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

Abstract

The purpose of the present disclosure is to obtain an iridium-containing oxide that achieves both high activity and high durability and that makes it possible to reduce the amount of catalyst used, when serving as a water splitting electrode catalyst in cation exchange membrane water electrolysis or a cation exchange membrane fuel cell, as a result of controlling the pore structure. An iridium-containing oxide according to the present disclosure is characterized by having a total pore volume of 0.20 cm3 / g or greater, as calculated by the BJH method from a nitrogen adsorption / desorption isotherm measurement, and by having a pore distribution in which the average pore diameter is 7.0 nm or greater.

Description

[Technical Field]

[0001] The present disclosure relates to an iridium-containing oxide that is highly active and has a long life when used as an electrode catalyst in the field of water electrolysis, a method for producing the same, and a catalyst containing the iridium-containing oxide. [Background technology]

[0002] Iridium oxide generally possesses excellent electrical conductivity and catalytic activity for water oxidation reactions. It also has excellent corrosion resistance under strongly acidic and strongly alkaline conditions, making it a popular electrode material. It has traditionally been used as a shape-stabilizing electrode material in fields such as soda electrolysis and electroplating. Recently, nanoparticles of iridium oxide have attracted attention as gas diffusion electrode catalysts for the 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 use as an electrode material for supercapacitors.

[0003] In particular, the catalysts that are expected to be widely used in practical applications as water electrolysis catalysts are cation exchange membrane water electrolysis anode catalysts and cation exchange membrane fuel cell reverse potential durable catalysts.

[0004] Cation exchange membrane water electrolysis has recently been attracting attention as a means of storing renewable energy in preparation for the coming hydrogen energy society, and development of larger, more efficient systems up to the megawatt level is accelerating.

[0005] Furthermore, development of cation exchange membrane fuel cells is accelerating as a clean means of transportation in the coming hydrogen energy society.

[0006] A cation exchange membrane water electrolysis cell is constructed by joining multiple membrane electrode assemblies (MEA) in series via separators. Each MEA is a catalyst coated membrane (CCM), which is made up of a cation exchange polymer electrolyte membrane such as Nafion (registered trademark) sandwiched between an anode catalyst layer and a cathode catalyst layer. The CCM is further sandwiched between gas diffusion layers on both sides of the membrane electrode assembly. When water is supplied to the anode catalyst layer, the reaction shown in Chemical Formula 1 occurs in the anode catalyst layer, and the reaction shown in Chemical Formula 2 occurs in the cathode catalyst layer, generating oxygen (O2) on the anode side and hydrogen (H2) on the cathode side. (Chemical formula 1)H2O(liq.)→ 1 / 2O2(g) + 2H + + 2e - (C2)2H + + 2e - → H2(g) The rate-determining step of the overall reaction is the oxidation of water on the anode side, the oxygen evolution reaction, and the mass activity of the anode catalyst for the oxygen evolution reaction (OER) is an important factor that determines the efficiency of the system.

[0007] Regarding oxygen generating anodes used in industrial electrolysis, a technology has been disclosed that reduces the oxygen generating overvoltage and enables the production of highly active and durable electrodes by setting the crystallite size of iridium oxide to 9.7 nm or less and increasing the degree of crystallinity (see, for example, Patent Document 1).

[0008] On the other hand, in a cation exchange membrane fuel cell, the reaction (chemical formula 3) occurs at the cathode and the reaction (chemical formula 4) occurs at the anode, and an electromotive force is generated as a whole by the reaction (chemical formula 5), ​​which is connected to an external circuit for use. (C3)1 / 2O2(g) + 2H + + 2e - → H2O (Chemical formula 4)H2(g)→ 2H + + 2e - (C5)1 / 2O2(g)+ H2(g)→ H2O However, when the fuel cell is started or stopped, if there is an insufficient supply of hydrogen to the anode side, the cell will be in a fuel-starved state. When a current is forced to flow from the other cells connected in series to this fuel-starved cell, the reaction shown below (Chemical Formula 6) will occur, causing oxidation and corrosion of the platinum-supported carbon-based electrode catalyst, rendering the fuel cell unusable. (C6)C + 2H2O → CO2+ 4H + + 4e - (7)2H2O → O2+ 4H + + 4e - In order to suppress the oxidative corrosion of the carbon support by water under such reverse potential conditions, the addition of an iridium oxide nanoparticle catalyst has been investigated as an electrocatalyst that electrolyzes water through the reaction of (Chemical Formula 7) (see, for example, Patent Document 2).

[0009] Although there is no mention of iridium oxide as a method for producing microparticles, a technique has been disclosed for producing microparticles using high-temperature, high-pressure water, in which water is passed through a pressurizing means and a heating means to become high-temperature, high-pressure water in a supercritical or subcritical state, and this high-temperature, high-pressure water and a fluid raw material are joined in a mixing section, mixed, and then guided to a reactor, in which the fluid raw material is cooled to a temperature lower than the critical temperature of water before being joined with the high-temperature, high-pressure water (see, for example, Patent Document 3).

[0010] As methods for producing iridium oxide catalysts for oxygen evolution reactions in cation exchange membrane water electrolysis, the sol-gel method, aqueous solution hydrolysis method, Adams fusion method, etc. have been disclosed in reviews (see, for example, Non-Patent Document 1).

[0011] A method for producing iridium oxide for use as an anode catalyst for oxygen generation in water electrolysis has been disclosed, in which an iridium salt is hydrolyzed using aqueous ammonia, a nitrate is added to the intermediate, and the resulting mixture is heated to dryness and melted (see, for example, Patent Document 4).

[0012] A method for testing the reverse potential durability of the anode of a cation exchange membrane fuel cell has been disclosed, and a comparison of durability between cases where a water electrolysis catalyst component is added to the anode and cases where it is not added is disclosed (see, for example, Non-Patent Document 2). [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Special Publication No. 2014-526608 [Patent Document 2] Special Publication No. 2003-508877 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-21724 [Patent Document 4] Japanese Patent Publication No. 2020-132465 [Non-patent literature]

[0014] [Non-Patent Document 1] PEM Electrolysis for Hydrogen Production-Principales and Applications,CRC Press(2016),53-55 [Non-patent document 2] Tsutomu Iokura and Kazuaki Yasuda, Abstracts of the 59th Battery Symposium (November 2018, Osaka), Lecture Number 1H23 Summary of the Invention [Problem to be solved by the invention]

[0015] Iridium is an expensive precious metal, with an annual production of only 9 tons compared to 454 tons for platinum group metals. However, large amounts of iridium must be used as an electrode catalyst, and there is a need to reduce the amount used and the frequency of electrode replacement. Therefore, there is a need for a highly efficient and durable electrode catalyst.

[0016] In developing a highly efficient iridium oxide, the inventors searched for a method for producing an iridium oxide with a large specific surface area in order to achieve high activity. However, they found that increasing the specific surface area improves catalytic activity but reduces durability. Therefore, it is important to increase catalytic activity while maintaining durability.

[0017] Iridium oxide has traditionally been used as an anode catalyst for oxygen evolution in industrial electrolysis. However, in Patent Document 1, the highly crystalline iridium oxide had a large crystallite size of about 6 nm to 10 nm, resulting in a low specific surface area and insufficient activity despite its durability.

[0018] Patent Document 2 discloses the remarkable effects of ruthenium oxide and a mixed oxide of ruthenium oxide and iridium oxide as water electrolysis catalyst components, but it states that the effect of iridium oxide alone is durable but insufficient in activity.

