Electrode including oxygen generating electrode catalyst, and method for manufacturing same

Abstract

An objective of the present invention is to provide at least one among: an electrode containing a manganese oxide which suppresses the elution of manganese during water electrolysis without reducing hydrogen productivity; and a method for manufacturing the electrode.　The electrode includes a conductive substrate, and an oxygen generating electrode catalyst containing iridium-manganese oxide. The content of iridium per geometric area of the conductive substrate is less than 10 μg / cm2.

Description

Electrode containing oxygen-evolving electrode catalyst and method for producing same

[0001] The present disclosure relates to electrodes that include oxygen evolving electrode catalysts that include manganese oxides and methods for making the same.

[0002] Due to the problems of fossil fuel depletion and environmental pollution, attention is being focused on the use of hydrogen as a clean energy source and methods for producing it. Water electrolysis is one effective means of producing high-purity hydrogen gas. In water electrolysis, iridium-based catalysts are widely known as highly active oxygen-evolving electrode catalysts (e.g., Non-Patent Document 1). However, iridium reserves are extremely scarce compared to other precious metals, and even if water electrolysis technology becomes widespread in the future, there will not be enough iridium available as catalyst.

[0003] Against this background, manganese oxides (Patent Document 1, Non-Patent Document 2) and iridium-manganese oxides (Patent Document 2), in which a small amount of iridium is introduced into manganese oxides, have been reported as oxygen-evolving electrode catalysts in which the amount of iridium used is reduced as compared to conventional methods.

[0004] International Publication No. 2019 / 117199 International Publication No. 2022 / 264960

[0005] F. Birol, World Energy Outlook 2016, International Energy Agency (IEA), Paris, 2016. Angew. Chem. Int. Ed, 58 (2019) 5054-5048

[0006] The oxygen generating electrode catalysts of Patent Documents 1 and 2 have oxygen generating electrode catalytic activity over a wide potential range (potential window), but some manganese is converted to MnO by water electrolysis. ４ － In addition, in Non-Patent Document 2, the current density is set to 10 mA / cm ２ However, a decrease in the current electrolysis density is accompanied by a decrease in hydrogen productivity.

[0007] An object of the present disclosure is to provide at least one of an electrode containing manganese oxide in which manganese elution during water electrolysis is suppressed without reducing hydrogen productivity, and a method for producing the same.

[0008] In this disclosure, it was discovered that the presence of iridium affects the elution of manganese during water electrolysis from an electrode containing an oxygen generating electrode catalyst containing manganese oxide, and an investigation was conducted focusing on the state of iridium. As a result, it was discovered that in an oxygen generating electrode catalyst containing iridium-manganese oxide, by controlling the amount of iridium from a perspective different from the oxygen generating catalytic ability of iridium, manganese elution during water electrolysis can be reduced without a decrease in hydrogen productivity.

[0009] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows: [1] An oxygen generating electrode comprising an oxygen generating electrode catalyst containing iridium-manganese oxide and a conductive substrate, wherein the content of iridium per geometric area of ​​the conductive substrate is 10 μg / cm ２ [2] An electrode in which the mass ratio of iridium to manganese is less than 3.0 × 10 －２ The electrode according to the above [1], which is: [3] The electrode according to [1] or [2], wherein the conductive substrate is a substrate containing titanium; [4] The electrode according to any one of [1] to [3], wherein platinum is present on a part or all of the surface of the conductive substrate; [5] The electrode according to any one of [1] to [4], wherein the conductive substrate has a mesh-like shape.

[0010] [6] A method for producing the electrode according to any one of [1] to [5] above, comprising: an electrodeposition step of electrolyzing a mixed solution containing sulfuric acid and manganese sulfate to deposit manganese oxide on a conductive substrate to obtain a manganese oxide-containing substrate; and an iridium-containing step of contacting the manganese oxide-containing substrate with an iridium salt solution and then annealing it. [7] A membrane-electrode assembly comprising the electrode according to any one of [1] to [5] above and an electrolyte membrane. [8] A water electrolytic cell comprising the membrane-electrode assembly according to [7] above. [9] A method for producing hydrogen, comprising water electrolysis using the water electrolytic cell according to [8] above.

[0011] The present disclosure can provide at least one of an electrode containing an iridium-manganese oxide in which manganese elution during water electrolysis is suppressed without reducing hydrogen productivity, and a method for producing the same.

