Electrochemical devices

Abstract

To provide an electrochemical device that can reduce energy consumption. [Solution] The electrochemical device 10 comprises an anode electrode 22 containing an anode catalyst, a first chamber 24 in which the anode electrode 22 is placed and a gas containing H2 is supplied, a cation exchange membrane 30 placed on the anode electrode 22, and a second chamber 28 adjacent to the first chamber 24 via the cation exchange membrane 30 and in which an aqueous solution containing carbonate ion species is supplied. The anode catalyst includes a first catalyst that promotes a hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes an oxygen evolution reaction in an acidic environment. When a voltage is applied to the anode electrode 22, protons generated at the anode electrode 22 are supplied to the second chamber 28 through the cation exchange membrane 30 and react with the carbonate ion species.

Description

Technical Field

[0001] The present invention relates to the technology of electrochemical devices.

Background Art

[0002] As a technology that can contribute to carbon neutralization, an electrolysis technology for obtaining CO2 reduction valuable substances from carbonate ion species or carbon dioxide, an electrodialysis technology for recovering carbon dioxide using an alkaline aqueous solution containing carbonate ion species (at least one of carbonate ions (CO3 2- ), and hydrogen carbonate ions (HCO3 - ), and separating and concentrating carbon dioxide from the recovered solution containing carbon dioxide, etc. There is interest in electrochemical devices that utilize such technologies.

[0003] In an electrochemical device, for example, protons generated at the anode electrode by applying a voltage are supplied through an ion exchange membrane to an alkaline aqueous solution containing carbonate ion species, and the carbonate ion species in the alkaline aqueous solution are activated to generate carbon dioxide (neutral CO2 molecules), etc. In the case of an electrochemical device using electrolysis technology, the generated carbon dioxide, etc. is reduced by, for example, the cathode electrode to generate CO2 reduction valuable substances such as CO, formic acid, and ethylene alcohol. For example, Patent Documents 1 to 6 and Non-Patent Documents 1 to 3 disclose electrolysis devices that apply a voltage to an anode electrode and a cathode electrode to generate CO2 reduction valuable substances. Also, for example, Patent Document 7 and Non-Patent Documents 4 and 5 disclose electrodialysis devices that apply a voltage to an anode electrode and a cathode electrode to separate and concentrate carbon dioxide.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] [Non-licensed Document 1] David A. Vermaas and Wilson A. Smith, “Synergistic Electrochemical CO2 Reduction and Water Oxidation with a Bipolar Membrane”, ACS Energy Lett., 1, 1143-1148(2016) [Non-licensed Document 2] Tengfei Li, Eric W. Lees, Maxwell Goldman, Danielle A. Salvatore, David M. Weekes, and Curtis P. Berlinguette, “Electrolytic Conversion of Bicarbonate into CO in a Flow Cell”, Joule, 3, 1487-1497(2019) [Non-licensed Document 3] Yuguang C. Li, Geonhui Lee, Tiange Yuan, Ying Wang, Dae-Hyun Nam, Ziyun Wang, F. Pelayo Garcia de Arquer, Yanwei Lum, Cao-Thang Dinh, Oleksandr Voanyy, and Edward H. Sargent, “CO2 Electroreduction from Carbonate Electrolyte”, ACS Energy Lett., 4, 1427-1431(2019) [Non-Patent Document 4] Matthew D. Eisaman, Luis Alvarado, Daniel Larner, Peng Wang, Bhaskar Garg, and Karl A. Littau (PaloAlto Research Center), “CO2 separation using polar membrane electrodialysis”, EnergyEnviron.Sci., 4, 1319-1328(2011). [Non-Patent Document 5] Reference [8] R. Sharifian, RM Wagterveld, IA Digdaya, C. Xiang, and DA Vermaas, “Electrochemical carbon dioxide capture to close the carbon cycle”, Energy Environ. Sci., 14, 781-814 (2021). [Overview of the project] [Problems that the invention aims to solve]

[0006] By the way, when performing electrolysis or electrodialysis using water as a medium, protons (H) are produced at the anode electrode due to the oxidation of water. +The reaction to produce carbon dioxide proceeds, but oxygen (O2) is also produced as a byproduct. From the standpoint of concentrating carbon dioxide or obtaining CO2 reduction products, oxygen is unnecessary, but it must be produced in order to carry out electrolysis or electrodialysis. As a result, the potential of the anode electrode must be raised to +1.23V or higher for the reaction at the cathode electrode (cathode potential: approximately 0V) (i.e., the applied voltage must be 1.23V or higher), which is the cause of high energy consumption.

[0007] Therefore, the present invention aims to provide an electrochemical device that can reduce energy consumption. [Means for solving the problem]

[0008] The electrochemical device according to this embodiment comprises an anode electrode containing an anode catalyst, a first chamber in which the anode electrode is placed and a gas containing H2 is supplied, a cation exchange membrane placed on the anode electrode, and a second chamber adjacent to the first chamber via the cation exchange membrane and in which an aqueous solution containing carbonate ion species is supplied, wherein the anode catalyst includes a first catalyst that promotes a hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes an oxygen evolution reaction in an acidic environment, and when a voltage is applied to the anode electrode, protons generated at the anode electrode are supplied to the second chamber through the cation exchange membrane and react with the carbonate ion species.

