Gas adsorption system and method for manufacturing electrochemical cell used in the same

Abstract

To provide a gas adsorption system having improved gas adsorption speed, and a method for manufacturing an electrochemical cell used in the same.SOLUTION: A gas adsorption system has a first electrode film 132 for adsorbing predetermined gas. The first electrode film 132 has a gas adsorption material 133, an action electrode side binder 135 and an electrolyte material 136, and at least a part of the electrolyte material 136 is a gelled gel electrolyte 137. In the first electrode film 132, a gap part 138 is formed which communicates with a surface layer on the side of a first power collection material 131 and the gel electrolyte 137 coating the surface layer, and becomes a gas vapor phase passage. The first electrode film 132 is formed by coating a paste containing a solvent, the gas adsorption material 133 and the action electrode side binder 135 into a sheet shape and forming a sheet body, then coating an electrolytic solution becoming an electrolytic material 136, and drying the solvent.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a gas adsorption system for adsorbing a predetermined gas and a method for manufacturing an electrochemical cell used therein. [Background technology]

[0002] A gas adsorption system capable of adsorbing and desorbing a predetermined gas, such as carbon dioxide (CO2), has been proposed in Patent Document 1. The gas adsorption system described in Patent Document 1 includes an electrochemical cell having a working electrode containing a CO2 adsorbent, a counter electrode, an insulating layer disposed between the working electrode and the counter electrode, and an electrolyte material covering the working electrode, the counter electrode, and the insulating layer. This gas adsorption system can control the adsorption and desorption of CO2 in the CO2 adsorbent in the working electrode by turning an electric field on and off, and can recover CO2 from a CO2-containing gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-177883 Summary of the Invention [Problem to be solved by the invention]

[0004] This type of gas adsorption system is required to further improve the gas adsorption rate. The gas adsorption system described in Patent Document 1 improves the CO2 gas adsorption rate by adsorbing CO2 using the Coulomb force of electrons, rather than by chemically bonding a specific element with CO2, but there is still room for improvement.

[0005] In the conventional gas adsorption system described above, the entire electrochemical cell is immersed in an electrolyte for the purpose of ion conduction. As a result of extensive research by the present inventors, it has been newly discovered that the dissolution and diffusion of gas in the electrolyte significantly affects the rate of gas adsorption at the working electrode when the working electrode is immersed in the electrolyte.

[0006] In view of the above, an object of the present disclosure is to provide a gas adsorption system with an improved gas adsorption rate and a method for manufacturing an electrochemical cell used therein. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, a gas adsorption system is a gas adsorption system for adsorbing a predetermined gas, comprising: a working electrode (130) having an electrode film (132) that adsorbs a predetermined gas; a counter electrode (140) that pairs with the working electrode; a separator (150) disposed between the working electrode and the counter electrode; The working electrode comprises a gas adsorbent (133) that adsorbs a predetermined gas, and an electrolyte material (136) that is in contact with the gas adsorbent; the electrolyte material is an at least partially gelled gel electrolyte (137); The working electrode has a void (138) formed therein, which connects one of the surfaces other than the surface in contact with the separator to the electrolyte material.

[0008] This gas adsorption system has a configuration in which at least a portion of the electrolyte material of the working electrode that is in contact with the gas adsorbent is gelled, and a void portion is formed in the working electrode that communicates with the electrolyte material on one of the surfaces other than the surface that is in contact with the separator. In this gas adsorption system, the gas to be adsorbed passes through the void portion, which serves as a gas phase passage, and reaches the gas adsorbent that is in contact with the electrolyte material. Therefore, compared to a conventional configuration in which the working electrode is immersed in the electrolyte material, the rate at which the gas reaches the gas adsorbent and therefore the gas adsorption rate are improved.

[0009] According to another aspect of the present disclosure, a method for manufacturing an electrochemical cell is a method for manufacturing an electrochemical cell for use in a gas adsorption system that adsorbs a predetermined gas, the method comprising: Applying a paste containing a polymer material (135), a gas adsorbent (133) that adsorbs a predetermined gas, and a solvent into a sheet; adding an electrolyte to the paste before drying the paste applied in a sheet form; After adding the electrolytic solution, the solvent in the sheet-like paste is dried to form a working electrode (130) having an electrode film (132) containing a gelled gel electrolyte (137).

[0010] This involves applying a paste containing a polymer material, a gas adsorbent, and a solvent to a sheet, adding an electrolyte before drying the applied paste, and then drying the solvent to form a gel electrolyte in which at least a portion of the polymer material is gelled by the electrolyte. This process then results in a working electrode containing a gel electrolyte and having voids formed that connect the surface layer to the gel electrolyte covering the gas adsorbent. This structure allows the gas to be adsorbed to reach the gas adsorbent through the voids, making it possible to manufacture an electrochemical cell with a faster adsorption rate for the gas compared to conventional structures in which the working electrode is immersed in an electrolyte material.

