Iridium-containing manganese oxides, catalysts, electrodes, and water electrolysis methods

Abstract

The present disclosure provides at least any one of an iridium-containing manganese oxide exhibiting high oxygen evolution electrode catalytic activity in a water electrolysis method, a catalyst including the same, an electrode including the catalyst, and a water electrolysis method using the electrode. The iridium-containing manganese oxide of the present invention has a molar ratio of iridium to manganese of 0.001 or more and 0.250 or less. In one mode, the above manganese oxide is manganese dioxide having a crystal structure of a β type. In addition, in one mode, 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] This disclosure relates to an iridium-containing manganese oxide, a catalyst, an electrode, and a method for water electrolysis. Background Technology

[0002] Due to the depletion of fossil fuels and environmental pollution, the utilization and production methods of hydrogen as a clean energy source have attracted attention. Water electrolysis is one of the effective methods for producing high-purity hydrogen.

[0003] Solid polymer membrane (PEM) type water electrolysis devices are typically constructed by stacking single cells (cells) in series, each having a membrane-electrode assembly (MEA) and a separator holding the MEA. The MEA comprises: a solid polymer electrolyte membrane (hereinafter also simply referred to as "electrolyte membrane") with proton conductivity, a catalyst layer, and a conductive substrate. As a conventional method for manufacturing an MEA, a conductive substrate is bonded to the catalyst layer of a catalyst-coated electrolyte membrane (CCM), on both sides of the electrolyte membrane, by heating and pressing (e.g., Patent Document 1).

[0004] CCM is easily manufactured on an industrial scale by coating an ink obtained by dispersing an oxygen generating electrode catalyst in a solvent onto an electrolyte membrane. Iridium-based catalysts are widely known to have very high activity as oxygen generating electrode catalysts (e.g., non-patent literature 1).

[0005] On the other hand, iridium is very expensive due to its scarcity and uneven distribution in specific regions, 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 obtained by introducing a small amount of iridium into α-MnO2. Patent Document 2 discloses an iridium-manganese oxide composite electrode material, which is obtained by introducing iridium into manganese oxide directly electrolytically deposited on a conductive substrate, rather than coating oxygen-generating electrode catalyst powder onto an electrolyte membrane.

[0006] Existing technical documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-22140

[0008] Patent Document 2: International Publication No. 2022 / 264960

[0009] Non-patent literature

[0010] Non-patent literature 1: F. Birol, World Energy Outlook 2016, International Energy Agency (IEA), Paris, 2016.

[0011] Non-patent literature 2: Nature Communications (2024) 15:95

[0012] Iridium-containing manganese oxides, such as those in Non-Patent Document 2 and Patent Document 2, have been studied as oxygen-generating electrode catalysts in water electrolysis, but their catalytic activity needs further improvement before practical application. Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] The purpose of this disclosure is to provide at least one of an iridium-containing manganese oxide exhibiting high oxygen-generating electrode catalytic activity, a catalyst comprising the same, an electrode comprising the catalyst, and a water electrolysis method using the electrode.

[0015] Technical solutions for solving the problem

[0016] This disclosure investigates various physical properties of iridium-containing manganese oxides. The results show that by controlling the preparation method of the manganese oxide and the iridium loading method, iridium-containing manganese oxides with specific molar compositions of iridium and manganese can be obtained, exhibiting significantly higher oxygen-generating electrode catalytic activity in water electrolysis compared to conventional iridium-containing manganese oxides.

[0017] That is, the present invention is as described in the claims, and the gist of this disclosure is as follows.

[0018] [1] An iridium-containing manganese oxide having an iridium to manganese molar ratio of more than 0.001 and less than 0.250.

[0019] [2] According to the iridium-containing manganese oxide described in [1] above, wherein the manganese oxide is manganese dioxide having a β-type crystal structure.

[0020] [3] According to the iridium-containing manganese oxide described in [2] above, the ratio of the lattice constant in the a-axis direction to the lattice constant in the c-axis direction is greater than 1.420 and less than 1.521.

[0021] [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.

[0022] [5] The iridium-containing manganese oxide according to any one of [1] to [4] above, wherein the BET specific surface area is 1 m². 2 / g or more and 200m 2 / g or less.

[0023] [6] According to any one of [1] to [5] above, the full width at half maximum (FWHM) of the peak appearing at 2θ = 28 ± 1.5° when using CuKα line as the X-ray source in the powder X-ray diffraction pattern is greater than 1.90° and less than 4.00°.

[0024] [7] A catalyst comprising any one of the above [1] to [6] iridium-containing manganese oxides.

[0025] [8] An electrode comprising the catalyst described in [7] above.

[0026] [9] A water electrolysis method using the electrodes described above [8].

[0027] Invention Effects

[0028] According to this disclosure, at least one of the following can be provided: an iridium-containing manganese oxide exhibiting high oxygen-generating electrode catalytic activity, a catalyst containing the same, an electrode containing the catalyst, and a water electrolysis method using the electrode. Detailed Implementation

[0029] The following description illustrates one embodiment of this disclosure. It should be noted that the main terminology used in this embodiment is as follows. Furthermore, the structures and parameters disclosed in this specification can be combined arbitrarily, and the upper and lower limits of the numerical values ​​disclosed in this specification can also be combined arbitrarily.

[0030] This embodiment is an iridium-containing manganese oxide containing iridium, wherein the molar ratio of iridium to manganese is 0.001 or more and 0.250 or less.

[0031] The manganese oxide can be any oxide of manganese (Mn), and can be selected from one or more of manganese oxide (MnO), manganese trioxide (Mn2O3), manganese dioxide (MnO2), and manganese tetroxide (Mn3O4). In order to have high catalytic activity of oxygen generating electrode, the manganese oxide in the iridium-containing manganese oxide of this embodiment preferably includes manganese dioxide, and more preferably electrolytic manganese dioxide.

[0032] Manganese dioxide is manganese dioxide with a γ-, β-, ε-, or α-type crystal structure. Considering that it readily exhibits high catalytic activity in the oxygen-generating electrode when containing iridium, manganese dioxide with a β-type crystal structure (hereinafter also referred to as "β-type manganese dioxide") is preferred. It should be noted that electrolytic manganese dioxide with a γ- or δ-type crystal structure is converted to manganese dioxide with a β-type crystal structure by incorporating iridium and subjecting it to heat treatment (e.g., at 200°C or higher). The iridium-containing manganese oxide of this embodiment may contain two or more types of manganese dioxide with 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.

[0033] The crystal structure of manganese oxides can be identified by comparing its powder X-ray diffraction (XRD) pattern with the XRD pattern registered in the ICDD (International Data Center for Diffraction) PDF (Powder Diffraction File, registered trademark) (hereinafter referred to as "reference pattern"). For example, the reference patterns for manganese dioxide with γ-type, β-type, ε-type, δ-type, or α-type crystal structures can be obtained using PDF No. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), 80-1098 (δ-type), or 44-0141 (α-type), respectively.

[0034] In this embodiment, the XRD pattern is obtained by XRD measurement under the following conditions using a conventional powder X-ray diffraction apparatus (e.g., apparatus name: UltimaIV Protectus, manufactured by Rigaku Co., Ltd.).

[0035] Accelerating current and voltage: 40mA·40kV

[0036] X-ray source: CuKα line (λ=1.5405Å)

[0037] Measurement mode: Continuous scanning

[0038] Scanning conditions: 4° / minute

[0039] Measurement range: 2θ = 10°~80°

[0040] Longitudinal diverging slit: 10mm

[0041] Diverging / Incident Slit: 1°

[0042] Light-receiving slit: open

[0043] Detector: D / teX Ultra

[0044] Using a Ni filter

[0045] In this embodiment, the XRD peak is the 2θ peak at the apex determined and detected during the analysis of XRD patterns using conventional analysis software (e.g., SmartLab StudioII, manufactured by Rigaku Co., Ltd.). The following conditions can be cited as criteria for XRD pattern analysis.

[0046] Fitting conditions: Automatic, refined background

[0047] Dispersed pseudo-Voigt function (peak shape)

[0048] For the manganese oxide of this embodiment, the crystal structure can be identified by comparing its powder X-ray diffraction (hereinafter also referred to as "XRD") pattern with the XRD pattern registered in the ICDD (International Data Center for Diffraction) PDF (Powder Diffraction File, registered trademark) (hereinafter also referred to as "reference pattern").