[0019] In Patent Document 3, which discloses a method for producing fine particles of metals, metal oxides, etc., repeated heating and cooling processes cause the crystallite size to repeatedly increase and decrease in size, which can lead to variations in crystallite size and makes it highly likely that the durability and catalytic activity will differ depending on the particle.

[0020] In Patent Document 4, the specific surface area is 150 m 2 / g or more and an average pore diameter of 2.3 nm or more and 4.0 nm or less has been disclosed, and although the activity is high, the durability is insufficient.

[0021] Non-Patent Document 1 reports various conventionally known methods for producing iridium oxide as an oxygen evolution reaction catalyst for cation exchange membrane water electrolysis, but does not describe a hydrothermal synthesis method using supercritical water or subcritical water in the reaction field.

[0022] Non-Patent Document 2 describes iridium black as a reverse potential durable water electrolytic catalyst component, but does not teach the catalytic action of iridium oxide.

[0023] Therefore, an object of the present disclosure is to provide an iridium-containing oxide that can exhibit high activity and high durability when used as an electrode catalyst by controlling the pore structure of the iridium oxide, and a method for producing the same. Another object of the present disclosure is to provide a highly active and durable water electrolysis catalyst containing such an iridium-containing oxide for use as a cation exchange membrane water electrolysis anode or a reverse potential durable electrode of a cation exchange membrane fuel cell. [Means for solving the problem]

[0024] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by an iridium-containing oxide having a specific pore structure that has not been found in the past and a method for producing the same, thereby completing the present invention. That is, the iridium-containing oxide has a total pore volume of 0.20 cm3 calculated by the BJH method from nitrogen adsorption / desorption isotherm measurements. 3 / g or more and has a pore distribution with an average pore diameter of 7.0 nm or more. The iridium-containing oxide is iridium oxide or a composite oxide of iridium and an element whose oxide has a rutile crystal structure, and the iridium oxide or composite oxide has a rutile crystal structure. It is characterized by:

[0025] In the iridium-containing oxide according to the present invention, it is preferable that the relative pressure (P / P) of the nitrogen adsorption / desorption isotherm has hysteresis in the region of 0.7 to 0.95. Furthermore, the BET specific surface area of ​​the oxide is preferably 100 m 2 / g or more, a catalyst having higher activity and durability can be obtained.

[0026] In the iridium-containing oxide according to the present invention, the iridium-containing oxide is in the form of a powder or dispersed particles, and the powder or dispersed particles have a total pore volume of 0.20 cm 3 calculated by the BJH method from nitrogen adsorption / desorption isotherm measurement. 3 / g or more and an average pore diameter as large as 7.0 nm. Furthermore, it is preferable that the relative pressure (P / P0) of the adsorption / desorption isotherm has hysteresis in the range of 0.7 to 0.95, and the BET specific surface area is 100 m 2 / g is preferable.

[0028] The method for producing an iridium-containing oxide according to the present invention is characterized by comprising: (1) step A of dispersing raw material iridium nanoparticles or iridium hydroxide particles in a medium to obtain a dispersion, or (2) step A of dissolving raw material iridium compound in a solvent to obtain a solution; step B of converting water into high-temperature, high-pressure water under high-temperature, high-pressure conditions of a heating temperature of 100°C or higher and a pressurization pressure of 0.1 MPa or higher; and step C of mixing the dispersion or solution obtained in step A with the high-temperature, high-pressure water obtained in step B.

[0029] In the method for producing an iridium-containing oxide according to the present invention, it is preferable that the solvent is at 15 to 30° C. and the raw material iridium compound is dissolved in the solvent in step A. An iridium-containing oxide having a large total pore volume can be produced, and an iridium-containing oxide having high activity and high durability can be obtained.

[0030] In the method for producing an iridium-containing oxide according to the present invention, step B preferably includes any one of the following steps: (1) adding an oxidizing agent that releases oxygen atoms to the water to form high-temperature, high-pressure water, (2) adding an oxidizing agent that releases oxygen atoms to the water to form high-temperature, high-pressure water, or (3) adding an oxidizing agent that releases oxygen atoms to the water to form high-temperature, high-pressure water, and further adding an oxidizing agent that releases oxygen atoms to the high-temperature, high-pressure water. The oxidation reaction can be efficiently carried out in step C.

[0031] The cation exchange membrane water electrolysis anode catalyst according to the present invention is characterized by containing the iridium-containing oxide according to the present invention. Because it is synthesized under hydrothermal conditions, it has a unique pore structure, with a particularly large average pore diameter of 7.0 nm or more. This increases the affinity of the ionomer molecules, such as Nafion®, which serve as binders for cation exchange resins with an average molecular diameter of approximately 10 nm during the preparation of the cation exchange membrane water electrolysis anode, thereby enabling the provision of highly active and durable electrodes.

[0032] Furthermore, the reverse potential durable catalyst for a cation exchange membrane fuel cell according to the present invention is characterized by containing the iridium-containing oxide according to the present invention in an electrode catalyst layer. Because it is synthesized under hydrothermal conditions, it has a unique pore structure, and in particular, the average pore diameter is large, at 7.0 nm or more. Therefore, when preparing electrodes for a cation exchange membrane fuel cell, it has high affinity with ionomer molecules, such as Nafion (registered trademark), which serve as binders for cation exchange resins with an average molecular diameter of about 10 nm, making it possible to provide electrodes that are highly active and have excellent durability. [Effects of the Invention]

[0033] The iridium-containing oxide according to the present disclosure has a total pore volume of 0.20 cm 3 calculated by the BJH method from nitrogen adsorption / desorption isotherm measurements. 3 / g or more and an average pore diameter of 7.0 nm or more. More preferably, the nitrogen adsorption / desorption isotherm has hysteresis in the relative pressure (P / P0) range of 0.7 to 0.95, and even more preferably, the BET specific surface area is 100 m 2 / g or more. When an iridium-containing oxide having such a pore distribution and physical properties is used as a cation exchange membrane water electrolysis anode catalyst or a reverse potential durability catalyst for a cation exchange membrane fuel cell, an electrode with unprecedented high activity and excellent durability can be obtained. Furthermore, the method for producing an iridium-containing oxide according to the present disclosure can produce an iridium-containing oxide having a unique pore structure with a large pore volume and a large average pore diameter, and can obtain an iridium-containing oxide that has high activity and high durability when used as an electrode catalyst.

