Electrochemical cell

Abstract

To provide an electrochemical cell which can improve adsorption performance of recovered gas.SOLUTION: An electrochemical cell 101 includes a working electrode 130 and a counter electrode 140. The working electrode 130 adsorbs and desorbs recovered gas by electrochemical reaction from mixed gas containing the recovered gas. The counter electrode 140 exchanges electrons with the working electrode 130. A volume porosity of the working electrode 130 is equal to or more than a volume porosity of the counter electrode 140. Thus, diffusion property of the recovered gas can be improved in the working electrode 130, which can secure permeability of the recovered gas. As a result, adsorption performance of the recovered gas can be improved.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an electrochemical cell.

Background Art

[0002] In Patent Document 1, an electrochemical cell used in a carbon dioxide recovery system for separating carbon dioxide, which is a gas to be recovered, from a mixed gas containing carbon dioxide (CO2) by an electrochemical reaction has been proposed. In Patent Document 1, in a state where a potential difference is applied between the cathode and the anode of the electrochemical cell, by supplying a carbon dioxide-containing gas to the cathode, an electrochemical reaction in which CO3 is generated from CO2 and an electrochemical reaction in which CO2 is generated from CO3 2- is carried out. 2- from CO2 is carried out.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when an electrochemical cell is used for an EDLC (electric double layer capacitor), in order to improve the energy density, a technique of increasing the density of the electrochemical cell by press working or the like is adopted.

[0005] However, according to the study by the present inventors, when an electrochemical cell is used in a carbon dioxide recovery system, it has been clarified that when the electrochemical cell is compressed by press working or the like, the adsorption performance of carbon dioxide decreases.

[0006] In view of the above points, an object of the present disclosure is to provide an electrochemical cell capable of improving the adsorption performance of a gas to be recovered.

Means for Solving the Problems

[0007] To achieve the above objective, the electrochemical cell described in claim 1 includes a working electrode (130) that performs adsorption and desorption of the gas to be recovered from a mixed gas containing the gas to be recovered by an electrochemical reaction, It comprises a counter electrode (140) that exchanges electrons with the working electrode, The volumetric porosity of the working electrode is greater than or equal to the volumetric porosity of the counter electrode. the law of nature, The gas to be recovered is carbon dioxide. The working electrode has a working electrode side electrode film (132), The counter electrode has a counter electrode side electrode film (142), Of the working electrode film and the counter electrode film, only the counter electrode film is pressure-molded. .

[0008] According to this, the diffusivity of the gas to be recovered can be improved at the working electrode (130), thereby ensuring the permeability of the gas to be recovered. As a result, it becomes possible to improve the adsorption performance of the gas to be recovered.

[0009] The reference numerals in parentheses next to 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 drawing]

[0010] [Figure 1] This is a conceptual diagram showing the overall configuration of a carbon dioxide capture system in one embodiment. [Figure 2] This is an explanatory diagram showing a carbon dioxide capture device in one embodiment. [Figure 3] This is a cross-sectional view showing an electrochemical cell in one embodiment. [Figure 4] This is an explanatory diagram illustrating the structure of the working electrode. [Figure 5] This is an explanatory diagram to illustrate the structure of opposing poles. [Figure 6] This is an explanatory diagram illustrating the working pole side vacancy. [Figure 7] This is an explanatory diagram for illustrating the void on the opposite side. [Figure 8] This figure shows the relationship between the number of cycles and the adsorption Faraday efficiency. [Figure 9] It is a diagram showing the relationship between the number of cycles and the integrated adsorption amount. [Figure 10] It is a diagram showing the relationship between the average circle equivalent diameter of the pores on the working electrode side and the molecular diffusion coefficient of carbon dioxide. [Figure 11] It is a diagram showing the relationship between the film thickness of the electrode film on the working electrode side and the calculated value of the carbon dioxide adsorption rate. [Figure 12] It is a diagram showing the relationship between the film thickness of the electrode film on the working electrode side and the measured value of the carbon dioxide adsorption rate. [Figure 13] It is a diagram showing the relationship between the film thickness of the electrode film on the working electrode side and the diffusion - reaching concentration.