[0009] Furthermore, in the electrochemical device, the gas containing H2 is preferably a humidifying gas containing H2.

[0010] Furthermore, in the electrochemical device, it is preferable that the anode electrode and the cation exchange membrane are joined together.

[0011] Furthermore, in the electrochemical device, it is preferable that the first catalyst contains at least one element selected from the group consisting of Pt, Pd, Rh, Re, Au, and Ni.

[0012] Furthermore, in the electrochemical device, it is preferable that the second catalyst includes at least one selected from the group consisting of Ir oxide, Ru oxide, a mixture containing Ir oxide and Ru oxide, and a composite oxide containing Ir and Ru.

[0013] Furthermore, in the electrochemical device, it is preferable that the first catalyst contains Pt and the second catalyst contains the Ir oxide.

[0014] Furthermore, in the electrochemical device, the content of the first catalyst is 0.04 mg / cm² per geometric area of ​​the anode electrode. 2 It is preferable that the above conditions are met.

[0015] Furthermore, in the electrochemical device, the content of the second catalyst is 0.37 mg / cm² per geometric area of ​​the anode electrode. 2 It is preferable that the above conditions are met. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an electrochemical device that can reduce energy consumption. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing an example of an electrochemical device according to this embodiment. [Figure 2] This is a schematic diagram showing another example of the electrochemical device according to this embodiment. [Figure 3] This is an exploded view of the electrochemical device used in the example. [Figure 4] Figure 3 is a schematic diagram of an electrolytic system equipped with the electrochemical device shown. [Figure 5] This figure shows the relationship between the applied voltage UH2O and the IrO2 content in the anode electrode, and the relationship between the voltage increase ΔUH2O and the IrO2 content. [Figure 6]This figure shows the relationship between hydrogen utilization rate and the IrO2 content in the anode electrode, and the relationship between the Pt content in the anode electrode and the IrO2 content. [Figure 7] This figure shows the relationship between the applied voltage UH2 and the IrO2 content in the anode electrode, and the relationship between the Pt content in the anode electrode and the IrO2 content. [Figure 8] This figure shows the relationship between the difference between the applied voltage UH2O and the applied voltage UH2 and the IrO2 content in the anode electrode, and the relationship between the Pt content in the anode electrode and the IrO2 content. [Modes for carrying out the invention]

[0018] Embodiments of the present invention will be described below. This embodiment is just one example of how the present invention can be implemented, and the present invention is not limited to this embodiment.

[0019] Figure 1 is a schematic diagram showing an example of an electrochemical device according to this embodiment. The electrochemical device 10 shown in Figure 1 can be used, for example, in an electrolysis apparatus for obtaining CO2 reduction valuable products. The electrochemical device 10 shown in Figure 1 has a first chamber 24 equipped with an anode electrode 22 and a diffusion layer 34, a cation exchange membrane 30 disposed on the anode electrode 22, a cathode electrode 26, a second chamber 28, and frame members 36a and 36b. The first chamber 24 is provided between the frame member 36a and the cation exchange membrane 30, and the anode electrode 22 and the diffusion layer 34 are arranged therein. The diffusion layer 34 is located between the anode electrode 22 and the frame member 36a. The second chamber 28 is adjacent to the first chamber 24 via the cation exchange membrane 30. That is, the cation exchange membrane 30 is sandwiched between the first chamber 24 and the second chamber 28. Furthermore, a cathode electrode 26 is placed in the second chamber 28, and a channel 32 through which an aqueous solution containing carbonate ion species flows is located between the cathode electrode 26 and the cation exchange membrane 30. Here, carbonate ion species refers to carbonate ions (CO3 2- ) and bicarbonate ions (HCO3) -refers to at least one of them. In the electrochemical device 10 shown in FIG. 1, the diffusion layer 34, the anode electrode 22, the cathode electrode 26, etc. are structurally supported by the frame members 36a and 36b. The frame members 36a and 36b are made of, for example, metal, plastic, glass members, etc.

[0020] The anode electrode 22 includes an anode catalyst. The anode catalyst includes a first catalyst that promotes the hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes oxygen generation in an acidic environment.

[0021] Reference numeral 70 shown in FIG. 1 is a power source that applies a voltage between the anode electrode 22 and the cathode electrode 26. The power source 70 is not particularly limited, and examples include chemical batteries (including primary batteries, secondary batteries, etc.), constant voltage sources, solar cell modules, etc.

[0022] Next, an operation example of the electrochemical device 10 shown in FIG. 1 will be described.

