Iridium-containing manganese oxide, catalyst, electrode, and water electrolysis method

Abstract

The present disclosure provides at least one of an iridium-containing manganese oxide that exhibits high oxygen-evolving electrode catalytic activity in a water electrolysis method, a catalyst containing the same, an electrode containing the catalyst, and a water electrolysis method using the electrode. The iridium-containing manganese oxide of the present invention is an iridium-containing manganese oxide having an iridium to manganese molar ratio of 0.001 or more and 0.250 or less. In one embodiment, the manganese oxide is manganese dioxide having a β-type crystal structure. In another embodiment, the ratio of the lattice constant in the a-axis direction to the lattice constant in the c-axis direction is 1.420 or more and less than 1.521.

Description

[Technical Field]

[0001] The present disclosure relates to an iridium-containing manganese oxide, a catalyst, an electrode, and a water electrolysis method. [Background technology]

[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. One effective method for producing high-purity hydrogen gas is water electrolysis.

[0003] A polymer electrolyte membrane (PEM) water electrolysis device is typically configured by serially stacking cells each including a membrane electrode assembly (MEA) and separators sandwiching the MEA. The MEA includes a proton-conductive solid polymer electrolyte membrane (hereinafter simply referred to as "electrolyte membrane"), a catalyst layer, and a conductive substrate. A typical MEA is fabricated by bonding a conductive substrate to the surface of the catalyst layer of a catalyst-coated membrane (CCM), which has catalyst layers formed on both sides of the electrolyte membrane, by heat and pressure bonding (see, for example, Patent Document 1).

[0004] CCM can be easily produced on an industrial scale by applying an ink in which an oxygen-evolving electrode catalyst is dispersed in a solvent to an electrolyte membrane. Iridium-based catalysts are widely known to have very high activity as oxygen-evolving electrode catalysts (e.g., Non-Patent Document 1).

[0005] On the other hand, iridium is very expensive due to its limited reserves and uneven distribution in certain regions, and therefore, the development of alternative catalysts using inexpensive transition metals is underway. In recent years, transition metal materials such as manganese (Mn) have been investigated as alternative catalysts. Non-Patent Document 2 reports an iridium-containing manganese oxide in which a small amount of iridium is introduced into α-MnO2. Patent Document 2 discloses an iridium-manganese oxide composite electrode material in which iridium is introduced into manganese oxide that is electrodeposited directly onto a conductive substrate, rather than by applying an oxygen evolution electrode catalyst powder to an electrolyte membrane. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-22140 [Patent Document 2] International Publication No. 2022 / 264960 [Non-patent literature]

[0007] [Non-Patent Document 1] F. Birol, World Energy Outlook 2016, International Energy Agency (IEA), Paris, 2016. [Non-patent document 2] Nature Communications (2024)15:95 Summary of the Invention [Problem to be solved by the invention]

[0008] Iridium-containing manganese oxides such as those described in Non-Patent Document 2 and Patent Document 2 have been investigated as oxygen-generating electrode catalysts in water electrolysis, but their catalytic activity needs to be further improved before they can be put to practical use.

[0009] An object of the present disclosure is to provide at least one of an iridium-containing manganese oxide that exhibits high oxygen evolution electrode catalytic activity, a catalyst containing the same, an electrode containing the catalyst, and a water electrolysis method using the electrode. [Means for solving the problem]

[0010] This disclosure investigates the physical properties of iridium-containing manganese oxides, and has found that by controlling the manganese oxide preparation method and the iridium loading method, it is possible to obtain iridium-containing manganese oxides with specific iridium and manganese molar compositions, which exhibit significantly higher oxygen evolution electrode catalytic activity in water electrolysis than conventional iridium-containing manganese oxides.

[0011] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] An iridium-containing manganese oxide having a molar ratio of iridium to manganese of 0.001 or more and 0.250 or less. [2] The iridium-containing manganese oxide according to [1] above, wherein the manganese oxide is manganese dioxide having a β-type crystal structure. [3] The iridium-containing manganese oxide according to [2] above, wherein the ratio of the lattice constant in the a-axis direction to the lattice constant in the c-axis direction is 1.420 or more and less than 1.521. [4] The iridium-containing manganese oxide according to any one of [1] to [3] above, wherein the D50 diameter in the volume particle size distribution is 0.1 μm or more and 50.0 μm or less. [5] BET specific surface area is 1m 2 / g or more 200m 2 / g or less. [6] The iridium-containing manganese oxide according to any one of [1] to [5], wherein in a powder X-ray diffraction pattern, when CuKα radiation is used as a radiation source, the full width at half maximum of a peak appearing at 2θ=28±1.5° is greater than 1.90° and not greater than 4.00°. [7] A catalyst comprising the iridium-containing manganese oxide according to any one of [1] to [6] above. [8] An electrode comprising the catalyst according to [7] above. [9] A water electrolysis method using the electrode according to [8] above. [Effects of the Invention]

[0012] The present disclosure can provide at least one of an iridium-containing manganese oxide that exhibits high oxygen evolution electrode catalytic activity, a catalyst containing the same, an electrode containing the catalyst, and a water electrolysis method using the electrode. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure will be described below with reference to an example embodiment. The main terms used in this embodiment are as follows: 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.

[0014] The present embodiment is an iridium-containing manganese oxide that contains iridium and has a molar ratio of iridium to manganese of 0.001 or more and 0.250 or less.

[0015] The manganese oxide may be any oxide of manganese (Mn), and may be one or more selected from the group consisting of manganese oxide (MnO), manganese sesquioxide (MnO), manganese dioxide (MnO), and manganese tetraoxide (MnO). In order to have high oxygen evolution electrode catalytic activity, the manganese oxide in the iridium-containing manganese oxide of this embodiment preferably contains manganese dioxide, and is preferably electrolytic manganese dioxide.

[0016] Manganese dioxide is manganese dioxide having a γ-, β-, ε-, or α-type crystal structure. Since manganese dioxide is likely to exhibit high oxygen-evolving electrode catalytic activity when containing iridium, manganese dioxide having a β-type crystal structure (hereinafter also referred to as "β-type manganese dioxide") is preferred. Electrolytic manganese dioxide is manganese dioxide having a γ- or δ-type crystal structure, but by containing iridium and subjecting it to heat treatment (e.g., at 200°C or higher), it becomes manganese dioxide having a β-type crystal structure. The manganese dioxide contained in the iridium-containing manganese oxide of this embodiment may contain two or more manganese dioxides having different crystal structures. That is, the iridium-containing manganese oxide of this embodiment preferably contains iridium-containing β-type manganese dioxide, and more preferably iridium-containing β-type manganese dioxide.

[0017] 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, registered trademark). For example, the reference patterns for manganese dioxide having a γ-, β-, ε-, δ-, or α-type crystal structure can be PDF Nos. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), 80-1098 (δ-type), or 44-0141 (α-type), respectively.

[0018] In this embodiment, the XRD pattern was obtained by XRD measurement using a general powder X-ray diffractometer (for example, device name: Ultima IV Protectus, manufactured by Rigaku Corporation) under the following conditions. Acceleration current / voltage: 40mA / 40kV Radiation source: CuKα radiation (λ=1.5405Å) Measurement mode: Continuous scan Scan condition: 4° / min Measurement range: 2θ=10° to 80° Divergence vertical limit slit: 10mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0019] In this embodiment, the XRD peak is a peak detected by identifying the 2θ of the peak top in an XRD pattern analysis using general analysis software (e.g., SmartLab Studio II, manufactured by Rigaku). The analysis conditions for the XRD pattern include the following: Fitting conditions: Automatic, refine background Dispersive pseudo-Voigt function (peak shape)

[0020] The crystal structure of the manganese oxide of this embodiment 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 (registered trademark) PDF.

[0021] In the iridium-containing manganese oxide of this embodiment, in an XRD pattern obtained using CuKα radiation (λ=1.5405 Å) as a radiation source, the full width at half maximum (hereinafter simply referred to as "half width") of the XRD peak (hereinafter also referred to as "Mn peak") having a peak top at 2θ=28.00±1.50° is preferably at least 0.50°, at least 1.00°, or greater than 1.90°, and preferably at most 4.00° or at most 3.50°. A preferred range for the full width at half maximum of the peak appearing at 2θ=28±1.5° is greater than 1.90° and less than 4.00°. When the half width of the Mn peak is within the above range, excellent oxygen evolution electrode catalytic activity is exhibited.