[0034] According to the present disclosure, when an iridium-containing oxide is used as an anode catalyst for cation exchange membrane water electrolysis, its high activity and durability make it possible to reduce the amount of iridium used per unit electrode area to approximately 1 / 2 to 1 / 5 of the conventional amount. Furthermore, adding an iridium-containing oxide to a platinum-on-carbon electrode catalyst in a cation exchange membrane fuel cell significantly improves reverse potential durability. Because the effects of fuel starvation are more severe on the anode side of a cation exchange membrane fuel cell, the water electrolysis catalyst is typically mixed with a hydrogen oxidation catalyst component in the anode. However, because the effects of reverse potential can also occur on the cathode side, the catalyst can also be mixed with an oxygen reduction catalyst component in the cathode catalyst layer. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is an example of an apparatus for producing an iridium-containing oxide according to the present embodiment. [Figure 2] 1 shows the nitrogen adsorption / desorption isotherm of the iridium-containing oxide in Example 1. [Figure 3] 1 shows nitrogen adsorption / desorption isotherms of iridium-containing oxide in Example 2. [Figure 4] 1 shows nitrogen adsorption / desorption isotherms of iridium-containing oxides in Example 3. [Figure 5] 1 shows the nitrogen adsorption / desorption isotherm of the iridium-containing oxide in Comparative Example 1. [Figure 6] 1 shows the nitrogen adsorption / desorption isotherm of the iridium-containing oxide in Comparative Example 2. [Figure 7] 1 is a graph showing a comparison of the OER mass activity of catalysts of the examples and comparative examples. [Figure 8] 1 is a graph showing a comparison of accelerated deterioration tests of single water electrolysis cells using catalysts of Examples and Comparative Examples as the anode. [Figure 9] 10 is a graph showing a comparison of a reverse potential durability test of a single fuel cell using electrodes in which the catalysts of the Examples and Comparative Examples are added to the anode. [Figure 10] 10 is a nitrogen adsorption / desorption isotherm of the iridium-containing oxide in Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will now be described in detail with reference to the following embodiments, but the present invention is not limited to these descriptions. Various modifications may be made to the embodiments as long as the effects of the present invention are achieved.

[0037] The iridium-containing oxide according to this embodiment has a total pore volume of 0.20 cm 3 calculated by the BJH method from nitrogen adsorption / desorption isotherm measurement. 3 The iridium-containing oxide according to the present invention is characterized in that it has a pore distribution with a pore size of 1.0 nm or more and an average pore diameter of 7.0 nm or more. In the iridium-containing oxide according to the present invention, it is preferable that the relative pressure (P / P) of the nitrogen adsorption / desorption isotherm has hysteresis in the region of 0.7 to 0.95, and that the BET specific surface area is 100 m 2 / g or more is even more preferable. This allows for the production of a catalyst with higher activity and durability. 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.

[0038] The iridium-containing oxide according to this embodiment is characterized by a nitrogen adsorption / desorption isotherm that is relatively flat from a relative pressure (P / P) of approximately 0.05 to 0.7, and then rises sharply from approximately 0.7 to 0.95. Furthermore, it is preferable for the isotherm to have a so-called hysteresis, in which a deviation occurs in the isotherm during the adsorption and desorption process. Hysteresis is believed to be caused by the phenomenon of capillary condensation of liquid nitrogen during the desorption process, and is considered to be a phenomenon unique to mesopore structures. The iridium-containing oxide according to this embodiment has a pore distribution that is almost devoid of micropores with a pore diameter of less than 2.0 nm or mesopores with a relatively small diameter of 2.0 nm to 5.0 nm, with the majority of pores being relatively large mesopores with a pore diameter of 5.0 nm to 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 0.20 cm. 3 / g or more, resulting in a large pore volume.

[0039] The iridium-containing oxide according to this embodiment is, in addition to iridium oxide (IrO), a composite oxide of Ir and an element having a rutile crystal structure, such as TiO, NbO, TaO, SnO, or RuO, and has an average pore diameter of 7.0 nm or more and a total pore volume of 0.20 cm. 3 / g or more. The iridium oxide or the composite oxide of iridium and an element whose oxide has a rutile crystal structure preferably has a rutile crystal structure. Note that the iridium-containing oxide according to this embodiment may contain impurities other than iridium and the additive element as long as they do not impair the properties of the oxide.

[0040] In the iridium-containing oxide according to this embodiment, the BET specific surface area is preferably 100 m 2 / g or more. The average pore diameter is 7.0 nm or more, and the total pore volume is 0.20 cm 3 / g or more, even if the specific surface area is large, durability is not reduced and activity is improved.

[0041] In the iridium-containing oxide according to this embodiment, the iridium-containing oxide is a monodisperse nanoparticle powder or aggregate particles thereof, and it is believed that the particle surfaces and aggregate interfaces form a unique pore structure.

[0042] The ratio of iridium to oxygen in the iridium-containing oxide according to this embodiment is preferably 30:70 to 40:60 in atomic %, and more preferably 32:68 to 34:66. When the iridium-containing oxide according to this embodiment is a composite oxide of Ir and an element that has a rutile crystal structure, such as TiO2, NbO2, TaO2, SnO2, or RuO2, the ratio of the total amount of iridium and the element that has a rutile crystal structure to oxygen is preferably 30:70 to 40:60 in atomic %, and more preferably 32:68 to 34:66.

[0043] The method for producing an iridium-containing oxide according to this embodiment includes the steps of: (1) dispersing raw material iridium nanoparticles or iridium hydroxide particles in a medium to obtain a dispersion; or (2) dissolving raw material iridium compounds in a solvent to obtain a solution; (3) converting water into high-temperature, high-pressure water under high-temperature, high-pressure conditions of a heating temperature of 100°C or higher and a pressurization pressure of 0.1 MPa or higher; and (4) mixing the dispersion or solution obtained in step A with the high-temperature, high-pressure water obtained in step B.

[0044] An example of an apparatus for producing an iridium-containing oxide will now be described with reference to FIG. 1. The apparatus for producing an iridium-containing oxide 100 according to this embodiment includes at least a first supply source (1) of a dispersion or solution containing iridium, a second supply source (2) of a liquid containing water, a heating unit (3) for heating the liquid containing water, a reaction unit (4) for joining the dispersion or solution containing iridium and the liquid containing water, a liquid transfer route (5) connecting the first supply source (1) and the reaction unit (4), a liquid transfer route (6) connecting the second supply source (2) and the reaction unit (4), a recovery unit (7) connected to the reaction unit (4) via a pipe and for recovering the generated reaction product, and a cooling unit (8) between the reaction unit (4) and the recovery unit (7). A pressure adjustment mechanism (11) is connected to the recovery unit (7). The pressure adjustment mechanism (11) may be connected between the cooling unit (8) and the recovery unit (7). According to the apparatus for producing an iridium-containing oxide according to this embodiment, it is possible to stably produce particles of an iridium-containing oxide.

[0045] In the apparatus for producing an iridium-containing oxide according to this embodiment, a dispersion or solution containing iridium is mixed with high-temperature, high-pressure water in the reaction section (4), thereby oxidizing the iridium in the dispersion or solution to produce an iridium-containing oxide. The high-temperature, high-pressure water is obtained by the heating section (3). The high-temperature, high-pressure water includes not only water in a high-temperature, high-pressure state, but also water containing an oxidizing agent such as oxygen, hydrogen peroxide, or ozone, which has been brought to a high-temperature, high-pressure state.

[0046] The liquid transfer route (5) connecting the first supply source (1) and the reaction section (4) includes a pipe. One method for adjusting the flow rate of the liquid flowing through the pipe is to place the first supply source (1) at a position higher than the reaction section (4) and utilize the difference in elevation. In this case, the iridium-containing dispersion or solution can be transported from the first supply source (1) to the reaction section (4) using only the pipe. In this case, a valve for throttling the flow rate, such as a needle valve or a stop valve, may be placed in the liquid transfer route (5).

[0047] The liquid transfer route (6) connecting the second supply source (2) and the reaction section (4) includes a pipe. One method for adjusting the flow rate of the liquid flowing through the pipe is to place the second supply source (2) at a higher position than the reaction section (4) and utilize the difference in elevation. In this case, the liquid containing water can be transported from the second supply source (2) to the reaction section (4) using only the pipe. In this case, a valve for throttling the flow rate, such as a needle valve or a stop valve, may be placed in the liquid transfer route (6), similar to the liquid transfer route (5).

