Carbon dioxide reduction reaction device

Abstract

A carbon dioxide reduction reaction device 1 comprises: an oxidation tank 11 into which an aqueous solution flows; a reduction tank 12 into which carbon dioxide flows; an oxidation electrode 14 which is inserted into the aqueous solution in the oxidation tank and is irradiated with light from outside of the oxidation tank; an electrolyte film 15 disposed between the oxidation tank and the reduction tank; and a reduction electrode 16 which is joined to the reduction tank side of the electrolyte film and is connected to the oxidation electrode by a conductor. The oxidation tank is provided with an anti-reflection structure 18 in a section where the light passes.

Description

Carbon dioxide reduction reactor

[0001] The present disclosure relates to a carbon dioxide reduction reactor.

[0002] There is a device that reduces carbon dioxide using light energy (Non-Patent Document 1). An electrolyte membrane is placed between an oxidation tank and a reduction tank, and the oxidation tank and reduction tank are each filled with an aqueous solution. An oxidation electrode is placed in the aqueous solution in the oxidation tank, and a reduction electrode is placed in the aqueous solution in the reduction tank, and the oxidation electrode and reduction electrode are connected by a wire. Carbon dioxide is then introduced into the aqueous solution in the reduction tank.

[0003] When light is irradiated onto the oxidation electrode, electron-hole pairs are generated and separated at the oxidation electrode, resulting in the oxidation reaction of water, which produces oxygen and protons. The electrons move from the oxidation electrode to the reduction electrode via the conductor, and the protons travel from the oxidation cell to the reduction cell via the electrolyte membrane. At the reduction electrode, the protons, electrons, and carbon dioxide undergo a reduction reaction, producing carbon monoxide, formic acid, methane, and other energy resources.

[0004] Satoshi Yotsuhashi and 6 others, “CO2 Conversion with Light and Water by GaN Photoelectrode”, Japanese Journal of Applied Physics, 51, 2012, p.02BP07-1-p.02BP07-3

[0005] The oxidation chamber is made of highly transparent quartz. However, due to differences in refractive index, light is reflected between the quartz and the air outside the oxidation chamber, and between the quartz and the aqueous solution in the oxidation chamber. This causes the light intensity to attenuate before it reaches the oxidation electrode. This reduces the efficiency of the oxidation reaction in the oxidation chamber.

[0006] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a technology that can improve the oxidation efficiency in an oxidation tank.

[0007] A carbon dioxide reduction reaction device according to one embodiment of the present disclosure comprises an oxidation tank into which an aqueous solution is introduced, a reduction tank into which carbon dioxide is introduced, an oxidation electrode inserted into the aqueous solution in the oxidation tank and irradiated with light from outside the oxidation tank, an electrolyte membrane disposed between the oxidation tank and the reduction tank, and a reduction electrode joined to the reduction tank side of the electrolyte membrane and connected to the oxidation electrode by a lead, and the oxidation tank has an anti-reflection structure in the portion through which the light passes.

[0008] According to the present disclosure, a technique can be provided that can improve the oxidation efficiency in an oxidation tank.

[0009] FIG. 1 is a diagram showing the configuration of a carbon dioxide reduction reaction apparatus. FIG. 2 is a diagram showing a decrease in light intensity due to a refractive index difference. FIG. 3 is a diagram showing an example of an antireflection structure. FIG. 4 is a diagram showing the antireflection structure of Example 1. FIG. 5 is a diagram showing the antireflection structure of Example 1. FIG. 6 is a diagram showing a method for fabricating the antireflection structure. FIG. 7 is a diagram showing a method for fabricating the antireflection structure. FIG. 8 is a diagram showing the results of measurement of light transmittance. FIG. 9 is a diagram showing the results of measurement of the amount of hydrogen produced. FIG. 10 is a diagram showing the antireflection structure of Example 2. FIG. 11 is a diagram showing the results of measurement of light transmittance. FIG. 12 is a diagram showing the results of measurement of the amount of hydrogen produced. FIG. 13 is a diagram showing the antireflection structure of Example 3.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0011] 1 is a diagram showing an example of the configuration of a carbon dioxide reduction reaction device according to this embodiment. The carbon dioxide reduction reaction device 1 is a device that applies light energy, such as sunlight, to an oxidation electrode and directly supplies gaseous carbon dioxide to a reduction electrode, thereby causing a carbon dioxide reduction reaction.

[0012] The carbon dioxide reduction reaction apparatus 1 includes an oxidation tank 11 and a reduction tank 12. An aqueous solution 13, which is an electrolyte, flows into the oxidation tank 11. An oxidation electrode 14 is inserted into the aqueous solution 13 in the oxidation tank 11. Carbon dioxide flows into the reduction tank 12.

