極。 [3] The above, wherein the n-type semiconductor layer contains at least one metal sulfide, oxide or hydroxide selected from Cd, Zn, In, Ga, Ti, Zr and Sn. The electrode for hydrogen generation according to [1] or [2].
［４］前記助触媒が、Ｐｔ、Ｒｕ、Ｒｈ、Ｉｒ、Ａｕ、Ａｇ、Ｐｄ及びＮｉから選択される少なくとも一種を含むことを特徴とする上記［１］～［３］のいずれか１つに記載の水素発生用電極。 [4] Any one of [1] to [3] above, wherein the co-catalyst contains at least one selected from Pt, Ru, Rh, Ir, Au, Ag, Pd and Ni An electrode for hydrogen evolution as described.
［５］前記集電層と前記ｐ型半導体層との間に、酸化物層を有することを特徴とする上記［１］～［４］のいずれか１つに記載の水素発生用電極。 [5] The electrode for hydrogen generation according to any one of [1] to [4] above, wherein an oxide layer is provided between the current collecting layer and the p-type semiconductor layer.
［６］前記酸化物層が、Ｔｉ、Ｚｒ、Ｈｆ、Ｚｎ、Ｃｄ、Ｓｎ、Ｇａ及びＩｎから選択される少なくとも一種以上の金属の酸化物を含むことを特徴とする上記［５］に記載の水素発生用電極。 [6] The above-mentioned [5], wherein the oxide layer contains an oxide of at least one metal selected from Ti, Zr, Hf, Zn, Cd, Sn, Ga and In. Electrodes for hydrogen generation.
［７］上記［１］～［６］のいずれかに１つに記載の水素発生用電極の製造方法であって、前記集電層上に前記ｐ型半導体層を形成するｐ型半導体層形成工程と、前記ｐ型半導体層上に前記ｎ型半導体層を形成するｎ型半導体層形成工程と、前記ｎ型半導体層上に前記助触媒を担持する助触媒担持工程と、を備えてなることを特徴とする水素発生用電極の製造方法。 [7] The method for producing a hydrogen generating electrode according to any one of [1] to [6] above, wherein the p-type semiconductor layer is formed on the current collecting layer. an n-type semiconductor layer forming step of forming the n-type semiconductor layer on the p-type semiconductor layer; and a co-catalyst carrying step of carrying the co-catalyst on the n-type semiconductor layer. A method for producing a hydrogen generating electrode, characterized by:
［８］前記ｐ型半導体層形成工程では、多元蒸着法によって前記ｐ型半導体層を形成することを特徴とする上記［７］に記載の水素発生用電極の製造方法。 [8] The method for producing a hydrogen generating electrode according to [7] above, wherein in the p-type semiconductor layer forming step, the p-type semiconductor layer is formed by a multi-source vapor deposition method.
本発明によれば、集電層上に、ｐ型半導体層及びｎ型半導体層をこの順に有し、ｎ型半導体層上に助触媒を担持し、ｐ型半導体層が、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有し、必要に応じてＺｎ及びＳｅの少なくとも一方を含有するｐ型半導体を含む水素発生用電極とすることにより、高い電流密度とより貴側のオンセット電位となる光電気化学特性を示す。この為、水を分解することにより水素を効率的に製造することができる。 According to the present invention, a p-type semiconductor layer and an n-type semiconductor layer are provided in this order on a current collecting layer, a co-catalyst is carried on the n-type semiconductor layer, and the p-type semiconductor layer contains Cu and S. , at least one of Ga and In, and an alkali metal as essential components, and optionally containing at least one of Zn and Se. It exhibits photoelectrochemical properties that result in a more noble onset potential. Therefore, hydrogen can be efficiently produced by decomposing water.
＜＜水素発生用電極＞＞
本発明の水素発生用電極は、光によって水から水素を発生させることができる電極であり、集電層上に、ｐ型半導体層と、ｎ型半導体層とをこの順に有し、ｎ型半導体層上に助触媒を担持している。このような水素発生用電極について、以下に詳述する。
<<Electrode for hydrogen generation>>
The electrode for hydrogen generation of the present invention is an electrode that can generate hydrogen from water by light, and has a p-type semiconductor layer and an n-type semiconductor layer in this order on a current collecting layer, and an n-type semiconductor A co-catalyst is carried on the layer. Such a hydrogen generating electrode will be described in detail below.
＜（１）集電層＞
本発明の水素発生用電極を構成する集電層は、導電性を有しかつ電気化学的に耐久性のある材料であれば特に制限されないが、耐熱性の観点から、Ｆｅ、Ｃｕ、Ａｌ、Ｎｉ、ステンレス鋼、Ｔｉ、Ｔａ、Ｍｏ、Ａｕ、Ｐｔなどの金属材料が好ましい。
<(1) Collecting layer>
The current collecting layer constituting the electrode for hydrogen generation of the present invention is not particularly limited as long as it is a material having conductivity and electrochemical durability. From the viewpoint of heat resistance, Fe, Cu, Al, Metal materials such as Ni, stainless steel, Ti, Ta, Mo, Au, Pt are preferred.
また、集電層は、ガラス等の絶縁材料からなる基板に導電層を被覆したものでもよい。導電層としては、上記の金属材料を用いることができる。水素発生用電極の製造時における耐反応性の点から、金属材料としてＭｏを用いることが好ましい。また、絶縁材料としては、石英、ソーダライムガラス等を用いることができる。ＣＩＧＳ（Ｃｕ－Ｉｎ－Ｇａ－Ｓｅ）太陽電池の分野においてソーダライムガラスからＣＩＧＳ層へのＮａ混入による高性能化が指摘されており、同効果の利用、および導電層と熱膨張係数が近い基材を用いなければ容易にクラックが導入されてしまうという観点から、ソーダライムガラスを用いることが好ましい。 Also, the current collecting layer may be a substrate made of an insulating material such as glass covered with a conductive layer. The above metal materials can be used as the conductive layer. It is preferable to use Mo as the metal material from the viewpoint of reaction resistance during the production of the hydrogen generating electrode. Further, as an insulating material, quartz, soda lime glass, or the like can be used. In the field of CIGS (Cu-In-Ga-Se) solar cells, it has been pointed out that mixing Na from soda-lime glass into the CIGS layer improves performance. It is preferable to use soda-lime glass from the viewpoint that cracks are easily introduced if the material is not used.
また、Ｍｏ等の金属材料からなる導電層とソーダライムガラス等の絶縁材料からなる基板との間に、密着性等を改善する目的で、導電層に含まれる金属以外の金属、例えば、Ｔｉ、Ａｌ、Ｎｉ、Ｓｎ、Ｆｅ、Ｚｎ等の金属を用いて、厚さ数ｎｍ～数百ｎｍの薄い層を有していてもよい。 In addition, for the purpose of improving adhesion between the conductive layer made of a metal material such as Mo and the substrate made of an insulating material such as soda lime glass, a metal other than the metal contained in the conductive layer, such as Ti, Metals such as Al, Ni, Sn, Fe, and Zn may be used to form a thin layer with a thickness of several nanometers to several hundreds of nanometers.
集電層の形状は特に限定されないが、厚さ１μｍ～１ｍｍ程度のシート状のものを用いることが好ましい。また、絶縁材料からなる基板に導電層を被覆したものを集電層として用いる場合は、導電層の厚さは、１００ｎｍ～１０μｍであることが好ましい。導電層の厚さが厚くなりすぎると、絶縁材料から剥離する虞がある。 Although the shape of the current collecting layer is not particularly limited, it is preferable to use a sheet-like one having a thickness of about 1 μm to 1 mm. Further, when a substrate made of an insulating material and coated with a conductive layer is used as the current collecting layer, the thickness of the conductive layer is preferably 100 nm to 10 μm. If the thickness of the conductive layer becomes too thick, there is a risk that it will separate from the insulating material.
＜（２）ｐ型半導体層＞
ｐ型半導体層は、正孔の移動によって電荷が運ばれる半導体である。
本発明の水素発生用電極を構成するｐ型半導体層は、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有し、必要に応じてＺｎおよびＳｅの少なくとも一方を含有するｐ型半導体を含む。
<(2) p-type semiconductor layer>
A p-type semiconductor layer is a semiconductor in which charge is carried by the movement of holes.
