WO2015133127A1 - Carbon dioxide reduction electrode and carbon dioxide reduction device in which same is used - Google Patents

Carbon dioxide reduction electrode and carbon dioxide reduction device in which same is used Download PDF

Info

Publication number
WO2015133127A1
WO2015133127A1 PCT/JP2015/001110 JP2015001110W WO2015133127A1 WO 2015133127 A1 WO2015133127 A1 WO 2015133127A1 JP 2015001110 W JP2015001110 W JP 2015001110W WO 2015133127 A1 WO2015133127 A1 WO 2015133127A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical semiconductor
type optical
reduction
electrode
substrate
Prior art date
Application number
PCT/JP2015/001110
Other languages
French (fr)
Japanese (ja)
Inventor
飯島　剛
土方　啓暢
裕明 世登
横野　照尚
村上　直也
Original Assignee
株式会社デンソー
国立大学法人九州工業大学
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社デンソー, 国立大学法人九州工業大学 filed Critical 株式会社デンソー
Publication of WO2015133127A1 publication Critical patent/WO2015133127A1/en

Links

Images

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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • 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
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction
    • 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

Definitions

  • the present disclosure relates to a CO 2 reduction electrode for reducing CO 2 and a CO 2 reduction device using the same.
  • Non-Patent Document 1 In recent years, research for synthesizing organic substances from carbon dioxide using light energy such as sunlight has been regarded as important for solving the fossil fuel depletion problem. So far, development of a suspension system in which a photocatalyst is suspended in water has been advanced. Specifically, a reduction catalyst has been developed in which a photocatalyst made of brookite-type titanium oxide is loaded with a promoter made of a noble metal (see Non-Patent Document 1).
  • the present disclosure has been made in view of such a background, and an object of the present disclosure is to provide a CO 2 reduction electrode and a CO 2 reduction device that can sufficiently obtain a reduction product made of an organic substance or the like.
  • the CO 2 reduction electrode includes a conductive substrate, a p-type optical semiconductor provided on the substrate, and an n-type optical semiconductor provided on the p-type optical semiconductor. Have.
  • the energy level of the conduction band of the p-type optical semiconductor is higher than the energy level of the conduction band of the n-type optical semiconductor, and the energy level of the valence band of the p-type optical semiconductor is n It is higher than the energy level of the valence band of the type optical semiconductor.
  • a CO 2 reduction device includes the CO 2 reduction electrode, an oxidation electrode, an aqueous electrolyte in which the oxidation electrode and the CO 2 reduction electrode are immersed, and the aqueous electrolyte.
  • An ion exchange membrane for separating the CO 2 reduction electrode and the oxidation electrode therein, a light source for irradiating the CO 2 reduction electrode with light, and a supply port for supplying CO 2 to the CO 2 reduction electrode.
  • the CO 2 reduction electrode (hereinafter referred to as “reduction electrode” as appropriate) has the p-type optical semiconductor and the n-type optical semiconductor provided thereon. That is, the reduction electrode has a stacked body of a p-type optical semiconductor and an n-type optical semiconductor, and has a pn junction. Therefore, it is possible to n-type optical semiconductor keep light irradiation conditions to reduce CO 2 Te transferring electrons to CO 2. At this time, an organic substance such as methanol is generated from CO 2 in the presence of water. On the other hand, holes are generated in the p-type optical semiconductor by light irradiation.
  • the reduction electrode the reduction can be performed by stably supplying electrons to CO 2 , and a reduction product made of an organic substance or the like can be sufficiently obtained.
  • the reduction electrode can suppress the reduction of water. Therefore, CO 2 can be selectively reduced while suppressing reduction of water even in the presence of water.
  • the energy levels of the p-type optical semiconductor and the n-type optical semiconductor are in the above relationship. Therefore, it is possible to pass a current when the reduction electrode is used as an electrode.
  • the CO 2 reduction device (hereinafter referred to as “reduction device” as appropriate) includes the reduction electrode. Therefore, taking advantage of the above-described excellent performance of the reduction electrode, the reduction device can sufficiently reduce CO 2 and generate a reduction product made of an organic substance or the like.
  • the reduction electrode and the oxidation electrode are separated by an ion exchange membrane. Therefore, it is possible to suppress the reduction product of CO 2 produced in the reduction electrode is oxidized again. Therefore, a sufficient reduction product can be obtained.
  • FIG. 3 is an explanatory diagram showing a cross-sectional configuration of a reduction electrode in Example 1.
  • FIG. 3 is an explanatory diagram illustrating a process of forming a p-type optical semiconductor on a substrate from the formation surface side of the FTO film of the substrate in Example 1.
  • FIG. 2B is an explanatory diagram showing a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 2A from the FTO film formation surface side of the substrate.
  • FIG. 2B is an explanatory diagram showing a step of forming a p-type optical semiconductor on the substrate subsequent to FIG.
  • FIG. 2D is an explanatory view showing a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 2C from the FTO film forming surface side of the substrate.
  • Explanatory drawing which shows the process of forming a p-type optical semiconductor on a board
  • FIG. 3B is an explanatory diagram showing a step of forming a p-type optical semiconductor on the substrate following FIG. 3A by a cross-sectional structure.
  • FIG. 3D is an explanatory diagram showing a cross-sectional structure of a process for forming a p-type optical semiconductor on a substrate following FIG. 3B.
  • FIG. 3D is an explanatory diagram illustrating, by a cross-sectional structure, a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 3C.
  • FIG. 3 is an explanatory diagram illustrating a method for forming an n-type optical semiconductor by electrophoresis in Example 1.
  • FIG. 3 is an explanatory diagram illustrating a cross-sectional configuration of the reduction device according to the first embodiment.
  • FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 7.
  • FIG. 10 is a schematic view of an electrodeposition apparatus for forming a p-type optical semiconductor in Example 7. The scanning electron micrograph of the magnification of 2000 times of the surface of the p-type optical semiconductor in Example 7.
  • FIG. 3D is an explanatory diagram illustrating, by a cross-sectional structure, a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 3C.
  • FIG. 3 is an explanatory diagram illustrating a method for
  • FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 8. Scanning electron micrograph of the surface of the p-type optical semiconductor in Example 8 at a magnification of 2000 times Scanning electron micrograph of the surface of the p-type optical semiconductor in Example 8 at a magnification of 50000 times
  • FIG. 10B is a diagram of the scanning electron micrograph shown in FIG. 10A.
  • FIG. 10B is a diagram of the scanning electron micrograph shown in FIG.
  • FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 9.
  • FIG. FIG. 12B is a diagram of the scanning electron micrograph shown in FIG. 12A.
  • FIG. 12B is a diagram of the scanning electron micrograph shown in FIG. 12B.
  • FIG. 3 is an enlarged cross-sectional view of a reduction electrode in Example 1.
  • FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 9.
  • FIG. 12B is a diagram of the scanning electron micrograph shown in FIG. 12A.
  • FIG. 14B is a diagram of the scanning electron micrograph shown in FIG. 14A.
  • FIG. 14B is a diagram of the scanning electron micrograph shown in FIG. 14B.
  • FIG. 6 is an explanatory diagram showing a comparison result of current densities of the reduction electrodes of Example 1 and Examples 7 to 9.
  • the substrate may be a substrate having a conductive layer on the surface, even if the substrate does not have overall conductivity.
  • substrate should just have electroconductivity,
  • the material can be selected suitably.
  • the shape of the p-type optical semiconductor and the n-type optical semiconductor is a film shape, for example.
  • the thickness can be changed as appropriate.
  • the n-type optical semiconductor on the p-type optical semiconductor is preferably formed with a thickness capable of transmitting light.
  • the thickness of the p-type optical semiconductor is, for example, 0.1 to 500 ⁇ m, and the thickness of the n-type optical semiconductor is, for example, 0.01 to 200 ⁇ m.
  • Examples of the material of the n-type optical semiconductor include TiO 2 , SrTiO 3 , BaTiO 3 , CaTiO 3 , WO 3 , BiVO 4 , BiFeO 3 , CuTaN 2 , FeTiO 2 , MgFe 2 O 4 , PbS, ZnO, graphene, and graphite Examples thereof include at least one selected from carbon nitride (CN), n-Si, n-SiC, n-GaN, n-AlGaN, and the like.
  • TiO 2 includes, for example, a rutile type, an anatase type, and a brookite type. Any of these materials may be used as the material of the n-type optical semiconductor, and a mixture of two or more types may be used.
  • Examples of the material of the p-type optical semiconductor include CuO, Cu 2 O, Mg-doped CuFe 2 O 4 , CaFe 2 O 4 , CoO 3 , Cr 2 O 3 , CuCrO 2 , Fe-doped TiO 2 , Cr-doped TiO 2 , and GaP. And at least one selected from InP, NiO, Rh-doped SrTiO 3 , p-Si, p-SiC, and the like.
  • the energy level of the conduction band of the p-type optical semiconductor is higher on the base side than the energy level of the conduction band of the n-type optical semiconductor.
  • the energy level of the valence band of the p-type optical semiconductor is higher than the energy level of the valence band of the n-type optical semiconductor.
  • materials of the p-type optical semiconductor and the n-type optical semiconductor are appropriately selected from, for example, the above-described substances.
  • the oxidation electrode is the counter electrode of the reduction electrode.
  • the oxidation electrode for example, an electrode made of a noble metal or the like can be used.
  • the aqueous electrolyte solution for example, an aqueous electrolyte solution can be used.
  • Various commercially available products can be used as the ion exchange membrane.
  • the light from the light source preferably includes ultraviolet light, visible light and the like. In this case, it becomes easier to activate the CO 2 reduction reaction at the reduction electrode. More preferably, the light from the light source includes at least ultraviolet rays.
  • Example 1 examples of the CO 2 reduction electrode and the CO 2 reduction device will be described.
  • the reduction electrode 1 of this example has a conductive substrate 11, a p-type optical semiconductor 12 provided thereon, and an n-type optical semiconductor 13 provided thereon.
  • the p-type optical semiconductor 12 is completely covered with the n-type optical semiconductor 13.
  • the p-type optical semiconductor 12 is made of copper oxide (CuO)
  • the n-type optical semiconductor 13 is made of brookite-type titanium oxide (TiO 2 ).
  • the p-type optical semiconductor 12 is formed on the substrate 11 by the squeegee method.
  • a quartz glass substrate 112 having a fluorine-doped tin oxide (FTO) film 111 formed on the surface was prepared as the conductive substrate 11 (see FIGS. 2A and 3A).
  • FTO fluorine-doped tin oxide
  • the substrate 11 a product of Meijo Kagaku Kogyo Co., Ltd. was used.
  • the FTO film 111 is laminated on one side of the quartz glass substrate 112.
  • the dimensions of the substrate 11 are 30 mm long ⁇ 30 mm wide ⁇ 1.8 mm thick.
  • a plate-like spacer 120 with a hollow interior was prepared.
  • the external dimensions of the spacer 120 are 30 mm long ⁇ 30 mm wide like the substrate 11, and the dimensions of the internal space are 25 mm long ⁇ 25 mm wide.
  • the thickness of the spacer 120 is 1 mm.
  • This spacer 120 was placed on the surface of the substrate 11 where the FTO film 111 is formed.
  • a CuO paste layer 121 was formed on the FTO film 111 of the substrate 11 by applying a CuO paste in the internal space of the spacer 120 by a squeegee method.
  • the CuO paste was obtained by mixing 500 mg of CuO (manufactured by Wako Pure Chemical Industries, Ltd.) and 2 ml of ethanol.
  • the spacer 120 was removed.
  • the substrate 11 on which the CuO paste layer 121 was laminated was baked at a temperature of 550 ° C. for 1 hour. Thereby, as shown in FIG. 2D and FIG. 3D, a film-like p-type optical semiconductor 12 having a thickness of 30 ⁇ m was formed on the substrate 11.
  • the p-type optical semiconductor 12 is formed on the FTO film 111 of the substrate 11.
  • substrate A the substrate 11 on which the p-type optical semiconductor 12 is formed is referred to as “substrate A” and is denoted by reference numeral 15.
  • the p-type optical semiconductor 12 is manufactured by the squeegee method.
  • the p-type optical semiconductor 12 can also be manufactured by, for example, a spin coater method, an electrophoresis method, an electrodeposition method, or the like.
  • an n-type optical semiconductor is formed by electrophoresis.
  • brookite type titanium oxide was prepared.
  • 0.6 g of titanium powder (“204-05205” manufactured by Wako Pure Chemical Industries, Ltd.), 10 ml of 25 mass% ammonia water (“010-03166” manufactured by Wako Pure Chemical Industries, Ltd.), 30 40 ml of a mass% hydrogen peroxide solution (“081-04215” manufactured by Wako Pure Chemical Industries, Ltd.) was mixed and stirred until all of the titanium powder was dissolved.
  • 1.426 g of glycolic acid (“075-01515” manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was further stirred at room temperature for 2 hours. The solution was then heated at a temperature of 100 ° C. with stirring.
  • a solution 131 for electrophoresis As shown in FIG. 4, the substrate A15 and the substrate 16 on which the p-type optical semiconductor is not formed (hereinafter, referred to as “substrate B” as appropriate) were completely immersed in the solution 131.
  • the substrate B16 is the same as the substrate before the p-type optical semiconductor is formed, and is a quartz glass substrate 162 on which the FTO film 161 is formed.
  • both were immersed in the solution 131 in a state where the distance between the substrate A15 and the substrate B16 was 1 mm.
  • Substrate A15 and substrate B16 were electrically connected to potentiostat 18.
  • the substrate A15 is a positive electrode
  • the substrate B16 is a negative electrode.
  • a voltage of 10V was applied between the substrate A15 and the substrate B16 for 120 seconds.
  • the n-type optical semiconductor 13 made of brookite-type titanium oxide was formed on the surface of the substrate A15 where the FTO film 111 is formed (see FIGS. 4 and 1).
  • the n-type optical semiconductor 13 has a thickness of 40 ⁇ m. This thickness is the thickness of the n-type optical semiconductor 13 in the stacked portion of the p-type optical semiconductor 12 and the n-type optical semiconductor 13.
  • the reduction includes the conductive substrate 11, the p-type optical semiconductor 12 stacked on the substrate 11, and the n-type optical semiconductor 13 covering the p-type optical semiconductor 12.
  • An electrode 1 was obtained.
  • FIG. 16 shows the material and thickness of the n-type optical semiconductor 13 and the material and thickness of the p-type optical semiconductor 12 in the reduction electrode 1 of this example.
  • the n-type optical semiconductor 13 is manufactured by electrophoresis.
  • the n-type optical semiconductor 13 can also be manufactured by, for example, a squeegee method, a spin coater method, or the like.
  • the reduction device 8 of this example includes a reduction electrode 1, an oxidation electrode 2, an aqueous electrolytic solution 3 (hereinafter referred to as “electrolytic solution 3” as appropriate), and an ion exchange membrane 4 (hereinafter referred to as “ A membrane 4 ”), a light source 5, and a supply port 6 for supplying CO 2 .
  • the electrolytic solution 3 is a KHCO 3 aqueous solution having a concentration of 0.2 mol / L.
  • 50 ml of the electrolytic solution 3 is injected into the case 80.
  • Case 80 is an H-type cell VB-9 manufactured by EC Frontier. That is, the case 80 is H-shaped and includes two cases 801 and 802 and a connecting portion 803 that connects the two cases.
  • the reduction electrode 1 and the reference electrode 19 made of Ag / AgCl are inserted.
  • the reduction electrode 1 and the reference electrode 19 are electrically connected.
  • the oxidation electrode 2 that is the counter electrode of the reduction electrode 1 is inserted.
  • the oxidation electrode 2 is made of a Pt wire.
  • a membrane 4 (Nafion membrane manufactured by Sigma-Aldrich) is disposed in the connecting portion 803 of the case 80. The membrane 4 exists between the reduction electrode 1 and the oxidation electrode 2 and separates them.
  • the reduction electrode 1, the reference electrode 19, the oxidation electrode 2, and the membrane 4 are immersed in the electrolytic solution 3.
  • the openings of the cases 801 and 802 are sealed with plugs 803 and 804.
  • a tube 60 for supplying CO 2 is inserted into the plug 803 on the case 801 side. CO 2 is supplied into the electrolytic solution 3 from the supply port 6 of the pipe 60.
  • the reducing device 8 includes a light source 5 for irradiating the reducing electrode 1 with light 51.
  • the light source 5 is arranged so that light is irradiated onto the surface of the reduction electrode 1 on which the p-type optical semiconductor 12 and the n-type optical semiconductor 13 are formed.
  • the light source 5 “MAX300W” manufactured by Asahi Spectroscopic Co., Ltd. was used.
  • the reduction device 8 is electrically connected to an electrochemical analyzer 9 including an ammeter 91 and a voltmeter 92 as shown in FIG.
  • the electrochemical analyzer 9 is an ALS model 660E manufactured by BAS.
  • the ammeter 91 is connected between the reduction electrode 1 and the oxidation electrode 2, and the voltmeter 92 is connected between the reduction electrode 1 and the reference electrode 19.
  • CO 2 was reduced using the reducing device 8 and the amount of reduction product produced was analyzed.
  • carbon dioxide gas (CO 2 ) having a G1 level, that is, a purity of 99.99995 vol% is supplied from the supply port 6 into the electrolyte 3 for 2 hours, and the wavelength of 340 nm or more is supplied from the light source 5.
  • the light 51 was irradiated to the reduction electrode 1 for 6 hours.
  • the flow rate of carbon dioxide gas is 5 ml / min, and the intensity of light is 10 mW / cm 2 .
  • the carbon dioxide gas supplied into the electrolytic solution 3 is reduced at the reduction electrode 1 irradiated with light.
  • This reduction reaction was carried out for 6 hours, and the amount of reduction product was detected by chromatography.
  • methanol, formic acid, hydrogen, and carbon monoxide were detected as products.
  • Methanol was detected by collecting the electrolytic solution 3 after the reduction reaction and injecting the electrolytic solution 3 into a gas chromatography apparatus (“GC-2014” manufactured by Shimadzu Corporation) using a syringe.
  • the column for chromatography is “DB-WAXetr” manufactured by Agilent Technologies.
  • the detection method is flame ionization detection (FID). The detection was performed under the condition that the temperature was maintained at 70 ° C. for 5 minutes.
  • Formic acid is detected by collecting the electrolytic solution 3 after the reduction reaction and injecting the electrolytic solution 3 into an ion chromatography apparatus (“Dionex IC-20” manufactured by Thermo Fisher Scientific Co., Ltd.) using a syringe. It was done by doing.
