JP2017150072A - Electrochemical reaction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the reduction efficiency of carbon dioxide.SOLUTION: Provided is an electrochemical reaction device comprising: the first electrolytic solution tank provided with the first storage part storing the first electrolytic solution including carbon dioxide and the second storage part storing the secondary electrolytic solution including water; the second electrolytic solution tank provided with a reduction electrode immersed into the first electrolytic solution, an oxidation electrode immersed into the second electrolytic solution, a power source electrically connected to the reduction electrode and oxidation electrode and the third storage part storing the third electrolytic solution including carbon dioxide; and a flow passage connecting the first storage part and the third storage part. The temperature of the third electrolytic solution is lower than the temperature of the first electrolytic solution.SELECTED DRAWING: Figure 1

Description

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

  In recent years, from the viewpoint of energy problems and environmental problems, development of artificial photosynthesis technology that imitates plant photosynthesis and converts sunlight into electrochemical chemicals has been promoted. For example, it is because the utility value is low even if the utility value is low such as a desert and the sunlight is converted into a chemical substance and transported to a remote place on a land that is not used for plant production. When sunlight is converted into chemicals and stored in cylinders or tanks, energy storage costs can be reduced and storage loss is less than when sunlight is converted into electricity and stored in storage batteries. There is an advantage.

As a photoelectrochemical reaction apparatus for converting sunlight into a chemical substance electrochemically, for example, it has an electrode having a reduction catalyst for reducing carbon dioxide (CO ₂ ) and an oxidation catalyst for oxidizing water (H ₂ O). There is known a two-electrode type apparatus that includes electrodes and immerses these electrodes 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 / 2O ₂ ) and a potential is obtained. In an electrode having a reduction catalyst, formic acid (HCOOH) or the like is generated by reducing carbon dioxide by obtaining a potential from an electrode that causes an oxidation reaction. As described above, in the two-electrode system, the reduction potential of carbon dioxide is obtained by two-stage excitation, so that the conversion efficiency from sunlight to chemical energy is low.

US Pat. No. 3,959,094 Japanese Patent No. 4811844

  The problem to be solved by the invention of the embodiment is to increase the reduction efficiency of carbon dioxide.

  The electrochemical reaction device according to the embodiment includes a first storage unit that stores a first electrolytic solution containing carbon dioxide, and a second storage unit that stores a second electrolytic solution containing water. An electrolyte bath, a reduction electrode immersed in the first electrolyte, an oxidation electrode immersed in the second electrolyte, a power source electrically connected to the reduction electrode and the oxidation electrode, and carbon dioxide A second electrolytic solution tank including a third storage unit that stores the third electrolytic solution including the first electrolytic unit; and a flow path that connects the first storage unit and the third storage unit. The temperature of the third electrolytic solution is lower than the temperature of the first electrolytic solution.

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

  Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic, and for example, the thickness and width of each component may differ from the actual component dimensions. In the embodiment, substantially the same constituent elements may be assigned the same reference numerals and description thereof may be omitted. In this specification, the term “connecting” is not limited to the case of direct connection, but may include the meaning of indirect connection.

  FIG. 1 is a schematic diagram showing a configuration example of an electrochemical reaction device. As shown in FIG. 1, the electrochemical reaction apparatus includes an electrolytic solution tank 11, an electrolytic solution tank 12, a reduction electrode 31, an oxidation electrode 32, a photoelectric conversion body 33, an ion exchange membrane 4, and a flow path 51. And a flow path 52.

  The electrolytic solution tank 11 includes a housing part 111 and a housing part 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 housing portion.

  The accommodating part 111 accommodates the electrolyte solution 21 containing a to-be-reduced substance. 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 contain hydrogen ions. By changing the amount of water contained in the electrolytic solution 21 and the electrolytic solution component, the reactivity can be changed, and the selectivity of the substance to be reduced and the ratio of the generated chemical substance can be changed.

  The accommodating part 112 accommodates the electrolyte solution 22 containing an oxidizable substance. 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 material as the electrolytic solution 21 may be contained in the electrolytic solution 22. In this case, the electrolytic solution 21 and the electrolytic solution 22 may be regarded as one electrolytic solution.

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

  The electrolytic solution tank 12 has a storage portion 113 that stores the electrolytic solution 23. The electrolytic solution 23 includes, for example, carbon dioxide. The electrolytic solution tank 12 has a function as a reduction catalyst absorption device. The temperature of the electrolytic solution 23 is lower than the temperature of the electrolytic solution 21.

The reduction electrode 31 is immersed in the electrolytic solution 21. The reduction electrode 31 includes, for example, a reduction catalyst for the substance to be reduced. The compound produced by the reduction reaction varies depending on the type of reduction catalyst. Examples of the compound produced by the reduction reaction include 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 compound produced by the reduction reaction may be recovered, for example, via the product flow path. At this time, the product flow path is connected to the accommodating part 111, for example. The compound produced by the reduction reaction may be recovered via another channel.

  The reduction electrode 31 may have, for example, a thin film, lattice, particle, or wire structure. The reduction catalyst does not necessarily have to be provided on the reduction electrode 31. A reduction catalyst provided other than the reduction electrode 31 may be electrically connected to the reduction electrode 31.

  The oxidation electrode 32 is immersed in the electrolytic solution 22. The oxidation electrode 32 includes, for example, an oxidation catalyst for the substance to be oxidized. The compound produced by the oxidation reaction varies depending on the type of oxidation catalyst. The compound produced | generated by an oxidation reaction is a hydrogen ion, for example. The compound produced by the oxidation reaction may be recovered, for example, via the product channel. At this time, the product flow path is connected to the accommodating portion 112, for example. The compound produced by the oxidation reaction may be recovered via another channel.

  The oxidation electrode 32 may have, for example, a thin film, lattice, particle, or wire structure. The oxidation electrode 32 does not necessarily have to be provided with the oxidation catalyst. An oxidation catalyst layer provided other than the oxidation electrode 32 may be electrically connected to the oxidation electrode 32.

  In the case where the oxidation electrode 32 is laminated 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, the oxidation electrode 32 is transparent. It is necessary to have sex. The light transmittance of the oxidation electrode 32 is, for example, preferably at least 10% or more, more preferably 30% or more, of the amount of light irradiated to the oxidation electrode 32. For example, the photoelectric converter 33 may be irradiated with light via the reduction electrode 31.

  The photoelectric converter 33 has a surface 331 electrically connected to the reduction electrode 31 and a surface 332 electrically connected to the oxidation electrode 32. In FIG. 1, the surface 331 and the reduction electrode 31 and the surface 332 and the oxidation electrode electrode 32 are connected by a heat transfer member such as a wire having heat transfer properties, for example. When the photoelectric converter and the reduction electrode or the oxidation electrode are connected by wiring or the like, the components are separated for each function, which is advantageous in terms of the system. The photoelectric conversion body 33 may be provided outside the electrolytic solution tank 11. Note that the photoelectric conversion body 33 is not necessarily provided. Another power source may be connected to the oxidation electrode 32 and the reduction electrode 31. The power source is not limited to a photoelectric conversion element including a photoelectric converter, and a power source device such as a system power source or a storage battery, or renewable energy such as wind power, hydraulic power, or geothermal heat may be used.

