Electrochemical cell

Abstract

To provide an electrochemical cell for gas adsorption having conductive particles and functional particles, which can make both securement of conductivity by the conductive particles and improvement in functionality by the functional particles compatible.SOLUTION: An electrochemical cell comprises a working electrode 104 and a counter electrode 106 and is configured so that when a voltage is applied between the working electrode and the counter electrode, the working electrode adsorbs and desorbs gas. At least either of the working electrode and the counter electrode has conductive particles 104b that contact each other to form a conductive path, and functional particles 104a that do not form the conductive path. Particle sizes of the conductive particles are equal to particle sizes of the functional particles or more.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention relates to an electrochemical cell for adsorbing gases. [Background technology]

[0002] Patent Document 1 discloses an electrochemical cell for recovering a specific gas from a mixed gas. The electrochemical cell of Patent Document 1 comprises a pair of electrodes consisting of a working electrode and a counter electrode, and adsorbs the specific gas by an electrochemical reaction. The working electrode includes a gas adsorbent that adsorbs the specific gas from the mixed gas and a conductive additive that forms a conductive path to the gas adsorbent. The counter electrode includes an electroactivating auxiliary material that exchanges electrons with the working electrode and a conductive additive that forms a conductive path to the electroactivating auxiliary material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2018-533470 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] For example, if conductive additives are made of conductive particles and gas adsorbents and electroactivation auxiliary materials are made of functional particles, in order to improve the gas adsorption efficiency of the electrochemical cell, it is necessary to ensure conductivity with the conductive particles while also enhancing functionality with the functional particles.

[0005] In view of the above points, the present invention aims to achieve both ensuring conductivity with conductive particles and improving functionality with functional particles in an electrochemical cell for gas adsorption having conductive particles and functional particles. [Means for solving the problem]

[0006] To achieve the above objective, the electrochemical cell described in claim 1 has a working electrode (104) and a counter electrode (106), and a voltage is applied between the working electrode and the counter electrode to adsorb and desorb gas. At least one of the electrodes, the working electrode and the counter electrode, has conductive particles (104b) that contact each other to form a conductive path and functional particles (104a) that do not form a conductive path. The particle size of the conductive particles is greater than or equal to the particle size of the functional particles.

[0007] This improves the contact rate of conductive particles at the electrodes, thereby improving the conductivity of the electrodes. Therefore, conductivity can be ensured even when the volume ratio of conductive particles is reduced. Furthermore, since the volume ratio of functional particles can be increased, the functionality provided by the functional particles can be improved.

[0008] The symbols in parentheses for each of the above components indicate their correspondence to the specific means described in the embodiments described later. [Brief explanation of the drawing]

[0009] [Figure 1] This is a conceptual diagram showing the overall configuration of the carbon dioxide capture system according to the first embodiment. [Figure 2] This is an explanatory diagram showing the configuration of a carbon dioxide capture device. [Figure 3] This is an explanatory diagram showing the configuration of an electrochemical cell in a carbon dioxide capture device. [Figure 4] This diagram shows the configuration of the working electrode in an electrochemical cell. [Figure 5] This is a magnified view of the materials that make up the working electrode. [Figure 6] This figure shows the relationship between the conductivity of an electrode containing conductive particles and the volume ratio of conductive particles in the electrode. [Figure 7] This figure shows the relationship between particle size and abundance ratio when particle size is adjusted. [Figure 8] This is an enlarged view of the material constituting the working electrode of the second embodiment.

Best Mode for Carrying Out the Invention

[0010] Hereinafter, a plurality of modes for implementing the present disclosure will be described with reference to the drawings. In each embodiment, the same reference numerals may be assigned to the parts corresponding to those described in the preceding embodiment, and duplicate descriptions may be omitted. When only a part of the configuration is described in each embodiment, other embodiments described previously can be applied to the other parts of the configuration. Not only the combinations of parts that are explicitly shown to be combinable in each embodiment, but also the embodiments can be partially combined with each other without particular hindrance to the combination, even if not explicitly stated.

[0011] (First Embodiment) Hereinafter, a first embodiment of an electrochemical cell according to the present invention will be described. In this embodiment, the electrochemical cell according to the present invention is applied to a carbon dioxide recovery system 1 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 the overall configuration diagram of FIG. 1, the carbon dioxide recovery system 1 of this embodiment includes a carbon dioxide recovery device 10, a pump 11, a flow path switching valve 12, a carbon dioxide utilization device 13, and a control device 14.

