JP2017057491A - Production system of reduced product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system capable of recovering a reduced product of carbon dioxide at a high efficiency.SOLUTION: According to the present embodiment, a system that produces a reduced product of carbon dioxide is provided. The system includes an electrolytic tank for oxidation reaction which is provided with an oxidation catalyst, and an electrolytic tank for reducing reaction which is provided with a reduction catalyst. The system further includes a chemical reactor that generates a reduced product by reducing carbon dioxide, an electrolytic solution supply unit that supplies an electrolytic solution to the electrolytic tank for reducing reaction, a carbon dioxide supply unit that increases a concentration of the reduced product in the electrolytic solution by continuing the reducing reaction in the electrolytic tank for reducing reaction by dissolving carbon dioxide in the electrolytic solution, and a separation unit for separating the reduced product from the electrolytic solution in which the concentration of the reduced product is increased.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a system for producing a carbon dioxide reduction product.

From the viewpoint of energy problems and environmental problems, it is required to efficiently reduce CO ₂ by light energy like plants. Plants use a system called the Z scheme that excites light energy in two stages. In a photochemical reaction using this system, water (H ₂ O) is oxidized to obtain electrons, and carbon dioxide (CO ₂ ) is reduced to synthesize cellulose and saccharides.

Currently, an artificial photosynthesis system has been developed that mimics such a plant Z-scheme and obtains the potential necessary for CO ₂ reduction from visible light.

JP 2011-68699 A JP 2014-74207 A Special table 2011-524342 gazette JP 2010-188243 A

Photoelectrochemical Reduction of Carbon Dioxide at Si (111) Electrode Modified by Viologen Molecular Layer with Metal Complex _ Chem. Lett. 2012, 41, 328330 CO2 Capture by Imidazolate-Based Ionic Liquids: Effect of Functionalized Cation and Dication Ind.Eng. Chem. Res., 2013, 52 (18), pp 6069-6075 acs.catal.2012.2.1684-1692

A CO ₂ reduction product that is difficult to dissolve in an electrolyte such as carbon monoxide, methane, and ethylene can be efficiently recovered with less energy. On the other hand, CO ₂ reduction products that are easily dissolved in an electrolytic solution such as methanol, ethanol, and ethylene glycol require a large amount of energy to recover from the electrolytic solution, resulting in a reduction in recovery efficiency. An object of this invention is to provide the system which can collect | recover the reduced product of a carbon dioxide with high efficiency.

  According to the embodiment, a system for producing a reduced product of carbon dioxide is provided. The system includes an oxidation reaction electrolytic cell equipped with an oxidation catalyst and a reduction reaction electrolytic cell equipped with a reduction catalyst, a chemical reaction device for reducing carbon dioxide to produce a reduced product, and the reduction reaction An electrolytic solution supply unit for supplying an electrolytic solution to the electrolytic cell for use, and increasing the concentration of the reduced product in the electrolytic solution by dissolving carbon dioxide in the electrolytic solution and maintaining the reduction reaction in the electrolytic cell for the reduction reaction And a separation unit that separates the reduced product from the electrolytic solution in which the concentration of the reduced product is increased.

The figure which shows an example of a structure of the reduced product production system which concerns on embodiment. The figure which shows the other example of a structure of the reduced product production system which concerns on embodiment. The figure which shows the other example of a structure of the reduced product production system which concerns on embodiment. The figure which shows the other example of a structure of the reduced product production system which concerns on embodiment. Sectional drawing which shows the structure of the chemical reaction cell used in the reduced product production system which concerns on embodiment. Sectional drawing which shows an example of the operation principle of the chemical reaction cell of FIG. Sectional drawing which shows the other example of the operation | movement principle of the chemical reaction cell of FIG. The perspective view which shows the structure of the chemical reaction apparatus with which the reduced product production system which concerns on embodiment is equipped. Sectional drawing of the chemical reaction apparatus of FIG. Sectional drawing which shows the structure of the modification 1 of the chemical reaction apparatus of FIG. Sectional drawing which shows the structure of the modification 2 of the chemical reaction apparatus of FIG. The schematic diagram which shows the structure of a 1st reduction catalyst. The schematic diagram which shows the structure of the reduction catalyst which concerns on the 1st aspect of a 1st reduction catalyst. The schematic diagram which shows an example of a structure of the reduction catalyst which concerns on the 2nd aspect of a 1st reduction catalyst. The schematic diagram which shows the structure of the reduction catalyst which concerns on a 2nd reduction catalyst. The schematic diagram which shows the structure of the reduction catalyst which concerns on the modification 1 of a 2nd reduction catalyst. The schematic diagram which shows an example of a structure of the reduction catalyst which concerns on the modification 1 of a 2nd aspect. The schematic diagram which shows an example of a structure of the reduction catalyst which concerns on the modification 2 of a 2nd aspect.

Hereinafter, embodiments will be described with reference to the drawings.
According to the embodiment, a reduced product production system for producing a reduced product of carbon dioxide is provided. This system has an oxidation reaction electrolytic cell equipped with an oxidation catalyst and a reduction reaction electrolytic cell equipped with a reduction catalyst, a chemical reaction device for reducing carbon dioxide to produce a reduced product, and the reduction reaction An electrolytic solution supply unit for supplying an electrolytic solution to the electrolytic cell, and a concentration of the reduced product in the electrolytic solution by dissolving carbon dioxide in the electrolytic solution and maintaining the reduction reaction in the electrolytic cell for the reduction reaction And a separation unit for separating the reductant from the electrolyte having an increased concentration of the reductant.

  In FIG. 1, an example of a structure of the reduced product production system 60 is shown. The reduced product production system 60 includes a chemical reaction device 61 having an oxidation reaction electrolytic bath 31a, a reduction reaction electrolytic bath 31b, and a diaphragm 31c, an electrolyte supply unit, a carbon dioxide supply unit, and a separation unit.

  The chemical reaction device 61 includes an oxidation catalyst in the oxidation reaction electrolytic bath 31a, and a reduction catalyst in the reduction reaction electrolytic bath 31b. Water is supplied to the oxidation reaction electrolytic bath 31a through the pipe 80a, and oxygen generated by the oxidation reaction is discharged together with water through the pipe 80b.

  An electrolytic solution containing carbon dioxide is supplied from the electrolytic solution supply unit to the reduction reaction electrolytic bath 31b. In the reduction reaction electrolytic bath 31b, carbon dioxide in the electrolytic solution is reduced by the reduction catalyst, and a reduced product is generated. As the reduction catalyst, not only carbon dioxide but also a catalyst capable of reducing intermediate products in which carbon dioxide is reduced, such as formic acid, formaldehyde, oxalic acid, glycolic acid and glycolaldehyde, is used. The reduction catalyst and the chemical reaction apparatus will be described in detail later.

  The electrolytic solution supply unit is a unit that supplies the electrolytic solution to the reduction reaction electrolytic bath 31b, and a storage tank 64 that stores the electrolytic solution, and a first electrolytic solution that supplies the electrolytic solution from the storage bath 64 to the reduction reaction electrolytic bath 31b. 1 piping 81 and the 2nd piping 82 which discharges electrolyte solution from electrolysis tank 31b for reduction reaction, and returns to storage tank 64 are provided. The electrolytic solution supply unit includes a liquid feeding pump 81a, and causes the electrolytic solution to circulate between the storage tank 64 and the reduction reaction electrolytic tank 31b by the liquid feeding pump 81a. In FIG. 1, an example in which the liquid feeding pump 81 a is provided in the first pipe 81 is shown, but the liquid feeding pump 81 a is not limited to this, and the liquid feeding pump 81 a is connected to at least one of the first pipe 81 and the second pipe 82. It only has to be provided.

  The electrolytic solution supply unit is connected to the separation unit, and the electrolytic solution circulating between the storage tank 64 and the reduction reaction electrolytic tank 31b is fed to the separation unit. For example, the first pipe 81 is provided with a three-way valve 81b, and the electrolytic solution is sent to the separation unit via the three-way valve 81b. The electrolytic solution circulating between the storage tank 64 and the reduction reaction electrolytic bath 31b is sent to the third pipe 83 of the separation unit via the three-way valve 81b after a predetermined time. Alternatively, a part of the electrolytic solution circulating between the storage tank 64 and the reduction reaction electrolytic tank 31b is continuously sent to the third pipe 83 of the separation unit via the three-way valve 81b.

  1 shows an example in which the three-way valve 81b is provided in the first pipe 81. However, the present invention is not limited to this, and the three-way valve 81b is provided in at least one of the first pipe 81 and the second pipe 82. It only has to be provided. Alternatively, a pipe having a valve instead of the three-way valve 81b may be provided in the storage tank 64.

  The storage tank 64 is provided with a pipe 92 having a valve, and a new electrolyte is supplied to the storage tank 64 through the pipe 92.

  The carbon dioxide supply unit is a unit that supplies carbon dioxide to the electrolytic solution supplied to the reduction reaction electrolytic bath 31b. The carbon dioxide supply unit is provided in at least one of the reduction reaction electrolytic bath 31 b, the storage tank 64, the first pipe 81, and the second pipe 82. For example, as shown in FIG. 1, the carbon dioxide supply unit may be a unit that sprays carbon dioxide directly into a pipe 66 having a valve and the inside of the electrolytic solution.

  The electrolytic solution supply unit preferably includes an exhaust unit that exhausts excess carbon dioxide gas that has not been dissolved in the electrolytic solution and gas generated by the reduction reaction. The exhaust unit may be a pipe 68 provided with a valve, and may be provided in the storage tank 64, for example.

The separation unit is a unit that recovers the CO ₂ reduction product from the electrolytic solution. The separation unit includes a third pipe 83 connected to the electrolytic solution supply unit via the three-way valve 81b, and a unit that separates the electrolyte and the reduced product from the electrolytic solution. Specifically, a crude distillation column 70 that separates the electrolyte from the electrolytic solution, and a rectifying column 72 that separates the reduced product from the liquid discharged from the crude distillation column 70 are provided.

  In one embodiment, as shown in FIG. 1, the rectification column 72 separates the first rectification column 72a for separating a reduced product having a boiling point lower than that of water and a reduced product having a boiling point higher than that of water. And a third rectifying column 72c. Reducts having a lower boiling point than water include, but are not limited to, methanol and ethanol. The reduced product having a boiling point higher than that of water includes, but is not limited to, ethylene glycol.

  The separation unit first supplies the electrolytic solution flowing from the electrolytic solution supply unit to the third pipe 83 via the three-way valve 81b to the crude distillation tower 70. In the crude distillation tower 70, the electrolytic solution is distilled and separated into a liquid component and an electrolyte. Distillation in the crude distillation column 70 can be performed by a conventional method. Specifically, the electrolytic solution is distilled under reduced pressure under a reduced pressure of 10 to 120 Torr. Thereby, 85-99 mass% of liquid components, such as a reduced product and water, contained in electrolyte solution evaporate, and it is discharged | emitted from a tower top part. On the other hand, the electrolyte is accumulated in the lower part of the tower and removed outside the tower.

  The liquid component discharged from the top of the crude distillation column 70 is supplied to the first rectification column 72a through the pipe 86 and is rectified. Rectification in the first rectification column 72a can be performed by a conventional method. Specifically, it can be carried out by vacuum distillation using the difference in boiling points. Thereby, a liquid component containing a reduced product having a boiling point lower than that of water such as methanol or ethanol is discharged from the top of the first rectifying column 72a through the pipe 88. On the other hand, a liquid containing a reduced product having a boiling point higher than that of water is discharged from the bottom of the column.

  The liquid component containing a reduced product having a boiling point lower than that of water, such as methanol or ethanol, discharged from the top of the first rectifying column 72a may be further refined into each component, or as described later. May be used to prepare a simple electrolyte.

  The liquid component discharged from the bottom of the first rectifying column 72a is then supplied to the third rectifying column 72c through the pipe 90 and rectified. Rectification in the third rectification column 72c can be performed by a conventional method. Specifically, it can be performed by distillation under reduced pressure using the difference in boiling points, water is separated from the top of the column, and a reduced product having a higher boiling point than water is discharged from the bottom of the column. An example of such a reduced product is ethylene glycol.

The electrolytic solution used in the reduced product production system 60 according to the embodiment preferably has a property of reducing the reduction potential of CO ₂ , having high ionic conductivity, and absorbing CO ₂ . Examples of the electrolyte contained in such an electrolyte include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium chloride, Sodium chloride, potassium chloride, lithium sulfate, lithium bromide, sodium bromide, potassium bromide, lithium iodide, sodium iodide, potassium iodide, lithium sulfate, sodium sulfate, potassium sulfate, lithium hydrogen sulfate, sodium hydrogen sulfate, Potassium hydrogen sulfate, lithium phosphate, sodium phosphate, potassium phosphate, lithium hydrogen phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, lithium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate included. As the solvent, water is preferably used. The concentration of the electrolyte in the electrolytic solution can be appropriately determined in consideration of CO ₂ solubility, ionic conductivity, viscosity, and the like. For example, a range of 0.01 to 1 mol / L is preferable.

  In the reduced product production system 60 according to the embodiment, by using the electrolytic solution containing the above electrolyte, it is possible to separate the electrolyte from the electrolytic solution and efficiently collect the reduced product.

  In one embodiment, the reduced product production system 60 may include a plurality of chemical reaction devices 61. The plurality of chemical reaction devices 61 may be connected in series or may be connected in parallel. By providing a plurality of chemical reaction devices 61, it is possible to increase the reduction efficiency.

  In one embodiment, as shown in FIG. 2, the reduced product production system 60 includes a first rectifying column 72a for separating methanol, a second rectifying column 72b for separating ethanol, and a third rectifying column 72b for separating ethylene glycol. A rectifying column 72c. The liquid component discharged from the crude distillation column 70 is supplied to the first rectification column 72a through the pipe 86 and is rectified. Rectification in the first rectification column 72a can be performed by a conventional method. Specifically, it can be carried out by vacuum distillation using the difference in boiling points. As a result, methanol is discharged from the top of the first rectifying column 72a through the pipe 88a, and other liquid components are discharged from the bottom of the column.

  The liquid component discharged from the bottom of the first rectifying column 72a is then supplied to the second rectifying column 72b through the pipe 90a and rectified. The rectification in the second rectification column 72b can be performed by a conventional method. Specifically, it can be carried out by vacuum distillation using the difference in boiling points. Thereby, ethanol is discharged | emitted from the tower top through the piping 88b, and another liquid component is discharged | emitted from the tower bottom part.

  The liquid component discharged from the bottom of the second rectifying column 72b is then supplied to the third rectifying column 72c through the pipe 90b and rectified. Rectification in the third rectification column 72c can be performed by a conventional method. Specifically, it can be carried out by vacuum distillation using the difference in boiling points. As a result, water is discharged from the top of the tower through the pipe 88c, and ethylene glycol is discharged from the bottom of the tower.

  According to such a configuration, each of methanol, ethanol and ethylene glycol can be recovered.

  In another embodiment, the reduced product production system 60 prepares a new electrolytic solution using the electrolyte separated in the crude distillation column 70 and the water separated in the rectifying column 72, as shown in FIG. A preparation tank 74 may be provided.

  The electrolyte separated in the crude distillation tower 70 is injected into the preparation tank 74 through the fifth pipe 78. The fifth pipe 78 may have a storage tank 79 for temporarily storing the electrolyte. Further, the water discharged from the top of the third rectifying column 72c is supplied to the preparation tank 74 through the pipe 88c.

  In the preparation tank 74, a new electrolytic solution is prepared using an electrolyte and water. The preparation tank 74 preferably includes a stirring mechanism such as a stirring blade inside. In order to adjust the electrolytic solution to a predetermined concentration, the concentration can be adjusted by a known method. For example, an electrolyte having a predetermined mass and water are mixed and stirred by a stirring mechanism to dissolve the electrolyte and prepare a uniform solution.

  The preparation tank 74 may include a pH meter or a conductivity meter that measures the hydrogen ion concentration and electrical conductivity. With these devices, it can be confirmed that the electrolyte is dissolved in water and the electrolyte solution of a predetermined concentration is prepared.

  The electrolyte prepared in the preparation tank 74 is supplied to the storage tank 64 through a fourth pipe 76 having a valve.

  According to such a configuration, the electrolytic solution can be continuously used stably, and the operation of the reduced product production system can be easily maintained. Moreover, since the separated electrolyte and water can be reused, the cost can be reduced.

In other embodiments, a reduced product production system 60, separation unit concentration of the reducing substance of CO ₂ to recover the reduced product from elevated electrolyte have other forms. A separation unit having another form will be described with reference to FIG.

  In the reduced product production system 60 shown in FIG. 3, the separation unit is connected to the electrolyte supply unit by a third pipe 83 via a three-way valve 81b.

This separation unit includes an extraction device 201 that extracts the reduced product and unreacted CO ₂ from an electrolytic solution in which the concentration of the CO ₂ reduction product has increased into an ionic liquid that is an extraction solvent, and a reduction exhausted from the extraction device 201. Carbon dioxide separation column 202 for separating CO ₂ from the ionic liquid containing the product and CO _2, and a rectifying column 72 for separating the reduced product from the ionic liquid containing the reduced product discharged from carbon dioxide separation column 202.