  The photoelectric conversion body 33 has a function of performing charge separation by the energy of light such as irradiated sunlight. Electrons generated by charge separation move to the reduction electrode side, and 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 the electrolytic solution tank 11, for example. Note that the photoelectric conversion body 33 may be formed by stacking a plurality of photoelectric conversion layers.

  The sizes 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 accommodating portion 111 and the accommodating portion 112. Examples of the ion exchange membrane 4 include Astom Neoceptor (registered trademark), Asahi Glass Selemion (registered trademark), Aciplex (registered trademark), Fumatech Fumasep (registered trademark), fumapem (registered trademark), DuPont's Nafion (registered trademark), which is a fluororesin obtained by sulfonating tetrafluoroethylene, LANWESS® lablane (registered trademark), IONTECH IONSEP (registered trademark), PALL Mustang (registered trademark), mega ralex (Registered trademark), Gore-Tex (registered trademark) manufactured by Gore-Tex Corporation, and the like can be used. In addition, the ion exchange membrane may be configured using a membrane having a basic skeleton of hydrocarbon, or a membrane having an amine group in anion exchange. Note that the ion exchange membrane 4 is not necessarily provided.

  The flow path 51 and the flow path 52 have a function as an electrolytic solution flow path for circulating the electrolytic solution. However, the present invention is not limited to this, and the electrolytic solution and the product resulting from the oxidation-reduction reaction may be circulated through the channel 51 and the channel 52. For example, a material that transmits light may be used as the electrolyte baths 11 and 12 and the flow paths 51 and 52. The electrolyte bath 12 is a material that can easily transfer heat to improve the efficiency of the electrolyte bath 12, and it is desirable to keep the inside of the bath uniform. When using solar heat, a material that easily absorbs heat or black It is preferable to use a material having a high heat absorption rate such as energy saving. In particular, it is more desirable in an electrochemical reaction apparatus in which the reaction proceeds when receiving sunlight. Moreover, in order to directly adjust the liquid temperature of the electrolytic solution inside the tank, it is possible to improve efficiency by using a material that transmits light and providing a material that absorbs sunlight inside.

  The flow path 51 connects the housing part 111 and the housing part 113. Ions and other substances contained in the electrolytic solution 21 can move to the electrolytic solution tank 12 through the flow path 51.

  The flow path 52 connects the housing part 111 and the housing part 113. Ions and other substances contained in the electrolytic solution 23 can move to the electrolytic solution tank 11 through the flow path 52.

  The shape of the flow path 51 and the flow path 52 is not particularly limited as long as it has a cavity capable of flowing an electrolyte such as a pipe. The electrolyte solution in at least one of the channel 51 and the channel 52 may be circulated by a circulation pump. At least a part of the electrolytic solution 21 moves to the accommodating portion 113 via the flow path 51, for example. At least a part of the electrolytic solution 23 moves to the accommodating portion 111 via the flow path 52, for example. The arrows shown in FIG. 1 indicate the circulation direction of the electrolytic solution.

  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, photoexcited 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. As light, sunlight is preferable, 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 electrolytic solution containing water and carbon dioxide as the electrolytic solution 21 and the electrolytic solution 22 will be described. In the vicinity of the oxidation electrode 32, an oxidation reaction of water occurs as shown in the following formula (1), the electrons are lost, and oxygen and hydrogen ions are generated. 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)

In the vicinity of the reduction electrode 31, a reduction reaction of carbon dioxide occurs as in the following formula (2), and hydrogen ions react with carbon dioxide while receiving electrons, thereby generating carbon monoxide and water. In addition to carbon monoxide, hydrogen ions are generated when hydrogen ions receive electrons as shown in the following formula (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 converter 33 needs to have an open circuit voltage equal to or greater 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 formula (1) is 1.23 [V]. The standard redox potential of the reduction reaction in Formula (2) is −0.03 [V]. The standard redox potential of the oxidation reaction in Formula (3) is 0V. At this time, in the reaction between the formula (1) and the formula (2), the open circuit voltage needs to be 1.26 [V] or more.

  The open-circuit voltage of the photoelectric converter 33 is preferably 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 overvoltage value. For example, the overvoltage of the oxidation reaction in Formula (1) and the reduction reaction in Formula (2) is 0.2 [V], respectively. In the reaction between Formula (1) and Formula (2), it is preferable to set the open circuit voltage to 1.66 [V] or higher. Similarly, in the reaction between Formula (1) and Formula (3), it is preferable to set the open circuit voltage to 1.63 [V] or higher.

  The reduction reaction of hydrogen ions or 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 deteriorated. Therefore, it is preferable to make the hydrogen ion concentration different between the electrolytic solution 21 and the electrolytic solution 22 so that the hydrogen ion can be easily moved by the concentration difference. The concentration of anions (for example, hydroxide ions) may be different between the electrolytic solution 21 and the electrolytic solution 22.

  The reaction efficiency of Formula (2) changes with the density | concentration of the carbon dioxide dissolved in electrolyte solution. The reaction efficiency increases as the carbon dioxide concentration increases, and decreases as it decreases. It is difficult to increase the carbon dioxide concentration in the electrolyte because of its low solubility. The reaction efficiency of formula (2) also changes depending on the bicarbonate ion concentration or carbonate ion concentration. However, since the bicarbonate ion concentration and the carbonate ion concentration can be adjusted by increasing the electrolyte concentration or adjusting the pH, it is easier to adjust than the carbon dioxide concentration. Even if an ion exchange membrane is provided between the oxidation electrode and the reduction electrode, carbon dioxide gas, carbonate ions, hydrogen carbonate ions, etc. will pass through the ion exchange membrane 4, so that it is difficult to completely prevent performance degradation. It is.

  As a method of increasing the carbon dioxide concentration, for example, a method of blowing carbon dioxide directly into the electrolytic solution tank 11 can be considered. However, when the reduction product is gaseous carbon monoxide or the like, it is necessary to separate carbon dioxide gas and carbon monoxide gas. Therefore, an increase in cost due to the complexity of the apparatus and energy required for separation are required, resulting in energy loss.

  The electrochemical reaction device of the present embodiment includes a first electrolytic solution tank used for the oxidation-reduction reaction, and a second electrolytic solution tank connected to the first electrolytic solution tank. The temperature of the electrolytic solution accommodated in the accommodating portion of the second electrolytic solution tank is lower than the electrolytic solution accommodated in the accommodating portion of the first electrolytic solution tank. For example, by cooling the accommodating part in the second electrolytic solution tank, the temperature of the electrolytic solution accommodated in the second electrolytic solution tank is lower than the electrolytic solution accommodated in the accommodating part of the first electrolytic solution tank. can do. The solubility of carbon dioxide in the second electrolyte bath is higher than the solubility of carbon dioxide in the first electrolyte bath.