[0048] The apparatus for producing an iridium-containing oxide according to this embodiment may include mechanisms (9) and (10) for unidirectionally transferring the liquid flowing in either the liquid feed route (5) or the liquid feed route (6), or both. The apparatus for producing an iridium-containing oxide 100 shown in FIG. 1 has mechanisms (9) and (10) in both the liquid feed route (5) and the liquid feed route (6). In this embodiment, the flow rates and flow velocities of the iridium-containing dispersion or solution and the water-containing liquid can be stably determined in the liquid feed route (5) and the liquid feed route (6), thereby enabling stable production of an iridium-containing oxide.

[0049] The mechanisms (9) and (10) are means for adjusting the flow rate of the liquid flowing through the pipe, and are, for example, plungers, cylinders, or regulators.

[0050] The dispersion medium for iridium nanoparticles or iridium hydroxide particles can be freely selected as long as it is a medium in which dispersion is possible, such as water, an organic solvent, etc. The solvent for dissolving the iridium compound can be freely selected as long as it is a solvent that is liquid at room temperature, such as water, an organic solvent, etc. In this embodiment, room temperature is 15°C to 30°C, and preferably 20°C to 25°C.

[0051] [Process A (1)] The particle size of the raw material iridium nanoparticles is preferably 3.0 nm or less, and more preferably 2.5 nm or less. If the particle size of the iridium nanoparticles is larger than 3.0 nm, iridium oxide particles of the desired crystallite size may not be obtained when iridium is reacted with oxygen, and oxidation may be insufficient. Furthermore, the particle size of the iridium hydroxide particles is preferably 3.0 nm or less, and more preferably 2.5 nm or less. If the iridium hydroxide particles are larger than 3.0 nm, iridium oxide particles of the desired crystallite size may not be obtained when iridium hydroxide is reacted with oxygen, and oxidation may be insufficient when iridium hydroxide is reacted with oxygen.

[0052] By adding iridium nanoparticles or iridium hydroxide particles that satisfy the above conditions to a medium, it is possible to obtain a dispersion in which the iridium nanoparticles or iridium hydroxide particles are dispersed in the medium, such as water or ethanol.

[0053] [Process A (2)] The iridium compound used as the raw material may be any of iridium-containing metal salts such as iridium nitrate, iridium sulfate, iridium acetate, and iridium chloride, as well as metal complexes such as iridium acetylacetonate and iridium carbonyl, but is preferably an iridium nitrate, iridium sulfate, or iridium acetate. Adding the iridium compound to a solvent can yield a solution in which the iridium compound is dissolved in the solvent. Examples of the solvent include water for iridium-containing metal salts and ethanol or ethyl acetate for iridium-containing metal complexes. In step A(2), the solvent is preferably at room temperature, e.g., 15°C to 30°C, and the raw iridium compound is dissolved in the solvent.

[0054] [Process B] Separately from step A, high-temperature, high-pressure water is obtained by heating water to a temperature of 100°C or higher and applying a 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. The heating temperature is, for example, 400°C. The pressure is 0.1 MPa or higher, more preferably 0.5 MPa or higher, and most preferably 22.1 MPa or higher. The pressure is, for example, 30 MPa. Pure water is preferably used as the water for obtaining high-temperature, high-pressure water, but a solution in which an oxidizing agent such as oxygen, hydrogen peroxide, or ozone is dissolved in water may also be used.

[0055] In order to efficiently carry out the oxidation reaction in step C, step B preferably includes any one of the following steps: (1) adding an oxidizing agent that releases oxygen atoms to the water, and then converting the water into high-temperature, high-pressure water; (2) converting the water into high-temperature, high-pressure water and then adding an oxidizing agent that releases oxygen atoms; or (3) adding an oxidizing agent that releases oxygen atoms to the water, converting the water into high-temperature, high-pressure water, and then adding an oxidizing agent that releases oxygen atoms to the high-temperature, high-pressure water. In the case of oxygen gas, it is preferable to convert water with a saturated oxygen concentration into a high-temperature, high-pressure state. Examples of oxidizing agents that release oxygen atoms include oxygen, hydrogen peroxide, and ozone.

[0056] [Process C] The dispersion or solution obtained in step A is mixed with the high-temperature, high-pressure water obtained in step B. The conditions for mixing are not particularly limited, but when a small-capacity pipe or the like is used, the pipe containing the dispersion or solution obtained in step A and the pipe containing the high-temperature, high-pressure water obtained in step B are joined together to produce a dispersion in which the iridium-containing oxide is dispersed in the high-temperature, high-pressure water. When a large-capacity container or the like is used, the dispersion or solution obtained in step A and the high-temperature, high-pressure water obtained in step B are placed in the container and mixed by stirring or the like to produce a dispersion in which the iridium-containing oxide is dispersed in the high-temperature, high-pressure water. In Figure 1, the mixing is performed in the reaction section (4).

[0057] The solution obtained in step C is cooled, for example, in the cooling section (8) shown in Figure 1, and then recovered in the recovery section (7). Thereafter, the sample is separated and washed by filtration, centrifugation, etc., and dehydrated in a dryer to obtain iridium-containing oxide nanoparticles.

[0058] [Cation exchange membrane water electrolysis anode catalyst] Next, the cation exchange membrane water electrolysis anode catalyst containing the iridium-containing oxide according to this embodiment will be described. Various cation exchange membranes, such as perfluorosulfonic acid-based, sulfonated polyethylene ether ketone-based, and sulfonated polybenzimidazole-based, are used as cation exchange membranes for water electrolysis cells. 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), and Aquivion (registered trademark, manufactured by Solvay) are preferred. Platinum black or platinum-supported carbon black catalysts, which have high hydrogen generation reaction activity, are typically used as cathode catalysts for cation exchange membrane water electrolysis cells. The iridium-containing oxide according to this embodiment is mixed with the same cation exchange resin ionomer as the cation exchange membrane component in a solvent by stirring to prepare an anode catalyst ink. The ratio of iridium-containing oxide to ionomer is not particularly limited, but a ratio of 1:0.2 to 1:0.05 is preferably used, and a ratio of 1:0.15 to 1:0.07 is more preferably used. The solvent is not particularly limited, but water or a mixture of water and a lower aliphatic alcohol such as ethanol, propanol, or butanol is preferably used. Similarly, a cathode catalyst is mixed with an ionomer to prepare a cathode catalyst ink. The method for preparing a CCM by coating the anode catalyst layer and cathode catalyst layer on the front and back surfaces of a cation exchange membrane using the anode catalyst ink and cathode catalyst ink prepared in this manner is not particularly limited, and known methods can be used, such as direct coating methods such as bar coating and spray coating, or coating the anode catalyst layer and cathode catalyst layer separately on Teflon (registered trademark) films in advance and then transferring them using hot pressing, etc. The amount of the cation exchange membrane water electrolysis anode catalyst according to this embodiment supported on the cation exchange membrane is not particularly limited, but is preferably 2.0 mg / cm. 2 ~0.1mg / cm 2 , and more preferably 1.0 mg / cm 2 ~0.3mg / cm 2 In this way, a current of 1.0 A / cm is obtained with a much smaller amount of iridium than that used in conventional cation exchange membrane water electrolysis cells. 2~5.0A / cm 2 This makes it possible to operate a water electrolysis cell at a higher current density than conventional methods and at a lower electrolysis voltage of 1.5 V to 1.7 V (internal resistance-free), and provides an anode catalyst that can maintain durability for tens of thousands of hours or more.

