Electrode comprising oxygen evolution electrode catalyst

Abstract

To provide an electrode that exhibits higher oxygen evolution electrode catalyst activity compared to an electrode using manganese-based oxide as an oxygen evolution electrode catalyst.SOLUTION: The electrode comprises an oxygen evolution 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.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an electrode including an oxygen generation electrode catalyst containing at least one of manganese oxide and iridium-manganese oxide.

Background Art

[0002] Due to the problems of depletion of fossil fuels and environmental pollution, attention has been focused on the use of hydrogen as a clean energy and its production methods. One of the effective means for producing high-purity hydrogen gas is the water electrolysis method. In the water electrolysis method, iridium-based catalysts are widely known as highly active oxygen generation electrode catalysts (for example, Non-Patent Document 1). However, iridium has an extremely small reserve compared to other precious metals, and even if water electrolysis technology spreads in the future, a sufficient amount of catalyst cannot be ensured.

[0003] Under such circumstances, 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 an oxygen generation electrode catalyst with a reduced conventional iridium usage amount.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Although the manganese oxides of Patent Document 1 and the iridium-manganese oxides of Patent Document 2 have high oxygen evolution electrode catalytic activity, further performance improvement is required to meet the growing demand for higher efficiency in recent water electrolysis. The present disclosure aims to provide at least one of an electrode showing high oxygen evolution electrode catalytic activity compared with a conventional electrode using manganese oxides and iridium-manganese oxides (hereinafter also referred to as "manganese-based oxides") as an oxygen evolution electrode catalyst, a water electrolysis method using the same, and a method for producing hydrogen using the same electrode.

Means for Solving the Problems

[0007] Regarding electrodes using conventional manganese-based oxides as in Patent Documents 1 and 2 as oxygen evolution electrode catalysts, the structure of the conductive base material constituting these electrodes has not been focused on. In the present disclosure, attention was paid to the relationship between the structure of the conductive base material constituting the oxygen evolution electrode and the catalyst. As a result, in an electrode using a manganese-based oxide as an oxygen evolution electrode catalyst, by controlling the thickness of the conductive base material, it was found that, as an anode of an electrolysis reaction involving oxygen evolution, it shows significantly higher oxygen evolution electrode catalytic activity compared with a conventional electrode using a manganese-based oxide as an oxygen evolution electrode catalyst.

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

[0009] According to the present disclosure, at least one of an electrode exhibiting high oxygen evolution electrode catalyst activity as compared with a conventional electrode using a manganese-based oxide as an oxygen evolution electrode catalyst, a water electrolysis method using the same, and a method for producing hydrogen using the electrode can be provided. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, an embodiment of the present disclosure will be described. The electrode of the present embodiment is an electrode including an oxygen evolution 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 evolution electrode catalyst contained in the electrode of the present embodiment is an oxygen evolution electrode catalyst containing at least one of manganese oxide and iridium-manganese oxide (hereinafter, also referred to as a "manganese-based electrode catalyst"). Thereby, the electrode of the present embodiment functions as an oxygen evolution electrode.

[0011] The manganese-based electrode catalyst preferably contains manganese oxide, more preferably contains manganese dioxide, still more preferably contains manganese dioxide having a crystal structure of γ-type, β-type, ε-type or α-type, 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 two or more kinds of manganese-based electrode catalysts having a single-phase crystal structure or a mixed phase having a plurality of crystal structures may also be used.

[0012] In the present 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 PDF (Powder Diffraction File) of the ICDD (International Center for Diffraction Data). As the reference pattern of manganese dioxide having a crystal structure of γ-type, β-type, ε-type or α-type, PDF No. 14-0644 (γ-type), 24-0735 (β-type), 30-0820 (ε-type) or 44-0141 (α-type) may be used respectively.

