JP6640686B2 - Electrochemical reactor - Google Patents

Description

  The invention of an embodiment relates to an electrochemical reaction device.

  2. Description of the Related Art In recent years, from the viewpoint of energy and environmental issues, development of an artificial photosynthesis technology for electrochemically converting sunlight into chemical substances by imitating photosynthesis of plants has been promoted. For example, energy can be sufficiently obtained by converting sunlight into a chemical substance and transporting it to a distant place in a land where the utility value is low such as a desert and is not used for plant production. When converting sunlight into chemical substances and storing it in cylinders or tanks, energy storage costs can be reduced and storage losses are lower than when converting sunlight into electricity and storing it in storage batteries. There is an advantage.

Examples of an electrochemical reaction device that electrochemically converts sunlight into a chemical substance include, for example, an electrode having a reduction catalyst for reducing carbon dioxide (carbon dioxide) and an electrode having an oxidation catalyst for oxidizing water (H ₂ O). There is known a two-electrode type device in which these electrodes are immersed in water in which carbon dioxide is dissolved. At this time, each electrode is electrically connected via an electric wire or the like. In an electrode having an oxidation catalyst, H ₂ O is oxidized by light energy to obtain oxygen (１ ／ O ₂ ) and to obtain a potential. In an electrode having a reduction catalyst, carbon dioxide is reduced by obtaining a potential from an electrode that causes an oxidation reaction to generate formic acid (HCOOH) and the like. As described above, in the two-electrode system, since the reduction potential of carbon dioxide is obtained by two-step excitation, the conversion efficiency from sunlight to chemical energy is low.

JP 2011-094194 A

S. Y. Reeece, et. al. , Science. vol. 334. pp. 645 (2011)

  A problem to be solved by the invention of the embodiment is to increase the generation efficiency of reduction products in an electrochemical reaction device.

The electrochemical reaction device according to the embodiment has a first liquid phase containing water and a second liquid phase containing an organic solvent, and at least one of the first liquid phase and the second liquid phase is covered. An electrolytic solution tank including a first storage portion for storing a first electrolyte solution further containing a reducing substance, and a second storage portion for storing a second electrolyte solution containing a substance to be oxidized; , A reduction electrode provided in the first storage section, and an oxidation electrode provided in the second storage section. A reduction electrode is provided for contacting the first liquid phase and includes a first region including the first reduction catalyst, and a second region provided for contacting the second liquid phase and including a second reduction catalyst. And a region.

It is a schematic diagram which shows the example of a structure of an electrochemical reaction apparatus. It is a schematic diagram which shows the example of a structure of a photoelectric conversion cell. It is a schematic diagram which shows the other example of a structure of an electrochemical reaction device. It is a schematic diagram which shows the other example of a structure of an electrochemical reaction device. It is a schematic diagram which shows the other example of a structure of an electrochemical reaction device. It is a schematic diagram which shows the other example of a structure of an electrochemical reaction device.

  Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic and, for example, dimensions such as thickness and width of each component may be different from actual dimensions of the component. In the embodiments, substantially the same components are denoted by the same reference numerals, and description thereof may be omitted. In this specification, the term “connect” is not limited to the case of direct connection, but may include the meaning of indirect connection.

  FIG. 1 is a schematic diagram illustrating a configuration example of an electrochemical reaction device. As shown in FIG. 1, the electrochemical reaction device includes an electrolyte tank 11, a reduction electrode 31, an oxidation electrode 32, a photoelectric converter 33, an ion exchange membrane 4, and channels 50a to 50c. I do.

  The electrolytic solution tank 11 has a storage section 111 and a storage section 112. The shape of the electrolytic solution tank 11 is not particularly limited as long as it is a three-dimensional shape having a cavity serving as a storage portion. As a material of the electrolytic solution tank 11, for example, a material that transmits light is used.

  The storage section 111 stores the electrolytic solution 21 containing the substance to be reduced. The substance to be reduced is a substance that is reduced by a reduction reaction. The substance to be reduced includes, for example, carbon dioxide. Further, the substance to be reduced may include hydrogen ions. By changing the amount of water contained in the electrolytic solution 21 and the components of the electrolytic solution, the reactivity can be changed, and the selectivity of the non-reducing substance and the ratio of the generated chemical substance can be changed.

  Further, the electrolytic solution 21 has a liquid phase 21a containing water and a liquid phase 21b containing an organic solvent and in contact with the liquid phase 21a. At least one liquid phase of the liquid phase 21a and the liquid phase 21b contains the substance to be reduced, and is in contact with the reduction electrode 31.

  The storage section 112 stores the electrolytic solution 22 containing the substance to be oxidized. The substance to be oxidized is a substance that is oxidized by an oxidation reaction. The substance to be oxidized is, for example, water, an organic substance such as alcohol or amine, or an inorganic oxide such as iron oxide. The same substance as the electrolyte 21 may be contained in the electrolyte 22. In this case, the electrolyte 21 and the electrolyte 22 may be regarded as one electrolyte.

  The pH of the electrolytic solution 22 is preferably higher than the pH of the electrolytic solution 21. This facilitates the movement of hydrogen ions, hydroxide ions, and the like. Further, the oxidation-reduction reaction can be effectively advanced by the liquid junction potential difference caused by the pH difference.

As the liquid phase 21a of the electrolytic solution 21, for example, an aqueous solution containing LiHCO ₃ , NaHCO ₃ , KHCO ₃ , CsHCO _3, phosphoric acid, boric acid, or the like may be used. The liquid phase 21a may contain alcohols such as methanol, ethanol, and acetone. The liquid phase 21a may be the same as the electrolytic solution 22. However, it is preferable that the absorption amount of carbon dioxide in the electrolytic solution containing carbon dioxide is high. Therefore, a different solution from the electrolyte containing water may be used as the electrolyte containing carbon dioxide. The electrolyte containing carbon dioxide is preferably an electrolyte containing a carbon dioxide absorbent that reduces the reduction potential of carbon dioxide, has high ion conductivity, and absorbs carbon dioxide.

As the liquid phase 21a, for example, an ionic liquid or an aqueous solution thereof composed of a salt of a cation such as an imidazolium ion or a pyridinium ion and an anion such as BF ₄ ⁻ or PF ₆ ⁻ in a liquid state in a wide temperature range is used. Can be used. Further, examples of the other electrolyte include an amine solution such as ethanolamine, imidazole, and pyridine or an aqueous solution thereof. Examples of the amine include a primary amine, a secondary amine, and a tertiary amine. These electrolytes may have high ion conductivity, have the property of absorbing carbon dioxide, and have the property of reducing reduction energy.

  Examples of the primary amine include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine and the like. The hydrocarbon of the amine may be substituted by an alcohol, halogen, or the like. Examples of amines in which hydrocarbons are substituted include methanolamine, ethanolamine, and chloromethylamine. Further, an unsaturated bond may be present. These hydrocarbons are the same for secondary amines and tertiary amines.

  Examples of the secondary amine include dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, dipropanolamine and the like. The substituted hydrocarbons can be different. This is the same for tertiary amines. For example, examples of different hydrocarbons include methylethylamine and methylpropylamine.

  Examples of the tertiary amine include trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, tripropanolamine, tributanolamine, triexanolamine, methyldiethylamine, and methyldipropylamine. Is mentioned.

  Examples of cations of the ionic liquid include 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl-3-methylimidazol ion, 1-methyl-3-pentylimidazolium ion , 1-hexyl-3-methylimidazolium ion and the like.

  The 2-position of the imidazolium ion may be substituted. Examples of the cation substituted at the 2-position of the imidazolium ion include 1-ethyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, and 1-butyl-2,3-dimethyl. Imidazolium ion, 1,2-dimethyl-3-pentylimidazolium ion, 1-hexyl-2,3-dimethylimidazolium ion and the like.

Examples of the pyridinium ion include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, hexylpyridinium and the like. Both the imidazolium ion and the pyridinium ion may be substituted with an alkyl group and may have an unsaturated bond. For example, an organic compound represented by the formula: [PEG _m (mim) ₂ ] (where PEG is polyethylene glycol, mim is methyl imidazolium, and m is a number of 10 or more and 10,000 or less) Can be used.