[0013] The carbon dioxide recovery device 10 separates and recovers carbon dioxide from the mixed gas. As the mixed gas, air, exhaust gas of an internal combustion engine, or the like can be used. The mixed gas contains gases such as oxygen in addition to carbon dioxide. The mixed gas is supplied to the carbon dioxide recovery device 10. The carbon dioxide recovery device 10 discharges the mixed gas after carbon dioxide is removed or the recovered carbon dioxide. The detailed configuration of the carbon dioxide recovery device 10 will be described later.

[0014] At the outlet of the carbon dioxide recovery device 10, the suction side of the pump 11 is connected. The pump 11 sucks the mixed gas after carbon dioxide is removed from the carbon dioxide recovery device 10, or the recovered carbon dioxide. Further, due to the suction action of the pump 11, the mixed gas is supplied to the carbon dioxide recovery device 10.

[0015] In this embodiment, an example in which the pump 11 is arranged on the downstream side in the gas flow direction of the carbon dioxide recovery device 10 is described, but the pump 11 may be arranged on the upstream side in the gas flow direction of the carbon dioxide recovery device 10.

[0016] At the discharge port of the pump 11, the inlet side of the flow path switching valve 12 is connected. The flow path switching valve 12 is a three-way valve that switches the flow path of the gas flowing out from the carbon dioxide recovery device 10. The flow path switching valve 12 switches between a flow path for allowing the gas flowing out from the carbon dioxide recovery device 10 to flow out to the atmosphere side and a flow path for allowing the gas flowing out from the carbon dioxide recovery device 10 to flow out to the carbon dioxide utilization device 13 side.

[0017] The carbon dioxide utilization device 13 is a device that utilizes carbon dioxide. As the carbon dioxide utilization device 13, for example, a storage tank for storing carbon dioxide or a conversion device for converting carbon dioxide into fuel can be used. The conversion device is a device that converts carbon dioxide into hydrocarbon fuel such as methane. The hydrocarbon fuel may be a gaseous fuel at normal temperature and pressure or a liquid fuel at normal temperature and pressure.

[0018] The control device 14 is composed of a well-known microcomputer including a CPU, ROM, RAM, etc. and its peripheral circuits. The control device 14 performs various calculations and processes based on the control program stored in the ROM and controls the operations of various controlled devices connected to the output side. More specifically, the control device 14 of this embodiment controls the operations of the carbon dioxide recovery device 10, the pump 11, and the flow path switching valve 12.

[0019] Here, the carbon dioxide recovery device 10 will be described.

[0020] As shown in Figure 2, the carbon dioxide capture device 10 has a housing 100 and a plurality of electrochemical cells 101. In this embodiment, the housing 100 is made of a metal material. The housing 100 may also be made of a resin material.

[0021] The housing 100 has a gas inlet and a gas outlet. The gas inlet is an opening for introducing the mixed gas into the housing 100. The gas outlet is an opening for releasing the mixed gas, after carbon dioxide has been removed, or the recovered carbon dioxide, from inside the housing 100.

[0022] The electrochemical cell 101 adsorbs carbon dioxide through an electrochemical reaction, separating and recovering it from the mixed gas. The electrochemical cell 101 also releases the adsorbed carbon dioxide through an electrochemical reaction. Multiple electrochemical cells 101 are housed in the enclosure 100.

[0023] The electrochemical cell 101 is formed in the shape of a rectangular flat plate. Multiple electrochemical cells 101 are stacked inside the housing 100 at regular intervals so that their plate surfaces are parallel to each other. Multiple gas channels are formed between adjacent electrochemical cells 101 to allow the mixed gas flowing in from the gas inlet to circulate.

[0024] As shown in Figure 3, the electrochemical cell 101 includes a working electrode current collector 103, a working electrode 104, a counter electrode current collector 105, a counter electrode 106, a separator 107, and an electrolyte layer 108. The working electrode current collector 103, the working electrode 104, the counter electrode current collector 105, the counter electrode 106, and the separator 107 are all formed in the shape of rectangular flat plates. The working electrode 104 and the counter electrode 106 constitute a pair of electrodes.

[0025] The electrochemical cell 101 is formed as a laminate of a working electrode current collector 103, a working electrode 104, a counter electrode current collector 105, a counter electrode 106, and a separator 107. The lamination direction in which the working electrode current collector 103, etc., are stacked in each individual electrochemical cell 101 coincides with the lamination direction in which multiple electrochemical cells 101 are stacked inside the housing 100.

[0026] The working electrode current collector 103 is a conductive member that contacts the working electrode 104 and electrically connects the working electrode 104 and the counter electrode 106. One flat surface of the working electrode current collector 103 is exposed to the mixed gas. The other flat surface of the working electrode current collector 103 is in contact with the working electrode 104.