[0013] In the present embodiment, the XRD pattern may be obtained from XRD measurement under the following conditions using a general powder X-ray diffractometer (for example, device name: Ultima IV Protectus, manufactured by Rigaku Corporation). Accelerating current and voltage: 40 mA·40 kV X-ray source: CuKα ray (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 / incidence slit: 1° Receiving slit: open Detector: D / teX Ultra Using Ni filter

[0014] The XRD peak is a peak at which 2θ of the peak top is detected in the analysis of the XRD pattern using general analysis software (for example, IGOR Pro 8 manufactured by WaveMetrics, or SmartLab StudioII manufactured by Rigaku). The content of the oxygen evolution electrode catalyst per geometric area of the electrode of the present embodiment (hereinafter, also referred to as "catalyst content") is 0.1 mg / cm 2 or more and 12.0 mg / cm 2 or less, preferably 0.5 mg / cm 2 or more and 11.0 mg / cm 2 or less, more preferably 0.8 mg / cm 2 or more and 10.0 mg / cm 2 or less is even more preferable.

[0015] The "geometric area" is an area corresponding to the projected area without considering the unevenness and voids on the surface, and is the projected area of the surface (geometric surface) facing the electrolyte membrane when constructing a membrane-electrode assembly (hereinafter, also referred to as "MEA"). The "geometric area of the electrode" is the projected area of the electrode, and is the area of the plane obtained from the length × width when the shape of the electrode is defined by length × width × thickness.

[0016] Since the activity as an oxygen evolution electrode catalyst is likely to be high, the manganese-based electrode catalyst is preferably a catalyst containing manganese oxide and iridium (iridium-manganese oxide). Examples of iridium-manganese oxide include those in which iridium is supported on manganese oxide and those in which iridium is dispersed and arranged 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 the oxygen evolution electrode, the content of iridium per geometric area of the electrode (hereinafter, also referred to as "iridium content") is 0.001 mg / cm 2 or more, preferably 0.005 mg / cm 2 or more, more preferably 0.01 mg / cm 2 or more, even more preferably 0.02 mg / cm2 It is particularly preferable that it is as described above, and the iridium content is 1.0 mg / cm 2 or less, preferably 0.75 mg / cm 2 or less, more preferably 0.5 mg / cm 2 or less, and even more preferably. By setting the upper limit value or the lower limit value of the iridium content to this value, when combined with the conductive substrate described later, it is easy to exhibit high oxygen evolution electrode catalytic activity. The iridium content is 0.001 mg / cm 2 or more and 1.0 mg / cm 2 or less, 0.005 mg / cm 2 or more and 0.75 mg / cm 2 or less, or 0.01 mg / cm 2 or more and 0.5 mg / cm 2 or less is preferable.

[0018] In 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. Also, 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. By setting the upper limit value or the lower limit value of the Ir / Mn molar ratio to this value, when combined with the conductive substrate described later, it is easy to exhibit high oxygen evolution electrode catalytic activity. 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 the present embodiment includes a conductive substrate having a thickness of 50 μm or more and less than 500 μm. Generally, the influence of the thickness of the conductive substrate on the oxygen evolution electrode catalytic activity is slight, and when the conductive substrate becomes thinner, the current efficiency is slightly improved (for example, S. Toghyani et al., Energy, 2018, 152, 237-246.). On the other hand, in the electrode of the present embodiment, when the thickness of the conductive substrate is less than 500 μm, a remarkable effect is achieved in which the oxygen evolution electrode catalytic activity of the manganese-based electrode catalyst is dramatically improved.

[0020] When the thickness of the conductive substrate is less than 50 μm, the mechanical strength of the conductive substrate decreases, and the electrode is likely to be damaged. On the other hand, when the thickness of the conductive substrate is 500 μm or more, the electrical resistance of the conductive substrate increases, and as a result, the oxygen generation electrode catalytic activity decreases. In order to exhibit more excellent oxygen generation electrode catalytic activity, the thickness of the conductive substrate is preferably 75 μm or more, more preferably 100 μm or more. Also, the thickness of the conductive substrate is preferably 450 μm or less, more preferably 300 μm or less, still more preferably less than 300 μm, and particularly preferably 250 μm or less. The range of the thickness of the conductive substrate is preferably 50 μm or more and 450 μm or less, more preferably 75 μm or more and 300 μm or less, and still more preferably 100 μm or more and 250 μm or less.