[0049] For the iridium-containing manganese oxide of this embodiment, in the XRD pattern using the CuKα line (λ = 1.5405 Å) as the X-ray source, the lower limit of the full width at half maximum (WHM) of the XRD peak (hereinafter also referred to as the "Mn peak") with a apex at 2θ = 28.00 ± 1.50° is preferably 0.50° or more, 1.00° or more, or greater than 1.90°, and the upper limit is preferably 4.00° or less or 3.50° or less. As a preferred range for the WHM of the peak appearing at the aforementioned 2θ = 28 ± 1.5°, values ​​greater than 1.90° and less than 4.00° are possible. By setting the WHM of the Mn peak to the above values, excellent oxygen-generating electrode catalytic activity is exhibited.

[0050] For the iridium-containing manganese oxide of this embodiment, when its crystal structure is β-type manganese dioxide (tetragonal), the ratio (hereinafter, also called "a / c ratio") of the lattice constant in the a-axis direction (hereinafter also called "lattice constant a") to the lattice constant in the c-axis direction (hereinafter also called "lattice constant c") is preferably 1.420 or more and less than 1.521. By making the a / c ratio the above value, iridium is uniformly dissolved in the manganese oxide, which helps to increase the amount of iridium in the reaction, and thus it is easy to obtain high oxygen generating electrode catalytic activity. From the viewpoint of easily obtaining higher oxygen generating electrode catalytic activity, the a / c ratio is preferably 1.420 or more, 1.450 or more, or 1.480 or more, and preferably less than 1.521 or less. As a specific combination of the upper and lower limits of the a / c ratio, it is preferably 1.420 or more and less than 1.521, and more preferably 1.480 or more and less than 1.520.

[0051] For the iridium-containing manganese oxide of this embodiment, when its crystal structure is β-type manganese dioxide (tetragonal), the lattice constant α is preferably 4.20 Å or more and 4.51 Å or less, more preferably 4.30 Å or more and 4.45 Å or less. Furthermore, for the iridium-containing manganese oxide of this embodiment, when its crystal structure is β-type manganese dioxide (tetragonal), the lattice constant c is preferably 2.70 Å or more and 3.18 Å or less, more preferably 2.80 Å or more and 3.10 Å or less.

[0052] For the lattice constants a and c, the lattice constants in the tetragonal crystal can be calculated from the peak positions of the XRD peaks (hereinafter referred to as "(110) peaks") on the tetragonal (110) plane with a peak at an interplanar spacing d = 3.11 ± 0.11 Å and the XRD peaks (hereinafter referred to as "(101) peaks") on the tetragonal (101) plane with a peak at an interplanar spacing d = 2.40 ± 0.10 Å. For the a / c ratio, the a / c ratio can be calculated using the following mathematical formula from the obtained lattice constants a and c.

[0053] a / c ratio = lattice constant a [Å] / lattice constant c [Å] (1)

[0054] In this embodiment, the iridium-containing manganese oxide only needs to contain iridium (Ir) in a state that interacts with the manganese oxide; preferably, the manganese oxide contains iridium. Examples of the state in which the manganese oxide contains iridium include one or more states selected from a state of being mixed with manganese oxide, a state of being loaded with manganese oxide, and a state of being dissolved in manganese oxide; preferably, at least a portion of the iridium is dissolved in the manganese oxide.

[0055] The form of iridium contained in the iridium-containing manganese oxide of this embodiment is arbitrary. Iridium may be contained in one or more forms selected from metals, cations, and compounds, and preferably in one or more forms selected from metals, cations, and oxides. The iridium contained in the iridium-containing manganese oxide of this embodiment is preferably contained in the manganese oxide in the form of iridium ions, and more preferably in a state in which at least a portion of the iridium ions replace the manganese ions of the manganese oxide, that is, in a state in which at least a portion of the iridium is dissolved in the manganese oxide.

[0056] For iridium supported on manganese oxide, it is sufficient that iridium is contained in one or more of the manganese oxide's surface, pores, and framework structure. For example, when iridium is supported on the surface of manganese oxide, examples include iridium as an oxide, and further, iridium supported in the form of iridium oxide. When iridium is supported within the pores of manganese oxide, examples include iridium contained in a cation state, and further, iridium cations contained at ion-exchangeable sites of the manganese oxide. When iridium is dissolved in manganese oxide, examples include at least a portion of the iridium cations replacing manganese ions in the manganese oxide.

[0057] In order to exhibit high oxygen generating electrode catalytic activity, the iridium-containing manganese oxide of this embodiment preferably contains iridium in at least one of the states in which iridium is supported on manganese oxide and in which it is dissolved in manganese oxide, and more preferably contains iridium in a state in which part or all of the iridium is dissolved in manganese oxide.

[0058] For the iridium-containing manganese oxide of this embodiment, in its XRD pattern, when the area intensity of the XRD peak with the largest area intensity is set to 100, the ratio of the area intensity of the XRD peak with a peak at 2θ = 35.00 ± 1.00° (hereinafter also referred to as the "Ir intensity ratio") is 3 or less. This can be considered as a state in which at least a portion of iridium is dissolved in the manganese oxide. For example, when the manganese oxide is β-type manganese dioxide, an XRD peak with a peak at 2θ = 28 ± 1° (hereinafter also referred to as the "Mn peak") can be cited as the XRD peak with the largest area intensity.

[0059] The XRD peak with a apex at 2θ = 35.00 ± 1.00° is considered to be the main peak of the iridium compound. In this embodiment, the iridium-containing manganese oxide preferably contains iridium in a state of solid solution within the manganese oxide; therefore, the Ir intensity ratio is preferably 0 or more and 3 or less, more preferably 0 or more and 1 or less. Furthermore, the crystal structure of the iridium-supported and solid-solidified manganese oxide is prone to strain. In this case, compared to the Mn peak of the iridium-supported and solid-solidified manganese oxide, the half-width of the Mn peak of the iridium-supported and solid-solidified manganese oxide tends to increase. For example, the half-width of the Mn peak in the iridium-supported and solid-solidified manganese oxide can be greater than 1.90°, 2.30° or more, or 2.50° or more; examples include greater than 1.90° and 4.00° or less, 2.30° and 3.50° or less, or 2.50° and 3.50° or less.

[0060] In this embodiment, the molar ratio (mol / mol; hereinafter also referred to as "Ir / Mn molar ratio") of the iridium-containing manganese oxide is 0.001 or more and 0.250 or less. If the Ir / Mn molar ratio is less than 0.001, the properties as a manganese oxide are enhanced, and the catalytic activity of the oxygen generating electrode is significantly reduced. On the other hand, if the Ir / Mn molar ratio is greater than 0.250, iridium is easily dissolved, and the catalytic activity of the oxygen generating electrode is easily reduced. The Ir / Mn molar ratio is preferably 0.004 or more or 0.008 or more, and preferably 0.200 or less or 0.150 or less. Furthermore, it is preferably 0.004 or more and 0.200 or less, or 0.008 or more and 0.150 or less.

[0061] The Ir / Mn molar ratio can be determined using a conventional ICP apparatus (Optima 830, manufactured by PerkinElmer) via inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, the Ir / Mn molar ratio of the iridium-containing manganese oxide is calculated by determining the manganese and iridium content of the iridium-containing manganese oxide using ICP and then retrieving the iridium content relative to the manganese content.

[0062] "Manganese content" and "iridium content" refer to the mass ratio of manganese and iridium relative to the mass of iridium-containing manganese oxide, which can be calculated using the following mathematical formula.

[0063] Manganese content [mass%] = (W Mn / W)×100(2)

[0064] Iridium content [mass%] = (W Ir / W)×100(3)

[0065] In the above formula, W Mn W is the mass [g] of manganese in iridium-containing manganese oxides. 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.

[0066] In the iridium-containing manganese oxide of this embodiment, in order to easily exert sufficient catalytic activity for the reaction with oxygen, the iridium content is preferably 0.2% by mass or more or 0.8% by mass or more, and preferably 35% by mass or less or 30% by mass or less, 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.

