WO2015146008A1 - Photoelectrochemical reaction system - Google Patents

Photoelectrochemical reaction system Download PDF

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Publication number
WO2015146008A1
WO2015146008A1 PCT/JP2015/001205 JP2015001205W WO2015146008A1 WO 2015146008 A1 WO2015146008 A1 WO 2015146008A1 JP 2015001205 W JP2015001205 W JP 2015001205W WO 2015146008 A1 WO2015146008 A1 WO 2015146008A1
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Prior art keywords
reaction
reduction
electrode
unit
photoelectrochemical
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PCT/JP2015/001205
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French (fr)
Japanese (ja)
Inventor
静君 黄
御子柴　智
昭彦 小野
良太 北川
由紀 工藤
田村　淳
栄史 堤
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株式会社 東芝
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Application filed by 株式会社 東芝 filed Critical 株式会社 東芝
Priority to JP2016509970A priority Critical patent/JP6258467B2/en
Publication of WO2015146008A1 publication Critical patent/WO2015146008A1/en
Priority to US15/247,178 priority patent/US20160362801A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
    • H01L31/0725—Multiple junction or tandem solar cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/02—Hydrogen or oxygen
    • C25B1/04—Hydrogen or oxygen by electrolysis of water
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/50—Processes
    • C25B1/55—Photoelectrolysis
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • 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
    • 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
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/054—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means
    • H01L31/056—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means the light-reflecting means being of the back surface reflector [BSR] type
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/52—PV systems with concentrators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight

Definitions

  • Embodiments of the present invention relate to photoelectrochemical reaction systems.
  • Plants use a system that is excited in two steps by light energy called a Z scheme. That is, a plant obtains electrons from water (H 2 O) by light energy and synthesizes cellulose and saccharides by reducing carbon dioxide (CO 2 ) using the electrons.
  • a Z scheme As an apparatus for artificial photosynthesis, development of a photoelectrochemical reaction apparatus for reducing (decomposing) CO 2 with light energy is in progress.
  • the artificial photoelectrochemical reaction device includes an electrode having a reduction catalyst for reducing carbon dioxide (CO 2 ) and an electrode having an oxidation catalyst for oxidizing water (H 2 O), and these electrodes are CO 2
  • CO 2 carbon dioxide
  • H 2 O oxidation catalyst for oxidizing water
  • a two-electrode system device in which water is immersed in dissolved water. When water is used as the electrolytic solution, the CO 2 decomposition efficiency can not be enhanced because the dissolved concentration of CO 2 is low.
  • a photoelectrochemical reaction device that decomposes water (H 2 O) with light energy to obtain oxygen (O 2 ) and hydrogen (H 2 ) a laminate in which a photovoltaic layer is sandwiched between a pair of electrodes is used Is being considered.
  • an aqueous solution containing an amine molecule, an ionic liquid, etc. have been studied.
  • an alkaline aqueous solution such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution or an aqueous amine solution is used as an electrolytic solution in a conventional CO 2 reduction device (CO 2 electrolysis device).
  • an aqueous amine solution used as a CO 2 absorbent has low chemical stability and is gradually oxidized even in a natural state. Since the oxidation electrode side of the photoelectrochemical reactor is a strong oxidizing environment, amine molecules in the aqueous solution are preferentially oxidized, and the aqueous amine solution can not be recovered or reused. For this reason, in the conventional photoelectrochemical reaction apparatus, the inside of the electrolytic cell is isolated to the oxidation electrode side and the reduction electrode side, but this causes the cell structure to be complicated and the like, which increases the apparatus cost, and further the apparatus Is easy to enlarge.
  • the ionic liquid is chemically stable, itself is expensive, which causes an increase in the cost of the apparatus.
  • the transportability and transport efficiency of CO 2 from the device that discharges CO 2 to the electrolyzer are not considered, and the configuration as a photoelectrochemical reaction system is not constructed.
  • the problem to be solved by the present invention is to provide a photoelectrochemical reaction system in which the efficiency of decomposition of CO 2 by light energy is enhanced and the efficiency of the entire system is improved.
  • the photoelectrochemical reaction system of the embodiment converts carbon dioxide into at least one intermediate substance selected from the group consisting of metal carbonates and metal hydrogencarbonates by an aqueous solution containing a metal hydroxide, and a reaction containing the intermediate substance
  • a conversion unit that generates a solution, a transfer unit that transfers a reaction solution containing an intermediate substance, a one-component reaction tank in which the reaction solution is introduced by the transfer unit, and an oxidation electrode that is immersed in the reaction solution to oxidize water
  • a reduction electrode which is immersed in the reaction solution and reduces the intermediate substance, and a photovoltaic element electrically connected to the oxidation electrode and the reduction electrode and performing charge separation by light energy.
  • FIG. 1st Embodiment It is a block diagram of the photoelectrochemical reaction system by 1st Embodiment. It is a figure which shows the 1st example of the photoelectrochemical module used for the photoelectrochemical reaction system shown in FIG. It is a figure which shows the 2nd example of the photoelectrochemical module used for the photoelectrochemical reaction system shown in FIG. It is a figure which shows the oxidation electrode used for the photoelectrochemical module shown in FIG. It is a figure which shows the reduction electrode used for the photoelectrochemical module shown in FIG. It is a figure which shows the photovoltaic device used for the photoelectrochemical module shown in FIG.
  • FIG. 1 is a view showing the configuration of a photoelectrochemical reaction system according to a first embodiment.
  • the photoelectrochemical reaction system 100 of the first embodiment is installed in addition to the CO 2 generation unit 100X that generates a gas containing carbon dioxide (CO 2 ).
  • the photoelectrochemical reaction system 100 includes a CO 2 conversion unit 102, a reaction solution transfer unit 103, a CO 2 reduction unit 104, a reaction solution adjustment unit 105, a reaction solution reflux unit 106, a product collection unit 107, and a reaction solution storage unit 108. Equipped with A power plant can be mentioned as a representative example of the CO 2 generation unit 100X.
  • the CO 2 generation unit 100X is not limited to this, and may be an iron factory, a chemical plant, a waste incineration site, or the like.
  • the CO2 generation unit 100X is not particularly limited.
  • the photoelectrochemical reaction system 100 according to the embodiment can reduce the size and the like of the CO 2 reducing unit 104 as described later, and is not limited to large plants such as a power plant and an iron factory, but may be a waste incineration site. It is also effective for small plants.
  • a gas containing CO 2 generated in the CO 2 generation unit 100 X for example, an exhaust gas discharged from a power plant, an iron factory, a chemical plant, a waste incineration plant or the like is sent to the CO 2 conversion unit 102 of the photoelectrochemical reaction system 100.
  • the impurities such as sulfur oxide in the exhaust gas may be removed and then sent to the CO 2 conversion unit 102.
  • the photoelectrochemical reaction system 100 may include the impurity removing unit 101.
  • the impurity removal unit 101 is not limited to between the CO 2 generation unit 100 X and the CO 2 conversion unit 102, and may be anywhere in the CO 2 circulation path.
  • the CO 2 conversion unit 102, the reaction solution transfer unit 103, It may be between any of the CO 2 reduction unit 104, the reaction solution reflux unit 106, and the reaction solution storage unit 108.
  • impurities not only components in the exhaust gas but also decomposition products of piping and reaction solution, chemically changed substances, substances eluted from piping and tank by reaction solution, metal ions from CO 2 reduction section 104, etc. are considered.
  • the impurity removing unit 101 may be a dry or wet gas processing apparatus, an ion exchange resin that absorbs metal ions, a filter that removes sulfur oxides or nitrogen oxides, physical decomposition products such as piping, tanks, and a stirrer. The filter to remove is mentioned.
  • CO 2 is converted to at least one intermediate selected from metal carbonates and metal hydrogen carbonates.
  • the CO 2 conversion unit 102 has a reaction vessel containing an aqueous solution containing a metal hydroxide that converts CO 2 into an intermediate substance.
  • a gas containing CO 2 is blown into the reaction vessel containing the aqueous solution of metal hydroxide by a gas supply pipe.
  • the CO 2 blown into the aqueous solution is converted by the metal hydroxide to at least one intermediate selected from metal carbonates and metal hydrogencarbonates.
  • a reaction solution (aqueous solution) containing the intermediate is generated in the reaction vessel. That is, the CO 2 conversion unit 102 generates a reaction solution (aqueous solution) containing water (H 2 O) and at least one intermediate substance selected from metal carbonates and metal hydrogencarbonates.
  • the metal hydroxide that converts CO 2 into an intermediate is preferably a hydroxide of at least one metal selected from an alkali metal (Group 1 element) and an alkaline earth metal (Group 2 element).
  • the metal hydroxide is at least selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), beryllium (Be), magnesium (Mg), calcium (Ca), and strontium (Sr) More preferably, it is a hydroxide of one metal.
  • the pH of the aqueous solution containing the metal hydroxide is preferably adjusted to a range of 7-14.
  • the pH of the aqueous solution containing the metal hydroxide In order to enhance the reactivity between CO 2 and the metal hydroxide, it is preferable to adjust the pH of the aqueous solution containing the metal hydroxide to a strongly alkaline region. On the other hand, in order to suppress corrosion of components such as the CO 2 conversion unit 102 and the CO 2 reduction unit 104, it is preferable to adjust the pH of the aqueous solution containing the metal hydroxide to a weakly alkaline region.
  • CO 2 is represented by the following formula (4) or (5) Converted to calcium carbonate or calcium hydrogen carbonate based on.
  • the other alkaline earth metals (group 2 elements) are almost the same.
  • the reaction solution (aqueous solution) containing the intermediate substance (metal carbonate or metal bicarbonate) generated in the CO 2 conversion unit 102 is sent to the CO 2 reduction unit 104 by the reaction solution transfer unit 103.
  • the CO 2 conversion unit 102 and the CO 2 reduction unit 104 do not have to be operated at the same time.
  • the reaction solution containing the intermediate substance generated by the CO 2 conversion unit 102 is a reaction solution It is stored in the storage unit 108.
  • the reaction solution stored in the reaction solution reservoir 108 is sent to the CO 2 reduction unit 104 during the operation of the CO 2 reduction unit 104.
  • the CO 2 reduction unit 104 includes the photoelectrochemical module 1 shown in FIGS. 2 and 3.
  • FIG. 2 shows a photoelectrochemical module 1A in which the photovoltaic element is disposed outside the reaction solution and the oxidation electrode and the reduction electrode are immersed in the reaction solution.
  • FIG. 3 shows a photoelectrochemical module 1B in which a laminate (photoelectrochemical cell) of an oxidation electrode, a photovoltaic layer and a reduction electrode is immersed in a reaction solution.
  • the photoelectrochemical module 1A (104) shown in FIG. 2 comprises a one-pack type reaction tank 3 containing the reaction solution 2, an oxidation electrode 4 and a reduction electrode 5 immersed in the reaction solution 2, and A photovoltaic element 6 disposed outside and electrically connected to the oxidation electrode 4 and the reduction electrode 5 is provided.
  • the reaction solution introduction pipe 7a for introducing the reaction solution 2 by the reaction solution transfer unit 103, the adjustment liquid introduction pipe 7b for introducing the adjustment solution of the reaction solution 2 from the reaction solution adjustment unit 105, and the reaction solution reflux unit 106 Connects the reaction solution discharge pipe 7c for discharging the solution after reaction, the reaction solution discharge pipe 7d for discharging the solution after reaction, and the product delivery pipe 7e for delivering gaseous reaction products to the product collection unit 107. It is done.
  • the reaction solution containing the intermediate substance generated by the CO 2 conversion unit 102 is introduced through the reaction solution introduction pipe 7a.
  • the introduction amount of the reaction solution is adjusted so that a predetermined space S is generated in the upper part of the reaction tank 3. Gaseous products generated by the oxidation-reduction reaction in the reaction tank 3 are collected in the upper space S of the reaction tank 3 and then sent to the product collection unit 107 via the product delivery pipe 7e.
  • An adjusting liquid is further introduced into the reaction tank 3 through the adjusting liquid introduction pipe 7b as necessary.
  • the reaction solution in the reaction tank 3 is adjusted with the adjusting liquid so as to have a desired concentration, properties and the like.
  • reaction solution in which the redox reaction has been performed in the reaction tank 3 is refluxed to the CO 2 converter 102 through the reaction solution discharge pipe 7 c.
  • a part of the reaction solution after the reaction is discharged out of the system through the reaction solution discharge pipe 7d as necessary.
  • the introduction and discharge of the reaction solution may be carried out continuously or batchwise at discrete times.
  • the reaction tank 3 is preferably formed of a material which does not react chemically with the reaction solution 2 and which is difficult to deteriorate by the energy of sunlight.
  • materials for example, polyetheretherketone (PEEK) resin, polyamide (PA) resin, polyvinylidene fluoride (PVDF) resin, polyacetal (POM) resin (copolymer), polyphenylene ether (PPE) resin, acrylonitrile-butadiene -Resin materials such as styrene copolymer (ABS), polypropylene (PP) resin, polyethylene (PE) resin and the like can be mentioned.
  • PEEK polyetheretherketone
  • PA polyamide
  • PVDF polyvinylidene fluoride
  • POM polyacetal
  • PPE polyphenylene ether
  • ABS styrene copolymer
  • PP polyprop
  • the reaction tank 3 may be provided with a stirrer for stirring the reaction solution 2.
  • the upper space S of the reaction vessel 3 is preferably completely sealed except for the product delivery pipe 7e in order to efficiently collect and discharge the gas product.
  • the reaction solution 2 introduced into the reaction tank 3 is adjusted by the reaction solution adjusting unit 105 so as to have a concentration and properties suitable for the oxidation reaction of H 2 O and the reduction reaction of the intermediate substance.
  • an aqueous solution of the same metal hydroxide as water or the CO 2 conversion unit 102 is added via the adjustment liquid introduction pipe 7 b so that the pH of the reaction solution 2 is in the range of 10.0 to 14.0. It is preferable to introduce it into the reaction tank 3.
  • a redox couple may be added to the reaction solution 2. Examples of the redox couple include Fe 3+ / Fe 2+ and IO 3 ⁇ / I ⁇ .
  • the oxidation electrode 4 and the reduction electrode 5 are disposed so as to be immersed in the reaction solution 2.
  • the oxidation electrode 4 has an oxidation catalyst layer 8 formed on both sides of the supporting substrate 4a.