Embodiments for Carrying Out the Invention

[0011] An embodiment in the present disclosure will be described with reference to the drawings. This embodiment applies the electrochemical cell in the present disclosure to a carbon dioxide recovery system that separates and recovers carbon dioxide from a mixed gas containing carbon dioxide. Therefore, the gas to be recovered in this embodiment is carbon dioxide.

[0012] As shown in FIG. 1, the carbon dioxide recovery system 10 of this embodiment is provided with a compressor 11, a carbon dioxide recovery device 100, a flow path switching valve 12, a carbon dioxide utilization device 13, and a control device 14.

[0013] The carbon dioxide recovery device 100 is a device that separates and recovers carbon dioxide from the mixed gas. The carbon dioxide recovery device 100 discharges the carbon dioxide - removed gas after carbon dioxide is recovered from the mixed gas, or the carbon dioxide recovered from the mixed gas. The configuration of the carbon dioxide recovery device 100 will be described in detail later.

[0014] The mixed gas is a carbon dioxide - containing gas containing carbon dioxide. The mixed gas also contains gases other than carbon dioxide. The mixed gas is air, or a high - concentration gas with a higher carbon dioxide content concentration than air. The high - concentration gas is discharged from, for example, an internal combustion engine or a factory. The mixed gas in this embodiment is air.

[0015] The compressor 11 pumps the mixed gas to the carbon dioxide recovery device 100. The flow path switching valve 12 is a three-way valve that switches the flow path of the exhaust gas from the carbon dioxide recovery device 100. When carbon dioxide removal gas is discharged from the carbon dioxide recovery device 100, the flow path switching valve 12 switches the exhaust gas flow path to the atmosphere side, and when carbon dioxide is discharged from the carbon dioxide recovery device 100, it switches the exhaust gas flow path to the carbon dioxide utilization device 13 side.

[0016] The carbon dioxide utilization device 13 is a device that utilizes carbon dioxide. The carbon dioxide utilization device 13 can include, for example, a storage tank for storing carbon dioxide or a conversion device for converting carbon dioxide into fuel. The conversion device can be one that converts carbon dioxide 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.

[0017] The control device 14 consists of a well-known microcomputer including a CPU, ROM, and RAM, and its peripheral circuits. The control device 14 performs various calculations and processes based on a control program stored in the ROM, and controls the operation of various controlled devices. In this embodiment, the control device 14 performs operation control of the compressor 11, operation control of the carbon dioxide recovery device 100, flow path switching control of the flow path switching valve 12, and the like.

[0018] As shown in Figure 2, the carbon dioxide capture device 100 is equipped with an electrochemical cell 101. The electrochemical cell 101 has a working electrode 130, a counter electrode 140, and a separator 150. Multiple electrochemical cells 101 are stacked and arranged inside the carbon dioxide capture device 100.

[0019] In the example shown in Figure 2, the working electrode 130, the counter electrode 140, and the separator 150 are each configured as plate-shaped components. Although Figure 2 shows the working electrode 130, the counter electrode 140, and the separator 150 spaced apart, in reality these components are arranged to be in contact with each other.

[0020] The electrochemical cell 101 may be housed in a container (not shown). The container may be provided with a gas inlet for introducing the mixed gas into the container and a gas outlet for releasing the carbon dioxide removal gas or carbon dioxide from the container.

[0021] The carbon dioxide recovery device 100 separates and recovers carbon dioxide from a mixed gas by adsorption and desorption through electrochemical reactions. The carbon dioxide recovery device 100 is equipped with a control power supply 120 that applies a predetermined voltage to the working electrode 130 and the counter electrode 140, and can change the potential difference between the working electrode 130 and the counter electrode 140. The working electrode 130 is the negative electrode, and the counter electrode 140 is the positive electrode.