[0011] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an application example of the gas adsorption system according to the first embodiment. [Figure 2] FIG. 1 illustrates a gas adsorption system. [Figure 3] FIG. 3 is a diagram corresponding to an enlarged view of region III in FIG. 2, and is an explanatory diagram of CO 2 adsorption at the working electrode. [Figure 4] FIG. 4 is a diagram corresponding to FIG. 3 and is an explanatory diagram of CO2 adsorption in a gas adsorption system of a comparative example. [Figure 5] FIG. 1 is a diagram showing the results of comparing the CO2 adsorption rates of Examples and Comparative Examples. [Figure 6] FIG. 3 is a diagram showing the results of observing a cross section of a first electrode film with a scanning electron microscope (SEM) in an example. [Figure 7]FIG. 1 is a diagram showing the relationship between the volume ratio of the gel electrolyte and the effective diffusion coefficient of ions. [Figure 8] 5A to 5C are diagrams illustrating a manufacturing process of the first electrode film. [Figure 9] FIG. 10 is a diagram showing the relationship between temperature and vapor pressure for a solvent, an electrolytic solution, and a gel electrolyte during the production of a first electrode film. [Figure 10] FIG. 10 is a diagram showing the Hansen distance between the solvent and the binder and the Hansen distance between the electrolyte and the binder during the production of the first electrode film. [Figure 11] FIG. 10 is a diagram illustrating an application example of the gas adsorption system according to the second embodiment. [Figure 12] FIG. 10 is a diagram showing the results of a comparison between the number of cycles and the amount of CO2 adsorption for each sample. [Figure 13] FIG. 1 is a diagram showing an example of the relationship between polymer water content and ionic conductivity. [Figure 14] FIG. 1 is an explanatory diagram of a presumed mechanism for improving ionic conductivity at a predetermined polymer water content. [Figure 15] FIG. 10 is a graph showing the change over time in weight retention rate for each humidification environment in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0014] (First embodiment) The following description will be given with reference to a gas adsorption system 100 of a first embodiment. The gas adsorption system 100 recovers a gas to be recovered from a mixed gas containing the gas to be recovered by an electrochemical reaction, for example. The gas to be recovered is, for example, an acidic gas such as CO2, NOx, or SOx. Examples of the mixed gas include the atmosphere, exhaust gas from an internal combustion engine, and exhaust gas from factory equipment such as a furnace. In this specification, a case where CO2 is recovered from a mixed gas will be described as a representative example.

[0015] The gas adsorption system 100 of this embodiment can be used as part of a CO2 recovery apparatus 10, as shown in FIG. 1 . The CO2 recovery apparatus 10 includes, for example, a compressor 11, a gas adsorption system 100, a flow path switching valve 12, a CO2 utilization device 13, and a control device 14. The compressor 11 pressurizes a CO2-containing gas (mixed gas) to the gas adsorption system 100. The flow path switching valve 12 is, for example, a three-way valve that switches the flow path of the exhaust gas from the gas adsorption system 100. When discharging a CO2-removed gas, the flow path of the exhaust gas is switched to the atmosphere, and when discharging CO2 gas, the flow path of the exhaust gas is switched to the CO2 utilization device 13. The CO2 utilization device 13 is a device that utilizes CO2, such as a storage tank that stores CO2 or a conversion device that converts CO2 into fuel. The control device 14 is composed of a well-known microcomputer including a CPU, ROM, RAM, etc., not shown, and its peripheral circuits. The CPU, ROM, and RAM are abbreviations for Central Processing Unit, Read Only Memory, and Random Access Memory, respectively. The control device 14 performs various calculations and processes based on control programs stored in the ROM, and controls the operation of various controlled devices. In this embodiment, the control device 14 controls the operation of each device, for example, the compressor 11, the gas adsorption system 100, and the flow path switching valve 12.

[0016] [Basic configuration] 2, the gas adsorption system 100 includes an electrochemical cell 110 and a control power supply 120, and is an electrosorption / desorption system in which gas adsorption and desorption occur through an electrochemical reaction in the electrochemical cell 110. The electrochemical cell 110 includes, for example, a plate-shaped first electrode 130, a second electrode 140, and a separator 150, with the separator 150 disposed between the first electrode 130 and the second electrode 140. The control power supply 120 is a power supply device for the gas adsorption system 100, and is controlled by, for example, a control device 14, and is used to switch the electrochemical cell 110 between a gas adsorption mode and a gas desorption mode.

[0017] The first electrode 130 is, for example, a negative electrode. The first electrode 130 includes a first current collector 131 and a first electrode film 132, as shown in FIG.

[0018] The first current collector 131 is made of a conductive material that allows gas to pass through, and is connected to the control power supply 120. The first current collector 131 is made of any conductive material, such as a carbonaceous material such as carbon paper, carbon cloth, nonwoven carbon mat, or porous gas diffusion layer (GDL), or a metal material such as Al, Ni, Ti, or SUS, and has a porous or mesh structure. GDL is an abbreviation for Gas Diffusion Layer.

[0019] The first electrode film 132 is a working electrode that adsorbs and desorbs a predetermined gas from a mixed gas containing the gas through an electrochemical reaction. The first electrode film 132 includes a gas adsorbent 133, a working electrode-side conductive additive 134, a working electrode-side binder 135, and an electrolyte material 136. The working electrode-side binder 135 and the electrolyte material 136 form a gel electrolyte 137. The first electrode film 132 also includes voids 138 that connect the surface of the first current collector 131 to the gel electrolyte 137 that covers the gas adsorbent 133. In other words, the first electrode film 132 does not have a configuration in which all of the gaps between the gas adsorbent 133, the working electrode-side conductive additive 134, and the working electrode-side binder 135 are filled with the electrolyte material 136, but instead has voids 138 that serve as gas-phase passages for the gas to be adsorbed.

[0020] The gas adsorbent 133 is, for example, a CO2 adsorbent that adsorbs and desorbs CO2. For example, when an electric field is applied by the control power supply 120, the gas adsorbent 133 adsorbs CO2 by receiving electrons via the first current collector 131, and desorbs the adsorbed CO2 by releasing electrons. When the gas adsorbent 133 is used as a CO2 adsorbent, for example, an organic compound such as polyanthraquinone, carbon, or a metal oxide can be used.

[0021] The working electrode-side conductive additive 134 is a conductive substance that forms a conductive path to the gas adsorbent 133. As the working electrode-side conductive additive 134, for example, a carbon material such as carbon nanotubes, carbon black, or graphene, or metal fine particles, a conductive polymer, or the like can be used.