[0012] The present disclosure will be described below with reference to exemplary embodiments. The configurations and parameters disclosed herein may be combined in any desired manner, and the upper and lower limits of the values ​​disclosed herein may be combined in any desired manner.

[0013] This embodiment includes an oxygen generating electrode catalyst containing iridium-manganese oxide and a conductive substrate, and the content of iridium per geometric area of ​​the conductive substrate is 10 μg / cm ２ By satisfying this constitution, manganese elution is significantly suppressed even during water electrolysis at a high current electrolysis density.

[0014] The present embodiment relates to an electrode, and in particular to an oxygen generating electrode, an electrolysis electrode in water electrolysis, an oxygen generating electrode in water electrolysis, and an anode in water electrolysis. ２ ) and oxygen (O ２ ) to generate water (H ２ The reaction of water electrolysis is shown by the following equation: Cathode: 2H ＋ +2e － → H ２ (1-1) Anode: 2H ２ O → O ２ +4H ＋ +4e － (1-2) Overall: 2H ２ O → 2H ２ +O ２ (1-3)

[0015] The oxygen generating reaction is a reaction that occurs at the anode during water electrolysis and is the rate-limiting process in water electrolysis. The oxygen generating reaction is a reaction represented by formula (1-2), in which four electrons, four protons, and one oxygen molecule are produced from two water molecules. The oxygen generating electrode catalyst allows the oxygen generating reaction to proceed with lower energy. The electrode of this embodiment includes an oxygen generating electrode catalyst containing iridium-manganese oxide (hereinafter also referred to as "Ir / Mn catalyst"). This allows the electrode of this embodiment to function as an oxygen generating electrode.

[0016] The Ir / Mn catalyst contains manganese oxide and iridium (Ir). Examples of the form of the Ir / Mn catalyst include one in which iridium is supported on an electrolytically deposited manganese oxide, and one in which iridium is dispersed on the surface of an electrolytically deposited manganese oxide. The manganese oxide contained in the Ir / Mn catalyst is preferably a manganese oxide obtained by electrolytic deposition, i.e., an electrolytic manganese oxide. The manganese oxide contained in the Ir / Mn catalyst may be any oxide of manganese (Mn) (MnOx; 0<x≦2), and examples thereof include one or more selected from the group consisting of manganese oxide, manganese dioxide, and trimanganese tetraoxide. Manganese dioxide is preferably contained.

[0017] The manganese dioxide is preferably manganese dioxide having any of γ-, β-, ε-, or α-type crystal structures, and more preferably manganese dioxide having a β-type crystal structure. The manganese oxide contained in the Ir / Mn catalyst may contain two or more types of manganese oxides, or may contain two or more types of manganese oxides having different crystal structures.

[0018] In this embodiment, the crystal structure of manganese oxide can be identified by comparing its powder X-ray diffraction (hereinafter also referred to as "XRD") pattern with the XRD pattern (hereinafter also referred to as "reference pattern") registered in the ICDD (International Center for Diffraction Data) Powder Diffraction File (PDF). For example, reference patterns for manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure are PDF Nos. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), and 44-0141 (α-type), respectively.

[0019] In this embodiment, the XRD pattern is obtained by XRD measurement using a general powder X-ray diffractometer (for example, an Ultima IV Protectus, manufactured by Rigaku Corporation) under the following conditions: Acceleration current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Continuous scan Scan condition: 4° / min Measurement range: 2θ=10° to 80° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0020] The XRD peak is a peak whose peak top 2θ is detected in an analysis of an XRD pattern using general analysis software (for example, IGOR Pro 8 manufactured by WaveMetrics, or SmartLab Studio II manufactured by Rigaku Corporation).

[0021] The electrode of this embodiment includes a conductive substrate. The conductive substrate may be any substrate made of a conductive material, and is preferably a substrate containing titanium, and more preferably a substrate made of titanium. The conductive substrate may have any shape that is suitable for use in an electrolytic cell, and examples thereof include one or more shapes selected from the group consisting of mesh, cloth, and plate. Since an increased surface area tends to increase the oxygen generating electrode catalytic activity, the conductive substrate is preferably in a mesh shape. Examples of conductive substrates having a mesh shape include metal meshes made of fibrous or powdered conductive metals, and sintered metal meshes that have been heat-treated. In order to facilitate the oxygen generating reaction at a lower voltage, the conductive substrate preferably has platinum on part or all of its surface. Particularly preferred conductive substrates include at least one of a titanium mesh having platinum on its surface (hereinafter also referred to as a "platinum-coated Ti mesh") and a sintered titanium mesh having platinum on its surface (hereinafter also referred to as a "platinum-coated sintered Ti mesh"), and even a platinum-coated Ti mesh.