[0022] When the iridium-containing manganese oxide of this embodiment has a β-type manganese dioxide (tetragonal) crystal structure, the ratio of the lattice constant in the a-axis direction (hereinafter also referred to as the "lattice constant a") to the lattice constant in the c-axis direction (hereinafter also referred to as the "lattice constant c") (hereinafter also referred to as the "a / c ratio") is preferably 1.420 or more and less than 1.521. When the a / c ratio is within the above range, iridium is uniformly dissolved in the manganese oxide, and more iridium contributes to the reaction, making it easier to achieve high oxygen evolving electrode catalytic activity. In terms of making it easier to achieve higher oxygen evolving electrode catalytic activity, the a / c ratio is preferably 1.420 or more, 1.450 or more, or 1.480 or more, and less than 1.521, or 1.520 or less. Specifically, the combination of the upper and lower limits of the a / c ratio is preferably 1.420 or more and less than 1.521, and more preferably 1.480 or more and 1.520 or less.

[0023] When the iridium-containing manganese oxide of this embodiment has a β-type manganese dioxide (tetragonal) crystal structure, the lattice constant a is preferably 4.20 Å or more and 4.51 Å or less, and more preferably 4.30 Å or more and 4.45 Å or less. When the iridium-containing manganese oxide of this embodiment has a β-type manganese dioxide (tetragonal) crystal structure, the lattice constant c is preferably 2.70 Å or more and 3.18 Å or less, and more preferably 2.80 Å or more and 3.10 Å or less.

[0024] The lattice constants a and c in the tetragonal crystal can be calculated from the position of the XRD peak corresponding to the tetragonal (110) plane (hereinafter also referred to as the "(110) peak"), which has its peak top at a lattice spacing d = 3.11 ± 0.11 Å, and the position of the XRD peak corresponding to the tetragonal (101) plane (hereinafter also referred to as the "(101) peak"), which has its peak top at a lattice spacing d = 2.40 ± 0.10 Å. The a / c ratio can be calculated from the obtained lattice constants a and c using the following formula: a / c ratio = lattice constant a[Å] / lattice constant c[Å] (1)

[0025] The iridium-containing manganese oxide of this embodiment contains iridium (Ir), and it is sufficient that the iridium is contained in a state in which it can interact with the manganese oxide, and it is preferable that the manganese oxide contains iridium. The state in which the manganese oxide contains iridium can be one or more states selected from the group consisting of a state in which the iridium is mixed with the manganese oxide, a state in which the iridium is supported on the manganese oxide, and a state in which the iridium is solid-solved in the manganese oxide, and it is preferable that at least a portion of the iridium is solid-solved in the manganese oxide.

[0026] The form of iridium contained in the iridium-containing manganese oxide of this embodiment is arbitrary, as long as it is contained in one or more forms selected from the group consisting of metals, cations, and compounds, and it is preferable that it is contained in one or more forms selected from the group consisting of metals, cations, and oxides. The iridium contained in the iridium-containing manganese oxide of this embodiment is preferably contained in the manganese oxide as at least iridium ions, and more preferably in a state where at least a portion of the iridium ions are substituted for manganese ions in the manganese oxide, i.e., at least a portion of the iridium is solid-solved in the manganese oxide.

[0027] The state in which iridium is supported on manganese oxide may be such that iridium is contained in one or more selected from the group consisting of the surface, pores, and skeletal structure of the manganese oxide. For example, when iridium is supported on the surface of manganese oxide, the iridium may be in the form of an oxide, or may be supported as iridium oxide. When iridium is supported in the pores of manganese oxide, the iridium may be contained as a cation, or may be contained as iridium cations in ion-exchangeable sites of the manganese oxide. When iridium is dissolved in manganese oxide, at least a portion of the iridium cations may be substituted for manganese ions of the manganese oxide.

[0028] In order to exhibit high oxygen evolution electrode catalytic activity, the iridium-containing manganese oxide of this embodiment preferably contains iridium in at least one of a state in which it is supported on manganese oxide and a state in which it is solid-solved in manganese oxide, and more preferably contains a part or all of the iridium in a state in which it is solid-solved in manganese oxide.

[0029] In the iridium-containing manganese oxide of this embodiment, if the ratio of the area intensity of the XRD peak having a peak top at 2θ=35.00±1.00° to the area intensity of the XRD peak with the greatest area intensity in its XRD pattern (hereinafter also referred to as the "Ir intensity ratio") is 3 or less, when the area intensity of the XRD peak with the greatest area intensity is taken as 100, then at least a portion of the iridium can be considered to be dissolved in the manganese oxide. For example, when the manganese oxide is β-type manganese dioxide, the XRD peak with the greatest area intensity is the XRD peak having a peak top at 2θ=28±1° (hereinafter also referred to as the "Mn peak").

[0030] The XRD peak with a peak top at 2θ=35.00±1.00° is considered to be the main peak of the iridium compound. Since the iridium-containing manganese oxide of this embodiment preferably contains iridium in a state of solid solution in the manganese oxide, the Ir intensity ratio is preferably 0 to 3, more preferably 0 to 1. Furthermore, the crystal structure of the manganese oxide on which iridium is supported and in which it is solid-solved is prone to distortion. In this case, the half-width of the Mn peak of the manganese oxide containing iridium in a solid-solution state tends to be larger than the half-width of the Mn peak of the manganese oxide on which iridium is supported and in which it is solid-solved, compared to the Mn peak of the manganese oxide not containing iridium in a solid-solution state. For example, the half-width of the Mn peak in the manganese oxide on which iridium is supported and in which it is solid-solved may be greater than 1.90°, 2.30° or more, or 2.50° or more. Examples of the half-width of the Mn peak may be greater than 1.90°, 2.30° or more, or 2.50° or more. Examples of the half-width may be greater than 1.90° and 4.0°, greater than 2.30° and 3.50°, or greater than 2.50° and 3.50°.

[0031] The iridium-containing manganese oxide of this embodiment has a molar ratio of iridium to manganese (mol / mol; hereinafter, also referred to as the "Ir / Mn molar ratio") of 0.001 or more and 0.250 or less. If the Ir / Mn molar ratio is less than 0.001, the properties of manganese oxide become stronger, and the oxygen generating electrode catalytic activity decreases significantly. On the other hand, if the Ir / Mn molar ratio exceeds 0.250, iridium becomes more likely to be eluted, and the oxygen generating electrode catalytic activity tends to decrease. The Ir / Mn molar ratio is preferably 0.004 or more or 0.008 or more, and is preferably 0.200 or less or 0.150 or less. Also, 0.004 or more and 0.200 or less, or 0.008 or more and 0.150 or less is preferred.

[0032] The Ir / Mn molar ratio can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a common ICP apparatus (apparatus name: Optima 830, manufactured by PerkinElmer). That is, the manganese content and iridium content of the iridium-containing manganese oxide are measured by the ICP method, and the Ir / Mn molar ratio of the iridium-containing manganese oxide can be determined from the obtained iridium content relative to the manganese content.

[0033] The "manganese content" and "iridium content" are the mass proportions of manganese and iridium, respectively, relative to the mass of the iridium-containing manganese oxide, and are calculated using the following formula: Manganese content [mass%] = (W Mn / W)×100 (2) Iridium content [mass%] = (W Ir / W)×100 (3)

[0034] In the above equation, W Mn is the mass of manganese in the iridium-containing manganese oxide [g], W Ir is the mass [g] of iridium in the iridium-containing manganese oxide, and W is the mass [g] of the iridium-containing manganese oxide determined by weighing.

[0035] In the iridium-containing manganese oxide of this embodiment, the iridium content is preferably 0.2% by mass or more or 0.8% by mass or more, and is preferably 35% by mass or less or 30% by mass or less, and is preferably 0.2% by mass or more and 35% by mass or less, or 0.8% by mass or more and 30% by mass or less, so that sufficient catalytic activity for the oxygen generation reaction is easily exhibited.