[0067] In order to facilitate the catalytic reaction and to ensure that the iridium can be easily and uniformly coated on the electrolyte membrane and conductive substrate when the anolyte catalyst ink is made, the D50 diameter of the iridium-containing manganese oxide in this embodiment is preferably 0.1 μm or more and 50.0 μm or less, preferably 0.3 μm or more or 0.5 μm or more, and preferably 30.0 μm or less, 10.0 μm or less or 3.0 μm or less, 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 less and 3.0 μm or less.

[0068] The standard deviation in the volumetric particle size distribution of the iridium-containing manganese oxide in this embodiment is preferably 0.05 μm or more, and preferably 5.0 μm or less, 3.0 μm or less, or 2.0 μm or less, and more 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.

[0069] In this embodiment, the D16 diameter of the iridium-containing manganese oxide is preferably 0.05 μm or more, 0.15 μm or more, or 0.25 μm or more. In addition, it 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 and 30.00 μm or less, 0.15 μm or more and 20.00 μm or less, or 0.25 μm or more and 10.00 μm or less.

[0070] In this embodiment, the D84 diameter of the iridium-containing manganese oxide is preferably 0.5 μm or more, 1.0 μm or more, or 1.5 μm or more. In addition, it 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.

[0071] In this embodiment, "D16 diameter," "D50 diameter," and "D84 diameter" refer to the particle sizes [μm] whose cumulative frequency of particle size distribution obtained by laser diffraction and scattering is equivalent to 16%, 50%, and 84% of the particle sizes [μm], respectively. It should be noted that D50 and "median particle size" are interchangeable.

[0072] The D16, D50, and D84 diameters of the iridium-containing manganese oxide in this embodiment can be measured using a conventional particle size distribution measuring device (e.g., device name: MT-3100II, manufactured by Macquarie-Baier) under the following conditions.

[0073] Measurement range: 0.02~2000μm

[0074] Particle refractive index: 2.2

[0075] Particle permeability: Transmission

[0076] Particle shape: Non-spherical

[0077] Solvent refractive index: 1.333

[0078] Ultrasonic pretreatment: 10 minutes

[0079] The standard deviation can be calculated using the following mathematical formula based on the obtained values ​​of the D16 and D84 diameters.

[0080] Standard deviation [μm] = (D84 diameter [μm] - D16 diameter [μm]) / 2 (4)

[0081] In this embodiment, the BET specific surface area of ​​the iridium-containing manganese oxide is preferably 1 m². 2 / g or more and 200m 2 / g or less, preferably 10m 2 / g or more or 19m 2 / g or more, and preferably 100m 2 / g or less, 50m 2 / g or less or 30m 2 / g or less, preferably 1m 2 / g or more and 100m 2 / g or less, 10m 2 / g or more and 50m 2 / g or less, or 19m 2 / g or more and 30m 2 / g or less.

[0082] BET surface area can be determined using conventional measuring apparatus (e.g., Macsorb, manufactured by MOUNTECH) with a 30 vol% nitrogen-70 vol% helium mixture as the adsorbate gas, via the one-point method specified in JIS Z8830:2013. Pretreatment of the sample involves placing it in a glass cuvette for BET surface area measurement and dehydrating it at 150°C for 20 minutes under a nitrogen-flowing atmosphere.

[0083] 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 can be used directly, or it can be used as a catalyst composition containing the iridium-containing manganese oxide of this embodiment (hereinafter, these are collectively referred to as "the catalyst of this embodiment"). The catalyst of this embodiment is preferably used as an oxygen generating electrode catalyst.

[0084] The catalyst of this embodiment can be used as an anode catalyst (oxygen generating electrode catalyst) in water electrolysis using a PEM-type electrolyzer, and high oxygen generating electrode catalytic activity can be expected.

[0085] The catalyst composition may be an anode catalyst ink containing iridium-containing manganese oxide as described in this embodiment, for example, it may be a composition obtained by mixing iridium-containing manganese oxide, water, ethanol and an ionomer (e.g., product name: Nafion dispersion, manufactured by Sigma-Aldrich). The composition may contain isopropanol for purposes such as adjusting viscosity.

[0086] The method for manufacturing iridium-containing manganese oxide according to this embodiment will be described below.

[0087] [Method for manufacturing iridium-containing manganese oxide according to this embodiment]

[0088] The method for manufacturing the iridium-containing manganese oxide in this embodiment is not particularly limited, as long as an iridium-containing manganese oxide having the above-described structure can be obtained, and as long as the manufacturing method can contain iridium in at least a portion of the manganese oxide, it is acceptable. Preferably, at least any of the following methods can be exemplified: a manufacturing method including a mixing step of contacting a manganese oxide source with an iridium salt solution to obtain the mixture, and a heat treatment step of heat-treating the mixture (hereinafter also referred to as the "powder method"); and a manufacturing method including an electrolytic step of electrolytically depositing manganese oxide on 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 the mixture and the conductive substrate, and a heat treatment step of heat-treating the mixture and the conductive substrate (hereinafter also referred to as the "electrolysis method").

[0089] <Powder Method>

[0090] As a preferred manufacturing method for the iridium-containing manganese oxide of this embodiment, the following manufacturing method can be cited, which 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. The iridium-containing manganese oxide of this embodiment can be obtained in powder form using a powder method.

[0091] Mixing process:

[0092] In the powder process, the manganese oxide source is contacted with an iridium salt solution during the mixing step. This allows the manganese oxide source to contain iridium.

[0093] Manganese oxide source:

[0094] As a manganese oxide source, examples include one or more selected from manganese dioxide (MnO2), manganese tetroxide (Mn3O4), and manganese trioxide (Mn2O3), with manganese dioxide and at least one of manganese tetroxide being preferred, and manganese dioxide being more preferred. From the viewpoint that it readily exhibits high oxygen-generating electrode catalytic activity when containing iridium, the manganese oxide source is preferably manganese dioxide having a γ-type crystal structure (hereinafter also referred to as "γ-type manganese dioxide").

[0095] When the manganese oxide source is γ-type manganese dioxide, the crystallite size of this γ-type manganese dioxide is preferably 2.4 nm or more and 4.0 nm or less. By setting the crystallite size of the γ-type manganese dioxide to the above values, the structure of the β-type manganese dioxide in the iridium-containing manganese oxide obtained in the heat treatment process described later is more prone to strain in the c-axis direction, thus the a / c ratio tends to decrease. As a result, higher catalytic activity of the oxygen generating electrode can be expected. The crystallite size of the γ-type manganese dioxide is more preferably 2.6 nm or more and 3.5 nm or less, and even more preferably 2.7 nm or more and 3.2 nm or less.

[0096] In this embodiment, the "crystal size of γ-type manganese dioxide" can be calculated using the following Scherrer formula based on the half-width of the XRD peak with a apex at 2θ = 22.5 ± 1.5° in the XRD pattern of γ-type manganese dioxide when CuKα line is used as the XRD source (λ = 1.5405 Å).

[0097] Microcrystal size [nm] = Scherer constant [-] × wavelength of X-ray source λ [nm] × 0.1 / (half-width [rad] × cosθ [rad]) (5)

[0098] Here, the Scherrer constant is 0.879, and θ is the Bragg angle.

[0099] 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 preferably 30.00 μm or less, 10.00 μm or less, or 5.00 μm or less, 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. By setting the D50 diameter of the manganese oxide source to the above values, an iridium-containing manganese oxide having the above-described D50 diameter can be easily obtained in the heat treatment process described later.

[0100] 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. It is also 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 and 30.00 μm or less, 0.15 μm or more and 20.00 μm or less, or 0.25 μm or more and 10.00 μm or less.

[0101] 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. In addition, it 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.

[0102] To achieve the aforementioned D50, D16, and D84 diameters of the manganese oxide source, the powder process may include a pulverization step before the mixing step. The pulverization of the manganese oxide source can be performed using known methods, such as wet pulverization or dry pulverization.

[0103] iridium:

[0104] The iridium salt solution supplied for the mixing process can be any solution containing an iridium salt, preferably a solution containing an iridium salt, more preferably an aqueous solution containing an iridium salt, and even more preferably an aqueous solution containing an iridium salt. Examples of iridium salts include iridium(III) chloride (IrCl3), iridium(IV) chloride (IrCl4), and iridium nitrate (Ir(NO3)4), with iridium(III) chloride (IrCl3) being the most preferred. The aqueous solution may use only one type of iridium salt or two or more types.