[0022] Since an increase in surface area tends to increase the oxygen generating electrode catalytic activity, it is preferable that the conductive substrate has voids. The porosity of the conductive substrate is preferably 30% or more, more preferably 40% or more, and is preferably 80% or less, more preferably 70% or less. The porosity range is preferably 30% or more and 80% or less, more preferably 40% or more and 70% or less.

[0023] In the electrode of this embodiment, the content of iridium per geometric area of ​​the conductive substrate (hereinafter also referred to as "Ir amount") is 10 μg / cm ２ The amount of Ir in the electrode is less than 10 μm / cm ２ If the amount of Ir is less than 0 μg / cm, the effect of suppressing manganese elution during water electrolysis can be obtained, and the amount of expensive iridium used can be reduced. The amount of Ir may be any amount that suppresses manganese elution during water electrolysis, but is preferably 0 μg / cm ２ More preferably, more than 1.0 μg / cm ２ or more, and 10 μg / cm ２ and preferably less than 9.0 μg / cm ２ The range of the Ir amount is 0 μg / cm２ Super 10μg / cm ２ Preferably, it is less than 1.0 μg / cm ２ 9.0 μg / cm or more ２ More preferably, it is:

[0024] The "geometric area" is an area equivalent to a projected area without taking into consideration irregularities or voids on the surface, and is the projected area of ​​the surface (geometric surface) that faces the electrolyte membrane when constituting a membrane-electrode assembly (hereinafter also referred to as "MEA"). The "geometric area of ​​a conductive substrate" is the projected area of ​​the conductive substrate, and is the area of ​​a plane calculated from the length x width when the shape of the conductive substrate is defined as length x width x depth.

[0025] The amount of Ir is calculated by immersing the electrode in a mixed solution of hydrochloric acid and nitric acid to dissolve the oxygen-generating electrode catalyst contained in the electrode to obtain a sample solution, and dividing the mass of iridium in the sample solution obtained from the concentration measured by inductively coupled plasma atomic emission spectrometry (hereinafter also referred to as "ICP-AES") using a general ICP apparatus (for example, apparatus name: OPTIMA5300DV, manufactured by PerkinElmer) by the geometric area of ​​the conductive substrate.

[0026] The electrode of this embodiment has a mass ratio of iridium to manganese (hereinafter also referred to as "Ir / Mn ratio") of 3.0 × 10 －２ Preferably, it is 2.0 × 10 or less. －２ This tends to further suppress manganese elution during water electrolysis. Furthermore, the Ir / Mn ratio is more preferably 1.0 × 10 or less. －２ Below, further 0.8 × 10 －２ The electrode of the present embodiment is only required to contain iridium, and the Ir / Mn ratio is preferably greater than 0, and is 5.0×10 －４ More preferably, it is 1.0 × 10 or more. －３ The preferred Ir / Mn ratio is more than 0 and 3.0×10 －２ More preferably, it is 5.0 × 10 －４ Above 3.0 x 10 －２ is preferably 1.0×10 or less. －３ Above 1.0 x 10－２ The following is the result.

[0027] In this embodiment, the Ir / Mn ratio is calculated by the following formula: Ir / Mn ratio=W Ｉｒ / W Ｍｎ In the above equation, W Ｉｒ is the amount of Ir [mg / cm ２ ] and W Ｍｎ is the manganese content per geometric area of ​​the conductive substrate in the electrode (hereinafter also referred to as "Mn amount"), and is calculated by immersing the electrode in a mixed solution of hydrochloric acid and nitric acid to dissolve the oxygen generating electrode catalyst contained in the electrode to obtain a sample solution, and dividing the mass of manganese in the sample solution obtained from the concentration obtained by measurement by ICP-AES using a general ICP device by the geometric area of ​​the conductive substrate.

[0028] The electrode of this embodiment can be used as an MEA including the electrode and an electrolyte membrane, and can also be used as a water electrolytic cell including the MEA, preferably a water electrolytic cell including the MEA. Hydrogen can be produced by water electrolysis using the electrode of this embodiment or a water electrolytic cell including an MEA including the electrode.