Examples of the anion include fluoride ion, chloride ion, bromide ion, iodide ion, BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ COO ⁻ , CF ₃ SO ₃ ⁻ , NO ₃ ⁻ , SCN ⁻ , and (CF ₃ SO _2). ) ₃ C ⁻ , bis (trifluoromethoxysulfonyl) imide, bis (perfluoroethylsulfonyl) imide, bistrifluoromethanesulfonylimide and the like. Zwitterions in which the cation and the anion of the ionic liquid are connected by a hydrocarbon may be used. Note that a buffer solution such as a potassium phosphate solution may be supplied to the storage units 111 and 112.

  Examples of the organic solvent of the liquid phase 21b include toluene, benzene, octane, octanol, dimethylformamide, hexane, xylene, chlorobenzene, ethyl acetate, chloroethylene, dichloroethylene, acetic acid, formalin, formic acid, acetaldehyde, tetrahydrofuran, cyclohexane, methanol, and ethanol. , Ethylene glycol, glyoxal, acetonitrile, methyl acetate, ethyl methyl ketone, dimethyl ether, acetone, diethyl ether, chloroform, methylene chloride, dimethyl sulfoxide (DMSO), dimethyl disulfide (DMDS), and hexadecane as an aprotic solvent. Methylphosphoric triamide (Hexamethylph) sphoric Triamide: HMPA), N, N'- dimethylpropyleneurea (N, N'-dimethylpropyleneurea: DMPU) and the like, can be used these alone or a mixture. When a hydrophilic organic solvent is used, it is preferably used in combination with, for example, another hydrophobic organic solvent so that the liquid phase 21b and the liquid phase 21a are separated. When the liquid phase 21b contains a substance to be reduced, the liquid phase 21b may contain an electrolytic solution applicable to the liquid phase 21a in addition to the organic solvent. The organic solvent may include, for example, an ionic liquid.

As the electrolytic solution 22, for example, an aqueous solution containing an arbitrary electrolyte can be used. Examples of the aqueous solution containing an electrolyte include phosphate ions (PO ₄ ²⁻ ), borate ions (BO ₃ ³⁻ ), sodium ions (Na ⁺ ), potassium ions (K ⁺ ), calcium ions (Ca ²⁺ ), and lithium ions. An aqueous solution containing ions (Li ⁺ ), cesium ions (Cs ⁺ ), magnesium ions (Mg ²⁺ ), chloride ions (Cl ⁻ ), hydrogen carbonate ions (HCO ₃ ⁻ ), and the like can be given. When the electrolytic solution 22 contains carbon dioxide, an electrolytic solution applicable to the liquid phase 21a may be used.

The reduction electrode 31 is immersed in the electrolyte 21 so as to be in contact with at least one of the liquid phases 21a and 21b. The reduction electrode 31 shown in FIG. 1 is in contact with the liquid phase 21a. The reduction electrode 31 includes, for example, a reduction catalyst for a substance to be reduced. It is preferable that at least one of the reduction catalysts is in contact with the liquid phase. The compound generated by the reduction reaction varies depending on the type of the reduction catalyst and the like. Compounds generated by the reduction reaction include, for example, carbon monoxide (CO), formic acid (HCOOH), methane (CH ₄ ), methanol (CH ₃ OH), ethane (C ₂ H ₆ ), and ethylene (C ₂ H ₄ ). , Ethanol (C ₂ H ₅ OH), formaldehyde (HCHO), carbon compounds such as ethylene glycol, or hydrogen.

  The reduction electrode 31 may have, for example, a thin film, lattice, particle, or wire structure. It is not always necessary to provide the reduction electrode 31 with a reduction catalyst. A reduction catalyst provided other than the reduction electrode 31 may be electrically connected to the reduction electrode 31.

  Oxidation electrode 32 is immersed in electrolyte solution 22. The oxidation electrode 32 includes, for example, an oxidation catalyst for a substance to be oxidized. The compound generated by the oxidation reaction differs depending on the type of the oxidation catalyst and the like. The compound generated by the oxidation reaction is, for example, a hydrogen ion.

  The oxidation electrode 32 may have, for example, a thin film, lattice, particle, or wire structure. It is not always necessary to provide the oxidation electrode 32 with an oxidation catalyst. An oxidation catalyst provided other than the oxidation electrode 32 may be electrically connected to the oxidation electrode 32.

  When the oxidation electrode 32 is laminated on the photoelectric conversion body 33 and immersed in the electrolytic solution 22 and the oxidation / reduction reaction is performed by irradiating the photoelectric conversion body 33 with light through the oxidation electrode 32, 32 needs to have translucency. The light transmittance of the oxidation electrode 32 is, for example, preferably at least 10% or more, more preferably 30% or more, of the irradiation amount of the light applied to the oxidation electrode 32. The present invention is not limited to this. For example, the photoelectric conversion body 33 may be irradiated with light via the reduction electrode 31.

  The ion diffusion efficiency increases as the distance between the reduction electrode 31 and the oxidation electrode 32 decreases. For this reason, it is preferable that the reduction electrode 31 faces the oxidation electrode 32. At this time, it is preferable that the electrode on the light receiving side is arranged perpendicular to the incident light, and the electrode on the side opposite to the light receiving side is arranged parallel to the incident light.

  The photoelectric conversion body 33 has a surface 331 electrically connected to the reduction electrode 31 and a surface 332 electrically connected to the oxidation electrode 32. Note that the photoelectric converter 33 does not necessarily have to be provided, and another power source may be connected to the oxidation electrode 32 and the reduction electrode 31. The power supply is not limited to a photoelectric conversion element including a photoelectric conversion body, and may use a system power supply, a power supply device such as a storage battery, or renewable energy such as wind power, hydraulic power, and geothermal power. The reduction electrode 31, the oxidation electrode 32, and the photoelectric conversion body 33 are stacked. The reduction electrode 31 is in contact with the surface 331, and the oxidation electrode 32 is in contact with the surface 332. At this time, the stacked body including the reduction electrode 31, the oxidation electrode 32, and the photoelectric conversion body 33 is also referred to as a photoelectric conversion cell. The photoelectric conversion cell penetrates the ion exchange membrane 4 and is immersed in the electrolytic solution 21 and the electrolytic solution 22.

  The photoelectric conversion body 33 has a function of performing charge separation by the energy of light such as irradiated sunlight. The electrons generated by the charge separation move to the reduction electrode side, and the holes move to the oxidation electrode side. Thereby, the photoelectric converter 33 can generate an electromotive force. As the photoelectric converter 33, for example, a pn junction type or pin junction type photoelectric converter can be used. The photoelectric conversion body 33 may be fixed to, for example, the electrolytic solution tank 11. Note that the photoelectric converter 33 may be formed by stacking a plurality of photoelectric converters. The size of the reduction electrode 31, the oxidation electrode 32, and the photoelectric conversion body 33 may be different from each other.

  The ion exchange membrane 4 is provided so as to separate the storage unit 111 from the storage unit 112. The ion exchange membrane 4 can pass specific ions. Examples of the ion-exchange membrane 4 include Neosepta (registered trademark) of Astom, Selemion (registered trademark) of Asahi Glass, Aciplex (registered trademark), Fumasep (registered trademark) of Fumatech, fumamem (registered trademark), and DuPont (registered trademark). Nafion (registered trademark), a fluororesin obtained by sulfonating and polymerizing tetrafluoroethylene, lewabrane (registered trademark) of LANXESS, IONSEP (registered trademark) of IONTECH, Mustang (registered trademark) of PALL, ralex of mega (Registered trademark), Gore-Tex (registered trademark) of Gore-Tex and the like can be used. Further, an ion exchange membrane may be formed using a membrane having a basic skeleton of a hydrocarbon or a membrane having an amine group in anion exchange.

  When the ion exchange membrane 4 is, for example, a proton exchange membrane, hydrogen ions can move to the electrolyte 21 side. By using an ion exchange membrane which is a solid polymer membrane such as Nafion, the transfer efficiency of ions can be increased. Note that the ion exchange membrane 4 does not necessarily have to be provided, and a salt bridge such as agar may be provided instead of the ion exchange membrane 4.

