Electrochemical cell

Abstract

This electrochemical cell has a working electrode (104) and a counter electrode (106), and adsorbs and desorbs a gas at the working electrode by applying a voltage between the working electrode and the counter electrode. At least one of the working electrode and the counter electrode has conductive particles (104b) that are in contact with each other and form a conductive path, and functional particles (104a) that do not form a conductive path. The particle diameter of the conductive particles is equal to or greater than the particle diameter of the functional particles.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on Japanese patent application No. 2022-109069 filed on July 6, 2022, and the contents thereof are cited herein. Technical Field

[0003] The present disclosure relates to gas adsorbed electrochemical cells. Background Art

[0004] Patent document 1 discloses an electrochemical cell for recovering a specific gas of a recovery object from a mixed gas. The electrochemical cell of Patent document 1 has a pair of electrodes consisting of a working electrode and a counter electrode, and adsorbs the specific gas through an electrochemical reaction. The working electrode includes a gas adsorbing material that adsorbs the specific gas from the mixed gas, and a conductive auxiliary agent that forms a conductive path to the gas adsorbing material. The counter electrode includes an electroactive auxiliary material that transmits and receives electrons with the working electrode, and a conductive auxiliary agent that forms a conductive path to the electroactive auxiliary material.

[0005] Patent Document 1: Japanese Patent Application No. 2018-533470

[0006] For example, when the conductive auxiliary agent is used as conductive particles and the gas adsorbent and electroactive auxiliary material are used as functional particles, in order to improve the gas adsorption efficiency of the electrochemical cell, it is necessary to ensure the conductivity of the conductive particles and improve the functionality of the functional particles. Summary of the invention

[0007] The present disclosure has been made in view of the above-mentioned viewpoints, and an object of the present disclosure is to achieve both ensuring the conductivity of the conductive particles and improving the functionality of the functional particles in an electrochemical cell for gas adsorption having conductive particles and functional particles.

[0008] In order to achieve the above-mentioned object, the electrochemical cell of the present disclosure has a working electrode and a counter electrode, and by applying a voltage between the working electrode and the counter electrode, a gas is adsorbed and desorbed at the working electrode. At least one of the working electrode and the counter electrode has conductive particles that contact each other and form a conductive path and functional particles that do not form a conductive path. The particle size of the conductive particles is greater than the particle size of the functional particles.

[0009] Thus, the contact rate of the conductive particles in the electrode can be increased, and the conductivity of the electrode can be increased. Therefore, even if the volume ratio of the conductive particles is reduced, the conductivity based on the conductive particles can be ensured. Moreover, the volume ratio of the functional particles can be increased, so the functionality based on the functional particles can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1It is a schematic diagram showing the overall structure of the carbon dioxide recovery system according to the first embodiment.

[0011] Figure 2 It is an explanatory diagram showing the structure of a carbon dioxide recovery device.

[0012] Figure 3 It is an explanatory diagram showing the structure of an electrochemical cell in a carbon dioxide recovery device.

[0013] Figure 4 It is a diagram showing the structure of a working electrode of an electrochemical cell.

[0014] Figure 5 This is an enlarged view of the material constituting the working electrode.

[0015] Figure 6 This is a diagram showing the relationship between the electrical conductivity of an electrode containing conductive particles and the volume ratio of the conductive particles in the electrode.

[0016] Figure 7 This is a diagram showing the relationship between the particle size and the abundance ratio when the particle size adjustment is performed.

[0017] Figure 8 This is an enlarged view of the material constituting the working electrode of the second embodiment. DETAILED DESCRIPTION

[0018] Hereinafter, multiple methods for implementing the present disclosure will be described with reference to the accompanying drawings. In each embodiment, the same reference numerals are sometimes used to mark the parts corresponding to the matters described in the previous embodiment, and repeated descriptions are omitted. In the case where only a part of the structure is described in each embodiment, other embodiments described previously can be applied to the other parts of the structure. Not only are the combinations of the parts that can be combined specifically indicated in each embodiment, but the embodiments can also be partially combined with each other even if not indicated, as long as there is no particular hindrance to the combination.

[0019] (First Embodiment)

[0020] A first embodiment of the electrochemical cell of the present disclosure is described below. In this embodiment, the electrochemical cell of the present disclosure is applied to a carbon dioxide recovery system 1 for separating and recovering carbon dioxide from a mixed gas containing carbon dioxide. Therefore, the recovery target gas of this embodiment is carbon dioxide.

[0021] like Figure 1 As shown in the overall configuration diagram of FIG. 1 , the carbon dioxide recovery system 1 of the present 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 .