[0027] As shown in Figure 4, the working electrode 104 is provided between the working electrode current collector 103 and the separator 107. As shown in Figures 4 and 5, the working electrode 104 includes a carbon dioxide adsorbent 104a, a conductive additive 104b, and a binder 104c. In Figures 4 and 5, the conductive additive 104b is shaded, and in Figure 4, the binder 104c is not shown. The carbon dioxide adsorbent 104a, the conductive additive 104b, and the binder 104c are not limited to the shapes and sizes shown in Figures 4 and 5.

[0028] The carbon dioxide adsorbent 104a, the conductive additive 104b, and the binder 104c are used in a mixture state. More specifically, in this embodiment, the particles of the carbon dioxide adsorbent 104a and the particles of the conductive additive 104b are used in a state in which they are held by the binder 104c. The working electrode 104 can adsorb and recover carbon dioxide from the mixed gas, and desorb and release the recovered carbon dioxide.

[0029] The carbon dioxide adsorbent 104a is an electroactive species that adsorbs carbon dioxide by accepting electrons and desorbs the adsorbed carbon dioxide by releasing electrons. The carbon dioxide adsorbent 104a is an example of a gas adsorbent. Examples of carbon dioxide adsorbents that can be used include polyanthraquinone, carbon materials, and metal oxides. In this embodiment, polyanthraquinone is used as the carbon dioxide adsorbent 104a.

[0030] The conductive additive 104b is a conductive material that forms a conductive path to the carbon dioxide adsorbent 104a. As the conductive additive 104b, carbon materials, metal porous materials, metal-supported ceramics, etc., can be used. The carbon material constituting the conductive additive 104b can be carbon black, carbon nanotubes, graphene, carbon fiber nonwoven fabric, etc.

[0031] Binder 104c is a polymeric binder that holds the carbon dioxide adsorbent 104a and the conductive additive 104b. Binder 104c binds the carbon dioxide adsorbent 104a to each other, the conductive additive 104b to each other, and the carbon dioxide adsorbent 104a to each other. As binder 104c, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used. In this embodiment, binder 104c uses a non-conductive polymer that does not have conductivity.

[0032] The working electrode 104 contains conductive particles whose primary purpose is to exhibit conductivity, and functional particles whose primary purpose is to exhibit functions other than conductivity. In this embodiment, the conductive particles contain a conductive additive 104b, and the functional particles contain a carbon dioxide adsorbent 104a.

[0033] The conductive particles are in contact with each other, forming conductive paths that are the pathways for electrons. The conductive particles are in continuous contact with adjacent conductive particles, constituting the conductive framework of the working electrode 104. The conductive framework is a continuous structure of conductive particles that form conductive paths. The dashed lines in Figure 4 indicate the conductive paths. In the working electrode 104, the conductive paths formed by the conductive additive 104b are formed in a three-dimensional manner.

[0034] Functional particles are basically materials that do not have conductivity, or materials that have lower conductivity than conductive particles. Adjacent functional particles are not in continuous contact with each other, and functional particles do not form conductive paths.

[0035] Conductive particles and functional particles are particulate matter. Conductive particles and functional particles are amorphous and include spherical, lumpy, tubular, sheet-like, and fibrous forms. Particles include not only primary particles but also secondary particles formed by the aggregation of primary particles.

[0036] In this embodiment, the particle size ratio of conductive particles to functional particles is controlled so that the particle size of the conductive particles is greater than or equal to the particle size of the functional particles. In this embodiment, the particle size of the conductive additive 104b, which is a conductive particle, is greater than or equal to the particle size of the carbon dioxide adsorbent 104a, which is a functional particle.

[0037] In this specification, the particle size of conductive particles and functional particles is the length of the part of the particle with the largest diameter, and can also be called the maximum diameter or longest diameter of the particle. In other words, it is sufficient that the length of at least one axial direction of the conductive particles is greater than or equal to the particle size of the functional particles. For fibrous particles such as carbon fiber nonwoven fabrics, the particle size is defined as the straight-line distance from one end to the other while the particle remains in a non-linear state, rather than the length when the particle is stretched in a straight line.

[0038] In this embodiment, the particle size is defined as the mode (peak value) of the particle size distribution. The particle size can be obtained as follows.

[0039] The geometric shape of particles is observed using electron microscopes (SEM, TEM) or atomic force microscopes (AFM), and the maximum diameter of the target particle is measured. The number of measurement samples N is, for example, 30 or more. The mode, estimated by assuming that the distribution of the maximum diameters of each measured particle follows a log-normal distribution, is obtained as the particle size.

[0040] By making the particle size of the conductive particles greater than or equal to the particle size of the functional particles, the particle size of the conductive additive 104b increases, making it easier for adjacent conductive additives 104b to come into contact with each other, thereby increasing the contact rate of the conductive additives 104b. As a result, conductive paths can be easily formed by the conductive additives 104b, and the conductivity per unit volume can be improved.

