Gas phase reduction device for carbon dioxide

Abstract

This gas phase reduction device for carbon dioxide comprises: an oxidation tank 1 that includes an oxidation electrode 2; a reduction tank 4 that is adjacent to the oxidation tank 1 and that is supplied with carbon dioxide; and a composite body 20 that is disposed between the oxidation tank 1 and the reduction tank 4 and that includes a plurality of reduction electrodes 5A and 5B and an electrolyte film 6. The plurality of reduction electrodes 5A and 5B are disposed on the reduction tank 4 side. The electrolyte film 6 is disposed on the oxidation tank 1 side. The plurality of reduction electrodes 5A and 5B are connected to the oxidation electrode 2 by a conducting wire 7 and each perform a different reduction reaction due to electrons flowing through the conducting wire 7.

Description

Gas-phase carbon dioxide reduction device

[0001] The present disclosure relates to a gas phase reduction device for carbon dioxide.

[0002] From the viewpoints of preventing global warming and ensuring a stable supply of energy, carbon dioxide reduction technologies have been attracting attention. Carbon dioxide reduction technologies include reduction devices that use artificial photosynthesis, which apply light energy such as sunlight to reduce carbon dioxide, and electrolysis devices that apply external electrical energy to reduce carbon dioxide.

[0003] Artificial photosynthesis is a technology that promotes the oxidation of water and the reduction of carbon dioxide by irradiating an oxidation electrode made of a photocatalyst with light. Electroreduction is a technology that promotes the oxidation of water and the reduction of carbon dioxide by applying a voltage between an oxidation electrode made of metal and a reduction electrode. Artificial photosynthesis technology that uses sunlight and electroreduction technology that uses electricity derived from renewable energy have attracted attention as technologies that can recycle carbon dioxide into carbon monoxide, formic acid, hydrocarbons such as ethylene, or alcohols such as methanol and ethanol, and have been actively researched in recent years.

[0004] Artificial photosynthesis and carbon dioxide electrolytic reduction technologies have used a reaction system in which a reduction electrode is immersed in an aqueous solution, and carbon dioxide dissolved in the aqueous solution is supplied to the reduction electrode for reduction (Non-Patent Documents 1 and 2). However, this reduction method has limitations on the concentration of carbon dioxide dissolved in the aqueous solution and the diffusion of carbon dioxide in the aqueous solution, which limits the amount of carbon dioxide that can be supplied to the reduction electrode.

[0005] To address this problem, research is being conducted into supplying gaseous carbon dioxide to the reduction electrode in order to increase the amount of carbon dioxide supplied to the reduction electrode. According to Non-Patent Document 3, by using a reaction device having a structure capable of supplying gaseous carbon dioxide to the reduction electrode, the amount of carbon dioxide supplied to the reduction electrode is increased, and the reduction reaction of carbon dioxide is promoted.

[0006] Satoshi Yotsuhashi and 6 others, “CO2Conversion with Light and Water by GaN Photoelectrode”, Japanese Journal of Applied Physics, 51, 2012, p.02BP07-1-p.02BP07-3Yoshio Hori and 2 others, “Formation of Hydrocarbons in the Electrochemical Reduction of Carbone Dioxide at a Copper Electrode in Aqueous Solution”, Journal of the Chemical Society, 85(8), 1989, p.2309-p.2326Ichitaro Waki ​​and others, “Direct Gas-phase CO2 Reduction for Solar Methane Generation Using a Gas Diffusion Electrode with a BiVO4:Mo and a Cu-In-Se Photoanode”, Chemistry Letter, 47, 2018, p.436-439

[0007] Equation (1) is the oxidation reaction of water. The carbon dioxide reduction reactions shown in equations (2) to (5) proceed in combination with the oxidation reaction of equation (1). As a side reaction, the hydrogen production reaction shown in equation (6) proceeds.

[0008] 2H ２ O + 4h ＋ → O ２ + 4H ＋ (1) CO ２ + 2H ＋ + 2e － → CO + H ２ O (2) CO ２ + 2H ＋ + 2e － → HCOOH (3) CO ２ + 6H ＋ + 6e － → CH ３ OH + H ２ O (4) CO２ + 8H ＋ + 8e － → CH ４ + 2H ２ O (5) 2H ＋ + 2e － → H ２ (6) The reduction reaction of carbon dioxide is most likely to produce carbon monoxide, which is produced with the fewest number of electrons (Equation (2)). However, carbon monoxide is rarely used industrially as it is, and is not further reduced to produce CH ３ OH, CH ４ Therefore, it is desirable to be able to directly produce useful products that are produced by reactions involving more electrons, such as those shown in formulas (4) and (5). However, it is difficult for multi-electron reactions to proceed all at once.