[0059] [Reverse potential durable catalyst for cation exchange membrane fuel cells] Next, we will describe a reverse-potential-durable water electrolysis catalyst for a cation exchange membrane fuel cell containing an iridium-containing oxide according to this embodiment in the electrode catalyst layer. Various cation exchange membranes, such as perfluorosulfonic acid-based, sulfonated polyethylene ether ketone-based, and sulfonated polybenzimidazole-based membranes, are used as cation exchange membranes in cation exchange membrane fuel cells. 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), and Aquivion (registered trademark, manufactured by Solvay) are preferred. Conventional oxygen reduction catalyst components for the cathode and hydrogen oxidation catalyst components for the anode of a cation exchange membrane fuel cell can be used. A typical oxygen reduction catalyst is graphitized carbon black supported on Pt or a platinum alloy such as Pt-Co, and a typical hydrogen oxidation catalyst is Pt supported on carbon black. The amount of the iridium-containing oxide water electrolysis catalyst added to the anode catalyst layer and the cathode catalyst layer to improve the reverse potential durability of the cation exchange membrane fuel cell is not particularly limited, but is preferably 2% to 50%, more preferably 5% to 20%, in mass percentage relative to the oxygen reduction catalyst component or the hydrogen oxidation catalyst component.

[0060] In this embodiment, the amount of iridium-containing oxide supported in the anode catalyst layer is 0.01 mg / cm per CCM unit area. 2 to 0.5 mg / cm 2 The range of 0.02 mg / cm is preferred. 2 to 0.1 mg / cm 2 is particularly preferred. 2 If it is less than 0.5 mg / cm, durability may be insufficient. 2If the catalyst exceeds this limit, the cost of the catalyst may increase in proportion to the performance.

[0061] In this embodiment, the cathode catalyst layer and the anode catalyst layer contain a proton-conductive ionomer in addition to the oxygen reduction catalyst, the fuel oxidation catalyst, and the water electrolysis catalyst. The reverse potential durability water electrolysis catalyst for a cation exchange membrane fuel cell using an iridium-containing oxide in this embodiment can maintain a longer life of reverse potential durability with a smaller amount of iridium used than conventional reverse potential durability catalysts. [Example]

[0062] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of added parts is a value calculated on a solid content basis.

[0063] Example 1: Preparation of iridium oxide IrO2 (IO-1) 100.86 g of iridium nitrate solution (Furuya Metal) (iridium content: 6.94 wt%) was added to 7 L of water, and a homogeneous iridium compound solution was prepared by stirring and ultrasonic treatment. This resulted in a metal compound solution serving as the raw material. Next, oxygen was bubbled into the water at room temperature (25°C) to achieve a saturated dissolved oxygen concentration. The water temperature was then adjusted to 420°C, and the water pressure was adjusted to 30 MPa to obtain high-temperature, high-pressure water. The resulting metal compound solution was then flowed into the reaction section (4) at a rate of 30 mL / min, and the resulting high-temperature, high-pressure water was also flowed into the reaction section (4) at a rate of 200 mL / min. Mixing was then carried out in the reaction section (4), yielding an iridium oxide dispersion. The mixed iridium oxide dispersion was then cooled to room temperature and atmospheric pressure (1 atmosphere, 20°C) in the cooling section (8) and recovered in the recovery section (7). Thereafter, the mixture was filtered through a membrane filter, and the filter cake was dried in an electric dryer at 80°C for 4 hours to obtain 8.62 g of iridium oxide IrO2.

[0064] The nitrogen adsorption and desorption isotherms of the obtained iridium oxide were measured using the "Adsorption and Desorption Isotherm" measurement program of the BELSORP-mini II automatic specific surface area / pore distribution analyzer (manufactured by BEL JAPAN, INC.). The adsorption and desorption isotherms are shown in Figure 2. As shown in Figure 2, the adsorption and desorption isotherms showed a steep rise from a relative pressure (P / P0) of approximately 0.7, and there was a discrepancy between the adsorption and desorption isotherms between relative pressures (P / P0) of 0.7 and 0.9, indicating the presence of so-called hysteresis.

[0065] The data on this adsorption / desorption isotherm was analyzed by the "BJH method" to determine the total pore volume and average pore diameter, and analyzed by the "BET method" to determine the specific surface area. The results are shown in Table 1. The total pore volume in Example 1 was 0.232 cm 3 / g, average pore diameter 7.88nm, specific surface area 118m 2 / g, and iridium oxide with a relatively large total pore volume, average pore diameter, and specific surface area was obtained.

[0066] [Table 1]

[0067] Example 2: Preparation of iridium oxide IrO2 (IO-2) 28.98 g of iridium nitrate solution (Furuya Metal) (iridium content: 6.94 wt%) was added to 2 L of water, and a homogeneous iridium compound solution was prepared by stirring and ultrasonic treatment. This resulted in a metal compound solution serving as the raw material. Next, 30% hydrogen peroxide water was added to adjust the water concentration to 1 g / L, and the water temperature was adjusted to 420°C and the water pressure to 30 MPa to obtain high-temperature, 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, high-pressure water obtained above was flowed into the reaction section (4) at a rate of 200 mL / min. Mixing was carried out in the reaction section (4), yielding an iridium oxide dispersion. The mixed iridium oxide dispersion was then cooled to room temperature and atmospheric pressure (1 atmosphere, 20°C) in the cooling section (8) and recovered in the recovery section (7). Thereafter, the mixture was filtered through a membrane filter, and the filter cake was dried in an electric dryer at 80°C for 4 hours to obtain 2.10 g of iridium oxide IrO2.

[0068] The nitrogen adsorption and desorption isotherms of the obtained iridium oxide were measured using the "Adsorption and Desorption Isotherm" measurement program of the BELSORP-mini II automatic specific surface area / pore distribution analyzer (manufactured by BEL JAPAN, INC.). The adsorption and desorption isotherms are shown in Figure 3. As shown in Figure 3, the adsorption and desorption isotherms rise at a relative pressure (P / P0) of approximately 0.8, and a sharp curve is obtained. Furthermore, a difference between the adsorption and desorption isotherms occurs at a relative pressure (P / P0) of 0.8, indicating the presence of so-called hysteresis.

[0069] The data on this adsorption / desorption isotherm was analyzed by the "BJH method" to determine the total pore volume and average pore diameter, and analyzed by the "BET method" to determine the specific surface area. The results are shown in Table 1. The total pore volume in Example 2 was 0.397 cm 3 / g, average pore diameter 12.5nm, specific surface area 127m 2 / g, and iridium oxide with a relatively large total pore volume, average pore diameter, and specific surface area was obtained.

[0070] Example 3: Preparation of iridium oxide IrO2 (IO-3) 23.44 g of iridium nitrate solution (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 obtain a metal compound solution as the raw material. Next, synthesis was performed in the same manner as in Example 2, except that 30% hydrogen peroxide water was added to adjust the water concentration to 2 g / L.

[0071] The nitrogen adsorption and desorption isotherms of the obtained iridium oxide were measured using the "Adsorption and Desorption Isotherm" measurement program of the BELSORP-mini II automatic specific surface area / pore distribution analyzer (manufactured by BEL JAPAN, INC.). The adsorption and desorption isotherms are shown in Figure 4. As shown in Figure 4, the adsorption and desorption isotherms rise at a relative pressure (P / P0) of approximately 0.8, and a sharp curve is obtained. Furthermore, a difference between the adsorption and desorption isotherms occurs at a relative pressure (P / P0) of 0.8, indicating the presence of so-called hysteresis.