The p-type semiconductor layer constituting the hydrogen generating electrode of the present invention contains Cu, S, at least one of Ga and In, and an alkali metal as essential components, and optionally at least one of Zn and Se. A p-type semiconductor containing
このように、本発明においては、集電層上に、ｐ型半導体層及びｎ型半導体層をこの順に有し、ｎ型半導体層上に助触媒を担持し、ｐ型半導体層が、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有するｐ型半導体を含むことにより、本発明の水素発生用電極は、後述する実施例に示すように、高い電流密度と、より貴側のオンセット電位（電流密度が立ち上がる電位）となる光電気化学特性を示す。この理由は現時点では判明していないが、本発明者らは以下の様に推測している。
本発明の水素発生用電極は、ＣｕとＧａ及びＩｎの少なくとも一方とを含むｐ型半導体層にＳが含まれることが、高い性能を発現する要因の一つではないかと考えられる。なお、特にこのＳは、ムラなく結晶に取り込まれていることが好ましい。
水素発生用電極のオンセット電位の最も貴側電位は、理論的には、用いられるｐ型半導体層のフェルミレベルに一致すると考えられる。従来のカルコゲナイド系Ｃｕ含有ｐ型光半導体においては、Ｓｅ系よりもＳ系の方が、より貴側にフェルミレベルが存在することが予想される。価電子帯上端の電位はＳｅ系に比してＳ系の方が０．３～０．５ｅＶほど貴側にあるとされ、これらｐ型半導体のフェルミレベルは価電子帯上端よりわずかに卑側にあるとされるので、Ｓｅ系よりＳ系の方がフェルミレベルも貴側にあることが予想される。従って、理論的には、Ｓ系Ｃｕ含有ｐ型光半導体のオンセット電位はＳｅ系Ｃｕ含有ｐ型光半導体よりも貴側を示すことが期待できる。
そして、本発明の水素発生用電極に含まれるアルカリ金属の存在が、Ｃｕ元素に由来する欠陥部位を何らかの形で補っていることも、高い性能を発現する大きな要因であると考えられる。なお、この系におけるＳとの組み合わせの観点では、アルカリ金属の中でもＮａやＬｉが好ましく、より好ましくはＬｉである。
Thus, in the present invention, the p-type semiconductor layer and the n-type semiconductor layer are provided in this order on the current collecting layer, the co-catalyst is carried on the n-type semiconductor layer, and the p-type semiconductor layer contains Cu and , S, at least one of Ga and In, and an alkali metal as essential components. , the onset potential (potential at which the current density rises) on the more noble side. Although the reason for this is not clear at present, the present inventors presume as follows.
The presence of S in the p-type semiconductor layer containing Cu and at least one of Ga and In is considered to be one of the reasons why the hydrogen generating electrode of the present invention exhibits high performance. In particular, it is preferable that the S is evenly incorporated into the crystal.
Theoretically, the most noble side potential of the onset potential of the hydrogen generating electrode is considered to match the Fermi level of the p-type semiconductor layer used. In conventional chalcogenide-based Cu-containing p-type optical semiconductors, it is expected that the S-based semiconductor has a Fermi level on the more noble side than the Se-based one. The potential at the top of the valence band is said to be 0.3 to 0.5 eV more noble in the S system than in the Se system. Therefore, it is expected that the Fermi level is also on the higher side in the S system than in the Se system. Therefore, theoretically, it can be expected that the onset potential of the S-based Cu-containing p-type optical semiconductor is on the nobler side than that of the Se-based Cu-containing p-type optical semiconductor.
The fact that the presence of the alkali metal contained in the hydrogen generating electrode of the present invention somehow compensates for the defective sites derived from the Cu element is also considered to be a major factor in achieving high performance. From the viewpoint of combination with S in this system, among alkali metals, Na and Li are preferable, and Li is more preferable.
上記ｐ型半導体のアルカリ金属の含有量は、Ｃｕ、Ｇａ、Ｉｎ、Ｚｎ、アルカリ金属の合計を１００モル％とした場合、０．００１～５．０モル％であることが好ましい。このアルカリ金属の含有量のより好ましい下限値は０．００５モル％であり、さらに好ましくは０．０１モル％であり、特に好ましくは０．０５モル％である。一方、アルカリ金属の含有量のより好ましい上限値は４．０モル％であり、さらに好ましくは３．０モル％であり、より好ましくは２．５モル％であり、特に好ましくは２．０モル％である。
アルカリ金属としては、リチウム、ナトリウム、カリウムから選ばれる元素が含まれることが好ましい。より好ましくは、リチウム、ナトリウムであり、さらに好ましくはリチウムである。これらの元素は２種以上含まれていてもよい。
The content of the alkali metal in the p-type semiconductor is preferably 0.001 to 5.0 mol % when the total of Cu, Ga, In, Zn and alkali metal is 100 mol %. A more preferable lower limit of the alkali metal content is 0.005 mol %, more preferably 0.01 mol %, and particularly preferably 0.05 mol %. On the other hand, the upper limit of the alkali metal content is more preferably 4.0 mol%, more preferably 3.0 mol%, more preferably 2.5 mol%, and particularly preferably 2.0 mol. %.
The alkali metal preferably contains an element selected from lithium, sodium, and potassium. Lithium and sodium are more preferred, and lithium is even more preferred. Two or more of these elements may be contained.
上記ｐ型半導体の化学式は、例えば下記式（Ａ）で表すことができる。
ＣｕａＧａｂＩｎｃＺｎｄＳ２－ｅＸｅＹｆ・・・（Ａ）
（上記式中、ａ、ｂ、ｃ、ｄ、ｅ、ｆは下記条件を満たし、ＸはＳｅを示し、Ｙはアルカリ金属を示す。
０＜ａ≦２、０＜（ｂ＋ｃ）≦１．６７、０≦ｄ＜２、０≦ｅ＜２、０＜ｆ＜０．１。）
なお、本発明におけるｐ型半導体が上記式（Ａ）で表されるｐ型半導体の場合は、ｐ型半導体中の全金属原子に対するアルカリ金属の含有量（モル％）は、ｆ／（ｆ＋ａ＋ｂ＋ｃ＋ｄ）×１００で求められる。
The chemical formula of the p-type semiconductor can be represented, for example, by the following formula (A).
CuaGabIncZndS2 - eXeYf ( A ) _
(In the above formula, a, b, c, d, e, and f satisfy the following conditions, X represents Se, and Y represents an alkali metal.
0<a≦2, 0<(b+c)≦1.67, 0≦d<2, 0≦e<2, 0<f<0.1. )
In addition, when the p-type semiconductor in the present invention is the p-type semiconductor represented by the above formula (A), the content (mol%) of the alkali metal with respect to the total metal atoms in the p-type semiconductor is f / (f + a + b + c + d) x100.
本発明における上記ｐ型半導体が含有する成分の含有量比は特に限定されないが、式（Ａ）において、好ましくは、０．２≦ａ≦１．２、０．０≦ｂ≦１．０、０．０≦ｃ≦１．０、０．０≦ｄ≦１．５、０．０≦ｅ≦１．０、０．０００１≦ｆ≦０．１００、より好ましくは、０．４≦ａ≦１．０、０．０≦ｂ≦０．８、０．０≦ｃ≦０．８、０．０≦ｄ≦１．２、０．０≦ｅ≦０．５、０．０００１≦ｆ≦０．０５０である。また、上述の通り、上記ｐ型半導体中のアルカリ金属の含有量（モル％）、すなわち、ｆ／（ｆ＋ａ＋ｂ＋ｃ＋ｄ）×１００は、好ましくは、０．００１～５．０、より好ましくは、０．０１～２．５である。 The content ratio of the components contained in the p-type semiconductor in the present invention is not particularly limited. 0.0≦c≦1.0, 0.0≦d≦1.5, 0.0≦e≦1.0, 0.0001≦f≦0.100, more preferably 0.4≦a≦ 1.0, 0.0≤b≤0.8, 0.0≤c≤0.8, 0.0≤d≤1.2, 0.0≤e≤0.5, 0.0001≤f≤ 0.050. Further, as described above, the content (mol %) of the alkali metal in the p-type semiconductor, that is, f/(f+a+b+c+d)×100 is preferably 0.001 to 5.0, more preferably 0.001 to 5.0. 01 to 2.5.
また、ｐ型半導体層を構成する上記ｐ型半導体の吸収波長は光電変換可能な波長域であれば特に限定されるものではない。吸収波長としては、太陽光の波長域、特に可視光域の波長域を含んでいればよいが、その吸収波長は６００ｎｍ以上、好ましくは７００ｎｍ以上の波長域を含んでいることが好ましい。 Further, the absorption wavelength of the p-type semiconductor constituting the p-type semiconductor layer is not particularly limited as long as it is in a wavelength range capable of photoelectric conversion. The absorption wavelength may include the wavelength range of sunlight, particularly the visible light range, and the absorption wavelength preferably includes the wavelength range of 600 nm or more, preferably 700 nm or more.