[0013] A composite in which an electrolyte membrane 15 and a reduction electrode 16 are bonded together is disposed between the oxidation chamber 11 and the reduction chamber 12. The electrolyte membrane 15 is disposed on the oxidation chamber 11 side, and the reduction electrode 16 is disposed on the reduction chamber 12 side. The oxidation electrode 14 and the reduction electrode 16 are connected by a conductor 17.

[0014] Next, the oxidation-reduction reaction will be described.

[0015] Nitrogen is flowed into the aqueous solution 13 in the oxidation tank 11, and carbon dioxide is flowed into the reduction tank 12. When light is irradiated onto the oxidation electrode 14 from outside the oxidation tank 11, electron-hole pairs are generated and separated at the oxidation electrode 14, and oxygen and protons (H ＋ ) is produced. － ) moves from the oxidation electrode 14 to the reduction electrode 16 via the lead wire 17. Protons reach the reduction electrode 16 from the oxidation vessel 11 via the electrolyte membrane 15.

[0016] At the reduction electrode 16, a reduction reaction of carbon dioxide occurs between protons, electrons, and carbon dioxide. At the same time, a side reaction of hydrogen production occurs due to the combination of protons and electrons. This reduction reaction of carbon dioxide produces carbon monoxide, formic acid, methane, and other substances that can be used as energy resources.

[0017] (Oxidation tank: Water oxidation reaction) 2H ２ O+4h ＋ →O ２ +4H ＋ (Reduction tank: carbon dioxide reduction reaction (target reaction)) CO ２ +2H ＋ +2e － →CO+H ２ O CO ２ +2H ＋ +2e － →HCOOH CO ２ +4H ＋ +4e － →HCHO+H ２ O CO ２ +6H ＋ +6e － →CH ３ OH+H ２ O CO ２ +8H ＋+8e － →CH ４ +2H ２ O (reduction tank: hydrogen production reaction (side reaction)) 2H ＋ +2e － →H ２ In the carbon dioxide reduction reaction device 1, the oxidation electrode 14 is generally made of a wide-gap semiconductor, which absorbs only light in the wavelength range up to ultraviolet. Therefore, quartz or synthetic quartz, which has high optical transparency, is used as the material for the light-transmitting window 18 of the oxidation vessel 11. Hereinafter, the quartz will be given the same reference numeral as the oxidation vessel 11.

[0018] However, as shown in FIG. 2, there is a difference in the refractive index n between the air outside the oxidation tank and the quartz 11, and between the quartz 11 and the aqueous solution 13 in the oxidation tank, so reflection occurs between them, reducing the intensity and amount of light reaching the oxidation electrode 14 and lowering the efficiency of water oxidation in the oxidation tank.

[0019] Specifically, the refractive index of quartz 11, n≈1.47 (wavelength 365 nm), is larger than that of air, n=1.00 (wavelength 365 nm), and the refractive index of aqueous solution 13, n≈1.35. Therefore, the difference in refractive index between the two materials causes reflection, and the incident light on oxidation electrode 14 is attenuated.

[0020] Therefore, in this embodiment, in the light-transmitting window 18 shown in FIG. 1, a first anti-reflection structure 20 is provided on the outer surface of the quartz 11, and a second anti-reflection structure 30 is provided on the inner surface of the quartz 11, as shown in FIG.

[0021] Specifically, a first anti-reflection film having a first anti-reflection structure 20 is formed and attached to the outer surface of the quartz 11. A second anti-reflection film having a second anti-reflection structure 30 is formed and attached to the inner surface of the quartz 11. The anti-reflection film is made of a material having a moth-eye structure or one or more layers of material having a refractive index within a predetermined range. The anti-reflection film is also made of a transparent material that does not absorb light in the wavelength range of 300 nm or more.

[0022] In this way, the first antireflection structure 20 and the second antireflection structure 30 are provided on the surface of the quartz 11 in the light-transmitting window 18, thereby preventing or suppressing reflections that occur between the air outside the oxidation tank and the quartz 11, and between the quartz 11 and the aqueous solution 13 in the oxidation tank. As a result, the light transmittance through the light-transmitting window 18 is improved, which improves the efficiency of water oxidation in the oxidation tank and the efficiency of carbon dioxide reduction in the reduction tank.

[0023] Furthermore, an alkaline aqueous solution is generally used as the aqueous solution 13, but since the quartz 11 is not resistant to alkali, if the quartz 11 is left in contact with the aqueous solution 13 for a long period of time, the glass surface of the quartz 11 is dissolved and etched, and the transparency of the quartz 11 decreases.

