Electrochemical cell

Abstract

To provide an electrochemical cell capable of suppressing a decrease in the amount of adsorption of gas to be recovered.SOLUTION: An electrochemical cell, which adsorbs and desorbs CO2 from mixed gas containing CO2 by electrochemical reaction, comprises an action electrode 103 and a counter electrode 105. A voltage is applied between the action electrode 103 and the counter electrode 105 so that an electron can be applied to the action electrode 103 from the counter electrode 105. The action electrode 103 adsorbs CO2 in association with supply of the electron, and the counter electrode 105 contains a metal oxide.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to electrochemical cells. [Background technology]

[0002] Conventionally, electrochemical cells have been known that adsorb and desorb a gas to be recovered (e.g., CO2) from a mixed gas containing the gas through an electrochemical reaction. Patent Document 1 discloses an electrochemical cell in which an adsorbent that adsorbs the gas to be recovered is provided on the working electrode and a counter electrode active material is provided on the counter electrode. The counter electrode active material is an electroactive species made of an organic material (e.g., polyvinylferrocene). By changing the potential difference between the working electrode and the counter electrode, the adsorbent can switch between adsorbing and desorbing the gas to be recovered, and the counter electrode active material exchanges electrons with the adsorbent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-67545 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when an electrochemical cell is operated in the presence of O2, such as in the atmosphere, charge transfer occurs to O2, which is a type of active oxygen. - (superoxide) is generated at the working electrode. O2 generated at the working electrode - If the active oxygen diffuses to the counter electrode, the organic counter electrode active material may be oxidized and decomposed by the active oxygen, which may reduce the amount of electrons supplied from the counter electrode to the working electrode. As a result, the amount of gas adsorbed by the working electrode may decrease.

[0005] In view of the above, an object of the present invention is to provide a battery chemical cell that can suppress a decrease in the amount of adsorption of the gas to be collected. [Means for solving the problem]

[0006] In order to achieve the above object, the electrochemical cell according to claim 1 is an electrochemical cell that adsorbs and desorbs a gas to be recovered from a mixed gas containing the gas to be recovered by electrochemical reaction, A working electrode (103) and a counter electrode (105) are provided. When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the working electrode adsorbs the gas to be collected as the electrons are supplied. The counter electrode contains a metal oxide.

[0007] According to this, O2 contained in the atmosphere etc. is converted to O2 - is produced, and O2 - Even if the gas reaches the counter electrode, the constituent material of the counter electrode is unlikely to be oxidatively decomposed. Therefore, it is possible to prevent a decrease in the amount of adsorption of the gas to be recovered by the electrochemical cell due to oxidative decomposition of the constituent material of the counter electrode.

[0008] The symbols in parentheses for each means described in this section and in the claims indicate the correspondence with the specific means described in the embodiments described later. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a carbon dioxide capture system according to one embodiment. [Figure 2] FIG. 1 illustrates a carbon dioxide capture device in one embodiment. [Figure 3] 2A and 2B are diagrams illustrating the operation of the carbon dioxide capture device in a CO2 capture mode and a CO2 release mode in one embodiment. [Figure 4] 1 is a graph showing the capacitance of each metal oxide in an electrochemical test. [Figure 5] FIG. 1 is a graph showing the relationship between the number of cycles in an electrochemical test and the deterioration rate of a working electrode. [Figure 6] FIG. 10 is a diagram showing an XPS spectrum when the working electrode is MnO2. [Figure 7]FIG. 10 is a diagram showing an XPS spectrum when the working electrode is RuO2. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present disclosure will be described below with reference to the drawings. In this embodiment, an electrochemical cell according to the present disclosure is applied to a carbon dioxide capture system that separates and captures CO from a CO2-containing mixed gas. Therefore, the gas to be captured in this embodiment is CO2. However, gases other than CO2 may also be used as the gas to be captured.