＜（３）ｎ型半導体層＞
ｎ型半導体層は、電子の移動によって電荷が運ばれる半導体であれば、特に制限されない。例えば、結晶構造がウルツ型、または、閃亜鉛鉱型であるｎ型半導体が挙げられる。このような結晶構造のｎ型半導体としては、例えば、ＣｄＳ、ＣｄＳｅ、ＣｄＴｅ、ＺｎＯ、ＺｎＳ、ＺｎＳｅ、ＺｎＴｅ、ＨｇＴｅ、ＡｌＰ、ＡｌＡｓ、ＡｌＳｂ、ＧａＰ、ＧａＡｓ、ＧａＳｂ、Ｉｎ２Ｓ３、ＩｎＰ、ＩｎＡｓ、ＩｎＳｂ、ＺｎＯ、ＧａＮ、ＭｇＳ、ＭｇＳｅ、ＢｅＳ、ＢｅＳｅ等が挙げられる。
中でも、本発明においては、ｎ型半導体層は、Ｃｄ、Ｚｎ、Ｉｎ、Ｇａ、Ｔｉ、Ｚｒ及びＳｎから選択される少なくとも一種の金属の、硫化物、酸化物又は水酸化物を含むことが好ましく、ＣｄＳ、ＺｎＳ、Ｉｎ２Ｓ３を含むことがより好ましい。ｎ型半導体層は、これら硫化物、酸化物や水酸化物の混合物であってもよい。２種以上を用いてもよいが、通常、１種のみを用いることでも十分に機能を発揮することができる。
<(3) n-type semiconductor layer>
The n-type semiconductor layer is not particularly limited as long as it is a semiconductor in which charges are carried by electron movement. For example, an n-type semiconductor having a wurtz-type crystal structure or a zinc-blende-type crystal structure can be used. Examples of n-type semiconductors having such a crystal structure include CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, HgTe, AlP, AlAs, AlSb, GaP, GaAs, GaSb, In 2 S 3 , InP, InAs , InSb, ZnO, GaN, MgS, MgSe, BeS, BeSe and the like.
Among them, in the present invention, the n-type semiconductor layer preferably contains at least one metal sulfide, oxide or hydroxide selected from Cd, Zn, In, Ga, Ti, Zr and Sn. , CdS, ZnS , In2S3 . The n-type semiconductor layer may be a mixture of these sulfides, oxides and hydroxides. Although two or more kinds may be used, the function can be sufficiently exhibited by using only one kind.
本発明では、ｎ型半導体となる物質は、ｐ型半導体層上に積層または担持されていることが好ましい。ｐ型半導体層の表面にｎ型半導体層が積層または担持されることでｐｎ接合が形成され、それによって励起電子がｐ型半導体ＣＧＩＺＳからｎ型半導体へ、さらに助触媒へと励起電子が効果的に運ばれる。その際に、励起電子と空孔との再結合を抑制することも同時に期待されるので、効率よい電荷分離が実現できると考えられる。
これらｎ型半導体の担持の形態としては、特に限定されないが、上記ｐ型半導体層の表面に、膜として積層または粒子として担持された状態が好ましい。積層の場合のｎ型半導体層の膜厚は通常０．１ｎｍ以上、５００ｎｍ以下、好ましくは１ｎｍ以上、２００ｎｍ以下である。また、担持の場合のｎ型半導体を構成する粒子の大きさは、平均直径が通常１ｎｍ以上、２００ｎｍ以下であり、２ｎｍ以上、１００ｎｍ以下の微粒子であることが好ましい。
In the present invention, it is preferable that the substance to be the n-type semiconductor is laminated or supported on the p-type semiconductor layer. A pn junction is formed by stacking or carrying an n-type semiconductor layer on the surface of the p-type semiconductor layer, whereby excited electrons are effectively transferred from the p-type semiconductor CGIZS to the n-type semiconductor and further to the promoter. carried to. At that time, it is also expected that the recombination of excited electrons and vacancies can be suppressed at the same time, so it is considered that efficient charge separation can be realized.
The form in which these n-type semiconductors are supported is not particularly limited, but the state in which they are laminated as a film or supported as particles on the surface of the p-type semiconductor layer is preferable. In the case of lamination, the thickness of the n-type semiconductor layer is usually 0.1 nm or more and 500 nm or less, preferably 1 nm or more and 200 nm or less. The size of the particles constituting the n-type semiconductor in the case of carrying is usually 1 nm or more and 200 nm or less in average diameter, preferably 2 nm or more and 100 nm or less.
＜（４）助触媒＞
本発明の水素発生用電極は、ｎ型半導体層上に助触媒が担持されている。
本発明の水素発生用電極は、光励起された電子を用いて水を還元して水素を生成するが、助触媒はその活性点として機能する。その際に、光励起された電子が助触媒の表面において水分子に電子を与えることで水素分子が生成すると考えられる。
助触媒としては、第６～１０族の遷移金属、遷移金属化合物、または、これらの混合物を用いることができる。より具体的には、例えば、Ｐｔ、Ｒｕ、Ｒｈ、Ｉｒ、Ａｕ、Ａｇ、Ｐｄ等の貴金属やＮｉが好ましく用いられる。特に、Ｐｔ、Ｉｒ、Ｒｕがより好ましい。助触媒は、２種以上を用いてもよいが、通常、１種のみを用いることでも十分に助触媒の機能を発揮することができる。
助触媒の担持の形態は、特に限定されないが、ｎ型半導体層の表面に粒子として担持された状態が好ましい。助触媒は、平均直径が０．１～１０ｎｍのナノサイズの微粒子であることが好ましい。
助触媒の担持量も特に限定されるものでなく、上述のｐ型半導体層１００質量％に対して、助触媒は０．１～１０質量％が好ましく、０．５～３質量％がより好ましい。
<(4) Cocatalyst>
In the hydrogen generating electrode of the present invention, a promoter is supported on the n-type semiconductor layer.
The hydrogen generating electrode of the present invention uses photoexcited electrons to reduce water to produce hydrogen, and the co-catalyst functions as its active site. At that time, it is thought that photoexcited electrons donate electrons to water molecules on the surface of the cocatalyst to generate hydrogen molecules.
As cocatalysts, transition metals of Groups 6 to 10, transition metal compounds, or mixtures thereof can be used. More specifically, for example, noble metals such as Pt, Ru, Rh, Ir, Au, Ag, Pd, and Ni are preferably used. In particular, Pt, Ir and Ru are more preferred. Two or more cocatalysts may be used, but normally, the cocatalyst function can be fully exhibited even when only one cocatalyst is used.
The form in which the co-catalyst is carried is not particularly limited, but it is preferably carried as particles on the surface of the n-type semiconductor layer. The co-catalyst is preferably nano-sized fine particles having an average diameter of 0.1 to 10 nm.
The amount of co-catalyst carried is not particularly limited, and the co-catalyst is preferably 0.1 to 10% by mass, more preferably 0.5 to 3% by mass, relative to 100% by mass of the p-type semiconductor layer. .
＜（５）酸化物層＞
本発明の水素発生用電極は、集電層とｐ型半導体層との間に、酸化物層を有していてもよい。酸化物層を有することにより、例えば、詳しくは後述するが、多元蒸着による成膜でのｐ型半導体層形成時の、集電層や集電層を構成する導電層の硫化を、抑制することができる。特に多元蒸着による成膜時にＳラジカルセルを用いてＳ源を導入する際には、反応性の高いＳ分が、集電層や集電層を構成する導電層の金属と反応して金属硫化物を生成する場合がある。例えば集電層や集電層を構成する導電層がＭｏを含む場合はＭｏＳ２が生成して、集電層や集電層を構成する導電層の機能を損なう場合がある。しかしながら、集電層上に酸化物層を有することにより、多元蒸着による成膜でのｐ型半導体層形成時の、集電層や集電層を構成する導電層の硫化を抑制することができるため、集電層や集電層を構成する導電層の機能を損なうことが抑制される。
酸化物層は、金属酸化物を含んでいることが好ましい。金属酸化物の金属としては、４族のＴｉ、Ｚｒ、Ｈｆ、１２族のＺｎ、Ｃｄ、１３族のＧａ、Ｉｎ、１４族のＳｎなどの酸化物が好ましく、Ｔｉ、Ｚｒ、Ｇａ、Ｚｎなどがより好ましい。
酸化物層の厚さは、１～１００ｎｍが好ましく、５～５０ｎｍがより好ましい。厚すぎると導電性が低下し、薄すぎると、Ｍｏ層等の導電層の硫化の抑制が十分でない場合がある。
<(5) Oxide layer>
The hydrogen generating electrode of the present invention may have an oxide layer between the collector layer and the p-type semiconductor layer. By having the oxide layer, for example, although details will be described later, sulfuration of the current collecting layer and the conductive layer constituting the current collecting layer during the formation of the p-type semiconductor layer by multi-source deposition can be suppressed. can be done. In particular, when an S source is introduced using an S radical cell during film formation by multi-source vapor deposition, the highly reactive S component reacts with the current collecting layer and the metal of the conductive layer that constitutes the current collecting layer, resulting in metal sulfidation. may produce things. For example, when the current collecting layer or the conductive layer constituting the current collecting layer contains Mo, MoS 2 may be generated, impairing the function of the current collecting layer or the conductive layer constituting the current collecting layer. However, by having an oxide layer on the current collecting layer, it is possible to suppress sulfuration of the current collecting layer and the conductive layer constituting the current collecting layer when forming the p-type semiconductor layer by multi-source deposition. Therefore, impairment of the function of the current collecting layer and the conductive layer constituting the current collecting layer is suppressed.