  • the column for chromatography is “IonPac AS20” manufactured by Thermo Fisher Scientific Co., Ltd.
  • a mixed solution of a 2.7 mmol / L Na 2 CO 3 aqueous solution and a 0.3 mmol / L NaHCO 3 aqueous solution was used as an electrolyte for chromatography.
  • the flow rate condition is 1.5 ml / min.
  • Hydrogen and carbon monoxide were detected by injecting the gas in the case 80 after the reduction reaction into a gas chromatography apparatus (“GC-2014” manufactured by Shimadzu Corporation).
  • the column for chromatography is “SHINCARBON ST” manufactured by Shimadzu Corporation.
  • the detection method is thermal conductivity detection (TCD). The detection was performed under the condition that the temperature was maintained at 40 ° C. for 12 minutes and then the temperature was increased to 200 ° C. at a temperature increase rate of 10 ° C./min.
  • Example 2 The reduction electrode 1 of Example 2 is an electrode manufactured in the same manner as in Example 1 except that the thickness of the n-type optical semiconductor 13 is changed to 15 ⁇ m.
  • the reduction electrode 1 of Example 3 is an electrode manufactured in the same manner as in Example 1 except that brookite type titanium oxide supporting metal (Ag) is used instead of brookite type titanium oxide. .
  • the brookite type titanium oxide supporting metal was prepared as follows.
  • catalyst powder AgNO 3
  • sacrificial reagent ethanol
  • N 2 nitrogen
  • a metal was supported on the reduction surface of brookite-type titanium oxide.
  • the addition amount of the catalyst powder can be adjusted in the range of 0.5 mg to 5 mg, for example, and the addition amount of the sacrificial reagent can be adjusted in the range of 0.5 ml to 5 ml, for example.
  • the reduction electrode 1 of Example 4 is an electrode produced in the same manner as in Example 1 except that the p-type optical semiconductor 12 is formed using CuFe 2 O 4 paste instead of CuO paste.
  • the reduction electrode 1 of Example 5 is made of general-purpose titanium oxide (“AEROXIDE (registered trademark) TiO 2 manufactured by Nippon Aerosil Co., Ltd.) instead of brookite-type titanium oxide.
  • the electrode was produced in the same manner as in Example 1 except that P25 ") was used.
  • the titanium oxide of this example is a mixture of a rutile type and an anatase type.
  • the reduction electrode 1 of Example 6 is an electrode manufactured in the same manner as Example 1 except that strontium titanate (SrTiO 3 ) was used instead of brookite-type titanium oxide.
  • the reduction device 8 having the same configuration as that of Example 1 was produced using each of these, and CO 2 was reduced.
  • the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description is referred to.
  • Comparative Examples 1 to 5 The reduction electrode of Comparative Example 1 is an electrode manufactured in the same manner as in Example 1 except that the n-type optical semiconductor was not formed.
  • the reduction electrode of Comparative Example 2 did not form an n-type optical semiconductor, and was the same as Example 1 except that a p-type optical semiconductor was formed using CuFe 2 O 4 paste instead of CuO paste. This is an electrode manufactured in this way.
  • the reduction electrode of Comparative Example 3 was manufactured in the same manner as in Example 1 except that the n-type optical semiconductor was not formed and that a p-type optical semiconductor was formed using InP paste instead of CuO paste. Electrode.
  • the reduction electrode of Comparative Example 4 is an electrode manufactured in the same manner as in Example 1 except that the n-type optical semiconductor was formed directly on the substrate without forming the p-type optical semiconductor.
  • the reduction electrode of Comparative Example 5 does not form a p-type optical semiconductor, and further uses general-purpose titanium oxide (“AEROXIDE (registered trademark) TiO 2 P25” manufactured by Nippon Aerosil Co., Ltd.) instead of brookite-type titanium oxide.
  • AEROXIDE registered trademark TiO 2 P25
  • the electrode was produced in the same manner as in Example 1 except that the n-type optical semiconductor was directly formed on the substrate.
  • the reduction electrode 1 of the embodiment has a stacked body of a p-type optical semiconductor 12 and an n-type optical semiconductor 13 and has a pn junction between them (see FIGS. 1 and 5). Therefore, reduction can be performed by supplying electrons to CO 2 stably under light irradiation conditions, and a reduction product composed of an organic substance or the like is sufficiently obtained.
  • methanol and formic acid are sufficiently generated from CO 2 , while generation of hydrogen and carbon monoxide is sufficiently suppressed. This is because, in the embodiment, it is possible to suppress the reduction of water and advance the reduction reaction that generates methanol and formic acid from water and carbon dioxide, not the reduction reaction that generates carbon monoxide from carbon dioxide. means.
  • the energy level of the conduction band of the p-type optical semiconductor 12 is higher than the energy level of the conduction band of the n-type optical semiconductor 13.
  • the energy level of the valence band of the p-type optical semiconductor 12 is higher on the base side than the energy level of the valence band of the n-type optical semiconductor 13. Since the p-type optical semiconductor 12 and the n-type optical semiconductor in such a combination are employed, it is possible to pass a current when the reduction electrode 1 is used as an electrode.
  • the p-type optical semiconductor 12 is completely covered with the n-type optical semiconductor 13 as in the embodiment. That is, it is preferable that the p-type optical semiconductor 12 is not exposed to the outside. In this case, since the p-type optical semiconductor 12 does not come into direct contact with the electrolytic solution 3 in the reducing device 8, the reduction of water is further suppressed. That is, the reduction electrode 1 can reduce CO 2 more selectively.
  • the n-type optical semiconductor 13 is preferably made of at least one selected from TiO 2 , SrTiO 3 , WO 3 and BiVO 4 . More preferably, the n-type optical semiconductor 13 is made of brookite-type titanium oxide. In this case, the reduction of water can be further suppressed, and CO 2 can be reduced more selectively. As a result, the amount of CO 2 reduction product can be further improved.
  • the p-type optical semiconductor 12 is preferably made of at least one selected from CuO, Cu 2 O, InP, p-SiC, and p-Si. In this case, the amount of reduction product of CO 2 can be further improved.
  • Example 3 titanium oxide supporting Ag as described above is used as the n-type optical semiconductor.
  • Other examples of the metal to be supported include Au, Rh, Cu, Ni, Ru, Ir, Re, and Pd. At least one of these metals can be used.
  • the reduction device 8 has an ion exchange membrane 4 that separates the reduction electrode 1 and the oxidation electrode 2 (see FIG. 5). Therefore, in the reduction device 8, the movement of the reduction product is limited. Therefore, reduction products such as methanol and formic acid can be prevented from being oxidized again at the oxidation electrode 2. Therefore, the reduction device 8 can obtain a sufficient reduction product.
  • Example 7 This example is an example of a reduction electrode having a p-type optical semiconductor having a branched structure.
  • the reduction electrode 1 of this example covers a conductive substrate 11, a p-type optical semiconductor 12 having a branched structure provided on the substrate 11, and the p-type optical semiconductor 12. and an n-type optical semiconductor 13.
  • the substrate 11 has a quartz glass substrate 112 and an FTO film 111 formed on the quartz glass substrate 112 in the same manner as in the first embodiment.
  • the p-type optical semiconductor 12 is an FTO film of the substrate 11. 111 is formed.
  • the p-type optical semiconductor 12 has a branched structure extending from the substrate 11 (FTO film 111) to the inside of the n-type optical semiconductor 13. Specifically, in the p-type optical semiconductor 12, a large number of branches 125 (projections 125) extending in a random direction from the substrate 11 are formed, and these branches 125 are branched structures. Is forming. It can be said that the p-type optical semiconductor 12 is a cauliflower-like structure in which a large number of protrusions 125 extending in a random direction are gathered. The p-type optical semiconductor 12 is formed on the substrate 11 with a predetermined surface roughness. The p-type optical semiconductor 12 is made of CuO as in the first embodiment.
  • the n-type optical semiconductor 13 covers the branched p-type optical semiconductor 12.
  • the n-type optical semiconductor 13 covers the p-type optical semiconductor 12 along the outer shape of the branched p-type optical semiconductor 12, and has a concavo-convex structure on the surface.
  • the n-type optical semiconductor 13 is made of brookite-type titanium oxide as in the first embodiment.
  • Example 1 a quartz glass substrate 112 having an FTO film 111 formed on the surface was prepared as the conductive substrate 11.
  • the counter electrode 17 was immersed.
  • the working electrode 14 and the counter electrode 17 are both composed of the above-described quartz glass substrate 112 having the FTO film 111 formed on the surface thereof, and are the above-described conductive substrate 11.
  • the reference electrode 19 is an Ag / AgCl electrode.
  • the working electrode 14 and the counter electrode 17 were disposed so that the FTO films 111 face each other.
  • the distance between the working electrode 14 and the counter electrode 17 is 4 mm.
  • An ammeter was installed between the working electrode 14 and the counter electrode 17, and a voltmeter was installed between the working electrode 14 and the reference electrode 19.
  • the working electrode 14 and the counter electrode 17 are electrically connected to the potentiostat 18, and a potential of ⁇ 0.75 V is applied between both electrodes for 1800 seconds so that the working electrode 14 has a negative potential with respect to the counter electrode 17. did.
  • the liquid temperature of the aqueous solution 129 at this time is room temperature (25 ° C.). Due to this potential difference, as shown in FIG. 7, Cu 2+ ions in the aqueous solution 129 are deposited as Cu on the FTO film 111 of the working electrode 14 (electrodeposition). Thereafter, the working electrode 14 was dried in a dryer at a temperature of 110 ° C. for 1 hour, and then the working electrode 14 was further fired at a temperature of 550 ° C. for 1 hour under atmospheric conditions.
  • the p-type optical semiconductor 12 having a branched structure made of copper oxide was formed on the FTO film 111 of the substrate 11 (see FIG. 6).
  • the crystal structure of the p-type optical semiconductor 12 was examined by an X-ray diffractometer using Cu—K ⁇ rays (RINT2000 manufactured by Rigaku Corporation), it was confirmed that the p-type optical semiconductor was made of CuO.
  • FIG. 8A The result of 2000 times magnification is shown in FIG. 8A, and the result of 50000 times magnification is shown in FIG. 8B.
  • 8C and 8D show diagrams of the SEM photographs shown in FIGS. 8A and 8B, respectively.
  • FIG. 8A An enlarged cross-sectional view of the p-type optical semiconductor 12 in Example 1 is shown in FIG.
  • FIG. 14A an SEM photograph at a magnification of 2000 times of the surface of the p-type optical semiconductor 12 in Example 1 is shown in FIG. 14A to be described later.
  • the SEM photograph at a magnification of 50000 is shown in FIG. 14B described later.
  • 14C and 14D show diagrams of the SEM photographs shown in FIGS. 14A and 14B, respectively.
  • the p-type optical semiconductor 12 in Example 1 is composed of an aggregate of particles made of copper oxide, whereas it is known from FIGS. 8A to 8D.
  • the p-type optical semiconductor 12 in this example has a branched structure extending from the FTO film 111 and extending.
  • the roughness of the surface of the p-type optical semiconductor 12 in this example was measured based on the arithmetic average roughness Ra (JIS 2001 standard).
  • a needle contact type surface shape measuring device “DEKTAK 6M STYLUS PROFILER” manufactured by VEECO / SLOAN was used.
  • the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor in this example was 2701.97 nm.
  • the surface roughness Ra of the p-type optical semiconductor 12 in Example 1 was 1237.09 nm.
  • an n-type optical semiconductor 13 was formed on the p-type optical semiconductor 12 of this example by the same electrophoresis method as in Example 1. As described above, as shown in FIG. 6, a reduction electrode 1 having a branched p-type optical semiconductor 12 and an n-type optical semiconductor 13 covering the branched p-type optical semiconductor 12 was obtained.
  • a reducing device 8 having the same configuration as that of Example 1 is assembled except that the reducing electrode 1 of this example is used and the electrolytic solution 3 is changed to Na 2 SO 4 having a concentration of 0.1 mol / L. (See FIG. 5). Subsequently, CO 2 was reduced by the reduction device 8.
  • G1 level CO 2 is supplied into the electrolyte 3 for 60 minutes, light 51 (pseudo sunlight) having an intensity of 100 W / cm 2 is irradiated from the light source 5 at intervals of 1 second, and CO 2 is reduced by the reducing device 8. Reduction of 2 was performed.
  • FIG. 15 also shows the measurement results of current density when using the reduction electrode of Example 1.
  • Example 8 This example is an example of a reduction electrode in which a p-type optical semiconductor is formed by changing the electrodeposition reaction time from that of Example 7 described above.
  • the p-type optical semiconductor 12 is a branch that extends from the substrate 11 (FTO film 111) to the inside of the n-type optical semiconductor 13, as in the seventh embodiment. It has a shape structure.
  • the p-type optical semiconductor 12 of this example there are more branches 125 (projections 125) than in Example 7, and the length thereof is longer. Other configurations are the same as those of the seventh embodiment.
  • the reduction electrode 1 of this example is the same as that of the above-described embodiment except that, when the p-type optical semiconductor 12 is formed, a potential of ⁇ 0.75 V is applied between the counter electrode 17 and the working electrode 14 for 3600 seconds. 7 (see FIG. 7). Also in this example, when the crystal structure of the p-type optical semiconductor 12 was examined with an X-ray diffractometer using a Cu—K ⁇ ray (RINT2000 manufactured by Rigaku Corporation) as in Example 7, the p-type optical semiconductor was examined. It was confirmed that 12 consists of CuO. Further, an SEM photograph on the surface of the p-type optical semiconductor 12 in this example was taken under the same conditions as in Example 7. An SEM photograph at a magnification of 2000 is shown in FIG.
  • FIG. 10A an SEM photograph at a magnification of 50000 is shown in FIG. 10B.
  • 10C and 10D show diagrams of the SEM photographs shown in FIGS. 10A and 10B, respectively.
  • the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor in this example was measured in the same manner as in Example 7. As a result, the surface roughness was 3174.66 nm.
  • the reduction device 8 is assembled in the same manner as in Example 7 (see FIG. 5), and the photocurrent density when the potential with respect to the standard hydrogen electrode is 0 V (current density flowing during light irradiation). ) The result is shown in FIG.
  • Example 9 is an example of a reduction electrode in which a p-type optical semiconductor is formed by changing the electrodeposition reaction time from Example 7 and Example 8 described above.
  • the p-type optical semiconductor is branched like extending from the substrate 11 (FTO film 111) to the inside of the n-type optical semiconductor 13 as in the seventh embodiment. It has a structure.
  • the p-type optical semiconductor 12 of this example has fewer branches 125 (projections 125) and a shorter length than that of the seventh embodiment. Other configurations are the same as those of the seventh embodiment.
  • the reduction electrode 1 of this example is the same as that of the above-described embodiment except that, when the p-type optical semiconductor 12 is formed, a potential of ⁇ 0.75 V is applied between the counter electrode 17 and the working electrode 14 for 600 seconds. 7 (see FIG. 7). Also in this example, when the crystal structure of the p-type optical semiconductor 12 was examined with an X-ray diffractometer using a Cu—K ⁇ ray (RINT2000 manufactured by Rigaku Corporation) as in Example 7, the p-type optical semiconductor was examined. It was confirmed that 12 consists of CuO. Further, an SEM photograph on the surface of the p-type optical semiconductor 12 in this example was taken under the same conditions as in Example 7. An SEM photograph at a magnification of 2000 is shown in FIG.
  • FIG. 12A an SEM photograph at a magnification of 50000 is shown in FIG. 12B.
  • 12C and 12D show diagrams of the SEM photographs shown in FIGS. 12A and 12B, respectively.
  • the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor in this example was measured in the same manner as in Example 7. As a result, the surface roughness was 2015.23 nm.
  • the reduction device 8 is assembled in the same manner as in Example 7 (see FIG. 5), and the photocurrent density when the potential with respect to the standard hydrogen electrode is 0 V (current density flowing during light irradiation). ) The result is shown in FIG.
  • Embodiments 7 to 7 having a p-type optical semiconductor 12 (see FIGS. 6, 8A to 12D) having a branched structure extending from the substrate 11 to the inside of the n-type optical semiconductor 13 and extending.
  • the reduction electrode 1 of 9 showed a higher current density than the reduction electrode 1 of Example 1 having the p-type optical semiconductor 12 (see FIGS. 13 and 14A to 14D) that did not have a branched structure. .
  • This improvement in current density means an improvement in the CO 2 reduction reaction rate. Therefore, it can be seen that by forming the p-type optical semiconductor 12 having a branched structure as in Examples 7 to 9, the reduction rate of CO 2 can be improved and the production rate of organic substances such as methanol can be further improved.
  • the reduction electrodes 1 of Examples 7 to 9 formed by the electrodeposition method have the p-type optical semiconductor 12 having a branched structure as described above, the p-type optical semiconductor 12 and the n-type optical semiconductor 12 are combined. Since the junction region with the type optical semiconductor 13 is widened, it is assumed that the current density is improved as described above (see FIGS. 6 and 8A to 12D). In Examples 7 to 9, it is speculated that the formation of the dense p-type optical semiconductor 12 also contributes to the improvement of the current density. On the other hand, in the p-type optical semiconductor 12 in Example 1 formed by the squeegee method, since many voids exist between CuO particles (FIGS. 13 and 14A to 14D), Examples 7 to It is assumed that the current density of about 9 was not reached.
  • the p-type optical semiconductor 12 having a branched structure as in Examples 7 to 9 can be formed by the above-described electrodeposition and subsequent firing. By adjusting the potential and reaction time during electrodeposition, the length and number of the branches 125 (projections 125) in the branched structure can be controlled.
  • FIG. 17 shows the formation method, form, and surface roughness of the p-type optical semiconductor 12 in Example 1 and Examples 7 to 9.
  • the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor is preferably 2000 nm or more. In this case, the current density can be sufficiently improved. More preferably, the surface roughness of the p-type optical semiconductor is 2500 nm or more. Moreover, from the viewpoint of realizable surface roughness by electrodeposition, the surface roughness of the p-type optical semiconductor is preferably 3200 nm or less.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Catalysts (AREA)

