Patent Application
20240410068
The present invention relates to an electrolyte membrane and a method for manufacturing an electrolyte membrane.
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.
As a way 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, it has not been possible to make chemical products using fossil fuels as raw materials.
As a method of simultaneously solving these issues, technology of reducing carbon dioxide using light energy has attracted attention. For example, Non Patent Literature 1 discloses a carbon dioxide reduction device using light illumination. In an oxidation tank, when an oxidation electrode is illuminated with light, electron-hole pairs are generated and separated at the oxidation electrode, and oxygen and protons (H+) are generated by an oxidation reaction of water in an electrolytic solution. The protons pass through an electrolyte membrane and reach a reduction tank, and electrons flow to the reduction electrode via a conducting wire. In the reduction tank, a carbon dioxide reduction reaction by protons, electrons, and carbon dioxide dissolved in a 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.
In the carbon dioxide reduction device of Non Patent Literature 1, the reduction electrode is immersed in a solution, and carbon dioxide is dissolved in the solution, and thereby the carbon dioxide is supplied to the reduction electrode. However, in such a method of reducing carbon dioxide, since the reduction electrode is immersed in the solution, there are limitations on a dissolved carbon dioxide concentration in the solution and a diffusion coefficient of carbon dioxide in the solution, and the amount of carbon dioxide supplied to the reduction electrode is limited.
In this respect, 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, a supply amount of carbon dioxide to the reduction electrode is increased, and the carbon dioxide reduction reaction is promoted.
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 membrane 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 carbon dioxide reduction device in the related art has a problem in that the reduction reaction efficiency of carbon dioxide decreases in several tens of hours.
The present invention has been made to address the problems described above, and an object of the present invention is to provide a technology capable of improving reduction reaction efficiency of carbon dioxide.
An electrolyte membrane according to an aspect of the present invention 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 which performs a carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode, the electrolyte membrane including: a water-repellent film on a part of a surface which is in contact with the electrolytic solution.
A method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of applying a water-soluble polymer to one surface of the electrolyte membrane; a step of removing moisture in the water-soluble polymer; a step of performing a water-repellent treatment on both surfaces of the electrolyte membrane; and a step of removing the water-soluble polymer from the one surface of the electrolyte membrane.
A method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of applying a water-repellent polymer to one surface of the electrolyte membrane; and a step of removing a solvent in the water-repellent polymer.
A method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of applying a water-soluble polymer to one surface of the electrolyte membrane; a step of removing moisture in the water-soluble polymer; a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on both surfaces of the electrolyte membrane; and a step of removing the water-soluble polymer from the one surface of the electrolyte membrane.
A method for manufacturing an electrolyte membrane according to an aspect of the present invention is a method for manufacturing the electrolyte membrane described above, the method including: a step of performing a water-repellent treatment of heating and depositing a water-repellent low molecular substance on one surface of the electrolyte membrane.
According to the present invention, carbon dioxide reduction reaction efficiency can be improved.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference signs are assigned to the same parts, and the description thereof is omitted.
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 or redox activity, such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex, on a surface of a sapphire substrate.
The oxidation tank 2 contains an electrolytic solution 3 in which the oxidation electrode 1 is immersed.
The electrolytic solution 3 is contained 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.
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 made of copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, cadmium, or an alloy thereof. Alternatively, the reduction electrode 4 may be made of 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.
The reduction tank 5 contains the reduction electrode 4 disposed inside and gas phase carbon dioxide supplied from the outside through a pipe.
The electrolyte membrane 6 is disposed between the oxidation tank 2 and the reduction tank 5. To be accurate, the electrolyte membrane 6 is disposed between the electrolytic solution 3 and the reduction electrode 4 to be in contact with both the electrolytic solution and the reduction electrode. The electrolyte membrane 6 is, for example, any one of Nafion (registered trademark), FORBLUE, and Aquivion that are an electrolyte membrane having a carbon-fluorine skeleton, or SELEMION, NEOSEPTA, or the like that is an electrolyte membrane having a carbon-hydrogen skeleton.
The conducting wire 7 physically and electrically connects the oxidation electrode 1 and the reduction electrode 4.
The light source 8 is disposed close to the oxidation tank 2. The light source 8 is, for example, sunlight, a xenon lamp, a pseudo sunlight source, a halogen lamp, a mercury lamp, or a combination thereof.