The oxide layer preferably contains a metal oxide. As the metal of the metal oxide, oxides such as Ti, Zr, and Hf of Group 4, Zn and Cd of Group 12, Ga and In of Group 13, and Sn of Group 14 are preferable, such as Ti, Zr, Ga, and Zn. is more preferred.
The thickness of the oxide layer is preferably 1-100 nm, more preferably 5-50 nm. If it is too thick, the conductivity will be lowered, and if it is too thin, the suppression of sulfuration of the conductive layer such as the Mo layer may not be sufficient.
＜＜水素発生用電極の製造方法＞＞
上記水素発生用電極は、公知の技術を特に制限なく用いて製造することができるが、例えば、集電層上にｐ型半導体層を形成するｐ型半導体層形成工程と、ｐ型半導体層上にｎ型半導体層を形成するｎ型半導体層形成工程と、ｎ型半導体層上に助触媒を担持する助触媒担持工程とを備えてなる、本発明の水素発生用電極の製造方法により、製造することができる。また、集電層とｐ型半導体層との間に酸化物層を有する水素発生用電極を製造する場合は、本発明の水素発生用電極の製造方法は、集電層上に酸化物層を形成する酸化物層形成工程をさらに備える。本発明の水素発生用電極の製造方法について、以下に詳述する。
<<Method for manufacturing electrode for hydrogen generation>>
The hydrogen generating electrode can be manufactured using known techniques without particular limitation. Manufactured by the method for manufacturing an electrode for hydrogen generation of the present invention, comprising an n-type semiconductor layer forming step of forming an n-type semiconductor layer in the n-type semiconductor layer and a co-catalyst supporting step of supporting a co-catalyst on the n-type semiconductor layer can do. Further, when manufacturing a hydrogen generating electrode having an oxide layer between the current collecting layer and the p-type semiconductor layer, the method for manufacturing the hydrogen generating electrode of the present invention includes forming the oxide layer on the current collecting layer. The step of forming an oxide layer is further provided. The method for producing the hydrogen generating electrode of the present invention will be described in detail below.
＜酸化物層形成工程＞
酸化物層形成工程では、集電層上に酸化物層を形成する。酸化物層形成工程は任意の工程である。
酸化物層の形成方法としては、スパッタ法、蒸着法、化学溶液析出法（ＣＢＤ法、Ｃｈｅｍｉｃａｌ Ｂａｔｈ Ｄｅｐｏｓｉｔｉｏｎ）などの成膜方法が適用できるが、スパッタ法がより適している。なお、スパッタ法および蒸着法においては、スパッタおよび蒸着直後は金属のまま酸化されていないが、成膜装置内から取り出されて空気に触れることによって表面が酸化されて酸化物になる。本発明において、酸化物層はこのような酸化物も含むものである。
<Oxide layer forming step>
In the oxide layer forming step, an oxide layer is formed on the current collecting layer. The oxide layer forming step is an optional step.
As a method for forming the oxide layer, film forming methods such as a sputtering method, a vapor deposition method, and a chemical solution deposition method (CBD method, Chemical Bath Deposition) can be applied, but the sputtering method is more suitable. In the sputtering method and vapor deposition method, the metal is not oxidized immediately after sputtering or vapor deposition, but the surface is oxidized to oxide when it is taken out from the film forming apparatus and exposed to air. In the present invention, the oxide layer also includes such an oxide.
＜ｐ型半導体層形成工程＞
ｐ型半導体層形成工程では、集電層上にｐ型半導体層を形成する。集電層上に酸化物層を形成した場合は、集電層上の酸化物層上に、ｐ型半導体層を形成する。
ｐ型半導体層は、公知の成膜方法で形成することができる。
<P-type semiconductor layer forming step>
In the p-type semiconductor layer forming step, a p-type semiconductor layer is formed on the collector layer. When an oxide layer is formed on the current collecting layer, a p-type semiconductor layer is formed on the oxide layer on the current collecting layer.
The p-type semiconductor layer can be formed by a known film formation method.
ｐ型半導体層の成膜方法は特に制限されないが、例えば、多元蒸着法、硫化法、スパッタ法、メカノケミカルプロセス法、スクリーン印刷法、近接昇華法、ＭＯＣＶＤ
（Metal Organic Chemical Vapor Deposition）法、およびスプレー法等が挙げられ、多元蒸着法が好ましく、ＭＢＥ（Ｍｏｌｅｃｕｌａｒ Ｂｅａｍ Ｅｐｉｔａｘｙ）装置を用いた多元蒸着法により成膜を行うことが好ましい。この多元蒸着法による成膜方法は、膜厚制御が比較的容易で、緻密で高品位な結晶が得られるだけでなく、蒸着条件を制御することによって膜の深さ方向に組成に傾斜をつけることができるなどの利点がある。
The method for forming the p-type semiconductor layer is not particularly limited.
(Metal Organic Chemical Vapor Deposition) method, spray method, etc., preferably multi-source vapor deposition method, and it is preferable to form a film by multi-source vapor deposition method using an MBE (Molecular Beam Epitaxy) apparatus. This film formation method using multi-source vapor deposition makes it relatively easy to control the film thickness, and not only does it yield dense, high-quality crystals, but it also allows the composition to be graded in the depth direction of the film by controlling the vapor deposition conditions. There are advantages such as being able to
多元蒸着法による成膜に用いる原料は、特に限定されないが、銅、ガリウム、インジウム、亜鉛、硫黄などの元素や単量体をそのまま用いることができる。また、硫化第一銅（Ｃｕ２Ｓ）、硫化ガリウム（Ｇａ２Ｓ３）、硫化インジウム（Ｉｎ２Ｓ３）、硫化亜鉛（ＺｎＳ）等の硫化物も用いることができる。また、アルカリ金属の原料には、Ｌｉ、Ｎａ、Ｋなどアルカリ金属のフッ化物、塩化物、硫化物などを用いることができ、アルカリ金属のフッ化物や硫化物が好ましく、アルカリ金属のフッ化物がより好ましい。多元蒸着法による成膜においては、ＬｉＦやＮａＦなどのアルカリフッ化物を用いるのが特に好ましい。さらに、基板のソーダライムガラスに含まれるナトリウム成分を、集電層を経由してｐ型半導体層に混入できる場合があり、この混入によってもナトリウムをｐ型半導体層に添加することも可能である。 Materials used for film formation by a multi-source vapor deposition method are not particularly limited, but elements and monomers such as copper, gallium, indium, zinc, and sulfur can be used as they are. Sulfides such as cuprous sulfide (Cu 2 S), gallium sulfide (Ga 2 S 3 ), indium sulfide (In 2 S 3 ), and zinc sulfide (ZnS) can also be used. In addition, as the alkali metal raw material, alkali metal fluorides, chlorides, sulfides, etc., such as Li, Na, and K can be used, and alkali metal fluorides and sulfides are preferable. more preferred. It is particularly preferable to use alkali fluorides such as LiF and NaF in film formation by multi-source vapor deposition. Furthermore, the sodium component contained in the soda-lime glass of the substrate may sometimes be mixed into the p-type semiconductor layer via the current collecting layer, and this mixing also makes it possible to add sodium to the p-type semiconductor layer. .
Ｓ（硫黄）分子は通常多量体で存在するので、Ｓの供給には多量体を分解して供給することが好ましい。例えば、Ｓラジカルセルと呼ばれる装置をＳ蒸着源に付帯させることが好ましい。このＳラジカルセルはＳ多量体をクラッキングにより分解して単量体やラジカルＳ原子に分解することができる。単量体やラジカルＳは多量体に比して反応性が高くかつムラなく供給できるので高品位の結晶成長が達成されると考えられる。実際、本発明者らの検討により、水素発生用電極において、光電流密度がより増大し、オンセット電位がより貴側になるという性能面でのメリットが確認されている。 Since S (sulfur) molecules usually exist in the form of polymers, it is preferable to supply S by decomposing the polymers. For example, it is preferable to attach a device called an S radical cell to the S vapor deposition source. This S radical cell can decompose S multimers by cracking into monomers and radical S atoms. Since the monomers and radicals S have higher reactivity than multimers and can be uniformly supplied, it is believed that high-quality crystal growth is achieved. In fact, the studies by the present inventors have confirmed that the electrode for hydrogen generation has merits in terms of performance that the photocurrent density is further increased and the onset potential is on the more noble side.
多元蒸着法を用いる成膜は、好ましくは圧力１×１０－３Ｐａ以下の高い真空度に保たれた容器中において原料を独立に加熱、蒸発させ、適度な温度に加熱された基板上で化合物薄膜をエピタキシャル成長させて薄膜を形成する方法である。各原料の供給量は原料を蒸発させる各セルの温度を制御することによってコントロールすることができる。 Film formation using a multi-source vapor deposition method preferably involves heating and evaporating raw materials independently in a container maintained at a high degree of vacuum at a pressure of 1×10 −3 Pa or less, and depositing a compound on a substrate heated to an appropriate temperature. This is a method of epitaxially growing a thin film to form a thin film. The supply amount of each raw material can be controlled by controlling the temperature of each cell that evaporates the raw material.