[0023] A gas containing H2 is supplied to the diffusion layer 34 of the first chamber 24. The gas containing H2 is, for example, a mixed gas of air supplied by a blower or the like and hydrogen gas supplied from a tank filled with hydrogen gas. Also, the gas containing H2 may be humidified by a humidifier before being supplied to the diffusion layer 34 of the first chamber 24 and supplied to the diffusion layer 34 of the first chamber 24 as a humidified gas containing moisture. Further, an aqueous solution containing carbonate ion species is supplied to the flow path 32 of the second chamber 28. The aqueous solution containing carbonate ion species is preferably an alkaline aqueous solution in terms of the solubility of the carbonate ion species, etc.

[0024] When a voltage is applied between the cathode electrode 26 and the anode electrode 22 by the power source 70, on the first chamber 24 side, when the gas containing H2 passing through the diffusion layer 34 contacts the anode electrode 22, for example, H2 in the gas is oxidized to generate protons (H + ). Also, water in the gas is oxidized to generate oxygen (O2) and protons (H +) and are produced. The oxidation reaction of H2 is mainly caused by the presence of the first catalyst in the anode electrode 22. The oxidation reaction of water (i.e., the oxygen evolution reaction) is mainly caused by the presence of the second catalyst in the anode electrode 22. The protons produced at the anode electrode 22 pass through the cation exchange membrane 30 and are supplied to the second chamber 28. Then, carbonate ions and bicarbonate ions in the aqueous solution supplied to the channel 32 of the second chamber 28 react with the protons that have moved to the second chamber 28 side through the cation exchange membrane 30, producing carbon dioxide (neutral CO2 molecules) or bicarbonate ions (derived from carbonate ions). At the cathode electrode 26, for example, CO2 reduction valuables and hydrogen (gas) are produced by the reduction of the produced carbon dioxide with water. CO2 reduction products include, for example, carbon monoxide (CO), formic acid (HCOOH), methane (CH4), methanol (CH3OH), ethane (C2H6), ethylene (C2H4), ethanol (C2H5OH), propanol (C3H7OH), etc. In this way, products containing at least one of carbon dioxide (gas), hydrogen (gas), and CO2 reduction products are generated in the second chamber 28. The products generated in the second chamber 28 are discharged from the flow path 32 together with the aqueous solution supplied to the second chamber 28, and are separated into gas and liquid by, for example, a gas-liquid separator and recovered. Alternatively, the gas-liquid separated liquid may be brought into contact with, for example, a gas containing carbon dioxide, and supplied to the second chamber 28 as an aqueous solution containing carbonate ion species.

[0025] In the electrochemical device 10 shown in Figure 1, the anode electrode 22 contains both a first catalyst that promotes the hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes oxygen evolution in an acidic environment, thereby promoting the H2O oxidation reaction. + In addition to generation (which requires an anode potential of 1.23V or higher), H2 is also produced by the H2 oxidation reaction. + Since the generation (anode potential can be 0 or higher) also proceeds, the applied voltage to the electrochemical device 10 can be reduced, and consequently, energy consumption can be reduced. On the other hand, with only the second catalyst, the H2O oxidation reaction does not proceed. +Since only generation proceeds, the applied voltage cannot be reduced, and this does not lead to a reduction in energy consumption. Also, with only the first catalyst, the H2 oxidation reaction does not proceed. + The process continues, but when the H2 supply is insufficient due to atmospheric fluctuations such as when the device is started, the H2O oxidation reaction will occur. + Since the generation is not promoted and a passive oxide film is formed on the anode electrode 22, the voltage of the electrochemical device 10 increases, which does not lead to a reduction in energy consumption.

[0026] Figure 2 is a schematic diagram showing another example of the electrochemical device of this embodiment. In the electrochemical device 11 shown in Figure 2, components similar to those in the electrochemical device 10 shown in Figure 1 are denoted by the same reference numerals, and their descriptions are omitted. The electrochemical device 11 shown in Figure 2 can be used, for example, in an electrodialysis machine. In the electrochemical device 11 shown in Figure 2, the cathode electrode 26 is located outside the second chamber 28, and a fluid passage chamber / ion exchange membrane group 29 related to electrodialysis is located between the second chamber 28 and the cathode electrode 26. The fluid passage chamber / ion exchange membrane group 29 consists of one or more fluid passage chambers and one or more ion exchange membranes, which are alternately arranged between the second chamber 28 and the cathode electrode 26. The second chamber 28 is provided between the ion exchange membrane and the cation exchange membrane 30 at one end of the fluid passage chamber / ion exchange membrane group 29. Although not shown in the diagram, the cathode electrode 26 may be adjacent to, for example, a liquid passage chamber located at the other end of the liquid passage chamber / ion exchange membrane group 29, or adjacent to an ion exchange membrane located at the other end of the liquid passage chamber / ion exchange membrane group 29. The anode electrode 22 is placed in the first chamber 24, and a flow path 23 through which a gas containing H2 flows is provided between the anode electrode 22 and the frame material 36a. The aforementioned diffusion layer 34 may be placed at the location of the flow path 23 or between the flow path 23 and the anode electrode 22.