[0011] As shown in FIG. 1, a carbon dioxide capture system 10 of this embodiment is provided with a compressor 11, a carbon dioxide capture device 100, a flow path switching valve 12, a carbon dioxide utilization device 13, and a control device .

[0012] The compressor 11 compresses and sends the CO2-containing gas to the carbon dioxide recovery unit 100. The CO2-containing gas is a mixed gas containing CO2 and a gas other than CO2. For example, the atmosphere can be used as the CO2-containing gas.

[0013] The carbon dioxide capture device 100 is a device that separates and captures CO2 from a CO2-containing gas. The carbon dioxide capture device 100 discharges a CO2-removed gas after CO2 has been captured from the CO2-containing gas, or CO2 captured from the CO2-containing gas. The configuration of the carbon dioxide capture device 100 will be described in detail later.

[0014] The flow path switching valve 12 is a three-way valve that switches the flow path of the exhaust gas from the carbon dioxide capture device 100. When CO2-removed gas is discharged from the carbon dioxide capture device 100, the flow path switching valve 12 switches the flow path of the exhaust gas to the atmosphere side. When CO2 is discharged from the carbon dioxide capture device 100, the flow path switching valve 12 switches the flow path of the exhaust gas to the carbon dioxide utilization device 13 side.

[0015] The carbon dioxide utilization device 13 is a device that utilizes CO2. As the carbon dioxide utilization device 13, for example, a storage tank that stores CO2 or a conversion device that converts CO2 into fuel can be used. The conversion device can be a device that converts CO2 into a hydrocarbon fuel such as methane. The hydrocarbon fuel may be a gaseous fuel at room temperature and normal pressure, or a liquid fuel at room temperature and normal pressure.

[0016] 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 control programs stored in the ROM, and controls the operation of various controlled devices. The control device 14 of this embodiment controls the operation of the compressor 11, the operation of the carbon dioxide capture device 100, and the flow path switching of the flow path switching valve 12, etc.

[0017] Next, the carbon dioxide capture device 100 will be described with reference to Fig. 2. As shown in Fig. 2, the carbon dioxide capture device 100 is provided with an electrochemical cell 101 of an electric field adsorption / desorption type that adsorbs and desorbs CO2 through an electrochemical reaction. The electrochemical cell 101 has a working electrode current collector 102, a working electrode 103, a counter electrode current collector 104, a counter electrode 105, an insulating layer 106, and an electrolyte 107. The working electrode current collector 102, the working electrode 103, the counter electrode current collector 104, the counter electrode 105, and the insulating layer 106 are provided in a laminated structure.

[0018] The electrochemical cell 101 may be housed in a container (not shown). The container may be provided with a gas inlet for allowing the CO2-containing gas to flow into the container and a gas outlet for allowing the CO2-removed gas and CO2 to flow out of the container.

[0019] The carbon dioxide capture device 100 adsorbs and desorbs CO2 through an electrochemical reaction in an electrochemical cell 101, and separates and captures CO2 from a CO2-containing gas. The carbon dioxide capture device 100 is provided with a power supply 108 that applies a predetermined voltage to a working electrode 103 and a counter electrode 105, and is capable of changing the potential difference between the working electrode 103 and the counter electrode 105. The working electrode 103 is a negative electrode, and the counter electrode 105 is a positive electrode.

[0020] The electrochemical cell 101 can be operated in a CO2 capture mode in which CO2 is captured by the working electrode 103, and a CO2 release mode in which CO2 is released from the working electrode 103, by changing the potential difference between the working electrode 103 and the counter electrode 105. The CO2 capture mode is a charge mode in which the electrochemical cell 101 is charged, and the CO2 release mode is a discharge mode in which the electrochemical cell 101 is discharged.

[0021] In the CO2 capture mode, a first voltage V1 is applied between the working electrode 103 and the counter electrode 105, and electrons are supplied from the counter electrode 105 to the working electrode 103. At the first voltage V1, the working electrode potential is less than the counter electrode potential. The first voltage V1 can be set within a range of 0.5 to 2.0 V, for example.