  • the support base 4 a of the oxidation electrode 4 is formed of a material having conductivity. Examples of the forming material of the supporting base 4 a include metals such as Cu, Al, Ti, Ni, Fe, Ag, an alloy containing at least one of these metals, and a conductive resin.
  • a metal plate or an alloy plate is used in consideration of the formability of the oxidation catalyst layer 8.
  • the support substrate 4a may be made of a porous material such as a metal, an alloy, or a conductive resin.
  • the oxidation catalyst layer 8 has a function of receiving holes from the supporting substrate 4 a of the oxidation electrode 4 and reacting with H 2 O in the reaction solution 2 to oxidize H 2 O.
  • the constituent material of the oxidation catalyst layer 8 preferably contains an oxide or hydroxide of at least one metal selected from Fe, Ni, Co, Cu, Ti, V, Mn, Ru, and Ir.
  • Specific materials of the oxidation catalyst layer 8 include RuO 2 , NiO, Ni (OH) 2 , NiOOH, Co 3 O 4 , Co (OH) 2 , CoOOH, FeO, Fe 2 O 3 , MnO 2 , and Mn.
  • One or more composite materials selected from 3 O 4 , Rh 2 O 3 , and IrO 2 can be mentioned.
  • the oxidation catalyst layer 8 promotes the oxidation reaction of H 2 O in the oxidation electrode 4, the oxidation catalyst layer 8 can be omitted if the reaction rate of the oxidation reaction by the supporting substrate 4 a of the oxidation electrode 4 is sufficient.
  • the reduction electrode 5 has a support base 5a and a reduction catalyst layer 9 formed on both sides thereof.
  • the support substrate 5 a of the reduction electrode 5 is formed of a material having conductivity.
  • the forming material of the supporting base 5a include metals such as Cu, Al, Ti, Ni, Fe, Ag, an alloy containing at least one of these metals, and a conductive resin.
  • a metal plate or an alloy plate is used in consideration of the formability of the reduction catalyst layer 9.
  • the support substrate 5a may be made of a porous body of metal, alloy, conductive resin or the like.
  • the reduction catalyst layer 9 has a function of receiving electrons from the supporting substrate 5 a of the reduction electrode 5 and reducing an intermediate substance in the reaction solution 2, that is, metal carbonate and metal hydrogen carbonate, and CO 2 generated thereby.
  • the constituent material of the reduction catalyst layer 9 is a metal such as Au, Ag, Zn, Cu, Hg, Cd, Pb, Ti, In, Sn, a metal complex such as a ruthenium complex or rhenium complex, graphene, CNT (carbon nanotube) It is preferable to contain carbon materials such as fullerene, ketjen black and the like. Since the reduction catalyst layer 9 promotes the reduction reaction of CO 2 in the reduction electrode 5, the reduction catalyst layer 9 can be omitted if the reaction rate of the reduction reaction by the support substrate 5 a of the reduction electrode 5 is sufficient.
  • the photovoltaic element 6 is electrically connected to the oxidation electrode 4 and the reduction electrode 5, thereby exchanging electrons and holes with the oxidation electrode 4 and the reduction electrode 5.
  • the photovoltaic element 6 performs charge separation by light energy.
  • the photovoltaic element 6 needs to create a potential difference higher than the difference between the standard redox potential of the oxidation reaction of H 2 O generated near the oxidation electrode 4 and the standard redox potential of the reduction reaction of CO 2 generated near the reduction electrode 5 There is. That is, the photovoltaic element 6 can provide the energy necessary for simultaneously causing the oxidation reaction of H 2 O and the reduction reaction of CO 2 .
  • the photovoltaic element 6 includes the first electrode layer 11, the photovoltaic layer 31, and the second electrode layer 21.
  • FIG. 7 shows a specific example of the photovoltaic element 6 using a silicon solar cell (pin junction) as the photovoltaic layer 31.
  • the second electrode layer 21 is formed of a metal such as Cu, Al, Ti, Ni, Fe, Ag, an alloy such as SUS containing at least one of these metals, a conductive resin, a semiconductor such as Si or Ge, or the like. Ru.
  • a metal plate, an alloy plate, a resin plate, a semiconductor substrate or the like is used for the second electrode layer 21, a metal plate, an alloy plate, a resin plate, a semiconductor substrate or the like is used.
  • the photovoltaic layer 31 is formed on the second electrode layer 21.
  • the photovoltaic layer 31 is composed of the reflective layer 32, the first photovoltaic layer 33, the second photovoltaic layer 34, and the third photovoltaic layer 35.
  • the reflective layer 32 is formed on the second electrode layer 21 and has a first reflective layer 32a and a second reflective layer 32b formed in order from the lower side.
  • a metal such as Ag, Au, Al, Cu, etc., which has light reflectivity and conductivity, an alloy containing at least one of these metals, or the like is used.
  • the second reflective layer 32 b is provided to adjust the optical distance to enhance the light reflectivity.
  • the second reflective layer 32 b is preferably made of a material having optical transparency and capable of making ohmic contact with the n-type semiconductor layer because the second reflective layer 32 b is joined to the n-type semiconductor layer of the photovoltaic layer 31 described later.
  • transparent conductive oxide such as ITO (indium tin oxide), zinc oxide (ZnO), FTO (fluorine-doped tin oxide), AZO (aluminum-doped zinc oxide), ATO (antimony-doped tin oxide), etc. The thing is used.
  • the first photovoltaic layer 33, the second photovoltaic layer 34, and the third photovoltaic layer 35 are each a solar cell using a pin junction semiconductor, and they have different light absorption wavelengths. By laminating these layers in a planar manner, the photovoltaic layer 31 can absorb light of a wide wavelength of sunlight, and energy of the sunlight can be efficiently used. Since the photovoltaic layers 33, 34, 35 are connected in series, a high open circuit voltage can be obtained.
  • the first photovoltaic layer 33 is formed on the reflective layer 32, and an n-type amorphous silicon (a-Si) layer 33a formed in order from the lower side, intrinsic amorphous silicon germanium (a-) And a p-type microcrystalline silicon (mc-Si) layer 33c.
  • the a-SiGe layer 33 b is a layer that absorbs light in a long wavelength region of about 700 nm. In the first photovoltaic layer 33, charge separation occurs due to light energy in the long wavelength region.
  • the second photovoltaic layer 34 is formed on the first photovoltaic layer 33, and an n-type a-Si layer 34a, an intrinsic a-SiGe layer 34b, which are sequentially formed from the lower side, And a p-type mc-Si layer 34c.
  • the a-SiGe layer 34 b is a layer that absorbs light in an intermediate wavelength region of about 600 nm. In the second photovoltaic layer 34, charge separation occurs by light energy in the intermediate wavelength region.
  • the third photovoltaic layer 35 is formed on the second photovoltaic layer 34, and is an n-type a-Si layer 35a, an intrinsic a-Si layer 35b, formed sequentially from the lower side, And a p-type mc-Si layer 35c.
  • the a-Si layer 35b is a layer that absorbs light in a short wavelength region of about 400 nm. In the third photovoltaic layer 35, charge separation occurs due to light energy in the short wavelength region.
  • the first electrode layer 11 is formed on the p-type semiconductor layer (p-type mc-Si layer 35 c) of the photovoltaic layer 31.
  • the first electrode layer 11 is preferably formed of a material capable of ohmic contact with the p-type semiconductor layer.
  • a metal such as Ag, Au, Al or Cu, an alloy containing at least one of these metals, a transparent conductive oxide such as ITO, ZnO, FTO, AZO, ATO or the like is used.
  • the first electrode layer 11 has, for example, a structure in which a metal and a transparent conductive oxide are laminated, a structure in which a metal and another conductive material are composited, and a transparent conductive oxide and another conductive material are composited It may have the same structure or the like.
  • the irradiation light passes through the first electrode layer 11 and reaches the photovoltaic layer 31.
  • the first electrode layer 11 has optical transparency to the irradiation light.
  • charge separation occurs due to the energy of the light of each wavelength region of the irradiation light (sunlight etc.).
  • an electromotive force is generated in the photovoltaic layer 31 by separating holes toward the first electrode layer 11 and electrons toward the second electrode layer 21. Therefore, the first electrode layer 11 to which holes move is electrically connected to the oxidation electrode 4, and the second electrode layer 21 to which electrons move is electrically connected to the reduction electrode 5.
  • FIG. 7 illustrates the photovoltaic layer 31 having a stacked structure of three photovoltaic layers as an example, the photovoltaic layer 31 is not limited to this.
  • the photovoltaic layer 31 may have a laminated structure of two or four or more photovoltaic layers. Instead of the photovoltaic layer 31 of the laminated structure, one photovoltaic layer 31 may be used.
  • the photovoltaic layer 31 is not limited to a solar cell using a pin junction type semiconductor, and may be a solar cell using a pn junction type semiconductor.
  • the semiconductor layer is not limited to Si or Ge, and may be a compound semiconductor such as GaAs, GaInP, AlGaInP, CdTe, CuInGaSe or the like.
  • FIG. 7 illustrates the photovoltaic layer 31 having a stacked structure of three photovoltaic layers as an example, the photovoltaic layer 31 is not limited to this.
  • the photovoltaic layer 31 may have a laminated structure of two or four or
  • the photovoltaic device 6 is not limited to a silicon solar cell, and another solar cell may be applied.
  • the light irradiation side is not limited to the p-type semiconductor layer, and may be an n-type semiconductor layer.
  • sodium hydrogen carbonate (NaHCO 3 ) will be described as a representative example of the intermediate substance, but the same applies to other metal carbonates and metal hydrogen carbonates.
  • NaHCO 3 sodium hydrogen carbonate
  • An oxidation reaction of H 2 O occurs in the vicinity of the oxidation electrode 4 from which the holes move.
  • the holes transferred to the oxidation electrode 4 combine with the electrons generated by the oxidation reaction.
  • a reduction reaction of intermediates and CO 2 occurs.
  • the electrons transferred to the reduction electrode 5 are used for the reduction reaction.
  • CO 2 is generated from a metal carbonate or metal hydrogen carbonate as an intermediate substance.
  • the CO 2 generated by the reaction of the metal carbonate or the metal hydrogencarbonate is reduced in the vicinity of the reduction electrode 5 (to obtain electrons).
  • CO 2 produced by the reaction of metal carbonates and metal hydrogen carbonates are produced by the oxidation electrode 4 side, the H + which has moved to the reduction electrode 5 side by diffusing the reaction solution 2, light It is generated by the charge separation in the electromotive force element 6 and reacts with the electrons transferred to the reduction electrode 5 to generate, for example, CO and H 2 O.
  • the reactions of the formulas (7) to (9) are an example of the reaction in the vicinity of the reduction electrode 5, and metal carbonates and metal hydrogencarbonates are directly reduced to produce CO and H 2 O. It may be generated.
  • metal carbonates and metal hydrogencarbonates are directly reduced to produce CO and H 2 O. It may be generated.
  • the photoelectrochemical module 1B (104) shown in FIG. 3 includes a one-pack type reaction tank 3 containing the reaction solution 2 and a photoelectrochemical cell immersed in the reaction solution 2, that is, an oxidation catalyst layer 12, an oxidation electrode A laminate 10 of a (first electrode) 11, a photovoltaic layer 31, a reduction electrode (second electrode) 21, and a reduction catalyst layer 22 is provided. According to the photoelectrochemical module 1B, simplification of the constituent elements can be achieved as compared to the photoelectrochemical module 1A shown in FIG.
  • the reaction tank 3 in the photoelectrochemical module 1B (104) has the same configuration (each piping, etc.) as the reaction tank 3 of the photoelectrochemical module 1A shown in FIG.
  • the reaction vessel 3 does not react chemically with the reaction solution 2 and is a material that transmits light, ie, 250 ⁇ It is made of a material having a low absorptivity of light in the wavelength region of 1100 nm.
  • Examples of materials for forming such a reaction vessel 3 include quartz, white sheet glass, polystyrene and methacrylate. Only the window for light irradiation may be formed of the above-described material, and the other portion may be the reaction tank 3 formed of the above-described resin material.
  • the oxidation catalyst layer 12 is formed on the first electrode (oxidation electrode) 11 of the photovoltaic element 6 shown in FIG. 7, and the second electrode (reduction electrode)
  • the structure which formed the reduction catalyst layer 22 on 21 is mentioned.
  • the catalyst layer disposed on the light irradiation side has light transparency.
  • the configuration of the photoelectrochemical cell 10 is not limited to this, and a pin junction having an oxidation catalyst layer and a reduction catalyst layer, a pn junction, an amorphous silicon solar cell, a multijunction solar cell, a single crystal silicon solar cell, many A crystalline silicon solar cell, a dye-sensitized solar cell, an organic thin film solar cell or the like can be applied.
  • the photoelectrochemical cell 10 needs to create a potential difference higher than the difference between the standard redox potential of the oxidation reaction of H 2 O generated near the oxidation electrode 11 and the standard redox potential of the reduction reaction of CO 2 generated near the reduction electrode 21. There is. That is, the photoelectrochemical cell 10 can provide the energy necessary for simultaneously causing the oxidation reaction of H 2 O and the reduction reaction of CO 2 .
  • 50% or more of light energy passes through the reaction vessel 3, the reaction solution 2, and the oxidation catalyst layer 12 from the outside of the reaction vessel 3. It is preferable to be configured to reach the electromotive force layer 31.
  • metals such as Ag, Au, Al and Cu, alloys containing at least one of these metals, and transparent such as ITO, ZnO, FTO, AZO, ATO A conductive oxide etc. are mentioned.
  • the oxidation electrode 11 of the photoelectrochemical cell 10 has been described as the light irradiation side, the present invention is not limited to this, and the reduction electrode 21 may be on the light irradiation side.
  • the constituent materials of the oxidation catalyst layer 12 and the reduction catalyst layer 22 are as described above.
  • the catalyst layer disposed on the light irradiation side of the oxidation catalyst layer 12 and the reduction catalyst layer 22 and the electrode disposed on the light irradiation side of the oxidation electrode 11 and the reduction electrode 21 have light transparency.
  • the photoelectrochemical cell 10 may be a laminate in which the oxidation catalyst layer 12, the oxidation electrode 11, the photovoltaic layer 31, the reduction electrode 21, and the reduction catalyst layer 22 are simply integrated, or such a laminate Alternatively, through holes may be formed in the stacking direction as ion passing holes. In order to transfer H + ions and the like efficiently between the oxidation reaction and the reduction reaction, it is preferable to provide a through hole in the photoelectrochemical cell 10, whereby the reaction efficiency is improved.