  The carbon dioxide concentration in the second electrolytic solution tank can also be increased by making the pressure applied to the electrolytic solution 23 higher than the pressure applied to the electrolytic solution 21. At this time, for example, the pressure in the housing part of the second electrolytic solution tank may be made higher than the pressure in the housing part of the first electrolytic solution tank. Further, a pressure regulator may be provided in the flow path 52.

  By supplying an electrolytic solution having a high carbon dioxide concentration adjusted in the second electrolytic solution tank to the first electrolytic solution tank, the carbon dioxide concentration of the electrolytic solution accommodated in the first electrolytic solution tank is increased. be able to. Therefore, the efficiency of the reduction reaction can be improved.

  When cooling the accommodating part of a 1st electrolyte solution tank, since reaction by a catalyst falls, reaction efficiency tends to fall. Moreover, when pressurizing the accommodating part of the first electrolytic solution tank, it is necessary to increase the pressure resistance of the electrolytic solution tank, so that the cost increases and the structure becomes complicated. Furthermore, if the pressure resistance is increased, the maintainability such as the exchange of the electrodes becomes complicated.

  In order to reduce the amount of carbon dioxide supplied and to efficiently absorb carbon dioxide in the electrolyte, it is necessary that the distance between the bubbles of carbon dioxide passing through the electrolyte is wide. However, by increasing the concentration of carbon dioxide, the distance between the bubbles is shortened, and the electrolyte bath can be made smaller. For example, the cooling temperature is preferably equal to or lower than the temperature of the electrolytic solution in the first electrolytic solution tank. When the temperature of the electrolytic solution rises due to the oxidation-reduction reaction, the cooling temperature is preferably room temperature or higher and lower than or equal to the electrolytic solution temperature of the first electrolytic bath. The cooling temperature is more preferably not less than the temperature at which the electrolyte does not freeze and not more than the electrolyte temperature.

The temperature of the electrolytic solution in the first electrolytic solution tank is preferably higher than the freezing temperature. For example, when an ion such as potassium ion or sodium ion is included for the purpose of improving carbon dioxide absorption, carbon dioxide ion, HCO ₃ ion concentration, and improving the solution resistance of the electrolyte, the electrolyte is at 0 ° C. Does not freeze. However, in order to cool extremely, a large-sized cooler is required, which leads to cost and energy loss. Moreover, since there are concerns about energy loss of the whole electrochemical reaction apparatus and reaction decrease due to extreme cooling of the electrolytic solution, 5 ° C. or higher or 10 ° C. or higher may be preferable.

  In order to suppress a decrease in reaction efficiency due to a decrease in the electrolyte temperature, a temperature controller may be provided in the electrolyte baths 11 and 12 and the flow paths 51 and 52. The reaction efficiency is improved by adjusting the temperature with the temperature controller. For example, a cooler may be provided in the flow path 51, and a heater may be provided in the flow path 52. Since the effect can be obtained even with a temperature difference of several degrees Celsius, it is added by irradiating sunlight to the electrolyte flow path or the electrolyte tank between the first electrolyte tank and the second electrolyte tank. It is efficient because natural energy can be used when heated. Furthermore, in the case where this reaction is performed by converting sunlight, which will be described later, into electric energy, the heat energy and light energy of sunlight can be used efficiently, so that the efficiency is further improved.

A structural example of each component in the electrochemical reaction device will be further described. As the electrolytic solution containing water applicable to the electrolytic solution, for example, an aqueous solution containing an arbitrary electrolyte can be used. This solution is preferably an aqueous solution that promotes the oxidation reaction of water. Examples of the aqueous solution containing an electrolyte include phosphate ion (PO ₄ ²⁻ ), borate ion (BO ₃ ³⁻ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), calcium ion (Ca ²⁺ ), lithium 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.

Examples of the electrolytic solution containing carbon dioxide applicable to the electrolytic solution include an aqueous solution containing LiHCO ₃ , NaHCO ₃ , KHCO ₃ , CsHCO _3, phosphoric acid, boric acid, and the like. The electrolytic solution containing carbon dioxide may contain alcohols such as methanol, ethanol, and acetone. The electrolytic solution containing water may be the same as the electrolytic solution containing carbon dioxide. However, it is preferable that the amount of carbon dioxide absorbed in the electrolytic solution containing carbon dioxide is high. Therefore, a solution different from the electrolyte solution containing water may be used as the electrolyte solution containing carbon dioxide. The electrolytic solution containing carbon dioxide is preferably an electrolytic solution containing a carbon dioxide absorbent that reduces the reduction potential of carbon dioxide, has high ionic conductivity, and absorbs carbon dioxide.

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

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

  Examples of secondary amines include dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, and dipropanolamine. The substituted hydrocarbon may be different. The same applies to tertiary amines. For example, those having different hydrocarbons include methylethylamine, methylpropylamine and the like.

  Tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, tripropanolamine, tributanolamine, tripropanolamine, triexanolamine, methyldiethylamine, methyl And dipropylamine.

  As the cation of the ionic liquid, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl-3-methylimidazole 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, 1-butyl-2,3-dimethyl. Examples include 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. In both the imidazolium ion and the pyridinium ion, an alkyl group may be substituted, and an unsaturated bond may exist.

As anions, fluoride ions, chloride ions, bromide ions, iodide ions, BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ COO ⁻ , CF ₃ SO ₃ ⁻ , NO ₃ ⁻ , SCN ⁻ , (CF ₃ SO _2). ) ₃ C ⁻ , bis (trifluoromethoxysulfonyl) imide, bis (trifluoromethoxysulfonyl) imide, bis (perfluoroethylsulfonyl) imide and the like. It may be a zwitterion in which a cation and an anion of an ionic liquid are connected by a hydrocarbon. In addition, you may supply buffer solutions, such as a potassium phosphate solution, to the accommodating parts 111 and 112. FIG.

  FIG. 2 is a diagram showing another example of an electrochemical reaction device. In the electrochemical reaction apparatus shown in FIG. 2, the electrochemical reaction apparatus shown in FIG. 1, the reduction electrode 31, the oxidation electrode 32, and the photoelectric conversion body 33 are different in the stacked configuration. 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.

  FIG. 3 is a schematic cross-sectional view illustrating a structural example of a photoelectric conversion cell. The photoelectric conversion cell shown in FIG. 3 includes a conductive substrate 30, a reduction electrode 31, an oxidation electrode 32, a photoelectric conversion body 33, a light reflector 34, a metal oxide body 35, and a metal oxide body 36. Prepare.