[0022] In the CO2 release mode, a second voltage V2 is applied between the working electrode 103 and the counter electrode 105, and electrons are supplied from the working electrode 103 to the counter electrode 105. The second voltage V2 is a voltage different from the first voltage V1. The second voltage V2 may be any voltage lower than the first voltage V1, and the magnitude relationship between the working electrode potential and the counter electrode potential is not limited. That is, in the CO2 release mode, the working electrode potential may be 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.

[0023] The working electrode current collector 102 is a porous conductive material having pores through which CO2-containing gas containing CO2 can pass. The working electrode current collector 102 can be made of, for example, a carbonaceous material or a metal material. The carbonaceous material constituting the working electrode current collector 102 can be, for example, carbon paper, carbon cloth, a nonwoven carbon mat, a porous gas diffusion layer (GDL), or the like. The metal material constituting the working electrode current collector 102 can be, for example, a mesh structure made of metal such as Al, Ni, or SUS.

[0024] The working electrode 103 is provided with a working electrode substrate 103a, which is an electrode substrate, and a CO2 adsorbent 103b. The working electrode substrate 103a is a conductive material that holds the CO2 adsorbent 103b. For example, a carbon sheet can be used as the working electrode substrate 103a.

[0025] The CO2 adsorbent 103b is an active material that receives and gives off electrons through an oxidation-reduction reaction. The CO2 adsorbent 103b adsorbs CO2 by receiving electrons and desorbs the adsorbed CO2 by releasing electrons. For example, carbon material, metal oxide, polyanthraquinone, etc. can be used as the CO2 adsorbent 103b.

[0026] The working electrode 103 may be provided with a conductive additive and a binder. The conductive additive forms a conductive path to the CO2 adsorbent 103b. The conductive additive may be a carbon material such as carbon nanotubes, carbon black, or graphene. The binder may be any material that can hold the CO2 adsorbent 103b on the working electrode substrate 103a and has conductivity. The binder may be a conductive resin such as an epoxy resin containing Ag or the like as a conductive filler, or a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF).

[0027] As an example, in this embodiment, the working electrode substrate 103a is formed to be porous. The CO2 adsorbent 103b, the conductive additive, and the binder are used in the form of a mixture. Specifically, a mixture of the CO2 adsorbent 103b, the conductive additive, and the binder is formed, and the mixture is applied to the working electrode substrate 103a and bonded thereto. That is, the CO2 adsorbent 103b, the conductive additive, and the binder are mixed and applied to the working electrode substrate 103a.

[0028] The counter electrode current collector 104 is a conductive material. The same material as the working electrode current collector 102 described above can be used as the counter electrode current collector 104.

[0029] Counter electrode substrate 105a and counter electrode active material 105b are provided on counter electrode 105. Counter electrode substrate 105a is a conductive material that holds counter electrode active material 105b. Counter electrode substrate 105a can be, for example, a carbon sheet.

[0030] The counter electrode active material 105b is a supplementary electroactive species that exchanges electrons with the working electrode 103. The counter electrode active material 105b contains a metal oxide. More specifically, the counter electrode active material 105b contains a metal oxide that has multiple valence states at a formation energy of −1.0 eV or less. Specifically, the counter electrode active material 105b contains at least one of RuO2, MnO2, IrO2, CuO, MoO2, V2O5, and WO3.

[0031] Next, the inventors conducted electrochemical tests on seven types of metal oxides: RuO2, MnO2, IrO2, CuO, MoO2, V2O5, and WO3. Specifically, a glassy carbon electrode coated with powder of each of the above metal oxides was used as the working electrode. An Ag / Ag + A Pt coil was used as the counter electrode. Electrochemical tests were performed in air using the ionic liquid [BMIM][PF6] as the electrolyte. The voltage range was -1.0 V to +1.0 V. The results are shown in Figure 4.