  The flow path 50a connects between the liquid phase 21a and the outside of the electrolytic solution tank 11. The flow path 50a is a flow path for collecting a product by a reduction reaction included in the liquid phase 21a. The shape of the flow path 50a is not particularly limited as long as the shape has a cavity such as a pipe. Separate recovery channels may be provided for each type of product. Alternatively, the product may be extracted and recovered by connecting the flow path 50a to a still or by providing a separation membrane or the like in the flow path 50a. Further, a flow path for feeding or discharging the liquid phase 21b may be provided separately from the flow path 50b. Further, a flow path for feeding or discharging the liquid phase 21a may be provided separately from the flow path 50a.

  The flow path 50b connects between the liquid phase 21b and the outside of the electrolytic solution tank 11. The flow path 50b is a flow path for collecting a product of the reduction reaction contained in the liquid phase 21b. The shape of the flow path 50b is not particularly limited as long as it has a cavity such as a pipe. Alternatively, the product may be extracted and recovered by connecting the flow path 50b to a still or by providing a separation membrane or the like in the flow path 50b. Further, a flow path for feeding or discharging the liquid phase 21b may be provided separately from the flow path 50b.

  The flow path 50c connects between the electrolytic solution 22 and the outside of the electrolytic solution tank 11. The flow path 50c is a flow path for collecting a product by an oxidation reaction contained in the electrolytic solution 22. Alternatively, the product may be extracted and recovered by connecting the flow path 50c to a still or by providing a separation membrane or the like in the flow path 50c. Further, a flow path for feeding or discharging the liquid phase 21b may be provided separately from the flow path 50b. The shape of the flow path 50c is not particularly limited as long as the shape has a cavity such as a pipe.

  Next, an operation example of the electrochemical reaction device shown in FIG. 1 will be described. When light enters the photoelectric converter 33, the photoelectric converter 33 generates photoexcited electrons and holes. At this time, photo-excited electrons gather at the reduction electrode 31 and holes gather at the oxidation electrode 32. Thereby, an electromotive force is generated in the photoelectric conversion body 33. The light is preferably sunlight, but light such as a light emitting diode or an organic EL may be incident on the photoelectric converter 33.

A case where carbon monoxide is generated using an electrolyte containing water and carbon dioxide as the liquid phase 21a of the electrolyte 21 and the electrolyte 22 will be described. Around the oxidation electrode 32, an oxidation reaction of water occurs as shown in the following formula (1), losing electrons, and generating oxygen and hydrogen ions. At least one of the generated hydrogen ions moves to the storage unit 111 via the ion exchange membrane 4.
^{_{2H 2 O → 4H + + O}} 2 + 4e - ··· (1)

Around the reduction electrode 31, a reduction reaction of carbon dioxide occurs as shown in the following formula (2), and hydrogen ions react with carbon dioxide while receiving electrons to generate carbon monoxide and water. In addition, hydrogen is generated when the hydrogen ions receive electrons as in the following equation (3). At this time, hydrogen may be generated simultaneously with carbon monoxide.
CO ₂ + 2H ⁺ + 2e ⁻ → CO + H ₂ O (2)
2H ⁺ + 2e ⁻ → H ₂ (3)

  The photoelectric conversion body 33 needs to have an open voltage equal to or higher than the potential difference between the standard oxidation-reduction potential of the oxidation reaction and the standard oxidation-reduction potential of the reduction reaction. For example, the standard oxidation-reduction potential of the oxidation reaction in the formula (1) is 1.23 [V]. The standard oxidation-reduction potential of the reduction reaction in the formula (2) is 0.03 [V]. The standard oxidation-reduction potential of the reduction reaction in the formula (3) is 0V. At this time, in the reaction between the equations (1) and (2), the open circuit voltage needs to be 1.26 [V] or more.

  It is preferable that the open-circuit voltage of the photoelectric conversion body 33 be higher than the potential difference between the standard oxidation-reduction potential of the oxidation reaction and the standard oxidation-reduction potential of the reduction reaction by at least the value of the overvoltage. For example, the overvoltages of the oxidation reaction in the formula (1) and the reduction reaction in the formula (2) are each 0.2 [V]. In the reaction between the equations (1) and (2), the open circuit voltage is preferably set to 1.66 [V] or more. Similarly, in the reaction between the formulas (1) and (3), the open circuit voltage is preferably set to 1.63 [V] or more.

  The reduction reaction of hydrogen ions and carbon dioxide is a reaction that consumes hydrogen ions. For this reason, when the amount of hydrogen ions is small, the efficiency of the reduction reaction is reduced. Therefore, it is preferable that the concentration of hydrogen ions be made different between the electrolytic solution 21 and the electrolytic solution 22 so that the hydrogen ions can be easily moved by the concentration difference. The concentration of the anion (for example, hydroxide ion or the like) may be different between the electrolytic solution 21 and the electrolytic solution 22. When a cation exchange membrane is used as an ion exchange membrane, cations are moved, and when an anion exchange membrane is used as an ion exchange membrane, anions are moved. Further, in order to increase the concentration difference of hydrogen ions, an inert gas (nitrogen, argon, or the like) containing no carbon dioxide is directly blown into the electrolytic solution 22, for example, to release the carbon dioxide contained in the electrolytic solution 22 so as to release the electrolytic solution. A method of lowering the hydrogen ion concentration in 22 is considered.

  The reaction efficiency of equation (2) changes depending on the concentration of carbon dioxide dissolved in the electrolyte. The reaction efficiency increases as the carbon dioxide concentration increases, and decreases as the carbon dioxide concentration decreases. The reaction efficiency of equation (2) also changes depending on the concentration of hydrogen carbonate ions and carbonate ions. However, since the hydrogen carbonate ion concentration and the carbonate ion concentration can be adjusted by increasing the concentration of the electrolytic solution and adjusting the pH, the concentration is easier to adjust than the carbon dioxide concentration. In addition, even if the ion exchange membrane 4 is provided between the oxidation electrode and the reduction electrode, carbon dioxide gas, carbonate ion, hydrogen carbonate ion and the like pass through the ion exchange membrane 4, so that it is impossible to completely prevent the performance from being deteriorated. Have difficulty. As a method of increasing the carbon dioxide concentration, for example, a method of directly blowing carbon dioxide into the electrolytic solution 21 can be considered. At this time, by providing a porous layer in the electrolytic solution 21 and supplying carbon dioxide through the porous layer, the concentration of carbon dioxide in the electrolytic solution 21 can be increased.

  In the electrochemical reaction device of the present embodiment, the electrolytic solution 21 has a liquid phase 21a containing water and a liquid phase 21b containing an organic solvent. When the liquid phase 21a comes into contact with the reduction electrode 31, the product generated by the reduction reaction dissolves in the liquid phase 21a. The product in the liquid phase 21a can move to the liquid phase 21b according to the distribution coefficient of the product between the liquid phase 21a and the liquid phase 21b. The value of the partition coefficient is determined, for example, by the type of the solvent contained in the liquid phase 21a and the liquid phase 21b and the type of the product in the solvent.

  When the organic solvent of the liquid phase 21b is, for example, xylene, and the product of the reduction reaction is, for example, ethanol, ethanol has a high hydrophilicity and a high affinity between ethanol and xylene. Dissolve in xylene. At this time, the ratio of the ethanol concentration in the liquid phase 21b to the ethanol concentration in the liquid phase 21a is a substantially constant value regardless of the amount of ethanol. The above concentration ratio is called a distribution coefficient.

  When the product is ethanol, by using a mixed solvent such as m-xylene and hexanol, the product can be easily extracted from the liquid phase 21a by distillation, membrane separation, or the like. As described above, by selecting a solvent that can be easily extracted according to the product to be extracted, the product can be easily moved from the liquid phase 21a to the liquid phase 21b. Therefore, the concentration of the product contained in the liquid phase 21b can be increased. For example, the reduction product concentration per unit volume of the liquid phase 21b can be higher than the reduction product concentration per unit volume of the liquid phase 21a. Therefore, the generation efficiency of the reduction product can be increased. Further, compared to the case where the liquid phase 21b is not provided, the energy required for separating the product by distillation, membrane separation, or the like can be reduced. Even when the product of the reduction reaction is hydrophilic and the product concentration in the liquid phase 21b is low, distillation or membrane separation containing a low-concentration product may occur due to differences in the boiling point, molecular size, and the like. Thus, the energy required for separating the product can be reduced.