The separation unit first supplies the electrolytic solution flowing from the electrolytic solution supply means to the third pipe 83 via the three-way valve 81 b to the extraction device 201. The extraction device 201 is filled with an ionic liquid as an extraction solvent. The extraction device 201 mixes, contacts, and performs liquid-liquid extraction with an electrolytic solution containing a reduced product and unreacted CO ₂ and an ionic liquid as an extraction solvent, so that the reduced product and unreacted CO are removed from the electrolytic solution. ₂ to the ionic liquid.

The operation of mixing and contacting the electrolytic solution containing the reduced product and unreacted CO ₂ and the ionic liquid to perform liquid-liquid extraction can be performed by a conventional method. Specifically, an electrolytic solution containing a reduced product and unreacted CO ₂ is supplied to the extraction device 201 filled with the ionic liquid through the third pipe 83. Although the reduction product and CO ₂ are extracted into the ionic liquid by stirring, the method of physically contacting the electrolytic solution and the ionic liquid includes shaking and ultrasonic waves, and is not limited.

From the viewpoint of extracting unreacted CO ₂ , it is preferable to pressurize in addition to stirring. By pressurizing, CO ₂ can be effectively dissolved in the ionic liquid. If the pressure to be applied is too low, it takes time to complete the absorption, and if it is too high, operation control becomes difficult. Therefore, it is 0 MPa or more and 50 MPa or less, preferably normal pressure (for example, 0.1 MPa) or more and 25 MPa or less, more preferably normal pressure or more and 12 MPa or less.

  In addition, the temperature condition for pressurization is -50 ° C or higher and 250 ° C or lower, preferably 0 ° C or higher and 200 ° C or lower, more preferably considering the thermal stability of the reduced product or ionic liquid, the fluidity of the solution, and the like. Is normal temperature (for example, 15-25 degreeC) or more and 100 degrees C or less.

The ionic liquid used as the extraction solvent is an ionic liquid composed of a cation and an anion. The ionic liquid is a compound containing an organic cation selected from, for example, an alkyl ammonium cation, a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, an imidazolium cation, and an alkylphosphonium cation. The anion include counter anion Xa in the following general formula Ia～VIa ^- can be the same anion as specific examples of. As the extraction solvent, two or more ionic liquids having different cation structures or anion structures may be mixed and used.

  Specific examples of the ionic liquid that can be suitably used as the extraction solvent include compounds represented by any one of the following general formulas Ia to VIa.

In the general formulas Ia to VIa, R _1a , R _2a , R _3a and R _4a each independently represents an alkyl group or a cycloalkyl group. Xa ^- represents a counter anion.

  As described above, the ionic liquid is an ionic liquid composed of a cation and an anion, and in one form, is a compound in which the lengths of the alkyl chains of the cation molecule are unbalanced. As a result of increasing the asymmetry of the molecular structure by making the length of the alkyl chain of the cation molecule non-uniform, it is in a solution state.

As an alkyl group represented by R _{< 1a>} , R _<2a> , R _<3a> and R _<4a >, a C1-C12 alkyl group is preferable, for example, and a C1-C6 alkyl group is preferable. Moreover, as a cycloalkyl group represented by R _{< 1a>} , R _<2a> , R _<3a> and R _<4a >, a C3-C8 cycloalkyl group is preferable, for example, and a C4-C6 cycloalkyl group is more preferable.

R _1a is preferably a group having a carbon number smaller than R _2a , R _3a and R _4a . Specifically, the difference in carbon number between R _1a and R _2a , R _3a and R _4a is preferably 1 or more and 11 or less, and more preferably 1 or more and 5 or less.

Examples of the counter anion represented by Xa ⁻ include BF ₄ ⁻ , PF ₆ ⁻ , fluoromethanesulfonate anion (CF ₃ SO ₃ ⁻ ), and bistrifluoromethanesulfonylimide anion ((CF ₃ SO ₃ ) ₂ N ^−. ) And (CN) ₂ N ⁻ , (CN) ₄ B ^— .

  The solubility of the ionic liquid in water varies depending on the combination of the cation and the anion. Since it is desired that the ionic liquid used as the extraction solvent in the extraction apparatus 201 does not dissolve in water, the cation and the anion may be appropriately selected from a combination that provides hydrophobicity.

Specific examples of the ionic liquid that can be used as the extraction solvent include the following.
1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-propyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-butyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-pentyl-3 -Methylimidazolium bistrifluoromethanesulfonylimide, 1-hexyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-octyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-nonyl-3-methylimidazolium bistri Fluoromethanesulfonylimide, 1-decyl-3-methylimidazolium bistrifluoromethanesulfonylimide, 1-undecyl-3-methylimidazolium bistrif Oro methanesulfonyl imide, 1-dodecyl-3-methylimidazolium bis-trifluoromethanesulfonyl imide,

1-ethyl-3-propylimidazolium hexafluorophosphate, 1-ethyl-3-hexylimidazolium tetracyanoborate, 1-ethyl-3-octylimidazolium trifluoromethanesulfonate, 1-ethyl-3-decylimidazolium Tetrafluoroborate, 1-dodecyl-3-methylimidazolium dicyanamide,
1-ethyl-4-methylpyridinium bistrifluoromethanesulfonylimide, 1-propyl-4-methylpyridinium bistrifluoromethanesulfonylimide, 1-butyl-4-methylpyridinium bistrifluoromethanesulfonylimide, 1-pentyl-4-methylpyridinium Bistrifluoromethanesulfonylimide, 1-hexyl-4-methylpyridinium bistrifluoromethanesulfonylimide, 1-octyl-4-methylpyridinium bistrifluoromethanesulfonylimide, 1-nonyl-4-methylpyridinium trifluoromethanesulfonylimide, 1- Decyl-4-methylpyridinium bistrifluoromethanesulfonylimide, 1-undecyl-4-methylpyridinium bistrifluoromethanesulfonyl Bromide, 1-dodecyl-4-methylpyridinium bistrifluoromethanesulfonylimide,

  1-ethyl-4-propylpyridinium hexafluorophosphate, 1-ethyl-4-pentylpyridinium tetracyanoborate, 1-ethyl-4-nonylpyridinium trifluoromethanesulfonate, 1-ethyl-4-undecylpyridinium tetrafluoroborate Lato, 1-ethyl-4-dodecylpyridinium dicyanamide,

1-ethyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-propyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-butyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1- Pentyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-hexyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-octyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-nonyl -1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-decyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide, 1-undecyl-1-methylpyrrolidinium trifluoro Lomethanesulfonylimide, 1-dodecyl-1-methylpyrrolidinium bistrifluoromethanesulfonylimide,
1-ethyl-1-butylpyrrolidinium hexafluorophosphate, 1-ethyl-1-hexylpyrrolidinium tetracyanoborate, 1-ethyl-1-octylpyrrolidinium trifluoromethanesulfonate, 1-ethyl-1- Decylpyrrolidinium tetrafluoroborate, 1-ethyl-1-dodecylpyrrolidinium pyridinium dicyanamide,

1-ethyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-propyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-butyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1- Pentyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-hexyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-octyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-nonyl -1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-decyl-1-methylpiperidinium bistrifluoromethanesulfonylimide, 1-undecyl-1-methylpiperidinium trifluoro Lomethanesulfonylimide, 1-dodecyl-1-methylpiperidinium bistrifluoromethanesulfonylimide,
1-ethyl-1-propylpiperidinium hexafluorophosphate, 1-ethyl-1-butylpiperidinium tetracyanoborate, 1-ethyl-1-hexylpiperidinium trifluoromethanesulfonate, 1-ethyl-1- Decylpiperidinium tetrafluoroborate, 1-ethyl-1-dodecylpiperidinium bisdicyanamide,

  Ethyltrimethylammonium bistrifluoromethanesulfonylimide, propyltrimethylammonium bistrifluoromethanesulfonylimide, butyltrimethylammonium bistrifluoromethanesulfonylimide, pentyltrimethylammonium bistrifluoromethanesulfonylimide, hexyltrimethylammonium bistrifluoromethanesulfonylimide, octyltrimethylammonium bistrifluoro Methanesulfonylimide, nonyltrimethylammonium trifluoromethanesulfonylimide, decyltrimethylammonium bistrifluoromethanesulfonylimide, undecyltrimethylammonium bistrifluoromethanesulfonylimide, dodecyltrimethylammonium bistrifluoro Tan imide,

  Butyltriethylammonium hexafluorophosphate, hexyltriethylammonium tetracyanoborate, octyltriethylammonium fluoromethanesulfonate, decyltriethylammonium tetrafluoroborate, ethyltributylammonium dicyanamide,

  Ethyltrimethylphosphonium bistrifluoromethanesulfonylimide, propyltrimethylphosphonium bistrifluoromethanesulfonylimide, butyltrimethylphosphonium bistrifluoromethanesulfonylimide, pentyltrimethylphosphonium bistrifluoromethanesulfonylimide, hexyltrimethylphosphonium bistrifluoromethanesulfonylimide, octyltrimethylphosphonium bistrifluoro Methanesulfonylimide, nonyltrimethylphosphonium trifluoromethanesulfonylimide, decyltrimethylphosphonium bistrifluoromethanesulfonylimide, undecyltrimethylphosphonium bistrifluoromethanesulfonylimide, dodecyltrimethylphosphonium bistrifluoro Tan imide,

  Butyltriethylphosphonium hexafluorophosphate, hexyltriethylphosphonium tetracyanoborate, octyltriethylphosphonium fluoromethanesulfonate, decyltriethylphosphonium tetrafluoroborate, ethyltributylphosphonium dicyanamide.

The electrolytic solution in which the reduced product and CO ₂ are extracted and removed, and the ionic liquid containing the reduced product and CO _2, which are generated in the extraction device 201, are discharged through separate pipes. Although depending on the density of the electrolytic solution and the ionic liquid, when the density of the ionic liquid containing the reduced product and CO ₂ is larger than that of the electrolytic solution, the ionic liquid is accumulated in the lower part of the extraction device 201 and passes through the pipe 100a. Is discharged out of the device. On the other hand, the electrolytic solution accumulated in the upper part of the extraction device 201 is discharged through the pipe 101a separately from the ionic liquid.

The ionic liquid discharged from the lower part of the extraction device 201 is supplied to the carbon dioxide separation tower 202 through the pipe 100a. In carbon dioxide separation column 202, by the ionic liquid depressurizing the ionic liquid at a pressure lower than the pressure applied upon absorption of CO ₂ in the extraction device 201, CO ₂ contained in the ionic liquid is separated and recovered Is done. Specifically, the pressure is lower than 0 MPa to 50 MPa, preferably 10 MPa to 35 MPa, more preferably 15 MPa to 25 MPa, but lower than the pressure when the ionic liquid absorbs CO _2. It can be selected as appropriate in consideration of the CO ₂ emission characteristics of the ionic liquid.

The ionic liquid from which CO ₂ has been separated and removed by the carbon dioxide separation tower 202 is supplied to the rectification tower 72 through the pipe 100b. In the rectification column 72, the reduced product contained in the ionic liquid can be separated from the ionic liquid by distillation by a conventional method. Specifically, it can be carried out by vacuum distillation using the difference in boiling points. Thereby, a reductant having a boiling point lower than that of water, such as methanol or ethanol, or a reductant such as ethylene glycol having a boiling point higher than that of water is taken out from the pipe 101c provided at the upper part of the rectifying column 72, and the vapor pressure is almost reduced. The ionic liquid that does not have is recovered from the bottom of the rectification column 72.

  In one embodiment, as shown in FIG. 3, in the reduced product production system 60, a rectification column 72 and an extraction device 201 are connected by a sixth pipe 100 c. The ionic liquid from which the reduced product has been separated and removed in the rectification column 72 is recovered from the bottom of the rectification column 72, passes through the sixth pipe 100c, and is filled into the extraction device 201.

In another aspect, as shown in FIG. 3, the reduced product production system 60 includes an electrolytic solution from which the reduced product and CO ₂ have been separated and removed by the extraction device 201, and CO that has been separated from the ionic liquid by the carbon dioxide separation tower 202. ₂ and a preparation tank 74 for preparing an electrolytic solution in which CO ₂ is dissolved.

  The preparation tank 74 is connected to the extraction device 201 and the carbon dioxide separation tower 202 by a pipe 101a and a pipe 101b, respectively.

The electrolytic solution in which CO ₂ prepared in the preparation tank 74 is dissolved is supplied to the storage tank 64 through a seventh pipe 84 having a valve.

Furthermore, in another aspect, the reduction product production system 60 has another configuration in which a separation unit that recovers the reduction product from the electrolytic solution in which the concentration of the CO ₂ reduction product is increased. A separation unit having another form will be described with reference to FIG.

  In the reduced product production system 60 shown in FIG. 4, the separation unit is connected to the electrolyte supply unit by the third pipe 83 via the three-way valve 81b.

The separation unit includes a carbon dioxide separation column 202 in which the concentration of the reducing of CO ₂ separates the CO ₂ of the unreacted elevated electrolyte, reduced product from the electrolyte to CO ₂ in the carbon dioxide separation column 202 is separated And a rectifying column 72 for separating the slag.

The electrolyte used in the reduced product production system 60 shown in FIG. 4 preferably has a property of reducing the reduction potential of CO ₂ , having high ionic conductivity, and absorbing CO ₂ . As such an electrolytic solution, for example, an ionic liquid aqueous solution can be used.

The ionic liquid that can be used as the electrolyte in the electrolytic solution is an ionic liquid composed of a cation and an anion. The ionic liquid is a compound containing an organic cation selected from, for example, an alkyl ammonium cation, a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, an imidazolium cation, and an alkylphosphonium cation. The anion include counter anion Xb in the following general formula Ib～VIb ^- can be the same anion as specific examples of. As the electrolyte in the electrolytic solution, two or more ionic liquids having different cation structures or anion structures may be mixed and used.

  Specific examples of the ionic liquid that can be suitably used as the electrolyte include compounds represented by any one of the following general formulas Ia to VIa.

In the general formulas I to VI, R _1b , R _2b , R _3b and R _4b each independently represent an alkyl group or a cycloalkyl group. Xb ⁻ represents a counter anion.

  As described above, the ionic liquid is an ionic liquid composed of a cation and an anion, and in one form, is a compound in which the lengths of the alkyl chains of the cation molecule are unbalanced. As a result of increasing the asymmetry of the molecular structure by making the length of the alkyl chain of the cation molecule non-uniform, it is in a solution state.

As an alkyl group represented by R _{< 1b>} , R _<2b> , R _<3b> and R _<4b >, a C1-C12 alkyl group is preferable, for example, and a C1-C6 alkyl group is preferable. Moreover, as a cycloalkyl group represented by R _{< 1b>} , R _<2b> , R _<3b> and R _<4b >, a C3-C8 cycloalkyl group is preferable, for example, and a C4-C6 cycloalkyl group is more preferable.

R _1b is preferably a group having a carbon number smaller than R _2b , R _3b and R _4b . Specifically, the difference in carbon number between R _1b and R _2b , R _3b and R _4b is preferably 1 or more and 11 or less, more preferably 1 or more and 5 or less.

Examples of the counter anion represented by Xb ⁻ include Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , (CN) ₄ B ⁻ and (CN) ₂ N ⁻ .

  The solubility of the ionic liquid in water varies depending on the combination of the cation and the anion. Since it is desired that the ionic liquid used for the electrolytic solution is dissolved in water, the cation and the anion may be appropriately selected from the combination that provides hydrophilicity.

  Specific examples of the ionic liquid that can be used as the electrolyte in the electrolytic solution include the following.