  • the through holes are provided to penetrate from the oxidation catalyst layer 12 which is one surface layer of the photoelectrochemical cell 10 to the reduction catalyst layer 22 which is the other surface layer.
  • the reduction reaction of the intermediate substance or CO 2 is performed based on the above-mentioned equations (7), (8), (9), etc. Occurs to form a carbon compound such as CO.
  • Gaseous products containing O 2 and intermediates produced by the oxidation reaction of H 2 O and carbon compounds (such as CO) produced by the reduction reaction of CO 2 were collected in the upper space S of the reaction vessel 3 Thereafter, it is sent to the product collection unit 107 via the product delivery pipe 7e.
  • the generated O 2 or carbon compound may be supplied, for example, as a carbon fuel containing a flame retardant to a combustion furnace such as a power plant, an iron factory, a chemical plant, or a waste disposal site. O 2 and carbon compounds can be separated and used individually.
  • Part or all of the reaction solution 2 in which the reaction is completed is refluxed to the CO 2 converter 102 through the reaction solution discharge pipe 7 c.
  • the reaction solution 2 was refluxed in CO 2 conversion unit 102 is reused in CO 2 conversion unit 102. A part of the reaction solution 2 after the reaction is discharged out of the system through the reaction solution discharge pipe 7d as necessary.
  • metal carbonate and metal hydrogen carbonate using CO 2 are metal hydroxides.
  • An aqueous solution containing an intermediate (a solution containing an intermediate and H 2 O) is used as a reaction solution after conversion into at least one intermediate selected from salts.
  • the reaction solution is alkaline, the oxidation reaction efficiency of H 2 O can be enhanced. Therefore, it is possible to provide the photoelectrochemical reaction system 100 which is excellent in reaction efficiency as a whole of the redox reaction, and is inexpensive and compact.
  • FIG. 10 is a block diagram of a photoelectrochemical reaction system according to a second embodiment.
  • the photoelectrochemical reaction system 110 according to the second embodiment includes a CO 2 conversion unit 102, a reaction solution transfer unit 103, a first CO 2 reduction unit 104A, a first reaction solution adjustment unit 105A, a first reaction solution reflux unit 106A, a first A 2CO 2 reduction unit 104B, a second reaction solution adjustment unit 105B, a second reaction solution reflux unit 106B, and a product collection unit 107 are provided.
  • the photoelectrochemical reaction system 110 of the second embodiment is installed in association with the CO 2 generation unit 100X.
  • the photoelectrochemical reaction system 110 may include the impurity removing unit 101 as in the first embodiment.
  • the photoelectrochemical reaction system 110 includes two systems of CO 2 reduction units 104 and reaction solution adjustment with respect to one system of CO 2 generation unit 100 X, CO 2 conversion unit 102, and reaction solution transfer unit 103. A portion 105 and a reaction solution reflux portion 106 are provided.
  • the other configuration is the same as that of the photoelectrochemical reaction system 100 of the first embodiment.
  • the detailed configuration of each part 101, 102, 103, 104, 105, 106, 107 is also the same as that of the photoelectrochemical reaction system 100 of the first embodiment.
  • the photoelectrochemical reaction system 110 may include a reaction solution storage unit.
  • the processing capability of CO 2 conversion unit 102 and the CO 2 reduction unit 104 can be one of a plurality of systems of systems including system and CO 2 reduction unit 104 including a CO 2 conversion unit 102.
  • FIG. 10 shows an example of the case where the processing capacity of the CO 2 conversion unit 102 is superior to the processing capacity of the CO 2 reduction unit 104.
  • the CO 2 conversion unit 102 can be operated efficiently by providing a plurality of systems including the CO 2 reduction unit 104 with respect to the system including the CO 2 conversion unit 102. This contributes to the improvement of the processing efficiency of the photoelectrochemical reaction system 110 as a whole.
  • first and second embodiments can be combined and applied, and can be partially replaced. While certain embodiments of the present invention have been described herein, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and at the same time, included in the invention described in the claims and the equivalents thereof.

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Abstract

A photoelectrochemical reaction system (100) according to one embodiment of the present invention is provided with a CO2 conversion unit (102) and a CO2 reduction unit (104). The CO2 conversion unit (102) converts CO2 into at least one intermediate selected from among metal carbonates and metal hydrogen carbonates by means of an aqueous solution containing a metal hydroxide, and produces a reaction solution containing the intermediate. The CO2 reduction unit (104) is provided with: a one-pack type reaction tank into which the reaction solution containing the intermediate is introduced; an oxidation electrode and a reduction electrode, which are immersed in the reaction solution; and a photovoltaic element which is electrically connected to the oxidation electrode and the reduction electrode. Consequently, O2 is produced in the vicinity of the oxidation electrode by oxidizing H2O, and a carbon compound is produced in the vicinity of the reduction electrode by reducing the intermediate.

Description

光電気化学反応システムPhotoelectrochemical reaction system
　本発明の実施形態は、光電気化学反応システムに関する。 Embodiments of the present invention relate to photoelectrochemical reaction systems.
　エネルギー問題や環境問題の観点から、植物のように光エネルギーによってＣＯ２を効率よく還元する技術が求められている。植物は、Ｚスキームと呼ばれる光エネルギーにより２段階で励起されるシステムを用いている。すなわち、植物は光エネルギーにより水（Ｈ２Ｏ）から電子を得ると共に、この電子を利用して二酸化炭素（ＣＯ２）を還元することによりセルロースや糖類を合成する。人工光合成を行う装置として、光エネルギーによりＣＯ２を還元（分解）する光電気化学反応装置の開発が進められている。 From the viewpoint of energy problems and environmental problems, there is a need for a technology that efficiently reduces CO 2 with light energy like plants. Plants use a system that is excited in two steps by light energy called a Z scheme. That is, a plant obtains electrons from water (H 2 O) by light energy and synthesizes cellulose and saccharides by reducing carbon dioxide (CO 2 ) using the electrons. As an apparatus for artificial photosynthesis, development of a photoelectrochemical reaction apparatus for reducing (decomposing) CO 2 with light energy is in progress.
　人工的な光電気化学反応装置としては、二酸化炭素（ＣＯ２）を還元する還元触媒を有する電極と、水（Ｈ２Ｏ）を酸化する酸化触媒を有する電極とを備え、これら電極をＣＯ２が溶解した水中に浸漬させる二電極方式の装置が知られている。電解液として水を用いた場合、ＣＯ２の溶存濃度が低いため、ＣＯ２の分解効率を高めることができない。さらに、光エネルギーにより水（Ｈ２Ｏ）を分解して酸素（Ｏ２）や水素（Ｈ２）を得る光電気化学反応装置として、一対の電極で光起電力層を挟持した積層体を用いることが検討されている。ＣＯ２吸収剤としては、アミン分子を含む水溶液、イオン性液体等が検討されている。光電気化学反応装置とは別に、従来のＣＯ２還元装置（ＣＯ２電解装置）においては、電解液として水酸化カリウム水溶液や水酸化ナトリウム水溶液等のアルカリ性水溶液、あるいはアミン水溶液が用いられている。 The artificial photoelectrochemical reaction device includes an electrode having a reduction catalyst for reducing carbon dioxide (CO 2 ) and an electrode having an oxidation catalyst for oxidizing water (H 2 O), and these electrodes are CO 2 There is known a two-electrode system device in which water is immersed in dissolved water. When water is used as the electrolytic solution, the CO 2 decomposition efficiency can not be enhanced because the dissolved concentration of CO 2 is low. Furthermore, as a photoelectrochemical reaction device that decomposes water (H 2 O) with light energy to obtain oxygen (O 2 ) and hydrogen (H 2 ), a laminate in which a photovoltaic layer is sandwiched between a pair of electrodes is used Is being considered. As a CO 2 absorbent, an aqueous solution containing an amine molecule, an ionic liquid, etc. have been studied. Aside from the photoelectrochemical reaction device, an alkaline aqueous solution such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution or an aqueous amine solution is used as an electrolytic solution in a conventional CO 2 reduction device (CO 2 electrolysis device).
　従来の光電気化学反応装置において、ＣＯ２吸収剤として用いられるアミン水溶液は、化学的な安定性が低く、自然な状態でも徐々に酸化されてしまう。光電気化学反応装置の酸化電極側は強度な酸化環境となるため、水溶液中のアミン分子が優先的に酸化され、アミン水溶液の回収や再利用ができなくなる。このため、従来の光電気化学反応装置では電解槽内を酸化電極側と還元電極側とに隔離しているが、これはセル構造の複雑化等を招くことから装置コストが増大し、さらに装置が大型化しやすい。イオン性液体は化学的に安定であるものの、それ自体が高価であるため、装置コストの増大等を招いてしまう。従来のＣＯ２電解装置では、ＣＯ２を排出する装置から電解装置までのＣＯ２の輸送性や輸送効率等が考慮されておらず、光電気化学反応システムとしての構成も構築されていない。 In the conventional photoelectrochemical reaction apparatus, an aqueous amine solution used as a CO 2 absorbent has low chemical stability and is gradually oxidized even in a natural state. Since the oxidation electrode side of the photoelectrochemical reactor is a strong oxidizing environment, amine molecules in the aqueous solution are preferentially oxidized, and the aqueous amine solution can not be recovered or reused. For this reason, in the conventional photoelectrochemical reaction apparatus, the inside of the electrolytic cell is isolated to the oxidation electrode side and the reduction electrode side, but this causes the cell structure to be complicated and the like, which increases the apparatus cost, and further the apparatus Is easy to enlarge. Although the ionic liquid is chemically stable, itself is expensive, which causes an increase in the cost of the apparatus. In the conventional CO 2 electrolyzer, the transportability and transport efficiency of CO 2 from the device that discharges CO 2 to the electrolyzer are not considered, and the configuration as a photoelectrochemical reaction system is not constructed.
特開２０１１－０９４１９４号公報JP, 2011-094194, A 特開２０１２－１１２００１号公報JP, 2012-112001, A
　本発明が解決しようとする課題は、光エネルギーによるＣＯ２の分解効率を高めると共に、システム全体の効率を向上させた光電気化学反応システムを提供することにある。 The problem to be solved by the present invention is to provide a photoelectrochemical reaction system in which the efficiency of decomposition of CO 2 by light energy is enhanced and the efficiency of the entire system is improved.
　実施形態の光電気化学反応システムは、金属水酸化物を含む水溶液により二酸化炭素を金属炭酸塩および金属炭酸水素塩からなる群より選ばれる少なくとも１つの中間物質に変換し、前記中間物質を含む反応溶液を生成する変換部と、中間物質を含む反応溶液を転送する転送部と、転送部により反応溶液が導入される一液型反応槽と、反応溶液中に浸漬され、水を酸化する酸化電極と、反応溶液中に浸漬され、中間物質を還元する還元電極と、酸化電極および還元電極と電気的に接続され、光エネルギーにより電荷分離を行う光起電力素子とを備える還元部とを具備する。 The photoelectrochemical reaction system of the embodiment converts carbon dioxide into at least one intermediate substance selected from the group consisting of metal carbonates and metal hydrogencarbonates by an aqueous solution containing a metal hydroxide, and a reaction containing the intermediate substance A conversion unit that generates a solution, a transfer unit that transfers a reaction solution containing an intermediate substance, a one-component reaction tank in which the reaction solution is introduced by the transfer unit, and an oxidation electrode that is immersed in the reaction solution to oxidize water And a reduction electrode which is immersed in the reaction solution and reduces the intermediate substance, and a photovoltaic element electrically connected to the oxidation electrode and the reduction electrode and performing charge separation by light energy. .
第１の実施形態による光電気化学反応システムの構成図である。It is a block diagram of the photoelectrochemical reaction system by 1st Embodiment. 図１に示す光電気化学反応システムに用いられる光電気化学モジュールの第１の例を示す図である。It is a figure which shows the 1st example of the photoelectrochemical module used for the photoelectrochemical reaction system shown in FIG. 図１に示す光電気化学反応システムに用いられる光電気化学モジュールの第２の例を示す図である。It is a figure which shows the 2nd example of the photoelectrochemical module used for the photoelectrochemical reaction system shown in FIG. 図２に示す光電気化学モジュールに用いられる酸化電極を示す図である。It is a figure which shows the oxidation electrode used for the photoelectrochemical module shown in FIG. 図２に示す光電気化学モジュールに用いられる還元電極を示す図である。It is a figure which shows the reduction electrode used for the photoelectrochemical module shown in FIG. 図２に示す光電気化学モジュールに用いられる光起電力素子を示す図である。It is a figure which shows the photovoltaic device used for the photoelectrochemical module shown in FIG. 図６に示す光起電力素子の具体例を示す図である。It is a figure which shows the specific example of the photovoltaic device shown in FIG. 図２に示す光電気化学モジュールの動作を説明する図である。It is a figure explaining operation | movement of the photoelectrochemical module shown in FIG. 図３に示す光電気化学モジュールの動作を説明する図である。It is a figure explaining operation | movement of the photoelectrochemical module shown in FIG. 第２の実施形態による光電気化学反応システムの構成図である。It is a block diagram of the photoelectrochemical reaction system by 2nd Embodiment.
　以下、実施形態の光電気化学反応システムについて、図面を参照して説明する。 Hereinafter, the photoelectrochemical reaction system of the embodiment will be described with reference to the drawings.
