Electrolyte Membrane and Manufacturing Method of Electrolyte Membrane

Abstract

An electrolyte film that is disposed between an electrolytic solution in an oxidation tank and a reduction electrode in a reduction tank to be in contact with both the electrolytic solution and the reduction electrode and is used in a carbon dioxide reduction device that performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode, the electrolyte film including: a water-repellent film on a part of a surface which is in contact with the reduction electrode.

Description

TECHNICAL FIELD

[0001] The present invention relates to an electrolyte film and an electrolyte film manufacturing method.BACKGROUND ART

[0002] An increase in the concentration of carbon dioxide in the atmosphere is mentioned as a main cause of global warming. Reduction of carbon dioxide emissions has become a long-term challenge on a global scale. Meanwhile, energy supply relying on fossil fuels is to be reviewed in the medium and long term as an energy problem, and creation of a next-generation energy supply source is awaited.

[0003] As a means of suppressing emission of carbon dioxide and obtaining energy, technologies have been developed for utilizing unused energy such as exhaust heat, snow and ice heat, vibration, and electromagnetic waves, and renewable energy such as sunlight. These power generation technologies enable only creation of electrical energy, and storage of energy is impossible with these technologies. In addition, creation of chemical products using fossil fuels as raw materials is also impossible.

[0004] As a method of simultaneously solving these problems, a technology of reducing carbon dioxide using light energy has attracted attention. For example, Non Patent Literature 1 discloses a carbon dioxide reduction device by light t irradiation. In an oxidation tank, when an oxidation electrode is irradiated with light, electron-hole pairs are generated and separated at the oxidation electrode, and oxygen and protons (H+) are generated by the oxidation reaction of water in an electrolytic solution. The protons pass through the electrolyte film and reach a reduction tank, and the electrons flow to a reduction electrode through a conductive wire. In the reduction tank, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide dissolved in the solution is caused at the reduction electrode in the solution. This reduction reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.

[0005] In the carbon dioxide reduction device of Non Patent Literature 1, the reduction electrode is immersed in the solution, and carbon dioxide is dissolved in the solution to supply the carbon dioxide to the reduction electrode. However, in this method for reducing carbon dioxide, since the reduction electrode is immersed in the solution, there are limitations on the concentration of carbon dioxide dissolved in the solution and the diffusion coefficient of carbon dioxide in the solution, and the amount of carbon dioxide supplied to the reduction electrode is limited.

[0006] Therefore, in order to increase the amount of carbon dioxide supplied to the reduction electrode, studies have been conducted to eliminate the solution in the reduction tank and directly supply carbon dioxide to the reduction electrode. In Non Patent Literature 2, by using a reduction tank having a structure in which carbon dioxide in a gas phase is directly supplied to a reduction electrode, the amount of carbon dioxide supplied to the reduction electrode is increased, and carbon dioxide reduction reaction is promoted.CITATION LISTNon Patent LiteratureNon Patent Literature 1: Satoshi Yotsuhashi, and six others, “CO2 Conversion with Light and Water by GaN Photoelectrode”, Japanese Journal of Applied Physics, 51, 2012, p. 02BP07-1-p. 02BP07-3

[0008] Non Patent Literature 2: Qingxin Jia, and two others, “Direct Gas-phase CO2 reduction for Solar Methane Generation Using a Gas Diffusion Electrode with a BiVO4:Mo and a Cu—In-e Photoanode”, Chem. Lett., 47, Jan. 13, 2018, p. 436-p. 439SUMMARY OF INVENTIONTechnical Problem

[0009] However, when the reduction reaction proceeds, reduction products of carbon dioxide are generated on a reaction surface of the reduction electrode, and not only hydrogen, carbon monoxide, and methane which are gases but also formic acid, methanol, ethanol, and the like which are liquids are generated. In addition, as time elapses, an electrolytic solution in an oxidation tank passes through an electrolyte film and is gradually exuded into the reduction tank. Therefore, the reaction surface (reaction site) of the reduction electrode is covered with these liquids, and the carbon dioxide reduction reaction does not proceed. Consequently, the conventional carbon dioxide reduction device has a problem in that the reduction reaction efficiency of carbon dioxide decreases in several tens of hours.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technology capable of improving the reduction reaction efficiency of carbon dioxide.Solution to Problem

[0011] An electrolyte film according to an aspect of the present invention is an electrolyte film that is disposed between an electrolytic solution in an oxidation tank and a reduction electrode in a reduction tank to be in contact with both the electrolytic solution and the reduction electrode and is used in a carbon dioxide reduction device that performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode, the electrolyte film including: a water-repellent film on a part of a surface which is in contact with the reduction electrode.

[0012] An electrolyte film manufacturing method according to an aspect of the present invention is an electrolyte film manufacturing method for manufacturing the electrolyte film, the electrolyte film manufacturing method performing: a step of heating a water-repellent polymer; a step of pressing the water-repellent polymer against one surface of the electrolyte film; and a step of forming a water-repellent film on a surface of the electrolyte film by sweeping the water-repellent polymer.

[0013] An electrolyte film manufacturing method according to an aspect of the present invention is an electrolyte film manufacturing method for manufacturing the electrolyte film, the electrolyte film manufacturing method performing: a step of attaching a mask having a penetration portion to one surface of the electrolyte film; a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on the one surface of the electrolyte film; and a step of removing the mask from the electrolyte film.

[0014] An electrolyte film manufacturing method according to an aspect of the present invention is an electrolyte film manufacturing method for manufacturing the electrolyte film, the electrolyte film manufacturing method performing: a step of attaching a mask having a penetration portion to one surface of the electrolyte film; a step of applying a dissolved water-repellent agent to the one surface of the electrolyte film; a step of removing a solvent contained in the water-repellent agent from the one surface of the electrolyte film; and a step of removing the mask from the electrolyte film.Advantageous Effects of Invention

[0015] According to the present invention, the reduction reaction efficiency of carbon dioxide can be improved.BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 is a diagram illustrating a configuration example of a carbon dioxide reduction device according to a first embodiment.

[0017] FIG. 2 is a diagram (bottom diagram of FIG. 1) illustrating a configuration example of a reduction electrode and a water-repellent film.

[0018] FIG. 3 is a diagram (right side surface of FIG. 1) illustrating a configuration example of a reduction electrode and a water-repellent film.

[0019] FIG. 4 is a diagram illustrating a first manufacturing method for the water-repellent film.

[0020] FIG. 5 is a diagram illustrating a second manufacturing method for the water-repellent film.

[0021] FIG. 6 is a diagram illustrating a third manufacturing method for the water-repellent film.

[0022] FIG. 7 is a diagram illustrating a measurement result of Faraday efficiency of formic acid according to the first embodiment.

[0023] FIG. 8 is a diagram illustrating a configuration example of a carbon dioxide reduction device according to a second embodiment.

[0024] FIG. 9 is a diagram illustrating a measurement result of Faraday efficiency of formic acid according to the second embodiment.DESCRIPTION OF EMBODIMENTS

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals, and description thereof is omitted.First Embodiment

[0026] FIG. 1 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a first embodiment. As illustrated in FIG. 1, the carbon dioxide reduction device 100 includes an oxidation electrode 1, an oxidation tank 2, an electrolytic solution 3, a reduction electrode 4, a reduction tank 5, an electrolyte film 6, a conductive wire 7, a light source 8, and a water-repellent film 9.

[0027] The oxidation electrode 1 is immersed in the electrolytic solution 3 in the oxidation tank 2. The oxidation electrode 1 is formed by forming a semiconductor on a substrate having a predetermined area. The oxidation electrode 1 is formed, for example, by forming a film of a compound exhibiting photoactivity, redox activity, or the like such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex, on a surface of a sapphire substrate.

[0028] The oxidation tank 2 holds the electrolytic solution 3 in which the oxidation electrode 1 is immersed.

[0029] The electrolytic solution 3 is placed in the oxidation tank 2. Examples of the electrolytic solution 3 include a potassium hydrogen carbonate aqueous solution, a sodium hydrogen carbonate aqueous solution, a potassium chloride aqueous solution, a sodium chloride aqueous solution, a potassium hydroxide aqueous solution, a rubidium hydroxide aqueous solution, and a cesium hydroxide aqueous solution.

[0030] The reduction electrode 4 is disposed in the reduction tank 5. The reduction electrode 4 is formed on a substrate having a predetermined area similarly to the oxidation electrode 1. The reduction electrode 4 is, for example, a porous body of copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, cadmium, or an alloy thereof. Additionally, the reduction electrode 4 may be a compound such as silver oxide, copper oxide, copper(II) oxide, nickel oxide, indium oxide, tin oxide, tungsten oxide, tungsten(VI) oxide, or copper oxide, or a porous metal complex having a metal ion and an anionic ligand.

[0031] The reduction tank 5 has the reduction electrode 4 disposed inside thereof, and holds carbon dioxide in a gas phase supplied from the outside through a pipe.