[0036] Because this makes it easier for iridium to contribute to the catalytic reaction and also makes it easier to uniformly apply the resulting anode catalyst ink to an electrolyte membrane or a conductive substrate, the D50 diameter of the iridium-containing manganese oxide of this embodiment is preferably 0.1 μm or more and 50.0 μm or less, more preferably 0.3 μm or more or 0.5 μm or more, and is also preferably 30.0 μm or less, 10.0 μm or less, or 3.0 μm or less, and more preferably 0.1 μm or more and 30.0 μm or less, 0.3 μm or more and 10.0 μm or less, or 0.5 μm or more and 3.0 μm or less.

[0037] The standard deviation in the volume particle size distribution of the iridium-containing manganese oxide of this embodiment is preferably 0.05 μm or more, and is preferably 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less, and is preferably 0.05 μm or more and 5.0 μm or less, 0.05 μm or more and 3.0 μm or less, or 0.05 μm or more and 2.0 μm or less.

[0038] The D16 diameter of the iridium-containing manganese oxide of this embodiment is preferably 0.05 μm or more, 0.15 μm or more, or 0.25 μm or more, and is preferably 30.00 μm or less, 20.00 μm or less, or 10.00 μm or less, and is preferably 0.05 μm or more to 30.00 μm or less, 0.15 μm or more to 20.00 μm or less, or 0.25 μm or more to 10.00 μm or less.

[0039] The D84 diameter of the iridium-containing manganese oxide of this embodiment is preferably 0.5 μm or more, 1.0 μm or more, or 1.5 μm or more, and is preferably 60.0 μm or less, 50.0 μm or less, or 30.0 μm or less, and is preferably 0.5 μm or more and 60.0 μm or less, 1.0 μm or more and 50.0 μm or less, or 1.5 μm or more and 30.0 μm or less.

[0040] In this embodiment, the "D16 diameter," "D50 diameter," and "D84 diameter" are the particle diameters [μm] corresponding to a cumulative frequency of 16%, 50%, and 84%, respectively, in the cumulative volume particle size distribution obtained by laser diffraction / scattering. D50 is used interchangeably with "median diameter."

[0041] The D16 diameter, D50 diameter, and D84 diameter of the iridium-containing manganese oxide of this embodiment may be measured using a general particle size distribution measuring device (for example, device name: MT-3100II, manufactured by Microtrack Bell) under the following conditions. Measurement range: 0.02 to 2000 μm Particle refractive index: 2.2 Particle permeability: permeation Particle shape: non-spherical Solvent refractive index: 1.333 Ultrasonic pretreatment: 10 minutes

[0042] The standard deviation can be calculated from the obtained D16 diameter and D84 diameter values ​​using the following formula. Standard deviation [μm] = (D84 diameter [μm] - D16 diameter [μm]) / 2 (4)

[0043] The BET specific surface area of ​​the iridium-containing manganese oxide of this embodiment is 1 m 2 / g or more 200m 2 / g or less is preferable, and 10m 2 / g or more or 19m 2 / g or more, and 100m 2 / g or less, 50m 2 / g or less or 30m 2 / g or less, and 1m 2 / g or more 100m 2 / g or less, 10m 2 / g or more 50m 2 / g or less or 19m 2 / g or more 30m 2It is more preferable that the saturation coefficient is 1 / g or less.

[0044] The BET specific surface area can be measured using a general measuring device (e.g., Macsorb, manufactured by MOUNTECH) and a mixed gas of 30% by volume nitrogen and 70% by volume helium as the adsorption gas, according to the one-point method specified in JIS Z8830: 2013. The sample to be measured is pretreated by placing it in a glass cell for BET specific surface area measurement and dehydrating it in a nitrogen flow atmosphere at 150°C for 20 minutes.

[0045] The iridium-containing manganese oxide of this embodiment can be used as a catalyst containing it. When using the iridium-containing manganese oxide of this embodiment as a catalyst, it may be used as is, or it may be used as a catalyst composition containing the iridium-containing manganese oxide of this embodiment (hereinafter, these are also collectively referred to as the "catalyst of this embodiment"). The catalyst of this embodiment can preferably be used as an oxygen generating electrode catalyst. The catalyst of this embodiment can be used as an anode catalyst (oxygen generating electrode catalyst) in a water electrolysis method using a PEM electrolytic cell, and is expected to have high oxygen generating electrode catalytic activity.

[0046] The catalyst composition may be an anode catalyst ink containing the iridium-containing manganese oxide of this embodiment, for example, a composition obtained by mixing the iridium-containing manganese oxide of this embodiment, water, ethanol, and an ionomer (for example, product name: Nafion Dispersion Solution, manufactured by Sigma-Aldrich). The composition may contain isopropyl alcohol for the purpose of adjusting viscosity, etc.

[0047] The method for producing the iridium-containing manganese oxide of this embodiment will be described below.

[0048] [Method for producing iridium-containing manganese oxide of this embodiment] The method for producing the iridium-containing manganese oxide of this embodiment is not particularly limited as long as it can produce an iridium-containing manganese oxide having the above-mentioned configuration, but it may be a production method in which at least a portion of the manganese oxide can contain iridium. Preferably, the method includes a production method (hereinafter also referred to as the "powder method") comprising a mixing step of contacting a manganese oxide source with an iridium salt solution to obtain a mixture, and a heat treatment step of heat-treating the mixture, as well as a production method (hereinafter also referred to as the "electrodeposition method") comprising an electrolysis step of electrolytically depositing manganese oxide on a conductive substrate, an iridium-containing step of contacting the manganese oxide source electrolytically deposited on a conductive substrate with an iridium salt solution to obtain a mixture and a conductive substrate, and a heat treatment step of heat-treating the mixture and the conductive substrate.

[0049] <Powder method> A preferred method for producing the iridium-containing manganese oxide of this embodiment includes a mixing step of contacting a manganese oxide source with an iridium salt solution to obtain a mixture, and a heat treatment step of heat-treating the mixture. By the powder method, the iridium-containing manganese oxide of this embodiment can be obtained in powder form.

[0050] Mixing process: In the powder method, the manganese oxide source is brought into contact with an iridium salt solution in the mixing step, thereby allowing iridium to be contained in the manganese oxide source.

[0051] Manganese oxide source: The manganese oxide source can be one or more selected from the group consisting of manganese dioxide (MnO), trimanganese tetraoxide (MnO), and manganese trioxide (MnO), with at least one of manganese dioxide and trimanganese tetraoxide, and manganese dioxide being more preferred. The manganese oxide source is preferably manganese dioxide having a γ-type crystal structure (hereinafter also referred to as "γ-type manganese dioxide"), since high oxygen evolution electrode catalytic activity is likely to be exhibited when iridium is contained.

[0052] When the manganese oxide source is γ-manganese dioxide, the crystallite diameter of the γ-manganese dioxide is preferably 2.4 nm or more and 4.0 nm or less. When the crystallite diameter of the γ-manganese dioxide is within the above range, the structure of the β-manganese dioxide is more likely to be distorted in the c-axis direction in the iridium-containing manganese oxide obtained in the heat treatment step described below, which tends to reduce the a / c ratio and, as a result, is expected to result in higher oxygen evolution electrode catalytic activity. The crystallite diameter of the γ-manganese dioxide is more preferably 2.6 to 3.5, and even more preferably 2.7 to 3.2.

[0053] In this embodiment, the "crystallite size of γ-type manganese dioxide" can be determined using the following Scherrer equation from the half-width of the XRD peak having a peak top at 2θ=22.5±1.5° in the XRD pattern of γ-type manganese dioxide when the radiation source is CuKα radiation (λ=1.5405 Å). Crystallite diameter [nm] = Scherrer constant [-] × wavelength of radiation source λ [nm] × 0.1 / (half-width [rad] × cosθ [rad]) (5) Here, the Scherrer constant is 0.879, and θ is the Bragg angle.