Abstract

　Provided are a CO2 reduction electrode and a CO2 reduction device making it possible to sufficiently obtain a reduction product comprising organic matter, etc. The reduction electrode (1) has an electroconductive substrate (11), a p-type optical semiconductor (12) provided thereon, and an n-type optical semiconductor (13) provided on the p-type optical semiconductor (12). The reduction electrode (1) is used in the reduction device (8). The energy level of the conduction band of the p-type optical semiconductor (12) is higher in the negative direction than the energy level of the conduction band of the n-type optical semiconductor (13). The energy level of the valence band of the p-type optical semiconductor (12) is higher in the negative direction than the energy level of the valence band of the n-type optical semiconductor (13).

Description

二酸化炭素還元電極及びこれを用いた二酸化炭素還元装置Carbon dioxide reduction electrode and carbon dioxide reduction apparatus using the same 関連出願の相互参照Cross-reference of related applications
　本出願は、２０１４年３月４日に出願された日本出願番号２０１４-４１７６１号および２０１４年１２月１２日に出願された日本出願番号２０１４-２５１４８５号に基づくもので、ここにその記載内容を援用する。 This application is based on Japanese Application No. 2014-41761 filed on Mar. 4, 2014 and Japanese Application No. 2014-251485 filed on Dec. 12, 2014. Incorporate.
　本開示は、ＣＯ2を還元するためのＣＯ2還元電極、及びこれを用いたＣＯ2還元装置に関する。 The present disclosure relates to a CO 2 reduction electrode for reducing CO 2 and a CO 2 reduction device using the same.
　近年、化石燃料枯渇問題の解決に向けて太陽光等の光エネルギーを利用して二酸化炭素から有機物を合成するための研究が重要視されている。これまでに、光触媒を水に懸濁してなる懸濁系での開発が進められてきた。具体的には、ブルッカイト型酸化チタンからなる光触媒に、貴金属からなる助触媒を担持した還元触媒が開発されている（非特許文献１参照）。 In recent years, research for synthesizing organic substances from carbon dioxide using light energy such as sunlight has been regarded as important for solving the fossil fuel depletion problem. So far, development of a suspension system in which a photocatalyst is suspended in water has been advanced. Specifically, a reduction catalyst has been developed in which a photocatalyst made of brookite-type titanium oxide is loaded with a promoter made of a noble metal (see Non-Patent Document 1).
　しかしながら、上述のように還元触媒を水に分散させてＣＯ2の還元を行っても、還元反応が十分に進行しない。その結果、還元生成物が十分に得られないという問題がある。 However, even if the reduction catalyst is dispersed in water and CO 2 is reduced as described above, the reduction reaction does not proceed sufficiently. As a result, there is a problem that a reduction product cannot be obtained sufficiently.
　本開示は、かかる背景に鑑みてなされたものであり、有機物等からなる還元生成物を十分に得ることができるＣＯ2還元電極、及びＣＯ2還元装置を提供しようとするものである。 The present disclosure has been made in view of such a background, and an object of the present disclosure is to provide a CO 2 reduction electrode and a CO 2 reduction device that can sufficiently obtain a reduction product made of an organic substance or the like.
　本開示の一態様によれば、ＣＯ2還元電極は、導電性の基板と、該基板上に設けられたｐ型光半導体と、該ｐ型光半導体上に設けられたｎ型光半導体とを有する。 According to one aspect of the present disclosure, the CO 2 reduction electrode includes a conductive substrate, a p-type optical semiconductor provided on the substrate, and an n-type optical semiconductor provided on the p-type optical semiconductor. Have.
　上記ｐ型光半導体の伝導帯のエネルギー準位は、上記ｎ型光半導体の伝導帯のエネルギー準位よりも卑側に高く、上記ｐ型光半導体の価電子帯のエネルギー準位は、上記ｎ型光半導体の価電子帯のエネルギー準位よりも卑側に高い。 The energy level of the conduction band of the p-type optical semiconductor is higher than the energy level of the conduction band of the n-type optical semiconductor, and the energy level of the valence band of the p-type optical semiconductor is n It is higher than the energy level of the valence band of the type optical semiconductor.
　本開示の他の態様によれば、ＣＯ2還元装置は、上記ＣＯ2還元電極と、酸化電極と、該酸化電極と上記ＣＯ2還元電極とが浸漬された水系電解液と、該水系電解液中において上記ＣＯ2還元電極と上記酸化電極とを隔てるイオン交換膜と、上記ＣＯ2還元電極に光を照射する光源と、上記ＣＯ2還元電極にＣＯ2を供給する供給口とを有する。 According to another aspect of the present disclosure, a CO 2 reduction device includes the CO 2 reduction electrode, an oxidation electrode, an aqueous electrolyte in which the oxidation electrode and the CO 2 reduction electrode are immersed, and the aqueous electrolyte. An ion exchange membrane for separating the CO 2 reduction electrode and the oxidation electrode therein, a light source for irradiating the CO 2 reduction electrode with light, and a supply port for supplying CO 2 to the CO 2 reduction electrode.
　上記ＣＯ2還元電極（以下、適宜「還元電極」という）は、上記ｐ型光半導体と、この上に設けられた上記ｎ型光半導体とを有している。即ち、上記還元電極は、ｐ型光半導体とｎ型光半導体との積層体を有し、ｐｎ接合を有している。そのため、光照射条件下おいてｎ型光半導体がＣＯ2に電子を受け渡してＣＯ2を還元することができる。このとき、水の存在下においてＣＯ2からメタノール等の有機物が生成される。一方、光照射によりｐ型光半導体には正孔が生じる。このとき、ｐ型光半導体において生じる余剰の電子がｐｎ接合を通ってｎ型光半導体へ補われる。また、ｐ型光半導体には、導電性の基板から電子が補われる。このように、上記還元電極においては、安定してＣＯ2に電子を供給して還元を行うことができ、有機物等からなる還元生成物を十分に得ることができる。 The CO 2 reduction electrode (hereinafter referred to as “reduction electrode” as appropriate) has the p-type optical semiconductor and the n-type optical semiconductor provided thereon. That is, the reduction electrode has a stacked body of a p-type optical semiconductor and an n-type optical semiconductor, and has a pn junction. Therefore, it is possible to n-type optical semiconductor keep light irradiation conditions to reduce CO 2 Te transferring electrons to CO 2. At this time, an organic substance such as methanol is generated from CO 2 in the presence of water. On the other hand, holes are generated in the p-type optical semiconductor by light irradiation. At this time, surplus electrons generated in the p-type optical semiconductor are supplemented to the n-type optical semiconductor through the pn junction. Further, electrons are supplemented from the conductive substrate to the p-type optical semiconductor. Thus, in the reduction electrode, the reduction can be performed by stably supplying electrons to CO 2 , and a reduction product made of an organic substance or the like can be sufficiently obtained.
　また、上記還元電極は、水の還元を抑制することが可能である。そのため、水の存在下においても、水の還元を抑制しつつＣＯ2を選択的に還元することができる。また、上記還元電極においては、ｐ型光半導体とｎ型光半導体とのエネルギー準位が上述の関係にある。そのため、還元電極を電極として用いた場合に電流を流すことが可能になる。 Further, the reduction electrode can suppress the reduction of water. Therefore, CO 2 can be selectively reduced while suppressing reduction of water even in the presence of water. In the reduction electrode, the energy levels of the p-type optical semiconductor and the n-type optical semiconductor are in the above relationship. Therefore, it is possible to pass a current when the reduction electrode is used as an electrode.
　次に、上記ＣＯ2還元装置（以下、適宜「還元装置」という）は、上記還元電極を備えている。そのため、還元電極が有する上述の優れた性能を生かして、上記還元装置は、ＣＯ2を還元して、有機物等からなる還元生成物を十分に生成することができる。また、上記還元装置においては、還元電極と酸化電極とがイオン交換膜により隔てられている。そのため、還元電極において生成されるＣＯ2の還元生成物が再度酸化されることを抑制することができる。そのため、還元生成物を十分に得ることができる。 Next, the CO 2 reduction device (hereinafter referred to as “reduction device” as appropriate) includes the reduction electrode. Therefore, taking advantage of the above-described excellent performance of the reduction electrode, the reduction device can sufficiently reduce CO 2 and generate a reduction product made of an organic substance or the like. In the reducing device, the reduction electrode and the oxidation electrode are separated by an ion exchange membrane. Therefore, it is possible to suppress the reduction product of CO 2 produced in the reduction electrode is oxidized again. Therefore, a sufficient reduction product can be obtained.
　本開示についての上記目的およびその他の目的、特徴や利点は、添付の図面を参照しながら下記の詳細な記述により、より明確になる。図面において、
実施例１における還元電極の断面構成を示す説明図。 実施例１における、基板上にｐ型光半導体を形成する工程を、基板のＦＴＯ膜の形成面側から示す説明図。 図２Ａに続く基板上にｐ型光半導体を形成する工程を、基板のＦＴＯ膜の形成面側から示す説明図。 図２Ｂに続く基板上にｐ型光半導体を形成する工程を、基板のＦＴＯ膜の形成面側から示す説明図。 図２Ｃに続く基板上にｐ型光半導体を形成する工程を、基板のＦＴＯ膜の形成面側から示す説明図。 実施例１における、基板上にｐ型光半導体を形成する工程を、断面構造により示す説明図。 図３Ａに続く基板上にｐ型光半導体を形成する工程を、断面構造により示す説明図。 図３Ｂに続く基板上にｐ型光半導体を形成する工程を、断面構造により示す説明図。 図３Ｃに続く基板上にｐ型光半導体を形成する工程を、断面構造により示す説明図。 実施例１における、電気泳動法によりｎ型光半導体を形成する方法を示す説明図。 実施例１における還元装置の断面構成を示す説明図。 実施例７における還元電極の拡大断面図。 実施例７におけるｐ型光半導体を形成するための電析装置の概略図。 実施例７におけるｐ型光半導体の表面の倍率２０００倍の走査型電子顕微鏡写真。 実施例７におけるｐ型光半導体の表面の倍率５００００倍の走査型電子顕微鏡写真。 図８Ａに示す走査型電子顕微鏡写真の線図。 図８Ｂに示す走査型電子顕微鏡写真の線図。 実施例８における還元電極の拡大断面図。 実施例８におけるｐ型光半導体の表面の倍率２０００倍の走査型電子顕微鏡写真 実施例８におけるｐ型光半導体の表面の倍率５００００倍の走査型電子顕微鏡写真 図１０Ａに示す走査型電子顕微鏡写真の線図。 図１０Ｂに示す走査型電子顕微鏡写真の線図。 実施例９における還元電極の拡大断面図。 実施例９におけるｐ型光半導体の表面の倍率２０００倍の走査型電子顕微鏡写真。 実施例９におけるｐ型光半導体の表面の倍率５００００倍の走査型電子顕微鏡写真。 図１２Ａに示す走査型電子顕微鏡写真の線図。 図１２Ｂに示す走査型電子顕微鏡写真の線図。 実施例１における還元電極の拡大断面図。 実施例１におけるｐ型光半導体の表面の倍率２０００倍の走査型電子顕微鏡写真。 実施例１におけるｐ型光半導体の表面の倍率５００００倍の走査型電子顕微鏡写真。 図１４Ａに示す走査型電子顕微鏡写真の線図。 図１４Ｂに示す走査型電子顕微鏡写真の線図。 実施例１、実施例７～実施例９の各還元電極の電流密度の比較結果を示す説明図。 各実施例及び各比較例における還元電極のｎ型光半導体の材質及び厚み、ｐ型光半導体の材質及び厚み、及び還元生成物を示す図。 各実施例における還元電極のｐ型光半導体について、形成方法、形態、及び表面粗さを示す図。 The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. In the drawing
FIG. 3 is an explanatory diagram showing a cross-sectional configuration of a reduction electrode in Example 1. FIG. 3 is an explanatory diagram illustrating a process of forming a p-type optical semiconductor on a substrate from the formation surface side of the FTO film of the substrate in Example 1. FIG. 2B is an explanatory diagram showing a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 2A from the FTO film formation surface side of the substrate. FIG. 2B is an explanatory diagram showing a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 2B from the FTO film formation surface side of the substrate. FIG. 2D is an explanatory view showing a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 2C from the FTO film forming surface side of the substrate. Explanatory drawing which shows the process of forming a p-type optical semiconductor on a board | substrate in Example 1 by sectional structure. FIG. 3B is an explanatory diagram showing a step of forming a p-type optical semiconductor on the substrate following FIG. 3A by a cross-sectional structure. FIG. 3D is an explanatory diagram showing a cross-sectional structure of a process for forming a p-type optical semiconductor on a substrate following FIG. 3B. FIG. 3D is an explanatory diagram illustrating, by a cross-sectional structure, a step of forming a p-type optical semiconductor on the substrate subsequent to FIG. 3C. FIG. 3 is an explanatory diagram illustrating a method for forming an n-type optical semiconductor by electrophoresis in Example 1. FIG. 3 is an explanatory diagram illustrating a cross-sectional configuration of the reduction device according to the first embodiment. FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 7. FIG. 10 is a schematic view of an electrodeposition apparatus for forming a p-type optical semiconductor in Example 7. The scanning electron micrograph of the magnification of 2000 times of the surface of the p-type optical semiconductor in Example 7. FIG. The scanning electron micrograph of the magnification of 50000 times of the surface of the p-type optical semiconductor in Example 7. FIG. FIG. 8B is a diagram of the scanning electron micrograph shown in FIG. 8A. FIG. 8B is a diagram of the scanning electron micrograph shown in FIG. 8B. FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 8. Scanning electron micrograph of the surface of the p-type optical semiconductor in Example 8 at a magnification of 2000 times Scanning electron micrograph of the surface of the p-type optical semiconductor in Example 8 at a magnification of 50000 times FIG. 10B is a diagram of the scanning electron micrograph shown in FIG. 10A. FIG. 10B is a diagram of the scanning electron micrograph shown in FIG. 10B. FIG. 10 is an enlarged cross-sectional view of a reduction electrode in Example 9. The scanning electron micrograph of the magnification of 2000 times of the surface of the p-type optical semiconductor in Example 9. FIG. The scanning electron micrograph of the magnification of 50000 times of the surface of the p-type optical semiconductor in Example 9. FIG. FIG. 12B is a diagram of the scanning electron micrograph shown in FIG. 12A. FIG. 12B is a diagram of the scanning electron micrograph shown in FIG. 12B. FIG. 3 is an enlarged cross-sectional view of a reduction electrode in Example 1. The scanning electron micrograph of the magnification of 2000 times of the surface of the p-type optical semiconductor in Example 1. FIG. The scanning electron micrograph of the magnification of 50000 times of the surface of the p-type optical semiconductor in Example 1. FIG. FIG. 14B is a diagram of the scanning electron micrograph shown in FIG. 14A. FIG. 14B is a diagram of the scanning electron micrograph shown in FIG. 14B. FIG. 6 is an explanatory diagram showing a comparison result of current densities of the reduction electrodes of Example 1 and Examples 7 to 9. The figure which shows the material and thickness of the n-type optical semiconductor of the reduction | restoration electrode in each Example and each comparative example, the material and thickness of a p-type optical semiconductor, and a reduction product. The figure which shows a formation method, a form, and surface roughness about the p-type optical semiconductor of the reduction electrode in each Example.
　次に、還元電極及び還元装置の好ましい実施形態について説明する。 Next, preferred embodiments of the reduction electrode and the reduction device will be described.
　還元電極において、基板は、全体が導電性を有していなくても、表面に導電性の層を有する基板であればよい。基板は、導電性を有していればよく、その材質は適宜選択できる。 In the reduction electrode, the substrate may be a substrate having a conductive layer on the surface, even if the substrate does not have overall conductivity. The board | substrate should just have electroconductivity, The material can be selected suitably.
　ｐ型光半導体及びｎ型光半導体の形状は、例えば膜状である。厚みは適宜変更することができる。ｐ型光半導体上のｎ型光半導体は、光を透過できる厚みで形成されていることが好ましい。ｐ型光半導体の厚みは、例えば０．１～５００μｍであり、ｎ型光半導体の厚みは、例えば０．０１～２００μｍである。 The shape of the p-type optical semiconductor and the n-type optical semiconductor is a film shape, for example. The thickness can be changed as appropriate. The n-type optical semiconductor on the p-type optical semiconductor is preferably formed with a thickness capable of transmitting light. The thickness of the p-type optical semiconductor is, for example, 0.1 to 500 μm, and the thickness of the n-type optical semiconductor is, for example, 0.01 to 200 μm.
　ｎ型光半導体の材質としては、例えばＴｉＯ2、ＳｒＴｉＯ3、ＢａＴｉＯ3、ＣａＴｉＯ3、ＷＯ3、ＢｉＶＯ4、ＢｉＦｅＯ3、ＣｕＴａＮ2、ＦｅＴｉＯ2、ＭｇＦｅ2Ｏ4、ＰｂＳ、ＺｎＯ、グラフェン、グラファイト状窒化炭素（ＣＮ）、ｎ－Ｓｉ、ｎ－ＳｉＣ、ｎ－ＧａＮ、ｎ－ＡｌＧａＮ等から選ばれる少なくとも１種が挙げられる。なお、ＴｉＯ2には、例えばルチル型、アナターゼ型、ブルッカイト型がある。ｎ型光半導体の材質としては、これらのいずれであってもよく、２種以上の混合物であってもよい。 Examples of the material of the n-type optical semiconductor include TiO 2 , SrTiO 3 , BaTiO 3 , CaTiO 3 , WO 3 , BiVO 4 , BiFeO 3 , CuTaN 2 , FeTiO 2 , MgFe 2 O 4 , PbS, ZnO, graphene, and graphite Examples thereof include at least one selected from carbon nitride (CN), n-Si, n-SiC, n-GaN, n-AlGaN, and the like. TiO 2 includes, for example, a rutile type, an anatase type, and a brookite type. Any of these materials may be used as the material of the n-type optical semiconductor, and a mixture of two or more types may be used.
　ｐ型光半導体の材質としては、例えばＣｕＯ、Ｃｕ2Ｏ、ＭｇドープＣｕＦｅ2Ｏ4、ＣａＦｅ2Ｏ4、ＣｏＯ3、Ｃｒ2Ｏ3、ＣｕＣｒＯ2、ＦｅドープＴｉＯ2、ＣｒドープＴｉＯ2、ＧａＰ、ＩｎＰ、ＮｉＯ、ＲｈドープＳｒＴｉＯ3、ｐ－Ｓｉ、ｐ－ＳｉＣ等から選ばれる少なくとも１種が挙げられる。 Examples of the material of the p-type optical semiconductor include CuO, Cu 2 O, Mg-doped CuFe 2 O 4 , CaFe 2 O 4 , CoO 3 , Cr 2 O 3 , CuCrO 2 , Fe-doped TiO 2 , Cr-doped TiO 2 , and GaP. And at least one selected from InP, NiO, Rh-doped SrTiO 3 , p-Si, p-SiC, and the like.
　還元電極において、ｐ型光半導体の伝導帯のエネルギー準位は、ｎ型光半導体の伝導帯のエネルギー準位よりも卑側に高い。また、ｐ型光半導体の価電子帯のエネルギー準位は、ｎ型光半導体の価電子帯のエネルギー準位よりも卑側に高い。このような関係となるように、ｐ型光半導体とｎ型光半導体との材質が例えば上述の物質の中から適宜選択される。 In the reduction electrode, the energy level of the conduction band of the p-type optical semiconductor is higher on the base side than the energy level of the conduction band of the n-type optical semiconductor. In addition, the energy level of the valence band of the p-type optical semiconductor is higher than the energy level of the valence band of the n-type optical semiconductor. In order to satisfy such a relationship, materials of the p-type optical semiconductor and the n-type optical semiconductor are appropriately selected from, for example, the above-described substances.