[0029] A method for producing the electrode of this embodiment will be described below. The method for producing the electrode of this embodiment is not particularly limited as long as it can produce an electrode having the above-described configuration. Preferred production methods include a production method comprising an electrolysis step of electrolytically depositing manganese oxide on a conductive substrate to obtain a manganese oxide-containing substrate, a contact step of contacting the manganese oxide-containing substrate with an iridium salt solution to obtain an iridium-manganese oxide-containing substrate, and a heat treatment step of heat-treating the iridium-manganese-containing substrate.

[0030] In the electrolysis step, manganese oxide is electrolytically deposited on the conductive substrate to obtain a manganese oxide-containing substrate. The electrolytic deposition method is not particularly limited as long as manganese oxide is electrolytically deposited on the surface of the conductive substrate, but examples include a method in which the conductive substrate is immersed in an electrolytic solution and manganese oxide is electrolytically deposited on the surface of the conductive substrate by electrolysis of the electrolytic solution. The conductive substrate used in the electrolysis step may be any of the above-mentioned conductive substrates, and is preferably a platinum-coated Ti mesh, or more preferably a platinum-coated sintered Ti mesh.

[0031] The electrolyte may be any solution containing manganese, such as manganese sulfate (MnSO ４ ), and more preferably a manganese sulfate aqueous solution, and more preferably a sulfuric acid-manganese sulfate aqueous solution. The manganese concentration of the electrolytic solution is preferably 5 g / L or more, more preferably 10 g / L or more, and also preferably 100 g / L or less, more preferably 90 g / L or less, and is preferably 5 g / L or more and 100 g / L or less, and more preferably 10 g / L or more and 90 g / L or less. The sulfuric acid concentration is preferably 5 g / L or more and 65 g / L or less, and more preferably 5 g / L or more and 50 g / L or less.

[0032] In the electrolysis, the conductive substrate is immersed in an electrolytic solution, and the electrolytic solution is electrolyzed. The electrolysis conditions may be any conditions that allow electrolytic deposition of manganese oxide on the conductive substrate. ２ The current density per ２ 20mA / cm or more ２ The electrolysis temperature is 93°C or higher and 98°C or lower.

[0033] In the contact step, the manganese oxide-containing substrate is brought into contact with an iridium salt solution to obtain an iridium-manganese oxide-containing substrate. The iridium salt solution used in the contact step may be any solution containing an iridium salt, and is preferably a solution containing an iridium salt and sulfuric acid, or more preferably an aqueous solution containing an iridium salt and sulfuric acid. Examples of iridium salts include potassium hexachloroiridate (K ２ IrCl ６ ) and hexachloroiridic acid (H ２ IrCl６ ) and furthermore potassium hexachloroiridate.

[0034] The iridium concentration of the iridium salt solution is preferably 0.0005 g / L or more, more preferably 0.0010 g / L or more, and preferably 0.0025 g / L or less, more preferably 0.0020 g / L or less, and the range of the iridium concentration is preferably 0.0005 g / L or more and 0.0025 g / L or less, and more preferably 0.0010 g / L or more and 0.0020 g / L or less. The higher the iridium concentration, the greater the amount of iridium in the obtained electrode tends to be.

[0035] The manganese oxide-containing substrate can be brought into contact with the iridium salt solution by immersing the manganese oxide-containing substrate in the iridium salt solution. The contact conditions are not particularly limited as long as the iridium salt solution impregnates the surface of the manganese oxide-containing substrate, but examples include immersing the manganese oxide-containing substrate in the iridium salt solution at a temperature of 20° C. or higher and 100° C. or lower. The contact time can be adjusted appropriately depending on the size of the manganese oxide-containing substrate, the concentration of the iridium salt solution, and the like, and can be, for example, 30 minutes to 24 hours.

[0036] In the heat treatment step, the iridium-manganese oxide-containing substrate is heat-treated. This increases the adhesion between the iridium-manganese oxide and the conductive substrate, resulting in the electrode of this embodiment. For example, the heat treatment atmosphere in the heat treatment step may be an air atmosphere or an inert atmosphere, or even an air atmosphere, and the heat treatment temperature may be 100°C or higher and 600°C or lower. The heat treatment time may be adjusted appropriately depending on the size of the conductive substrate to be subjected to the heat treatment, and may be, for example, 10 minutes to 24 hours.