[0054] The D50 diameter of the manganese oxide source is preferably 0.05 μm or more and 50.00 μm or less, preferably 0.07 μm or more or 0.10 μm or more, and also preferably 30.00 μm or less, 10.00 μm or less, or 5.00 μm or less, and preferably 0.05 μm or more and 30.00 μm or less, 0.07 μm or more and 10.00 μm or less, or 0.10 μm or more and 3.00 μm or less. When the D50 diameter of the manganese oxide source is within the above range, it becomes easier to obtain an iridium-containing manganese oxide having the above-mentioned D50 diameter in the heat treatment step described below.

[0055] The D16 diameter of the manganese oxide source is preferably 0.05 μm or more, 0.15 μm or more, or 0.25 μm or more, and is preferably 30.00 μm or less, 20.00 μm or less, or 10.00 μm or less, and more preferably 0.05 μm or more to 30.00 μm or less, 0.15 μm or more to 20.00 μm or less, or 0.25 μm or more to 10.00 μm or less.

[0056] The D84 diameter of the manganese oxide source is preferably 0.5 μm or more, 1.0 μm or more, or 1.5 μm or more, and is preferably 60.0 μm or less, 50.0 μm or less, or 30.0 μm or less, and more preferably 0.5 μm or more and 60.0 μm or less, 1.0 μm or more and 50.0 μm or less, or 1.5 μm or more and 30.0 μm or less.

[0057] The powder method may include a grinding step of grinding the manganese oxide source prior to the mixing step so that the D50, D16, and D84 diameters of the manganese oxide source are within the above ranges. The manganese oxide source can be ground by a known method, such as wet grinding or dry grinding.

[0058] iridium: The iridium salt solution to be subjected to the mixing step may be any solution containing an iridium salt, and is preferably a solution containing an iridium salt, or even more preferably an aqueous solution containing an iridium salt, with an aqueous iridium salt solution being more preferred. Examples of iridium salts include iridium chloride (III) (IrCl), iridium chloride (IV) (IrCl), and iridium nitrate (Ir(NO)), with iridium chloride (III) (IrCl) being preferred. The aqueous iridium salt solution may contain one type of iridium salt, or two or more types.

[0059] The iridium concentration of the iridium salt solution is preferably 0.001 g / L or more and 20 g / L or less.

[0060] The method for contacting a manganese oxide source with an iridium salt solution is not particularly limited as long as the conditions are such that the desired amount of iridium can be contained in the manganese oxide. Specific conditions for this method include a contact temperature of 20°C or higher and 100°C or lower, and a contact time of 30 minutes or higher and 100 hours or lower. By keeping the contact time and contact temperature within the above ranges, it is believed that the iridium content on the surface of the manganese oxide can be controlled. That is, the higher the contact temperature and the longer the contact time, the more likely the iridium content of the manganese oxide tends to increase. Furthermore, when the contact temperature is high, manganese atoms within the crystal structure of the manganese oxide are more likely to be replaced by iridium atoms. Therefore, it is believed that the higher the contact temperature, the more easily iridium substitutes for manganese in the manganese oxide and forms a solid solution, and at least a portion of the iridium is more likely to be solid-dissolved in the manganese oxide. From this perspective, the contact temperature is preferably 70°C or higher, and, for example, 70°C or higher and 100°C or lower is preferred.

[0061] Heat treatment process: In the powder method, the heat treatment step involves heat treating the mixture obtained in the mixing step. This replaces manganese atoms within the crystal structure of the manganese oxide with iridium atoms contained on the surface and in the pores of the manganese oxide, resulting in even more iridium being dissolved in the manganese oxide. The heat treatment atmosphere in the heat treatment step is preferably air or an inert atmosphere, more preferably air, and the heat treatment temperature is preferably 100°C or higher and 600°C or lower. The heat treatment time may be set appropriately depending on the amount of manganese oxide, etc., to be subjected to the heat treatment, and may be, for example, 10 minutes to 24 hours.

[0062] By the powder method, it is possible to obtain an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide, and more preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide and wherein the a / c ratio is 1.420 or more and less than 1.521.

[0063] The iridium-containing manganese oxide obtained by the powder method is preferably in the form of a powder.

[0064] <Electrodeposition method> Another preferred method for producing the iridium-containing manganese oxide of this embodiment includes an electrolysis step of electrolytically depositing manganese oxide onto a conductive substrate, an iridium-containing step of contacting the manganese oxide source electrolytically deposited on the conductive substrate with an iridium salt solution to obtain a mixture and a conductive substrate, and a heat treatment step of heat-treating the mixture and the conductive substrate. This allows the iridium-containing manganese oxide of this embodiment to be obtained in a state where it coats at least a portion of the conductive substrate.

[0065] Electrolysis process: In the electrodeposition method, manganese oxide is electrolytically deposited on a conductive substrate in the electrolysis step, thereby obtaining manganese oxide electrolytically deposited on the conductive substrate (hereinafter also referred to as "electrodeposited manganese oxide source").

[0066] Electrolytic Method Any electrolytic deposition method may be used as long as the manganese oxide source is electrolytically deposited on the surface of the conductive substrate, and any method may be used as long as the conductive substrate is immersed in an electrolyte and electrolyzed.

[0067] The conductive substrate to be subjected to the electrolysis step may have a thickness of less than 500 μm, preferably 300 μm or less, and may be made of a conductive material, preferably containing titanium.

[0068] The conductive substrate may have one or more shapes selected from the group consisting of mesh, cloth, and plate. Mesh is preferred because it is likely to enhance the oxygen generating electrode catalytic activity. Specific conductive substrates include titanium mesh made of fibrous or powdered conductive titanium metal, and sintered titanium mesh obtained by heat-treating the titanium mesh. These conductive substrates are preferably coated on the surface with platinum, as this facilitates the development of high oxygen generating electrode catalytic properties. Platinum-coated titanium mesh, and platinum-coated sintered titanium mesh are more preferred as the conductive substrate.

[0069] The electrodeposited manganese oxide source is preferably manganese dioxide having a δ-type structure (hereinafter also referred to as "δ-type manganese dioxide"). This makes it easier to obtain iridium-containing manganese oxide in the iridium-containing step described below, which contains iridium, and γ-type manganese dioxide having a crystallite diameter of 2.4 nm to 4.0 nm.

[0070] The electrolytic solution may be a solution containing manganese, as long as the electrolytic manganese oxide source is electrolytically deposited on the surface of the conductive substrate. The manganese concentration of the electrolytic solution is preferably 0.05 mol / L or more and 1.00 mol / L or less. The electrolytic solution is preferably a solution containing manganese sulfate, more preferably a manganese sulfate aqueous solution. In this case, the sulfuric acid concentration is preferably 0.05 mol / L or more and 1.00 mol / L or less, and the manganese concentration is preferably 0.05 mol / L or more and 1.00 mol / L or less.

[0071] The electrolyte preferably contains an ammonium salt. The inclusion of an ammonium salt facilitates the production of δ-type manganese dioxide as an electrolytic manganese oxide source. Ammonium ions have a template effect for forming a layered structure of δ-type manganese dioxide. Furthermore, by incorporating ammonium ions between the layers of δ-type manganese dioxide, the crystal growth of δ-type manganese dioxide can be directed in a specific plane direction. As a result, in the iridium-containing step described below, the iridium-containing manganese oxide contains iridium and is likely to produce γ-type manganese dioxide having a crystallite diameter of 2.4 nm to 4.0 nm. In this case, the ammonium salt concentration in the electrolyte may be 0.1 mol / L to 3.0 mol / L. The ammonium salt may be one or more selected from the group consisting of ammonium sulfate, ammonium nitrate, and ammonium chloride, with ammonium sulfate being preferred.

[0072] In the electrolytic deposition, a conductive substrate is immersed in an electrolyte and electrolyzed. The electrolytic deposition conditions are sufficient as long as manganese oxide is electrolytically deposited, and the current density is 0.3 mA / cm per geometric area of ​​the conductive substrate. 2 More than 20mA / cm 2 and the electrolysis temperature is 93°C or higher and 98°C or lower.