　還元装置において、酸化電極は還元電極の対極である。酸化電極としては、例えば貴金属等からなる電極を用いることができる。水系電解液としては、例えば電解質の水溶液を用いることができる。イオン交換膜としては、各種市販品を採用することができる。 In the reduction device, the oxidation electrode is the counter electrode of the reduction electrode. As the oxidation electrode, for example, an electrode made of a noble metal or the like can be used. As the aqueous electrolyte solution, for example, an aqueous electrolyte solution can be used. Various commercially available products can be used as the ion exchange membrane.
　光源からの光は、紫外線、可視光等を含むことが好ましい。この場合には、還元電極におけるＣＯ2の還元反応をより活性化し易くなる。より好ましくは、光源からの光は、少なくとも紫外線を含むことがよい。 The light from the light source preferably includes ultraviolet light, visible light and the like. In this case, it becomes easier to activate the CO 2 reduction reaction at the reduction electrode. More preferably, the light from the light source includes at least ultraviolet rays.
　（実施例１）
　次に、ＣＯ2還元電極及びＣＯ2還元装置の実施例について説明する。 Example 1
Next, examples of the CO 2 reduction electrode and the CO 2 reduction device will be described.
　図１に示すごとく、本例の還元電極１は、導電性の基板１１と、この上に設けられたｐ型光半導体１２と、この上に設けられたｎ型光半導体１３とを有する。ｐ型光半導体１２は、ｎ型光半導体１３に完全に被覆されている。本例において、ｐ型光半導体１２は、酸化銅（ＣｕＯ）からなり、ｎ型光半導体１３は、ブルッカイト型酸化チタン（ＴｉＯ2）からなる。 As shown in FIG. 1, the reduction electrode 1 of this example has a conductive substrate 11, a p-type optical semiconductor 12 provided thereon, and an n-type optical semiconductor 13 provided thereon. The p-type optical semiconductor 12 is completely covered with the n-type optical semiconductor 13. In this example, the p-type optical semiconductor 12 is made of copper oxide (CuO), and the n-type optical semiconductor 13 is made of brookite-type titanium oxide (TiO 2 ).
　本例の還元電極１の製造方法について説明する。まず、スキージ法により基板１１上にｐ型光半導体１２を形成する。具体的には、まず、導電性の基板１１として、フッ素ドープ酸化スズ（ＦＴＯ）膜１１１が表面に形成された石英ガラス基板１１２を準備した（図２Ａ、図３Ａ参照）。基板１１としては、名城科学工業(株)の製品を用いた。基板１１において、ＦＴＯ膜１１１は、石英ガラス基板１１２の片側面に積層されている。基板１１の寸法は、縦３０ｍｍ×横３０ｍｍ×厚み１．８ｍｍである。 A method for manufacturing the reduction electrode 1 of this example will be described. First, the p-type optical semiconductor 12 is formed on the substrate 11 by the squeegee method. Specifically, first, a quartz glass substrate 112 having a fluorine-doped tin oxide (FTO) film 111 formed on the surface was prepared as the conductive substrate 11 (see FIGS. 2A and 3A). As the substrate 11, a product of Meijo Kagaku Kogyo Co., Ltd. was used. In the substrate 11, the FTO film 111 is laminated on one side of the quartz glass substrate 112. The dimensions of the substrate 11 are 30 mm long × 30 mm wide × 1.8 mm thick.
　次に、図２Ｂ、図３Ｂに示すごとく、内部がくり抜かれた板状のスペーサ１２０を準備した。スペーサ１２０の外形寸法は基板１１と同様に縦３０ｍｍ×横３０ｍｍであり、内部空間の寸法は縦２５ｍｍ×横２５ｍｍである。スペーサ１２０の厚みは１ｍｍである。このスペーサ１２０を基板１１のＦＴＯ膜１１１の形成面上に載置した。次いで、図２Ｃ、図３Ｃに示すごとく、スキージ法により、スペーサ１２０の内部空間内にＣｕＯペーストを塗布することにより、基板１１のＦＴＯ膜１１１上にＣｕＯペースト層１２１を形成した。ＣｕＯペーストは、ＣｕＯ（和光純薬（株）製）５００ｍｇとエタノール２ｍｌとを混合して得られた。 Next, as shown in FIG. 2B and FIG. 3B, a plate-like spacer 120 with a hollow interior was prepared. The external dimensions of the spacer 120 are 30 mm long × 30 mm wide like the substrate 11, and the dimensions of the internal space are 25 mm long × 25 mm wide. The thickness of the spacer 120 is 1 mm. This spacer 120 was placed on the surface of the substrate 11 where the FTO film 111 is formed. Next, as shown in FIGS. 2C and 3C, a CuO paste layer 121 was formed on the FTO film 111 of the substrate 11 by applying a CuO paste in the internal space of the spacer 120 by a squeegee method. The CuO paste was obtained by mixing 500 mg of CuO (manufactured by Wako Pure Chemical Industries, Ltd.) and 2 ml of ethanol.
　次いで、ＣｕＯペースト層１２１を温度５０℃で１時間乾燥させた後、スペーサ１２０を取り外した。次いで、ＣｕＯペースト層１２１が積層された基板１１を温度５５０℃で１時間焼成した。これにより、図２Ｄ、図３Ｄに示すごとく、厚み３０μｍの膜状のｐ型光半導体１２を基板１１上に形成した。ｐ型光半導体１２は、基板１１のＦＴＯ膜１１１上に形成されている。以下、ｐ型光半導体１２が形成された基板１１を「基板Ａ」といい、符号１５で示す。 Next, after the CuO paste layer 121 was dried at a temperature of 50 ° C. for 1 hour, the spacer 120 was removed. Next, the substrate 11 on which the CuO paste layer 121 was laminated was baked at a temperature of 550 ° C. for 1 hour. Thereby, as shown in FIG. 2D and FIG. 3D, a film-like p-type optical semiconductor 12 having a thickness of 30 μm was formed on the substrate 11. The p-type optical semiconductor 12 is formed on the FTO film 111 of the substrate 11. Hereinafter, the substrate 11 on which the p-type optical semiconductor 12 is formed is referred to as “substrate A” and is denoted by reference numeral 15.
　なお、上述の例においては、スキージ法により、ｐ型光半導体１２を作製したが、ｐ型光半導体１２は、例えばスピンコータ法、電気泳動法、電析法等により作製することもできる。 In the above example, the p-type optical semiconductor 12 is manufactured by the squeegee method. However, the p-type optical semiconductor 12 can also be manufactured by, for example, a spin coater method, an electrophoresis method, an electrodeposition method, or the like.
　次に、電気泳動法により、ｎ型光半導体を形成する。 Next, an n-type optical semiconductor is formed by electrophoresis.
　具体的には、まず、ブルッカイト型酸化チタンを調整した。まず、チタン粉末（和光純薬工業(株)製の「２０４－０５２０５」）０．６ｇと、２５質量％アンモニア水（和光純薬工業(株)製の「０１０－０３１６６」）１０ｍｌと、３０質量％過酸化水素水（和光純薬工業(株)製の「０８１－０４２１５」）４０ｍｌとを混合し、チタン粉末がすべて溶けるまで撹拌を行った。得られた溶液に、グリコール酸（和光純薬工業(株)製の「０７５－０１５１５」）１．４２６ｇを添加し、室温でさらに２時間の撹拌を行った。その後、撹拌しながら溶液を温度１００℃で加熱した。続けて、加熱及び撹拌を行うことにより、溶液からアンモニア、過酸化水素を蒸発させた。得られたゲル状の固体にイオン交換水４０ｍｌを添加し、固体を再度溶解させた。次いで、溶液を撹拌しながらアンモニア水を添加することにより、溶液のｐＨを１０に調整した。次いで、溶液にイオン交換水を添加し、総量を５０ｍｌまでメスアップした。次に、温度２００℃、４８時間という条件で水熱合成を行った。そして、得られた生成物の上澄み液を除去した。その後、固体状の沈殿物にイオン交換水を加えて、遠心分離を行った。そして、得られた物質の電気伝導度を測定した。この電気伝導度の値が１０μＳ／ｃｍとなるまで、イオン交換水の添加から遠心分離までの操作を繰り返し行った。次に、温度６０℃、２４時間という条件で真空乾燥を実施した。その後、得られた物質を、乳鉢を用いて解砕することにより、粉末状のブルッカイト型酸化チタンを得た。 Specifically, first, brookite type titanium oxide was prepared. First, 0.6 g of titanium powder (“204-05205” manufactured by Wako Pure Chemical Industries, Ltd.), 10 ml of 25 mass% ammonia water (“010-03166” manufactured by Wako Pure Chemical Industries, Ltd.), 30 40 ml of a mass% hydrogen peroxide solution (“081-04215” manufactured by Wako Pure Chemical Industries, Ltd.) was mixed and stirred until all of the titanium powder was dissolved. To the obtained solution, 1.426 g of glycolic acid (“075-01515” manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was further stirred at room temperature for 2 hours. The solution was then heated at a temperature of 100 ° C. with stirring. Subsequently, ammonia and hydrogen peroxide were evaporated from the solution by heating and stirring. To the obtained gel-like solid, 40 ml of ion-exchanged water was added to dissolve the solid again. Next, the pH of the solution was adjusted to 10 by adding aqueous ammonia while stirring the solution. Subsequently, ion exchange water was added to the solution, and the total amount was made up to 50 ml. Next, hydrothermal synthesis was performed under conditions of a temperature of 200 ° C. and 48 hours. And the supernatant liquid of the obtained product was removed. Thereafter, ion-exchanged water was added to the solid precipitate and centrifuged. And the electrical conductivity of the obtained substance was measured. The operation from the addition of ion exchange water to centrifugation was repeated until the value of electrical conductivity reached 10 μS / cm. Next, vacuum drying was performed under conditions of a temperature of 60 ° C. and 24 hours. Thereafter, the obtained substance was pulverized using a mortar to obtain powdered brookite type titanium oxide.
　次いで、ブルッカイト型酸化チタン０．５ｇをエタノール２５ｍｌに添加し混合することにより、電気泳動用の溶液１３１を作製した（図４参照）。図４に示すごとく、この溶液１３１中に、基板Ａ１５と、ｐ型光半導体が形成されていない基板１６（以下、適宜「基板Ｂ」という）を完全に浸漬させた。基板Ｂ１６は、ｐ型光半導体が形成される前の基板と同じものであり、ＦＴＯ膜１６１が表面に形成された石英ガラス基板１６２である。 Next, 0.5 g of brookite type titanium oxide was added to 25 ml of ethanol and mixed to prepare a solution 131 for electrophoresis (see FIG. 4). As shown in FIG. 4, the substrate A15 and the substrate 16 on which the p-type optical semiconductor is not formed (hereinafter, referred to as “substrate B” as appropriate) were completely immersed in the solution 131. The substrate B16 is the same as the substrate before the p-type optical semiconductor is formed, and is a quartz glass substrate 162 on which the FTO film 161 is formed.
　図４に示すごとく、基板Ａ１５と基板Ｂ１６との間隔を１ｍｍにした状態で両者を溶液１３１に浸漬した。基板Ａ１５と基板Ｂ１６をポテンショスタット１８に電気的に接続した。基板Ａ１５が正極、基板Ｂ１６が負極である。そして、基板Ａ１５と基板Ｂ１６との間に１０Ｖの電圧を１２０秒間印加した。これにより、基板Ａ１５のＦＴＯ膜１１１の形成面側にブルッカイト型酸化チタンからなるｎ型光半導体１３を形成した（図４及び図１参照）。ｎ型光半導体１３の厚みは、４０μｍである。なお、この厚みは、ｐ型光半導体１２とｎ型光半導体１３との積層部分におけるｎ型光半導体１３の厚みである。 As shown in FIG. 4, both were immersed in the solution 131 in a state where the distance between the substrate A15 and the substrate B16 was 1 mm. Substrate A15 and substrate B16 were electrically connected to potentiostat 18. The substrate A15 is a positive electrode, and the substrate B16 is a negative electrode. A voltage of 10V was applied between the substrate A15 and the substrate B16 for 120 seconds. Thus, the n-type optical semiconductor 13 made of brookite-type titanium oxide was formed on the surface of the substrate A15 where the FTO film 111 is formed (see FIGS. 4 and 1). The n-type optical semiconductor 13 has a thickness of 40 μm. This thickness is the thickness of the n-type optical semiconductor 13 in the stacked portion of the p-type optical semiconductor 12 and the n-type optical semiconductor 13.
　以上のようにして、図１に示すごとく、導電性の基板１１と、基板１１上に積層されたｐ型光半導体１２と、ｐ型光半導体１２を被覆するｎ型光半導体１３とを有する還元電極１を得た。本例の還元電極１におけるｎ型光半導体１３の材質及び厚み、ｐ型光半導体１２の材質及び厚みを図１６に示す。 As described above, as shown in FIG. 1, the reduction includes the conductive substrate 11, the p-type optical semiconductor 12 stacked on the substrate 11, and the n-type optical semiconductor 13 covering the p-type optical semiconductor 12. An electrode 1 was obtained. FIG. 16 shows the material and thickness of the n-type optical semiconductor 13 and the material and thickness of the p-type optical semiconductor 12 in the reduction electrode 1 of this example.
　なお、上述の例においては、電気泳動法により、ｎ型光半導体１３を作製したが、ｎ型光半導体１３は、例えばスキージ法、スピンコータ法等により作製することもできる。 In the above example, the n-type optical semiconductor 13 is manufactured by electrophoresis. However, the n-type optical semiconductor 13 can also be manufactured by, for example, a squeegee method, a spin coater method, or the like.
　次に、本例の還元電極１を用いて還元装置を組み立てた。 Next, a reduction device was assembled using the reduction electrode 1 of this example.
　図５に示すごとく、本例の還元装置８は、還元電極１と、酸化電極２と、水系電解液３（以下、適宜「電解液３」という）と、イオン交換膜４（以下、適宜「膜４」という）と、光源５と、ＣＯ2を供給するための供給口６とを有する。電解液３は、濃度０．２ｍｏｌ／ＬのＫＨＣＯ3水溶液である。還元装置８においては、５０ｍｌの電解液３がケース８０内に注入されている。ケース８０は、（株）イーシーフロンティア製のＨ型セルＶＢ－９である。即ち、ケース８０は、Ｈ型であり、２つのケース８０１、８０２と両者を連結する連結部８０３とからなる。 As shown in FIG. 5, the reduction device 8 of this example includes a reduction electrode 1, an oxidation electrode 2, an aqueous electrolytic solution 3 (hereinafter referred to as “electrolytic solution 3” as appropriate), and an ion exchange membrane 4 (hereinafter referred to as “ A membrane 4 ”), a light source 5, and a supply port 6 for supplying CO 2 . The electrolytic solution 3 is a KHCO 3 aqueous solution having a concentration of 0.2 mol / L. In the reducing device 8, 50 ml of the electrolytic solution 3 is injected into the case 80. Case 80 is an H-type cell VB-9 manufactured by EC Frontier. That is, the case 80 is H-shaped and includes two cases 801 and 802 and a connecting portion 803 that connects the two cases.
　ケース８０１内には、還元電極１と、Ａｇ／ＡｇＣｌからなる参照電極１９とが挿入されている。還元電極１と参照電極１９とは電気的に接続されている。一方、ケース８０２内には、還元電極１の対極である酸化電極２が挿入されている。酸化電極２は、Ｐｔワイヤからなる。ケース８０の連結部８０３には、膜４（シグマアルドリッチ社製のナフィオン膜）が配置されている。膜４は、還元電極１と酸化電極２との間に存在し、両者を分離している。ケース８０内において、還元電極１、参照電極１９、酸化電極２、及び膜４は、電解液３中に浸されている。 In the case 801, the reduction electrode 1 and the reference electrode 19 made of Ag / AgCl are inserted. The reduction electrode 1 and the reference electrode 19 are electrically connected. On the other hand, in the case 802, the oxidation electrode 2 that is the counter electrode of the reduction electrode 1 is inserted. The oxidation electrode 2 is made of a Pt wire. A membrane 4 (Nafion membrane manufactured by Sigma-Aldrich) is disposed in the connecting portion 803 of the case 80. The membrane 4 exists between the reduction electrode 1 and the oxidation electrode 2 and separates them. In the case 80, the reduction electrode 1, the reference electrode 19, the oxidation electrode 2, and the membrane 4 are immersed in the electrolytic solution 3.
　各ケース８０１、８０２の開口部は、栓８０３、８０４により密閉されている。ケース８０１側の栓８０３には、ＣＯ2を供給する管６０が挿入されている。この管６０の供給口６から電解液３中にＣＯ2が供給される。 The openings of the cases 801 and 802 are sealed with plugs 803 and 804. A tube 60 for supplying CO 2 is inserted into the plug 803 on the case 801 side. CO 2 is supplied into the electrolytic solution 3 from the supply port 6 of the pipe 60.
　また、図５に示すごとく、還元装置８は、還元電極１に光５１を照射するための光源５を備えている。光源５は、還元電極１におけるｐ型光半導体１２とｎ型光半導体１３とが形成された面に光が照射されるように配置されている。光源５としては、朝日分光(株)製の「ＭＡＸ３００Ｗ」を用いた。 Further, as shown in FIG. 5, the reducing device 8 includes a light source 5 for irradiating the reducing electrode 1 with light 51. The light source 5 is arranged so that light is irradiated onto the surface of the reduction electrode 1 on which the p-type optical semiconductor 12 and the n-type optical semiconductor 13 are formed. As the light source 5, “MAX300W” manufactured by Asahi Spectroscopic Co., Ltd. was used.
　また、還元装置８は、図５に示すように、電流計９１及び電圧計９２を備える電気化学アナライザ９に電気的に接続されている。電気化学アナライザ９は、ビー・エー・エス(株)製のＡＬＳモデル６６０Ｅである。電流計９１は、還元電極１と酸化電極２との間に接続されており、電圧計９２は、還元電極１と参照電極１９との間に接続されている。 Further, the reduction device 8 is electrically connected to an electrochemical analyzer 9 including an ammeter 91 and a voltmeter 92 as shown in FIG. The electrochemical analyzer 9 is an ALS model 660E manufactured by BAS. The ammeter 91 is connected between the reduction electrode 1 and the oxidation electrode 2, and the voltmeter 92 is connected between the reduction electrode 1 and the reference electrode 19.
　次に、還元装置８を用いて、ＣＯ2の還元を行い、還元生成物の生成量の分析を行った。具体的には、図５に示すごとく、供給口６から電解液３中に、Ｇ１レベル、即ち純度９９．９９９９５ｖｏｌ％の炭酸ガス（ＣＯ2）を２時間供給し、光源５から波長３４０ｎｍ以上の光５１を還元電極１に６時間照射した。炭酸ガスの流速は、５ｍｌ／ｍｉｎであり、光の強度は、１０ｍＷ／ｃｍ2である。このとき、電解液３中に供給された炭酸ガスは、光が照射された還元電極１において還元される。この還元反応を６時間実施し、還元生成物の量をクロマトグラフィにより検出した。なお、本例においては、生成物として、メタノール、ギ酸、水素、一酸化炭素の検出を行った。 Next, CO 2 was reduced using the reducing device 8 and the amount of reduction product produced was analyzed. Specifically, as shown in FIG. 5, carbon dioxide gas (CO 2 ) having a G1 level, that is, a purity of 99.99995 vol% is supplied from the supply port 6 into the electrolyte 3 for 2 hours, and the wavelength of 340 nm or more is supplied from the light source 5. The light 51 was irradiated to the reduction electrode 1 for 6 hours. The flow rate of carbon dioxide gas is 5 ml / min, and the intensity of light is 10 mW / cm 2 . At this time, the carbon dioxide gas supplied into the electrolytic solution 3 is reduced at the reduction electrode 1 irradiated with light. This reduction reaction was carried out for 6 hours, and the amount of reduction product was detected by chromatography. In this example, methanol, formic acid, hydrogen, and carbon monoxide were detected as products.
　メタノールの検出は、還元反応後の電解液３を採取し、シリンジを用いて電解液３をガスクロマトグラフィ装置（(株)島津製作所製の「ＧＣ－２０１４」）に注入することにより行った。なお、クロマトグラフィ用のカラムは、アジレント・テクノロジー(株)製の「ＤＢ－ＷＡＸｅｔｒ」である。検出方法は、水素炎イオン化検出（ＦＩＤ）である。検出は、温度７０℃で５分間保持するという条件で行った。 Methanol was detected by collecting the electrolytic solution 3 after the reduction reaction and injecting the electrolytic solution 3 into a gas chromatography apparatus (“GC-2014” manufactured by Shimadzu Corporation) using a syringe. The column for chromatography is “DB-WAXetr” manufactured by Agilent Technologies. The detection method is flame ionization detection (FID). The detection was performed under the condition that the temperature was maintained at 70 ° C. for 5 minutes.
　ギ酸の検出は、還元反応後の電解液３を採取し、シリンジを用いて電解液３をイオンクロマトグラフィ装置（(株)サーモフィッシャーサイエンティフィック(株)製の「Ｄｉｏｎｅｘ　ＩＣ－２０」）に注入することにより行った。なお、クロマトグラフィ用のカラムは、(株)サーモフィッシャーサイエンティフィック(株)製の「ＩｏｎＰａｃ　ＡＳ２０」である。検出には、濃度２．７ｍｍｏｌ／ＬのＮａ2ＣＯ3水溶液と濃度０．３ｍｍｏｌ／ＬのＮａＨＣＯ3水溶液との混合溶液をクロマトグラフィ用の電解液として用いた。流速条件は、１．５ｍｌ／ｍｉｎである。 Formic acid is detected by collecting the electrolytic solution 3 after the reduction reaction and injecting the electrolytic solution 3 into an ion chromatography apparatus (“Dionex IC-20” manufactured by Thermo Fisher Scientific Co., Ltd.) using a syringe. It was done by doing. The column for chromatography is “IonPac AS20” manufactured by Thermo Fisher Scientific Co., Ltd. For the detection, a mixed solution of a 2.7 mmol / L Na 2 CO 3 aqueous solution and a 0.3 mmol / L NaHCO 3 aqueous solution was used as an electrolyte for chromatography. The flow rate condition is 1.5 ml / min.