[0022] The carbon dioxide recovery device 10 separates carbon dioxide from the mixed gas and recovers it. As the mixed gas, the atmosphere, the exhaust gas of an internal combustion engine, etc. 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 from which carbon dioxide has been removed or the recovered carbon dioxide. The detailed structure of the carbon dioxide recovery device 10 will be described later.

[0023] The outlet of the carbon dioxide recovery device 10 is connected to the suction port side of the pump 11. The pump 11 sucks the mixed gas from which carbon dioxide has been removed or the recovered carbon dioxide from the carbon dioxide recovery device 10. The mixed gas is supplied to the carbon dioxide recovery device 10 by the suction action of the pump 11.

[0024] In the present embodiment, an example in which the pump 11 is arranged downstream of the carbon dioxide recovery device 10 in the gas flow direction is described, but the pump 11 may be arranged upstream of the carbon dioxide recovery device 10 in the gas flow direction.

[0025] The discharge port of the pump 11 is connected to the inlet side of the flow path switching valve 12. The flow path switching valve 12 is a three-way valve that switches the flow path of the gas flowing out of the carbon dioxide recovery device 10. The flow path switching valve 12 switches the flow path for the gas flowing out of the carbon dioxide recovery device 10 to flow to the atmosphere side and the flow path for the gas flowing out of the carbon dioxide recovery device 10 to flow to the carbon dioxide utilization device 13 side.

[0026] 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 fuels such as methane. The hydrocarbon fuel can be a gaseous fuel at normal temperature and pressure, or a liquid fuel at normal temperature and pressure.

[0027] The control device 14 is composed of a well-known microcomputer including a CPU, a ROM, a RAM, etc. and its peripheral circuits. The control device 14 performs various calculations and processes based on the control program stored in the ROM to control the operation of various control target devices connected to the output side. More specifically, the control device 14 of this embodiment controls the operation of the carbon dioxide recovery device 10, the pump 11, and the flow path switching valve 12.

[0028] Here, the carbon dioxide recovery device 10 will be described.

[0029] like Figure 2 As shown, the carbon dioxide recovery device 10 includes a housing 100 and a plurality of electrochemical cells 101. The housing 100 of this embodiment is formed of a metal material. The housing 100 may also be formed of a resin material.

[0030] The housing 100 has a gas inlet and a gas outlet. The gas inlet is an opening for allowing the mixed gas to flow into the housing 100. The gas outlet is an opening for allowing the mixed gas from which carbon dioxide has been removed or the recovered carbon dioxide to flow out of the housing 100.

[0031] The electrochemical cell 101 absorbs carbon dioxide through an electrochemical reaction, separates carbon dioxide from the mixed gas, and recovers it. In addition, the electrochemical cell 101 desorbs carbon dioxide through an electrochemical reaction, and releases the absorbed carbon dioxide. A plurality of electrochemical cells 101 are accommodated in the housing 100 .

[0032] The electrochemical cell 101 is formed in a rectangular flat plate shape. A plurality of electrochemical cells 101 are stacked and arranged at a certain interval in the frame 100 so that the plate surfaces are parallel to each other. A plurality of gas flow paths are formed between adjacent electrochemical cells 101 to allow the mixed gas flowing from the gas inlet to flow.

[0033] like Figure 3 As shown, the electrochemical cell 101 has a working electrode current collecting material 103, a working electrode 104, a counter electrode current collecting material 105, a counter electrode 106, a separator 107, and an electrolyte layer 108. The working electrode current collecting material 103, the working electrode 104, the counter electrode current collecting material 105, the counter electrode 106, and the separator 107 are all formed into a rectangular flat plate shape. The working electrode 104 and the counter electrode 106 constitute a pair of electrodes.

[0034] The electrochemical cell 101 is formed as a stacked body formed by stacking the working electrode current collector material 103, the working electrode 104, the counter electrode current collector material 105, the counter electrode 106, and the separator 107. The stacking direction of the working electrode current collector material 103 and the like in each electrochemical cell 101 is consistent with the stacking direction of the plurality of electrochemical cells 101 stacked inside the frame 100.

[0035] The working electrode collector 103 is a conductive member that contacts the working electrode 104 to electrically connect the working electrode 104 and the counter electrode 106. One flat surface of the working electrode collector 103 is exposed to the mixed gas. The other flat surface of the working electrode collector 103 contacts the working electrode 104.

[0036] like Figure 4 As shown, the working electrode 104 is disposed between the working electrode current collector material 103 and the separator 107. Figure 4 , Figure 5 As shown, the working electrode 104 includes a carbon dioxide adsorbent 104a, a conductive additive 104b, and a binder 104c. Figure 4 , Figure 5In the figure, the conductive auxiliary agent 104b is marked with oblique lines. Figure 4 The carbon dioxide adsorbent 104a, the conductive additive 104b, and the adhesive 104c are not limited to Figure 4 , Figure 5 The shapes and sizes shown.