[0073] Iridium-containing processes: In the electrodeposition method, the iridium-containing step involves contacting the conductive substrate and the manganese oxide electrolytically deposited on the conductive substrate (hereinafter referred to as the "manganese oxide-containing substrate") with an iridium salt solution. The manganese oxide (electrodeposited manganese oxide source) in the manganese oxide-containing substrate obtained in the electrolysis step is in a state of being adhered and deposited on the conductive substrate, so the iridium-containing step provides a mixture in which iridium is contained in the electrodeposited manganese oxide source (hereinafter also referred to as the "iridium-containing electrolytic manganese oxide source"). This results in the mixture and the conductive substrate (hereinafter also referred to as the "iridium-manganese oxide-containing substrate").

[0074] The iridium salt solution used in the iridium-containing 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 the iridium salt include one or more selected from the group consisting of iridium(III) chloride (IrCl), iridium(IV) chloride (IrCl), iridium nitrate (Ir(NO)), potassium hexachloroiridate (KIrCl), and hexachloroiridate (HIrCl).

[0075] When the electrolytic manganese oxide source is δ-type manganese dioxide, δ-type manganese dioxide has cation exchange properties and is easily reactive with δ-type manganese dioxide. Therefore, the iridium salt is preferably an iridium salt from which iridium dissociates as a cation in solution. Specifically, one or more selected from the group consisting of IrCl3, IrCl4, and Ir(NO3)4 are preferred, with IrCl3 being more preferred.

[0076] The iridium concentration of the iridium salt solution is preferably 0.001 mmol / L or more and 5,000 mmol / L or less.

[0077] The manganese oxide-containing substrate can be contacted 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 surface of the manganese oxide-containing substrate is impregnated with iridium, and examples of the contact temperature include 20°C to 100°C. The contact time can be adjusted appropriately depending on the size of the manganese oxide-containing substrate, and is, for example, 30 minutes to 24 hours.

[0078] The mixture in which iridium is contained in the electrodeposited manganese oxide source (hereinafter also referred to as "iridium-containing electrolytic manganese oxide source") is preferably γ-type manganese dioxide containing iridium, and more preferably γ-type manganese dioxide containing iridium and having a crystallite diameter of 2.4 nm to 4.0 nm. By using δ-type manganese dioxide as the electrodeposited manganese oxide source, when iridium is added to it, the crystal structure can be changed to γ-type manganese dioxide containing iridium.

[0079] Heat treatment process: In the electrodeposition method, the heat treatment step involves heat treating the iridium-manganese oxide-containing substrate. This increases the adhesion between the iridium-containing manganese oxide and the conductive substrate. The heat treatment atmosphere in the heat treatment step can be an air atmosphere or an inert atmosphere, or even an air atmosphere, and the heat treatment temperature can be 100°C or higher and 600°C or lower. The heat treatment time can be adjusted appropriately depending on the size of the conductive substrate to be subjected to the heat treatment, and can be, for example, 10 minutes to 24 hours.

[0080] By the electrodeposition method, it is possible to obtain an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.300 or less, preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.300 or less, a β-type crystal structure, and an a / c ratio of 1.420 or more and less than 1.521, and further an electrode including a catalyst containing this (the catalyst of the present embodiment) and a conductive substrate.

[0081] The iridium-containing manganese oxide obtained by electrodeposition is a production method in which iridium-containing manganese oxide is electrolytically deposited on a conductive substrate, and therefore it is possible to directly produce an electrode containing the iridium-containing manganese oxide of this embodiment and a conductive substrate (hereinafter referred to as the "electrode of this embodiment"), and further an electrode containing the catalyst of this embodiment and a conductive substrate.

[0082] The iridium-containing manganese oxide of this embodiment obtained by either the powder method or the electrodeposition method can be used as a catalyst containing it (the catalyst of this embodiment), and can be preferably used as an oxygen generating electrode catalyst.

[0083] The catalyst of this embodiment can be used as an anode catalyst for an MEA in a water electrolysis method using a PEM-type electrolytic cell. An MEA may be constructed using the iridium-containing manganese oxide obtained by the powder method as the anode catalyst of a CCM, or an MEA may be constructed using an electrode obtained by an electrodeposition method and a CCM consisting only of a cathode catalyst and an electrolyte membrane. In either case, the MEA obtained by either manufacturing method can exhibit significantly higher oxygen evolution electrode catalytic activity than conventional iridium-containing manganese oxides.

[0084] By the electrolysis method, it is possible to obtain, on a conductive substrate, an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide, and more preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide and wherein the a / c ratio is 1.420 or more and less than 1.521.

[0085] The iridium-containing manganese oxide obtained by the electrolysis method is preferably in the form of a catalyst containing the iridium-containing manganese oxide and an electrode containing a conductive substrate.

[0086] electrode: The electrode of this embodiment can be used as the anode catalyst and conductive substrate of an MEA in a water electrolysis method using a PEM electrolytic cell. In this case, an MEA can be constructed by combining the electrode of this embodiment with a CCM consisting only of a cathode catalyst and an electrolyte membrane (i.e., a CCM without an anode catalyst).

[0087] The electrode of the present embodiment comprises a catalyst and a conductive substrate, the catalyst including an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide, and more preferably an iridium-containing manganese oxide having an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide and wherein the a / c ratio is 1.420 or more and less than 1.521.

[0088] The metal content per geometric area of ​​the electrode of this embodiment (hereinafter also referred to as the "metal content of the electrode") is 0.1 mg / cm 2 More than 0.5mg / cm 2 or more than 0.8 mg / cm 2 It is preferable that the concentration is 12.0 mg / cm or more. 2 Below, 11.0mg / cm 2 or less than 10.0 mg / cm 2 Preferably less than 0.1 mg / cm 2 More than 12.0mg / cm 2 Below, 0.5mg / cm 2 More than 11.0mg / cm 2 Below, 0.8mg / cm 2 More than 10.0mg / cm 2 The metal content of the electrode is 0.1 mg / cm 2 By satisfying the above conditions, the coverage of the iridium-containing manganese oxide on the conductive substrate is improved, and high oxygen evolution electrode catalytic activity is more likely to be exhibited.

[0089] On the other hand, the metal content of the electrode is 12.0 mg / cm 2 When the electrode resistance is equal to or less than this, the electrode has a low electrical resistance, and as a result, high oxygen evolution electrode catalytic activity is easily exhibited. The metal content of the electrode of this embodiment can be calculated using the following formula. Metal content of electrode [mg / cm 2 ] = (manganese content of electrode [mg] + iridium content of electrode [mg]) / geometric area of ​​electrode [cm 2 ] (6)

[0090] The manganese content and iridium content of the electrode can be determined by the ICP method in the same way as for the measurement of the manganese content and iridium content of the iridium-containing manganese oxide. 2 The electrode is impregnated with the catalyst and the catalyst contained in the electrode is dissolved. The mixed solution with the dissolved catalyst is used as a measurement sample, and the manganese content and iridium content of the measurement sample are determined by ICP method, and these are taken as the manganese content and iridium content of the electrode.

[0091] The "geometric area" is the area equivalent to the projected area, without taking into account surface irregularities or voids, 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 ​​an electrode" is the projected area of ​​an electrode, and is the area of ​​a plane calculated by multiplying the length and width when the shape of the electrode is specified as length x width x depth.

[0092] The molar ratio of iridium to manganese per geometric area of ​​the electrode of this embodiment (hereinafter also referred to as the "Ir / Mn molar ratio of the electrode") may be the same as the Ir / Mn molar ratio of the iridium-containing manganese oxide of this embodiment.

[0093] Furthermore, the crystal structure, a / c ratio, lattice constant a, lattice constant c, Ir / Mn molar ratio, manganese content, and iridium content of the iridium-containing manganese oxide contained in the electrode of this embodiment are the same as those of the iridium-containing manganese oxide of this embodiment, and therefore description thereof will be omitted.

[0094] The conductive substrate may be any substrate made of a conductive material, and is preferably a substrate containing titanium.

[0095] The conductive substrate may have one or more shapes selected from the group consisting of mesh, cloth, and plate. Mesh is preferred because it is likely to enhance the oxygen generating electrode catalytic activity. Specific conductive substrates include titanium mesh made of fibrous or powdered conductive titanium metal, and sintered titanium mesh obtained by heat-treating the titanium mesh. These conductive substrates are preferably coated on the surface with platinum, as this facilitates the development of high oxygen generating electrode catalytic properties. Platinum-coated titanium mesh, and platinum-coated sintered titanium mesh are more preferred as the conductive substrate.

