JP6302038B2 - Photochemical reaction system - Google Patents

Description

  Embodiments of the present invention relate to a photochemical reaction system.

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 that excites light energy in two stages, called the Z scheme. By the photochemical reaction of such a system, plants obtain electrons from water (H ₂ O) and reduce carbon dioxide (CO ₂ ) to synthesize cellulose and saccharides.

However, the technique of decomposing CO ₂ by obtaining electrons from water without using a sacrificial reagent by an artificial photochemical reaction has only very low efficiency.

For example, Patent Document 1 discloses, as a photochemical reaction device, an oxidation reaction electrode that oxidizes H ₂ O to generate oxygen (O ₂ ), and a reduction reaction electrode that reduces CO ₂ to generate a carbon compound. Prepare. The oxidation reaction electrode is provided with an oxidation catalyst for oxidizing H ₂ O on the surface of the photocatalyst, and obtains a potential by light energy. The reduction reaction electrode is provided with a reduction catalyst for reducing CO ₂ on the surface of the photocatalyst, and is connected to the oxidation reaction electrode with an electric wire. The reduction reaction electrode obtains a reduction potential of CO ₂ from the oxidation reaction electrode, thereby reducing CO ₂ to generate formic acid (HCOOH). As described above, in order to obtain a potential necessary for reducing CO _{2 with} a photocatalyst using visible light, a Z-scheme type artificial photosynthesis system imitating a plant is used.

  However, in patent document 1, the solar energy conversion efficiency is as very low as about 0.04%. This is due to the low energy efficiency of the photocatalyst excited with visible light. Further, since the reduction reaction electrode is connected to the oxidation reaction electrode by the electric wire, the efficiency of taking out electricity (current) is reduced by the wiring resistance, and as a result, the efficiency is lowered.

In Patent Document 2, a configuration is considered in which a silicon solar cell is used in order to obtain a reaction potential, and a catalyst is provided on both sides to cause a reaction. In Non-Patent Document 1, an electrolytic reaction of H ₂ O is performed by using a structure in which silicon solar cells are stacked in order to obtain a reaction potential, and providing a catalyst on both surfaces thereof. The solar energy conversion efficiency in these is as high as 2.5%.

  In addition, since this device has a structure that does not require wiring, it is easy to increase the size. Further, since the cell itself can act as a partition plate to isolate the product, the product separation step is unnecessary.

However, in these apparatuses, there is no example of successful CO ₂ reduction reaction. Further, for the reduction reaction of CO ₂ , ions having a positive charge generated on the oxidation side and ions having a negative charge generated on the reduction side need to move to the counter electrode. This is not taken into account in the laminated structure. In particular, in a redox reaction using H ₂ O as an electron donor without using a sacrificial catalyst, it is essential to move protons (hydrogen ions (H ⁺ )).

Thus, a CO ₂ decomposition technique that uses light energy and has high photoreaction efficiency is required.

JP 2011-094194 A JP-A-10-290017

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

A photochemical reaction system having a CO ₂ decomposition technology with high photoreaction efficiency is provided.

Photochemical reaction system according to this embodiment includes a CO ₂ generator 111 for generating CO _2, and CO ₂ absorption means 112 for absorbing the CO ₂ generated by the CO ₂ generator, _{O 2} and oxidizing of _{H 2} O Formed between the oxidation catalyst layer 19 for generating H ⁺ and the reduction catalyst layer 20 for reducing the CO ₂ absorbed by the CO ₂ absorption means to generate a carbon compound, and the oxidation catalyst layer and the reduction catalyst layer. A CO ₂ reduction means 110 comprising: a stack having a semiconductor layer 17 that separates charges by light energy; and an ion transfer path that moves ions between the oxidation catalyst layer side and the reduction catalyst layer side; It comprises.

Sectional drawing which shows the structure of the photochemical reaction cell which concerns on embodiment. Sectional drawing which shows the operation | movement principle of the photochemical reaction cell which concerns on embodiment. The perspective view which shows the structure of the photochemical reaction apparatus which concerns on 1st Embodiment. Sectional drawing which shows the structure of the photochemical reaction apparatus which concerns on 1st Embodiment. Sectional drawing which shows the structure of the modification 1 in the photochemical reaction apparatus which concerns on 1st Embodiment. Sectional drawing which shows the structure of the modification 2 in the photochemical reaction apparatus which concerns on 1st Embodiment. Sectional drawing which shows the structure of the modification 3 in the photochemical reaction apparatus which concerns on 1st Embodiment. Sectional drawing which shows the structure of the modification 4 in the photochemical reaction apparatus which concerns on 1st Embodiment. The top view which shows the structure of the photochemical reaction apparatus which concerns on 1st Embodiment. The top view which shows the structure of the photochemical reaction apparatus which concerns on 1st Embodiment. The top view which shows the structure of the photochemical reaction apparatus which concerns on 1st Embodiment. Experiments showing the photoreduction efficiency of CO ₂ in Example 1 for Comparative Example result. Sectional drawing which shows the structure of the photochemical reaction apparatus which concerns on 2nd Embodiment. The graph which shows the relationship between the periodic width of the through-hole in the photochemical reaction apparatus which concerns on 2nd Embodiment, and the light absorption rate by a multijunction solar cell. The graph which shows the relationship between the circle equivalent diameter of the through-hole in the photochemical reaction device which concerns on 2nd Embodiment, and the light absorption rate by a multijunction solar cell. Sectional drawing which shows the structure of the photochemical reaction apparatus which concerns on 2nd Embodiment. Experiments showing the photoreduction efficiency of CO ₂ in Example 2 for Comparative Example result. Experiments showing the photoreduction efficiency of CO ₂ in Example 3 for Comparative Example result. FIG. 6 is a plan view showing the structure of a photochemical reaction device in Example 3. Sectional drawing which shows the structure of the photochemical reaction apparatus in Example 3. FIG. Sectional drawing which shows the electrolytic vessel which measures the photochemical reaction apparatus in Example 3 and a comparative example. Sectional drawing which shows the structure of the modification 1 in the photochemical reaction apparatus which concerns on 2nd Embodiment. Sectional drawing which shows the structure of the modification 2 in the photochemical reaction apparatus which concerns on 2nd Embodiment. The perspective view which shows the structure of the photochemical reaction apparatus which concerns on 3rd Embodiment. Sectional drawing which shows the structure of the photochemical reaction apparatus which concerns on 3rd Embodiment. The perspective view which shows the modification of the structure of the photochemical reaction apparatus which concerns on 3rd Embodiment. Sectional drawing which shows the modification of the structure of the photochemical reaction apparatus which concerns on 3rd Embodiment. The top view which shows the example of application of the photochemical reaction apparatus which concerns on 3rd Embodiment. The block diagram which shows the structure of the photochemical reaction system which concerns on embodiment. The block diagram which shows the structure of the modification 1 of the photochemical reaction system which concerns on embodiment. The block diagram which shows the structure of the modification 2 of the photochemical reaction system which concerns on embodiment. The block diagram which shows the structure of the modification 3 of the photochemical reaction system which concerns on embodiment. Sectional drawing which shows the operation | movement principle of the photochemical reaction cell in the modification 3 of the photochemical reaction system which concerns on embodiment. Sectional drawing which shows the operation | movement principle of the photochemical reaction cell in the modification 3 of the photochemical reaction system which concerns on embodiment.

The present embodiment will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals. In addition, redundant description will be given as necessary.
1. Photochemical Reaction Cell The photochemical reaction cell according to this embodiment will be described below with reference to FIGS. 1 and 2.

  FIG. 1 is a cross-sectional view showing the structure of the photochemical reaction cell according to the present embodiment.

  As shown in FIG. 1, the photochemical reaction cell according to this embodiment includes a substrate 11, a reflective layer 12, a reduction electrode layer 13, a multijunction solar cell 17, an oxidation electrode layer 18, an oxidation catalyst layer 19, and a reduction catalyst layer. 20 is provided. On the surface (light incident surface) of the substrate 11, a reflective layer 12, a reduction electrode layer 13, a multijunction solar cell 17, an oxidation electrode layer 18, and an oxidation catalyst layer 19 are formed. On the other hand, a reduction catalyst layer 20 is formed on the back surface of the substrate 11.

  The substrate 11 is provided to support the photochemical reaction cell and increase its mechanical strength. The substrate 11 has conductivity and is made of a metal plate such as Cu, Al, Ti, Ni, Fe, or Ag, or an alloy plate such as SUS including at least one of them. Alternatively, the substrate 11 may be made of a conductive resin or the like. Further, the substrate 11 may be composed of a semiconductor substrate such as Si or Ge. As will be described later, the substrate 11 may be formed of an ion exchange membrane.

  The reflective layer 12 is formed on the surface of the substrate 11. The reflection layer 12 is made of a material capable of reflecting light, and is made of, for example, a distributed Bragg reflection layer made of a metal layer or a semiconductor multilayer film. The reflection layer 12 is formed between the substrate 11 and the multijunction solar cell 17, thereby reflecting light that could not be absorbed by the multijunction solar cell 17 and entering the multijunction solar cell 17 again. Let Thereby, the light absorption rate in the multijunction solar cell 17 can be improved.

  The reduction electrode layer 13 is formed on the reflective layer 12. The reduction electrode layer 13 is formed on the surface of the 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 desirable that the reduction electrode layer 13 be made of a material that can make 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 configured with a structured.

  The multi-junction solar cell 17 is formed on the reduction electrode layer 13 and includes a first solar cell 14, a second solar cell 15, and a third solar cell 16. Each of the first solar cell 14, the second solar cell 15, and the third solar cell 16 is a solar cell using a pin junction semiconductor and has different light absorption wavelengths. By laminating these in a planar shape, the multi-junction solar cell 17 can absorb light with a wide wavelength of sunlight, and can utilize solar energy more efficiently. Moreover, since each solar cell is connected in series, a high open circuit voltage can be obtained.

  More specifically, the first solar cell 14 includes an n-type amorphous silicon (a-Si) layer 14a, an intrinsic amorphous silicon germanium (a-SiGe) layer 14b, p, formed in order from the lower side. A type microcrystalline silicon (μc-Si) layer 14c. Here, the a-SiGe layer 14b is a layer that absorbs light in a short wavelength region of about 400 nm. That is, in the first solar cell 14, charge separation occurs 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, which are sequentially formed from the lower side. Here, the a-SiGe layer 15b is a layer that absorbs light in the intermediate wavelength region of about 600 nm. That is, in the second solar cell 15, charge separation occurs 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 formed in this order from the lower side. Here, the a-Si layer 16b is a layer that absorbs light in a long wavelength region of about 700 nm. That is, in the third solar cell 16, charge separation occurs due to light energy in the long wavelength region.

  Thus, in the multi-junction 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, the multijunction solar cell 17 generates an electromotive force.

  In the above description, the multi-junction solar cell 17 configured with a stacked structure of three solar cells has been described as an example, but the present invention is not limited thereto. The multi-junction solar cell 17 may be composed of a laminated structure of two or four or more solar cells. 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, the solar cell using a pn junction type semiconductor may be sufficient. Moreover, although the example comprised by Si and Ge was shown as a semiconductor layer, it is not restricted to this, For example, you may comprise by GaAs, GaInP, AlGaInP, CdTe, CuInGaSe. Furthermore, various forms such as single crystal, polycrystal, and amorphous can be applied.

  The oxidation electrode layer 18 is formed on the multi-junction solar cell 17. The oxidation electrode layer 18 is formed on the p-type semiconductor layer (p-type μc-Si layer 16 c) surface of the multi-junction solar cell 17. For this reason, it is desirable that the oxidation electrode layer 18 be made of a material capable of ohmic contact with the p-type semiconductor layer. The oxidation electrode layer 18 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 oxidation electrode layer 18 is made of a transparent conductive oxide such as ITO, ZnO, FTO, AZO, or ATO. 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 configured with a structured.

  In this example, the irradiation light passes through the oxidation electrode layer 18 and reaches the multi-junction solar cell 17. For this reason, the oxidation electrode layer 18 disposed on the light irradiation surface side has light transmittance with respect to the irradiation light. More specifically, the permeability of the oxidation electrode layer 18 on the irradiation surface side is preferably at least 10% or more, more preferably 30% or more, of the irradiation amount of irradiation light.

The oxidation catalyst layer 19 is formed on the oxidation electrode layer 18. The oxidation catalyst layer 19 is formed on the positive electrode side of the multi-junction solar cell 17 and oxidizes H ₂ O to generate O ₂ and H ⁺ . For this reason, the oxidation catalyst layer 19 is made of a material that reduces activation energy for oxidizing H ₂ O. In other words, it is made of a material that reduces the overvoltage when H ₂ O is oxidized to generate O ₂ and H ⁺ . 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, but may be a lattice, a particle, or a wire.