[0032] The electrolyte film 6 is disposed between the oxidation tank 2 and the reduction tank 5. To be precise, the electrolyte film 6 is disposed between the electrolytic solution 3 and the reduction electrode 4 in contact with the electrolytic solution 3 and the reduction electrode 4. The electrolyte film 6 is, for example, Nafion (registered trademark), FORBLUE, or Aquivion each of which is an electrolyte film having a carbon-fluorine skeleton, or SELEMION or NEOSEPTA that is an electrolyte film having a carbon-hydrogen skeleton.

[0033] The conductive wire 7 physically and electrically connects the oxidation electrode 1 and the reduction electrode 4.

[0034] The light source 8 is disposed close to the oxidation tank 2. The light source 8 is, for example, a light source of sunlight, a xenon lamp, a pseudo sunlight source, a halogen lamp, a mercury lamp, or a combination thereof.

[0035] In FIG. 1, the reduction electrode 4 and the electrolyte film 6 are drawn so as to have a large width in the lateral direction of the paper surface, but the width in the lateral direction of the paper surface may be reduced to have a thin plate shape with a flat surface in the depth direction of the paper surface. By bonding the reduction electrode 4 and the electrolyte film 6 to each other in their planes, the reaction field of the contact surface can be maximized.

[0036] In the carbon dioxide reduction device 100 described above, in the oxidation tank 2, the oxidation reaction of water in the electrolytic solution 3 is performed by irradiation light (light energy) from the light source 8 using the electrolytic solution 3 and the oxidation electrode 1 of the semiconductor immersed in the electrolytic solution 3. In the reduction tank 5, the carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the oxidation electrode 1 via the conductive wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4.

[0037] Specifically, when the light source 8 emits light from the bottom of the oxidation tank 2, electron-hole pairs are generated and separated at the oxidation electrode 1 within the oxidation tank 2 that has received the emitted light, and oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3. The protons pass through the electrolyte film 6 and reach the reduction electrode 4 in the reduction tank 5 from the electrolytic solution 3 in the oxidation tank 2. The electrons flow from the oxidation electrode 1 in the oxidation tank 2 to the reduction electrode 4 in the reduction tank 5 via the conductive wire 7. In the reduction tank 5, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide in a gas phase brought into direct contact with the reduction electrode 4 is caused at the reduction electrode 4. This oxidation-reduction reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.

[0038] At this time, when a strong alkaline aqueous solution, for example, a 1.0 mol / L aqueous solution of sodium hydroxide is used as the electrolytic solution 3 in the oxidation tank 2, the electrolyte film 6 swells, and the electrolytic solution 3 passes through the pores of the electrolyte film 6 and exudes to the surface of the reduction electrode 4 in the reduction tank 5. In order to prevent such exudation of the electrolytic solution 3 from the electrolyte film 6, it is sufficient if a surface of the electrolyte film 6 on the oxidation tank 2 side is subjected to a water-repellent treatment, the surface being in contact with the electrolytic solution 3. However, since it is necessary to move protons as a raw material of the reduction reaction using water in the electrolyte film 6 as a medium, the reduction reaction may not proceed on the reduction tank 5 side when the surface of the electrolyte film 6 on the oxidation tank 2 side is fully covered by the water-repellent treatment.

[0039] Therefore, in the present embodiment, as illustrated in FIGS. 1 and 2, the water-repellent film 9 is disposed on a part of the surface of the electrolyte film 6 on the reduction tank 5 side. Specifically, as enlarged in FIG. 2, the water-repellent film 9 is provided on a part of the surface between the electrolyte film 6 and the reduction electrode 4 so as not to cover the entire surface of the electrolyte film 6. For example, a plurality of water-repellent films 9 is disposed in parallel to be separated from each other on the surface of the electrolyte film 6 on the reduction tank 5 side. As enlarged in FIG. 3, the water-repellent films 9 are parallel to a z direction that is the direction of gravity. Therefore, a droplet of the electrolytic solution 3 or the like does not spread in a y direction but easily falls in the z direction, and the slidability of the droplet has anisotropy.

[0040] By forming such a water-repellent film 9 on the surface of the electrolyte film 6 on the reduction tank 5 side, when the electrolytic solution 3 in the oxidation tank 2 exudes between the electrolyte film 6 and the reduction tank 5, the droplet easily fall, a state in which the droplet does not cover the surface of the electrolyte film 6 can be maintained, and the reaction site of the reduction electrode 4 is not filled with the electrolytic solution 3. In addition, since the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte film 6, a state in which protons can reach between the electrolyte film 6 and the reduction electrode 4 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in the reduction reaction efficiency can be suppressed.

[0041] In addition, in order to maintain the anisotropy of slidability, it is preferable that the structure of the reduction electrode 4 be also parallel to the z direction. For example, as enlarged in FIG. 2, a plurality of reduction electrodes 4 is disposed and formed on the surface of the electrolyte film 6 on the reduction tank 5 side in parallel with the z direction to be separated from each other. The plurality of water-repellent films 9 is disposed between two adjacent reduction electrodes 4 in parallel with the z direction to be separated from each other. The water-repellent film 9 has a rectangular parallelepiped shape, and the longitudinal direction of the water-repellent film 9 coincides with the longitudinal direction of the reduction electrode 4 having a plate shape. Since the reduction electrode 4 also does not cover the entire surface of the electrolyte film 6, a carbon dioxide reduction reaction can be caused.

[0042] Next, a method for manufacturing the water-repellent film 9 will be described.

[0043] Examples of the water-repellent treatment for manufacturing the water-repellent film 9 include a friction transfer method, a gas phase method, and a liquid phase method.

[0044] The friction transfer method is a method of forming an alignment film of a fluorine-based polymer on the surface of the electrolyte film 6 by heating the fluorine-based polymer having a water-repellent surface with small surface energy to around a glass transition temperature to make the fluorine-based polymer flexible, then pressing the fluorine-based polymer against the electrolyte film 6, which is an object, and then sweeping the fluorine-based polymer while maintaining the pressure.

[0045] The gas phase method is a method in which a mask having a penetration portion is attached to the surface of the electrolyte film 6, an object and a fluorine-based low molecular substance (silane coupling agent), which is a water-repellent agent, are put in the same sealed space, the fluorine-based low molecular substance is heated to be evaporated, and then the fluorine-based low molecular substance is deposited on the surface of the object.

[0046] The liquid phase method is a method in which a mask having a penetration portion is attached to the surface of the electrolyte film 6, an object is immersed in a fluorine-based solvent obtained by dissolving a fluorine-based polymer, which is a water-repellent agent, by a dip coating method or the like, and then the fluorine-based polymer is precipitated by performing heating or the like on the object and removing the solvent.

[0047] Another method of the liquid phase method is a method in which a film of the fluorine-based solvent is formed by a cast coating method, a spin coating method, or the like instead of the dip coating step, and then the fluorine-based polymer is precipitated by performing heating or the like on the object and removing the solvent.

[0048] FIG. 4 is a diagram illustrating a first manufacturing method for the water-repellent film 9. The first manufacturing method is a method for manufacturing the water-repellent film 9 by the friction transfer method. Nafion was used for the electrolyte film 6. Polytetrafluoroethylene (PTFE) was used for a water-repellent block.

[0049] First, the water-repellent block is heated to 110° C., which is near the glass transition temperature (first step S101). By making the surface of the water-repellent block flexible, the polymer on the surface of the water-repellent block can be transferred to the electrolyte film. Thereafter, the water-repellent block is pressed against the electrolyte film at a pressure of 0.5 MPa (second step S102), and then the water-repellent block is swept at a speed of 10 mm / min (third step S103). When the water-repellent block can be swept over the entire electrolyte film, the water-repellent block is pulled up (fourth step S104). Through this step, a part of the surface of the electrolyte film can be covered with a water-repellent block material, and a water-repellent film on which droplets easily slide in one direction can be formed.

[0050] FIG. 5 is a diagram illustrating a second manufacturing method for the water-repellent film 9. The second manufacturing method is a method for manufacturing the water-repellent film 9 by the gas phase method. Nafion was used for the electrolyte film 6. As the water-repellent agent, a fluorine-based silane coupling agent (for example, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane) was used.

[0051] First, a mask having a penetration portion is attached to the electrolyte film (first step S201). Next, the electrolyte film and the water-repellent agent (water-repellent low molecular substance) are put in a Teflon container and sealed (second step S202). Next, the Teflon container is put in an oven and heated at 100° C. (third step S203). Through this step, the water-repellent agent evaporates, and a water-repellent film is formed on the surface of the electrolyte film in a portion of the mask having the penetration portion. The water-repellent film is formed on the surface of the mask in a portion not having the penetration portion. Finally, the mask is removed from the electrolyte film (fourth step S204).

[0052] FIG. 6 is a diagram illustrating a third manufacturing method for the water-repellent film 9. The third manufacturing method is a method for manufacturing the water-repellent film 9 by the liquid phase method. Nafion was used for the electrolyte film 6. As the water-repellent agent, OPTOOL DSX (water-repellent polymer) was used.

[0053] First, a mask having a penetration portion is attached to the electrolyte film (first step S301). Next, a water-repellent agent is dropped on the electrolyte film and the surface of the mask using a spin coating method (second step S302). Thereafter, the electrolyte film is left to evaporate the solvent in the water-repellent agent (third step S303). Finally, the mask is removed from the electrolyte film (fourth step S304). Through this step, a water-repellent film is formed on the surface of the electrolyte film in a portion of the mask having the penetration portion.

