Carbon dioxide capture system

Abstract

To provide a carbon dioxide recovery system capable of suppressing the generation of organic gas accompanied by reaction of a substance which contains oxygen, with an electrode.SOLUTION: A carbon dioxide recovery system separates CO2 from CO2 containing gas which contains CO2 by electrochemical reaction. The carbon dioxide recovery system includes an electrochemical cell 201. The electrochemical cell 201 includes an operation electrode 210 which has CO2 adsorption material 212 for adsorbing CO2 and a counter electrode 220. In the electrochemical cell 201, an electron is supplied from the counter electrode 220 to the operation electrode 210 by applying a voltage between the operation electrode 210 and the counter electrode 220, and the CO2 adsorption material 212 is combined with CO2 accompanying that the electron is supplied thereto. The operation electrode 210 has an operation electrode side conductive assistant 213 which forms a conductive path to the CO2 adsorption material 212. The operation electrode side conductive assistant 213 is a metal oxide having such a structure that oxygen elements are arranged around a metal element.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide capture system for capturing CO2 from a CO2-containing gas. [Background technology]

[0002] A gas separation system that separates CO2 from a CO2-containing gas by an electrochemical reaction has been proposed in, for example, Patent Document 1. The gas separation system includes an electrochemical cell having electrodes. The electrodes are made of carbonaceous materials such as carbon nanotubes, carbon black, ketjen black, graphene, or carbon-containing materials such as polyanthraquinone and polyvinylferrocene. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2018-533470 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional technology, the carbon-containing electrode is in contact with the atmosphere, which causes a reaction between the electrode and oxygen-containing substances such as H2O and O2 in the atmosphere, resulting in the generation of organic gases.

[0005] The generation of organic gases reduces the purity of CO2 capture. Also, the purity of CO2 capture relative to the energy used to capture it decreases, resulting in a decrease in energy efficiency. Furthermore, the electrode wears out as a result of the reaction between oxygen-containing substances and the electrode, reducing the electrode's durability during repeated use.

[0006] In view of the above, an object of the present invention is to provide a carbon dioxide recovery system that can suppress the generation of organic gases that accompany the reaction between an oxygen-containing substance and an electrode. [Means for solving the problem]

[0007] In order to achieve the above object, claims 1 to The described invention is a carbon dioxide capture system for separating CO2 from a CO2-containing gas containing CO2 by an electrochemical reaction, comprising an electrochemical cell (201).

[0008] The electrochemical cell includes a working electrode (210) having a CO2 adsorbent (212) that adsorbs CO2, and a counter electrode (220). When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO2 adsorbent bonds with CO2 as the electrons are supplied.

[0009] In the invention described in claim 1, the working electrode has a working electrode-side conductive additive (213) that forms a conductive path to the CO2 adsorbent. The working electrode-side conductive additive is a metal oxide having a structure in which oxygen elements are arranged around a metal element. The metal oxide serving as the conductive additive on the working electrode side is manganese dioxide.

[0010] According to this, since the working electrode-side conductive additive is a metal oxide that does not contain carbon, no reaction occurs between the oxygen-containing substance in the CO2-containing gas and the working electrode-side conductive additive, thereby suppressing the generation of organic gases.

[0015] The symbols in parentheses for each means described in this section and in the claims indicate the correspondence with the specific means described in the embodiments described later. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing a carbon dioxide capture system according to a first embodiment. [Figure 2] FIG. 1 is a diagram showing a CO2 capture device. [Figure 3] FIG. 1 is a cross-sectional view of an electrochemical cell. [Figure 4] FIG. 1 is a graph showing the CO2 selective permeability and hydrophobicity of a negative electrode binder. [Figure 5] FIG. 2 is an enlarged cross-sectional view of the vicinity of the surface of the negative electrode of the electrochemical cell. [Figure 6] 2 is a diagram for explaining a CO2 capture mode and a CO2 release mode of the CO2 capture device. FIG. [Figure 7] FIG. 1 is a diagram showing the reaction between a working electrode-side conductive additive, which is a metal oxide, and O 2 − . [Figure 8] FIG. 10 is a diagram showing the reaction of a working electrode-side conductive additive, which is a carbon material, with O 2 − as a comparative example. [Figure 9] FIG. 10 is a diagram showing the decomposition reaction of polyvinylferrocene in the second embodiment. [Figure 10] FIG. 1 is a diagram showing the molecular structure of decamethylferrocene according to a second embodiment. [Figure 11] FIG. 10 is a diagram showing the molecular structure of phenothiazine in a third embodiment. [Figure 12] FIG. 10 is a diagram showing the molecular structure of phenoxazine according to a third embodiment. [Figure 13] FIG. 10 is a diagram showing the molecular structure of methylphenothiazine according to a third embodiment. [Figure 14] FIG. 10 is a diagram showing the molecular structure of phenylphenothiazine according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts are designated by the same reference numerals in the drawings.

