JPWO2019172014A1 - Photocatalytic electrode for water decomposition and water decomposition equipment - Google Patents
Photocatalytic electrode for water decomposition and water decomposition equipment Download PDFInfo
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- JPWO2019172014A1 JPWO2019172014A1 JP2020504938A JP2020504938A JPWO2019172014A1 JP WO2019172014 A1 JPWO2019172014 A1 JP WO2019172014A1 JP 2020504938 A JP2020504938 A JP 2020504938A JP 2020504938 A JP2020504938 A JP 2020504938A JP WO2019172014 A1 JPWO2019172014 A1 JP WO2019172014A1
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- semiconductor layer
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- electrode
- photocatalyst electrode
- photocatalyst
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 74
- 230000001699 photocatalysis Effects 0.000 title claims abstract description 21
- 238000000354 decomposition reaction Methods 0.000 title abstract description 26
- 239000004065 semiconductor Substances 0.000 claims abstract description 175
- 239000011941 photocatalyst Substances 0.000 claims abstract description 93
- 150000001875 compounds Chemical class 0.000 claims abstract description 47
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 39
- 239000001257 hydrogen Substances 0.000 claims abstract description 39
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 37
- 229910052738 indium Inorganic materials 0.000 claims abstract description 31
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 31
- 229910052733 gallium Inorganic materials 0.000 claims abstract description 30
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 29
- 239000001301 oxygen Substances 0.000 claims abstract description 29
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- 229910052711 selenium Inorganic materials 0.000 claims abstract description 13
- 229910052802 copper Inorganic materials 0.000 claims abstract description 11
- 238000011049 filling Methods 0.000 claims abstract description 7
- 230000001678 irradiating effect Effects 0.000 claims abstract description 5
- 239000007864 aqueous solution Substances 0.000 claims description 24
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
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- 150000002431 hydrogen Chemical class 0.000 description 2
- 238000009616 inductively coupled plasma Methods 0.000 description 2
- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
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- 229910052715 tantalum Inorganic materials 0.000 description 2
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 229910052723 transition metal Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- 238000002834 transmittance Methods 0.000 description 2
- LWIHDJKSTIGBAC-UHFFFAOYSA-K tripotassium phosphate Chemical compound [K+].[K+].[K+].[O-]P([O-])([O-])=O LWIHDJKSTIGBAC-UHFFFAOYSA-K 0.000 description 2
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- 229910052692 Dysprosium Inorganic materials 0.000 description 1
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- 230000005678 Seebeck effect Effects 0.000 description 1
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 1
- 229910021607 Silver chloride Inorganic materials 0.000 description 1
- 229910004121 SrRuO Inorganic materials 0.000 description 1
- 229910003071 TaON Inorganic materials 0.000 description 1
- 229910052771 Terbium Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Natural products NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 1
- 239000004327 boric acid Substances 0.000 description 1
- 235000010338 boric acid Nutrition 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- UHYPYGJEEGLRJD-UHFFFAOYSA-N cadmium(2+);selenium(2-) Chemical compound [Se-2].[Cd+2] UHYPYGJEEGLRJD-UHFFFAOYSA-N 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
- 150000002484 inorganic compounds Chemical class 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000003014 ion exchange membrane Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910000403 monosodium phosphate Inorganic materials 0.000 description 1
- 235000019799 monosodium phosphate Nutrition 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
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- 229920000573 polyethylene Polymers 0.000 description 1
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- 229920002223 polystyrene Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 235000011118 potassium hydroxide Nutrition 0.000 description 1
- 229910000160 potassium phosphate Inorganic materials 0.000 description 1
- 235000011009 potassium phosphates Nutrition 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 239000005297 pyrex Substances 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 229940065287 selenium compound Drugs 0.000 description 1
- 150000003343 selenium compounds Chemical class 0.000 description 1
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000005092 sublimation method Methods 0.000 description 1
- 150000004763 sulfides Chemical class 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000010408 sweeping Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/50—Processes
- C25B1/55—Photoelectrolysis
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
- B01J27/04—Sulfides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
- B01J27/057—Selenium or tellurium; Compounds thereof
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
- C01B13/02—Preparation of oxygen
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/042—Electrodes formed of a single material
- C25B11/049—Photocatalysts
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- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
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- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
- C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
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- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
- C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
- C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
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- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
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- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/50—Cells or assemblies of cells comprising photoelectrodes; Assemblies of constructional parts thereof
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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
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Electrochemistry (AREA)
- Metallurgy (AREA)
- Inorganic Chemistry (AREA)
- Combustion & Propulsion (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Catalysts (AREA)
- Oxygen, Ozone, And Oxides In General (AREA)
Abstract
本発明の課題は、オンセットポテンシャルに優れた水分解用光触媒電極および水分解装置の提供である。本発明の水分解装置は、水素発生用の光触媒電極および酸素発生用の光触媒電極に光を照射することによって、水素発生用の光触媒電極および酸素発生用の光触媒電極から気体を発生させる水分解装置であって、電解水溶液を満たすための槽と、槽内に配置された水素発生用の光触媒電極および酸素発生用の光触媒電極と、を有し、水素発生用の光触媒電極が、ｐ型半導体層と、ｐ型半導体層上に設けられたｎ型半導体層と、ｎ型半導体層の上に設けられた助触媒を有し、ｐ型半導体層が、Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体を含む半導体層であり、ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である。An object of the present invention is to provide a photocatalytic electrode for water decomposition and a water decomposition device having excellent onset potential. The water splitting apparatus of the present invention is a water splitting apparatus that generates gas from the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation by irradiating the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation with light. A tank for filling the electrolytic solution, a photocatalyst electrode for hydrogen generation and a photocatalyst electrode for oxygen generation arranged in the tank are provided, and the photocatalyst electrode for hydrogen generation is a p-type semiconductor layer. A CIGS compound having an n-type semiconductor layer provided on the p-type semiconductor layer and a cocatalyst provided on the n-type semiconductor layer, wherein the p-type semiconductor layer contains Cu, In, Ga, and Se. It is a semiconductor layer containing a semiconductor, and the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.
Description
本発明は、水分解用光触媒電極および水分解装置に関する。 The present invention relates to a photocatalytic electrode for water decomposition and a water decomposition device.
太陽電池の光吸収層として、優れた太陽光変換効率を有する等の点から、Ｃｕ、Ｉｎ、ＧａおよびＳｅの合金からなるＣＩＧＳ化合物を用いることが知られている。例えば、非特許文献１には、太陽電池の光吸収層に用いるＣＩＧＳ化合物として、ＧａおよびＩｎの合計量に対する、Ｇａのモル比が０．３の場合に、太陽光変換効率が特に優れることが開示されている。
近年、上述の太陽電池等の光を電気に変換する光電変換装置の他に、太陽エネルギーの利用方法として、光触媒を用いて水を分解して、水素および酸素を製造する技術に注目が集まっている。As a light absorption layer of a solar cell, it is known to use a CIGS compound composed of an alloy of Cu, In, Ga and Se from the viewpoint of having excellent sunlight conversion efficiency. For example, Non-Patent Document 1 states that as a CIGS compound used in the light absorption layer of a solar cell, the solar conversion efficiency is particularly excellent when the molar ratio of Ga to the total amount of Ga and In is 0.3. It is disclosed.
In recent years, in addition to the above-mentioned photoelectric conversion device that converts light such as a solar cell into electricity, as a method of utilizing solar energy, attention has been focused on a technique for decomposing water using a photocatalyst to produce hydrogen and oxygen. There is.
水分解用光触媒電極には、気体の発生量を増加させるために、水分解装置に適用した際に生じる電流値が高いことが求められる。この場合、その電流値を取り出せる電位（オンセットポテンシャル）も重要である。
ここで、水素発生用の光触媒電極と酸素発生用の光触媒電極とを用い、可視光照射下で水を分解して、水素および酸素の両方を発生できる系（いわゆる、「Ｚスキーム」）を利用した水分解装置が知られている。
このようなＺスキームを利用した２つの光触媒電極を有する水分解装置に着目した場合、１つの光触媒電極において、水の分解に必要とされる電圧（約１．２３Ｖ）の約半分以上の電圧をもつような電位（オンセットポテンシャル）で電流を取り出せることが水分解装置の性能の指針となる。
このような観点から、本発明者らが、上記文献に記載された太陽電池に使用されているＣＩＧＳ化合物半導体を水分解用光触媒電極に適用したところ、オンセットポテンシャルが不充分であり、水分解装置に求められる性能を満たしていないことを知見した。The photocatalyst electrode for water decomposition is required to have a high current value when applied to a water decomposition apparatus in order to increase the amount of gas generated. In this case, the potential (onset potential) from which the current value can be taken out is also important.
Here, using a photocatalyst electrode for hydrogen generation and a photocatalyst electrode for oxygen generation, a system capable of decomposing water under visible light irradiation to generate both hydrogen and oxygen (so-called "Z scheme") is used. The water splitting device is known.
Focusing on a water splitting device having two photocatalyst electrodes using such a Z scheme, one photocatalyst electrode can generate a voltage of about half or more of the voltage required for water decomposition (about 1.23 V). The ability to extract current with a potential (onset potential) is a guideline for the performance of the water splitting device.
From this point of view, when the present inventors applied the CIGS compound semiconductor used in the solar cell described in the above document to the photocatalytic electrode for water splitting, the onset potential was insufficient and the water splitting occurred. It was found that the performance required for the device was not satisfied.
そこで、本発明は、オンセットポテンシャルに優れた水分解用光触媒電極および水分解装置の提供を課題とする。 Therefore, an object of the present invention is to provide a photocatalytic electrode for water decomposition and a water decomposition device having excellent onset potential.
本発明者らは、上記課題について鋭意検討した結果、ＣＩＧＳ化合物半導体を含む半導体層を有する水分解用光触媒電極を水分解装置に適用した場合において、ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計量に対するＧａのモル比が所定範囲内にあれば、オンセットポテンシャルに優れることを見出し、本発明に至った。
また、本発明者らは、ｐ型半導体層とｎ型半導体層とを有する水分解用光触媒電極を有する水分解装置において、ｐ型半導体層の伝導帯の下端のポテンシャルと、ｎ型半導体層の伝導帯の下端のポテンシャルとの差であるバンドオフセットが所定値以下であれば、水分解用光触媒電極のオンセットポテンシャルに優れることを見出し、本発明に至った。
すなわち、本発明者らは、以下の構成により上記課題が解決できることを見出した。As a result of diligent studies on the above problems, the present inventors have applied a photocatalytic electrode for water splitting having a semiconductor layer containing a CIGS compound semiconductor to a water splitting device, with respect to the total amount of Ga and In in the CIGS compound semiconductor. We have found that the onset potential is excellent when the molar ratio of Ga is within a predetermined range, and have reached the present invention.
Further, the present inventors have determined the potential of the lower end of the conduction band of the p-type semiconductor layer and the potential of the n-type semiconductor layer in a water decomposition apparatus having a photocatalytic electrode for water decomposition having a p-type semiconductor layer and an n-type semiconductor layer. We have found that when the band offset, which is the difference from the potential at the lower end of the conduction band, is equal to or less than a predetermined value, the onset potential of the photocatalyst electrode for water splitting is excellent, and the present invention has been made.
