Iridium-containing oxide, method for producing the same, and catalyst containing the iridium-containing oxide

Abstract

The present invention is an iridium oxide-containing material, a method for producing the same, and a catalyst containing the iridium oxide-containing material. The present invention aims to provide an iridium oxide-containing material which is used as a water-splitting electrode catalyst for a cation exchange membrane water electrolysis or a cation exchange membrane fuel cell, has high activity and high durability, and can reduce the amount of catalyst used by controlling the pore structure. The iridium oxide-containing material of the present invention is characterized by having a total pore volume of 0.20 cm 3 / g or more and a pore distribution having an average pore diameter of 7.0 nm or more, as determined from a nitrogen adsorption / desorption isotherm and calculated by the BJH method.

Description

Technical Field

[0001] This invention relates to an iridium-containing oxide that has high activity and long lifespan when used as an electrode catalyst in fields such as water electrolysis, a method for manufacturing the same, and catalysts containing iridium-containing oxides. Background Technology

[0002] Generally, iridium oxides possess good electrical conductivity and a high catalytic ability for water oxidation reactions. Furthermore, they exhibit very high corrosion resistance even under strong acidic and alkaline conditions, thus making them suitable for various electrode materials. Historically, they have been used as shape-stabilizing electrode materials in fields such as sodium alkali electrolysis and electroplating. More recently, by nanoparticleizing iridium oxides, they have attracted attention as gas diffusion electrode catalysts for oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and chlorine evolution reaction (CER) in applications such as cation exchange membrane water electrolysis, cation exchange membrane fuel cells, seawater electrolysis, and photocatalytic water splitting, as well as for applications as electrode materials in supercapacitors.

[0003] In particular, cation exchange membrane anode catalysts for water electrolysis and cation exchange membrane fuel cell reverse potential durability catalysts are expected to be widely used as water electrolysis catalysts.

[0004] In preparation for the coming hydrogen society, the use of cation exchange membrane water electrolysis for renewable energy storage has attracted attention in recent years, and large-scale, high-efficiency megawatt-level electrolysis is being developed at an accelerated pace.

[0005] In addition, cation exchange membrane fuel cells are being developed at an accelerated pace as a clean transportation method for the upcoming hydrogen society.

[0006] A cation exchange membrane electrolyzer consists of a catalyst-coated membrane (CCM) formed by sandwiching a cation exchange polymer electrolyte membrane, such as Nafion (registered trademark), between the anode and cathode catalyst layers. A gas diffusion layer then sandwiches both sides of the catalyst-coated membrane to form a membrane electrode assembly (MEA). Multiple MEAs are connected in series as a structural unit, separated by a separating membrane. When water is supplied to the anode catalyst layer, a reaction occurs in the anode catalyst layer (Chemical 1), and a reaction occurs in the cathode catalyst layer (Chemical 2). Oxygen (O2) is produced on the anode side, and hydrogen (H2) is produced on the cathode side.

[0007] (Chemical 1) H₂O(liq.) → 1 / 2O₂(g) + 2H₂O + +2e -

[0008] (Chemical 2)2H + +2e - →H2(g)

[0009] The rate-limiting phase of the entire reaction is the oxidation of water and the oxygen evolution reaction on the anode side. The oxygen evolution reaction (OER) quality activity of the anode catalyst is an important factor determining the system efficiency.

[0010] Regarding oxygen evolution anodes used in industrial electrolysis, a technique is disclosed that can reduce oxygen evolution overvoltage by setting the crystallite size of iridium oxide to below 9.7 nm and increasing crystallinity to produce a highly active and durable electrode (for example, see Patent Document 1).

[0011] On the other hand, in a cation exchange membrane fuel cell, a reaction occurs at the cathode (Chemical 3) and at the anode (Chemical 4). Overall, an electromotive force is generated through (Chemical 5), which is then connected to an external circuit for use.

[0012] (Chemicals 3)1 / 2O2(g) + 2H + +2e - →H2O

[0013] (Chemicals 4)H2(g)→2H + +2e -

[0014] (Chemicals 5) 1 / 2O2(g) + H2(g) → H2O

[0015] However, when starting or stopping the fuel cell, if the hydrogen supplied to the anode side is insufficient, it will become a fuel-deficient state. Current will be forced to flow from other cells connected in series with the cell in this fuel-deficient state, and the following reaction will occur (Chemical 6): the platinum-supported carbon electrode catalyst will be oxidized and corroded, and it will be unable to be used as a fuel cell.

[0016] (Chemicals 6) C + 2H₂O → CO₂ + 4H₂O + +4e -

[0017] (Chem. 7) 2H₂O → O₂ + 4H₂O + +4e -

[0018] To suppress the oxidative corrosion of carbon supports by water under such reverse potential conditions, the addition of iridium oxide nanoparticle catalysts has been studied as electrolytic catalysts for water electrolysis via reaction (Chem. 7) (see, for example, Patent Document 2).

[0019] While iridium oxide is not mentioned as a method for manufacturing microparticles, the following technology is disclosed: a method for manufacturing microparticles using high-temperature and high-pressure water. This method uses a pressurizing member and a heating member to turn water into high-temperature and high-pressure water in a supercritical or subcritical state. The high-temperature and high-pressure water is then mixed with a fluid raw material in a mixing section. After mixing, the mixture is guided to a reactor. Before the fluid raw material is mixed with the high-temperature and high-pressure water, it is cooled to a temperature below the critical temperature of water (for example, see Patent Document 3).

[0020] Methods for manufacturing iridium oxide as a catalyst for the oxygen evolution reaction in cation exchange membrane water electrolysis are generally disclosed, including sol-gel method, aqueous solution hydrolysis method, or Adams melting method (for example, see Non-Patent Literature 1).

[0021] In the application of oxygen anode catalysts in water electrolysis, a method for producing iridium oxide is disclosed, which uses ammonia water to hydrolyze iridium salts and adds nitrates to the intermediates, then heats and dries and melts them (for example, see Patent Document 4).

[0022] A test method for the reverse potential durability of the anode of a cation exchange membrane fuel cell is disclosed, and a comparison of durability with and without the addition of a water electrolysis catalyst component to the anode is disclosed (for example, see Non-Patent Literature 2).

[0023] Existing technical documents

[0024] Patent documents

[0025] Patent Document 1: Japanese Patent Publication No. 2014-526608

[0026] Patent Document 2: Japanese Patent Publication No. 2003-508877

[0027] Patent Document 3: Japanese Patent Application Publication No. 2005-21724

[0028] Patent Document 4: Japanese Patent Application Publication No. 2020-132465

[0029] Non-patent literature

[0030] Non-patent literature 1: PEM Electrolysis for Hydrogen Production - Principales and Applications, CRC Press (2016), 53-55

[0031] Non-Patent Document 2: Abstracts of the 59th Battery Symposium (November 2018, Osaka) by Tsutomu Ikuzo and Kazuaki Yasuda, Presentation No. 1H23 Summary of the Invention

[0032] [The problem the invention aims to solve]

[0033] Compared to the platinum group metals, which have an annual production of 454 tons, iridium has an annual production of only 9 tons, making it an expensive precious metal. However, iridium must be used extensively as an electrode catalyst, necessitating reductions in its usage or the frequency of electrode replacement. Therefore, highly efficient and durable electrode catalysts are required.

[0034] In the process of developing high-efficiency iridium oxides, the inventors explored a method for preparing iridium oxides with a large specific surface area to achieve high activity. However, they learned that while increasing the specific surface area improves catalytic activity, it reduces durability. Therefore, it is important to increase catalytic activity while maintaining durability.

[0035] Previously, iridium oxide was used as the anode catalyst for oxygen evolution in industrial electrolysis. However, in Patent Document 1, the crystallite size of highly crystalline iridium oxide is as large as about 6 nm to 10 nm, and the specific surface area is correspondingly low. Although it has durability, its activity is insufficient.