（第１の実施形態）
　図１は第１の実施形態による光電気化学反応システムの構成を示す図である。第１の実施形態の光電気化学反応システム１００は、二酸化炭素（ＣＯ２）含むガスを発生するＣＯ２発生部１００Ｘに付随して設置される。光電気化学反応システム１００は、ＣＯ２変換部１０２、反応溶液転送部１０３、ＣＯ２還元部１０４、反応溶液調整部１０５、反応溶液還流部１０６、生成物収集部１０７、および反応溶液貯蔵部１０８を具備している。ＣＯ２発生部１００Ｘの代表例としては、発電所が挙げられる。ＣＯ２発生部１００Ｘはこれに限られるものではなく、鉄工所、化学工場、ごみ焼却場等であってもよい。ＣＯ２発生部１００Ｘは特に限定されない。実施形態による光電気化学反応システム１００は、後述するようにＣＯ２還元部１０４の小型化等を図ることができるため、発電所や鉄工所等の大型プラントに限らず、ごみ焼却場のような小型プラントに対しても有効である。 First Embodiment
FIG. 1 is a view showing the configuration of a photoelectrochemical reaction system according to a first embodiment. The photoelectrochemical reaction system 100 of the first embodiment is installed in addition to the CO 2 generation unit 100X that generates a gas containing carbon dioxide (CO 2 ). The photoelectrochemical reaction system 100 includes a CO 2 conversion unit 102, a reaction solution transfer unit 103, a CO 2 reduction unit 104, a reaction solution adjustment unit 105, a reaction solution reflux unit 106, a product collection unit 107, and a reaction solution storage unit 108. Equipped with A power plant can be mentioned as a representative example of the CO 2 generation unit 100X. The CO 2 generation unit 100X is not limited to this, and may be an iron factory, a chemical plant, a waste incineration site, or the like. The CO2 generation unit 100X is not particularly limited. The photoelectrochemical reaction system 100 according to the embodiment can reduce the size and the like of the CO 2 reducing unit 104 as described later, and is not limited to large plants such as a power plant and an iron factory, but may be a waste incineration site. It is also effective for small plants.
　ＣＯ２発生部１００Ｘで発生したＣＯ２を含むガス、例えば発電所、鉄工所、化学工場、ごみ焼却場等から排出される排ガスは、光電気化学反応システム１００のＣＯ２変換部１０２に送られる。ＣＯ２発生部１００Ｘから排出される排ガスの成分等によっては、排ガス中の硫黄酸化物のような不純物を除去した後にＣＯ２変換部１０２に送ってもよい。光電気化学反応システム１００は、不純物除去部１０１を備えていてもよい。不純物除去部１０１は、ＣＯ２発生部１００ＸとＣＯ２変換部１０２との間に限らず、ＣＯ２の循環経路のどこかにあってもよく、ＣＯ２変換部１０２、反応溶液転送部１０３、ＣＯ２還元部１０４、反応溶液還流部１０６、および反応溶液貯蔵部１０８のいずれの装置の間にあってもよい。不純物としては、排ガス中の成分のみならず、配管や反応溶液の分解物や化学的に変化した物質、反応溶液による配管やタンクからの溶出物、ＣＯ２還元部１０４からの金属イオン等が考えられる。不純物除去部１０１としては、乾式または湿式のガス処理装置、金属イオンを吸収するイオン交換樹脂や、硫黄酸化物や窒素酸化物を除去するフィルタ、配管、タンク、撹拌装置等の物理的分解物を除去するフィルタが挙げられる。 A gas containing CO 2 generated in the CO 2 generation unit 100 X, for example, an exhaust gas discharged from a power plant, an iron factory, a chemical plant, a waste incineration plant or the like is sent to the CO 2 conversion unit 102 of the photoelectrochemical reaction system 100. Depending on the components and the like of the exhaust gas discharged from the CO 2 generation unit 100X, the impurities such as sulfur oxide in the exhaust gas may be removed and then sent to the CO 2 conversion unit 102. The photoelectrochemical reaction system 100 may include the impurity removing unit 101. The impurity removal unit 101 is not limited to between the CO 2 generation unit 100 X and the CO 2 conversion unit 102, and may be anywhere in the CO 2 circulation path. The CO 2 conversion unit 102, the reaction solution transfer unit 103, It may be between any of the CO 2 reduction unit 104, the reaction solution reflux unit 106, and the reaction solution storage unit 108. As impurities, not only components in the exhaust gas but also decomposition products of piping and reaction solution, chemically changed substances, substances eluted from piping and tank by reaction solution, metal ions from CO 2 reduction section 104, etc. are considered. Be The impurity removing unit 101 may be a dry or wet gas processing apparatus, an ion exchange resin that absorbs metal ions, a filter that removes sulfur oxides or nitrogen oxides, physical decomposition products such as piping, tanks, and a stirrer. The filter to remove is mentioned.
　ＣＯ２変換部１０２において、ＣＯ２は金属炭酸塩および金属炭酸水素塩から選ばれる少なくとも１つの中間物質に変換される。ＣＯ２変換部１０２は、ＣＯ２を中間物質に変換する金属水酸化物を含む水溶液が収容された反応槽を有する。金属水酸化物の水溶液が収容された反応槽内には、ガス供給管によりＣＯ２を含むガスが吹き込まれる。水溶液中に吹き込まれたＣＯ２は、金属水酸化物により金属炭酸塩および金属炭酸水素塩から選ばれる少なくとも１つの中間物質に変換される。ＣＯ２を金属水酸化物で中間物質に変換することによって、反応槽内には中間物質を含む反応溶液（水溶液）が生成される。すなわち、ＣＯ２変換部１０２では金属炭酸塩および金属炭酸水素塩から選ばれる少なくとも１つの中間物質と水（Ｈ２Ｏ）とを含む反応溶液（水溶液）が生成される。 In the CO 2 converter 102, CO 2 is converted to at least one intermediate selected from metal carbonates and metal hydrogen carbonates. The CO 2 conversion unit 102 has a reaction vessel containing an aqueous solution containing a metal hydroxide that converts CO 2 into an intermediate substance. A gas containing CO 2 is blown into the reaction vessel containing the aqueous solution of metal hydroxide by a gas supply pipe. The CO 2 blown into the aqueous solution is converted by the metal hydroxide to at least one intermediate selected from metal carbonates and metal hydrogencarbonates. By converting CO 2 into an intermediate with metal hydroxide, a reaction solution (aqueous solution) containing the intermediate is generated in the reaction vessel. That is, the CO 2 conversion unit 102 generates a reaction solution (aqueous solution) containing water (H 2 O) and at least one intermediate substance selected from metal carbonates and metal hydrogencarbonates.
　ＣＯ２を中間物質に変換する金属水酸化物は、アルカリ金属（第１族元素）およびアルカリ土類金属（第２族元素）から選ばれる少なくとも１つの金属の水酸化物であることが好ましい。金属水酸化物は、リチウム（Ｌｉ）、ナトリウム（Ｎａ）、カリウム（Ｋ）、ルビジウム（Ｒｂ）、ベリリウム（Ｂｅ）、マグネシウム（Ｍｇ）、カルシウム（Ｃａ）、およびストロンチウム（Ｓｒ）から選ばれる少なくとも１つの金属の水酸化物であることがより好ましい。金属水酸化物を含む水溶液のｐＨは、７～１４の範囲に調整することが好ましい。ＣＯ２と金属水酸化物との反応性を高めるためには、金属水酸化物を含む水溶液のｐＨを強アルカリ領域に調整することが好ましい。一方、ＣＯ２変換部１０２やＣＯ２還元部１０４等の構成部品の腐食を抑制するためには、金属水酸化物を含む水溶液のｐＨを弱アルカリ領域に調整することが好ましい。 The metal hydroxide that converts CO 2 into an intermediate is preferably a hydroxide of at least one metal selected from an alkali metal (Group 1 element) and an alkaline earth metal (Group 2 element). The metal hydroxide is at least selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), beryllium (Be), magnesium (Mg), calcium (Ca), and strontium (Sr) More preferably, it is a hydroxide of one metal. The pH of the aqueous solution containing the metal hydroxide is preferably adjusted to a range of 7-14. In order to enhance the reactivity between CO 2 and the metal hydroxide, it is preferable to adjust the pH of the aqueous solution containing the metal hydroxide to a strongly alkaline region. On the other hand, in order to suppress corrosion of components such as the CO 2 conversion unit 102 and the CO 2 reduction unit 104, it is preferable to adjust the pH of the aqueous solution containing the metal hydroxide to a weakly alkaline region.
　金属水酸化物として水酸化ナトリウム（ＮａＯＨ）を用いた場合を例として説明すると、金属水酸化物の水溶液が収容された反応槽に吹き込まれたＣＯ２は、下記の（１）式や（２）式に基づいて炭酸ナトリウムや炭酸水素ナトリウムに変換される。
　　ＮａＯＨ＋ＣＯ２　→　ＮａＨＣＯ３　…（１）
　　２ＮａＯＨ＋ＣＯ２　→　Ｎａ２ＣＯ３＋Ｈ２Ｏ　…（２）
　炭酸ナトリウムは、下記の（３）式に基づいて、さらに炭酸水素ナトリウムに変換される場合もある。
　　Ｎａ２ＣＯ３＋ＣＯ２＋Ｈ２Ｏ　→　２ＮａＨＣＯ３　…（３）
　他のアルカリ金属（第１族元素）もほぼ同様である。 Taking sodium hydroxide (NaOH) as the metal hydroxide as an example, CO 2 blown into the reaction vessel containing the aqueous solution of metal hydroxide is expressed by the following formula (1) or (2) ) Converted to sodium carbonate or sodium hydrogen carbonate based on the formula.
NaOH + CO 2 → NaHCO 3 (1)
2 NaOH + CO 2 → Na 2 CO 3 + H 2 O (2)
Sodium carbonate may be further converted to sodium hydrogen carbonate based on the following formula (3).
Na 2 CO 3 + CO 2 + H 2 O → 2 NaHCO 3 (3)
The other alkali metals (group 1 elements) are almost the same.
　金属水酸化物として水酸化カルシウム（Ｃａ（ＯＨ）２）等のアルカリ土類金属（第２族元素）の水酸化物を用いた場合、ＣＯ２は下記の（４）式や（５）式に基づいて炭酸カルシウムや炭酸水素カルシウムに変換される。
　　Ｃａ（ＯＨ）２＋ＣＯ２　→　ＣａＣＯ３＋Ｈ２Ｏ　…（４）
　　ＣａＣＯ３＋Ｈ２Ｏ＋ＣＯ２　→　Ｃａ（ＨＣＯ３）２　…（５）
　他のアルカリ土類金属（第２族元素）もほぼ同様である。 When a hydroxide of an alkaline earth metal (group 2 element) such as calcium hydroxide (Ca (OH) 2 ) is used as the metal hydroxide, CO 2 is represented by the following formula (4) or (5) Converted to calcium carbonate or calcium hydrogen carbonate based on.
Ca (OH) 2 + CO 2 → CaCO 3 + H 2 O (4)
CaCO 3 + H 2 O + CO 2 → Ca (HCO 3 ) 2 ... (5)
The other alkaline earth metals (group 2 elements) are almost the same.
　ＣＯ２変換部１０２で生成された中間物質（金属炭酸塩や金属炭酸水素塩）を含む反応溶液（水溶液）は、反応溶液転送部１０３によりＣＯ２還元部１０４に送られる。ＣＯ２変換部１０２とＣＯ２還元部１０４とは、必ずしも同時に運転しなければならないものではない。例えば、ＣＯ２変換部１０２は夜間も運転するのに対し、ＣＯ２還元部１０４の運転は夜間については休止する場合、ＣＯ２変換部１０２で生成された中間物質を含む反応溶液は、反応溶液貯蔵部１０８に貯蔵される。反応溶液貯蔵部１０８に貯蔵された反応溶液は、ＣＯ２還元部１０４の運転時にＣＯ２還元部１０４に送られる。 The reaction solution (aqueous solution) containing the intermediate substance (metal carbonate or metal bicarbonate) generated in the CO 2 conversion unit 102 is sent to the CO 2 reduction unit 104 by the reaction solution transfer unit 103. The CO 2 conversion unit 102 and the CO 2 reduction unit 104 do not have to be operated at the same time. For example, when the operation of the CO 2 reduction unit 104 is stopped at night while the CO 2 conversion unit 102 is also operated at night, the reaction solution containing the intermediate substance generated by the CO 2 conversion unit 102 is a reaction solution It is stored in the storage unit 108. The reaction solution stored in the reaction solution reservoir 108 is sent to the CO 2 reduction unit 104 during the operation of the CO 2 reduction unit 104.
　ＣＯ２還元部１０４は、図２や図３に示す光電気化学モジュール１を備えている。図２は光起電力素子を反応溶液外に配置し、酸化電極と還元電極とを反応溶液内に浸漬した光電気化学モジュール１Ａを示している。図３は酸化電極と光起電力層と還元電極との積層体（光電気化学セル）を反応溶液内に浸漬した光電気化学モジュール１Ｂを示している。 The CO 2 reduction unit 104 includes the photoelectrochemical module 1 shown in FIGS. 2 and 3. FIG. 2 shows a photoelectrochemical module 1A in which the photovoltaic element is disposed outside the reaction solution and the oxidation electrode and the reduction electrode are immersed in the reaction solution. FIG. 3 shows a photoelectrochemical module 1B in which a laminate (photoelectrochemical cell) of an oxidation electrode, a photovoltaic layer and a reduction electrode is immersed in a reaction solution.
　図２に示す光電気化学モジュール１Ａ（１０４）は、反応溶液２を収容する一液型の反応槽３と、反応溶液２中に浸漬される酸化電極４および還元電極５と、反応槽３の外部に配置され、酸化電極４および還元電極５と電気的に接続された光起電力素子６とを備えている。反応槽３には、反応溶液転送部１０３により反応溶液２を導入する反応溶液導入管７ａ、反応溶液調整部１０５から反応溶液２の調整液を導入する調整液導入管７ｂ、反応溶液還流部１０６により反応後の溶液を導出する反応溶液導出管７ｃ、反応後の溶液を排出する反応溶液排出管７ｄ、およびガス状の反応生成物を生成物収集部１０７に送出する生成物送出管７ｅが接続されている。 The photoelectrochemical module 1A (104) shown in FIG. 2 comprises a one-pack type reaction tank 3 containing the reaction solution 2, an oxidation electrode 4 and a reduction electrode 5 immersed in the reaction solution 2, and A photovoltaic element 6 disposed outside and electrically connected to the oxidation electrode 4 and the reduction electrode 5 is provided. The reaction solution introduction pipe 7a for introducing the reaction solution 2 by the reaction solution transfer unit 103, the adjustment liquid introduction pipe 7b for introducing the adjustment solution of the reaction solution 2 from the reaction solution adjustment unit 105, and the reaction solution reflux unit 106 Connects the reaction solution discharge pipe 7c for discharging the solution after reaction, the reaction solution discharge pipe 7d for discharging the solution after reaction, and the product delivery pipe 7e for delivering gaseous reaction products to the product collection unit 107. It is done.