ｐ型半導体層は、固相法で成膜してもよい。固相法では、例えば、硫化第一銅（Ｃｕ２Ｓ）、硫化ガリウム（Ｇａ２Ｓ３）、硫化インジウム（Ｉｎ２Ｓ３）、硫化亜鉛（ＺｎＳ）等の硫化物を原料にして、不活性雰囲気ガス下、または、真空封管中にて、５００～１０００℃にて熱処理を行うことによって製造される。空気中や、酸素含有ガス雰囲気下において熱処理を行うと、硫化物は容易に酸化されてしまう傾向があるのが、不活性ガス雰囲気下あるいは真空雰囲気が好ましい理由である。 The p-type semiconductor layer may be deposited by a solid phase method. In the solid-phase method, for example, sulfides such as cuprous sulfide (Cu 2 S), gallium sulfide (Ga 2 S 3 ), indium sulfide (In 2 S 3 ), and zinc sulfide (ZnS) are used as raw materials, It is produced by heat treatment at 500 to 1000° C. in an active atmosphere gas or in a vacuum sealed tube. The reason why the inert gas atmosphere or vacuum atmosphere is preferable is that the sulfide tends to be easily oxidized when the heat treatment is performed in air or in an oxygen-containing gas atmosphere.
＜ｎ型半導体層形成工程＞
ｎ型半導体層形成工程では、ｐ型半導体層上にｎ型半導体層を形成する。
ｎ型半導体層は、公知の成膜方法で形成することができる。
ｎ型半導体が金属の硫化物である場合は、例えば、含浸法、化学溶液析出法（ＣＢＤ法、Ｃｈｅｍｉｃａｌ Ｂａｔｈ Ｄｅｐｏｓｉｔｉｏｎ）、光電着法、電気泳動法、スパッタ法などが好適に用いられる。特に化学溶液析出法がより好ましい。
一例として、化学溶液析出法で、ｎ型半導体層としてＣｄＳをｐ型半導体層に担持する場合について説明する。Ｃｄ源には、硫酸カドミウムや酢酸カドミウムなどのＣｄ塩、硫黄源にはチオ尿素、中和剤としてアンモニア水が好適に用いられる。具体的には、Ｃｄ塩とチオ尿素とアンモニア水とを含む水溶液に、集電層上に形成されたｐ型半導体層を、４０～８０℃に加温した状態で浸漬する。ｐ型半導体層表面にＣｄＳが析出するので、所定時間浸漬した後、取り出して水で洗浄する。
<N-type semiconductor layer forming step>
In the n-type semiconductor layer forming step, an n-type semiconductor layer is formed on the p-type semiconductor layer.
The n-type semiconductor layer can be formed by a known film formation method.
When the n-type semiconductor is a metal sulfide, for example, an impregnation method, a chemical solution deposition method (CBD method, Chemical Bath Deposition), a photoelectrodeposition method, an electrophoresis method, a sputtering method, and the like are preferably used. A chemical solution deposition method is particularly preferred.
As an example, a case where CdS is carried on a p-type semiconductor layer as an n-type semiconductor layer by a chemical solution deposition method will be described. A Cd salt such as cadmium sulfate or cadmium acetate is preferably used as the Cd source, thiourea is preferably used as the sulfur source, and aqueous ammonia is preferably used as the neutralizing agent. Specifically, the p-type semiconductor layer formed on the current collecting layer is immersed in an aqueous solution containing Cd salt, thiourea, and aqueous ammonia while being heated to 40 to 80.degree. Since CdS is deposited on the surface of the p-type semiconductor layer, the substrate is immersed for a predetermined time, then taken out and washed with water.
＜助触媒担持工程＞
助触媒担持工程では、ｎ型半導体層上に助触媒を担持する。
助触媒は、公知の方法でｎ型半導体上に担持することができ、助触媒の担持方法は、特に限定されず、例えば、含浸法、光電着法（光電析法）、電気泳動法、スパッタ法、ドロップキャスト法等などが挙げられる。中でも、光電析法が好ましい。光電着法（光電析法）では、上記で作製された、集電層上にｐ型半導体層及びｎ型半導体層を形成したものと金属塩とを電解質水溶液中に共存させ、光照射によって金属塩を還元し、金属または金属化合物としてｎ型半導体層上に担持させる。
このような本発明の水素発生用電極の製造方法で、上記本発明の水素発生用電極を製造することができる。なお、安定性付与のための表面処理として、ＴｉＯ２などの酸化物を電極表面に膜として積層してもよい。
<Promoter supporting step>
In the co-catalyst carrying step, the co-catalyst is carried on the n-type semiconductor layer.
The co-catalyst can be supported on the n-type semiconductor by a known method, and the method for supporting the co-catalyst is not particularly limited. method, drop cast method, and the like. Among them, the photoelectrolysis method is preferable. In the photoelectrodeposition method (photoelectrodeposition method), the p-type semiconductor layer and the n-type semiconductor layer formed on the current collecting layer prepared above and a metal salt are allowed to coexist in an aqueous electrolyte solution, and the metal salt is formed by light irradiation. The salt is reduced and deposited on the n-type semiconductor layer as a metal or metal compound.
The hydrogen generating electrode of the present invention can be manufactured by such a method for manufacturing the hydrogen generating electrode of the present invention. As a surface treatment for imparting stability, an oxide such as TiO 2 may be laminated as a film on the electrode surface.
＜＜水分解による水素発生方法＞＞
上記本発明の水素発生用電極は、光によって水から水素を発生させることができる。具体的には、本発明の水素発生用電極と、別途用意された酸素発生用の電極とを、電線などの導電性材料で接続した後、液体状または気体状の水を供給しながら光を照射することで、各々の電極表面より水素ガスおよび酸素ガスが発生して水分解反応を進行させることができる。必要に応じて電極間に電位差を設けることで、水分解反応を促進することができる。通常は、水または電解質水溶液に各電極を浸漬して光照射することで水分解が進行する。
<<Method of generating hydrogen by water decomposition>>
The hydrogen generating electrode of the present invention can generate hydrogen from water by light. Specifically, after connecting the electrode for hydrogen generation of the present invention and the separately prepared electrode for oxygen generation with a conductive material such as an electric wire, light is emitted while liquid or gaseous water is supplied. By irradiating, hydrogen gas and oxygen gas are generated from the surface of each electrode, and the water splitting reaction can proceed. The water-splitting reaction can be promoted by providing a potential difference between the electrodes as necessary. Normally, each electrode is immersed in water or an aqueous electrolyte solution and irradiated with light to promote water decomposition.
本発明においては、集電層上に、ｐ型半導体層及びｎ型半導体層をこの順に有し、ｎ型半導体層上に助触媒を担持し、ｐ型半導体層が、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有するｐ型半導体を含むため、水分解反応において、高い電流密度とより貴側のオンセット電位となる光電気化学特性を示す。 In the present invention, a p-type semiconductor layer and an n-type semiconductor layer are provided in this order on the current collecting layer, a co-catalyst is carried on the n-type semiconductor layer, and the p-type semiconductor layer comprises Cu, S, Since it contains a p-type semiconductor containing at least one of Ga and In and an alkali metal as essential components, it exhibits photoelectrochemical properties such as a high current density and a more noble onset potential in a water splitting reaction.
照射する光の光源としては、太陽のほか、キセノンランプ、メタルハライドランプ等の太陽光近似光ないし疑似太陽光を照射可能なランプ、水銀ランプ、ＬＥＤ等が挙げられる。 Examples of the light source for irradiation include, in addition to the sun, lamps capable of irradiating near-sunlight or pseudo-sunlight, such as xenon lamps and metal halide lamps, mercury lamps, and LEDs.
この水分解の活性評価は、電極の光電気化学特性を評価することで代用するのが一般的である。例えば、実施例で示すように、３電極（特性評価用電極、Ｐｔ対照電極、Ａｇ／ＡｇＣｌ参照電極）を一つのセル内の電解質水溶液に浸漬し、ポテンショスタットを用いて特性評価用電極にある電位からある電位まで印加しながら一定の速度で掃引し、その間、ソーラーシミュレーターによる光照射をｏｎとｏｆｆを交互に繰り返すことで、電流－電位曲線を得るという評価方法で、水分解の活性を評価することができる。上述のとおり、この際に得られる電流－電位曲線から、電流密度が大きいほど水素発生活性が高いこと、および、オンセット電位がより貴側にあれば酸素発生用電極との組合せによる水分解が有効に機能することが期待できる。 This water-splitting activity evaluation is generally substituted by evaluating the photoelectrochemical properties of the electrode. For example, as shown in the Examples, three electrodes (characterization electrode, Pt control electrode, Ag/AgCl reference electrode) are immersed in an aqueous electrolyte solution in one cell and a potentiostat is used to The activity of water splitting is evaluated by an evaluation method in which a current-potential curve is obtained by sweeping at a constant speed while applying a potential to a certain potential, during which the light irradiation by the solar simulator is alternately turned on and off. can do. As described above, from the current-potential curve obtained at this time, it can be seen that the higher the current density, the higher the hydrogen generation activity, and that if the onset potential is on the more noble side, the water splitting due to the combination with the oxygen generation electrode will occur. It can be expected to function effectively.