[0041] Furthermore, by increasing the particle size of the conductive additive 104b, the number of conductive additive 104b particles constituting the conductive path decreases, reducing the number of grain boundaries per unit of transmission distance. As a result, the grain boundary resistance caused by the multiple conductive additives 104b forming the conductive path is reduced, and the conductivity can be further improved.

[0042] Here, the relationship between the conductivity of an electrode containing conductive particles and the volume ratio of conductive particles in the electrode is explained using Figure 6. In Figure 6, the vertical axis is the logarithm of the electrode's conductivity, and the horizontal axis is the volume ratio of conductive particles. In Figure 6, carbon black with a particle size of 0.04 μm and RuO2 with a particle size of 0.5 μm are used as conductive particles. In Figure 6, conductive particles with a particle size of 0.5 μm are shown as circles and solid lines, and conductive particles with a particle size of 0.04 μm are shown as squares and dashed lines. Note that the effect of the difference in conductivity inherent in the RuO2 and carbon black materials themselves on the electrode's conductivity can be ignored compared to the effect of particle size on the electrode's conductivity.

[0043] As shown in Figure 6, when compared at the same volume ratio, conductive particles with a particle size of 0.5 μm exhibit higher conductivity than conductive particles with a particle size of 0.04 μm. In other words, conductive particles with a particle size of 0.5 μm can achieve the same conductivity by reducing their volume ratio compared to conductive particles with a particle size of 0.04 μm. In the example shown in Figure 6, conductive particles with a particle size of 0.04 μm achieve a conductivity of 1 S / m at a volume ratio of approximately 0.6, while conductive particles with a particle size of 0.5 μm achieve a conductivity of 1 S / m at a volume ratio of approximately 0.4.

[0044] As shown in Figure 6, regardless of the particle size of the conductive particles, there is a volume ratio at which the conductivity increases sharply as the volume ratio of conductive particles increases from zero. This volume ratio at which conductivity increases sharply is called the critical volume ratio. When the volume ratio of conductive particles is increased above the critical volume ratio, the rate of increase in conductivity becomes gradual, and conductivity does not increase easily even when the volume ratio of conductive particles increases. In the example shown in Figure 6, conductive particles with a particle size of 0.5 μm have a critical volume ratio of about 0.3, and conductive particles with a particle size of 0.04 μm have a critical volume ratio of about 0.5.

[0045] In regions where the volume ratio of conductive particles is lower than the critical volume ratio, the conductivity is almost zero. Therefore, the volume ratio of conductive particles must be equal to or greater than the critical volume ratio.

[0046] In this embodiment, the conductivity of the working electrode 104 in the thickness direction is set to 1 / 10 or more of the conductivity when the volume ratio of the conductive additive 104b is set to 100%. This makes it possible to maintain the volume ratio of the conductive additive 104b in the working electrode 104 above the limit volume ratio. In other words, it is possible to ensure contact between adjacent conductive additives 104b on the working electrode 104, and to avoid interruptions in the conductive path formed by the conductive additive 104b. The thickness direction of the working electrode 104 is the direction connecting the working electrode current collector 103 and the separator 107 with the working electrode 104 in between.

[0047] The conductivity per unit volume can be obtained as the reciprocal of the volume resistivity. Volume resistivity is the electrical resistance value per unit volume and can be calculated using the following formula.

[0048] Volume resistivity (Ω m) = Electrical resistance (Ω) x Area (m 2 ) / Thickness (m) A working electrode 104 containing conductive additive 104b and conductive particles of the same material and particle size distribution as conductive additive 104b are cut or molded into cylindrical, prismatic, or sheet-like shapes to create measurement samples. The conductive particles of the same material and particle size distribution as conductive additive 104b are measurement samples of conductive additive 100% by volume. The working electrode 104 and the measurement samples of the conductive particles for comparison are fastened together with the same load in the thickness direction using a metal plate, and the electrical resistance is measured. The volume resistivity can be calculated using the above formula, along with the measured electrical resistance and the area and thickness of the measurement samples.

[0049] In this embodiment, the volume ratio of the conductive additive 104b in the working electrode 104 is set to be equal to or greater than the volume ratio of the binder 104c. This ensures that the volume ratio of the conductive additive 104b in the working electrode 104 is maintained, and that the volume ratio of the conductive additive 104b in the working electrode 104 is equal to or greater than the limit volume ratio.

[0050] The particle size of conductive and functional particles can be adjusted as needed. For example, to reduce the particle size, the particles can be crushed using a planetary ball mill or the like to achieve the target particle size.