[0027] An example of the operation of the electrochemical device 11 shown in Figure 2 will be described. An alkaline aqueous solution containing carbonate ions is supplied into the second chamber 28, and a gas containing H2 is supplied to the flow path 23 of the first chamber 24. When a voltage is applied between the cathode electrode 26 and the anode electrode 22 by the power supply 70, on the first chamber 24 side, when the gas containing H2 comes into contact with the anode electrode 22, for example, the H2 in the gas is oxidized to form protons (H + ) is generated, and the water in the gas is oxidized to produce oxygen (O2) and protons (H + ) are generated. Protons are supplied to the second chamber 28 through the cation exchange membrane 30. In the second chamber 28, carbonate ions and bicarbonate ions in the alkaline aqueous solution react with the protons that have moved to the second chamber 28 through the cation exchange membrane 30, generating carbon dioxide (neutral CO2 molecules) or bicarbonate ions from carbonate ions. The generated carbon dioxide is discharged from the second chamber 28 along with the aqueous solution and recovered. In addition, cations generated in the carbon dioxide generation (for example, alkali metal ions, etc.) move from the second chamber 28 to the liquid-passing chamber through the ion exchange membrane of the liquid-passing chamber / ion exchange membrane group 29, and are used, for example, for alkaline aqueous solution or H2 generation.

[0028] In the electrochemical device 11 shown in Figure 2, similar to the electrochemical device 10 shown in Figure 1, the anode electrode contains both a first catalyst that promotes the hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes oxygen evolution in an acidic environment, thereby promoting the H2O oxidation reaction. + H2 is produced and oxidized by the H2 oxidation reaction. + Since both generation processes proceed, the applied voltage to the electrochemical device 11 can be reduced, and consequently, energy consumption can be reduced.

[0029] The following describes in detail the cation exchange membrane 30, anode electrode 22, cathode electrode 26, aqueous solution containing carbonate ion species, gas containing H2, etc.

[0030] While conventionally known cation exchange membranes can be used for the cation exchange membrane 30, perfluorosulfonic acid polymer membranes such as Nafion or Flemion are preferred in terms of hydrogen ion conductivity and water permeability, for example.

[0031] As described above, the anode electrode 22 includes a first catalyst that promotes the hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes the oxygen evolution reaction in an acidic environment.

[0032] The first catalyst that promotes the hydrogen oxidation reaction in an acidic environment is a catalyst that satisfies the following condition (1). (1) The electrochemical device shown in Figure 3, which was used in the example described later, is used. A 1M aqueous KOH solution is supplied to the second chamber at 10 mL / min, and He gas containing 3.5% H2 is supplied to the first chamber at 20 mL / min, so that the current density between the anode electrode and the cathode electrode is 10 mA / cm². 2 A catalyst that achieves an H2 utilization rate of 90% or more at the anode electrode when a constant current is applied. The anode electrode is a catalyst sheet made by coating a catalyst ink, which is a mixture of the catalyst, Nafion solution, pure water, and ethanol, into a sheet, and the catalyst content is 0.11 mg / cm² per geometric area of ​​the anode electrode. 2 Furthermore, the catalyst sheet is thermocompressed and bonded to the cation exchange film. The cathode electrode is made of Pt deposited at a density of 250 nm on carbon paper, and generates H2 with 100% current efficiency.

[0033] The second catalyst that promotes the oxygen evolution reaction in an acidic environment is a catalyst that satisfies the following condition (I). (I) The electrochemical device shown in Figure 3, used in the examples described later, is used (the conditions for preparing the anode and cathode electrodes are the same as in the case of the first catalyst). A 1M aqueous KOH solution is supplied to the second chamber at 10 mL / min, and He gas containing 3.5% H2 is supplied to the first chamber at 20 mL / min, so that the current density between the anode and cathode electrodes is 10 mA / cm². 2A catalyst that, when a constant current is applied, exhibits a current efficiency of 90% or more for the oxygen evolution reaction at the anode electrode. The anode electrode is a catalyst sheet prepared by coating a sheet with a catalyst ink, which is a mixture of the catalyst, Nafion solution, pure water, and ethanol. The catalyst content is 2 mg / cm² per geometric area of ​​the anode electrode. 2 Furthermore, the catalyst sheet is thermocompressed and bonded to the cation exchange film. The cathode electrode is made of Pt deposited at a density of 250 nm on carbon paper, and generates H2 with 100% current efficiency.

[0034] The first catalyst is not particularly limited as long as it satisfies the aforementioned conditions, but for example, H2 oxidation reaction + To further promote the formation of the product, the catalyst is preferably one that contains at least one element selected from the group consisting of Pt, Pd, Rh, Re, Au, and Ni. Specifically, it may be the metals Pt, Pd, Rh, Re, Au, or Ni, or an alloy or compound containing such metal. The compound containing such metal may be an oxide, hydroxide, or complex. The first catalyst may be a single type or two or more types may be used in combination.