[0022] The electrochemical cell 101 can operate by changing the potential difference between the working electrode 130 and the counter electrode 140, thereby switching between a recovery mode in which carbon dioxide is recovered at the working electrode 130 and a release mode in which carbon dioxide is released from the working electrode 130. The recovery mode is a charging mode in which the electrochemical cell 101 is charged, and the release mode is a discharge mode in which the electrochemical cell 101 is discharged.

[0023] In recovery mode, a first voltage V1 is applied between the working electrode 130 and the counter electrode 140, and electrons are supplied from the counter electrode 140 to the working electrode 130. At the first voltage V1, the working electrode potential is less than the counter electrode potential. The first voltage V1 can be, for example, in the range of 0.5 to 2.0 V.

[0024] In emission mode, a second voltage V2 lower than the first voltage V1 is applied between the working electrode 130 and the counter electrode 140, supplying electrons from the working electrode 130 to the counter electrode 140. The second voltage V2 only needs to be lower than the first voltage V1, and the relative magnitudes of the working electrode potential and the counter electrode potential are not limited. In other words, in emission mode, the working electrode potential may be less than the counter electrode potential, the working electrode potential may be equal to the counter electrode potential, or the working electrode potential may be greater than the counter electrode potential.

[0025] As shown in Figures 3 and 4, the working electrode 130 in the electrochemical cell 101 has a working electrode-side current collector 131 and a working electrode-side electrode film 132. The working electrode-side current collector 131 is connected to the control power supply 120 and is a porous conductive member that can pass a mixed gas through.

[0026] As the working electrode side current collector 131, for example, a carbonaceous material or a metallic material can be used. As the carbonaceous material constituting the working electrode side current collector 131, for example, carbon paper, carbon cloth, nonwoven carbon mat, porous gas diffusion layer (GDL), etc. can be used. As the metallic material constituting the working electrode side current collector 131, for example, a mesh structure of metals such as Al, Ni, and SUS can be used.

[0027] The working electrode side electrode film 132 adsorbs and desorbs carbon dioxide from the mixed gas by an electrochemical reaction. The working electrode side electrode film 132 includes a carbon dioxide adsorbent 133, a working electrode side conductive additive 134, and a working electrode side binder 135.

[0028] Hereinafter, the materials constituting the working electrode side electrode film 132, such as the carbon dioxide adsorbent 133, the working electrode side conductive additive 134, and the working electrode side binder 135, will also be referred to as the working electrode side constituent materials 136. In this embodiment, the working electrode side constituent materials 136 are formed in particulate form.

[0029] The carbon dioxide adsorbent 133 is an electroactive species that adsorbs carbon dioxide by accepting electrons and desorbs the adsorbed carbon dioxide by releasing electrons. For example, carbon materials, metal oxides, polyanthraquinones, etc., can be used as the carbon dioxide adsorbent 133.

[0030] The working electrode side conductive additive 134 is a conductive material that forms a conductive path to the carbon dioxide adsorbent 133. As the working electrode side conductive additive 134, carbon materials such as carbon nanotubes, carbon black, and graphene can be used.

[0031] The working electrode binder 135 holds the carbon dioxide adsorbent 133 and the working electrode conductive additive 134 to the working electrode current collector 131. Specifically, a mixture of the carbon dioxide adsorbent 133, the working electrode conductive additive 134, and the working electrode binder 135 is formed, and this mixture is adhered to the working electrode current collector 131.

[0032] For example, a conductive resin can be used as the working electrode binder 135. As the conductive resin, epoxy resins containing Ag or the like as a conductive filler, or fluororesins such as PTFE (polytetrafluoroethylene) and PVDF (polyvinylidene fluoride) can be used.

[0033] As shown in Figures 3 and 5, the counter electrode 140 in the electrochemical cell 101 has a counter electrode current collector 141 and a counter electrode electrode film 142. The counter electrode current collector 141 is a conductive member connected to the control power supply 120. The counter electrode current collector 141 may be made of the same material as the working electrode current collector 131, or it may be made of a different material.

[0034] The counter electrode film 142 exchanges electrons with the working electrode film 132. The counter electrode film 142 includes a counter active material 143, a counter conductive additive 144, and a counter binder 145.