[0022] The working electrode side binder 135 is a retaining material that retains the gas adsorbent 133 and the working electrode side conductive assistant 134 on the first current collector 131. As the working electrode side binder 135, for example, a polymer material such as epoxy resin, polyimide, or a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) is used. Note that the working electrode side binder 135 may be configured to include, in addition to the above-mentioned polymer material, a conductive filler made of a conductive material such as Ag.

[0023] The electrolyte material 136 contacts the gas adsorbent 133 and faces the void 138. The electrolyte material 136 contains ions, which are transferred to the gas adsorbent 133 and serve to correct any imbalance in the charge in the gas adsorbent 133. Examples of the electrolyte material 136 include an ionic liquid and an aqueous electrolyte solution. At least a portion of the electrolyte material 136 gels together with the working electrode binder 135 during the manufacturing process of the first electrode film 132 (described later), forming a non-fluid gel electrolyte 137 as a whole. Because the electrolyte material 136 is in a gelled state, it does not flow freely like a liquid, and is thus prevented from imbalance due to the influence of airflow, gravity, and the like during operation of the gas adsorption system 100. This improves the flexibility of mounting the electrochemical cell 110.

[0024] Examples of ionic liquids that can be used include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TfN]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TfN]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF]), 1-ethyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide. Examples of aqueous electrolytes that can be used include aqueous solutions containing electrolytes such as HSO, NaSO, HPO, KOH, NaOH, NaCl, and KCl.

[0025] The gel electrolyte 137 is obtained, for example, by swelling the working electrode-side binder 135 with the electrolyte material 136 and gelling the electrolyte material 136. The gel electrolyte 137 contacts or covers, for example, at least one of the gas adsorbent 133 and the working electrode-side conductive assistant 134. The gel electrolyte 137 is also in contact with the voids 138, and gas from the first current collector 131 side or the side surface reaches the gel electrolyte 137 in a gaseous state through the voids 138. Because the gel electrolyte 137 is in a non-fluid gel state, it is fixed in contact with the gas adsorbent 133 and can stably maintain the voids 138.

[0026] As shown in FIG. 3 , the void 138 is a space that connects the gel electrolyte 137 to a surface of the first electrode film 132 other than the surface that contacts the separator 150. While FIG. 3 shows a representative example of the void 138 connecting the surface of the first electrode film 132 facing the first current collector 131 to the gel electrolyte 137, the void 138 is not limited to this, and the void 138 may also be one that connects the side surface to the gel electrolyte 137. The void 138 is a gas-phase passage that allows the gas to be adsorbed to pass in a gaseous state between the surface or side surface facing the first current collector 131 and the gel electrolyte 137. The formation of the void 138 will be described later. In addition to the void 138, the first electrode film 132 may also include a void that is an internal space that is not connected to the outside.

[0027] The second electrode 140 is, for example, a positive electrode, and includes a second current collector 141 and a second electrode film 142. The second current collector 141 is a conductive member connected to the control power supply 120. The second current collector 141 may be made of the same material as the first current collector 131, or may be made of a different material.

[0028] The second electrode film 142 is a counter electrode that exchanges electrons with the first electrode film 132. The second electrode film 142 is, for example, configured by mixing multiple materials, similar to the first electrode film 132, and has a counter electrode-side active material, a counter electrode-side conductive additive, and a counter electrode-side binder, which are not shown.

[0029] The counter electrode active material is an electroactive species that exchanges electrons with the gas adsorbent 133 of the first electrode film 132. Examples of the counter electrode active material include metal complexes in which the valence of metal ions changes, such as cyclopentadienyl metal complexes (e.g., ferrocene, nickelocene, or cobaltocene), or porphyrin metal complexes, allowing electron exchange. Examples of the counter electrode active material include transition metal oxides (e.g., Ru, Mn, Fe, or Mo) that allow electron exchange by changing the valence of the transition metal. The counter electrode conductive additive is a conductive material that forms a conductive path to the counter electrode active material. For example, the same conductive material as the working electrode conductive additive 134 may be used, or a different conductive material may be used. The counter electrode binder is composed of a material that can hold the counter electrode active material and the counter electrode conductive additive on the second current collector 141. The counter electrode side binder may be made of, for example, the same material as the working electrode side binder 135, or may be made of a different material.

[0030] The separator 150 is disposed between the first electrode film 132 and the second electrode film 142, and is a member that prevents physical contact between the first electrode film 132 and the second electrode film 142. The separator 150 suppresses electrical short circuits between the first electrode film 132 and the second electrode film 142. The separator 150 can be made of an insulating material such as a cellulose film, a polymer, a composite material of a polymer and ceramic, or a porous body.

[0031] The basic configuration of the gas adsorption system 100 has been described above.

[0032] [Gas adsorption and desorption steps] In the gas adsorption system 100, the control device 14 controls the potential applied between the first electrode 130 and the second electrode 140, thereby performing, for example, a CO 2 adsorption process and a desorption process.

[0033] For example, in the adsorption process, the control device 14 controls the control power supply 120 to apply an adsorption potential between the first electrode 130 and the second electrode 140 of the electrochemical cell 110. At this time, in the gas adsorption system 100, the counter electrode active material of the second electrode film 142 simultaneously donates electrons and the first electrode film 132 supplies electrons to the gas adsorbent 133 through the application of a voltage. When the adsorption potential is applied between the first electrode film 132 and the second electrode film 142, the counter electrode active material of the second electrode film 142 releases electrons and supplies them to the first electrode film 132. Then, the gas adsorbent 133 receives the electrons, increasing its bonding strength with CO2 and adsorbing CO2 contained in the mixed gas. This allows the electrochemical cell 110 to capture CO2 from the mixed gas. The mixed gas after CO2 has been recovered by the gas adsorption system 100, that is, the CO2-removed gas, is released into the atmosphere by the control device 14 switching the flow path of the flow path switching valve 12.