[0037] The carbon dioxide adsorbent 104a, the conductive aid 104b, and the binder 104c are used in a mixed state. More specifically, in this embodiment, the particles of the carbon dioxide adsorbent 104a and the particles of the conductive aid 104b are used in a state 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.

[0038] 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. As the carbon dioxide adsorbent, for example, polyanthraquinone, carbon material, metal oxide, etc. can be used. In this embodiment, polyanthraquinone is used as the carbon dioxide adsorbent 104a.

[0039] The conductive agent 104b is a conductive substance that forms a conductive path to the carbon dioxide adsorbent 104a. Carbon materials, metal porous materials, metal-supported ceramics, etc. can be used as the conductive agent 104b. Carbon materials constituting the conductive agent 104b can use carbon black, carbon nanotubes, graphene, carbon fiber nonwoven fabrics, etc.

[0040] The adhesive 104c is a polymer binder that holds the carbon dioxide adsorbent 104a and the conductive aid 104b. The adhesive 104c allows the carbon dioxide adsorbent 104a and the carbon dioxide adsorbent 104a, the conductive aid 104b and the conductive aid 104b, and the carbon dioxide adsorbent 104a and the conductive aid 104b to adhere. As the adhesive 104c, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used. The adhesive 104c of this embodiment uses a non-conductive polymer that does not have conductivity.

[0041] The working electrode 104 includes conductive particles that mainly exhibit conductivity and functional particles that mainly exhibit functions other than conductivity. In this embodiment, the conductive particles include a conductive auxiliary agent 104b, and the functional particles include a carbon dioxide adsorbent 104a.

[0042] The conductive particles are in contact with each other to form a conductive path that is a passage for electrons. The conductive particles are in continuous contact with adjacent conductive particles to form a conductive skeleton of the working electrode 104. The conductive skeleton is a continuous structure of conductive particles that form a conductive path. Figure 4 The dotted line in represents a conductive path. In the working electrode 104, the conductive path based on the conductive auxiliary agent 104b is formed in a three-dimensional shape.

[0043] The functional particles are substantially non-conductive or have lower conductivity than the conductive particles. The adjacent functional particles are not in continuous contact with each other, and the functional particles do not form a conductive path.

[0044] Conductive particles and functional particles are particulate materials. Conductive particles and functional particles are amorphous and include spherical, blocky, tubular, flake and fibrous shapes. Particles include not only primary particles but also secondary particles formed by the aggregation of primary particles.

[0045] In this embodiment, the particle size ratio of the conductive particles and the functional particles is controlled so that the particle size of the conductive particles is equal to or larger than the particle size of the functional particles. In this embodiment, the particle size of the conductive additive 104b as the conductive particles is equal to or larger than the particle size of the carbon dioxide adsorbent 104a as the functional particles.

[0046] In this specification, the particle size of conductive particles and functional particles is the length of the largest diameter part of the particle, which can also be referred to as the maximum diameter or major diameter of the particle. In other words, the length of at least one axial direction of the conductive particles is equal to or greater than the particle size of the functional particles. For fibrous particles such as carbon fiber nonwoven fabrics, the particle size is not the length extending linearly, but the linear distance from one end to the other end in a non-linear state.

[0047] In this embodiment, the mode (peak value) of the particle size distribution of the particles is used as the particle size. The particle size of the particles can be obtained as follows.

[0048] The geometric shape of the particles is observed by electron microscopy (SEM, TEM) or atomic force microscopy (AFM), and the maximum diameter of the particles to be measured is measured. The number of samples N is set to 30 or more, for example. The mode value estimated by assuming that the distribution of the maximum diameter of each particle measured is a log-normal distribution is obtained as the particle size.

[0049] By setting the particle size of the conductive particles to be larger than the particle size of the functional particles, the particle size of the conductive additive 104b as the conductive particles becomes larger, and adjacent conductive additives 104b are more likely to contact each other, which can increase the contact rate of the conductive additives 104b. Therefore, the conductive additives 104b can easily form a conductive path, which can increase the conductivity per unit volume.

[0050] Furthermore, by increasing the particle size of the conductive additive 104b, the number of conductive additive 104b particles constituting the conductive path decreases, and the number of grain boundaries passed through per transmission distance decreases. Therefore, the grain boundary resistance generated by the conductive additives 104b forming the conductive path is reduced, and the conductivity can be further improved.