  In this example, similarly to the oxidation electrode layer 18, the irradiation light passes through the oxidation catalyst layer 19 and reaches the multi-junction solar cell 17. For this reason, the oxidation catalyst layer 19 disposed on the light irradiation surface side is light transmissive to the irradiation light. More specifically, the permeability of 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 formed on the back surface of the substrate 11. The reduction catalyst layer 20 is formed on the negative electrode side of the multi-junction solar cell 17 and reduces CO ₂ to reduce carbon dioxide (for example, carbon monoxide (CO), formic acid (HCOOH), methane (CH ₄ ), methanol ( CH ₃ OH), ethanol (C ₂ H ₅ OH), etc.). For this reason, the reduction catalyst layer 20 is made of a material that reduces activation energy for reducing CO ₂ . In other words, it is composed of a material that reduces the overvoltage when CO ₂ is reduced to produce a carbon compound. Examples of such materials include Au, Ag, Cu, Pt, C, Ni, Zn, C, graphene, CNT (carbon nanotube), fullerene, ketjen black, or a metal such as Pd or an alloy containing at least one of them. Or metal complexes, such as Ru complex or Re complex, are mentioned. Further, the form of the reduction catalyst layer 20 is not limited to a thin film shape, and may be a lattice shape, a particle shape, or a wire shape.

  The arrangement relationship between the polarity of the multi-junction solar cell 17 and the substrate 11 is arbitrary. In this example, the oxidation catalyst layer 19 is disposed on the light incident surface side, but the reduction catalyst layer 20 may be disposed on the light incident surface side. That is, in the photochemical reaction cell, the positions of the oxidation catalyst layer 19 and the reduction catalyst layer 20, the positions of the oxidation electrode layer 18 and the reduction electrode layer 13, and the polarity of the multijunction solar cell may be interchanged. In this case, it is desirable that the reduction catalyst layer 20 and the reduction electrode layer 13 have transparency.

Further, a protective layer is disposed 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 this example). May be. The protective layer has conductivity and 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, Al2O 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. FIG. 2 is a cross-sectional view showing the operation principle of the photochemical reaction cell according to the present embodiment. Here, the reflection layer 12, the reduction electrode layer 13, and the oxidation electrode layer 18 are omitted.

  As shown in FIG. 2, when light is incident from the surface side, the incident light passes through the oxidation catalyst layer 19 and the oxidation electrode layer 18 and reaches the multi-junction solar cell 17. When the multi-junction solar cell 17 absorbs light, it generates photoexcited electrons and holes paired therewith and separates them. That is, in each solar cell (the first solar cell 14, the second solar cell 15, and the third solar cell 16), the photoexcited electrons move to the n-type semiconductor layer side (reduction catalyst layer 20 side), and the p-type Charge separation occurs in which holes generated as pairs of photoexcited electrons move to the semiconductor layer side (oxidation catalyst layer 19 side). Thereby, an electromotive force is generated in the multi-junction solar cell 17.

  Thus, the 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, and the holes are used for the oxidation reaction in the oxidation catalyst layer 19 that is the positive electrode. . As a result, the reaction of the formula (1) occurs near the oxidation catalyst layer 19, and the reaction of the formula (2) occurs near the reduction catalyst layer 20.

2H ₂ O → 4H ⁺ + O ₂ + 4e ⁻ (1)
2CO ₂ + 4H ⁺ + 4e ⁻ → 2CO + 2H ₂ O (2)
As shown in the formula (1), in the vicinity of the oxidation catalyst layer 19, H ₂ O is oxidized (loses electrons) to generate O ₂ and H ⁺ . Then, H ⁺ generated on the oxidation catalyst layer 19 side moves to the reduction catalyst layer 20 side through an ion movement path described later.

As shown in the equation (2), in the vicinity of the reduction catalyst layer 20, CO ₂ and the transferred H ⁺ react to generate carbon monoxide (CO) and H ₂ O.

  At this time, the multi-junction solar cell 17 needs to have an open circuit voltage equal to or higher than the potential difference between the standard oxidation-reduction potential of the oxidation reaction occurring in the oxidation catalyst layer 19 and the standard oxidation-reduction potential of the reduction reaction occurring in the reduction catalyst layer 20. . For example, the standard redox potential of the oxidation reaction in the formula (1) is 1.23 [V], and the standard redox potential of the reduction reaction in the formula (2) is −0.1 [V]. For this reason, the open 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 the potential difference including the overvoltage. More specifically, for example, when the overvoltage of the oxidation reaction in Formula (1) and the reduction reaction in Formula (2) is 0.2 [V], the open circuit voltage may be 1.73 [V] or more. desirable.

Not only the reduction reaction from CO ₂ to CO shown in formula (2) but also the reduction reaction from CO ₂ to HCOOH, CH ₄ , CH ₃ OH, C ₂ H ₅ OH, etc. is a reaction that consumes H ^+. . For this reason, when the H ⁺ produced in the oxidation catalyst layer 19 cannot move to the counter reduction catalyst layer 20, the overall reaction efficiency is low. In contrast, the present embodiment, by forming the ion transfer path for moving the H ^+, realizes a high light reaction efficiency by improving the transport of H ^+.
2. Photochemical Reaction Device A photochemical reaction device using the photochemical reaction cell according to the present embodiment will be described below with reference to FIGS.
<2-1. First Embodiment>
The photochemical reaction device according to the first embodiment will be described with reference to FIGS.

The photochemical reaction device according to the first embodiment includes an oxidation catalyst layer 19, a reduction catalyst layer 20, a photochemical reaction cell including a stacked body of multijunction solar cells 17 formed therebetween, an oxidation catalyst An ion movement path for moving ions between the layer 19 and the reduction catalyst layer 20 is an example. Accordingly, H ⁺ produced on the oxidation catalyst layer 19 side can be moved to the reduction catalyst layer 20 with high photoreaction efficiency, and carbon dioxide can be decomposed on the reduction catalyst layer 20 side by this H ⁺ . it can. Hereinafter, the first embodiment will be described in detail.
[Structure of First Embodiment]
First, the structure of the photochemical reaction device according to the first embodiment will be described.

  FIG. 3 is a perspective view showing the structure of the photochemical reaction device according to the first embodiment. FIG. 4 is a cross-sectional view showing the structure of the photochemical reaction device according to the first embodiment. In FIG. 3, an ion movement path to be described later is omitted.

  As shown in FIGS. 3 and 4, the photochemical reaction device according to the first embodiment is connected to the photochemical reaction cell, the electrolytic cell 31 including the photochemical reaction cell therein, and the electrolytic cell 31 as an ion transfer path. And an electrolytic cell channel 41.

  The photochemical reaction cell is formed in a flat plate shape, and at least the substrate 11 separates the electrolytic cell 31 into two. That is, the electrolytic cell 31 includes an oxidation reaction electrolytic cell 45 in which the photocatalytic reaction cell oxidation catalyst layer 19 is disposed, and a reduction reaction electrolytic cell 46 in which the photochemical reaction cell reduction catalyst layer 20 is disposed. In the oxidation reaction electrolytic tank 45 and the reduction reaction electrolytic tank 46, it is possible to supply separate electrolytic solutions.

The oxidation reaction electrolytic tank 45 is filled with, for example, a liquid containing H ₂ O as an electrolytic solution. Examples of such an electrolytic solution include those containing an arbitrary electrolyte, but it is desirable to promote an oxidation reaction of H ₂ O. In the oxidation reaction electrolytic tank 45, H ₂ O is oxidized by the oxidation catalyst layer 19 to generate O ₂ and H ⁺ .

The electrolytic cell for reduction reaction 46 is filled with a liquid containing, for example, CO ₂ as an electrolytic solution. It is desirable that the electrolytic solution in the reduction reaction electrolytic tank 46 has a CO ₂ absorbent that reduces the reduction potential of CO ₂ , has high ionic conductivity, and absorbs CO ₂ . As such an electrolytic solution, an ionic liquid or an aqueous solution thereof, which consists of a salt of a cation such as imidazolium ion or pyridinium ion and an anion such as BF ₄ ⁻ or PF ₆ ⁻ and is in a liquid state in a wide temperature range. Can be mentioned. Alternatively, examples of the electrolytic solution include amine solutions such as ethanolamine, imidazole, and pyridine, or aqueous solutions thereof. The amine may be any of primary amine, secondary amine, and tertiary amine. Examples of primary amines include methylamine, ethylamine, propylamine, butylamine, pentylamine, and hexylamine. The amine hydrocarbon may be substituted with alcohol or halogen. Examples of the substituted amine hydrocarbon include methanolamine, ethanolamine, and chloromethylamine. Moreover, an unsaturated bond may exist. These hydrocarbons are the same for secondary amines and tertiary amines. Secondary amines include dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, dipropanolamine, and the like. The substituted hydrocarbon may be different. The same applies to tertiary amines. For example, examples of hydrocarbons that are different include methylethylamine and methylpropylamine. Tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, tripropanolamine, tributanolamine, tripropanolamine, triexanolamine, methyldiethylamine, methyl Such as dipropylamine. As the cation of the ionic liquid, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl-3-methylimidazole ion, 1-methyl-3-pentylimidazolium ion 1-hexyl-3-methylimidazolium ion and the like. Further, the 2-position of the imidazolium ion may be substituted. For example, 1-ethyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl 2,3-dimethylimidazolium ion, 1,2-dimethyl-3-pentylimidazole Examples include a lithium ion and a 1-hexyl-2,3-dimethylimidazolium ion. Examples of the pyridinium ion include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, hexylpyridinium, and the like. In both the imidazolium ion and the pyridinium ion, an alkyl group may be substituted and an unsaturated bond may exist. As anions, fluoride ions, chloride ions, bromide ions, iodide ions, BF ⁴⁻ , PF ⁶⁻ , CF ₃ COO ⁻ , CF ₃ SO ³⁻ , NO ³⁻ , SCN ⁻ , (CF ₃ SO _{2). 3} C ⁻ , bis (trifluoromethoxysulfonyl) imide, bis (trifluoromethoxysulfonyl) imide, bis (perfluoroethylsulfonyl) imide and the like. Moreover, the zwitterion which connected the cation and the anion of the ionic liquid with the hydrocarbon may be sufficient. In the electrolytic cell 46 for reduction reaction, CO ₂ is reduced by the reduction catalyst layer 20 to generate a carbon compound. In addition, water (H ₂ O) can be reduced to produce hydrogen (H ₂ ).

Incidentally, by changing the amount of water in the electrolyte, it is possible to change the reducing substance of CO ₂ produced. For example, the production ratio of HCOOH, CH ₄ , CH ₃ OH, C ₂ H ₅ OH, hydrogen, or the like can be changed.

The temperature of the electrolytic solution filled in the oxidation reaction electrolytic tank 45 and the reduction reaction electrolytic tank 46 may be the same or different depending on the use environment. For example, when the electrolytic solution used in the reduction reaction electrolytic bath 46 is an amine absorbing solution containing CO ₂ discharged from the factory, the temperature of the electrolytic solution is higher than the atmospheric temperature. In this case, the temperature of the electrolytic solution is 30 ° C. or higher and 150 ° C. or lower, more preferably 40 ° C. or higher and 120 ° C. or lower.

  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 45, and the other is connected to the reduction reaction electrolytic cell 46. That is, the electrolytic cell channel 41 connects the oxidation reaction electrolytic cell 45 and the reduction reaction electrolytic cell 46.

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 are moved through the electrolytic cell channel 41 provided with the ion exchange membrane 43 while separating the electrolytic solution between the electrolytic cell 45 for oxidation reaction and the electrolytic cell 46 for reduction reaction. be able to. That is, the photochemical reaction device has a partition structure through which a substance is selectively passed. Here, the ion exchange membrane 43 is a proton exchange membrane, and H ⁺ generated in the oxidation reaction electrolytic cell 45 can be moved to the reduction reaction electrolytic cell 46 side. More specifically, examples of the ion exchange membrane 43 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 that can move ions and that can separate the electrolyte, for example, agar such as a salt bridge may be used. In general, when a proton exchangeable solid polymer membrane represented by Nafion is used, ion transfer performance is good.

Further, a circulation mechanism 42 such as a pump may be provided in the electrolytic cell channel 41. Thereby, the circulation of ions (H ⁺ ) can be improved between the oxidation reaction electrolytic cell 45 and the reduction reaction electrolytic cell 46. Further, two electrolytic cell channels 41 may be provided, and the reduction reaction is performed from the oxidation reaction electrolytic cell 45 through 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 46, and may be moved from the reduction reaction electrolytic cell 46 to the oxidation reaction electrolytic cell 45 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. Further, by transporting the liquid, the generated gas bubbles do not stay on the electrode surface or the electrolytic layer surface, and the efficiency reduction and light quantity distribution due to the scattering of sunlight by the bubbles may be suppressed.

  In addition, a temperature difference is generated in the electrolytic solution by using heat raised by irradiating light on the surface of the multi-junction solar cell 17, thereby reducing ion diffusion and circulating ions more efficiently. Also good. In other words, ion movement can be promoted by convection other than ion diffusion.

  On the other hand, a temperature adjusting mechanism 44 for adjusting the temperature of the electrolytic solution is provided in the electrolytic cell channel 41 or the electrolytic cell 31, and the solar cell performance and the catalyst performance can be controlled by temperature control. Thereby, in order to stabilize and improve the performance of a solar cell or a catalyst, for example, the temperature of the reaction system can be made uniform. In addition, temperature rise can be prevented for system stability. Temperature control can change the selectivity of the solar cell and the catalyst, and can also control the product.

Moreover, in this example, the edge part of the board | substrate 11 protrudes rather than the edge part of the multijunction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20, but it is not restricted to this. The substrate 11, the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 may have a flat plate shape having the same area.
[Modification of First Embodiment]
Next, a modification of the photochemical reaction device according to the first embodiment will be described.