[0051] Figure 7 shows the relationship between particle size and abundance ratio when particle size is reduced through particle size adjustment. In Figure 7, I, II, III, and IV show the particle size distribution as particle size adjustment progresses in order. As shown in Figure 7, the particle size decreases as particle size adjustment progresses. Furthermore, as particle size adjustment progresses, the range of the particle size distribution narrows and the particle size becomes more averaged.

[0052] Furthermore, increasing the particle size can be achieved by generating secondary particles, which are aggregates of primary particles, from primary particles. For example, secondary particles can be obtained by compressing primary particles or by agglomerating them with a binder.

[0053] Here, we will explain the manufacturing method of the working electrode 104.

[0054] For example, a working electrode 104 can be manufactured by dispersing or dissolving the carbon dioxide adsorbent 104a, the conductive additive 104b, and the binder 104c in a solvent to form a paste, and then applying the resulting electrode paste to the working electrode current collector 103 or the separator 107. The carbon dioxide adsorbent 104a and the conductive additive 104b may be used as mixed particles, or the carbon dioxide adsorbent 104a may be supported on the conductive additive 104b and then kneaded with the binder 104c. The carbon dioxide adsorbent 104a can be supported on the conductive additive 104b by coating the conductive additive 104b with the carbon dioxide adsorbent 104a dispersed or dissolved in a solvent.

[0055] Alternatively, the working electrode 104 may be manufactured by forming a conductive skeleton with the conductive additive 104b and then supporting the carbon dioxide adsorbent 104a on the conductive additive 104b. In this case, the conductive additive 104b and the binder 104c are dispersed or dissolved in a solvent to form a paste, which is then applied to the working electrode current collector 103 or separator 107 and dried to create a porous body consisting of the conductive additive 104b and the binder 104c. Then, a liquid material in which the carbon dioxide adsorbent 104a is dispersed or dissolved in a solvent is applied to the porous body prepared earlier by penetration or spraying, and the solvent is then removed to fix the carbon dioxide adsorbent 104a to the conductive additive 104b. The solvent used to disperse or dissolve the carbon dioxide adsorbent 104a is one that does not dissolve the binder 104c. As a result, a coating of carbon dioxide adsorbent 104a or binder 104c is formed on the surface of the conductive additive 104b with a thickness of, for example, 1 / N (where N is any integer) or less of the particle size of the conductive additive 104b.

[0056] Returning to Figure 3, the counter electrode current collector 105 is a conductive member that contacts the counter electrode 106 and electrically connects the working electrode 104 and the counter electrode 106. One flat surface of the counter electrode current collector 105 is exposed to the mixed gas. The other flat surface of the counter electrode current collector 105 is in contact with the counter electrode 106.

[0057] The counter electrode 106 exchanges electrons with the working electrode 104 when the carbon dioxide adsorbent adsorbs or desorbs carbon dioxide. The counter electrode 106 comprises an electroactivating agent, a conductive additive, and a binder. The electroactivating agent, conductive additive, and binder are used in a mixture state. More specifically, in this embodiment, the particles of the electroactivating agent and the particles of the conductive additive are used in a state in which they are held by the binder.

[0058] The conductive additive and binder of the counter electrode 106 can be made of the same materials as those used for the conductive additive and binder of the working electrode 104. The electroactivating additive is an auxiliary electroactive species that facilitates electron transfer between the working electrode 104 and the carbon dioxide adsorbent, and is an active material with redox properties. As the active material, an organic compound having a π bond, a transition metal compound with multiple oxidation states, or a metal complex that enables electron transfer by changing the valence of a metal ion can be used.

[0059] Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickerosene, and cobaltocene, or porphyrin metal complexes. These metal complexes may be polymers or monomers.

[0060] The separator 107 is positioned between the working electrode 104 and the counter electrode 106, separating them. The separator 107 is an insulating ion-permeable membrane that prevents physical contact between the working electrode 104 and the counter electrode 106, thereby suppressing electrical short circuits, while also allowing ions to pass through. As the separator 107, a cellulose membrane, a polymer, a composite material of polymer and ceramic, etc., can be used.

[0061] The electrolyte layer 108 is an immersion layer in which the working electrode 104, separator 107, and counter electrode 106 are immersed. For example, an ionic liquid can be used as the electrolyte layer 108. An ionic liquid is a salt of a liquid that is non-volatile at room temperature and pressure.

[0062] Furthermore, a power supply 109 is connected to the working electrode current collector 103 and the counter electrode current collector 105 of the electrochemical cell 101. The power supply 109 can apply a predetermined voltage to the working electrode 104 and the counter electrode 106, thereby changing the potential difference between the working electrode 104 and the counter electrode 106. The working electrode 104 is the negative electrode. Therefore, the opposite electrode 106 is the positive electrode.