[0032] As is clear from Figure 4, when RuO2, MnO2, or IrO2 was used as the electrode active material, the capacitance was larger than when other metal oxides were used. Therefore, it is desirable that the counter electrode active material 105b contain at least one of RuO2, MnO2, and IrO2. As an example, the counter electrode active material 105b of this embodiment contains MnO2.

[0033] A conductive additive and a binder may be provided on the counter electrode 105. The conductive additive and binder of the counter electrode 105 may be the same as those of the working electrode 103 described above.

[0034] The insulating layer 106 is disposed between the working electrode 103 and the counter electrode 105, and separates the working electrode 103 from the counter electrode 105. The insulating layer 106 is an insulating ion-permeable membrane that prevents physical contact between the working electrode 103 and the counter electrode 105 to suppress electrical short circuits, and also allows ions to pass through.

[0035] A separator or a gas layer such as air can be used as the insulating layer 106. In this embodiment, a porous separator is used as the insulating layer 106. The separator can be made of a cellulose film, a polymer, a composite material of polymer and ceramic, or the like.

[0036] An ionically conductive electrolyte 107 is provided between the working electrode 103 and the counter electrode 105. The electrolyte 107 is provided between the working electrode 103 and the counter electrode 105 via an insulating layer 106. The electrolyte 107 is provided so as to cover the working electrode 103, the counter electrode 105, and the insulating layer 106.

[0037] As an example, in this embodiment, an aprotic electrolyte 107 is used. The aprotic electrolyte 107 is a proton (H + ) is an electrolyte that does not donate protons. Therefore, charge does not move to the electrolyte 107 for proton generation, and a decrease in current efficiency during CO2 adsorption can be suppressed.

[0038] An ionic liquid can be used as the aprotic electrolyte 107. An ionic liquid is a liquid salt that is nonvolatile at room temperature and normal pressure. When an ionic liquid is used as the electrolyte 107, the ionic liquid may be gelled to prevent elution from the electrochemical cell 101. Examples of the aprotic ionic liquid that can be used include [BMIM][TFSI], [TMPA][TFSI], [Pyrro][TFSI], [BMIM][Tfb], [EMIM][TFSI], and the like.

[0039] Next, the operation of the carbon dioxide capture system 10 of this embodiment will be described. As shown in Fig. 3, the carbon dioxide capture system 10 operates by alternately switching between a CO2 capture mode and a CO2 release mode. The operation of the carbon dioxide capture system 10 is controlled by a control device 14.

[0040] First, the CO2 capture mode will be described. In the CO2 capture mode, the compressor 11 operates to supply CO2-containing gas to the carbon dioxide capture device 100. In the carbon dioxide capture device 100, a voltage applied between the working electrode 103 and the counter electrode 105 is set to a first voltage V1. This allows the counter electrode 105 to donate electrons and the working electrode 103 to withdraw electrons simultaneously.

[0041] The counter electrode active material 105b of the counter electrode 105 releases electrons, which are then supplied from the counter electrode 105 to the working electrode 103. The CO2 adsorbent 103b of the working electrode 103 adsorbs CO2 as the electrons are supplied. In this embodiment, CO2 is ·- , C2O4 2- , HCO3 - and adsorbed onto the working electrode 103. In this way, the carbon dioxide capture device 100 can capture CO2 from the CO2-containing gas.

[0042] After CO2 is captured by the carbon dioxide capture device 100, the CO2-containing gas is discharged from the carbon dioxide capture device 100 as a CO2-removed gas that does not contain CO2. The flow path switching valve 12 switches the gas flow path to the atmosphere side, and the CO2-removed gas discharged from the carbon dioxide capture device 100 is discharged to the atmosphere.