  FIG. 2 is a schematic cross-sectional view illustrating a structural example of the photoelectric conversion cell. The photoelectric conversion cell shown in FIG. 2 includes a conductive substrate 30, a reduction electrode 31, an oxidation electrode 32, a photoelectric converter 33, a light reflector 34, a metal oxide body 35, and a metal oxide body 36. Prepare.

  The conductive substrate 30 is provided so as to be in contact with the reduction electrode 31. Note that the conductive substrate 30 may be regarded as a part of the reduction electrode. Examples of the conductive substrate 30 include a substrate including at least one or more of Cu, Al, Ti, Ni, Fe, and Ag. For example, a stainless steel substrate including stainless steel such as SUS may be used. The present invention is not limited to this, and the conductive substrate 30 may be formed using a conductive resin. Further, the conductive substrate 30 may be formed using a semiconductor substrate such as Si or Ge. Further, a resin film or the like may be used as the conductive substrate 30. For example, a film applicable to the ion exchange film 4 may be used as the conductive substrate 30.

  The conductive substrate 30 has a function as a support. The conductive substrate 30 may be provided so as to separate the housing 111 from the housing 112. By providing the conductive substrate 30, the mechanical strength of the photoelectric conversion cell can be improved. Further, the conductive substrate 30 may be regarded as a part of the reduction electrode 31. Further, the conductive substrate 30 need not always be provided.

  The reduction electrode 31 preferably contains a reduction catalyst. The reduction electrode 31 may include both a conductive material and a reduction catalyst. Examples of the reduction catalyst include a material that reduces activation energy for reducing hydrogen ions and carbon dioxide. In other words, a material that reduces an overvoltage when generating hydrogen or a carbon compound by a reduction reaction of hydrogen ions or carbon dioxide can be used. For example, a metal material or a carbon material can be used. As the metal material, for example, in the case of hydrogen, a metal such as platinum or nickel, or an alloy containing the metal can be used. In the reduction reaction of carbon dioxide, a metal such as gold, aluminum, copper, silver, platinum, palladium, or nickel, or an alloy containing the metal can be used. As the carbon material, for example, graphene, carbon nanotube (Carbon Nanotube: CNT), fullerene, Ketjen black, or the like can be used. Note that the present invention is not limited thereto, and a metal complex such as a Ru complex or a Re complex, or an organic molecule having an imidazole skeleton or a pyridine skeleton may be used as the reduction catalyst. Further, a plurality of materials may be mixed.

  The oxidation electrode 32 preferably contains an oxidation catalyst. Oxidation electrode 32 may include both a conductive material and a reduction catalyst. Examples of the oxidation catalyst include a material that reduces activation energy for oxidizing water. In other words, a material that reduces an overvoltage when oxygen and hydrogen ions are generated by an oxidation reaction of water is given. For example, iridium, iron, platinum, cobalt, manganese, or the like can be given. As the oxidation catalyst, a binary metal oxide, a ternary metal oxide, a quaternary metal oxide, or the like can be used. Examples of the binary metal oxide include manganese oxide (Mn-O), iridium oxide (Ir-O), nickel oxide (Ni-O), cobalt oxide (Co-O), iron oxide (Fe-O), Examples include tin oxide (Sn-O), indium oxide (In-O), and ruthenium oxide (Ru-O). Examples of the ternary metal oxide include Ni-Co-O, La-Co-O, Ni-La-O, and Sr-Fe-O. Examples of the quaternary metal oxide include Pb-Ru-Ir-O and La-Sr-Co-O. Note that the invention is not limited thereto, and a metal complex such as a Ru complex or an Fe complex can be used as the oxidation catalyst. Further, a plurality of materials may be mixed.

  At least one of the reduction electrode 31 and the oxidation electrode 32 may have a porous structure. Examples of the material applicable to the electrode having a porous structure include, in addition to the above materials, carbon black such as Ketjen black and Vulcan XC-72, activated carbon, and fine metal powder. By having a porous structure, the area of the active surface that contributes to the oxidation-reduction reaction can be increased, so that the conversion efficiency can be increased.

  The porous structure preferably has a pore distribution of 5 nm or more and 100 nm or less. By having the above pore distribution, the catalytic activity can be enhanced. Further, the porous structure preferably has a plurality of pore distribution peaks. As a result, it is possible to simultaneously increase the surface area, improve the diffusivity of ions and reactants, and achieve high conductivity. For example, a reduction catalyst layer containing fine particles of metal or alloy applicable to the above reduction catalyst (fine particle reduction catalyst) of 100 nm or less is stacked on a conductive layer of the above material having a pore distribution of 5 μm or more and 10 μm or less to reduce The electrode 31 may be configured. At this time, the fine particles may have a porous structure, but may not necessarily have a porous structure from the viewpoint of conductivity and the relationship between reaction sites and substance diffusion. Further, the fine particles may be supported on another material.

  The reduction electrode 31 may have a laminated structure of a porous conductive layer and a porous catalyst layer containing a reduction catalyst. For example, a mixture of conductive particles such as Nafion and Ketjen black can be used as the porous conductive layer, and a gold catalyst can be used as the porous catalyst layer. Further, by forming irregularities of 5 μm or less on the surface of the porous catalyst layer, the reaction efficiency can be increased. Furthermore, the reduction electrode 31 having a nanoparticle structure can be formed by oxidizing the surface of the porous catalyst layer by applying a high frequency and then electrochemically reducing the surface. Other than gold, metals such as copper, palladium, silver, zinc, tin, bismuth, and lead are preferred. Further, the porous conductive layer may further have a laminated structure in which each layer has a different pore size. With the laminated structure having different pore sizes, it is possible to improve the efficiency by adjusting the difference in the reaction due to, for example, the difference in the concentration of the reaction product near the electrode or the difference in the pH depending on the pore size.

  When an electrode reaction with a low current density is performed using irradiation energy of relatively low light, there are a wide range of options for a catalyst material. Therefore, it is easy to carry out the reaction using, for example, a ubiquitous metal, and it is relatively easy to obtain the selectivity of the reaction. On the other hand, when the photoelectric conversion body 33 is not provided in the electrolytic solution tank 11 and the photoelectric conversion body 33 is electrically connected to at least one of the reduction electrode 31 and the oxidation electrode 32 by wiring or the like, the size of the electrolyte solution bath is reduced. For this reason, the electrode area is generally small, and the reaction may be performed at a high current density. In this case, it is preferable to use a noble metal as the catalyst.

  The photoelectric conversion body 33 has a stacked structure including a photoelectric conversion layer 33x, a photoelectric conversion layer 33y, and a photoelectric conversion layer 33z. The number of stacked photoelectric conversion layers is not limited to FIG.

  The photoelectric conversion layer 33x includes, for example, an n-type semiconductor layer 331n including n-type amorphous silicon, an i-type semiconductor layer 331i including intrinsic amorphous silicon germanium, and a p-type semiconductor layer including p-type microcrystalline silicon. 331p. The i-type semiconductor layer 331i is a layer that absorbs light in a short wavelength region including, for example, 400 nm. Therefore, in the photoelectric conversion layer 33x, charge separation occurs due to light energy in the short wavelength region.

  The photoelectric conversion layer 33y includes, for example, an n-type semiconductor layer 332n including n-type amorphous silicon, an i-type semiconductor layer 332i including intrinsic amorphous silicon germanium, and a p-type semiconductor layer 332p including p-type microcrystalline silicon. Having. The i-type semiconductor layer 332i is a layer that absorbs light in an intermediate wavelength region including, for example, 600 nm. Therefore, in the photoelectric conversion layer 33y, charge separation occurs due to light energy in the intermediate wavelength region.

  The photoelectric conversion layer 33z includes, for example, an n-type semiconductor layer 333n including n-type amorphous silicon, an i-type semiconductor layer 333i including intrinsic amorphous silicon, and a p-type semiconductor layer 333p including p-type microcrystalline silicon. Have. The i-type semiconductor layer 333i is a layer that absorbs light in a long wavelength region including, for example, 700 nm. Therefore, in the photoelectric conversion layer 33z, charge separation occurs due to light energy in a long wavelength region.