[0018] (First embodiment) The carbon dioxide capture system according to this embodiment separates CO2 from a CO2-containing gas by an electrochemical reaction. As shown in Fig. 1, the carbon dioxide capture system 1 includes a compressor 100, a CO2 capture device 200, a flow path switching valve 300, a CO2 utilization device 400, and a control device 500.

[0019] The compressor 100 compresses and sends the CO2-containing gas to the CO2 recovery device 200. The CO2-containing gas is a mixed gas containing CO2 and gases other than CO2. The CO2-containing gas is, for example, the atmosphere or exhaust gas from an internal combustion engine.

[0020] The CO2 capture device 200 is a device that separates and captures CO2 from a CO2-containing gas. The CO2 capture device 200 discharges a CO2-removed gas after CO2 has been captured from the CO2-containing gas, or discharges CO2 captured from the CO2-containing gas.

[0021] The flow path switching valve 300 is a three-way valve that switches the flow path of the exhaust gas from the CO2 recovery device 200. When CO2-removed gas is discharged from the CO2 recovery device 200, the flow path switching valve 300 switches the flow path of the exhaust gas to the atmosphere. When CO2 is discharged from the CO2 recovery device 200, the flow path switching valve 300 switches the flow path of the exhaust gas to the CO2 utilization device 400.

[0022] The CO2 utilization device 400 is a device for utilizing CO2. For example, a storage tank for storing CO2 or a conversion device for converting CO2 into fuel can be used as the CO2 utilization device 400. The conversion device can be a device that converts CO2 into a hydrocarbon fuel such as methane. The hydrocarbon fuel may be a gaseous fuel at room temperature and pressure, or a liquid fuel at room temperature and pressure.

[0023] The control device 500 is composed of a well-known microcomputer including a CPU, ROM, RAM, etc., and its peripheral circuits. The control device 500 performs various calculations and processes according to a control program stored in the ROM. The control device 500 also controls the compressor 100, the CO2 recovery device 200, and the flow path switching control of the flow path switching valve 300.

[0024] Next, a specific configuration of the CO2 recovery apparatus 200 will be described. As shown in Figures 2 and 3, the CO2 recovery apparatus 200 includes an electrochemical cell 201. The electrochemical cell 201 has a working electrode 210, a counter electrode 220, an insulating layer 230, and an ion-conductive member 240.

[0025] 2 shows an example in which the working electrode 210, the counter electrode 220, and the insulating layer 230 are each configured in a plate shape. Note that in FIG. 2, the working electrode 210, the counter electrode 220, and the insulating layer 230 are arranged with a gap between them, but in reality, these components are arranged so as to be in contact with each other.

[0026] The electrochemical cell 201 may be housed in a container (not shown). The container may be provided with a gas inlet for allowing the CO2-containing gas to flow into the container and a gas outlet for allowing the CO2-removed gas and CO2 to flow out of the container.

[0027] The CO2 recovery device 200 adsorbs and desorbs CO2 through an electrochemical reaction, separating and recovering CO2 from a CO2-containing gas. The CO2 recovery device 200 has a power supply 202 that applies a predetermined voltage to a working electrode 210 and a counter electrode 220. The power supply 202 can change the potential difference between the working electrode 210 and the counter electrode 220. The working electrode 210 is a negative electrode. The counter electrode 220 is a positive electrode.

[0028] The electrochemical cell 201 can operate in a CO2 capture mode in which CO2 is captured by the working electrode 210, and a CO2 release mode in which CO2 is released from the working electrode 210. The CO2 capture mode and CO2 release mode are switched by changing the potential difference between the working electrode 210 and the counter electrode 220. The CO2 capture mode is a charge mode in which the electrochemical cell 201 is charged. The CO2 release mode is a discharge mode in which the electrochemical cell 201 is discharged.

[0029] In the CO2 capture mode, a first voltage is applied between the working electrode 210 and the counter electrode 220. This causes electrons to be supplied from the counter electrode 220 to the working electrode 210. At the first voltage, the working electrode potential is smaller than the counter electrode potential. The first voltage can be set within a range of 0.5V to 2.0V, for example.

[0030] In the CO2 release mode, a second voltage lower than the first voltage is applied between the working electrode 210 and the counter electrode 220. This causes electrons to be supplied from the working electrode 210 to the counter electrode 220. The second voltage may be any voltage lower than the first voltage, and the magnitude relationship between the working electrode potential and the counter electrode potential is not limited. That is, in the CO2 release mode, the working electrode potential may be lower than the counter electrode potential, the working electrode potential may be equal to the counter electrode potential, or the working electrode potential may be higher than the counter electrode potential.