  5 to 8 are cross-sectional views showing the structures of Modifications 1 to 4 in the photochemical reaction device according to the first embodiment. In the modified example of the photochemical reaction device according to the first embodiment, differences from the above structure will be mainly described.

  As shown in FIG. 5, Modification 1 of the photochemical reaction device according to the first embodiment is formed on the substrate 11 as a photochemical reaction cell, an electrolytic cell 31 including the photochemical reaction cell inside, and an ion transfer path. And an opening 51.

  The opening 51 is provided, for example, so as to penetrate the end portion of the substrate 11 from the oxidation reaction electrolytic bath 45 side to the reduction reaction electrolytic bath 46 side. Thus, the opening 51 connects the oxidation reaction electrolytic cell 45 and the reduction reaction electrolytic cell 46.

  A part of the opening 51 is filled with an ion exchange membrane 43, and the ion exchange membrane 43 allows only specific ions to pass therethrough. Thus, only specific ions can be moved through the opening 51 provided with the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic tank 45 and the reduction reaction electrolytic tank 46. it can.

  As shown in FIG. 6, Modification 2 of the photochemical reaction device according to the first embodiment includes a photochemical reaction cell, an electrolytic cell 31 including the photochemical reaction cell, a substrate 11 as an ion transfer path, and a multi-junction type. And an opening 51 formed in the solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20.

  The opening 51 is provided so as to penetrate, for example, the substrate 11, the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 from the oxidation reaction electrolytic tank 45 side to the reduction reaction electrolytic tank 46 side. Yes. Thus, the opening 51 connects the oxidation reaction electrolytic cell 45 and the reduction reaction electrolytic cell 46.

  A part of the opening 51 is filled with an ion exchange membrane 43, and the ion exchange membrane 43 allows only specific ions to pass therethrough. Thus, only specific ions can be moved through the opening 51 provided with the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic tank 45 and the reduction reaction electrolytic tank 46. it can.

  In FIG. 6, the ion exchange membrane 43 is formed in part of the opening 51, but the ion exchange membrane 43 may be formed so as to fill the opening 51.

  As shown in FIG. 7, the modification 3 in the photochemical reaction device according to the first embodiment includes a photochemical reaction cell, an electrolytic cell 31 including the photochemical reaction cell inside, a substrate 11 as an ion transfer path, and a multi-junction type. And an opening 51 formed in the solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20.

  The opening 51 is provided so as to penetrate, for example, the substrate 11, the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 from the oxidation reaction electrolytic tank 45 side to the reduction reaction electrolytic tank 46 side. Yes. Thus, the opening 51 connects the oxidation reaction electrolytic cell 45 and the reduction reaction electrolytic cell 46.

  Moreover, the ion exchange membrane 43 is provided so that the light irradiation surface (surface of the oxidation catalyst layer 19) of a photochemical reaction cell may be covered. As a result, the oxidation reaction electrolytic cell 45 side of the opening 51 is covered with the ion exchange membrane 43. The ion exchange membrane 43 allows only specific ions to pass through. Thus, only specific ions can be moved through the opening 51 provided with the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic tank 45 and the reduction reaction electrolytic tank 46. it can.

  In the third modification, the surface of the oxidation catalyst layer 19 is covered with the ion exchange membrane 43. Thereby, the ion exchange membrane 43 functions as the oxidation catalyst layer 19 and further as a protective layer of the multi-junction solar cell 17.

  As shown in FIG. 8, the modification 4 in the photochemical reaction device according to the first embodiment includes a photochemical reaction cell, an electrolytic cell 31 including the photochemical reaction cell inside, and a multi-junction solar cell 17 as an ion transfer path. And an opening 51 formed in the oxidation catalyst layer 19 and the reduction catalyst layer 20.

  In Modification 4, an ion exchange membrane 43 is provided instead of the substrate 11. That is, the multi-junction solar cell 17 and the oxidation catalyst layer 19 are formed on the surface of the ion exchange membrane 43, and the reduction catalyst layer 20 is formed on the back surface.

  The opening 51 is provided so as to penetrate, for example, the multi-junction solar cell 17 and the oxidation catalyst layer 19 from the oxidation reaction electrolytic cell 45 side to the reduction reaction electrolytic cell 46 side, and the reduction catalyst layer 20 is subjected to oxidation reaction electrolysis. It is provided so as to penetrate from the tank 45 side to the reduction reaction electrolytic tank 46 side. Thereby, the ion exchange membrane 43 is provided in the opening 51. In other words, the oxidation reaction electrolytic cell 45 side and the reduction reaction electrolytic cell 46 are separated only by the ion exchange membrane 43.

  The ion exchange membrane 43 allows only specific ions to pass through. Thus, only specific ions can be moved through the opening 51 provided with the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic tank 45 and the reduction reaction electrolytic tank 46. it can. Also, ions can be moved not only at the opening 51 but also at the end of the protruding ion exchange membrane 43.

  9 to 11 are plan views showing the structure of the photochemical reaction device according to the first embodiment, mainly showing an example of the planar shape of the opening 51.

  As shown in FIG. 9, for example, the opening 51 penetrates the substrate 11, the multijunction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20, and the planar shape thereof is formed as a circular through hole 52. Is done. In this case, a plurality of through holes 52 may be formed. The arrangement configuration of the plurality of through holes 52 is, for example, a quadrangular lattice (tetragonal lattice) in the first direction and the second direction orthogonal to the first direction.

The lower limit of the diameter (equivalent circle diameter) of the through hole 52 is such a size that H ⁺ can move, and is preferably 0.3 nm or more. The equivalent circle diameter is defined by ((4 × area) / π) ^0.5 .

  The planar shape of the through hole 52 is not limited to a circular shape, and may be an elliptical shape, a triangular shape, or a rectangular shape. Further, the arrangement configuration of the plurality of through holes 52 is not limited to a rectangular lattice shape, but may be a triangular lattice shape or a random lattice shape. Moreover, the through-hole 52 should just have the space | gap which continued from the oxidation catalyst layer 19 to the reduction catalyst layer 20 except the ion-exchange membrane 43 part, and the magnitude | size of the diameter of the through-hole 52 in each layer is as follows. It doesn't have to be the same. For example, the diameter of the through hole 52 from the oxidation catalyst layer 19 to the multijunction solar cell 17 may be different from the diameter of the through hole 52 from the reduction catalyst layer 20 to the multijunction solar cell 17. . Further, even if burrs and roughness are generated on the side wall of the through hole 52, the effect is not lost.

  Further, as shown in FIG. 10, the opening 51 penetrates, for example, the substrate 11, the multijunction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20, and the planar shape thereof is a slit 53 having a rectangular shape. It is formed. In this case, a plurality of slits 53 may be formed. For example, the plurality of slits 53 extend in parallel in the first direction and are arranged side by side in the second direction.

The lower limit of the width (short width) of the slit 53 is such a size that H ⁺ can move, and is preferably 0.3 nm or more.

As shown in FIG. 11, the opening 51 separates, for example, the substrate 11, the multijunction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20, and has a planar shape as a slit 54. It is formed. That is, a plurality of laminated bodies composed of the substrate 11, the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 are formed, and a slit 54 is formed between the plurality of laminated bodies. In addition, a some laminated body is supported by the flame | frame etc. which are not shown in figure. In this case, a plurality of slits 54 may be formed. For example, the plurality of slits 54 extend in parallel in the first direction and are arranged side by side in the second direction.
[Production Method of First Embodiment]
Next, the manufacturing method of the photochemical reaction device according to the first embodiment will be described. Here, the case where the through-hole 52 is formed as the opening part 51 used as an ion movement path | route is demonstrated to an example.

  First, a structure composed of the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multijunction solar cell 17, and the oxidation electrode layer 18 is prepared. The reflective layer 12, the reduction electrode layer 13, the multi-junction solar cell 17, and the oxidation electrode layer 18 are sequentially formed on the surface of the substrate 11. As the solar cell, a multijunction solar cell 17 including a first solar cell 14, a second solar cell 15, and a third solar cell 16 using a pin junction semiconductor is used.

  Next, an oxidation catalyst layer 19 is formed on the oxidation electrode layer 18 by, for example, sputtering or coating. The oxidation catalyst layer 19 is made of, for example, manganese oxide (Mn—O), iridium oxide (Ir—O), nickel oxide (Ni—O), cobalt oxide (Co—O), iron oxide (Fe—O), or ruthenium oxide. Binary metal oxides such as (Ru—O), ternary metal oxides such as Ni—Co—O, La—Co—O, Ni—La—O, Sr—Fe—O, Pb—Ru— It is composed of a quaternary metal oxide such as Ir—O or La—Sr—Co—O, or a metal complex such as a Ru complex or an Fe complex. The form of the oxidation catalyst layer 19 is not limited to a thin film, but may be a lattice, a particle, or a wire.

  Further, the reduction catalyst layer 20 is formed on the back surface of the substrate 11 by, for example, a vacuum deposition method, a sputtering method, or a coating method. The reduction catalyst layer 20 is made of, for example, a metal such as Au, Ag, Cu, Pt, C, Ni, Zn, graphene, CNT, fullerene, ketjen black, or Pd, or an alloy containing at least one of them, or a Ru complex or It is composed of a metal complex such as an Re complex. Further, the form of the reduction catalyst layer 20 is not limited to a thin film shape, and may be a lattice shape, a particle shape, or a wire shape.

  Thus, a photochemical reaction cell composed of a laminate of the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multijunction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20. It is formed.

  Next, a through hole 52 penetrating from the oxidation catalyst layer 19 to the reduction catalyst layer 20 is formed in the photochemical reaction cell.

  As a method of forming the through hole 52, for example, there is a method of etching after forming a mask pattern. More specifically, after a mask pattern is formed on the oxidation catalyst layer 19 (front surface side) or the reduction catalyst layer 20 (back surface side), the substrate 11, the reflective layer 12, and the reduction electrode layer 13 are formed using this mask pattern. The multi-junction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20 are etched.

  Examples of the method for forming the mask pattern include a method of forming by general optical lithography or electron beam lithography. Moreover, the method using an imprint, the method using the self-organization pattern of a block copolymer or particle | grains may be used. Examples of the etching method include dry etching using a reactive gas such as chlorine gas, or wet etching using an acid solution or an alkali solution. Further, direct processing by laser processing, press processing, or cutting processing has an advantage that the number of steps is small and is useful.

In this way, through holes 52 are formed in the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multijunction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20. Then, the photochemical reaction cell in which the through-hole 52 was formed is installed in the electrolytic cell 31, and a photochemical reaction apparatus is formed.
[Effect of the first embodiment]
According to the first embodiment, the photochemical reaction device includes an oxidation catalyst layer 19, a reduction catalyst layer 20, and a photochemical reaction cell including a multilayer body of multijunction solar cells 17 formed therebetween. And an ion movement path for moving ions (H ⁺ ) between the oxidation catalyst layer 19 and the reduction catalyst layer 20. As a result, H ⁺ generated in the oxidation catalyst layer 19 can be transported to the reduction catalyst layer 20 via the ion transfer path. As a result, CO ₂ reductive decomposition reaction in the reduction catalyst layer 20 can be promoted, and high photoreduction efficiency can be obtained.

By the way, the energy (potential) required for the oxidation of H ₂ O in the vicinity of the oxidation catalyst layer 19 and the reduction of CO _{2 in} the vicinity of the reduction catalyst layer 20 is supplied by the electromotive force generated in the multi-junction solar cell 17. Usually, in the solar cell in the comparative example, an electrode is provided for taking out the photoexcited electrons subjected to charge separation, but a transparent electrode is used for entering light. However, since the transparent electrode has high resistance, the efficiency of taking out electricity is reduced. For this reason, a non-transparent metal wiring or the like may be connected to the transparent electrode as an auxiliary electrode. However, in this case, the light is blocked by the metal wiring and the amount of incident light is reduced, so that the efficiency is lowered. Further, the metal wiring is formed long and thin, and electricity (electrons) is collected through the metal wiring, so that the resistance becomes high.

  On the other hand, in the first embodiment, the planar oxidation catalyst layer 19 and the reduction catalyst layer 20 are formed on the front and back surfaces of the multi-junction solar cell 17. For this reason, an oxidation-reduction reaction takes place by the catalyst on the spot where the multi-junction solar cell 17 is separated by charge. In other words, charge separation occurs over the entire surface of the multi-junction solar cell 17, and a redox reaction occurs over the entire surface of the oxidation catalyst layer 19 and the reduction catalyst layer 20. Thereby, resistance is not increased by metal wiring or the like, and the electromotive force generated by the multi-junction solar cell 17 can be efficiently applied to the oxidation catalyst layer 19 and the reduction catalyst layer 20. In addition, since it is not necessary to form metal wiring or the like, the structure can be simplified.

  In addition, when electricity is collected from the solar cell in the comparative example by the metal wiring and reacted, the structure becomes complicated and the area other than the electrode becomes large. For this reason, in order to reduce the size, the electrode area is reduced, and it is necessary to react at a high current density. In this case, high-performance catalysts capable of reacting at a high current density are limited, and noble metals are often used.

  On the other hand, in the first embodiment, since the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 are stacked, an area other than the electrodes is unnecessary. For this reason, even if the size is reduced, the electrode area can be increased, and the reaction is possible at a relatively low current density. As a result, a wide range of options for the catalyst metal can be used, and a general-purpose metal can be used. It is also easy to obtain reaction selectivity.