　光電気化学モジュール１Ａの反応槽３内には、ＣＯ２変換部１０２で生成された中間物質を含む反応溶液が反応溶液導入管７ａを介して導入される。反応溶液の導入量は、反応槽３の上部に所定の空間Ｓが生じるように調整される。反応槽３内での酸化還元反応により生じるガス状の生成物は、反応槽３の上部空間Ｓに集められた後、生成物送出管７ｅを介して生成物収集部１０７に送られる。反応槽３内には、さらに調整液導入管７ｂを介して調整液が必要に応じて導入される。反応槽３内の反応溶液は、所望の濃度や性質等を有するように調整液で調整される。反応槽３内で酸化還元反応が行われた反応溶液は、反応溶液導出管７ｃを介してＣＯ２変換部１０２に還流される。反応後の反応溶液の一部は、必要に応じて反応溶液排出管７ｄを介して系外に排出される。反応溶液の導入および導出は、連続的に実施してもよいし、不連続にバッチ式で実施してもよい。 In the reaction tank 3 of the photoelectrochemical module 1A, the reaction solution containing the intermediate substance generated by the CO 2 conversion unit 102 is introduced through the reaction solution introduction pipe 7a. The introduction amount of the reaction solution is adjusted so that a predetermined space S is generated in the upper part of the reaction tank 3. Gaseous products generated by the oxidation-reduction reaction in the reaction tank 3 are collected in the upper space S of the reaction tank 3 and then sent to the product collection unit 107 via the product delivery pipe 7e. An adjusting liquid is further introduced into the reaction tank 3 through the adjusting liquid introduction pipe 7b as necessary. The reaction solution in the reaction tank 3 is adjusted with the adjusting liquid so as to have a desired concentration, properties and the like. The reaction solution in which the redox reaction has been performed in the reaction tank 3 is refluxed to the CO 2 converter 102 through the reaction solution discharge pipe 7 c. A part of the reaction solution after the reaction is discharged out of the system through the reaction solution discharge pipe 7d as necessary. The introduction and discharge of the reaction solution may be carried out continuously or batchwise at discrete times.
　反応槽３は、反応溶液２と化学的に反応せず、かつ太陽光のエネルギーにより変質しづらい材料で形成することが好ましい。そのような材料としては、例えばポリエーテルエーテルケトン（ＰＥＥＫ）樹脂、ポリアミド（ＰＡ）樹脂、ポリフッ化ビニリデン（ＰＶＤＦ）樹脂、ポリアセタール（ＰＯＭ）樹脂（コポリマー）、ポリフェニレンエーテル（ＰＰＥ）樹脂、アクリロニトリル－ブタジエン－スチレン共重合体（ＡＢＳ）、ポリプロピレン（ＰＰ）樹脂、ポリエチレン（ＰＥ）樹脂等の樹脂材料が挙げられる。 The reaction tank 3 is preferably formed of a material which does not react chemically with the reaction solution 2 and which is difficult to deteriorate by the energy of sunlight. As such materials, for example, polyetheretherketone (PEEK) resin, polyamide (PA) resin, polyvinylidene fluoride (PVDF) resin, polyacetal (POM) resin (copolymer), polyphenylene ether (PPE) resin, acrylonitrile-butadiene -Resin materials such as styrene copolymer (ABS), polypropylene (PP) resin, polyethylene (PE) resin and the like can be mentioned.
　反応溶液２の酸化還元反応時において、反応槽３内で均一かつ効率よく反応を行うために、反応槽３は反応溶液２を撹拌する撹拌機を備えていてもよい。反応槽３の上部空間Ｓは、気体生成物を効率よく収集して排出するために、生成物送出管７ｅを除いて完全な密閉状態であることが好ましい。反応槽３の上部空間Ｓを維持する上で、反応溶液２は反応槽３の内部容量に対して５０～９０％の範囲となるように導入することが好ましく、さらに反応槽３の７０～９０％の範囲となるように導入することがより好ましい。 In order to carry out the reaction uniformly and efficiently in the reaction tank 3 during the oxidation-reduction reaction of the reaction solution 2, the reaction tank 3 may be provided with a stirrer for stirring the reaction solution 2. The upper space S of the reaction vessel 3 is preferably completely sealed except for the product delivery pipe 7e in order to efficiently collect and discharge the gas product. In order to maintain the upper space S of the reaction tank 3, it is preferable to introduce the reaction solution 2 in a range of 50 to 90% with respect to the internal volume of the reaction tank 3. It is more preferable to introduce it in the range of%.
　反応槽３内に導入された反応溶液２は、Ｈ２Ｏの酸化反応および中間物質の還元反応に適した濃度や性質を有するように反応溶液調整部１０５により調整される。具体的には、反応溶液２のｐＨが１０．０～１４．０の範囲となるように、水やＣＯ２変換部１０２と同一の金属水酸化物の水溶液を、調整液導入管７ｂを介して反応槽３内に導入することが好ましい。反応溶液２には、必要に応じて酸化還元対を添加してもよい。酸化還元対としては、例えばＦｅ３＋／Ｆｅ２＋やＩＯ３－／Ｉ－が挙げられる。 The reaction solution 2 introduced into the reaction tank 3 is adjusted by the reaction solution adjusting unit 105 so as to have a concentration and properties suitable for the oxidation reaction of H 2 O and the reduction reaction of the intermediate substance. Specifically, an aqueous solution of the same metal hydroxide as water or the CO 2 conversion unit 102 is added via the adjustment liquid introduction pipe 7 b so that the pH of the reaction solution 2 is in the range of 10.0 to 14.0. It is preferable to introduce it into the reaction tank 3. If necessary, a redox couple may be added to the reaction solution 2. Examples of the redox couple include Fe 3+ / Fe 2+ and IO 3− / I − .
　反応溶液２が導入された反応槽３内には、反応溶液２中に浸漬するように酸化電極４および還元電極５が配置されている。酸化電極４は、例えば図４に示すように、支持基材４ａとのその両面に形成された酸化触媒層８とを有している。酸化電極４の支持基材４ａは、導電性を有する材料で形成される。支持基材４ａの形成材料としては、Ｃｕ、Ａｌ、Ｔｉ、Ｎｉ、Ｆｅ、Ａｇ等の金属、それら金属を少なくとも１つ含む合金、導電性樹脂等が挙げられる。支持基材４ａには、酸化触媒層８の形成性を考慮して、例えば金属板や合金板が用いられる。支持基材４ａは、金属、合金、導電性樹脂等の多孔質体で構成してもよい。 In the reaction tank 3 into which the reaction solution 2 is introduced, the oxidation electrode 4 and the reduction electrode 5 are disposed so as to be immersed in the reaction solution 2. For example, as shown in FIG. 4, the oxidation electrode 4 has an oxidation catalyst layer 8 formed on both sides of the supporting substrate 4a. The support base 4 a of the oxidation electrode 4 is formed of a material having conductivity. Examples of the forming material of the supporting base 4 a include metals such as Cu, Al, Ti, Ni, Fe, Ag, an alloy containing at least one of these metals, and a conductive resin. For the support base 4 a, for example, a metal plate or an alloy plate is used in consideration of the formability of the oxidation catalyst layer 8. The support substrate 4a may be made of a porous material such as a metal, an alloy, or a conductive resin.
　酸化触媒層８は、酸化電極４の支持基材４ａから正孔を受け取り、反応溶液２中のＨ２Ｏと反応してＨ２Ｏを酸化させる機能を有する。酸化触媒層８の構成材料は、Ｆｅ、Ｎｉ、Ｃｏ、Ｃｕ、Ｔｉ、Ｖ、Ｍｎ、Ｒｕ、およびＩｒから選ばれる少なくとも１種の金属の酸化物または水酸化物を含むことが好ましい。酸化触媒層８の具体的な構成材料としては、ＲｕＯ２、ＮｉＯ、Ｎｉ（ＯＨ）２、ＮｉＯＯＨ、Ｃｏ３Ｏ４、Ｃｏ（ＯＨ）２、ＣｏＯＯＨ、ＦｅＯ、Ｆｅ２Ｏ３、ＭｎＯ２、Ｍｎ３Ｏ４、Ｒｈ２Ｏ３、およびＩｒＯ２から選ばれる１つまたは２つ以上の複合材料が挙げられる。酸化触媒層８は、酸化電極４におけるＨ２Ｏの酸化反応を促進させるものであるため、酸化電極４の支持基材４ａによる酸化反応の反応速度が十分であれば省略することができる。 The oxidation catalyst layer 8 has a function of receiving holes from the supporting substrate 4 a of the oxidation electrode 4 and reacting with H 2 O in the reaction solution 2 to oxidize H 2 O. The constituent material of the oxidation catalyst layer 8 preferably contains an oxide or hydroxide of at least one metal selected from Fe, Ni, Co, Cu, Ti, V, Mn, Ru, and Ir. Specific materials of the oxidation catalyst layer 8 include RuO 2 , NiO, Ni (OH) 2 , NiOOH, Co 3 O 4 , Co (OH) 2 , CoOOH, FeO, Fe 2 O 3 , MnO 2 , and Mn. One or more composite materials selected from 3 O 4 , Rh 2 O 3 , and IrO 2 can be mentioned. Since the oxidation catalyst layer 8 promotes the oxidation reaction of H 2 O in the oxidation electrode 4, the oxidation catalyst layer 8 can be omitted if the reaction rate of the oxidation reaction by the supporting substrate 4 a of the oxidation electrode 4 is sufficient.
　還元電極５は、図５に示すように支持基材５ａとのその両面に形成された還元触媒層９とを有している。還元電極５の支持基材５ａは、導電性を有する材料で形成される。支持基材５ａの形成材料としては、Ｃｕ、Ａｌ、Ｔｉ、Ｎｉ、Ｆｅ、Ａｇ等の金属、それら金属を少なくとも１つ含む合金、導電性樹脂等が挙げられる。支持基材５ａには、還元触媒層９の形成性を考慮して、例えば金属板や合金板が用いられる。支持基材５ａは、金属、合金、導電性樹脂等の多孔質体で構成してもよい。 As shown in FIG. 5, the reduction electrode 5 has a support base 5a and a reduction catalyst layer 9 formed on both sides thereof. The support substrate 5 a of the reduction electrode 5 is formed of a material having conductivity. Examples of the forming material of the supporting base 5a include metals such as Cu, Al, Ti, Ni, Fe, Ag, an alloy containing at least one of these metals, and a conductive resin. For the support base 5 a, for example, a metal plate or an alloy plate is used in consideration of the formability of the reduction catalyst layer 9. The support substrate 5a may be made of a porous body of metal, alloy, conductive resin or the like.
　還元触媒層９は、還元電極５の支持基材５ａから電子を受け取り、反応溶液２中の中間物質、すなわち金属炭酸塩や金属炭酸水素塩、およびそれにより生じるＣＯ２を還元させる機能を有する。還元触媒層９の構成材料は、Ａｕ、Ａｇ、Ｚｎ、Ｃｕ、Ｈｇ、Ｃｄ、Ｐｂ、Ｔｉ、Ｉｎ、Ｓｎ等の金属、ルテニウム錯体やレニウム錯体のような金属錯体、グラフェン、ＣＮＴ（ｃａｒｂｏｎ　ｎａｎｏｔｕｂｅ）、フラーレン、ケッチェンブラック等の炭素材料等を含むことが好ましい。還元触媒層９は、還元電極５におけるＣＯ２の還元反応を促進させるものであるため、還元電極５の支持基材５ａによる還元反応の反応速度が十分であれば省略することができる。 The reduction catalyst layer 9 has a function of receiving electrons from the supporting substrate 5 a of the reduction electrode 5 and reducing an intermediate substance in the reaction solution 2, that is, metal carbonate and metal hydrogen carbonate, and CO 2 generated thereby. The constituent material of the reduction catalyst layer 9 is a metal such as Au, Ag, Zn, Cu, Hg, Cd, Pb, Ti, In, Sn, a metal complex such as a ruthenium complex or rhenium complex, graphene, CNT (carbon nanotube) It is preferable to contain carbon materials such as fullerene, ketjen black and the like. Since the reduction catalyst layer 9 promotes the reduction reaction of CO 2 in the reduction electrode 5, the reduction catalyst layer 9 can be omitted if the reaction rate of the reduction reaction by the support substrate 5 a of the reduction electrode 5 is sufficient.
　光起電力素子６は、酸化電極４および還元電極５に電気的に接続されており、これにより酸化電極４および還元電極５との間で電子や正孔をやり取りする。光起電力素子６は、光エネルギーにより電荷分離を行うものである。光起電力素子６としては、ｐｉｎ接合、ｐｎ接合、アモルファスシリコン太陽電池、多接合型太陽電池、単結晶シリコン太陽電池、多結晶シリコン太陽電池、色素増感型太陽電池、有機薄膜太陽電池等が挙げられる。光起電力素子６は、酸化電極４付近で生じるＨ２Ｏの酸化反応の標準酸化還元電位と還元電極５付近で生じるＣＯ２の還元反応の標準酸化還元電位との差より高い電位差を作り出す必要がある。すなわち、光起電力素子６はＨ２Ｏの酸化反応およびＣＯ２の還元反応を同時に生じさせるために必要なエネルギーを提供し得るものである。 The photovoltaic element 6 is electrically connected to the oxidation electrode 4 and the reduction electrode 5, thereby exchanging electrons and holes with the oxidation electrode 4 and the reduction electrode 5. The photovoltaic element 6 performs charge separation by light energy. As the photovoltaic element 6, a pin junction, a pn junction, an amorphous silicon solar cell, a multijunction solar cell, a single crystal silicon solar cell, a polycrystalline silicon solar cell, a dye-sensitized solar cell, an organic thin film solar cell, etc. It can be mentioned. The photovoltaic element 6 needs to create a potential difference higher than the difference between the standard redox potential of the oxidation reaction of H 2 O generated near the oxidation electrode 4 and the standard redox potential of the reduction reaction of CO 2 generated near the reduction electrode 5 There is. That is, the photovoltaic element 6 can provide the energy necessary for simultaneously causing the oxidation reaction of H 2 O and the reduction reaction of CO 2 .