  The conductive substrate 30 is provided in contact with the reduction electrode 31. The conductive substrate 30 may be regarded as a part of the reduction electrode. Examples of the conductive substrate 30 include a substrate containing at least one or more of Cu, Al, Ti, Ni, Fe, and Ag. For example, a stainless steel substrate containing stainless steel such as SUS may be used. Without being limited thereto, the conductive substrate 30 may be configured using a conductive resin. Moreover, you may comprise the electroconductive board | substrate 30 using semiconductor substrates, 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 membrane 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 portion 111 and the housing portion 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. Furthermore, the conductive substrate 30 is not necessarily provided.

  The reduction electrode 31 preferably includes a reduction catalyst. The reduction electrode 31 may include both a conductive material and a reduction catalyst. Examples of the reduction catalyst include materials that reduce activation energy for reducing hydrogen ions and carbon dioxide. In other words, a material that reduces the overvoltage when hydrogen or a carbon compound is generated 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 (CNT), fullerene, ketjen black, or the like can be used. Note that the present invention is not limited thereto, and for example, 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 a reduction catalyst. A plurality of materials may be mixed.

  The oxidation electrode 32 preferably includes an oxidation catalyst. The oxidation electrode 32 may include both a conductive material and an oxidation catalyst. Examples of the oxidation catalyst include a material that reduces activation energy for oxidizing water. In other words, a material that reduces the overvoltage when oxygen and hydrogen ions are generated by an oxidation reaction of water can be used. For example, iridium, platinum, cobalt, manganese, etc. are mentioned. As the oxidation catalyst, a binary metal oxide, a ternary metal oxide, a quaternary metal oxide, or the like can be used. Examples of binary metal oxides include manganese oxide (Mn—O), iridium oxide (Ir—O), nickel oxide (Ni—O), cobalt oxide (Co—O), iron oxide (Fe—O), Examples thereof 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 present invention is not limited to this, and a metal complex such as a Ru complex or an Fe complex can also be used as an oxidation catalyst. 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 materials 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 metal fine powder. By having a porous structure, the area of the active surface contributing to the oxidation-reduction reaction can be increased, so that the conversion efficiency can be increased.

  When an electrode reaction with a low current density is performed using a relatively low light irradiation energy, there are a wide range of options for the catalyst material. Therefore, for example, it is easy to perform the reaction using ubiquitous metal or the like, 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 and at least one of the reduction electrode 31 and the oxidation electrode 32 are electrically connected by wiring or the like, the electrolytic solution tank is downsized, etc. 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 a catalyst.

  The photoelectric conversion body 33 includes 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 containing n-type amorphous silicon, an i-type semiconductor layer 331i containing intrinsic amorphous silicon germanium, and a p-type semiconductor layer containing 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 containing n-type amorphous silicon, an i-type semiconductor layer 332i containing intrinsic amorphous silicon germanium, a p-type semiconductor layer 332p containing p-type microcrystalline silicon, Have 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 the 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 the semiconductor layer; however, the present invention is not limited thereto, and for example, a compound semiconductor layer or the like can be used. As the compound semiconductor layer, for example, a semiconductor layer containing GaAs, GaInP, AlGaInP, CdTe, CuInGaSe, or the like can be used. In addition, 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 single crystal, 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 made of a laminate of a metal layer or a semiconductor layer can be cited. By providing the light reflector 34, the light that could not be absorbed by the photoelectric conversion body 33 can be reflected and incident on either the photoelectric conversion layer 33x or the photoelectric conversion layer 33z, so that light is converted into a chemical substance. Efficiency can be increased. As the light reflector 34, for example, a layer such as a metal such as Ag, Au, Al, or Cu, or an alloy including at least one of these metals can be used.

  The metal oxide body 35 is provided between the light reflector 34 and the photoelectric conversion body 33. The metal oxide body 35 has a function of increasing the light reflectivity by adjusting the optical distance, for example. As the metal oxide body 35, it is preferable to use a material capable of ohmic contact with the n-type semiconductor layer 331n. Examples of the metal oxide body 35 include 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-containing 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 that suppresses destruction of the photoelectric conversion cell due to an oxidation reaction. By providing the metal oxide body 36, corrosion of the photoelectric conversion body 33 can be suppressed and the lifetime of the photoelectric conversion cell can be extended. Note that the metal oxide body 36 is not necessarily 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 to obtain conductivity by the tunnel effect. Examples of the metal oxide body 36 include indium tin oxide (ITO), zinc oxide (ZnO), tin oxide containing fluorine (FTO), zinc oxide containing aluminum (AZO), and tin oxide containing antimony (ATO). A metal oxide layer having light properties 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 other conductive materials are combined, or a combination of a transparent conductive oxide and other conductive materials. 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. 3, the surface opposite to the contact surface of the n-type semiconductor layer 331n with the i-type semiconductor layer 331i is 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, the photoelectric conversion cell shown in FIG. 3 can absorb light of a wide wavelength of sunlight by stacking the photoelectric conversion layer 33x to the photoelectric conversion layer 33z, thereby more efficiently using solar energy. Can be used. At this time, a high voltage can be obtained because the photoelectric conversion layers are connected in series.

  In FIG. 3, since the electrodes are stacked on the photoelectric conversion body 33, the charge-separated electrons and holes can be used for the oxidation-reduction reaction as they are. Further, it is not necessary to electrically connect the photoelectric converter 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 connection. A two-junction type or single layer type photoelectric converter may be used. You may have the lamination | stacking of the photoelectric conversion body of 2 layers or 4 layers or more. Instead of stacking a plurality of photoelectric conversion layers, a single photoelectric conversion layer may be used.

  The electrochemical reaction device of this embodiment is a simplified system in which a reduction electrode, an oxidation electrode, and a photoelectric conversion body are integrated to reduce the number of components. Thus, for example, at least one of manufacture, installation, and maintenance is facilitated. Furthermore, since the wiring etc. which connect a photoelectric conversion body, a reduction electrode, and an oxidation electrode become unnecessary, a light transmittance can be improved and a light-receiving area can be enlarged.

  In some cases, the photoelectric conversion body 33 is corroded because of contact with the electrolytic solution, and the corrosion product is dissolved in the electrolytic solution, thereby causing deterioration of the electrolytic solution. In order to prevent corrosion, a protective layer may be provided. However, the protective layer component may be dissolved in the electrolytic solution. Therefore, 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 electrochemical reaction device of the present embodiment is a technique suitable for measures against surplus power, and is required to utilize solar energy. When the illuminance of sunlight is strong, energy is obtained as much as possible when there is no surplus power, and energy is used for electrolyte circulation or the like for consumption when there is surplus power. Thereby, an energy mix is performed efficiently and the energy utilization rate as a whole can be increased. When a buffer solution is used as the electrolytic solution, the change in pH due to the reaction is small when the reaction amount is small. Therefore, by reducing the electrolyte solution by circulating the electrolyte solution when it is not reacted to keep the electrolyte solution components uniform and restricting or stopping the supply of the electrolyte solution during the reaction, it is possible to suppress the reduction in total efficiency and cost. For example, it is preferable to perform the oxidation-reduction reaction by circulating the electrolytic solution using wind power at night or surplus power with low cost, and stopping the circulation of the electrolytic solution during the day or reacting with a minimum supply amount.