[0035] The second catalyst is not particularly limited as long as it satisfies the aforementioned conditions, but for example, H2O oxidation reaction + In terms of further promoting generation, it is preferable to include at least one selected from the group consisting of Ir oxide, Ru oxide, a mixture containing Ir oxide and Ru oxide, and a composite oxide containing Ir and Ru.

[0036] As for the first and second catalysts, it is preferable that the first catalyst contains Pt and the second catalyst contains Ir oxide, for example, in order to further reduce the energy consumption of the electrochemical device.

[0037] The content of the first catalyst is 0.04 mg / cm² per geometric area of ​​the anode electrode 22, for example, in that it can further reduce the energy consumption of the electrochemical device. 2It is preferable that the above is true. Furthermore, the content of the second catalyst is, for example, 0.37 mg / cm² per geometric area of ​​the anode electrode 22, in order to further reduce the energy consumption of the electrochemical device. 2 The above is preferable. If the content of the first and second catalysts becomes too high, it may lead to an increase in the cost of the electrochemical device. Therefore, the upper limit for the content of the first and second catalysts is 1.5 mg / cm² per geometric area of ​​the anode electrode 22, respectively. 2 The following is preferable:

[0038] It is preferable that the anode electrode 22 and the cation exchange membrane 30 are joined together. This reduces the resistance when protons generated at the anode electrode 22 move to the second chamber 28. As a result, it becomes possible to improve the amount of protons supplied to the second chamber 28 per unit area of ​​the anode electrode 22, and consequently, to increase the amount of neutral CO2 molecules generated in the second chamber 28.

[0039] The anode electrode 22 may contain a polymer. The polymer functions, for example, as a binder to increase the bonding strength between the anode electrode 22 and the cation exchange film 30. Examples of polymers include cation exchange resins and anion exchange resins, but cation exchange resins are preferred in terms of bonding strength and proton conductivity, and perfluorosulfonic acid ions such as Nafion® (manufactured by DuPont) and Flemion (manufactured by Asahi Glass Co., Ltd.) are particularly preferred.

[0040] The polymer content is, for example, 0.06 mg / cm² per unit area of ​​the anode electrode 22, in order to increase the bonding strength between the anode electrode 22 and the cation exchange membrane 30. 2 It is preferable that the polymer content is as described above. Furthermore, if the polymer content becomes too high, the conductivity of the anode electrode 22 may decrease, which may lead to a decrease in the catalytic activity of the first and second catalysts. Therefore, the upper limit of the polymer content is 0.20 mg / cm² per unit area of ​​the anode electrode 22. 2 The following is preferable:

[0041] The anode electrode 22 may contain a conductive material. Examples of conductive materials include carbon materials such as carbon black, activated carbon, fullerene, carbon nanotubes, graphene, Ketjenblack, and diamond; transparent conductive oxides such as indium tin oxide, fluorine-doped tin oxide, aluminum-doped zinc oxide, and antimony-doped tin oxide; metals such as copper, aluminum, titanium, silver, and tungsten; or alloys containing at least one of these metals.

[0042] An example of a method for joining the anode electrode 22 and the cation exchange membrane 30 will be described. First, a catalyst ink containing a first catalyst, a second catalyst, a polymer, etc., is applied to a PTFE substrate to create a sheet-like anode electrode 22. Then, the anode electrode 22 is placed on the cation exchange membrane 30, and the two are joined by heat pressing.

[0043] The diffusion layer 34 may be made of, for example, a porous metal body or metal mesh made of titanium, titanium alloy, or stainless steel, or a porous conductive substrate such as carbon paper. In this embodiment of the electrochemical device, it is not necessary to install the diffusion layer 34 in the first chamber 24.

[0044] The H2-containing gas supplied to the first chamber 24 is, for example, a mixture of air or an inert gas (e.g., nitrogen gas, noble gas, etc.) and hydrogen gas, and is preferably a humidified gas. The hydrogen gas concentration in the gas may be, for example, 1% or more and 20% or less. Furthermore, the degree of humidification of the humidified gas is preferably such that the moisture content is higher than that of air at 25°C and 50% humidity. Specifically, the moisture content in the humidified gas is 11.5 g / m³. 3 It is preferable that the above conditions are met.

[0045] The cathode electrode 26 may contain a cathode catalyst, for example, in that it promotes the generation of CO2 reduction valuable products. Examples of cathode catalysts include catalysts containing at least one element from among Sn, In, Co, Au, Ag, Zn, Cu, Pd, Pt, and Mo, and specifically include metals such as Sn, In, Co, Au, Ag, Zn, Cu, Pd, Pt, and Mo, alloys containing such metals, and compounds containing such metals. The cathode catalyst is not limited to the above, and may also be a carbon material such as graphene, carbon nanotubes, fullerenes, or Ketjenblack, or a metal complex such as a Ru complex or Re complex, or an organic molecule having an imidazole skeleton or a pyridine skeleton. The cathode catalyst may also be a mixture of multiple materials. The cathode electrode 26 may have a structure in which the cathode catalyst is supported on a conductive substrate.