[0054] Through these steps, the water-repellent film having anisotropy can be formed only on one side of the electrolyte film. In the method of using the gas phase method and the liquid phase method described above, an extremely thin water-repellent film having a thickness on the order of several tens of nanometers can be formed in principle. In addition, since the distance between the water-repellent films depends on the distance of the penetration portion of the mask, the range from the nanometer order to the millimeter order can be controlled by processing.

[0055] On the other hand, in the method by the friction transfer method, in principle, it is possible to form a range from a thickness on the order of several tens of nanometers to a thickness on the order of micrometers. The distance between the water-repellent films can be controlled by preliminarily subjecting the surface of the water-repellent block on the side to be pressed against the electrolyte film to irregularity processing. The width of the water-repellent film and the width between the water-repellent films can be controlled by changing the width of the irregularity.

[0056] Next, electrochemical measurement by the carbon dioxide reduction device 100 described above and a measurement result thereof will be described.

[0057] First, a thin film of gallium nitride (GaN) as an n-type semiconductor and aluminum gallium nitride (AlGaN) were epitaxially grown in this order on a sapphire substrate, and nickel (Ni) was vacuum-deposited thereon and heat treatment was performed, so that a cocatalyst thin film of nickel oxide (NiO) was formed. Then, the cocatalyst thin film was used as the oxidation electrode 1, and the oxidation electrode 1 was immersed in the electrolytic solution 3 of a 1.0 mol / L potassium hydroxide aqueous solution in the oxidation tank 2.

[0058] In addition, as the reduction electrode 4, a copper plate having a vertical width of 2 cm, a horizontal width of 2 cm, and a height of 0.1 mm was used, and penetration portions having a vertical width of 1.7 cm and a horizontal width of 0.1 mm were formed every 0.1 mm in a range of a vertical width of 1.7 cm and a horizontal width of 1.7 cm. The reduction electrode 4 was connected to the oxidation electrode 1 by the conductive wire 7, and the reduction electrode 4 was installed in the reduction tank 5.

[0059] In addition, Nafion was used for the electrolyte film 6 physically separating the oxidation tank 2 and the reduction tank 5. Of both surfaces of the electrolyte film 6, one surface on which the water-repellent film 9 was formed was disposed to be in contact with the reduction electrode 4 in the reduction tank 5, and the other surface was disposed to be in contact with the electrolytic solution 3 in the oxidation tank 2. In order to reduce the contact resistance between the electrolyte film 6 and the reduction electrode 4, for example, a method in which the electrolyte film 6 is heated to near the glass transition temperature so as to be press-bonded may be applied.

[0060] In addition, as the light source 8, a 300 W xenon lamp was used. A wavelength of 450 nm or more was cut with a filter, and the illuminance was set to 6.6 mW / cm2. An irradiation surface of the oxidation electrode 1 was set to 2.5 cm2.

[0061] Then, nitrogen and carbon dioxide were supplied to the oxidation tank 2 and the reduction tank 5 at a flow rate of 5 ml / min and a pressure of 0.5 MPa, respectively. The bubbling of nitrogen into the oxidation tank 2 was carried out for the purpose of analyzing the reaction products. The inside of each of the oxidation tank 2 and the reduction tank 5 was sufficiently replaced with nitrogen and carbon dioxide, respectively, and light was emitted from the light source 8. Thereafter, the carbon dioxide reduction reaction proceeded on the surface of the copper porous body, which is the reduction electrode 4.

[0062] At this time, the current flowing between the oxidation electrode 1 and the reduction electrode 4 by the irradiation light was measured with an electrochemical measurement device (Model 1287 Potentiogalvanostat manufactured by Solartron). In addition, gases and liquids generated in the oxidation tank 2 and the reduction tank 5 were collected, and the reaction products were analyzed using a gas chromatograph, a liquid chromatograph, and a gas chromatograph mass spectrometer.

[0063] In particular, in the present embodiment, an effect of the water-repellent film 9 formed on the surface of the electrolyte film 6 was examined by determining the Faraday efficiency of the carbon dioxide reduction reaction. Note that a method for calculating the Faraday efficiency of the carbon dioxide reduction reaction will be described below.

[0064] In a first example, Nafion was used as the electrolyte film 6, PTFE was used as the water-repellent block, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 was installed so that the direction of the water-repellent film 9 and the direction of gravity were parallel, that is, 0°.

[0065] In a second example, Nafion was used as the electrolyte film 6, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane was used as the water-repellent low molecular substance, the water-repellent film 9 manufactured by the second manufacturing method was used, and the water-repellent film 9 was installed so that the direction of the water-repellent film 9 and the direction of gravity were parallel, that is, 0°.

[0066] In a third example, Nafion was used as the electrolyte film 6, OPTOOL DSX was used as the water-repellent agent, the water-repellent film 9 manufactured by the third manufacturing method was used, and the water-repellent film 9 was installed so that the direction of the water-repellent film 9 and the direction of gravity were parallel, that is, 0°.

[0067] In a first comparative example, Nafion on which the water-repellent film 9 was not formed was used as it was as the electrolyte film 6.

[0068] In a second comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that a long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°.

[0069] In a third comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were perpendicular, that is, 90°.

[0070] FIG. 7 is a diagram showing a measurement result of the Faraday efficiency of formic acid according to the first embodiment. In the first comparative example in which the water-repellent film 9 was not formed, the Faraday efficiency decreased after six hours. On the other hand, in the first example to the third example in which the water-repellent film 9 was formed, the Faraday efficiency did not decrease even after six hours. This is because, as a result of introducing the water-repellent film 9 into the electrolyte film 6, the liquid on the surface of the reduction electrode 4 as a result of liquid leakage easily slides down, and the reaction site of the reduction electrode 4 was not covered with the electrolytic solution 3.

[0071] In addition, in the second comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°, the ease of water sliding was slightly improved, and the reduction rate of decrease in Faraday efficiency after the test time of 6 hours was suppressed. In the third comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 90°, the water was less likely to slide down than in the first comparative example in which the water-repellent film was not formed, and the decrease in Faraday efficiency was deteriorated.

[0072] Here, a method for calculating the Faraday efficiency of the carbon dioxide reduction reaction will be described. The Faraday efficiency of carbon dioxide indicates the ratio of the number of electrons used in the carbon dioxide reduction reaction to the number of electrons moved between the oxidation electrode 1 and the reduction electrode 4 by light irradiation or application of a current voltage, and can be calculated by Formula (1).Faraday⁢ efficiency={number⁢ of⁢ electrons⁢ in⁢ reduction⁢ reaction} / {number⁢ of⁢ electrons⁢ moved⁢ between⁢ electrodes}(1)

[0073] The “number of electrons in reduction reaction” in Formula (1) is determined by converting the measured value of the integrated amount of the generated carbon dioxide reduction product into the number of electrons required for the production reaction. For example, the “number of electrons in reduction reaction” when the reduction product is a gas can be calculated by Formula (2).Number⁢ of⁢ electrons⁢ in⁢ each⁢ reduction⁢ reaction⁢ (C)={A×B×Z×F×T×10-6)} / Vg(2)

[0074] A is a concentration (ppm) of the reduction reaction product. B is a flow rate (L / sec) of the carrier gas. Z is the number of electrons required for the reduction reaction. F is the Faraday constant (C / mol). T is a light irradiation time or a current voltage application time (sec). Vg is a molar volume of the gas (L / mol).

[0075] The “number of electrons in reduction reaction” when the reduction product is a liquid can be calculated by Formula (3).Number⁢ of⁢ electrons⁢ in⁢ each⁢ reduction⁢ reaction⁢ (C)=C×V1×Z×F(3)

[0076] C is a concentration (mol / L) of the reduction reaction product. V1 is a volume (L) of the liquid sample. Z is the number of electrons required for the reduction reaction. F is the Faraday constant (C / mol).

[0077] The first embodiment has been described above. With the carbon dioxide reduction device 100 according to the first embodiment, it is possible to provide the carbon dioxide reduction device 100 capable of allowing the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.

[0078] That is, in the first embodiment, in the carbon dioxide reduction device 100 including the oxidation tank 2 that performs the oxidation reaction of water by irradiation light from the light source 8 by using the electrolytic solution 3 and the oxidation electrode 1 of a semiconductor immersed in the electrolytic solution 3, the reduction tank 5 that performs the carbon dioxide reduction reaction by using the reduction electrode 4 connected to the oxidation electrode 1 via the conductive wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4, and the electrolyte film 6 disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution 3 and the reduction electrode 4, the electrolyte film 6 includes the water-repellent film 9 on a part of the surface which is in contact with the reduction electrode 4.

[0079] Therefore, the water-repellent anisotropy of the water-repellent film 9 provided on the surface of the electrolyte film 6 causes the liquid on the surface of the reduction electrode 4, which is a result of exudation of the electrolytic solution 3 in the oxidation tank 2 to the outside of the electrolyte film 6, easily slides down, and the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3. In addition, since the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte film 6, a state in which protons can reach between the electrolyte film 6 and the reduction electrode 4 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in the reduction reaction efficiency can be suppressed.