[0009] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a gas-phase reduction device for carbon dioxide that facilitates the progress of a multi-electron reaction.

[0010] A gas-phase carbon dioxide reduction device according to one aspect of the present disclosure comprises an oxidation tank including an oxidation electrode, a reduction tank adjacent to the oxidation tank and supplied with carbon dioxide, and a composite including a plurality of reduction electrodes and an electrolyte membrane disposed between the oxidation tank and the reduction tank, wherein the plurality of reduction electrodes are disposed on the reduction tank side, the electrolyte membrane is disposed on the oxidation tank side, and the plurality of reduction electrodes are connected to the oxidation electrode by conductors, and each of the reduction electrodes performs a different reduction reaction using electrons flowing through the conductors.

[0011] According to the present disclosure, it is possible to provide a gas-phase carbon dioxide reduction device that facilitates the progress of a multi-electron reaction.

[0012] Fig. 1 is a diagram showing an example of the configuration of a gas phase carbon dioxide reduction device according to an embodiment, and Fig. 2 is a diagram showing an example of the configuration of a gas phase carbon dioxide reduction device according to a comparative example.

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to the embodiments described below, and modifications may be made without departing from the spirit and scope of the present disclosure.

[0014] 1 is a configuration diagram showing an example of a gas-phase reduction device for carbon dioxide according to the present embodiment (hereinafter referred to as the "gas-phase reduction device"). The gas-phase reduction device is a reduction device (artificial photosynthesis device) that causes a carbon dioxide reduction reaction at a reduction electrode by irradiating an oxidation electrode with light.

[0015] The gas-phase reduction device of this embodiment comprises an oxidation tank 1 including an oxidation electrode 2, a reduction tank 4 adjacent to the oxidation tank 1 and supplied with carbon dioxide, and a composite 20 including a plurality of reduction electrodes 5A, 5B and an electrolyte membrane 6, which is disposed between the oxidation tank 1 and the reduction tank 4. The plurality of reduction electrodes 5A, 5B are disposed on the reduction tank 4 side, and the electrolyte membrane 6 is disposed on the oxidation tank 1 side. The plurality of reduction electrodes 5A, 5B are connected to the oxidation electrode 2 by a conductor 7, and each of the reduction electrodes 5A, 5B performs a different reduction reaction by electrons flowing through the conductor 7.

[0016] Specifically, the illustrated gas-phase reduction device comprises an oxidation tank 1 and a reduction tank 4 formed by dividing the internal space of a single housing in two. The oxidation tank 1 is filled with an aqueous solution 3, into which an oxidation electrode 2 is inserted. The reduction tank 4 adjacent to the oxidation tank 1 is filled with carbon dioxide gas or a gas containing carbon dioxide.

[0017] A semiconductor, a metal complex, or the like can be used for the oxidation electrode 2. For example, the oxidation electrode 2 may be a compound that exhibits photoactivity or redox activity, such as a nitride semiconductor, titanium oxide, amorphous silicon, a ruthenium complex, or a rhenium complex.

[0018] The aqueous solution 3 may be, for example, an aqueous potassium hydrogen carbonate solution, an aqueous sodium hydrogen carbonate solution, an aqueous potassium chloride solution, an aqueous sodium chloride solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous rubidium hydroxide solution, or an aqueous cesium hydroxide solution.

[0019] A composite 20 is disposed between the oxidation tank 1 and the reduction tank 4. The composite 20 includes a plurality of reduction electrodes 5A, 5B and an electrolyte membrane 6. The composite 20 is formed by joining the plurality of reduction electrodes 5A, 5B and the electrolyte membrane 6. The electrolyte membrane 6 is disposed on the oxidation tank 1 side, and a plurality of reduction electrodes 5A, 5B are disposed on the reduction tank 4 side. The oxidation electrode 2 and the reduction electrodes 5A, 5B are connected in parallel by a conductor 7.

[0020] The composite 20 of this embodiment includes multiple types of reduction electrodes 5A and 5B. Specifically, the composite 20 includes a first reduction electrode 5A and a second reduction electrode 5B, where the first reduction electrode 5A reduces carbon dioxide to a first gas and the second reduction electrode 5B reduces the first gas to a second gas. For example, the composite 20 may include a first reduction electrode 5A made of gold and a second reduction electrode 5B made of copper oxide, where the first reduction electrode 5A reduces carbon dioxide to carbon monoxide and the second reduction electrode 5B reduces carbon monoxide to methane.