[0046] The aqueous solution containing carbonate ions supplied to the second chamber 28 is an aqueous solution containing at least one of carbonate ions and bicarbonate ions, and is preferably an alkaline aqueous solution. An alkaline aqueous solution is an aqueous solution containing alkali metal ions such as potassium hydroxide and sodium hydroxide. Examples of such alkaline aqueous solutions containing carbonate ions include aqueous solutions containing alkali metal bicarbonates or alkali metal carbonates such as lithium bicarbonate (LiHCO3), sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and cesium bicarbonate (CsHCO3). The alkali metal ion concentration in the aqueous solution is preferably in the range of 0.1 M to 3 M.

[0047] Furthermore, the alkaline aqueous solution containing carbonate ions may also contain alcohols such as methanol, ethanol, and acetone. Additionally, the alkaline aqueous solution containing carbonate ions may contain, for example, cations such as imidazolium ions and pyridinium ions, and BF4 - PF6 - It may also contain an ionic liquid or an aqueous solution thereof, which consists of a salt with anions such as the above and is in a liquid state over a wide temperature range. [Examples]

[0048] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0049] <Example 1> Figure 3 shows an exploded view of the electrochemical device used in the example. The electrochemical device 13 shown in Figure 3 includes a Ti current collector plate 80, an anode electrode 82, a cation exchange film 84 (Nafion N-115 film) bonded to the anode electrode 82, a Teflon® spacer 86, a cathode electrode 88, an Au-coated SUS mesh 90, and a SUS current collector plate 92. In the assembled electrochemical device 13, the anode electrode 82 and the Ti current collector plate 80 are in contact, and the space between the Ti current collector plate 80 and the cation exchange film 84 forms the first chamber. A gas containing H2 is supplied to the anode electrode 82 in the first chamber through a channel (not shown) formed in the Ti current collector plate 80. Furthermore, in the assembled electrochemical device 13, the cathode electrode 88 is fitted into a through hole 86a formed in the Teflon spacer 86, with one side of the SUS mesh 90 in contact with the cathode electrode 88 and the other side in contact with the SUS current collector plate 92. The space between the SUS current collector plate 92 and the cation exchange membrane 84 forms the second chamber. The second chamber is located on the opposite side of the first chamber via the cation exchange membrane. An alkaline aqueous solution containing carbonate ions is supplied to the SUS mesh 90 and cathode electrode 88 in the second chamber through a channel (not shown) formed in the SUS current collector plate 92.

[0050] The cathode electrode 88 used in Example 1 was made by depositing 250 nm of Pt onto one side of carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.) using the sputtering method. The electrode geometric area was 3 cm × 3 cm.

[0051] The anode electrode 82 used in Example 1 was prepared as follows: Specific surface area 8.1 m² 2An IrO2 and Pt catalyst ink was prepared by mixing IrO2 powder (at a concentration of 1 / g), Pt-supported carbon powder with a Pt concentration of 29% by mass, Nafion solution, pure water, and ethanol. Using a coating applicator, the prepared catalyst ink was spread to a uniform thickness on a PTFE sheet and heated and dried at 80°C to produce an IrO2 and Pt catalyst sheet. This IrO2 and Pt catalyst sheet was used as the anode electrode 82. The anode electrode 82 and the cation exchange film 84 were then joined by placing the sheet on one side and heat-pressing. The IrO2 content in the anode electrode 82 was 0.918 mg / cm² per geometric area of ​​the anode electrode 82, and the Pt content in the anode electrode 82 was 0.065 mg / cm² per geometric area of ​​the anode electrode 82. 2 That was the case.

[0052] An electrolytic system 1, shown in Figure 4, was constructed using the electrochemical device 13 shown in Figure 3. The performance of the electrochemical device 13 was then evaluated by operating the electrolytic system 1 according to the following procedure. First, humidified He gas was supplied at 30 mL / min from piping 94a to the first chamber 13a of the electrochemical device 13, and then discharged through the first chamber 13a via piping 94c. Pump 98 was also operated to supply 10 mL / min of 1 M K2CO3 aqueous solution from reservoir 100 to the second chamber 13b via piping 94b. The supply of humidified He gas and K2CO3 aqueous solution was continued for 30 minutes. Subsequently, a current density of 10 mA / cm² was measured between the electrodes in the first chamber 13a and the second chamber 13b using the potentiostat 102. 2 An electrolytic test was performed for 30 minutes while applying a constant current. The product generated in the second chamber during the electrolytic test was discharged from pipe 94d along with the K2CO3 aqueous solution, the K2CO3 aqueous solution was recovered in reservoir 100, and the product was discharged and recovered from pipe 94e.