[0080] Note that, in the above experiment, light is generated by a xenon lamp in order to quantitatively manage the emission amount of light with respect to the oxidation electrode 1, but it is also possible to cause an oxidation reaction using sunlight or the like.Second Embodiment

[0081] In the first embodiment, the case where the light source 8 and the oxidation electrode 1 including a semiconductor are used has been described. In the second embodiment, instead of these, an oxidation / reduction reaction is allowed to proceed using an external power supply and the oxidation electrode 1 including a metal. For comparison, the same voltage value and current value as those in the first embodiment were adjusted and applied.

[0082] FIG. 8 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a second embodiment. The oxidation electrode 1 is platinum. Additionally, the oxidation electrode 1 may be, for example, gold or silver. An external power supply 10 is an electrochemical measurement device, and is connected in series to a conductive wire 7 connecting the oxidation electrode 1 and a reduction electrode 4. The power supply 10 may be another power supply device. Other components are the same as those of the first embodiment.

[0083] In the carbon dioxide reduction device 100 according to the present embodiment, in an oxidation tank 2, the oxidation reaction of water in an electrolytic solution 3 is performed by a current voltage (electrical energy) from the power supply 10 using the electrolytic solution 3 and the oxidation electrode 1 of platinum (metal) immersed in the electrolytic solution 3. In a reduction tank 5, the carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the power supply 10 (source of electrical energy) and carbon dioxide brought into direct contact with the reduction electrode 4.

[0084] Specifically, when the power supply 10 applies a current voltage to the conductive wire 7, oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3. The protons pass through the electrolyte film 6 and reach the reduction electrode 4 in the reduction tank 5 from the electrolytic solution 3 in the oxidation tank 2. The electrons flow from the power supply 10 to the reduction electrode 4 in the reduction tank 5 via the conductive wire 7. In the reduction tank 5, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide in a gas phase brought into direct contact with the reduction electrode 4 is caused at the reduction electrode 4.

[0085] Also in the second embodiment, similarly to the first embodiment, a water-repellent film 9 is provided on a part of the surface of the electrolyte film 6 on the reduction tank 5 side so as not to cover the entire surface of the electrolyte film 6. As a method for manufacturing the water-repellent film 9, the first manufacturing method to the third manufacturing method are used similarly to the first embodiment.

[0086] FIG. 9 is a diagram showing a measurement result of the Faraday efficiency of formic acid according to the second embodiment. Examples using the same electrolyte film 6 as in the first example to the third example described in the first embodiment are referred to as a fourth example to a sixth example, respectively. In a fourth comparative example, Nafion on which the water-repellent film 9 was not formed was used as it was as the electrolyte film 6. In a fifth comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that a long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°. In a sixth comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were perpendicular, that is, 90°.

[0087] In the fourth comparative example in which the water-repellent film 9 was not formed, the Faraday efficiency decreased after six hours. On the other hand, in the fourth example to the sixth example in which the water-repellent film 9 was formed, the Faraday efficiency did not decrease even after six hours. This is because, as a result of introducing the water-repellent film 9 into the electrolyte film 6, the liquid on the surface of the reduction electrode 4 as a result of liquid leakage easily slides down, and the reaction site of the reduction electrode 4 was not covered with the electrolytic solution 3.

[0088] In addition, in the fifth comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°, the ease of water sliding was slightly improved, and the reduction rate of decrease in Faraday efficiency after the test time of 6 hours was suppressed. In the sixth comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 90°, the water was less likely to slide down than in the first comparative example in which the water-repellent film was not formed, and the decrease in Faraday efficiency was deteriorated.

[0089] The second embodiment has been described above. With the carbon dioxide reduction device 100 according to the second embodiment, it is possible to provide the carbon dioxide reduction device 100 capable of allowing the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.

[0090] That is, in the second embodiment, in the carbon dioxide reduction device 100 including the oxidation tank 2 that performs the oxidation reaction of water by the current voltage from the power supply 10 by using the electrolytic solution 3 and the oxidation electrode 1 of platinum (metal) immersed in the electrolytic solution 3, the reduction tank 5 that performs the carbon dioxide reduction reaction by using the reduction electrode 4 connected to the power supply 10 and carbon dioxide brought into direct contact with the reduction electrode 4, and the electrolyte film 6 disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution 3 and the reduction electrode 4, the electrolyte film 6 includes the water-repellent film 9 on a part of the surface which is in contact with the reduction electrode 4.

[0091] Therefore, the water-repellent anisotropy of the water-repellent film 9 provided on the surface of the electrolyte film 6 causes the liquid on the surface of the reduction electrode 4, which is a result of exudation of the electrolytic solution 3 in the oxidation tank 2 to the outside of the electrolyte film 6, easily slides down, and the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3. In addition, since the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte film 6, a state in which protons can reach between the electrolyte film 6 and the reduction electrode 4 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in the reduction reaction efficiency can be suppressed.Others

[0092] The present invention can be widely used in the field related to the recycling of carbon dioxide. Although light energy is used in the first embodiment and electrical energy is used in the second embodiment, other renewable energy may be used. In addition, the first embodiment and the second embodiment can be combined.

[0093] The present invention can be also applied to any electrolyte film as long as it is the electrolyte film 6 that is disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 in contact with the electrolytic solution 3 and the reduction electrode 4 and is used in the carbon dioxide reduction device 100 that performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode 4.REFERENCE SIGNS LIST1 Oxidation electrode

[0095] 2 Oxidation tank

[0096] 3 Electrolytic solution

[0097] 4 Reduction electrode

[0098] 5 Reduction tank

[0099] 6 Electrolyte film

[0100] 7 Conductive wire

[0101] 8 Light source

[0102] 9 Water-repellent film

[0103] 10 Power supply

[0104] 100 Carbon dioxide reduction device

Examples

first embodiment

[0026]FIG. 1 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a first embodiment. As illustrated in FIG. 1, the carbon dioxide reduction device 100 includes an oxidation electrode 1, an oxidation tank 2, an electrolytic solution 3, a reduction electrode 4, a reduction tank 5, an electrolyte film 6, a conductive wire 7, a light source 8, and a water-repellent film 9.

[0027]The oxidation electrode 1 is immersed in the electrolytic solution 3 in the oxidation tank 2. The oxidation electrode 1 is formed by forming a semiconductor on a substrate having a predetermined area. The oxidation electrode 1 is formed, for example, by forming a film of a compound exhibiting photoactivity, redox activity, or the like such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex, on a surface of a sapphire substrate.

[0028]The oxidation tank 2 holds the electrolytic solution 3 in which the oxidation...

second embodiment

[0081]In the first embodiment, the case where the light source 8 and the oxidation electrode 1 including a semiconductor are used has been described. In the second embodiment, instead of these, an oxidation / reduction reaction is allowed to proceed using an external power supply and the oxidation electrode 1 including a metal. For comparison, the same voltage value and current value as those in the first embodiment were adjusted and applied.

[0082]FIG. 8 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a second embodiment. The oxidation electrode 1 is platinum. Additionally, the oxidation electrode 1 may be, for example, gold or silver. An external power supply 10 is an electrochemical measurement device, and is connected in series to a conductive wire 7 connecting the oxidation electrode 1 and a reduction electrode 4. The power supply 10 may be another power supply device. Other components are the same as those of the first embod...

TECHNICAL FIELD

[0001] The present invention relates to an electrolyte film and an electrolyte film manufacturing method.BACKGROUND ART

[0002] An increase in the concentration of carbon dioxide in the atmosphere is mentioned as a main cause of global warming. Reduction of carbon dioxide emissions has become a long-term challenge on a global scale. Meanwhile, energy supply relying on fossil fuels is to be reviewed in the medium and long term as an energy problem, and creation of a next-generation energy supply source is awaited.

[0003] As a means of suppressing emission of carbon dioxide and obtaining energy, technologies have been developed for utilizing unused energy such as exhaust heat, snow and ice heat, vibration, and electromagnetic waves, and renewable energy such as sunlight. These power generation technologies enable only creation of electrical energy, and storage of energy is impossible with these technologies. In addition, creation of chemical products using fossil fuels as raw materials is also impossible.

[0004] As a method of simultaneously solving these problems, a technology of reducing carbon dioxide using light energy has attracted attention. For example, Non Patent Literature 1 discloses a carbon dioxide reduction device by light t irradiation. In an oxidation tank, when an oxidation electrode is irradiated with light, electron-hole pairs are generated and separated at the oxidation electrode, and oxygen and protons (H+) are generated by the oxidation reaction of water in an electrolytic solution. The protons pass through the electrolyte film and reach a reduction tank, and the electrons flow to a reduction electrode through a conductive wire. In the reduction tank, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide dissolved in the solution is caused at the reduction electrode in the solution. This reduction reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.

[0005] In the carbon dioxide reduction device of Non Patent Literature 1, the reduction electrode is immersed in the solution, and carbon dioxide is dissolved in the solution to supply the carbon dioxide to the reduction electrode. However, in this method for reducing carbon dioxide, since the reduction electrode is immersed in the solution, there are limitations on the concentration of carbon dioxide dissolved in the solution and the diffusion coefficient of carbon dioxide in the solution, and the amount of carbon dioxide supplied to the reduction electrode is limited.