[0021] The reduction electrodes 5A and 5B may be made of, for example, a porous body containing copper, platinum, gold, silver, indium, palladium, gallium, nickel, tin, cadmium, or an alloy thereof; a porous body containing silver oxide, copper oxide, copper(II) oxide, nickel oxide, indium oxide, tin oxide, tungsten oxide, tungsten(VI) oxide, copper oxide, or the like; or a porous body containing a porous metal complex having a metal ion and an anionic ligand.

[0022] The electrolyte membrane 6 may be, for example, Nafion (registered trademark), Forblue, or Aquivion, which are electrolyte membranes having a skeleton made of carbon and fluorine, or Selemion or Neocepta, which are electrolyte membranes having a hydrocarbon skeleton.

[0023] The reduction tank 4 is provided with a gas inlet 11 for introducing (inputting) carbon dioxide into the reduction tank 4. The reduction tank 4 also has a gas inlet 11 for introducing (inputting) carbon dioxide into the reduction tank 4. The gas inlet 11 is also provided with a gas inlet 11 for introducing (inputting) carbon dioxide into the reduction tank 4. ４ , C.H. ３ The oxidation vessel 1 is provided with a gas outlet 12 for outputting gas (e.g., OH). A tube (not shown) for introducing helium into the aqueous solution 3 in the oxidation vessel 1 may be inserted into the oxidation vessel 1.

[0024] To operate the gas-phase reduction device, a light source 30 is disposed opposite the oxidation electrode 2. The light source 30 is, for example, a xenon lamp, a solar simulator, a halogen lamp, a mercury lamp, sunlight, or a combination thereof.

[0025] The reduction electrodes 5A and 5B shown in FIG. 1 are arranged in parallel on the electrolyte membrane 6 at a predetermined interval.

[0026] When the first reduction electrode 5A is a reduction electrode that reduces carbon dioxide with a smaller number of reaction electrons than the second reduction electrode 5B, it is preferable that the first reduction electrode 5A be disposed on the gas inlet 11 side of the reduction tank 4, and the second reduction electrode 5B be disposed on the gas outlet 12 side of the reduction tank 4.

[0027] Although the gas-phase reduction device of this embodiment uses two reduction electrodes 5A and 5B as an example, three or more reduction electrodes may be used. When three or more reduction electrodes are arranged in the electrolyte membrane 6, it is preferable to arrange a predetermined reduction electrode on the front side of the carbon dioxide flow path (close to the carbon dioxide flow path). The predetermined reduction electrode is a reduction electrode made of a metal catalyst material that reduces carbon dioxide through a reaction with the fewest number of reaction electrons among all the reduction electrodes, thereby producing a gaseous product. In other words, when the composite body 20 of the gas-phase reduction device includes three or more reduction electrodes, it is preferable that the reduction electrode that reduces carbon dioxide with the fewest number of reaction electrons among the three or more reduction electrodes be arranged closest to the gas input port 11 of the reduction tank 4.

[0028] [Example 1] Next, a gas phase reduction apparatus of Example 1 will be described. The gas phase reduction apparatus of Example 1 is the same as the gas phase reduction apparatus shown in FIG. 1. In Example 1, the target product of the gas phase reduction apparatus is methane (CH ４ By changing the reduction electrode or the atmosphere in the cell, it is possible to produce the target product as an alcohol such as methanol or ethanol, or other useful substances.

[0029] (Preparation of Composite) A method for preparing the composite 20 of Example 1 will be described below. The composite 20 of Example 1 is formed by joining two reduction electrodes 5A and 5B and an electrolyte membrane 6 together.

[0030] In Example 1, a cation exchange membrane was used as the electrolyte membrane 6. Two types of reduction electrodes 5A and 5B were placed on the electrolyte membrane 6. The reduction electrode 5A was made of a porous gold (Au) material, and the reduction electrode 5B was made of a copper oxide (Cu ２ A compact (porous body) of SiO2 (O) was used. The electrolyte membrane 6 with the reduction electrodes 5A and 5B arranged thereon was placed between two copper plates, and this sample was placed between a thermocompression bonding device. While heating, pressure was applied in the direction perpendicular to the copper plate on the reduction electrodes 5A and 5B side. After a certain time had passed, the sample was cooled and removed, thereby obtaining a composite in which the electrolyte membrane 6 and the two reduction electrodes 5A and 5B were joined together.

[0031] (Electrochemical Measurement and Measurement of Amounts of Gas and Liquid Produced) The amounts of products produced in Example 1 were verified by the following method. The verification results are shown in Table 1.