[0034] Furthermore, for example, in the desorption step, the control device 14 controls the control power supply 120 to apply a desorption potential between the first electrode 130 and the second electrode 140 of the electrochemical cell 110. At this time, in the gas adsorption system 100, the applied voltage causes the gas adsorbent 133 of the first electrode film 132 to donate electrons and the second electrode film 142 to supply electrons to the counter electrode active material. When this desorption potential is applied, the gas adsorbent 133 releases electrons and the bonding strength with CO2 decreases, causing the gas adsorbent 133 to desorb and release CO2. The electrons released by the gas adsorbent 133 are supplied to the counter electrode active material of the second electrode film 142. Then, the control device 14 switches the flow path of the flow path switching valve 12, and the CO2 gas released by the gas adsorbent 133 of the gas adsorption system 100 is sent to the CO2 utilization device 13. The gas adsorption system 100 repeatedly executes the cycle of the gas adsorption step and the desorption step.

[0035] [Improvement of gas adsorption speed] Next, the improvement in the gas adsorption rate in the gas adsorption system 100 of this embodiment will be described in comparison with the structure of a gas adsorption system of a comparative example shown in FIG.

[0036] The gas adsorption system of the comparative example differs from the gas adsorption system 100 in the structure of the first electrode 200. As shown in FIG. 4 , the first electrode 200 includes a first current collector 131, a gas adsorbent 133, and an electrolyte 210. The electrolyte 210, which is an ionic liquid, remains in a liquid state in the first electrode 200. In addition, the entire space between the first current collector 131 and the separator 150 of the first electrode 200, except for the gas adsorbent 133, is impregnated with the electrolyte 210.

[0037] In the gas adsorption system of the comparative example, in order for CO2 gas from the first current collector 131 to reach the gas adsorbent 133, CO2 must first be dissolved in the electrolyte 210. Then, the CO2 dissolved in the electrolyte 210 must diffuse through the electrolyte 210 and move to the surface of the gas adsorbent 133. In other words, the gas adsorption system of the comparative example must go through two stages: dissolution of CO2 in the electrolyte 210 and diffusion of CO2 in the electrolyte 210, and it takes time for the CO2 to dissolve and diffuse in the liquid.

[0038] As a result of intensive research by the present inventors, they have devised a gas adsorption system 100 in which a first electrode film 132 is formed with voids 138 that serve as gas-phase passages through which CO2 gas can diffuse in a gaseous state, as shown in Fig. 3. The first electrode film 132 has an electrolyte material 136 gelled only on the surface of the gas adsorbent 133 to form a gel electrolyte 137, and the surface on the first current collector 131 side is connected to the gel electrolyte 137 by the voids 138. Therefore, the first electrode film 132 has a structure in which CO2 gas reaches the gel electrolyte 137 through the voids 138 and then reaches the gas adsorbent 133 via the gel electrolyte 137. Furthermore, the diffusion rate of CO2 is much faster in the gas phase than in a liquid, and CO2 gas dissolves in the electrolyte near the gas adsorbent 133. As a result, the gas adsorption system 100 of this embodiment has a smaller effect on the dissolution of CO2 gas into the electrolyte than the comparative example, and the diffusion rate of CO2 gas in the first electrode film 132 is very high, thereby improving the adsorption rate of CO2 gas.

[0039] The CO2 gas adsorption rate was measured under the same conditions for the gas adsorption system of the comparative example and the gas adsorption system 100 of the example, and the results shown in Figure 5 were obtained. The CO2 gas adsorption rate of the gas adsorption system 100 was approximately 1.8, with the CO2 gas adsorption rate of the gas adsorption system of the comparative example being set to 1. The gas adsorption rate can be obtained, for example, by flowing a constant concentration of CO2 gas through the gas adsorption system and calculating the rate based on the CO2 concentration after the adsorption process, or by filling the gas adsorption system with a constant amount of CO2 gas and calculating the rate based on the CO2 concentration after the adsorption process.

[0040] Note that, as a result of observing the cross section of the first electrode film 132 with a scanning electron microscope (SEM), it was confirmed that voids 138 were formed, as shown in Fig. 6. In the SEM photograph shown in Fig. 6, the black areas are the voids 138, the gray areas are the gel electrolyte 137, and the white areas are the gas adsorbent 133 or the working electrode-side conductive assistant 134.

[0041] From the viewpoint of ensuring both ionic conductivity and gas diffusibility, it is preferable that the volume of the voids 138 in the first electrode film 132 be larger than the volume of the gel electrolyte 137. Electrical conduction in the first electrode film 132 is induced by the electric field from the control power supply 120, so as long as the conductive path is connected, it is easy to maintain conductivity. On the other hand, gas diffusion in the first electrode film 132 depends on the volume of the gas phase passage because there is no driving force such as an electric field. In view of these relationships, it is preferable that the first electrode film 132 be configured to prioritize the gas diffusion rate in the film over ionic conduction, which can be assisted by the application of an electric field, i.e., the volume of the voids 138 is larger than the volume of the gel electrolyte 137.