Hereinafter, in the first embodiment, the photoreduction efficiency of CO ₂ when the through hole 52 is formed as the ion movement path will be described.

FIG. 12 is an experimental result showing the photoreduction efficiency of CO ₂ in Example 1 with respect to the comparative example. More specifically, the photoreduction efficiency of CO ₂ in Example 1 (1-1 to 1-12) when the photoreduction efficiency of CO _{2 in} the comparative example is set to 1.00 is made relative. Hereinafter, FIG. 12 will be described in more detail.

Example 1 is an example of a photochemical reaction cell in the photochemical reaction device according to the first embodiment. More specifically, the photochemical reaction cell in Example 1 has a through-hole 52 that can only transport H ⁺ and has a relatively large equivalent circle diameter. Here, 12 different types of photochemical reaction cells (evaluation cell numbers 1-1 to 1-12) having an equivalent circle diameter of the through-hole 52 of 50, 100, 200 μm and an area ratio of 10, 20, 30, 40% were used. It was prepared and its photoreduction efficiency of CO ₂ was evaluated. These photochemical reaction cells in Example 1 were produced as follows.

  First, a multi-junction solar cell 17 composed of a pin-type a-Si layer, an a-SiGe layer, and an a-SiGe layer, an oxidation electrode layer 18 composed of ITO formed on the surface of the multi-junction solar cell 17, The reduction electrode layer 13 made of ZnO formed on the back surface of the multi-junction solar cell 17, the reflective layer 12 made of Ag formed on the back surface of the reduction electrode layer 13, and the back surface of the reflection layer 12. A structure having the SUS substrate 11 is prepared. Here, the multi-junction solar cell 17 has a thickness of 500 nm, the oxidation electrode layer 18 has a thickness of 100 nm, the reduction electrode layer 13 has a thickness of 300 nm, the reflective layer 12 has a thickness of 200 nm, and the SUS substrate 11 has a thickness. Is 1.5 mm. The oxidation catalyst layer 19 is disposed on the p-type surface of the multijunction semiconductor, and the reduction catalyst layer 20 is disposed on the n-type surface.

Next, an oxidation catalyst layer 19 made of Co ₃ O ₄ is formed on the surface of the oxidation electrode layer 18 by sputtering. Further, a reduction catalyst layer 20 made of Au is formed on the back surface of the SUS substrate 11 by vacuum deposition. Here, the film thickness of the oxidation catalyst layer 19 is 100 nm, and the film thickness of the reduction catalyst layer 20 is 100 nm.

In this manner, a laminate (cell) including the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multi-junction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20 is formed. Thereafter, the laminate is irradiated with light from the surface of the oxidation catalyst layer 19 by a solar simulator (AM1.5, 1000 W / m ² ), and the open voltage of the cell at that time is measured. As a result, the open circuit voltage of the cell is set to 1.9 [V].

  Next, the through hole 52 is formed in the cell. The through-hole 52 is formed by irradiating the obtained cell with laser light. The laser light irradiation conditions are a wavelength of 515 nm, a pulse width of 15 ps, and a repetition frequency of 82 MHz. This laser beam is condensed by a 10 × objective lens and irradiated to the cell. As a result, a plurality of through holes 52 having a triangular lattice shape are formed in the cell. Thereafter, trimming is again performed using laser light so that each through hole 52 has a vertical shape.

Next, the cell in which the through hole 52 is formed is cut into a square shape, and the edge portion is sealed with an epoxy resin so that the area of the exposed portion becomes 1 cm ² . Then, after photographing with an optical microscope or a scanning electron microscope at an angle of view where about 100 through-holes 52 are contained, the average equivalent circle diameter and area ratio of the through-holes 52 of each cell are measured by image processing software. Thus, photochemical reaction cells (evaluation cell numbers 1-1 to 1-12) in Example 1 were produced.

  On the other hand, the comparative example is a photochemical reaction cell that does not have the through-hole 52, and has a structure similar to that of the first embodiment except for the through-hole 52.

Moreover, the photoreduction efficiency of CO ₂ was measured as follows. First, the cell is immersed in a closed water tank (electrolysis tank 31) containing a 0.1M (mol / l) KHCO ₃ solution in which CO ₂ gas is bubbled for 10 minutes. Next, light is irradiated for 10 minutes from the oxidation catalyst layer 19 surface side by a solar simulator (AM1.5, 1000 W / m ² ). Then, the quantitative analysis of the gas in a water tank was performed by gas chromatogram mass spectrometry (GCMS). As a result of the analysis, the detected gas species were O ₂ , H ₂ , and CO. The generated CO is generated by reduction of CO ₂ . The amount of CO generated in the cell in the comparative example was set to 1.00, and the amount of CO obtained in the various cells in Example 1 calculated as a relative value was defined as the photoreduction efficiency of CO ₂ .

As shown in FIG. 12, when the equivalent circle diameter of the through hole 52 is the same in Example 1, the smaller the area ratio of the through hole 52, the higher the CO ₂ photoreduction efficiency compared to the comparative example. More specifically, regardless of the equivalent circle diameter of the through hole 52, high CO ₂ photoreduction efficiency can be obtained if the area ratio of the through hole 52 is 10, 20, and 30%. This is to minimize the area ratio of the through-hole 52, while suppressing the decrease in efficiency due to the absorption loss of light by suppressing the area reduction of the multijunction solar cell 17, the efficiency improvement by H ⁺ transport improvement This is because it is reflected. However, when the area ratio is 40% or more, the contribution of the decrease in efficiency due to the absorption loss of light is greater than the improvement in efficiency due to the improvement of H ⁺ transport, and the obtained effect is lower than that of the comparative example. From the results of Example 1, it can be said that the area ratio of the through-holes 52 of the cell is preferably 40% or less, more preferably 10% or less. However, when the light diffraction and scattering effects can be used as described later in the second embodiment, the area ratio is not limited to this.

In Example 1, when the through hole 52 has the same area ratio, the larger the equivalent circle diameter of the through hole 52, the higher the CO ₂ photoreduction efficiency compared to the comparative example. This is because the structure composed of the through-holes 52 having a larger equivalent circle diameter has a larger processing area (processing area) per unit area and is less affected by processing damage.

As described above, in the first embodiment, when the through hole 52 is formed as the ion movement path, by adjusting the equivalent circle diameter and the area ratio of the through hole 52, the CO ₂ having a higher CO ₂ than the comparative example. Photoreduction efficiency can be obtained.
<2-2. Second Embodiment>
A photochemical reaction device according to the second embodiment will be described with reference to FIGS. 13 to 19.

According to the experimental results in FIG. 12, the photoreduction efficiency of CO ₂ when the through hole 52 is formed as the ion migration path is mainly not only the H ⁺ transport efficiency by the through hole 52 but also the multijunction solar cell 17. It is also determined by the amount of light absorbed by. This is because when the through-hole 52 is provided in the photochemical reaction cell, the area of the multi-junction solar cell 17 is reduced, resulting in a decrease in light absorption. As a result, the number of electrons and holes generated by light decreases, and the reaction efficiency of the oxidation-reduction reaction decreases. For this reason, it is required to suppress the loss of light absorption by the multi-junction solar cell 17 caused by the formation of the through hole 52.

On the other hand, 2nd Embodiment is an example which suppresses the loss of the amount of light absorption accompanying the area reduction of the multijunction type solar cell 17 by adjusting the size, shape, or structure of the through-hole 52. . The second embodiment will be described in detail below. Note that in the second embodiment, description of the same points as in the first embodiment will be omitted, and different points will be mainly described.
[Structure of Second Embodiment]
First, the structure of the photochemical reaction device according to the second embodiment will be described.

  FIG. 13 is a cross-sectional view showing the structure of the photochemical reaction device according to the second embodiment, and is a cross-sectional view along the line AA shown in FIG.

  As shown in FIG. 13, the second embodiment is different from the first embodiment in that the size of the through hole 52 is defined. More specifically, the periodic width (pitch) w1 of the through hole 52 is 3 μm or less, or the equivalent circle diameter (diameter) w2 is 1 μm or less. That is, the through hole 52 in the second embodiment is formed relatively finely. The basis for this will be described below.

  FIG. 14 is a graph showing the relationship between the periodic width w1 of the through hole 52 and the light absorptance of the multi-junction solar cell 17 in the photochemical reaction device according to the second embodiment. FIG. 15 is a graph showing the relationship between the equivalent circle diameter w2 of the through hole 52 and the light absorption rate by the multi-junction solar cell 17 in the photochemical reaction device according to the second embodiment.

  Here, the amount of solar light absorption obtained by the RCWA (Rigorous Coupled Wave Analysis) method when a plurality of through-holes 52 having a square lattice-like arrangement configuration are formed in an a-Si layer having a thickness of 550 nm is shown. More specifically, after calculating the light absorption rate α (λ) up to a wavelength of 300 to 1000 nm when incident light is perpendicularly incident on the sample surface using Diffract MD (manufactured by Rsoft), the solar spectrum I ( The amount of sunlight absorbed A = Σα (λ) × I (λ) was calculated by multiplying by λ). FIG. 14 and FIG. 15 each show a relative value when the amount of sunlight absorbed by the photochemical reaction device (hereinafter referred to as a comparative example) without the through hole 52 is 1. The area ratio of the through hole 52 is calculated as 9, 30, 50, 70%.

  As shown in FIG. 14, when the periodic width w1 of the through-hole 52 is increased, the light absorption rate is reduced as compared with the comparative example (becomes 1 or less). Similarly, as shown in FIG. 15, when the equivalent circle diameter w <b> 2 of the through hole 52 is increased, the light absorption rate is reduced as compared with the comparative example. This is because the incident light and the through-hole structure interact geometrically and the amount of light absorption is reduced by the volume of the through-hole 52.

  However, when the periodic width w1 is 3 μm or less or the equivalent circle diameter w2 is 1 μm or less, the amount of absorption does not decrease compared to the comparative example, and a high amount of absorption can be obtained. This is because incident light is diffracted and scattered in the a-Si layer by the formed through-hole structure. That is, it is considered that incident light enters the a-Si layer due to diffraction and scattering, further increases the optical path length, and increases the amount of light absorbed by the a-Si layer.

In addition, although the plurality of through holes 52 whose arrangement configuration is a square lattice shape has been described, the same result can be obtained even when the arrangement configuration is a triangular lattice shape. Further, the planar shape of the through hole 52 is not limited to a circular shape, and may be an elliptical shape, a quadrangular shape, or a triangular shape. In addition, it does not have to be a regular shape and arrangement, and a diffraction effect can be obtained if the structure has fluctuations in period and diameter, and even a random structure can reduce the amount of light absorbed by the light scattering effect. An increase is obtained.
[Manufacturing Method of Second Embodiment]
Next, a method for manufacturing a photochemical reaction device according to the second embodiment will be described.

  First, as in the first embodiment, the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multi-junction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20 are configured. A photochemical reaction cell is formed.

  Next, a through hole 52 penetrating from the oxidation catalyst layer 19 to the reduction catalyst layer 20 is formed in the photochemical reaction cell.

  More specifically, first, a resist is applied on the oxidation catalyst layer 19 and baked. Thereafter, the resist is irradiated with light or an electron beam by an exposure apparatus or an electron beam drawing apparatus, and then a resist pattern is formed by pre-baking and development processing.

  Next, etching is performed from the oxidation catalyst layer 19 to the reduction catalyst layer 20 by RIE (Reactive Ion Etching) using the resist pattern as a mask. That is, the oxidation catalyst layer 19, the oxidation electrode layer 18, the multi-junction solar cell 17, the reduction electrode layer 13, the reflection layer 12, the substrate 11, and the reduction catalyst layer 20 are etched in order. Thereafter, the resist is removed by an ashing process.

  In this way, through holes 52 are formed in the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multijunction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20. Then, the photochemical reaction cell in which the through-hole 52 was formed is installed in the electrolytic cell 31, and a photochemical reaction apparatus is formed.

  Here, the substrate 11 has a large film thickness and can be formed of a material that is difficult to process by dry etching such as RIE. For this reason, it becomes difficult to form the fine through holes 52 in the second embodiment on the substrate 11. From such a manufacturing point of view, as shown in FIG. 16, the through hole 52 may be formed as follows.

  First, a resist is applied and baked on the oxidation catalyst layer 19 (on the surface). Thereafter, the resist is irradiated with light or an electron beam by an exposure apparatus or an electron beam drawing apparatus, and then a resist pattern is formed by pre-baking and development processing.

  Next, etching is performed by RIE from the oxidation catalyst layer 19 to the reflective layer 12 using the resist pattern as a mask. That is, the oxidation catalyst layer 19, the oxidation electrode layer 18, the multijunction solar cell 17, the reduction electrode layer 13, and the reflection layer 12 are sequentially etched from the surface side, and the through hole 52 is formed. At this time, the substrate 11 and the reduction catalyst layer 20 are not etched. Thereafter, the resist is removed by an ashing process.

  Next, a resist is formed and protected on the exposed surfaces of the processed oxidation catalyst layer 19, oxidation electrode layer 18, multi-junction solar cell 17, reduction electrode layer 13, and reflection layer 12. Thereafter, a resist is applied on the reduction catalyst layer 20 (on the back surface) and baked. Thereafter, the resist is irradiated with light or an electron beam by an exposure apparatus or an electron beam drawing apparatus, and then a resist pattern is formed by pre-baking and development processing.