[0032] The oxidation tank 1 was filled with an aqueous solution 3. To form the oxidation electrode 2, a thin film of gallium nitride (GaN), an n-type semiconductor, was epitaxially grown on a sapphire substrate, and then a thin film of aluminum gallium nitride (AlGaN) was epitaxially grown on the gallium nitride (GaN) thin film. Then, nickel (Ni) was vacuum-deposited on the aluminum gallium nitride (AlGaN) thin film, followed by heat treatment, to form a nickel oxide (NiO) promoter thin film. The oxidation electrode 2 thus formed was placed in the oxidation tank 1 so as to be immersed in the aqueous solution 3.

[0033] The aqueous solution 3 was a 1.0 mol / L aqueous potassium hydroxide solution. The light source 30 was a 300 W high-pressure xenon lamp (cutting wavelengths of 450 nm or more, illuminance 2.2 mW / cm ２ The surface of the oxidation electrode 2 on which the oxidation promoter of the semiconductor photoelectrode was formed (the surface on which NiO was formed) was fixed to the irradiated surface. The light irradiation area of ​​the oxidation electrode 2 was set to 2.3 cm ２ It was decided.

[0034] Helium was introduced into the oxidation vessel 1 through a tube (not shown), and carbon dioxide was introduced into the reduction vessel 4 through a gas inlet 11 at a flow rate of 30 ml / min and a pressure of 0.2 MPa. In this system, the reduction reaction of carbon dioxide can proceed at the three-phase interface of [electrolyte membrane-reduction electrode-gas phase carbon dioxide] within the composite 20.

[0035] After the oxidation tank 1 and the reduction tank 4 were thoroughly substituted with helium and carbon dioxide, respectively, light was uniformly irradiated onto the oxidation electrode 2 using the light source 30. By irradiating the oxidation electrode 2 with light, electrons flowed between the oxidation electrode 2 and the reduction electrode 5A, and between the oxidation electrode 2 and the reduction electrode 5B. As a result, different reduction reactions proceeded at the two reduction electrodes 5A and 5B. First, the reduction reaction of formula (7) proceeded at the reduction electrode 5A, and then the reduction reaction of formula (8) proceeded at the reduction electrode 5B.

[0036] CO ２ + 2H ＋ + 2e － → CO + H ２ O (7) CO + 6H ＋ + 6e － → CH ４ + H ２ O (8) That is, in the reduction tank 4, carbon dioxide (CO ２ ) into carbon monoxide (CO), and the converted carbon monoxide (CO) is converted into methane (CH ４ ) In this example, therefore, the reduction reaction of carbon dioxide was allowed to proceed in multiple stages at each of the reduction electrodes 5A and 5B.

[0037] The current value between the oxidation electrode 2 and the reduction electrodes 5A and 5B during light irradiation was measured using an electrochemical measurement device (Solartron, Model 1287 potentiogalvanostat). Furthermore, gas and liquid samples were collected from the oxidation tank 1 and the reduction tank 4 at any time during light irradiation, and the reaction products were analyzed using a gas chromatograph, a liquid chromatograph, and a gas chromatograph mass spectrometer. As a result, it was confirmed that oxygen was produced in the oxidation tank 1 and methane was produced in the reduction tank 4.

[0038] [Comparative Example 1] Fig. 2 is a configuration diagram showing an example of the configuration of a gas-phase reduction device for carbon dioxide in Comparative Example 1. The gas-phase reduction device of Comparative Example 1 differs from the gas-phase reduction device of Example 1 shown in Fig. 1 in that it includes one reduction electrode 5, but is otherwise similar to Example 1. The reduction electrode 5 of Comparative Example 1 uses a porous gold (Au) body, similar to the reduction electrode 5A of Example 1.

[0039] The composite 20A of Comparative Example 1 was produced by bonding a reduction electrode 5 and an electrolyte membrane 6. Specifically, similar to Example 1, gold (Au) was used for the reduction electrode 5, and a cation exchange membrane was used for the electrolyte membrane 6. The reduction electrode 5 was placed on the electrolyte membrane 6, and the electrolyte membrane 6 with the reduction electrode 5 placed thereon was placed between two copper plates. This sample was placed between a thermocompression bonding device, and pressure was applied vertically to the copper plate of the reduction electrode 5 while heating. After a certain period of time had passed, the sample was cooled and removed, thereby obtaining a composite 20A in which the electrolyte membrane 6 and a plurality of reduction electrodes 5 were bonded together.

[0040] The electrochemical measurement and the measurement of the amount of gas and liquid produced in Comparative Example 1 were carried out in the same manner as in Example 1. The verification results of the amount of product produced in Comparative Example 1 are shown in Table 1.