[0036] Patent document 2 discloses the significant effects of ruthenium oxide, in particular, and mixed oxides of ruthenium oxide and iridium oxide, as components of water electrolysis catalysts. However, regarding the effect of iridium oxide alone, although it has durability, its activity is insufficient.

[0037] Patent document 3 discloses a method for manufacturing microparticles such as metals or metal oxides. Due to repeated heating and cooling, the crystallite size increases and decreases repeatedly. Therefore, the crystallite size may deviate, and the durability or catalytic activity may vary from particle to particle.

[0038] Patent document 4 discloses a specific surface area of ​​150 m². 2 Iridium oxide with a concentration of 1 g or more and an average pore diameter of 2.3 nm or more and 4.0 nm or less has high activity but insufficient durability.

[0039] Non-patent document 1 reports various known methods for manufacturing iridium oxide as a catalyst for the oxygen evolution reaction in cation exchange membrane water electrolysis, but does not describe a hydrothermal synthesis method using supercritical or subcritical water in the reaction field.

[0040] Non-patent document 2 describes iridium black as a component of a reverse potential durable water electrolysis catalyst, but does not reveal the catalytic effect of iridium oxide.

[0041] Therefore, the object of the present invention is to provide an iridium-containing oxide that exhibits high activity and high durability when used as an electrode catalyst by controlling the microporous structure of the iridium oxide, and a method for manufacturing the same. Furthermore, the present invention provides a highly active and highly durable water electrolysis catalyst comprising such an iridium-containing oxide for use as a cation exchange membrane water electrolysis anode or as a reverse potential durable electrode in a cation exchange membrane fuel cell.

[0042] [Technical means to solve the problem]

[0043] The inventors conducted extensive research to solve the aforementioned problems, and as a result, discovered that these problems were solved by using an iridium-containing oxide with a specific microporous structure and its manufacturing method, which were previously unknown, thus completing this invention. Specifically, this iridium-containing oxide is characterized by a total micropore volume of 0.20 cm³, determined by nitrogen adsorption-desorption isotherms and calculated using the BJH (Barrett-Joyner-Halenda) method. 3 It has a pore distribution with an average pore diameter of 7.0 nm or more and a pore size of 7.0 nm or more.

[0044] The iridium-containing oxide of the present invention preferably exhibits hysteresis in the region where the relative pressure (P / P0) of the nitrogen adsorption-desorption isotherm is between 0.7 and 0.95. Furthermore, its BET (Brunauer-Emmett-Teller) specific surface area is preferably 100 m². 2 / g or more. Catalysts with higher activity and greater durability can be obtained.

[0045] In the iridium-containing oxide of the present invention, the iridium-containing oxide is a powder or dispersed particles, which has the following characteristics: a total pore volume of up to 0.20 cm³, determined by the nitrogen adsorption-desorption isotherm and calculated by the BJH method. 3 The surface area is greater than / g, and the average pore diameter is as large as 7.0 nm. Furthermore, it is preferable to have hysteresis in the region where the relative pressure (P / P0) of its adsorption-desorption isotherm is 0.7 to 0.95, and even more preferably, the BET specific surface area is as large as 100 m². 2 / g.

[0046] In the iridium-containing oxide of the present invention, the iridium-containing oxide is iridium oxide, or a composite oxide of an element having a rutile crystal structure and iridium, including the iridium oxide or composite oxide having a rutile crystal structure.

[0047] The method for manufacturing iridium oxide of the present invention is characterized by the following steps: Step A, (1) dispersing iridium nanoparticles or iridium hydroxide particles as raw materials in a medium to obtain a dispersion, or (2) dissolving an iridium compound as raw materials in a solvent to obtain a solution; Step B, making water into high-temperature and high-pressure water under high-temperature and high-pressure conditions of heating temperature above 100°C and pressure above 0.1 MPa; and Step C, mixing the dispersion or solution obtained in Step A with the high-temperature and high-pressure water obtained in Step B.

[0048] In the method for manufacturing iridium-containing oxides of the present invention, in step A, the solvent is preferably set at 15–30°C, in which the iridium compound used as a raw material is dissolved. This method enables the production of iridium-containing oxides with a large total pore volume, resulting in iridium-containing oxides with high activity and high durability.

[0049] In the method for manufacturing iridium oxide of the present invention, step B preferably includes any of the following steps: (1) adding an oxidant that releases oxygen atoms to the water and then making the water high-temperature and high-pressure water; (2) making the water high-temperature and high-pressure water and then adding an oxidant that releases oxygen atoms; or (3) adding an oxidant that releases oxygen atoms to the water and then making the water high-temperature and high-pressure water, and then adding an oxidant that releases oxygen atoms to the high-temperature and high-pressure water. This allows for highly efficient oxidation reaction in step C.

[0050] The cation exchange membrane water electrolysis anode catalyst of the present invention is characterized by containing the iridium-containing oxide of the present invention. Because it is synthesized under hydrothermal conditions, it has a unique microporous structure, especially with an average micropore diameter of 7.0 nm or more. Therefore, when preparing the electrode for the cation exchange membrane water electrolysis anode, the affinity with ionic polymer molecules, such as Nafion (registered trademark), which serve as a binder for the cation exchange resin and has an average molecular diameter of about 10 nm, is improved, resulting in an electrode with high activity and excellent durability.

[0051] Furthermore, the reverse potential durability catalyst for cation exchange membrane fuel cells of the present invention is characterized in that the electrode catalyst layer contains the iridium-containing oxide of the present invention. Because it is synthesized under hydrothermal conditions, it has a unique microporous structure, especially with an average micropore diameter of 7.0 nm or more. Therefore, when preparing the electrode for the cation exchange membrane fuel cell, the affinity with ionomer molecules, such as Nafion (registered trademark), which serve as a binder for the cation exchange resin and has an average molecular diameter of about 10 nm, is improved, resulting in an electrode with high activity and excellent durability.

[0052] [The effects of the invention]

[0053] The iridium-containing oxide of the present invention has a unique microporous structure, namely, the total micropore volume is as large as 0.20 cm³, as determined by the nitrogen adsorption-desorption isotherm and calculated by the BJH method. 3 The nitrogen content is greater than 7.0 nm / g, and the average pore diameter is greater than 7.0 nm. Furthermore, it is preferable to have hysteresis in the region where the relative pressure (P / P0) of the nitrogen adsorption-desorption isotherm is 0.7 to 0.95, and it is even more preferable to provide a BET specific surface area of ​​greater than 100 m². 2 Iridium-containing oxides with a density of / g or higher. Iridium-containing oxides with this micropore distribution and physical properties, when used as anode catalysts for cation exchange membrane water electrolysis or as reverse potential durability catalysts for cation exchange membrane fuel cells, can produce electrodes with unprecedentedly high activity and excellent durability. Furthermore, the method for manufacturing iridium-containing oxides according to the present invention can produce iridium-containing oxides with a unique micropore structure having a large micropore volume and a large average micropore diameter, thus obtaining iridium-containing oxides with high activity and high durability when used as electrode catalysts.

[0054] According to the present invention, when iridium-containing oxides are used as the anode catalyst for cation exchange membrane water electrolysis, they exhibit high activity and durability, thus reducing the amount of iridium used per unit electrode area to approximately 1 / 2 to 1 / 5 compared to conventional methods. Furthermore, by adding iridium-containing oxides to the platinum-supported carbon-based electrode catalyst of the cation exchange membrane fuel cell, reverse potential durability can be significantly improved. Additionally, the effects of fuel scarcity are more severe on the anode side of the cation exchange membrane fuel cell; therefore, the water electrolysis catalyst is used in combination with the anode's hydroxide catalyst components. However, the effects of reverse potential can also occur on the cathode side; therefore, the cathode catalyst layer can also be mixed with oxygen reduction catalyst components. Attached Figure Description

[0055] Figure 1 This is an example of an iridium oxide manufacturing apparatus according to this embodiment.