　光起電力素子６は、図６に示すように、第１電極層１１、光起電力層３１、および第２電極層２１で構成される。図７は光起電力層３１としてシリコン太陽電池（ｐｉｎ接合）用いた光起電力素子６の具体例を示している。第２電極層２１は、Ｃｕ、Ａｌ、Ｔｉ、Ｎｉ、Ｆｅ、Ａｇ等の金属、それら金属を少なくとも１つ含むＳＵＳのような合金、導電性樹脂、ＳｉやＧｅのような半導体等により形成される。第２電極層２１には、金属板、合金板、樹脂板、半導体基板等が用いられる。 As shown in FIG. 6, the photovoltaic element 6 includes the first electrode layer 11, the photovoltaic layer 31, and the second electrode layer 21. FIG. 7 shows a specific example of the photovoltaic element 6 using a silicon solar cell (pin junction) as the photovoltaic layer 31. The second electrode layer 21 is formed of a metal such as Cu, Al, Ti, Ni, Fe, Ag, an alloy such as SUS containing at least one of these metals, a conductive resin, a semiconductor such as Si or Ge, or the like. Ru. For the second electrode layer 21, a metal plate, an alloy plate, a resin plate, a semiconductor substrate or the like is used.
　光起電力層３１は、第２電極層２１上に形成されている。光起電力層３１は、反射層３２、第１光起電力層３３、第２光起電力層３４、および第３光起電力層３５で構成されている。反射層３２は、第２電極層２１上に形成されており、下部側から順に形成された第１反射層３２ａおよび第２反射層３２ｂを有している。第１反射層３２ａには、光反射性と導電性とを有する、Ａｇ、Ａｕ、Ａｌ、Ｃｕ等の金属、それら金属を少なくとも１つ含む合金等が用いられる。第２反射層３２ｂは、光学的距離を調整して光反射性を高めるために設けられる。第２反射層３２ｂは、後述する光起電力層３１のｎ型半導体層と接合されるため、光透過性を有し、ｎ型半導体層とオーミック接触が可能な材料で形成することが好ましい。第２反射層３２ｂには、ＩＴＯ（酸化インジウムスズ）、酸化亜鉛（ＺｎＯ）、ＦＴＯ（フッ素ドープ酸化スズ)、ＡＺＯ（アルミニウムドープ酸化亜鉛）、ＡＴＯ（アンチモンドープ酸化スズ）等の透明導電性酸化物が用いられる。 The photovoltaic layer 31 is formed on the second electrode layer 21. The photovoltaic layer 31 is composed of the reflective layer 32, the first photovoltaic layer 33, the second photovoltaic layer 34, and the third photovoltaic layer 35. The reflective layer 32 is formed on the second electrode layer 21 and has a first reflective layer 32a and a second reflective layer 32b formed in order from the lower side. For the first reflective layer 32a, a metal such as Ag, Au, Al, Cu, etc., which has light reflectivity and conductivity, an alloy containing at least one of these metals, or the like is used. The second reflective layer 32 b is provided to adjust the optical distance to enhance the light reflectivity. The second reflective layer 32 b is preferably made of a material having optical transparency and capable of making ohmic contact with the n-type semiconductor layer because the second reflective layer 32 b is joined to the n-type semiconductor layer of the photovoltaic layer 31 described later. In the second reflective layer 32b, transparent conductive oxide such as ITO (indium tin oxide), zinc oxide (ZnO), FTO (fluorine-doped tin oxide), AZO (aluminum-doped zinc oxide), ATO (antimony-doped tin oxide), etc. The thing is used.
　第１光起電力層３３、第２光起電力層３４、および第３光起電力層３５は、それぞれｐｉｎ接合半導体を使用した太陽電池であり、光の吸収波長が異なる。これらを平面状に積層することによって、光起電力層３１で太陽光の幅広い波長の光を吸収することができ、太陽光のエネルギーを効率よく利用することが可能となる。光起電力層３３、３４、３５は直列に接続されているため、高い開放電圧を得ることができる。 The first photovoltaic layer 33, the second photovoltaic layer 34, and the third photovoltaic layer 35 are each a solar cell using a pin junction semiconductor, and they have different light absorption wavelengths. By laminating these layers in a planar manner, the photovoltaic layer 31 can absorb light of a wide wavelength of sunlight, and energy of the sunlight can be efficiently used. Since the photovoltaic layers 33, 34, 35 are connected in series, a high open circuit voltage can be obtained.
　第１光起電力層３３は、反射層３２上に形成されており、下部側から順に形成されたｎ型のアモルファスシリコン（ａ－Ｓｉ）層３３ａ、真性（ｉｎｔｒｉｎｓｉｃ）のアモルファスシリコンゲルマニウム（ａ－ＳｉＧｅ）層３３ｂ、およびｐ型の微結晶シリコン（ｍｃ－Ｓｉ）層３３ｃを有している。ａ－ＳｉＧｅ層３３ｂは、７００ｎｍ程度の長波長領域の光を吸収する層である。第１光起電力層３３においては、長波長領域の光エネルギーにより電荷分離が生じる。 The first photovoltaic layer 33 is formed on the reflective layer 32, and an n-type amorphous silicon (a-Si) layer 33a formed in order from the lower side, intrinsic amorphous silicon germanium (a-) And a p-type microcrystalline silicon (mc-Si) layer 33c. The a-SiGe layer 33 b is a layer that absorbs light in a long wavelength region of about 700 nm. In the first photovoltaic layer 33, charge separation occurs due to light energy in the long wavelength region.
　第２光起電力層３４は、第１光起電力層３３上に形成されており、下部側から順に形成されたｎ型のａ－Ｓｉ層３４ａ、真性（ｉｎｔｒｉｎｓｉｃ）のａ－ＳｉＧｅ層３４ｂ、およびｐ型のｍｃ－Ｓｉ層３４ｃを有している。ａ－ＳｉＧｅ層３４ｂは、６００ｎｍ程度の中間波長領域の光を吸収する層である。第２光起電力層３４においては、中間波長領域の光エネルギーにより電荷分離が生じる。 The second photovoltaic layer 34 is formed on the first photovoltaic layer 33, and an n-type a-Si layer 34a, an intrinsic a-SiGe layer 34b, which are sequentially formed from the lower side, And a p-type mc-Si layer 34c. The a-SiGe layer 34 b is a layer that absorbs light in an intermediate wavelength region of about 600 nm. In the second photovoltaic layer 34, charge separation occurs by light energy in the intermediate wavelength region.
　第３光起電力層３５は、第２光起電力層３４上に形成されており、下部側から順に形成されたｎ型のａ－Ｓｉ層３５ａ、真性（ｉｎｔｒｉｎｓｉｃ）のａ－Ｓｉ層３５ｂ、およびｐ型のｍｃ－Ｓｉ層３５ｃを有している。ａ－Ｓｉ層３５ｂは、４００ｎｍ程度の短波長領域の光を吸収する層である。第３光起電力層３５においては、短波長領域の光エネルギーにより電荷分離が生じる。 The third photovoltaic layer 35 is formed on the second photovoltaic layer 34, and is an n-type a-Si layer 35a, an intrinsic a-Si layer 35b, formed sequentially from the lower side, And a p-type mc-Si layer 35c. The a-Si layer 35b is a layer that absorbs light in a short wavelength region of about 400 nm. In the third photovoltaic layer 35, charge separation occurs due to light energy in the short wavelength region.
　第１電極層１１は、光起電力層３１のｐ型半導体層（ｐ型のｍｃ－Ｓｉ層３５ｃ）上に形成されている。第１電極層１１は、ｐ型半導体層とオーミック接触が可能な材料で形成することが好ましい。第１電極層１１には、Ａｇ、Ａｕ、Ａｌ、Ｃｕ等の金属、それら金属を少なくとも１つ含む合金、ＩＴＯ、ＺｎＯ、ＦＴＯ、ＡＺＯ、ＡＴＯ等の透明導電性酸化物等が用いられる。第１電極層１１は、例えば金属と透明導電性酸化物とが積層された構造、金属とその他の導電性材料とが複合された構造、透明導電性酸化物とその他の導電性材料とが複合された構造等を有していてもよい。 The first electrode layer 11 is formed on the p-type semiconductor layer (p-type mc-Si layer 35 c) of the photovoltaic layer 31. The first electrode layer 11 is preferably formed of a material capable of ohmic contact with the p-type semiconductor layer. For the first electrode layer 11, a metal such as Ag, Au, Al or Cu, an alloy containing at least one of these metals, a transparent conductive oxide such as ITO, ZnO, FTO, AZO, ATO or the like is used. The first electrode layer 11 has, for example, a structure in which a metal and a transparent conductive oxide are laminated, a structure in which a metal and another conductive material are composited, and a transparent conductive oxide and another conductive material are composited It may have the same structure or the like.
　図７に示す光起電力素子６において、照射光は第１電極層１１を通過して光起電力層３１に到達する。第１電極層１１は、照射光に対して光透過性を有している。光起電力層３１においては、照射光（太陽光等）の各波長領域の光のエネルギーにより電荷分離が生じる。図７に示す光起電力素子６では、正孔が第１電極層１１側に、電子が第２電極層２１側に分離することによって、光起電力層３１に起電力が発生する。従って、正孔が移動してくる第１電極層１１は酸化電極４と電気的に接続され、電子が移動してくる第２電極層２１は還元電極５と電気的に接続される。 In the photovoltaic element 6 shown in FIG. 7, the irradiation light passes through the first electrode layer 11 and reaches the photovoltaic layer 31. The first electrode layer 11 has optical transparency to the irradiation light. In the photovoltaic layer 31, charge separation occurs due to the energy of the light of each wavelength region of the irradiation light (sunlight etc.). In the photovoltaic device 6 shown in FIG. 7, an electromotive force is generated in the photovoltaic layer 31 by separating holes toward the first electrode layer 11 and electrons toward the second electrode layer 21. Therefore, the first electrode layer 11 to which holes move is electrically connected to the oxidation electrode 4, and the second electrode layer 21 to which electrons move is electrically connected to the reduction electrode 5.
　図７では３つの光起電力層の積層構造を有する光起電力層３１を例に説明したが、光起電力層３１はこれに限らない。光起電力層３１は、２つまたは４つ以上の光起電力層の積層構造を有していてもよい。積層構造の光起電力層３１に代えて、１つの光起電力層３１を用いてもよい。光起電力層３１は、ｐｉｎ接合型半導体を使用した太陽電池に限らず、ｐｎ接合型半導体を使用した太陽電池であってもよい。半導体層はＳｉやＧｅに限らず、例えばＧａＡｓ、ＧａＩｎＰ、ＡｌＧａＩｎＰ、ＣｄＴｅ、ＣｕＩｎＧａＳｅ等の化合物半導体であってもよい。なお、図７は光起電力素子６の一例を示したものであり、光起電力素子６はシリコン太陽電池に限らず、他の太陽電池を適用してもよい。光照射側はｐ型半導体層に限られるものではなく、ｎ型半導体層であってもよい。 Although FIG. 7 illustrates the photovoltaic layer 31 having a stacked structure of three photovoltaic layers as an example, the photovoltaic layer 31 is not limited to this. The photovoltaic layer 31 may have a laminated structure of two or four or more photovoltaic layers. Instead of the photovoltaic layer 31 of the laminated structure, one photovoltaic layer 31 may be used. The photovoltaic layer 31 is not limited to a solar cell using a pin junction type semiconductor, and may be a solar cell using a pn junction type semiconductor. The semiconductor layer is not limited to Si or Ge, and may be a compound semiconductor such as GaAs, GaInP, AlGaInP, CdTe, CuInGaSe or the like. In addition, FIG. 7 shows an example of the photovoltaic device 6, and the photovoltaic device 6 is not limited to a silicon solar cell, and another solar cell may be applied. The light irradiation side is not limited to the p-type semiconductor layer, and may be an n-type semiconductor layer.
　光電気化学モジュール１Ａ（１０４）の動作および酸化還元反応について、図８を参照して説明する。ここでは、中間物質の代表例として炭酸水素ナトリウム（ＮａＨＣＯ３）について説明するが、他の金属炭酸塩や金属炭酸水素塩の場合も同様である。太陽光等が光起電力素子６に照射されると、光のエネルギーにより電荷分離が生じる。電荷分離により生じた正孔は酸化電極４に移動し、電子は還元電極５に移動する。正孔が移動してくる酸化電極４付近でＨ２Ｏの酸化反応が生起される。酸化電極４に移動した正孔は、酸化反応により生じた電子と結合する。電子が移動してくる還元電極５付近で中間物質およびＣＯ２の還元反応が生起される。還元電極５に移動した電子は、還元反応に使用される。 The operation and redox reaction of the photoelectrochemical module 1A (104) will be described with reference to FIG. Here, sodium hydrogen carbonate (NaHCO 3 ) will be described as a representative example of the intermediate substance, but the same applies to other metal carbonates and metal hydrogen carbonates. When sunlight or the like is irradiated to the photovoltaic element 6, charge separation occurs due to the energy of light. Holes generated by charge separation move to the oxidation electrode 4 and electrons move to the reduction electrode 5. An oxidation reaction of H 2 O occurs in the vicinity of the oxidation electrode 4 from which the holes move. The holes transferred to the oxidation electrode 4 combine with the electrons generated by the oxidation reaction. In the vicinity of the reduction electrode 5 from which the electrons move, a reduction reaction of intermediates and CO 2 occurs. The electrons transferred to the reduction electrode 5 are used for the reduction reaction.
　酸化電極４付近においては、下記の（６）式に示す反応が生じる。反応溶液２に含まれるＨ２Ｏが酸化されて（電子を失い）、酸素（Ｏ２）と水素イオン（Ｈ＋）が生成される。
　　２Ｈ２Ｏ　→　４Ｈ＋＋Ｏ２＋４ｅ－　…（６）
　還元電極５付近においては、まず下記の（７）式や（８）式に示す反応、さらに下記の（９）式に示す反応が生じる。
　　ＮａＨＣＯ３　→　ＮａＯＨ＋ＣＯ２　…（７）
　　２ＮａＨＣＯ３　→　Ｎａ２ＣＯ３＋ＣＯ２＋Ｈ２Ｏ　…（８）
　　２ＣＯ２＋４Ｈ＋＋４ｅ－　→　２ＣＯ＋２Ｈ２Ｏ　…（９） In the vicinity of the oxidation electrode 4, a reaction represented by the following equation (6) occurs. H 2 O contained in the reaction solution 2 is oxidized (los electrons) to generate oxygen (O 2 ) and hydrogen ions (H + ).
2H 2 O → 4H + + O 2 + 4e - ... (6)
In the vicinity of the reduction electrode 5, first, reactions shown by the following equations (7) and (8) and reactions shown by the following equation (9) occur.