[0041] (Evaluation of Example 1 and Comparative Example 1) Table 1 shows the proportions of reduction products resulting from the reduction reaction of carbon dioxide in Example 1 and Comparative Example 1. ４ The production rate of methane (CH ４ As can be seen from Table 1, Example 1 had a higher production rate of methane (CH ４ This is because, in Example 1, carbon dioxide is reduced to carbon monoxide at the gold reduction electrode 5A, and carbon monoxide (CO) is further reduced to methane (CH ４ In Example 1, by performing the reduction reaction stepwise using a plurality of types of reduction electrodes 5A and 5B, it is possible to perform the multi-electron reduction more effectively than by performing the multi-electron reaction using a single type of reduction electrode.

[0042] As described above, the gas-phase carbon dioxide reduction device of this embodiment comprises: an oxidation tank 1 including an oxidation electrode 2; a reduction tank 4 adjacent to the oxidation tank 1 and supplied with carbon dioxide; and a composite 20 disposed between the oxidation tank 1 and the reduction tank 4, the composite 20 including a plurality of reduction electrodes 5A, 5B and an electrolyte membrane 6, wherein the plurality of reduction electrodes 5A, 5B are disposed on the reduction tank 4 side, and the electrolyte membrane 6 is disposed on the oxidation tank 1 side, and the plurality of reduction electrodes 5A, 5B are connected to the oxidation electrode 2 by a conductor 7, and each of the reduction electrodes 5A, 5B performs a different reduction reaction by electrons flowing through the conductor 7.

[0043] As described above, in the gas-phase reduction device of this embodiment, multiple types of reduction electrodes 5A, 5B are arranged in one cell (reduction tank 4), the reduction reaction of carbon dioxide is carried out in multiple stages, and a multi-electron reaction, which is normally difficult to occur, is carried out in stages, thereby making it easier to convert carbon dioxide into more useful organic substances.

[0044] For example, the first reduction electrode 5A is ２ ) into carbon monoxide (CO), and the converted carbon monoxide (CO) is converted into methane (CH ４ This makes it easier to carry out multi-step reduction rather than directly reducing carbon dioxide through a multi-electron reaction.

[0045] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0046] DESCRIPTION OF SYMBOLS 1: Oxidation tank 2: Oxidation electrode 3: Aqueous solution 4: Reduction tank 5A, 5B, 5: Reduction electrode 6: Electrolyte membrane 7: Conductor 11: Gas inlet (inlet) 12: Gas outlet (output) 20, 20A: Composite 30: Light source

Claims

1. A gas-phase carbon dioxide reduction device comprising: an oxidation tank including an oxidation electrode; a reduction tank adjacent to the oxidation tank and supplied with carbon dioxide; and a composite including a plurality of reduction electrodes and an electrolyte membrane arranged between the oxidation tank and the reduction tank, wherein the plurality of reduction electrodes are arranged on the reduction tank side and the electrolyte membrane is arranged on the oxidation tank side, and the plurality of reduction electrodes are connected to the oxidation electrode by conductors, and each of the reduction electrodes performs a different reduction reaction by electrons flowing through the conductors.

2. The gas-phase carbon dioxide reduction device according to claim 1, wherein the composite comprises a plurality of types of reduction electrodes.

3. The gas-phase carbon dioxide reduction device according to claim 1, wherein the composite comprises a first reduction electrode and a second reduction electrode, the first reduction electrode reduces the carbon dioxide to a first gas, and the second reduction electrode reduces the first gas to a second gas.

4. The gas-phase carbon dioxide reduction device according to claim 1, wherein the composite comprises a first reduction electrode made of gold and a second reduction electrode made of copper oxide, the first reduction electrode reducing the carbon dioxide to carbon monoxide, and the second reduction electrode reducing the carbon monoxide to methane.

5. The gas-phase carbon dioxide reduction device according to claim 1, wherein the reduction tank comprises an input port for inputting the carbon dioxide and an output port for outputting the gas produced by the reduction reaction, the composite comprises a first reduction electrode and a second reduction electrode, the first reduction electrode is a reduction electrode that reduces the carbon dioxide with a smaller number of reaction electrons than the second reduction electrode, the first reduction electrode is arranged on the input port side of the reduction tank, and the second reduction electrode is arranged on the output port side of the reduction tank.

6. The gas-phase carbon dioxide reduction device according to claim 1, wherein the reduction tank has an input port for inputting the carbon dioxide, the composite has three or more reduction electrodes, and the reduction electrode that reduces the carbon dioxide with the smallest number of reaction electrons among the three or more reduction electrodes is positioned closest to the input port of the reduction tank.

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