[0042] Furthermore, the relationship between the ratio of the volume of the gel electrolyte 137 to the volume of the solid portion of the first electrode film 132 (hereinafter referred to as the "gel volume ratio" for convenience) and the effective ion diffusion coefficient was examined, and the results shown in FIG. 7 were obtained. The effective ion diffusion coefficient was approximately 0.013 when the gel volume ratio was approximately 0.22, approximately 0.763 when the gel volume ratio was approximately 0.42, approximately 0.936 when the gel volume ratio was approximately 0.59, and approximately 0.943 when the gel volume ratio was approximately 0.70. The effective ion diffusion coefficient was approximately 0.934 when the gel volume ratio was approximately 0.80, approximately 0.982 when the gel volume ratio was approximately 0.86, and approximately 0.986 when the gel volume ratio was approximately 0.92. Based on these results, from the viewpoint of ensuring ionic conductivity, a gel volume ratio of 0.22 or more is preferable, and 0.5 or more is more preferable. Furthermore, when the gel volume ratio is 1, the gel electrolyte 137 is present in an amount equal to the solid portion, and there are no voids 138, so it is considered preferable that the gel volume ratio be 0.95 or less. The effective diffusion coefficient of ions can be calculated by a known method such as the random walk method.

[0043] [Step of forming first electrode film] Next, the process of forming the first electrode film 132 of the electrochemical cell 110 will be described with reference to FIGS.

[0044] First, a first kneading step is performed in which a polymer material, i.e., the working electrode side binder 135, is mixed with a solvent. The solvent used is, for example, one that dissolves the working electrode side binder 135. Examples of solvents that can be used include, but are not limited to, protonophilic solvents such as dimethylformamide, dimethyl sulfoxide, 1-methyl-2-pyrrolidone, tetrahydrofuran, pyridine, and hexamethylphosphoramide, and protonphobic solvents such as acetonitrile, propylene carbonate, ethylbenzene, cyclohexanone, cyclohexane, p-cymene, benzyl benzoate, butyl benzoate, dimethylcyclohexane, xylene, toluene, and methylcyclohexane. For example, the solvent may be a mixed solvent containing a plurality of solvents, or may contain other protonophilic, protonphobic, or amphoteric solvents. Furthermore, it is preferable to use a solvent with a boiling point at least lower than that of the electrolyte solution in order to gel the electrolyte solution, as described below. Specifically, to form the first electrode film 132 having the gel electrolyte 137 and the voids 138, it is preferable to use a solvent whose saturated vapor pressure is higher than that of the electrolyte solution, as shown in Fig. 9. The electrolyte solution becomes a gelled electrolyte solution in the drying step described below, and the saturated vapor pressure of the gelled electrolyte solution becomes lower than that of the electrolyte solution, thereby further suppressing evaporation and ensuring the ionic conductivity of the first electrode film 132.

[0045] In addition, as the working electrode side binder 135 (polymer material), since it is necessary to form the gel electrolyte 137 that gels with the electrolyte solution used in the subsequent process, a material that dissolves in the solvent and does not dissolve in the electrolyte solution is selected. Specifically, the solubility parameters between the polymer material and the solvent, and between the polymer material and the electrolyte solution are adjusted. As the solubility parameter, for example, as shown in FIG. 10, the Hansen distance determined by the dispersion term dD, the polarization term dP, and the hydrogen bond term dH of the solvent is known. The Hansen distance is a value representing the solubility of a substance, and the smaller the value, the easier it is to dissolve. For example, taking the Hansen distance between the polymer material and the solvent as HD1 and the Hansen distance between the polymer material and the electrolyte solution as HD2, it is preferable to select the working electrode side binder 135, the solvent, and the electrolyte solution (electrolyte material 136) such that HD1 < HD2. Thereby, it becomes possible to more reliably form the gel electrolyte 137. Note that depending on the type of the polymer material, the gel electrolyte 137 can be formed even if the above-mentioned relationship of the Hansen distance does not hold, so HD1 < HD2 is not an essential condition.

[0046] Subsequently, a second kneading step is performed in which the gas adsorbent 133 is added to and mixed with the product obtained in the first kneading step. Then, a third kneading step is performed in which the working electrode side conductive aid 134 is added to and mixed with the product obtained in the second kneading step. And, using the paste obtained in the third kneading step, a first coating step of coating it in a sheet shape by a coating method such as a printing method using, for example, screen printing, metal mask printing, doctor blade, applicator, wire bar, gravure, slot die, etc. is performed. Hereinafter, for the sake of convenience of explanation, the sheet-shaped paste obtained in the first coating step is referred to as a "sheet body". Note that the mixing ratio etc. of the solvent, the gas adsorbent 133, the working electrode side conductive aid 134, the working electrode side binder 135, etc. are appropriately set so that coating using the paste obtained in the first to third kneading steps becomes possible.

[0047] Next, before the solvent contained in the sheet is dried, a second coating step is performed in which an electrolyte solution, i.e., an electrolyte material 136, is applied to the sheet. The second coating step can be performed by any coating method that can apply the electrolyte solution to the surface of the sheet, such as spray coating, dip coating, bar coating, liquid immersion, vacuum impregnation, or inkjet printing. The electrolyte solution can be, for example, the ionic liquid described above or an aqueous solution containing an electrolyte. By applying the electrolyte solution, the polymer material (working electrode-side binder 135) of the sheet is swelled and gelled by the electrolyte solution (electrolyte material 136), forming a gel electrolyte 137.

[0048] Finally, the sheet body to which the electrolytic solution has been applied in the second application step is subjected to a drying step in which the solvent is evaporated by any method, such as heating, air drying, or vacuum drying. This drying step volatilizes the solvent that dissolved the polymer material from the sheet body, leaving only the electrolytic solution. In the drying step, the sheet body is configured to have a gel electrolyte 137 formed by the aggregation of the polymer material through gelation, and becomes a non-fluid plate as a whole. Then, as the sheet body aggregates and the solvent evaporates, spaces, i.e., voids 138, are formed in the sheet body that communicate between the gel electrolyte 137 and the surface layer.