[0021] "Thickness" corresponds to the length in the direction perpendicular to the geometric surface. "The thickness of the conductive substrate" corresponds to the length in the direction perpendicular to the geometric surface of the conductive substrate, and corresponds to the width when the shape of the electrode is defined as length × width × height.

[0022] The conductive substrate may be a substrate made of a conductive material, and is preferably a substrate containing titanium. Examples of the shape of the conductive substrate include one or more selected from the group of mesh, cloth, and plate shapes, and a mesh shape is preferred because the oxygen generation electrode catalytic activity is likely to be high. Specific examples of the conductive substrate include a titanium mesh composed of fibrous or powdery conductive metal titanium, and a sintered titanium mesh obtained by heat-treating this. From the viewpoint of easily exhibiting high oxygen generation electrode catalytic activity, the surface of these conductive substrates is preferably coated with platinum, and the conductive substrate is more preferably a platinum-coated titanium mesh, and further preferably a platinum-coated sintered titanium mesh.

[0023] 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, the porosity is defined as the volume of the space portion without the conductive substrate or the like in the volume of the conductive substrate. As a method for measuring the porosity, for example, the mercury pressure method can be mentioned. When the porosity is within the above range, the mechanical strength of the electrode is increased, and an excellent effect can be obtained in that the supply of water, which is the reaction quality of oxygen generation, can be smoothly performed.

[0024] The electrode of the present embodiment only needs to contain a manganese-based electrode catalyst and a conductive substrate, and is preferably composed of a composite electrode material in which at least a part of the conductive substrate is coated with the manganese-based electrode catalyst (hereinafter, also referred to as "composite electrode material"). The manganese oxide composite electrode material is one in which at least a part of the conductive substrate is coated with the above-described manganese oxide, and the iridium-manganese oxide composite electrode material is one in which at least a part of the conductive substrate is coated with the above-described iridium-manganese oxide.

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

[0026] The electrode of the present embodiment can be used as an oxygen generation electrode, and more preferably as an oxygen generation 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 this electrode.

[0027] Hereinafter, a method for manufacturing the electrode of the present embodiment will be described. The method for manufacturing the electrode of the present embodiment is not particularly limited as long as an electrode having the above configuration can be obtained. As a preferred manufacturing method, an electrolysis step of electrochemically 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 are included.

[0028] In the electrolysis process, manganese oxide is electrodeposited on a conductive substrate. Thereby, a manganese oxide-containing substrate is obtained. If manganese oxide is electrodeposited on the surface of the conductive substrate, the electrodeposition method is arbitrary, and any method may be used as long as the conductive substrate is immersed in the electrolytic solution and electrolyzed.

[0029] The electrolytic solution may be a 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, and more preferably an aqueous solution of manganese sulfate. In this case, the sulfuric acid concentration is 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 used in the electrolysis process may be the above-mentioned conductive substrate, and its thickness may be less than 500 μm, preferably 300 μm or less, and more preferably a platinum-coated titanium mesh or a platinum-coated sintered titanium mesh.

[0031] In electrolysis, the conductive substrate may be immersed in the electrolytic solution and electrolyzed. The electrolysis conditions may be any conditions under which manganese oxide is electrodeposited, and the current density is 0.3 mA / cm per geometric area of the conductive substrate 2 or more and 20 mA / cm 2 or less, and the electrolysis temperature may be 93 °C or more and 98 °C or less.

[0032] In the heat treatment step, a manganese oxide-containing substrate is heat treated. Thereby, the adhesion between the manganese oxide and the conductive substrate is enhanced. The heat treatment in the heat treatment step may be any condition under which the manganese oxide in the manganese oxide-containing substrate can maintain the above-described crystal structure. Examples of the heat treatment atmosphere include an air atmosphere or an inert atmosphere, and more preferably an air atmosphere. The heat treatment temperature may be 100°C or higher and 600°C or lower. The heat treatment time may be appropriately adjusted according to the size of the conductive substrate to be heat treated. For example, it may be 10 minutes or longer and 24 hours or shorter.