[0051] Here, use Figure 6 The relationship between the electrical conductivity of an electrode including conductive particles and the volume ratio of the conductive particles in the electrode will be described. Figure 6 The vertical axis is the logarithm of the conductivity of the electrode, and the horizontal axis is the volume ratio of the conductive particles. Figure 6 In the present invention, 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. Figure 6 In the figure, the conductive particles with a particle size of 0.5 μm are represented by a circle figure and a solid line, and the conductive particles with a particle size of 0.04 μm are represented by a quadrilateral figure and a dotted line. In addition, the difference in conductivity between the RuO2 and carbon black materials themselves has an influence on the conductivity of the electrode that can be ignored compared to the influence of the particle size on the conductivity of the electrode.

[0052] like Figure 6 As shown in FIG. 1 , when the conductive particles with a particle size of 0.5 μm are compared with the conductive particles with a particle size of 0.04 μm, the conductivity is improved. In other words, in order to obtain the same conductivity, the volume ratio of the conductive particles with a particle size of 0.5 μm can be reduced compared with the conductive particles with a particle size of 0.04 μm. Figure 6 In the example shown, conductive particles having a particle size of 0.04 μm give a conductivity of 1 S / m at a volume ratio of about 0.6, whereas conductive particles having a particle size of 0.5 μm give a conductivity of 1 S / m at a volume ratio of about 0.4.

[0053] like Figure 6 As shown in FIG. 1 , regardless of the particle size of the conductive particles, if the volume ratio of the conductive particles is increased from zero, there is a volume ratio at which the conductivity increases sharply. The volume ratio at which the conductivity increases sharply is defined as the limiting volume ratio. If the volume ratio of the conductive particles is increased above the limiting volume ratio, the increase rate of the conductivity becomes slow, and the conductivity is not easy to increase even if the volume ratio of the conductive particles increases. Figure 6In the example shown, the limiting volume ratio of the conductive particles having a particle size of 0.5 μm is approximately 0.3, and the limiting volume ratio of the conductive particles having a particle size of 0.04 μm is approximately 0.5.

[0054] In a region where the volume ratio of the conductive particles is lower than the limiting volume ratio, the electrical conductivity is substantially 0. Therefore, the volume ratio of the conductive particles needs to be equal to or higher than the limiting volume ratio.

[0055] In this embodiment, the conductivity of the working electrode 104 is set to be 1 / 10 or more of the conductivity when the volume ratio of the conductive auxiliary agent 104b is 100% in the thickness direction of the working electrode 104. As a result, the volume ratio of the conductive auxiliary agent 104b in the working electrode 104 can be maintained above the limit volume ratio. In other words, the contact between adjacent conductive auxiliary agents 104b in the working electrode 104 can be ensured, and the interruption of the conductive path formed by the conductive auxiliary agent 104b can be avoided. In addition, the thickness direction of the working electrode 104 is the direction of connecting the working electrode current collector 103 and the separator 107 with the working electrode 104 sandwiched therebetween.

[0056] The electrical conductivity per unit volume can be obtained as the reciprocal of the volume resistivity. The volume resistivity is the resistance value per unit volume and can be calculated by the following formula.

[0057] Volume resistivity (Ω·m) = resistance (Ω) × area (m 2 ) / Thickness(m)

[0058] The working electrode 104 containing the conductive auxiliary agent 104b and the conductive particles of the same material and the same particle size distribution as the conductive auxiliary agent 104b are cut or formed into a cylindrical, prism-shaped or sheet-shaped shape to prepare a measurement sample. The conductive particles of the same material and the same particle size distribution as the conductive auxiliary agent 104b are the measurement sample of the conductive auxiliary agent 104b with a volume ratio of 100%. The working electrode 104 and the measurement sample of the conductive particles as a comparison object are respectively fastened with the same load in the thickness direction using a metal flat plate, and the resistance is measured. The volume resistivity can be calculated by the above formula using the measured value of the resistance and the area and thickness of the measurement sample.

[0059] In this embodiment, the volume ratio of the conductive auxiliary agent 104b is set to be greater than the volume ratio of the binder 104c in the working electrode 104. Thus, the volume ratio of the conductive auxiliary agent 104b in the working electrode 104 can be ensured and the volume ratio of the conductive auxiliary agent 104b in the working electrode 104 can be greater than the limit volume ratio.

[0060] The particle size of the conductive particles and the functional particles can be adjusted as desired. For example, when the particle size of the particles is reduced by adjusting the particle size, the particles can be pulverized using a planetary ball mill or the like to obtain a target particle size.