1-ethyl-3-methylimidazolium tetrafluoroborate, 1-propyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-pentyl-3-methylimidazole 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-nonyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate Decyl-3-methylimidazolium tetrafluoroborate, 1-undecyl-3-methylimidazolium tetrafluoroborate, 1-dodecyl-3-methylimidazolium tetrafluoroborate,
1-ethyl-3-propylimidazolium chloride, 1-ethyl-3-hexylimidazolium bromide, 1-ethyl-3-octylimidazolium iodide, 1-ethyl-3-decylimidazolium tetracyanoborate, 1- Dodecyl-3-methylimidazolium dicyanamide,

  1-ethyl-4-methylpyridinium tetrafluoroborate, 1-propyl-4-methylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, 1-pentyl-4-methylpyridinium tetrafluoroborate 1-hexyl-4-methylpyridinium tetrafluoroborate, 1-octyl-4-methylpyridinium tetrafluoroborate, 1-nonyl-4-methylpyridinium tetrafluoroborate, 1-decyl-4-methylpyridinium Tetrafluoroborate, 1-undecyl-4-methylpyridinium tetrafluoroborate, 1-dodecyl-4-methylpyridinium tetrafluoroborate,

  1-ethyl-4-propylpyridinium chloride, 1-ethyl-4-pentylpyridinium bromide, 1-ethyl-4-nonylpyridinium iodide, 1-ethyl-4-undecylpyridinium tetracyanoborate, 1-ethyl-4 -Dodecylpyridinium dicyanamide,

  1-ethyl-1-methylpyrrolidinium tetrafluoroborate, 1-propyl-1-methylpyrrolidinium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium tetrafluoroborate, 1-pentyl-1 -Methylpyrrolidinium tetrafluoroborate, 1-hexyl-1-methylpyrrolidinium tetrafluoroborate, 1-octyl-1-methylpyrrolidinium tetrafluoroborate, 1-nonyl-1-methylpyrrolidi Nium tetrafluoroborate, 1-decyl-1-methylpyrrolidinium tetrafluoroborate, 1-undecyl-1-methylpyrrolidinium tetrafluoroborate, 1-dodecyl-1-methylpyrrolidinium tetrafluoroborate ,

  1-ethyl-1-butylpyrrolidinium bromide, 1-ethyl-1-hexylpyrrolidinium chloride, 1-ethyl-1-octylpyrrolidinium iodide, 1-ethyl-1-decylpyrrolidinium tetracyanoborate 1-ethyl-1-dodecylpyrrolidinium pyridinium dicyanamide,

  1-ethyl-1-methylpiperidinium tetrafluoroborate, 1-propyl-1-methylpiperidinium tetrafluoroborate, 1-butyl-1-methylpiperidinium tetrafluoroborate, 1-pentyl-1 -Methylpiperidinium tetrafluoroborate, 1-hexyl-1-methylpiperidinium tetrafluoroborate, 1-octyl-1-methylpiperidinium tetrafluoroborate, 1-nonyl-1-methylpiperidi Nium tetrafluoroborate, 1-decyl-1-methylpiperidinium tetrafluoroborate, 1-undecyl-1-methylpiperidinium tetrafluoroborate, 1-dodecyl-1-methylpiperidinium tetrafluoroborate ,

  1-ethyl-1-propylpiperidinium chloride, 1-ethyl-1-butylpiperidinium bromide, 1-ethyl-1-hexylpiperidinium iodide, 1-ethyl-1-decylpiperidinium tetracyanoborate 1-ethyl-1-dodecylpiperidinium bisdicyanamide,

Ethyltrimethylammonium tetrafluoroborate, propyltrimethylammonium tetrafluoroborate, butyltrimethylammonium tetrafluoroborate, pentyltrimethylammonium tetrafluoroborate, hexyltrimethylammonium tetrafluoroborate, octyltrimethylammonium tetrafluoroborate, nonyltrimethyl Ammonium tetrafluoroborate, decyltrimethylammonium tetrafluoroborate, undecyltrimethylammonium tetrafluoroborate, dodecyltrimethylammonium tetrafluoroborate,
Butyltriethylammonium chloride, hexyltriethylammonium bromide, octyltriethylammonium iodide, decyltriethylammonium tetracyanoborate, ethyltributylammonium dicyanamide,

Ethyltrimethylphosphonium tetrafluoroborate, propyltrimethylphosphonium tetrafluoroborate, butyltrimethylphosphonium tetrafluoroborate, pentyltrimethylphosphonium tetrafluoroborate, hexyltrimethylphosphonium tetrafluoroborate, octyltrimethylphosphonium tetrafluoroborate, nonyltrimethyl Phosphonium tetrafluoroborate, decyltrimethylphosphonium tetrafluoroborate, undecyltrimethylphosphonium tetrafluoroborate, dodecyltrimethylphosphonium tetrafluoroborate,
Butyltriethylphosphonium bromide, hexyltriethylphosphonium chloride, octyltriethylphosphonium iodide, decyltriethylphosphonium tetracyanoborate, ethyltributylphosphonium dicyanamide.

The concentration of the electrolyte in the electrolytic solution, that is, the concentration of the ionic liquid can be appropriately determined in consideration of the solubility of CO ₂ , ionic conductivity, fluidity, and the like. For example, a range of 0.1 to 15 mol / L is preferable.

In the reduced product production system 60 shown in FIG. 4, when the aqueous solution of the ionic liquid described above is used as the electrolytic solution, the supply of CO ₂ to the electrolytic solution in the carbon dioxide supply unit is performed in addition to the direct spraying means described above. The following means may be used.

That is, in the storage tank 64, CO ₂ can be dissolved by pressurizing the aqueous solution of the ionic liquid that is the electrolytic solution. If the pressure to be applied is too low, it takes time to complete the absorption, and if it is too high, operation control becomes difficult. Therefore, for example, it is 0 MPa or more and 50 MPa or less, preferably normal pressure (for example, 0.1 MPa) or more and 25 MPa or less, more preferably normal pressure or more and 12 MPa or less.

  In addition, the temperature condition for pressurization is -50 ° C or higher and 250 ° C or lower, preferably 0 ° C or higher and 200 ° C or lower, more preferably considering the thermal stability of the reduced product or ionic liquid, the fluidity of the solution, and the like. Is normal temperature (for example, 15-25 degreeC) or more and 100 degrees C or less.

  In the reduced product production system 60 shown in FIG. 4, the separation unit first supplies the electrolytic solution flowing from the electrolytic solution supply means to the third pipe 83 through the three-way valve 81 b to the carbon dioxide separation column 202.

The carbon dioxide separation tower 202 separates unreacted CO ₂ from the electrolytic solution (ionic liquid aqueous solution) in which the concentration of the CO ₂ reduction product is increased. CO ₂ dissolved in the aqueous solution of the ionic liquid can be separated from the ionic liquid by a conventional method. For example, when the supply of CO ₂ to the electrolytic solution in the carbon dioxide supply unit is performed by pressurizing CO ₂ to the aqueous solution of the ionic liquid in the storage tank 64, it can be performed by the following method.

In the carbon dioxide separation tower 202, the aqueous solution of the ionic liquid is decompressed to a pressure lower than the pressure applied when the aqueous solution of the ionic liquid absorbs CO ₂ in the storage tower 64, so that it is contained in the aqueous solution of the ionic liquid. CO ₂ is separated and recovered. Specifically, the pressure is lower than 0 MPa to 50 MPa, preferably 10 MPa to 35 MPa, more preferably 15 MPa to 25 MPa, lower than the pressure applied when the aqueous ionic liquid solution absorbs CO _2. The ionic liquid can be appropriately selected in consideration of the CO ₂ release characteristics and the like.

The aqueous solution of the ionic liquid from which CO ₂ has been separated and removed by the carbon dioxide separation tower 202 is supplied to the rectification tower 72 through the pipe 100b. The reduced product contained in the aqueous solution of the ionic liquid can be separated by distillation by a conventional method. Specifically, it can be carried out by vacuum distillation using the difference in boiling points. Thereby, a reductant having a boiling point lower than that of water, such as methanol or ethanol, or a reductant such as ethylene glycol having a boiling point higher than that of water is taken out from the pipe 101c provided at the upper part of the rectifying column 72, and the vapor pressure is almost reduced. The aqueous solution of the ionic liquid that does not have is recovered from the bottom of the rectification column 72.

In one embodiment, as shown in FIG. 4, the reductant production system 60 separates CO ₂ separated from the electrolyte (ionic liquid aqueous solution) in the carbon dioxide separation column 202 and the reductant in the rectification column 72. by using the removed electrolyte, the electrolytic solution CO ₂ is dissolved may comprise a preparation tank 74 to prepare.

In the carbon dioxide separation tower 202, CO ₂ separated from the aqueous solution of the ionic liquid is supplied to the preparation tank 74 through the pipe 101b.

  The aqueous solution of the ionic liquid from which the reduced product recovered from the bottom of the rectifying column 72 is separated is divided into the ionic liquid and water, and filled into the preparation tank 74 through the pipes 100d and 100e, respectively.

In the preparation tank 74, CO ₂ , ionic liquid, and water are supplied from the pipes 101b, 100d, and 100e, respectively, and an electrolytic solution containing CO ₂ , ionic liquid, and water is prepared. In order to effectively dissolve CO ₂ in the ionic liquid aqueous solution, CO ₂ can be pressurized to the ionic liquid aqueous solution. If the pressure to be applied is too low, it takes time to complete the absorption, and if it is too high, operation control becomes difficult. Therefore, for example, it is 0 MPa or more and 50 MPa or less, preferably normal pressure (for example, 0.1 MPa) or more and 25 MPa or less, more preferably normal pressure or more and 12 MPa or less.

  In addition, the temperature condition for pressurization is -50 ° C or higher and 250 ° C or lower, preferably 0 ° C or higher and 200 ° C or lower, more preferably considering the thermal stability of the reduced product or ionic liquid, the fluidity of the solution, and the like. Is normal temperature (for example, 15-25 degreeC) or more and 100 degrees C or less.

The electrolytic solution containing CO ₂ , ionic liquid and water prepared in the preparation tank 74 is supplied to the storage tank 64 through a seventh pipe 84 having a valve.

  In the reduced product production system according to the embodiment described above, the electrolytic solution containing the reduced product is circulated between the storage tank 64 and the reduction reaction electrolytic tank 31b. In addition, carbon dioxide, which is a reducing material, is replenished to the electrolytic solution. Therefore, the reduction reaction continues in the reduction reaction electrolytic bath 31b, and the concentration of the reduced product contained in the electrolytic solution increases. In addition, since the generated reduction product does not participate in the reduction reaction in the reduction reaction electrolytic bath 31b, the reduction reaction can be continued regardless of the concentration of the reduction product in the electrolytic solution.

  If the concentration of the reduced product contained in the electrolyte is low, the energy input to recover the reduced product from the electrolyte may be larger than the amount of energy stored in the reduced product, making it impossible to make a profit on the manufacturing cost. There is. However, the reduced product production system according to the embodiment can obtain an electrolytic solution containing the reduced product at a high concentration. Therefore, the reduced product can be recovered with high efficiency. In order to improve the recovery efficiency, it is preferable to supply an electrolytic solution containing the reduced product at a concentration of 0.01 to 50 wt% to the separation unit. Here, the concentration of the reduced product is preferably the concentration of ethylene glycol.

  Also, if the electrolyte contains a small amount of reductant, the separation process becomes complicated, and the energy input to recover the reductant from the electrolyte becomes larger than the amount of energy stored in the reductant. There is a risk that the manufacturing cost may not be profitable. However, in the reduced product production system according to the embodiment, the electrolytic solution is circulated between the storage tank 64 and the reduction reaction electrolytic tank 31b, and the reduction reaction of the reduced product of carbon dioxide is continuously performed. Therefore, multi-electron reduction proceeds and is converted to methanol, ethanol, ethylene glycol, and the like. Therefore, high recovery efficiency can be realized while using a simple separation process.

[Chemical reactor]
Next, the chemical reaction device 61 will be described with reference to FIGS. The chemical reaction device 61 includes a chemical reaction cell 30 having an oxidation catalyst layer and a reduction catalyst layer, an oxidation reaction electrolytic bath 31a, a reduction reaction electrolytic bath 31b, an oxidation reaction electrolytic bath 31a, and a reduction reaction electrolytic bath 31b. An ion transfer path that separates the electrolyte solution and allows ions to move.

  First, the chemical reaction cell 30 will be described with reference to FIGS. The chemical reaction cell includes an oxidation catalyst layer 19, a reduction catalyst layer 20, and a power supply element connected to each of the oxidation catalyst layer 19 and the reduction catalyst layer 20. Moreover, it has a diaphragm which separates the oxidation catalyst layer 19 and the reduction catalyst layer 20. The power supply element supplies power to the oxidation catalyst layer 19 and the reduction catalyst layer 20 to apply a voltage necessary for electrolysis.

  The power supply element may be an external power supply, but is preferably a semiconductor layer that separates charges by light energy. As the power supply element, for example, a solar cell can be used. The semiconductor layer is preferably disposed between the oxidation catalyst layer 19 and the reduction catalyst layer 20. When a semiconductor layer is disposed between the oxidation catalyst layer 19 and the reduction catalyst layer 20, the semiconductor layer is used as a diaphragm.

  FIG. 5 is a cross-sectional view showing the structure of the chemical reaction cell 30. As shown in FIG. 5, the chemical reaction cell 30 includes a reduction catalyst layer 20, a substrate 11, a reflection layer 12, a reduction electrode layer 13, a multi-junction solar cell 17, an oxidation electrode layer 18, and an oxidation catalyst layer 19 in this order. It is the laminated body laminated | stacked by. In the chemical reaction cell 30, the reduction catalyst layer 20 side is the back surface, and the oxidation catalyst layer 19 side is the surface on which light is incident.

  The substrate 11 is provided to support the chemical reaction cell 30 and increase its mechanical strength. The substrate 11 is made of a conductive material. For example, a metal plate made of a metal selected from the group consisting of Au, Ag, Cu, Pt, Zn, Fe, Ti, Sn, In, Bi and Ni, or an alloy plate containing at least one of these metals Can be configured. For example, an alloy plate such as SUS can be used as the alloy plate. Or the board | substrate 11 can be comprised with resin etc. which have electroconductivity. The substrate 11 can be formed of a semiconductor substrate such as Si or Ge. The substrate 11 can also be composed of an ion exchange membrane.

  The reflective layer 12 is formed on the surface of the substrate 11. The reflective layer 12 is made of a material that can reflect light. For example, it can be composed of a metal layer or a distributed Bragg reflection layer made of a semiconductor multilayer film. The reflective layer 12 is disposed between the substrate 11 and the multijunction solar cell 17. Therefore, the light that has not been absorbed by the multi-junction solar cell 17 can be reflected and incident again on the multi-junction solar cell 17. Thereby, the light absorption rate in the multijunction solar cell 17 can be improved.

  The reduction electrode layer 13 is disposed on the reflective layer 12 and is sandwiched between the reflective layer 12 and an n-type semiconductor layer (an n-type amorphous silicon layer 14a described later) of the multi-junction solar cell 17. For this reason, it is preferable that the reduction electrode layer 13 is made of a material capable of ohmic contact with the n-type semiconductor layer. The reduction electrode layer 13 is made of, for example, a metal such as Ag, Au, Al, or Cu, or an alloy containing at least one of them. Alternatively, the reduction electrode layer 13 is made of transparent conductive material such as ITO (Indium Tin Oxide) or zinc oxide (ZnO), FTO (fluorine-doped tin oxide), AZO (aluminum-doped zinc oxide), or ATO (antimony-doped tin oxide). Consists of oxides. The reduction electrode layer 13 is, 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 of a transparent conductive oxide and another conductive material. It may be a structured.

  The multi-junction solar cell 17 is disposed on the reduction electrode layer 13. It has the structure by which the 1st solar cell 14, the 2nd solar cell 15, and the 3rd solar cell 16 were laminated | stacked in order from the reduction electrode layer 13 side. These are all solar cells using pin junction semiconductors. The first solar cell 14, the second solar cell 15, and the third solar cell 16 have different light absorption wavelengths. By laminating these in a planar shape, the multi-junction solar cell 17 can absorb light having a wide wavelength of sunlight. Therefore, it becomes possible to use solar energy more efficiently. Moreover, since each solar cell is connected in series, a high open circuit voltage can be obtained.

  The first solar cell 14 includes an n-type amorphous silicon (a-Si) layer 14a, an intrinsic amorphous silicon-germanium (a-SiGe) layer 14b, and a p-type microelectrode in order from the reduction electrode layer 13 side. A crystalline silicon (μc-Si) layer 14c is provided. The a-SiGe layer 14b is a layer that absorbs light in a short wavelength region of about 400 nm. Therefore, charge separation occurs in the first solar cell 14 due to light energy in the short wavelength region.

  The second solar cell 15 includes an n-type a-Si layer 15a, an intrinsic a-SiGe layer 15b, and a p-type μc-Si layer 15c in this order from the reduction electrode layer 13 side. The a-SiGe layer 15b is a layer that absorbs light in the intermediate wavelength region of about 600 nm. Therefore, charge separation occurs in the second solar cell 15 due to light energy in the intermediate wavelength region.

  The third solar cell 16 includes an n-type a-Si layer 16a, an intrinsic a-Si layer 16b, and a p-type μc-Si layer 16c in this order from the reduction electrode layer 13 side. The a-Si layer 16b is a layer that absorbs light in a long wavelength region of about 700 nm. Therefore, charge separation occurs in the third solar cell 16 due to light energy in the long wavelength region.

  In the multijunction solar cell 17, charge separation occurs due to light in each wavelength region. That is, holes are separated on the positive electrode side (front surface side) and electrons are separated on the negative electrode side (back surface side). Thereby, an electromotive force is generated in the multi-junction solar cell 17.

  In addition, although the multi-junction solar cell 17 comprised by the laminated structure of three solar cells was demonstrated here as an example, it is not limited to this, It is comprised by the laminated structure of two or four or more solar cells. It is also possible to use a multi-junction solar cell. Alternatively, one solar cell may be used instead of the multi-junction solar cell 17. Moreover, although the solar cell using a pin junction semiconductor was demonstrated, you may use the solar cell using a pn junction type semiconductor. Further, for example, a semiconductor layer made of GaAs, GaInP, AlGaInP, CdTe, CuInGaSe, or the like may be used. Further, various forms such as a single crystal, a polycrystal, and an amorphous state can be applied as the semiconductor layer.