[0006] Therefore, in order to increase the amount of carbon dioxide supplied to the reduction electrode, studies have been conducted to eliminate the solution in the reduction tank and directly supply carbon dioxide to the reduction electrode. In Non Patent Literature 2, by using a reduction tank having a structure in which carbon dioxide in a gas phase is directly supplied to a reduction electrode, the amount of carbon dioxide supplied to the reduction electrode is increased, and carbon dioxide reduction reaction is promoted.CITATION LISTNon Patent LiteratureNon Patent Literature 1: Satoshi Yotsuhashi, and six others, “CO2 Conversion with Light and Water by GaN Photoelectrode”, Japanese Journal of Applied Physics, 51, 2012, p. 02BP07-1-p. 02BP07-3

[0008] Non Patent Literature 2: Qingxin Jia, and two others, “Direct Gas-phase CO2 reduction for Solar Methane Generation Using a Gas Diffusion Electrode with a BiVO4:Mo and a Cu—In-e Photoanode”, Chem. Lett., 47, Jan. 13, 2018, p. 436-p. 439SUMMARY OF INVENTIONTechnical Problem

[0009] However, when the reduction reaction proceeds, reduction products of carbon dioxide are generated on a reaction surface of the reduction electrode, and not only hydrogen, carbon monoxide, and methane which are gases but also formic acid, methanol, ethanol, and the like which are liquids are generated. In addition, as time elapses, an electrolytic solution in an oxidation tank passes through an electrolyte film and is gradually exuded into the reduction tank. Therefore, the reaction surface (reaction site) of the reduction electrode is covered with these liquids, and the carbon dioxide reduction reaction does not proceed. Consequently, the conventional carbon dioxide reduction device has a problem in that the reduction reaction efficiency of carbon dioxide decreases in several tens of hours.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technology capable of improving the reduction reaction efficiency of carbon dioxide.Solution to Problem

[0011] An electrolyte film according to an aspect of the present invention is an electrolyte film that is disposed between an electrolytic solution in an oxidation tank and a reduction electrode in a reduction tank to be in contact with both the electrolytic solution and the reduction electrode and is used in a carbon dioxide reduction device that performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode, the electrolyte film including: a water-repellent film on a part of a surface which is in contact with the reduction electrode.

[0012] An electrolyte film manufacturing method according to an aspect of the present invention is an electrolyte film manufacturing method for manufacturing the electrolyte film, the electrolyte film manufacturing method performing: a step of heating a water-repellent polymer; a step of pressing the water-repellent polymer against one surface of the electrolyte film; and a step of forming a water-repellent film on a surface of the electrolyte film by sweeping the water-repellent polymer.

[0013] An electrolyte film manufacturing method according to an aspect of the present invention is an electrolyte film manufacturing method for manufacturing the electrolyte film, the electrolyte film manufacturing method performing: a step of attaching a mask having a penetration portion to one surface of the electrolyte film; a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on the one surface of the electrolyte film; and a step of removing the mask from the electrolyte film.

[0014] An electrolyte film manufacturing method according to an aspect of the present invention is an electrolyte film manufacturing method for manufacturing the electrolyte film, the electrolyte film manufacturing method performing: a step of attaching a mask having a penetration portion to one surface of the electrolyte film; a step of applying a dissolved water-repellent agent to the one surface of the electrolyte film; a step of removing a solvent contained in the water-repellent agent from the one surface of the electrolyte film; and a step of removing the mask from the electrolyte film.Advantageous Effects of Invention

[0015] According to the present invention, the reduction reaction efficiency of carbon dioxide can be improved.BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 is a diagram illustrating a configuration example of a carbon dioxide reduction device according to a first embodiment.

[0017] FIG. 2 is a diagram (bottom diagram of FIG. 1) illustrating a configuration example of a reduction electrode and a water-repellent film.

[0018] FIG. 3 is a diagram (right side surface of FIG. 1) illustrating a configuration example of a reduction electrode and a water-repellent film.

[0019] FIG. 4 is a diagram illustrating a first manufacturing method for the water-repellent film.

[0020] FIG. 5 is a diagram illustrating a second manufacturing method for the water-repellent film.

[0021] FIG. 6 is a diagram illustrating a third manufacturing method for the water-repellent film.

[0022] FIG. 7 is a diagram illustrating a measurement result of Faraday efficiency of formic acid according to the first embodiment.

[0023] FIG. 8 is a diagram illustrating a configuration example of a carbon dioxide reduction device according to a second embodiment.

[0024] FIG. 9 is a diagram illustrating a measurement result of Faraday efficiency of formic acid according to the second embodiment.DESCRIPTION OF EMBODIMENTS

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals, and description thereof is omitted.First Embodiment

[0026] FIG. 1 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a first embodiment. As illustrated in FIG. 1, the carbon dioxide reduction device 100 includes an oxidation electrode 1, an oxidation tank 2, an electrolytic solution 3, a reduction electrode 4, a reduction tank 5, an electrolyte film 6, a conductive wire 7, a light source 8, and a water-repellent film 9.

[0027] The oxidation electrode 1 is immersed in the electrolytic solution 3 in the oxidation tank 2. The oxidation electrode 1 is formed by forming a semiconductor on a substrate having a predetermined area. The oxidation electrode 1 is formed, for example, by forming a film of a compound exhibiting photoactivity, redox activity, or the like such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex, on a surface of a sapphire substrate.

[0028] The oxidation tank 2 holds the electrolytic solution 3 in which the oxidation electrode 1 is immersed.

[0029] The electrolytic solution 3 is placed in the oxidation tank 2. Examples of the electrolytic solution 3 include a potassium hydrogen carbonate aqueous solution, a sodium hydrogen carbonate aqueous solution, a potassium chloride aqueous solution, a sodium chloride aqueous solution, a potassium hydroxide aqueous solution, a rubidium hydroxide aqueous solution, and a cesium hydroxide aqueous solution.

[0030] The reduction electrode 4 is disposed in the reduction tank 5. The reduction electrode 4 is formed on a substrate having a predetermined area similarly to the oxidation electrode 1. The reduction electrode 4 is, for example, a porous body of copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, cadmium, or an alloy thereof. Additionally, the reduction electrode 4 may be a compound such as silver oxide, copper oxide, copper(II) oxide, nickel oxide, indium oxide, tin oxide, tungsten oxide, tungsten(VI) oxide, or copper oxide, or a porous metal complex having a metal ion and an anionic ligand.

[0031] The reduction tank 5 has the reduction electrode 4 disposed inside thereof, and holds carbon dioxide in a gas phase supplied from the outside through a pipe.

[0032] The electrolyte film 6 is disposed between the oxidation tank 2 and the reduction tank 5. To be precise, the electrolyte film 6 is disposed between the electrolytic solution 3 and the reduction electrode 4 in contact with the electrolytic solution 3 and the reduction electrode 4. The electrolyte film 6 is, for example, Nafion (registered trademark), FORBLUE, or Aquivion each of which is an electrolyte film having a carbon-fluorine skeleton, or SELEMION or NEOSEPTA that is an electrolyte film having a carbon-hydrogen skeleton.

[0033] The conductive wire 7 physically and electrically connects the oxidation electrode 1 and the reduction electrode 4.

[0034] The light source 8 is disposed close to the oxidation tank 2. The light source 8 is, for example, a light source of sunlight, a xenon lamp, a pseudo sunlight source, a halogen lamp, a mercury lamp, or a combination thereof.

[0035] In FIG. 1, the reduction electrode 4 and the electrolyte film 6 are drawn so as to have a large width in the lateral direction of the paper surface, but the width in the lateral direction of the paper surface may be reduced to have a thin plate shape with a flat surface in the depth direction of the paper surface. By bonding the reduction electrode 4 and the electrolyte film 6 to each other in their planes, the reaction field of the contact surface can be maximized.

[0036] In the carbon dioxide reduction device 100 described above, in the oxidation tank 2, the oxidation reaction of water in the electrolytic solution 3 is performed by irradiation light (light energy) from the light source 8 using the electrolytic solution 3 and the oxidation electrode 1 of the semiconductor immersed in the electrolytic solution 3. In the reduction tank 5, the carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the oxidation electrode 1 via the conductive wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4.

[0037] Specifically, when the light source 8 emits light from the bottom of the oxidation tank 2, electron-hole pairs are generated and separated at the oxidation electrode 1 within the oxidation tank 2 that has received the emitted light, and oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3. The protons pass through the electrolyte film 6 and reach the reduction electrode 4 in the reduction tank 5 from the electrolytic solution 3 in the oxidation tank 2. The electrons flow from the oxidation electrode 1 in the oxidation tank 2 to the reduction electrode 4 in the reduction tank 5 via the conductive wire 7. In the reduction tank 5, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide in a gas phase brought into direct contact with the reduction electrode 4 is caused at the reduction electrode 4. This oxidation-reduction reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.