[0035] Hereinafter, the materials constituting the counter electrode film 142, such as the counter electrode active material 143, the counter electrode conductive additive 144, and the counter electrode binder 145, will also be referred to as the counter electrode constituent material 146. In this embodiment, the counter electrode constituent material 146 is formed in particulate form.

[0036] The counter electrode active material 143 is an auxiliary electroactive species that exchanges electrons with the carbon dioxide adsorbent 133. The counter electrode active material 143 is a material that can exchange electrons through changes in the valence state of the metal or through charge exchange in and out of the π electron cloud.

[0037] As the counter-electrode active material 143, for example, a metal complex that enables electron transfer by changing the valence of a metal ion can be used. Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickerosene, and cobaltocene, or porphyrin metal complexes.

[0038] In this embodiment, a compound having a ferrocene skeleton is used as the counter electrode active material 143. Specifically, PVFc (polyvinylferrocene), which is polymerized ferrocene, is used as the counter electrode active material 143.

[0039] The counter electrode conductive additive 144 is a conductive material that forms a conductive path to the counter electrode active material 143. The counter electrode conductive additive 144 is used in mixture with the counter electrode active material 143. The counter electrode conductive additive 144 may be made of the same material as the working electrode conductive additive 134, or it may be made of a different material. The counter electrode conductive additive 144 is, for example, in particulate form.

[0040] The counter electrode binder 145 is a material that can hold the counter electrode active material 143 and the counter electrode conductive additive 144 to the counter electrode current collector 141, and is also conductive. The counter electrode binder 145 may be made of the same material as the working electrode binder 135, or it may be made of a different material. In this embodiment, PVDF is used as the counter electrode binder 145.

[0041] The separator 150 is placed between the working electrode film 132 and the counter electrode film 142. The separator 150 separates the working electrode film 132 and the counter electrode film 142. In other words, the separator 150 prevents physical contact between the working electrode film 132 and the counter electrode film 142. The separator 150 also suppresses electrical short circuits between the working electrode film 132 and the counter electrode film 142.

[0042] As the separator 150, a separator made of a cellulose membrane, a polymer, a composite material of a polymer and ceramic, etc., can be used. A porous separator may also be used as the separator 150.

[0043] An electrolyte solution 160, which is an electrolyte material, is provided between the working electrode film 132 and the separator 150, and between the counter electrode film 142 and the separator 150. The working electrode 130 and the counter electrode 140 are covered with the electrolyte solution 160. The electrolyte solution 160 promotes conductivity to the carbon dioxide adsorbent 133.

[0044] The electrolyte 160 can be, for example, an ionic liquid. An ionic liquid is a salt of a liquid that is non-volatile at room temperature and pressure. When an ionic liquid is used as the electrolyte 160, the ionic liquid may be gelled to prevent elution from the electrochemical cell 101.

[0045] As shown in Figures 4 and 6, the working electrode side electrode film 132 is formed by filling it with the working electrode side constituent material 136. In the working electrode side electrode film 132, working electrode side vacancies 137 are formed in the gaps between the filled working electrode side constituent material 136. In Figure 6, the working electrode side constituent material 136 and the working electrode side vacancies 137 are schematically shown for ease of explanation. In the working electrode side electrode film 132, carbon dioxide molecules flow from the surface of the working electrode side electrode film 132 into the working electrode side vacancies 137, flow through the working electrode side vacancies 137, and diffuse.

[0046] As shown in Figures 5 and 7, the counter electrode film 142 is formed by filling it with counter electrode constituent material 146. Counter electrode voids 147 are formed in the gaps between the filled counter electrode constituent material 146 in the counter electrode film 142. In Figure 7, the counter electrode constituent material 146 and the counter electrode voids 147 are schematically shown for ease of explanation.

[0047] As shown in Figures 4 to 7, the average equivalent diameter of the working electrode void 137 is greater than or equal to the equivalent diameter of the counter electrode void 147. Therefore, the volumetric porosity of the working electrode film 132 is greater than or equal to the volumetric porosity of the counter electrode film 142. Consequently, the volumetric porosity of the working electrode 130 is greater than or equal to the volumetric porosity of the counter electrode 140.