　水素、一酸化炭素の検出は、還元反応後のケース８０内のガスをガスクロマトグラフィ装置（(株)島津製作所製の「ＧＣ－２０１４」）に注入することにより行った。なお、クロマトグラフィ用のカラムは、(株)島津製作所製の「ＳＨＩＮＣＡＲＢＯＮ　ＳＴ」である。検出方法は、熱伝導度検出（ＴＣＤ）である。検出は、温度４０℃で１２分間保持した後、昇温速度１０℃／ｍｉｎで温度２００℃まで昇温させるという条件で行った。 Hydrogen and carbon monoxide were detected by injecting the gas in the case 80 after the reduction reaction into a gas chromatography apparatus (“GC-2014” manufactured by Shimadzu Corporation). The column for chromatography is “SHINCARBON ST” manufactured by Shimadzu Corporation. The detection method is thermal conductivity detection (TCD). The detection was performed under the condition that the temperature was maintained at 40 ° C. for 12 minutes and then the temperature was increased to 200 ° C. at a temperature increase rate of 10 ° C./min.
　各還元生成物の量を図１６に示す。 The amount of each reduction product is shown in FIG.
　（実施例２～６）
　実施例２の還元電極１は、ｎ型光半導体１３の厚みを１５μｍに変更した点を除いては、実施例１と同様にして作製した電極である。 (Examples 2 to 6)
The reduction electrode 1 of Example 2 is an electrode manufactured in the same manner as in Example 1 except that the thickness of the n-type optical semiconductor 13 is changed to 15 μm.
　実施例３の還元電極１は、ブルッカイト型酸化チタンの代わりに、金属（Ａｇ）を担持させたブルッカイト型酸化チタンを用いた点を除いては、実施例１と同様にして作製した電極である。金属を担持させたブルッカイト型酸化チタンは、次のようにして調整した。 The reduction electrode 1 of Example 3 is an electrode manufactured in the same manner as in Example 1 except that brookite type titanium oxide supporting metal (Ag) is used instead of brookite type titanium oxide. . The brookite type titanium oxide supporting metal was prepared as follows.
　即ち、まず、ブルッカイト型酸化チタン５ｇを分散した水５０ｍｌに、触媒粉末（ＡｇＮＯ3）０．５ｍｇと犠牲試薬（エタノール）５ｍｌとを添加した。次いで、これらの混合液に窒素（Ｎ2）ガスを３０分間供給した後、ＬＥＤ光源（波長３６５ｎｍ）からの光を強度０．３ｍＷ／ｃｍ2で２４時間照射した。この光電着法により、ブルッカイト型酸化チタンの還元面に金属を担時させた。なお、触媒粉末の添加量は、例えば０．５ｍｇ～５ｍｇの範囲で調整が可能であり、犠牲試薬の添加量は、例えば０．５ｍｌ～５ｍｌの範囲で調整が可能である。 That is, first, 0.5 mg of catalyst powder (AgNO 3 ) and 5 ml of sacrificial reagent (ethanol) were added to 50 ml of water in which 5 g of brookite-type titanium oxide was dispersed. Next, nitrogen (N 2 ) gas was supplied to these mixed solutions for 30 minutes, and then light from an LED light source (wavelength 365 nm) was irradiated for 24 hours at an intensity of 0.3 mW / cm 2 . By this photodeposition method, a metal was supported on the reduction surface of brookite-type titanium oxide. The addition amount of the catalyst powder can be adjusted in the range of 0.5 mg to 5 mg, for example, and the addition amount of the sacrificial reagent can be adjusted in the range of 0.5 ml to 5 ml, for example.
　実施例４の還元電極１は、ＣｕＯペーストの代わりにＣｕＦｅ2Ｏ4ペーストを用いてｐ型光半導体１２を形成した点を除いては、実施例１と同様にして作製した電極である。 The reduction electrode 1 of Example 4 is an electrode produced in the same manner as in Example 1 except that the p-type optical semiconductor 12 is formed using CuFe 2 O 4 paste instead of CuO paste.
　実施例５の還元電極１は、ブルッカイト型酸化チタンの代わりに汎用の酸化チタン（日本エアロジル(株)製の「ＡＥＲＯＸＩＤＥ（登録商標）　ＴｉＯ2
　Ｐ２５」）を用いた点を除いては、実施例１と同様にして作製した電極である。なお、本例の酸化チタンは、ルチル型とアナターゼ型との混合物である。 The reduction electrode 1 of Example 5 is made of general-purpose titanium oxide (“AEROXIDE (registered trademark) TiO 2 manufactured by Nippon Aerosil Co., Ltd.) instead of brookite-type titanium oxide.
The electrode was produced in the same manner as in Example 1 except that P25 ") was used. In addition, the titanium oxide of this example is a mixture of a rutile type and an anatase type.
　実施例６の還元電極１は、ブルッカイト型酸化チタンの代わりにチタン酸ストロンチウム（ＳｒＴｉＯ3）を用いた点を除いては、実施例１と同様にして作製した電極である。 The reduction electrode 1 of Example 6 is an electrode manufactured in the same manner as Example 1 except that strontium titanate (SrTiO 3 ) was used instead of brookite-type titanium oxide.
　上述の実施例２～６の還元電極１についても、これらをそれぞれ用いて実施例１と同様の構成の還元装置８を作製し、ＣＯ2の還元を行った。なお、実施例２～６において、実施例１と同じ符号は、同一の構成を示し、先行する説明を参照する。 For the reduction electrodes 1 of Examples 2 to 6 described above, the reduction device 8 having the same configuration as that of Example 1 was produced using each of these, and CO 2 was reduced. In the second to sixth embodiments, the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description is referred to.
　（比較例１～５）
　比較例１の還元電極は、ｎ型光半導体を形成しなかった点を除いては、実施例１と同様にして作製した電極である。 (Comparative Examples 1 to 5)
The reduction electrode of Comparative Example 1 is an electrode manufactured in the same manner as in Example 1 except that the n-type optical semiconductor was not formed.
　比較例２の還元電極は、ｎ型光半導体を形成せず、さらにＣｕＯペーストの代わりにＣｕＦｅ2Ｏ4ペーストを用いてｐ型光半導体を形成した点を除いては、実施例１と同様にして作製した電極である。 The reduction electrode of Comparative Example 2 did not form an n-type optical semiconductor, and was the same as Example 1 except that a p-type optical semiconductor was formed using CuFe 2 O 4 paste instead of CuO paste. This is an electrode manufactured in this way.
　比較例３の還元電極は、ｎ型光半導体を形成せず、さらにＣｕＯペーストの代わりにＩｎＰペーストを用いてｐ型光半導体を形成した点を除いては、実施例１と同様にして作製した電極である。 The reduction electrode of Comparative Example 3 was manufactured in the same manner as in Example 1 except that the n-type optical semiconductor was not formed and that a p-type optical semiconductor was formed using InP paste instead of CuO paste. Electrode.
　比較例４の還元電極は、ｐ型光半導体を形成せずに、基板上に直接ｎ型光半導体を形成した点を除いては、実施例１と同様にして作製した電極である。 The reduction electrode of Comparative Example 4 is an electrode manufactured in the same manner as in Example 1 except that the n-type optical semiconductor was formed directly on the substrate without forming the p-type optical semiconductor.
　比較例５の還元電極は、ｐ型光半導体を形成せずに、さらに、ブルッカイト型酸化チタンの代わりに汎用の酸化チタン（日本エアロジル社製の「ＡＥＲＯＸＩＤＥ（登録商標）　ＴｉＯ2　Ｐ２５」）を用いて基板上に直接ｎ型光半導体を形成した点を除いては、実施例１と同様にして作製した電極である。 The reduction electrode of Comparative Example 5 does not form a p-type optical semiconductor, and further uses general-purpose titanium oxide (“AEROXIDE (registered trademark) TiO 2 P25” manufactured by Nippon Aerosil Co., Ltd.) instead of brookite-type titanium oxide. The electrode was produced in the same manner as in Example 1 except that the n-type optical semiconductor was directly formed on the substrate.
　比較例１～５の還元電極についても、これらをそれぞれ用いて実施例１と同様の構成の還元装置を作製し、ＣＯ2の還元を行った。 For the reduction electrodes of Comparative Examples 1 to 5, a reduction device having the same configuration as that of Example 1 was produced using each of these reduction electrodes, and CO 2 was reduced.
　（実施例１～６と比較例１～５との比較）
　各実施例１～６及び比較例１～５における還元生成物の生成量は、図１６に示す通りである。なお、図１６中の「Ｎ．Ｄ．」は、不検出を意味する。 (Comparison between Examples 1 to 6 and Comparative Examples 1 to 5)
The amount of reduction product produced in each of Examples 1 to 6 and Comparative Examples 1 to 5 is as shown in FIG. Note that “ND” in FIG. 16 means non-detection.
　図１６より知られるように、実施例の還元電極１を用いた電極装置８においては、ＣＯ2の還元生成物であるメタノールやギ酸が十分に生成されていた。これに対し、比較例の還元電極を用いた還元装置においては、メタノールやギ酸の生成量が不十分であった。即ち、実施例の還元電極１は、ｐ型光半導体１２とｎ型光半導体１３との積層体を有し、両者の間にｐｎ接合を有している（図１及び図５参照）。そのため、光照射条件下おいて安定してＣＯ2に電子を供給して還元を行うことができ、有機物等からなる還元生成物が十分に得られる。また、各実施例においては、上述のように、ＣＯ2からメタノールやギ酸が十分に生成される一方で、水素や一酸化炭素の生成が十分に抑制されている。これは、実施例においては、水の還元を抑制できると共に、二酸化炭素から一酸化炭素を生成する還元反応ではなく、水と二酸化炭素からメタノールやギ酸を生成する還元反応を進行させることができることを意味する。 As can be seen from FIG. 16, in the electrode device 8 using the reduction electrode 1 of the example, methanol and formic acid, which are reduction products of CO 2 , were sufficiently generated. On the other hand, in the reduction apparatus using the reduction electrode of the comparative example, the amount of methanol or formic acid produced was insufficient. That is, the reduction electrode 1 of the embodiment has a stacked body of a p-type optical semiconductor 12 and an n-type optical semiconductor 13 and has a pn junction between them (see FIGS. 1 and 5). Therefore, reduction can be performed by supplying electrons to CO 2 stably under light irradiation conditions, and a reduction product composed of an organic substance or the like is sufficiently obtained. In each example, as described above, methanol and formic acid are sufficiently generated from CO 2 , while generation of hydrogen and carbon monoxide is sufficiently suppressed. This is because, in the embodiment, it is possible to suppress the reduction of water and advance the reduction reaction that generates methanol and formic acid from water and carbon dioxide, not the reduction reaction that generates carbon monoxide from carbon dioxide. means.
　また、実施例の還元電極１においては、ｐ型光半導体１２の伝導帯のエネルギー準位は、ｎ型光半導体１３の伝導帯のエネルギー準位よりも卑側に高い。また、ｐ型光半導体１２の価電子帯のエネルギー準位は、ｎ型光半導体１３の価電子帯のエネルギー準位よりも卑側に高い。このような組み合わせのｐ型光半導体１２とｎ型光半導体が採用されているため、還元電極１を電極として用いた場合に電流を流すことが可能になる。 Further, in the reduction electrode 1 of the example, the energy level of the conduction band of the p-type optical semiconductor 12 is higher than the energy level of the conduction band of the n-type optical semiconductor 13. In addition, the energy level of the valence band of the p-type optical semiconductor 12 is higher on the base side than the energy level of the valence band of the n-type optical semiconductor 13. Since the p-type optical semiconductor 12 and the n-type optical semiconductor in such a combination are employed, it is possible to pass a current when the reduction electrode 1 is used as an electrode.
　また、還元電極１においては、実施例のようにｐ型光半導体１２がｎ型光半導体１３に完全に被覆されていることが好ましい。即ち、ｐ型光半導体１２は、外部に露出していないことが好ましい。この場合には、還元装置８において、ｐ型光半導体１２が電解液３と直接接触することがないため、水の還元がより一層抑制される。即ち、還元電極１は、ＣＯ2をより選択的に還元することができる。 Moreover, in the reduction electrode 1, it is preferable that the p-type optical semiconductor 12 is completely covered with the n-type optical semiconductor 13 as in the embodiment. That is, it is preferable that the p-type optical semiconductor 12 is not exposed to the outside. In this case, since the p-type optical semiconductor 12 does not come into direct contact with the electrolytic solution 3 in the reducing device 8, the reduction of water is further suppressed. That is, the reduction electrode 1 can reduce CO 2 more selectively.
　ｎ型光半導体１３は、ＴｉＯ2、ＳｒＴｉＯ3、ＷＯ3、ＢｉＶＯ4から選ばれる少なくとも１種からなることが好ましい。より好ましくは、ｎ型光半導体１３は、ブルッカイト型酸化チタンからなることがよい。この場合には、水の還元をより一層抑制することができ、ＣＯ2をより選択的に還元することができる。その結果、ＣＯ2の還元生成物の量をより向上させることができる。 The n-type optical semiconductor 13 is preferably made of at least one selected from TiO 2 , SrTiO 3 , WO 3 and BiVO 4 . More preferably, the n-type optical semiconductor 13 is made of brookite-type titanium oxide. In this case, the reduction of water can be further suppressed, and CO 2 can be reduced more selectively. As a result, the amount of CO 2 reduction product can be further improved.
　また、ｐ型光半導体１２は、ＣｕＯ、Ｃｕ2Ｏ、ＩｎＰ、ｐ－ＳｉＣ、ｐ－Ｓｉから選ばれる少なくとも１種からなることが好ましい。この場合には、ＣＯ2の還元生成物の生成量をより向上させることができる。 The p-type optical semiconductor 12 is preferably made of at least one selected from CuO, Cu 2 O, InP, p-SiC, and p-Si. In this case, the amount of reduction product of CO 2 can be further improved.
　なお、実施例３においては、ｎ型光半導体として、上述のようにＡｇを担持させた酸化チタンを用いている。担持させる金属としては、その他にも例えばＡｕ、Ｒｈ、Ｃｕ、Ｎｉ、Ｒｕ、Ｉｒ、Ｒｅ、Ｐｄ等を用いることができる。これらの金属は少なくとも１種を用いることができる。 In Example 3, titanium oxide supporting Ag as described above is used as the n-type optical semiconductor. Other examples of the metal to be supported include Au, Rh, Cu, Ni, Ru, Ir, Re, and Pd. At least one of these metals can be used.
　また、還元装置８は、還元電極１と酸化電極２とを分離するイオン交換膜４を有している（図５参照）。そのため、還元装置８においては、還元生成物の移動が制限される。それ故、メタノール、ギ酸等の還元生成物が酸化電極２において再度酸化されてしまうことを抑制することができる。したがって、還元装置８においては、還元生成物をより十分得ることができる。 The reduction device 8 has an ion exchange membrane 4 that separates the reduction electrode 1 and the oxidation electrode 2 (see FIG. 5). Therefore, in the reduction device 8, the movement of the reduction product is limited. Therefore, reduction products such as methanol and formic acid can be prevented from being oxidized again at the oxidation electrode 2. Therefore, the reduction device 8 can obtain a sufficient reduction product.
　（実施例７）
　本例は、分枝状構造のｐ型光半導体を有する還元電極の例である。 (Example 7)
This example is an example of a reduction electrode having a p-type optical semiconductor having a branched structure.
　図６に示すごとく、本例の還元電極１は、導電性の基板１１と、この基板１１上に設けられた分枝状構造のｐ型光半導体１２と、このｐ型光半導体１２を被覆するｎ型光半導体１３とを有する。基板１１は、実施例１と同様に、石英ガラス基板１１２と、この石英ガラス基板１１２上に積層形成されたＦＴＯ膜１１１とを有しており、ｐ型光半導体１２は、基板１１のＦＴＯ膜１１１上に形成されている。 As shown in FIG. 6, the reduction electrode 1 of this example covers a conductive substrate 11, a p-type optical semiconductor 12 having a branched structure provided on the substrate 11, and the p-type optical semiconductor 12. and an n-type optical semiconductor 13. The substrate 11 has a quartz glass substrate 112 and an FTO film 111 formed on the quartz glass substrate 112 in the same manner as in the first embodiment. The p-type optical semiconductor 12 is an FTO film of the substrate 11. 111 is formed.
　ｐ型光半導体１２は、基板１１（ＦＴＯ膜１１１）上からｎ型光半導体１３の内部に広がって伸びる分枝状構造を有している。具体的には、ｐ型光半導体１２においては、基板１１上からランダムな方向に広がって伸びる多数の分枝１２５（突起物１２５）が形成されており、これらの分枝１２５が分枝状構造を形成している。ｐ型光半導体１２は、ランダムな方向に伸びる突起物１２５が多数集合してなるカリフラワー状の構造体であるともいえる。ｐ型光半導体１２は、所定の表面粗さで基板１１上に形成されている。ｐ型光半導体１２は、実施例１と同様にＣｕＯからなる。 The p-type optical semiconductor 12 has a branched structure extending from the substrate 11 (FTO film 111) to the inside of the n-type optical semiconductor 13. Specifically, in the p-type optical semiconductor 12, a large number of branches 125 (projections 125) extending in a random direction from the substrate 11 are formed, and these branches 125 are branched structures. Is forming. It can be said that the p-type optical semiconductor 12 is a cauliflower-like structure in which a large number of protrusions 125 extending in a random direction are gathered. The p-type optical semiconductor 12 is formed on the substrate 11 with a predetermined surface roughness. The p-type optical semiconductor 12 is made of CuO as in the first embodiment.
　また、図６に示すごとく、ｎ型光半導体１３は、分枝状構造のｐ型光半導体１２を被覆している。ｎ型光半導体１３は、分枝状構造のｐ型光半導体１２の外形に沿ってｐ型光半導体１２を被覆しており、表面に凹凸構造を有する。ｎ型光半導体１３は、実施例１と同様にブルッカイト型酸化チタンからなる。 Also, as shown in FIG. 6, the n-type optical semiconductor 13 covers the branched p-type optical semiconductor 12. The n-type optical semiconductor 13 covers the p-type optical semiconductor 12 along the outer shape of the branched p-type optical semiconductor 12, and has a concavo-convex structure on the surface. The n-type optical semiconductor 13 is made of brookite-type titanium oxide as in the first embodiment.
　次に、本例の還元電極１の製造方法について説明する。具体的には、まず、実施例１と同様に、導電性の基板１１として、ＦＴＯ膜１１１が表面に形成された石英ガラス基板１１２を準備した。次いで、図７に示すごとく、硫酸銅とグリシンとの濃度がそれぞれ０．０２ｍｏｌ／ｌ、０．１ｍｏｌ／ｌに調整された水溶液１２９を調整し、この水溶液１２９中に参照電極１９、作用電極１４、対極１７を浸漬した。作用電極１４と対極１７は、いずれもＦＴＯ膜１１１が表面に形成された上述の石英ガラス基板１１２からなり、上述の導電性の基板１１である。参照電極１９は、Ａｇ／ＡｇＣｌ電極である。作用電極１４と対極１７とは、互いのＦＴＯ膜１１１が対向するように配置した。作用電極１４と対極１７との間隔は４ｍｍである。そして、作用電極１４と対極１７との間に電流計を設置すると共に、作用電極１４と参照極１９との間に電圧計を設置した。 Next, a method for manufacturing the reduction electrode 1 of this example will be described. Specifically, first, as in Example 1, a quartz glass substrate 112 having an FTO film 111 formed on the surface was prepared as the conductive substrate 11. Next, as shown in FIG. 7, an aqueous solution 129 in which the concentrations of copper sulfate and glycine are adjusted to 0.02 mol / l and 0.1 mol / l, respectively, is prepared, and the reference electrode 19 and the working electrode 14 are contained in the aqueous solution 129. The counter electrode 17 was immersed. The working electrode 14 and the counter electrode 17 are both composed of the above-described quartz glass substrate 112 having the FTO film 111 formed on the surface thereof, and are the above-described conductive substrate 11. The reference electrode 19 is an Ag / AgCl electrode. The working electrode 14 and the counter electrode 17 were disposed so that the FTO films 111 face each other. The distance between the working electrode 14 and the counter electrode 17 is 4 mm. An ammeter was installed between the working electrode 14 and the counter electrode 17, and a voltmeter was installed between the working electrode 14 and the reference electrode 19.