[0033] When manufacturing an electrode in which the manganese-based electrode catalyst is iridium-manganese oxide, it is preferable to have a contact step of bringing a manganese oxide-containing substrate into contact with an iridium salt solution prior to the heat treatment step. Thereby, an iridium-manganese oxide-containing substrate is obtained, and in the heat treatment step, the iridium-manganese oxide-containing substrate may be used instead of the manganese oxide-containing substrate.

[0034] The iridium salt solution used in the contact step may be any solution containing an iridium salt. A solution containing an iridium salt and sulfuric acid, and more preferably an aqueous solution containing an iridium salt and sulfuric acid, are preferred. Examples of the iridium salt include at least one of potassium hexachloroiridate (K2IrCl6) and hexachloroiridic acid (H2IrCl6). The iridium concentration of the iridium salt solution is preferably 0.001 g / L or higher and 10 g / L or lower.

[0035] The contact between the manganese oxide-containing substrate and the iridium salt solution may be achieved by immersing the manganese oxide-containing substrate in the iridium salt solution. The contact is not particularly limited as long as the surface of the manganese oxide-containing substrate is impregnated with iridium. Examples of the contact temperature include 20°C or higher and 100°C or lower. The contact time may be appropriately adjusted according to the size of the manganese oxide-containing substrate. For example, it may be 30 minutes or longer and 24 hours or shorter.

Example

[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. <Metal amount analysis 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 to dissolve the oxygen evolution electrode catalyst contained in the electrode, thereby obtaining a sample solution. The composition of the sample solution was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) using a general ICP device (device name: Optima 830, manufactured by PerkinElmer). <Identification of crystal structure>

[0038] A general powder X-ray diffractometer (device name: Ultima IV Protectus, manufactured by Rigaku) was used to obtain an XRD pattern under the following conditions. Accelerating current and voltage: 40 mA·40 kV X-ray source: CuKα ray (λ = 1.5405 Å) Measurement mode: Continuous scan Scan condition: 4° / min Measurement range: 2θ = 10° to 80° Divergent vertical limiting slit: 10 mm Divergent / incident slit: 1° Receiving slit: open Detector: D / teX Ultra Using Ni filter

[0039] The crystal phase of the sample was identified by comparing the obtained XRD pattern with the XRD pattern registered in the PDF (Powder Diffraction File) of the ICDD (International Center for Diffraction Data) (hereinafter also referred to as the "reference pattern"). The reference patterns of manganese dioxide having a γ-type, β-type, ε-type, or α-type crystal structure used 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 catalyst activity>

[0040] A PEM type water electrolysis cell with the electrodes of the examples and comparative examples as the working electrode (anode) was used, and 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 / second 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. Also, the ratio of the current density of the electrodes of the examples and comparative examples to the current density of the electrode with a conductive substrate thickness of 500 μm (hereinafter, also referred to as "relative current density") was determined.

[0042] <Manganese oxide> Example 1 The electrolytic cell was filled with a sulfuric acid-manganese sulfate mixed solution having 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 therein. A current of 7 mA / cm 2 was applied to the conductive substrate for 10 minutes to electrochemically deposit manganese oxide on the conductive substrate.

[0043] The obtained conductive substrate on which manganese oxide was electrochemically deposited was annealed in an air atmosphere at 450 °C for 5 hours to obtain a manganese oxide composite electrode material, which was used as the electrode of this example. The electrode of this example is an electrode having an oxygen evolution electrode catalyst composed 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 200 μm, and the manganese content is 1.2 mg / cm 2 and the iridium content is 0 g / cm 2 and the Ir / Mn molar ratio is 0).