That is, the present inventors have found that the above problems can be solved by the following configuration.
［１］
水素発生用の光触媒電極および酸素発生用の光触媒電極に光を照射することによって、上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極から気体を発生させる水分解装置であって、
電解水溶液を満たすための槽と、
上記槽内に配置された上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極と、を有し、
上記水素発生用の光触媒電極が、ｐ型半導体層と、上記ｐ型半導体層上に設けられたｎ型半導体層と、上記ｎ型半導体層の上に設けられた助触媒を有し、
上記ｐ型半導体層が、Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体を含む半導体層であり、
上記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である、水分解装置。
［２］
上記ｎ型半導体層がＣｄＳを含む、［１］に記載の水分解装置。
［３］
さらに、上記ｎ型半導体層と上記助触媒との間に設けられた金属層を有する、［１］または［２］に記載の水分解装置。
［４］
上記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．５〜０．７である、［１］〜［３］のいずれか１つに記載の水分解装置。
［５］
水素発生用の光触媒電極および酸素発生用の光触媒電極に光を照射することによって、上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極から気体を発生させる水分解装置であって、
電解水溶液を満たすための槽と、
上記槽内に配置された上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極と、を有し、
上記水素発生用の光触媒電極が、ｐ型半導体層と、上記ｐ型半導体層上に設けられたｎ型半導体層と、上記ｎ型半導体層の上に設けられた助触媒を有し、
上記ｐ型半導体層の伝導帯の下端のポテンシャルｐ−ＣＢＭと、上記ｎ型半導体層の伝導帯の下端のポテンシャルｎ−ＣＢＭと、の差であるバンドオフセットΔＥが以下の関係を満たす、水分解装置。
ΔＥ＝（ｎ−ＣＢＭ）−（ｐ−ＣＢＭ）≦０．１［ｅＶ］
［６］
Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体を含む半導体層を有し、
上記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である、水分解用光触媒電極。[1]
A water splitting device that generates gas from the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode by irradiating the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode with light.
A tank for filling the electrolytic aqueous solution and
It has the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen evolution arranged in the tank.
The photocatalyst electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer.
The p-type semiconductor layer is a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga and Se.
A water splitting apparatus in which the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.
[2]
The water splitting apparatus according to [1], wherein the n-type semiconductor layer contains CdS.
[3]
The water splitting apparatus according to [1] or [2], further comprising a metal layer provided between the n-type semiconductor layer and the co-catalyst.
[4]
The water splitting apparatus according to any one of [1] to [3], wherein the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.5 to 0.7.
[5]
A water splitting device that generates gas from the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode by irradiating the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode with light.
A tank for filling the electrolytic aqueous solution and
It has the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen evolution arranged in the tank.
The photocatalyst electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer.
Hydrolysis in which the band offset ΔE, which is the difference between the potential p-CBM at the lower end of the conduction band of the p-type semiconductor layer and the potential n-CBM at the lower end of the conduction band of the n-type semiconductor layer, satisfies the following relationship. apparatus.
ΔE = (n-CBM)-(p-CBM) ≤ 0.1 [eV]
[6]
It has a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga and Se.
A photocatalytic electrode for water splitting, wherein the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.
以下に示すように、本発明によれば、オンセットポテンシャルに優れた水分解用光触媒電極および水分解装置を提供できる。 As shown below, according to the present invention, it is possible to provide a photocatalytic electrode for water decomposition and a water decomposition device having excellent onset potential.
以下に、本発明について説明する。
なお、本発明において「〜」を用いて表される数値範囲は、「〜」の前後に記載される数値を下限値および上限値として含む範囲を意味する。
本発明において、可視光とは、電磁波のうちヒトの目で見える波長の光であり、具体的には３８０〜７８０ｎｍの波長域の光を示す。
なお、本明細書において、オンセットポテンシャルに優れるとは、オンセットポテンシャルの値が０．６Ｖ（ｖｓ．ＲＨＥ）以上であることを意味する。ここで、ＲＨＥは、reversible hydrogen electrode（可逆水素電極）の略である。光触媒電極として用いる場合に、０．６Ｖ（ｖｓ．ＲＨＥ）でより多くの電流が得られることが好ましい。The present invention will be described below.
In the present invention, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.
In the present invention, the visible light is light having a wavelength visible to the human eye among electromagnetic waves, and specifically, light having a wavelength range of 380 to 780 nm.
In the present specification, excellent onset potential means that the value of onset potential is 0.6 V (vs. RHE) or more. Here, RHE is an abbreviation for reversible hydrogen electrode. When used as a photocatalytic electrode, it is preferable that a larger current can be obtained at 0.6 V (vs. RHE).
以下において、本発明の水分解装置について、実施形態毎に詳細に説明する。 Hereinafter, the water splitting apparatus of the present invention will be described in detail for each embodiment.
［第１実施形態］
本発明の水分解装置の一実施形態は、水素発生用の光触媒電極および酸素発生用の光触媒電極に光を照射することによって、上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極から気体を発生させる水分解装置であって、電解水溶液を満たすための槽と、上記槽内に配置された上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極と、を有し、上記水素発生用の光触媒電極が、ｐ型半導体層と、上記ｐ型半導体層上に設けられたｎ型半導体層と、上記ｎ型半導体層の上に設けられた助触媒を有し、上記ｐ型半導体層が、Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体を含む半導体層であり、上記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である。本明細書において、上記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計量に対するＧａのモル比を、単に「Ｇａ比」と略記する場合がある。[First Embodiment]
In one embodiment of the water splitting apparatus of the present invention, the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation are irradiated with light, so that the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation are gas. It is a water splitting apparatus that generates the above-mentioned hydrogen, and has a tank for filling an electrolytic aqueous solution, the above-mentioned photocatalyst electrode for hydrogen generation and the above-mentioned photocatalyst electrode for generating oxygen, which are arranged in the tank. The photocatalyst electrode for use has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer, and the p-type semiconductor layer. Is a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga and Se, and the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8. is there. In the present specification, the molar ratio of Ga to the total amount of Ga and In in the CIGS compound semiconductor may be simply abbreviated as "Ga ratio".
第１実施形態の水分解装置における光触媒電極（具体的には、水素発生用の光触媒電極）は、優れたオンセットポテンシャルを示す。この理由の詳細は明らかになっていないが、概ね以下の理由によるものと推測される。
すなわち、太陽電池を構成する光吸収層として最適な組成であるＧａ比が０．３のＣＩＧＳ化合物半導体を光触媒電極に適用した場合、ＣＩＧＳ化合物半導体の伝導帯端（伝導帯の最底部）と、これと隣接する層（例えば、後述するｎ型半導体層）の伝導帯端（伝導帯の最底部）とのオフセット電位が大きく、これが障壁となって、キャリア輸送を阻害するためと考えられる。そのため、ＣＩＧＳ化合物半導体の伝導帯端（伝導帯の最底部）は、これと隣接する層（例えば、後述するｎ型半導体層）の伝導帯端（伝導帯の最底部）と同等または浅い方が好ましい。具体的には、ｐ型半導体層の伝導帯の下端のポテンシャルｐ−ＣＢＭと、ｎ型半導体層の伝導帯の下端のポテンシャルｎ−ＣＢＭと、の差であるバンドオフセットΔＥ（下記式参照）は、０．１ｅＶ以下が好ましく、０ｅＶ以下がより好ましい。また、ΔＥの下限値は、−０．５ｅＶ以上が好ましい。
ΔＥ＝（ｎ−ＣＢＭ）−（ｐ−ＣＢＭ）
Ｇａ比が０．４以上であれば、ＣＩＧＳ化合物半導体の伝導帯端（伝導帯の最底部）が浅くなるので、ＣＩＧＳ化合物半導体と隣接する層とのオフセット電位が小さくなる結果、優れたオンセットポテンシャルを示すものになったと推測される。The photocatalytic electrode (specifically, the photocatalytic electrode for hydrogen generation) in the water splitting apparatus of the first embodiment exhibits excellent onset potential. The details of this reason have not been clarified, but it is presumed that it is due to the following reasons.
That is, when a CIGS compound semiconductor having a Ga ratio of 0.3, which is an optimum composition as a light absorption layer constituting a solar cell, is applied to a photocatalyst electrode, the conduction band end (the bottom of the conduction band) of the CIGS compound semiconductor and It is considered that the offset potential between this and the conduction band end (the bottom of the conduction band) of the adjacent layer (for example, the n-type semiconductor layer described later) is large, which acts as a barrier and hinders carrier transport. Therefore, the conduction band end (bottom of the conduction band) of the CIGS compound semiconductor should be equal to or shallower than the conduction band end (bottom of the conduction band) of a layer adjacent to the CIGS compound semiconductor (for example, an n-type semiconductor layer described later). preferable. Specifically, the band offset ΔE (see the following formula), which is the difference between the potential p-CBM at the lower end of the conduction band of the p-type semiconductor layer and the potential n-CBM at the lower end of the conduction band of the n-type semiconductor layer, is , 0.1 eV or less is preferable, and 0 eV or less is more preferable. The lower limit of ΔE is preferably −0.5 eV or higher.
ΔE = (n-CBM)-(p-CBM)
When the Ga ratio is 0.4 or more, the conduction band end (the bottom of the conduction band) of the CIGS compound semiconductor becomes shallow, and as a result, the offset potential between the CIGS compound semiconductor and the adjacent layer becomes small, resulting in excellent onset. It is presumed that it has become an indicator of potential.
本発明において、ｐ−ＣＢＭおよびｎ−ＣＢＭは、大気中光電子分光装置（製品名「ＡＣ−３」、理研計器社製）を用いて価電子帯の上端のポテンシャルを求めて、それに紫外可視分光光度計（製品名「Ｖ−７７０」、日本分光社製）から求めたバンドギャップの値を加えて得られる値である。
なお、本発明において、伝導帯の下端のポテンシャルの値は、真空準位を基準（０ｅＶ）として、マイナス側に軸を取った場合の値である。In the present invention, p-CBM and n-CBM use an atmospheric photoelectron spectrometer (product name "AC-3", manufactured by RIKEN KEIKI) to determine the potential of the upper end of the valence band, and ultraviolet-visible spectroscopy. It is a value obtained by adding the value of the band gap obtained from a photometric meter (product name "V-770", manufactured by JASCO Corporation).
In the present invention, the potential value at the lower end of the conduction band is a value when the axis is taken to the minus side with the vacuum level as a reference (0 eV).
以下において、第１実施形態の水分解装置の構成について、図面を参照しながら説明する。
図１は、第１実施形態の水分解装置の一例である水分解装置１を模式的に示す側面図である。水分解装置１は、光Ｌの照射によって、アノード電極１０（酸素発生用の光触媒電極）およびカソード電極２０（水素発生用の光触媒電極）から気体を発生させる装置である。具体的には、光Ｌによって水が分解して、アノード電極１０から酸素が発生し、カソード電極２０から水素が発生する。
図１に示すように、水分解装置１は、電解水溶液Ｓで満たされた槽４０と、槽４０内に配置されたアノード電極１０およびカソード電極２０と、アノード電極１０とカソード電極２０との間であって槽４０内に配置された隔膜３０と、を有する。アノード電極１０、隔膜３０およびカソード電極２０は、光Ｌの進行方向と交差する方向に沿って、この順に配置されている。
照射される光Ｌとしては、太陽光などの可視光、紫外光または赤外光などが利用でき、その中でも、その量が無尽蔵である太陽光が好ましい。Hereinafter, the configuration of the water splitting device of the first embodiment will be described with reference to the drawings.