The p-type semiconductor layer or the n-type semiconductor layer can be formed, for example, by adding an element serving as a donor or an acceptor to a semiconductor material. Note that in the photoelectric conversion layer, a semiconductor layer containing silicon, germanium, or the like is used as a semiconductor layer; however, the present invention is not limited to this, and a compound semiconductor layer or the like can be used, for example. As the compound semiconductor layer, for example, a semiconductor layer containing GaAs, GaInP, AlGaInP, CdTe, CuInGaSe, or the like can be used. Further, a layer containing a material such as TiO ₂ or WO ₃ may be used as long as photoelectric conversion is possible. Further, each semiconductor layer may be monocrystalline, polycrystalline, or amorphous. Further, a zinc oxide layer may be provided on the photoelectric conversion layer.

  The light reflector 34 is provided between the conductive substrate 30 and the photoelectric converter 33. As the light reflector 34, for example, a distributed Bragg reflector composed of a stack of metal layers or semiconductor layers can be used. By providing the light reflector 34, light that could not be absorbed by the photoelectric converter 33 can be reflected and incident on any of the photoelectric conversion layers 33x to 33z. Efficiency can be increased. As the light reflector 34, for example, a layer of a metal such as Ag, Au, Al, or Cu, or an alloy containing at least one of these metals can be used.

  The metal oxide body 35 is provided between the light reflector 34 and the photoelectric converter 33. The metal oxide body 35 has, for example, a function of adjusting an optical distance to enhance light reflectivity. As the metal oxide body 35, it is preferable to use a material that can make ohmic contact with the n-type semiconductor layer 331n. Examples of the metal oxide body 35 include indium tin oxide (Indium Tin Oxide: ITO), zinc oxide (ZnO), tin oxide containing fluorine (Fluorine-doped Tin Oxide: FTO), and zinc oxide containing aluminum (Aluminum-doped). A layer of a light-transmitting metal oxide such as Zinc Oxide (AZO) or antimony-doped Tin Oxide (ATO) can be used.

  The metal oxide body 36 is provided between the oxidation electrode 32 and the photoelectric conversion body 33. The metal oxide body 36 may be provided on the surface of the photoelectric conversion body 33. The metal oxide body 36 has a function as a protective layer for suppressing destruction of the photoelectric conversion cell due to the oxidation reaction. By providing the metal oxide body 36, corrosion of the photoelectric conversion body 33 can be suppressed, and the life of the photoelectric conversion cell can be prolonged. Note that the metal oxide body 36 does not necessarily have to be provided.

As the metal oxide body 36, for example, a dielectric thin film such as TiO ₂ , ZrO ₂ , Al ₂ O ₃ , SiO ₂ , or HfO ₂ can be used. The thickness of the metal oxide body 36 is preferably 10 nm or less, more preferably 5 nm or less. This is for obtaining conductivity by a tunnel effect. Examples of the metal oxide body 36 include transparent materials such as indium tin oxide (ITO), zinc oxide (ZnO), tin oxide containing fluorine (FTO), zinc oxide containing aluminum (AZO), and tin oxide containing antimony (ATO). A light-emitting metal oxide layer may be used.

  The metal oxide body 36 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 combined, or a composite in which a transparent conductive oxide and another conductive material are combined. It may have a structure. With the above structure, the number of parts can be reduced, the weight can be reduced, the manufacturing can be facilitated, and the cost can be reduced. The metal oxide body 36 may have a function as a protective layer, a conductive layer, and a catalyst layer.

  In the photoelectric conversion cell shown in FIG. 2, the surface of the n-type semiconductor layer 331n opposite to the contact surface with the i-type semiconductor layer 331i becomes the first surface of the photoelectric conversion body 33, and the i-type semiconductor layer 333i of the p-type semiconductor layer 333p. The surface opposite to the contact surface is the second surface. As described above, by stacking the photoelectric conversion layers 33x to 33z, the photoelectric conversion cell illustrated in FIG. 2 can absorb light of a wide wavelength range of sunlight, and can more efficiently reduce sunlight energy. Can be used. At this time, a high voltage can be obtained because the photoelectric conversion layers are connected in series.

  In FIG. 2, since the electrodes are stacked on the photoelectric conversion body 33, the electrons and holes separated from the charge can be used as they are in the oxidation-reduction reaction. Further, it is not necessary to electrically connect the photoelectric conversion body 33 and the electrode by wiring or the like. Therefore, the oxidation-reduction reaction can be performed with high efficiency.

  A plurality of photoelectric converters may be electrically connected in parallel. A two-junction or single-layer photoelectric converter may be used. It may have a laminate of two or four or more photoelectric converters. Instead of stacking a plurality of photoelectric conversion layers, a single photoelectric conversion layer may be used.

  The electrochemical reaction device of the present embodiment is a simplified system in which a reduction electrode, an oxidation electrode, and a photoelectric converter are integrated, and the number of parts is reduced. Thus, for example, at least one of manufacturing, installation, and maintenance is facilitated. Further, since wiring and the like for connecting the photoelectric converter to the reduction electrode and the oxidation electrode are not required, the light transmittance can be increased and the light receiving area can be increased.

  The photoelectric conversion body 33 may be corroded due to contact with the electrolyte, and the corrosion product may be dissolved in the electrolyte to deteriorate the electrolyte. In order to prevent corrosion, a protective layer may be provided. However, the components of the protective layer may be dissolved in the electrolyte. Therefore, the deterioration of the electrolytic solution is suppressed by providing a filter such as a metal ion filter in the flow path or the electrolytic solution tank.

  The structural example of the electrochemical reaction device is not limited to FIG. 3 to 6 are schematic views showing other examples of the electrochemical reaction device. In the electrochemical reaction device shown in FIG. 3, the photoelectric conversion body 33 is provided outside the electrolytic solution tank 11. The surface 331 and the reduction electrode 31 and the surface 332 and the oxidation electrode 32 are connected by a conductive member such as a wiring. When the photoelectric converter is connected to the reduction electrode or the oxidation electrode by wiring or the like, the components are separated for each function, which is systemically advantageous.

  In the electrochemical reaction device shown in FIG. 4, the liquid phase 21b is in contact with the reduction electrode 31. In this case, the product of the reduction reaction generated in the liquid phase 21b can be moved to the liquid phase 21a according to the distribution coefficient of the product between the liquid phase 21a and the liquid phase 21b. Therefore, the generation efficiency of the reduction product is improved. Further, both the liquid phase 21a and the liquid phase 21b may be in contact with the reduction electrode 31.

  The product to be extracted from the liquid phase 21b by distillation, membrane separation, or the like may be selected in consideration of, for example, the boiling points of the components of the liquid phase 21a and the liquid phase 21b, the affinity between the product and the liquid phase 21a, and the like. preferable. For example, consider the case where ethanol is distilled from water and xylene, respectively. The boiling point of water is 100 ° C. at 1 atm, the boiling point of xylene is 144 ° C. at 1 atm, and the boiling point of ethanol is 78 ° C. at 1 atm. It can be seen that it is easier to extract ethanol from xylene than from water because of the difference in boiling point and the difference in ease of azeotropic distillation. The present invention is not limited to this, and the product of the reduction reaction generated in xylene may be moved into water and extracted by distillation.

  Even if a product is extracted by distillation from a solvent having a lower concentration in relation to the above-mentioned partition coefficient, these relations are arbitrary from the viewpoint of overall energy, cost and system properties. Therefore, the product may be extracted by distillation or the like from the liquid phase having the lower concentration of the product to be extracted, of the liquid phase 21a and the liquid phase 21b. The same applies to membrane separation, and a solvent having higher resolvability can be selected depending on differences in molecular size, shape, hydrophobicity, and the like.

  The liquid phase 21a may contain a salt. Examples of the salt include a first salt having at least one element of sodium, potassium, magnesium, calcium, iron, nickel, and cobalt, or a second salt having at least one element of fluorine, chlorine, bromine, and iodine. And the like. Further, as the first salt, for example, sodium chloride, magnesium hydroxide, potassium sulfate, calcium carbonate, cobalt hydroxide, or the like is preferably used. As the second salt, for example, sodium chloride, magnesium chloride, iron chloride, cobalt chloride, cobalt iodide, or the like is preferably used. By mixing the salt into the liquid phase 21a, the distribution coefficient of the reduction product between the liquid phase 21a and the liquid phase 21b can be changed. Organic compounds and the like have a property that they are not dissolved or hardly dissolved in a high-concentration salt solution. For example, when a salt is added to an aqueous solution, hydration power is strong, so that water molecules can be fixed as hydration water. Therefore, it is possible to easily move the product of the reduction reaction to be recovered to the liquid phase 21b. The same effect can be obtained with low molecular weight organic substances. For example, by adding a salt to, for example, methanol, ethanol, butanol, and ethylene glycol, the product can be easily moved to the liquid phase 21b.