[0061] Figure 7 This shows the relationship between the particle size and the abundance ratio when the particle size is reduced by particle size adjustment. Figure 7 In the figure, I, II, III, and IV represent the particle size distribution when the particle size is adjusted. Figure 7 As shown, as the particle size adjustment proceeds, the particle size of the particles becomes smaller. Furthermore, as the particle size adjustment proceeds, the range of the particle size distribution becomes narrower, and the particle size becomes averaged.

[0062] In the case of increasing the particle size, this can be achieved by generating secondary particles, which are aggregates of primary particles, from primary particles. For example, secondary particles can be obtained by compacting primary particles or aggregating primary particles with a binder.

[0063] Here, a method for manufacturing the working electrode 104 will be described.

[0064] For example, the carbon dioxide adsorbent 104a, the conductive agent 104b, and the binder 104c are dispersed or dissolved in a solvent and paste-formed, and the obtained electrode paste is applied to the working electrode current collector 103 or the separator 107, thereby manufacturing the working electrode 104. The carbon dioxide adsorbent 104a and the conductive agent 104b can be used as mixed particles, or the carbon dioxide adsorbent 104a can be supported on the conductive agent 104b and then kneaded with the binder 104c. The carbon dioxide adsorbent 104a can be supported on the conductive agent 104b by applying the carbon dioxide adsorbent 104a dispersed or dissolved in the solvent to the conductive agent 104b.

[0065] Alternatively, the working electrode 104 may be manufactured by supporting the carbon dioxide adsorbent 104a on the conductive aid 104b after forming a conductive skeleton with the conductive aid 104b. In this case, the conductive aid 104b and the binder 104c are dispersed or dissolved in a solvent and made into a paste, which is then applied to the working electrode current collector 103 or the separator 107 and dried to form a porous body composed of the conductive aid 104b and the binder 104c. Then, a liquid material in which the carbon dioxide adsorbent 104a is dispersed or dissolved in a solvent is attached to the previously manufactured porous body by immersion or spraying, and then the solvent is removed to fix the carbon dioxide adsorbent 104a to the conductive aid 104b. The solvent in which the carbon dioxide adsorbent 104a is dispersed or dissolved uses a solvent that does not dissolve the binder 104c. Thus, a film of the carbon dioxide adsorbent 104a and the binder 104c is formed on the surface of the conductive auxiliary agent 104b with a film thickness of, for example, 1 / N (N is an arbitrary integer) or less of the particle size of the conductive auxiliary agent 104b.

[0066] Return 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 contacts the counter electrode 106 .

[0067] The counter electrode 106 transmits and receives electrons with the working electrode 104 when the carbon dioxide adsorbent adsorbs or desorbs carbon dioxide. The counter electrode 106 comprises an electroactive auxiliary material, a conductive auxiliary agent and a binder. The electroactive auxiliary material, the conductive auxiliary agent and the binder are used in a state of a mixture. More specifically, in this embodiment, the particles of the electroactive auxiliary material and the particles of the conductive auxiliary agent are used in a state held by the binder.

[0068] The conductive auxiliary agent and the binder of the counter electrode 106 can use the same materials as those of the conductive auxiliary agent and the binder of the working electrode 104. The electroactive auxiliary material is an auxiliary electroactive species that performs electron transmission and reception between the working electrode 104 and the carbon dioxide adsorbent, and is an active material having redox properties. As the active material, an organic compound having a π bond, a transition metal compound having multiple oxidation numbers, and a metal complex that can transmit and receive electrons by changing the valence of metal ions can be used.

[0069] Examples of such metal complexes include cyclopentadienyl metal complexes such as ferrocene, nickelocene, and cobaltocene, and porphyrin metal complexes, etc. These metal complexes may be polymers or monomers.

[0070] The separator 107 is disposed between the working electrode 104 and the counter electrode 106 to separate the working electrode 104 from the counter electrode 106. The separator 107 is an insulating ion permeable membrane that prevents physical contact between the working electrode 104 and the counter electrode 106, suppresses electrical short circuits, and allows ions to pass through. As the separator 107, a cellulose membrane, a polymer, a composite material of a polymer and ceramics, etc. can be used.

[0071] The electrolyte layer 108 is an impregnation layer in which the working electrode 104, the separator 107, and the counter electrode 106 are impregnated. For example, an ionic liquid can be used as the electrolyte layer 108. The ionic liquid is a liquid salt having non-volatility at normal temperature and pressure.

[0072] Furthermore, a power source 109 is connected to the working electrode current collector 103 and the counter electrode current collector 105 of the electrochemical cell 101. The power source 109 applies a predetermined voltage to the working electrode 104 and the counter electrode 106, and can change the potential difference between the working electrode 104 and the counter electrode 106. The working electrode 104 is a negative electrode, and the counter electrode 106 is a positive electrode.