FIG. 1 is a side view schematically showing a water splitting device 1 which is an example of the water splitting device of the first embodiment. The water decomposition device 1 is a device that generates gas from the anode electrode 10 (photocatalyst electrode for oxygen generation) and the cathode electrode 20 (photocatalyst electrode for hydrogen generation) by irradiation with light L. Specifically, water is decomposed by light L, oxygen is generated from the anode electrode 10, and hydrogen is generated from the cathode electrode 20.
As shown in FIG. 1, the water splitting device 1 is located between a tank 40 filled with an electrolytic aqueous solution S, an anode electrode 10 and a cathode electrode 20 arranged in the tank 40, and an anode electrode 10 and a cathode electrode 20. It has a diaphragm 30 arranged in the tank 40. The anode electrode 10, the diaphragm 30, and the cathode electrode 20 are arranged in this order along the direction intersecting the traveling direction of the light L.
As the light L to be irradiated, visible light such as sunlight, ultraviolet light, infrared light and the like can be used, and among them, sunlight whose amount is inexhaustible is preferable.
＜槽＞
槽４０内は、隔膜３０によって、アノード電極１０が配置されたアノード電極室４２と、カソード電極２０が配置されたカソード電極室４４と、に区画されている。
槽４０は、これに限定されないが、アノード電極１０およびカソード電極２０に対する単位面積当たりの入射光量が大きくなるように、傾けて配置されている。また、槽４０を傾けた状態で電解水溶液Ｓが流れ出ないように、槽４０は密封されている。
槽４０を構成する材料の具体例としては、耐腐食性（特に、耐アルカリ性）に優れた材料が好ましく、ポリアクリレート、ポリメタクリレート、ポリカーボネート、ポリプロピレン、ポリエチレン、ポリスチレン、ガラスが挙げられる。<Tank>
The inside of the tank 40 is divided by a diaphragm 30 into an anode electrode chamber 42 in which the anode electrode 10 is arranged and a cathode electrode chamber 44 in which the cathode electrode 20 is arranged.
The tank 40 is tilted so as to increase the amount of incident light per unit area with respect to the anode electrode 10 and the cathode electrode 20, but not limited to this. Further, the tank 40 is sealed so that the electrolytic aqueous solution S does not flow out when the tank 40 is tilted.
Specific examples of the material constituting the tank 40 are preferably a material having excellent corrosion resistance (particularly alkali resistance), and examples thereof include polyacrylate, polymethacrylate, polycarbonate, polypropylene, polyethylene, polystyrene, and glass.
（電解水溶液）
図１に示すように、槽４０内は電解水溶液Ｓで満たされており、アノード電極１０、カソード電極２０および隔膜３０の全体が電解水溶液Ｓに浸漬している。
電解水溶液Ｓは、電解質を水に溶解させた溶液である。電解質の具体例としては、硫酸、硫酸ナトリウム、水酸化カリウム、リン酸カリウム、および、ホウ酸が挙げられる。
電解水溶液ＳのｐＨは、６〜１１が好ましい。電解水溶液ＳのｐＨが上記範囲内にあれば、安全に取り扱いができるという利点がある。なお、電解水溶液ＳのｐＨは、公知のｐＨメータを用いて測定でき、測定温度は２５℃である。
電解水溶液Ｓ中の電解質の濃度は、特に限定されないが、電解水溶液ＳのｐＨが上記範囲内になるように調整されるのが好ましい。(Electrolytic aqueous solution)
As shown in FIG. 1, the inside of the tank 40 is filled with the electrolytic aqueous solution S, and the entire anode electrode 10, the cathode electrode 20, and the diaphragm 30 are immersed in the electrolytic aqueous solution S.
The electrolytic aqueous solution S is a solution in which an electrolyte is dissolved in water. Specific examples of the electrolyte include sulfuric acid, sodium sulfate, potassium hydroxide, potassium phosphate, and boric acid.
The pH of the electrolytic aqueous solution S is preferably 6 to 11. If the pH of the electrolytic aqueous solution S is within the above range, there is an advantage that it can be handled safely. The pH of the electrolytic aqueous solution S can be measured using a known pH meter, and the measurement temperature is 25 ° C.
The concentration of the electrolyte in the electrolytic aqueous solution S is not particularly limited, but it is preferable that the pH of the electrolytic aqueous solution S is adjusted to be within the above range.
＜アノード電極＞
アノード電極１０は、アノード電極室４２内に配置されている。
アノード電極１０は、第１基板１２と、第１基板１２上に配置された第１導電層１４と、第１導電層１４上に配置された第１光触媒層１６と、を有する。アノード電極１０は、光Ｌが照射される側から、第１光触媒層１６、第１導電層１４、および、第１基板１２の順になるように、槽４０内に配置されている。
図１の例では、アノード電極１０は平板状であるが、これに限定されない。アノード電極１０は、パンチングメタル状、メッシュ状、格子状、または、貫通した細孔を持つ多孔体であってもよい。
アノード電極１０は、導線５０によってカソード電極２０と電気的に接続されている。図１では、アノード電極１０とカソード電極２０とが導線５０によって接続されている例を示したが、電気的に接続されていれば、接続方式は特に限定されない。
アノード電極１０の厚みは、０．１〜５ｍｍが好ましく、０．５〜２ｍｍがより好ましい。<Anode electrode>
The anode electrode 10 is arranged in the anode electrode chamber 42.
The anode electrode 10 has a first substrate 12, a first conductive layer 14 arranged on the first substrate 12, and a first photocatalyst layer 16 arranged on the first conductive layer 14. The anode electrodes 10 are arranged in the tank 40 in the order of the first photocatalyst layer 16, the first conductive layer 14, and the first substrate 12 from the side irradiated with the light L.
In the example of FIG. 1, the anode electrode 10 has a flat plate shape, but the present invention is not limited to this. The anode electrode 10 may be a punched metal-like, mesh-like, lattice-like, or porous body having penetrating pores.
The anode electrode 10 is electrically connected to the cathode electrode 20 by a lead wire 50. FIG. 1 shows an example in which the anode electrode 10 and the cathode electrode 20 are connected by a lead wire 50, but the connection method is not particularly limited as long as they are electrically connected.
The thickness of the anode electrode 10 is preferably 0.1 to 5 mm, more preferably 0.5 to 2 mm.
（第１基板）
第１基板１２は、第１導電層１４および第１光触媒層１６を支持する層である。
第１基板１２を構成する材料の具体例としては、金属、有機化合物（例えば、ポリアクリレート、ポリメタクリレート）、無機化合物（例えば、ＳｒＴｉＯ３等の金属酸化物、ガラス、セラミックス）が挙げられる。
第１基板１２の厚みは、０．１〜５ｍｍが好ましく、０．５〜２ｍｍがより好ましい。(1st board)
The first substrate 12 is a layer that supports the first conductive layer 14 and the first photocatalyst layer 16.
Specific examples of the material constituting the first substrate 12 include metals, organic compounds (for example, polyacrylates and polymethacrylates), and inorganic compounds (for example, metal oxides such as SrTIO 3 , glass, and ceramics).
The thickness of the first substrate 12 is preferably 0.1 to 5 mm, more preferably 0.5 to 2 mm.
（第１導電層）
アノード電極１０が第１導電層１４を有することで、アノード電極１０に対する光Ｌの入射によって生じた電子が、導線５０を介してカソード電極２０の第２導電層２４（後述）に移動する。
第１導電層１４を構成する材料の具体例としては、金属（例えば、Ｓｎ、Ｔｉ、Ｔａ、Ａｕ）、ＳｒＲｕＯ３、ＩＴＯ（酸化インジウムスズ）、酸化亜鉛系の透明導電材料（Ａｌ：ＺｎＯ，Ｉｎ：ＺｎＯ，Ｇａ：ＺｎＯなど）が挙げられる。なお、Ａｌ：ＺｎＯなどの「金属原子：金属酸化物」との表記は、金属酸化物を構成する金属（Ａｌ：ＺｎＯの場合には、Ｚｎ）の一部を、金属原子（Ａｌ：ＺｎＯの場合には、Ａｌ）で置換したものを意味する。
第１導電層１４の厚みは、５０ｎｍ〜１μｍが好ましく、１００〜５００ｎｍがより好ましい。
第１導電層１４を形成する方法としては、特に限定されず、例えば、気相成長法（例えば、化学気相成長法、スパッタ法）が挙げられる。(First conductive layer)
Since the anode electrode 10 has the first conductive layer 14, the electrons generated by the incident light L on the anode electrode 10 move to the second conductive layer 24 (described later) of the cathode electrode 20 via the conducting wire 50.
Specific examples of the material constituting the first conductive layer 14 include metals (for example, Sn, Ti, Ta, Au), SrRuO 3 , ITO (indium tin oxide), and zinc oxide-based transparent conductive materials (Al: ZnO, In: ZnO, Ga: ZnO, etc.). In addition, the notation of "metal atom: metal oxide" such as Al: ZnO refers to a part of the metal (Zn in the case of Al: ZnO) constituting the metal oxide as a metal atom (Al: ZnO). In the case, it means the one replaced with Al).
The thickness of the first conductive layer 14 is preferably 50 nm to 1 μm, more preferably 100 to 500 nm.
The method for forming the first conductive layer 14 is not particularly limited, and examples thereof include a vapor phase growth method (for example, a chemical vapor deposition method and a sputtering method).
（第１光触媒層）
アノード電極１０に光Ｌが照射されると、第１光触媒層１６で生じた電子が、第１導電層１４に移動する。一方、第１光触媒層１６で生じたホール（正孔）が水と反応することで、アノード電極１０から酸素が発生する。
第１光触媒層１６の厚みは、１００ｎｍ〜１０μｍが好ましく、３００ｎｍ〜２μｍがより好ましい。(1st photocatalyst layer)
When the anode electrode 10 is irradiated with light L, the electrons generated in the first photocatalyst layer 16 move to the first conductive layer 14. On the other hand, the holes generated in the first photocatalyst layer 16 react with water to generate oxygen from the anode electrode 10.
The thickness of the first photocatalyst layer 16 is preferably 100 nm to 10 μm, more preferably 300 nm to 2 μm.