[0038] At this time, when a strong alkaline aqueous solution, for example, a 1.0 mol / L aqueous solution of sodium hydroxide is used as the electrolytic solution 3 in the oxidation tank 2, the electrolyte film 6 swells, and the electrolytic solution 3 passes through the pores of the electrolyte film 6 and exudes to the surface of the reduction electrode 4 in the reduction tank 5. In order to prevent such exudation of the electrolytic solution 3 from the electrolyte film 6, it is sufficient if a surface of the electrolyte film 6 on the oxidation tank 2 side is subjected to a water-repellent treatment, the surface being in contact with the electrolytic solution 3. However, since it is necessary to move protons as a raw material of the reduction reaction using water in the electrolyte film 6 as a medium, the reduction reaction may not proceed on the reduction tank 5 side when the surface of the electrolyte film 6 on the oxidation tank 2 side is fully covered by the water-repellent treatment.

[0039] Therefore, in the present embodiment, as illustrated in FIGS. 1 and 2, the water-repellent film 9 is disposed on a part of the surface of the electrolyte film 6 on the reduction tank 5 side. Specifically, as enlarged in FIG. 2, the water-repellent film 9 is provided on a part of the surface between the electrolyte film 6 and the reduction electrode 4 so as not to cover the entire surface of the electrolyte film 6. For example, a plurality of water-repellent films 9 is disposed in parallel to be separated from each other on the surface of the electrolyte film 6 on the reduction tank 5 side. As enlarged in FIG. 3, the water-repellent films 9 are parallel to a z direction that is the direction of gravity. Therefore, a droplet of the electrolytic solution 3 or the like does not spread in a y direction but easily falls in the z direction, and the slidability of the droplet has anisotropy.

[0040] By forming such a water-repellent film 9 on the surface of the electrolyte film 6 on the reduction tank 5 side, when the electrolytic solution 3 in the oxidation tank 2 exudes between the electrolyte film 6 and the reduction tank 5, the droplet easily fall, a state in which the droplet does not cover the surface of the electrolyte film 6 can be maintained, and the reaction site of the reduction electrode 4 is not filled with the electrolytic solution 3. In addition, since the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte film 6, a state in which protons can reach between the electrolyte film 6 and the reduction electrode 4 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in the reduction reaction efficiency can be suppressed.

[0041] In addition, in order to maintain the anisotropy of slidability, it is preferable that the structure of the reduction electrode 4 be also parallel to the z direction. For example, as enlarged in FIG. 2, a plurality of reduction electrodes 4 is disposed and formed on the surface of the electrolyte film 6 on the reduction tank 5 side in parallel with the z direction to be separated from each other. The plurality of water-repellent films 9 is disposed between two adjacent reduction electrodes 4 in parallel with the z direction to be separated from each other. The water-repellent film 9 has a rectangular parallelepiped shape, and the longitudinal direction of the water-repellent film 9 coincides with the longitudinal direction of the reduction electrode 4 having a plate shape. Since the reduction electrode 4 also does not cover the entire surface of the electrolyte film 6, a carbon dioxide reduction reaction can be caused.

[0042] Next, a method for manufacturing the water-repellent film 9 will be described.

[0043] Examples of the water-repellent treatment for manufacturing the water-repellent film 9 include a friction transfer method, a gas phase method, and a liquid phase method.

[0044] The friction transfer method is a method of forming an alignment film of a fluorine-based polymer on the surface of the electrolyte film 6 by heating the fluorine-based polymer having a water-repellent surface with small surface energy to around a glass transition temperature to make the fluorine-based polymer flexible, then pressing the fluorine-based polymer against the electrolyte film 6, which is an object, and then sweeping the fluorine-based polymer while maintaining the pressure.

[0045] The gas phase method is a method in which a mask having a penetration portion is attached to the surface of the electrolyte film 6, an object and a fluorine-based low molecular substance (silane coupling agent), which is a water-repellent agent, are put in the same sealed space, the fluorine-based low molecular substance is heated to be evaporated, and then the fluorine-based low molecular substance is deposited on the surface of the object.

[0046] The liquid phase method is a method in which a mask having a penetration portion is attached to the surface of the electrolyte film 6, an object is immersed in a fluorine-based solvent obtained by dissolving a fluorine-based polymer, which is a water-repellent agent, by a dip coating method or the like, and then the fluorine-based polymer is precipitated by performing heating or the like on the object and removing the solvent.

[0047] Another method of the liquid phase method is a method in which a film of the fluorine-based solvent is formed by a cast coating method, a spin coating method, or the like instead of the dip coating step, and then the fluorine-based polymer is precipitated by performing heating or the like on the object and removing the solvent.

[0048] FIG. 4 is a diagram illustrating a first manufacturing method for the water-repellent film 9. The first manufacturing method is a method for manufacturing the water-repellent film 9 by the friction transfer method. Nafion was used for the electrolyte film 6. Polytetrafluoroethylene (PTFE) was used for a water-repellent block.

[0049] First, the water-repellent block is heated to 110° C., which is near the glass transition temperature (first step S101). By making the surface of the water-repellent block flexible, the polymer on the surface of the water-repellent block can be transferred to the electrolyte film. Thereafter, the water-repellent block is pressed against the electrolyte film at a pressure of 0.5 MPa (second step S102), and then the water-repellent block is swept at a speed of 10 mm / min (third step S103). When the water-repellent block can be swept over the entire electrolyte film, the water-repellent block is pulled up (fourth step S104). Through this step, a part of the surface of the electrolyte film can be covered with a water-repellent block material, and a water-repellent film on which droplets easily slide in one direction can be formed.

[0050] FIG. 5 is a diagram illustrating a second manufacturing method for the water-repellent film 9. The second manufacturing method is a method for manufacturing the water-repellent film 9 by the gas phase method. Nafion was used for the electrolyte film 6. As the water-repellent agent, a fluorine-based silane coupling agent (for example, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane) was used.

[0051] First, a mask having a penetration portion is attached to the electrolyte film (first step S201). Next, the electrolyte film and the water-repellent agent (water-repellent low molecular substance) are put in a Teflon container and sealed (second step S202). Next, the Teflon container is put in an oven and heated at 100° C. (third step S203). Through this step, the water-repellent agent evaporates, and a water-repellent film is formed on the surface of the electrolyte film in a portion of the mask having the penetration portion. The water-repellent film is formed on the surface of the mask in a portion not having the penetration portion. Finally, the mask is removed from the electrolyte film (fourth step S204).

[0052] FIG. 6 is a diagram illustrating a third manufacturing method for the water-repellent film 9. The third manufacturing method is a method for manufacturing the water-repellent film 9 by the liquid phase method. Nafion was used for the electrolyte film 6. As the water-repellent agent, OPTOOL DSX (water-repellent polymer) was used.

[0053] First, a mask having a penetration portion is attached to the electrolyte film (first step S301). Next, a water-repellent agent is dropped on the electrolyte film and the surface of the mask using a spin coating method (second step S302). Thereafter, the electrolyte film is left to evaporate the solvent in the water-repellent agent (third step S303). Finally, the mask is removed from the electrolyte film (fourth step S304). Through this step, a water-repellent film is formed on the surface of the electrolyte film in a portion of the mask having the penetration portion.

[0054] Through these steps, the water-repellent film having anisotropy can be formed only on one side of the electrolyte film. In the method of using the gas phase method and the liquid phase method described above, an extremely thin water-repellent film having a thickness on the order of several tens of nanometers can be formed in principle. In addition, since the distance between the water-repellent films depends on the distance of the penetration portion of the mask, the range from the nanometer order to the millimeter order can be controlled by processing.

[0055] On the other hand, in the method by the friction transfer method, in principle, it is possible to form a range from a thickness on the order of several tens of nanometers to a thickness on the order of micrometers. The distance between the water-repellent films can be controlled by preliminarily subjecting the surface of the water-repellent block on the side to be pressed against the electrolyte film to irregularity processing. The width of the water-repellent film and the width between the water-repellent films can be controlled by changing the width of the irregularity.

[0056] Next, electrochemical measurement by the carbon dioxide reduction device 100 described above and a measurement result thereof will be described.

[0057] First, a thin film of gallium nitride (GaN) as an n-type semiconductor and aluminum gallium nitride (AlGaN) were epitaxially grown in this order on a sapphire substrate, and nickel (Ni) was vacuum-deposited thereon and heat treatment was performed, so that a cocatalyst thin film of nickel oxide (NiO) was formed. Then, the cocatalyst thin film was used as the oxidation electrode 1, and the oxidation electrode 1 was immersed in the electrolytic solution 3 of a 1.0 mol / L potassium hydroxide aqueous solution in the oxidation tank 2.

[0058] In addition, as the reduction electrode 4, a copper plate having a vertical width of 2 cm, a horizontal width of 2 cm, and a height of 0.1 mm was used, and penetration portions having a vertical width of 1.7 cm and a horizontal width of 0.1 mm were formed every 0.1 mm in a range of a vertical width of 1.7 cm and a horizontal width of 1.7 cm. The reduction electrode 4 was connected to the oxidation electrode 1 by the conductive wire 7, and the reduction electrode 4 was installed in the reduction tank 5.