  Next, etching is performed by wet etching from the reduction catalyst layer 20 to the substrate 11 using the resist pattern as a mask. That is, the reduction catalyst layer 20 and the substrate 11 are etched in order from the back side.

  At this time, the substrate 11 and the reduction catalyst layer 20 are isotropically etched by wet etching. For this reason, as shown in FIG. 16, a through hole 62 having a larger equivalent circle diameter than the through hole 52 is formed in the substrate 11 and the reduction catalyst layer 20.

  Thereafter, the resist on the oxidation catalyst layer 19, the oxidation electrode layer 18, the multijunction solar cell 17, the reduction electrode layer 13, and the reflection layer 12 and the resist on the reduction catalyst layer 20 are subjected to ultrasonic cleaning in an organic solvent. Is removed.

In this way, the through hole 52 is formed in the oxidation catalyst layer 19, the oxidation electrode layer 18, the multi-junction solar cell 17, the reduction electrode layer 13, and the reflection layer 12, and the through hole 62 is formed in the reduction catalyst layer 20 and the substrate 11. Is formed. Then, the photochemical reaction cell in which the through-hole 52 was formed is installed in the electrolytic cell 31, and a photochemical reaction apparatus is formed.
[Effects of Second Embodiment]
According to the second embodiment, the same effect as in the first embodiment can be obtained.

  Furthermore, according to the second embodiment, the periodic width w1 of the through-hole 52 formed in the photochemical reaction cell is 3 μm or less, and the equivalent circle diameter w2 is 1 μm or less. Thereby, incident light can be diffracted and scattered. As a result, the light incident on the surface of the through-hole 52 enters the multi-junction solar cell 17, so that loss of light absorption by the multi-junction solar cell 17 can be suppressed. Further, the amount of light absorbed by the multi-junction solar cell 17 can be increased by increasing the optical path length.

Hereinafter, the photoreduction efficiency of CO ₂ in the second embodiment will be described.

FIG. 17 is an experimental result showing the photoreduction efficiency of CO ₂ in Example 2 with respect to the comparative example. More specifically, the photoreduction efficiency of CO ₂ in Example 2 (2-1 to 2-4) when the photoreduction efficiency of CO _{2 in} the comparative example is set to 1.00 is made relative. Hereinafter, FIG. 17 will be described in more detail.

Example 2 is an example of a photochemical reaction cell in the photochemical reaction device according to the second embodiment. More specifically, the photochemical reaction cell in Example 2 has a through hole 52 that can only transport H ⁺ and has a relatively small equivalent circle diameter. Here, four different types of evaluation holes (evaluation cell numbers 2-1 to 2-4) in which the equivalent circle diameter of the through hole 52 is 0.1, 0.5, 1.0, 2.0 μm and the area ratio is 30%. A photochemical reaction cell was prepared and its photoreduction efficiency of CO ₂ was evaluated. These photochemical reaction cells in Example 2 were produced as follows.

  First, a multi-junction solar cell 17 composed of a pin-type a-Si layer, an a-SiGe layer, and an a-SiGe layer, an oxidation electrode layer 18 composed of ITO formed on the surface of the multi-junction solar cell 17, The reduction electrode layer 13 made of ZnO formed on the back surface of the multi-junction solar cell 17, the reflective layer 12 made of Ag formed on the back surface of the reduction electrode layer 13, and the back surface of the reflection layer 12. A structure having the SUS substrate 11 is prepared. Here, the multi-junction solar cell 17 has a thickness of 500 nm, the oxidation electrode layer 18 has a thickness of 100 nm, the reduction electrode layer 13 has a thickness of 300 nm, the reflective layer 12 has a thickness of 200 nm, and the SUS substrate 11 has a thickness. Was 1.5 mm.

  Next, an oxidation catalyst layer 19 made of nickel oxide is formed on the surface of the oxidation electrode layer 18 by sputtering. Further, a reduction catalyst layer 20 made of Ag is formed on the back surface of the SUS substrate 11 by vacuum deposition. Here, the film thickness of the oxidation catalyst layer 19 was 50 nm, and the film thickness of the reduction catalyst layer 20 was 100 nm.

  In this manner, a laminate (cell) including the substrate 11, the reflective layer 12, the reduction electrode layer 13, the multi-junction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20 is formed.

  Next, the through hole 52 and the through hole 62 are formed in the cell. The through hole 52 and the through hole 62 are formed as follows.

  First, an i-line exposure positive resist or a positive electron beam resist is applied on the oxidation catalyst layer 19 (on the surface) by spin coating and baked. Thereafter, the resist is irradiated with light or an electron beam by an exposure apparatus or an electron beam drawing apparatus, and then a resist pattern having a triangular lattice opening pattern is formed by pre-baking and development processing.

  Next, etching is performed from the oxidation catalyst layer 19 to the reflective layer 12 by inductively coupled plasma (ICP) RIE using a chlorine-argon mixed gas, using the resist pattern as a mask. That is, the oxidation catalyst layer 19, the oxidation electrode layer 18, the multijunction solar cell 17, the reduction electrode layer 13, and the reflection layer 12 are sequentially etched from the surface side, and the through hole 52 is formed. At this time, the substrate 11 and the reduction catalyst layer 20 are not etched. Thereafter, the resist is removed by an ashing process.

  Next, a resist is formed and protected on the exposed surfaces of the processed oxidation catalyst layer 19, oxidation electrode layer 18, multi-junction solar cell 17, reduction electrode layer 13, and reflection layer 12. Thereafter, a positive resist for i-line exposure is applied on the reduction catalyst layer 20 (on the back surface) and baked. Thereafter, the resist is irradiated with light or an electron beam by an exposure apparatus or an electron beam drawing apparatus, and then a resist pattern is formed by pre-baking and development processing.

  Next, etching is performed from the reduction catalyst layer 20 to the substrate 11 by wet etching using an acid, using the resist pattern as a mask. That is, the reduction catalyst layer 20 and the substrate 11 are etched in order from the back side.

  At this time, the substrate 11 and the reduction catalyst layer 20 are isotropically etched by wet etching. Therefore, a through hole 62 having a larger equivalent circle diameter than the through hole 52 is formed in the substrate 11 and the reduction catalyst layer 20. The equivalent circle diameter of the through hole 62 is 15 μm, and the area ratio is 10%. The arrangement configuration of the plurality of through holes 62 is a triangular lattice shape.

  Thereafter, the resist on the oxidation catalyst layer 19, the oxidation electrode layer 18, the multijunction solar cell 17, the reduction electrode layer 13, and the reflection layer 12 and the resist on the reduction catalyst layer 20 are subjected to ultrasonic cleaning in an organic solvent. Is removed.

Next, the cell in which the through hole 52 is formed is cut into a square shape, and the edge portion is sealed with an epoxy resin so that the area of the exposed portion becomes 1 cm ² . Then, after photographing with an optical microscope or a scanning electron microscope at an angle of view where about 100 through holes 52 were accommodated, the average equivalent circle diameter and area ratio of the through holes 52 of each cell were measured by image processing software. Thus, the photochemical reaction cells (evaluation cell numbers 2-1 to 2-4) in Example 2 were produced.

  On the other hand, the comparative example is a photochemical reaction cell that does not have the through hole 52 (and the through hole 62), and has the same structure as that of the second embodiment except for the through hole 52.

Moreover, the photoreduction efficiency of CO ₂ was measured as follows. First, the cell is immersed in a closed water tank (electrolysis tank 31) containing a 0.1M (mol / l) KHCO ₃ solution in which CO ₂ gas is bubbled for 10 minutes. Next, light is irradiated for 10 minutes from the oxidation catalyst layer 19 surface side by a solar simulator (AM1.5, 1000 W / m ² ). Then, the quantitative analysis of the gas in a water tank was performed by gas chromatogram mass spectrometry (GCMS). As a result of the analysis, the detected gas species were O ₂ , H ₂ , and CO. The generated CO is generated by reduction of CO ₂ . The amount of CO generated in the cell in the comparative example was set to 1.00, and the amount of CO obtained in the various cells in Example 2 was calculated as a relative value to be the CO ₂ photoreduction efficiency.

As shown in FIG. 17, in Example 2, when the equivalent circle diameter is 0.1, 0.5, and 1.0 μm, higher photoreduction efficiency of CO ₂ can be obtained as compared with the comparative example. This is because the increase in efficiency due to the improvement in H ⁺ transport is reflected, and incident light is diffracted and scattered by making the equivalent circle diameter relatively small, and the amount of light absorbed by the multijunction solar cell 17 is increased. . Particularly, in the evaluation cell number 2-2 (equivalent circle diameter W2 is 0.5 μm), higher CO ₂ photoreduction efficiency can be obtained. However, when the equivalent circle diameter is 2.0 μm, the influence of the diffraction effect is reduced, and the obtained effect is lower than that of the comparative example.

Thus, in Example 2 in the second embodiment, by adjusting the equivalent circle diameter of the through hole 52 to 1 μm or less, it is possible to obtain a higher CO ₂ photoreduction efficiency compared to the comparative example.

FIG. 18 is an experimental result showing the photoreduction efficiency of CO ₂ in Example 3 with respect to the comparative example. More specifically, the photoreduction efficiency of CO ₂ in Example 3 (3-1 to 3-2) when the photoreduction efficiency of CO _{2 in} the comparative example is set to 1.00 is made relative. FIG. 19 is a plan view showing the structure of the photochemical reaction device in Example 3. FIG. 20 is a cross-sectional view showing the structure of the photochemical reaction device in Example 3. Hereinafter, FIGS. 18 to 20 will be described in more detail.

Example 3 is an example of a photochemical reaction cell in the photochemical reaction device according to the second embodiment. More specifically, the photochemical reaction cell in Example 2 has a through hole 52 that can only transport H ⁺ and has a relatively small equivalent circle diameter.

  Further, as shown in FIGS. 19 and 20, in the photochemical reaction device in Example 3, the equivalent circle diameters and the arrangement configuration of the plurality of through holes 52 are random. Furthermore, in Example 3, the electrolyte solution in contact with the reduction catalyst layer 20 and the electrolyte solution in contact with the oxidation catalyst layer 19 are different, and light is irradiated from the reduction catalyst layer 20 side to develop a photochemical reaction.

Here, two types of photochemical reaction cells, one having the ion exchange membrane 43 inside the through-hole 52 (evaluation cell number 3-1) and one not having (evaluation cell number 3-2), are prepared, and the CO The photoreduction efficiency of ₂ was evaluated. The gas product detected at that time was also examined. These photochemical reaction cells in Example 3 were produced as follows.

  First, a multijunction solar cell 17 composed of an InGaP layer (third solar cell 16) having an pn junction, an InGaAs layer (second solar cell 15), and a Ge layer (first solar cell 14), a multijunction solar cell A structure having a reduction electrode layer 13 made of ITO formed on the surface (light incident surface) 17 and an oxidation electrode layer 18 made of Au formed on the back surface of the multi-junction solar cell 17 is prepared. Here, the p-type surface of the multi-junction solar cell 17 is disposed on the oxidation electrode layer 18 side, and the n-type surface is disposed on the reduction electrode layer 13 side.

  The detailed structure of the multi-junction solar cell 17 is n-InGaAs (contact layer) / n-AlInP (window layer) / n-InGaP / p-InGaP / p-AlInP (Back Surface Field (BSF) layer) / p-AlGaAs (tunnel layer) / p-InGaP (tunnel layer) / n-InGaP (window layer) / n-InGaAs / p-InGaP (BSF layer) / p-GaAs (tunnel layer) / n-GaAs (tunnel layer) ) / N-InGaAs / p-Ge (Substrate).

  Next, an oxidation catalyst layer 19 made of nickel oxide is formed on the back surface of the oxidation electrode layer 18 by sputtering. Further, a reduction catalyst layer 20 made of Ag is formed on the surface of the reduction electrode layer 13 by vacuum vapor deposition. Here, the film thickness of the oxidation catalyst layer 19 was 50 nm, and the film thickness of the reduction catalyst layer 20 was 15 nm.

At this time, as a result of measuring the open voltage of the cell when light irradiation was performed from the reduction catalyst layer 20 side using a solar simulator (AM1.5, 1000 W / m ² ), the open voltage was 2.4V.

  Thus, a laminate (cell) composed of the reduction electrode layer 13, the multi-junction solar cell 17, the oxidation electrode layer 18, the oxidation catalyst layer 19, and the reduction catalyst layer 20 is formed.

  Next, the through hole 52 and the through hole 62 are formed in the cell. The through hole 52 and the through hole 62 are formed as follows.

  First, a positive thermosetting resist for i-line exposure is applied on the reduction catalyst layer 20 (on the surface) by spin coating and baked on a hot plate. Next, a quartz stamper as a mold is prepared. The stamper pattern is produced by transferring the self-assembled pattern of the block copolymer. The pattern formed on the stamper has an average equivalent circle diameter of 120 nm (standard deviation of 31 nm), and has an arrangement configuration in which pillars with irregular diameters are irregularly arranged. At this time, as a release treatment, the surface of the stamper is coated with a fluorine-based release agent such as perfluoropolyether, and the release energy is improved by lowering the surface energy of the stamper.