以下、実施例に基づいて本発明の水素発生用電極について具体的に説明するが、本発明はこれらの実施例に限定されるものではない。
＜実施例１＞ Ｐｔ／ＣｄＳ／ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極の作製および光電気化学特性評価
［Ｍｏコートソーダライムガラス（Ｍｏ／ＳＬＧ）基板の作製］
１０×１０×１．１ｍｍのソーダライムガラス（ＳＬＧ）板に、Ｍｏ薄膜をＲＦマグネトロンスパッタ法にて成膜し、Ｍｏ／ＳＬＧ基板を得た。具体的には、Ｍｏ成膜時の試料温度を３５０℃、成膜チャンバー内のＡｒ分圧を２．５×１０－１Ｐａ、ＲＦ出力を２００Ｗに設定し、成膜時間は４５分間とし、厚さ５００ｎｍのＭｏ薄膜（Ｍｏ層）を、ＳＬＧ上に形成した。
The hydrogen generating electrode of the present invention will be specifically described below based on Examples, but the present invention is not limited to these Examples.
<Example 1> Production of Pt/CdS/CGIZSSe/TiO x /Mo/SLG electrode and photoelectrochemical property evaluation [Production of Mo-coated soda lime glass (Mo/SLG) substrate]
A Mo thin film was formed on a soda lime glass (SLG) plate of 10×10×1.1 mm by RF magnetron sputtering to obtain a Mo/SLG substrate. Specifically, the sample temperature during Mo deposition was set to 350° C., the Ar partial pressure in the deposition chamber was set to 2.5×10 −1 Pa, the RF output was set to 200 W, and the deposition time was set to 45 minutes. A Mo thin film (Mo layer) with a thickness of 500 nm was formed on the SLG.
［酸化チタンコート層（ＴｉＯｘ／Ｍｏ／ＳＬＧ）の作製］
上記手法で得たＭｏ／ＳＬＧ基板の上に、反応性スパッタ法にて酸化チタン膜を成膜し、ＴｉＯｘ／Ｍｏ／ＳＬＧ基板を得た。具体的には、成膜装置にはスパッタ成膜装置（アルバック機工製、ＭＰＳ－２５４）を、Ｔｉターゲットには豊島製作所製（３Ｎ）のものを用い、試料温度を１５０℃、ガス流量をＯ２：５ｓｃｃｍ、Ａｒ：１０ｓｃｃｍとし、成膜チャンバー内圧力を６．０×１０－１Ｐａ、ＲＦ出力を１００Ｗに設定し、成膜時間は６０分とし、厚さが３０ｎｍの酸化チタン層をＭｏ／ＳＬＧ基板上に形成した。
[Preparation of titanium oxide coat layer (TiO x /Mo/SLG)]
A TiO x /Mo/SLG substrate was obtained by depositing a titanium oxide film by a reactive sputtering method on the Mo/SLG substrate obtained by the above method. Specifically, a sputtering film deposition device (manufactured by ULVAC KIKO, MPS-254) was used as the film deposition device, and a Ti target (3N) manufactured by Toyoshima Seisakusho was used. 2 : 5 sccm, Ar: 10 sccm, the pressure in the deposition chamber was set to 6.0 × 10 -1 Pa, the RF output was set to 100 W, the deposition time was set to 60 minutes, and the titanium oxide layer having a thickness of 30 nm was Mo. /SLG substrate.
［Ｌｉ－ＣＧＩＺＳＳｅ層（ｐ型半導体層）の作製）］
ＴｉＯｘ／Ｍｏ／ＳＬＧ基板上に多元蒸着法によってＬｉ－ＣＧＩＺＳＳｅ層を成膜することによって、集電層上にｐ型半導体層を積層した。具体的には、成膜装置にはＭＢＥ装置（（株）エピクエスト製、ＲＣ６１００）を用い、原料として、Ｃｕ（フルウチ化学製、６Ｎ）、Ｉｎ（フルウチ化学製、６Ｎ）、Ｇａ（高純度化学製、７Ｎ）、Ｚｎ（高純度化学製、６Ｎ）、Ｓｅ（フルウチ化学製、６Ｎ）、ＬｉＦ（高純度化学製、３Ｎ）をそれぞれ熱分解用のセル内にセットし、Ｓ（高純度化学製、５Ｎ）はＳ用バルブドクラッカーセル（Ｖｅｅｃｏ製 Ｍａｒｋ Ｖ ５００ｃｃ）にセットして、独立に加熱、蒸発させて、その蒸気を、同じく圧力１×１０－３Ｐａ以下に保たれた成膜チャンバー内に配置されたＴｉＯｘ／Ｍｏ／ＳＬＧ基板に照射することにより堆積させた。原料供給量の制御は、各原料の堆積速度を各セルの温度により制御することにより行った。また、５５０℃で３０分間以上脱ガス処理を行った後、３５０℃から６００℃まで温度を上昇させながら合計１７０分間蒸着を実施した。
以上の操作によって約１．５μｍ厚のＬｉ－ＣＧＩＺＳＳｅ薄膜を得た。走査型電子顕微鏡（ＳＥＭ）による形態観察時におけるエネルギー分散型Ｘ線分析法（ＥＤＸ）による組成分析から、上記式（Ａ）に基づくと、組成は、モル基準で、Ｃｕ：Ｇａ：Ｉｎ：Ｚｎ：Ｓ：Ｓｅ＝０．９９：０．３５：０．６５：０．３６：１．８１：０．１９であることが確認された。またＩＣＰ分析により、リチウムの含有量（モル％）、すなわち上記式（Ａ）のｆ／（ｆ＋ａ＋ｂ＋ｃ＋ｄ）×１００の値が０．２であることを確認した。
[Production of Li-CGIZSSe layer (p-type semiconductor layer)]
A p-type semiconductor layer was deposited on the current collecting layer by depositing a Li-CGIZSSe layer on the TiO x /Mo/SLG substrate by multi-source deposition. Specifically, an MBE device (manufactured by Epiquest Co., Ltd., RC6100) is used as a film forming device, and Cu (manufactured by Furuuchi Chemical Co., Ltd., 6N), In (manufactured by Furuuchi Chemical Co., Ltd., 6N), Ga (high-purity Kagaku, 7N), Zn (Koujundo Kagaku, 6N), Se (Furuuchi Kagaku, 6N), and LiF (Koujundo Kagaku, 3N) are set in respective thermal decomposition cells, and S (Koujundo Kagaku, 3N) Kagaku, 5N) was set in a valved cracker cell for S (Veeco Mark V 500cc), heated and evaporated independently, and the vapor was similarly kept at a pressure of 1 × 10 -3 Pa or less. It was deposited by irradiation on a TiO x /Mo/SLG substrate placed in a film chamber. The amount of raw material supplied was controlled by controlling the deposition rate of each raw material by the temperature of each cell. After degassing at 550° C. for 30 minutes or more, vapor deposition was performed for a total of 170 minutes while raising the temperature from 350° C. to 600° C.
A Li-CGIZSSe thin film having a thickness of about 1.5 μm was obtained by the above operation. From composition analysis by energy dispersive X-ray spectroscopy (EDX) during morphological observation with a scanning electron microscope (SEM), based on the above formula (A), the composition is Cu:Ga:In:Zn on a molar basis. :S:Se=0.99:0.35:0.65:0.36:1.81:0.19. Also, by ICP analysis, it was confirmed that the lithium content (mol %), that is, the value of f/(f+a+b+c+d)×100 in the above formula (A) was 0.2.
［ＣＢＤ法によるＣｄＳ（ｎ型半導体層）の形成］
ガラス製ビーカーに純水２５ｍＬを採取し、アンモニア水（和光純薬、２８％）２５ｍＬ、酢酸カドミウム二水和物（関東化学、９８．０％）０．３３ｇを加え、６０℃に昇温した後、チオ尿素（関東化学、９８．０％）１．４２ｇを加えた後ただちに上記Ｌｉ－ＣＧＩＺＳＳｅ層を液中に約１０分間浸漬した。その後、純水で洗浄した後、２００℃に加熱したホットプレート上で１分間加熱して乾燥させて、Ｌｉ－ＣＧＩＺＳＳｅ層上にＣｄＳ層を形成した。
[Formation of CdS (n-type semiconductor layer) by CBD method]
25 mL of pure water was collected in a glass beaker, 25 mL of ammonia water (Wako Pure Chemical, 28%), and 0.33 g of cadmium acetate dihydrate (Kanto Chemical, 98.0%) were added, and the temperature was raised to 60 ° C. After that, 1.42 g of thiourea (Kanto Kagaku, 98.0%) was added, and the Li-CGIZSSe layer was immediately immersed in the liquid for about 10 minutes. Then, after washing with pure water, it was dried by heating on a hot plate heated to 200° C. for 1 minute to form a CdS layer on the Li—CGIZSSe layer.