NaHCO 3 → NaOH + CO 2 (7)
2 NaHCO 3 → Na 2 CO 3 + CO 2 + H 2 O (8)
2CO 2 + 4H + + 4e - → 2CO + 2H 2 O ... (9)
　還元電極５付近においては、例えば中間物質としての金属炭酸塩や金属炭酸水素塩からＣＯ２が生じる。金属炭酸塩や金属炭酸水素塩の反応により生じたＣＯ２は、還元電極５付近で還元される（電子を得る）。具体的には、金属炭酸塩や金属炭酸水素塩の反応により生じたＣＯ２は、酸化電極４側で生成され、反応溶液２内を拡散して還元電極５側に移動したＨ＋と、光起電力素子６内での電荷分離により生じ、還元電極５に移動した電子と反応し、例えばＣＯとＨ２Ｏとが生成される。なお、（７）式ないし（９）式の反応は、還元電極５付近の反応の一例を示したものであり、金属炭酸塩や金属炭酸水素塩が直接還元されてＣＯとＨ２Ｏとが生成される場合もある。以下では、中間物質やＣＯ２の還元反応と記すが、これは上述したいずれかの反応を示すものである。 In the vicinity of the reduction electrode 5, for example, CO 2 is generated from a metal carbonate or metal hydrogen carbonate as an intermediate substance. The CO 2 generated by the reaction of the metal carbonate or the metal hydrogencarbonate is reduced in the vicinity of the reduction electrode 5 (to obtain electrons). Specifically, CO 2 produced by the reaction of metal carbonates and metal hydrogen carbonates are produced by the oxidation electrode 4 side, the H + which has moved to the reduction electrode 5 side by diffusing the reaction solution 2, light It is generated by the charge separation in the electromotive force element 6 and reacts with the electrons transferred to the reduction electrode 5 to generate, for example, CO and H 2 O. The reactions of the formulas (7) to (9) are an example of the reaction in the vicinity of the reduction electrode 5, and metal carbonates and metal hydrogencarbonates are directly reduced to produce CO and H 2 O. It may be generated. Hereinafter, although it is described as a reduction reaction of an intermediate substance or CO 2 , this indicates any of the reactions described above.
　還元電極５付近においては、（９）式に示すＣＯ２からＣＯへの還元反応だけでなく、ＣＯ２からギ酸（ＨＣＯＯＨ）、メタン（ＣＨ４）、エチレン（Ｃ２Ｈ４）、メタノール（ＣＨ３ＯＨ）、エタノール（Ｃ２Ｈ５ＯＨ）等の炭素化合物への還元反応を生じさせることができる。反応溶液２中のＨ２Ｏの還元反応を生じさせ、Ｈ２を発生させることもできる。還元触媒９の種類によって、生成されるＣＯ２の還元物質を変えることができる。 In the vicinity of the reduction electrode 5, not only the reduction reaction from CO 2 to CO shown in the equation (9) but also CO 2 to formic acid (HCOOH), methane (CH 4 ), ethylene (C 2 H 4 ), methanol (CH 2 ) A reduction reaction to carbon compounds such as 3 OH), ethanol (C 2 H 5 OH) and the like can be produced. It is also possible to generate a reduction reaction of H 2 O in the reaction solution 2 to generate H 2 . Depending on the type of reduction catalyst 9, the reduced substance of CO 2 produced can be changed.
　図３に示す光電気化学モジュール１Ｂ（１０４）は、反応溶液２を収容する一液型の反応槽３と、反応溶液２中に浸漬される光電気化学セル、すなわち酸化触媒層１２、酸化電極（第１電極）１１、光起電力層３１、還元電極（第２電極）２１、および還元触媒層２２の積層体１０とを備えている。光電気化学モジュール１Ｂによれば、図２に示す光電気化学モジュール１Ａに比べて構成要素の簡素化等を図ることができる。 The photoelectrochemical module 1B (104) shown in FIG. 3 includes a one-pack type reaction tank 3 containing the reaction solution 2 and a photoelectrochemical cell immersed in the reaction solution 2, that is, an oxidation catalyst layer 12, an oxidation electrode A laminate 10 of a (first electrode) 11, a photovoltaic layer 31, a reduction electrode (second electrode) 21, and a reduction catalyst layer 22 is provided. According to the photoelectrochemical module 1B, simplification of the constituent elements can be achieved as compared to the photoelectrochemical module 1A shown in FIG.
　光電気化学モジュール１Ｂ（１０４）における反応槽３は、図２に示す光電気化学モジュール１Ａの反応槽３と同様な構成（各配管等）を有している。ただし、光起電力層３１を含む光電気化学セル１０が反応槽３内に配置されるため、反応槽３は反応溶液２と化学的に反応せず、かつ光を透過する材料、すなわち２５０～１１００ｎｍの波長領域の光の吸収率が低い材料で構成される。このような反応槽３の形成材料としては、石英、白板ガラス、ポリスチロール、メタクリレート等が挙げられる。光照射用の窓部のみを上記した材料で形成し、他の部位は前述した樹脂材料で構成された反応槽３であってもよい。 The reaction tank 3 in the photoelectrochemical module 1B (104) has the same configuration (each piping, etc.) as the reaction tank 3 of the photoelectrochemical module 1A shown in FIG. However, since the photoelectrochemical cell 10 including the photovoltaic layer 31 is disposed in the reaction vessel 3, the reaction vessel 3 does not react chemically with the reaction solution 2 and is a material that transmits light, ie, 250 ̃ It is made of a material having a low absorptivity of light in the wavelength region of 1100 nm. Examples of materials for forming such a reaction vessel 3 include quartz, white sheet glass, polystyrene and methacrylate. Only the window for light irradiation may be formed of the above-described material, and the other portion may be the reaction tank 3 formed of the above-described resin material.
　光電気化学セル１０の具体的な構成としては、図７に示した光起電力素子６の第１電極（酸化電極）１１上に酸化触媒層１２を形成すると共に、第２電極（還元電極）２１上に還元触媒層２２を形成した構造が挙げられる。酸化触媒層１２および還元触媒層２２のうち、光照射側に配置される触媒層は光透過性を有する。光電気化学セル１０の構成はこれに限られるものではなく、酸化触媒層と還元触媒層とを有するｐｉｎ接合、ｐｎ接合、アモルファスシリコン太陽電池、多接合型太陽電池、単結晶シリコン太陽電池、多結晶シリコン太陽電池、色素増感型太陽電池、有機薄膜太陽電池等を適用することができる。光電気化学セル１０は、酸化電極１１付近で生じるＨ２Ｏの酸化反応の標準酸化還元電位と還元電極２１付近で生じるＣＯ２の還元反応の標準酸化還元電位との差より高い電位差を作り出す必要がある。すなわち、光電気化学セル１０は、Ｈ２Ｏの酸化反応およびＣＯ２の還元反応を同時に生じさせるために必要なエネルギーを提供し得るものである。 As a specific configuration of the photoelectrochemical cell 10, the oxidation catalyst layer 12 is formed on the first electrode (oxidation electrode) 11 of the photovoltaic element 6 shown in FIG. 7, and the second electrode (reduction electrode) The structure which formed the reduction catalyst layer 22 on 21 is mentioned. Of the oxidation catalyst layer 12 and the reduction catalyst layer 22, the catalyst layer disposed on the light irradiation side has light transparency. The configuration of the photoelectrochemical cell 10 is not limited to this, and a pin junction having an oxidation catalyst layer and a reduction catalyst layer, a pn junction, an amorphous silicon solar cell, a multijunction solar cell, a single crystal silicon solar cell, many A crystalline silicon solar cell, a dye-sensitized solar cell, an organic thin film solar cell or the like can be applied. The photoelectrochemical cell 10 needs to create a potential difference higher than the difference between the standard redox potential of the oxidation reaction of H 2 O generated near the oxidation electrode 11 and the standard redox potential of the reduction reaction of CO 2 generated near the reduction electrode 21. There is. That is, the photoelectrochemical cell 10 can provide the energy necessary for simultaneously causing the oxidation reaction of H 2 O and the reduction reaction of CO 2 .
　図３に示す光電気化学モジュール１Ｂにおいて、反応に必要なエネルギー源である光エネルギーの５０％以上は、反応槽３の外部より反応槽３、反応溶液２、および酸化触媒層１２を通って光起電力層３１に到達するように構成することが好ましい。光照射側となる酸化電極１１の構成材料としては、前述したようにＡｇ、Ａｕ、Ａｌ、Ｃｕ等の金属、それら金属を少なくとも１つ含む合金、ＩＴＯ、ＺｎＯ、ＦＴＯ、ＡＺＯ、ＡＴＯ等の透明導電性酸化物等が挙げられる。ここでは光電気化学セル１０の酸化電極１１を光照射側として説明したが、これに限られるものではなく、還元電極２１が光照射側であってもよい。酸化触媒層１２および還元触媒層２２の構成材料は、前述した通りである。酸化触媒層１２および還元触媒層２２のうちの光照射側に配置される触媒層、さらに酸化電極１１および還元電極２１のうちの光照射側に配置される電極は、光透過性を有する。 In the photoelectrochemical module 1B shown in FIG. 3, 50% or more of light energy, which is an energy source necessary for the reaction, passes through the reaction vessel 3, the reaction solution 2, and the oxidation catalyst layer 12 from the outside of the reaction vessel 3. It is preferable to be configured to reach the electromotive force layer 31. As a constituent material of the oxidation electrode 11 on the light irradiation side, as described above, metals such as Ag, Au, Al and Cu, alloys containing at least one of these metals, and transparent such as ITO, ZnO, FTO, AZO, ATO A conductive oxide etc. are mentioned. Here, although the oxidation electrode 11 of the photoelectrochemical cell 10 has been described as the light irradiation side, the present invention is not limited to this, and the reduction electrode 21 may be on the light irradiation side. The constituent materials of the oxidation catalyst layer 12 and the reduction catalyst layer 22 are as described above. The catalyst layer disposed on the light irradiation side of the oxidation catalyst layer 12 and the reduction catalyst layer 22 and the electrode disposed on the light irradiation side of the oxidation electrode 11 and the reduction electrode 21 have light transparency.
　光電気化学セル１０は、酸化触媒層１２、酸化電極１１、光起電力層３１、還元電極２１、および還元触媒層２２を単に一体化した積層体であってもよいし、そのような積層体にイオン通過孔として貫通孔を積層方向に形成したものであってもよい。酸化反応と還元反応との間でＨ＋イオン等を効率よく移動させるためには、光電気化学セル１０に貫通孔を設けることが好ましく、これにより反応効率が向上する。貫通孔は、光電気化学セル１０の一方の表面層である酸化触媒層１２から他方の表面層である還元触媒層２２まで貫通するように設けられる。ただし、図３に示す光電気化学モジュール１Ｂでは、一液型の反応槽３内に光電気化学セル１０を浸漬しているため、そのような構成自体でもＨ＋イオン等の移動効率に優れるものである。図２に示す光電気化学モジュール１Ａも同様である。Ｈ＋イオン等の拡散を促進するために、反応槽３に撹拌機等を設けてもよい。 The photoelectrochemical cell 10 may be a laminate in which the oxidation catalyst layer 12, the oxidation electrode 11, the photovoltaic layer 31, the reduction electrode 21, and the reduction catalyst layer 22 are simply integrated, or such a laminate Alternatively, through holes may be formed in the stacking direction as ion passing holes. In order to transfer H + ions and the like efficiently between the oxidation reaction and the reduction reaction, it is preferable to provide a through hole in the photoelectrochemical cell 10, whereby the reaction efficiency is improved. The through holes are provided to penetrate from the oxidation catalyst layer 12 which is one surface layer of the photoelectrochemical cell 10 to the reduction catalyst layer 22 which is the other surface layer. However, in the photoelectrochemical module 1B shown in FIG. 3, since the photoelectrochemical cell 10 is immersed in the one-pack type reaction tank 3, even such a configuration itself is excellent in the transfer efficiency of H + ions etc. It is. The same applies to the photoelectrochemical module 1A shown in FIG. A stirrer or the like may be provided in the reaction tank 3 to promote the diffusion of H + ions and the like.
　図３に示す光電気化学モジュール１Ｂ（１０４）においては、図９に示すように、図２に示す光電気化学モジュール１Ａと同様な酸化還元反応が生じる。すなわち、反応槽３に照射された太陽光等が反応槽３や反応溶液２等を介して光電気化学セル１０に到達すると、光のエネルギーにより電荷分離が生じる。電荷分離により生じた正孔は酸化電極１１に移動し、電子は還元電極２１に移動する。正孔が移動してくる酸化電極１１上に設けられた酸化触媒層１２付近において、上述した（６）式に基づいてＨ２Ｏの酸化反応が生じてＯ２とＨ＋が生成される。電子が移動してくる還元電極２１上に設けられた還元触媒層２２付近において、上述した（７）式、（８）式、（９）式等に基づいて、中間物質やＣＯ２の還元反応が生じてＣＯ等の炭素化合物が生成される。 In the photoelectrochemical module 1B (104) shown in FIG. 3, as shown in FIG. 9, the same redox reaction as the photoelectrochemical module 1A shown in FIG. 2 occurs. That is, when sunlight or the like irradiated to the reaction tank 3 reaches the photoelectrochemical cell 10 via the reaction tank 3 or the reaction solution 2 etc, charge separation occurs due to the energy of light. Holes generated by charge separation move to the oxidation electrode 11 and electrons move to the reduction electrode 21. In the vicinity of the oxidation catalyst layer 12 provided on the oxidation electrode 11 from which holes move, an oxidation reaction of H 2 O occurs based on the above-mentioned equation (6) to generate O 2 and H + . In the vicinity of the reduction catalyst layer 22 provided on the reduction electrode 21 from which the electrons move, the reduction reaction of the intermediate substance or CO 2 is performed based on the above-mentioned equations (7), (8), (9), etc. Occurs to form a carbon compound such as CO.