[0105] The iridium concentration of the iridium salt solution is preferably above 0.001 g / L and below 20 g / L.

[0106] The method of contacting the manganese oxide source with the iridium salt solution is not particularly limited as long as the manganese oxide contains a desired amount of iridium. Specifically, the contact temperature is preferably 20°C or higher and 100°C or lower, and the contact time is preferably 30 minutes or higher and 100 hours or lower. It is believed that by keeping the contact time and contact temperature within the above ranges, 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 will increase. Furthermore, at higher contact temperatures, manganese atoms within the crystal structure of the manganese oxide are more easily replaced by iridium atoms. Therefore, it is believed that the higher the contact temperature, the more easily iridium replaces and dissolves with the manganese in the manganese oxide, and the more easily at least a portion of iridium is dissolved in the manganese oxide. Based on the above viewpoints, the contact temperature is preferably 70°C or higher, for example, preferably 70°C or higher and 100°C or lower.

[0107] Heat treatment process:

[0108] In the powder process, the mixture obtained in the above-mentioned mixing process is heat-treated in a heat treatment step. As a result, manganese atoms within the crystal structure of the manganese oxide are replaced by iridium atoms contained in the surface and pores of the manganese oxide, thereby further enabling the solid dissolution of iridium in the manganese oxide. The heat treatment atmosphere in the heat treatment step is preferably atmospheric or an inactive atmosphere, more preferably atmospheric, and the heat treatment temperature is preferably 100°C or higher and 600°C or lower. The heat treatment time can be appropriately set according to the amount of manganese oxide, etc., supplied for heat treatment; for example, 10 minutes or more and 24 hours or less can be used.

[0109] By means of powder method, it is possible to obtain iridium-containing manganese oxides with an Ir / Mn molar ratio of 0.001 or more and 0.250 or less. Preferably, it is possible to obtain iridium-containing manganese oxides with an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, wherein the manganese oxide is β-type manganese dioxide. More preferably, it is possible to obtain iridium-containing manganese oxides with 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 an a / c ratio of 1.420 or more and less than 1.521.

[0110] The preferred form of iridium-containing manganese oxide obtained by the powder method is powder.

[0111] Electrolysis

[0112] As another preferred manufacturing method for the iridium-containing manganese oxide of this embodiment, a manufacturing method comprising the following steps is provided: an electrolytic step of electrolytically depositing manganese oxide on a conductive substrate; an iridium-containing step of contacting the electrolytically deposited manganese oxide source 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. Thus, the iridium-containing manganese oxide of this embodiment can be obtained in a state where at least a portion of the conductive substrate is coated.

[0113] Electrolysis process:

[0114] In the electrolysis method, manganese oxide is electrolytically deposited on a conductive substrate during the electrolysis process. This yields manganese oxide electrolytically deposited on a conductive substrate (hereinafter also referred to as "electrolysis manganese oxide source").

[0115] The process simply involves electrolytically depositing manganese oxide onto the surface of a conductive substrate. The electrolytic deposition method is arbitrary, as long as it involves immersing the conductive substrate in an electrolyte solution and then electrolyzing it.

[0116] The thickness of the conductive substrate supplied for the electrolysis process only needs to be less than 500 μm, and preferably less than 300 μm. Furthermore, the conductive substrate only needs to be a substrate containing a conductive material, and preferably a substrate containing titanium.

[0117] The conductive substrate can be exemplified by one or more of the following shapes: mesh, cloth, and plate. Mesh conductive substrates are preferred because they tend to exhibit higher activity in the oxygen generating electrode catalyst. Specifically, examples of conductive substrates include titanium meshes made of fibrous or powdered conductive titanium, which are then heat-treated to form sintered titanium meshes. From the viewpoint of easily achieving high oxygen generating electrode catalyst activity, these conductive substrates are preferably coated with platinum; platinum-coated titanium meshes are more preferred, and platinum-coated sintered titanium meshes are even more preferred.

[0118] The preferred source of manganese oxide for electrolysis is manganese dioxide with a delta-shaped structure (hereinafter also referred to as "delta-shaped manganese dioxide"). Therefore, in the iridium-containing process described later, it is easy to obtain γ-shaped manganese dioxide containing iridium and with a crystallite size of 2.4 nm or more and 4.0 nm or less as an iridium-containing manganese oxide.

[0119] The electrolyte can be any solution containing manganese, as long as it enables the electrolytic deposition of manganese oxide source onto the surface of a conductive substrate. The manganese concentration in the electrolyte is preferably 0.05 mol / L or higher and 1.00 mol / L or lower. The electrolyte is preferably a solution containing manganese sulfate, and more preferably an aqueous solution of manganese sulfate. In this case, the sulfuric acid concentration is preferably 0.05 mol / L or higher and 1.00 mol / L or lower, and the manganese concentration is preferably 0.05 mol / L or higher and 1.00 mol / L or lower.

[0120] Furthermore, the electrolyte preferably contains an ammonium salt. By containing an ammonium salt, delta-type manganese dioxide can easily be obtained as a source of manganese oxide in the electrolytic process. Ammonium ions have a template effect for forming the layered structure of delta-type manganese dioxide. In addition, ammonium ions are incorporated into the interlayer of delta-type manganese dioxide, thereby enabling the crystal growth of delta-type manganese dioxide to be oriented towards a specific crystal plane. As a result, in the iridium-containing process described later, iridium-containing gamma-type manganese dioxide with a crystallite size of 2.4 nm or more and 4.0 nm or less can easily be obtained as an iridium-containing manganese oxide. In this case, the concentration of the ammonium salt in the electrolyte can be 0.1 mol / L or more and 3.0 mol / L or less. As the ammonium salt, one or more selected from ammonium sulfate, ammonium nitrate and ammonium chloride can be mentioned, with ammonium sulfate being preferred.

[0121] In electrolytic deposition, a conductive substrate is immersed in an electrolyte and then electrolyzed. The conditions for electrolytic deposition are identical to those for manganese oxide electrolytic deposition; for example, a current density of 0.3 mA / cm² per geometric area of ​​the conductive substrate can be used. 2 Above and 20mA / cm 2 The electrolysis temperature is above 93℃ and below 98℃.

[0122] Iridium-containing processes:

[0123] In the electrochemical process, during the iridium-containing step, a conductive substrate and manganese oxide electrolytically deposited on the conductive substrate (hereinafter referred to as "manganese oxide substrate") are contacted with an iridium salt solution. By allowing the manganese oxide (electrochemical manganese oxide source) in the manganese oxide substrate obtained in the above electrochemical step to be in a state of being deposited and adhered to the conductive substrate, a mixture containing iridium in the electrochemical manganese oxide source (hereinafter also referred to as "iridium-containing electrochemical manganese oxide source") is obtained through the iridium-containing step. Thus, this mixture and the conductive substrate (hereinafter also referred to as "iridium-manganese oxide substrate") are obtained.

[0124] The iridium salt solution supplied for the iridium-containing process can be any solution containing an iridium salt, preferably a solution containing an iridium salt and sulfuric acid, and more preferably an aqueous solution containing an iridium salt and sulfuric acid. Examples of iridium salts include one or more selected from iridium(III) chloride (IrCl3), iridium(IV) chloride (IrCl4), iridium nitrate (Ir(NO3)4), potassium hexachloroiridate (K2IrCl6), and hexachloroiridic acid (H2IrCl6).

[0125] When the electrolytic manganese oxide source is delta-type manganese dioxide, delta-type manganese dioxide has cation exchange properties. From the perspective of easily reacting with delta-type manganese dioxide, the iridium salt is preferably an iridium salt in which iridium dissociates as a cation in solution. Specifically, it is preferably selected from one or more of IrCl3, IrCl4 and Ir(NO3)4, and more preferably IrCl3.

[0126] The iridium concentration of the iridium salt solution is preferably above 0.001 mmol / L and below 5.000 mmol / L.