  The oxidation electrode layer 18 is disposed on the multi-junction solar cell 17 and is sandwiched between the p-type semiconductor layer of the multi-junction solar cell 17 and the oxidation catalyst layer 19. The oxidation electrode layer 18 is preferably made of a transparent material that can make ohmic contact with the p-type semiconductor layer. The oxidation electrode layer 18 is made of a transparent conductive oxide such as ITO (Indium Tin Oxide) or zinc oxide (ZnO), FTO (fluorine doped tin oxide), AZO (aluminum doped zinc oxide), or ATO (antimony doped tin oxide). Consists of. In addition, the oxidation electrode layer 18 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 be a structured.

The oxidation catalyst layer 19 is disposed on the positive electrode side of the multi-junction solar cell 17 and is formed on the oxidation electrode layer 18. When the hydrogen ion concentration of the electrolytic solution is lower than 7 (pH <7), the oxidation catalyst layer 19 oxidizes H ₂ O to generate O ₂ and H ⁺ . On the other hand, when the hydrogen ion concentration of the electrolytic solution is higher than 7 (pH> 7), OH ⁻ is oxidized to generate O ₂ and H ₂ O. For this reason, the oxidation catalyst layer 19 is made of a material that reduces activation energy for causing an oxidation reaction. In other words, it is made of a material that lowers the overvoltage when a reaction is performed to oxidize H ₂ O or OH ⁻ to extract electrons.

  As such materials, manganese oxide (Mn—O), iridium oxide (Ir—O), nickel oxide (Ni—O), cobalt oxide (Co—O), iron oxide (Fe—O), tin oxide (Sn) -O), indium oxide (In-O), binary metal oxides such as ruthenium oxide (Ru-O), Ni-Co-O, La-Co-O, Ni-La-O, Sr-Fe Examples thereof include ternary metal oxides such as —O, quaternary metal oxides such as Pb—Ru—Ir—O and La—Sr—Co—O, and metal complexes such as Ru complexes and Fe complexes.

  The form of the oxidation catalyst layer 19 is not limited to a thin film shape, and may be a lattice shape, a particle shape, or a wire shape.

  In the chemical reaction cell 30, the irradiation light passes through the oxidation catalyst layer 19 and the oxidation electrode layer 18 and reaches the multi-junction solar cell 17. For this reason, the oxidation electrode layer 18 and the oxidation catalyst layer 19 disposed on the light irradiation surface side have light transmittance with respect to the irradiation light. More specifically, the transparency of the oxidation electrode layer 18 and the oxidation catalyst layer 19 on the irradiation surface side is at least 10% or more, more desirably 30% or more, of the irradiation amount of irradiation light.

  The reduction catalyst layer 20 is disposed on the negative electrode side of the multi-junction solar cell 17 and is formed on the back surface of the substrate 11. The reduction catalyst layer 20 is a layer made of a reduction catalyst that reduces carbon dioxide to produce a reduced product. As the reduction catalyst, a first reduction catalyst or a second reduction catalyst described later is used. Reduction products produced by these reduction catalysts include carbon monoxide, formic acid, formaldehyde, methane, methanol, acetic acid, acetaldehyde, ethanol, ethylene glycol, and the like. The first reduction catalyst or the second reduction catalyst is not limited to carbon dioxide as a reducing raw material, and carbon monoxide, formic acid, formaldehyde, methane, methanol, acetic acid, acetaldehyde, and ethanol can be further reduced.

Conductivity on the surface of the multi-junction solar cell 17 or between the electrode layer on the light irradiation surface side and the catalyst layer (between the oxidation electrode layer 18 and the oxidation catalyst layer 19 in the chemical reaction cell 30). A protective layer may be disposed. The protective layer prevents corrosion of the multijunction solar cell 17 in the oxidation-reduction reaction. As a result, the lifetime of the multijunction solar cell 17 can be extended. Moreover, a protective layer has a light transmittance as needed. As the protective layer, for example _{TiO 2, ZrO 2, Al 2} O 3, SiO 2, or a dielectric thin film of HfO ₂ and the like. The film thickness is preferably 10 nm or less, more preferably 5 nm or less in order to obtain conductivity by the tunnel effect.

  6 and 7 are cross-sectional views for explaining the operating principle of the chemical reaction cell 30. FIG. Here, the reflection layer 12, the reduction electrode layer 13, and the oxidation electrode layer 18 are omitted.

  As shown in FIGS. 6 and 7, when light (L) is incident from the surface side (oxidation electrode layer 18 side), the incident light passes through the oxidation catalyst layer 19 (and oxidation electrode layer 18), and the multijunction solar The battery 17 is reached. When the multi-junction solar cell 17 absorbs light, photoexcited electrons and holes paired therewith are generated and separated. Specifically, in each solar cell (first solar cell 14, second solar cell 15, and third solar cell 16), photoexcited electrons move to the n-type semiconductor layer side (reduction catalyst layer 20 side), Holes generated as a pair of photoexcited electrons move to the p-type semiconductor layer side (oxidation catalyst layer 19 side). That is, charge separation occurs. Thereby, an electromotive force is generated in the multi-junction solar cell 17.

  Photoexcited electrons generated in the multi-junction solar cell 17 are used for the reduction reaction in the reduction catalyst layer 20 that is the negative electrode. The holes are used for the oxidation reaction in the oxidation catalyst layer 19 that is the positive electrode.

FIG. 6 shows an example in which the hydrogen ion concentration of the electrolytic solution is an acidic solution smaller than 7. In the vicinity of the oxidation catalyst layer 19, the reaction of the following formula (1) occurs. That is, H ₂ O is oxidized to generate O ₂ , H ⁺ and electrons. The H ⁺ generated here moves to the reduction catalyst layer 20 side through an ion movement path described later. In the vicinity of the reduction catalyst layer 20, the reaction of the following formula (2) occurs. That is, CO ₂ is reduced by the transferred H ⁺ and electrons, and carbon monoxide (CO) and H ₂ O are generated.
2H ₂ O → 4H ⁺ + O ₂ + 4e ⁻ (1)
2CO ₂ + 4H ⁺ + 4e ⁻ → 2CO + 2H ₂ O (2)
On the other hand, FIG. 7 shows an example in which the hydrogen ion concentration of the electrolytic solution is a basic solution larger than 7. In the vicinity of the oxidation catalyst layer 19, the reaction of the following formula (3) occurs. That is, OH ⁻ is oxidized to generate O ₂ , H ₂ O, and electrons. In the vicinity of the reduction catalyst layer 20, the reaction of the following formula (4) occurs. That is, CO ₂ undergoes a reduction reaction that receives electrons together with H ₂ O, and carbon monoxide (CO) and OH ⁻ are generated. OH ⁻ generated on the reduction catalyst layer 20 side moves to the oxidation catalyst layer 19 side via an ion migration path described later.
4OH ⁻ → O ₂ + 2H ₂ O + 4e ⁻ (3)
2CO ₂ + 2H ₂ O + 4e ⁻ → 2CO + 4OH ⁻ (4)
The multi-junction solar cell 17 needs to have an open circuit voltage that is greater than or equal to the potential difference between the standard redox potential of the oxidation reaction occurring in the oxidation catalyst layer 19 and the standard redox potential of the reduction reaction occurring in the reduction catalyst layer 20. For example, when the hydrogen ion concentration (pH) of the reaction solution is 0, the standard oxidation-reduction potential of the oxidation reaction in equation (1) is +1.23 [V], and the standard oxidation-reduction potential of the reduction reaction in equation (2) Is −0.1 [V]. For this reason, the open circuit voltage of the multi-junction solar cell 17 needs to be 1.33 [V] or more.

  More preferably, the open circuit voltage needs to be equal to or greater than a potential difference including an overvoltage. More specifically, for example, when the overvoltage of the oxidation reaction in the formula (1) and the reduction reaction in the formula (2) is 0.2 [V], the open circuit voltage may be 1.73 [V] or more. preferable.

The reduction reaction in the above formulas (2) and (4) is a reduction reaction from CO ₂ to CO. However, the reduction reaction is not limited to this, and CO ₂ to HCOOH, HCHO, CH ₄ , CH ₃ OH, Reduction reactions to C ₂ H ₅ OH, HOCH ₂ CH ₂ OH, etc. can also occur. Any reduction reaction consumes H ⁺ or produces OH ⁻ . For this reason, when the H ⁺ generated in the oxidation catalyst layer 19 cannot move to the reduction catalyst layer 20 of the counter electrode, or the OH ⁻ generated in the reduction catalyst layer 20 cannot move to the oxidation catalyst layer 19 of the counter electrode, the entire reaction Efficiency is reduced. In contrast, in the chemical reactor 61, H ⁺ or OH ^- by providing the ion transfer path for moving, H ⁺ or OH ^- can improve transport. Therefore, high photoreaction efficiency can be realized.

  Next, the chemical reaction apparatus 61 using the chemical reaction cell 30 will be described with reference to FIGS. Here, the oxidation-reduction reaction (the above formulas (1) and (2)) in the case of an acidic solution in which the hydrogen ion concentration of the electrolytic solution is smaller than 7 will be described as an example. In the case of a basic solution in which the hydrogen ion concentration of the electrolytic solution is higher than 7, an oxidation-reduction reaction according to the above formulas (3) and (4) occurs.

  FIG. 8 is a perspective view showing the structure of the chemical reaction device 61. FIG. 9 is a cross-sectional view showing the structure of the chemical reaction device 61. The chemical reaction device 61 includes a photochemical reaction cell 30, an electrolytic cell 31 that houses the photochemical reaction cell, and an electrolytic cell channel 41 that is connected to the electrolytic cell 31 as an ion movement path. In FIG. 8, the ion movement path is omitted. As described above, the photochemical reaction cell 30 includes the oxidation catalyst layer 19, the reduction catalyst layer 20, the multi-junction solar cell 17 formed therebetween, and the laminate of the substrate 11.

The electrolytic bath 31 includes an oxidation reaction electrolytic bath 31a in which the oxidation catalyst layer 19 is disposed, and a reduction reaction electrolytic bath 31b in which the reduction catalyst layer 20 is disposed. In the oxidation reaction electrolytic bath 31a, the oxidation catalyst layer 19 oxidizes H ₂ O to generate O ₂ and H ⁺ . In the reduction reaction electrolytic bath 31b, CO ₂ is reduced by the reduction catalyst layer 20 to generate CO and H ₂ O. These two electrolytic cells are separated into two by the substrate 11 of the chemical reaction cell 30. In this example, the end portion of the substrate 11 protrudes from the end portions of the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20. The junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 may be a laminate having the same area.

  Separate electrolytic solutions are supplied to the oxidation reaction electrolytic bath 31a and the reduction reaction electrolytic bath 31b. The electrolytic cell channel 41 that enables the movement of ions connects the oxidation reaction electrolytic cell 31a and the reduction reaction electrolytic cell 31b.

As described above, according to the configuration including the electrolytic cell channel 41, H ⁺ produced on the oxidation catalyst layer 19 side can be moved to the reduction catalyst layer 20, and the reduction catalyst layer 20 side can be moved by this H ⁺ . Can decompose carbon dioxide. Therefore, high photoreaction efficiency can be achieved.

  The electrolytic cell channel 41 will be described in more detail. The electrolytic cell channel 41 is provided on the side of the electrolytic cell 31, for example. One of the electrolytic cell channels 41 is connected to the oxidation reaction electrolytic cell 31a, and the other is connected to the reduction reaction electrolytic cell 31b. That is, the electrolytic cell channel 41 connects the oxidation reaction electrolytic cell 31a and the reduction reaction electrolytic cell 31b. Thereby, ions can move between the oxidation catalyst layer 19 and the reduction catalyst layer 20.

  A portion of the electrolytic cell channel 41 is filled with an ion exchange membrane 43, and the ion exchange membrane 43 allows only specific ions to pass therethrough. Thereby, only specific ions can be moved while separating the electrolytic solution between the oxidation reaction electrolytic bath 31a and the reduction reaction electrolytic bath 31b.

The ion exchange membrane 43 is a proton exchange membrane, and can move H ⁺ produced in the oxidation reaction electrolytic bath 31a to the reduction reaction electrolytic bath 31b side. Examples of the proton exchange membrane include a cation exchange membrane such as Nafion or Flemion, and an anion exchange membrane such as Neoceptor or Selemion.

  Instead of the ion exchange membrane 43, a material such as agar that can move ions and separate the electrolytic solution may be used. For example, a salt bridge is used. In general, when a proton exchangeable solid polymer membrane represented by Nafion is used, ion transfer performance can be improved.

Further, a circulation mechanism 42 such as a pump may be provided in the electrolytic cell channel 41. By promoting the circulation of the electrolytic solution by the circulation mechanism 42, it is possible to improve the circulation of ions (H ⁺ ) between the oxidation reaction electrolytic bath 31a and the reduction reaction electrolytic bath 31b. Further, two electrolytic cell channels 41 may be provided, and the reduction reaction is performed from the oxidation reaction electrolytic cell 31a via one electrolytic cell channel 41 using the circulation mechanism 42 provided in at least one of them. The ions may be moved to the electrolytic cell 31b and moved from the electrolytic cell 31b for the reduction reaction to the electrolytic cell 31a for the oxidation reaction via the other electrolytic cell channel 41. A plurality of circulation mechanisms 42 may be provided. In order to reduce ion diffusion and to circulate ions more efficiently, a plurality (three or more) of electrolytic cell channels 41 may be provided.

  By creating a liquid flow with the circulation mechanism 42, it is possible to suppress the generated gas bubbles from staying on the electrode surface and the electrolytic cell surface, and to suppress the efficiency reduction and the light amount distribution due to the scattering of sunlight by the bubbles. You can also.

  In addition, heat may be generated on the surface of the multi-junction solar cell 17 when irradiated with light. Convection may be generated using the temperature difference generated in the electrolytic solution by this heat, and ions may be circulated more efficiently. In this case, the movement of ions can be promoted more than the ion diffusion.

  A temperature adjustment mechanism 44 for adjusting the temperature of the electrolytic solution may be provided in the electrolytic cell channel 41 or the electrolytic cell 31. By controlling the temperature using the temperature adjusting mechanism 44, the solar cell performance and the catalyst performance can be controlled. For example, by making the temperature of the reaction system uniform, the performance of the solar cell and the catalyst can be stabilized and improved. Also, temperature rise can be prevented for system stability. The temperature control can change the selectivity of the solar cell and the catalyst, and the product can be controlled.

The oxidation reaction electrolytic bath 31a may be filled with an electrolytic solution containing an arbitrary electrolyte, and is preferably an electrolytic solution that promotes an oxidation reaction of H ₂ O. Alternatively, it may be filled with water. The oxidation catalyst layer 19 is immersed in this electrolytic solution. The electrolytic cell 31b for reduction reaction is filled with the above-described electrolytic solution. The reduction catalyst layer 20 is immersed in this electrolytic solution. The temperature of the electrolytic solution filling the oxidation reaction electrolytic bath 31a and the temperature of the electrolytic solution filling the reduction reaction electrolytic bath 31b may be the same or different depending on the use environment.

  Next, a modified example of the chemical reaction device 61 will be described. FIG. 10 is a cross-sectional view showing the structure of the chemical reaction device 62 according to the first modification. FIG. 11 is a cross-sectional view showing the structure of the chemical reaction device 63 according to the second modification. Below, the structure different from the chemical reaction apparatus 61 mentioned above is demonstrated.

  As shown in FIG. 10, the chemical reaction device 62 according to the first modification includes a chemical reaction cell 30, an electrolytic bath 31 that accommodates the chemical reaction cell 30, and an opening 51 formed in the substrate 11 as an ion movement path. Is provided.

  The opening 51 is provided so as to penetrate the end of the substrate 11 from the oxidation reaction electrolytic bath 31a side to the reduction reaction electrolytic bath 31b side. Part of the opening 51 is filled with an ion exchange membrane 43, and the oxidation reaction electrolytic bath 31 a and the reduction reaction electrolytic bath 31 b are separated by the substrate 11 and the ion exchange membrane 43. The ion exchange membrane 43 allows only specific ions to pass through.

  With such a configuration, it is possible to move only specific ions through the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic bath 31a and the reduction reaction electrolytic bath 31b.

  As illustrated in FIG. 11, the chemical reaction device 63 according to the second modification includes a chemical reaction cell 30, an electrolytic cell 31 that accommodates the chemical reaction cell 30, and an opening 52 that is formed as an ion movement path. The opening 52 is provided so as to penetrate the reduction catalyst layer 20, the substrate 11, the multijunction solar cell 17, and the oxidation catalyst layer 19 from the oxidation reaction electrolytic bath 31 a side to the reduction reaction electrolytic bath 31 b side. ing.

  Part of the opening 52 is filled with an ion exchange membrane 43, and the oxidation reaction electrolytic bath 31 a and the reduction reaction electrolytic bath 31 b are separated by the substrate 11 and the ion exchange membrane 43. The ion exchange membrane 43 allows only specific ions to pass through.

  With such a configuration, it is possible to move only specific ions through the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic bath 31a and the reduction reaction electrolytic bath 31b.

  In the chemical reaction device 63 according to the second modification of FIG. 11, the ion exchange membrane 43 is installed only in a part of the opening 52, but the ion exchange membrane 43 may be installed in the entire opening 52. Good.