[0031] 3, the working electrode 210 has a working electrode-side substrate 211, a CO adsorbent 212, a working electrode-side conductive additive 213, and a working electrode-side binder 214. For convenience, in FIG. 3, the CO adsorbent 212, the working electrode-side conductive additive 213, and the working electrode-side binder 214 are shown as being located outside the working electrode-side substrate 211. In reality, the CO adsorbent 212, the working electrode-side conductive additive 213, and the working electrode-side binder 214 are provided inside the porous working electrode-side substrate 211.

[0032] The working electrode side substrate 211 is a porous conductive material that allows CO2 to pass through. For example, a carbonaceous material or a metal material can be used as the working electrode side substrate 211. For example, carbonaceous materials that constitute the working electrode side substrate 211 can be carbon paper, carbon cloth, nonwoven carbon mats, porous gas diffusion layers (GDLs), etc. For example, metal materials that constitute the working electrode side substrate 211 can be a mesh structure made of metals such as Al and Ni.

[0033] The CO2 adsorbent 212 is an electroactive species that has redox activity and can undergo reversible oxidation-reduction reactions. The CO2 adsorbent 212 can bind and adsorb CO2 in a reduced state and can release CO2 in an oxidized state.

[0034] The CO2 adsorbent 212 has a functional group that bonds with CO2. The functional group that bonds with CO2 receives and gives off electrons to become a CO2 adsorption site. Examples of the functional group that bonds with CO2 include functional groups containing elements with high electronegativity such as F, O, N, Cl, and S. For example, a ketone group (C=O) can be used as the functional group that bonds with CO2.

[0035] In this embodiment, polyanthraquinone, an organic polymer having a ketone group, is used as the CO2 adsorbent 212. Examples of polyanthraquinone that can be used include poly-(1,4-anthraquinone), poly-(1,5-anthraquinone), poly-(1,8-anthraquinone), and poly-(2,6-anthraquinone). In this embodiment, the following poly-(1,4-anthraquinone) is used as the CO2 adsorbent 212.

[0036] [ka] The working electrode-side conductive additive 213 is a conductive material that forms a conductive path to the CO2 adsorbent 212. The working electrode-side conductive additive 213 is used by mixing it with the CO2 adsorbent 212. Note that, although the working electrode-side conductive additive 213 is depicted in FIG. 3 as being separated from the CO2 adsorbent 212, in reality the working electrode-side conductive additive 213 is in contact with the CO2 adsorbent 212.

[0037] The CO2 adsorbent 212 and the working electrode-side conductive additive 213 can be mixed by dissolving the working electrode-side conductive additive 213 in an organic solvent such as NMP (N-methylpyrrolidone) and bringing the working electrode-side conductive additive 213 dispersed in the organic solvent into contact with the CO2 adsorbent 212. The contact between the working electrode-side conductive additive 213 and the CO2 adsorbent 212 can be achieved by a method such as dip coating, in which the working electrode-side substrate 211 containing the CO2 adsorbent 212 is immersed in a solvent in which the working electrode-side conductive additive 213 is dispersed. This allows the working electrode-side conductive additive 213 to come into uniform contact with the CO2 adsorbent 212.

[0038] The working electrode-side conductive additive 213 is a metal oxide having a structure in which oxygen elements are arranged around a metal element. Metal oxides are stable conductive additives that do not undergo chemical reactions other than the main reaction with gas species in the atmosphere except for CO2. Metal oxides are stable conductive additives that do not undergo chemical reactions other than the main reaction with electrode components of the working electrode 210 other than the working electrode-side conductive additive 213. The main reaction is when a voltage is applied between the working electrode 210 and the counter electrode 220 in the electrochemical cell 201, causing electrons to be supplied from the counter electrode 220 to the working electrode 210, and the CO2 adsorbent 212 to bond with CO2 as the electrons are supplied.

[0039] Examples of the metal element include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Alternatively, examples of the metal element include Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag. Alternatively, examples of the metal element include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Examples of the metal oxide include ruthenium oxide and manganese dioxide. The working electrode side conductive additive 213 is, for example, in a particulate form.

[0040] The working electrode-side binder 214 is a retaining material for retaining the CO2 adsorbent 212 and the working electrode-side conductive additive 213 on the working electrode-side substrate 211. The working electrode-side binder 214 has adhesive strength. Furthermore, the working electrode-side binder 214 retains the CO2 adsorbent 212 and the working electrode-side conductive additive 213 on the working electrode-side substrate 211. This ensures the transfer of electrons among the working electrode-side substrate 211, the CO2 adsorbent 212, and the working electrode-side conductive additive 213. Furthermore, the CO2 adsorbent 212 is less likely to peel off from the working electrode-side substrate 211, which can prevent the CO2 adsorption amount of the electrochemical cell 201 from decreasing over time.

[0041] The working electrode side binder 214 may be a conductive material having electrical conductivity, which can prevent the working electrode side binder 214 from interfering with the flow of electrons between the working electrode side base material 211 and the CO adsorbent 212.