[0127] Contact between the manganese oxide substrate and the iridium salt solution can be achieved by immersing the manganese oxide substrate in the iridium salt solution. The contact condition is simply that the iridium is present on the surface of the manganese oxide substrate; there are no particular limitations. For the contact temperature, examples include 20°C or higher and 100°C or lower. The contact time can be adjusted appropriately according to the size of the manganese oxide substrate; for example, it can be 30 minutes or more and 24 hours or less.

[0128] The mixture containing iridium in the electrolytic manganese oxide source (hereinafter also referred to as "iridium-containing electrolytic manganese oxide source") is preferably iridium-containing gamma-type manganese dioxide, and more preferably iridium-containing gamma-type manganese dioxide with a crystallite size of 2.4 nm or more and 4.0 nm or less. By making the electrolytic manganese oxide source delta-type manganese dioxide, when it contains iridium, the crystal structure can be changed to iridium-containing gamma-type manganese dioxide.

[0129] Heat treatment process:

[0130] In the electrolysis method, the iridium-manganese oxide substrate is heat-treated during a heat treatment process. This improves the adhesion between the iridium-containing manganese oxide and the conductive substrate. The heat treatment atmosphere can be atmospheric or an inert atmosphere, preferably atmospheric, and the heat treatment temperature can be above 100°C and below 600°C. The heat treatment time can be adjusted appropriately according to the size of the conductive substrate to be heat-treated, for example, from 10 minutes to 24 hours.

[0131] By electrolysis, iridium-containing manganese oxides with an Ir / Mn molar ratio of 0.001 or higher and 0.300 or lower can be obtained. Preferably, iridium-containing manganese oxides with an Ir / Mn molar ratio of 0.001 or higher and 0.300 or lower, having a β-type crystal structure, and an a / c ratio of 1.420 or higher and less than 1.521 can be obtained. Furthermore, electrodes containing the catalyst (the catalyst of this embodiment) and conductive substrate can be obtained.

[0132] The iridium-containing manganese oxide obtained by electrolysis is produced by a manufacturing method that electrolytically deposits iridium-containing manganese oxide on a conductive substrate. Therefore, it is possible to directly manufacture an electrode containing the iridium-containing manganese oxide and the conductive substrate of this embodiment (hereinafter referred to as "the electrode of this embodiment"), and further, it is possible to manufacture an electrode containing the catalyst and the conductive substrate of this embodiment.

[0133] The iridium-containing manganese oxides obtained by the powder method and electrolysis method in this embodiment can be used as catalysts containing them (catalysts in this embodiment), and are preferably used as oxygen generating electrode catalysts.

[0134] The catalyst of this embodiment can be used as the anode catalyst of MEA in water electrolysis using a PEM-type electrolyzer. The MEA can be constructed by using an iridium-containing manganese oxide obtained by the powder method as the anode catalyst of the CCM, or by using an electrode obtained by the electrolysis method and a CCM consisting only of a cathode catalyst and an electrolyte membrane. Regardless of the manufacturing method used, the MEA can exhibit significantly higher oxygen generation electrode catalytic activity compared to conventional iridium-containing manganese oxides.

[0135] By electrolysis, an iridium-containing manganese oxide with an Ir / Mn molar ratio of 0.001 or higher and 0.250 or lower can be obtained on a conductive substrate. Preferably, the manganese oxide is an iridium-containing manganese oxide with an Ir / Mn molar ratio of 0.001 or higher and 0.250 or lower, and the manganese oxide is β-type manganese dioxide. More preferably, an iridium-containing manganese oxide is obtained with an Ir / Mn molar ratio of 0.001 or higher and 0.250 or lower, and the manganese oxide is β-type manganese dioxide, and the a / c ratio is 1.420 or higher and less than 1.521.

[0136] The form of iridium-containing manganese oxide obtained by electrolysis is preferably an electrode containing a catalyst and a conductive substrate.

[0137] electrode:

[0138] The electrode of this embodiment can be used as an anode catalyst and conductive substrate in water electrolysis using a PEM-type electrolyzer. 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).

[0139] The electrode of this embodiment includes a catalyst and a conductive substrate. The catalyst includes an iridium-containing manganese oxide with an Ir / Mn molar ratio of 0.001 or more and 0.250 or less. Preferably, it includes an iridium-containing manganese oxide with an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, and the manganese oxide is β-type manganese dioxide. More preferably, it includes an iridium-containing manganese oxide with an Ir / Mn molar ratio of 0.001 or more and 0.250 or less, and the manganese oxide is β-type manganese dioxide. The a / c ratio is 1.420 or more and less than 1.521.

[0140] The metal content per geometric area of ​​the electrode in this embodiment (hereinafter also referred to as "metal content of the electrode") is preferably 0.1 mg / cm². 2 Above, 0.5 mg / cm 2 Above or 0.8 mg / cm 2 The above is preferably 12.0 mg / cm³. 2 Below, 11.0 mg / cm 2 Below or 10.0 mg / cm 2 The following examples illustrate the effect of 0.1 mg / cm². 2 Above and 12.0 mg / cm 2 Below, 0.5 mg / cm 2 Above and 11.0 mg / cm 2 Below, 0.8 mg / cm 2 Above and 10.0 mg / cm 2 The following is an example. The metal content of the electrode is set to 0.1 mg / cm³. 2 In summary, the increased coverage of iridium-containing manganese oxides on conductive substrates makes it easier to exhibit high oxygen-generating electrode catalytic activity.

[0141] On the other hand, by making the metal content of the electrode 12.0 mg / cm³ 2 As the electrode resistance decreases, it is easier to exhibit high oxygen-generating electrode catalytic activity.

[0142] The metal content of the electrode in this embodiment is calculated using the following mathematical formula.

[0143] Electrode metal content [mg / cm³] 2 ]

[0144] = (Manganese content of the electrode [mg] + Iridium content of the electrode [mg]) / Geometric area of ​​the electrode [cm²] 2 (6)

[0145] The manganese and iridium content of the electrode can be determined by ICP in the same way as the determination of the manganese and iridium content of iridium-containing manganese oxides. That is, the electrode with a geometric area of ​​1 cm²... 2 The electrode is immersed in a mixed aqueous solution of hydrochloric acid and nitric acid to dissolve the catalyst contained in the electrode. The mixed solution containing the dissolved catalyst is used as the test sample. The manganese and iridium contents of the test sample are determined by ICP method, and these are used as the manganese and iridium contents of the electrode.

[0146] "Geometric area" refers to the area equivalent to the projected area, without considering surface irregularities or gaps, and is the projected area of ​​the surface (geometric surface) opposite the electrolyte membrane when forming a membrane-electrode junction (hereinafter also referred to as "MEA"). "Electrode geometric area" refers to the projected area of ​​the electrode, which is the area of ​​the plane obtained by calculating the length × width when the shape of the electrode is specified as length × width × thickness.

[0147] The molar ratio of iridium to manganese per geometric area of ​​the electrode in this embodiment (hereinafter also referred to as "the Ir / Mn molar ratio of the electrode") can be the same as the Ir / Mn molar ratio of the iridium-containing manganese oxide in this embodiment.

[0148] 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 included in the electrode of this embodiment are the same as those of the iridium-containing manganese oxide of this embodiment, and therefore the description is omitted.

[0149] The conductive substrate can be any substrate made of conductive material, and preferably a substrate containing titanium.

[0150] The conductive substrate can be exemplified by one or more of the following shapes: mesh, cloth, and plate. Since the activity of the oxygen generating electrode catalyst is easily increased, a mesh shape is preferred. As a specific conductive substrate, a titanium mesh made of fibrous or powdered conductive titanium and then heat-treated to form a sintered titanium mesh can be exemplified. From the viewpoint of easily achieving high oxygen generating electrode catalyst activity, these conductive substrates are preferably coated with platinum, and platinum-coated titanium meshes are more preferred, and platinum-coated sintered titanium meshes are even more preferred.

[0151] In conductive substrates, where the surface is coated with platinum, the platinum content per geometric area is preferably 0.5 mg / cm² to exhibit high conductivity. 2 Above and 10.0 mg / cm 2 The following is more preferably 1.0 mg / cm³2 Above and 8.0 mg / cm 2 Hereinafter, 1.0 mg / cm³ is further preferred. 2 Above and 6.0 mg / cm 2 the following.

[0152] In order to exhibit excellent oxygen generating electrode catalytic activity, 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.