[0048] More specifically, in this embodiment, the average equivalent diameter of the working electrode side void 137 is greater than the equivalent diameter of the counter electrode side void 147. Therefore, the volumetric porosity of the working electrode side electrode film 132 is greater than the volumetric porosity of the counter electrode side electrode film 142. Consequently, the volumetric porosity of the working electrode 130 is greater than the volumetric porosity of the counter electrode 140.

[0049] Next, the working electrode formation process for forming the working electrode 130 of the electrochemical cell 101 of this embodiment will be described. In the working electrode formation process, first, a working electrode side mixing process is performed in which the working electrode side constituent materials 136 are mixed.

[0050] Next, a heating step is performed to heat the mixed working electrode component material 136. In the heating step of this embodiment, the mixed working electrode component material is applied to the working electrode current collector 131 and then fired. As a result, a working electrode electrode film 132 is formed on the surface of the working electrode current collector 131. Thus, the working electrode formation step is completed.

[0051] Next, the counter electrode formation process for forming the counter electrode 140 of the electrochemical cell 101 in this embodiment will be described. In the counter electrode formation process, first, a counter electrode side mixing process is performed in which the counter electrode side constituent materials 146 are mixed.

[0052] Next, a compression step is performed to compress the mixed counter electrode component material 146. In the compression step of this embodiment, the mixed counter electrode component material 146 is pressed onto the counter electrode current collector 141 using a press machine. As a result, a counter electrode film 142 is formed on the surface of the counter electrode current collector 141. In other words, the counter electrode film 142 is pressure-molded. Thus, the counter electrode formation step is completed.

[0053] Next, the adsorption efficiency and adsorption amount of carbon dioxide in the electrochemical cell 101 will be explained using examples and comparative examples. Specifically, the combination of the recovery mode and the release mode was considered as one cycle, and the adsorption Faraday efficiency and carbon dioxide adsorption amount were measured in each cycle. The results are shown in Figures 8 and 9.

[0054] The normalized Faraday efficiency on the vertical axis of Figure 8 is the adsorption Faraday efficiency normalized to 1, where the adsorption Faraday efficiency for the first cycle in the example described later is set to 1. The adsorption Faraday efficiency represents the ratio of the number of carbon dioxide molecules adsorbed on the carbon dioxide adsorbent 133 to the number of electrons that flowed through the carbon dioxide adsorbent 133 of the electrochemical cell 101.

[0055] The normalized adsorption amount on the vertical axis of Figure 9 is the cumulative adsorption amount normalized to 1, where the cumulative adsorption amount for the first cycle in the example described later is set to 1. The cumulative adsorption amount represents the total amount of carbon dioxide adsorbed up to each cycle.

[0056] The example uses an electrochemical cell 101 in which the counter electrode film 142 is pressure-molded, while the working electrode film 132 is not pressure-molded. Comparative Example 1 uses an electrochemical cell 101 in which the working electrode film 132 is pressure-molded, while the counter electrode film 142 is not pressure-molded. Comparative Example 2 uses an electrochemical cell 101 in which neither the counter electrode film 142 nor the working electrode film 132 is pressure-molded.

[0057] As shown in Figure 8, the adsorption Faraday efficiency of the electrochemical cell 101 in the example was approximately four times that of the electrochemical cell 101 in Comparative Example 1. On the other hand, the adsorption Faraday efficiency of the electrochemical cell 101 in the example and Comparative Example 2 was almost the same.

[0058] As shown in Figure 9, the cumulative amount of carbon dioxide adsorbed in the electrochemical cell 101 in the example was approximately four times the cumulative amount of carbon dioxide adsorbed in the electrochemical cell 101 in comparative example 1. On the other hand, the cumulative amount of carbon dioxide adsorbed in the electrochemical cell 101 was almost the same between the example and comparative example 2.