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

[0045] Next, a Nafion membrane (product name: Nafion 115, manufactured by Sigma-Aldrich) was washed and protonated by boiling it in 3% by mass hydrogen peroxide solution for 1 hour, pure water for 1 hour, 1M sulfuric acid aqueous solution for 1 hour, and pure water for 1 hour in this order, and this was used as the electrolyte membrane.

[0046] Using the sample electrode as the working electrode (anode), sandwiching the electrolyte membrane between the catalytic surfaces of the working electrode (anode) and the counter electrode, and using a hot press machine (product name: SA-302, manufactured by Tester Sangyo Co., Ltd.), hot pressing was performed at 135 °C and a molding pressure of 400 kg / cm 2 for 3 minutes to obtain the MEA. The obtained MEA was attached to the housing of the PEM water electrolyzer (product name: WE-4S-RICW, manufactured by EFCE Co., Ltd.) to fabricate the PEM water electrolyzer.

[0047] The oxygen evolution electrode catalytic activity was evaluated using the obtained PEM water electrolyzer.

[0048] Example 2 The 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 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 evolution electrode catalyst composed of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of a 300-μm-thick Pt-coated Ti fiber, and the manganese content is 1.2 mg / cm2 It was (iridium content was 0 g / cm 2 , and the Ir / Mn molar ratio was 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 The electrode of this comparative example was obtained in the same manner as in Example 1, except that a Ti fiber coated with Pt (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 evolution electrode catalyst composed of manganese dioxide (manganese oxide) having a β-type crystal structure on a conductive substrate made of a 500-μm-thick Pt-coated Ti fiber, and the manganese content is 1.2 mg / cm 2 It was (iridium content was 0 g / cm 2 , and 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 evaluation results of Example 1, Example 2, and Comparative Example 1 are shown in the following table. The current density in the following table is the value at a voltage of 2 V.

[0052]

Table 1

[0053] Example 3 The electrode of this example was obtained in the same manner as in Example 1, except that a Ti fiber coated with Pt (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, and the current application time was 20 minutes. The electrode of this example is an electrode having an oxygen generation electrode catalyst composed 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 the manganese content is 2.4 mg / cm 2 (the iridium content was 0 g / cm 2 , and the Ir / Mn molar ratio was 0). The oxygen generation electrode catalyst 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 The electrode of this comparative example was obtained in the same manner as in Example 3, except that Pt-coated Ti fibers (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% were used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generation electrode catalyst composed 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 500 μm, and the manganese content is 2.4 mg / cm 2 (the iridium content was 0 g / cm 2 , and the Ir / Mn molar ratio was 0). The oxygen generation electrode catalyst 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 following table. The current density in the following table is the value at a voltage of 2V.

[0056]

Table 2

[0057] Example 4 The electrode of this example was obtained in the same manner as in Example 3, except that the current application time was 5 minutes. The electrode of this example is an electrode having an oxygen evolution electrode catalyst composed 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 200 μm, and the manganese content is 0.6 mg / cm 2 (the iridium content was 0 g / cm 2 , and the Ir / Mn molar ratio was 0). The oxygen evolution electrode catalyst 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 The electrode of this comparative example was obtained in the same manner as in Example 4, except that 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 evolution electrode catalyst composed 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 the manganese content is 0.6 mg / cm 2 (the iridium content was 0 g / cm 2 , and the Ir / Mn molar ratio was 0). The oxygen evolution electrode catalyst 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 following table. The current density in the following table is the value at a voltage of 2V.

[0060]

Table 3

[0061] It was confirmed that for an electrode using manganese oxide as an oxygen evolution electrode catalyst, the oxygen evolution electrode catalyst activity was significantly improved compared to a conventional electrode (with a conductive substrate thickness of 500 μm) using manganese oxide as an oxygen evolution electrode catalyst, by reducing the thickness of the conductive substrate.