  The structural example of an electrochemical reaction device is not limited to FIG. FIG. 4 is a schematic view showing another example of an electrochemical reaction device. The electrochemical reaction device shown in FIG. 4 is at least different from the electrochemical reaction device shown in FIG. 1 in that the separation tank 13, the separation tank 14, and the flow path 53 to the flow path 55 are further provided.

  The separation tank 13 includes a storage portion 114a that stores the electrolytic solution 24 and a gas-liquid separation membrane 114b that is provided so as to divide the storage portion 114a into a plurality of regions. The gas-liquid separation membrane 114b includes, for example, a hollow fiber membrane. Hollow fiber membranes are, for example, silicone resins and fluorine-based resins (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 electrochemical reaction apparatus shown in FIG. 4, a partial product of the reduction product in the electrolytic solution tank 11 is extracted in the separation tank 13. The outer side of the gas-liquid separation membrane 114b (on the side opposite to the contact surface of the electrolyte solution 24) is decompressed and the electrolyte solution 24 containing a gaseous product efficiently passes through the gas-liquid separation membrane 114b to generate a gas efficiently. And carbon dioxide can be separated. For example, when the product is carbon monoxide, only the carbon monoxide gas can be separated by gas-liquid separation in the separation tank 13.

  The flow path 51 is connected to the accommodating part 114a. The flow path 53 connects the accommodating part 113 and the accommodating part 114a. The separation tank 14 includes a storage portion 115a for storing the electrolytic solution 25 and a gas-liquid separation membrane 115b provided so as to divide the storage portion 115a into a plurality of regions. The flow path 54 connects the accommodating part 112 and the accommodating part 115a. The flow path 55 connects the accommodating part 112 and the accommodating part 115a. At least a part of the electrolytic solution 22 is supplied to the accommodating portion 115 a via the flow path 54. At least a part of the electrolytic solution 25 is supplied to the housing portion 112 via the flow path 55. A circulation pump or the like may be provided in the flow channel 54 and the flow channel 55.

  The pressure outside the gas-liquid separation membrane 115b (the surface opposite to the contact surface of the electrolyte solution 25) is reduced, and the electrolyte containing the gaseous product passes through the gas-liquid separation membrane 115b. Dissolved oxygen can be separated. Although it is conceivable that the oxygen gas generated in the electrolytic solution tank 11 is directly recovered and used, the oxygen gas is dissolved in the electrolytic solution 22 and it is difficult to completely recover the oxygen gas. It is desirable to recover the dissolved oxygen in the form of gas because it causes a reduction in the performance of the oxidation electrode. Unlike gas separation in the electrolytic solution tank 11, it is possible to collect the gas generated in a plurality of cells at a time. Therefore, the total flow path length for gas recovery is shortened, and the system can be simplified. In this case, in order to efficiently recover the oxygen gas, similarly to the electrolytic solution tank 12, the separation tank 14, the flow path 54, and the flow path 55 are provided with temperature control devices to efficiently separate oxygen from the electrolytic solution. It can be carried out.

  By providing a temperature control device in the separation tank 13 or the flow path 51, the product separation efficiency can be increased. In order to perform gas separation completely, it is preferable to remove dissolved gas in the electrolyte as much as possible. In order to improve the removal efficiency of dissolved gas due to temperature distribution or the like, it is preferable that a stirring means is provided in the separation tank 13.

  The difference between the temperature of the electrolytic solution 24 in the separation tank 13 and the temperature of the electrolytic solution 21 in the electrolytic solution tank 11 may be −10 ° C. or more and 10 ° C. or less. If the temperature of the electrolytic solution 24 in the separation tank 13 is too high, dissolved carbon dioxide is vaporized, and the gas concentration of the product tends to decrease. Since energy loss due to heating is large, extreme heating causes a reduction in efficiency.

  When the product is a water-soluble liquid substance such as methanol or ethanol, the separation method of the separation tank 13 may be, for example, distillation or membrane separation. At this time, it is desirable to provide a temperature control device to improve the separation efficiency. The separation membrane may be, for example, zeolite. In particular, since the upstream heat is large, the overall efficiency tends to decrease. On the other hand, a decrease in efficiency can be prevented by providing a heat insulating material in the separation tank 13.

  When an ion exchange membrane or a flow path is provided between the oxidation electrode and the reduction electrode in the electrolytic solution tank, the electrolytic solution in contact with the oxidation electrode may be different from the electrolytic solution in contact with the reduction electrode. With the above configuration, oxygen which is a reaction product on the oxidation side can be easily separated and extracted.

  Each catalyst has a suitable electrolyte, and the efficiency can be improved by changing the electrolyte in contact with each catalyst layer. Further, when the pH is increased on the oxidation side and the reduction side, there is an advantage that the liquid-liquid potential caused by the difference in pH can be supplemented with a potential with insufficient reaction.

  The electrochemical reaction device shown in FIG. 5 includes the configuration shown in the electrochemical reaction device shown in FIG. 4, the flow path 56, the cooler 61 a, the cooler 61 b, the heater 62 a, the heater 62 b, and the pump 71. And a pressurizing valve 72.

  The flow path 56 is connected to the accommodating part of the electrolytic solution tank 12. For example, the flow path 56 is connected to the carbon dioxide generation source 80.

  The cooler 61 a has a function of cooling the electrolyte flowing through the flow path 56. The cooler 61a may be provided inside or outside the flow channel 56, for example.

  The cooler 61 b has a function of cooling the electrolytic solution 23. The cooler 61b may be provided inside or outside the accommodating portion 113, for example.

  The heater 62a has a function of heating the electrolytic solution 25. The heater 62a may be provided inside or outside the accommodating portion 115a, for example.

  The heater 62 b has a function of heating the electrolyte flowing through the flow path 54. The heater 62b may be provided inside or outside the flow channel 54, for example.

  The pump 71 has a function of accelerating the supply of the electrolytic solution from the storage portion 114a to the storage portion 113. The pump 71 is provided, for example, inside or outside the flow path 53. The pump 71 is not necessarily provided.

  The pressurizing valve 72 has a function of accelerating the supply of the electrolytic solution from the storage unit 113 to the storage unit 111. The pressurizing valve 72 is provided, for example, inside or outside the flow path 52. Examples of the pressurizing valve 72 include an orifice valve and a pulse valve. Note that the pressurization valve 72 is not necessarily provided.

  Heat exchange may be performed between the separation tank 13 and the separation tank 14. For example, heat exchange can be performed by providing a heat transfer member 91 that connects between the separation tank 13 and the separation tank 14. For example, the heat transfer member 91 may be provided so as to connect the housing portion 114a and the housing portion 115a. Moreover, you may connect a heat exchanger etc. separately.