  Next, a stamper is pressed against the resist using a heater plate press at a temperature of 128 ° C. and a pressure of 60 kN. And after returning to room temperature over 1 hour, the mold reversal pattern is formed in the resist by releasing vertically. Thereby, a resist pattern having an opening is created. Using this resist pattern as an etching mask, the reduction catalyst layer 20 made of Ag is etched by ion milling, and the reduction-side electrode layer 13 made of ITO is etched by wet etching using oxalic acid. Further, the InGaP layer 16 and the InGaAs layer 15 of the multi-junction solar cell 17 are etched by ICP-RIE using chlorine gas. As a result, through holes 52 are formed in the reduction catalyst layer 20, the reduction-side electrode layer 13, the InGaP layer 16, and the InGaAs layer 15. At this time, the Ge layer 14, the oxidation electrode layer 18, and the oxidation catalyst layer 19 are not etched. Thereafter, the resist is removed by an ashing process.

  Next, a resist is formed on the exposed surfaces of the processed reduction catalyst layer 20, reduction electrode layer 13, InGaP layer 16, and InGaAs layer 15 to protect them. Thereafter, a positive resist for i-line exposure is applied on the oxidation catalyst layer 19 (on the back surface) and baked. Thereafter, the resist is exposed to light and developed to form an open resist pattern.

  Next, after the oxidation catalyst layer 19 made of nickel oxide and the oxidation electrode layer 18 made of Au are etched by ion milling, the Ge layer 14 is etched by a wet etching process using an acid. As a result, through holes 62 are formed in the oxidation catalyst layer 19, the oxidation side electrode layer 18, and the Ge layer 14. At this time, the equivalent circle diameter of the through hole 62 is 30 μm, and the area ratio is 15%. Moreover, the arrangement configuration of the through holes 62 is a triangular lattice shape.

  Thereafter, the resist on the reduction catalyst layer 20, the reduction electrode layer 19, the InGaP layer 16, and the InGaAs layer 15 and the resist on the oxidation catalyst layer 19 are removed by ultrasonic cleaning in an organic solvent.

  Furthermore, in the evaluation cell number 3-1, the ion exchange membrane 43 is filled in the through holes 52 and 62. More specifically, the ion exchange membrane 43 is filled in the through holes 52 and 62 by dipping and drying the Nafion solution.

Next, the cell in which the through hole 52 is formed is cut into a square shape, and the edge portion is sealed with an epoxy resin so that the area of the exposed portion becomes 1 cm ² . Thus, the photochemical reaction cell in evaluation cell number 3-1 was produced.

  In addition, the photochemical reaction cell in evaluation cell number 3-2 is a photochemical reaction cell which does not have the ion exchange membrane 43 in the through-hole 52 (and through-hole 62), and other than evaluation cell number 3-1 It has the same structure.

  On the other hand, the comparative example is a photochemical reaction cell that does not have the through hole 52 (and the through hole 62) and the ion exchange membrane 43. Except for the through hole 52, Example 3 (Evaluation cell numbers 3-1 and 3). -2).

  FIG. 21 is a cross-sectional view showing an electrolytic cell 31 for measuring the photochemical reaction device in Example 3 and Comparative Example.

As shown in FIG. 21, the cells in Example 3 and the comparative example are set at the center of a closed H-type electrolytic layer 31. In other words, the electrolytic cell 31 has an oxidation reaction electrolytic cell 45 and a reduction reaction electrolytic cell 46, and the widths of these connecting portions are formed small. A cell is disposed in the connection portion having the small width. At this time, the cell oxidation catalyst layer 19 was placed in the oxidation reaction electrolytic bath 45 and the cell reduction catalyst layer 20 was placed in the reduction reaction electrolytic bath 46. As the electrolytic solution in the oxidation reaction electrolytic tank 45, a 0.5 mol / L sodium sulfate aqueous solution was used. On the other hand, as the electrolytic solution in the electrolytic cell 46 for reduction reaction, an aqueous solution of 2-aminoethanol (monoethanolamine) (40 wt%) obtained by bubbling CO ₂ gas at 40 ° C. for 2 hours was used.

In addition, the photoreduction efficiency and gas product of CO ₂ were measured as follows. First, light is irradiated for 10 minutes from the reduction catalyst layer 20 surface side by a solar simulator (AM1.5, 1000 W / m ² ). Then, the quantitative analysis of the gas in each water tank was performed by gas chromatogram mass spectrometry (GCMS). The amount of CO ₂ reducing substance generated in the cell in the comparative example was set to 1.00, and the amount of CO obtained in the various cells in Example 3 was calculated as a relative value as the CO ₂ photoreduction efficiency. .

As shown in FIG. 18, in the evaluation cell number 3-1, unlike the evaluation cell number 3-2, only H ⁺ is selected by the effect of the ion exchange membrane 43 filled in the through hole 52 (and the through hole 62). Can be moved. For this reason, the product produced | generated by each tank was isolate | separated and detected. More specifically, H ₂ and CO ₂ were detected in the reduction reaction electrolytic cell 46, and O ₂ was detected in the oxidation reaction electrolytic cell 45.

Further, even when the size (equivalent circle diameter) and the arrangement configuration of the plurality of through holes 52 (and the through holes 62) are random as in the third embodiment, the light of CO ₂ is sufficiently high compared to the comparative example. Reduction efficiency can be obtained. Furthermore, in Example 3, the photoreduction efficiency of CO ₂ higher than that in Example 2 can be obtained. This is because when the electrolytic solution in the oxidation reaction electrolytic tank 45 and the electrolytic solution in the reduction reaction electrolytic tank 46 are partitioned by cells, the comparison does not have an H ⁺ movement path (through hole 52 and through hole 62). This is because the photoreduction reaction of CO ₂ is extremely low in the example. This means that, in the case of a photochemical reaction cell that does not have an H ⁺ transfer path, as the cell size increases, the transfer of H ⁺ becomes difficult and the photoreaction efficiency obtained decreases. Thus, by providing the movement path of H ⁺ , high photoreaction efficiency can be obtained even when the cell is enlarged.
[Modification of Second Embodiment]
Next, a modification of the photochemical reaction device according to the second embodiment will be described.

  22 and 23 are cross-sectional views showing the structures of Modification 1 and Modification 2 in the photochemical reaction device according to the second embodiment. In the modified example of the photochemical reaction device according to the second embodiment, differences from the above structure will be mainly described.

  As shown in FIG. 22, in the first modification of the photochemical reaction device according to the second embodiment, the through hole 52 has an equivalent circle diameter w2 that increases from the front surface side (incident surface side) to the back surface side. Formed. That is, the through hole 52 has a tapered shape such that the equivalent circle diameter w2 increases from the oxidation catalyst layer 19 toward the reduction catalyst layer 20. For this reason, the equivalent circle diameter of the through hole 52 on the front surface side of the multi-junction solar cell 17 is larger than the equivalent circle diameter of the through hole 52 on the back surface side. The equivalent circle diameter of the through hole 52 on the back surface side of the multi-junction solar cell 17 is preferably about 10 to 90% of the equivalent circle diameter of the through hole 52 on the front surface side.

  The through hole 52 having a tapered shape is formed by adjusting an etching gas in the etching process by ICP-RIE. More specifically, the through-hole 52 having a tapered shape is formed by isotropic etching using a chlorine-argon mixed gas in which the ratio of argon is increased as an etching gas.

By forming the through hole 52 in a tapered shape, a GI (Graded Index) effect that gives a gradient in the refractive index distribution from the front surface side to the back surface side can be provided. Thereby, the antireflection effect which suppresses the light reflection component which generate | occur | produces when light injects can be acquired. In other words, since more light enters the multi-junction solar cell 17, more light can be absorbed. As a result of measuring the photoreduction efficiency of CO _{2 in} the same manner as in Example 2, the efficiency obtained by the various cells of Example 2 was improved by about 10% to 15% due to the light reflection preventing effect.

As shown in FIG. 23, in the second modification of the photochemical reaction device according to the second embodiment, a protective layer 61 is formed on the inner surface of the through hole 52. In other words, the protective layer 61 is formed on the side surfaces of the substrate 11, the multijunction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 in the through hole 52. The protective layer 61 is composed of a dielectric (insulator) thin film such as SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , or HfO ₂ , and the film thickness of the protective layer 61 is, for example, about 30 nm. It is.

  The protective layer 61 is formed on the inner surface of the through hole 52 by an ALD (Atomic Layer Deposition) method or a CVD (chemical vapor deposition) method after the etching process by ICP-RIE and before removing the resist on the oxidation catalyst layer 19. And formed on the resist. Thereafter, the protective layer 61 and the resist on the resist are removed, so that the protective layer 61 is formed only on the inner surface of the through hole 52.

  The formation of the protective layer 61 is not limited to the ALD method and the CVD method. An immersion method in which the cell is immersed in a solution containing metal ions and then heat treatment is also effective.

By forming the protective layer 61 as the side wall of the through hole 52, leakage of electrons and holes from the multijunction solar cell 17 can be suppressed, and corrosion of the multijunction solar cell 17 due to the solution can be prevented. . As a result of measuring the photoreduction efficiency of CO _{2 in} the same manner as in Example 2, the efficiency obtained by various cells of Example 2 was improved by about 5% to 10% due to leakage prevention.
<2-3. Third Embodiment>
A photochemical reaction device according to the third embodiment will be described with reference to FIGS. The third embodiment is an example in which the photochemical reaction cell is applied to tubular (pipe-shaped) piping. Thus, while decomposing the CO _2, a compound produced by the oxidation catalyst layer 19 and the reduction catalyst layer 20 can be easily transported, it can be used as chemical energy. Hereinafter, the third embodiment will be described in detail. Note that in the third embodiment, description of the same points as in the first photochemical reaction device will be omitted, and different points will be mainly described.
[Structure of Third Embodiment]
First, the structure of the photochemical reaction device according to the third embodiment will be described.

  FIG. 24 is a perspective view showing the structure of the photochemical reaction device according to the third embodiment. FIG. 25 is a cross-sectional view showing the structure of the photochemical reaction device according to the third embodiment. In FIG. 24, the ion movement path is omitted.

  As shown in FIGS. 24 and 25, in the photochemical reaction device according to the third embodiment, a pipe 101 is used as the electrolytic cell 31. The photochemical reaction device according to the third embodiment includes a photochemical reaction cell, a photochemical reaction cell inside (enclosed), a tubular pipe 101 having optical transparency, a substrate 11 as an ion movement path, and a multi-junction. Type solar cell 17, oxidation catalyst layer 19, and opening 51 formed in reduction catalyst layer 20. Here, “piping” means a pipe or pipe system for guiding a fluid.

  The photochemical reaction cell is formed in a cylindrical shape (tubular shape) with the light irradiation surface side (oxidation catalyst layer 19 side) as the outside. That is, the photochemical reaction cell has a tubular structure in which the oxidation catalyst layer 19, the multi-junction solar cell 17, the substrate 11, and the reduction catalyst layer 20 are formed in order from the outside. By this tubular structure, the inside of the pipe 101 is separated into two along the flow direction. The tubular photochemical reaction cell and the tubular pipe 101 may not have a common central axis. In other words, these cross-sectional shapes may not be concentric. Accordingly, the pipe 101 includes an outer oxidation reaction electrolytic cell 102 in which the photocatalytic reaction cell oxidation catalyst layer 19 is disposed, and an inner reduction reaction electrolytic cell 103 in which the photochemical reaction cell reduction catalyst layer 20 is disposed. Is provided. In the oxidation reaction electrolytic cell 102 and the reduction reaction electrolytic cell 103, it is possible to supply separate electrolytic solutions. In addition, a structure in which the cell structure is reversed (a structure in which the reduction catalyst layer 20, the multijunction solar cell 17, the substrate 11, and the oxidation catalyst layer 19 are sequentially formed from the outside) may be used. 102 and the electrolytic cell 103 for reduction reaction are reversed.

The electrolytic reaction electrolytic cell 102 is filled with, for example, a liquid containing H ₂ O as an electrolytic solution. In the oxidation reaction electrolytic cell 102, H ₂ O is oxidized by the oxidation catalyst layer 19 to generate O ₂ and H ⁺ .

The electrolytic cell 103 for reduction reaction is filled with a liquid containing, for example, CO ₂ as an electrolytic solution. In the reduction reaction electrolytic cell 103, CO ₂ is reduced by the reduction catalyst layer 20 to generate a carbon compound.

  The opening 51 is provided so as to penetrate, for example, the substrate 11, the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 from the oxidation reaction electrolytic cell 102 side to the reduction reaction electrolytic cell 103 side. Yes. As a result, the opening 51 connects the oxidation reaction electrolytic cell 102 and the reduction reaction electrolytic cell 103.

A part of the opening 51 is filled with an ion exchange membrane 43, and the ion exchange membrane 43 allows only specific ions to pass therethrough. Thereby, it is possible to move only specific ions through the opening 51 provided with the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic cell 102 and the reduction reaction electrolytic cell 103. it can. Here, the ion exchange membrane 43 is a proton exchange membrane, and H ⁺ generated in the oxidation reaction electrolytic cell 102 can be moved to the reduction reaction electrolytic cell 103 side.

Further, the photochemical reaction device according to the third embodiment is constituted by a pipe 101. Therefore, O ₂ generated in the oxidation reaction electrolytic cell 102 and CO generated in the reduction reaction electrolytic cell 103 can be easily transported by flowing along the flow direction of the pipe 101. Thus, at each facility, it is possible to use the product by decomposition of CO ₂ as chemical energy.
[Modification of Third Embodiment]
Next, a modification of the photochemical reaction device according to the third embodiment will be described.

