Electrode containing oxygen generating electrode catalyst

Abstract

Provided is an electrode exhibiting high oxygen generating electrode catalytic activity as compared with conventional electrodes using manganese-based oxide as an oxygen generating electrode catalyst.

Description

Electrode containing oxygen evolution electrode catalyst

[0001] The present disclosure relates to an electrode that includes an oxygen evolution electrocatalyst that includes manganese oxide and / or iridium-manganese oxide.

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

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

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

[0005] F. Birol, World Energy Outlook 2016, International Energy Agency (IEA), Paris, 2016.

[0006] Although the manganese oxide of Patent Document 1 and the iridium-manganese oxide of Patent Document 2 have high oxygen evolving electrode catalytic activity, further performance improvements are required to meet the strong demand in recent years for higher efficiency in water electrolysis.The present disclosure aims to provide at least one of an electrode that exhibits higher oxygen evolving electrode catalytic activity than conventional electrodes that use manganese oxide and iridium-manganese oxide (hereinafter also referred to as "manganese-based oxide") as the oxygen evolving electrode catalyst, a water electrolysis method using the electrode, and a method for producing hydrogen using the electrode.

[0007] In studies of conventional electrodes using manganese-based oxides as oxygen generating electrode catalysts, such as those in Patent Documents 1 and 2, no attention was paid to the structure of the conductive substrate that constitutes those electrodes. In the present disclosure, attention was focused on the relationship between the structure of the conductive substrate that constitutes the oxygen generating electrode and the catalyst. As a result, it was found that, by controlling the thickness of the conductive substrate, an electrode using a manganese-based oxide as an oxygen generating electrode catalyst exhibits significantly higher oxygen generating electrode catalytic activity as an anode for an electrolytic reaction involving oxygen generation, compared to conventional electrodes using a manganese-based oxide as an oxygen generating electrode catalyst.

[0008] That is, the present invention is as set forth in the claims, and the gist thereof is as follows: [1] An electrode comprising an oxygen generating electrode catalyst containing at least one of manganese oxide and iridium-manganese oxide, and a conductive substrate having a thickness of 50 μm or more and less than 500 μm. [2] A content of the oxygen generating electrode catalyst per geometric area of ​​the electrode is 0.1 mg / cm. ２ 12.0mg / cm or more ２ [3] The electrode according to [1] above, wherein the oxygen generating electrode catalyst is an iridium-manganese oxide. [4] The iridium content is 0.01 mg / cm or less per geometric area of ​​the electrode. ２ 1.0mg / cm or more ２ [5] The electrode according to [3] above, wherein the molar ratio of iridium to manganese is 0.001 or more and 0.100 or less. [6] The electrode according to any one of [1] to [5] above, wherein the conductive base material contains titanium. [7] A water electrolysis device comprising the electrode according to any one of [1] to [6] above. [8] A method for producing hydrogen by water electrolysis using the electrode according to any one of [1] to [6] above.

[0009] The present disclosure can provide at least one of an electrode that exhibits higher oxygen generating electrode catalytic activity than conventional electrodes that use manganese-based oxides as oxygen generating electrode catalysts, a water electrolysis method using the electrode, and a method for producing hydrogen using the electrode.

[0010] An embodiment of the present disclosure will be described below. The electrode of this embodiment includes an oxygen generating electrode catalyst containing at least one of manganese oxide and iridium-manganese oxide, and a conductive substrate having a thickness of 50 μm or more and less than 500 μm. The oxygen generating electrode catalyst included in the electrode of this embodiment is an oxygen generating electrode catalyst containing at least one of manganese oxide and iridium-manganese oxide (hereinafter also referred to as a "manganese-based electrode catalyst"). This allows the electrode of this embodiment to function as an oxygen generating electrode.

[0011] The manganese-based electrode catalyst preferably contains manganese oxide, more preferably contains manganese dioxide, further preferably contains manganese dioxide having a γ-, β-, ε- or α-type crystal structure, and even more preferably contains manganese dioxide having a β-type crystal structure. The crystal structure of the manganese-based electrode catalyst is preferably a single phase, but may be two or more types of manganese-based electrode catalysts having a single-phase crystal structure, or a mixed phase having a plurality of crystal structures.

[0012] In this embodiment, the crystal structure of the manganese-based electrode catalyst 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) PDF (Powder Diffraction File). The reference patterns for manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure may be PDF No. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), or 44-0141 (α-type), respectively.