[0042] In this embodiment, a mixture of a CO2 adsorbent 212, a working electrode-side conductive additive 213, and a working electrode-side binder 214 is formed, and this mixture is adhered to the working electrode-side substrate 211. The CO2 adsorbent 212 and the working electrode-side conductive additive 213 are held inside the working electrode-side binder 214. Therefore, the working electrode-side binder 214 can firmly hold the CO2 adsorbent 212 and the working electrode-side conductive additive 213. In addition, the CO2 adsorbent 212 and the working electrode-side conductive additive 213 are less likely to peel off from the working electrode-side substrate 211.

[0043] The working electrode side binder 214 has CO2 permeability, which allows CO2 to pass through. Furthermore, the working electrode side binder 214 has CO2 selective permeability, which allows CO2 to selectively pass through among multiple types of gases contained in the CO2-containing gas. In addition, the working electrode side binder 214 is hydrophobic.

[0044] 4, CO2 contained in the CO2-containing gas can permeate the working electrode-side binder 214 and reach the CO2 adsorbent 212 located inside the working electrode-side binder 214. That is, even if the CO2-containing gas cannot directly contact the CO2 adsorbent 212, CO2 can permeate the working electrode-side binder 214 and reach the CO2 adsorbent 212. Therefore, even if the CO2 adsorbent 212 is located inside the working electrode-side binder 214, it is possible to capture CO2 by the CO2 adsorbent 212.

[0045] On the other hand, gases other than CO2, such as N2 and O2, contained in the CO2-containing gas, cannot permeate the working electrode-side binder 214, which has CO2 selective permeability. This makes it possible to prevent gases other than CO2 contained in the CO2-containing gas from reaching the working electrode-side binder 214. This makes it possible to increase the concentration of CO2 reaching the CO2 adsorbent 212. Furthermore, it is possible to increase the amount of CO2 adsorbed by the CO2 adsorbent 212.

[0046] Furthermore, when moisture (H2O) is contained in the CO2-containing gas, the moisture does not penetrate into the hydrophobic working electrode-side binder 214. Therefore, even in the presence of moisture (H2O), it is possible to prevent H2O from reaching the working electrode-side binder 214. This makes it possible to prevent H2O from preferentially reacting with the CO2 adsorbent 212, thereby increasing the amount of CO2 adsorbed by the CO2 adsorbent 212.

[0047] A non-fluid substance that does not have fluidity can be used as the working electrode side binder 214. Examples of the non-fluid substance include a gel-like substance and a solid-like substance. Examples of the gel-like substance include an ionic liquid gel. Examples of the solid-like substance include a solid electrolyte, a conductive resin, or the like.

[0048] When a solid electrolyte is used as the working electrode side binder 214, it is desirable to use an ionomer made of a polymer electrolyte or the like in order to increase the contact area with the CO2 adsorbent 212. When a conductive resin is used as the working electrode side binder 214, an epoxy resin containing Ag or the like as a conductive filler, or a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) can be used.

[0049] The raw material of the working electrode-side binder 214 may be a liquid substance having fluidity. In this case, the CO adsorbent 212 may be dispersed or mixed in the raw material of the working electrode-side binder 214, and the raw material may be attached to the working electrode-side base material 211 by impregnation, coating, or the like. Thereafter, the raw material of the working electrode-side binder 214 may be gelled or solidified under predetermined conditions. The predetermined conditions are conditions such as a specific pressure, a specific temperature, and a specific time that can gel or solidify the raw material of the working electrode-side binder 214.

[0050] 5, the working electrode side binder 214 is fixed by entering holes and gaps in the unevenness formed on the surface of the working electrode side substrate 211. The working electrode side binder 214 can generate a mechanical bonding force between itself and the working electrode side substrate 211 due to an anchoring effect.

[0051] In this embodiment, an ionic liquid gel obtained by gelling an ionic liquid is used as the working electrode-side binder 214. The ionic liquid gel is a gel-like structure in which an ionic liquid is held in a polymer network structure. Using the ionic liquid gel as the working electrode-side binder 214 makes it easier for the CO adsorbent 212 and the working electrode-side binder 214 to come into contact with each other, thereby improving conductivity.

[0052] The structure disclosed in Japanese Patent Laid-Open No. 2015-25056 can be used as the ionic liquid gel. In this structure, an ionic liquid is held in a three-dimensional network structure made of two different types of polymer chains. The three-dimensional network structure includes a first network structure formed by condensation polymerization and a second network structure formed by radical polymerization.

[0053] Tetraethoxyorthosilicate (TEOS) can be used as a monomer for condensation polymerization. TEOS also functions as a cross-linking agent for condensation polymerization.