[0153] "Thickness" refers to the length perpendicular to the geometric surface. "Thickness of conductive substrate" refers to the length perpendicular to the geometric surface of the conductive substrate, which is the thickness when the shape of the electrode is specified in length × width × thickness.

[0154] The porosity of the conductive substrate is preferably 30% or more and 80% or less, more preferably 40% or more and 70% or less. Here, porosity is defined as the volume of the conductive substrate excluding the space containing the conductive substrate, and methods for measuring porosity include, for example, mercury porosimetry. If the porosity is within the above range, the mechanical strength of the electrode is improved, and excellent results can be obtained in terms of ensuring a smooth supply of water, the reactive substance that generates oxygen.

[0155] The porosity in this embodiment is calculated using the following mathematical formula.

[0156] Porosity (%) = {1 - (bulk density of conductive substrate (g / cm³)} 3 )

[0157] / Skeleton density of conductive substrate (g / cm³) 3 ))}×100

[0158] The bulk density and skeleton density of the conductive substrate are values ​​obtained using the following mathematical formulas, based on the pore volume and the volume of the conductive substrate, which can be measured by mercury porosimetry using a conventional mercury porosimetry apparatus (AutoPore 9510, manufactured by Micromeritics).

[0159] Bulk density of conductive substrate (g / cm³) 3 = Mass of conductive substrate (g) / Volume of conductive substrate (cc)

[0160] Spatial density of conductive substrate (g / cm³) 3 = Mass of conductive substrate (g) / {Volume of conductive substrate - Volume of pores} (cc)

[0161] In the two formulas above, the volume of the conductive substrate can also be determined by measuring it with a laser volume gauge (device name: 3D scanner type coordinate measuring machine VL-700 series (controller VL-700, worktable VL-750 / VL-C35, measuring unit VL-770), manufactured by KEYENCE). In addition, the mass of the conductive substrate is determined by measuring the mass using an electronic balance.

[0162] The following conditions can be cited as specific measurement conditions for mercury porosimeter.

[0163] Sample volume: 40mg

[0164] Mercury infusion pressure: 601.6 psia ~ 36,098.1 psia

[0165] (4.1MPa~248.9MPa)

[0166] Pore ​​diameter measured: 5 nm to 500 μm

[0167] Using a cuvette: Press in a 5.3cc glass cuvette.

[0168] Mercury surface tension: 480 dyn

[0169] Mercury contact angle: 130°

[0170] Pretreatment conditions: Degassing at 110℃ for more than 1 hour under atmospheric conditions.

[0171] [Method for manufacturing the electrode according to this embodiment]

[0172] In this embodiment, the iridium-containing manganese oxide is obtained by electrolysis. Since the iridium-containing manganese oxide is integrated with the conductive substrate, it can be directly used as the electrode in this embodiment.

[0173] On the other hand, in the case where the iridium-containing manganese oxide in this embodiment is obtained by a powder method, the electrode of this embodiment is obtained by preparing a catalyst ink from the iridium-containing manganese oxide and coating the catalyst ink onto a conductive substrate. The catalyst ink described above only needs to be an Ir-Mn oxide dispersed in a solvent, and the solvent can be water, alcohol, or a mixture of water and alcohol.

[0174] Example

[0175] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the present invention is not limited to the embodiments shown below.

[0176] <Composition Analysis>

[0177] The prepared sample was dissolved using a hydrochloric acid-nitric acid mixture. The manganese and iridium contents of the sample were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) with a standard ICP apparatus (Optima 830, manufactured by PerkinElmer). The Ir / Mn molar ratio of the prepared sample was then calculated from the obtained manganese and iridium contents.

[0178] <Particle Size Distribution>

[0179] The volumetric particle size distribution was determined using a laser diffraction-scattering particle size distribution measuring device (Microtrac MT3300EXII, manufactured by Microtrac Bayer). The measurement conditions are as follows.

[0180] Measurement range: 0.02~2000μm

[0181] Particle refractive index: 2.2

[0182] Particle permeability: Transmission

[0183] Particle shape: Non-spherical

[0184] Solvent refractive index: 1.333

[0185] Ultrasonic pretreatment: 10 minutes

[0186] Based on the obtained volumetric particle size distribution, the D16 diameter [μm], D50 diameter (median particle size) [μm], and D84 diameter [μm] of the prepared sample are determined. Furthermore, the standard deviation is calculated using equation (4) above based on the obtained D16 and D84 diameter values.

[0187] <BET specific surface area>

[0188] The BET specific surface area of ​​the prepared sample was determined according to JIS Z 8830:2013. Specifically, 0.3 g of the prepared sample was placed in a glass unit for BET specific surface area determination and dehydrated at 150°C for 20 minutes under a nitrogen atmosphere as a pretreatment. Using a standard BET specific surface area determination apparatus (product name: Macsorb (registered trademark), manufactured by MOUNTECH), a mixed gas of 30 vol% nitrogen and 70 vol% helium was used as the adsorbent gas, and the BET specific surface area of ​​the pretreated sample was determined using a single-point method.

[0189] <Half-width Full Width (FWHM)>

[0190] The XRD pattern was obtained using a conventional powder X-ray diffraction apparatus (Ultima IV Protectus, manufactured by Rigaku Co., Ltd.) under the following conditions.

[0191] Accelerating current and voltage: 40mA·40kV

[0192] X-ray source: CuKα line (λ=1.5405Å)

[0193] Measurement mode: Continuous scanning

[0194] Scanning conditions: 4° / minute

[0195] Measurement range: 2θ = 10°~80°

[0196] Longitudinal diverging slit: 10mm

[0197] Diverging / Incident Slit: 1°

[0198] Light-receiving slit: open

[0199] Detector: D / teX Ultra

[0200] Using a Ni filter

[0201] The crystalline phase of the prepared sample was identified by comparing the obtained XRD pattern with the reference pattern. The reference patterns were PDF No. 14-0644 (γ-type MnO2), 24-0735 (β-type MnO2), 30-0820 (ε-type MnO2), 80-1098 (δ-type), or 44-0141 (α-type MnO2).

[0202] The XRD pattern of the prepared sample was analyzed using the analytical software attached to the powder X-ray diffraction apparatus (product name: PDXL2, manufactured by Rigaku Corporation). The full width at half maximum (FWHM) of the XRD peak with a apex at 2θ = 28 ± 1.5° was determined and used as the FWHM (°).

[0203] In addition, the background was subtracted from the obtained XRD pattern using the analytical software attached to the powder X-ray diffraction apparatus (product name: PDXL2, manufactured by Rigaku Corporation). Then, the interplanar spacing d [Å] was calculated using the diffraction angles [°] of the peaks of (110) and (101) and Bragg's formula, and the lattice constants a [Å] and c [Å] of the tetragonal crystal were calculated. From the obtained lattice constants a and c, the a / c ratio was calculated using the above equation (1).

[0204] Example 1:

[0205] <Preparation of Iridium-Containing Manganese Oxide Powder>

[0206] Electrolytic manganese dioxide (product name: HMR-AF, manufactured by Tosoh Corporation) was pulverized using a jet mill to obtain a median particle size of 0.5 μm and a BET specific surface area of ​​47 m². 2 / g of manganese dioxide powder (manganese oxide source). This manganese dioxide is γ-type manganese dioxide with a microcrystalline particle size of 3.0nm.

[0207] 500 mg of manganese dioxide powder was immersed in an iridium salt solution tank filled with 33.2 mL of an aqueous solution of potassium hexachloroiridate (K2IrCl6) at a concentration of 1.60 g / L (equivalent to 53 mg of K2IrCl6). The solution was then immersed at 95 °C for 48 hours, followed by solid-liquid separation to obtain a mixture. This mixture was dried at 90 °C for 2 hours in atmospheric atmosphere, then allowed to cool naturally to room temperature. Finally, it was annealed at 450 °C for 5 hours in atmospheric atmosphere to obtain iridium-containing manganese oxide powder.

[0208] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.12 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0209] Example 2:

[0210] 33.2 mL of a K2IrCl6 aqueous solution with a concentration of 3.98 g / L (equivalent to 132 mg of K2IrCl6) was used as the K2IrCl6 aqueous solution. Otherwise, the same method as in Example 1 was used to obtain iridium-containing manganese oxide powder.