[0024] Therefore, an organic or inorganic material is used as the material for the second anti-reflection coating provided on the inner surface of the quartz 11. Since the inner surface of the quartz 11 is coated with an organic or inorganic material, dissolution and etching of the glass surface of the quartz 11 by the aqueous solution 13 can be suppressed.

[0025] Example 1 In Example 1, a case where an organic material having a moth-eye structure is used will be described.

[0026] 3, a polymer 21 having a moth-eye structure is attached to the outer surface of quartz 11 as shown in Fig. 4. Hereinafter, the polymer having a moth-eye structure will be referred to as a moth-eye polymer.

[0027] The moth-eye polymer 21 is made of a polymer material having a refractive index between the refractive index of air and the refractive index of quartz 11 (for example, a polymer material having a refractive index of 1 to 1.5), and is made of a material that is transparent in the wavelength region of 300 nm or more. Such a material can be made of, for example, polymethylpentene, fluorine-based resin, ultraviolet-transmitting acrylic, or polystyrene.

[0028] The moth-eye structure has multiple curved spindle-shaped protrusions, and the shape of these protrusions gradually changes the refractive index of incident light from various angles, resulting in almost no reflection. As a result, the refractive index changes continuously between the air outside the oxidation tank, the moth-eye polymer 21, and the quartz 11, reducing the refractive index difference and reducing surface reflection.

[0029] As shown in FIG. 5, the second anti-reflection structure 30 shown in FIG. 3 is formed by attaching a moth-eye polymer 31 and a low refractive index polymer 32 to the inner surface of the quartz 11 .

[0030] The moth-eye polymer 31 is made of a polymer material having a refractive index within a range between the refractive index of the quartz 11 and the refractive index of the low refractive index polymer 32, and is made of a material that is transparent in the wavelength region of 300 nm or more.

[0031] The low refractive index polymer 32 is made of a polymer material having a refractive index within the range between the refractive index of the moth-eye polymer 31 and the refractive index of the aqueous solution 13, and is made of a material that is transparent in the wavelength region of 300 nm or more.

[0032] Note that the moth-eye structure of the moth-eye polymer 31 is not destroyed if the moth-eye polymer 31 is coated with a material having the same refractive index as the aqueous solution 13. Therefore, it is preferable to use a fluorine-based polymer (n≈1.33) as the low-refractive-index polymer 32.

[0033] The moth-eye polymer 31 and the low-refractive-index polymer 32 cause the refractive index to change continuously among the quartz 11-moth-eye polymer 31-low-refractive-index polymer 32-aqueous solution 13 in the oxidation bath, thereby mitigating the refractive index difference and reducing surface reflection.

[0034] Furthermore, the moth-eye polymer 31 and the low-refractive-index polymer 32 have low surface free energy, making them less susceptible to contamination (dirt), and therefore have alkali resistance, which can prevent the glass surface of the quartz 11 from being dissolved and etched by the aqueous solution 13, thereby preventing a decrease in the transparency of the quartz 11.

[0035] 6 is a diagram showing a method for producing a moth-eye polymer by thermal nanoimprinting. A thermoplastic resin polymer film is formed on quartz (step S101). Next, the polymer is heated, and a moth-eye structure template is pressed against the polymer surface (step S102). Finally, the polymer is cooled, and the template is removed from the polymer (step S103). This produces moth-eye polymers 21 and 31 with a moth-eye structure on their surfaces.

[0036] 7 is a diagram showing a method for producing a moth-eye polymer using photo-nanoimprinting. A film of a photocurable resin monomer is formed on quartz (step S201). Next, a moth-eye structure template is pressed against the surface of the monomer (step S202). Finally, ultraviolet light is irradiated onto the monomer, and the template is removed from the polymer that has been transformed by the ultraviolet light irradiation (step S203). This produces moth-eye polymers 21 and 31 with a moth-eye structure on their surfaces.

[0037] 8 is a diagram showing the results of measuring light transmittance. By providing an anti-reflection structure with a moth-eye structure on one side of the quartz 11, the light transmittance was improved compared to when there was no anti-reflection structure. This shows that providing an anti-reflection structure on only one side of the quartz 11 is effective. Furthermore, by providing an anti-reflection structure on both sides of the quartz 11, the light transmittance was improved more than when there was an anti-reflection structure on only one side of the quartz 11. This shows that providing an anti-reflection structure on both sides of the quartz 11 is more effective.