  By providing a temperature controller for adjusting the temperature of the electrolytic solution 21 and the electrolytic solution 22 in, for example, the electrolytic solution tank 11, the temperature difference between the electrolytic solution 21 and the electrolytic solution 22 can be reduced, and the efficiency of product separation can be increased. . In addition, a rise in the temperature of the electrochemical reaction device can be suppressed. Furthermore, the selectivity of the catalyst can be varied.

  When the specific gravity of the liquid phase 21b is larger than the specific gravity of the liquid phase 21a, the liquid phase 21b is passed through the liquid phase 21a from above the liquid phase 21a in the direction of gravity, and the contact with the liquid phase 21a is improved. It is possible to efficiently transfer the reduced product dissolved in the liquid phase 21a to the liquid phase 21b. It is possible to improve the reaction efficiency by taking out the liquid phase 21b containing the above product, separating or reacting at least a part of the product, and then circulating the liquid phase 21b again above the liquid phase 21a in the direction of gravity. it can.

  At least a part of the electrolytic solution 21 containing at least one of the liquid phase 21a and the liquid phase 21b containing the product may be supplied to another electrolytic solution tank 11 via a flow path. Thereby, the reaction product can be continuously reacted. Therefore, a solvent suitable for the reaction in the next-stage electrolytic solution tank 11 can be used for the liquid phase 21b or the liquid phase 21a in the next-stage electrolytic solution 21, and there is no need to perform solvent replacement. Further, a solvent suitable for separation and purification of the reaction product in the next electrolytic solution tank 11 can be selected, so that the reaction efficiency can be improved.

  Since the distribution coefficient changes depending on the product generated by the reduction reaction in the electrolytic bath 11 in the next stage, the product can be concentrated by continuously reacting. Therefore, the generation efficiency of the reduction product can be further increased. In addition, since the concentration of the reduction product first generated by the subsequent reaction, distillation, membrane separation, or the like decreases, the product moves according to the distribution coefficient.

  When the product generated in the liquid phase 21a moves to the liquid phase 21b and the concentration of the product in the liquid phase 21b is reduced by the next reaction or distillation, the product contained in the liquid phase 21a is converted into the liquid phase 21b according to the chemical equilibrium. Go to Therefore, the reaction is not only efficient because the reaction is performed continuously, but also the reaction efficiency can be increased without being affected by the reaction diffusion of the product in the liquid phase 21a or being restricted by the solubility. At this time, the relationship between the positions and reactions of the reduction electrode 31, the liquid phase 21a, and the liquid phase 21b is arbitrary, and the same effect can be obtained by selecting an appropriate combination in any combination.

  In the case where impurities are generated by the oxidation-reduction reaction and hinder the oxidation-reduction reaction, or when the production efficiency of the product is reduced due to the life of the electrochemical reaction device or corrosion of the electrolytic solution tank 11, for example, one of the liquid phase 21a and the liquid phase 21b May capture impurities and perform a reduction reaction on the other hand. Thereby, the continuity of the reduction reaction can be improved. This liquid phase relationship is arbitrary, and a similar effect can be obtained by selecting an appropriate combination in any combination.

  When there are a plurality of kinds of reduction products, one kind of a plurality of kinds of reduction products can be recovered from the liquid phase 21a, and the other kind can be recovered from the liquid phase 21b. Thereby, each product can be efficiently collected. Further, one product may be recovered from the liquid phase 21a by utilizing the difference in the reaction rate, and another product having a slow reaction rate may be recovered from the liquid phase 21b. Further, when surplus power, nighttime power, or natural energy is used, the product can be recovered according to the sunshine, wind conditions, and the like.

  When the liquid phase 21a and the liquid phase 21b are in contact with the reduction electrode 31, the proportion of the product can be changed by changing the contact area. The contact area is adjusted, for example, by changing the volume (liquid amount) of the liquid phase 21a and the liquid phase 21b to be supplied. Thereby, the reaction can be performed more efficiently according to the demand for electric power, natural environment, and products. Therefore, for example, it is possible to perform a reaction according to a situation such as low-cost operation and high-efficiency operation.

  In the electrochemical reactor shown in FIG. 5, the reduction electrode 31 includes the first reduction catalyst and is in contact with the liquid phase 21b, and the first electrode has a second reduction catalyst different from the first reduction catalyst and is in contact with the liquid phase 21a. And As the first reduction catalyst and the second reduction catalyst, a material applicable as a reduction catalyst can be appropriately used. Thereby, a reduction reaction suitable for each liquid phase can be advanced.

  In the case of the above configuration, the oxidation-reduction reaction can be continuously performed. For example, the product generated by the reduction reaction in the liquid phase 21a is moved to the liquid phase 21b, and the reduction reaction of the product is performed in the liquid phase 21b, so that another compound can be continuously generated. At this time, the relationship between the positions and reactions of the reduction electrode 31, the liquid phase 21a, and the liquid phase 21b is arbitrary, and the same effect can be obtained by selecting an appropriate combination in any combination.

  The electrochemical reaction device shown in FIG. 6 includes, in addition to the components shown in FIG. 1, an electrolytic solution tank 12, a separation tank 6 for separating a part of a product contained in a liquid phase 21b, and at least one of non-reducing substances. And a collecting device 7 for collecting the part. At this time, the flow path 50a shown in FIG. 6 connects between the liquid phase 21a and the recovery device 7, and the flow path 50b connects between the liquid phase 21b and the separation tank 6. Further, the electrochemical reaction device shown in FIG. 6 includes a flow path 50 d connecting between the separation tank 6 and the liquid phase 21 a, a flow path 50 e connecting between the electrolytic solution tank 12 and the recovery device 7, And a flow path 50f for discharging the product to the outside of the liquid tank 12. About the same part as the component shown in FIG. 1, the description of FIG. 1 can be used as appropriate. Note that the separation tank 6 and the recovery device 7 do not necessarily need to be provided.

  The electrolytic solution tank 12 has a storage section 121 for storing the electrolytic solution 23. In addition, the description of the electrolytic solution tank 11 can be appropriately referred to as the description of the electrolytic solution tank 12. Electrolyte solution 23 includes a liquid phase 23a and a liquid phase 23b in contact with liquid phase 23a. The liquid phase 23a contains, for example, water. The liquid phase 23a is connected to the recovery device 7 via the flow path 50e. The liquid phase 23a may include a material applicable to the liquid phase 21a. The liquid phase 23b is connected to the separation tank 6 via the flow path 50d. The liquid phase 23b contains, for example, an organic solvent. As the organic solvent, for example, an organic solvent applicable to the liquid phase 21b can be used. At least one of the liquid phases 23a and 23b contains a substance to be reduced. In the electrolytic solution tank 12, a membrane separation, a distillation tower, or the like may be performed. Further, a product recovery channel may be provided in the electrolytic solution tank 12.

  The separation tank 6 can separate at least a part of the product from the electrolyte supplied from the electrolyte tank 11. The separation method in the separation tank 6 is, for example, distillation or membrane separation. FIG. 6 illustrates an example in which a product is separated by membrane separation as an example.

  The separation tank 6 shown in FIG. 6 has a storage section 161a for storing the electrolytic solution 24 and a gas-liquid separation membrane 161b provided to divide the storage section 161a into a plurality of regions. The electrolytic solution 24 is at least a part of the liquid phase 21b supplied via the flow path 50b. The gas-liquid separation membrane 161b includes, for example, a hollow fiber membrane or the like. The hollow fiber membrane is made of, for example, silicone resin or fluorine resin (perfluoroalkoxyalkane (PFA), perfluoroethylene propene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene / tetrafluoroethylene copolymer (ETFE), polyfluorinated Vinylidene (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like.

  In the separation tank 6 shown in FIG. 6, for example, the outside of the gas-liquid separation membrane 161b (the side opposite to the contact surface of the electrolyte 24) is depressurized, and the electrolyte 24 containing gaseous products forms the gas-liquid separation membrane 161b. By passing through, gaseous products can be efficiently separated.