The reduction electrode 4 and the electrolyte membrane 6 may be formed of the same material. For example, the present invention can be realized by using a gas diffusion electrode (GDE (registered trademark)) composed of a porous material and a catalyst. Since the gas diffusion electrode can separate liquid and gas and enables cations to move in the electrode, the gas diffusion electrode has actions equivalent to actions of both the reduction electrode 4 and the electrolyte membrane 6.
In addition, in
In the carbon dioxide reduction device 100 described above, in the oxidation tank 2, an oxidation reaction of water in the electrolytic solution 3 is performed by illumination light (light energy) from the light source 8 by using the electrolytic solution 3 and the semiconductor oxidation electrode 1 immersed in the electrolytic solution 3. In the reduction tank 5, a carbon dioxide reduction reaction is performed using the reduction electrode 4 connected to the oxidation electrode 1 via the conducting wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4.
Specifically, when the light source 8 emits light from the bottom of the oxidation tank 2, generation and separation of electron-hole pairs occur in the oxidation electrode 1 in the oxidation tank 2 that has received the illumination light, and oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3. The protons pass through the electrolyte membrane 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 conducting wire 7. In the reduction tank 5, a carbon dioxide reduction reaction is caused by the protons, the electrons, and carbon dioxide in a gas phase brought in direct contact with the reduction electrode 4 in the reduction electrode 4. This redox reaction generates carbon monoxide, formic acid, methane, and the like that can be used as energy resources.
In this case, in a case where a strong alkaline aqueous solution, for example, a 1.0 mol/L sodium hydroxide aqueous solution is used as the electrolytic solution 3 in the oxidation tank 2, the electrolyte membrane 6 swells, and the electrolytic solution 3 passes through pores of the electrolyte membrane 6 and is exuded to a 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 membrane 6, a surface of the electrolyte membrane 6 on the side of the oxidation tank 2 may be 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 membrane 6 as a medium, the reduction reaction may not proceed on the side of the reduction tank 5 when the surface of the electrolyte membrane 6 is completely covered.
In this respect, in this embodiment, as illustrated in
Next, a method for manufacturing the water-repellent film 9 will be described.
Examples of the water-repellent treatment for manufacturing the water-repellent film 9 include a liquid phase method and a gas phase method. The liquid phase method is a method in which an object is immersed in a fluorine-based solvent obtained by dissolving a fluorine-based polymer as a water repellent agent, by a dip coating method or the like, and then the fluorine-based polymer is deposited by performing heating or the like on the object and removing the solvent. Another method of the liquid phase method is a method in which a film of the fluorine-based solvent is formed on a surface of an object by a cast coating method, a spin coating method, or the like, and then the fluorine-based polymer is deposited by performing heating or the like on the object and removing the solvent. The gas phase method is a method in which 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.
First, a water-soluble polymer is dissolved in pure water to prepare a polyvinyl alcohol aqueous solution with a concentration of 1% (first step S101). Next, the polyvinyl alcohol aqueous solution is dropped onto one surface of the Nafion membrane by a spin coating method, and a polyvinyl alcohol film is formed on the one surface (second step S102).
Next, the Nafion membrane is left in an oven at 60° C. for one hour to evaporate moisture in polyvinyl alcohol (third step S103). Through this step, a polymer film (water-soluble polymer) is formed on the one surface of the Nafion membrane. Next, dip coating is performed by immersing the Nafion membrane in an OPTOOL DSX solution (water-repellent polymer) for one minute and pulling up the Nafion membrane (fourth step S104). Through this step, water-repellent films are formed on both surfaces of the Nafion membrane.
Finally, the Nafion membrane is washed with pure water (fifth step S105). Through this step, polyvinyl alcohol (water-soluble polymer) coated with the water-repellent film can be removed. That is, the polymer film (water-soluble polymer) is removed from one surface of the Nafion membrane, and the water-repellent film on the polymer film is also removed.
Through these steps, a water-repellent film can be formed only on one surface of the Nafion membrane. In the method of forming the water-repellent film using the dip coating method, a relatively thick water-repellent film on the order of micrometers can be formed.
First, the OPTOOL DSX (water-repellent polymer) is dropped on one surface of the Nafion membrane using a spin coating method (first step S201). Thereafter, the Nafion membrane is left, and the solvent in OPTOOL DSX is evaporated (second step S202). Through this step, a polymer film (water-repellent film) is formed on one surface of the Nafion membrane.