[0054] N,N-dimethylacrylamide (DMAAm) can be used as a monomer for radical polymerization. In radical polymerization, N,N'-methylenebisacrylamide (MBAA) can be used as a crosslinking agent. In addition, 2,2'-azobis(isobutyronitrile) (AIBN) can be used as an initiator.

[0055] The ionic liquid that constitutes the ionic liquid gel functions as a solvent for the monomers that constitute the first network structure and the monomers that constitute the second network structure. After the first network structure and the second network structure are formed, the first network structure and the second network structure become entangled with each other, and the ionic liquid is entrapped in these network structures.

[0056] Examples of ionic liquids that can be used to form the ionic liquid gel include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TfN]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TfN]), and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF]).

[0057] It is desirable to use a hydrophobic ionic liquid as the ionic liquid constituting the ionic liquid gel in order to impart hydrophobicity to the working electrode side binder 214. As the hydrophobic ionic liquid, [EMIM][TfN] or [BMIM][TfN] can be used.

[0058] The ionic liquid gel of this embodiment can be obtained by independently conducting condensation polymerization of a monomer (e.g., TEOS) that forms the first network structure and radical polymerization of a monomer (e.g., DMAAm) that forms the second network structure in an ionic liquid. The method for producing the ionic liquid gel of this embodiment includes the steps of mixing the monomers that form the first network structure and the monomers that form the second network structure in an ionic liquid, forming the first network structure by condensation polymerization, and forming the second network structure by radical polymerization. Radical polymerization may be performed after condensation polymerization, or condensation polymerization and radical polymerization may be performed simultaneously.

[0059] 3 has the same configuration as the working electrode 210. That is, the counter electrode 220 has a counter electrode-side substrate 221, a counter electrode-side active material 222, a counter electrode-side conductive additive 223, and a counter electrode-side binder 224.

[0060] The counter electrode substrate 221 is made of a conductive material. The counter electrode substrate 221 may be made of the same material as the working electrode substrate 211, or may be made of a different material.

[0061] The counter electrode side active material 222 is an auxiliary electroactive species whose redox state is opposite to that of the CO adsorbent 212 and which transfers electrons to and from the CO adsorbent 212. For example, a metal complex that allows electron transfer by changing the valence of the metal ion can be used as the counter electrode side active material 222. Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickelocene, and cobaltocene, and porphyrin metal complexes. In this embodiment, polyvinylferrocene shown below is used as the counter electrode side active material 222.

[0062] [ka] The counter electrode-side conductive additive 223 is a conductive material that forms a conductive path to the counter electrode-side active material 222. The counter electrode-side conductive additive 223 is used by mixing with the counter electrode-side active material 222. Note that, although the counter electrode-side conductive additive 223 is depicted in FIG. 3 as being separated from the counter electrode-side active material 222, in reality the counter electrode-side conductive additive 223 is in contact with the counter electrode-side active material 222.

[0063] The counter electrode-side conductive additive 223 is a metal oxide having a structure in which oxygen elements are arranged around a metal element. The counter electrode-side conductive additive 223 may be made of the same material as or a different material from the working electrode-side conductive additive 213. The counter electrode-side conductive additive 223 is, for example, in a particulate form.

[0064] The counter electrode side binder 224 may be any material as long as it can hold the counter electrode side active material 222 and the counter electrode side conductive assistant 223 on the counter electrode side base material 221 and has conductivity. The counter electrode side binder 224 may be made of the same material as the working electrode side binder 214, or may be made of a different material.

[0065] The insulating layer 230 is disposed between the working electrode 210 and the counter electrode 220. The insulating layer 230 separates the working electrode 210 and the counter electrode 220. The insulating layer 230 prevents physical contact between the working electrode 210 and the counter electrode 220. The insulating layer 230 also suppresses electrical short-circuiting between the working electrode 210 and the counter electrode 220.

[0066] A separator or a gas layer such as air can be used as the insulating layer 230. In this embodiment, a porous separator is used as the insulating layer 230. The separator may be made of a cellulose film, a polymer, a composite material of polymer and ceramic, or the like.

[0067] The ion conductive member 240 is provided between the working electrode 210 and the counter electrode 220. Specifically, the ion conductive member 240 is provided between the working electrode side substrate 211 and the counter electrode side substrate 221 with the insulating layer 230 interposed therebetween.

[0068] The ion conductive member 240 is in contact with the CO adsorbent 212 inside the working electrode side substrate 211. The ion conductive member 240 has ion conductivity. This allows the ion conductive member 240 to promote conduction to the CO adsorbent 212. The ions contained in the ion conductive member 240 do not directly react with the functional groups contained in the CO adsorbent 212 that bond to CO.