第１光触媒層１６を構成し得る材料としては、Ｂｉ２ＷＯ６、ＢｉＶＯ４、ＢｉＹＷＯ６、Ｉｎ２Ｏ３（ＺｎＯ）３、ＩｎＴａＯ４、ＩｎＴａＯ４：Ｎｉ（「化合物：Ｍ」は、光半導体にＭをドープしていることを示す。以下同様。）、ＴｉＯ２：Ｎｉ、ＴｉＯ２：Ｒｕ、ＴｉＯ２Ｒｈ、ＴｉＯ２：Ｎｉ／Ｔａ（「化合物：Ｍ１／Ｍ２」は、光半導体にＭ１とＭ２を共ドープしていることを示す。以下同様。）、ＴｉＯ２：Ｎｉ／Ｎｂ、ＴｉＯ２：Ｃｒ／Ｓｂ、ＴｉＯ２：Ｎｉ／Ｓｂ、ＴｉＯ２：Ｓｂ／Ｃｕ、ＴｉＯ２：Ｒｈ／Ｓｂ、ＴｉＯ２：Ｒｈ／Ｔａ、ＴｉＯ２：Ｒｈ／Ｎｂ、ＳｒＴｉＯ３：Ｎｉ／Ｔａ、ＳｒＴｉＯ３：Ｎｉ／Ｎｂ、ＳｒＴｉＯ３：Ｃｒ、ＳｒＴｉＯ３：Ｃｒ／Ｓｂ、ＳｒＴｉＯ３：Ｃｒ／Ｔａ、ＳｒＴｉＯ３：Ｃｒ／Ｎｂ、ＳｒＴｉＯ３：Ｃｒ／Ｗ、ＳｒＴｉＯ３：Ｍｎ、ＳｒＴｉＯ３：Ｒｕ、ＳｒＴｉＯ３：Ｒｈ、ＳｒＴｉＯ３：Ｒｈ／Ｓｂ、ＳｒＴｉＯ３：Ｉｒ、ＣａＴｉＯ３：Ｒｈ、Ｌａ２Ｔｉ２Ｏ７：Ｃｒ、Ｌａ２Ｔｉ２Ｏ７：Ｃｒ／Ｓｂ、Ｌａ２Ｔｉ２Ｏ７：Ｆｅ、ＰｂＭｏＯ４：Ｃｒ、ＲｂＰｂ２Ｎｂ３Ｏ１０、ＨＰｂ２Ｎｂ３Ｏ１０、ＰｂＢｉ２Ｎｂ２Ｏ９、ＢｉＶＯ４、ＢｉＣｕ２ＶＯ６、ＢｉＳｎ２ＶＯ６、ＳｎＮｂ２Ｏ６、ＡｇＮｂＯ３、ＡｇＶＯ３、ＡｇＬｉ１／３Ｔｉ２／３Ｏ２、ＡｇＬｉ１／３Ｓｎ２／３Ｏ２、ＷＯ３、ＢａＢｉ１−ｘＩｎｘＯ３、ＢａＺｒ１−ｘＳｎｘＯ３、ＢａＺｒ１−ｘＧｅｘＯ３、およびＢａＺｒ１−ｘＳｉｘＯ３などの酸化物、ＬａＴｉＯ２Ｎ、Ｃａ０．２５Ｌａ０．７５ＴｉＯ２．２５Ｎ０．７５、ＴａＯＮ、ＣａＮｂＯ２Ｎ、ＢａＮｂＯ２Ｎ、ＣａＴａＯ２Ｎ、ＳｒＴａＯ２Ｎ、ＢａＴａＯ２Ｎ、ＬａＴａＯ２Ｎ、Ｙ２Ｔａ２Ｏ５Ｎ２、（Ｇａ１−ｘＺｎｘ）（Ｎ１−ｘＯｘ）、（Ｚｎ１＋ｘＧｅ）（Ｎ２Ｏｘ）（ｘは、０−１の数値を表す）、およびＴｉＮｘＯｙＦｚなどの酸窒化物、ＮｂＮ、およびＴａ３Ｎ５などの窒化物、ＣｄＳなどの硫化物、ＣｄＳｅなどのセレン化物、Ｌｘ ２Ｔｉ２Ｓ２Ｏ５（Ｌｘ：Ｐｒ、Ｎｄ、Ｓｍ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、またはＥｒ）、ならびにＬａ、Ｉｎを含むオキシサルファイド化合物（Chemistry Letters、2007,36,854−855）が挙げられるが、ここに例示した材料に限定されるものではない。Materials that can form the first photocatalyst layer 16 include Bi 2 WO 6 , BiVO 4 , BiYWO 6 , In 2 O 3 (ZnO) 3 , InTaO 4 , InTaO 4 : Ni (“Compound: M” is an optical semiconductor. (The same applies hereinafter), TiO 2 : Ni, TiO 2 : Ru, TiO 2 Rh, TiO 2 : Ni / Ta ("Compound: M1 / M2" is M1 in the photosemiconductor. And M2 are co-doped. The same applies hereinafter.), TiO 2 : Ni / Nb, TiO 2 : Cr / Sb, TiO 2 : Ni / Sb, TiO 2 : Sb / Cu, TiO 2 : Rh / Sb, TiO 2 : Rh / Ta, TiO 2 : Rh / Nb, SrTIO 3 : Ni / Ta, SrTIO 3 : Ni / Nb, SrTIO 3 : Cr, SrTIO 3 : Cr / Sb, SrTIO 3 : Cr / Ta, SrTIO 3 : Cr / Nb, SrTIO 3 : Cr / W, SrTIO 3 : Mn, SrTIO 3 : Ru, SrTIO 3 : Rh, SrTIO 3 : Rh / Sb, SrTIO 3 : Ir, CaTIO 3 : Rh, La 2 Ti 2 O 7 : Cr, La 2 Ti 2 O 7 : Cr / Sb, La 2 Ti 2 O 7 : Fe, PbMoO 4 : Cr, RbPb 2 Nb 3 O 10 , HPb 2 Nb 3 O 10 , PbBi 2 Nb 2 O 9 , BiVO 4 , BiCu 2 VO 6 , BiSn 2 VO 6 , SnNb 2 O 6 , AgNbO 3 , AgVO 3 , AgLi 1/3 Ti 2/3 O 2 , AgLi 1/3 Sn 2/3 O 2 , WO 3 B Oxides such as 1-x InxO 3 , BaZr 1-x Sn x O 3 , BaZr 1-x Ge x O 3 , and BaZr 1-x Si x O 3 , LaTIO 2 N, Ca 0.25 La 0.75 TiO 2.25 N 0.75 , TaON, CaNbO 2 N, BaNbO 2 N, CaTaO 2 N, SrTaO 2 N, BaTaO 2 N, LaTaO 2 N, Y 2 Ta 2 O 5 N 2 , (Ga 1-x Zn) x ) (N 1-x O x ), (Zn 1 + x Ge) (N 2 O x ) (x represents the value of 0-1), and TiN x O y F z, etc. Nitride, NbN, and nitrides such as Ta 3 N 5 , sulfides such as CdS, selenium compounds such as CdSe, L x 2 Ti 2 S 2 O 5 (L x : Pr, Nd, Sm, Gd, Tb) , Dy, Ho, or Er), and oxysulfide compounds containing La, In (Chemistry Letters, 2007, 36, 854-855), but are not limited to the materials exemplified herein.
第１光触媒層１６の形成方法としては、特に限定されず、例えば、気相成長法（例えば、化学気相成長法、スパッタ法、パルスレーザーデポジション法など）および粒子転写法が挙げられる。 The method for forming the first photocatalyst layer 16 is not particularly limited, and examples thereof include a vapor phase growth method (for example, a chemical vapor deposition method, a sputtering method, a pulse laser deposition method, etc.) and a particle transfer method.
第１光触媒層１６は、その表面に助触媒が担持されていてもよい。助触媒が担持されていれば、オンセットポテンシャルや気体生成効率が良好になる。助触媒の具体例は、上述の通りである。
助触媒を担持させる方法としては、特に限定されず、例えば、浸漬法（例えば、助触媒を含む懸濁液中に光触媒層を浸漬させる方法）および気相成長法（例えば、スパッタ法）が挙げられる。A co-catalyst may be supported on the surface of the first photocatalyst layer 16. If the co-catalyst is supported, the onset potential and gas generation efficiency are improved. Specific examples of the co-catalyst are as described above.
The method for supporting the co-catalyst is not particularly limited, and examples thereof include a dipping method (for example, a method of immersing the photocatalyst layer in a suspension containing a co-catalyst) and a vapor phase growth method (for example, a sputtering method). Be done.
＜カソード電極＞
カソード電極１０は、絶縁基板２２の表面２２ａ上に、導電層２４と、ｐ型半導体層２６と、ｎ型半導体層２８と、助触媒３２とが、この順で積層されている。図１の例では、ｐ型半導体層２６とｎ型半導体層２８とで半導体層２９が構成される。<Cathode electrode>
In the cathode electrode 10, the conductive layer 24, the p-type semiconductor layer 26, the n-type semiconductor layer 28, and the co-catalyst 32 are laminated in this order on the surface 22a of the insulating substrate 22. In the example of FIG. 1, the semiconductor layer 29 is composed of the p-type semiconductor layer 26 and the n-type semiconductor layer 28.
（絶縁基板）
絶縁基板２２は、導電層２４および半導体層２９を支持する基板であり、電気絶縁性を有する材料で構成される。
絶縁基板２２は、特に限定されないが、例えば、ソーダライムガラス基板（以下、ＳＬＧ基板という）またはセラミックス基板を用いることができる。
また、絶縁基板２２には、金属基板上に絶縁層が形成されたものを用いてもよい。
また、絶縁基板２２には、高歪点ガラスおよび無アルカリガラス等のガラス板、または、ポリイミド材を用いることもできる。
絶縁基板２２は、フレキシブルなものであっても、そうでなくてもよい。(Insulated substrate)
The insulating substrate 22 is a substrate that supports the conductive layer 24 and the semiconductor layer 29, and is made of a material having electrical insulating properties.
The insulating substrate 22 is not particularly limited, but for example, a soda lime glass substrate (hereinafter referred to as SLG substrate) or a ceramic substrate can be used.
Further, as the insulating substrate 22, one in which an insulating layer is formed on a metal substrate may be used.
Further, as the insulating substrate 22, a glass plate such as high-strain point glass and non-alkali glass, or a polyimide material can also be used.
The insulating substrate 22 may or may not be flexible.
絶縁基板２２の厚みは、特に限定されるものではなく、例えば、２０〜２００００μｍ程度あればよく、１００〜１００００μｍが好ましく、１０００〜５０００μｍがより好ましい。 The thickness of the insulating substrate 22 is not particularly limited, and may be, for example, about 20 to 20000 μm, preferably 100 to 10000 μm, and more preferably 1000 to 5000 μm.
（導電層）
導電層２４は、絶縁基板２２の表面２２ａに形成され、例えば、半導体層２９に電圧を印加するために使用される。
導電層２４は、導電性を有していれば、特に限定されるものではないが、例えば、Ｍｏ、ＣｒおよびＷ等の金属、またはこれらを組み合わせたものにより構成される。これらの中でも、導電層２４は、Ｍｏで構成することが好ましい。
導電層２４は、単層構造でもよいし、２層構造等の積層構造でもよい。
導電層２４の膜厚は、一般的に、その厚みが８００ｎｍ程度であるが、導電層２４は厚みが４００ｎｍ〜１μｍであることが好ましい。(Conductive layer)
The conductive layer 24 is formed on the surface 22a of the insulating substrate 22, and is used, for example, to apply a voltage to the semiconductor layer 29.