［光電着法によるＰｔ（助触媒）の担持］
上記［ＣＢＤ法によるＣｄＳ（ｎ型半導体層）の形成］にてＬｉ－ＣＧＩＺＳＳｅ層上にＣｄＳを形成した後、エポキシ樹脂を用いて裏面と横面など不用な部分を封止し、さらにＩｎ導線を集電層に接着することで、ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を得た。
下記の参照電極を備えたフラスコに電解液１００ｍＬを仕込み、アルゴン置換した後、塩化白金酸（和光純薬、９８．５％）５０μＬを加えた。その後、上記で得られた電極を液中に浸して－０．２Ｖ ｖｓ ＲＨＥの電位にて下記のソーラーシミュレーターを光源に用いて光照射を行った。観測される光カソード電流値が飽和したところで電着を終了して、Ｐｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を得た。処理時間は約４０分であった。
・光源：ソーラーシミュレーター ＡＭ１．５Ｇ（三永電機 ＸＥＳ－４０Ｓ１、１００ｍＷ／ｃｍ２）
・電解液：０．５Ｍ Ｎａ２ＳＯ４、０．２５Ｍ Ｎａ２ＨＰＯ４、０．２５Ｍ ＮａＨ２ＰＯ４ ｐＨ６．３
・参照電極：Ａｇ／ＡｇＣｌ、対電極 Ｐｔワイヤ
・アルゴン雰囲気
[Supporting of Pt (promoter) by photoelectrodeposition]
After forming CdS on the Li-CGIZSSe layer in the above [Formation of CdS (n-type semiconductor layer) by CBD method], use epoxy resin to seal unnecessary parts such as the back and side surfaces, and further In conducting wire was adhered to the current collecting layer to obtain a CdS/Li-CGIZSSe/TiO x /Mo/SLG electrode.
100 mL of the electrolytic solution was charged into a flask equipped with the following reference electrode, and after argon substitution, 50 μL of chloroplatinic acid (Wako Pure Chemical Industries, Ltd., 98.5%) was added. Thereafter, the electrode obtained above was immersed in a liquid and irradiated with light at a potential of −0.2 V vs. RHE using the following solar simulator as a light source. Electrodeposition was terminated when the observed photocathode current value was saturated to obtain a Pt/CdS/Li-CGIZSSe/TiO x /Mo/SLG electrode. Processing time was about 40 minutes.
・Light source: Solar simulator AM1.5G (Mitsunaga Electric XES-40S1, 100mW/cm 2 )
- Electrolyte: 0.5M Na2SO4 , 0.25M Na2HPO4 , 0.25M NaH2PO4 pH 6.3
・Reference electrode: Ag/AgCl, counter electrode Pt wire ・Argon atmosphere
［光電気化学特性評価］
上記で得られたＰｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を用いて、Ｐｔ対照電極、Ａｇ／ＡｇＣｌ参照電極（東洋製；ＴＲＥ－１０）を備えた３電極１セル方式にて、ポテンショスタット（北斗電工製、ＨＳＶ－１１０）を用いて、以下の測定条件にて光電気化学特性を調べた。印加電圧を０．０Ｖ ｖｓ ＲＨＥから１．０Ｖ ｖｓ ＲＨＥまで２０ｍＶ／ｓの速度で掃引し、その間、ソーラーシミュレーターによる光照射をｏｎとｏｆｆを２秒ずつ交互に繰り返し行った。得られた電流－電位曲線を図１に示す。また、図１から求めた、０．６ＶｖｓＲＨＥにおける電流密度（ｍＡ／ｃｍ２）及びオンセット電位ＶｖｓＲＨＥを表１に示す。
・光源：ソーラーシミュレーター ＡＭ１．５Ｇ（三永電機製 ＸＥＳ－４０Ｓ１、１００ｍＷ／ｃｍ２）
・電解液：０．５Ｍ Ｎａ２ＳＯ４、０．２５Ｍ Ｎａ２ＨＰＯ４、０．２５Ｍ ＮａＨ２ＰＯ４ ｐＨ ６．３
・参照電極 Ａｇ／ＡｇＣｌ、対電極 Ｐｔワイヤ
・アルゴン雰囲気
[Photoelectrochemical property evaluation]
Using the Pt/CdS/Li-CGIZSSe/TiO x /Mo/SLG electrode obtained above, a three-electrode one-cell system equipped with a Pt control electrode and an Ag/AgCl reference electrode (Toyo; TRE-10) was used. Using a potentiostat (manufactured by Hokuto Denko, HSV-110), photoelectrochemical properties were examined under the following measurement conditions. The applied voltage was swept from 0.0 V vs. RHE to 1.0 V vs. RHE at a rate of 20 mV/s, during which light irradiation from the solar simulator was alternately turned on and off for 2 seconds each. The resulting current-potential curve is shown in FIG. Table 1 shows the current density (mA/cm 2 ) at 0.6 V vs RHE and the onset potential V vs RHE obtained from FIG.
・Light source: Solar simulator AM1.5G (Mitsunaga Electric XES-40S1, 100mW/cm2)
- Electrolyte: 0.5M Na2SO4 , 0.25M Na2HPO4 , 0.25M NaH2PO4 pH 6.3
・Reference electrode Ag/AgCl, counter electrode Pt wire ・Argon atmosphere
＜実施例２＞
実施例１の［酸化チタンコート層（ＴｉＯｘ／Ｍｏ／ＳＬＧ）の作製］おいて、Ｔｉスパッタする代わりにＧａスパッタを行うことで酸化ガリウム膜（ＧａＯｘ層）を成膜したこと以外は、実施例１と同様にして、Ｐｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＧａＯｘ／Ｍｏ／ＳＬＧ電極を作製した。ＧａＯｘの膜厚は約２０ｎｍであった。Ｌｉ－ＣＧＩＺＳＳｅ層の各組成およびＬｉ含有量は、実施例１と同じであった。
実施例１と同様に光電気化学特性評価を行うことで得た電流－電位曲線を図１に示す。
<Example 2>
In [Preparation of titanium oxide coat layer (TiO x /Mo/SLG)] of Example 1, Ga sputtering was performed instead of Ti sputtering to form a gallium oxide film (GaO x layer). Similar to Example 1, a Pt/CdS/Li-CGIZSSe/GaO x /Mo/SLG electrode was produced. The GaO x film thickness was about 20 nm. Each composition and Li content of the Li-CGIZSSe layer were the same as in Example 1.
A current-potential curve obtained by evaluating photoelectrochemical properties in the same manner as in Example 1 is shown in FIG.
＜実施例３＞
Ｔｉをスパッタせず、すなわち酸化チタンコート層を積層しなかったこと以外は、実施例１と同様にして、Ｐｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／Ｍｏ／ＳＬＧ電極を作製した。Ｌｉ－ＣＧＩＺＳＳｅ層の各組成およびＬｉ含有量は、実施例１と同じであった。
実施例１と同様に光電気化学特性評価を行うことで得た電流－電位曲線を図１に示す。
<Example 3>
A Pt/CdS/Li-CGIZSSe/Mo/SLG electrode was produced in the same manner as in Example 1, except that Ti was not sputtered, that is, a titanium oxide coating layer was not laminated. Each composition and Li content of the Li-CGIZSSe layer were the same as in Example 1.
A current-potential curve obtained by evaluating photoelectrochemical properties in the same manner as in Example 1 is shown in FIG.
＜実施例４＞
Ｌｉ－ＣＧＩＺＳＳｅ層の作製において、多元蒸着時の原料の堆積速度を変更したこと以外は、実施例１と同様にして、Ｐｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を作製した。Ｌｉ－ＣＧＩＺＳＳｅ層について、実施例１と同様の組成分析を行ったところ、組成は、Ｃｕ：Ｇａ：Ｉｎ：Ｚｎ：Ｓ：Ｓｅ＝１．０４：０．４９：０．５５：０．３５：１．８７：０．１３であった。
電解液にＫＯＨ水溶液を追加使用してｐＨ１３．０とした以外は実施例１と同様にして光電気化学特性を評価した。得られた電流－電位曲線を図２に示す。
<Example 4>
A Pt/CdS/Li-CGIZSSe/TiO x /Mo/SLG electrode was produced in the same manner as in Example 1, except that the deposition rate of the raw materials during multi-source deposition was changed in the production of the Li-CGIZSSe layer. When the composition analysis of the Li-CGIZSSe layer was performed in the same manner as in Example 1, the composition was Cu:Ga:In:Zn:S:Se=1.04:0.49:0.55:0.35: 1.87:0.13.
The photoelectrochemical properties were evaluated in the same manner as in Example 1, except that an aqueous KOH solution was additionally used as the electrolyte to adjust the pH to 13.0. The resulting current-potential curve is shown in FIG.