  The electrochemical reaction device shown in FIG. 6 further includes a cooler 61c in addition to the configuration shown in FIG.

  The flow path 53 connects the housing part 111 and the housing part 113. The flow path 56 is connected to the accommodating portion 111. The flow path 56 connects the accommodating part 111 and the carbon dioxide generation source 80, for example. The carbon dioxide generation source 80 may be provided inside or outside the electrochemical reaction device.

  Heat exchange may be performed between the electrolytic solution tank 12 and the separation tank 14. For example, heat exchange can be performed by providing a heat transfer member 92 that connects between the electrolytic solution tank 12 and the separation tank 14. For example, the heat transfer member 92 may be provided so as to connect between the flow path 53 and the flow path 54. Moreover, you may connect a heat exchanger etc. separately.

  The cooler 61 c has a function of cooling the electrolyte flowing through the flow path 53. The cooler 61c is provided inside or outside the flow path 53, for example.

  The pump 71 has a function of accelerating the supply of the electrolytic solution from the storage unit 113 to the storage unit 111. The pump 71 is provided in the flow path 52, for example.

  The pressurizing valve 72 has a function of accelerating the supply of the electrolytic solution from the storage unit 111 to the storage unit 113. The pressurizing valve 72 is provided, for example, inside or outside the flow path 52. Examples of the pressurizing valve 72 include an orifice valve and a pulse valve. Note that the pressurization valve 72 is not necessarily provided.

  In the electrochemical reaction apparatus shown in FIGS. 5 and 6, the temperature of the electrolyte solution on the reduction side can be easily lowered by using a cooler. Moreover, the temperature of the electrolyte solution on the oxidation side can be easily increased by using a heater. Therefore, the reaction efficiency can be increased.

  Hot carbon dioxide is generated in power plants and incinerators. When the high temperature carbon dioxide is directly supplied to the electrolytic solution tank 11, the temperature is improved. For this reason, it is preferable to provide a cooler in the flow path 56 between the carbon dioxide generation source 80 and the electrolyte bath 11 to suppress the temperature rise. Even if the cooler has a configuration in which the flow path is cooled by, for example, air, seawater, river water, or the like, a sufficient effect can be obtained.

  By supplying carbon dioxide pressurized by a carbon dioxide generation source 80 such as a power plant or an incinerator to the electrolytic solution tank 11 or the electrolytic solution tank 12 through a flow path without using a pump or the like, energy loss is reduced. can do. A pressure regulator may be provided to stabilize the pressure. Carbon dioxide can be absorbed into the electrolyte solution at a stable pressure by the pressure regulator. Therefore, the stability of the entire apparatus can be improved. Further, the voltage between the reduction electrode and the oxidation electrode, the temperature management of the electrochemical reaction device, and the pressure management are performed according to the supply amount and temperature of the carbon dioxide from the electrolytic solution tank 11 and the operation signal of the carbon dioxide supply device. If the efficiency is improved, the capacity of the device can be utilized to the maximum and the efficiency is improved.

  When the separation tank 13 is heated, the efficiency is improved because the energy loss is reduced by heating using heat from a carbon dioxide generation source or the like. On the other hand, by using the heat of the high-temperature carbon dioxide gas supplied from the carbon dioxide generation source, the temperature of the carbon dioxide gas supplied to the electrolytic solution tank 12 is lowered and the efficiency is improved.

  The electrochemical reaction device shown in FIG. 7 includes, in addition to the configuration of the electrochemical reaction device shown in FIG. 6, a distiller 81a, a reduction reaction device 81b, and a flow path 57 that connects the accommodating portion 113 and the reduction reaction device 81b. Are further provided. Moreover, the electrochemical reaction apparatus has a cooler 61d instead of the cooler 61c. Note that both the cooler 61c and the cooler 61d may be provided.

  The cooler 61 d has a function of cooling the electrolyte flowing in the flow path 52. The cooler 61d is provided inside or outside the flow path 52, for example.

  The distiller 81a has a function of distilling the product in the storage unit 113. The distiller 81 a is connected to the storage unit 113. The distiller 81a is provided on the electrolytic solution tank 12, for example. In the electrochemical reaction apparatus shown in FIG. 7, since the high-temperature carbon dioxide gas can be efficiently used from the heat deprived by distillation in the distiller 81a and the carbon dioxide generation source, the efficiency can be improved. However, since an efficient heat exchanger leads to an increase in cost, the effect can be obtained even by a simple heat exchange method such as connecting a pipe or the like with a heat transfer member. Further, the heat of the high-temperature carbon dioxide gas supplied from the carbon dioxide generation source 80 can be exchanged between the carbon dioxide generation source 80 and the separation tank 13.

The reduction reaction device 81b has a function of reducing the product in the storage unit 113. In the reduction reaction device 81b, for example, a catalyst in which a metal such as an oxide of copper, palladium, silver or Cu—ZnO, Pd—ZnO, Cu—Zn—Cr is supported on Al ₂ O ₃ is used. For example, methanol can be produced by flowing raw material hydrogen and CO gas at 150 to 300 ° C. under pressure. In addition, methanol can be produced by a liquid phase method in which hydrogen and CO gas are passed through the catalyst slurry under pressure. The reduction reaction device 81b includes a heat exchanger for removing heat generated by the reaction, for example. The reduction reaction device 81b may be a device that produces methane using ethanol, nickel, or ruthenium using rhodium or the like.

  The product of the reduction reaction in the reduction reaction device 81b is, for example, hydrocarbons such as methane, methanol, ethanol, acetic acid, dimethyl ether, wax, olefin, naphtha, and light oil. The heat source may include not only carbon dioxide from, for example, a carbon dioxide generation source, but also at least part of the heat of reaction between the reduction product of carbon dioxide and hydrogen. For example, the efficiency is improved by utilizing mutual heat utilizing a part of reaction heat when methanol is generated from the reaction between carbon monoxide and hydrogen by the reduction reaction device 81b.

  Heat exchange may be performed between the carbon dioxide generation source 80 and the electrolytic solution tank 12. For example, heat exchange can be performed by providing a heat transfer member 93 that connects between the carbon dioxide generation source 80 and the electrolyte bath 12. For example, the heat transfer member 93 may be provided so as to connect between the flow path 56 and the distiller 81a. Moreover, you may connect a heat exchanger etc. separately.

  Heat exchange may be performed between the reduction reaction device 81b and the distiller 81a. For example, heat exchange can be performed by providing a heat transfer member 94 that connects the reduction reaction device 81b and the distiller 81a. Moreover, you may connect a heat exchanger etc. separately.

  In the electrochemical reaction apparatus shown in FIG. 7, heat from the heat source can be efficiently exhausted by heat exchange between the flow path 56 and the distiller 81a and heat exchange between the distiller 81a and the reduction reaction apparatus 81b.