The conductive layer 24 is not particularly limited as long as it has conductivity, but is composed of, for example, a metal such as Mo, Cr, and W, or a combination thereof. Among these, the conductive layer 24 is preferably composed of Mo.
The conductive layer 24 may have a single-layer structure or a laminated structure such as a two-layer structure.
The thickness of the conductive layer 24 is generally about 800 nm, but the thickness of the conductive layer 24 is preferably 400 nm to 1 μm.
（半導体層）
半導体層２９は、起電力を発生するものである。半導体層２９は、導電層２４の表面２４ａに形成されたｐ型半導体層２６と、ｐ型半導体層２６の表面２６ａに形成されたｎ型半導体層２８と有し、ｐ型半導体層２６とｎ型半導体層２８との界面でｐｎ接合が形成される。
半導体層２９に入射した光は、半導体層２９内で吸収されて、半導体の価電子帯から伝導帯へ電子を励起する。そして、ｐｎ接合が作る内部電界によって励起されたキャリアのうち、電子はｎ型半導体側へ、正孔はｐ型半導体側へ移動させられる。
ここで、半導体層２９内において、ｐ型半導体層２６およびｎ型半導体層２８の伝導タイプは、ゼーベック効果を利用した計測装置（製品名「ＰＮ−１２α」、ＮＡＰＳＯＮ社製）により測定できる。(Semiconductor layer)
The semiconductor layer 29 generates an electromotive force. The semiconductor layer 29 includes a p-type semiconductor layer 26 formed on the surface 24a of the conductive layer 24 and an n-type semiconductor layer 28 formed on the surface 26a of the p-type semiconductor layer 26, and the p-type semiconductor layer 26 and n. A pn junction is formed at the interface with the type semiconductor layer 28.
The light incident on the semiconductor layer 29 is absorbed in the semiconductor layer 29 and excites electrons from the valence band to the conduction band of the semiconductor. Then, among the carriers excited by the internal electric field created by the pn junction, electrons are moved to the n-type semiconductor side and holes are moved to the p-type semiconductor side.
Here, in the semiconductor layer 29, the conduction type of the p-type semiconductor layer 26 and the n-type semiconductor layer 28 can be measured by a measuring device (product name “PN-12α”, manufactured by NAPSON) using the Seebeck effect.
ｐ型半導体層２６は、Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体から構成されている。Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体は、具体的には、Ｃｕ（Ｉｎ，Ｇａ）Ｓｅ２で表される化合物であってもよいし、Ｃｕ（Ｉｎ，Ｇａ）Ｓｅ２におけるＳｅの一部がＳで置換されたＣｕ（Ｉｎ，Ｇａ）（Ｓｅ，Ｓ）２で表される化合物であってもよい。
ｐ型半導体層２６を構成するＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計量に対する、Ｇａのモル比（Ｇａ比）は、０．４〜０．８である。
Ｇａ比は、０．４以上であり、０．４５以上が好ましく、０．５以上がより好ましい。これにより、ｐ型半導体層２６の伝導帯端が浅くなって、ｎ型半導体層２８とのバンド不連続（バンド障壁）が解消されるため、電子がｎ型半導体層２８に流れやすくなる。
Ｇａ比が大きくなるほどオンセットポテンシャルは優れるという利点がある一方で、Ｇａ比が大きすぎると、バンドギャップが広くなること、ＣＩＧＳ化合物半導体の融点上昇によって粒成長が阻害されて粒径が小さくなること、および、ＣＩＧＳ化合物半導体の結晶性が低下すること等の問題が生じる場合がある。特に、Ｇａ比が０．７を超えると、このような問題が顕著になって、電流値が小さくなる。したがって、Ｇａ比は、０．７以下が好ましく、０．６５以下がより好ましく、０．６以下がさらに好ましい。
本発明において、Ｇａ比は、高周波誘導結合プラズマ発光分光分析法（ＩＣＰ−ＡＥＳ）を用いて、半導体層（ＣＩＧＳ化合物半導体）全体の元素分析に基づいて、算出される。The p-type semiconductor layer 26 is composed of a CIGS compound semiconductor containing Cu, In, Ga and Se. Cu, an In, CIGS compound containing Ga and Se semiconductor, specifically, Cu (In, Ga) may be a compound represented by the Se 2, Cu (In, Ga) in the Se 2 of Se It may be a compound represented by Cu (In, Ga) (Se, S) 2 , which is partially substituted with S.
The molar ratio of Ga (Ga ratio) to the total amount of Ga and In in the CIGS compound semiconductor constituting the p-type semiconductor layer 26 is 0.4 to 0.8.
The Ga ratio is 0.4 or more, preferably 0.45 or more, and more preferably 0.5 or more. As a result, the conduction band end of the p-type semiconductor layer 26 becomes shallow, and the band discontinuity (band barrier) with the n-type semiconductor layer 28 is eliminated, so that electrons can easily flow into the n-type semiconductor layer 28.
The larger the Ga ratio, the better the onset potential. On the other hand, if the Ga ratio is too large, the band gap becomes wider and the grain growth is hindered by the increase in the melting point of the CIGS compound semiconductor, resulting in a smaller particle size. , And problems such as a decrease in the crystallinity of the CIGS compound semiconductor may occur. In particular, when the Ga ratio exceeds 0.7, such a problem becomes remarkable and the current value becomes small. Therefore, the Ga ratio is preferably 0.7 or less, more preferably 0.65 or less, and even more preferably 0.6 or less.
In the present invention, the Ga ratio is calculated based on elemental analysis of the entire semiconductor layer (CIGS compound semiconductor) using radio frequency inductively coupled plasma emission spectroscopy (ICP-AES).
ｐ型半導体層２６（ＣＩＧＳ化合物半導体）の形成方法としては、例えば、多元蒸着法（好ましくは３段階法）、セレン化法、スパッタ法、ハイブリッドスパッタ法、メカノケミカルプロセス法等、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（ウェット成膜法）等が挙げられ、これらの中でも、多元蒸着法が好ましく、３段階法がより好ましい。 Examples of the method for forming the p-type semiconductor layer 26 (CIGS compound semiconductor) include a multi-element vapor deposition method (preferably a three-step method), a selenium deposition method, a sputtering method, a hybrid sputtering method, a mechanochemical process method, and a screen printing method. Proximity sublimation method, MOCVD (Metal Organic Chemical Vapor Deposition) method, spray method (wet film formation method) and the like can be mentioned. Among these, the multi-element vapor deposition method is preferable, and the three-step method is more preferable.
ｐ型半導体層２６の膜厚は、０．５〜３．０μｍが好ましく、１．０〜２．０μｍがより好ましい。 The film thickness of the p-type semiconductor layer 26 is preferably 0.5 to 3.0 μm, more preferably 1.0 to 2.0 μm.
ｎ型半導体層２８は、上述のようにｐ型半導体層２６との界面でｐｎ接合を形成するものである。また、ｎ型半導体層２８は、入射した光Ｌをｐ型半導体層２６に到達させるため、光Ｌが透過する層であるのが好ましい。
ｎ型半導体層２８を構成する材料としては、例えば、Ｃｄ、Ｚｎ、ＳｎおよびＩｎからなる群より選ばれる少なくとも１種の金属元素を含む金属硫化物が挙げられる。金属硫化物は、１種単独で用いても２種以上を併用してもよい。
金属硫化物としては、例えば、ＣｄＳ、ＺｎＳ、Ｚｎ（Ｓ，Ｏ）、Ｚｎ（Ｓ，Ｏ，ＯＨ）、Ｉｎ２Ｓ３、ＳｎＳ、および、ＳｎＳｘＳｅ１−ｘ（Ｘは０以上１未満の数値を表す。）が挙げられ、ＣｄＳおよびＺｎＳが好ましく、ＣｄＳがより好ましい。特に、ＣｄＳは、ＣＩＧＳ化合物半導体との格子整合の観点から好ましい。この場合、ＣＩＧＳ化合物半導体上にＣｄＳを格子整合させた状態（エピタキシャル）で成膜でき、接合界面の欠陥を減らすことができる。
ｎ型半導体層２８の膜厚は、１０ｎｍ〜２μｍが好ましく、１５〜２００ｎｍがより好ましい。
ｎ型半導体層２８の形成には、例えば、化学浴析出法（以下、ＣＢＤ法という）が用いられる。
なお、ｎ型半導体層２８上に、例えば、窓層を設けてもよい。この窓層は、例えば、厚み１０ｎｍ程度のＺｎＯ層で構成される。The n-type semiconductor layer 28 forms a pn junction at the interface with the p-type semiconductor layer 26 as described above. Further, the n-type semiconductor layer 28 is preferably a layer through which the light L is transmitted so that the incident light L reaches the p-type semiconductor layer 26.
Examples of the material constituting the n-type semiconductor layer 28 include metal sulfides containing at least one metal element selected from the group consisting of Cd, Zn, Sn and In. The metal sulfide may be used alone or in combination of two or more.
Examples of metal sulfides include CdS, ZnS, Zn (S, O), Zn (S, O, OH), In 2 S 3 , SnS, and SnS x Se 1-x (X is 0 or more and less than 1). CdS and ZnS are preferable, and CdS is more preferable. In particular, CdS is preferable from the viewpoint of lattice matching with the CIGS compound semiconductor. In this case, the film can be formed in a state (epitaxial) in which CdS is lattice-matched on the CIGS compound semiconductor, and defects at the bonding interface can be reduced.
The film thickness of the n-type semiconductor layer 28 is preferably 10 nm to 2 μm, more preferably 15 to 200 nm.
For the formation of the n-type semiconductor layer 28, for example, a chemical bath precipitation method (hereinafter referred to as CBD method) is used.
For example, a window layer may be provided on the n-type semiconductor layer 28. This window layer is composed of, for example, a ZnO layer having a thickness of about 10 nm.
（助触媒）
助触媒３２は、半導体層２９上、すなわち、ｎ型半導体層２８の表面２８ａに形成されている。助触媒３２は、カソード電極２０のオンセットポテンシャルおよび光電流密度をより良好にできる。
助触媒３２は、ｎ型半導体層２８の表面全体に形成されていてもよく、点在するように島状に形成されていてもよい。
助触媒３２を構成する材料としては、例えば、Ｐｔ、Ｐｄ、Ｎｉ、Ａｕ、Ａｇ、Ｒｕ、Ｃｕ、Ｃｏ、Ｒｈ、ＩｒまたはＭｎ等により構成される単体、およびそれらを組み合わせた合金、ならびにその酸化物が挙げられる。これらの中でも、本発明の効果がより発揮される点から、Ｐｔ、ＲｈまたはＲｕが好ましい。
助触媒３２のサイズは、特に限定されるものではなく、０．５ｎｍ〜１μｍであり、高さが数ｎｍ程度であるのが好ましい。
助触媒３２は、例えば、塗布焼成法、光電着法、真空蒸着法、スパッタ法または含浸法等により形成できる。(Co-catalyst)
The co-catalyst 32 is formed on the semiconductor layer 29, that is, on the surface 28a of the n-type semiconductor layer 28. The co-catalyst 32 can improve the onset potential and photocurrent density of the cathode electrode 20.
The co-catalyst 32 may be formed on the entire surface of the n-type semiconductor layer 28, or may be formed in an island shape so as to be scattered.