[0059] As shown in Figures 8 and 9, it was found that when the working electrode side electrode film 132 is pressure-molded, the diffusibility of carbon dioxide in the working electrode side electrode film 132 decreases, resulting in a decrease in carbon dioxide adsorption performance. On the other hand, it was found that even when the counter electrode side electrode film 142 is pressure-molded to increase its density, there is almost no effect on the carbon dioxide adsorption performance compared to when the counter electrode side electrode film 142 is not pressure-molded.

[0060] Next, Figure 10 shows the relationship between the average circular equivalent diameter of the working electrode side pores 137 and the molecular diffusion coefficient of carbon dioxide in the working electrode side electrode film 132 of this embodiment.

[0061] The horizontal axis of the graph in Figure 10 shows the value obtained by dividing the average circle equivalent diameter of the working electrode side vacancy 137 by the mean free path of carbon dioxide. In this specification, "mean free path of carbon dioxide" refers to the mean free path of carbon dioxide at the operating temperature of the electrochemical cell 101.

[0062] The vertical axis of the graph in Figure 10 shows the ratio to the molecular diffusion coefficient of carbon dioxide in a gas. A ratio greater than 0.5 indicates that molecular diffusion is dominant.

[0063] As shown in Figure 10, by setting the average circle equivalent diameter of the working electrode vacancy 137 to more than four times the mean free path of carbon dioxide, molecular diffusion of carbon dioxide becomes more than 80%. By setting the average circle equivalent diameter of the working electrode vacancy 137 to more than ten times the mean free path of carbon dioxide, molecular diffusion of carbon dioxide becomes more than 90%.

[0064] Therefore, it is desirable to set the average circle equivalent diameter of the working electrode side vacancy 137 to four times or more the mean free path of carbon dioxide. Furthermore, it is even more desirable to set the average circle equivalent diameter of the working electrode side vacancy 137 to ten times or more the mean free path of carbon dioxide.

[0065] Next, the inventors investigated the film thickness of the working electrode side electrode film 132. Figure 11 shows the relationship between the film thickness of the working electrode side electrode film 132 and the carbon dioxide adsorption rate calculated by the calculation (hereinafter referred to as the calculation data).

[0066] The normalized CO2 adsorption rate on the vertical axis of Figure 11 is the carbon dioxide adsorption rate normalized to the saturation value of the carbon dioxide adsorption rate in the calculation data, which is set to 1. The saturation value of the carbon dioxide adsorption rate in the calculation data refers to the average value of the carbon dioxide adsorption rate when the film thickness of the working electrode side electrode film 132 is between 50 and 500 μm.

[0067] As shown in Figure 11, increasing the film thickness of the working electrode side electrode film 132 increases the carbon dioxide adsorption rate. When the film thickness of the working electrode side electrode film 132 exceeds a certain film thickness, the carbon dioxide adsorption rate does not increase further and plateaus. This carbon dioxide adsorption rate is called the upper limit. In this embodiment, the film thickness of the working electrode side electrode film 132 is set to be less than or equal to the film thickness at which the carbon dioxide adsorption rate reaches the upper limit (30 μm in this example). Also, the film thickness of the working electrode side electrode film 132 is less than or equal to the film thickness of the counter electrode side electrode film 142.

[0068] Here, Equation 1 shows the result of converting the gas diffusion equation to an equation that derives the diffusion concentration c for the carbon dioxide recovery system 10 of this embodiment.

[0069]

number

[0070] However, x is the thickness of the working electrode film 132, t is the operating time of the carbon dioxide recovery system 10, a is the specific surface area of ​​the working electrode film 132, η is the distance conversion coefficient, and D is the diffusion coefficient of carbon dioxide.

[0071] The distance conversion coefficient η is a value between 1 and 100. In this embodiment, the diffusion distance of carbon dioxide in the working electrode side electrode film 132 is a value obtained by correcting the film thickness of the working electrode side electrode film 132 by the specific surface area a, and the ratio of the specific surface area a to the geometric surface area of ​​the working electrode side electrode film 132 is used. Specifically, the distance conversion coefficient η can be calculated as follows.