  The recovery device 7 causes a substance to be reduced such as carbon dioxide contained in at least a part of the liquid phase 23a supplied through the flow path 50e to be adsorbed to, for example, an amine solution or zeolite, and is released again by heat or the like. Thereby, the concentration and purity of the substance to be reduced can be increased. By burying the re-discharged reduced substance in the ground or mining natural gas or shale gas, it is possible to suppress an increase in the concentration of the reduced substance in the atmosphere. In addition, at least a part of the liquid phase 23a is supplied to the recovery device 7 through the flow path 50e, and the electrolytic solution containing the high-concentration reduced substance obtained by the recovery device 7 is supplied again to the storage unit 111. In addition, the redox efficiency can be increased. As described above, by using the recovery device 7, for example, it is possible to realize a system capable of reducing the emission amount of carbon dioxide as a reduced substance, improving the overall system efficiency by utilizing oxygen, and obtaining valuable resources. it can.

  Next, an operation example of the electrochemical reaction device shown in FIG. 6 will be described. In the electrochemical reaction device shown in FIG. 6, as in the electrochemical reaction device shown in FIG. 1, a product is generated by the oxidation-reduction reaction. At this time, the liquid phase 21b contains the product.

  In the electrochemical reaction device shown in FIG. 6, the temperature of the liquid phase 21a differs from the temperature of the liquid phase 23b. For example, the temperature of the liquid phase 21a is set lower than that of the liquid phase 23a. At this time, the temperature of the liquid phase 21a is preferably 80 ° C. or lower, and more preferably 0 ° C. to 40 ° C. The temperature of the liquid phase 23a is preferably 100C or lower, more preferably 50 to 80C. As a result, the stability of the products and the components of the electrolytic solution can be increased, and the energy efficiency can be increased.

  In order to make the temperature of the liquid phase 21a different from the temperature of the liquid phase 23b, a heater for heating the electrolytic solution 23 and a cooler for cooling the electrolytic solution supplied to the liquid phase 21a or the recovery device 7 are electrically connected. It may be provided in a chemical reaction device. Each of the cooler and the heater is controlled by, for example, a temperature controller.

  When at least one of the liquid phases 21a and 21b contains an ionic liquid, the ionic liquid containing the substance to be reduced moves to the liquid phase 21a. That is, by increasing the temperature of the electrolytic solution, the ionic liquid moves to the liquid phase 21a containing the organic solvent. At least a part of the liquid phase 21a moves to the separation tank 6 via the flow path 50b. The separation tank 6 separates at least a part of the product from the electrolytic solution.

  The electrolytic solution separated by the separation tank 6 moves to the electrolytic solution tank 12 via the flow path 50d. When the electrolytic solution 23 contains an ionic liquid and the temperature of the liquid phase 23b is higher than the temperature of the liquid phase 21a, the ionic liquid containing the substance to be reduced and the product moves to the liquid phase 23b. Thus, organic products such as methanol and ethylene glycol can be efficiently recovered from the liquid phase containing the ionic liquid. In this way, by forming a temperature difference of several tens of degrees Celsius and performing separation, a target product can be taken out with low energy. Therefore, cost can be reduced.

  The boiling point of the organic solvent is usually about 60C to 150C. On the other hand, the boiling point of the ionic liquid is about 300 ° C. Therefore, for example, when methanol is separated as a product by distillation, azeotropy between the ionic liquid and methanol hardly occurs, so that only methanol can be extracted by one distillation.

  When performing membrane separation, the product can be easily separated by using an ionic liquid containing a large-sized molecule. Further, by adding a salt applicable to the liquid phase 21a to the mixture of the separated product and the ionic liquid, the product may be taken out after changing the ion balance to change the ionic liquid from a liquid to a solid. .

  When the temperature of the liquid phase 23b is higher than the temperature of the liquid phase 21a, the to-be-reduced substances dissolved in the liquid phase 23b can be efficiently discharged through the flow path 50f. At this time, the substance to be reduced may be released by membrane separation or the like.

  By using an ionic liquid, overvoltage can be reduced during the reduction reaction of carbon dioxide. In addition, by collecting or removing impurities in a liquid phase containing water during the reaction, the reaction can be allowed to proceed continuously. Even if the liquid is not an ionic liquid, the distribution coefficient changes. Therefore, by concentrating the product in this way, the efficiency of separation and recovery of the product can be increased. Further, it is preferable to use a material that reduces the reduction potential of carbon dioxide, has high ion conductivity, and has carbon dioxide absorption performance even if it is not an ionic liquid.

  By using an organic substance having a high absorptivity of carbon dioxide, mainly ionic liquid and amine, the substance to be reduced can be absorbed in the electrolyte on the low temperature side and carbon dioxide can be released on the high temperature side. As a result, the electrochemical reaction device can function as a carbon dioxide separation and recovery system, and at least a part of the recovered to-be-reduced substance can be efficiently reduced and obtained as an energy substance. Can be improved.

  At least a portion of the liquid phase 23a is supplied to the recovery device 7 via the flow path 50e. When the electrolytic solution supplied to the recovery device 7 is cooled, a part of the substance to be reduced becomes difficult to be dissolved. The recovery device 7 recovers the to-be-reduced substance that is not dissolved. The recovered electrolyte is supplied to the liquid phase 21a via the flow path 50a. The electrolyte may be circulated between the electrolyte tank 11 and the electrolyte tank 12 using a pump or the like.

  The temperature of the liquid phase 21a may be higher than the temperature of the liquid phase 23a. Thereby, the activity of the reduction catalyst in contact with the liquid phase 21a is increased, and the reaction is performed in the ionic liquid. Further, the electrolytic solution after the reaction is cooled in the electrolytic solution tank 12, the ionic liquid is moved to a liquid phase containing water, and the product can be separated.

(Example 1)
An electrochemical reactor equipped with the structure was manufactured. The structure includes a three-junction photoelectric converter with a thickness of 500 nm, a ZnO layer with a thickness of 300 nm provided on the first surface of the three-junction photoelectric converter, and a thickness with which a ZnO layer is provided. It has a 200 nm Ag layer, a 1.5 mm thick SUS substrate provided on the Ag layer, and a 100 nm thick ITO layer provided on the second surface of the three junction type photoelectric converter. Each layer on the SUS substrate has a texture structure on the order of sub-microns in order to obtain an optical confinement effect.

  The three-junction type photoelectric converter includes a first photoelectric conversion layer that absorbs light in a short wavelength region, a second photoelectric conversion layer that absorbs light in a medium wavelength region, and a third photoelectric conversion layer that absorbs light in a long wavelength region. And a photoelectric conversion layer. The first photoelectric conversion layer has a p-type microcrystalline silicon layer, an i-type amorphous silicon layer, and an n-type amorphous silicon layer. The second photoelectric conversion layer has a p-type microcrystalline silicon layer, an i-type amorphous silicon germanium layer, and an n-type amorphous silicon layer. The third photoelectric conversion layer has a p-type microcrystalline silicon germanium layer, an i-type amorphous silicon layer, and an n-type amorphous silicon layer.

Next, a Ni catalyst layer having a thickness of 5 nm was formed as an oxidation catalyst on the ITO layer by an atomic layer deposition method. In addition, a conductor was connected to the back surface of the SUS substrate. A composite substrate (4 cm square) having a SUS substrate with a thickness of 1.5 mm and a copper-carrying carbon film with a carrying amount of 0.5 mg / cm ² on the SUS substrate connected via a conductive wire was prepared. An ion exchange membrane (Nafion 117, 6 cm square) was provided between the composite substrate and the structure, and a potassium carbonate solution was supplied into the module. The composite substrate was used as a reduction electrode, the oxidation catalyst side of the structure was used as an oxidation electrode, and a silver-silver chloride electrode was used as a reference electrode. Using a galvanostat, an electric current was applied under the condition of 0.5 mA / cm ² to reduce carbon dioxide to produce methanol and ethanol. At this time, 2 ml of toluene and 10 ml of an aqueous solution of potassium hydrogen carbonate were supplied as the electrolyte on the reducing side.

The structure was irradiated with light using a solar simulator (AM 1.5, 1000 W / m ² ) to collect gas generated from the reduction electrode side, and to measure the conversion efficiency of carbon dioxide. The gas was recovered above the reduction electrode, and the generated gas was sampled and identified and quantified by gas chromatography.