Examples of the material constituting the co-catalyst 32 include a simple substance composed of Pt, Pd, Ni, Au, Ag, Ru, Cu, Co, Rh, Ir, Mn and the like, an alloy combining them, and oxidation thereof. Things can be mentioned. Among these, Pt, Rh or Ru is preferable from the viewpoint that the effect of the present invention is more exhibited.
The size of the co-catalyst 32 is not particularly limited, and is preferably 0.5 nm to 1 μm and a height of about several nm.
The co-catalyst 32 can be formed by, for example, a coating firing method, a photoelectric adhesion method, a vacuum deposition method, a sputtering method, an impregnation method, or the like.
（カソード電極に含まれ得る他の部材）
カソード電極２０は、ｎ型半導体層２８と助触媒３２との間に金属層（図示せず）を有していてもよい。この場合、助触媒３２は、金属層の表面に形成される。
金属層は、ｎ型半導体層２８の表層に導電性を付与できる。そのため、半導体層２９で生成したキャリア（電子）が、金属層によって助触媒３２側に容易に移動できる。
金属層は、４族以上の遷移金属で構成することが好ましい。４族以上の遷移金属としては、例えば、Ｔｉ、Ｚｒ、Ｍｏ、ＴａおよびＷが挙げられる。
なお、金属層の厚みは、８ｎｍ以下が好ましく、６ｎｍ以下がより好ましい。金属層の下限は、上述の機能を良好に発揮でき、かつ製造上可能な厚みであれば、特に限定されない。
金属層は、例えば、スパッタ法、真空蒸着法、および電子ビーム蒸着法等で形成できる。(Other members that may be included in the cathode electrode)
The cathode electrode 20 may have a metal layer (not shown) between the n-type semiconductor layer 28 and the co-catalyst 32. In this case, the co-catalyst 32 is formed on the surface of the metal layer.
The metal layer can impart conductivity to the surface layer of the n-type semiconductor layer 28. Therefore, the carriers (electrons) generated in the semiconductor layer 29 can be easily moved to the co-catalyst 32 side by the metal layer.
The metal layer is preferably composed of a group 4 or higher transition metal. Examples of the Group 4 or higher transition metal include Ti, Zr, Mo, Ta and W.
The thickness of the metal layer is preferably 8 nm or less, more preferably 6 nm or less. The lower limit of the metal layer is not particularly limited as long as it can satisfactorily exhibit the above-mentioned functions and has a thickness that can be manufactured.
The metal layer can be formed by, for example, a sputtering method, a vacuum vapor deposition method, an electron beam vapor deposition method, or the like.
カソード電極２０は、上記以外の他の層を有していてもよい。他の層としては、例えば、光触媒電極３２上に形成可能な表面保護層が挙げられる。 The cathode electrode 20 may have a layer other than the above. Examples of the other layer include a surface protective layer that can be formed on the photocatalyst electrode 32.
なお、図１において、カソード電極２０が、絶縁基板１２を有する態様を例に挙げて説明したが、本発明の効果が発揮できるのであれば、これらの部材のうち、いずれかの部材を有していなくてもよい。 In addition, in FIG. 1, the embodiment in which the cathode electrode 20 has the insulating substrate 12 has been described as an example, but if the effect of the present invention can be exhibited, any of these members is provided. It does not have to be.
＜隔膜＞
隔膜３０は、電解水溶液Ｓに含まれるイオンがアノード電極室４２およびカソード電極室４４に自由に出入りできるが、アノード電極１０で発生した気体とカソード電極２０で発生した気体とが混合しないように、アノード電極１０とカソード電極２０との間に配置されている。
隔膜３０を構成する材料としては、特に限定されず、公知のイオン交換膜などが挙げられる。
なお、図１では、隔膜３０が設けられている例を示したが、これに限定されず、隔膜３０が設けられていなくてもよい。<Septum>
The diaphragm 30 allows ions contained in the electrolytic solution S to freely enter and exit the anode electrode chamber 42 and the cathode electrode chamber 44, but the gas generated at the anode electrode 10 and the gas generated at the cathode electrode 20 are not mixed. It is arranged between the anode electrode 10 and the cathode electrode 20.
The material constituting the diaphragm 30 is not particularly limited, and examples thereof include known ion exchange membranes.
Although FIG. 1 shows an example in which the diaphragm 30 is provided, the present invention is not limited to this, and the diaphragm 30 may not be provided.
＜その他の構成＞
アノード電極１０で発生した気体は、アノード電極室４２と接続された図示しない配管から回収できる。カソード電極２０で発生した気体は、カソード電極室４４と接続された図示しない配管から回収できる。
図示していないが、槽４０には、電解水溶液Ｓを供給するための供給管およびポンプなどが接続されていてもよい。<Other configurations>
The gas generated in the anode electrode 10 can be recovered from a pipe (not shown) connected to the anode electrode chamber 42. The gas generated in the cathode electrode 20 can be recovered from a pipe (not shown) connected to the cathode electrode chamber 44.
Although not shown, the tank 40 may be connected to a supply pipe, a pump, or the like for supplying the electrolytic aqueous solution S.
図１では、槽４０内が電解水溶液Ｓで満たされた例を示したが、これに限定されず、水分解装置の駆動時に槽４０内を電解水溶液Ｓで満たせばよい。
図１では、アノード電極１０およびカソード電極２０がいずれも、光触媒電極である場合を示したが、これに限定されず、カソード電極２０のみが光触媒電極であってもよい。FIG. 1 shows an example in which the inside of the tank 40 is filled with the electrolytic aqueous solution S, but the present invention is not limited to this, and the inside of the tank 40 may be filled with the electrolytic aqueous solution S when the water decomposition apparatus is driven.
FIG. 1 shows a case where both the anode electrode 10 and the cathode electrode 20 are photocatalyst electrodes, but the present invention is not limited to this, and only the cathode electrode 20 may be a photocatalyst electrode.
図１では、アノード電極１０、隔膜３０およびカソード電極２０が、光Ｌの進行方向と交差する方向に沿ってこの順に配置されている例を示したが、これに限定されず、本発明の水分解装置は、図２に示す構造であってもよい。
図２は、本発明の水分解装置の一実施形態である水分解装置１００を模式的に示す側面図である。水分解装置１００は、光Ｌの照射によってアノード電極１１０およびカソード電極１２０から気体を発生させる装置である。具体的には、光Ｌによって水が分解して、アノード電極１１０から酸素が発生し、カソード電極１２０から水素が発生する。
図３に示すように、水分解装置１００は、電解水溶液Ｓで満たされた槽４０と、槽４０内に配置されたアノード電極１１０およびカソード電極１２０と、アノード電極１１０とカソード電極１２０との間であって槽４０内に配置された隔膜３０と、を有する。アノード電極１１０、隔膜３０およびカソード電極１２０は、光Ｌの進行方向に沿って、この順に配置されている。水分解装置１００は、アノード電極１１０の配置、カソード電極１２０の配置、および光Ｌの照射方向が図１の水分解装置１と相違する以外は、水分解装置１と同様であるので、異なる部分について主に説明する。FIG. 1 shows an example in which the anode electrode 10, the diaphragm 30, and the cathode electrode 20 are arranged in this order along the direction intersecting the traveling direction of the light L, but the present invention is not limited to this. The disassembling device may have the structure shown in FIG.
FIG. 2 is a side view schematically showing the water splitting device 100, which is an embodiment of the water splitting device of the present invention. The water decomposition device 100 is a device that generates gas from the anode electrode 110 and the cathode electrode 120 by irradiation with light L. Specifically, water is decomposed by light L, oxygen is generated from the anode electrode 110, and hydrogen is generated from the cathode electrode 120.
As shown in FIG. 3, the water splitting device 100 is located between the tank 40 filled with the electrolytic aqueous solution S, the anode electrode 110 and the cathode electrode 120 arranged in the tank 40, and the anode electrode 110 and the cathode electrode 120. It has a diaphragm 30 arranged in the tank 40. The anode electrode 110, the diaphragm 30, and the cathode electrode 120 are arranged in this order along the traveling direction of the light L. The water decomposition device 100 is the same as the water decomposition device 1 except that the arrangement of the anode electrodes 110, the arrangement of the cathode electrodes 120, and the irradiation direction of the light L are different from those of the water decomposition device 1 of FIG. Will be mainly explained.
アノード電極１１０は、光Ｌが照射される側から、第１光触媒層１１６、第１導電層１１４および第１基板１１２の順になるように、槽４０内に配置されている。
カソード電極１２０は、光Ｌが照射される側から、助触媒１３２と、ｎ型半導体層１２８と、ｐ型半導体層１２６と、導電層１２４と、絶縁基板１２２とが、この順になるように、槽４０内に配置されている。なお、ｐ型半導体層１２６とｎ型半導体層１２８とで半導体層１２９が構成される。
アノード電極１１０およびカソード電極１２０は、単位面積当たりの入射光量が大きくなるように傾けて配置されている。
水分解装置１００において、第１基板１１２および第１導電層１１４は、カソード電極１２０に光Ｌを入射させるために、透明であるのが好ましい。これにより、第１光触媒層１１６が吸収できなかった光を、カソード電極１２０が利用できるので、単位面積あたりの光の利用効率が向上するという利点がある。
本発明において「透明」とは、波長３８０ｎｍ〜７８０ｎｍの領域における光透過率が６０％以上であるのを意味する。光透過率は分光光度計により測定される。分光光度計としては、例えば、紫外可視分光光度計である日本分光社製のＶ−７７０（製品名）が用いられる。The anode electrode 110 is arranged in the tank 40 in the order of the first photocatalyst layer 116, the first conductive layer 114, and the first substrate 112 from the side irradiated with the light L.
In the cathode electrode 120, the co-catalyst 132, the n-type semiconductor layer 128, the p-type semiconductor layer 126, the conductive layer 124, and the insulating substrate 122 are arranged in this order from the side irradiated with the light L. It is arranged in the tank 40. The semiconductor layer 129 is composed of the p-type semiconductor layer 126 and the n-type semiconductor layer 128.
The anode electrode 110 and the cathode electrode 120 are arranged at an angle so that the amount of incident light per unit area is large.
In the water decomposition apparatus 100, the first substrate 112 and the first conductive layer 114 are preferably transparent in order to allow light L to enter the cathode electrode 120. As a result, the cathode electrode 120 can use the light that the first photocatalyst layer 116 could not absorb, so that there is an advantage that the light utilization efficiency per unit area is improved.
In the present invention, "transparent" means that the light transmittance in the wavelength region of 380 nm to 780 nm is 60% or more. The light transmittance is measured by a spectrophotometer. As the spectrophotometer, for example, V-770 (product name) manufactured by JASCO Corporation, which is an ultraviolet-visible spectrophotometer, is used.
本発明の水分解用光触媒電極は、Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体を含む半導体層を有し、ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である。本発明の水分解用光触媒電極の詳細は、水分解装置１におけるカソード電極２０で説明した通りであるのでその説明を省略する。 The photocatalytic electrode for water splitting of the present invention has a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga and Se, and the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is determined. It is 0.4 to 0.8. The details of the photocatalyst electrode for water decomposition of the present invention are as described with respect to the cathode electrode 20 in the water decomposition device 1, and thus the description thereof will be omitted.