[0037] Hereinafter, the present disclosure will be described with reference to examples and comparative examples, but the present disclosure is not limited to the following. <Analysis of Metal Content of Electrode>

[0038] A sample electrode measuring 10 mm in length and 10 mm in width was immersed in 10 mL of a mixed solution of hydrochloric acid and nitric acid to dissolve the oxygen-generating electrode catalyst contained in the electrode, yielding a sample solution. The composition of the sample solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) using a common ICP device (device name: OPTIMA 5300DV, manufactured by PerkinElmer).

[0039] The electrode used in the water electrolysis test was used as a sample electrode to measure the composition of the sample solution, and the amounts of iridium and manganese in the sample solution were calculated from the obtained iridium and manganese concentrations.

[0040] Furthermore, the iridium content (Ir content) and manganese content (Mn content) per geometric area of ​​the conductive substrate were calculated using the following formulas: W １ = W Ｉｒ / S W ２ = W Ｍｎ / S In the above formula, W １ is the amount of Ir [×10 －２ mg / cm ２ ], W Ｉｒ is the amount of iridium obtained by composition analysis [× 10 －２ mg], W ２ is the Mn content [mg / cm ２ ], W Ｍｎ is the amount of manganese obtained by composition analysis [mg], and S is the geometric area of ​​the sample electrode [1 cm ２ ].

[0041] Using the electrode as a sample electrode before and after the water electrolysis test, the composition of the sample solution was measured, and the manganese elution rate [mass %] was calculated from the obtained manganese amount using the following formula. Ｍｎ = {(W Ｍｎ１ -W Ｍｎ２ ) / W Ｍｎ１}×100 In the above formula, C Ｍｎ is the manganese elution rate [mass%], W Ｍｎ１ is the amount of manganese [mg] obtained by the composition analysis before the water electrolysis test, and W Ｍｎ２ is the amount of manganese [mg] obtained by composition analysis after the water electrolysis test. <Identification of crystal structure>

[0042] An XRD pattern was obtained using a general powder X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Rigaku Corporation) under the following conditions: Acceleration current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Continuous scan Scan condition: 4° / min Measurement range: 2θ=10° to 80° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0043] The crystalline phase of the sample was identified by comparing the obtained XRD pattern with the XRD pattern (hereinafter also referred to as "reference pattern") registered in the PDF (Powder Diffraction File) of the ICDD (International Center for Diffraction Data). The reference patterns for manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure were PDF No. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), or 44-0141 (α-type), respectively. <Water Electrolysis Test>

[0044] A PEM-type water electrolysis cell was fabricated using the electrode of this example as the working electrode and equipped with a membrane-electrode assembly (hereinafter also referred to as "MEA") fabricated by the following method. A conductive catalyst ink was prepared by mixing a 20% by mass platinum-supported carbon catalyst (product name: 20% Platinum on Vulcan XC-72, manufactured by Sigma-Aldrich) with a solution containing water, ethanol, and an ionomer (product name: Nafion dispersion, manufactured by Sigma-Aldrich). This was applied to carbon paper (product name: TGP-H-060, manufactured by Toray Industries, Inc.) and air-dried to form a counter electrode.

[0045] Next, a Nafion membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was washed and protonated by boiling in 3% by mass hydrogen peroxide solution for 1 hour, pure water for 1 hour, 1 M sulfuric acid solution for 1 hour, and pure water for 1 hour, in that order, to obtain an electrolyte membrane. The sample electrode was used as the working electrode, and the electrolyte membrane was sandwiched between the catalytic surfaces of the working electrode and the counter electrode. The membrane was then heated at 135°C and a clamping force of 400 kg / cm using a hot press (product name: SA-302, manufactured by Tester Sangyo Co., Ltd.). ２ The resulting MEA was attached to a housing of a PEM water electrolysis cell (product name: WE-4S-RICW, manufactured by FC Development Co., Ltd.) to prepare a PEM water electrolysis cell.

[0046] Using the obtained PEM-type water electrolyzer, a water electrolysis test and hydrogen production were carried out by applying a constant current to a two-electrode system under the following conditions: Applied current density: 1 A / cm ２ Water temperature: 80℃ Water supply rate: 2mL / min

[0047] Example 1 An electrolytic cell was filled with a sulfuric acid-manganese sulfate mixed solution with a sulfuric acid concentration of 35 g / L and a manganese sulfate concentration of 55 g / L, and a conductive substrate made of a 2.25 cm x 2.25 cm Ti fiber sintered body (Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) made of a sintered and rolled platinum-coated titanium nonwoven fabric was immersed in the solution. A current density of 7 mA / cm was applied to the conductive substrate. ２ A current was applied for 10 minutes at 40°C to electrochemically deposit manganese oxide onto the conductive substrate.