[0056] Figure 2 It is the nitrogen adsorption-desorption isotherm containing iridium oxide in Example 1.

[0057] Figure 3 This is the nitrogen adsorption-desorption isotherm containing iridium oxide in Example 2.

[0058] Figure 4 This is the nitrogen adsorption-desorption isotherm containing iridium oxide in Example 3.

[0059] Figure 5 This is the nitrogen adsorption-desorption isotherm of the iridium oxide-containing sample in Comparative Example 1.

[0060] Figure 6 This is the nitrogen adsorption-desorption isotherm of the iridium oxide-containing compound in Comparative Example 2.

[0061] Figure 7 This is a graph showing the comparison of the OER mass activity of the catalysts in the examples and comparative examples.

[0062] Figure 8 This is a graph showing the comparison of accelerated degradation tests in a single water electrolysis cell using the catalysts of the examples and comparative examples as anodes.

[0063] Figure 9 This is a graph showing the comparison of single-cell reverse potential durability tests of fuel cells using the catalysts of the examples and comparative examples added to the electrodes in the anode.

[0064] Figure 10 It is the nitrogen adsorption-desorption isotherm containing iridium oxide in Example 7. Detailed Implementation

[0065] The present invention will now be described in detail with reference to embodiments, but the invention is not limited to these descriptions. Various variations may be made to the embodiments as long as the effects of the invention are achieved.

[0066] The iridium-containing oxide of this embodiment is characterized in that the total micropore volume, determined by the nitrogen adsorption-desorption isotherm and calculated by the BJH method, is 0.20 cm³. 3 The iridium oxide has a density of 7.0 nm or more per g and a fine pore distribution with an average pore diameter of 7.0 nm or more. In the iridium oxide of the present invention, it is further preferable to have a hysteresis in the region where the relative pressure (P / P0) of the nitrogen adsorption-desorption isotherm is 0.7 to 0.95, and it is even more preferable to have a BET specific surface area of ​​100 m². 2 / g or higher. Catalysts with higher activity and durability can be obtained. Furthermore, the relative pressure (P / P0) is defined as the ratio of the pressure P when nitrogen molecules are adsorbed on a solid surface to the saturated vapor pressure P0 of nitrogen.

[0067] The iridium-containing oxide of this embodiment is characterized by a relatively flat relative pressure (P / P0) before reaching approximately 0.05 to 0.7, followed by a steep rise from approximately 0.7 to approximately 0.95 in its nitrogen adsorption-desorption isotherm. Furthermore, it preferably exhibits a so-called hysteresis loop, a shift in the isotherm during adsorption and desorption. This hysteresis is caused by capillary condensation of liquid nitrogen during desorption, a phenomenon unique to mesoporous and microporous structures. The iridium-containing oxide of this embodiment contains almost no micropores with a diameter less than 2.0 nm or relatively small-aperture mesoporous pores with a diameter of 2.0 nm or more but less than 5.0 nm; most pores have a micropore distribution comprising relatively large-aperture mesoporous pores with diameters of 5.0 nm or more but less than 50 nm. As a result, the average pore diameter calculated by the BJH method is 7.0 nm or more, and the total pore volume is as large as 0.20 cm³. 3A fine pore volume of / g or more.

[0068] The iridium-containing oxide in this embodiment includes, in addition to iridium oxide (IrO2), composite oxides of Ir with elements having rutile crystal structures such as TiO2, NbO2, TaO2, SnO2, and RuO2, and has an average micropore diameter of 7.0 nm or more and a total micropore volume of up to 0.20 cm³. 3 Pore ​​volume of / g or more. The iridium oxide, or a composite oxide of iridium and an element having a rutile crystal structure, preferably has a rutile crystal structure. Furthermore, impurities other than iridium or additive elements may be included, provided that the properties of the iridium-containing oxide of this embodiment are not impaired.

[0069] In the iridium-containing oxide of this embodiment, the BET specific surface area is preferably 100 m². 2 / g or higher. As long as the average pore diameter is 7.0nm or higher and the total pore volume is 0.20cm³. 3 If the specific surface area is above a certain value, then even if the specific surface area is large, the durability will not be reduced and the activity will be improved.

[0070] In the iridium-containing oxide of this embodiment, the iridium-containing oxide is a monodisperse nanoparticle powder or its aggregate particles, and it is believed that its particle surface and aggregate interface constitute a unique microporous structure.

[0071] In this embodiment, the ratio of iridium to oxygen in the iridium-containing oxide is preferably 30:70 to 40:60 in atomic percent, and more preferably 32:68 to 34:66. In the case where the iridium-containing oxide in this embodiment is a composite oxide of Ir and elements with a rutile crystal structure such as TiO2, NbO2, TaO2, SnO2, or RuO2, the ratio of the total amount of iridium and the rutile crystal structure to oxygen in atomic percent is preferably 30:70 to 40:60, and more preferably 32:68 to 34:66.

[0072] The method for manufacturing iridium oxides according to this embodiment includes the following steps: Step A, (1) dispersing iridium nanoparticles or iridium hydroxide particles as raw materials in a medium to obtain a dispersion, or (2) dissolving an iridium compound as raw materials in a solvent to obtain a solution; Step B, making water into high-temperature and high-pressure water under high-temperature and high-pressure conditions of heating temperature above 100°C and pressure above 0.1 MPa; and Step C, mixing the dispersion or solution obtained in Step A with the high-temperature and high-pressure water obtained in Step B.

[0073] Here, refer to Figure 1An example of an apparatus for manufacturing iridium oxides will be described. The apparatus 100 for manufacturing iridium oxides according to this embodiment includes at least: a first supply source (1) of an iridium-containing dispersion or solution; a second supply source (2) of an aqueous liquid; a heating section (3) for heating the aqueous liquid; a reaction section (4) for merging the iridium-containing dispersion or solution with the aqueous liquid; a liquid delivery path (5) connecting the first supply source (1) and the reaction section (4); a liquid delivery path (6) connecting the second supply source (2) and the reaction section (4); a recovery section (7) connected to the reaction section (4) via piping and recovering the generated reactants; and a cooling section (8) located between the reaction section (4) and the recovery section (7). A pressure adjustment mechanism (11) is connected to the recovery section (7). Alternatively, the pressure adjustment mechanism (11) may be connected between the cooling section (8) and the recovery section (7). According to the apparatus for manufacturing iridium oxides according to this embodiment, iridium oxide particles can be stably produced.

[0074] In the apparatus for manufacturing iridium oxides according to this embodiment, in the reaction section (4), iridium oxides are produced by oxidizing the iridium in the dispersion or solution by mixing it with high-temperature and high-pressure water. The high-temperature and high-pressure water is obtained from the heating section (3). The high-temperature and high-pressure water includes not only water in a high-temperature and high-pressure state, but also water containing oxidants such as oxygen, hydrogen peroxide, and ozone that has been converted into a high-temperature and high-pressure state.

[0075] The liquid delivery path (5) connecting the first supply source (1) and the reaction unit (4) includes piping. One method for adjusting the flow rate of the liquid flowing through the piping is to position it above the first supply source (1) and the reaction unit (4), utilizing the elevation difference. In this case, the iridium-containing dispersion or solution can be delivered from the first supply source (1) to the reaction unit (4) using only the piping. Alternatively, a flow-limiting valve such as a needle valve or a stop valve can be installed in the liquid delivery path (5).

[0076] The liquid delivery path (6) connecting the second supply source (2) and the reaction section (4) includes piping. One method for adjusting the flow rate of the liquid flowing through the piping is to position the second supply source (2) above the reaction section (4) to utilize the elevation difference. In this case, aqueous liquid can be transported from the second supply source (2) to the reaction section (4) using only piping. Similarly to the liquid delivery path (5), flow-limiting valves such as needle valves and stop valves can also be installed in the liquid delivery path (6).