[0013] In this embodiment, the XRD pattern may be obtained by XRD measurement using a general powder X-ray diffractometer (for example, an Ultima IV Protectus manufactured by Rigaku Corporation) under the following conditions: Acceleration current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Continuous scan Scan conditions: 4° / min Measurement range: 2θ=10° to 80° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0014] The XRD peak is a peak whose peak top 2θ is detected in an XRD pattern analysis using general analysis software (e.g., IGOR Pro 8 manufactured by WaveMetrics or SmartLab Studio II manufactured by Rigaku Corporation). The content of the oxygen generating electrode catalyst per geometric area of ​​the electrode of this embodiment (hereinafter also referred to as the "catalyst content") is 0.1 mg / cm. ２ 12.0mg / cm or more ２ Preferably, it is 0.5 mg / cm or less. ２ 11.0mg / cm or more ２ More preferably, 0.8 mg / cm or less ２ 10.0mg / cm or more ２ The following is even more preferred:

[0015] The "geometric area" is the area equivalent to the projected area without taking into consideration irregularities or voids on the surface, and is the projected area of ​​the surface (geometric surface) that faces the electrolyte membrane when constituting a membrane-electrode assembly (hereinafter also referred to as "MEA"). The "geometric area of ​​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 defined as length, width, and width.

[0016] The manganese-based electrode catalyst is preferably a catalyst containing manganese oxide and iridium (iridium-manganese oxide) because it tends to have high activity as an oxygen generating electrode catalyst. Examples of iridium-manganese oxide include iridium supported on manganese oxide and iridium dispersed on the surface of manganese oxide. The average metal valence of iridium is preferably 3.1 or more and 3.8 or less.

[0017] In an electrode using iridium-manganese oxide as an oxygen generating electrode, the iridium content per geometric area of ​​the electrode (hereinafter also referred to as "iridium content") is 0.001 mg / cm ２ It is preferable that the concentration is 0.005 mg / cm or more. ２ More preferably, it is 0.01 mg / cm or more. ２ More preferably, it is 0.02 mg / cm or more. ２ It is particularly preferable that the iridium content is 1.0 mg / cm or more. ２ Preferably, it is 0.75 mg / cm or less. ２ More preferably, it is 0.5 mg / cm or less. ２ When the upper or lower limit of the iridium content is within this range, high oxygen evolution electrode catalytic activity is likely to be achieved when combined with a conductive substrate, which will be described later. The iridium content is 0.001 mg / cm or less. ２ 1.0mg / cm or more ２ Below, 0.005mg / cm ２ 0.75mg / cm or more ２ or less, or 0.01 mg / cm ２ 0.5mg / cm or more ２ The following is preferred:

[0018] In the iridium-manganese oxide, the molar ratio of iridium to manganese (hereinafter also referred to as "Ir / Mn molar ratio") is preferably 0.001 or more, more preferably 0.002 or more, and even more preferably 0.010 or more. The Ir / Mn molar ratio is preferably 0.100 or less, more preferably 0.075 or less, and even more preferably 0.050 or less. When the upper or lower limit of the Ir / Mn molar ratio is within this range, high oxygen generating electrode catalytic activity is likely to be achieved when combined with a conductive base material described below. The Ir / Mn molar ratio is preferably 0.001 or more and 0.100 or less, 0.002 or more and 0.075 or less, or 0.010 or more and 0.050 or less.

[0019] The electrode of this embodiment includes a conductive substrate having a thickness of 50 μm or more and less than 500 μm. Generally, the thickness of the conductive substrate has little effect on the oxygen evolving electrode catalytic activity, and a thinner conductive substrate slightly improves the current efficiency (e.g., S. Toghyani et al., Energy, 2018, 152, 237-246). In contrast, in the electrode of this embodiment, the thickness of the conductive substrate is less than 500 μm, which significantly improves the oxygen evolving electrode catalytic activity of the manganese-based electrode catalyst.