[0063] The electrochemical cell 101 operates in a carbon dioxide capture mode, where carbon dioxide is captured at the working electrode 104, and a carbon dioxide release mode, where carbon dioxide is released from the working electrode 104, by changing the potential difference between the working electrode 104 and the counter electrode 106. The carbon dioxide capture mode is a charging mode that charges the electrochemical cell 101, and the carbon dioxide release mode is a discharge mode that discharges the electrochemical cell 101.

[0064] Specifically, in carbon dioxide capture mode, a first voltage V1 is applied between the working electrode 104 and the counter electrode 106, and electrons are supplied from the counter electrode 106 to the working electrode 104. 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.

[0065] In the carbon dioxide emission mode, a second voltage V2 is applied between the working electrode 104 and the counter electrode 106, supplying electrons from the working electrode 104 to the counter electrode 106. The second voltage V2 is different from the first voltage V1. 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 the carbon dioxide 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.

[0066] Next, the operation of the carbon dioxide capture system 1 of this embodiment will be described. As described above, the carbon dioxide capture system 1 operates by alternately switching between a carbon dioxide capture mode and a carbon dioxide release mode. The operation of the carbon dioxide capture system 1 is controlled by the control device 14.

[0067] First, let's explain the carbon dioxide recovery mode. In carbon dioxide recovery mode, the pump 11 is activated. This supplies the mixed gas to the carbon dioxide recovery device 10. In the carbon dioxide recovery device 10, the voltage applied between the working electrode 104 and the counter electrode 106 of the electrochemical cell 101 is defined as the first voltage V1. This allows for the simultaneous donation of electrons to the electroactivating auxiliary material of the counter electrode 106 and the withdrawal of electrons to the carbon dioxide adsorbent of the working electrode 104.

[0068] The carbon dioxide adsorbent on the working electrode 104, having received electrons from the counter electrode 106, has increased carbon dioxide binding affinity and adsorbs carbon dioxide contained in the mixed gas. As a result, the carbon dioxide recovery device 10 can recover carbon dioxide from the mixed gas. The mixed gas, after carbon dioxide has been removed, is discharged from the carbon dioxide recovery device 10.

[0069] In carbon dioxide recovery mode, the flow path switching valve 12 switches to a flow path that allows the mixed gas discharged from the carbon dioxide recovery device 10 to flow out to the atmosphere. As a result, the mixed gas discharged from the carbon dioxide recovery device 10 is released into the atmosphere.

[0070] Next, the carbon dioxide release mode will be described. In the carbon dioxide release mode, the pump 11 is stopped. This stops the supply of the mixed gas to the carbon dioxide recovery device 10. In the carbon dioxide recovery device 10, the voltage applied between the working electrode 104 and the counter electrode 106 of the electrochemical cell 101 is set to the second voltage V2. This allows for the simultaneous donation of electrons to the carbon dioxide adsorbent of the working electrode 104 and the withdrawal of electrons to the electroactivating auxiliary material of the counter electrode 106.

[0071] The carbon dioxide adsorbent at the working electrode 104 releases electrons and enters an oxidized state. The carbon dioxide adsorbent's binding force to carbon dioxide decreases, and it desorbs and releases carbon dioxide. The carbon dioxide released from the carbon dioxide adsorbent is discharged from the carbon dioxide recovery device 10.

[0072] In carbon dioxide release mode, the flow path switching valve 12 switches to a flow path that allows carbon dioxide emitted from the carbon dioxide recovery device 10 to flow out to the inlet side of the carbon dioxide utilization device 13. As a result, the carbon dioxide emitted from the carbon dioxide recovery device 10 is supplied to the carbon dioxide utilization device 13.

[0073] According to the embodiment described above, in the working electrode 104, the particle size of the conductive additive 104b, which is a conductive particle, is set to be greater than or equal to the particle size of the carbon dioxide adsorbent 104a, which is a functional particle. This improves the contact rate of the conductive additive 104b in the working electrode 104, thereby improving the conductivity per unit volume. Furthermore, as the particle size of the conductive additive 104b increases, the number of particles per unit distance of the conductive path decreases, and the number of grain boundaries to be traversed decreases. As a result, the grain boundary resistance caused by the multiple conductive additives 104b forming the conductive path is reduced, and the conductivity per unit volume can be further improved.

[0074] Furthermore, by making the particle size of the conductive additive 104b greater than or equal to the particle size of the carbon dioxide adsorbent 104a, conductivity can be ensured even if the volume ratio of the conductive additive 104b is reduced, and the volume ratio of the functional particle carbon dioxide adsorbent 104a can be increased. As a result, the functionality of the functional particle carbon dioxide adsorbent 104a can be improved, and the carbon dioxide adsorption efficiency of the working electrode 104 can be improved.