[0077] In the iridium oxide manufacturing apparatus of this embodiment, there may be mechanisms (9) and (10) for unidirectionally transferring liquid flowing in either or both of the liquid delivery paths (5) and (6). Figure 1The apparatus 100 for manufacturing iridium oxide shown includes mechanisms (9) and (10) in both the liquid delivery path (5) and the liquid delivery path (6). In this configuration, the flow rate and velocity of the iridium dispersion or solution and the aqueous liquid can be stably controlled in both the liquid delivery path (5) and the liquid delivery path (6), thus enabling the stable manufacture of iridium oxide.

[0078] Mechanisms (9) and (10) are means of adjusting the flow rate of liquid flowing through the piping, such as plungers, measuring cylinders or regulators.

[0079] As the dispersion medium for iridium nanoparticles or iridium hydroxide particles, any medium capable of dispersion can be freely chosen, such as water or an organic solvent. As the solvent for dissolving the iridium compound, any solvent that is liquid at room temperature can be freely chosen, such as water or an organic solvent. In this embodiment, room temperature refers to 15°C to 30°C, preferably 20°C to 25°C.

[0080] [Step A of (1)]

[0081] The particle size of the iridium nanoparticles used as raw materials is preferably 3.0 nm or less, more preferably 2.5 nm or less. If the particle size of the iridium nanoparticles is greater than 3.0 nm, then when iridium reacts with oxygen, iridium oxide particles of the target crystallite size cannot be obtained, and oxidation may be insufficient. Furthermore, the particle size of the iridium hydroxide particles is preferably 3.0 nm or less, more preferably 2.5 nm or less. If the iridium hydroxide particles are greater than 3.0 nm, then when iridium hydroxide reacts with oxygen, iridium oxide particles of the target crystallite size cannot be obtained, and oxidation may be insufficient.

[0082] By adding iridium nanoparticles or iridium hydroxide particles that meet the aforementioned conditions to a medium, a dispersion in which iridium nanoparticles or iridium hydroxide particles are dispersed in the medium can be obtained. Examples of media include water and ethanol.

[0083] [Step A of (2)]

[0084] The iridium compound used as a raw material can be any of the following: iridium nitrate, iridium sulfate, iridium acetic acid, iridium chloride, or iridium metal salts, or metal complexes such as iridium acetylacetonate and iridium carbonyl compounds, preferably iridium nitrate, iridium sulfate, or iridium acetic acid. By adding the iridium compound to a solvent, a solution in which the iridium compound is dissolved in the solvent can be obtained. The solvent is, for example, water in the case of iridium metal salts, and ethanol or ethyl acetate in the case of iridium metal complexes. In step A (2), the solvent is at room temperature, for example, 15°C to 30°C, and it is preferable that the iridium compound used as a raw material is dissolved in this solvent.

[0085] [Step B]

[0086] Unlike step A, high-temperature, high-pressure water is obtained by treating water at a heating temperature of 100°C or higher and a pressurization pressure of 0.1 MPa or higher. The heating temperature is 100°C or higher, more preferably 150°C or higher, and most preferably 374°C or higher. For example, the heating temperature is 400°C. The pressurization pressure is 0.1 MPa or higher, more preferably 0.5 MPa or higher, and most preferably 22.1 MPa or higher. For example, the pressurization pressure is 30 MPa. The water used to obtain the high-temperature, high-pressure water is preferably pure water, but it can also be a solution obtained by dissolving oxidants such as oxygen, hydrogen peroxide, or ozone in water.

[0087] To ensure efficient oxidation reaction in step C, step B preferably includes any of the following steps: (1) adding an oxidant that releases oxygen atoms to the water and then making the water high-temperature, high-pressure water; (2) making the water high-temperature, high-pressure water and then adding an oxidant that releases oxygen atoms; or (3) adding an oxidant that releases oxygen atoms to the water and then making the water high-temperature, high-pressure water, and then adding an oxidant that releases oxygen atoms to the high-temperature, high-pressure water. In the case of oxygen, it is preferable to make the water, which has a saturated oxygen concentration, into a high-temperature, high-pressure state. Furthermore, the oxidant that releases oxygen atoms can be oxygen, hydrogen peroxide, ozone, etc.

[0088] [Step C]

[0089] The dispersion or solution obtained in step A is mixed with the high-temperature, high-pressure water obtained in step B. There are no particular limitations on the mixing conditions. When using a small-capacity pipe, mixing can be achieved by merging the pipe containing the dispersion or solution obtained in step A with the pipe containing the high-temperature, high-pressure water obtained in step B, thereby obtaining a dispersion of iridium oxide dispersed in high-temperature, high-pressure water. Alternatively, when using a large-capacity container, the dispersion or solution obtained in step A and the high-temperature, high-pressure water obtained in step B can be placed in the container and mixed by stirring, etc., to obtain a dispersion of iridium oxide dispersed in high-temperature, high-pressure water. Figure 1 In the reaction section (4), the mixture is mixed.

[0090] The solution obtained in step C is, for example... Figure 1 After cooling in the cooling section (8) shown, the sample is recovered by the recovery section (7). Then, the sample is separated and washed by filtration or centrifugation, and dehydrated by a dryer, thereby obtaining nanoparticles containing iridium oxide.

[0091] [Cation exchange membrane water electrolysis anode catalyst]

[0092] Next, the iridium oxide-containing cation exchange membrane anode catalyst for water electrolysis according to this embodiment will be described. Various cation exchange membranes, such as perfluorosulfonic acid-based, sulfonated polyvinyl ether ketone-based, and sulfonated polybenzimidazole-based membranes, are used as cation exchange membranes for the water electrolyzer. Among these, perfluorosulfonic acid-based membranes such as Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by AGC), Aciplex (registered trademark, manufactured by Asahi Kasei), Fumion (registered trademark, manufactured by Fumatech), or Aquivion (registered trademark, manufactured by Solvay) are preferred. As the cathode catalyst for the cation exchange membrane water electrolyzer, platinum black or platinum-supported carbon black catalysts with high hydrogen evolution reaction activity are typically used. The iridium oxide of this embodiment is prepared by stirring and mixing it in a solvent with a cation exchange resin ionomer, which has the same composition as the cation exchange membrane described above, to prepare the anode catalyst ink. The ratio of the iridium oxide to the ionomer is not particularly limited, but a composition of 1:0.2 to 1:0.05 is preferred, and a composition of 1:0.15 to 1:0.07 is more preferred. The solvent is not particularly limited, but water, or a mixture of water and lower aliphatic alcohols such as ethanol, propanol, or butanol, is preferred. The cathode catalyst is also similarly mixed with the ionomer to prepare the cathode catalyst ink. The method for preparing the CCM by coating the anode catalyst layer and cathode catalyst layer onto the front and back sides of the cation exchange membrane using the anode catalyst ink and cathode catalyst ink prepared in this manner is not particularly limited; known methods can be used, such as direct coating methods using rod coating or spray coating, or transfer printing after pre-coating the anode catalyst layer and cathode catalyst layer onto a Teflon membrane using a hot press, etc. The loading amount of the cation exchange membrane water electrolysis anode catalyst on the cation exchange membrane in this embodiment is not particularly limited, but 2.0 mg / cm³ is preferred. 2 ~0.1mg / cm 2 Within the range, and therefore preferably using 1.0 mg / cm³. 2 ~0.3mg / cm 2 Within this range, an iridium amount that can be far less than that used in conventional cation exchange membrane water electrolyzers is provided, at 1.0 A / cm². 2 ~5.0A / cm 2 This anode catalyst enables the water electrolyzer to operate at a higher current density than before, a lower electrolysis voltage of 1.5V to 1.7V (without internal resistance), and maintains durability for tens of thousands of hours.