[0049] The above is the process of forming the first electrode film 132.

[0050] Another possible method for forming a gel is to premix the electrolyte solution with the paste obtained in the third kneading process. However, in systems containing fine particles such as the gas adsorbent 133 and the working electrode-side conductive additive 134, gelation (aggregation) is a significant factor, making it difficult to adjust the viscosity and solvent ratio to an appropriate level for the sheet coating process. Another possible method involves drying the solvent before coating the sheet with the electrolyte solution, and then coating the sheet with the electrolyte solution. However, this process makes it difficult to induce gelation in the sheet. Furthermore, although this process leaves some voids in the sheet after the solvent dries, applying the electrolyte solution at a level sufficient to achieve the required ionic conductivity would fill the voids.

[0051] Therefore, in forming the first electrode film 132, three conditions must be met: (1) obtaining a paste that can be applied to a sheet body, (2) causing gelation between a polymer material and an electrolyte solution, and (3) forming voids by volatilizing the solvent while gelling the electrolyte solution. Therefore, as shown in Fig. 8, the first electrode film 132 can be obtained by applying a paste made of a polymer material, a solvent, a gas adsorbent, and a conductive additive to a sheet, applying the electrolyte solution to the obtained sheet body, and then performing a formation process in which the solvent is dried.

[0052] According to the present embodiment, the gas adsorption system 100 is configured such that at least a portion of the electrolyte material 136 in contact with the gas adsorbent 133 of the working electrode is gelled to form a gel electrolyte 137, and a void 138 is formed that connects the surface layer of the first electrode film 132 with the electrolyte material 136. The gas adsorption system 100 includes an electrochemical cell 110 configured such that the gas to be adsorbed passes through the void 138, which is a gas phase passage, and reaches the gas adsorbent 133 in contact with the electrolyte material 136. Therefore, compared to a conventional configuration in which the working electrode is immersed in the electrolyte material, the gas adsorption system 100 achieves an effect of further improving the speed at which the gas reaches the gas adsorbent 133, and therefore the gas adsorption speed.

[0053] The method for manufacturing the electrochemical cell 110 according to this embodiment includes at least the following three steps. The first step is to obtain a sheet body by applying a paste containing a working electrode-side binder 135, a gas adsorbent 133, and a solvent. The second step is to add an electrolyte solution to the paste before drying the sheet body. The third step is to dry the solvent from the sheet-like paste after adding the electrolyte solution, thereby forming a first electrode film 132 containing a gelled gel electrolyte 137. This results in a first electrode film 132 containing the gel electrolyte 137 and having voids 138 connecting the surface layer and the gel electrolyte 137 covering the gas adsorbent 133. This structure allows the gas to be adsorbed to reach the gas adsorbent 133 through the voids 138, making it possible to manufacture an electrochemical cell 110 with a faster gas adsorption rate than conventional structures in which the working electrode is immersed in an electrolyte material.

[0054] (Second embodiment) A gas adsorption system 100 according to a second embodiment will be described.

[0055] The gas adsorption system 100 of this embodiment is configured such that, in addition to the first electrode film 132, the second electrode film 142 and the separator 150 have a gelled electrolyte material, and a water-based electrolyte material is used as the electrolyte material. Furthermore, as shown in FIG. 11 , the gas adsorption system 100 also includes an evaporation suppression unit 160 that suppresses evaporation of water in the electrochemical cell 110. The gas adsorption system 100 of this embodiment differs from the first embodiment in the above-mentioned respects. This difference will be mainly described in this embodiment.

[0056] Conventional electrochemical cells are configured with the entire cell impregnated with an ionic liquid. Ionic liquids are non-volatile at room temperature and normal pressure, but depending on the composition, the recovered gas may have an odor. In addition, they are more expensive than aqueous electrolytes, which increases the manufacturing cost of electrochemical cells. On the other hand, aqueous electrolytes do not give off an odor to the recovered gas and are cheaper than ionic liquids, but they evaporate at room temperature and normal pressure, resulting in a decrease in water content and a decrease in cycle performance. In addition, aqueous electrolytes have lower ionic conductivity than ionic liquids, and a side reaction of the water splitting reaction occurs during operation of the electrochemical cell, resulting in a decrease in gas adsorption and desorption performance.

[0057] Therefore, through intensive research by the present inventors, it has been found that by using an aqueous gel electrolyte (described below) with a predetermined water absorption rate while suppressing water evaporation, it is possible to significantly improve the amount of gas adsorption and desorption compared to a configuration that simply uses an aqueous electrolyte solution.

[0058] In this embodiment, the first electrode film 132, the second electrode film 142, and the separator 150 are configured to have a gel electrolyte (hereinafter referred to as an "aqueous gel electrolyte") in which a highly water-absorbent polymer material is gelled with an aqueous electrolyte solution. Examples of highly water-absorbent polymer materials that can be used include highly water-absorbent polymers such as sodium polyacrylate, natural polymer materials such as gelatin, agarose, and alginic acid, and synthetic polymer materials such as polyvinyl alcohol and polyamino acids. Examples of aqueous electrolyte solutions that can be used include aqueous solutions of aqueous electrolytes such as Na2SO4, H2SO4, KOH, and NaCl. For example, the aqueous electrolyte solution is a 1 mol / L Na2SO4 aqueous solution, but is not limited to this.

[0059] The evaporation suppression unit 160 is for suppressing evaporation of water contained in the electrochemical cell 110 of this embodiment. The evaporation suppression unit 160 is, for example, a low-temperature device that lowers the temperature in the operating atmosphere of the electrochemical cell 110 to reduce the saturated vapor pressure, a supply device that directly supplies water to the electrochemical cell 110, or a humidifier that humidifies the gas to be supplied to the electrochemical cell 110. The evaporation suppression unit 160 may be any mechanism that can suppress evaporation of water in the electrochemical cell 110, and may be one or a combination of two or more of the above, or other known methods may be employed.