Through these steps, the water-repellent film can be formed only on one side of the Nafion membrane. In the method of forming the water-repellent film using the spin coating method, since a centrifugal force is used, a thin water-repellent film of sub-micrometer order can be formed in principle.
First, a water-soluble polymer is dissolved in pure water to prepare a polyvinyl alcohol aqueous solution with a concentration of 1% (first step S301). Next, the polyvinyl alcohol aqueous solution is dropped onto one surface of the Nafion membrane by a spin coating method, and a polyvinyl alcohol film is formed on the one surface (second step S302).
Next, the Nafion membrane is left in an oven at 60° C. for one hour to evaporate moisture in polyvinyl alcohol (third step S303). Through this step, a polymer film (water-soluble polymer) is formed on the one surface of the Nafion membrane. Next, the Nafion membrane and a fluorine-based silane coupling agent (water-repellent low molecular substance) are put in a Teflon container and sealed (fourth step S304).
Next, the Teflon container is put in an oven and heated at 150° C. (fifth step S305). Through this step, the fluorine-based silane coupling agent is evaporated, and water-repellent films are formed on both surfaces of the Nafion membrane. Finally, the Nafion membrane is washed with pure water (sixth step S306). Through this step, polyvinyl alcohol (water-soluble polymer) coated with the water-repellent film can be removed. That is, the polymer film (water-soluble polymer) is removed from one surface of the Nafion membrane, and the water-repellent film on the polymer film is also removed.
Through these steps, the water-repellent film can be formed only on one side of the Nafion membrane. In this gas phase method, since a monomolecular film is formed on the surface of Nafion, a very thin water-repellent film on the order of nanometers can be formed.
First, the Nafion membrane is left in close contact with a bottom of the Teflon container, and a fluorine-based silane coupling agent (water-repellent low molecular substance) is put thereon and sealed (first step S401). Finally, while this state is maintained, the Teflon container is put in an oven and heated at 150° C. (second step S402). Through this step, the fluorine-based silane coupling agent is evaporated, and a water-repellent film is formed on one surface of the Nafion membrane.
Through these steps, the water-repellent film can be formed only on one side of the Nafion membrane. In this gas phase method, since a monomolecular film is formed on the surface of Nafion, a very thin water-repellent film on the order of nanometers can be formed.
Next, electrochemical measurement by the carbon dioxide reduction device 100 and a measurement result thereof will be described.
First, a nickel oxide (NiO) co-catalyst thin film was formed by epitaxially growing a thin film of gallium nitride (GaN) which is an n-type semiconductor and aluminum gallium nitride (AlGaN) in this order on a sapphire substrate, vacuum-depositing nickel (Ni) thereon, and performing heat treatment. Accordingly, the co-catalyst 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.
In addition, the reduction electrode 4 was formed using a copper porous body, the reduction electrode 4 was connected to the oxidation electrode 1 by the conducting wire 7, and the reduction electrode 4 was installed in the reduction tank 5.
In addition, Nafion was used for the electrolyte membrane 6 which physically separates the oxidation tank 2 and the reduction tank 5 from each other. Of both surfaces of the electrolyte membrane 6, one surface on which the water-repellent film 9 was formed was disposed to be in contact with the electrolytic solution 3 in the oxidation tank 2, and the other surface was disposed to be in contact with the reduction electrode 4 in the reduction tank 5.
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 illumination area of the oxidation electrode 1 was set to 2.5 cm2.
Accordingly, nitrogen and carbon dioxide were supplied to the oxidation tank 2 and the reduction tank 5, respectively, at a flow rate of 5 ml/min and a pressure of 0.5 MPa. The bubbling of nitrogen into the oxidation tank 2 was performed for the purpose of analyzing reaction products. The insides of the oxidation tank 2 and the reduction tank 5 were sufficiently replaced with nitrogen and carbon dioxide, respectively, and were illuminated with light 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.
In this case, the current that flows between the oxidation electrode 1 and the reduction electrode 4 by the illumination light was measured by an electrochemical measurement device (potentiogalvanostat Model 1287 manufactured by Solartron Analytical). 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.