　Ｈ２Ｏの酸化反応により生成されるＯ２や中間物質およびＣＯ２の還元反応により生成される炭素化合物（ＣＯ等）を含むガス状生成物は、反応槽３の上部空間Ｓに集められた後、生成物送出管７ｅを介して生成物収集部１０７に送られる。生成されたＯ２や炭素化合物は、例えば発電所、鉄工所、化学工場、ごみ処理場等の燃焼炉に助燃剤を含む炭素燃料として供給してもよい。Ｏ２と炭素化合物とを分離し、個々に利用することもできる。反応が終了した反応溶液２の一部または全ては、反応溶液導出管７ｃを介してＣＯ２変換部１０２に還流される。ＣＯ２変換部１０２に還流された反応溶液２は、ＣＯ２変換部１０２で再利用される。反応後の反応溶液２の一部は、必要に応じて反応溶液排出管７ｄを介して系外に排出される。 Gaseous products containing O 2 and intermediates produced by the oxidation reaction of H 2 O and carbon compounds (such as CO) produced by the reduction reaction of CO 2 were collected in the upper space S of the reaction vessel 3 Thereafter, it is sent to the product collection unit 107 via the product delivery pipe 7e. The generated O 2 or carbon compound may be supplied, for example, as a carbon fuel containing a flame retardant to a combustion furnace such as a power plant, an iron factory, a chemical plant, or a waste disposal site. O 2 and carbon compounds can be separated and used individually. Part or all of the reaction solution 2 in which the reaction is completed is refluxed to the CO 2 converter 102 through the reaction solution discharge pipe 7 c. The reaction solution 2 was refluxed in CO 2 conversion unit 102 is reused in CO 2 conversion unit 102. A part of the reaction solution 2 after the reaction is discharged out of the system through the reaction solution discharge pipe 7d as necessary.
　実施形態の光電気化学反応システム１００においては、酸化されやすいアミン分子や高価なイオン性液体分子でＣＯ２を吸収することに代えて、ＣＯ２を金属水酸化物により金属炭酸塩および金属炭酸水素塩から選ばれる少なくとも１つの中間物質に変換し、中間物質を含む水溶液（中間物質とＨ２Ｏを含む溶液）を反応溶液として用いている。このような反応溶液を使用することによって、一液型の反応槽３を適用することが可能になると共に、電極構造やセル構造を簡素化することができる。ＣＯ２還元部１０４の装置コストの削減、小型化等を図ることが可能になる。反応溶液はアルカリ性であるため、Ｈ２Ｏの酸化反応効率を高めることができる。従って、酸化還元反応の全体としての反応効率に優れ、かつ安価で小型な光電気化学反応システム１００を提供することが可能になる。 In the photoelectrochemical reaction system 100 according to the embodiment, instead of absorbing CO 2 with amine molecules that are easily oxidized or expensive ionic liquid molecules, metal carbonate and metal hydrogen carbonate using CO 2 are metal hydroxides. An aqueous solution containing an intermediate (a solution containing an intermediate and H 2 O) is used as a reaction solution after conversion into at least one intermediate selected from salts. By using such a reaction solution, it is possible to apply the one-pack type reaction tank 3 and simplify the electrode structure and the cell structure. It is possible to reduce the device cost of the CO 2 reduction unit 104 and to miniaturize it. Since the reaction solution is alkaline, the oxidation reaction efficiency of H 2 O can be enhanced. Therefore, it is possible to provide the photoelectrochemical reaction system 100 which is excellent in reaction efficiency as a whole of the redox reaction, and is inexpensive and compact.
（第２の実施形態）
　図１０は第２の実施形態による光電気化学反応システムの構成図である。第２の実施形態の光電気化学反応システム１１０は、ＣＯ２変換部１０２、反応溶液転送部１０３、第１ＣＯ２還元部１０４Ａ、第１反応溶液調整部１０５Ａ、第１反応溶液還流部１０６Ａ、第２ＣＯ２還元部１０４Ｂ、第２反応溶液調整部１０５Ｂ、第２反応溶液還流部１０６Ｂ、および生成物収集部１０７を具備している。第２の実施形態の光電気化学反応システム１１０は、ＣＯ２発生部１００Ｘに付随して設置される。光電気化学反応システム１１０は、第１の実施形態と同様に不純物除去部１０１を備えていてもよい。 Second Embodiment
FIG. 10 is a block diagram of a photoelectrochemical reaction system according to a second embodiment. The photoelectrochemical reaction system 110 according to the second embodiment includes a CO 2 conversion unit 102, a reaction solution transfer unit 103, a first CO 2 reduction unit 104A, a first reaction solution adjustment unit 105A, a first reaction solution reflux unit 106A, a first A 2CO 2 reduction unit 104B, a second reaction solution adjustment unit 105B, a second reaction solution reflux unit 106B, and a product collection unit 107 are provided. The photoelectrochemical reaction system 110 of the second embodiment is installed in association with the CO 2 generation unit 100X. The photoelectrochemical reaction system 110 may include the impurity removing unit 101 as in the first embodiment.
　第２の実施形態の光電気化学反応システム１１０は、１系統のＣＯ２発生部１００Ｘ、ＣＯ２変換部１０２、および反応溶液転送部１０３に対して、２系統のＣＯ２還元部１０４、反応溶液調整部１０５、および反応溶液還流部１０６を備えている。それ以外については、第１の実施形態の光電気化学反応システム１００と同様な構成を備えている。各部１０１、１０２、１０３、１０４、１０５、１０６、１０７の詳細構成も、第１の実施形態の光電気化学反応システム１００と同様である。図１０では図示を省略したが、光電気化学反応システム１１０は反応溶液貯蔵部を備えていてもよい。 The photoelectrochemical reaction system 110 according to the second embodiment includes two systems of CO 2 reduction units 104 and reaction solution adjustment with respect to one system of CO 2 generation unit 100 X, CO 2 conversion unit 102, and reaction solution transfer unit 103. A portion 105 and a reaction solution reflux portion 106 are provided. The other configuration is the same as that of the photoelectrochemical reaction system 100 of the first embodiment. The detailed configuration of each part 101, 102, 103, 104, 105, 106, 107 is also the same as that of the photoelectrochemical reaction system 100 of the first embodiment. Although not shown in FIG. 10, the photoelectrochemical reaction system 110 may include a reaction solution storage unit.
　ＣＯ２変換部１０２とＣＯ２還元部１０４の処理能力によっては、ＣＯ２変換部１０２を含む系統とＣＯ２還元部１０４を含む系統の一方を複数系統とすることができる。図１０はＣＯ２変換部１０２の処理能力がＣＯ２還元部１０４の処理能力に比べて優れる場合の例である。このような場合、ＣＯ２変換部１０２を含む系統に対してＣＯ２還元部１０４を含む系統を複数とすることによって、ＣＯ２変換部１０２を効率よく運転することができる。これは光電気化学反応システム１１０全体としての処理効率の向上に寄与する。逆の場合も同様であり、ＣＯ２還元部１０４の処理能力がＣＯ２変換部１０２の処理能力に比べて優れる場合には、ＣＯ２還元部１０４を含む系統に対してＣＯ２変換部１０２を含む系統を複数とすることができる。その他の効果は第１の実施形態と同様である。 The processing capability of CO 2 conversion unit 102 and the CO 2 reduction unit 104 can be one of a plurality of systems of systems including system and CO 2 reduction unit 104 including a CO 2 conversion unit 102. FIG. 10 shows an example of the case where the processing capacity of the CO 2 conversion unit 102 is superior to the processing capacity of the CO 2 reduction unit 104. In such a case, the CO 2 conversion unit 102 can be operated efficiently by providing a plurality of systems including the CO 2 reduction unit 104 with respect to the system including the CO 2 conversion unit 102. This contributes to the improvement of the processing efficiency of the photoelectrochemical reaction system 110 as a whole. In the opposite case is also, when the processing capability of CO 2 reduction unit 104 is excellent as compared with the processing capability of CO 2 conversion unit 102, the CO 2 conversion unit 102 with respect to system including a CO 2 reduction unit 104 There can be multiple strains included. The other effects are the same as in the first embodiment.
　なお、第１および第２の実施形態の構成は、それぞれ組合せて適用することができ、また一部置き換えることも可能である。ここでは、本発明のいくつかの実施形態を説明したが、これらの実施形態は例として提示したものであり、発明の範囲を限定することは意図するものではない。これら実施形態は、その他の様々な形態で実施し得るものであり、発明の要旨を逸脱しない範囲で、種々の省略、置き換え、変更を行うことができる。これら実施形態やその変形は、発明の範囲や要旨に含まれると同時に、特許請求の範囲に記載された発明とその均等の範囲に含まれる。 The configurations of the first and second embodiments can be combined and applied, and can be partially replaced. While certain embodiments of the present invention have been described herein, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and at the same time, included in the invention described in the claims and the equivalents thereof.

Claims (14)

  1. 　金属水酸化物を含む水溶液により二酸化炭素を金属炭酸塩および金属炭酸水素塩からなる群より選ばれる少なくとも１つの中間物質に変換し、前記中間物質を含む反応溶液を生成する変換部と、
    　前記中間物質を含む反応溶液を転送する転送部と、
    　前記転送部により前記反応溶液が導入される一液型反応槽と、前記反応溶液中に浸漬され、水を酸化する酸化電極と、前記反応溶液中に浸漬され、前記中間物質を還元する還元電極と、前記酸化電極および前記還元電極と電気的に接続され、光エネルギーにより電荷分離を行う光起電力素子とを備える還元部と
    を具備する光電気化学反応システム。     A conversion unit which converts carbon dioxide into at least one intermediate substance selected from the group consisting of metal carbonates and metal hydrogencarbonates by an aqueous solution containing a metal hydroxide to produce a reaction solution containing the intermediate substance;
    A transfer unit for transferring a reaction solution containing the intermediate substance;
    A one-component reaction vessel into which the reaction solution is introduced by the transfer unit, an oxidation electrode which is immersed in the reaction solution and which oxidizes water, and a reduction electrode which is immersed in the reaction solution and which reduces the intermediate substance A photoelectrochemical reaction system, comprising: a reduction unit electrically connected to the oxidation electrode and the reduction electrode and including a photovoltaic element that performs charge separation by light energy.
  2. 　前記変換部は、前記金属水酸化物としてアルカリ金属およびアルカリ土類金属からなる群より選ばれる少なくとも１つの金属の水酸化物を含む水溶液を備える、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, wherein the conversion part comprises an aqueous solution containing a hydroxide of at least one metal selected from the group consisting of an alkali metal and an alkaline earth metal as the metal hydroxide.
  3. 　前記還元部は、前記反応溶液中に浸漬された前記酸化電極および前記還元電極と、前記一液型反応槽の外部に配置された前記光起電力素子とを備える、請求項１に記載の光電気化学反応システム。 The light according to claim 1, wherein the reduction unit includes the oxidation electrode and the reduction electrode immersed in the reaction solution, and the photovoltaic element disposed outside the one-pack reaction tank. Electrochemical reaction system.
  4. 　前記還元部は、前記酸化電極と前記光起電力素子と前記還元電極とが一体化された積層体を備え、前記積層体は前記反応溶液中に浸漬される、請求項１に記載の光電気化学反応システム。 The photoelectric conversion device according to claim 1, wherein the reduction unit includes a laminate in which the oxidation electrode, the photovoltaic device, and the reduction electrode are integrated, and the laminate is immersed in the reaction solution. Chemical reaction system.
  5. 　前記還元部は、前記酸化電極で水を酸化することにより酸素および水素イオンを生成し、前記還元電極で前記中間物質を還元することにより炭素化合物を生成する、請求項１に記載の光電気化学反応システム。 The photoelectrochemistry according to claim 1, wherein the reduction unit generates oxygen and hydrogen ions by oxidizing water at the oxidation electrode, and generates a carbon compound by reducing the intermediate substance at the reduction electrode. Reaction system.
  6. 　さらに、前記還元部で生成された酸素および気体状の前記炭素化合物の少なくとも一方を収集する収集部を具備する、請求項５に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 5, further comprising a collection unit that collects at least one of oxygen generated in the reduction unit and the gaseous carbon compound.
  7. 　前記還元部は、前記酸化電極上に設けられた酸化触媒層と、前記還元電極上に設けられた還元触媒層とを備える、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, wherein the reduction unit comprises an oxidation catalyst layer provided on the oxidation electrode, and a reduction catalyst layer provided on the reduction electrode.
  8. 　前記酸化触媒層は、Ｆｅ、Ｎｉ、Ｃｏ、Ｃｕ、Ｔｉ、Ｖ、Ｍｎ、Ｒｕ、およびＩｒからなる群より選ばれる少なくとも１つの金属の酸化物または水酸化物を含む、請求項７に記載の光電気化学反応システム。 The oxide catalyst layer according to claim 7, wherein the oxidation catalyst layer comprises an oxide or hydroxide of at least one metal selected from the group consisting of Fe, Ni, Co, Cu, Ti, V, Mn, Ru, and Ir. Photoelectrochemical reaction system.
  9. 　さらに、前記還元部で酸化還元反応を生じさせた前記反応溶液を前記変換部に還流する還流部を具備する、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, further comprising a reflux unit that refluxes the reaction solution in which the redox reaction is caused in the reduction unit to the conversion unit.
  10. 　さらに、前記変換部で生成された前記反応溶液を一旦貯蔵する貯蔵部を具備する、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, further comprising a storage unit for temporarily storing the reaction solution generated in the conversion unit.
  11. 　さらに、前記還元部に導入された前記反応溶液の濃度およびｐＨの少なくとも一方を調整する調整部を具備する、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, further comprising: a control unit configured to control at least one of the concentration and pH of the reaction solution introduced into the reduction unit.
  12. 　さらに、前記変換部に送られる前記二酸化炭素、および前記反応溶液の少なくとも一方から不純物を除去する不純物除去部を具備する、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, further comprising an impurity removing unit configured to remove an impurity from at least one of the carbon dioxide sent to the conversion unit and the reaction solution.
  13. 　前記変換部は、前記金属水酸化物を含む水溶液を収容する反応槽と、前記反応槽内に収容された前記水溶液に二酸化炭素を含むガスを吹き込むガス供給管とを備える、請求項１に記載の光電気化学反応システム。 The said conversion part is provided with the reaction tank containing the aqueous solution containing the said metal hydroxide, and the gas supply pipe which blows the gas containing a carbon dioxide into the said aqueous solution stored in the said reaction tank. Photoelectrochemical reaction system.
  14. 　前記転送部は、複数の前記還元部に接続されている、請求項１に記載の光電気化学反応システム。 The photoelectrochemical reaction system according to claim 1, wherein the transfer unit is connected to a plurality of the reduction units.
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