[0093] [Reverse Potential Durable Catalyst for Cation Exchange Membrane Fuel Cells]

[0094] Next, the reverse potential durable water electrolysis catalyst for a cation exchange membrane fuel cell containing iridium oxide of this embodiment will be described. Various cation exchange membranes, such as perfluorosulfonic acid-based, sulfonated polyvinyl ether ketone-based, and sulfonated polybenzimidazole-based membranes, are used as the cation exchange membrane in the cation exchange membrane fuel cell. Among these, perfluorosulfonic acid-based membranes such as Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by AGC), Aciplex (registered trademark, manufactured by Asahi Kasei), Fumion (registered trademark, manufactured by Fumatech), or Aquivion (registered trademark, manufactured by Solvay) are preferred. The oxygen reduction catalyst component at the cathode and the hydrogen hydroxide catalyst component at the anode of the cation exchange membrane fuel cell are conventionally known. A representative oxygen reduction catalyst is graphitized carbon black supported on a platinum alloy such as Pt or Pt-Co, and a representative hydrogen hydroxide catalyst is Pt-supported carbon black. To improve the reverse potential durability of cation exchange membrane fuel cells, the loading of iridium oxide water electrolysis catalyst added to the anode catalyst layer and cathode catalyst layer is not particularly limited, but is preferably 2% to 50% by mass relative to the oxygen reduction catalyst component or the hydroxide catalyst component, and more preferably 5% to 20%.

[0095] In this embodiment, the preferred loading of iridium oxide in the anode catalyst layer is 0.01 mg / cm² CCM. 2 Up to 0.5 mg / cm 2 The range is particularly preferred to be 0.02 mg / cm³. 2 Up to 0.1 mg / cm 2 If it does not reach 0.01 mg / cm³ 2 If the concentration exceeds 0.5 mg / cm³, then there may be insufficient durability. 2 Therefore, there are situations where the catalyst cost increases despite better performance.

[0096] In this embodiment, the cathode catalyst layer or anode catalyst layer, in addition to containing an oxygen reduction catalyst or fuel oxidation catalyst and a water electrolysis catalyst, also contains a proton-conducting ion polymer. Compared to conventional reverse potential durability catalysts, the iridium oxide-containing cation exchange membrane fuel cell reverse potential durability water electrolysis catalyst of this embodiment can maintain a longer reverse potential durability lifespan with less iridium used.

[0097] [Example]

[0098] The following examples illustrate the invention in more detail, but the invention is not limited to these examples. Furthermore, unless otherwise specified, "parts" and "%" in the examples refer to "parts by mass" and "% by mass," respectively. Additionally, the number of parts added is a value converted from the solids content.

[0099] <Example 1> Preparation of Iridium Oxide (IrO2(IO-1))

[0100] 100.86 g of iridium nitrate solution (manufactured by Furuya Metal) (iridium content 6.94 wt%) was added to 7 L of water and homogenized by stirring and ultrasonic treatment to prepare an iridium compound solution, thereby obtaining a metal compound solution as a raw material. Next, oxygen was introduced into the water at room temperature (25°C) to achieve a saturated dissolved oxygen concentration. Then, the water temperature was adjusted to 420°C and the water pressure was adjusted to 30 MPa to obtain high-temperature and high-pressure water. Next, the metal compound solution obtained above was flowed into the reaction section (4) at a rate of 30 ml / min, and the high-temperature and high-pressure water obtained above was flowed into the reaction section (4) at a rate of 200 ml / min, thereby mixing in the reaction section (4) to obtain an iridium oxide dispersion. Then, the iridium oxide dispersion mixed in the cooling section (8) was cooled to room temperature and pressure (1 atmosphere, 20°C) and recovered using the recovery section (7). Subsequently, after filtration using a membrane filter, the filter cake was dried using an electric dryer at 80°C for 4 hours, thereby obtaining 8.62 g of iridium oxide (IrO2).

[0101] For the obtained iridium oxide, nitrogen adsorption-desorption isotherms were determined using the "Adsorption-Desorption Isotherm" program of the BELSORP-miniII automated specific surface area / pore size distribution measuring device (manufactured by BEL JAPAN, INC.). The adsorption-desorption isotherms are shown below. Figure 2 In the middle. For example Figure 2 As shown, the adsorption-desorption isotherm rises sharply from around 0.7 relative pressure (P / P0), and there is a shift between the adsorption and desorption isotherms between 0.7 and 0.9 relative pressure (P / P0), which is called hysteresis.

[0102] Furthermore, the data from the adsorption-desorption isotherm were analyzed using the BJH method to determine the total micropore volume and average micropore diameter, and the specific surface area was determined using the BET method. The results are shown in Table 1. The total micropore volume in Example 1 was 0.232 cm³. 3 / g, with an average pore diameter of 7.88nm and a specific surface area of ​​118m². 2 / g, yielding iridium oxide with relatively large total micropore volume, average micropore diameter, and specific surface area.

[0103] [Table 1]

[0104]

[0105] <Example 2> Preparation of Iridium Oxide (IrO2(IO-2))

[0106] 28.98 g of iridium nitrate solution (manufactured by Furuya Metal) (iridium content 6.94 wt%) was added to 2 L of water and homogenized by stirring and ultrasonic treatment to prepare an iridium compound solution, thereby obtaining a metal compound solution as raw material. Next, 30% hydrogen peroxide water was added to adjust the water to 1 g / L, and the water temperature was adjusted to 420°C and the water pressure was adjusted to 30 MPa to obtain high-temperature and high-pressure water. Next, the metal compound solution obtained above was flowed into the reaction section (4) at a rate of 30 ml / min, and the high-temperature and high-pressure water obtained above was flowed into the reaction section (4) at a rate of 200 ml / min, thereby mixing in the reaction section (4) to obtain an iridium oxide dispersion. Subsequently, the iridium oxide dispersion mixed in the cooling section (8) was cooled to room temperature and pressure (1 atmosphere, 20°C) and recovered using the recovery section (7). Subsequently, the filter cake was filtered using a membrane filter and then dried using an electric dryer at 80°C for 4 hours to obtain 2.10 g of iridium oxide (IrO2).

[0107] For the obtained iridium oxide, nitrogen adsorption-desorption isotherms were determined using the "Adsorption-Desorption Isotherm" program of the BELSORP-miniII automated specific surface area / pore size distribution measuring device (manufactured by BEL JAPAN, INC.). The adsorption-desorption isotherms are shown below. Figure 3 In the middle. For example Figure 3 As shown, the adsorption-desorption isotherm curves that rise from around 0.8 relative pressure (P / P0) are steep, and there is a shift between the adsorption and desorption isotherms starting from 0.8 relative pressure (P / P0) and there is a so-called hysteresis.

[0108] Furthermore, the data from the adsorption-desorption isotherm were analyzed using the BJH method to determine the total micropore volume and average micropore diameter, and the specific surface area was determined using the BET method. The results are shown in Table 1. The total micropore volume in Example 2 was 0.397 cm³. 3 / g, with an average pore diameter of 12.5nm and a specific surface area of ​​127m². 2 / g, yielding iridium oxide with relatively large total micropore volume, average micropore diameter, and specific surface area.

[0109] <Example 3> Preparation of Iridium Oxide (IrO2(IO3))

[0110] 23.44 g of iridium nitrate solution (manufactured by Furuya Metal) (iridium content 8.66 wt%) was added to 2 L of water, and the solution was homogeneously dissolved by stirring and ultrasonic treatment to prepare an iridium compound solution, thereby obtaining a metal compound solution as a raw material. Next, 30% hydrogen peroxide water was added to adjust the water to 2 g / L, and the synthesis was carried out in the same manner as in Example 2.

[0111] For the obtained iridium oxide, nitrogen adsorption-desorption isotherms were determined using the "Adsorption-Desorption Isotherm" program of the BELSORP-miniII automated specific surface area / pore size distribution measuring device (manufactured by BEL JAPAN, INC.). The adsorption-desorption isotherms are shown below. Figure 4 In the middle. For example Figure 4 As shown, the adsorption-desorption isotherm curves that rise from around 0.8 relative pressure (P / P0) are steep, and there is a shift between the adsorption and desorption isotherms starting from 0.8 relative pressure (P / P0) and there is a so-called hysteresis.