  Note that the electrochemical reactor shown in FIG. 7 may be provided with the separation tank 14, the flow path 54, and the flow path 55 shown in FIG. Moreover, in order to improve the separation efficiency of dissolved gas due to temperature distribution or the like, a stirring means may be provided in the oxygen gas separation device. At this time, the efficiency can be improved by using the carbon dioxide generation source 80, the high-temperature carbon dioxide gas obtained from the carbon dioxide generation source 80, or the heat generated by the reduction reaction device 81b or the like as the heat source. The combination of these heats is arbitrary, and the efficiency can be improved by performing an operation method for exchanging heat with each other. Moreover, in order to mutually utilize these heat, efficiency can be improved by connecting a flow path etc. with a heat-transfer member. The accommodating part 114a may be connected to at least one of the accommodating part 112 and the accommodating part 115a via a heat transfer member, for example.

Example 1
An electrochemical reaction device having a structure was produced. The structure includes a three-junction photoelectric converter having a thickness of 500 nm, a ZnO layer having a thickness of 300 nm provided on the first surface of the three-junction photoelectric converter, and a thickness provided on the ZnO layer. 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 photoelectric conversion body.

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

The open circuit voltage was measured when the structure was irradiated with light using a solar simulator (AM1.5, 1000 W / m ² ). The open circuit voltage was 2.1V.

A Ni (OH) ₂ layer having a thickness of 200 nm was formed as an oxidation catalyst on the ITO layer on the structure of the three-junction photoelectric conversion body by an electrodeposition method using nickel nitrate. A gold nanoparticle layer supported on carbon having a thickness of 500 nm was formed on a SUS substrate as a reduction catalyst.

  The said structure was cut out in square shape, and the edge part was sealed with the thermosetting epoxy resin. The structure was surrounded by an ion exchange membrane (Nafion (registered trademark)) to form a sheet. This ion exchange membrane and a plurality of cells were combined to produce a 10 cm square unit, and 10 units were arranged vertically and horizontally to produce a 100 cm square photoelectrochemical reaction unit. For example, a photoelectric conversion cell may be embedded in a plurality of holes of one ion exchange membrane having a plurality of holes to form a sheet. A plurality of structures each having a photoelectric conversion cell embedded in a hole of an ion exchange membrane having one hole may be arranged in a sheet shape. An ion exchange membrane may be embedded in the hole of the photoelectric conversion cell having the hole.

This sheet-like photoelectrochemical reaction unit was sandwiched between a pair of 3 cm-thick frames having a hollow portion of 100 cm in length and 100 cm in width, and a silicone resin layer was formed between the pair of frames. A window made of non-reflective solar cell glass was produced so as to cover one hollow portion of the pair of frames. An acrylic resin plate was formed so as to cover the other hollow part of the pair of frames. This produced the sealing body which sealed the photoelectrochemical reaction unit. A flow path was provided on each of the Ni (OH) ₂ layer side and the gold nanoparticle layer side of the photoelectrochemical reaction unit. As the electrolytic solution, a 0.5 M potassium hydrogen phosphate aqueous solution saturated with carbon dioxide gas was used. A gas recovery channel for collecting the generated gas was provided in a part of the electrolytic solution tank. Thus, a photoelectrochemical reaction module was produced. An acrylic container having an internal volume of 30 cm × 3 cm × 3 cm was connected to the Pt layer side of the module as a mixing tank.

A 50 cc / min CO ₂ gas was blown into the module using a cylindrical glass container having a capacity of 30 cc as an electrolytic solution tank to dissolve the CO ₂ gas in the electrolytic solution. This electrolytic solution was supplied to the reduction electrode side of the module at a flow rate of 0.1 cc / min, and the electrolytic solution was circulated. Further, the potassium borate buffer solution on the oxidation electrode side was circulated through a buffer tank of a cylindrical container having a capacity of 30 cc at a flow rate of 0.1 cc / min without blowing CO ₂ .

In the module of Example 1, when AM1.5 artificial sunlight was irradiated from the oxidation electrode side and reacted for 0.5 hour, the initial current value was around 1 mA / cm ² , but 0.4 mA / cm 2. Decreased to ² .

In the module of Example 1, AM1.5 artificial sunlight was irradiated from the oxidation electrode side, reacted for 0.5 hour, and then the electrolyte bath was cooled by placing it in ice water and the current value was around 0.7 mA / cm ^2. It recovered until. This shows that the reaction efficiency can be improved by cooling the electrolytic solution containing carbon dioxide.

  In the module of Example 1, when the artificial sunlight of AM1.5 was irradiated from the oxidation electrode side and the flow rate was 0.2 cc / min, the current drop time could be increased by about 1.7 times. From this, it can be seen that a decrease in current can be suppressed by increasing the circulation flow rate.

(Example 2)
A composite substrate (4 cm square) having a SUS substrate having a thickness of 1.5 mm connected to a power source via a conductive wire and a gold-carrying carbon film having a supported amount of 0.25 mg / cm ² on the SUS substrate, and a platinum foil (4 cm square) were prepared. The power source is a solar cell simulation device. A flow path and a gas flow path were formed on each of the oxidation electrode side and the reduction electrode side of an acrylic frame having a 5 cm square and a thickness of 1 cm. A composite substrate and a platinum foil are encapsulated in a frame, an ion exchange membrane (Nafion 117, 6 cm square) is provided between the composite substrate and the platinum foil, and a silicon rubber sheet and an acrylic are provided on both the outside of the composite substrate and the outside of the platinum foil. A module sandwiched between plates (length 7 cm × width 7 cm × thickness 3 mm) was produced. A pH 7 potassium phosphate buffer solution was fed into the module. The composite substrate was a reduction electrode, the platinum foil was an oxidation electrode, and the silver-silver chloride electrode was a reference electrode. Using a galvanostat, carbon dioxide was decomposed by applying an electric current under the conditions of 37 mA: 2.3 mA / cm ² . A 50 cc / min CO ₂ gas was blown into the module using a cylindrical glass container having a capacity of 30 cc as an electrolytic solution tank to dissolve the CO ₂ gas in the electrolytic solution. This electrolytic solution was supplied to the reduction electrode side of the module at a flow rate of 0.1 cc / min, and the electrolytic solution was circulated. The potassium borate buffer solution on the oxidation electrode side was circulated through a buffer tank of a 30 cc cylindrical container at a flow rate of 0.1 cc / min without blowing CO ₂ .

  In the module of Example 2, when the reaction was performed for 0.5 hour at a current of 37 mA and a circulation flow rate of 0.1 cc / min, the initial potential was around −1V, but it dropped to −1.4V.

  In the module of Example 2, after reacting at a current of 37 mA and a circulation flow rate of 0.1 cc / min for 0.5 hours, the potential was recovered to around −0.8 V when the electrolytic bath was cooled by being immersed in ice water. This shows that the reaction efficiency can be improved by cooling the electrolytic solution containing carbon dioxide.