[0020] When the thickness of the conductive substrate is less than 50 μm, the mechanical strength of the conductive substrate decreases, making the electrode more susceptible to damage. On the other hand, when the thickness of the conductive substrate is 500 μm or more, the electrical resistance of the conductive substrate increases, resulting in a decrease in oxygen generating electrode catalytic activity. In order to exhibit better oxygen generating electrode catalytic activity, the thickness of the conductive substrate is preferably 75 μm or more, more preferably 100 μm or more. Furthermore, the thickness of the conductive substrate is preferably 450 μm or less, more preferably 300 μm or less, even more preferably less than 300 μm, and particularly preferably 250 μm or less. The thickness of the conductive substrate is preferably in the range of 50 μm or more and 450 μm or less, more preferably 75 μm or more and 300 μm or less, and even more preferably 100 μm or more and 250 μm or less.

[0021] 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.

[0022] The conductive substrate may be any substrate made of a conductive material, and is preferably a substrate containing titanium. The conductive substrate may have one or more shapes selected from the group consisting of mesh, cloth, and plate. Mesh-like shapes are preferred because they tend to increase oxygen generating electrode catalytic activity. Specific conductive substrates include titanium meshes made of fibrous or powdered conductive titanium metal, and sintered titanium meshes obtained by heat-treating these. In order to easily achieve high oxygen generating electrode catalytic activity, it is preferred that the surface of these conductive substrates be coated with platinum. Platinum-coated titanium meshes, and platinum-coated sintered titanium meshes are more preferred as conductive substrates.

[0023] 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 occupied by the conductive substrate and the conductive substrate is not present in the volume of the conductive substrate. The porosity can be measured by, for example, 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.

[0024] The electrode of this embodiment only needs to include a manganese-based electrode catalyst and a conductive substrate, and is preferably configured by a conductive substrate at least partially coated with the manganese-based electrode catalyst (hereinafter also referred to as a "composite electrode material"). A manganese oxide composite electrode material is a conductive substrate at least partially coated with the above-mentioned manganese oxide, and an iridium-manganese oxide composite electrode material is a conductive substrate at least partially coated with the above-mentioned iridium-manganese oxide.

[0025] Examples of the electrode structure of this embodiment include an electrode having a structure in which manganese oxide is supported on the surface of a conductive substrate, an electrode having a structure in which manganese oxide and iridium are supported on the surface of a conductive substrate, and an electrode having a structure in which manganese oxide is supported on the surface of a conductive substrate and iridium is supported on the manganese oxide.

[0026] The electrode of the present embodiment can be used as an oxygen generating electrode, and is preferably used as an oxygen generating electrode in a water electrolysis device. The electrode of the present embodiment can be used in a method for producing hydrogen by electrolyzing water using the electrode.

[0027] The method for producing the electrode of this embodiment is not particularly limited as long as it can produce an electrode having the above-described configuration, but a preferred production method includes an electrolysis step of electrolytically depositing manganese oxide on a conductive substrate to obtain a manganese oxide-containing substrate, and a heat treatment step of heat-treating the manganese oxide-containing substrate.

[0028] In the electrolysis step, manganese oxide is electrolytically deposited on the conductive substrate, thereby obtaining a manganese oxide-containing substrate. Any electrolytic deposition method may be used as long as manganese oxide 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.

[0029] The electrolytic solution may be any solution containing manganese. The manganese concentration of the electrolytic solution is preferably 5 g / L or more and 50 g / 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 5 g / L or more and 65 g / L or less, and the manganese concentration is preferably 5 g / L or more and 50 g / L or less.

[0030] The conductive substrate to be subjected to the electrolysis step may be any of the above-mentioned conductive substrates, and may have a thickness of less than 500 μm, preferably 300 μm or less, and more preferably a platinum-coated titanium mesh, or even a platinum-coated sintered titanium mesh.

[0031] In the electrolysis, the conductive substrate is immersed in an electrolyte solution and electrolyzed. The electrolysis conditions may be any conditions that allow electrolytic deposition of manganese oxide, and the current density per geometric area of ​​the conductive substrate is 0.3 mA / cm. ２ 20mA / cm or more ２ and the electrolysis temperature is 93°C or higher and 98°C or lower.

[0032] In the heat treatment step, the manganese oxide-containing substrate is heat-treated. This increases the adhesion between the manganese oxide and the conductive substrate. The heat treatment in the heat treatment step may be performed under conditions that allow the manganese oxide in the manganese oxide-containing substrate to maintain the above-mentioned crystal structure. The heat treatment atmosphere may be an air atmosphere or an inert atmosphere, or even an air atmosphere, and the heat treatment temperature may be 100°C or higher and 600°C or lower. The heat treatment time may be adjusted appropriately depending on the size of the conductive substrate to be subjected to the heat treatment, and may be, for example, 10 minutes to 24 hours.