[0069] A non-fluidic substance that does not have fluidity can be used as the ion conductive member 240. Examples of the non-fluidic substance include a gel-like substance and a solid substance. Examples of the non-fluidic substance that can be used include an ionic liquid gel and a solid electrolyte. The ion conductive member 240 may be made of the same material as the working electrode-side binder 214, or may be made of a material different from that of the working electrode-side binder 214. In this way, using a non-fluidic substance as the ion conductive member 240 can prevent the ion conductive member 240 from eluting from between the working electrode 210 and the counter electrode 220.

[0070] Next, a description will be given of the operation of the carbon dioxide capture system 1. As shown in Fig. 6, the carbon dioxide capture system 1 alternately switches between a CO2 capture mode and a CO2 release mode. The carbon dioxide capture system 1 is controlled by a control device 500.

[0071] First, the CO2 capture mode will be described. In the CO2 capture mode, the compressor 100 operates to supply CO2-containing gas to the CO2 capture device 200. In the CO2 capture device 200, a voltage applied between the working electrode 210 and the counter electrode 220 is set as a first voltage. This allows electron donation by the counter electrode side active material 222 of the counter electrode 220 and electron attraction by the CO2 adsorbent 212 of the working electrode 210 to be achieved simultaneously.

[0072] When a voltage is applied between the working electrode 210 and the counter electrode 220, the counter electrode side active material 222 of the counter electrode 220 emits electrons and becomes oxidized, and the electrons are supplied from the counter electrode 220 to the working electrode 210. The CO2 adsorbent 212 of the working electrode 210 receives the electrons and becomes reduced.

[0073] The reduced CO2 adsorbent 212 has a higher CO2 binding strength and binds to and adsorbs CO2 contained in the CO2-containing gas. In this way, when a voltage is applied between the working electrode 210 and the counter electrode 220 in the electrochemical cell 201, electrons are supplied from the counter electrode 220 to the working electrode 210, and the CO2 adsorbent 212 binds to CO2 as the electrons are supplied. Thus, the CO2 recovery device 200 can recover CO2 from the CO2-containing gas.

[0074] After CO2 from the CO2-containing gas is captured by the CO2 capture device 200, a CO2-removed gas that does not contain CO2 is discharged from the CO2 capture device 200. The flow path switching valve 300 switches the gas flow path to the atmosphere side. Therefore, the CO2-removed gas discharged from the CO2 capture device 200 is released into the atmosphere.

[0075] Next, the CO2 release mode will be described. In the CO2 release mode, the compressor 100 stops, and the supply of CO2-containing gas to the CO2 recovery device 200 stops. In the CO2 recovery device 200, the voltage applied between the working electrode 210 and the counter electrode 220 is set to a second voltage. This allows electron donation by the CO2 adsorbent 212 of the working electrode 210 and electron attraction by the counter electrode side active material 222 of the counter electrode 220 to be achieved simultaneously.

[0076] The CO2 adsorbent 212 of the working electrode 210 releases electrons and becomes oxidized. The CO2 adsorbent 212 loses its bond strength with CO2, and desorbs and releases CO2. The counter electrode active material 222 of the counter electrode 220 receives electrons and becomes reduced.

[0077] The CO2 released from the CO2 adsorbent 212 is discharged from the CO2 recovery device 200. The flow path switching valve 300 switches the gas flow path to the CO2 utilization device 400 side. Therefore, the CO2 discharged from the CO2 recovery device 200 is supplied to the CO2 utilization device 400.

[0078] As described above, in this embodiment, the working electrode 210 includes the working electrode-side conductive additive 213. The working electrode-side conductive additive 213 is a metal oxide that does not contain carbon. In the metal oxide, oxygen elements are already bonded around the metal elements. For this reason, as shown in FIG. 7, no reaction occurs between the oxygen-containing substance in the CO2-containing gas and the working electrode-side conductive additive 213. When a negative voltage is applied to the electrochemical cell 201, the oxygen-containing substance is converted into O2 by an electric field reaction of the oxygen contained in the CO2-containing gas. 2- Therefore, an example of the reaction between the substance containing oxygen and the working electrode side conductive additive 213 is 2O 2- →O2+4e - is.

[0079] In this way, no reaction occurs between the oxygen-containing substance contained in the CO2-containing gas and the working electrode-side conductive additive 213, and only oxygen is produced, so the working electrode-side conductive additive 213 is not consumed by the oxygen-containing substance. In other words, the working electrode 210 is not consumed. Of course, the conductivity of the working electrode-side conductive additive 213 is maintained. The same applies to the counter electrode-side conductive additive 223 of the counter electrode 220. Therefore, it is possible to suppress the generation of organic gas on both the working electrode 210 side and the counter electrode 220 side.

[0080] Suppressing the generation of organic gases can improve the purity of CO2 recovery. Also, since the purity of CO2 recovery relative to the energy used to recover CO2 is improved, energy efficiency can be improved. Furthermore, since the working electrode 210 and the counter electrode 220 are not consumed in association with reactions with oxygen-containing substances, the repeated durability of the working electrode 210 and the counter electrode 220 can be improved.