[First reduction catalyst]
Next, the first reduction catalyst among the first reduction catalyst and the second reduction catalyst used in the embodiment will be described in detail.

  The first reduction catalyst includes a current collector having a metal layer on the surface, and a modified organic molecule bonded to the surface of the metal layer and containing a quaternary nitrogen cation.

  Hereinafter, the first reduction catalyst will be described with reference to FIGS. FIG. 12 is a schematic diagram showing the configuration of the first reduction catalyst. As shown in FIG. 12, the first reduction catalyst 1 includes a current collector 101 and a modified organic molecule 112 containing a quaternary nitrogen cation. The current collector 101 has a metal layer 102 on the surface thereof. The modified organic molecule 112 containing a quaternary nitrogen cation is bonded to the metal layer 102 to form a monomolecular layer (Self-Assembled Monolayer: SAM).

  The current collector 101 is made of a material having electrical conductivity. For example, a stainless steel substrate can be used as the current collector 101.

  The metal layer 102 on the surface of the current collector 101 contains at least one metal selected from the group consisting of Au, Ag, Cu, Zn, Pt, Fe, Ti, Ni, Sn, In, and Bi. The metal layer 102 may contain components other than metal, but is preferably made of only metal. The metal layer 102 and the current collector 101 may be made of the same material. In this case, the metal constituting the metal layer 102 may also serve as the current collector 101.

  The metal contained in the metal layer 102 functions as a catalyst that activates the reduction reaction. In order to improve the activity of the catalyst, the metal contained in the metal layer 102 is preferably in a fine particle state.

  The average particle diameter of the metal fine particles contained in the metal layer 102 is preferably 1 nm or more and 300 nm or less. When the average particle size is 300 nm or less, the activity efficiency of the catalyst can be increased. Moreover, it is difficult to produce metal fine particles having an average particle size of less than 1 nm. The average particle size of the metal fine particles is more preferably 150 nm or less because the activity efficiency of the catalyst is further improved. The metal fine particles may be primary particles having an average particle diameter of 50 nm or less, or may be secondary particles in which such primary particles are aggregated.

  The modified organic molecule 112 containing a quaternary nitrogen cation has a skeleton 110, a reactive functional group 109 located at the end on the metal layer 102 side, and a terminal functional group 111 located at the opposite end.

  The reactive functional group 109 has an affinity for the metal layer 102 and is chemically bonded to the metal layer 102. Thereby, the modified organic molecule 112 is fixed to the metal layer 102. The reactive functional group 109 is preferably a functional group capable of covalent bonding with the metal layer 102, and is preferably selected from, for example, a thiol group, a disulfide group, and a thiocyanate group. A thiol group is more preferred because of its excellent binding strength.

The modified organic molecule 112 containing a quaternary nitrogen cation may form a salt with a counter anion. Counter anions include, but are not limited to, fluoride ions, chloride ions, bromide ions, iodide ions, SO ₄ ²⁻ , HCO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ COO ⁻ , CF ₃ SO ^{_{3 -, NO 3 -, SCN}} -, N (CN) 2 -, C (CN) 3 - (CF 3 SO 2) 3 C -, bis (trifluoromethoxy) imide anion, bis (trifluoromethoxy sulfonyl) It may be an anion such as an imide anion and a bis (perfluoroethylsulfonyl) imide anion. In FIG. 12, the counter anion is omitted.

[First aspect]
Next, the reduction catalyst 2 according to the first aspect of the first reduction catalyst will be described with reference to FIG.
In the reduction catalyst 2 of the first aspect, the modified organic molecule 112 is an organic molecule having a quaternary nitrogen cation as the terminal functional group 111. The quaternary nitrogen cation is preferably, for example, an ammonium cation, an imidazole cation, a pyridinium cation, a piperidinium cation, or a pyrrolidinium cation. The quaternary nitrogen cation has a function of promoting a CO ₂ reduction reaction by the metal layer 102 composed of metal fine particles. The quaternary nitrogen cation is preferably an imidazole cation because it is excellent in improving CO ₂ reduction activity.

In the reduction catalyst 2, the skeleton 110 of the modified organic molecule 112 may be an alkyl chain. When the alkyl chain length is remarkably increased, the quaternary nitrogen cation is less likely to participate in the CO ₂ reduction reaction of the metal layer 102. Therefore, the alkyl chain length of the skeleton 110 is preferably 2 to 16 carbon atoms.

  Examples of modified organic molecules 112 include the following molecules: 11-mercaptoundecane-1-trimethylammonium chloride, 1- (2-mercaptoethyl) -3-methylimidazolium bromide, 1- (2-mercaptoethyl) ) -3-Methylimidazolium bromide, 1- (3-mercaptopropyl) -3-methylimidazolium bromide, 1- (4-mercaptobutyl) -3-methylimidazolium bromide, 1- (4-mercaptobutyl)- 3-methylimidazolium bromide, 1- (5-mercaptopentyl) -3-methylimidazolium bromide, 1- (6-mercaptohexyl) -3-methylimidazolium bromide, 1- (8-mercaptooctyl) -3 -Methylimidazolium bromide, 1- (9-mercaptononyl)- -Methylimidazolium bromide, 1- (10-mercaptodecyl) -3-methylimidazolium bromide, 1- (11-mercaptoundecyl) -3-methylimidazolium bromide, 1- (12-mercaptododecyl) -3- Methylimidazolium bromide, 1- (2-mercaptoethyl) -3-ethylimidazolium bromide, 1- (4-mercaptobutyl) -2,3-dimethylimidazolium bromide, 1- (2-mercaptoethyl) -4- Methylpyridinium bromide, 1- (3-mercaptopropyl) -4-methylpyridinium bromide, 1- (4-mercaptobutyl) -4-methylpyridinium bromide, 1- (5-mercaptopentyl) -4-methylpyridinium bromide, 1 -(6-Mercaptohexyl) -4-methyl Lidinium bromide, 1- (8-mercaptooctyl) -4-methylpyridinium bromide, 1- (9-mercaptononyl) -4-methylpyridinium bromide, 1- (10-mercaptodecyl) -4-methylpyridinium bromide, 1 -(11-mercaptoundecyl) -4-methylpyridinium bromide, 1- (12-mercaptododecyl) -4-methylpyridinium bromide, 1- (4-mercaptobutyl) pyridinium bromide, 1- (2-mercaptoethyl)- 1-methylpyrrolidinium bromide, 1- (3-mercaptopropyl) -1-methylpyrrolidinium bromide, 1- (4-mercaptobutyl) -1-methylpyrrolidinium bromide, 1- (5-mercaptopentyl) -1-methylpyrrolidinium bromide, 1- (6-methyl Lucaptohexyl) -1-methylpyrrolidinium bromide, 1- (8-mercaptooctyl) -1-methylpyrrolidinium bromide,

  1- (9-mercaptononyl) -1-methylpyrrolidinium bromide, 1- (10-mercaptodecyl) -1-methylpyrrolidinium bromide, 1- (11-mercaptoundecyl) -1-methylpyrrolidinium Bromide, 1- (12-mercaptododecyl) -1-methylpyrrolidinium bromide, 1- (2-mercaptoethyl) -1-methylpiperidinium bromide, 1- (3-mercaptopropyl) -1-methylpiperidi Nitrobromide, 1- (4-mercaptobutyl) -1-methylpiperidinium bromide, 1- (5-mercaptopentyl) -1-methylpiperidinium bromide, 1- (6-mercaptohexyl) -1-methyl Piperidinium bromide, 1- (8-mercaptooctyl) -1-methylpiperidinium bromide, 1- ( -Mercaptononyl) -1-methylpiperidinium bromide, 1- (10-mercaptodecyl) -1-methylpiperidinium bromide, 1- (11-mercaptoundecyl) -1-methylpiperidinium bromide, 1- (12-mercaptododecyl) -1-methylpiperidinium bromide.

[Second embodiment]
Next, the reduction catalyst 3 according to the second aspect of the first reduction catalyst will be described with reference to FIG.
In the reduction catalyst 3 of the second embodiment, the modified organic molecule 112 is an organic molecule having a quaternary nitrogen cation in the skeleton 110 portion and an amino group as the terminal functional group 111. Such a modified organic molecule 112 is represented by any one of the following general formulas I to V.

(In the general formulas I to V, R ₁ is a primary, secondary or tertiary amino group. R ₂ and R ₃ may be the same or different, and each independently represents H or 1 A secondary, tertiary or tertiary amino group, p, q, r and n are each independently an integer of 1 to 12. Y is a reactive functional group and X ⁻ represents a counter anion. .)

In the reduction catalyst 3 of the second embodiment, the quaternary nitrogen cation is at least one cation selected from an alkyl ammonium cation, a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, and an imidazolium cation. The modified organic molecule 112 forms a salt with the counter anion represented by X ⁻ in the general formulas I to V. Specifically, an ammonium salt, piperidinium salt, pyrrolidinium salt, pyridinium salt or imidazolium salt is formed. As will be described later, since the effect of improving the reduction activity is high, it is more preferable that the quaternary nitrogen cation is an imidazolium cation and the modified organic molecule 112 forms an imidazolium salt.

  The skeleton 110 includes a quaternary nitrogen cation and an alkyl group that is a substituent of the cation. The number of carbon atoms of the alkyl group corresponds to p, q, r and n in general formulas I to V, and each independently represents an integer of 1 to 12. In the general formulas I to V, when p, q, r, and n are 1 or more and 12 or less, the quaternary nitrogen cation and the amino group, and the quaternary nitrogen cation and the metal layer 102 are not separated too much, which will be described later. Thus, the effect that the quaternary nitrogen cation improves the reduction efficiency can be obtained. More preferably, p, q, r and n are integers of 2 or more and 6 or less.

  In FIG. 14, bromide ions are shown as counter anions. The reactive functional group 109 corresponds to Y in the general formulas I to V.

In the reduction catalyst 3 of the second embodiment, the terminal functional group 111 is an amino group, and corresponds to R ₁ in the general formulas I to V and optionally R ₂ and R ₃ . The amino group may be a primary, secondary, or tertiary amino group. When the amino group is a secondary or tertiary amino group, the substituent is preferably one or two C ₁ -C ₁₂ alkyl groups. When the carbon atom of the alkyl group is 12 or less, the quaternary nitrogen cation and the amino group are not separated from each other, and the effect that the amino group improves the reduction efficiency can be obtained as described later. The carbon atom of the alkyl group is more preferably 2 or more and 6 or less. The amino group may form a salt with hydrofluoric acid, hydrochloric acid, odorous acid, iodic acid, sulfuric acid, nitric acid, phosphoric acid or the like.

  Examples of modified organic molecules 112 in the second embodiment include the following molecules: 1- (2-mercaptoethyl) -3-aminomethylimidazolium bromide, 1- (3-mercaptopropyl) -3-aminomethyl. Imidazolium bromide, 1- (4-mercaptobutyl) -3-aminomethylimidazolium bromide, 1- (5-mercaptopentyl) -3-aminomethylimidazolium bromide, 1- (6-mercaptohexyl) -3- Aminomethylimidazolium bromide, 1- (8-mercaptooctyl) -3-aminomethylimidazolium bromide, 1- (9-mercaptononyl) -3-aminomethylimidazolium bromide, 1- (10-mercaptodecyl) -3 -Aminomethylimidazolium bromide, 1- (11-mercaptoundec ) -3-Aminomethylimidazolium bromide, 1- (12-mercaptododecyl) -3-aminomethylimidazolium bromide, 1- (2-mercaptoethyl) -3- (2-aminoethyl) imidazolium bromide, 1- (2-mercaptoethyl) -3- (3-aminopropyl) imidazolium bromide, 1- (2-mercaptoethyl) -3- (4-aminobutyl) imidazolium bromide, 1- (2-mercaptoethyl) -3 -(5-Aminopentyl) imidazolium bromide, 1- (2-mercaptoethyl) -3- (6-aminohexyl) imidazolium bromide, 1- (2-mercaptoethyl) -3- (8-aminooctyl) imidazo Rium bromide, 1- (2-mercaptoethyl) -3- (9-aminononyl) imidazolium 1- (2-mercaptoethyl) -3- (10-aminodecyl) imidazolium bromide, 1- (2-mercaptoethyl) -3- (11-aminoundecyl) imidazolium bromide, 1- (2-mercapto Ethyl) -3- (12-aminododecyl) imidazolium bromide,

  1- (4-mercaptobutyl) -3- (2-methylaminoethyl) imidazolium bromide, 1- (6-mercaptohexyl) -3- (3-dimethylaminopropyl) imidazolium bromide, 1- (8-mercapto (Hexyl) -3- (4-ethylmethylaminobutyl) imidazolium bromide, 1- (2-mercaptoethyl) -4-aminomethylpyridinium bromide, 1- (3-mercaptopropyl) -4-aminomethylpyridinium bromide, 1 -(4-mercaptobutyl) -4-aminomethylpyridinium bromide, 1- (5-mercaptopentyl) -4-aminomethylpyridinium bromide, 1- (6-mercaptohexyl) -4-aminomethylpyridinium bromide, 1- (8-mercaptooctyl) -4-aminomethylpyridy Umbromide, 1- (9-mercaptononyl) -4-aminomethylpyridinium bromide, 1- (10-mercaptodecyl) -4-aminomethylpyridinium bromide, 1- (11-mercaptoundecyl) -4-aminomethylpyridinium bromide 1- (12-mercaptododecyl) -4-aminomethylpyridinium bromide, 1- (2-mercaptoethyl) -4- (2-aminoethyl) pyridinium bromide, 1- (2-mercaptoethyl) -4- (3 -Aminopropyl) pyridinium bromide, 1- (2-mercaptoethyl) -4- (4-aminobutyl) pyridinium bromide, 1- (2-mercaptoethyl) -4- (5-aminopentyl) pyridinium bromide, 1- ( 2-mercaptoethyl) -4- (6-aminohexyl) pi Dinium bromide, 1- (2-mercaptoethyl) -4- (8-aminooctyl) pyridinium bromide, 1- (2-mercaptoethyl) -4- (9-aminononyl) pyridinium bromide, 1- (2-mercaptoethyl) ) -4- (10-aminodecyl) pyridinium bromide,

  1- (2-mercaptoethyl) -4- (11-aminoundecyl) pyridinium bromide, 1- (2-mercaptoethyl) -4- (12-aminododecyl) pyridinium bromide, 1- (5-mercaptopentyl)- 4- (3-methylaminopropyl) pyridinium bromide, 1- (9-mercaptononyl) -4- (4-dimethylaminobutyl) pyridinium bromide, 1- (11-mercaptoundecyl) -4- (6-ethylmethyl) Aminohexyl) pyridinium bromide, 1- (2-mercaptoethyl) -1-aminomethylpyrrolidinium bromide, 1- (3-mercaptopropyl) -1-aminomethylpyrrolidinium bromide, 1- (4-mercaptobutyl) -1-aminomethylpyrrolidinium bromide, 1- (5-mercaptopenti ) -1-aminomethylpyrrolidinium bromide, 1- (6-mercaptohexyl) -1-aminomethylpyrrolidinium bromide, 1- (8-mercaptooctyl) -1-aminomethylpyrrolidinium bromide, 1- (9-mercaptononyl) -1-aminomethylpyrrolidinium bromide, 1- (10-mercaptodecyl) -1-aminomethylpyrrolidinium bromide, 1- (11-mercaptoundecyl) -1-aminomethylpyrrolidi Nitrobromide, 1- (12-mercaptododecyl) -1-aminomethylpyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (2-aminoethyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) ) -1- (3-Aminopropyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (4-aminobutyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (6-aminohexyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (8- Aminooctyl) pyrrolidinium bromide,

  1- (2-mercaptoethyl) -1- (9-aminononyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (10-aminodecyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (11-aminoundecyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (12-aminododecyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1- (4 -Methylaminobutyl) pyrrolidinium bromide, 1- (3-mercaptopropyl) -1- (8-dimethylaminooctyl) pyrrolidinium bromide, 1- (4-mercaptobutyl) -1- (9-ethylmethylamino) Nonyl) pyrrolidinium bromide, 1- (2-mercaptoethyl) -1-aminomethylpiperidinium bromide, 1- (3 Mercaptopropyl) -1-aminomethylpiperidinium bromide, 1- (4-mercaptobutyl) -1-aminomethylpiperidinium bromide, 1- (5-mercaptopentyl) -1-aminomethylpiperidinium bromide, 1 -(6-mercaptohexyl) -1-aminomethylpiperidinium bromide, 1- (8-mercaptooctyl) -1-aminomethylpiperidinium bromide, 1- (9-mercaptononyl) -1-aminomethylpimide Peridinium bromide, 1- (10-mercaptodecyl) -1-aminomethylpiperidinium bromide, 1- (11-mercaptoundecyl) -1-aminomethylpiperidinium bromide, 1- (12-mercaptododecyl)- 1-aminomethylpiperidinium bromide, 1- (2-mercaptoeth ) -1- (2-aminoethyl) piperidinium bromide, 1- (2-mercaptoethyl) -1- (3-aminopropyl) piperidinium bromide, 1- (2-mercaptoethyl) -1- (4 -Aminobutyl) piperidinium bromide, 1- (2-mercaptoethyl) -1- (6-aminohexyl) piperidinium bromide,