  In the module of Example 2, when the reaction was performed at a current of 37 mA and a circulation flow rate of 0.1 cc / min for 0.5 hours and the flow rate was set to 0.2 cc / min, the potential decrease time could be approximately doubled. From this, it is understood that a decrease in potential can be suppressed by increasing the circulation flow rate.

  The above embodiment is presented as an example, and is not intended to limit the scope of the invention. The above embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. The above-described embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and equivalents thereof.

  DESCRIPTION OF SYMBOLS 4 ... Ion exchange membrane, 11 ... Electrolyte tank, 12 ... Electrolyte tank, 13 ... Separation tank, 14 ... Separation tank, 21 ... Electrolyte, 22 ... Electrolyte, 23 ... Electrolyte, 24 ... Electrolyte, 25 ... Electrolytic solution, 30 ... conductive substrate, 31 ... reduction electrode, 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, 51-57 ... Channel, 61a ... Cooler, 61b ... Cooler, 61c ... Cooler, 61d ... Cooler, 62a ... Heater, 62b ... Heater, 71 ... Pump, 72 ... pressurizing valve, 80 ... carbon dioxide generation source, 81a ... distiller, 81b ... reduction reaction device, 91 ... heat transfer member, 92 ... heat transfer member, 93 ... heat transfer member, 94 ... heat transfer member, 111 ... accommodating part, 112 ... accommodating part, 113 ... accommodating part, 114a ... accommodating part, 14b ... gas-liquid separation membrane, 115a ... housing portion, 115b ... gas-liquid separation membrane, 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.

Claims (14)

A first electrolyte tank comprising: a first container that contains a first electrolyte containing carbon dioxide; and a second container that contains a second electrolyte containing water;
A reduction electrode immersed in the first electrolytic solution;
An oxidation electrode immersed in the second electrolytic solution;
A power source electrically connected to the reduction electrode and the oxidation electrode;
A second electrolytic solution tank comprising a third accommodating portion for accommodating a third electrolytic solution containing carbon dioxide;
A flow path connecting the first housing portion and the third housing portion,
An electrochemical reaction device, wherein a temperature of the third electrolytic solution is lower than a temperature of the first electrolytic solution. 1st separation tank provided with the 4th accommodating part which accommodates the 4th electrolyte solution containing a carbon dioxide, and the 1st gas-liquid separation membrane provided so that the said 4th accommodating part may be divided into a plurality of fields When,
A second separation tank comprising a fifth housing portion for housing a fifth electrolyte containing water and a second gas-liquid separation membrane provided so as to divide the fifth housing portion into a plurality of regions; ,
A second flow path connecting the first housing portion and the fourth housing portion;
A third flow path connecting the third housing portion and the fourth housing portion;
2. The electrochemical reaction device according to claim 1, further comprising a fourth flow path connecting the second storage portion and the fifth storage portion. A carbon dioxide generating source containing carbon dioxide having a temperature higher than that of the first electrolytic solution;
A reduction reaction device for reducing a product resulting from the reduction reaction of carbon dioxide;
A distiller provided on the third accommodating portion;
A fifth flow path connecting the first housing part and the carbon dioxide generation source;
The electrochemical reaction device according to claim 2, further comprising a sixth flow path that connects the third storage unit and the reduction reaction device. A first cooler provided in the third accommodating portion;
A first heater provided in the second flow path;
A second cooler provided in the fourth flow path;
The electrochemical reaction device according to claim 3, further comprising a second heater provided in the fifth flow path.   Between the second electrolyte tank and the second separation tank, between the first separation tank and the second separation tank, between the reduction reaction device and the second electrolyte tank. The electrochemical reaction device according to claim 3, wherein heat exchange is performed between at least one of the carbon dioxide generation source and the distiller and between the reduction reaction device and the distiller.   A heat transfer member connecting between the second electrolyte tank and the second separation tank, a heat transfer member connecting between the first separation tank and the second separation tank, and the reduction reaction A heat transfer member connecting between the apparatus and the second electrolytic solution tank, a heat transfer member connecting between the carbon dioxide generating source and the distiller, and between the reduction reaction apparatus and the distiller. The electrochemical reaction device according to claim 3, further comprising at least one heat transfer member of the heat transfer member to be connected.   The said power supply is provided with the photoelectric conversion body which has the 1st surface electrically connected to the said reduction | restoration electrode, and the 2nd surface electrically connected to the said oxidation electrode. The electrochemical reaction apparatus as described in any one.   The electrochemical reaction device according to any one of claims 1 to 7, further comprising an ion exchange membrane provided between the first housing portion and the second housing portion.   The electrochemical reaction device according to any one of claims 1 to 8, wherein a pressure applied to the third electrolytic solution is higher than a pressure applied to the first electrolytic solution. A first electrolyte tank comprising: a first container that contains a first electrolyte containing carbon dioxide; and a second container that contains a second electrolyte containing water;
A reduction electrode immersed in the first electrolytic solution;
An oxidation electrode immersed in the second electrolytic solution;
A power source electrically connected to the reduction electrode and the oxidation electrode;
A second electrolytic solution tank comprising a third accommodating portion for accommodating a third electrolytic solution containing carbon dioxide;
A flow path connecting the first housing portion and the third housing portion,
An electrochemical reaction device, wherein a pressure applied to the third electrolytic solution is higher than a pressure applied to the first electrolytic solution. 1st separation tank provided with the 4th accommodating part which accommodates the 4th electrolyte solution containing a carbon dioxide, and the 1st gas-liquid separation membrane provided so that the said 4th accommodating part may be divided into a plurality of fields When,
A second separation tank comprising a fifth housing portion for housing a fifth electrolyte containing water and a second gas-liquid separation membrane provided so as to divide the fifth housing portion into a plurality of regions; ,
A second flow path connecting the first housing portion and the fourth housing portion;
A third flow path connecting the third housing portion and the fourth housing portion;
11. The electrochemical reaction device according to claim 10, further comprising a fourth flow path connecting the second storage portion and the fifth storage portion. A carbon dioxide generating source containing carbon dioxide having a temperature higher than that of the first electrolytic solution;
A reduction reaction device for reducing a product resulting from the reduction reaction of carbon dioxide;
A distiller provided on the third accommodating portion;
A fifth flow path connecting the first housing part and the carbon dioxide generation source;
The electrochemical reaction device according to claim 11, further comprising a sixth flow path that connects the third storage unit and the reduction reaction device.   The said power supply is provided with the photoelectric conversion body which has the 1st surface electrically connected to the said reduction electrode, and the 2nd surface electrically connected to the said oxidation electrode. The electrochemical reaction apparatus as described in any one.   The electrochemical reaction device according to any one of claims 10 to 13, further comprising an ion exchange membrane provided between the first housing portion and the second housing portion.

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