[0062] <Iridium-Manganese Oxide> Example 5 As the conductive substrate, 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. A manganese oxide composite electrode material was obtained in the same manner as in Example 1 except for this. Next, the manganese oxide composite electrode material was immersed in an iridium salt solution of 0.05 g / L of potassium hexachloroiridate (K2IrCl6) 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 is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and having iridium supported on the surface on a conductive substrate composed of a 200-μm-thick Pt-coated Ti fiber, and the manganese content is 1.2 mg / cm 2 and the iridium content is 0.20 mg / cm 2 (the Ir / Mn molar ratio was 0.048). The oxygen evolution electrode catalyst 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 As the conductive substrate, 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. The electrode of this comparative example was obtained in the same manner as in Example 5 except for this. The electrode of this comparative example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and having iridium supported on the surface on a conductive substrate composed of a 500-μm-thick Pt-coated Ti fiber, and the manganese content is 1.2 mg / cm 2 and the iridium content is 0.20 mg / cm 2 (the 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 following table. The current density in the following table is the value at a voltage of 2V.

[0065]

Table 4

[0066] Example 6 A manganese oxide composite electrode material was obtained in the same manner as in Example 1, except that Pt-coated Ti fibers (product name: Pt-plated Ti fiber sintered body, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., thickness 100 μm, Pt thickness 0.5 μm, porosity 56%) were used as the conductive substrate. Next, an electrode of this example was obtained in the same manner as in Example 5, except that the concentration of K2IrCl6 in the iridium salt solution was 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 evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and iridium supported on the surface on a conductive substrate composed 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 is 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 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%) were used as the conductive substrate.

[0069] The electrode of this example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and supporting iridium on the 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 (the Ir / Mn molar ratio is 0.024). The oxygen evolution electrode catalyst 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 Pt-coated Ti fibers (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% were used as the conductive substrate.

[0071] The electrode of this example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and supporting iridium on the 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 (the Ir / Mn molar ratio is 0.024). The oxygen evolution electrode catalyst 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 Pt-coated Ti fibers (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% were used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and supporting iridium on the surface, on a conductive substrate made of Pt-coated Ti fibers with a thickness of 500 μm, and the manganese content is 1.2 mg / cm 2 and the iridium content is 0.10 mg / cm 2 (the Ir / Mn molar ratio was 0.024). The oxygen evolution electrode catalyst 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 evaluation results of Examples 6 to 8 and Comparative Example 5 are shown in the following table. The current density in the following table is the value at a voltage of 2V.

[0074]

Table 5

[0075] Example 9 The electrode of this example was obtained in the same manner as in Example 7, except that the concentration of K2IrCl6 in the iridium salt solution was 0.01 g / L. The electrode of this example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and supporting iridium on the 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 0.01 mg / cm 2 (the Ir / Mn molar ratio was 0.002). The oxygen evolution electrode catalyst 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 The electrode of this comparative example was obtained in the same manner as in Example 9, except that Pt-coated Ti fibers (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% were used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and supporting iridium on the surface on a conductive substrate made of Pt-coated Ti fibers with a thickness of 500 μm, and the manganese content is 1.2 mg / cm 2 and the iridium content is 0.01 mg / cm 2 (the Ir / Mn molar ratio was 0.002). The oxygen evolution electrode catalyst 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 the value at a voltage of 2V.

[0077]

Table 6

[0078] Example 10 A manganese oxide composite electrode material was obtained in the same manner as in Example 3. Next, the electrode of this example was obtained in the same manner as in Example 7 except that the manganese oxide composite electrode material was used. The electrode of this example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and supporting iridium on the surface on a conductive substrate made of Pt-coated Ti fibers with a thickness of 200 μm, and the manganese content is 2.4 mg / cm 2 and the iridium content is 0.10 mg / cm 2 (the Ir / Mn molar ratio was 0.012). The oxygen evolution electrode catalyst 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 The electrode of this comparative example was obtained in the same manner as in Example 10 except that Pt-coated Ti fibers (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% were used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen generation electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and having iridium supported on the surface on a conductive substrate made of Pt-coated Ti fibers with a thickness of 500 μm, with a manganese content of 2.4 mg / cm 2 and an iridium content of 0.10 mg / cm 2 (the Ir / Mn molar ratio was 0.012). The oxygen generation electrode catalyst 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]