  1- (2-mercaptoethyl) -1- (8-aminooctyl) piperidinium bromide, 1- (2-mercaptoethyl) -1- (9-aminononyl) piperidinium bromide, 1- (2-mercaptoethyl) ) -1- (10-aminodecyl) piperidinium bromide, 1- (2-mercaptoethyl) -1- (11-aminoundecyl) piperidinium bromide, 1- (2-mercaptoethyl) -1- (12 -Aminododecyl) piperidinium bromide, 1- (10-mercaptodecyl) -1- (9-methylaminononyl) piperidinium bromide, 1- (11-mercaptoundecyl) -1- (10-dimethylaminodecyl) ) Piperidinium bromide, 1- (12-mercaptododecyl) -1- (12-ethylmethylaminododecyl) piperidi Umbromide, 2-mercaptoethyl- (aminomethyl) dimethylammonium bromide, 3-mercaptopropyl- (aminomethyl) dimethylammonium bromide, 4-mercaptobutyl- (aminomethyl) dimethylammonium bromide, 5-mercaptopentyl- (aminomethyl) Dimethylammonium bromide, 6-mercaptohexyl- (aminomethyl) dimethylammonium bromide, 8-mercaptooctyl- (aminomethyl) dimethylammonium bromide, 9-mercaptononyl- (aminomethyl) dimethylammonium bromide, 10-mercaptodecyl- (amino Methyl) dimethylammonium bromide, 11-mercaptoundecyl- (aminomethyl) dimethylammonium bromide, 12-mercaptododecy -(Aminomethyl) dimethylammonium bromide, 2-mercaptoethyl- (3-aminopropyl) dimethylammonium bromide, 2-mercaptoethyl- (4-aminobutyl) dimethylammonium bromide, 2-mercaptoethyl- (5-aminopentyl) Dimethylammonium bromide,

  2-mercaptoethyl- (6-aminohexyl) dimethylammonium bromide, 2-mercaptoethyl- (8-aminooctyl) dimethylammonium bromide, 2-mercaptoethyl- (9-aminononyl) dimethylammonium bromide, 2-mercaptoethyl- ( 10-aminodecyl) dimethylammonium bromide, 2-mercaptoethyl- (11-aminoundecyl) dimethylammonium bromide, 2-mercaptoethyl- (12-aminododecyl) dimethylammonium bromide, 5-mercaptopentyl- (8-methylaminononyl) ) Ethylmethylammonium bromide, 6-mercaptohexyl- (6-dimethylaminohexyl) methylpropylammonium bromide, and 8-mercaptooctyl- (4-ethylmethyl) Ruaminobuchiru) butyl hexyl ammonium bromide.

[Reduction reaction in the first reduction catalyst]
The reduction reaction in the first reduction catalyst will be described by taking CO ₂ reduction as an example. The elementary reaction of CO ₂ reduction, CO ₂ is the CO ₂ radical anion by one-electron reduction reaction. This reaction requires a large overvoltage. This overvoltage is a loss of energy and causes a decrease in energy conversion efficiency. In addition, a reduction reaction of water and hydrogen ions occurs as a side reaction together with the CO ₂ reduction reaction, and hydrogen is generated. This side reaction reduces the Faraday efficiency of the CO ₂ reduction reaction. However, the first reduction catalyst described above has high reduction efficiency.

In the first reduction catalyst, a quaternary nitrogen cation form of CO ₂ and reaction intermediate. Therefore, it contributes to the generation and stabilization of the CO ₂ radical anion. Therefore, the first reduction catalyst can cause a CO ₂ reduction reaction with low energy. As a result, the energy conversion efficiency of the first reduction catalyst is improved. The quaternary nitrogen cation has an effect of inhibiting water and hydrogen ions from approaching the metal layer 102. For this reason, the quaternary nitrogen cation can impart reaction selectivity to the reduction reaction in the metal layer 102. That is, generation of hydrogen due to side reactions can be suppressed, and Faraday efficiency can be improved.

  Since the first reduction catalyst has high reduction efficiency, it is possible to provide a reduction product production system that can recover the reduction product with high efficiency.

Moreover, the reduction catalyst 3 of the second aspect can achieve even higher reduction efficiency. This is because the amino group in the modified organic molecule 112 reacts with the CO ₂ molecule to form a carbonate, so that the CO ₂ molecule necessary for the reduction reaction is attracted and supplied to the quaternary nitrogen cation or the metal layer 102. Because it can. In addition, the amino group forms a salt with carboxylic acids (for example, formic acid, acetic acid, oxalic acid, etc.) generated by CO ₂ reduction. Therefore, it has the effect of promoting a multi-electron reduction reaction in which reduction occurs continuously. As a result, the reduction efficiency can be further improved. Therefore, the reduced product production system which can collect a reduced product with higher efficiency can be provided.

  The reduction catalyst 3 of the second aspect can produce ethylene glycol with high selectivity. Therefore, by using the reduction catalyst 3, it is possible to provide a reduced product production system that produces ethylene glycol with high selectivity.

  The reduced product changes depending on the interaction between the quaternary nitrogen cation, the metal layer 102, and the reducing material. Details will be described below.

A reduction potential is applied to the metal layer 102 of the reduction catalyst. Therefore, among the electrolyte components, in particular, ions containing CO ₂ (for example, hydrogen carbonate ions) or physically dissolved CO ₂ are contained in the metal layer 102 and the modified organic molecules 112 fixed on the surface thereof. Subject to electrostatic attraction near the secondary nitrogen cation. As a result, the CO ₂ , the metal layer 102 and the quaternary nitrogen cation form an electric double layer at the catalyst / electrolyte interface.

At this interface, the CO ₂ reduction reaction by charge transfer reaction proceeds. In the reduction reaction electrolytic bath 31b, CO ₂ is reduced by the reduction catalyst layer 20 to generate a carbon compound. Specifically, CO ₂ is carbon monoxide (CO), formic acid (HCOOH), formaldehyde (HCHO), methanol (CH ₃ OH), acetic acid (CH ₃ COOH), acetaldehyde (CH ₃ CHO) ethanol (CH ₃ CH ₂ OH) and ethylene glycol (HOCH ₂ CH ₂ OH). Further, water (H ₂ O) can be reduced as a side reaction to generate hydrogen (H ₂ ).

  When carbon dioxide undergoes a two-electron reduction reaction, formic acid is generated in addition to carbon monoxide. When formic acid undergoes a two-electron reduction reaction, formaldehyde is produced. Further, when formaldehyde undergoes a two-electron reduction reaction, methanol is generated. When methanol is produced using the first reduction catalyst 1, formic acid or formaldehyde may be selected as a reducing raw material in addition to carbon dioxide. For this reason, it is desirable that at least one reducing material selected from carbon dioxide, formic acid, and formaldehyde is absorbed in the electrolytic solution in the reduction reaction electrolytic bath 31b. For example, sodium hydrogen carbonate solution is mentioned as electrolyte solution in the electrolytic tank 31b for reduction reaction.

  Further, when carbon dioxide undergoes a two-electron reduction reaction, oxalic acid may be generated. When oxalic acid undergoes a two-electron reduction reaction, glycolic acid is produced. Furthermore, when glycolic acid undergoes a two-electron reduction reaction, glyoxal or glycolic acid is produced. Further, when glyoxal or glycolic acid undergoes a two-electron reduction reaction, glycolaldehyde is produced. Further, when glycol aldehyde undergoes a two-electron reduction reaction, ethylene glycol is generated. When ethylene glycol is produced using the first reduction catalyst 1, oxalic acid, glycolic acid, or glycol aldehyde may be selected as a reducing raw material in addition to carbon dioxide. For this reason, at least one reducing material selected from oxalic acid, glycolic acid or glycolaldehyde may be absorbed in the electrolytic solution in the electrolytic cell 31b for reduction reaction.

  When carbon dioxide undergoes an 8-electron reduction reaction, acetic acid may be generated. When acetic acid undergoes a two-electron reduction reaction, acetaldehyde is produced. Furthermore, when acetaldehyde undergoes a two-electron reduction reaction, ethanol is generated. When ethanol is generated using the first reduction catalyst 1, acetic acid or acetaldehyde may be selected as a reducing raw material in addition to carbon dioxide. For this reason, the electrolytic solution in the electrolytic cell 31b for reduction reaction may have absorbed at least one reducing raw material selected from carbon dioxide, acetic acid, and acetaldehyde.

As described above, carbon dioxide is reduced to produce formic acid, formaldehyde, and methanol, and carbon dioxide is reduced to produce oxalic acid, glycolic acid, glyoxal or glycolic acid, glycolaldehyde, and ethylene glycol. The reaction and the reaction in which carbon dioxide is reduced to produce acetic acid, acetaldehyde, and ethanol depend on the density of the modified organic molecules 112 in the first reduction catalyst 1. For example, when the density of the modified organic molecules 112 with respect to the metal layer 102 is 1 × 10 ¹¹ atoms / cm ² or less, a reaction in which mainly formic acid, formaldehyde, and methanol are generated occurs. On the other hand, for example, when the density of the modified organic molecule 112 is 1 × 10 ¹² to 10 ¹⁵ atoms / cm ² , a reaction in which acetic acid, acetaldehyde, and ethanol are generated in addition to formic acid, formaldehyde, and methanol occurs. In particular, when the density of the modified organic molecule 112 is 1 × 10 ¹³ to 10 ¹⁵ atoms / cm ² , a reaction in which mainly acetic acid, acetaldehyde, and ethanol are generated occurs.

The binding state and molecular density of the modified organic molecule 112 can be calculated based on the analysis result by X-ray photoelectron spectroscopy (XPS). The analysis conditions can be the following conditions. The detection angle indicates an angle formed between the sample normal and the detector input lens axis.
Model used PHI Quantera-SXM
Irradiation X-ray source Single crystal spectroscopy AlKα ray Output 50W
Analysis area φ200μm
Pass Energy Wide Scan-280.0eV (1.0eV / Step)
Narrow Scan-69.0eV (0.125eV / Step)
Detection angle 45 °
Charge-neutralized electron gun Ar ⁺ , e ^{− is} used together As a charge correction (horizontal axis energy correction), the C—C / H coupling component of the C1s spectrum is adjusted to 284.80 eV.

  The bond density (molecular density) of the modified organic molecule 112 is the number of Au atoms per unit area estimated from the following equation (5) and the number of S atoms normalized by the number of Au atoms as a result of semi-quantitative analysis (S / Au). From the above, it is calculated by the following equation (6).

Au (atoms / cm ² ) = density (g / cm ³ ) × detection depth (nm) × N / Mw (5)
Molecular density (atoms / cm ² ) = Au (atoms / cm ² ) × S / Au (atomic ratio) (6)
Here, the density is 19.3 g / cm ³ , the detection depth is 5 nm, N is the Avogadro number (atoms / mol), and Mw is 197 g / mol.

  In the first reduction catalyst 1, the reaction in which carbon dioxide is reduced and ethylene glycol is generated via oxalic acid, glycolic acid or glycol aldehyde is selectively generated by maintaining the electrode at the reduction potential. That is, by maintaining the electrode at the reduction potential, the orientation of the modified organic molecules 112 becomes uniform, so that a reaction for generating ethylene glycol occurs. As an electrolysis condition in which the electrode is held at the reduction potential, in a three-electrode cell using an electrode substrate as a working electrode, silver silver chloride as a reference electrode, and Pt as a counter electrode, −0.8 V to −1 is applied to the working electrode. It is preferable that a potential of 3 V is applied for 5 hours or longer, more preferably 3 hours or longer, and still more preferably 1 hour or longer. The orientation of the modified organic molecules 112 can be observed using a scanning tunneling microscope (STM).

[Production method of first reduction catalyst]
Next, the manufacturing method of a 1st reduction catalyst is demonstrated.
First, the metal layer 102 is formed on the surface of the current collector 101. As the method, a known vacuum film forming method such as a sputtering method, a vapor deposition method, or an ALD (Atomic Layer Deposition) method can be used.

  Next, the modified organic molecule 112 is fixed to the metal layer 102 by bonding the reactive functional group 109 to the metal layer 102. As the method, a known method can be used. For example, a method in which the current collector 101 including the metal layer 102 is brought into contact with a solution in which the modified organic molecule 112 is dissolved, the modified organic molecule 112 is evaporated in a high vacuum, and a film is formed on the surface of the current collector 101. For example, a method of spraying the modified organic molecules 112 on the surface of the current collector 101 by a method, spraying, or the like can be used.

  In the method using the solution in which the modified organic molecule 112 is dissolved, the modified organic molecule 112 chemically adsorbed on the metal layer 102 spontaneously forms an aggregate by van der Waals force or hydrophobic interaction between the adsorbed molecules. . Then, the adsorbed molecules gather densely to form a monomolecular layer with uniform alignment.

  As a solvent for dissolving the modified organic molecule 112, any solvent that can dissolve the organic molecule may be used. For example, it can be selected from alcohols such as ethanol and aromatic or aliphatic organic solvents such as toluene and hexane. Since the modified organic molecule 112 is highly soluble and easy to handle, it is preferable to use ethanol.

An example of a method for fixing the modified organic molecules 112 to the metal layer 102 will be described in more detail.
First, a preparation solution in which the modified organic molecule 112 is dissolved is prepared. Next, the current collector 101 on which the metal layer 102 is formed is immersed in this prepared solution. The immersion time is from several minutes to several hours. Thereby, the modified organic molecule 112 is fixed on the surface of the metal layer 102. Conditions such as the concentration of the modified organic molecule 112, the immersion time, and the immersion temperature can be changed as appropriate according to the structure of the modified organic molecule 112 and the like. These conditions affect the formation state of the monomolecular layer composed of the modified organic molecules 112.

  If the concentration of the prepared solution is too low, it takes time until a monomolecular layer is formed. On the other hand, if the concentration is too high, more molecules may be adsorbed on the monomolecular layer and a laminated film may be formed. For this reason, the concentration of the modified organic molecule 112 is preferably 0.1 mM or more and 100 mM or less, and more preferably 1 mM or more and 10 mM or less.

  The immersion time is preferably sufficient to form a dense monolayer with uniform orientation. It is preferably 1 minute or longer and 100 hours or shorter, and preferably 12 hours or longer and 72 hours or shorter.

  The temperature of the prepared solution during the immersion affects the formation of a dense and aligned monolayer. For this reason, it is desirable that the temperature is from room temperature (25 ° C.) to 60 ° C. in consideration of the vapor pressure and boiling point of the solvent.

Whether the modified organic molecule 112 is immobilized on the surface of the metal layer 102 can be confirmed by a known electrochemical method or surface analysis method.
As an electrochemical method, a cyclic voltammetry method can be used. A specific example will be described below. First, 0.2M in which 1 mM hexacyanoiron (III) potassium (K ₃ [Fe (CN) ₆ ]) or 1 mM hexaammineruthenium (III) chloride ([Ru (NH ₃ ) ₆ ] Cl ₃ ) was dissolved. An aqueous potassium chloride (KCl) solution is prepared. In this aqueous solution, the electrochemical response of the current collector 101 before and after the process of adsorbing the modified organic molecules 112 is measured, and the results are compared.

  As an electrochemical response, a reaction current due to an electrochemical redox reaction of a hexacyanoiron (III) anion or a hexaammineruthenium (III) cation is measured. The reaction current for the current collector 101 to which the modified organic molecule 112 is fixed decreases as compared with the reaction current for the current collector 101 to which the modified organic molecule 112 is not fixed. This is because the oxidation-reduction reaction of the hexacyanoiron (III) anion or the hexaammineruthenium (III) cation is inhibited by fixing the modified organic molecule 112 to the metal layer 102. Thus, by measuring the above reaction current, it can be indirectly confirmed that the modified organic molecule 112 is immobilized.

  As a surface analysis method, a Fourier transform infrared spectrophotometer (FT-IR) using a reflection method can be used. According to this method, the infrared spectrum of the thin film and the molecularly adsorbed species on the surface of the current collector 101 can be measured with high sensitivity. That is, it is possible to know the structure of the organic molecule, particularly information on the functional group. Moreover, X-ray photoelectron spectroscopy (XPS) can also be used as a surface analysis method. According to this method, when the modified organic molecule 112 and the modified organic molecule 112 have an anion, the composition of the anion can be measured. Moreover, the presence or absence of the modified organic molecule 112 can also be determined from the difference in water wettability using a contact angle meter.

[Second reduction catalyst]
Next, of the first reduction catalyst and the second reduction catalyst used in the embodiment, the second reduction catalyst will be described in detail.

  The second reduction catalyst includes a current collector having a surface layer, a spacer organic molecular layer formed on the surface layer, and metal fine particles bonded to the surface of the spacer organic molecular layer.

  Hereinafter, the second reduction catalyst will be described with reference to FIGS. 15 to 18. In the drawing, the same parts as those of the first reduction catalyst are denoted by the same reference numerals. In addition, redundant description will be given as necessary.