[0033] When producing an electrode in which the manganese-based electrode catalyst is iridium-manganese oxide, it is preferable to have a contact step of contacting the manganese oxide-containing substrate with an iridium salt solution prior to the heat treatment step, thereby obtaining an iridium-manganese oxide-containing substrate, and then providing the iridium-manganese oxide-containing substrate in place of the manganese oxide-containing substrate in the heat treatment step.

[0034] The iridium salt solution to be subjected to the contact step may be any solution containing an iridium salt, and is preferably a solution containing an iridium salt and sulfuric acid, or more preferably an aqueous solution containing an iridium salt and sulfuric acid. ２ IrCl ６ ) and hexachloroiridic acid (H ２ IrCl ６ The iridium concentration of the iridium salt solution is preferably 0.001 g / L or more and 10 g / L or less.

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

[0036] Hereinafter, the present disclosure will be described in detail with reference to examples and comparative examples, but the present disclosure is not limited to these examples. <Analysis of Metal Content of Electrode>

[0037] A sample electrode measuring 10 mm in length and 10 mm in width was immersed in 10 mL of a mixed solution of hydrochloric acid and nitric acid, and the oxygen-generating electrode catalyst contained in the electrode was dissolved to obtain a sample solution. The composition of the sample solution was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a common ICP device (device name: Optima 830, manufactured by PerkinElmer). <Identification of crystal structure>

[0038] An XRD pattern was obtained using a general powder X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Rigaku Corporation) under the following conditions: Acceleration current / voltage: 40 mA / 40 kV Radiation source: CuKα radiation (λ=1.5405 Å) Measurement mode: Continuous scan Scan condition: 4° / min Measurement range: 2θ=10° to 80° Divergence vertical limiting slit: 10 mm Divergence / entrance slit: 1° Receiving slit: open Detector: D / teX Ultra Ni filter used

[0039] The crystalline phase of the sample was identified by comparing the obtained XRD pattern with the XRD pattern (hereinafter also referred to as "reference pattern") registered in the PDF (Powder Diffraction File) of the ICDD (International Center for Diffraction Data). The reference patterns for manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure were PDF No. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type), or 44-0141 (α-type), respectively. <Measurement of Oxygen Evolution Electrode Catalytic Activity>

[0040] Using a PEM-type water electrolysis cell in which the electrodes of the Examples and Comparative Examples were used as the working electrodes (anodes), the oxygen evolution electrode catalytic activity was evaluated by linear sweep voltammetry (LSV) of a two-electrode system under the following conditions.

[0041] Voltage increase rate: 10 mV / sec Water temperature: 80°C Water supply rate: 2 mL / min From this evaluation, the current density at a voltage of 2 V (hereinafter also simply referred to as "current density") was determined. In addition, the ratio of the current density of the electrodes of the example and comparative examples to the current density of an electrode having a conductive substrate with a thickness of 500 μm (hereinafter also referred to as "relative current density") was determined.

[0042] <Manganese oxide> Example 1 An electrolytic cell was filled with a sulfuric acid-manganese sulfate mixed solution with a sulfuric acid concentration of 35 g / L and a manganese sulfate concentration of 31 g / L, and a conductive substrate made of Pt-coated Ti fiber (product name: titanium fiber sintered body 2GDL08N-020 BS05PT platinum-plated product, manufactured by Bekaert, thickness 200 μm, Pt thickness 0.5 μm, porosity 56%) was immersed in the solution. A current density of 7 mA / cm was applied to the conductive substrate. ２ A current was applied for 10 minutes at 40°C to electrochemically deposit manganese oxide onto the conductive substrate.

[0043] The conductive substrate on which the obtained manganese oxide was electrochemically deposited was subjected to annealing treatment in an air atmosphere at 450°C for 5 hours to obtain a manganese oxide composite electrode material, which was used as the electrode of this example. The electrode of this example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) with a β-type crystal structure on a conductive substrate made of Pt-coated Ti fibers with a thickness of 200 µm, and a manganese content of 1.2 mg / cm ２ (iridium content was 0 g / cm ２ , Ir / Mn molar ratio is 0).

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

[0045] Next, a Nafion membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was washed and protonated by boiling in 3 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 this order, to prepare an electrolyte membrane.