[0060] The relationship between the number of CO2 adsorption and desorption cycles and the amount of CO2 adsorbed was confirmed for three electrochemical cells: one configured using an aqueous electrolyte, one configured using an aqueous gel electrolyte, and one configured using an aqueous gel electrolyte with humidification, and the results shown in Figure 12 were obtained. The results shown in Figure 12 compare the change in the amount of CO2 adsorbed for each number of CO2 adsorption and desorption cycles performed under the same conditions, with the maximum amount of CO2 adsorbed for each of the three electrochemical cells configured as 1.

[0061] One cycle of CO2 adsorption and desorption was performed, for example, in the following order: control to the adsorption potential, fixation at the adsorption potential, control to the resting potential, fixation at the resting potential, control to the desorption potential, fixation at the desorption potential, and switching from the desorption potential to the adsorption potential.

[0062] The configuration using aqueous electrolyte showed the greatest decrease in CO2 adsorption with increasing cycle count compared to the other two configurations. The number of cycles required for the configuration using aqueous electrolyte to drop to 0.1 or less was about one-quarter of that required for the configuration using aqueous gel electrolyte.

[0063] Although the amount of CO2 adsorbed in the configuration using the aqueous gel electrolyte gradually decreased with increasing cycle count, the rate of decrease was significantly slower than in the configuration using the aqueous electrolyte. This is thought to be because the aqueous electrolyte was gelled by the polymer material, which bound the water to the polymer material and prevented it from evaporating.

[0064] In the humidified configuration using the aqueous gel electrolyte, the CO adsorption amount remained almost constant even with an increase in the number of cycles. This is thought to be because the supply of moisture to the electrochemical cell 110 by humidification keeps the moisture content in the aqueous gel electrolyte almost constant, thereby maintaining the ionic conductivity of the separator 150.

[0065] Furthermore, through extensive research, the inventors have found that by setting the water absorption rate of an aqueous gel electrolyte within a predetermined range, the ionic conductivity can be made higher than that of an aqueous electrolyte solution alone. Specifically, as shown in FIG. 13, when the polymer water content of the aqueous gel electrolyte was approximately 100% or 200%, the ionic conductivity was approximately 0.02 S / cm or less, which was lower than the value of the aqueous electrolyte solution indicated by the dashed line. On the other hand, when the polymer water content of the aqueous gel electrolyte was approximately 300% or approximately 500%, the ionic conductivity was approximately 0.1 S / cm, which was higher than that of the aqueous electrolyte solution. The polymer water content shown in FIG. 13 is a value calculated using the following formula (1), where the weight of the polymer material is the polymer amount and the weight of the aqueous electrolyte solution is the electrolyte amount.

[0066] Polymer water content (%) = electrolyte volume / polymer volume × 100 (1) The dashed lines in FIG. 13 are approximation curves obtained based on plots of polymer water contents of approximately 100%, 200%, 300%, and 500%. According to the approximation curve in FIG. 13, the aqueous gel electrolyte exhibits higher ionic conductivity than aqueous electrolyte solutions when the polymer water content is within a range of approximately 240% to approximately 500%. This is thought to be due to the formation of high-salt concentration regions on the particle surfaces of the polymer material when the polymer water content is within a certain range, as shown in FIG. 14, for example. The reason for the low ionic conductivity when the polymer water content is low is thought to be due to the strong bond between the polymer material and water, which makes it difficult for free water to exist, and the high particle density of the polymer material, which inhibits the movement of electrolyte salt. Furthermore, when the polymer water content is high, a large amount of free water is present around the polymer material particles, which is thought to bring the ionic conductivity closer to that of aqueous electrolyte solutions. However, when the polymer water content is within a certain range, the moderate amount of free water is present around the polymer material particles, and regions with high electrolyte salt concentrations are formed, which is thought to result in higher ionic conductivity than aqueous electrolyte solutions alone. The thick arrows shown in FIG. 14 indicate ion conduction, with solid lines indicating that ions are conducted and dashed lines indicating that ions are not conducted.

[0067] Furthermore, when humidifying the electrochemical cell 110, the evaporation suppression unit 160 controls the relative humidity of the operating environment of the electrochemical cell 110 to preferably 70% (RH 70%) or higher, and more preferably 80% (RH 80%) or higher. When the relative humidity was changed at predetermined intervals to check the change in weight retention rate for two electrochemical cells, one using an aqueous electrolyte solution and the other using an aqueous gel electrolyte, the results shown in Fig. 15 were obtained.

[0068] The relative humidity was 40% for a predetermined time from the start of the test, 80% for a predetermined time after 40%, and 70% for the time after 80%. The elapsed time shown in Figure 15 is a relative time where the time required from the start of the test to the end of 40% RH is set to 1.

[0069] The weight retention rate in FIG. 15 is a value calculated using the following formula (2) with the weight immediately after preparation as the initial weight at zero elapsed time.

[0070] Weight retention rate (%) = weight after elapsed time / initial weight × 100 (2) Since the weights of the polymer material and aqueous electrolyte in an aqueous gel electrolyte and the aqueous electrolyte in an aqueous electrolyte solution do not change, the weight retention rate can be said to be an index of whether the weight of water is maintained.

[0071] As shown in Figure 15, the weight retention rate of the configuration using an aqueous electrolyte solution decreased linearly to about 20% at RH 40%, and then decreased gradually at RH 80%, but then decreased to about 5% at about 3 hours elapsed, and was below about 1% at the start of RH 70%. This result suggests that it is difficult to suppress water evaporation in the configuration using an aqueous electrolyte solution, even when humidified.