[0211] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.40 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0212] Example 3:

[0213] 33.2 mL of a K2IrCl6 aqueous solution with a concentration of 9.97 g / L (331 mg based on K2IrCl6 content) was used as the K2IrCl6 aqueous solution. Otherwise, the same method as in Example 1 was used to obtain iridium-containing manganese oxide powder.

[0214] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.99 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0215] Example 4:

[0216] 33.2 mL of a K2IrCl6 aqueous solution with a concentration of 19.91 g / L (661 mg based on K2IrCl6 content) was used as the K2IrCl6 aqueous solution. Otherwise, the same method as in Example 1 was used to obtain iridium-containing manganese oxide powder.

[0217] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.99 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0218] Example 5:

[0219] Instead of pulverized manganese dioxide, a material with a γ-type crystal structure, a crystallite size of 2.5 nm, a median particle size of 2.3 μm, and a BET specific surface area of ​​45 m² is used. 2 / g of electrolytic manganese dioxide powder (product name: FM, manufactured by Tosoh Corporation) was immersed in an iridium salt solution tank filled with 99.8mL of K2IrCl6 aqueous solution with a K2IrCl6 concentration of 2.504g / L (250mg based on K2IrCl6 content) for 24 hours. Otherwise, the same method as in Example 1 was used to obtain iridium-containing manganese oxide powder.

[0220] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.20 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0221] Example 6:

[0222] Instead of pulverized manganese dioxide, a material with a γ-type crystal structure, a crystallite size of 2.5 nm, a median particle size of 2.3 μm, and a BET specific surface area of ​​45 m² is used. 2 / g of electrolytic manganese dioxide powder (product name: FM, manufactured by Tosoh Corporation) was immersed in an iridium salt solution tank filled with 99.8mL of K2IrCl6 aqueous solution with a K2IrCl6 concentration of 2.504g / L (250mg based on K2IrCl6 content) for 96 hours. Otherwise, the same method as in Example 1 was used to obtain iridium-containing manganese oxide powder.

[0223] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.91 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0224] Example 7:

[0225] As manganese dioxide, a median particle size of 7.9 μm and a BET specific surface area of ​​36 m² were used. 2 Electrolytic manganese dioxide powder (product name: LM-10P, manufactured by Tosoh Corporation) was immersed in an iridium salt solution tank filled with 13.9 mL of K2IrCl6 aqueous solution with a K2IrCl6 concentration of 20.00 g / L (278 mg based on K2IrCl6 content) for 96 hours. Otherwise, the same method as in Example 1 was used to obtain iridium-containing manganese oxide powder.

[0226] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.52 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0227] Example 8:

[0228] Two kilograms of electrolytic manganese dioxide raw material powder (product name: HMR-AF, manufactured by Tosoh Corporation) were mixed with pure water to prepare a slurry with a solid content concentration of 20% by mass. The slurry was then pulverized for 3 hours using a pulverizer (device name: DYNO-MILL, manufactured by Shinmaru Enterprises) under conditions of a 0.5 mm diameter zirconium oxide medium, a filling rate of 80% by volume, and a circumferential speed of 14 m / s. After pulverization, the slurry was dried overnight at 90°C in an atmospheric atmosphere to obtain electrolytic manganese dioxide powder. This electrolytic manganese dioxide is a γ-type manganese dioxide with a microcrystalline particle size of 3.0 nm and a D50 diameter of 0.4 μm.

[0229] 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 at 90 °C for 2 hours in atmospheric atmosphere and then allowed to cool naturally to room temperature. Next, it was annealed at 450 °C for 5 hours in atmospheric atmosphere to obtain the iridium-containing manganese oxide powder of this embodiment. Its XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.51 for the Mn peak, thus indicating that it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid dissolved state within the manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0230] Example 9:

[0231] Using 68.6 mL of an Ir(NO3)4 aqueous solution (Ir(NO3)4 concentration: 0.005 mol / L) as the iridium salt solution, the iridium-containing manganese oxide powder of this embodiment was obtained using the same method as in Example 8. Its XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.45 for the Mn peak, thus indicating that it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid dissolved state within the manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0232] Example 10:

[0233] Using 114.3 mL of an Ir(NO3)4 aqueous solution (Ir(NO3)4 concentration: 0.005 mol / L) as the iridium salt solution, the iridium-containing manganese oxide powder of this embodiment was obtained using the same method as in Example 8. Its XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.77 for the Mn peak, thus indicating that it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid dissolved state within the manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0234] Example 11:

[0235] Using 45.7 mL of an IrCl4 aqueous solution (IrCl4 concentration: 0.004 mol / L) as the iridium salt solution, the iridium-containing manganese oxide powder of this embodiment was obtained using the same method as in Example 8. Its XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.70 for the Mn peak, thus indicating that it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid dissolved state within the manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0236] Example 12:

[0237] Using 96.0 mL of an IrCl4 aqueous solution (IrCl4 concentration: 0.004 mol / L) as the iridium salt solution, the iridium-containing manganese oxide powder of this embodiment was obtained using the same method as in Example 8. Its XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.35 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid dissolved state within the manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0238] Example 13:

[0239] Using 160.0 mL of an IrCl4 aqueous solution (IrCl4 concentration: 0.004 mol / L) as the iridium salt solution, the iridium-containing manganese oxide powder of this embodiment was obtained using the same method as in Example 8. Its XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.19 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid dissolved state within the manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0240] Example 14:

[0241] An electrolytic cell was filled with a mixed solution of sulfuric acid, manganese sulfate, and ammonium sulfate, containing 0.3 mol / L sulfuric acid, 0.5 mol / L manganese sulfate, and 1.5 mol / L ammonium sulfate. A conductive substrate containing a platinum-coated Ti fiber sintered body (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Precious Metals Industry Co., Ltd.) was impregnated in this solution. A current density of 7 mA / cm² was applied to the conductive substrate. 2 When an electric current is applied for 10 minutes, manganese oxide is electrochemically deposited on the conductive substrate. This manganese oxide is delta-type manganese dioxide.

[0242] Next, the conductive substrate with manganese oxide precipitated as described above was immersed in an iridium salt solution containing 0.1 mmol / L iridium(III) chloride (IrCl3) and 0.01 mol / L sulfuric acid at 95°C for 24 hours to obtain a mixture and a conductive substrate. This mixture is γ-type manganese dioxide containing iridium with a microcrystalline particle size of 3.1 nm. The mixture and the conductive substrate were annealed at 450°C for 5 hours under atmospheric atmosphere to obtain the iridium-containing manganese oxide precipitated on the conductive substrate according to this embodiment.

[0243] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.03 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0244] Example 15:

[0245] An electrolytic cell was filled with a sulfuric acid-manganese sulfate mixed solution with a sulfuric acid concentration of 0.36 mol / L and a manganese sulfate concentration of 0.36 mol / L. Otherwise, manganese oxide was electrochemically deposited on a conductive substrate using the same method as in Example 14. This manganese oxide was γ-type manganese dioxide.

[0246] Next, the conductive substrate with manganese oxide precipitated as described above 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. This mixture is γ-type manganese dioxide containing iridium with a microcrystalline particle size of 3.8 nm. The mixture and the conductive substrate were annealed at 450°C for 5 hours under atmospheric atmosphere to obtain the iridium-containing manganese oxide precipitated on the conductive substrate according to this embodiment.

[0247] The XRD pattern shows that the powder has a β-type crystal structure, an Ir intensity ratio of 0, and a half-width of 2.29 for the Mn peak. Therefore, it is iridium-containing β-type manganese dioxide containing at least a portion of iridium in a solid-dissolved state in manganese oxide. The evaluation results of this iridium-containing β-type manganese dioxide are shown in the table below.

[0248] Comparative Example 1:

[0249] Electrolytic manganese dioxide (product name: HMR-AF, manufactured by Tosoh Corporation) was pulverized to obtain a median particle size of 0.5 μm and a BET specific surface area of ​​47 m². 2 / g of manganese dioxide powder (manganese oxide source).

[0250] 500 mg of the obtained manganese dioxide powder (manganese oxide source) was annealed at 450 °C for 5 hours in an atmospheric atmosphere to obtain β-type manganese dioxide powder, which was used as the powder in this comparative example. The half-width of the Mn peak was 2.06. Furthermore, the D16 diameter of this powder 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. The evaluation results of this powder are shown in the table below.