[0075] Furthermore, in this embodiment, the volume ratio of the conductive additive 104b in the working electrode 104 is set to be equal to or greater than the volume ratio of the binder 104c. This ensures that the volume ratio of the conductive additive 104b in the working electrode 104 is maintained, thereby ensuring conductivity by the conductive additive 104b.

[0076] (Second Embodiment) Next, a second embodiment of the present invention will be described. Only the parts that differ from the first embodiment described above will be explained below.

[0077] In the second embodiment, in the working electrode 104, carbon materials are used as the carbon dioxide adsorbent 104a and the conductive assistant 104b. The carbon material used for the carbon dioxide adsorbent 104a and the carbon material used for the conductive assistant 104b may be the same carbon material or different carbon materials. In the second embodiment, the carbon dioxide adsorbent 104a and the conductive assistant 104b are included in the conductive particles, and the catalyst is included in the functional particles. The catalyst promotes a chemical reaction that proceeds with at least either the adsorption of carbon dioxide by the working electrode 104 or the desorption of carbon dioxide from the working electrode 104. The catalyst will be described later.

[0078] When a carbon material is used as the carbon dioxide adsorbent 104a, in the carbon dioxide recovery mode, at the working electrode 104, the oxygen reduction reaction shown in the following reaction formula (1) and the carbonate ion generation reaction shown in the reaction formula (2) proceed, and carbon dioxide is adsorbed on the working electrode 104. That is, the oxygen reduction reaction triggers the adsorption of carbon dioxide at the working electrode 104.

[0079] O2 + 2e - → O2 - ···(1) O2 - + CO2 → 1 / 2O2 + CO3 2- ···(2) At the working electrode 104, oxygen contained in the mixed gas receives electrons and is reduced, and an oxygen reduction reaction that generates superoxide O2 - which is a kind of active oxygen, occurs. The active oxygen O2 - generated by the oxygen reduction reaction is highly reactive, and a carbonate ion generation reaction that oxidizes carbon dioxide to generate carbonate ions CO3 2- which are oxide ions of carbon dioxide, occurs, and carbon dioxide is adsorbed on the working electrode 104. That is, the active oxygen O2 - generated by the oxygen reduction reaction contributes to the adsorption of carbon dioxide at the working electrode 104.

[0080] In the carbon dioxide release mode, at least either of the carbonate ion dissociation reactions shown in the following reaction formula (3) and reaction formula (4) proceeds at the working electrode 104. In the carbonate ion dissociation reaction, the carbonate ion CO32- The carbonate ion is dissociated, producing carbon dioxide. In other words, the carbonate ion dissociation reaction triggers the desorption of carbon dioxide at the working electrode 104.

[0081] CO3 2- +C → 3CO2 + 4e - ...(3) 2CO3 2- →O2+2CO2+4e - ...(4) As shown in Figure 8, the working electrode 104 of this second embodiment is equipped with a catalyst 104d that promotes at least one of the oxygen reduction reaction and the carbonate ion dissociation reaction. As such a catalyst 104d, metal particles consisting of at least one of Al, Cu, Ni, Ag, Au, and Pt, or metal oxide particles consisting of at least one of RuO2, MnO2, and MoO2 can be used. For example, the catalyst 104d can be used supported on a conductive additive 104b.

[0082] As described above, in this second embodiment, the catalyst 104d is included in the functional particles. Even if the conductivity of the material used as catalyst 104d is higher than that of the conductive particles, the catalyst 104d is not primarily intended to exhibit conductivity, and since catalyst 104d does not form conductive paths, catalyst 104d is included in the functional particles.

[0083] In this second embodiment as well, the particle sizes of the conductive particles, the carbon dioxide adsorbent 104a and the conductive additive 104b, are greater than or equal to the particle size of the functional particle, the catalyst 104d. Therefore, as in the first embodiment, the contact rate of the conductive particles at the working electrode 104 can be improved, and the conductivity per unit volume can be improved.

[0084] Furthermore, by making the particle size of the conductive additive 104b greater than or equal to the particle size of the carbon dioxide adsorbent 104a, conductivity can be ensured even when the volume ratio of the conductive additive 104b is reduced, and the volume ratio of the functional particle catalyst 104d can be increased. This improves the functionality of the functional particle catalyst 104d and improves the carbon dioxide adsorption efficiency of the working electrode 104.

[0085] (Third embodiment) Next, a third embodiment of the present invention will be described. Only the parts that differ from the above embodiments will be described below.

[0086] In this third embodiment, a conductive polymer is used as the binder 104c of the working electrode 104. The conductive polymer is a polymer having π bonds, and examples include polyacetylene, polypyrrole, poly(p-phenylene), poly(3-methylthiophene), and poly(3-hexylthiophene).