[0073] The electrochemical cell 101 operates in a carbon dioxide recovery mode for recovering carbon dioxide through the working electrode 104 and a carbon dioxide release mode for releasing carbon dioxide from the working electrode 104 by changing the potential difference between the working electrode 104 and the counter electrode 106. The carbon dioxide recovery mode is a charging mode for charging the electrochemical cell 101, and the carbon dioxide release mode is a discharge mode for discharging the electrochemical cell 101.

[0074] Specifically, in the carbon dioxide recovery 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. In the first voltage V1, the working electrode potential < the counter electrode potential. The first voltage V1 can be set within a range of 0.5 to 2.0V, for example.

[0075] In the carbon dioxide release mode, a second voltage V2 is applied between the working electrode 104 and the counter electrode 106, and electrons are supplied from the working electrode 104 to the counter electrode 106. The second voltage V2 is a voltage different from the first voltage V1. As long as the second voltage V2 is a voltage lower than the first voltage V1, the magnitude relationship between the working electrode potential and the counter electrode potential is not limited. In other words, in the carbon dioxide release mode, the working electrode potential can be < the counter electrode potential, the working electrode potential can be = the counter electrode potential, and the working electrode potential can be > the counter electrode potential.

[0076] Next, the operation of the carbon dioxide recovery system 1 of this embodiment will be described. As described above, the carbon dioxide recovery system 1 operates by alternately switching between the carbon dioxide recovery mode and the carbon dioxide release mode. The operation of the carbon dioxide recovery system 1 is controlled by the control device 14 .

[0077] First, the carbon dioxide recovery mode is described. In the carbon dioxide recovery mode, the pump 11 is operated. Thus, the mixed gas is supplied 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 a first voltage V1. Thus, the electron donation of the electroactive auxiliary material of the counter electrode 106 and the electron withdrawal of the carbon dioxide adsorbent material of the working electrode 104 can be achieved simultaneously.

[0078] The carbon dioxide adsorbent of the working electrode 104 that receives electrons from the counter electrode 106 has a higher carbon dioxide binding force, and binds and adsorbs carbon dioxide contained in the mixed gas. Thus, the carbon dioxide recovery device 10 can recover carbon dioxide from the mixed gas. The mixed gas from which carbon dioxide has been removed is discharged from the carbon dioxide recovery device 10.

[0079] In the carbon dioxide recovery mode, the flow path switching valve 12 switches the flow path so as to allow the mixed gas exhausted from the carbon dioxide recovery device 10 to flow toward the atmosphere. Thus, the mixed gas exhausted from the carbon dioxide recovery device 10 is exhausted to the atmosphere.

[0080] Next, the carbon dioxide release mode is described. In the carbon dioxide release mode, the pump 11 is stopped. Thus, the supply of the mixed gas to the carbon dioxide recovery device 10 is stopped. 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. Thus, the electron donation of the carbon dioxide adsorbent material of the working electrode 104 and the electron withdrawal of the electroactive auxiliary material of the counter electrode 106 can be achieved simultaneously.

[0081] The carbon dioxide adsorbent of the working electrode 104 releases electrons and becomes oxidized. The carbon dioxide adsorbent's carbon dioxide binding force decreases, and carbon dioxide is desorbed and released. The carbon dioxide released from the carbon dioxide adsorbent is discharged from the carbon dioxide recovery device 10.

[0082] In the carbon dioxide release mode, the flow path switching valve 12 switches the flow path so that the carbon dioxide exhausted from the carbon dioxide recovery device 10 flows toward the inlet side of the carbon dioxide utilization device 13. Thus, the carbon dioxide exhausted from the carbon dioxide recovery device 10 is supplied to the carbon dioxide utilization device 13.

[0083] According to the present embodiment described above, in the working electrode 104, the particle size of the conductive auxiliary agent 104b as conductive particles is set to be greater than the particle size of the carbon dioxide adsorbent 104a as functional particles. As a result, the contact rate of the conductive auxiliary agent 104b in the working electrode 104 can be increased, and the conductivity per unit volume can be increased. In addition, as the particle size of the conductive auxiliary agent 104b increases, the number of particles per unit distance of the conductive path decreases, and the number of particles passing through the grain boundaries decreases. Therefore, the grain boundary resistance generated by the plurality of conductive auxiliary agents 104b forming the conductive path is reduced, and the conductivity per unit volume can be further increased.