　次いで、作用電極１４と対極１７とをポテンショスタット１８に電気的に接続し、対極１７に対して作用電極１４が負の電位になるように、両極間に－０．７５Ｖの電位を１８００秒間印加した。このときの水溶液１２９の液温は室温（２５℃）である。この電位差により、図７に示すごとく、水溶液１２９中のＣｕ2+イオンが作用電極１４のＦＴＯ膜１１１上でＣｕとして析出する（電析）。その後、温度１１０℃の乾燥機内で作用電極１４を１時間乾燥させた後、さらに大気条件下、温度５５０℃で作用電極１４を１時間焼成した。これにより、基板１１のＦＴＯ膜１１１上に、酸化銅からなる分枝状構造のｐ型光半導体１２を形成した（図６参照）。このｐ型光半導体１２の結晶構造を、Ｃｕ－Ｋα線を用いたＸ線回折装置（（株）リガク製のＲＩＮＴ２０００）により調べたところ、ｐ型光半導体はＣｕＯからなることが確認された。 Next, the working electrode 14 and the counter electrode 17 are electrically connected to the potentiostat 18, and a potential of −0.75 V is applied between both electrodes for 1800 seconds so that the working electrode 14 has a negative potential with respect to the counter electrode 17. did. The liquid temperature of the aqueous solution 129 at this time is room temperature (25 ° C.). Due to this potential difference, as shown in FIG. 7, Cu 2+ ions in the aqueous solution 129 are deposited as Cu on the FTO film 111 of the working electrode 14 (electrodeposition). Thereafter, the working electrode 14 was dried in a dryer at a temperature of 110 ° C. for 1 hour, and then the working electrode 14 was further fired at a temperature of 550 ° C. for 1 hour under atmospheric conditions. Thereby, the p-type optical semiconductor 12 having a branched structure made of copper oxide was formed on the FTO film 111 of the substrate 11 (see FIG. 6). When the crystal structure of the p-type optical semiconductor 12 was examined by an X-ray diffractometer using Cu—Kα rays (RINT2000 manufactured by Rigaku Corporation), it was confirmed that the p-type optical semiconductor was made of CuO.
　次に、ｐ型光半導体１２の表面を走査型電子顕微鏡（ＳＥＭ；日本電子(株)製の「ＪＳＭ－６７００Ｆ」）を用いて観察した。ＳＥＭの観察条件は、加速電圧が５．０ｋＶ（反射電子像）であり、観察倍率が２０００倍、及び５００００倍である。倍率２０００倍の結果を図８Ａに示し、倍率５００００倍の結果を図８Ｂに示す。図８Ｃ及び図８Ｄは、それぞれ、図８Ａ及び図８Ｂに示すＳＥＭ写真の線図を示す。なお、比較用として、実施例１におけるｐ型光半導体１２の拡大断面図を後述の図１３に示し、実施例１におけるｐ型光半導体１２の表面の倍率２０００倍のＳＥＭ写真を後述の図１４Ａに示し、倍率５００００倍のＳＥＭ写真を後述の図１４Ｂに示す。図１４Ｃ及び図１４Ｄは、それぞれ、図１４Ａ及び図１４Ｂに示すＳＥＭ写真の線図を示す。 Next, the surface of the p-type optical semiconductor 12 was observed using a scanning electron microscope (SEM; “JSM-6700F” manufactured by JEOL Ltd.). The SEM observation conditions are an acceleration voltage of 5.0 kV (reflected electron image), and observation magnifications of 2000 times and 50000 times. The result of 2000 times magnification is shown in FIG. 8A, and the result of 50000 times magnification is shown in FIG. 8B. 8C and 8D show diagrams of the SEM photographs shown in FIGS. 8A and 8B, respectively. For comparison, an enlarged cross-sectional view of the p-type optical semiconductor 12 in Example 1 is shown in FIG. 13 to be described later, and an SEM photograph at a magnification of 2000 times of the surface of the p-type optical semiconductor 12 in Example 1 is shown in FIG. 14A to be described later. The SEM photograph at a magnification of 50000 is shown in FIG. 14B described later. 14C and 14D show diagrams of the SEM photographs shown in FIGS. 14A and 14B, respectively.
　図１３、図１４Ａ～図１４Ｄより知られるように、実施例１におけるｐ型光半導体１２が酸化銅からなる粒子の凝集体から構成されているのに対し、図８Ａ～図８Ｄより知られるように、本例におけるｐ型光半導体１２は、ＦＴＯ膜１１１上から広がって伸びる分枝状構造を有している。また、本例におけるｐ型光半導体１２の表面の粗さを算術平均粗さＲａ（ＪＩＳ　２００１年規格）に基づいて計測した。計測には、ＶＥＥＣＯ／ＳＬＯＡＮ社製の針接触式表面形状測定装置「ＤＥＫＴＡＫ　６Ｍ　ＳＴＹＬＵＳ　ＰＲＯＦＩＬＥＲ」を用いた。その結果、本例におけるｐ型光半導体の表面粗さ（算術平均粗さＲａ）は、２７０１．９７ｎｍであった。一方、実施例１におけるｐ型光半導体１２の表面粗さＲａは、１２３７．０９ｎｍであった。 As is known from FIGS. 13 and 14A to 14D, the p-type optical semiconductor 12 in Example 1 is composed of an aggregate of particles made of copper oxide, whereas it is known from FIGS. 8A to 8D. In addition, the p-type optical semiconductor 12 in this example has a branched structure extending from the FTO film 111 and extending. Further, the roughness of the surface of the p-type optical semiconductor 12 in this example was measured based on the arithmetic average roughness Ra (JIS 2001 standard). For measurement, a needle contact type surface shape measuring device “DEKTAK 6M STYLUS PROFILER” manufactured by VEECO / SLOAN was used. As a result, the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor in this example was 2701.97 nm. On the other hand, the surface roughness Ra of the p-type optical semiconductor 12 in Example 1 was 1237.09 nm.
　次に、本例のｐ型光半導体１２上に、実施例１と同様の電気泳動法によりｎ型光半導体１３を形成した。以上のようにして、図６に示すごとく、分枝状構造のｐ型光半導体１２と、これを被覆するｎ型光半導体１３とを有する還元電極１を得た。 Next, an n-type optical semiconductor 13 was formed on the p-type optical semiconductor 12 of this example by the same electrophoresis method as in Example 1. As described above, as shown in FIG. 6, a reduction electrode 1 having a branched p-type optical semiconductor 12 and an n-type optical semiconductor 13 covering the branched p-type optical semiconductor 12 was obtained.
　次に、本例の還元電極１を用い、さらに電解液３を濃度０．１ｍｏｌ／ＬのＮａ2ＳＯ4に変更した点を除いては、実施例１と同様の構成の還元装置８を組み立てた（図５参照）。次いで、この還元装置８によりＣＯ2の還元を行った。本例においては、Ｇ１レベルのＣＯ2を電解液３中に６０分間供給し、光源５から強度１００Ｗ／ｃｍ2の光５１（疑似太陽光）を１秒間隔で照射し、還元装置８によりＣＯ2の還元を行った。このとき、電気化学アナライザ９（ビー・エー・エス(株)製のＡＬＳモデル６６０Ｅ）により、掃引速度１０ｍＶ／ｓで電位を０．６Ｖから－０．１Ｖまで変化させたときの電流密度を測定した。そして、標準水素電極に対する電位が０Ｖのときの光電流密度（光照射時に流れる電流密度）を求めた。その結果を後述の図１５に示す。図１５には、比較のために、実施例１の還元電極を用いた時の電流密度の測定結果を併記している。 Next, a reducing device 8 having the same configuration as that of Example 1 is assembled except that the reducing electrode 1 of this example is used and the electrolytic solution 3 is changed to Na 2 SO 4 having a concentration of 0.1 mol / L. (See FIG. 5). Subsequently, CO 2 was reduced by the reduction device 8. In this example, G1 level CO 2 is supplied into the electrolyte 3 for 60 minutes, light 51 (pseudo sunlight) having an intensity of 100 W / cm 2 is irradiated from the light source 5 at intervals of 1 second, and CO 2 is reduced by the reducing device 8. Reduction of 2 was performed. At this time, the current density when the potential was changed from 0.6 V to −0.1 V at a sweep speed of 10 mV / s was measured by an electrochemical analyzer 9 (ALS model 660E manufactured by BAS Co., Ltd.). did. Then, the photocurrent density when the electric potential with respect to the standard hydrogen electrode was 0 V (current density flowing during light irradiation) was obtained. The result is shown in FIG. For comparison, FIG. 15 also shows the measurement results of current density when using the reduction electrode of Example 1.
　なお、本例及び後述の実施例８及び実施例９において、実施例１と同じ符号は、同一の構成を示し、先行する説明を参照する。 In addition, in this example and Example 8 and Example 9 to be described later, the same reference numerals as those in Example 1 indicate the same configurations, and refer to the preceding description.
　（実施例８）
　本例は、上述の実施例７とは電析の反応時間を変更して、ｐ型光半導体を形成した還元電極の例である。図９に示すごとく、本例の還元電極１において、ｐ型光半導体１２は、実施例７と同様に、基板１１（ＦＴＯ膜１１１）上からｎ型光半導体１３の内部に広がって伸びる分枝状構造を有している。本例のｐ型光半導体１２においては、実施例７よりも分枝１２５（突起物１２５）が多く、その長さが長くなっている。その他の構成は、実施例７と同様である。 (Example 8)
This example is an example of a reduction electrode in which a p-type optical semiconductor is formed by changing the electrodeposition reaction time from that of Example 7 described above. As shown in FIG. 9, in the reduction electrode 1 of this example, the p-type optical semiconductor 12 is a branch that extends from the substrate 11 (FTO film 111) to the inside of the n-type optical semiconductor 13, as in the seventh embodiment. It has a shape structure. In the p-type optical semiconductor 12 of this example, there are more branches 125 (projections 125) than in Example 7, and the length thereof is longer. Other configurations are the same as those of the seventh embodiment.
　本例の還元電極１は、ｐ型光半導体１２を形成する際に、対極１７と作用電極１４との間に－０．７５Ｖの電位を３６００秒間印加した点を除いては、上述の実施例７と同様にして作製した（図７参照）。本例においても、実施例７と同様にｐ型光半導体１２の結晶構造を、Ｃｕ－Ｋα線を用いたＸ線回折装置（（株）リガク製のＲＩＮＴ２０００）により調べたところ、ｐ型光半導体１２はＣｕＯからなることが確認された。また、本例におけるｐ型光半導体１２の表面におけるＳＥＭ写真を実施例７と同様の条件で撮影した。倍率２０００倍のＳＥＭ写真を図１０Ａに示し、倍率５００００倍のＳＥＭ写真を図１０Ｂに示す。図１０Ｃ及び図１０Ｄは、それぞれ、図１０Ａ及び図１０Ｂに示すＳＥＭ写真の線図を示す。また、本例のけるｐ型光半導体の表面粗さ（算術平均粗さＲａ）を実施例７と同様にして計測した。その結果、表面粗さは、３１７４．６６ｎｍであった。 The reduction electrode 1 of this example is the same as that of the above-described embodiment except that, when the p-type optical semiconductor 12 is formed, a potential of −0.75 V is applied between the counter electrode 17 and the working electrode 14 for 3600 seconds. 7 (see FIG. 7). Also in this example, when the crystal structure of the p-type optical semiconductor 12 was examined with an X-ray diffractometer using a Cu—Kα ray (RINT2000 manufactured by Rigaku Corporation) as in Example 7, the p-type optical semiconductor was examined. It was confirmed that 12 consists of CuO. Further, an SEM photograph on the surface of the p-type optical semiconductor 12 in this example was taken under the same conditions as in Example 7. An SEM photograph at a magnification of 2000 is shown in FIG. 10A, and an SEM photograph at a magnification of 50000 is shown in FIG. 10B. 10C and 10D show diagrams of the SEM photographs shown in FIGS. 10A and 10B, respectively. Further, the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor in this example was measured in the same manner as in Example 7. As a result, the surface roughness was 3174.66 nm.
　また、本例の還元電極１を用いて、実施例７と同様にして還元装置８を組み立て（図５参照）、標準水素電極に対する電位が０Ｖのときの光電流密度（光照射時に流れる電流密度）を求めた。その結果を後述の図１５に示す。 Further, using the reduction electrode 1 of this example, the reduction device 8 is assembled in the same manner as in Example 7 (see FIG. 5), and the photocurrent density when the potential with respect to the standard hydrogen electrode is 0 V (current density flowing during light irradiation). ) The result is shown in FIG.
　（実施例９）
　本例は、上述の実施例７及び実施例８とは電析の反応時間を変更して、ｐ型光半導体を形成した還元電極の例である。図１１に示すごとく、本例の還元電極１において、ｐ型光半導体は、実施例７と同様に、基板１１（ＦＴＯ膜１１１）上からｎ型光半導体１３の内部に広がって伸びる分枝状構造を有している。本例のｐ型光半導体１２は、実施例７よりも分枝１２５（突起物１２５）が少なく、その長さが短くなっている。その他の構成は、実施例７と同様である。 Example 9
This example is an example of a reduction electrode in which a p-type optical semiconductor is formed by changing the electrodeposition reaction time from Example 7 and Example 8 described above. As shown in FIG. 11, in the reduction electrode 1 of the present example, the p-type optical semiconductor is branched like extending from the substrate 11 (FTO film 111) to the inside of the n-type optical semiconductor 13 as in the seventh embodiment. It has a structure. The p-type optical semiconductor 12 of this example has fewer branches 125 (projections 125) and a shorter length than that of the seventh embodiment. Other configurations are the same as those of the seventh embodiment.
　本例の還元電極１は、ｐ型光半導体１２を形成する際に、対極１７と作用電極１４との間に－０．７５Ｖの電位を６００秒間印加した点を除いては、上述の実施例７と同様にして作製した（図７参照）。本例においても、実施例７と同様にｐ型光半導体１２の結晶構造を、Ｃｕ－Ｋα線を用いたＸ線回折装置（（株）リガク製のＲＩＮＴ２０００）により調べたところ、ｐ型光半導体１２はＣｕＯからなることが確認された。また、本例におけるｐ型光半導体１２の表面におけるＳＥＭ写真を実施例７と同様の条件で撮影した。倍率２０００倍のＳＥＭ写真を図１２Ａに示し、倍率５００００倍のＳＥＭ写真を図１２Ｂに示す。図１２Ｃ及び図１２Ｄは、それぞれ、図１２Ａ及び図１２Ｂに示すＳＥＭ写真の線図を示す。また、本例のけるｐ型光半導体の表面粗さ（算術平均粗さＲａ）を実施例７と同様にして計測した。その結果、表面粗さは、２０１５．２３ｎｍであった。 The reduction electrode 1 of this example is the same as that of the above-described embodiment except that, when the p-type optical semiconductor 12 is formed, a potential of −0.75 V is applied between the counter electrode 17 and the working electrode 14 for 600 seconds. 7 (see FIG. 7). Also in this example, when the crystal structure of the p-type optical semiconductor 12 was examined with an X-ray diffractometer using a Cu—Kα ray (RINT2000 manufactured by Rigaku Corporation) as in Example 7, the p-type optical semiconductor was examined. It was confirmed that 12 consists of CuO. Further, an SEM photograph on the surface of the p-type optical semiconductor 12 in this example was taken under the same conditions as in Example 7. An SEM photograph at a magnification of 2000 is shown in FIG. 12A, and an SEM photograph at a magnification of 50000 is shown in FIG. 12B. 12C and 12D show diagrams of the SEM photographs shown in FIGS. 12A and 12B, respectively. Further, the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor in this example was measured in the same manner as in Example 7. As a result, the surface roughness was 2015.23 nm.
　また、本例の還元電極１を用いて、実施例７と同様にして還元装置８を組み立て（図５参照）、標準水素電極に対する電位が０Ｖのときの光電流密度（光照射時に流れる電流密度）を求めた。その結果を後述の図１５に示す。 Further, using the reduction electrode 1 of this example, the reduction device 8 is assembled in the same manner as in Example 7 (see FIG. 5), and the photocurrent density when the potential with respect to the standard hydrogen electrode is 0 V (current density flowing during light irradiation). ) The result is shown in FIG.
　（実施例１、実施例７～実施例９との比較）
　図１５より知られるように、基板１１上からｎ型光半導体１３の内部に広がって伸びる分枝状構造のｐ型光半導体１２（図６、図８Ａ～図１２Ｄ参照）を有する実施例７～９の還元電極１は、分枝状構造を有していないｐ型光半導体１２（図１３及び図１４Ａ～図１４Ｄ参照）を有する実施例１の還元電極１よりも高い電流密度を示していた。この電流密度の向上は、ＣＯ2の還元反応速度の向上を意味する。したがって、実施例７～９のように分枝状構造のｐ型光半導体１２を形成することにより、ＣＯ2の還元速度を向上させ、メタノール等の有機物の生成速度をより向上できることがわかる。 (Comparison with Example 1 and Examples 7 to 9)
As is known from FIG. 15, Embodiments 7 to 7 having a p-type optical semiconductor 12 (see FIGS. 6, 8A to 12D) having a branched structure extending from the substrate 11 to the inside of the n-type optical semiconductor 13 and extending. The reduction electrode 1 of 9 showed a higher current density than the reduction electrode 1 of Example 1 having the p-type optical semiconductor 12 (see FIGS. 13 and 14A to 14D) that did not have a branched structure. . This improvement in current density means an improvement in the CO 2 reduction reaction rate. Therefore, it can be seen that by forming the p-type optical semiconductor 12 having a branched structure as in Examples 7 to 9, the reduction rate of CO 2 can be improved and the production rate of organic substances such as methanol can be further improved.
　電析法により形成された実施例７～実施例９の還元電極１においては、上述のように、分枝状構造のｐ型光半導体１２を有しているため、ｐ型光半導体１２とｎ型光半導体１３との接合領域が広くなるため、上述のように電流密度が向上したと推察される（図６、図８Ａ～図１２Ｄ参照）。また、実施例７～９においては、緻密なｐ型光半導体１２が形成されていることも電流密度の向上に寄与していると推察される。一方、スキージ法により形成された実施例１におけるｐ型光半導体１２においては、ＣｕＯ粒子間に多数の空隙が存在しているため（図１３及び図１４Ａ～図１４Ｄ）、実施例７～実施例９ほどの電流密度には達しなかったものと推察される。 Since the reduction electrodes 1 of Examples 7 to 9 formed by the electrodeposition method have the p-type optical semiconductor 12 having a branched structure as described above, the p-type optical semiconductor 12 and the n-type optical semiconductor 12 are combined. Since the junction region with the type optical semiconductor 13 is widened, it is assumed that the current density is improved as described above (see FIGS. 6 and 8A to 12D). In Examples 7 to 9, it is speculated that the formation of the dense p-type optical semiconductor 12 also contributes to the improvement of the current density. On the other hand, in the p-type optical semiconductor 12 in Example 1 formed by the squeegee method, since many voids exist between CuO particles (FIGS. 13 and 14A to 14D), Examples 7 to It is assumed that the current density of about 9 was not reached.
　実施例７～９のような分枝状構造のｐ型光半導体１２は、上述の電析及びその後の焼成により形成することができる。電析時の電位及び反応時間を調整することにより、分枝状構造における分枝１２５（突起物１２５）の長さや数を制御することができる。実施例１、実施例７～９におけるｐ型光半導体１２について、形成方法、形態、及び表面粗さを図１７に示す。 The p-type optical semiconductor 12 having a branched structure as in Examples 7 to 9 can be formed by the above-described electrodeposition and subsequent firing. By adjusting the potential and reaction time during electrodeposition, the length and number of the branches 125 (projections 125) in the branched structure can be controlled. FIG. 17 shows the formation method, form, and surface roughness of the p-type optical semiconductor 12 in Example 1 and Examples 7 to 9.
　図１７及び図１５の結果から知られるごとく、ｐ型光半導体の表面粗さ（算術平均粗さＲａ）は２０００ｎｍ以上であることが好ましい。この場合には、電流密度を十分に向上させることが可能になる。より好ましくは、ｐ型光半導体の表面粗さは２５００ｎｍ以上がよい。また、電析による実現可能な表面粗さという観点から、ｐ型光半導体の表面粗さは、３２００ｎｍ以下であることが好ましい。 As known from the results of FIGS. 17 and 15, the surface roughness (arithmetic average roughness Ra) of the p-type optical semiconductor is preferably 2000 nm or more. In this case, the current density can be sufficiently improved. More preferably, the surface roughness of the p-type optical semiconductor is 2500 nm or more. Moreover, from the viewpoint of realizable surface roughness by electrodeposition, the surface roughness of the p-type optical semiconductor is preferably 3200 nm or less.
　以上、本開示の実施例について詳細に説明したが、本開示は上記実施例に限定されるものではなく、本開示の趣旨を損なわない範囲内で種々の変更が可能である。
  As mentioned above, although the Example of this indication was described in detail, this indication is not limited to the said Example, A various change is possible within the range which does not impair the meaning of this indication.