[0087] In this third embodiment, by using a conductive polymer as the binder 104c, the binder 104c itself can be made conductive. The binder 104c is provided so as to cover at least the conductive additive 104b. By using a binder 104c made of a conductive polymer, it is possible to maintain conductivity through the binder 104c even if the entire conductive additive 104b is covered with the binder 104c.

[0088] The binder 104c that coats the conductive additive 104b can complement the conductive paths formed by the conductive additive 104b. In other words, even if there is a gap between adjacent conductive additives 104b and they are connected via the binder 104c, a conductive path can be formed by the conductive additive 104b and the binder 104c. The binder 104c, which is made of a conductive polymer, forms a conductive framework together with the conductive additive 104b.

[0089] The binder 104c may contain a non-conductive polymer in addition to the conductive polymer. A binder 104c consisting of a non-conductive polymer has superior binding properties compared to a binder 104c consisting of a conductive polymer. In a binder 104c containing both a conductive polymer and a non-conductive polymer, it is desirable to use a conductive polymer in the part that comes into contact with the conductive additive 104b and a non-conductive polymer in the other parts. This allows the binder 104c to ensure conductivity in the part that comes into contact with the conductive additive 104b, while improving binding properties in the other parts.

[0090] (Other embodiments) The present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of the invention. Furthermore, the means disclosed in each of the above embodiments may be combined as appropriate to the extent that they are feasible.

[0091] For example, in each of the above embodiments, an example was described in which carbon dioxide contained in the mixed gas is adsorbed by the electrochemical cell 101. However, the electrochemical cell 101 is not limited to this, and other types of gases such as oxygen may also be adsorbed from the mixed gas.

[0092] Furthermore, in each of the above embodiments, the particle size of the conductive particles in the working electrode 104 is set to be equal to or greater than the particle size of the functional particles. However, the embodiment is not limited to this, and the particle size of the conductive particles in the counter electrode 106 may also be equal to or greater than the particle size of the functional particles. In this case, the conductive particles contain the conductive additive of the counter electrode 106, and the functional particles contain the electroactivating auxiliary material of the counter electrode 106.

[0093] The characteristics of the electrochemical cell disclosed herein are as follows: (Item 1) An electrochemical cell having a working electrode (104) and a counter electrode (106), wherein a voltage is applied between the working electrode and the counter electrode to adsorb and desorb gas at the working electrode, At least one of the working electrode and the counter electrode has conductive particles (104b) that come into contact with each other to form a conductive path, and functional particles (104a) that do not form the conductive path. An electrochemical cell in which the particle size of the conductive particles is equal to or greater than the particle size of the functional particles. (Item 2) The functional particles are a gas adsorbent that adsorbs and desorbs the gas, as described in item 1, in the electrochemical cell. (Item 3) The electrochemical cell according to item 1 or 2, wherein the functional particles are catalysts (104d) that promote a chemical reaction that proceeds in conjunction with at least one of the adsorption of gas by the working electrode and the desorption of gas from the working electrode. (Item 4) The electrode has a binder (104c), The electrochemical cell according to any one of items 1 to 3, wherein the volume ratio of the conductive particles in the electrode is equal to or greater than the volume ratio of the binder. (Item 5) The electrochemical cell according to item 4, wherein the binder contains a conductive polymer and together with the conductive particles forms the conductive path. [Explanation of Symbols]

[0094] 104 Working electrode 104a Carbon dioxide adsorbent (functional particles, gas adsorbent) 104b Conductive additive (conductive particles) 104c Binder 104d Catalyst 106 Opposite

Claims

1. An electrochemical cell having a working electrode (104) and a counter electrode (106), wherein a voltage is applied between the working electrode and the counter electrode to adsorb and desorb gas at the working electrode, At least one of the working electrode and the counter electrode has conductive particles (104b) that come into contact with each other to form a conductive path, and functional particles (104a) that do not form the conductive path. An electrochemical cell in which the particle size of the conductive particles is equal to or greater than the particle size of the functional particles.

2. The electrochemical cell according to claim 1, wherein the functional particles are a gas adsorbent that adsorbs and desorbs the gas.

3. The electrochemical cell according to claim 1, wherein the functional particles are catalysts (104d) that promote a chemical reaction that proceeds in conjunction with at least one of the adsorption of gas by the working electrode and the desorption of gas from the working electrode.

4. The electrode has a binder (104c), The electrochemical cell according to claim 1, wherein the volume ratio of the conductive particles in the electrode is equal to or greater than the volume ratio of the binder.

5. The electrochemical cell according to claim 4, wherein the binder contains a conductive polymer and together with the conductive particles forms the conductive path.

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