[0084] In addition, by setting the particle size of the conductive auxiliary agent 104b to be larger than the particle size of the carbon dioxide adsorbent 104a, the conductivity can be ensured even if the volume ratio of the conductive auxiliary agent 104b is reduced, and the volume ratio of the carbon dioxide adsorbent 104a as a functional particle can be increased. Therefore, the functionality of the carbon dioxide adsorbent 104a as a functional particle can be improved, and the carbon dioxide adsorption efficiency of the working electrode 104 can be improved.

[0085] In this embodiment, the volume ratio of the conductive agent 104b is set to be equal to or greater than the volume ratio of the binder 104c in the working electrode 104. This ensures the volume ratio of the conductive agent 104b in the working electrode 104 and the conductivity of the conductive agent 104b.

[0086] (Second Embodiment)

[0087] Next, a second embodiment of the present disclosure will be described. Only the parts that are different from the first embodiment will be described below.

[0088] In the second embodiment, in the working electrode 104, a carbon material is used as the carbon dioxide adsorbent 104a and the conductive aid 104b. The carbon material used for the carbon dioxide adsorbent 104a and the carbon material used for the conductive aid 104b may be the same carbon material or different carbon materials. In the second embodiment, the carbon dioxide adsorbent 104a and the conductive aid 104b are contained in conductive particles, and the catalyst is contained in functional particles. The catalyst promotes a chemical reaction accompanied by at least one of the adsorption of carbon dioxide by the working electrode 104 and the desorption of carbon dioxide from the working electrode 104. The catalyst will be described later.

[0089] When a carbon material is used as the carbon dioxide adsorbent 104a, in the carbon dioxide recovery mode, the oxygen reduction reaction shown in the following reaction formula (1) and the carbonate ion generation reaction shown in the reaction formula (2) are performed in the working electrode 104, and carbon dioxide is adsorbed in the working electrode 104. In other words, the oxygen reduction reaction becomes the trigger for carbon dioxide adsorption in the working electrode 104.

[0090] O2+2e － →O2 － …(1)

[0091] O2 － +CO2→1 / 2O2+CO3 2－ …(2)

[0092] In the working electrode 104, the oxygen contained in the mixed gas receives electrons and is reduced to generate peroxide O2, which is a kind of active oxygen. － Oxygen reduction reaction. The active oxygen O2 generated by the oxygen reduction reaction － The reactivity is high, and it oxidizes carbon dioxide to generate carbonate ions CO3, which are oxide ions of carbon dioxide. 2－ Carbonate ion generation reaction, carbon dioxide is adsorbed on the working electrode 104. That is, the active oxygen O2 generated by the oxygen reduction reaction － Helps in the adsorption of carbon dioxide in the working electrode 104 .

[0093] In the carbon dioxide release mode, at least one of the carbonate ion dissociation reactions shown in the following reaction formula (3) and reaction formula (4) is performed in the working electrode 104. In the carbonate ion dissociation reaction, carbonate ions CO3 2－ In other words, the carbonate ion dissociation reaction becomes an opportunity for the carbon dioxide in the working electrode 104 to be desorbed.

[0094] CO3 2－ +C→3CO2+4e － …(3)

[0095] 2CO3 2－ →O2+2CO2+4e － …(4)

[0096] like Figure 8As shown, a catalyst 104d that promotes at least one of the oxygen reduction reaction and the carbonate ion dissociation reaction is added to the working electrode 104 of the second embodiment. As such a catalyst 104d, metal particles composed of at least any one of Al, Cu, Ni, Ag, Au and Pt, and metal oxide particles composed of at least any one of RuO2, MnO2 and MoO2 can be used. For example, the catalyst 104d can be supported on the conductive auxiliary agent 104b for use.

[0097] As described above, in the second embodiment, the catalyst 104d is included in the functional particles. Even if the material used as the catalyst 104d has higher conductivity than the conductive particles, the catalyst 104d does not mainly provide conductivity and does not form a conductive path, so the catalyst 104d is included in the functional particles.

[0098] In the second embodiment, the particle sizes of the carbon dioxide adsorbent 104a and the conductive additive 104b as conductive particles are also equal to or larger than the particle size of the catalyst 104d as functional particles. Therefore, as in the first embodiment, the contact rate of the conductive particles in the working electrode 104 can be increased, and the conductivity per unit volume can be increased.

[0099] In addition, by setting the particle size of the conductive auxiliary agent 104b to be larger than the particle size of the carbon dioxide adsorbent 104a, the conductivity can be ensured even if the volume ratio of the conductive auxiliary agent 104b is reduced, and the volume ratio of the catalyst 104d as a functional particle can be increased. Thus, the functionality of the catalyst 104d as a functional particle can be improved, and the carbon dioxide adsorption efficiency of the working electrode 104 can be improved.