[0251] [Table 1]

[0252]

[0253] [Table 2]

[0254]

[0255] [Table 3]

[0256]

[0257] Measurement Example 1:

[0258] <Evaluation of Oxygen Generating Electrode Catalysts>

[0259] The following method was used to prepare a membrane-electrode assembly (hereinafter also referred to as "MEA") with iridium-containing manganese oxide as an anode catalyst, as described in the examples and comparative examples, and a PEM-type water electrolyzer equipped with the MEA.

[0260] Fabrication of PEM-type water electrolyzers using Examples 1-13 and Comparative Example 1:

[0261] A cathode catalyst ink was prepared by mixing a solution containing water, ethanol, and an ionomer (product name: Nafion dispersion, manufactured by Sigma-Aldrich) with 20% by mass of a 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 set to 55.5:43.5:1.0. This resulted in a platinum loading of 0.3 mg / cm² per geometric area. 2 The cathode electrode is made by coating carbon paper (product name: TGP-H-060H, manufactured by Toray Industries, Inc.) with the coating material and then air-drying it.

[0262] Next, the cation exchange membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was successively boiled in 3% hydrogen peroxide water for 1 hour, in pure water for 1 hour, and in 1M sulfuric acid aqueous solution for 1 hour to clean and protonate, thus producing an electrolyte membrane.

[0263] Furthermore, the iridium-containing manganese oxides of Examples 1-13 and Comparative Example 1 were respectively mixed into solutions containing water, isopropanol, and ionomer (product name: Nafion dispersion, manufactured by Sigma-Aldrich) to prepare anode catalyst inks. The mass ratio of water:isopropanol:ionomer in the anode catalyst ink was set to 55.9:43.8:0.3. An Ir loading of 0.1 mg / cm² per geometric area was achieved. 2 The catalyst layer is coated onto a 0.05mm thick PTFE sheet (manufactured by Tokyo Glass Equipment Co., Ltd.) and then air-dried to produce a sheet with a catalyst layer.

[0264] The anolyte-coated side of the sheet with the catalyst layer is stacked opposite the electrolyte membrane, and the process is carried out using a hot press (product name: SA-302, manufactured by TESTER Sangyo Co., Ltd.) at 140°C and a clamping force of 80 kg / cm². 2 After hot pressing for 10 minutes, the PTFE sheet is peeled off to obtain a catalyst-coated electrolyte membrane.

[0265] The layers are stacked in the following order: anode current collector, catalyst-coated electrolyte membrane, and cathode electrode, such that the platinum-coated Ti fiber sintered body (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Precious Metals Industry Co., Ltd.; hereinafter also referred to as "anode current collector") faces the side of the catalyst-coated electrolyte membrane coated with the anode catalyst, and the side of the catalyst-coated electrolyte membrane without catalyst coating faces the side of the cathode electrode coated with the cathode catalyst. The resulting laminate is then pressed using a hot press at 130°C and a clamping force of 50 kg / cm². 2 The MEA is obtained by hot pressing for 3 minutes. The obtained MEA is installed in the shell of the PEM type water electrolyzer (product name: WE-4S-RICW, manufactured by FC Development Co., Ltd.) to manufacture the PEM type water electrolyzer.

[0266] Fabrication of the PEM-type water electrolyzers used in Examples 14 and 15:

[0267] The conductive substrates containing iridium-containing manganese oxides of Examples 14 and 1 were used as working electrodes (anodes).

[0268] A solution of water, ethanol, and ionomer (product name: Nafion dispersion, manufactured by Sigma-Aldrich) was mixed with 20% by mass of platinum-supported carbon catalyst (product name: 20% Platinum on Vulcan XC-72, manufactured by Sigma-Aldrich) to prepare a conductive catalyst ink. This ink was coated onto carbon paper (product name: TGP-H-060, manufactured by Toray Industries) and air-dried to serve as the counter electrode.

[0269] Next, the Nafion membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was successively boiled in 3% hydrogen peroxide water for 1 hour, in pure water for 1 hour, in 1M sulfuric acid aqueous solution for 1 hour, and in pure water for 1 hour to clean and protonate it, and used it as an electrolyte membrane.

[0270] The electrolyte membrane is held between the catalyst surfaces of the working electrode (anode) and the counter electrode, and then pressed using a hot press (product name: SA-302, manufactured by TESTER Sangyo Co., Ltd.) at 135°C and a clamping force of 400 kg / cm². 2The MEA is obtained by hot pressing for 3 minutes. The obtained MEA is installed in the shell of the PEM type water electrolyzer (product name: WE-4S-RICW, manufactured by FC Development Co., Ltd.) to manufacture the PEM type water electrolyzer.

[0271] <Evaluation of the catalytic performance of the oxygen generating electrode>

[0272] Using a PEM-type water electrolyzer, the current density at a voltage of 2V was measured by linear sweep voltammetry (LSV) of a two-electrode system under the following conditions, and this was used to evaluate the catalytic performance of the oxygen generating electrode.

[0273] Voltage increase rate: 10mV / second

[0274] Water temperature: 80℃

[0275] Water supply rate: 2 mL / min

[0276] An anode electrode catalyst (MEA) containing powders from the examples and comparative examples was prepared, along with a PEM-type water electrolyzer equipped with the MEA, and the oxygen generation electrode catalyst was evaluated. The results are shown in the table below.

[0277] [Table 4]

[0278]

[0279] As can be confirmed from Table 1, compared with Comparative Example 1 which does not contain iridium, the iridium-supported manganese oxide powder containing iridium and having an Ir / Mn molar ratio of 0.001 or more and 0.25 or less exhibits high oxygen generation electrode catalytic activity.

[0280] It can be confirmed that the current density increases with the increase of the Ir / Mn molar ratio, and the sample with an Ir / Mn molar ratio of 0.065 mol / mol achieved 2 A / cm. 2 The above current density.

[0281] The D16 diameter of Examples 1-4 and Comparative Example 1 was 0.5 μm, the D50 diameter was 0.7 μm, and the D84 diameter was 1.9 μm, with a standard deviation of 0.7 μm. This confirms that the treatment with K2IrCl6 aqueous solution and the subsequent heat treatment had no effect on the particle size.

[0282] It can be confirmed that the current density increases as the a / c ratio decreases, and iridium-containing manganese oxides with an a / c ratio of less than 1.521 exhibit high oxygen-generating electrode catalysis.

[0283] Industrial availability

[0284] This disclosure provides at least one of an iridium-containing manganese oxide exhibiting high oxygen-generating electrode catalytic activity, a catalyst comprising the same, an electrode comprising the catalyst, and a water electrolysis method using the electrode.

Claims

1. An iridium-containing manganese oxide, characterized in that, The molar ratio of iridium to manganese is greater than 0.001 and less than 0.

250.

2. The iridium-containing manganese oxide according to claim 1, wherein, The manganese oxide is manganese dioxide with a β-type crystal structure.

3. The iridium-containing manganese oxide according to claim 2, wherein, The ratio of the lattice constant of the iridium-containing manganese oxide in the a-axis direction to the lattice constant in the c-axis direction is greater than 1.420 and less than 1.

521.

4. The iridium-containing manganese oxide according to any one of claims 1 to 3, wherein, The D50 diameter in the volumetric particle size distribution of the iridium-containing manganese oxide is greater than 0.1 μm and less than 50.0 μm.

5. The iridium-containing manganese oxide according to any one of claims 1 to 3, wherein, The BET specific surface area of ​​the iridium-containing manganese oxide is 1 m². 2 / g or more and 200m 2 / g or less.

6. The iridium-containing manganese oxide according to any one of claims 1 to 3, wherein, In powder X-ray diffraction patterns, when using CuKα lines as the X-ray source, the peak at 2θ = 28 ± 1.5° has a full width at half maximum (FWHM) greater than 1.90° and less than 4.00°.

7. A catalyst, characterized in that, It comprises an iridium-containing manganese oxide according to any one of claims 1 to 3.

8. An electrode, characterized in that, It includes the catalyst as described in claim 7.

9. A method for water electrolysis, characterized in that, Use the electrode as described in claim 8.

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