  After a reaction time of 1 hour, extraction of the product from toluene was repeated, and then the extract was distilled. The amount of the obtained methanol was 0.03 mg, and the amount of ethanol was 0.005 mg. This indicates that the product of the reduction reaction moves to the liquid phase containing the organic solvent.

(Example 2)
In the electrochemical reaction device of Example 1, as the electrolytic solution on the reducing side, the formula: [PEG _m (mim) ₂ ] [NTf ₂ ] ₂ (wherein PEG is polyethylene glycol and NTf is bistrifluoromethanesulfonylimide) And im is methyl imidazolium, m is 500), and 1 ml of an organic compound represented by the formula: To the electrolytic solution on the reduction side, 3 ml of methanol and ethyl acetate were added as simulation products. The change of the electrolytic solution when the temperature of the electrolytic solution was raised from 20 ° C. to 50 ° C. was observed. At 20 ° C., the electrolyte containing methanol separated into a liquid phase containing methanol and ethyl acetate, and a liquid phase containing ionic liquid and water. When the temperature was raised to 50 ° C., a liquid phase containing water and a liquid phase containing methanol-containing ionic liquid and ethyl acetate were separated.

(Example 3)
In the electrochemical reaction apparatus of Example 1, 1 ml of polyethylene glycol m (methylimidazolium) 2bistrifluoromethanesulfonylimide (m = 500) and 10 ml of water were supplied as an electrolytic solution on the reduction side. To the electrolytic solution on the reduction side, 3 ml of ethylene glycol and ethyl acetate were added as simulation products. The change of the electrolytic solution when the temperature of the electrolytic solution was raised from 20 ° C. to 50 ° C. was observed. At 20 ° C., the electrolyte containing ethylene glycol was separated into a liquid phase containing ethylene glycol and ethyl acetate and a liquid phase containing ionic liquid and water. When the temperature was raised to 50 ° C., a liquid phase containing water and a liquid phase containing an ionic liquid containing ethylene glycol and ethyl acetate were separated. From the results of Example 2 and Example 3, the efficiency of phase separation can be increased by changing the temperature of the electrolytic solution.

  The above embodiments have been presented by way of example, and are not intended to limit the scope of the invention. The embodiment described above can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. The above-described embodiment and its modifications are included in the scope and spirit of the invention, and are also included in the invention described in the claims and their equivalents.

  DESCRIPTION OF SYMBOLS 4 ... Ion exchange membrane, 6 ... Separation tank, 7 ... Collection | recovery apparatus, 11 ... Electrolyte tank, 12 ... Electrolyte tank, 21 ... Electrolyte, 21a ... Liquid phase, 21b ... Liquid phase, 22 ... Electrolyte, 23 ... Electrolyte, 23a ... liquid phase, 23b ... liquid phase, 24 ... electrolyte, 30 ... conductive substrate, 31 ... reduction electrode, 31a ... area, 31b ... area, 32 ... oxidation electrode, 33 ... photoelectric conversion body, 33x ... Photoelectric conversion layer, 33y photoelectric conversion layer, 33z photoelectric conversion layer, 34 light reflector, 35 metal oxide body, 36 metal oxide body, 331 plane, 331i i-type semiconductor layer, 331n n-type semiconductor Layer, 331p ... p-type semiconductor layer, 332 ... plane, 332i ... i-type semiconductor layer, 332n ... n-type semiconductor layer, 332p ... p-type semiconductor layer, 333i ... i-type semiconductor layer, 333n ... n-type semiconductor layer, 333p ... p-type semiconductor layers, 50a to 50f ... flow paths.

Claims (10)

A first liquid phase including water and a second liquid phase including an organic solvent, wherein at least one of the first liquid phase and the second liquid phase further includes a substance to be reduced; An electrolytic solution tank comprising: a first accommodating portion for accommodating an electrolytic solution; and a second accommodating portion for accommodating a second electrolytic solution containing a substance to be oxidized.
A reduction electrode provided in the first storage section,
An oxidizing electrode provided in the second housing portion,
The reduction electrode is provided for contacting the first liquid phase and includes a first region including a first reduction catalyst, and a second region provided for contacting the second liquid phase. And a second region comprising:   The electrochemical reaction device according to claim 1, wherein the organic solvent includes a hydrophobic organic compound.   The first liquid phase has a first salt having at least one element of sodium, potassium, magnesium, calcium, iron, nickel, and cobalt, or at least one element of fluorine, chlorine, bromine, and iodine. The electrochemical reactor according to claim 1 or 2, further comprising a second salt.   The electrochemical reaction device according to claim 1, wherein the organic solvent includes an ionic liquid. A first flow path for connecting between the first liquid phase and the outside of the electrolytic solution tank;
The electrochemical device according to any one of claims 1 to 4, further comprising a second flow path for connecting between the second liquid phase and the outside of the electrolytic solution tank. Reactor. A first liquid phase containing water and a second liquid phase containing an organic solvent, and at least one of the first liquid phase and the second liquid phase further contains a substance to be reduced; and Each of the first liquid phase and the second liquid phase includes a first storage part for storing a first electrolyte further containing a product of a reduction reaction of the substance to be reduced, and a substance to be oxidized. An electrolyte bath including a second storage unit for storing a second electrolyte,
A reduction electrode provided in the first storage section,
An oxidation electrode provided in the second housing portion;
It has a third liquid phase containing the water and a fourth liquid phase containing the organic solvent, and at least one of the third liquid phase and the fourth liquid phase further converts the substance to be reduced. A second electrolyte bath for containing a third electrolyte containing
A first flow path for connecting between the first liquid phase and the third liquid phase;
A second flow path for connecting between the second liquid phase and the fourth liquid phase,
Each of the first liquid phase and the fourth liquid phase includes an ionic liquid,
The electrochemical reaction device, wherein a temperature of the first liquid phase is different from a temperature of the fourth liquid phase.   The electricity according to claim 6, further comprising at least one of a cooler for cooling the electrolyte supplied to the first liquid phase and a heater for heating the fourth liquid phase. Chemical reactor. A first liquid phase containing water and a second liquid phase containing an organic solvent, and at least one of the first liquid phase and the second liquid phase further contains a substance to be reduced; and Each of the first liquid phase and the second liquid phase includes a first storage part for storing a first electrolyte further containing a product of a reduction reaction of the substance to be reduced, and a substance to be oxidized. An electrolyte bath including a second storage unit for storing a second electrolyte,
A reduction electrode provided in the first storage section,
An oxidation electrode provided in the second housing portion;
It has a third liquid phase containing the water and a fourth liquid phase containing the organic solvent, and at least one of the third liquid phase and the fourth liquid phase further converts the substance to be reduced. A second electrolyte bath for containing a third electrolyte containing
A separation tank for separating a part of the product contained in the second liquid phase,
A recovery device for recovering at least a part of the substance to be reduced contained in the third liquid phase,
A first flow path for connecting between the first liquid phase and the recovery device;
A second flow path for connecting between the second liquid phase and the separation tank;
A third flow path for connecting between the third liquid phase and the recovery device;
A fourth flow path for connecting between the separation tank and the fourth liquid phase;
A fifth flow path for connecting between the fourth liquid phase and the outside of the second electrolytic solution tank,
Each of the first liquid phase and the fourth liquid phase includes an ionic liquid,
The electrochemical reaction device, wherein a temperature of the first liquid phase is different from a temperature of the fourth liquid phase.   9. The apparatus according to claim 8, further comprising at least one of a cooler for cooling the first liquid phase or the electrolyte supplied to the recovery device, and a heater for heating the fourth liquid phase. Electrochemical reactor. A first liquid phase including water and a second liquid phase including an organic solvent, wherein at least one of the first liquid phase and the second liquid phase further includes a substance to be reduced; An electrolytic solution tank comprising: a first accommodating portion for accommodating an electrolytic solution; and a second accommodating portion for accommodating a second electrolytic solution containing a substance to be oxidized.
A reduction electrode provided in the first storage section,
An oxidizing electrode provided in the second housing portion ,
The second liquid phase is taken out from the first storage part, and at least a part of a product of the reduction reaction of the substance to be reduced contained in the second liquid phase is separated or reacted, and the second liquid phase is taken out. the liquid phase Ru is circulated on the first liquid phase of said first housing portion, the electrochemical reactor.

Images