[0100] (Third Embodiment)

[0101] Next, a third embodiment of the present disclosure will be described. Hereinafter, only the parts different from the above-mentioned embodiments will be described.

[0102] In the third embodiment, a conductive polymer is used as the binder 104c of the working electrode 104. The conductive polymer is a polymer having a π bond, and examples thereof include polyacetylene, polypyrrole, poly(p-phenylene), poly(3-methylthiophene), and poly(3-hexylthiophene).

[0103] In the third embodiment, by using a conductive polymer as the binder 104c, the binder 104c itself can be made conductive. The binder 104c is provided to cover at least the conductive auxiliary agent 104b. By using the binder 104c composed of a conductive polymer, even if the entire conductive auxiliary agent 104b is covered by the binder 104c, the conductivity can be maintained through the binder 104c.

[0104] The adhesive 104c covering the conductive additive 104b can supplement the conductive path formed by the conductive additive 104b. That is, even if there is a gap between adjacent conductive additives 104b, the conductive additive 104b and the adhesive 104c can form a conductive path by connecting them via the adhesive 104c. The adhesive 104c composed of a conductive polymer and the conductive additive 104b together form a conductive skeleton.

[0105] The adhesive 104c may also contain a non-conductive polymer in addition to the conductive polymer. The adhesive 104c composed of the non-conductive polymer has better adhesion than the adhesive 104c composed of the conductive polymer. It is preferred that the adhesive 104c containing the conductive polymer and the non-conductive polymer use the conductive polymer in the portion in contact with the conductive auxiliary agent 104b and use the non-conductive polymer in the other portions. Thus, the adhesive 104c can ensure conductivity in the portion in contact with the conductive auxiliary agent 104b and improve adhesion in the other portions.

[0106] The present disclosure is not limited to the above-described embodiments, and various modifications can be made as follows without departing from the gist of the present disclosure. In addition, the means disclosed in the above-described embodiments can be appropriately combined within the scope of implementation.

[0107] For example, in the above-mentioned embodiments, an example in which carbon dioxide contained in the mixed gas is adsorbed by the electrochemical cell 101 is described, but the present invention is not limited thereto, and other types of gases such as oxygen may be adsorbed from the mixed gas by the electrochemical cell 101 .

[0108] In addition, in each of the above-mentioned embodiments, the particle size of the conductive particles in the working electrode 104 is set to be equal to or larger than the particle size of the functional particles, but the present invention is not limited thereto, and the particle size of the conductive particles in the counter electrode 106 may be set to be equal to or larger than the particle size of the functional particles. In this case, the conductive particles contain a conductive auxiliary agent for the counter electrode 106, and the functional particles contain an electroactive auxiliary material for the counter electrode 106.

[0109] The characteristics of the electrochemical cell disclosed in this specification are shown below.

[0110] (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 a gas in the working electrode, wherein:

[0111] At least one of the working electrode and the counter electrode comprises conductive particles (104b) that are in contact with each other and form a conductive path, and functional particles (104a) that do not form the conductive path.

[0112] The particle diameter of the conductive particles is equal to or larger than the particle diameter of the functional particles.

[0113] (Item 2) The electrochemical cell according to Item 1, wherein:

[0114] The functional particles are gas adsorbents that adsorb and desorb the gas.

[0115] (Item 3) The electrochemical cell according to Item 1 or 2, wherein:

[0116] The functional particles are catalysts (104d) that promote a chemical reaction that is accompanied by at least one of adsorption of gas by the working electrode and desorption of gas from the working electrode.

[0117] (Item 4) The electrochemical cell according to any one of Items 1 to 3, wherein

[0118] The electrode has a binder (104c),

[0119] In the electrode, the volume ratio of the conductive particles is equal to or greater than the volume ratio of the binder.

[0120] (Item 5) The electrochemical cell according to Item 4, wherein:

[0121] The binder includes a conductive polymer and forms the conductive path together with the conductive particles.

[0122] The present disclosure is described based on the embodiments, but it should be understood that the present disclosure is not limited to the embodiments and structures. The present disclosure also includes various modifications and modifications within the equivalent range. Among them, various combinations and methods are shown in the present disclosure, but other combinations and methods that only include one element, more than one, or less than one of them are also included in the scope and scope of thought of the present disclosure.

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 a gas at the working electrode, wherein: At least one of the working electrode and the counter electrode has conductive particles (104b) that are in contact with each other and form a conductive path, and functional particles (104a) that do not form the conductive path. The particle diameter of the conductive particles is equal to or larger than the particle diameter of the functional particles.

2. The electrochemical cell according to claim 1, wherein The functional particles are gas adsorbing materials that adsorb and desorb the gas.

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

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

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

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