[0112] Furthermore, the data from the adsorption-desorption isotherm were analyzed using the BJH method to determine the total micropore volume and average micropore diameter, and the specific surface area was determined using the BET method. The results are shown in Table 1. The total micropore volume in Example 3 was 0.349 cm³. 3 / g, with an average pore diameter of 11.2nm and a specific surface area of ​​125m². 2 / g, yielding iridium oxide with relatively large total micropore volume, average micropore diameter, and specific surface area.

[0113] <Example 7> Preparation of Iridium Oxide (IrO2(IO-6))

[0114] 1.0 L of iridium hydroxide slurry solution (manufactured by Furuya Metal) (iridium content 0.629 g / L) was adjusted, and NaOH was added to adjust the pH to 12.5 to obtain a metal compound dispersion as a raw material. Next, 30% hydrogen peroxide water was added to adjust the water to 2 g / L, and the synthesis was carried out in the same manner as in Example 3.

[0115] For the obtained iridium oxide, the nitrogen adsorption-desorption isotherm was determined using the "Adsorption-Desorption Isotherm" program of the BELSORP-miniII automated specific surface area / pore size distribution measuring device (manufactured by BEL JAPAN, INC.). The adsorption-desorption isotherm is shown below. Figure 10 In the middle. For example Figure 10As shown, the adsorption-desorption isotherm curves that rise from around 0.8 relative pressure (P / P0) are steep, and there is a shift between the adsorption and desorption isotherms starting from 0.8 relative pressure (P / P0) and there is a so-called hysteresis.

[0116] Furthermore, the data from the adsorption-desorption isotherm were analyzed using the BJH method to determine the total micropore volume and average micropore diameter, and the specific surface area was determined using the BET method. The results are shown in Table 1. The total micropore volume in Example 7 was 0.407 cm³. 3 / g, with an average pore diameter of 11.5nm and a specific surface area of ​​141m². 2 / g, yielding iridium oxide with relatively large total micropore volume, average micropore diameter, and specific surface area.

[0117] <Comparative Example 1> Preparation of Iridium Oxide (IrO2(IO4-))

[0118] Add 50g of tetravalent iridium chloride (H2IrCl6·nH2O manufactured by Furuya Metal) by weight of Ir to a 5L Teflon (registered trademark) beaker, along with 1.6L of pure water. Heat the solution to 80°C and stir for 1 hour to prepare an iridium chloride solution. Next, dissolve 7.8 times the amount of NaOH in 9 times the amount of pure water to prepare a 10% NaOH solution. Add the 10% NaOH solution dropwise to the iridium chloride solution at a rate of 12.5ml / min. After the addition is complete, maintain the temperature at 80°C and stir for 10 hours. Allow the resulting slurry to cool to room temperature and let it stand, then decant the supernatant. Add 1300ml of pure water to the Teflon (registered trademark) beaker containing the remaining slurry, heat again to 80°C, stir for 1 hour, allow to cool to room temperature, let it stand, and decant the supernatant again. This decantation washing process was continued until the conductivity of the supernatant was below 2 mS / m. Subsequently, the supernatant was filtered using a membrane filter, and the filter cake was dried using an electric dryer at 60°C for 20 hours. Finally, it was calcined in an electric furnace at 400°C for 10 hours in the atmosphere to obtain 58 g of iridium oxide (IrO2).

[0119] For the obtained iridium oxide, nitrogen adsorption-desorption isotherms were determined using the "Adsorption-Desorption Isotherm" program of the BELSORP-miniII automated specific surface area / pore size distribution measuring device (manufactured by BEL JAPAN, INC.). The adsorption-desorption isotherms are shown below. Figure 5 In the middle. For example Figure 5As shown, the adsorption-desorption isotherms exhibit a stable sloping curve before the relative pressure (P / P0) reaches 0.1 to 0.8, and there is almost no shift between the adsorption and desorption isotherms near the relative pressure (P / P0) of 0.1 to 0.8, indicating that there is almost no so-called hysteresis.

[0120] Furthermore, the total micropore volume and average micropore diameter were determined by analyzing the adsorption-desorption isotherm data using the BJH method, and the specific surface area was determined by analyzing the data using the BET method. The results are shown in Table 1. The total micropore volume in Comparative Example 1 was 0.083 cm³. 3 / g, with an average pore diameter of 5.03nm and a specific surface area of ​​65.9m². 2 / g, compared with the iridium oxide in Examples 1-3 and Example 7, iridium oxide with significantly smaller total pore volume, average pore diameter and specific surface area was obtained.

[0121] <Comparative Example 2> Preparation of Iridium Oxide (IrO2(IO5))

[0122] Add 3.45 g of tetravalent iridium chloride (H2IrCl6·nH2O manufactured by FuruyaMetal) based on the weight of Ir to a 1 L glass three-necked flask, along with 620 ml of 2-propanol. Stir at room temperature (25 °C) for 1.5 hours to dissolve. Add sodium nitrate (50 times the weight of Ir salt) in powder form, pre-crushed in a mortar, to the solution and stir at room temperature for 1 hour. Concentrate and dry the slurry under reduced pressure for 3 hours using a rotary evaporator at a water bath temperature of 50 °C and a vacuum degree of 50 hPa. Crush the obtained solid in a mortar, place it in an alumina tray, and add it to a muffle furnace at atmospheric pressure. Melt the mixture at 400 °C for 5 hours. After cooling to room temperature, 1L of pure water was added to the molten solidified material for dissolution and extraction. The obtained slurry was filtered using a membrane filter and washed with warm water until the conductivity of the filtrate was below 1mS / m. Then, it was dried using an electric dryer at 60℃ for 16 hours to obtain 4.0g of iridium oxide (IrO2).

[0123] For the obtained iridium oxide, nitrogen adsorption-desorption isotherms were determined using the "Adsorption-Desorption Isotherm" program of the BELSORP-miniII automated specific surface area / pore size distribution measuring device (manufactured by BEL JAPAN, INC.). The adsorption-desorption isotherms are shown below. Figure 6 In the middle. For example Figure 6As shown, the adsorption-desorption isotherms exhibit a steep upward curve before the relative pressure (P / P0) reaches 0.01 to 0.2, but become a smooth, sloping curve before the relative pressure (P / P0) reaches 0.2 to 0.8. Furthermore, there is almost no shift between the adsorption and desorption isotherms before the relative pressure (P / P0) reaches 0.2 to 0.8, indicating no so-called hysteresis, thus obtaining adsorption-desorption isotherms with a typical microporous structure.

[0124] Furthermore, the data from the adsorption-desorption isotherm were analyzed using the BJH method to determine the total micropore volume and average micropore diameter, and the specific surface area was determined using the BET method. The results are shown in Table 1. The total micropore volume in Comparative Example 2 was 0.140 cm³. 3 / g, with an average pore diameter of 2.58nm and a specific surface area of ​​217m². 2 / g, compared with the iridium oxide in Examples 1-3 and Example 7, iridium oxide with a significantly larger specific surface area and significantly smaller total pore volume and average pore diameter was obtained.