  FIG. 15 is a schematic diagram showing the configuration of the second reduction catalyst 4. As shown in FIG. 15, the second reduction catalyst 4 includes a current collector 101, a spacer organic molecular layer 100, and metal fine particles 107. The current collector 101 has a surface layer 120 on the surface thereof.

  The current collector 101 is made of a material having electrical conductivity, like the first reduction catalyst. For example, a stainless steel substrate can be used as the current collector 101.

  The surface layer 120 on the surface of the current collector 101 is a metal layer or an oxide layer. When the surface layer 120 is a metal layer, the surface layer 120 includes at least one metal selected from the group consisting of Au, Ag, Cu, Zn, Pt, Fe, Ti, Ni, Sn, In, and Bi. . The metal layer 102 may contain components other than metal, but is preferably made of only metal. The metal layer 102 and the current collector 101 may be made of the same material. In this case, the metal constituting the metal layer 102 may also serve as the current collector 101.

When the surface layer 120 of the current collector 101 is an oxide layer, the surface layer 120 is composed of titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ). And at least one oxide selected from the group consisting of zinc oxide (ZnO), tin-doped indium oxide (ITO), and fluorine-doped tin oxide (FTO). Alternatively, the surface layer 120 may be an oxide film layer formed on the surface of the stainless steel substrate. Note that the oxide layer is generally an insulator except for a transparent conductive film such as ITO or FTO. In order to ensure conduction by a tunnel current, the thickness of the oxide layer is preferably 10 nm or less, and more preferably 5 nm or less.

  The spacer organic molecular layer 100 is a monomolecular layer (Self-Assembled Monolayer) formed by the chemical adsorption of the spacer organic molecules 106 on the surface of the surface layer 120 and self-assembly. The spacer organic molecule 106 has a function of fixing the metal fine particles 107 to the current collector 101 and electrically connecting them.

  The spacer organic molecule 106 has a skeleton 104 and a first reactive functional group 103 and a second reactive functional group 105 bonded to the ends thereof.

  As the chain length of the spacer organic molecule 106 becomes longer, a dense and aligned molecular layer is formed on the surface layer 120. Therefore, by increasing the chain length, the metal fine particles 107 can be easily fixed and a molecular layer having high durability can be formed. On the other hand, if the chain length is too long, the resistance of the tunnel current in the spacer organic molecular layer 100 increases, so that the electrode resistance of the second reduction catalyst 4 increases. Therefore, the total number of carbon atoms contained in the spacer organic molecule 106 is preferably in the range of 2 to 12, and more preferably in the range of 2 to 6.

  The first reactive functional group 103 has an affinity for the surface layer 120 and chemically reacts with and binds to the surface layer 120. Thereby, the spacer organic molecule 106 is fixed to the surface layer 120. The first reactive functional group 103 is preferably a functional group capable of covalent bonding with the surface layer 120. When the surface layer 120 is formed of a metal layer, the first reactive functional group 103 is preferably selected from a thiol group, a disulfide group, and a thiocyanate group. A thiol group is more preferred because of its excellent binding strength. When the surface layer 120 is composed of an oxide layer or an oxide film layer on the stainless steel substrate surface, the first reactive functional group 103 is selected from a carboxylic acid group, a phosphonic acid group, a phosphate ester group, and an alkoxysilyl group. It is preferable. A phosphonic acid group is more preferred because of its excellent bonding strength.

  The second reactive functional group 105 has an affinity for the metal fine particles 107 and is chemically bonded to the metal fine particles 107. Thereby, the metal fine particles 107 are fixed to the surface of the spacer organic molecular layer 100. The second reactive functional group 105 is preferably a functional group capable of electrostatic bonding with the charged metal fine particles 107, and is preferably selected from, for example, an amino group and a carboxyl group. Alternatively, the second reactive functional group 105 is preferably a functional group that can be covalently bonded to the metal fine particle 107, and is preferably selected from functional groups such as a thiol group, a disulfide group, and a thiocyanate group. . A thiol group is more preferred because of its excellent binding strength.

  Examples of the spacer organic molecule 106 include a molecule similar to the example of the modified organic molecule 112 in the first embodiment of the first reduction catalyst.

  The metal fine particles 107 function as a catalyst that activates the reduction reaction. As the material of the metal fine particles, at least one element selected from the group consisting of Au, Ag, Cu, Pt, Zn, Fe, Ti, Sn, In, Bi, and Ni is used. Since the catalytic activity is particularly high, it is preferable to use metal fine particles made of Au or Ag as the metal fine particles 107.

  The average particle diameter of the metal fine particles 107 is preferably 1 nm or more and 300 nm or less. When the average particle size is 300 nm or less, the activity efficiency of the catalyst can be increased. Moreover, it is difficult to produce the metal fine particles 107 having an average particle size of less than 1 nm. The average particle size of the metal fine particles 107 is more preferably 150 nm or less because the catalyst activation efficiency is further improved. The metal fine particles 107 may be primary particles having an average particle diameter of 50 nm or less, or may be secondary particles in which such primary particles are aggregated.

  The average particle diameter of the metal fine particles 107 can be measured by particle size distribution measurement by a dynamic light scattering method. Specifically, the solution in which the metal fine particles 107 are dispersed is irradiated with laser light, and the fluctuation of the scattered light reflecting the diffusion coefficient is detected. From the result, the particle diameter can be calculated using the Stokes-Einstein equation. In the frequency distribution obtained from the appearance ratio for each particle diameter, the largest particle diameter or the maximum value of the distribution is the mode diameter, and this is the average particle diameter.

  The metal fine particle includes an organic molecule 108 having a charge on a part of its surface. Thereby, the surface of the metal fine particle 107 is charged. The metal fine particles 107 are immobilized on the surface of the spacer organic molecular layer 100 by electrostatic attraction (electrostatic coupling) between the charge on the surface of the metal fine particles 107 and the charge of the second reactive functional group 105. The charge of the organic molecule 108 may be either a positive charge or a negative charge.

  When the organic molecule 108 has a negative charge, the surface of the metal fine particle 107 also has a negative charge. In this case, the metal fine particles 107 can be immobilized by using the spacer organic molecule 106 having an amino group as the second reactive functional group 105.

  On the other hand, when the charge of the organic molecule 108 is positive, the metal fine particle 107 can be immobilized by using the spacer organic molecule 106 having a carboxyl group as the second reactive functional group 105.

  When the metal fine particles 107 have a charge, an electrostatic repulsive force is generated between the particles, so that nanoparticle-sized fine particles can be prevented from being aggregated and coarsened.

  The charge on the surface of the metal fine particle 107 can be provided with a charge due to the organic molecule 108 resulting from the manufacturing method of the metal fine particle 107 or a charge due to the organic molecule 108 due to processing after the production. For example, when a reducing agent such as citric acid is used when reducing and depositing the metal fine particles 107 from the liquid layer, citric acid is applied to the surface of the metal fine particles 107, and the surface of the metal fine particles 107 is negatively charged. When a molecule having an amino group is electrostatically coupled to the surface of the negatively charged metal fine particle 107, the surface of the metal fine particle 107 is positively charged. On the other hand, even when an amine molecule having a covalent reactive group such as thiol is reacted on the surface of the metal fine particle 107, the metal particle 107 is positively charged. That is, an amine molecule having a covalent reactive group such as thiol can be used regardless of the presence / absence of charge on the surface of the metal fine particle 107 and whether the charge is positive or negative.

[Modification 1]
Modification 1 of the second reduction catalyst will be described with reference to FIGS. 16 and 17.
FIG. 16 is a schematic diagram illustrating a configuration of the second reduction catalyst 5 according to the first modification. FIG. 17 is a schematic diagram illustrating in detail an example of the configuration of the second reduction catalyst 5 according to the first modification.

  As shown in FIG. 16, the second reduction catalyst 5 is bonded to the current collector 101 having the surface layer 120, the spacer organic molecular layer 100 formed on the surface of the surface layer 120, and the surface of the spacer organic molecular layer 100. Metal fine particles 107 and modified organic molecules 112 containing quaternary nitrogen cations bonded to the metal fine particles 107.

  As the current collector 101, the surface layer 120, the spacer organic molecules 106, and the metal fine particles 107, the same materials as those of the second reduction catalyst 4 can be used. Further, as the modified organic molecule 112, the same one as the reduction catalyst according to the first aspect of the first reduction catalyst can be used. That is, in Modification 1, the modified organic molecule 112 is an organic molecule having a quaternary nitrogen cation as the terminal functional group 111.

The reactive functional group 109 of the modified organic molecule 112 has an affinity for the metal fine particle 107 and is chemically bonded to the metal fine particle 107. Thereby, the modified organic molecule 112 is fixed to the metal fine particle 107. The modified organic molecule 112 is bonded to the metal fine particle 107 and has a function of promoting the CO ₂ reduction reaction generated in the metal fine particle 107.

  Examples of the modified organic molecule 112 used in Modification 1 include the same molecules as the modified organic molecule 112 in the first embodiment of the first reduction catalyst.

The modified organic molecule 112 containing a quaternary nitrogen cation may form a salt with a counter anion. Counter anions include, but are not limited to, fluoride ions, chloride ions, bromide ions, iodide ions, SO ₄ ²⁻ , HCO ₃ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ COO ⁻ , CF ₃ SO ^{_{3 -, NO 3 -, SCN}} -, N (CN) 2 -, C (CN) 3 - (CF 3 SO 2) 3 C -, bis (trifluoromethoxy) imide anion, bis (trifluoromethoxy sulfonyl) It may be an anion such as an imide anion and a bis (perfluoroethylsulfonyl) imide anion. In FIG. 15 and FIG. 16, the counter anion is omitted.

[Modification 2]
Modification 2 of the second reduction catalyst will be described with reference to FIG.
FIG. 18 is a schematic diagram illustrating in detail an example of the configuration of the second reduction catalyst 6 according to the second modification.

  As shown in FIG. 18, the second reduction catalyst 6 is bonded to the current collector 101 having the surface layer 120, the spacer organic molecular layer 100 formed on the surface of the surface layer 120, and the surface of the spacer organic molecular layer 100. Metal fine particles 107 and modified organic molecules 112 containing a quaternary nitrogen cation bonded to the metal fine particles 107.

  As the current collector 101, the surface layer 120, the spacer organic molecules 106, and the metal fine particles 107, the same materials as those of the second reduction catalyst 4 can be used. Further, as the modified organic molecule 112, the same one as the reduction catalyst according to the second aspect of the first reduction catalyst can be used. That is, in Modification 2, the modified organic molecule 112 is an organic molecule having a quaternary nitrogen cation in the skeleton 110 portion and an amino group as the terminal functional group 111.

  Examples of the modified organic molecule 112 used in Modification 2 include molecules similar to those of the modified organic molecule 112 described in the second embodiment of the first reduction catalyst.

  The modified organic molecule 112 containing a quaternary nitrogen cation may form a salt with a counter anion as in the first modification. In FIG. 18, bromide ions are shown as counter anions. The amino group may form a salt with hydrofluoric acid, hydrochloric acid, odorous acid, iodic acid, sulfuric acid, nitric acid, phosphoric acid or the like.

[Reduction reaction in the second reduction catalyst]
The reduction reaction in the second reduction catalyst will be described by taking CO ₂ reduction as an example. As described for the first reduction catalyst, the elementary reaction of the normal CO ₂ reduction reaction has a problem that the Faraday efficiency is low. However, the second reduction catalyst can achieve high reduction efficiency.

In the second reduction catalyst, the reduction reaction occurs in the metal fine particles 107. By using the metal fine particles 107, the reaction area (surface area) can be increased as compared with the flat metal layer. As a result, the CO ₂ reduction reaction efficiency can be increased.

The quaternary nitrogen cation contained in the modified organic molecule 112 forms a reaction intermediate with CO ₂ . Therefore, it contributes to the generation and stabilization of the CO ₂ radical anion. Therefore, the second reduction catalyst in which the modified organic molecules 112 are immobilized on the metal fine particles 107 can cause a CO ₂ reduction reaction with lower energy. As a result, the energy conversion efficiency of the reduction catalyst can be improved. The quaternary nitrogen cation has an effect of inhibiting water and hydrogen ions from approaching the metal fine particles 107. For this reason, the quaternary nitrogen cation can impart reaction selectivity to the reduction reaction in the metal fine particles 107. That is, generation of hydrogen due to a side reaction can be suppressed and Faraday efficiency can be improved.

Further, when an amino group is contained at the terminal of the modified organic molecule 112, the amino group reacts with the CO ₂ molecule to form a carbonate. Therefore, CO ₂ molecules necessary for the reduction reaction can be attracted and supplied to the quaternary nitrogen cation and the metal fine particles 107. In addition, the amino group forms a salt with carboxylic acids (for example, formic acid, acetic acid, oxalic acid, etc.) generated by CO ₂ reduction. Therefore, it has the effect of promoting a multi-electron reduction reaction in which reduction occurs continuously. As a result, reduction efficiency can be improved.

  From the above, the second reduction catalyst can achieve high reduction efficiency. Therefore, by using the second reduction catalyst, it is possible to provide a reduced product production system that can recover the reduced product with high efficiency.

The 2nd reduction catalyst can use the raw material selected from the group which consists of oxalic acid, glycolic acid, and glycol aldehyde other than a carbon dioxide as a reducing raw material. The reduced product changes depending on the interaction between the quaternary nitrogen cation, the surface layer 120, and the reducing material. For example, when CO _{2 is} used as a raw material, carbon monoxide (CO), formic acid (HCOOH), formaldehyde (HCHO), methanol (CH ₃ OH), acetic acid (CH ₃ COOH), acetaldehyde (CH ₃ CHO), ethanol ( CH ₃ CH ₂ OH), oxalic acid ((COOH) ₂ ), glycolic acid (C ₂ H ₂ O ₃ ), glycol aldehyde (C ₂ H ₂ O ₂ ), and ethylene glycol (HOCH ₂ CH ₂ OH) Can occur.

  Furthermore, as in Modification 2, the second reduction catalyst using the modified organic molecule 112 having an amino group as the terminal functional group 111 can generate ethylene glycol with high selectivity. Therefore, the reduced product production system which produces ethylene glycol with high selectivity can be provided by using the reduction catalyst of the modification 2.

[Method for producing second reduction catalyst]
Next, the manufacturing method of a 2nd reduction catalyst is demonstrated.
First, the surface layer 120 is formed on the surface of the current collector 101. As the method, a known vacuum film forming method such as a sputtering method, a vapor deposition method, or an ALD (Atomic Layer Deposition) method can be used.

  Next, the spacer organic molecule 106 is fixed to the surface layer 120 to form the spacer organic molecule layer 100. As the method, the same method as the method of fixing the modified organic molecule 112 to the metal layer 102 in the manufacturing method of the first reduction catalyst can be used.

  The formation of the spacer organic molecular layer 100 on the surface of the surface layer 120 is the same as the method for confirming that the modified organic molecule 112 is fixed to the metal layer 102 in the manufacturing method of the first reduction catalyst 1. Can be confirmed by the method.

Next, metal fine particles 107 are prepared. The charged organic molecules 108 are fixed to the metal fine particles. Examples of the method include the following first method and second method.
(First Method) In the method of preparing metal fine particles, a reducing agent such as citric acid is used when the metal fine particles are reduced and deposited from the liquid layer. Thereby, citric acid is provided to the surface of the metal fine particles. As a result, the surface of the metal fine particles is negatively charged. Then, molecules having amino groups are electrostatically bonded to the surface of the negatively charged metal fine particles.
(Second Method) An amine molecule having a covalent reactive group such as thiol is bonded to the surface of uncharged metal fine particles. Thereby, the metal fine particles are positively charged. According to this method, the charged organic molecule 108 can be fixed regardless of the presence / absence of charge on the surface of the metal fine particle and the sign of the charge.

  Next, the metal fine particles 107 to which the organic molecules 108 having electric charges are fixed are fixed to the surface of the spacer organic molecular layer 100. Specifically, the metal fine particles 107 are dispersed in an aqueous solution to prepare a dispersion. The current collector 101 on which the spacer organic molecular layer 100 is formed is immersed in this dispersion. As a result, the second reactive functional group 105 of the spacer organic molecular layer 100 and the organic molecules 108 on the surface of the metal fine particles 107 are electrostatically coupled, and the metal fine particles 107 are fixed to the spacer organic molecular layer 100.

  The solution in which the metal fine particles 107 are dispersed is not particularly limited as long as the metal fine particles 107 can be stably dispersed. For example, water, ethanol, toluene or the like can be used. Since handling is easy, it is preferable to use water or ethanol.

Conditions such as the concentration of the dispersion, the immersion time, and the immersion temperature depend on the method for synthesizing the metal fine particles 107 and the stability, and thus are changed as appropriate.
If the concentration of the dispersion is too low, it takes time to fix the metal fine particles 107. On the other hand, if the concentration is too high, the metal fine particles 107 aggregate in the dispersion and may not be fixed to the spacer organic molecular layer 100. For this reason, the concentration of the metal fine particles in the dispersion is preferably 0.01 mM or more and 10 mM or less, and more preferably 0.1 mM or more and 1 mM or less.