［第２実施形態］
本発明の水分解装置の一実施形態は、水素発生用の光触媒電極および酸素発生用の光触媒電極に光を照射することによって、上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極から気体を発生させる水分解装置であって、電解水溶液を満たすための槽と、上記槽内に配置された上記水素発生用の光触媒電極および上記酸素発生用の光触媒電極と、を有し、上記水素発生用の光触媒電極が、ｐ型半導体層と、上記ｐ型半導体層上に設けられたｎ型半導体層と、上記ｎ型半導体層の上に設けられた助触媒を有し、上記ｐ型半導体層の伝導帯の下端のポテンシャルｐ−ＣＢＭと、上記ｎ型半導体層の伝導帯の下端のポテンシャルｎ−ＣＢＭと、の差であるバンドオフセットΔＥが以下の関係を満たす。
ΔＥ＝（ｎ−ＣＢＭ）−（ｐ−ＣＢＭ）≦０．１［ｅＶ］[Second Embodiment]
In one embodiment of the water splitting apparatus of the present invention, the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation are irradiated with light to generate a gas from the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation. It is a water splitting device for generating the above hydrogen, and has a tank for filling the electrolytic aqueous solution, the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen generation arranged in the tank. The photocatalyst electrode for this purpose has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a cocatalyst provided on the n-type semiconductor layer, and the p-type semiconductor layer. The band offset ΔE, which is the difference between the potential p-CBM at the lower end of the conduction band and the potential n-CBM at the lower end of the conduction band of the n-type semiconductor layer, satisfies the following relationship.
ΔE = (n-CBM)-(p-CBM) ≤ 0.1 [eV]
第２実施形態の水分解装置における光触媒電極（具体的には、水素発生用の光触媒電極）は、優れたオンセットポテンシャルを示す。この理由の詳細は明らかになっていないが、概ね以下の理由によるものと推測される。
すなわち、ΔＥが０．１ｅＶ以下であれば、キャリア輸送が阻害されにくくなる。そのため、第２実施形態の水分解装置における光触媒電極は、優れたオンセットポテンシャルを示すものになったと推測される。
第２実施形態において、ΔＥは、０．１ｅＶ以下であり、光触媒電極のオンセットポテンシャルがより優れる点から、０ｅＶ以下がより好ましい。また、ΔＥの下限値は、−０．５ｅＶ以上が好ましい。The photocatalytic electrode (specifically, the photocatalyst electrode for hydrogen generation) in the water splitting apparatus of the second embodiment exhibits an excellent onset potential. The details of this reason have not been clarified, but it is presumed that it is due to the following reasons.
That is, when ΔE is 0.1 eV or less, carrier transport is less likely to be inhibited. Therefore, it is presumed that the photocatalytic electrode in the water splitting apparatus of the second embodiment shows an excellent onset potential.
In the second embodiment, ΔE is 0.1 eV or less, and 0 eV or less is more preferable from the viewpoint that the onset potential of the photocatalyst electrode is more excellent. The lower limit of ΔE is preferably −0.5 eV or higher.
第２実施形態におけるｐ型半導体層は、ΔＥを０．１ｅＶ以下にできるのであれば、特に限定されないが、ΔＥを０．１ｅＶ以下にするのが容易である点から、第１実施形態で説明したｐ型半導体層を用いるのが好ましい。
第２実施形態におけるｎ型半導体層は、ΔＥを０．１ｅＶ以下にできるのであれば、特に限定されないが、ΔＥを０．１ｅＶ以下にするのが容易である点から、第１実施形態で説明したｎ型半導体層を用いるのが好ましい。The p-type semiconductor layer in the second embodiment is not particularly limited as long as ΔE can be set to 0.1 eV or less, but is described in the first embodiment because it is easy to set ΔE to 0.1 eV or less. It is preferable to use the p-type semiconductor layer.
The n-type semiconductor layer in the second embodiment is not particularly limited as long as ΔE can be set to 0.1 eV or less, but is described in the first embodiment because it is easy to set ΔE to 0.1 eV or less. It is preferable to use the n-type semiconductor layer.
第２実施形態の水分解装置において、ｐ型半導体層およびｎ型半導体層以外の構成は、第１実施形態の水分解装置と同様であるので、その説明を省略する。 In the water splitting apparatus of the second embodiment, the configurations other than the p-type semiconductor layer and the n-type semiconductor layer are the same as those of the water splitting apparatus of the first embodiment, and thus the description thereof will be omitted.
以下に実施例に基づいて本発明をさらに詳細に説明する。以下の実施例に示す材料、使用量、割合、処理内容、および、処理手順等は、本発明の趣旨を逸脱しない限り適宜変更することができる。したがって、本発明の範囲は以下に示す実施例により限定的に解釈されるべきものではない。 The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as limiting by the examples shown below.
［実施例１］
実施例１の光触媒電極を次のようにして作製した。
まず、マグネトロンスパッタ装置（製品名「ＣＦＳ−１２Ｐ」、芝浦エレテック社製）を用いたＤＣ（直流）マグネトロンスパッタリング法によって、ソーダライムガラス基板（絶縁基板）の表面に、厚み６００ｎｍのＭｏからなる層（導電層）を形成した。
次に、導電層の表面に、多元蒸着装置（製品名「ＥＷ−１０」、エイコーエンジニアリング社製）を用いた３段階法によって、厚み２μｍのＣＩＧＳ化合物半導体からなる層（ｐ型半導体層）を形成した。具体的には、蒸着源として、Ｃｕ、Ｉｎ、ＧａおよびＳｅを用いて、１段目の基板温度を４００℃、２段目および３段目の基板温度を５２０℃とした。Ｇａ比（Ｇａ／（Ｇａ＋Ｉｎ））は、ＧａとＩｎの蒸着速度を制御して調整した。
次に、ｐ型半導体層の表面に、１．５ｍＭのＣｄＳＯ４、１．５ＭのＮＨ４ＯＨ、７．５ｍＭのチオ尿素水溶液を用いた化学浴析出法（ＣＢＤ法）によって、厚み７０ｎｍのＣｄＳからなる層（ｎ型半導体層）を作製した。なお、ＣＢＤ法は７０℃で４０分間行った。
次に、ｎ型半導体層の表面に、マグネトロンスパッタ装置（製品名「ＭＳＰ−３０Ｔ」、真空デバイス社製）を用いたＤＣマグネトロンスパッタリング法によって、サイズが０．５ｎｍのＰｔからなる粒子（助触媒）を担持させた。
このようにして、図１の光触媒電極１０と同様の構造をもつ、実施例１の光触媒電極（水素発生用の光触媒電極）を得た。[Example 1]
The photocatalyst electrode of Example 1 was prepared as follows.
First, a layer made of Mo having a thickness of 600 nm was applied to the surface of a soda lime glass substrate (insulating substrate) by a DC (DC) magnetron sputtering method using a magnetron sputtering device (product name "CFS-12P", manufactured by Shibaura Eletech). (Conductive layer) was formed.
Next, a layer (p-type semiconductor layer) made of a CIGS compound semiconductor having a thickness of 2 μm was formed on the surface of the conductive layer by a three-step method using a multi-element vapor deposition apparatus (product name “EW-10”, manufactured by Eiko Engineering Co., Ltd.). Formed. Specifically, Cu, In, Ga and Se were used as the vapor deposition sources, and the substrate temperature of the first stage was set to 400 ° C., and the substrate temperature of the second and third stages was set to 520 ° C. The Ga ratio (Ga / (Ga + In)) was adjusted by controlling the vapor deposition rates of Ga and In.
Next, CdS having a thickness of 70 nm was subjected to a chemical bath precipitation method (CBD method) using 1.5 mM CdSO 4 , 1.5 M NH 4 OH, and 7.5 mM thiourea aqueous solution on the surface of the p-type semiconductor layer. A layer made of (n-type semiconductor layer) was produced. The CBD method was carried out at 70 ° C. for 40 minutes.
Next, on the surface of the n-type semiconductor layer, particles (auxiliary catalyst) composed of Pt having a size of 0.5 nm were subjected to a DC magnetron sputtering method using a magnetron sputtering device (product name "MSP-30T", manufactured by Vacuum Device Co., Ltd.). ) Was carried.
In this way, the photocatalyst electrode (photocatalyst electrode for hydrogen generation) of Example 1 having the same structure as the photocatalyst electrode 10 of FIG. 1 was obtained.
［実施例２〜５、比較例１］
ｐ型半導体層を形成する際に、ＧａとＩｎの蒸着速度を適宜変更して、Ｇａ比が表１に示す値になるようにした以外は、実施例１の光触媒電極の作製と同様にして、実施例２〜５および比較例１の光触媒電極（水素発生用の光触媒電極）を得た。[Examples 2 to 5, Comparative Example 1]
When the p-type semiconductor layer was formed, the vapor deposition rates of Ga and In were appropriately changed so that the Ga ratio became the value shown in Table 1 in the same manner as in the production of the photocatalyst electrode of Example 1. , Photocatalyst electrodes (photocatalyst electrodes for hydrogen generation) of Examples 2 to 5 and Comparative Example 1 were obtained.
［Ｇａ比の測定］
高周波誘導結合プラズマ発光分光分析法（ＩＣＰ−ＡＥＳ）を測定原理とする装置（製品名「ＩＣＰ−ＡＥＳ ８１００」、島津製作所製）を用いて、ｐ型半導体層（ＣＩＧＳ化合物半導体）の全体的な元素分析を行って、ＧａおよびＩｎのモル量を算出し、得られたモル量から、Ｇａ比（Ｇａ／（Ｇａ＋Ｉｎ））を算出した。具体的には、上記のｐ型半導体層に含まれるＣＩＧＳ化合物半導体を適切な溶解液（フッ酸）で溶解させて、定量測定を行った。結果を表１に示す。[Measurement of Ga ratio]
An overall p-type semiconductor layer (CIGS compound semiconductor) using a device (product name "ICP-AES 8100", manufactured by Shimadzu Corporation) based on high frequency inductively coupled plasma emission spectroscopy (ICP-AES). Elemental analysis was performed to calculate the molar amounts of Ga and In, and the Ga ratio (Ga / (Ga + In)) was calculated from the obtained molar amounts. Specifically, the CIGS compound semiconductor contained in the p-type semiconductor layer was dissolved in an appropriate solution (hydrofluoric acid), and quantitative measurement was performed. The results are shown in Table 1.