In particular, in this embodiment, an effect of the water-repellent film 9 formed on the surface of the electrolyte membrane 6 was examined by computing the Faraday efficiency of the carbon dioxide reduction reaction. Further, a method of calculating the Faraday efficiency of the carbon dioxide reduction reaction will be described below.
In Example 1, the water-repellent film 9 manufactured by Manufacturing Method 1 using Nafion as the electrolyte membrane 6, OPTOOL DSX as the water-repellent agent, and a polyvinyl alcohol aqueous solution with a concentration of 1% dissolved in pure water as the water-soluble polymer was used.
In Example 2, the water-repellent film 9 manufactured by Manufacturing Method 2 using Nafion as the electrolyte membrane 6 and using OPTOOL DSX as the water-repellent agent was used.
In Example 3, the water-repellent film 9 manufactured by Manufacturing Method 3 using Nafion as the electrolyte membrane 6, heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane as the water-repellent agent, and a polyvinyl alcohol aqueous solution with a concentration of 1% dissolved in pure water as the water-soluble polymer was used.
In Example 4, the water-repellent film 9 manufactured by Manufacturing Method 4 using Nafion as the electrolyte membrane 6 and heptadecafluoro-1,1,2,2-tetrahydrodecyltrimethoxysilane as the water-repellent agent was used.
In a comparative example, Nafion on which the water-repellent film 9 was not formed was directly used as the electrolyte membrane 6.
In addition, a coverage rate of the water-repellent film 9 to the Nafion membrane was estimated using the Cassie-Baxter equation. When a contact angle of the Nafion membrane coated with the water-repellent film 9 is denoted by θ, a contact angle of the surface of the Nafion membrane is denoted by θ1, a proportion of the surface of the Nafion membrane is denoted by f1, a contact angle of a surface of the water-repellent film 9 is denoted by θ2, and a proportion of the surface of the water-repellent film 9 is denoted by f2, a relationship of Expression (1) is established.
In Examples 1 to 4, the contact angles θ of the Nafion membrane coated with the water-repellent film 9 were 100°, 95°, 75°, and 70°, respectively. In addition, the coverage rates of the water-repellent film 9 to the Nafion membrane were estimated to be 84%, 79%, 64%, and 60%, respectively. This suggests that the water-repellent film 9 not covering the entire surface of the electrolyte membrane 6 could be formed.
Here, a method for calculating the Faraday efficiency of the carbon dioxide reduction reaction will be described. The Faraday efficiency of carbon dioxide indicates a 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 illumination or current/voltage application, and can be calculated by Equation (2).
Here, the “number of electrons in the reduction reaction” in Equation (2) is obtained by converting the measured value of the integrated amount of the generated carbon dioxide reduction products into the number of electrons required for the production reaction. For example, the “number of electrons in the reduction reaction” in a case where the reduction product is a gas can be calculated by Equation (3).
Number of electrons in each reduction reaction
A denotes a concentration (ppm) of the reduction reaction product. B denotes a flow rate (L/sec) of carrier gas. Z denotes the number of electrons required for the reduction reaction. F denotes the Faraday constant (C/mol). T denotes a light illumination time or a current/voltage application time (sec). Vg denotes a molar volume of gas (L/mol).
The “number of electrons in the reduction reaction” in a case where the reduction product is a liquid can be calculated by Equation (4).
Number of electrons in each reduction reaction
C denotes a concentration (mol/L) of the reduction reaction product. V1 denotes a volume (L) of a liquid sample. Z denotes the number of electrons required for the reduction reaction. F denotes the Faraday constant (C/mol).
A first embodiment of the present invention will be described. According to the carbon dioxide reduction device 100 of the first embodiment, it is possible to provide the carbon dioxide reduction device 100 that enables the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.
That is, in the first embodiment, the carbon dioxide reduction device 100 includes the oxidation tank 2 that performs the oxidation reaction of water by the illumination light from the light source 8 by using the electrolytic solution 3 and the semiconductor oxidation electrode 1 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 conducting wire 7 and carbon dioxide brought into direct contact with the reduction electrode 4, and the electrolyte membrane 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 and the reduction electrode, in which the electrolyte membrane 6 includes the water-repellent film 9 on a part of the surface which is in contact with the electrolytic solution 3.