[0043] Next, the CO2 release mode will be described. In the CO2 release mode, the compressor 11 stops operating, and the supply of CO2-containing gas to the CO2 capture device 100 stops. In the carbon dioxide capture device 100, the voltage applied between the working electrode 103 and the counter electrode 105 is set to a second voltage V2. This allows electron donation by the CO2 adsorbent 103b of the working electrode 103 and electron attraction by the counter electrode active material 105b of the counter electrode 105 to be achieved simultaneously.

[0044] The CO2 adsorbent 103b desorbs and releases the CO2. ·- , C2O4 2- , HCO3 - is desorbed in the form converted to CO2.

[0045] The CO2 released from the CO2 adsorbent 103b is discharged from the CO2 recovery device 100. The flow path switching valve 12 switches the gas flow path to the CO2 utilization device 13 side, and the CO2 discharged from the CO2 recovery device 100 is supplied to the CO2 utilization device 13.

[0046] Next, the inventors conducted a comparative study on the durability of the counter electrode 105 when MnO2, RuO2, and PVFc (polyvinylferrocene) were used as the counter electrode active material 105b. Specifically, electrochemical tests were conducted on the following Examples 1 and 2 and Comparative Example.

[0047] Example 1 MnO2 was used as the working electrode, and Ag / Ag was used as the reference electrode. + The electrode was used as a counter electrode, and Pt was used as a counter electrode. Electrochemical tests were performed in air using [TMPA][TFSI] as the electrolyte. The voltage range was -1.5 V to +1.0 V, and each potential was maintained for 5 minutes.

[0048] Example 2 The same procedure as in Example 1 was carried out except that RuO2 was used as the working electrode.

[0049] (Comparative Example) The same procedure as in Example 1 was carried out except that PVFc was used as the working electrode.

[0050] (Durability test) For Examples 1 and 2 and the Comparative Example, an electrochemical test was performed for 600 cycles, and the degradation rate was measured. The relationship between the number of cycles of the electrochemical test and the degradation rate of the working electrode is shown in Figure 4. The degradation rate is expressed as the capacitance ratio when the capacitance before the electrochemical test is set to 1.

[0051] As is clear from Figure 4, in the comparative example, the capacitance decreased in proportion to the increase in the number of cycles in the electrochemical test. On the other hand, in Examples 1 and 2, the capacitance hardly decreased even when the number of cycles in the electrochemical test increased. In other words, in Examples 1 and 2, there was almost no deterioration in performance compared to the capacitance before the electrochemical test, and therefore it can be said that durability was improved compared to the comparative example.

[0052] (ICP analysis) For Examples 1 and 2 and the Comparative Example, the concentrations of eluted metals (Fe, Mn, Ru) in each electrolyte were measured by inductively coupled plasma atomic emission spectroscopy (ICP / AES) before the electrochemical test and after 100 cycles of the electrochemical test. Specifically, the Mn concentration was measured in Example 1, the Ru concentration was measured in Example 2, and the Fe concentration was measured in the Comparative Example. The results are shown in Table 1. The concentrations of the eluted metals were measured using an ICP atomic emission spectrometer "ICPS-8100 (Shimadzu Corporation)," with an integration time of 15 seconds per element per level (measurement time 5 seconds × accumulation number 3 times).

[0053] [Table 1] As shown in Table 1, in the comparative example, the Fe concentration after the electrochemical test was high at 9300 μg / g, which was approximately 13.4 times higher than before the electrochemical test. On the other hand, in Example 1, the Mn concentration after the electrochemical test was very low at 19.4 μg / g, which was approximately 2.2 times higher than before the electrochemical test. Similarly, in Example 2, the Ru concentration after the electrochemical test was very low at 14.4 μg / g, which was approximately 1.6 times higher than before the electrochemical test.

[0054] This indicates that in the comparative example, PVFc was decomposed by the electrochemical test, and a large amount of Fe ions were eluted into the electrolyte. On the other hand, in Examples 1 and 2, the electrochemical test indicated that MnO2 and RuO2 were not easily decomposed, and the elution of Mn and Ru into the electrolyte could be suppressed. Therefore, it can be said that the electrochemical cell 101 using MnO2 or RuO2 as the counter electrode active material 105b can have improved durability compared to the electrochemical cell 101 using PVFc as the counter electrode active material 105b.