[0081] As a comparative example, when the working electrode-side conductive additive 213 is a carbon material, a reaction occurs between the oxygen-containing substance in the CO2-containing gas and the working electrode-side conductive additive 213, as shown in FIG. 8. An example of the reaction between the oxygen-containing substance and the working electrode-side conductive additive 213 is 2- +C→CO2+4e - In this way, the carbon in the working electrode-side conductive additive 213 is used in the reaction, and the working electrode-side conductive additive 213 is consumed. In other words, the working electrode-side conductive additive 213 decreases. Therefore, the conductivity of the working electrode-side conductive additive 213 decreases.

[0082] As a modified example, the counter electrode 220 may not include the counter electrode-side conductive additive 223. Alternatively, the counter electrode 220 may include a conductive additive different from the counter electrode-side conductive additive 223.

[0083] (Second embodiment) In this embodiment, differences from the first embodiment will be mainly described. As shown in FIG. 9, when the counter electrode side active material 222 is polyvinylferrocene, Fe is a reaction site, and therefore, Fe and O in the polyvinylferrocene are reacted with a substance containing oxygen. 2- This may result in the formation of iron oxide and cyclopentadiene.

[0084] Therefore, in this embodiment, a substance in which a functional group is modified at the vertex of the five-membered ring constituting a cyclopentadienyl metal complex is used as the counter electrode active material 222. Specifically, the counter electrode active material 222 is decamethylferrocene in which a methyl group is modified at the vertex of the five-membered ring constituting ferrocene, which is a cyclopentadienyl metal complex.

[0085] The counter electrode side active material 222 is a stable active material that does not undergo any chemical reaction other than the main reaction with gas species in the atmosphere except for CO. The counter electrode side active material 222 is a stable active material that does not undergo any chemical reaction other than the main reaction with electrode members of the counter electrode 220 other than the counter electrode side active material 222.

[0086] As shown in Figure 10, the functional group acts as a steric hindrance, making it difficult for oxygen-containing substances to physically approach the Fe that constitutes decamethylferrocene. This suppresses the decomposition reaction of decamethylferrocene by oxygen-containing substances. This also prevents the generation of organic gases.

[0087] As a modified example, the counter electrode active material 222 is not limited to decamethylferrocene. For example, a five-membered ring having a long distance between C and H at the vertex may be used. Alternatively, a five-membered ring having a benzene ring attached to the vertex may be used.

[0088] (Third embodiment) In this embodiment, differences from the first and second embodiments will be mainly described. In this embodiment, the counter electrode active material 222 is a heterocyclic compound in which benzene rings are fused to both ends of a thiazine containing sulfur and nitrogen elements, and the sulfur element is substituted with an element other than sulfur.

[0089] Here, as shown in Figure 11, a heterocyclic compound in which benzene rings are condensed at both ends of a thiazine containing sulfur and nitrogen elements is phenothiazine. In phenothiazine, -NH and S are reactive sites, and O 2- Therefore, in this embodiment, the sulfur element in phenothiazine is substituted with an oxygen element, as shown in Fig. 12. That is, the counter electrode side active material 222 is phenoxazine.

[0090] In this way, by substituting some elements of phenothiazine, it is possible to improve the structural stability of the counter electrode side active material 222. This makes it possible to suppress the reaction between the oxygen-containing substance contained in the CO2-containing gas and the counter electrode side active material 222. This makes it possible to suppress the generation of organic gas.

[0091] As a modified example, a substance in which the nitrogen atom of phenothiazine has been modified with a functional group may be used as the counter electrode side active material 222. As shown in Fig. 13, for example, the counter electrode side active material 222 is methylphenothiazine in which the nitrogen atom of a heterocyclic compound has been modified with a methyl group. Alternatively, as shown in Fig. 14, the counter electrode side active material 222 is phenylphenothiazine in which the nitrogen atom of phenothiazine has been modified with a phenyl group.

[0092] (Fourth embodiment) In this embodiment, differences from the first to third embodiments will be mainly described. In this embodiment, the voltage applied between the working electrode 210 and the counter electrode 220 is greater than −0.9 V and less than 0 V. This voltage condition is adopted in either or both of the CO2 capture mode and the CO2 release mode.

[0093] As described above, a negative voltage is applied to the electrochemical cell 201 to 2- The specific electric field reaction is O2 + 2e - →2O 2- The inventors have found through experiments that the above electric field reaction occurs when the voltage applied to the electrochemical cell 201 is −0.9 V or less, but that the above electric field reaction is less likely to occur in the voltage range between −0.9 V and 0 V.

[0094] Therefore, by setting the voltage applied to the electrochemical cell 201 within this voltage range, O that easily reacts with the working electrode side conductive additive 213, the counter electrode side conductive additive 223, and the counter electrode side active material 222 can be easily removed. 2- Therefore, the generation of organic gases on both the working electrode 210 side and the counter electrode 220 side can be further suppressed.