[0046] The sample electrode was used as the working electrode (anode), and the electrolyte membrane was sandwiched between the catalytic surfaces of the working electrode (anode) and the counter electrode. The electrode was then heated at 135°C and a clamping force of 400 kg / cm using a hot press (product name: SA-302, manufactured by Tester Sangyo Co., Ltd.). ２ The resulting MEA was attached to a housing of a PEM water electrolysis cell (product name: WE-4S-RICW, manufactured by FC Development Co., Ltd.) to prepare a PEM water electrolysis cell.

[0047] The resulting PEM-type water electrolyzer was used to evaluate the oxygen evolution electrode catalytic activity.

[0048] Example 2 An electrode of this example was obtained in the same manner as in Example 1, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered compact, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 300 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of Pt-coated Ti fiber with a thickness of 300 μm, and a manganese content of 1.2 mg / cm ２ (iridium content was 0 g / cm ２ , Ir / Mn molar ratio is 0).

[0049] The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0050] Comparative Example 1 An electrode of this comparative example was obtained in the same manner as in Example 1, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 1.2 mg / cm ２ (iridium content was 0 g / cm ２ , the Ir / Mn molar ratio was 0.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0051] The following table shows the evaluation results of Examples 1 and 2 and Comparative Example 1. The current density in the table is the value at a voltage of 2V.

[0052]

[0053] Example 3 An electrode of this example was obtained in the same manner as in Example 1, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 200 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate, and the current application time was set to 20 minutes. The electrode of this example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) with a β-type crystal structure on a conductive substrate made of Pt-coated Ti fiber with a thickness of 200 μm, and a manganese content of 2.4 mg / cm ２ (iridium content was 0 g / cm ２ , Ir / Mn molar ratio was 0.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0054] Comparative Example 2 An electrode of this comparative example was obtained in the same manner as in Example 3, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered compact, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 2.4 mg / cm ２ (iridium content was 0 g / cm ２ , the Ir / Mn molar ratio was 0.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0055] The evaluation results of Example 3 and Comparative Example 2 are shown in the table below. The current density in the table below is the value at a voltage of 2V.

[0056]

[0057] Example 4 An electrode of this example was obtained in the same manner as in Example 3, except that the current application time was set to 5 minutes. The electrode of this example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of Pt-coated Ti fibers with a thickness of 200 μm, and the manganese content was 0.6 mg / cm. ２ (iridium content was 0 g / cm ２ , Ir / Mn molar ratio was 0.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0058] Comparative Example 3 An electrode of this comparative example was obtained in the same manner as in Example 4, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered compact, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 0.6 mg / cm ２ (iridium content was 0 g / cm ２ , the Ir / Mn molar ratio was 0.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0059] The evaluation results of Example 4 and Comparative Example 3 are shown in the table below. The current density in the table below is a value at a voltage of 2V.

[0060]

[0061] It was confirmed that the electrode using manganese oxide as the oxygen generating electrode catalyst has a significantly improved oxygen generating electrode catalytic activity compared to a conventional electrode (with a conductive substrate thickness of 500 μm) using manganese oxide as the oxygen generating electrode catalyst, due to the reduced thickness of the conductive substrate.

[0062] <Iridium-Manganese Oxide> Example 5 A manganese oxide composite electrode material was obtained in the same manner as in Example 1, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 200 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. ２ IrCl ６ The manganese oxide composite electrode material was immersed in an iridium salt solution containing 0.05 g / L of manganese dioxide and 0.5 g / L of sulfuric acid at 95°C for 168 hours, and then annealed in an air atmosphere at 450°C for 5 hours to obtain an iridium-manganese oxide composite electrode material, which was used as the electrode of this example. The electrode of this example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) with a β-type crystal structure and iridium supported on its surface, on a conductive substrate made of Pt-coated Ti fibers and having a thickness of 200 μm, and the manganese content was 1.2 mg / cm. ２ and the iridium content is 0.20 mg / cm ２ (Ir / Mn molar ratio was 0.048) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0063] Comparative Example 4 An electrode of this comparative example was obtained in the same manner as in Example 5, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 1.2 mg / cm ２ and the iridium content is 0.20 mg / cm ２ (Ir / Mn molar ratio was 0.048) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0064] The evaluation results of Example 5 and Comparative Example 4 are shown in the table below. The current density in the table below is a value at a voltage of 2V.