[0072] On the other hand, the weight retention rate of the configuration using an aqueous gel electrolyte decreased linearly at 40% RH, but the degree of decrease was smaller than that of the configuration using an aqueous electrolyte solution, reaching approximately 81% at the end of 40% RH. The weight retention rate of the configuration using an aqueous gel electrolyte remained nearly constant at 80% RH, reaching approximately 72% at approximately 7 hours after RH. It then gradually decreased at 70% RH, reaching approximately 65% ​​at approximately 10 hours after RH. This result suggests that for configurations using an aqueous gel electrolyte, water evaporation is suppressed in an environment with a certain relative humidity or higher, and that ionic conductivity can be ensured by maintaining a relative humidity of 70% RH or higher, preferably 80% RH or higher. Furthermore, the suppression of weight retention rate decrease by humidification in the aqueous gel electrolyte is thought to be due to the fact that the water in the aqueous gel electrolyte is bound by the polymer material due to gelation, thereby suppressing water evaporation compared to non-gelled aqueous electrolyte solutions.

[0073] The gas adsorption system 100 of this embodiment also provides the same effects as those of the first embodiment. Furthermore, by using an aqueous gel electrolyte, the proportion of ionic liquid used is reduced, resulting in a gas adsorption system 100 that reduces the odor of the recovered gas and manufacturing costs.

[0074] Although the electrochemical cell 110 in which the first electrode film 132, the second electrode film 142, and the separator 150 are all made of an aqueous gel electrolyte has been described as a representative example, this is not limiting. In the electrochemical cell 110, for example, some of the first electrode film 132, the second electrode film 142, and the separator 150 may be made of an aqueous gel electrolyte. For example, when the first electrode film 132 is made of an aqueous gel electrolyte, the working electrode binder 135 is a highly absorbent polymer, the electrolyte material 136 is an aqueous electrolyte solution, and the gel electrolyte 137 is an aqueous gel electrolyte. For example, when the second electrode film 142 is made of an aqueous gel electrolyte, the second electrode film 142 has the same configuration as above. Even in this case, the proportion of ionic liquid used is reduced, which results in the effects of reducing the odor in the collected gas and the manufacturing cost of the electrochemical cell 110.

[0075] (Other embodiments) Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one, or less than one, are also within the scope and spirit of the present disclosure.

[0076] It goes without saying that in each of the above embodiments, the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle. Furthermore, in each of the above embodiments, when numerical values ​​such as the number, values, amounts, and ranges of the components of the embodiments are mentioned, they are not limited to the specific numbers unless they are specifically stated as essential or are clearly limited to a specific number in principle. Furthermore, in each of the above embodiments, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., unless they are specifically stated or are clearly limited to a specific shape, positional relationship, etc. in principle. [Explanation of symbols]

[0077] 110 Electrochemical Cell 130 1st electrode (working electrode) 132 First electrode film 133 Gas absorbent 135 Working electrode binder (polymer material) 136 Electrolyte Materials 137 Gel Electrolyte 140 Second electrode (counter electrode) 150 Separator 160 Evaporation suppression section

Claims

1. 1. A gas adsorption system for adsorbing a predetermined gas, comprising: a working electrode (130) having an electrode film (132) that adsorbs the predetermined gas; a counter electrode (140) that pairs with the working electrode; a separator (150) disposed between the working electrode and the counter electrode; The working electrode comprises a gas adsorbent (133) that adsorbs the predetermined gas, and an electrolyte material (136) that is in contact with the gas adsorbent, the electrolyte material is an at least partially gelled gel electrolyte (137); The gas adsorption system, wherein the working electrode has a void portion (138) formed therein, the void portion communicating the electrolyte material with a surface other than the surface in contact with the separator.

2. The gas adsorption system according to claim 1 , wherein a volume of the void portion in the electrode film is larger than a volume of the gel electrolyte in the electrode film.

3. 2. The gas adsorption system according to claim 1, wherein, when the volume of the solid portion of the electrode film is taken as 1, the volume of the gel electrolyte relative to the solid portion of the electrolyte material is 0.22 or more.

4. 4. The gas adsorption system according to claim 1, wherein the gel electrolyte is a polymer material (135) gelled with an aqueous electrolyte solution, and the water content of the gel electrolyte is within a range of 240% or more and 500% or less, where the water content is a value obtained by dividing the weight of the aqueous electrolyte solution by the weight of the polymer material.

5. 5. The gas adsorption system according to claim 4, further comprising an evaporation suppression unit (160) that adds water to the working electrode or humidifies an environment in which the working electrode is placed, thereby suppressing evaporation of water from the working electrode.

6. The gas adsorption system according to claim 5 , wherein the evaporation suppression unit performs control to maintain the water content within a range of 240% to 500%.

7. 1. A method for manufacturing an electrochemical cell (110) for use in a gas adsorption system for adsorbing a predetermined gas, comprising: Applying a paste containing a polymer material (135), a gas adsorbent (133) that adsorbs the predetermined gas, and a solvent into a sheet form; adding an electrolyte to the paste before drying the paste applied in a sheet form; and after adding the electrolytic solution, drying the solvent in the sheet-like paste to form a working electrode (130) having an electrode film (132) containing a gelled gel electrolyte (137).

8. The method for producing an electrochemical cell according to claim 7 , wherein the solvent used in applying the paste into a sheet has a boiling point lower than that of the electrolytic solution.

9. 9. The method for manufacturing an electrochemical cell according to claim 7 or 8, wherein the electrolytic solution is added to the paste so that the Hansen distance between the polymer material and the electrolytic solution is shorter than the Hansen distance between the polymer material and the solvent.

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