[0072] The data on this adsorption / desorption isotherm was analyzed by the "BJH method" to determine the total pore volume and average pore diameter, and analyzed by the "BET method" to determine the specific surface area. The results are shown in Table 1. The total pore volume in Example 3 was 0.349 cm 3 / g, average pore diameter 11.2nm, specific surface area 125m 2 / g, and iridium oxide with a relatively large total pore volume, average pore diameter, and specific surface area was obtained.

[0073] Example 7: Preparation of iridium oxide IrO2 (IO-6) 1.0 L of iridium hydroxide slurry solution (Furuya Metal) (iridium content 0.629 g / L) was prepared, and NaOH was added to adjust the pH to 12.5 to obtain a metal compound dispersion liquid as a raw material. Next, synthesis was performed in the same manner as in Example 3, except that 30% hydrogen peroxide water was added to adjust the water content to 2 g / L.

[0074] The nitrogen adsorption and desorption isotherms of the obtained iridium oxide were measured using the "Adsorption and Desorption Isotherm" measurement program of the BELSORP-mini II automatic specific surface area / pore distribution analyzer (manufactured by BEL JAPAN, INC.). The adsorption and desorption isotherms are shown in Figure 10. As shown in Figure 10, the adsorption and desorption isotherms rise at a relative pressure (P / P0) of approximately 0.8, and a sharp curve is obtained. Furthermore, a difference between the adsorption and desorption isotherms occurs at a relative pressure (P / P0) of 0.8, indicating the presence of so-called hysteresis.

[0075] The data on this adsorption / desorption isotherm was analyzed by the BJH method to determine the total pore volume and average pore diameter, and analyzed by the BET method to determine the specific surface area. The results are shown in Table 1. The total pore volume in Example 7 was 0.407 cm 3 / g, average pore diameter 11.5 nm, specific surface area 141 m 2 / g, and iridium oxide with a relatively large total pore volume, average pore diameter, and specific surface area was obtained.

[0076] <Comparative Example 1> Preparation of iridium oxide IrO2 (IO-4) A 50 g iridium chloride tetravalent preparation (H2IrCl6·nH2O, manufactured by Furuya Metals) was placed in a 5 L Teflon beaker, and 1.6 L of pure water was added. The solution was heated to 80 °C and stirred for 1 hour to prepare an iridium chloride solution. Next, a 10% NaOH solution was prepared by dissolving 7.8 times the molar equivalent of NaOH in 9 times the amount of pure water. This 10% NaOH solution was added dropwise to the iridium chloride solution at a rate of 12.5 mL / min. After the addition, the solution was stirred for an additional 10 hours while maintaining the temperature at 80 °C. The resulting slurry was allowed to cool to room temperature and then allowed to stand, and the supernatant was decanted. 1300 mL of pure water was added to the remaining slurry in the Teflon beaker, and the mixture was stirred for 1 hour while again heating to 80 °C. After cooling to room temperature, the mixture was allowed to stand, and the supernatant was again decanted. This decantation washing was continued until the conductivity of the supernatant liquid became 2 mS / m or less. After that, it was filtered through a membrane filter, and the filter cake was dried in an electric dryer at 60 °C for 20 hours, and then calcined in an electric furnace in the air at 400 °C for 10 hours, obtaining 58 g of iridium oxide IrO2.

[0077] The nitrogen adsorption and desorption isotherms of the obtained iridium oxide were measured using the "Adsorption and Desorption Isotherm" measurement program of the BELSORP-mini II automatic specific surface area / pore distribution analyzer (manufactured by BEL JAPAN, INC.). The adsorption and desorption isotherms are shown in Figure 5. As shown in Figure 5, the adsorption and desorption isotherms showed a gently sloping curve at relative pressures (P / P0) ranging from approximately 0.1 to 0.8, and there was almost no difference between the adsorption and desorption isotherms at relative pressures (P / P0) ranging from approximately 0.1 to 0.8, indicating that there was almost no hysteresis.

[0078] The data on this adsorption / desorption isotherm was analyzed by the "BJH method" to determine the total pore volume and average pore diameter, and analyzed by the "BET method" to determine the specific surface area. The results are shown in Table 1. The total pore volume in Comparative Example 1 was 0.083 cm 3 / g, average pore diameter 5.03 nm, specific surface area 65.9 m 2 / g, and iridium oxide having significantly smaller total pore volume, average pore diameter, and specific surface area than the iridium oxides of Examples 1 to 3 and Example 7 was obtained.

[0079] Comparative Example 2: Preparation of iridium oxide IrO2 (IO-5) A 1-L glass three-neck flask was charged with 3.45 g of tetravalent iridium chloride (H2IrCl6·nH2O, manufactured by Furuya Metals), and 620 ml of 2-propanol was added. The solution was stirred and dissolved at room temperature (25°C) for 1.5 hours. Sodium nitrate, pre-ground in a mortar, was added to the solution in a 50-fold ratio by weight of the iridium salt, and the mixture was stirred at room temperature for 1 hour. The resulting slurry was concentrated to dryness under reduced pressure in a rotary evaporator at a water bath temperature of 50°C and a vacuum of 50 hPa for 3 hours. The resulting solid was crushed in a mortar, placed in an alumina tray, and placed in a muffle furnace in the atmosphere. It was then heated and melted at 400°C for 5 hours. After cooling to room temperature, 1 L of pure water was added to the molten solidified material to dissolve and extract it. The resulting slurry was filtered through a membrane filter and washed with warm water until the filtrate conductivity was 1 mS / m or less. It was then dried in an electric dryer at 60°C for 16 hours to obtain 4.0 g of iridium oxide IrO2.

[0080] The nitrogen adsorption and desorption isotherms of the obtained iridium oxide were measured using the "Adsorption and Desorption Isotherm" measurement program of the BELSORP-mini II automatic specific surface area / pore distribution analyzer (manufactured by BEL JAPAN, INC.). The adsorption and desorption isotherms are shown in Figure 6. As shown in Figure 6, the adsorption and desorption isotherms showed a steeply rising curve from a relative pressure (P / P0) of approximately 0.01 to 0.2, but a gentler slope was obtained from a relative pressure (P / P0) of approximately 0.2 to 0.8. Furthermore, there was almost no difference between the adsorption and desorption isotherms from a relative pressure (P / P0) of approximately 0.2 to 0.8, meaning there was almost no hysteresis, and an adsorption and desorption isotherm typical of a micropore structure was obtained.

[0081] The data on this adsorption / desorption isotherm was analyzed by the "BJH method" to determine the total pore volume and average pore diameter, and analyzed by the "BET method" to determine the specific surface area. The results are shown in Table 1. The total pore volume in Comparative Example 2 was 0.140 cm 3 / g, average pore diameter 2.58nm, specific surface area 217m 2 / g, which is significantly larger in specific surface area than the iridium oxides of Examples 1 to 3 and Example 7, and the obtained iridium oxide had significantly smaller total pore volume and average pore diameter.