[0065]

[0066] Example 6 A manganese oxide composite electrode material was obtained in the same manner as in Example 1, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 100 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. ２ IrCl ６ An electrode of this example was obtained in the same manner as in Example 5, except that the concentration was set to 0.02 g / L and the manganese oxide composite electrode material was immersed in the iridium salt solution for 24 hours.

[0067] The electrode of this example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fibers with a thickness of 100 μm, and the manganese content is 1.2 mg / cm ２ and the iridium content is 0.10 mg / cm ２ (Ir / Mn molar ratio was 0.024) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0068] Example 7 An electrode of this example was obtained in the same manner as in Example 6, except that a Pt-coated Ti fiber (trade name: titanium fiber sintered body 2GDL08N-020 BS05PT platinum-plated product, manufactured by Bekaert, thickness 200 μm, Pt thickness 0.5 μm, porosity 56%) was used as the conductive substrate.

[0069] The electrode of this example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fibers with a thickness of 200 μm, and the manganese content is 1.2 mg / cm ２ and the iridium content is 0.10 mg / cm ２(Ir / Mn molar ratio was 0.024) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0070] Example 8 An electrode of this example was obtained in the same manner as in Example 6, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 300 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate.

[0071] The electrode of this example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fibers with a thickness of 300 μm, and the manganese content is 1.2 mg / cm ２ and the iridium content is 0.10 mg / cm ２ (Ir / Mn molar ratio was 0.024) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0072] Comparative Example 5 An electrode of this comparative example was obtained in the same manner as in Example 6, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 1.2 mg / cm ２ and the iridium content is 0.10 mg / cm ２ (Ir / Mn molar ratio was 0.024) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0073] The following table shows the evaluation results of Examples 6 to 8 and Comparative Example 5. The current density in the table is the value at a voltage of 2V.

[0074]

[0075] Example 9 K in iridium salt solution ２ IrCl ６ The electrode of this example was obtained in the same manner as in Example 7, except that the concentration was 0.01 g / L. The electrode of this example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fibers with a thickness of 200 μm, and the manganese content was 1.2 mg / cm ２ and the iridium content is 0.01 mg / cm ２ (Ir / Mn molar ratio was 0.002.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0076] Comparative Example 6 An electrode of this comparative example was obtained in the same manner as in Example 9, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered compact, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 1.2 mg / cm ２ and the iridium content is 0.01 mg / cm ２ (Ir / Mn molar ratio was 0.002). The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode). The evaluation results of Example 9 and Comparative Example 6 are shown in the table below. The current density in the table below is a value at a voltage of 2 V.

[0077]

[0078] Example 10 A manganese oxide composite electrode material was obtained in the same manner as in Example 3. Next, an electrode of this example was obtained in the same manner as in Example 7, except that this manganese oxide composite electrode material was used. The electrode of this example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) with a β-type crystal structure and iridium supported on its surface, on a conductive substrate made of Pt-coated Ti fibers and having a thickness of 200 μm, and the manganese content was 2.4 mg / cm ２ and the iridium content is 0.10 mg / cm ２ (Ir / Mn molar ratio was 0.012.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0079] Comparative Example 7 An electrode of this comparative example was obtained in the same manner as in Example 10, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 2.4 mg / cm ２ and the iridium content is 0.10 mg / cm ２ (Ir / Mn molar ratio was 0.012) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0080] The evaluation results of Example 10 and Comparative Example 7 are shown in the table below. The current density in the table below is the value at a voltage of 2V.

[0081]

[0082] Example 11 A manganese oxide composite electrode material was obtained in the same manner as in Example 4. Next, an electrode of this example was obtained in the same manner as in Example 7, except that this manganese oxide composite electrode material was used. The electrode of this example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) with a β-type crystal structure and iridium supported on its surface, on a conductive substrate made of Pt-coated Ti fibers and having a thickness of 200 μm, and the manganese content was 0.6 mg / cm ２ and the iridium content is 0.05 mg / cm ２ (Ir / Mn molar ratio was 0.024) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this example was used as the working electrode (anode).

[0083] Comparative Example 8 An electrode of this comparative example was obtained in the same manner as in Example 11, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example was an electrode having an oxygen generating electrode catalyst made of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and carrying iridium on its surface, on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and a manganese content of 0.6 mg / cm ２ and the iridium content is 0.05 mg / cm ２ (Ir / Mn molar ratio was 0.024) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0084] The evaluation results of Example 11 and Comparative Example 8 are shown in the table below. The current density in the table below is a value at a voltage of 2V.