  The dipping time is preferably 1 hour or more and 50 hours or less, and more preferably 5 hours or more and 24 hours or less in order to fix a sufficient amount of the metal fine particles 107.

  The temperature of the dispersion during immersion is preferably from room temperature (25 ° C.) to 35 ° C. If the temperature is too high, the dispersion stability of the metal fine particles 107 may decrease, and the metal fine particles 107 may aggregate.

Whether the metal fine particles 107 are fixed on the surface of the spacer organic molecular layer 100 can be confirmed by a known electrochemical method or surface analysis method.
As an electrochemical method, a cyclic voltammetry method can be used. A specific example will be described below. First, 0.2M in which 1 mM hexacyanoiron (III) potassium (K ₃ [Fe (CN) ₆ ]) or 1 mM hexaammineruthenium (III) chloride ([Ru (NH ₃ ) ₆ ] Cl ₃ ) was dissolved. An aqueous potassium chloride (KCl) solution is prepared. In this aqueous solution, the electrochemical response of the current collector 101 before and after the step of fixing the metal fine particles 107 is measured, and the results are compared.

  As an electrochemical response, a reaction current due to an electrochemical redox reaction of a hexacyanoiron (III) anion or a hexaammineruthenium (III) cation is measured. The reaction current for the current collector 101 to which the metal fine particles 107 are fixed increases as compared with the reaction current for the current collector 101 to which the metal fine particles 107 are not fixed. This is due to the oxidation-reduction reaction of the hexacyanoiron (III) anion or the hexaammineruthenium (III) cation caused by the metal fine particles 107 being fixed to the spacer organic molecular layer 100. As described above, by measuring the reaction current, it can be indirectly confirmed that the metal fine particles 107 are fixed.

  As a surface analysis method, it can be directly observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM), an atomic force electron microscope (AFM), or a scanning transmission electron microscope (STEM). The metal composition can be evaluated by energy dispersive X-ray analysis (EDX), electron microanalyzer (EPMA), X-ray photoelectron spectroscopy (XPS), or the like.

  Furthermore, in the reduction catalyst manufactured as described above, the reduction catalyst of Modification 1 or Modification 2 can be manufactured by fixing the modified organic molecules 112 to the metal fine particles 107. Specifically, the modified organic molecules 112 are fixed to the metal fine particles 107 fixed to the spacer organic molecular layer 100. As the method, the same method as the method of fixing the modified organic molecule 112 to the metal layer 102 in the manufacturing method of the first reduction catalyst can be used.

An example of a method for fixing the modified organic molecules 112 to the metal fine particles 107 will be described in more detail.
First, a preparation solution in which the modified organic molecule 112 is dissolved is prepared. Next, the current collector 101 on which the metal fine particles 107 are formed is immersed in this prepared solution. The immersion time is from several minutes to several hours. Thereby, the modified organic molecule 112 is fixed on the surface of the metal fine particle 107. Conditions such as the concentration of the modified organic molecule 112, the immersion time, and the immersion temperature can be changed as appropriate according to the structure of the modified organic molecule 112 and the like.

  If the concentration of the prepared solution is too low, it takes time until a sufficient amount of the modified organic molecule 112 is fixed. On the other hand, if the concentration is too high, excessive modified organic molecules 112 may be adsorbed and molecules may be stacked. For this reason, the concentration of the modified organic molecule 112 is preferably 0.1 mM or more and 100 mM or less, and more preferably 1 mM or more and 10 mM or less.

  The immersion time is preferably sufficient to form a dense monolayer with uniform orientation. It is preferably 1 minute or longer and 100 hours or shorter, and preferably 12 hours or longer and 72 hours or shorter.

  The temperature of the prepared solution during the immersion affects the formation of a dense and aligned monolayer. For this reason, it is desirable that the temperature is from room temperature (25 ° C.) to 60 ° C. in consideration of the vapor pressure and boiling point of the solvent.

  The solvent of the preparation solution is not limited as long as the modified organic molecule can be dissolved. For example, an alcohol such as ethanol, or an aromatic or aliphatic organic solvent such as toluene or hexane can be used. From the viewpoint of solubility of the modified organic molecule 112 and ease of handling, it is preferable to use ethanol.

  By the above method, the reduction catalyst of the modification 1 or the modification 2 can be manufactured. In the reduction catalyst thus obtained, the metal fine particles 107 can be further laminated on the modified organic molecule 112. An example of a method for further laminating the modified organic molecules 112 and the metal fine particles 107 will be described in detail below.

  The quaternary nitrogen cation contained in the modified organic molecule 112 has a positive charge. For this reason, when the modified organic molecule 112 is brought into contact with an aqueous solution in which an anion containing a metal element constituting the metal fine particle 107 is dissolved, the quaternary nitrogen cation and the anion containing the metal element are electrostatically charged by an anion exchange reaction. Join. Then, metal nanoparticles can be supported on the surface of the quaternary nitrogen cation by performing electrochemical reduction or hydrogen gas reduction in an aqueous solution. These metal nanoparticles correspond to the metal fine particles 107.

Au or Pt can be used as the metal element that can be deposited in the vicinity of the quaternary nitrogen cation. As an anion raw material containing Au or Pt, sodium tetrachloroaurate (III) dihydrate (Na [AuCl ₄ ] 2H ₂ O), potassium chloroaurate (III) potassium (K [AuCl ₄ ]), tetrachloro Salts such as potassium platinum acid (II) (K ₂ [PtCl ₄ ]) and potassium hexachloroplatinate (IV) (K ₂ [PtCl ₆ ]) can be used.

  This method will be described more specifically. First, anion exchange is performed by immersing the current collector 101 in which the fine metal particles 107 in which the modified organic molecules 112 are fixed is fixed in a solution in which an anion containing Au or Pt is dissolved. Thereby, an anion containing Au or Pt is electrostatically bound to the quaternary nitrogen cation contained in the modified organic molecule 112. The concentration of the salt of the anion containing Au or Pt in the solution in which the anion is dissolved is preferably 0.1 mM or more and 100 mM or less. The anion exchange time is preferably from 30 minutes to 2 hours.

  Next, the current collector 101 after the anion exchange is immersed in an alkaline aqueous solution, and reduction is performed by constant potential reduction electrolysis. As the alkaline aqueous solution, an aqueous sodium hydrogen carbonate solution having a concentration of 0.5M can be used. For electrolysis, a three-electrode cell using the current collector 101 as a working electrode, silver-silver chloride as a reference electrode, and Pt as a counter electrode, and applying a potential of -0.5 V to the working electrode for about 1 hour To do.

Alternatively, the current collector 101 after the anion exchange is reduced by being immersed in an aqueous solution in which H ₂ gas is dissolved. Immersion may be on the order of 1 hour. Thereby, the metal fine particles 107 can be formed on the surface of the quaternary nitrogen cation.

  Next, a modified organic molecule 112 further containing a quaternary nitrogen cation is immobilized on the surface of the Au or Pt nanoparticles deposited in the vicinity of the quaternary nitrogen cation. Thus, the amount of the metal fine particles 107 can be increased by repeating the step of depositing the metal fine particles 107 near the quaternary nitrogen cation and the step of fixing the modified organic molecules 112.

  According to this embodiment described above, it is possible to provide a system that can recover a reduced product of carbon dioxide with high efficiency.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These 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 the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 1st reduction catalyst, 2 1st aspect reduction catalyst, 2nd aspect reduction catalyst, 4, 5, 6 2nd reduction catalyst, 11 board | substrate, 12 reflection layer, 13 reduction electrode layer, 14 1st solar cell, 15 second solar cell, 16 third solar cell, 17 multi-junction solar cell, 18 oxidation electrode layer, 19 oxidation catalyst layer, 20 reduction catalyst layer, 30 chemical reaction cell, 31 electrolytic cell, 31a electrolytic cell for oxidation reaction, 31b Electrolysis tank for reduction reaction, 43 Ion exchange membrane, 44 Temperature control mechanism, 51 Opening part, 52 Opening part, 60 Reduct product production system, 61 Chemical reaction apparatus, 64 Storage tank, 70 Coarse distillation tower, 72 Rectification tower, 72a 1st fractionator, 72b 2nd fractionator, 72c 3rd fractionator, 74 preparation tank, 76 4th pipe, 78 5th pipe, 79 storage tank, 81 1st pipe, 81a liquid feed pump, 81b Three-way valve, 2 Second piping, 83 Third piping, 84 7th piping, 100 Spacer organic molecular layer, 101 Current collector, 102 Metal layer, 103 First reactive functional group, 104 Skeleton, 105 Second reactive functional group , 106 spacer organic molecule, 107 metal fine particle, 108 organic molecule, 109 reactive functional group, 110 skeleton, 111 terminal functional group, 112 modified organic molecule, 120 surface layer, 100a piping, 100b piping, 100c sixth piping, 100d piping , 100e piping, 101a piping, 101b piping, 101c piping, 201 extraction device, 202 carbon dioxide separation tower.

Claims (32)

A system for producing a reduction product of carbon dioxide,
An oxidation reaction electrolytic cell equipped with an oxidation catalyst, and a reduction reaction electrolytic cell equipped with a reduction catalyst,
A chemical reactor that reduces carbon dioxide to produce a reduced product;
An electrolytic solution supply unit for supplying an electrolytic solution to the electrolytic cell for reduction reaction;
A carbon dioxide supply unit for increasing the concentration of the reduced product in the electrolytic solution by dissolving carbon dioxide in the electrolytic solution and maintaining the reduction reaction in the electrolytic cell for reduction reaction;
A separation unit for separating the reduced product from the electrolyte having an increased concentration of the reduced product;
Reduced product production system.   The electrolytic solution supply unit includes a storage tank that stores an electrolytic solution, a first pipe that supplies the electrolytic solution from the storage tank to the electrolytic reaction tank, and an electrolytic solution that is discharged from the electrolytic reaction tank. The system according to claim 1, further comprising a second pipe that returns to the storage tank, wherein the carbon dioxide supply unit is provided in at least one of the storage tank, the first pipe, and the second pipe.   The separation unit includes: a crude distillation column that separates the electrolytic solution having an increased concentration of the reduced product into an electrolyte and a liquid component; and a rectifying column that separates a carbon dioxide reductant from the liquid component separated in the crude distillation column. The system of Claim 1 or 2 provided with these.   The rectification column includes a first rectification column for separating methanol from the liquid, a second rectification column for separating ethanol, and a third rectification column for separating ethylene glycol. The described system.   Using the electrolyte separated in the crude distillation tower and the water separated in the rectification tower, a preparation tank for preparing a new electrolyte, and the electrolyte from the preparation tank to the electrolyte supply unit The system according to claim 3, further comprising a pipe for feeding liquid.   The separation unit includes an extraction device that extracts the reduced product and carbon dioxide from the electrolyte in which the concentration of the reduced product is increased into an ionic liquid that is an extraction solvent, and the reduced product and the carbon dioxide that are extracted in the extraction device. The carbon dioxide separation tower which isolate | separates a carbon dioxide from the ionic liquid containing this, and the rectification tower which isolate | separates the said reduced material from the ionic liquid from which the carbon dioxide was isolate | separated in the said carbon dioxide separation tower. The system described in.   The extraction solvent contains, as an ionic liquid, at least one compound containing an organic cation selected from an alkyl ammonium cation, a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, an imidazolium cation, and an alkylphosphonium cation. 6. The system according to 6. The system according to claim 6 or 7, wherein the extraction solvent contains at least one compound represented by any one of the following general formulas Ia to VIa as an ionic liquid.
In the general formulas Ia to VIa, R _1a , R _2a , R _3a and R _4a each independently represents an alkyl group or a cycloalkyl group. Xa ^- represents a counter anion. The extraction solvent is BF ₄ ⁻ , PF ₆ ⁻ , fluoromethanesulfonate anion (CF ₃ SO ₃ ⁻ ), bistrifluoromethanesulfonylimide anion ((CF ₃ SO ₃ ) ₂ N ⁻ ) and (CN) as ionic liquids. ^{_{) 2 N -, (CN)}} 4 B - comprising at least one compound containing an anion selected from, the system according to any one of claims 6-8.   The rectifying column includes a first rectifying column that separates methanol from the ionic liquid from which carbon dioxide has been separated, a second rectifying column that separates ethanol, and a third rectifying column that separates ethylene glycol. The system according to any one of claims 6 to 9.   The system according to any one of claims 6 to 10, further comprising a pipe for sending the ionic liquid from which the reduced product has been separated in the rectification column to the extraction device from the rectification column.   A preparation tank for preparing an electrolytic solution in which carbon dioxide is dissolved using the electrolytic solution from which the reduced product and carbon dioxide have been separated in the extraction device, and the carbon dioxide separated in the carbon dioxide separation tower; The system according to any one of claims 6 to 11, further comprising a pipe for feeding the electrolyte prepared in a preparation tank from the preparation tank to the electrolyte supply unit.   The separation unit includes a carbon dioxide separation tower that separates carbon dioxide from the electrolyte having an increased concentration of the reduced product, and a rectification that separates the reduced product from the electrolyte from which carbon dioxide has been separated in the carbon dioxide separation tower. The system according to claim 1, comprising a tower.   The aqueous solution containing at least one ionic liquid containing an organic cation selected from an alkylammonium cation, a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, an imidazolium cation and an alkylphosphonium cation is used as the electrolytic solution. The system described in. The system according to claim 13 or 14, wherein an aqueous solution containing at least one ionic liquid represented by any one of the following general formulas Ib to VIb is used as the electrolytic solution.
In the general formulas I to VI, R _1b , R _2b , R _3b and R _4b each independently represent an alkyl group or a cycloalkyl group. Xb ⁻ represents a counter anion. The aqueous solution containing at least one ionic liquid containing an anion selected from Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , (CN) ₄ B ⁻ and (CN) ₂ N ^{− is} used as the electrolytic solution. The system according to any one of 13 to 15.   Using the ionic liquid and water contained in the electrolytic solution from which the reduced product has been separated in the rectification column and the carbon dioxide separated in the carbon dioxide separation tower, carbon dioxide, ionic liquid and water are obtained. The preparation tank which prepares the electrolyte solution to contain, The piping which sends the electrolyte solution prepared by this preparation tank from the said preparation tank to the said electrolyte solution supply unit is further provided. The system described in.   The rectifying column includes a first rectifying column that separates methanol from the electrolyte solution from which carbon dioxide has been separated and removed, a second rectifying column that separates ethanol, and a third rectifying column that separates ethylene glycol. The system according to claim 13, comprising:   The system according to claim 1, wherein the chemical reaction device further includes a power supply element connected to an oxidation catalyst layer made of the oxidation catalyst and a reduction catalyst layer made of the reduction catalyst.   The system of claim 19, wherein the power element comprises a semiconductor layer that separates charges by light energy. The reduction catalyst is
A current collector having a metal layer on the surface;
21. The system according to any one of claims 1 to 20, comprising a modified organic molecule bonded to the surface of the metal layer and comprising a quaternary nitrogen cation.   24. The system of claim 21, wherein the modified organic molecule comprises at least one quaternary nitrogen cation selected from alkyl ammonium cations, pyridinium cations, piperidinium cations, and imidazolium cations. The system according to claim 21 or 22, wherein the modified organic molecule is represented by any one of the following general formulas I to V.
In the general formulas I to V, R ₁ is a primary, secondary or tertiary amino group, and R ₂ and R ₃ may be the same or different and are each independently H or primary. It is a secondary or tertiary amino group, p, q, r, and n are each independently an integer of 1 to 12, Y is a reactive functional group, and X ⁻ represents a counter anion. The system according to claim 23, wherein, in the general formulas I to V, the R ₁ is an amino group substituted by at least one substituent selected from a C _{1 to} C ₁₂ alkyl group.   The system according to any one of claims 21 to 24, wherein the metal layer includes metal fine particles.   The system according to any one of claims 21 to 25, wherein the metal layer includes at least one metal fine particle selected from gold, silver, platinum, copper, and zinc. The reduction catalyst is
A current collector having a surface layer;
A spacer organic molecular layer formed on the surface layer;
Metal fine particles bonded to the surface of the spacer organic molecular layer;
The system according to claim 1, comprising:   28. The system of claim 27, further comprising a modified organic molecule comprising a quaternary nitrogen cation bound to the surface of the metal particulate.   30. The system of claim 28, wherein the modified organic molecule comprises at least one quaternary nitrogen cation selected from an alkyl ammonium cation, a pyridinium cation, a piperidinium cation, and an imidazolium cation. The system according to claim 28 or 29, wherein the modified organic molecule is represented by any one of the following general formulas I to V.
In the general formulas I to V, R ₁ is a primary, secondary or tertiary amino group, and R ₂ and R ₃ may be the same or different and are each independently H or primary. It is a secondary or tertiary amino group, p, q, r, and n are each independently an integer of 1 to 12, Y is a reactive functional group, and X ⁻ represents a counter anion. In Formula l-V, wherein R ₁ is at least one substituted from substituent amino group is selected from C ₁ -C ₁₂ alkyl group, The system of claim 30.   The system according to any one of claims 27 to 31, wherein the metal fine particles are at least one metal fine particle selected from gold, silver, platinum, copper, and zinc.