[0038] 9 is a diagram showing the measurement results of the amount of hydrogen produced in the reduction tank 12. By providing an anti-reflection structure with a moth-eye structure on one side of the quartz 11, the amount of hydrogen produced increased. This shows that the efficiency of carbon dioxide reduction was improved. By providing an anti-reflection structure on both sides of the quartz 11, the amount of hydrogen produced increased even more. This shows that the efficiency of carbon dioxide reduction was improved even more.

[0039] Example 2 In Example 2, a case where one or more layers of inorganic materials having a refractive index within a predetermined range are used will be described.

[0040] 10, a single layer film 22 is attached to the outer surface of the quartz 11 as the first antireflection structure 20 shown in Fig. 3. A single layer film 33 is attached to the inner surface of the quartz 11 as the second antireflection structure 30 shown in Fig. 3.

[0041] The single layer film 22 is made of an inorganic material (for example, a polymer material having a refractive index of 1 to 1.5) that has a refractive index between the refractive index of air and the refractive index of the quartz 11, and is made of a material that is transparent in the wavelength region of 300 nm or more. ２ is.

[0042] As a result, the refractive index changes continuously between the air outside the oxidation chamber, the single layer film 22, and the quartz 11, so that the difference in refractive index is alleviated and the surface reflection is reduced.

[0043] The single layer film 33 is made of an inorganic material having a refractive index between the refractive index of the quartz 11 and the refractive index of the aqueous solution 13, and is transparent in the wavelength region of 300 nm or more. For example, the single layer film 33 is made of MgF ２ is.

[0044] As a result, the refractive index changes continuously between the quartz 11, the single layer film 33 and the aqueous solution 13 in the oxidation bath, so that the difference in refractive index is alleviated and the surface reflection is reduced.

[0045] Furthermore, since the inner surface of the quartz 11 is coated with the inorganic single layer film 33, the quartz 11 is provided with alkali resistance. This makes it possible to suppress dissolution and etching of the glass surface of the quartz 11 by the aqueous solution 13, and prevents a decrease in the transparency of the quartz 11.

[0046] 11 is a diagram showing the measurement results of the light transmittance. ２ By providing a single-layer anti-reflection structure, the light transmittance was improved compared to when there was no anti-reflection structure. This shows that there is an effect even when an anti-reflection structure is provided on only one side of the quartz 11. Furthermore, by providing anti-reflection structures on both sides of the quartz 11, the light transmittance was improved more than when there was an anti-reflection structure on only one side of the quartz 11. This shows that there is a greater effect when an anti-reflection structure is provided on both sides of the quartz 11.

[0047] 12 is a diagram showing the measurement results of the amount of hydrogen generated in the reduction chamber 12. ２ By providing a single-layer anti-reflection structure, the amount of hydrogen produced increased, which indicates that the efficiency of carbon dioxide reduction was improved. By providing anti-reflection structures on both sides of the quartz 11, the amount of hydrogen produced increased further, which indicates that the efficiency of carbon dioxide reduction was improved further.

[0048] 13, a laminated film 23 is attached to the outer surface of the quartz 11 as the first antireflection structure 20 shown in FIG. 3. A laminated film 34 is attached to the inner surface of the quartz 11 as the second antireflection structure 30 shown in FIG.

[0049] The laminated film 23 is composed of a single layer film 23a made of an inorganic material having a refractive index in the range between the refractive index of air and the refractive index of the single layer film 23b, and a single layer film 23b made of an inorganic material having a refractive index in the range between the refractive index of the single layer film 23a and the refractive index of the quartz 11. The laminated film 23 is made of a material that is transparent in the wavelength range of 300 nm or more. For example, the laminated film 23 is made of MgF ２ and ZrO ２ is.

[0050] As a result, the refractive index changes more continuously between the air outside the oxidation chamber, the laminated film 23 and the quartz 11 than in Example 2, so the refractive index difference is further alleviated and the surface reflection is further reduced.

[0051] The laminated film 34 is composed of a single layer film 34a made of an inorganic material having a refractive index in the range between the refractive index of the quartz 11 and the refractive index of the single layer film 34b, and a single layer film 34b made of an inorganic material having a refractive index in the range between the refractive index of the single layer film 34a and the refractive index of the aqueous solution 13. The laminated film 34 is made of an inorganic material that is transparent in the wavelength range of 300 nm or more. For example, the laminated film 34 is made of MgF ２ and ZrO ２ is.

[0052] As a result, the refractive index changes more continuously between the quartz 11, the laminated film 34, and the aqueous solution 13 in the oxidation bath than in Example 2, so the refractive index difference is further alleviated and the surface reflection is further reduced.