Claims (7)

  1. 　導電性の基板（１１）と、該基板（１１）上に設けられたｐ型光半導体（１２）と、該ｐ型光半導体（１２）上に設けられたｎ型光半導体（１３）とを有し、
    　上記ｐ型光半導体（１２）の伝導帯のエネルギー準位は、上記ｎ型光半導体（１３）の伝導帯のエネルギー準位よりも卑側に高く、上記ｐ型光半導体（１２）の価電子帯のエネルギー準位は、上記ｎ型光半導体（１３）の価電子帯のエネルギー準位よりも卑側に高いＣＯ2還元電極。     A conductive substrate (11), a p-type optical semiconductor (12) provided on the substrate (11), and an n-type optical semiconductor (13) provided on the p-type optical semiconductor (12). Have
    The energy level of the conduction band of the p-type optical semiconductor (12) is higher than the energy level of the conduction band of the n-type optical semiconductor (13), and the valence electrons of the p-type optical semiconductor (12). A CO 2 reduction electrode in which the energy level of the band is higher on the base side than the energy level of the valence band of the n-type optical semiconductor (13).
  2. 　上記ｐ型光半導体（１２）は、上記ｎ型光半導体（１３）に完全に被覆されている請求項１に記載のＣＯ2還元電極。 The CO 2 reduction electrode according to claim 1, wherein the p-type optical semiconductor (12) is completely covered with the n-type optical semiconductor (13).
  3. 　上記ｎ型光半導体（１３）は、ＴｉＯ2、ＳｒＴｉＯ3、ＷＯ3、及びＢｉＶＯ4から選ばれる少なくとも１種からなる請求項１又は２に記載のＣＯ2還元電極。 The CO 2 reduction electrode according to claim 1 or 2, wherein the n-type optical semiconductor (13) is made of at least one selected from TiO 2 , SrTiO 3 , WO 3 , and BiVO 4 .
  4. 　上記ｎ型光半導体（１３）は、ブルッカイト型酸化チタンからなる請求項１～３のいずれか１項に記載のＣＯ2還元電極。 The CO 2 reduction electrode according to any one of claims 1 to 3, wherein the n-type optical semiconductor (13) is made of brookite-type titanium oxide.
  5. 　上記ｐ型光半導体（１２）は、ＣｕＯ、Ｃｕ2Ｏ、ＩｎＰ、ｐ－ＳｉＣ、及びｐ－Ｓｉから選ばれる少なくとも１種からなる請求項１～４のいずれか１項に記載のＣＯ2還元電極。 The CO 2 reduction according to any one of claims 1 to 4, wherein the p-type optical semiconductor (12) comprises at least one selected from CuO, Cu 2 O, InP, p-SiC, and p-Si. electrode.
  6. 　上記ｐ型光半導体（１２）は、上記基板（１１）上から上記ｎ型光半導体（１３）の内部に広がって伸びる分枝状構造を有している請求項１～５のいずれか１項に記載のＣＯ2還元電極。 The p-type optical semiconductor (12) has a branched structure extending from the substrate (11) to the inside of the n-type optical semiconductor (13). The CO 2 reduction electrode according to 1.
  7. 　請求項１～６のいずれか１項に記載のＣＯ2還元電極と、酸化電極（２）と、該酸化電極（２）と上記ＣＯ2還元電極とが浸漬された水系電解液（３）と、該水系電解液（２）中において上記ＣＯ2還元電極と上記酸化電極（２）とを隔てるイオン交換膜（４）と、上記ＣＯ2還元電極に光を照射する光源（５）と、上記ＣＯ2還元電極にＣＯ2を供給する供給口（６）とを有するＣＯ2還元装置。 The CO 2 reduction electrode according to any one of claims 1 to 6, an oxidation electrode (2), an aqueous electrolyte (3) in which the oxidation electrode (2) and the CO 2 reduction electrode are immersed. An ion exchange membrane (4) separating the CO 2 reduction electrode and the oxidation electrode (2) in the aqueous electrolyte (2), a light source (5) for irradiating the CO 2 reduction electrode with light, and A CO 2 reduction device having a supply port (6) for supplying CO 2 to the CO 2 reduction electrode.
PCT/JP2015/001110 2014-03-04 2015-03-03 Carbon dioxide reduction electrode and carbon dioxide reduction device in which same is used WO2015133127A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2014-041761 2014-03-04
JP2014041761 2014-03-04
JP2014251485A JP2015180765A (en) 2014-03-04 2014-12-12 Carbon dioxide reduction electrode and carbon dioxide reduction device in which the same is used
JP2014-251485 2014-12-12