[0096] When the surface of the conductive substrate is coated with platinum, the amount of platinum per geometric area is 0.5 mg / cm to exhibit high conductivity. 2 More than 10.0mg / cm 2 Preferably less than 1.0 mg / cm 2 More than 8.0mg / cm 2 Less than 1.0 mg / cm is more preferable. 2 More than 6.0mg / cm 2 The following is even more preferred:

[0097] The thickness of the conductive substrate is preferably 50 μm or more and 500 μm or less, more preferably 100 μm or more and 400 μm or less, and even more preferably 150 μm or more and 300 μm or less, in order to exhibit excellent oxygen evolution electrode catalytic activity.

[0098] The "thickness" refers to the length corresponding to the length in the direction perpendicular to the geometric surface. The "thickness of the conductive substrate" refers to the length corresponding to the length in the direction perpendicular to the geometric surface of the conductive substrate, and is the length corresponding to the width when the shape of the electrode is defined as length x width x depth.

[0099] The porosity of the conductive substrate is preferably 30% to 80%, more preferably 40% to 70%. Here, the porosity is defined as the volume of the space that is free of the conductive substrate within the volume of the conductive substrate, and the porosity can be measured, for example, by mercury plethysmography. When the porosity is within the above range, excellent effects can be obtained in that the mechanical strength of the electrode is increased and water, which is a reactive gas for oxygen generation, can be smoothly supplied.

[0100] The porosity in this embodiment is calculated from the following formula. Porosity (%) = {1 - (bulk density of conductive substrate (g / cm 3 ) / skeletal density of conductive substrate (g / cm 3 ))}×100

[0101] The bulk density and skeletal density of the conductive substrate are values ​​that can be calculated using the following formulas from the pore volume measured by the mercury pressure method using a general mercury porosimeter (device name: AutoPore 9510, manufactured by Micromeritics) and the volume of the conductive substrate. Bulk density of conductive substrate (g / cm 3 ) = Mass of conductive substrate (g) / Volume of conductive substrate (cc) Skeletal density of conductive substrate (g / cm 3 ) = Mass of conductive substrate (g) / {Volume of conductive substrate - Pore volume} (cc)

[0102] In the above two equations, the volume of the conductive substrate is a value that can also be determined by measurement with a laser volume meter (device name: 3D scanner-type coordinate measuring machine VL-700 series (controller VL-700, stage VL-750 / VL-C35, measurement unit VL-770), manufactured by Keyence Corporation), and the mass of the conductive substrate is a value that can be determined by mass measurement using an electronic balance.

[0103] Specific measurement conditions for the mercury porosimeter are as follows. Sample amount: 40 mg Mercury introduction pressure: 601.6 psia to 36,098.1 psia (4.1MPa~248.9MPa) Measuring pore diameter: 5nm~500μm Cell used: Pressurized volume 5.3cc glass cell Mercury surface tension: 480dyn Mercury contact angle: 130° Pretreatment conditions: Degassing in air at 110°C for at least 1 hour

[0104] [Method for manufacturing electrode according to this embodiment] When the iridium-containing manganese oxide of this embodiment is an iridium-containing manganese oxide obtained by electrodeposition, the iridium-containing manganese oxide is integrated with the conductive substrate, and therefore this may be used as is as the electrode of this embodiment.

[0105] On the other hand, when the iridium-containing manganese oxide of this embodiment is obtained by a powder method, the electrode of this embodiment can be obtained by forming the iridium-containing manganese oxide into a catalyst ink and applying the catalyst ink to a conductive substrate. The catalyst ink can be in a state where the Ir-Mn oxide is dispersed in a solvent, and the solvent can be water, alcohol, or a mixture of water and alcohol. [Example]

[0106] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0107] <Composition analysis> The prepared sample was dissolved in a mixed solution of hydrochloric acid and nitric acid, and the manganese and iridium contents of the prepared sample were measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a general ICP device (device name: Optima 830, manufactured by PerkinElmer). The Ir / Mn molar ratio of the prepared sample was calculated from the obtained manganese and iridium contents.

[0108] <Particle size distribution> The volume particle size distribution was determined by measuring the volume particle size distribution using a laser diffraction / scattering particle size distribution analyzer (device name: Microtrac MT3300EXII, manufactured by Microtrac Bell). The measurement conditions are as follows: Measurement range: 0.02 to 2000 μm Particle refractive index: 2.2 Particle permeability: permeation Particle shape: non-spherical Solvent refractive index: 1.333 Ultrasonic pretreatment: 10 minutes

[0109] From the obtained volume particle size distribution, the D16 diameter [μm], D50 diameter (median diameter) [μm], and D84 diameter [μm] of the prepared sample were obtained. Also, from the obtained values of the D16 diameter and D84 diameter, the standard deviation was calculated using the above formula (4).

[0110] <BET specific surface area> The BET specific surface area of the prepared sample was determined by measurement according to JIS Z 8830:2013. That is, 0.3 g of the prepared sample was placed in a glass cell for BET specific surface area measurement, and dehydration treatment was performed at 150 °C for 20 minutes in a nitrogen flow atmosphere as a pretreatment. Using a general BET specific surface area measuring device (product name: Macsorb (registered trademark), manufactured by MOUNTECH Co., Ltd.), the BET specific surface area of the prepared sample after pretreatment was measured by the one-point method using a mixed gas of 30% by volume of nitrogen - 70% by volume of helium as the adsorption gas.

[0111] <Full width at half maximum (FWHM)><00​​​​​​​​​​​​​​​​​​​​​​​​The crystalline phase of the prepared samples was identified by comparing the obtained XRD patterns with reference patterns, PDF Nos. 14-0644 (γ-type MnO), 24-0735 (β-type MnO), 30-0820 (ε-type MnO), 80-1098 (δ-type), and 44-0141 (α-type MnO).

[0113] The XRD pattern of the prepared sample was analyzed using the analysis software (product name: PDXL2, manufactured by Rigaku Corporation) attached to the powder X-ray diffractometer, and the full width at half maximum (°) of the XRD peak having a peak top at 2θ = 28 ± 1.5° was calculated and used as the half width (°).

[0114] The background was removed from the obtained XRD pattern using the analysis software (product name: PDXL2, manufactured by Rigaku Corporation) attached to the powder X-ray diffractometer. Then, the interplanar spacing d [Å] was calculated using the diffraction angles [°] of the (110) and (101) peak tops and the Bragg equation, and the lattice constants a [Å] and c [Å] in the tetragonal crystal were calculated. The a / c ratio was calculated from the obtained lattice constants a and c using the above formula (1).

[0115] Example 1: <Preparation of iridium-containing manganese oxide powder> Electrolytic manganese dioxide (product name: HMR-AF, manufactured by Tosoh Corporation) was jet milled to a median diameter of 0.5 μm and a BET specific surface area of ​​47 m 2 / g of manganese dioxide powder (manganese oxide source) was obtained. The manganese dioxide was γ-type manganese dioxide with a crystallite diameter of 3.0 nm.

[0116] 500 mg of the manganese dioxide powder was immersed in an iridium salt solution bath filled with 33.2 mL of potassium hexachloroiridate (K2IrCl6) aqueous solution (53 mg of K2IrCl6 content) with a K2IrCl6 concentration of 1.60 g / L at 95°C for 48 hours, and a mixture was obtained by solid-liquid separation. The resulting mixture was dried in the air at 90°C for 2 hours, then allowed to cool to room temperature by natural cooling, and then annealed in the air at 450°C for 5 hours, yielding an iridium-containing manganese oxide powder.

[0117] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.12, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0118] Example 2: An iridium-containing manganese oxide powder was obtained in the same manner as in Example 1, except that 33.2 mL of a K2IrCl6 aqueous solution with a K2IrCl6 concentration of 3.98 g / L (K2IrCl6 content: 132 mg) was used as the K2IrCl6 aqueous solution.

[0119] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of the Mn peak of 2.40, which indicated that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0120] Example 3: An iridium-containing manganese oxide powder was obtained in the same manner as in Example 1, except that 33.2 mL of a K2IrCl6 aqueous solution with a K2IrCl6 concentration of 9.97 g / L (K2IrCl6 content: 331 mg) was used as the K2IrCl6 aqueous solution.