[0095] (Other embodiments) The configuration of the carbon dioxide capture system 1 shown in each of the above embodiments is an example, and the present invention is not limited to the configuration shown above, and other configurations are also possible that can realize the present invention. For example, although the compressor 100 is arranged upstream of the CO2 capture device 200, the compressor 100 may also be arranged downstream of the CO2 capture device 200.

[0096] In the above embodiment, the working electrode 210, counter electrode 220, and insulating layer 230 of the electrochemical cell 201 are each plate-shaped members, but they may also be cylindrical members. In this case, the working electrode 210 may be disposed on the innermost side, the counter electrode 220 may be disposed on the outermost side, and the insulating layer 230 may be disposed between the working electrode 210 and the counter electrode 220. This allows the space formed inside the working electrode 210 to serve as a gas flow path through which the CO2-containing gas passes.

[0097] In the above embodiment, the working electrode side binder 214 is used which has hydrophobicity, but the working electrode side binder 214 does not necessarily have to have hydrophobicity.

[0098] In the above embodiment, the working electrode side binder 214 that selectively permeates CO2 is used, but the working electrode side binder 214 does not necessarily have to have selective CO2 permeability.

[0099] In the above embodiment, the CO2 adsorbent 212 is disposed inside the working electrode-side binder 214, but the CO2 adsorbent 212 may be disposed on the surface of the working electrode-side binder 214. In this case, since the CO2 adsorbent 212 can come into direct contact with the CO2-containing gas, the working electrode-side binder 214 does not necessarily have to be CO2 permeable. [Explanation of symbols]

[0100] 201 Electrochemical Cell 210 Working electrode 212 CO2 absorbent 213 Working electrode side conductive additive 220 Opposite 222 Counter electrode active material 223 Counter electrode conductive additive

Claims

1. CO by electrochemical reaction ２ CO containing ２ from the CO ２ A carbon dioxide capture system for separating The CO ２ CO adsorbed ２ The device comprises a working electrode (210) having an adsorbent (212) and a counter electrode (220), and when a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the CO ２ The adsorbent absorbs the CO ２ an electrochemical cell (201) coupled to the The working electrode is ２ a working electrode-side conductive assistant (213) that forms a conductive path to the adsorbent; the working electrode-side conductive additive is a metal oxide having a structure in which oxygen elements are arranged around a metal element, The carbon dioxide recovery system, wherein the metal oxide serving as the working electrode-side conductive assistant is manganese dioxide.

2. The counter electrode has a counter electrode-side active material (222) that emits electrons when a voltage is applied between the working electrode and the counter electrode, and a counter electrode-side conductive assistant (223) that forms a conductive path to the counter electrode-side active material, The carbon dioxide recovery system according to claim 1 , wherein the counter electrode side conductive assistant is a metal oxide having a structure in which oxygen elements are arranged around a metal element.

3. A carbon dioxide recovery system as described in claim 2, wherein the metal oxide serving as the counter electrode side conductive aid is ruthenium oxide or manganese dioxide.

4. The counter electrode has a counter electrode side active material (222) that emits electrons when a voltage is applied between the working electrode and the counter electrode, 4. The carbon dioxide recovery system according to claim 1, wherein the counter electrode active material is a substance in which a functional group is modified at a vertex of a five-membered ring constituting a cyclopentadienyl metal complex.

5. 5. The carbon dioxide recovery system according to claim 4, wherein the counter electrode active material is decamethylferrocene in which a vertex of the five-membered ring constituting the ferrocene that is the cyclopentadienyl metal complex is modified with a methyl group.

6. The counter electrode has a counter electrode side active material (222) that emits electrons when a voltage is applied between the working electrode and the counter electrode, 4. The carbon dioxide recovery system according to claim 1, wherein the counter electrode active material is a heterocyclic compound in which benzene rings are fused to both ends of a thiazine containing a sulfur element and a nitrogen element, and the sulfur element is substituted with an element different from the sulfur element, or a heterocyclic compound in which the nitrogen element is modified with a functional group.

7. 7. The carbon dioxide recovery system according to claim 6, wherein the counter electrode active material is phenoxazine in which the sulfur element in the heterocyclic compound is substituted with an oxygen element.

8. 7. The carbon dioxide recovery system according to claim 6, wherein the counter electrode active material is methylphenothiazine in which the nitrogen element of the heterocyclic compound is modified with a methyl group.

9. 7. The carbon dioxide recovery system according to claim 6, wherein the counter electrode active material is phenylphenothiazine in which the nitrogen element of the heterocyclic compound is modified with a phenyl group.

10. 10. The carbon dioxide recovery system according to claim 1, wherein the voltage applied between the working electrode and the counter electrode is greater than −0.9 V and less than 0 V.

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