［評価試験］
＜オンセットポテンシャル測定＞
作製した光触媒電極のオンセットポテンシャルの評価は、ポテンショスタット（製品名「ＨＺ−７０００」、北斗電工製）を用いた３電極系での電気化学測定により行った。
具体的には、パイレックスガラス製の電気化学セルを用い、作用極として上記実施例および比較例の各光触媒電極、参照極にＡｇ／ＡｇＣｌ電極、対極にＰｔワイヤーを用いた。電解水溶液には、０．５Ｍの硫酸ナトリウム、０．２５Ｍのリン酸二水素ナトリウムおよび０．２５Ｍのリン酸水素二ナトリウムを含む水溶液を用いた。
電気化学セル内部はアルゴンで満たし、かつ、測定前に十分にバブリングを行うことによって溶存する酸素、二酸化炭素を除去した。
光源には、ソーラーシミュレータ（ＡＭ１．５Ｇ）（製品名「ＸＥＳ−７０Ｓ１」、三永電機製作所製）を用いた。
そして、２０ｍＶ／ｓで０Ｖ（ｖｓ．ＲＨＥ）から０．８Ｖ（ｖｓ．ＲＨＥ）まで掃引して、上記ソーラーシュミレータによる疑似太陽光照射下における電流電位曲線を得た。
得られたオンセットポテンシャルの値に基づいて、以下の評価基準により評価を行った。評価結果を表１に示す。
Ａ：オンセットポテンシャルの値が０．６Ｖ（ｖｓ．ＲＨＥ）以上
Ｂ：オンセットポテンシャルの値が０．６Ｖ（ｖｓ．ＲＨＥ）未満[Evaluation test]
<Onset potential measurement>
The onset potential of the produced photocatalytic electrode was evaluated by electrochemical measurement with a 3-electrode system using a potentiostat (product name "HZ-7000", manufactured by Hokuto Denko).
Specifically, an electrochemical cell made of Pyrex glass was used, and the photocatalytic electrodes of the above Examples and Comparative Examples were used as working electrodes, Ag / AgCl electrodes were used as reference electrodes, and Pt wire was used as the counter electrode. As the electrolytic aqueous solution, an aqueous solution containing 0.5 M sodium sulfate, 0.25 M sodium dihydrogen phosphate and 0.25 M disodium hydrogen phosphate was used.
The inside of the electrochemical cell was filled with argon, and dissolved oxygen and carbon dioxide were removed by sufficient bubbling before measurement.
A solar simulator (AM1.5G) (product name "XES-70S1", manufactured by Sannaga Denki Seisakusho) was used as the light source.
Then, the current potential curve was obtained under pseudo-sunlight irradiation by the above solar simulator by sweeping from 0 V (vs. RHE) to 0.8 V (vs. RHE) at 20 mV / s.
Based on the obtained onset potential value, evaluation was performed according to the following evaluation criteria. The evaluation results are shown in Table 1.
A: Onset potential value is 0.6V (vs. RHE) or more B: Onset potential value is less than 0.6V (vs. RHE)
＜光電流密度＞
上記オンセットポテンシャル測定で得られた電流電圧曲線から、０．６Ｖ（ｖｓ．ＲＨＥ）における光電流密度（ｍＡ／ｃｍ２）を読み取り、以下の評価基準により評価を行った。評価結果を表１に示す。
Ａ：光電流密度が４ｍＡ／ｃｍ２以上
Ｂ：光電流密度が０ｍＡ／ｃｍ２超４ｍＡ／ｃｍ２未満
Ｃ：光電流密度が０ｍＡ／ｃｍ２以下<Light current density>
From the current-voltage curve obtained by the above-mentioned onset potential measurement, the photocurrent density (mA / cm 2 ) at 0.6 V (vs. RHE) was read and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.
A: photocurrent density 4mA / cm 2 or more B: less than photocurrent density 0 mA / cm 2 ultra 4mA / cm 2 C: photocurrent density 0 mA / cm 2 or less
＜バンドオフセットΔＥ＞
大気中光電子分光装置（製品名「ＡＣ−３」、理研計器社製）を用いて、作製した光触媒電極のｐ型半導体層の価電子帯の上端のポテンシャルを求めた。また、紫外可視分光光度計（製品名「Ｖ−７７０」、日本分光社製）を用いて、作製した光触媒電極のｐ型半導体層のバンドギャップの値を求めた。このようにして得たｐ型半導体層の価電子帯の上端のポテンシャルにバンドギャップの値を加えて、光触媒電極におけるｐ型半導体層のｐ−ＣＢＭを求めた。
また、ｎ型半導体層を用いた以外はｐ−ＣＢＭの測定と同様にして、光触媒電極におけるｎ型半導体層のｎ−ＣＢＭを求めた。
得られたｐ−ＣＢＭとｎ−ＣＢＭの値からΔＥを求めた。結果を表１に示す。<Band offset ΔE>
Using an atmospheric photoelectron spectrometer (product name "AC-3", manufactured by RIKEN Keiki Co., Ltd.), the potential of the upper end of the valence band of the p-type semiconductor layer of the produced photocatalyst electrode was determined. Further, the value of the band gap of the p-type semiconductor layer of the produced photocatalyst electrode was determined using an ultraviolet-visible spectrophotometer (product name "V-770", manufactured by JASCO Corporation). The bandgap value was added to the potential at the upper end of the valence band of the p-type semiconductor layer thus obtained to obtain the p-CBM of the p-type semiconductor layer in the photocatalyst electrode.
Further, the n-CBM of the n-type semiconductor layer in the photocatalyst electrode was obtained in the same manner as in the measurement of p-CBM except that the n-type semiconductor layer was used.
ΔE was calculated from the obtained values of p-CBM and n-CBM. The results are shown in Table 1.
表１に示すように、Ｇａ比が０．４〜０．８であるＣＩＧＳ化合物半導体を含む半導体層を有する光触媒電極を用いれば、オンセットポテンシャルに優れることが確認できた（実施例１〜５）。
また、表１に示すように、ΔＥが０．１ｅＶ以下である光触媒電極を用いれば、オンセットポテンシャルに優れることが確認できた（実施例１〜５）。
また、実施例１〜５の対比から、Ｇａ比が０．５〜０．６であるＣＩＧＳ化合物半導体を含む半導体層を有する光触媒電極を用いれば（実施例２および実施例３）、光電流密度に優れることが確認できた。
一方で、表１に示すように、Ｇａ比が０．４未満であるＣＩＧＳ化合物半導体を含む半導体層を有する光触媒電極を用いると、オンセットポテンシャルが劣ることが確認できた（比較例１）。As shown in Table 1, it was confirmed that the onset potential was excellent when a photocatalytic electrode having a semiconductor layer containing a CIGS compound semiconductor having a Ga ratio of 0.4 to 0.8 was used (Examples 1 to 5). ).
Further, as shown in Table 1, it was confirmed that the onset potential was excellent when the photocatalyst electrode having ΔE of 0.1 eV or less was used (Examples 1 to 5).
Further, from the comparison of Examples 1 to 5, if a photocatalytic electrode having a semiconductor layer containing a CIGS compound semiconductor having a Ga ratio of 0.5 to 0.6 is used (Examples 2 and 3), the photocurrent density It was confirmed that it was excellent.
On the other hand, as shown in Table 1, it was confirmed that the onset potential was inferior when a photocatalytic electrode having a semiconductor layer containing a CIGS compound semiconductor having a Ga ratio of less than 0.4 was used (Comparative Example 1).
１，１００ 装置
１０，１１０ アノード電極
１２，１１２ 第１基板
１４，１１４ 第１導電層
１６，１１６ 第１光触媒層
２０，１２０ カソード電極
２２，１２２ 絶縁基板
２２ａ、２４ａ、２６ａ、２８ａ 表面
２４，１２４ 導電層
２６，１２６ ｐ型半導体層
２８，１２８ ｎ型半導体層
２９，１２９ 半導体層
３０ 隔膜
３２，１３２ 助触媒
４０ 槽
４２ アノード電極室
４４ カソード電極室
５０ 導線
Ｓ 電解液
Ｌ 光1,100 Equipment 10,110 Anode electrode 12,112 First substrate 14,114 First conductive layer 16,116 First photocatalyst layer 20,120 Cathode electrode 22,122 Insulated substrate 22a, 24a, 26a, 28a Surface 24,124 Conductive layer 26,126 p-type semiconductor layer 28,128 n-type semiconductor layer 29,129 Semiconductor layer 30 Diaphragm 32,132 Auxiliary catalyst 40 tank 42 Anode electrode room 44 Cathode electrode room 50 Conductor S Electrolyte L
Claims (6)
電解水溶液を満たすための槽と、
前記槽内に配置された前記水素発生用の光触媒電極および前記酸素発生用の光触媒電極と、を有し、
前記水素発生用の光触媒電極が、ｐ型半導体層と、前記ｐ型半導体層上に設けられたｎ型半導体層と、前記ｎ型半導体層の上に設けられた助触媒を有し、
前記ｐ型半導体層が、Ｃｕ、Ｉｎ、ＧａおよびＳｅを含むＣＩＧＳ化合物半導体を含む半導体層であり、
前記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である、水分解装置。A water splitting device that generates gas from the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode by irradiating the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode with light.
A tank for filling the electrolytic aqueous solution and
It has the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen evolution arranged in the tank.
The photocatalyst electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer.
The p-type semiconductor layer is a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga and Se.
A water splitting apparatus in which the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.
電解水溶液を満たすための槽と、
前記槽内に配置された前記水素発生用の光触媒電極および前記酸素発生用の光触媒電極と、を有し、
前記水素発生用の光触媒電極が、ｐ型半導体層と、前記ｐ型半導体層上に設けられたｎ型半導体層と、前記ｎ型半導体層の上に設けられた助触媒を有し、
前記ｐ型半導体層の伝導帯の下端のポテンシャルｐ−ＣＢＭと、前記ｎ型半導体層の伝導帯の下端のポテンシャルｎ−ＣＢＭと、の差であるバンドオフセットΔＥが以下の関係を満たす、水分解装置。
ΔＥ＝（ｎ−ＣＢＭ）−（ｐ−ＣＢＭ）≦０．１［ｅＶ］A water splitting device that generates gas from the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode by irradiating the hydrogen generation photocatalyst electrode and the oxygen generation photocatalyst electrode with light.
A tank for filling the electrolytic aqueous solution and
It has the photocatalyst electrode for hydrogen generation and the photocatalyst electrode for oxygen evolution arranged in the tank.
The photocatalyst electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer.
Hydrolysis in which the band offset ΔE, which is the difference between the potential p-CBM at the lower end of the conduction band of the p-type semiconductor layer and the potential n-CBM at the lower end of the conduction band of the n-type semiconductor layer, satisfies the following relationship. apparatus.
ΔE = (n-CBM)-(p-CBM) ≤ 0.1 [eV]
前記ＣＩＧＳ化合物半導体中のＧａおよびＩｎの合計モル量に対する、Ｇａのモル比が、０．４〜０．８である、水分解用光触媒電極。It has a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga and Se.
A photocatalytic electrode for water splitting, wherein the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.
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| JP5993768B2 (en) * | 2013-03-28 | 2016-09-14 | 富士フイルム株式会社 | Gas production equipment |
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| JP2006167652A (en) * | 2004-12-17 | 2006-06-29 | Tokyo Univ Of Science | Black photocatalyst for forming hydrogen absorbing all visible light |
| JP2012046385A (en) * | 2010-08-27 | 2012-03-08 | Mitsubishi Chemical Holdings Corp | Electrode for water decomposition by light, method for producing the same and method for decomposing water |
| WO2016024452A1 (en) * | 2014-08-11 | 2016-02-18 | 富士フイルム株式会社 | Hydrogen generating electrode and artificial photosynthesis module |
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