[0085]

[0086] It was confirmed that the electrode using iridium-manganese oxide as the oxygen generating electrode catalyst has a significantly improved oxygen generating electrode catalytic activity compared to a conventional electrode (with a conductive substrate thickness of 500 μm) using iridium-manganese oxide as the oxygen generating electrode catalyst, due to the reduced thickness of the conductive substrate.

[0087] <Iridium Oxide> Comparative Example 9 A conductive catalyst ink containing 4.7 g / L of iridium oxide was prepared by mixing commercially available iridium oxide powder (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with pure water, and this was applied to a conductive substrate consisting of Pt-coated Ti fibers (product name: Titanium fiber sintered body 2GDL08N-020 BS05PT platinum-plated product, manufactured by Bekaert, thickness 200 μm, Pt thickness 0.5 μm, porosity 56%) and air-dried. The resulting conductive substrate containing iridium oxide was annealed in air at 450°C for 5 hours to obtain an iridium oxide composite electrode material, which was used as the electrode of this comparative example.

[0088] The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of iridium oxide on a conductive substrate made of Pt-coated Ti fiber with a thickness of 200 μm, and the iridium content is 0.1 mg / cm ２ (manganese content was 0 g / cm ２ , the Ir / Mn molar ratio is ∞.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0089] Comparative Example 10 An electrode of this comparative example was obtained in the same manner as in Comparative Example 9, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 300 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of iridium oxide on a conductive substrate made of Pt-coated Ti fiber with a thickness of 300 μm, and an iridium content of 0.1 mg / cm ２ (manganese content was 0 g / cm ２ , Ir / Mn molar ratio is ∞).

[0090] The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0091] Comparative Example 11 An electrode of this comparative example was obtained in the same manner as in Comparative Example 9, except that a Pt-coated Ti fiber (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) with a thickness of 500 μm, a Pt thickness of 0.5 μm, and a porosity of 56% was used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generating electrode catalyst made of iridium oxide on a conductive substrate made of Pt-coated Ti fiber with a thickness of 500 μm, and an iridium content of 0.1 mg / cm ２ (manganese content was 0 g / cm ２ , the Ir / Mn molar ratio is ∞.) The oxygen evolution electrode catalytic activity was evaluated in the same manner as in Example 1, except that the electrode of this comparative example was used as the working electrode (anode).

[0092] The evaluation results of Comparative Examples 9 to 11 are shown in the table below. Note that the current density in the table below is the value at a voltage of 2V.

[0093]

[0094] In the case of an electrode using iridium oxide as the oxygen evolution electrode catalyst, even if the thickness of the conductive substrate was reduced, the change in the oxygen evolution electrode catalytic activity was small.

[0095] From the above results, it was confirmed that the significant improvement in oxygen evolution electrode catalytic activity due to the reduction in the thickness of the conductive substrate is a behavior unique to manganese oxide and iridium-manganese oxide. The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-135670, filed on August 23, 2023, and the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2024-100953, filed on June 24, 2024, are hereby incorporated by reference as part of the disclosure of the specification of the present disclosure.

Claims

1. An electrode comprising an oxygen generating electrode catalyst containing at least one of manganese oxide and iridium-manganese oxide, and a conductive substrate having a thickness of 50 μm or more and less than 500 μm.

2. The content of the oxygen generating electrode catalyst is 0.1 mg / cm per geometric area of ​​the electrode. ２ 12.0mg / cm or more ２ 2. The electrode of claim 1 , wherein:

3. The electrode according to claim 1 or 2, wherein the oxygen evolution electrode catalyst is iridium-manganese oxide.

4. The iridium content is 0.01 mg / cm2 per geometric area of ​​the electrode. ２ 1.0mg / cm or more ２ 4. The electrode of claim 3, wherein:

5. The electrode according to claim 3 or 4, wherein the molar ratio of iridium to manganese is 0.001 or more and 0.100 or less.

6. The electrode of any one of claims 1 to 5, wherein the conductive substrate comprises titanium.

7. A water electrolysis device comprising the electrode according to any one of claims 1 to 6.

8. A method for producing hydrogen by electrolysis of water using the electrode according to any one of claims 1 to 6.

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