[0053] The voltage of the electrochemical device 13 during the electrolysis test was measured to be 2.56V. Next, an electrolysis test was performed under the same conditions as in the example, except that humidified He gas containing 3.5% H2 (hereinafter referred to as humidified H2 / He gas) was supplied at a rate of 20 mL / min from piping 94a to the first chamber 13a of the electrochemical device 13. The voltage of the electrochemical device 13 during the electrolysis test was measured to be 2.13V. The H2 utilization rate at the anode electrode at this time was 92.7%. In other words, by using an anode electrode containing two catalysts, IrO2 and Pt, a hydrogen oxidation reaction occurred, and as a result, the voltage of the electrochemical device 13 was reduced. This reduces energy consumption.

[0054] <Example 2> The IrO2 content per geometric area of ​​the anode electrode should be 0 mg / cm². 2 ~2.02 mg / cm³ 2 The Pt content per geometric area of ​​the anode electrode is changed within the specified range, and the Pt content per geometric area of ​​the anode electrode is set to 0 mg / cm². 2 ~0.12 mg / cm³ 2 Multiple anode electrodes were fabricated with modifications within the specified range. The method for fabricating the anode electrodes was the same as in Example 1. Then, using each anode electrode, an electrochemical device 13, as shown in Figure 3, was fabricated, and the electrolytic system 1 shown in Figure 4 was constructed using the fabricated electrochemical device 13.

[0055] Humidified helium gas was supplied at a rate of 30 mL / min from piping 94a to the first chamber 13a of the electrochemical device 13. Pump 98 was also operated to supply 0.1 M KOH aqueous solution from reservoir 100 at a rate of 10 mL / min from piping 94b to the second chamber 13b. The supply of humidified helium gas and KOH aqueous solution was continued for 30 minutes. Subsequently, a current density of 10 mA / cm² was applied between the electrodes in both chambers 13a and 23b by the potentiostat 102. 2 An electrolytic test was performed for 30 minutes while applying a constant current. The voltage of the electrochemical device 13 during the electrolytic test (hereinafter referred to as the applied voltage U) H2O The applied voltage U was measured. H2O The IrO2 content is 2.02 mg / cm³.2 And the Pt content is 0 mg / cm³ 2 For the electrochemical device 13 using the anode electrode, the difference between the voltage of the electrochemical device 13 when the above electrolytic test was performed and the voltage of the electrochemical device 13 (hereinafter referred to as the voltage increase ΔU) H2O The result was calculated. The result is shown in Figure 5.

[0056] Figure 5 shows the applied voltage U H2O The relationship between the IrO2 content in the anode electrode and the voltage increase ΔU H2O This figure shows the relationship between the applied voltage U and the IrO2 content. As shown in Figure 5, the less IrO2 content there is, the more the applied voltage U H2O The voltage of the electrochemical device 13 increased. Furthermore, considering cases where a sufficient concentration of H2 is not supplied to the anode electrode, such as during device operation, the voltage increase ΔU H2O It is desirable that the IrO2 content be 1V or less. However, although not plotted in Figure 5, the IrO2 content is 0 mg / cm³. 2 In the case of an anode electrode containing only Pt, the voltage increase ΔU H2O The result was over 1V. This result indicates that the voltage reduction effect is not sufficiently obtained with an anode electrode containing only Pt as a catalyst. On the other hand, by using an anode electrode containing both Pt and IrO2 as catalysts, the voltage increase ΔU H2O It can be reduced to less than 1V. And the voltage increase ΔU H2O In terms of being able to further reduce the amount, the IrO2 content is 0.37 mg / cm³. 2 It is preferable that this be the case.

[0057] Next, humidified H2 / He gas was supplied at 20 mL / min from piping 94a to the first chamber 13a of the electrochemical device 13. Pump 98 was also operated to supply 0.1 M KOH aqueous solution from reservoir 100 at 10 mL / min from piping 94b to the second chamber 13b. The supply of humidified H2 / He gas and KOH aqueous solution was continued for 30 minutes. Afterward, a current density of 10 mA / cm² was applied between the electrodes in both chambers 13a and 23b by the potentiostat 102. 2An electrolytic test was performed for 30 minutes while applying a constant current. The voltage of the electrochemical device 13 at this time (hereinafter referred to as the applied voltage U) H2 The applied voltage U at each electrochemical device 13 was measured. H2O and applied voltage U H2 The difference was calculated. These results are shown in Figures 6-8.

[0058] Figure 6 shows the relationship between hydrogen utilization rate and the IrO2 content in the anode electrode, and the relationship between the Pt content in the anode electrode and the IrO2 content. 2 When using the anode electrode described above, the hydrogen utilization rate was almost 0%. From this result, it can be concluded that both Pt and IrO2 are necessary as catalysts for the hydrogen oxidation reaction to occur at the anode electrode.

[0059] Figure 7 shows the applied voltage U H2 This figure shows the relationship between the applied voltage U and the IrO2 content in the anode electrode, and the relationship between the Pt content in the anode electrode and the IrO2 content. The lower the IrO2 content and the higher the Pt content, the higher the applied voltage U H2 It decreased.