[0121] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.99, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0122] Example 4: An iridium-containing manganese oxide powder was obtained in the same manner as in Example 1, except that 33.2 mL of a K2IrCl6 aqueous solution with a K2IrCl6 concentration of 19.91 g / L (K2IrCl6 content: 661 mg) was used as the K2IrCl6 aqueous solution.

[0123] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.99, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0124] Example 5: Instead of manganese dioxide after grinding, it has a γ-type crystal structure, a crystallite diameter of 2.5 nm, a median diameter of 2.3 μm, and a BET specific surface area of ​​45 m 2 An iridium-containing manganese oxide powder was obtained in the same manner as in Example 1, except that electrolytic manganese dioxide powder (product name: FM, manufactured by Tosoh Corporation) with a KIrCl concentration of 2.504 g / L was used, and the manganese dioxide powder was immersed for 24 hours in an iridium salt solution bath filled with 99.8 mL of a KIrCl aqueous solution (containing 250 mg of KIrCl) with a KIrCl concentration of 2.504 g / L.

[0125] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of the Mn peak of 2.20, which indicated that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0126] Example 6: Instead of manganese dioxide after grinding, it has a γ-type crystal structure, a crystallite diameter of 2.5 nm, a median diameter of 2.3 μm, and a BET specific surface area of ​​45 m 2 An iridium-containing manganese oxide powder was obtained in the same manner as in Example 1, except that electrolytic manganese dioxide powder (product name: FM, manufactured by Tosoh Corporation) with a KIrCl concentration of 2.504 g / L was used, and the manganese dioxide powder was immersed for 96 hours in an iridium salt solution bath filled with 99.8 mL of a KIrCl aqueous solution (containing 250 mg of KIrCl) with a KIrCl concentration of 2.504 g / L.

[0127] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.91, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0128] Example 7: As manganese dioxide, the median diameter is 7.9 μm and the BET specific surface area is 36 m 2 An iridium-containing manganese oxide powder was obtained in the same manner as in Example 1, except that electrolytic manganese dioxide powder (product name: LM-10P, manufactured by Tosoh Corporation) with a KIrCl concentration of 20.00 g / L was used and the manganese dioxide powder was immersed for 96 hours in an iridium salt solution bath filled with 13.9 mL of an aqueous KIrCl solution (containing 278 mg of KIrCl) with a KIrCl concentration of 20.00 g / L.

[0129] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of the Mn peak of 2.52, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0130] Example 8: 2 kg of electrolytic manganese dioxide raw material powder (product name: HMR-AF, manufactured by Tosoh Corporation) was mixed with pure water to prepare a slurry with a solids concentration of 20% by mass. The slurry was then pulverized for 3 hours in a mill (device name: Dynomill, manufactured by Shinmaru Enterprises) using 0.5 mm diameter zirconia media, a filling rate of 80% by volume, and a peripheral speed of 14 m / s. After pulverization, the mixture was dried overnight at 90°C in an air atmosphere to obtain electrolytic manganese dioxide powder. The electrolytic manganese dioxide was a gamma-type manganese dioxide with a crystallite diameter of 3.0 nm and a D50 diameter of 0.4 μm.

[0131] 500 mg of electrolytic manganese dioxide powder was immersed in an iridium salt solution bath filled with 68.6 mL of IrCl3 aqueous solution (IrCl3 concentration: 0.005 mol / L) at 95°C for 24 hours, followed by solid-liquid separation to obtain a mixture. The resulting mixture was dried in an air atmosphere at 90°C for 2 hours and then allowed to cool naturally to room temperature. Annealing was then performed in an air atmosphere at 450°C for 5 hours to obtain the iridium-containing manganese oxide powder of this example. The XRD pattern of this powder showed a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.51, indicating that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0132] Example 9: The iridium-containing manganese oxide powder of this example was obtained in the same manner as in Example 8, except that 68.6 mL of an Ir(NO3)4 aqueous solution (Ir(NO3)4 concentration: 0.005 mol / L) was used as the iridium salt solution. The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.45, indicating that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0133] Example 10: The iridium-containing manganese oxide powder of this example was obtained in the same manner as in Example 8, except that 114.3 mL of an Ir(NO3)4 aqueous solution (Ir(NO3)4 concentration: 0.005 mol / L) was used as the iridium salt solution. The XRD pattern of this powder revealed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.77, indicating that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0134] Example 11: The iridium-containing manganese oxide powder of this example was obtained in the same manner as in Example 8, except that 45.7 mL of an IrCl4 aqueous solution (IrCl4 concentration: 0.004 mol / L) was used as the iridium salt solution. The XRD pattern of this powder revealed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.70, indicating that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0135] Example 12: The iridium-containing manganese oxide powder of this example was obtained in the same manner as in Example 8, except that 96.0 mL of an IrCl4 aqueous solution (IrCl4 concentration: 0.004 mol / L) was used as the iridium salt solution. The XRD pattern of this powder revealed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.35, indicating that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0136] Example 13: The iridium-containing manganese oxide powder of this example was obtained in the same manner as in Example 8, except that 160.0 mL of an IrCl4 aqueous solution (IrCl4 concentration: 0.004 mol / L) was used as the iridium salt solution. The XRD pattern of this powder revealed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.19, indicating that it was iridium-containing β-type manganese dioxide, containing at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0137] Example 14: The electrolytic cell was filled with a sulfuric acid-manganese sulfate-ammonium sulfate mixed solution with a sulfuric acid concentration of 0.3 mol / L, a manganese sulfate concentration of 0.5 mol / L, and an ammonium sulfate concentration of 1.5 mol / L, and a conductive substrate made of platinum-coated Ti fiber sintered body (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was immersed in the solution. The conductive substrate was subjected to a current density of 7 mA / cm. 2 A current was applied for 10 minutes at 40°C to electrochemically deposit manganese oxide onto the conductive substrate. The manganese oxide was δ-type manganese dioxide.

[0138] Next, the conductive substrate on which the manganese oxide obtained above had been precipitated was immersed in an iridium salt solution of 0.1 mmol / L iridium chloride (III) (IrCl3) and 0.01 mol / L sulfuric acid at 95°C for 24 hours to obtain a mixture and a conductive substrate. The mixture was a γ-type manganese dioxide containing iridium with a crystallite diameter of 3.1 nm. The mixture and conductive substrate were annealed in air at 450°C for 5 hours to obtain the iridium-containing manganese oxide of this example precipitated on the conductive substrate.

[0139] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.03, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0140] Example 15: Manganese oxide was electrochemically deposited on the conductive substrate in the same manner as in Example 14, except that the electrolytic cell was filled with a sulfuric acid-manganese sulfate mixed solution having a sulfuric acid concentration of 0.36 mol / L and a manganese sulfate concentration of 0.36 mol / L. The manganese oxide was γ-type manganese dioxide.

[0141] Next, the conductive substrate on which the manganese oxide obtained above had been precipitated was immersed in an iridium salt solution of 0.1 mmol / L potassium hexachloroiridate (K2IrCl6) and 0.01 mol / L sulfuric acid at 95°C for 24 hours to obtain a mixture and a conductive substrate. The mixture was a γ-type manganese dioxide containing iridium with a crystallite diameter of 3.8 nm. The mixture and conductive substrate were annealed in air at 450°C for 5 hours to obtain the iridium-containing manganese oxide of this example precipitated on the conductive substrate.

[0142] The XRD pattern of this powder showed that it had a β-type crystal structure, an Ir intensity ratio of 0, and a Mn peak half-width of 2.29, indicating that it was iridium-containing β-type manganese dioxide, which contains at least a portion of iridium in a solid solution state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0143] Comparative Example 1: Electrolytic manganese dioxide (product name: HMR-AF, manufactured by Tosoh Corporation) was pulverized to a median diameter of 0.5 μm and a BET specific surface area of ​​47 m 2 / g of manganese dioxide powder (manganese oxide source) was obtained.