＜実施例５＞
ｎ型半導体としてＣｄＳの代わりにＣｄＳ及びＩｎ２Ｓ３を積層し、また、助触媒としてＰｔの代わりにＲｕＯ２を担持させたこと以外は実施例１と同様にして、ＲｕＯ２／Ｉｎ２Ｓ３／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を作製した。具体的には、実施例１における［ＣＢＤ法によるＣｄＳ（ｎ型半導体層）の形成］において、ＣｄＳを積層後、さらに、硫酸インジウムｎ水和物０．６５ｍｇを用いて同様の操作を行うことでｎ型半導体としてＣｄＳとＩｎ２Ｓ３を積層した。また、実施例１における［光電着法によるＰｔ（助触媒）の担持］においては、塩化白金酸の代わりにＲｕ源として過ルテニウム酸カリウム（ＫＲｕＯ４）２６．５ｍｇを用いて、同様の処方により、Ｐｔの代わりにＲｕＯ２を光電着によって担持した。
Ｌｉ－ＣＧＩＺＳＳｅ層について、実施例１と同様の組成分析を行ったところ、組成は、Ｃｕ：Ｇａ：Ｉｎ：Ｚｎ：Ｓ：Ｓｅ＝０．９３：０．４９：０．６５：０．２５：１．８２：０．１８であった。
電解液を、ＮａＯＨ水溶液を用いてｐＨ９．０としたこと以外は実施例１と同様にして、光電気化学特性を評価した。得られた電流－電位曲線を図２に示す。
<Example 5>
RuO 2 / In 2 S was fabricated in the same manner as in Example 1, except that CdS and In 2 S 3 were stacked instead of CdS as n-type semiconductors, and RuO 2 was supported instead of Pt as a co-catalyst. 3 /CdS/Li-CGIZSSe/TiO x /Mo/SLG electrodes were fabricated. Specifically, in [Formation of CdS (n-type semiconductor layer) by CBD method] in Example 1, after laminating CdS, the same operation is performed using 0.65 mg of indium sulfate n-hydrate. CdS and In 2 S 3 were stacked as n-type semiconductors. In addition, in [supporting Pt (promoter) by photoelectrodeposition] in Example 1, 26.5 mg of potassium perruthenate (KRuO 4 ) was used as the Ru source instead of chloroplatinic acid, and the same formulation was used. , RuO instead of Pt was supported by photodeposition.
When the composition analysis of the Li-CGIZSSe layer was performed in the same manner as in Example 1, the composition was Cu:Ga:In:Zn:S:Se=0.93:0.49:0.65:0.25: 1.82:0.18.
Photoelectrochemical properties were evaluated in the same manner as in Example 1, except that the electrolytic solution was adjusted to pH 9.0 using an aqueous NaOH solution. The resulting current-potential curve is shown in FIG.
＜実施例６＞
Ｌｉ－ＣＧＩＺＳＳｅ層の作製において多元蒸着時の原料の堆積速度を変更したこと以外は、実施例５と同様にして、ＲｕＯ２／Ｉｎ２Ｓ３／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を作製した。Ｌｉ－ＣＧＩＺＳＳｅ層について、実施例１と同様の組成分析を行ったところ、組成は、Ｃｕ：Ｇａ：Ｉｎ：Ｚｎ：Ｓ：Ｓｅ＝１．０４：０．４９：０．５５：０．３５：１．８７：０．１３であった。
電解液を、ＮａＯＨ水溶液を用いてｐＨ１３．０とした以外は実施例１と同様にして、光電気化学特性評価を行った。得られた電流－電位曲線を図２に示す。
<Example 6>
RuO 2 /In 2 S 3 /CdS/Li-CGIZSSe/TiO x /Mo/SLG in the same manner as in Example 5, except that the deposition rate of the raw materials during multi-source deposition was changed in the production of the Li-CGIZSSe layer. An electrode was produced. When the composition analysis of the Li-CGIZSSe layer was performed in the same manner as in Example 1, the composition was Cu:Ga:In:Zn:S:Se=1.04:0.49:0.55:0.35: 1.87:0.13.
Photoelectrochemical characteristics were evaluated in the same manner as in Example 1, except that the electrolytic solution was adjusted to pH 13.0 using an aqueous NaOH solution. The resulting current-potential curve is shown in FIG.
＜実施例７＞
酸化チタン層（ＴｉＯｘ層）の厚さを２０ｎｍとし、Ｌｉ－ＣＧＩＺＳＳｅ層の作製において多元蒸着時の原料の堆積速度を変更したこと以外は、実施例１と同様にして、Ｐｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／ＴｉＯｘ／Ｍｏ／ＳＬＧ電極を作製した。Ｌｉ－ＣＧＩＺＳＳｅ層について、実施例１と同様の組成分析を行ったところ、組成は、Ｃｕ：Ｇａ：Ｉｎ：Ｚｎ：Ｓ：Ｓｅ＝１．０４：０．３６：０．６２：０．１５：１．７５：０．２５であった。
実施例１と同様にして光電気化学特性を評価して得られた電流－電位曲線を図３に示す。
<Example 7>
Pt/CdS/Li was prepared in the same manner as in Example 1, except that the thickness of the titanium oxide layer (TiO x layer) was set to 20 nm, and the deposition rate of the raw materials during multi-source deposition was changed in the preparation of the Li-CGIZSSe layer. - CGIZSSe/TiO x /Mo/SLG electrodes were fabricated. When the composition analysis of the Li-CGIZSSe layer was performed in the same manner as in Example 1, the composition was Cu:Ga:In:Zn:S:Se=1.04:0.36:0.62:0.15: 1.75:0.25.
A current-potential curve obtained by evaluating photoelectrochemical properties in the same manner as in Example 1 is shown in FIG.
＜実施例８＞
ＴｉＯｘ層を積層しないこと以外は実施例７と同様にしてＰｔ／ＣｄＳ／Ｌｉ－ＣＧＩＺＳＳｅ／Ｍｏ／ＳＬＧ電極を作製した。Ｌｉ－ＣＧＩＺＳＳｅ層の組成は実施例７と同じであった。
実施例１と同様に光電気化学特性評価を行うことで得た電流－電位曲線を図３に示す。
<Example 8>
A Pt/CdS/Li-CGIZSSe/Mo/SLG electrode was fabricated in the same manner as in Example 7 except that the TiO x layer was not laminated. The composition of the Li-CGIZSSe layer was the same as in Example 7.
A current-potential curve obtained by evaluating photoelectrochemical properties in the same manner as in Example 1 is shown in FIG.
図１～３及び表１に示されているように、実施例１～８の水素発生用電極は、オンセット電位は０．８～１．０Ｖ ｖｓ ＲＨＥ付近にあり、０．６～１．０Ｖ ｖｓ ＲＨＥ付近の電流密度は数ｍＡ／ｃｍ２の高い電流密度が認められる。 As shown in FIGS. 1 to 3 and Table 1, the electrodes for hydrogen generation of Examples 1 to 8 have onset potentials of around 0.8 to 1.0 V vs RHE, and 0.6 to 1.0 V vs. RHE. A high current density of several mA/cm 2 is observed near 0 V vs RHE.
Claims (7)
集電層上に、ｐ型半導体層及びｎ型半導体層をこの順に有し、前記ｎ型半導体層上に助触媒を担持し、
前記ｐ型半導体層が、Ｃｕと、Ｓと、Ｇａ及びＩｎの少なくとも一方と、アルカリ金属とを必須成分として含有し、必要に応じてＺｎ及びＳｅの少なくとも一方を含有するｐ型半導体を含み、
前記アルカリ金属が、Ｌｉを含むことを特徴とする水素発生用電極。 A hydrogen generating electrode for generating hydrogen from water by light,
A p-type semiconductor layer and an n-type semiconductor layer are provided in this order on a current collecting layer, and a promoter is supported on the n-type semiconductor layer;
The p-type semiconductor layer contains Cu, S, at least one of Ga and In, and an alkali metal as essential components, and optionally contains a p-type semiconductor containing at least one of Zn and Se. ,
The electrode for hydrogen generation , wherein the alkali metal contains Li .
前記集電層上に前記ｐ型半導体層を形成するｐ型半導体層形成工程と、
前記ｐ型半導体層上に前記ｎ型半導体層を形成するｎ型半導体層形成工程と、
前記ｎ型半導体層上に前記助触媒を担持する助触媒担持工程と、
を備えてなることを特徴とする水素発生用電極の製造方法。 A method for producing a hydrogen generating electrode according to any one of claims 1 to 5 ,
a p-type semiconductor layer forming step of forming the p-type semiconductor layer on the current collecting layer;
an n-type semiconductor layer forming step of forming the n-type semiconductor layer on the p-type semiconductor layer;
a co-catalyst supporting step of supporting the co-catalyst on the n-type semiconductor layer;
A method for producing a hydrogen generating electrode, comprising:
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