[0055] (XPS analysis) For Examples 1 and 2 and the Comparative Example, the working electrodes before and after 100 cycles of the electrochemical test were analyzed by X-ray photoelectron spectroscopy (XPS), and the results are shown in FIGS.

[0056] In XPS, the surface of a working electrode is irradiated with X-rays, the energy of the photoelectrons generated is measured, and the constituent elements and their electronic states of the material present on the surface of the working electrode can be analyzed. In this embodiment, the structural changes of the metal oxide are analyzed by checking the XPS peak positions.

[0057] Specifically, we checked whether the peak position characteristic of the oxide constituting the working electrode shifted before and after the electrochemical test. If the peak position characteristic of the oxide constituting the working electrode shifted, it can be determined that the oxide has changed to a different compound and the working electrode has deteriorated. The XPS instrument used was a PHI5000 Quantera II manufactured by ULVAC-PHI, with an incident lattice energy of 1486.6 eV (AlKα).

[0058] As shown in FIG. 5, in Example 1, the peak position specific to Mn oxide did not shift before and after the electrochemical test. Similarly, as shown in FIG. 6, in Example 2, the peak position specific to Ru oxide did not shift before and after the electrochemical test. This indicates that the working electrode did not deteriorate due to the electrochemical test in both Examples 1 and 2. Therefore, it can be said that the durability of the electrochemical cell 101 using MnO2 or RuO2 as the counter electrode active material 105b can be improved.

[0059] In the present embodiment described above, a substance containing a metal oxide is used as the counter electrode active material 105b. Metal oxides are compounds in which metals have already been oxidized, and therefore have low reactivity with oxygen. Therefore, the counter electrode active material 105b has low reactivity with oxygen, such as O2 and O2 - As a result, O2 in the atmosphere and CO2-containing gases is converted to O2 - is produced, and O2 - reaches the counter electrode active material 105b, the counter electrode active material 105b is unlikely to be oxidatively decomposed. This makes it possible to prevent a decrease in the CO adsorption amount of the electrochemical cell 101 due to oxidative decomposition of the counter electrode active material 105b. In other words, by using a substance containing a metal oxide as the counter electrode active material 105b, oxidative decomposition of the counter electrode active material 105b can be prevented, thereby improving the durability of the counter electrode 105. As a result, the durability of the electrochemical cell 101 can be improved.

[0060] (Other embodiments) The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention, as follows: For example, the CO2-containing gas is not limited to the atmosphere, and may be any gas containing CO2, such as exhaust gas from an internal combustion engine. [Explanation of symbols]

[0061] 103 Working electrode 105 Opposite

Claims

1. An electrochemical cell that adsorbs and desorbs a gas to be recovered from a mixed gas containing the gas to be recovered by electrochemical reaction, A working electrode (103) and a counter electrode (105) are provided. When a voltage is applied between the working electrode and the counter electrode, electrons are supplied from the counter electrode to the working electrode, and the working electrode adsorbs the gas to be recovered in response to the supply of electrons; The counter electrode of the electrochemical cell contains a metal oxide.

2. 2. The electrochemical cell according to claim 1, wherein the metal oxide has multiple valence states at a formation energy of −1.0 eV or less.

3. The counter electrode is made of RuO ２ , MnO ２ , IrO ２ , CuO, MoO ２ , V ２ O ５ , W.O. ３ 2. The electrochemical cell according to claim 1, comprising at least one of the following:

4. The counter electrode is made of RuO ２ , MnO ２ , IrO ２ 2. The electrochemical cell according to claim 1, comprising at least one of the following:

5. The gas to be recovered is CO ２ 5. The electrochemical cell according to claim 1, wherein

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