[0053] Furthermore, since the inner surface of the quartz 11 is coated with the inorganic material laminated film 34, the quartz 11 is provided with alkali resistance. This makes it possible to suppress dissolution and etching of the glass surface of the quartz 11 by the aqueous solution 13, and prevents a decrease in the transparency of the quartz 11.

[0054] Example 4 In Example 3, a laminated film formed by stacking two single layer films was described, but a laminated film formed by stacking three or more single layer films may also be used. Two single layer films with different refractive indices may be alternately stacked, or three or more single layer films with different refractive indices may be stacked.

[0055] (Example 5) Example 2 may be combined with Examples 3 and 4. For example, a single layer film is attached to the outer surface of the quartz 11, and a multilayer film is attached to the inner surface of the quartz 11.

[0056] Example 6 Example 1 may be combined with Examples 2 to 4. For example, a moth-eye polymer is attached to the outer surface of the quartz 11, and a monolayer film is attached to the inner surface of the quartz 11.

[0057] As described above, according to this embodiment, the light-transmitting window 18 of the oxidation basin 11 is provided with an anti-reflection structure (a moth-eye structure, a layer having a refractive index within the above-mentioned range), thereby improving the light transmittance through the light-transmitting window 18 and improving the efficiency of water oxidation in the oxidation basin.

[0058] Furthermore, according to this embodiment, the anti-reflection structure provided on the light-transmitting window 18 of the oxidation tank 11 is made of organic and inorganic materials, so that the dissolution and etching of the glass surface of the quartz 11 by the aqueous solution 13 in the oxidation tank can be suppressed.

[0059] REFERENCE SIGNS LIST 1 Carbon dioxide reduction reaction device 11 Oxidation tank (quartz) 12 Reduction tank 13 Aqueous solution 14 Oxidation electrode 15 Electrolyte film 16 Reduction electrode 17 Conductor 18 Light-transmitting window 20 First anti-reflection structure 21 Moth-eye polymer 22 Single layer film 23 Laminated film 23a, 23b Single layer film 30 Second anti-reflection structure 31 Moth-eye polymer 32 Low refractive index polymer 33 Single layer film 34 Laminated film 34a, 34b Single layer film

Claims

1. A carbon dioxide reduction reaction device comprising: an oxidation vessel into which an aqueous solution is flowed; a reduction vessel into which carbon dioxide is flowed; an oxidation electrode inserted into the aqueous solution in the oxidation vessel and irradiated with light from outside the oxidation vessel; an electrolyte membrane disposed between the oxidation vessel and the reduction vessel; and a reduction electrode joined to the reduction vessel side of the electrolyte membrane and connected to the oxidation electrode by a lead, wherein the oxidation vessel has an anti-reflection structure in a portion through which the light passes.

2. A carbon dioxide reduction reaction apparatus as described in claim 1, wherein the anti-reflection structure is provided on the outer surface of the oxidation tank and has a moth-eye structure.

3. A carbon dioxide reduction reaction device as described in claim 2, wherein the moth-eye structure is made of a material having a refractive index within the range between the refractive index of air and the refractive index of the oxidation tank, and is made of a material that is transparent in the wavelength region of 300 nm or more.

4. A carbon dioxide reduction reaction device as described in claim 1, wherein the anti-reflection structure is provided on the inner surface of the oxidation tank and is made of an organic material having a moth-eye structure and a specified organic material.

5. A carbon dioxide reduction reaction device as described in claim 4, wherein the organic material of the moth-eye structure is composed of a material having a refractive index within a range between the refractive index of the oxidation tank and the refractive index of the specified organic material, and is composed of a material that is transparent in the wavelength region of 300 nm or more.

6. A carbon dioxide reduction reaction device as described in claim 4, wherein the predetermined organic material is composed of a material having a refractive index within a range between the refractive index of the organic material of the moth-eye structure and the refractive index of the aqueous solution, and is composed of a material that is transparent in the wavelength region of 300 nm or more.

7. A carbon dioxide reduction reaction device as described in claim 1, wherein the anti-reflection structure is a single layer film provided on the outer surface of the oxidation tank and made of a material having a refractive index within the range between the refractive index of air and the refractive index of the oxidation tank, or a laminated film made of the material and having multiple layers with different refractive indices.

8. A carbon dioxide reduction reaction device as described in claim 1, wherein the anti-reflection structure is a single layer film provided on the inner surface of the oxidation tank and made of an inorganic material having a refractive index within a range between the refractive index of the oxidation tank and the refractive index of the aqueous solution, or a laminated film made of the inorganic material and having multiple layers with different refractive indexes.

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