[0048] Next, the potassium hexachloroiridate concentration (K ２ IrCl ６ The obtained manganese oxide composite electrode material was immersed in an aqueous sulfuric acid solution of potassium hexachloroiridate with a sulfuric acid concentration of 0.002 g / L and a sulfuric acid concentration of 1.0 g / L at 95°C for 24 hours, and then annealed in an air atmosphere at 450°C for 5 hours to obtain an electrode comprising an oxygen generating electrode catalyst containing iridium-manganese oxide and a conductive substrate, which was used as the electrode of this example.

[0049] Example 2 As a potassium hexachloroiridate solution, potassium hexachloroiridate concentration (K ２ IrCl ６ The electrode of this example was obtained in the same manner as in Example 1, except that the aqueous sulfuric acid solution was changed to an aqueous solution of potassium hexachloroiridate having a sulfuric acid concentration of 0.001 g / L and a sulfuric acid concentration of 1.0 g / L.

[0050] Example 3 A conductive substrate was subjected to a current density of 7 mA / cm ２ An electrode of this example was obtained in the same manner as in Example 1, except that a current was applied for 1 minute at 400° C. to electrochemically deposit manganese oxide on the conductive substrate.

[0051] Example 4 A conductive substrate was subjected to a current density of 7 mA / cm ２ An electrode of this example was obtained in the same manner as in Example 1, except that a current was applied for 5 minutes at 400 kJ / cm 2 at 400 kJ / cm 2 for electrochemical deposition of manganese oxide onto the conductive substrate.

[0052] Example 5 A conductive substrate was subjected to a current density of 7 mA / cm ２ The electrode of this example was obtained in the same manner as in Example 1, except that a current was applied for 20 minutes to electrochemically deposit manganese oxide on the conductive substrate.

[0053] Comparative Example 1 Manganese oxide was electrochemically deposited on a conductive substrate in the same manner as in Example 1, and the resulting manganese oxide composite electrode material was annealed in an air atmosphere at 450°C for 5 hours to obtain a manganese oxide composite electrode material, which was used as the electrode of this comparative example. The evaluation results of the electrodes (working electrodes) obtained in the example and comparative example are shown in Table 1.

[0054]

[0055] From Table 1, in comparison with Comparative Example 1 which does not contain iridium, －２ In the following Examples, it was confirmed that manganese elution was suppressed. Furthermore, it was confirmed from Examples 1, 3, and 4 that the Mn elution rate tended to decrease as the Ir / Mn ratio decreased. In the Examples, when the Ir / Mn ratio was 0.7 × 10 －２ Less than (0.3 x 10 －２ More than 0.7 x 10－２ It was confirmed that Mn elution did not occur in Example 5 (see below). Furthermore, compared to Example 3, the amounts of manganese oxide and iridium in Example 5 were twice as high, but it was confirmed that Mn elution was similarly suppressed. The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-138797, filed on August 29, 2023, are hereby incorporated by reference as part of the disclosure of the specification of the present disclosure.

Claims

1. An oxygen generating electrode catalyst comprising an iridium-manganese oxide and a conductive substrate, the content of iridium per geometric area of ​​the conductive substrate being 10 μg / cm ２ Less than 1000 .mu.m.

2. The mass ratio of iridium to manganese is 3.0 x 10 －２ 2. The electrode of claim 1 , wherein:

3. The electrode according to claim 1 or 2, wherein the conductive substrate is a substrate containing titanium.

4. The electrode according to any one of claims 1 to 3, wherein the conductive substrate has platinum on a part or the whole of its surface.

5. The electrode according to any one of claims 1 to 4, wherein the conductive substrate has a mesh-like shape.

6. A method for producing an electrode according to any one of claims 1 to 5, comprising: an electrodeposition step of electrolyzing a mixed solution containing sulfuric acid and manganese sulfate to deposit manganese oxide on a conductive substrate to obtain a manganese oxide-containing substrate; and an iridium-containing step of contacting the manganese oxide-containing substrate with an iridium salt solution and then annealing the resulting substrate.

7. A membrane-electrode assembly comprising the electrode according to any one of claims 1 to 5 and an electrolyte membrane.

8. A water electrolysis cell comprising the membrane-electrode assembly according to claim 7.

9. A method for producing hydrogen, comprising electrolyzing water using the water electrolytic cell according to claim 8.

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