  FIG. 26 is a perspective view showing a modification of the structure of the photochemical reaction device according to the third embodiment. FIG. 27 is a cross-sectional view showing a modification of the structure of the photochemical reaction device according to the third embodiment. In FIG. 26, the ion movement path is omitted.

  As shown in FIGS. 26 and 27, in the modification of the photochemical reaction device according to the third embodiment, a pipe 101 is used as the electrolytic cell 31. In the photochemical reaction device according to the third embodiment, the photochemical reaction cell provided in the pipe 101 is formed in a flat plate shape. With this flat plate-like structure, the pipe 101 is separated into two along the flow direction. That is, the piping 101 is, for example, an upper-side oxidation reaction electrolytic cell 102 in which the photochemical reaction cell oxidation catalyst layer 19 is arranged, and a lower-side electrolysis reaction electrolysis cell in which the photochemical reaction cell reduction catalyst layer 20 is arranged. A tank 103. In the oxidation reaction electrolytic cell 102 and the reduction reaction electrolytic cell 103, it is possible to supply separate electrolytic solutions.

The electrolytic reaction electrolytic cell 102 is filled with, for example, a liquid containing H ₂ O as an electrolytic solution. In the oxidation reaction electrolytic cell 102, H ₂ O is oxidized by the oxidation catalyst layer 19 to generate O ₂ and H ⁺ .

The electrolytic cell 103 for reduction reaction is filled with a liquid containing, for example, CO ₂ as an electrolytic solution. In the reduction reaction electrolytic cell 103, CO ₂ is reduced by the reduction catalyst layer 20 to generate a carbon compound.

  The opening 51 is provided so as to penetrate, for example, the substrate 11, the multi-junction solar cell 17, the oxidation catalyst layer 19, and the reduction catalyst layer 20 from the oxidation reaction electrolytic cell 102 side to the reduction reaction electrolytic cell 103 side. Yes. As a result, the opening 51 connects the oxidation reaction electrolytic cell 102 and the reduction reaction electrolytic cell 103.

A part of the opening 51 is filled with an ion exchange membrane 43, and the ion exchange membrane 43 allows only specific ions to pass therethrough. Thereby, it is possible to move only specific ions through the opening 51 provided with the ion exchange membrane 43 while separating the electrolytic solution between the oxidation reaction electrolytic cell 102 and the reduction reaction electrolytic cell 103. it can. Here, the ion exchange membrane 43 is a proton exchange membrane, and H ⁺ generated in the oxidation reaction electrolytic cell 102 can be moved to the reduction reaction electrolytic cell 103 side.
[Effect of the third embodiment]
According to the third embodiment, the same effect as in the first embodiment can be obtained.

Furthermore, in the third embodiment, the photochemical reaction cell is applied to a tubular pipe. Thus, while decomposing CO _2, it can be easily transported along a compound produced by the oxidation catalyst layer 19 and the reduction catalyst layer 20 in the flow direction through a pipe structure. And the produced | generated compound can be utilized as chemical energy.

Moreover, since the liquid is flowed and transported, the generated gas bubbles do not stay on the electrode surface or the electrolytic layer surface. Thereby, the efficiency fall and light quantity distribution resulting from scattering of the sunlight by a bubble can be suppressed.
[Application Example of Third Embodiment]
Next, an application example of the photochemical reaction device according to the third embodiment will be described.

  FIG. 28 is a plan view showing an application example of the photochemical reaction device according to the third embodiment. More specifically, it is an example in which a photochemical reaction device that is a tubular pipe according to the third embodiment is used as a system.

As shown in FIG. 28, the piping structure includes a piping 101 composed of the above-described outer oxidation reaction electrolytic cell 102 and inner reduction reaction electrolytic cell 103, a CO ₂ flow path 104 connected thereto, and H ₂ O. A channel 106, a CO channel 105, and an O ₂ channel 107.

The CO ₂ channel 104 is connected to one side of the reduction reaction electrolytic cell 103, and the CO channel 105 is connected to the other side of the reduction reaction electrolytic cell 103. The H ₂ O channel 106 is connected to one side of the oxidation reaction electrolytic cell 102, and the O ₂ channel 107 is connected to the other side of the oxidation reaction electrolytic cell 102. That is, the reduction reaction electrolytic cell 103 and the oxidation reaction electrolytic cell 102 constituting the pipe 101 are branched on one side to become the CO ₂ flow path 104 and the H ₂ O flow path 106. Further, the reduction reaction electrolytic bath 103 and the oxidation reaction electrolytic bath 102 constituting the pipe 101 are branched on the other side to become a CO flow path 105 and an O ₂ flow path 107.

The CO ₂ flow path 104, CO ₂ is introduced from the outside. In the CO ₂ flow path 104, CO ₂ may be introduced as a gas, or may be introduced as an electrolytic solution containing a CO ₂ absorbent. CO ₂ flow path 104 (an integral), which is the connected to the reduction reaction electrolyzer 103 for, consists of those forming the photochemical reaction cell in tubular, not limited to this, CO ₂ and a gas an electrolytic solution containing a CO ₂ absorbent may be made in what can flow.

The H ₂ O flow path 106, _{H 2} O is introduced from the outside. In the H ₂ O flow channel 106, H ₂ O may be introduced as a gas or a liquid. Since the H ₂ O flow path 106 is connected (integrated) with the oxidation reaction electrolytic cell 102, it is configured by the same thing as the tubular pipe 101 having light permeability, but is not limited thereto, and of H _{2 O} liquid may be made in what can be supplied.

H ₂ O that has flowed from the H ₂ O flow path 106 flows into the oxidation reaction electrolytic cell 102. Then, H ₂ O is oxidized by the oxidation catalyst layer 19 to generate O ₂ and H ⁺ . On the other hand, CO _{2 that} has flowed from the CO ₂ flow path 104 flows into the electrolytic cell 103 for reduction reaction. Then, CO ₂ is reduced by the reduction catalyst layer 20 to generate a carbon compound (CO or the like).

  The CO channel 105 flows out a carbon compound such as CO generated in the reduction reaction electrolytic cell 103 to the outside. In the CO channel 105, CO may flow out as a gas or liquid. The CO channel 105 is connected to the other of the reduction reaction electrolytic cell 103. For this reason, although it is comprised with what formed the photochemical reaction cell in the shape of a tube, not only this but what should just be comprised with what can flow out CO which is gas and liquid.

The O ₂ flow path 107 flows out O ₂ generated in the oxidation reaction electrolytic cell 102 to the outside. In the O ₂ flow path 107, O ₂ may flow out as a gas or may flow out as a liquid. The O ₂ flow path 107 is connected to the other side of the oxidation reaction electrolytic cell 102. Therefore, composed of the same as the pipe 101 of the tubular having light transmittance, not limited thereto, and may be made of the O ₂ gas and liquid in what can flow.

  Further, the reflecting plate 108 may be disposed on the light exit surface side of the pipe 101. The reflection plate 108 is, for example, a concave mirror along the tubular pipe 101, and can reflect light and enter the pipe 101 again. Thereby, the improvement of photochemical reaction efficiency can be aimed at. In addition, the reflection condition can be changed by filling the pipe 101 with a liquid. Thereby, the light can enter the pipe 101 by reflection or refraction at the pipe 101 or the gas-liquid interface, and the photochemical reaction efficiency can be improved.

In this way, by using the photochemical reaction device which is a tubular pipe according to the third embodiment, CO ₂ flowing from the outside is decomposed, and the products generated thereby are separated on the reduction side and the oxidation side. And can flow out to the outside.
3. Photochemical Reaction System The photochemical reaction system according to this embodiment will be described below with reference to FIGS. 29 to 34. The photochemical reaction system according to the present embodiment can be designed by a piping structure shown in FIG. 28, for example.

  FIG. 29 is a block diagram showing the configuration of the photochemical reaction system according to this embodiment.

As shown in FIG. 29, a CO ₂ reducing unit 110, a CO ₂ generating unit 111, and a CO ₂ absorbing unit 112 are provided.

The CO ₂ reduction unit 110 is, for example, the above-described photochemical reaction device. CO ₂ reduction unit 110 flows out the electrolytic solution containing CO ₂ absorbent to CO ₂ absorption means 112, the electrolyte flows into the containing CO ₂ absorbent having absorbed CO ₂ from the CO ₂ absorbing means 112. Then, CO ₂ reduction unit 110, by reducing the CO ₂ absorbed by the CO ₂ absorbent, CO, HCOOH, _CH 3 OH or generates carbon compounds CH _4, etc., these CO ₂ generating means, It flows out to 111. Further, the CO ₂ reducing unit 110 generates O ₂ by oxidizing H ₂ O together with the reduction of CO ₂ , and flows it out to the CO ₂ generating unit 111.

The CO ₂ generation means 111 is, for example, a power plant. The CO ₂ generation means 111 flows in the carbon compound such as CO, HCOOH, CH ₃ OH, or CH ₄ generated by the CO ₂ reduction means 110. The CO ₂ generation means 111 obtains energy and generates CO ₂ by burning carbon fuel such as CH ₃ OH or CH ₄ . The CO ₂ generation means 111 flows the generated CO _{2 out} to the CO ₂ absorption means 112. Further, the CO ₂ generation means 111 flows in O ₂ generated by the CO ₂ generation means 111. By using this O ₂ as a combustion aid, the combustion efficiency of the carbon fuel can be improved and the total CO ₂ emission can be reduced.

The CO ₂ absorption means 112 is, for example, CCS (Carbon Dioxide Capture and Storage). CO ₂ absorption means 112 uses the CO ₂ absorbent that is flowing from the CO ₂ reduction unit 110, to absorb the CO ₂ produced by the CO ₂ generation unit 111. Thereby, the CO ₂ absorption means 112 collects and stores CO ₂ . Then, the CO ₂ absorbing unit 112 flows out the electrolytic solution containing CO ₂ absorbent having absorbed CO ₂ in the CO ₂ reduction unit 110.

Thus, according to the photochemical reaction system according to this embodiment, it generates CO ₂ with obtaining energy by burning carbon fuels by CO ₂ generation unit 111, the CO ₂ produced by the CO ₂ absorbing means 112 It is absorbed and CO ₂ is reduced and decomposed by the CO ₂ reducing means 110. Then, again flows into CO ₂ generating unit 111 carbon compound produced with reductive decomposition of CO ₂ by CO ₂ reduction unit 110 as a carbon fuel. As a result, CO ₂ can be efficiently decomposed, and energy can be efficiently obtained using the product produced thereby.

The present invention is not limited to the power plant as a CO ₂ generating unit 111 for discharging the CO ₂ by burning carbon fuels, ironworks, chemical plants or landfills, etc. may be mentioned. In ironworks, high temperatures are required, and CO ₂ emissions and O ₂ consumption are increased, so the above system is suitable. Further, in chemical plants and the like, energy, carbon compounds, and O _2, and therefore the necessary all, the system is suitable.

In addition, by supplying O ₂ generated by the CO ₂ reducing means 110 to organisms such as fish in the farm, there are effects of promoting growth and preventing diseases. Then, the CO ₂ discharged from the organism can be reduced by the CO ₂ reduction means 110, and the generated O ₂ can be supplied again to the organism. Moreover, energy such as heat and electricity can be obtained by burning a carbon compound produced by reducing CO ₂ as carbon fuel by the CO ₂ generating means 111. It is also possible to supply this to the farm again.

Further, by supplying O ₂ generated by the CO ₂ reduction means 110 to sewage treatment bacteria or the like, the efficiency of the treatment can be improved. Similarly, energy such as heat and electricity can be obtained by burning a carbon compound produced by reducing CO ₂ as a carbon fuel. And it is also possible to supply this to a sewage treatment plant again. Thereby, the operating cost of a sewage treatment plant can be reduced. Further, by using the by-product H ₂ generated by the CO ₂ reduction means 110 together with the reductive decomposition of CO ₂ , a carbon compound such as CH ₃ OH, C ₂ H ₅ OH, or CH ₄ is generated by bacteria. Also good.

Moreover, O ₂ produced | generated by the CO ₂ reduction | restoration means 110 can be supplied to a hospital. Similarly, it is possible to obtain energy such as heat and electricity by supplying the carbon compound produced by reducing CO ₂ as carbon fuel by the CO ₂ generating means 111 and supplying it to the hospital. . Furthermore, chemical energy may be obtained by supplying CO ₂ such as private power generation to the CO ₂ reduction means 110 again.

Further, O ₂ may be used as an oxidizing power for an air purification system, a water purification system, or a system for cleaning contaminated organic substances. Then, the obtained energy may be used for system operation, CO ₂ generated by energy supply used in these systems may be absorbed and converted again into chemical energy by the CO ₂ reducing means 110 and the CO ₂ generating means 111, and cycled.

  FIG. 30 is a block diagram showing a configuration of Modification 1 of the photochemical reaction system according to the present embodiment. FIG. 31 is a block diagram showing a configuration of Modification 2 of the photochemical reaction system according to the present embodiment. FIG. 32 is a block diagram showing a configuration of Modification 3 of the photochemical reaction system according to the present embodiment.

The CO ₂ reduction unit 110 (reduction catalyst layer 20), although it is possible to decompose the CO ₂ to form CO or HCOOH, it is difficult to generate at once as a carbon fuel _CH 3 OH or CH _4, etc. . That is, after CO or HCOOH is formed by the CO ₂ reducing means 110, it is necessary to convert them into CH ₃ OH or CH ₄ or the like.