[0059] In addition, Nafion was used for the electrolyte film 6 physically separating the oxidation tank 2 and the reduction tank 5. Of both surfaces of the electrolyte film 6, one surface on which the water-repellent film 9 was formed was disposed to be in contact with the reduction electrode 4 in the reduction tank 5, and the other surface was disposed to be in contact with the electrolytic solution 3 in the oxidation tank 2. In order to reduce the contact resistance between the electrolyte film 6 and the reduction electrode 4, for example, a method in which the electrolyte film 6 is heated to near the glass transition temperature so as to be press-bonded may be applied.

[0060] In addition, as the light source 8, a 300 W xenon lamp was used. A wavelength of 450 nm or more was cut with a filter, and the illuminance was set to 6.6 mW / cm2. An irradiation surface of the oxidation electrode 1 was set to 2.5 cm2.

[0061] Then, nitrogen and carbon dioxide were supplied to the oxidation tank 2 and the reduction tank 5 at a flow rate of 5 ml / min and a pressure of 0.5 MPa, respectively. The bubbling of nitrogen into the oxidation tank 2 was carried out for the purpose of analyzing the reaction products. The inside of each of the oxidation tank 2 and the reduction tank 5 was sufficiently replaced with nitrogen and carbon dioxide, respectively, and light was emitted from the light source 8. Thereafter, the carbon dioxide reduction reaction proceeded on the surface of the copper porous body, which is the reduction electrode 4.

[0062] At this time, the current flowing between the oxidation electrode 1 and the reduction electrode 4 by the irradiation light was measured with an electrochemical measurement device (Model 1287 Potentiogalvanostat manufactured by Solartron). In addition, gases and liquids generated in the oxidation tank 2 and the reduction tank 5 were collected, and the reaction products were analyzed using a gas chromatograph, a liquid chromatograph, and a gas chromatograph mass spectrometer.

[0063] In particular, in the present embodiment, an effect of the water-repellent film 9 formed on the surface of the electrolyte film 6 was examined by determining the Faraday efficiency of the carbon dioxide reduction reaction. Note that a method for calculating the Faraday efficiency of the carbon dioxide reduction reaction will be described below.

[0064] In a first example, Nafion was used as the electrolyte film 6, PTFE was used as the water-repellent block, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 was installed so that the direction of the water-repellent film 9 and the direction of gravity were parallel, that is, 0°.

[0065] In a second example, Nafion was used as the electrolyte film 6, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane was used as the water-repellent low molecular substance, the water-repellent film 9 manufactured by the second manufacturing method was used, and the water-repellent film 9 was installed so that the direction of the water-repellent film 9 and the direction of gravity were parallel, that is, 0°.

[0066] In a third example, Nafion was used as the electrolyte film 6, OPTOOL DSX was used as the water-repellent agent, the water-repellent film 9 manufactured by the third manufacturing method was used, and the water-repellent film 9 was installed so that the direction of the water-repellent film 9 and the direction of gravity were parallel, that is, 0°.

[0067] In a first comparative example, Nafion on which the water-repellent film 9 was not formed was used as it was as the electrolyte film 6.

[0068] In a second comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that a long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°.

[0069] In a third comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were perpendicular, that is, 90°.

[0070] FIG. 7 is a diagram showing a measurement result of the Faraday efficiency of formic acid according to the first embodiment. In the first comparative example in which the water-repellent film 9 was not formed, the Faraday efficiency decreased after six hours. On the other hand, in the first example to the third example in which the water-repellent film 9 was formed, the Faraday efficiency did not decrease even after six hours. This is because, as a result of introducing the water-repellent film 9 into the electrolyte film 6, the liquid on the surface of the reduction electrode 4 as a result of liquid leakage easily slides down, and the reaction site of the reduction electrode 4 was not covered with the electrolytic solution 3.

[0071] In addition, in the second comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°, the ease of water sliding was slightly improved, and the reduction rate of decrease in Faraday efficiency after the test time of 6 hours was suppressed. In the third comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 90°, the water was less likely to slide down than in the first comparative example in which the water-repellent film was not formed, and the decrease in Faraday efficiency was deteriorated.

[0072] Here, a method for calculating the Faraday efficiency of the carbon dioxide reduction reaction will be described. The Faraday efficiency of carbon dioxide indicates the ratio of the number of electrons used in the carbon dioxide reduction reaction to the number of electrons moved between the oxidation electrode 1 and the reduction electrode 4 by light irradiation or application of a current voltage, and can be calculated by Formula (1).Faraday⁢ efficiency={number⁢ of⁢ electrons⁢ in⁢ reduction⁢ reaction} / {number⁢ of⁢ electrons⁢ moved⁢ between⁢ electrodes}(1)

[0073] The “number of electrons in reduction reaction” in Formula (1) is determined by converting the measured value of the integrated amount of the generated carbon dioxide reduction product into the number of electrons required for the production reaction. For example, the “number of electrons in reduction reaction” when the reduction product is a gas can be calculated by Formula (2).Number⁢ of⁢ electrons⁢ in⁢ each⁢ reduction⁢ reaction⁢ (C)={A×B×Z×F×T×10-6)} / Vg(2)

[0074] A is a concentration (ppm) of the reduction reaction product. B is a flow rate (L / sec) of the carrier gas. Z is the number of electrons required for the reduction reaction. F is the Faraday constant (C / mol). T is a light irradiation time or a current voltage application time (sec). Vg is a molar volume of the gas (L / mol).

[0075] The “number of electrons in reduction reaction” when the reduction product is a liquid can be calculated by Formula (3).Number⁢ of⁢ electrons⁢ in⁢ each⁢ reduction⁢ reaction⁢ (C)=C×V1×Z×F(3)

[0076] C is a concentration (mol / L) of the reduction reaction product. V1 is a volume (L) of the liquid sample. Z is the number of electrons required for the reduction reaction. F is the Faraday constant (C / mol).

[0077] The first embodiment has been described above. With the carbon dioxide reduction device 100 according to the first embodiment, it is possible to provide the carbon dioxide reduction device 100 capable of allowing the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.

[0078] That is, in the first embodiment, in the carbon dioxide reduction device 100 including the oxidation tank 2 that performs the oxidation reaction of water by irradiation light from the light source 8 by using the electrolytic solution 3 and the oxidation electrode 1 of a semiconductor immersed in the electrolytic solution 3, the reduction tank 5 that performs the carbon dioxide reduction reaction by using the reduction electrode 4 connected to the oxidation electrode 1 via the conductive wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4, and the electrolyte film 6 disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution 3 and the reduction electrode 4, the electrolyte film 6 includes the water-repellent film 9 on a part of the surface which is in contact with the reduction electrode 4.

[0079] Therefore, the water-repellent anisotropy of the water-repellent film 9 provided on the surface of the electrolyte film 6 causes the liquid on the surface of the reduction electrode 4, which is a result of exudation of the electrolytic solution 3 in the oxidation tank 2 to the outside of the electrolyte film 6, easily slides down, and the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3. In addition, since the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte film 6, a state in which protons can reach between the electrolyte film 6 and the reduction electrode 4 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in the reduction reaction efficiency can be suppressed.

[0080] Note that, in the above experiment, light is generated by a xenon lamp in order to quantitatively manage the emission amount of light with respect to the oxidation electrode 1, but it is also possible to cause an oxidation reaction using sunlight or the like.Second Embodiment

[0081] In the first embodiment, the case where the light source 8 and the oxidation electrode 1 including a semiconductor are used has been described. In the second embodiment, instead of these, an oxidation / reduction reaction is allowed to proceed using an external power supply and the oxidation electrode 1 including a metal. For comparison, the same voltage value and current value as those in the first embodiment were adjusted and applied.

[0082] FIG. 8 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a second embodiment. The oxidation electrode 1 is platinum. Additionally, the oxidation electrode 1 may be, for example, gold or silver. An external power supply 10 is an electrochemical measurement device, and is connected in series to a conductive wire 7 connecting the oxidation electrode 1 and a reduction electrode 4. The power supply 10 may be another power supply device. Other components are the same as those of the first embodiment.

[0083] In the carbon dioxide reduction device 100 according to the present embodiment, in an oxidation tank 2, the oxidation reaction of water in an electrolytic solution 3 is performed by a current voltage (electrical energy) from the power supply 10 using the electrolytic solution 3 and the oxidation electrode 1 of platinum (metal) immersed in the electrolytic solution 3. In a reduction tank 5, the carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the power supply 10 (source of electrical energy) and carbon dioxide brought into direct contact with the reduction electrode 4.

[0084] Specifically, when the power supply 10 applies a current voltage to the conductive wire 7, oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3. The protons pass through the electrolyte film 6 and reach the reduction electrode 4 in the reduction tank 5 from the electrolytic solution 3 in the oxidation tank 2. The electrons flow from the power supply 10 to the reduction electrode 4 in the reduction tank 5 via the conductive wire 7. In the reduction tank 5, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide in a gas phase brought into direct contact with the reduction electrode 4 is caused at the reduction electrode 4.