[0072] Figure 12 shows the relationship between the film thickness of the working electrode side electrode film 132 and the actually measured adsorption rate (hereinafter referred to as "measured data").

[0073] The normalized CO2 adsorption rate on the vertical axis of Figure 12 is the carbon dioxide adsorption rate normalized to the saturation value of the carbon dioxide adsorption rate in the measured data, which is set to 1. The saturation value of the carbon dioxide adsorption rate in the measured data refers to the average value of the carbon dioxide adsorption rates at the four rightmost points in Figure 12.

[0074] The distance conversion coefficient η is calculated when the calculated data shown in Figure 11 is fitted to the measured data shown in Figure 12. In this embodiment, the calculated distance conversion coefficient η was 25.

[0075] Using the distance conversion coefficient η calculated in this manner in Equation 1 above, the relationship between the film thickness x of the working electrode side electrode film 132 and the diffusion-achieved concentration c is calculated and the result is shown in Figure 13.

[0076] As shown in Figure 13, at a depth of approximately 40 μm from the surface of the working electrode side electrode film 132, 10⁻² of the total amount of carbon dioxide, or 1%, can reach. In other words, 99% of the carbon dioxide is present between the surface of the working electrode side electrode film 132 and a depth of 40 μm. Therefore, in this embodiment, the film thickness x of the working electrode side electrode film 132 is set such that c > 10 in the above equation 1. -4 It is set to satisfy the following conditions.

[0077] As described above, in the electrochemical cell 101 of this embodiment, the volumetric porosity of the working electrode 130 is set to be greater than or equal to the volumetric porosity of the counter electrode 140. More specifically, the volumetric porosity of the working electrode side electrode film 132 is set to be greater than or equal to the volumetric porosity of the counter electrode side electrode film 142. Specifically, the volumetric porosity of the working electrode side electrode film 132 is set to be greater than the volumetric porosity of the counter electrode side electrode film 142.

[0078] According to this, the diffusivity of carbon dioxide can be improved in the working electrode film 132, thereby ensuring carbon dioxide permeability. As a result, it becomes possible to improve the carbon dioxide adsorption performance.

[0079] Here, the counter electrode 140 does not need to diffuse carbon dioxide; it is sufficient for the electrolyte 160 to permeate it. For this reason, in this embodiment, the volume porosity of the counter electrode film 142 is reduced and its density is increased. Specifically, the counter electrode film 142 is pressure-molded.

[0080] According to this, the overall thickness dimension of the electrochemical cell 101 (i.e., the length in the stacking direction of the electrochemical cell 101) is reduced, so the number of electrochemical cells 101 housed in one carbon dioxide recovery device 100 can be increased. As a result, the amount of carbon dioxide adsorbed by the carbon dioxide recovery device 100 as a whole can be increased. In other words, the carbon dioxide adsorption capacity per unit volume can be improved.

[0081] Furthermore, in the electrochemical cell 101 of this embodiment, the average circular diameter of the working electrode side vacancy 137 is set to be greater than or equal to the average circular diameter of the counter electrode side vacancy 147. Specifically, the average circular diameter of the working electrode side vacancy 137 is made larger than the average circular diameter of the counter electrode side vacancy 147.

[0082] According to this, carbon dioxide molecules that flow from the surface of the working electrode side electrode film 132 into the working electrode side pores 137 are more easily diffused at the working electrode 130. As a result, the diffusion rate of carbon dioxide in the working electrode side electrode film 132 increases. This improves the adsorption rate of carbon dioxide. Consequently, it becomes possible to improve the carbon dioxide adsorption performance.

[0083] Furthermore, in this embodiment, the average circle equivalent diameter of the working electrode side vacancy 137 is set to be four times or more the mean free path of carbon dioxide at the operating temperature. This improves the diffusion rate of carbon dioxide in the working electrode side vacancy 137, thereby improving the adsorption rate of carbon dioxide. As a result, it becomes possible to improve the carbon dioxide adsorption performance.