  On the other hand, as shown in FIG. 30, the photochemical reaction system in the first modification includes a first chemical process means 113 and a buffer tank 114.

The first chemical process means 113 and the buffer tank 114 are provided in a flow path between the CO ₂ reducing means 110 and the CO ₂ generating means 111. The first chemical process means 113 chemically reacts CO or HCOOH produced by the CO ₂ reduction means 110 to produce CH ₃ OH or CH ₄ or the like. That is, the 1st chemical process means 113 performs the intermediate process in the production | generation of carbon fuel. At this time, if the ratio of CO and H ₂ produced by the CO ₂ reducing means 110 is adjusted to a ratio suitable for the first chemical process means 113 by adjusting the chemical structure of the electrolytic solution and the amount of water in the electrolytic solution. Good. For example, when producing CH ₃ OH, the reaction is carried out according to the following formula (3).

CO + H ₂ → CH ₃ OH (3)
(3) As shown in equation, when generating a _CH 3 OH from CO and _{H 2,} stoichiometrically CO: H = 1: 2 by reaction proceeds. Therefore, the ratio of CO and _{H 2} generated by the CO ₂ reduction unit 110 is preferably adjusted to the rate.

  In an actual process, in order to consider energy efficiency and cost, the ratio is often different from this, but can be adjusted to a suitable ratio.

  In addition, the product may change depending on device temperature, light intensity, and wavelength. In order to cope with this variation, a buffer tank 114 is provided.

By the way, when the CO ₂ reduction means 110 uses solar energy, there arises a problem that the buffer tank 114 is increased in size in response to a long-term change due to the rainy season or the like.

  On the other hand, as shown in FIG. 31, the photochemical reaction system in Modification 2 further includes second chemical process means 115.

The second chemical process means 115 is provided in a flow path between the CO ₂ reduction means 110 and the CO ₂ generation means 111, and is provided as a flow path different from the first chemical process means 113. The second chemical process means 115 is a manufacturing apparatus and a manufacturing method different from the first chemical process means 113.

  As described above, the first chemical process means 113 and the second chemical process means 115 may be provided as different flow paths, and these may be switched as appropriate, thereby solving fluctuations in the chemical reaction due to weather conditions and temperature conditions.

Note that the reaction conditions of the first chemical process means 113 and the second chemical process means 115 may be changed, or the product may be changed. At this time, there may be a case where the first chemical process means 113 and the second chemical process means 115 change depending on the tank capacities of the products. Moreover, the _{O 2} generated by the CO ₂ reduction unit 110 may be supplied thereto. These combinations are merely examples, and there are no restrictions on combinations with a plurality of chemical process means or multistage processes. In addition, the reflection condition can be changed by changing the angle or position of the reflection plate 108 or changing the amount of liquid in the tube. As a result, the amount of light incident on the pipe 101 can be changed by reflection and refraction at the pipe and the gas-liquid interface. As a result, the photochemical reaction efficiency is improved and the product is selectively reshaped. Can do.

By the way, in the photochemical reaction cell in the CO ₂ reduction means 110, when sunlight is irradiated, charge separation occurs in the multi-junction solar cell 17, and H ₂ O is oxidized by the oxidation catalyst layer 19 to generate H ⁺ and O _2. Is done. At this time, electrons move to the reduction catalyst layer 20 of the counter electrode by the oxidation reaction by the oxidation catalyst layer 19. Due to the transferred electrons, the reduction reaction of CO ₂ by the reduction catalyst layer 20 proceeds. However, the energy for oxidizing H ₂ O is very large. For this reason, there is a large potential difference between the oxidation potential of H ₂ O and the reduction potential of CO ₂ . Therefore, advancing the oxidation reaction of H ₂ O and the reduction reaction of CO ₂ requires a large amount of energy and is very difficult.

Therefore, an example is known in which a sacrificial reagent such as triethanolamine is used as the electron source (reduced form) on the oxidation catalyst layer 19 side. By using a reductant such as a sacrificial reagent instead of the reaction of decomposing H ₂ O into H ⁺ and O ₂ by the oxidation catalyst layer 19, the potential difference between the oxidation reaction and the reduction reaction can be reduced. As a result, the oxidation reaction and the reduction reaction proceed relatively easily. As a result, the number of junctions of a multi-junction solar cell can be reduced, or the solar cell can be configured as a single layer. Further, even when the same solar cell is used, the reaction proceeds more because the current increases. These combinations can be arbitrarily set according to the potential difference between oxidation and reduction, the output of the substitute battery, or a combination of catalysts. Further, the sacrificial reagent species such as triethanolamine is changed as an electron source (reduced form) on the oxidation catalyst layer 19 side, the concentration is changed by supplying triethanolamine as an aqueous solution, or the triethanolamine is converted into water. By substituting, it is possible to suppress a decrease in response due to changes in weather or to change the product.

  As shown in FIG. 32, in the photochemical reaction system in Modification 3, a reductant obtained in large quantities from the natural world 116 is used as a reductant that reduces the potential difference in the oxidation-reduction reaction as described above. In addition, a reductant shows what has a reducing power here. In other words, the reductant refers to a substance that is oxidized and loses electrons, and reduces other substances by the electrons.

Examples of the reductant obtained from the natural world 116 include iron divalent ions (Fe ²⁺ ) and the like present in wastewater from the mine. There is no limitation as long as it is a reductant existing in nature, such as hydrogen sulfide or sulfur. In the photochemical reaction system in Modification 3, Fe ²⁺ obtained from the natural world 116 is used as the reaction on the oxidation catalyst layer 19 side in the CO ₂ reduction means 110. Hereinafter, the chemical reaction of the photochemical reaction cell in the CO ₂ reduction means 110 will be described in detail.

  FIG. 33 is a cross-sectional view showing the operation principle of the photochemical reaction cell in Modification 3 of the photochemical reaction system according to the present embodiment. Here, the reflection layer 12, the reduction electrode layer 13, and the oxidation electrode layer 18 are omitted.

As shown in FIG. 29, in the vicinity of the oxidation catalyst layer 19, Fe ²⁺ obtained from the natural world is oxidized (loses electrons) to generate iron trivalent ions (Fe ³⁺ ). Electrons generated by this oxidation reaction move to the reduction catalyst layer 20. In the vicinity of the reduction catalyst layer 20, a reduction reaction is caused by the moved electrons. More specifically, CO ₂ is reduced to produce CO, or H ₂ O is reduced to produce H ₂ .

At this time, the potential difference between the oxidation reaction of Fe ^{2+ and} the reduction reaction of CO ₂ or H ₂ O is small. For this reason, these oxidation reactions and reduction reactions can proceed relatively easily.

The above-described Fe ²⁺ is present in large quantities in mines around the world, and many of them are present in mine wastewater containing sulfur. For this reason, low pH sulfuric acid produced by oxidation of sulfur in a tunnel or the like is an environmental problem. In particular, Fe ²⁺ needs to be neutralized with a neutralizing agent such as inexpensive calcium carbonate. However, Fe ²⁺ hardly reacts with calcium carbonate. For this reason, in order to oxidize Fe ^{< 2+>} to Fe ^<3+> , there exists a problem that energy is consumed using bacteria.

On the other hand, according to the third modification of the photochemical reaction system according to the present embodiment, anti-waste water (mineral waste water) containing Fe ²⁺ obtained from the natural world 116 is used as the electrolytic solution on the oxidation catalyst layer 19 side. When this Fe ²⁺ becomes a reductant, energy substances such as H ₂ and CO can be easily obtained by the reduction catalyst layer 20. At the same time, it becomes possible to oxidize Fe ^{2+ in the} natural world 116, and environmental problems due to Fe ²⁺ can be solved.

  In addition, it is more preferable that the energy obtained in this way is used as mining wastewater treatment facility or mining energy because there is no loss due to energy transfer.

As shown in FIG. 34, it is also effective to reduce ferric hydroxide (Fe (OH) ₃ ) precipitated as Fe ³⁺ as an electrolytic solution on the reduction catalyst layer 20 side. Thereby, Fe ^<2+> is produced ^| generated and can be cycled as a reductant by using again as electrolyte solution by the side of the oxidation catalyst layer 19 side.

  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 11 ... Board | substrate, 17 ... Multijunction type solar cell, 19 ... Oxidation catalyst layer, 20 ... Reduction catalyst layer, 31 ... Electrolyzer, 41 ... Electrolyzer flow path, 42 ... Circulation mechanism, 43 ... Ion exchange membrane, 44 ... Temperature adjusting mechanism, 45 ... oxidation reaction electrolyzer, 46 ... reduction electrolyzer, 51 ... opening, 52 ... through hole, 61 ... protective layer, 110 ... CO ₂ reduction unit, 111 ... CO ₂ generating unit, 112 ... CO ₂ absorption means, 113 ... chemical process means, 116 ... nature.

Claims (17)

Formed between an oxidation catalyst layer that oxidizes H ₂ O to generate O ₂ and H ⁺ , a reduction catalyst layer that reduces C ₂ O ₂ to generate a carbon compound, the oxidation catalyst layer, and the reduction catalyst layer; comprising a CO ₂ reduction hand stage comprising a laminate having a semiconductor layer for charge separation by light energy,
The laminate has a plurality of openings including a first opening that penetrates the laminate and moves ions between the oxidation catalyst layer side and the reduction catalyst layer side,
The photochemical reaction system, wherein the size of the first opening on the oxidation catalyst layer side is different from the size of the first opening on the reduction catalyst layer side . CO ₂ generating means for generating CO ₂ is further provided,
The CO ₂ reduction means flows the generated carbon compound to the CO ₂ generation means,
_2. The photochemical reaction system according to claim 1, wherein the CO ₂ generating unit obtains energy by burning a carbon compound discharged from the CO ₂ reducing unit. The CO ₂ reduction means flows out the generated O ₂ to the CO ₂ generation means,
The CO ₂ generating means, photochemical according to claim 2, wherein the CO and O ₂ flowing out from the ₂ reduction means, is characterized by using a carbon compound that is flowing out of the CO ₂ reduction unit as a combustion improver for burning Reaction system. 4. The photochemical reaction system according to claim 2, further comprising chemical process means for chemically changing the carbon compound flowing out from the CO ₂ reducing means and flowing it out to the CO ₂ generating means. 5. The photochemical reaction system according to claim 1, wherein the CO ₂ reduction unit supplies the generated O ₂ to a chemical process unit. 6. The CO ₂ reduction means, the generated O _2, power plants, ironworks, chemical plants, waste treatment plants, farms claims 1 and supplying sewage treatment plant, or to the hospital 5. The photochemical reaction system according to any one of 4 above.   The photochemical reaction system according to any one of claims 1 to 6, wherein an area ratio of the plurality of openings in the stacked body is 40% or less. It said first opening, photochemical reactions according to any one of claims 1 to 7, characterized in that size from the incident surface of the light toward the rear surface side is larger tapered system. The plurality of openings further include a second opening that moves ions between the oxidation catalyst layer side and the reduction catalyst layer side, penetrates the stacked body, and is adjacent to the first opening. ,
The photochemical reaction system according to claim 1 , wherein the second opening has a size different from that of the first opening . Formed between an oxidation catalyst layer that oxidizes H ₂ O to generate O ₂ and H ⁺ , a reduction catalyst layer that reduces C ₂ O ₂ to generate a carbon compound, the oxidation catalyst layer, and the reduction catalyst layer; comprising a CO ₂ reduction hand stage comprising a laminate having a semiconductor layer for charge separation by light energy, and,
The laminate has a plurality of openings including a first opening that penetrates the laminate and moves ions between the oxidation catalyst layer side and the reduction catalyst layer side,
A photochemical reaction system, wherein a protective layer made of a dielectric is formed on an inner surface of the first opening. The photochemical reaction system according to claim 10, wherein the protective layer includes any one of TiO ₂ , ZrO ₂ , Al ₂ O ₃ , SiO ₂ , and HfO ₂ . CO ₂ generating means for generating CO ₂ is further provided,
The CO ₂ reduction means flows the generated carbon compound to the CO ₂ generation means,
The photochemical reaction system according to claim 10 or 11, wherein the CO ₂ generating means obtains energy by combusting a carbon compound discharged from the CO ₂ reducing means. The CO ₂ reduction means flows out the generated O ₂ to the CO ₂ generation means,
The CO ₂ generating means, photochemical of claim 12, the O ₂ flowing out from the CO ₂ reduction means, is characterized by using a carbon compound that is flowing out of the CO ₂ reduction unit as a combustion improver for burning Reaction system. 14. The photochemical reaction system according to claim 12, further comprising chemical process means for chemically changing the carbon compound flowing out from the CO ₂ reducing means and flowing it out to the CO ₂ generating means. The photochemical reaction system according to any one of claims 10 to 14, wherein the CO ₂ reducing unit supplies the generated O ₂ to a chemical process unit. The CO ₂ reduction means, the generated O _2, power plants, ironworks, chemical plants, waste treatment plants, farms claims 10 to and supplying sewage treatment plant, or to the hospital 14. The photochemical reaction system according to any one of 14.   The photochemical reaction system according to any one of claims 10 to 16, wherein an area ratio of the plurality of openings in the stacked body is 40% or less.