[0085] Also in the second embodiment, similarly to the first embodiment, a water-repellent film 9 is provided on a part of the surface of the electrolyte film 6 on the reduction tank 5 side so as not to cover the entire surface of the electrolyte film 6. As a method for manufacturing the water-repellent film 9, the first manufacturing method to the third manufacturing method are used similarly to the first embodiment.

[0086] FIG. 9 is a diagram showing a measurement result of the Faraday efficiency of formic acid according to the second embodiment. Examples using the same electrolyte film 6 as in the first example to the third example described in the first embodiment are referred to as a fourth example to a sixth example, respectively. In a fourth comparative example, Nafion on which the water-repellent film 9 was not formed was used as it was as the electrolyte film 6. In a fifth comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that a long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°. In a sixth comparative example, the water-repellent film 9 manufactured by the first manufacturing method was used, and the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were perpendicular, that is, 90°.

[0087] In the fourth comparative example in which the water-repellent film 9 was not formed, the Faraday efficiency decreased after six hours. On the other hand, in the fourth example to the sixth example in which the water-repellent film 9 was formed, the Faraday efficiency did not decrease even after six hours. This is because, as a result of introducing the water-repellent film 9 into the electrolyte film 6, the liquid on the surface of the reduction electrode 4 as a result of liquid leakage easily slides down, and the reaction site of the reduction electrode 4 was not covered with the electrolytic solution 3.

[0088] In addition, in the fifth comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the long axis direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 45°, the ease of water sliding was slightly improved, and the reduction rate of decrease in Faraday efficiency after the test time of 6 hours was suppressed. In the sixth comparative example in which the water-repellent film 9 and the reduction electrode 4 were installed so that the direction of the water-repellent film 9 and the reduction electrode 4 and the direction of gravity were 90°, the water was less likely to slide down than in the first comparative example in which the water-repellent film was not formed, and the decrease in Faraday efficiency was deteriorated.

[0089] The second embodiment has been described above. With the carbon dioxide reduction device 100 according to the second embodiment, it is possible to provide the carbon dioxide reduction device 100 capable of allowing the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.

[0090] That is, in the second embodiment, in the carbon dioxide reduction device 100 including the oxidation tank 2 that performs the oxidation reaction of water by the current voltage from the power supply 10 by using the electrolytic solution 3 and the oxidation electrode 1 of platinum (metal) immersed in the electrolytic solution 3, the reduction tank 5 that performs the carbon dioxide reduction reaction by using the reduction electrode 4 connected to the power supply 10 and carbon dioxide brought into direct contact with the reduction electrode 4, and the electrolyte film 6 disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 to be in contact with both the electrolytic solution 3 and the reduction electrode 4, the electrolyte film 6 includes the water-repellent film 9 on a part of the surface which is in contact with the reduction electrode 4.

[0091] Therefore, the water-repellent anisotropy of the water-repellent film 9 provided on the surface of the electrolyte film 6 causes the liquid on the surface of the reduction electrode 4, which is a result of exudation of the electrolytic solution 3 in the oxidation tank 2 to the outside of the electrolyte film 6, easily slides down, and the reaction site of the reduction electrode 4 is not covered with the electrolytic solution 3. In addition, since the water-repellent film 9 is formed not on the entire surface but on a part of the surface of the electrolyte film 6, a state in which protons can reach between the electrolyte film 6 and the reduction electrode 4 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in the reduction reaction efficiency can be suppressed.Others

[0092] The present invention can be widely used in the field related to the recycling of carbon dioxide. Although light energy is used in the first embodiment and electrical energy is used in the second embodiment, other renewable energy may be used. In addition, the first embodiment and the second embodiment can be combined.

[0093] The present invention can be also applied to any electrolyte film as long as it is the electrolyte film 6 that is disposed between the electrolytic solution 3 in the oxidation tank 2 and the reduction electrode 4 in the reduction tank 5 in contact with the electrolytic solution 3 and the reduction electrode 4 and is used in the carbon dioxide reduction device 100 that performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode 4.REFERENCE SIGNS LIST1 Oxidation electrode

[0095] 2 Oxidation tank

[0096] 3 Electrolytic solution

[0097] 4 Reduction electrode

[0098] 5 Reduction tank

[0099] 6 Electrolyte film

[0100] 7 Conductive wire

[0101] 8 Light source

[0102] 9 Water-repellent film

[0103] 10 Power supply

[0104] 100 Carbon dioxide reduction device

Examples

first embodiment

[0026]FIG. 1 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a first embodiment. As illustrated in FIG. 1, the carbon dioxide reduction device 100 includes an oxidation electrode 1, an oxidation tank 2, an electrolytic solution 3, a reduction electrode 4, a reduction tank 5, an electrolyte film 6, a conductive wire 7, a light source 8, and a water-repellent film 9.

[0027]The oxidation electrode 1 is immersed in the electrolytic solution 3 in the oxidation tank 2. The oxidation electrode 1 is formed by forming a semiconductor on a substrate having a predetermined area. The oxidation electrode 1 is formed, for example, by forming a film of a compound exhibiting photoactivity, redox activity, or the like such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex, on a surface of a sapphire substrate.

[0028]The oxidation tank 2 holds the electrolytic solution 3 in which the oxidation...

second embodiment

[0081]In the first embodiment, the case where the light source 8 and the oxidation electrode 1 including a semiconductor are used has been described. In the second embodiment, instead of these, an oxidation / reduction reaction is allowed to proceed using an external power supply and the oxidation electrode 1 including a metal. For comparison, the same voltage value and current value as those in the first embodiment were adjusted and applied.

[0082]FIG. 8 is a diagram illustrating a configuration example of a carbon dioxide reduction device 100 according to a second embodiment. The oxidation electrode 1 is platinum. Additionally, the oxidation electrode 1 may be, for example, gold or silver. An external power supply 10 is an electrochemical measurement device, and is connected in series to a conductive wire 7 connecting the oxidation electrode 1 and a reduction electrode 4. The power supply 10 may be another power supply device. Other components are the same as those of the first embod...

Claims

1. An electrolyte film that is disposed between an electrolytic solution in an oxidation tank and a reduction electrode in a reduction tank to be in contact with both the electrolytic solution and the reduction electrode and is used in a carbon dioxide reduction device that performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode, the electrolyte film comprising: a water-repellent film on a part of a surface which is in contact with the reduction electrode.

2. The electrolyte film according to claim 1, whereinthe oxidation tank performs an oxidation reaction of water with light energy by using the electrolytic solution and an oxidation electrode of a semiconductor immersed in the electrolytic solution, andthe reduction tank performs a carbon dioxide reduction reaction using the reduction electrode connected to the oxidation electrode via a conductive wire and carbon dioxide brought into direct contact with the reduction electrode.

3. The electrolyte film according to claim 1, whereinthe oxidation tank performs an oxidation reaction of water with electrical energy by using the electrolytic solution and an oxidation electrode of metal immersed in the electrolytic solution, andthe reduction tank performs a carbon dioxide reduction reaction by using the reduction electrode connected to a source of the electrical energy and carbon dioxide brought into direct contact with the reduction electrode.

4. The electrolyte film according to claim 1, wherein the water-repellent film has a rectangular parallelepiped shape, and a longitudinal direction of the water-repellent film coincides with a longitudinal direction of the reduction electrode having a plate shape.

5. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 1, the electrolyte film manufacturing method performing:a step of heating a water-repellent polymer;a step of pressing the water-repellent polymer against one surface of the electrolyte film; anda step of forming a water-repellent film on a surface of the electrolyte film by sweeping the water-repellent polymer.

6. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 1, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

7. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 1, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of applying a dissolved water-repellent agent to the one surface of the electrolyte film;a step of removing a solvent contained in the water-repellent agent from the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

8. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 2, the electrolyte film manufacturing method performing:a step of heating a water-repellent polymer;a step of pressing the water-repellent polymer against one surface of the electrolyte film; anda step of forming a water-repellent film on a surface of the electrolyte film by sweeping the water-repellent polymer.

9. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 3, the electrolyte film manufacturing method performing:a step of heating a water-repellent polymer;a step of pressing the water-repellent polymer against one surface of the electrolyte film; anda step of forming a water-repellent film on a surface of the electrolyte film by sweeping the water-repellent polymer.

10. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 4, the electrolyte film manufacturing method performing:a step of heating a water-repellent polymer;a step of pressing the water-repellent polymer against one surface of the electrolyte film; anda step of forming a water-repellent film on a surface of the electrolyte film by sweeping the water-repellent polymer.

11. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 2, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

12. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 3, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

13. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 4, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

14. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 2, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of applying a dissolved water-repellent agent to the one surface of the electrolyte film;a step of removing a solvent contained in the water-repellent agent from the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

15. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 3, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of applying a dissolved water-repellent agent to the one surface of the electrolyte film;a step of removing a solvent contained in the water-repellent agent from the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

16. An electrolyte film manufacturing method for manufacturing the electrolyte film according to claim 4, the electrolyte film manufacturing method performing:a step of attaching a mask having a penetration portion to one surface of the electrolyte film;a step of applying a dissolved water-repellent agent to the one surface of the electrolyte film;a step of removing a solvent contained in the water-repellent agent from the one surface of the electrolyte film; anda step of removing the mask from the electrolyte film.

Images