[0125] <Example 4> Evaluation of the quality activity of oxygen evolution reaction (OER) as a catalyst for water electrolysis

[0126] For the iridium oxide (IO⁻¹) to (IO⁻⁶) of the above examples and comparative examples, 14.7 mg of iridium oxide was dispersed by ultrasound in a mixed solution of 15 ml of ultrapure water, 10 ml of 2-propanol (hereinafter referred to as IPA), and 0.1 ml of 5% Nafion dispersion (manufactured by DuPont). The resulting dispersion was then added to a rotating disk gold electrode using a micropipette to prepare a 30 μg / cm³ iridium oxide solution. 2 The catalyst-coated electrode was used. A rectangular wave durability test was conducted on the electrode using an electrochemical measurement system (HZ-7000, manufactured by Beidou Electric Co., Ltd.). The electrolyte was a liquid prepared by adjusting a 60% by mass perchloric acid solution (precision analytical reagent, manufactured by Kanto Chemical Co., Ltd.) to 0.1M and degassing it with Ar gas. The measurement method employed a three-electrode approach, using a platinum black hydrogen standard electrode with hydrogen gas passed through it as the reference electrode, and the measurement was performed in a constant temperature bath at 25°C. For the evaluation of the mass activity of the oxygen evolution reaction (hereinafter also referred to as OER), the voltage range of 1.0V–1.8V was scanned at a rate of 10mV / sec, and the current density (mA / cm²) at 1.5V was used. 2 Divide by the amount of catalyst coated on the electrode (30 μg / cm²) 2 The calculation is performed, and the result is shown below. Figure 7And as shown in Table 2. The sample prepared in Example 1 showed 1.28 times higher OER mass activity compared to the sample in Comparative Example 1; the sample prepared in Example 2 showed 1.60 times higher OER mass activity compared to the sample in Comparative Example 1; the sample prepared in Example 3 showed 1.57 times higher OER mass activity compared to the sample in Comparative Example 1; and the sample prepared in Example 7 showed 1.08 times higher OER mass activity compared to the sample in Comparative Example 1. High activity as an anode catalyst for water electrolysis was confirmed in all examples. In contrast, the sample prepared in Comparative Example 2 showed approximately the same 1.02 times higher OER mass activity compared to the sample in Comparative Example 1, which is lower. Despite its higher specific surface area, the catalyst in Comparative Example 2 showed lower OER mass activity, indicating that the contribution of micropores to the catalytic activity of water electrolysis is significantly lower.

[0127] [Table 2]

[0128]

[0129] <Example 5> Single-cell evaluation of solid polymer membrane water electrolysis electrode catalyst

[0130] [5-1) Manufacturing of anode catalyst sheets for water electrolyzers]

[0131] Iridium oxide (IO⁻¹) to (IO⁻⁵) from the above examples and comparative examples were weighed separately, and added to ultrapure water, 2-propanol, and 5% Nafion dispersion (manufactured by DuPont). The mixture was stirred using a magnetic stirrer, followed by dispersion using a powerful ultrasonic disperser. Finally, the mixture was stirred again using a magnetic stirrer to obtain an anode catalyst paste. A 50 μm thick Teflon sheet was placed in close contact with the glass surface of a wire rod coater (PM-9050MC, manufactured by MSTE) with a doctor blade. The anode catalyst paste was added to the surface of the Teflon sheet and coated using a blade scanning method. After air-drying the wet sheet for 15 hours, it was dried using a vacuum dryer at 120°C for 1.5 hours to obtain an anode catalyst sheet. The catalyst coating amount per unit area of ​​the catalyst sheet was adjusted to 1.0 mg / cm². 2 Using a Thomson scalpel, a 9 cm² electrode effective area was cut from the dried anode catalyst sheet to evaluate its required area. 2 The anode catalyst sheet AS-1 using the catalyst of Example 1, AS-2 using the catalyst of Example 2, AS-3 using the catalyst of Example 3, AS-4 using the catalyst of Comparative Example 1, and AS-5 using the catalyst of Comparative Example 2 were obtained to evaluate the durability of the cation exchange membrane water electrolysis single cell.

[0132] [5-2) Manufacturing of cathode catalyst sheets for water electrolyzers]

[0133] Ketjen Black EC300J (manufactured by AKZO NOBEL) was ultrasonically dispersed in deionized water, and high specific surface area platinum black (FHPB manufactured by Furuya Metal, with a BET specific surface area of ​​85 m²) was added to it. 2 A slurry of 50% Pt carbon (by mass) was prepared by ultrasonic dispersion in deionized water and used as a cathode catalyst. 50% Pt carbon powder was weighed and added to ultrapure water, 2-ethoxyethanol, 2-propanol, and 5% Nafion dispersion (manufactured by DuPont). The mixture was stirred and mixed using a magnetic stirrer and a powerful ultrasonic disperser to obtain a cathode catalyst paste. A 50 μm thick Teflon sheet was placed in close contact with the glass surface of a wire rod coater equipped with a doctor blade. The cathode catalyst paste was added to the surface of the Teflon sheet and coated by blade scanning. After air drying for 15 hours, it was dried in a vacuum dryer at 120°C for 1.5 hours to obtain a cathode catalyst sheet. The catalyst coating amount per unit area of ​​the catalyst sheet was adjusted to 1.0 mg / cm². 2 Use a Thomson scalpel to cut a 9cm section of the electrode to the effective area from the dried cathode catalyst sheet. 2 The cathode catalyst sheet CS-1 is circular and used for durability assessment of a single cell in cation exchange membrane water electrolysis.

[0134] [5-3] Manufacturing of CCM (Catalyst Coated Memblen) for water electrolysis cells]

[0135] A cation exchange membrane, Nafion 115 (manufactured by DuPont), was cut into φ70mm pieces. These pieces were then sandwiched in the middle, with the catalyst-coated surfaces of the anode catalyst sheets AS-1, AS-2, AS-3, AS-4 or AS-5 (cut to the effective area of ​​the electrodes) and the cathode catalyst sheet CS-1 as their inner sides, aligned center-to-center. A high-precision hot press (manufactured by TESTER SANGYO) was used at 145°C and a pressure of 0.5kN / cm². 2 Pressurize for 3 minutes. After pressurization, peel off the Teflon (registered trademark) sheets attached to the anode and cathode respectively to obtain the CCM M-1 (AS-1 / CS-1), M-2 (AS-2 / CS-1), M-3 (AS-3 / CS-1) of the catalysts of the examples and the CCM M-4 (AS-4 / CS-1) and M-5 (AS-5 / CS-1) of the catalysts of the comparative examples.

[0136] [5-4] Durability assessment of accelerated degradation in a single cell of solid polymer membrane water electrolysis]

[0137] Prepare an electrode with an effective area of ​​9cm² 2 The water electrolysis cell unit (manufactured by FC Development) was used. A Pt-plated Ti sintered body was used as a gas diffusion layer at the anode, and carbon paper was used as a gas diffusion layer at the cathode. These were assembled into a single cell with the CCMs M-1, M-2, and M-3 of the catalysts from the examples prepared above, or the CCMs M-4 and M-5 of the comparative examples, and secured with bolts. The anode and cathode sides of this single cell were connected to the pure water supply line and gas supply line of the water electrolysis / fuel cell evaluation device (AUTO-PE, manufactured by Toyo Technica), respectively. In the accelerated degradation durability evaluation of the cation exchange membrane water electrolysis single cell, the cell temperature was set to 80°C, and warm pure water with a conductivity of less than 0.1 mS / m was supplied to the anode at a flow rate of 30 ml / min for initial IV characteristics measurement. Subsequently, at a scan rate of 0.5V / second, 1V to 2V and 2V to 1V were performed as one cycle, for a total of 10,000 cycles, and finally the IV characteristics were measured again. Figure 8 The table shows a comparison of accelerated degradation tests in a single water electrolysis cell using the catalysts of the examples and comparative examples as anodes. It illustrates the shift in mass activity per 1000 cycles in durability tests prior to 10,000 cycles for each of the CCMs M-1, M-2, and M-3 of the examples and the CCMs M-4 and M-5 of the comparative examples. Tafel-Plot was performed based on the IV characteristics, and the activity retention rate was calculated from the ratio of mass activity before and after the aforementioned cycle tests at an electrolysis voltage of 1.5V with no internal resistance (IR). Table 3 shows a comparison of the OER mass activity and its retention rate in a single water electrolysis cell using the catalysts of the examples and comparative examples as anodes before and after the cycle tests. Compared to the comparative example catalyst CCM M-4, the initial activities of the catalysts in the examples at 1.5V were 1.97 times higher in M-1, 2.29 times higher in M-2, and 1.63 times higher in M-3. Furthermore, regarding the activity retention rate, the comparative example catalyst CCM M-4 had a retention rate of 63.9%, while the examples' catalysts CCM M-1, M-2, and M-3 had retention rates as high as 74.7%, 71.0%, and 75.3%, respectively. This demonstrates that the examples' catalysts exhibit high performance as anode catalysts for water electrolysis in terms of both activity and durability. On the other hand, it is evident that the initial activity of the catalyst CCM M-5 in Comparative Example 2 was 0.902 times lower than that of the catalyst CCM M-4 in Comparative Example 1. Even with a high activity retention rate of 98.1%, the OER mass activity after durability was far inferior to that of the examples' catalysts.