Table 7

[0082] Example 11 A manganese oxide composite electrode material was obtained in the same manner as in Example 4. Next, the electrode of this example was obtained in the same manner as in Example 7 except that the manganese oxide composite electrode material was used. The electrode of this example is an electrode having an oxygen generation electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and having iridium supported on the surface on a conductive substrate made of Pt-coated Ti fibers with a thickness of 200 μm, with a manganese content of 0.6 mg / cm 2 and an iridium content of 0.05 mg / cm 2 (the Ir / Mn molar ratio was 0.024). The oxygen generation electrode catalyst 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 As the conductive substrate, except that Pt-coated Ti fibers (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% were used, the electrodes of this comparative example were obtained in the same manner as in Example 11. The electrode of this comparative example is an electrode having an oxygen evolution electrode catalyst composed of manganese dioxide (iridium-manganese oxide) having a β-type crystal structure and having iridium supported on the surface on a conductive substrate made of Pt-coated Ti fibers with a thickness of 500 μm, and the manganese content is 0.6 mg / cm 2 and the iridium content is 0.05 mg / cm 2 (the Ir / Mn molar ratio was 0.024). The oxygen evolution electrode catalyst 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 following table. The current density in the following table is the value at a voltage of 2V.

[0085]

Table 8

[0086] It was confirmed that for an electrode using iridium-manganese oxide as the oxygen evolution electrode catalyst, the oxygen evolution electrode catalyst activity was significantly improved compared to a conventional electrode (with a conductive substrate thickness of 500 μm) using iridium-manganese oxide as the oxygen evolution electrode catalyst, by reducing the 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.) and pure water, and this was applied to a conductive substrate made 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 obtained conductive substrate containing iridium oxide was annealed in an air atmosphere 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 evolution electrode catalyst made of iridium oxide on a conductive substrate composed of Pt-coated Ti fibers with a thickness of 200 μm, and the iridium content is 0.1 mg / cm 2 (the manganese content is 0 g / cm 2 , and the Ir / Mn molar ratio is ∞). The oxygen evolution electrode catalyst 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 The electrode of this comparative example was obtained in the same manner as in Comparative Example 9, except that Pt-coated Ti fibers (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% were used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen evolution electrode catalyst made of iridium oxide on a conductive substrate composed of Pt-coated Ti fibers with a thickness of 300 μm, and the iridium content is 0.1 mg / cm 2 (the manganese content is 0 g / cm 2 , and the Ir / Mn molar ratio is ∞).

[0090] The oxygen evolution electrode catalyst 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 The electrode of this comparative example was obtained in the same manner as in Comparative Example 9, except that Pt-coated Ti fibers (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% were used as the conductive substrate. The electrode of this comparative example is an electrode having an oxygen evolution electrode catalyst made of iridium oxide on a conductive substrate composed of Pt-coated Ti fibers with a thickness of 500 μm, and the iridium content is 0.1 mg / cm 2It was (manganese content was 0 g / cm 2 , Ir / Mn molar ratio was ∞). 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 following table. The current density in the following table is the value at a voltage of 2V.

[0093]

Table 9

[0094] For the electrode using iridium oxide as the oxygen evolution electrode catalyst, even when the thickness of the conductive substrate was reduced, the change in the oxygen evolution electrode catalytic activity was slight.

[0095] From the above results, it was confirmed that the significant improvement in the oxygen evolution electrode catalytic activity due to the reduction in the thickness of the conductive substrate is a behavior peculiar 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 and made a part of the disclosure of this specification.

Claims

1. The electrode includes an oxygen generating electrode catalyst containing an 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 0.5 mg / cm per geometric area of ​​the electrode. ２ 11.0mg / cm or more ２ 2. The electrode of claim 1 , wherein:

3. 3. The electrode according to claim 1, wherein the molar ratio of iridium to manganese is 0.001 or more and 0.100 or less.

4. 3. The electrode of claim 1 or 2, wherein the conductive substrate comprises titanium.

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