[0144] 500 mg of the obtained manganese dioxide powder (manganese oxide source) was annealed in an air atmosphere at 450°C for 5 hours to obtain a β-type manganese dioxide powder, which was the powder of this comparative example. The half-width of the Mn peak was 2.06. The powder also had a D16 diameter of 0.5 μm, a D50 diameter of 0.7 μm, and a D84 diameter of 1.9 μm, with a standard deviation of 0.7 μm. The evaluation results of the powder are shown in the table below.

[0145] [Table 1]

[0146] [Table 2]

[0147] [Table 3]

[0148] Measurement example 1: <Oxygen Evolution Electrode Catalyst Evaluation> Membrane-electrode assemblies (hereinafter also referred to as "MEAs") each having an iridium-containing manganese oxide of each of the examples and comparative examples as an anode catalyst, and PEM-type water electrolyzers each having the MEA were fabricated by the following methods.

[0149] Preparation of PEM-type water electrolyzer using Examples 1 to 13 and Comparative Example 1: A cathode catalyst ink was prepared by mixing a solution containing water, ethanol, and ionomer (product name: Nafion dispersion solution, manufactured by Sigma-Aldrich) with a 20% by mass platinum-supported carbon catalyst (product name: 20% Platinum on Vulcan XC-72, manufactured by Sigma-Aldrich). The mass ratio of water:ethanol:ionomer in the cathode catalyst ink was 55.5:43.5:1.0. This resulted in a platinum loading per geometric area of ​​0.3 mg / cm. 2 The solution was applied to carbon paper (product name: TGP-H-060H, manufactured by Toray Industries, Inc.) so that the solution satisfies the following formula: and air-dried to prepare a cathode electrode. Next, a cation exchange membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was boiled and washed in 3% by mass hydrogen peroxide solution for 1 hour, purified water for 1 hour, and 1 M sulfuric acid solution for 1 hour, and then protonated to prepare an electrolyte membrane.

[0150] Furthermore, the iridium-containing manganese oxides of Examples 1 to 13 and Comparative Example 1 were mixed with a solution containing water, isopropanol, and ionomer (product name: Nafion dispersion solution, manufactured by Sigma-Aldrich) to prepare anode catalyst inks. The mass ratio of water:isopropanol:ionomer in the anode catalyst inks was 55.9:43.8:0.3. This resulted in an Ir loading per geometric area of ​​0.1 mg / cm. 2 The solution was applied to a PTFE sheet (manufactured by Tokyo Glass Instruments Co., Ltd.) having a thickness of 0.05 mm so as to give the following composition, and then air-dried to obtain a sheet with a catalyst layer.

[0151] The catalyst layer-attached sheet was laminated on the electrolyte membrane so that the surface coated with the anode catalyst faced the electrolyte membrane, and then heated at 140°C with a clamping force of 80 kg / cm using a hot press (product name: SA-302, manufactured by Tester Sangyo Co., Ltd.). 2 The PTFE sheet was then peeled off to obtain a catalyst-coated electrolyte membrane.

[0152] The anode current collector, catalyst-coated electrolyte membrane, and cathode electrode were stacked in this order, with the platinum-coated Ti fiber sintered compact (product name: Pt-plated Ti fiber sintered compact, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.; hereinafter also referred to as the "anode current collector") facing the anode catalyst-coated surface of the catalyst-coated electrolyte membrane, and with the catalyst-free surface of the catalyst-coated electrolyte membrane facing the cathode catalyst-coated surface of the cathode electrode. The resulting stack was then heated in a hot press at 130°C with a clamping force of 50 kg / cm. 2 The MEA was obtained by hot pressing for 3 minutes at 100°C. The obtained MEA was attached to the housing of a PEM water electrolyzer (product name: WE-4S-RICW, manufactured by FC Development Co., Ltd.) to prepare a PEM water electrolyzer.

[0153] Preparation of PEM-type water electrolyzer using Examples 14 and 15: The conductive substrates provided with the iridium-containing manganese oxides of Example 14 and Example 1 were each used as working electrodes (anodes).

[0154] A conductive catalyst ink was prepared by mixing a 20% platinum-supported carbon catalyst (product name: 20% Platinum on Vulcan XC-72, Sigma-Aldrich) with a solution containing water, ethanol, and ionomer (product name: Nafion dispersion, Sigma-Aldrich). This ink was then applied to carbon paper (product name: TGP-H-060, Toray Industries, Inc.) and air-dried to form the counter electrode.

[0155] Next, a Nafion membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was washed and protonated by boiling it in 3% by mass hydrogen peroxide solution for 1 hour, pure water for 1 hour, 1 M sulfuric acid aqueous solution for 1 hour, and pure water for 1 hour, in that order, to prepare an electrolyte membrane.

[0156] The electrolyte membrane was sandwiched between the catalytic surfaces of the working electrode (anode) and the counter electrode, and the mixture was heated at 135°C and a clamping force of 400 kg / cm using a hot press machine (product name: SA-302, manufactured by Tester Sangyo Co., Ltd.). 2The MEA was obtained by hot pressing for 3 minutes at 100°C. The obtained MEA was attached to the housing of a PEM water electrolyzer (product name: WE-4S-RICW, manufactured by FC Development Co., Ltd.) to prepare a PEM water electrolyzer.

[0157] <Evaluation of oxygen evolution electrode catalyst performance> Using a PEM-type water electrolyzer, the current density at a voltage of 2 V was measured by linear sweep voltammetry (LSV) of a two-electrode system under the following conditions, and the performance of the oxygen evolution electrode catalyst was evaluated. Voltage increase rate: 10mV / sec Water temperature: 80℃ Water supply rate: 2mL / min

[0158] MEAs each containing the powders of the Examples and Comparative Examples as anode catalysts and PEM-type water electrolyzers each containing the MEAs were fabricated, and the oxygen generating electrode catalysts were evaluated. The results are shown in the table below.

[0159] [Table 4]

[0160] Table 1 confirms that, compared to Comparative Example 1 which does not contain iridium, the iridium-supported manganese oxide powder which contains iridium and has an Ir / Mn molar ratio of 0.001 or more and 0.25 or less exhibits high oxygen evolution electrode catalytic activity.

[0161] The current density increased with increasing Ir / Mn molar ratio, reaching 2 A / cm for the sample with an Ir / Mn molar ratio of 0.065 mol / mol. 2 It was confirmed that the above current density could be obtained.

[0162] In Examples 1 to 4 and Comparative Example 1, the D16 diameter was 0.5 μm, the D50 diameter was 0.7 μm, the D84 diameter was 1.9 μm, and the standard deviation was 0.7 μm, confirming that the treatment with the KIrCl aqueous solution and the subsequent heat treatment had no effect on the particle diameter.

[0163] The current density increased as the a / c ratio decreased, and it was confirmed that iridium-containing manganese oxides with a / c ratios of less than 1.521 exhibited high oxygen evolution electrode catalytic properties. [Industrial Applicability]

[0164] The present disclosure provides at least one of an iridium-containing manganese oxide that exhibits high oxygen evolution electrode catalytic activity, a catalyst containing the same, an electrode containing the catalyst, and a water electrolysis method using the electrode.

Claims

1. An iridium-containing manganese oxide, wherein the molar ratio of iridium to manganese is 0.001 or more and 0.250 or less, the ratio of the lattice constant in the a-axis direction to the lattice constant in the c-axis direction is 1.420 or more and less than 1.521, and the full width at half maximum of a peak appearing at 2θ = 28 ± 1.5° when CuKα radiation is used as the radiation source in a powder X-ray diffraction pattern is more than 1.90° and 4.00° or less, wherein the manganese oxide in the iridium-containing manganese oxide is manganese dioxide having a β-type crystal structure.

2. The iridium-containing manganese oxide according to claim 1, wherein the D50 diameter in the volume particle size distribution is 0.1 μm or more and 50.0 μm or less.

3. BET specific surface area is 1m ２ / g or more 200m ２ The iridium-containing manganese oxide according to claim 1 or 2, wherein the iridium content is 1 / g or less.

4. A catalyst comprising the iridium-containing manganese oxide according to claim 1 or 2.

5. An electrode comprising the catalyst of claim 4.

6. A water electrolysis method using the electrode according to claim 5.

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