[0138] [Table 3]

[0139]

[0140] <Example 6> Reverse Potential Durability Assessment of Cation Exchange Membrane Fuel Cell Using Water Electrolysis Catalyst

[0141] [6-1) Manufacturing of electrode catalyst sheets for fuel cells]

[0142] In Example 5.5-2), 50% by mass of Pt carbon-supported material was prepared using highly graphitized carbon black FCX-80 (manufactured by CABOT) instead of Ketjen Black EC300J, and used. Otherwise, it was treated in the same manner as in Example 5.5-2) to obtain cathode catalyst sheet CS-2 for fuel cell reverse potential durability evaluation. The catalyst coating weight per unit area was adjusted to 1.0 mg / cm². 2 Additionally, a catalyst paste was prepared by mixing 50% by weight of Pt carbon supported on FCX-80 with catalyst IO-1 from Example 1 at a weight ratio of 95:5, and used. Otherwise, it was treated in the same manner as in Example 5 (5-2) to obtain anode catalyst sheet AS-6 for fuel cell reverse potential durability evaluation. The catalyst coating amount per unit area was adjusted to 1.0 mg / cm². 2 Furthermore, in preparing AS-6, catalyst IO-4 of Comparative Example 1 was used instead of catalyst IO-1 of Example 1, and otherwise the process was carried out in the same manner as described above to obtain anode catalyst sheet AS-7 for evaluating the reverse potential durability of fuel cells.

[0143] [6-2) Manufacturing of CCM for Fuel Cells]

[0144] A cation exchange membrane, Nafion NRE-212 (manufactured by DuPont), was cut into 100mm × 100mm pieces. These pieces were sandwiched between the cathode catalyst sheet (CS-2) manufactured in Example 6 (6-1) and the anode catalyst sheet (AS-6) containing catalyst IO-1 from Example 1 manufactured in Example 6 (6-1), with their respective catalyst-coated surfaces facing inwards. The pieces were then pressed using a hot press (a high-precision hot press for MEA fabrication, manufactured by TESTER SANGYO) at 140°C with a pressure of 2kN / cm. 2 Apply pressure for 3 minutes. After removal, peel off the Teflon (registered trademark) sheets from both sides to obtain CCM M-6 (AS-6 / CS-2) of Example 6.

[0145] Alternatively, instead of the anode catalyst sheet (AS-6), an anode catalyst sheet (AS-7) was used, and the same treatment as described above was performed to obtain the comparative example CCM M-7 (AS-7 / CS-2).

[0146] [6-3] Evaluation of reverse potential durability of fuel cells

[0147] A PEFC single cell (manufactured by FC Development) was prepared according to the standard cell specifications of JARI (Japan Automobile Research Institute), except that the effective electrode area was set to 30mm × 30mm. A CCM M-6 containing the catalyst of Example 1 as a water electrolysis catalyst was assembled into the single cell, and the fastening bolts were tightened with a torque of 4 Nm. The single cell was connected to the gas supply line of the fuel cell evaluation device (AUTO-PE, manufactured by Toyo Technica). The reverse potential durability test was conducted according to the method of Non-Patent Document 3 as follows: The cell temperature was set to 40°C, hydrogen was humidified to the dew point of 40°C at the anode using a humidifier, and air (Zero Air gas) was humidified to the dew point of 40°C at the cathode using a humidifier. Hydrogen was supplied to the anode at a flow rate of 200 ml / min, and air was supplied to the cathode at a flow rate of 600 ml / min. The fuel cell single cell was operated for 1 hour to determine the initial IV characteristics. Subsequently, the anode gas was completely replaced with nitrogen gas, and 0.2 A / cm was forcibly supplied from an external power source. 2 The reverse potential state is simulated by adjusting the current density. The time-varying change in the tank voltage is monitored, starting from an initial current density of 0.2 A / cm². 2 The time required for the cell voltage to exceed -2.0V from the initial current density was 27,123 seconds, which was taken as the reverse potential endurance time. The same evaluation as in Example 6 was performed on CCM M-7, which included the catalyst of Comparative Example 1 as the water electrolysis catalyst. The current density was increased from 0.2 A / cm². 2 The time required for the current density to start to rise until the tank voltage exceeds -2.0V is 12,216 seconds. Figure 9 The results of the reverse potential durability assessment test are shown in the figure. Figure 9 This indicates that the CCM for fuel cells using the catalyst from the added examples as a water electrolysis catalyst exhibits significantly higher reverse potential durability compared to the CCM for fuel cells using the catalyst from the comparative examples.

[0148] [Explanation of Symbols]

[0149] (1) First source of supply

[0150] (2) Second source of supply

[0151] (3) Heating section

[0152] (4) Reaction section

[0153] (5) Liquid delivery path

[0154] (6) Liquid delivery path

[0155] (7) Recycling Department

[0156] (8) Cooling section

[0157] (9) Mechanism for unidirectional liquid transfer

[0158] (10) Mechanism for unidirectional liquid transfer

[0159] (11) Pressure adjustment mechanism.

Claims

1. An iridium-containing oxide, characterized in that, The total micropore volume, determined by nitrogen adsorption-desorption isotherms and calculated using the BJH method, is 0.20 cm³. 3 The iridium oxide is iridium oxide or iridium oxide, or a composite oxide of an element having a rutile crystal structure and iridium oxide having a rutile crystal structure. The iridium oxide or composite oxide has a rutile crystal structure.

2. The iridium-containing oxide according to claim 1, characterized in that, BET has a specific surface area of ​​100 m² 2 / g or more.

3. A method for manufacturing iridium oxide, characterized in that, It is the manufacturing method of iridium oxide according to claim 1 or 2, and The manufacturing method comprises the following steps: Step A, (1) disperse iridium nanoparticles or iridium hydroxide particles as raw materials in a medium to obtain a dispersion, or (2) dissolve iridium compounds as raw materials in a solvent to obtain a solution; Step B involves heating the water to a temperature above 100°C and pressurizing it to a pressure above 0.1 MPa to create high-temperature, high-pressure water. and Step C: Mix the dispersion or solution obtained in step A with the high-temperature, high-pressure water obtained in step B.

4. The method for manufacturing iridium oxide according to claim 3, characterized in that, In step A, the solvent is at 15–30°C, in which the iridium compound used as a raw material is dissolved.

5. The method for manufacturing iridium-containing oxides according to claim 3 or 4, characterized in that, Step B includes any of the following steps: (1) adding an oxidant that releases oxygen atoms to the water to make the water high temperature and high pressure water; (2) making the water high temperature and high pressure water and then adding an oxidant that releases oxygen atoms; or (3) adding an oxidant that releases oxygen atoms to the water to make the water high temperature and high pressure water, and then adding an oxidant that releases oxygen atoms to the high temperature and high pressure water.

6. A cation exchange membrane water electrolysis anode catalyst, characterized in that... It contains an iridium-containing oxide as described in claim 1 or 2.

7. A reverse potential durability catalyst for cation exchange membrane fuel cells, characterized in that, The electrode catalyst layer contains an iridium-containing oxide as described in claim 1 or 2.

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