Publications (1)

Publication Number Publication Date
WO2015133127A1 true WO2015133127A1 (en) 2015-09-11

Family

ID=54054943

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2015/001110 WO2015133127A1 (en) 2014-03-04 2015-03-03 Carbon dioxide reduction electrode and carbon dioxide reduction device in which same is used

Country Status (2)

Country Link
JP (1) JP2015180765A (en)
WO (1) WO2015133127A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017170199A1 (en) * 2016-03-31 2017-10-05 株式会社デンソー Carbon dioxide reduction electrode and carbon dioxide reduction device using same

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6569495B2 (en) * 2015-11-19 2019-09-04 株式会社豊田中央研究所 Semiconductor electrode, light energy conversion device, and method of manufacturing semiconductor electrode
FR3046425B1 (en) * 2016-01-04 2018-01-12 Commissariat A L'energie Atomique Et Aux Energies Alternatives PHOTOCATHODE FOR A PHOTOELECTROLYTIC DEVICE, A METHOD FOR MANUFACTURING SUCH A PHOTOCATHODE AND A PHOTOELECTROLYTIC DEVICE
KR101791515B1 (en) 2016-12-09 2017-11-20 서강대학교산학협력단 Carbon dioxide reduction device
CN107099815B (en) * 2017-04-24 2018-11-16 太原师范学院 A kind of application of Bipolar Membrane surface powder state photochemical catalyst in CO2 reduction
CN107974691B (en) * 2017-12-01 2020-04-21 宁波大学 Phosphide/copper oxide electrode and preparation method thereof
US20240124996A1 (en) * 2021-05-25 2024-04-18 Nippon Telegraph And Telephone Corporation Carbon Dioxide Gas-Phase Reduction Device And Carbon Dioxide Gas-Phase Reduction Method

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH05311476A (en) * 1992-05-13 1993-11-22 Hitachi Ltd Electrode for electrochemical reduction and device for utilizing the same
JPH07188961A (en) * 1993-12-27 1995-07-25 Hitachi Ltd Carbon dioxide reducing electrode and carbon dioxide converter
JP2005133174A (en) * 2003-10-31 2005-05-26 Toyota Motor Corp Water decomposition type hydrogen generation cell
WO2005063393A1 (en) * 2003-12-26 2005-07-14 Kansai Technology Licensing Organization Co., Ltd. Method for electrolyzing water using organic photocatalyst
JP2010050115A (en) * 2008-08-19 2010-03-04 Hirosaki Univ Reaction cell for organic optical response element
JP5259889B1 (en) * 2011-08-29 2013-08-07 パナソニック株式会社 How to reduce carbon dioxide

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102484303B (en) * 2010-03-31 2015-12-09 松下知识产权经营株式会社 The energy system of Optical Electro-Chemistry element and this element of use

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH05311476A (en) * 1992-05-13 1993-11-22 Hitachi Ltd Electrode for electrochemical reduction and device for utilizing the same
JPH07188961A (en) * 1993-12-27 1995-07-25 Hitachi Ltd Carbon dioxide reducing electrode and carbon dioxide converter
JP2005133174A (en) * 2003-10-31 2005-05-26 Toyota Motor Corp Water decomposition type hydrogen generation cell
WO2005063393A1 (en) * 2003-12-26 2005-07-14 Kansai Technology Licensing Organization Co., Ltd. Method for electrolyzing water using organic photocatalyst
JP2010050115A (en) * 2008-08-19 2010-03-04 Hirosaki Univ Reaction cell for organic optical response element
JP5259889B1 (en) * 2011-08-29 2013-08-07 パナソニック株式会社 How to reduce carbon dioxide

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017170199A1 (en) * 2016-03-31 2017-10-05 株式会社デンソー Carbon dioxide reduction electrode and carbon dioxide reduction device using same

Also Published As

Publication number Publication date
JP2015180765A (en) 2015-10-15

Similar Documents

Publication Publication Date Title
WO2015133127A1 (en) Carbon dioxide reduction electrode and carbon dioxide reduction device in which same is used
Hu et al. Efficient photoelectrochemical water splitting over anodized p-type NiO porous films
Zhu et al. Nanostructured tungsten trioxide thin films synthesized for photoelectrocatalytic water oxidation: a review
Mohapatra et al. Water photooxidation by smooth and ultrathin α-Fe2O3 nanotube arrays
Wu et al. Stable cobalt nanoparticles and their monolayer array as an efficient electrocatalyst for oxygen evolution reaction
Sun et al. Enabling silicon for solar-fuel production
Kim et al. Synthesis of transparent mesoporous tungsten trioxide films with enhanced photoelectrochemical response: application to unassisted solar water splitting
Liu et al. Highly Efficient Photoelectrochemical Hydrogen Generation Using Zn x Bi2S3+ x Sensitized Platelike WO3 Photoelectrodes
Baran et al. Effect of different nano-structured Ag doped TiO2-NTs fabricated by electrodeposition on the electrocatalytic hydrogen production
Allam et al. Photoelectrochemical water oxidation characteristics of anodically fabricated TiO2 nanotube arrays: Structural and optical properties
Bledowski et al. Improving the performance of hybrid photoanodes for water splitting by photodeposition of iridium oxide nanoparticles
Lee et al. Electrodeposited heterogeneous nickel-based catalysts on silicon for efficient sunlight-assisted water splitting
Lu et al. In situ integration of ReS2/Ni3S2 pn heterostructure for enhanced photoelectrocatalytic performance
Garcia-Esparza et al. Photoelectrochemical and electrocatalytic properties of thermally oxidized copper oxide for efficient solar fuel production
Ma et al. Solar water splitting with p-SiC film on p-Si: Photoelectrochemical behavior and XPS characterization
Chang et al. Cu2O loaded titanate nanotube arrays for simultaneously photoelectrochemical ibuprofen oxidation and hydrogen generation
Siavash Moakhar et al. AuPd bimetallic nanoparticle decorated TiO 2 rutile nanorod arrays for enhanced photoelectrochemical water splitting
Minggu et al. Bilayer n-WO3/p-Cu2O photoelectrode with photocurrent enhancement in aqueous electrolyte photoelectrochemical reaction
Shi et al. CuO-functionalized silicon photoanodes for photoelectrochemical water splitting devices
Ojani et al. Photoinduced deposition of palladium nanoparticles on TiO2 nanotube electrode and investigation of its capability for formaldehyde oxidation
Zhang et al. Enhanced photoelectrochemical oxidation of water over Ti-doped α-Fe2O3 electrodes by surface electrodeposition InOOH
Janáky et al. On the substantially improved photoelectrochemical properties of nanoporous WO 3 through surface decoration with RuO 2
Yu et al. Enhanced photoelectrochemical performance of coaxial-nanocoupled strontium-rich SrTiO3/TiO2 {001} nanotube arrays
Hosseini et al. Evaluation of the Performance of Platinum Nanoparticle–Titanium Oxide Nanotubes as a New Refreshable Electrode for Formic Acid Electro‐oxidation
Costa Bassetto et al. Print-Light-Synthesis of Ni and NiFe-nanoscale catalysts for oxygen evolution

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 15758442

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 15758442

Country of ref document: EP

Kind code of ref document: A1