Therefore, the water repellency of the water-repellent films 9 provided on a surface of the electrolytic solution 3 causes the electrolytic solution 3 in the oxidation tank 2 to be suppressed from infiltrating into the electrolyte membrane 6 and causes liquid leakage of the electrolytic solution 3 to the reduction electrode 4 to be suppressed, and thus 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 provided on a part of the surface of the electrolyte membrane 6, a state in which protons can pass through the electrolyte membrane 6 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in reduction reaction efficiency can be suppressed.
Further, in the above experiment, light is generated by a xenon lamp in order to quantitatively manage an illumination amount of light with respect to the oxidation electrode 1, but it is also possible to cause an oxidation reaction by using sunlight or the like.
In the first embodiment, the case where the light source 8 and the oxidation electrode 1 made of a semiconductor are used has been described. In the second embodiment, instead, an oxidation/reduction reaction is caused to proceed using an external power supply and an oxidation electrode 1 composed of a metal.
In the carbon dioxide reduction device 100 according to this embodiment, in the oxidation tank 2, the oxidation reaction of water in the electrolytic solution 3 is performed by current and voltage (electrical energy) from the power supply 10 by using the electrolytic solution 3 and the platinum (metal) oxidation electrode 1 immersed in the electrolytic solution 3. In the reduction tank 5, a 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.
Specifically, when the power supply 10 applies current and voltage to the conducting wire 7, generation and separation of electron-hole pairs occur in the oxidation electrode 1 in the oxidation tank 2, and oxygen and protons are generated by the oxidation reaction of water in the electrolytic solution 3. The protons pass through the electrolyte membrane 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 conducting wire 7. In the reduction tank 5, a carbon dioxide reduction reaction is caused by the protons, the electrons, and carbon dioxide in a gas phase brought in direct contact with the reduction electrode 4 in the reduction electrode 4.
Also in the second embodiment, similarly to the first embodiment, the water-repellent film 9 is provided on a part of the surface of the electrolyte membrane 6 which is in contact with the electrolytic solution 3 so as not to cover the entire surface of the electrolyte membrane 6. For example, a plurality of water-repellent films 9 are formed on the surface at predetermined intervals. In addition, the water-repellent film 9 is manufactured by the first to fourth manufacturing methods, similarly to the first embodiment.
In Examples 5 to 8, the Faraday efficiency did not decrease even after six hours passed. This is because, as a result of introducing the water-repellent film 9 to the Nafion membrane, liquid leakage of the electrolytic solution 3 to the reduction electrode 4 was suppressed, and the reaction site of the reduction electrode 4 was not covered with the electrolytic solution 3.
As described above, the second embodiment is described. According to the carbon dioxide reduction device 100 of the second embodiment, it is possible to provide the carbon dioxide reduction device 100 that enables the carbon dioxide reduction reaction to proceed without reducing the Faraday efficiency.
That is, in the second embodiment, the carbon dioxide reduction device 100 includes the oxidation tank 2 that performs the oxidation reaction of water by the current and voltage from the power supply 10 by using the electrolytic solution 3 and the platinum (metal) oxidation electrode 1 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 membrane 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 and the reduction electrode, in which the electrolyte membrane 6 includes the water-repellent film 9 on a part of the surface which is in contact with the electrolytic solution 3.
Therefore, the water repellency of the water-repellent films 9 provided on a surface of the electrolytic solution 3 causes the electrolytic solution 3 in the oxidation tank 2 to be suppressed from infiltrating into the electrolyte membrane 6 and causes liquid leakage of the electrolytic solution 3 to the reduction electrode 4 to be suppressed, and thus 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 provided on a part of the surface of the electrolyte membrane 6, a state in which protons can pass through the electrolyte membrane 6 can be maintained. As a result, the carbon dioxide reduction reaction can proceed, and a decrease in reduction reaction efficiency can be suppressed.
The present invention can be widely used in the field related to the recycling of carbon dioxide. The light energy is used in the first embodiment, and the electrical energy is used in the second embodiment; however, other renewable energy may be used. In addition, the first embodiment and the second embodiment can be combined.
The present invention can also be applied to any electrolyte membrane as long as the electrolyte membrane 6 is 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 and the reduction electrode and is used in the carbon dioxide reduction device 100 which performs the carbon dioxide reduction reaction by bringing carbon dioxide into direct contact with the reduction electrode 4.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/041514 | 11/11/2021 | WO |