[0082] Example 4: Evaluation of mass activity of oxygen evolution reaction (OER) as a water electrolysis catalyst For each of the iridium oxides (IO-1) to (IO-6) in the above Examples and Comparative Examples, 14.7 mg of iridium oxide was ultrasonically dispersed 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 a 5 mass % Nafion dispersion (manufactured by DuPont). The dispersion was added to a rotating gold disk electrode using a micropipette, and the concentration was 30 μg / cm 2A catalyst-coated electrode was prepared. The electrode thus prepared was subjected to a square wave durability test using an electrochemical measurement system (HZ-7000, manufactured by Hokuto Denko Corporation). The electrolyte used was a 60 mass % perchloric acid solution (precision analytical reagent, manufactured by Kanto Chemical Co., Ltd.) prepared to 0.1 M and degassed with Ar gas. A three-electrode method was employed as the measurement method, and a hydrogen reference electrode in which hydrogen gas was passed over platinum black was used as the reference electrode. Measurements were carried out in a thermostatic chamber at 25°C. The mass activity of the oxygen evolution reaction (hereinafter also referred to as OER: Oxyge Evolution Reaction) was evaluated by sweeping the voltage range of 1.0 V to 1.8 V at a rate of 10 mV / sec, and measuring the current density (mA / cm) at 1.5 V. 2 ) is the catalyst coating amount (30 μg / cm 2 ) and calculated. The results are shown in FIG. 7 and Table 2. The sample prepared in Example 1 had an OER mass activity 1.28 times higher than the sample prepared in Comparative Example 1, the sample prepared in Example 2 had an OER mass activity 1.60 times higher than the sample prepared in Comparative Example 1, the sample prepared in Example 3 had an OER mass activity 1.57 times higher than the sample prepared in Comparative Example 1, and the sample prepared in Example 7 had an OER mass activity 1.08 times higher than the sample prepared in Comparative Example 1, demonstrating that all Examples were highly active as water electrolysis anode catalysts. In contrast, the OER mass activity of the sample prepared in Comparative Example 2 was 1.02 times lower than the sample prepared in Comparative Example 1, which was almost the same. The low OER mass activity of the catalyst of Comparative Example 2 despite its high specific surface area suggests that the contribution of micropores to water electrolysis catalytic activity is significantly low.

[0083] [Table 2]

[0084] Example 5: Single cell evaluation of solid polymer membrane water electrolysis electrode catalyst [5-1) Manufacturing of anode catalyst sheets for water electrolysis cells] The iridium oxides (IO-1) to (IO-5) of the above examples and comparative examples were each weighed, and ultrapure water, 2-propanol, and a 5% by mass Nafion dispersion (manufactured by Dupont) were added. The mixture was stirred with a magnetic stirrer, and then the iridium oxide was dispersed using a powerful ultrasonic disperser. Finally, the mixture was stirred and mixed again using a magnetic stirrer to obtain an anode catalyst paste. A 50 μm-thick Teflon® sheet was attached to the glass surface of a wire bar coater with a doctor blade (PM-9050MC, manufactured by MST Corporation). The anode catalyst paste was applied to the surface of the Teflon® sheet, and the blade was swept to coat the anode catalyst paste. The wet sheet was air-dried for 15 hours and then dried in 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 1.0 mg / cm. 2 The dried anode catalyst sheet was cut with a Thomson blade to obtain an electrode effective area of ​​9 cm2 required for evaluation. 2 The anode catalyst sheet was cut into circular shapes to obtain anode catalyst sheets 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, all for evaluating the durability of single cation exchange membrane water electrolysis cells.

[0085] [5-2) Manufacturing of cathode catalyst sheets for water electrolysis cells] Ketjen Black EC300J (AKZO NOBEL) was ultrasonically dispersed in deionized water, and high specific surface area platinum black (FHPB from Furuya Metal, BET specific surface area 85 m) was added. 2A slurry of 50% by mass Pt-loaded carbon was prepared by ultrasonically dispersing 50% by mass Pt (Pt / g) in deionized water and adding it to the deionized water. This was used as the cathode catalyst. The 50% by mass Pt-loaded carbon powder was weighed, and ultrapure water, 2-ethoxyethanol, 2-propanol, and a 5% by mass Nafion dispersion (manufactured by DuPont) were added. 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 attached to the glass surface of a wire bar coater equipped with a doctor blade. The cathode catalyst paste was applied to the surface of the Teflon® sheet and then coated with a sweeping blade. The sheet was air-dried for 15 hours and then 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 1.0 mg / cm. 2 The dried cathode catalyst sheet was cut with a Thomson blade to obtain a 9 cm2 electrode effective area. 2 The cathode catalyst sheet CS-1 was obtained for evaluating the durability of a single cation exchange membrane water electrolysis cell.

[0086] [5-3) Manufacture of CCM (Catalyst Coated Membrane) for water electrolysis cells] A cation exchange membrane Nafion 115 (manufactured by Dupont) was cut to a diameter of 70 mm, and this was sandwiched between the anode catalyst sheet AS-1, AS-2, AS-3, AS-4 or AS-5 cut to the above electrode effective area and the cathode catalyst sheet CS-1, with the catalyst coated surface facing inward, aligned in the center, and pressed in a high-precision hot press (manufactured by Tester Sangyo) at 145°C and 0.5 kN / cm. 2 After pressing, the Teflon (registered trademark) sheets attached to the anode and cathode were peeled off to obtain example catalysts CCM M-1 (AS-1 / CS-1), M-2 (AS-2 / CS-1), and M-3 (AS-3 / CS-1) and comparative catalysts CCM M-4 (AS-4 / CS-1) and M-5 (AS-5 / CS-1).

[0087] [5-4) Evaluation of accelerated degradation durability of solid polymer membrane water electrolysis single cell] Effective electrode area: 9cm 2A water electrolysis cell unit (manufactured by FC Development Co., Ltd.) was prepared. A platinum-plated Ti sintered body was used as the anode, and carbon paper was used as the cathode gas diffusion layer. These and the catalysts CCM M-1, M-2, and M-3 of the examples or CCM M-4 and M-5 of the comparative examples were assembled into a single cell and fastened with bolts. The anode and cathode sides of this single cell were connected to the pure water supply line and gas supply line of a water electrolysis / fuel cell evaluation system (AUTO-PE, manufactured by Toyo Corporation), respectively. The accelerated degradation durability of the cation exchange membrane water electrolysis single cell was evaluated by measuring the initial IV characteristics at a cell temperature of 80°C and supplying warm pure water with a conductivity of 0.1 mS / m or less to the anode at a flow rate of 30 ml / min. Subsequently, a total of 10,000 cycles were performed, with a sweep rate of 0.5 V / s from 1 V to 2 V and from 2 V to 1 V, and the IV characteristics were measured again at the end. Figure 8 shows a comparison of accelerated aging tests of single water electrolysis cells using the catalysts of the Examples and Comparative Examples as the anode, showing the changes in mass activity every 1,000 cycles in durability tests up to 10,000 cycles for the catalysts CCM M-1, M-2, and M-3 of the Examples and the catalysts CCM M-4 and M-5 of the Comparative Examples. Tafel plots were performed on the IV characteristics, and the activity retention rates were calculated from the ratios of mass activity before and after the cycle tests at an internal resistance (IR)-free electrolysis voltage of 1.5 V. Table 3 shows a comparison of the OER mass activity and its retention rate before and after the cycle tests of single water electrolysis cells using the catalysts of the Examples and Comparative Examples as the anode. The catalysts CCM M-1, M-2, and M-3 of the examples had initial activities at 1.5 V that were 1.97 times higher for M-1, 2.29 times higher for M-2, and 1.63 times higher for M-3 than the catalyst CCM M-4 of the comparative example. Furthermore, the catalysts CCM M-1, M-2, and M-3 had activity retention rates of 74.7%, 71.0%, and 75.3%, respectively, compared with 63.9% for the catalyst CCM M-4 of the comparative example. These results demonstrate the high performance of the catalysts of the examples as water electrolysis anode catalysts in terms of both activity and durability. On the other hand, the catalyst CCM M-5 of the comparative example 2 had an initial activity that was 0.902 times lower than that of the catalyst CCM M-4 of the comparative example 1. Despite its high activity retention rate of 98.1%, its OER mass activity after durability testing fell far short of that of the catalysts of the examples.