[0084] (Other embodiments) This disclosure is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of this disclosure, as follows.

[0085] For example, in the embodiment described above, an example was described in which press working was performed using a press machine in the compression step of the counter electrode formation step, but the press working is not limited to this embodiment. For example, press working may be performed using a roll press or a hydraulic press.

[0086] (others) The characteristics of the electrochemical cell disclosed herein are as follows: (Item 1) A working electrode (130) that performs adsorption and desorption of the gas to be recovered from a mixed gas containing the gas to be recovered by an electrochemical reaction, The system comprises a counter electrode (140) that exchanges electrons with the working electrode, An electrochemical cell in which the volume porosity of the working electrode is greater than or equal to the volume porosity of the counter electrode. (Item 2) The electrochemical cell according to item 1, wherein the volume porosity of the working electrode side electrode film (132), which is the electrode film of the working electrode, is greater than or equal to the volume porosity of the counter electrode side electrode film (142), which is the electrode film of the counter electrode. (Item 3) The working electrode side electrode film is provided with a working electrode side void (137), The counter electrode film is provided with a counter electrode void (147), The electrochemical cell according to item 2, wherein the average circular equivalent diameter of the working electrode side vacancy is equal to or greater than the average circular equivalent diameter of the counter electrode side vacancy. (Item 4) The working electrode side electrode film (132), which is the electrode film of the working electrode, is provided with a working electrode side void (137). The electrochemical cell according to any one of items 1 to 3, wherein the average circular equivalent diameter of the working electrode side vacancy is 4 times or more the mean free path of the recovered gas at the operating temperature. (Item 5) The counter electrode film (142), which is the counter electrode film, is pressure-molded in the electrochemical cell according to any one of items 1 to 4. (Item 6) The electrochemical cell according to any one of items 1 to 5, wherein the thickness of the working electrode side electrode film (132), which is the electrode film of the working electrode, is less than or equal to the thickness of the counter electrode side electrode film (142), which is the electrode film of the counter electrode. (Item 7) The electrochemical cell according to any one of items 1 to 6, wherein the thickness of the working electrode side electrode film (132), which is the electrode film of the working electrode, is less than or equal to the thickness at which the adsorption rate of the gas to be recovered reaches its upper limit. [Explanation of Symbols]

[0087] 130 Working electrode 140 opposite poles

Claims

1. A working electrode (130) that performs adsorption and desorption of the gas to be recovered from a mixed gas containing the gas to be recovered by an electrochemical reaction, It comprises a counter electrode (140) that exchanges electrons with the working electrode, The volumetric porosity of the working electrode is greater than or equal to that of the counter electrode. The gas to be recovered is carbon dioxide. The working electrode has a working electrode side electrode film (132), The counter electrode has a counter electrode side electrode film (142), An electrochemical cell in which, of the working electrode side electrode film and the counter electrode side electrode film, only the counter electrode side electrode film is pressure-molded.

2. The electrochemical cell according to claim 1, wherein the volume porosity of the working electrode side electrode film (132) is equal to or greater than the volume porosity of the counter electrode side electrode film (142).

3. The working electrode side electrode film is provided with a working electrode side void (137), The counter electrode film is provided with a counter electrode void (147), The electrochemical cell according to claim 2, wherein the average circular equivalent diameter of the working electrode side vacancy is equal to or greater than the average circular equivalent diameter of the counter electrode side vacancy.

4. The working electrode side electrode film (132) is provided with a working electrode side void (137), The electrochemical cell according to any one of claims 1 to 3, wherein the average circular equivalent diameter of the working electrode side vacancy is four times or more the mean free path of the recovered gas at the operating temperature.

5. The electrochemical cell according to any one of claims 1 to 3, wherein the thickness of the working electrode side electrode film (132) is less than or equal to the thickness of the counter electrode side electrode film (142).

6. The electrochemical cell according to any one of claims 1 to 3, wherein the thickness of the working electrode side electrode film (132) is less than or equal to the thickness at which the adsorption rate of the gas to be recovered reaches an upper limit.

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