[0060] Figure 8 shows the applied voltage U H2O and applied voltage U H2 This figure shows the relationship between the difference and the IrO2 content in the anode electrode, and the relationship between the Pt content in the anode electrode and the IrO2 content. Applied voltage U H2O and applied voltage U H2 The larger the difference, the greater the effect of reducing the applied voltage of the electrochemical device. H2O and applied voltage U H2 The difference between these values ​​should preferably be 0.05V or greater, and satisfying this condition, the Pt content is 0.04 mg / cm³. 2 It is preferable that the above conditions are met.

[0061] "Note": Structure of the present invention Configuration 1: an anode electrode containing an anode catalyst, The anode electrode is placed in a first chamber to which a gas containing H2 is supplied, A cation exchange membrane disposed on the anode electrode, The system comprises a second chamber adjacent to the first chamber via the cation exchange membrane, to which an aqueous solution containing carbonate ion species is supplied, The anode catalyst comprises a first catalyst that promotes a hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes an oxygen evolution reaction in an acidic environment. An electrochemical device characterized in that, when a voltage is applied to the anode electrode, protons generated at the anode electrode are supplied to the second chamber through the cation exchange membrane and react with the carbonate ion species. Configuration 2: The electrochemical device according to configuration 1, characterized in that the gas containing H2 is a humidifying gas containing H2. Configuration 3: The electrochemical device according to configuration 1 or 2, characterized in that the anode electrode and the cation exchange membrane are joined together. Configuration 4: The electrochemical device according to any one of configurations 1 to 3, characterized in that the first catalyst contains at least one element selected from the group consisting of Pt, Pd, Rh, Re, Au, and Ni. Configuration 5: The electrochemical device according to any one of configurations 1 to 4, characterized in that the second catalyst comprises at least one selected from the group consisting of Ir oxide, Ru oxide, a mixture containing Ir oxide and Ru oxide, and a composite oxide containing Ir and Ru. Configuration 6: An electrochemical device according to any one of configurations 1 to 4, characterized in that the first catalyst contains Pt and the second catalyst contains the Ir oxide. Composition 7: The content of the first catalyst is 0.04 mg / cm² per geometric area of ​​the anode electrode. 2 An electrochemical device according to any one of configurations 1 to 6, characterized by the above. Composition 8: The content of the second catalyst is 0.37 mg / cm² per geometric area of ​​the anode electrode. 2 An electrochemical device according to any one of configurations 1 to 7, characterized by the above. [Explanation of symbols]

[0062] 1 Electrolytic system, 10,11,13 Electrochemical devices, 22,82 Anode electrodes, 23,32 Flow channels, 24,13a First chamber, 26,88 Cathode electrodes, 28,13b Second chamber, 29 Liquid passage chamber / ion exchange membrane group, 30,84 Cation exchange membrane, 34 Diffusion layer, 36a,36b Frame material, 70 Power supply, 80,92 Current collector plate, 86 Teflon spacer, 86a Through hole, 90 Mesh, 94a~94e Piping, 98 Pump, 100 Reservoir, 102 Potentiostat.

Claims

1. an anode electrode containing an anode catalyst, The anode electrode is arranged, H ２ A first room is supplied with gas containing, A cation exchange membrane disposed on the anode electrode, The system comprises a second chamber adjacent to the first chamber via the cation exchange membrane, to which an aqueous solution containing carbonate ion species is supplied, The anode catalyst comprises a first catalyst that promotes a hydrogen oxidation reaction in an acidic environment and a second catalyst that promotes an oxygen evolution reaction in an acidic environment. An electrochemical device characterized in that, when a voltage is applied to the anode electrode, protons generated at the anode electrode are supplied to the second chamber through the cation exchange membrane and react with the carbonate ion species.

2. The aforementioned H ２ Gases containing H ２ The electrochemical device according to claim 1, characterized in that it is a humidifying gas containing the above.

3. The electrochemical device according to claim 1 or 2, characterized in that the anode electrode and the cation exchange membrane are joined together.

4. The electrochemical device according to claim 1 or 2, characterized in that the first catalyst comprises at least one element selected from the group consisting of Pt, Pd, Rh, Re, Au, and Ni.

5. The electrochemical device according to claim 1 or 2, characterized in that the second catalyst comprises at least one selected from the group consisting of Ir oxide, Ru oxide, a mixture containing Ir oxide and Ru oxide, and a composite oxide containing Ir and Ru.

6. The electrochemical device according to claim 1 or 2, characterized in that the first catalyst contains Pt and the second catalyst contains the Ir oxide.

7. The content of the first catalyst is 0.04 mg / cm² per geometric area of ​​the anode electrode. ２ The electrochemical device according to claim 1 or 2, characterized in that it is as described above.

8. The content of the second catalyst is 0.37 mg / cm² per geometric area of ​​the anode electrode. ２ The electrochemical device according to claim 1 or 2, characterized in that it is as described above.

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