[0088] [Table 3]

[0089] Example 6: Evaluation of the reverse potential durability of water electrolysis catalysts in cation exchange membrane fuel cells [6-1) Manufacturing of electrode catalyst sheets for fuel cells] In Example 5, 5-2), a 50% by mass Pt-loaded carbon was prepared using highly graphitized carbon black FCX-80 (manufactured by CABOT) instead of Ketjen Black EC300J. The same procedure as in Example 5, 5-2) was repeated except for using this, to obtain a cathode catalyst sheet CS-2 for evaluating fuel cell reverse potential durability. The catalyst coating amount per unit area was 1.0 mg / cm. 2 In addition, a catalyst paste was prepared by mixing 50 mass% Pt-supported carbon using FCX-80 and catalyst IO-1 of Example 1 in a weight ratio of 95:5, and the same treatment as in Example 5 5-2) was carried out except for using this to obtain anode catalyst sheet AS-6 for evaluating fuel cell reverse potential durability. The catalyst coating amount per unit area was 1.0 mg / cm 2 Furthermore, the same treatment as above was carried out except that in the preparation of AS-6, catalyst IO-4 of Comparative Example 1 was used instead of catalyst IO-1 of Example 1, to obtain an anode catalyst sheet AS-7 for evaluating the reverse potential durability of a fuel cell.

[0090] [6-2) Manufacturing of CCM for fuel cells] A cation exchange membrane Nafion NRE-212 (manufactured by DuPont) was cut into a 100 mm x 100 mm piece, and the cathode catalyst sheet (CS-2) produced in Example 6 6-1) and the anode catalyst sheet (AS-6) containing the catalyst IO-1 of Example 1 produced in Example 6 6-1) were sandwiched together with their respective catalyst-coated surfaces facing inward, aligned in the center, and then pressed in a hot press (a high-precision hot press for MEA production, manufactured by Tester Sangyo) at 140°C and 2 kN / cm. 2 After removal, the Teflon (registered trademark) sheets on the front and back were peeled off to obtain CCM M-6 (AS-6 / CS-2) of Example 6.

[0091] Furthermore, a comparative example, CCM M-7 (AS-7 / CS-2), was obtained by carrying out the same treatment as above, except that the anode catalyst sheet (AS-7) was used instead of the anode catalyst sheet (AS-6).

[0092] [6-3) Evaluation of fuel cell reverse potential durability] A PEFC single cell (manufactured by FC Development Co., Ltd.) was prepared according to the standard cell specifications of the Japan Automobile Research Institute (JARI), except that the electrode effective area was 30 mm × 30 mm. 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 to a torque of 4 Nm. This single cell was connected to the gas supply line of a fuel cell evaluation device (AUTO-PE, manufactured by Toyo Corporation). A reverse potential durability test was performed as follows, following the method described in Non-Patent Document 3. The cell temperature was set to 40°C, and hydrogen was supplied to the anode and air (zero air gas) to the cathode, each humidified with a humidifier to a dew point of 40°C. Hydrogen was supplied to the anode at a flow rate of 200 ml / min and air to the cathode at a flow rate of 600 ml / min. The single fuel cell was operated for 1 hour, and the initial IV characteristics were measured. The anode gas was then completely replaced with nitrogen gas, and a current of 0.2 A / cm was supplied from an external power source. 2 The current density of 0.2 A / cm was forced to flow to simulate a reverse potential state. The change in the cell voltage over time was monitored, and 2 The time required for the cell voltage to exceed -2.0 V from the start of current application at a current density of 0.2 A / cm was 27,123 seconds, which was defined as the reverse potential endurance time. CCM M-7 containing the catalyst of Comparative Example 1 as a water electrolysis catalyst was evaluated in the same manner as in Example 6. 2 The time required for the cell voltage to exceed -2.0 V from the start of current flow at this current density was 12,216 seconds. Figure 9 shows the results of the reverse potential durability evaluation test. Figure 9 reveals that the CCM for fuel cells to which the catalyst of the example was added as a water electrolysis catalyst exhibited significantly higher reverse potential durability than that of the catalyst of the comparative example. [Explanation of symbols]

[0093] (1) First Source (2) Secondary Source (3) Heating section (4) Reaction section (5) Liquid delivery route (6) Liquid delivery route (7) Recovery section (8) Cooling section (9) Mechanism for transporting liquid in one direction (10) Mechanism for transporting liquid in one direction (11) Pressure adjustment mechanism

Claims

1. The total pore volume calculated by the BJH method from nitrogen adsorption / desorption isotherm measurements was 0.20 cm ３ / g or more and a pore distribution with an average pore diameter of 7.0 nm or more, The iridium-containing oxide is iridium oxide or a composite oxide of iridium and an element whose oxide has a rutile crystal structure, and the iridium oxide or composite oxide has a rutile crystal structure.

2. Relative pressure (P / P) of nitrogen adsorption / desorption isotherm ０ 2. The iridium-containing oxide according to claim 1, wherein the hysteresis is in the range of 0.7 to 0.

95.

3. BET specific surface area is 100m ２ 3. The iridium-containing oxide according to claim 1, wherein the iridium content is 1 / g or more.

4. A method for producing an iridium-containing oxide according to any one of claims 1 to 3, (1) Step A of dispersing raw material iridium nanoparticles or iridium hydroxide particles in a medium to obtain a dispersion, or (2) Step A of dissolving raw material iridium compounds in a solvent to obtain a solution; A process B converts water into high-temperature, high-pressure water under high-temperature, high-pressure conditions of a heating temperature of 100°C or higher and a pressurized pressure of 0.1 MPa or higher; a step C of mixing the dispersion or the solution obtained in the step A with the high-temperature, high-pressure water obtained in the step B; 1. A method for producing an iridium-containing oxide, comprising:

5. 5. The method for producing an iridium-containing oxide according to claim 4, wherein in step A, the solvent is at 15 to 30° C., and the iridium compound as the raw material is dissolved in the solvent.

6. 6. The method for producing an iridium-containing oxide according to claim 4, wherein the step B includes any one of the steps of: (1) adding an oxidizing agent that releases oxygen atoms to the water to form high-temperature, high-pressure water; (2) converting the water into high-temperature, high-pressure water and then adding an oxidizing agent that releases oxygen atoms to the water; or (3) adding an oxidizing agent that releases oxygen atoms to the water to form high-temperature, high-pressure water, and further adding an oxidizing agent that releases oxygen atoms to the high-temperature, high-pressure water.

7. A cation exchange membrane water electrolysis anode catalyst comprising the iridium-containing oxide according to any one of claims 1 to 3.

8. A reverse potential durable catalyst for a cation exchange membrane fuel cell, comprising the iridium-containing oxide according to any one of claims 1 to 3 in an electrode catalyst layer.

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