Electrode member and method for manufacturing an electrode member

Abstract

To provide electrode components with good durability. [Solution] The electrode member 1 is formed by laminating a metal substrate 2, a conductive oxide layer 3 with a film thickness of 1 nm or more and less than 200 nm, and a metal layer 4 containing at least 50% by weight of iron in this order. The manufacturing method of the electrode member 1 includes step A of forming a conductive oxide layer 3 with a film thickness of 1 nm or more and less than 200 nm on the metal member 2, and step B of forming a metal layer 4 containing at least 50% by weight of iron on the conductive oxide layer 3, thereby forming an electrode member 1 in which the metal substrate 2, the conductive oxide layer 3, and the metal layer 4 are laminated in this order.

Description

[Technical Field]

[0001] The present technology relates to an electrode member and a method for producing the electrode member. [Background Art]

[0002] Conventionally, water electrolysis technology for producing hydrogen by electrolyzing water has been widely researched and industrialized. Examples include alkaline water electrolysis (AWE) using a potassium hydroxide (KOH) solution, PEM (Polymer Electrolyte Membrane) type water electrolysis in which electrolysis is performed with a polymer electrolyte having electrode catalysts coated on both sides of a proton exchange membrane, and SOEC (Solid Oxide Electrolysis Cell) type water electrolysis in which hydrogen is produced by electrolyzing water vapor using a ceramic membrane as an electrolyte. Among such water electrolysis technologies, alkaline water electrolysis technology has been adopted for large-scale facilities because of its advantages that the facility is relatively simple and no noble metal catalyst or the like is required.

[0003] In recent years, CO2 emissions caused by the use of fossil fuels have become a problem, and attention has been focused on renewable energy that does not use fossil fuels and hydrogen production using renewable energy. Hydrogen produced by electrolyzing water can be stored for a long time and used as an energy source, and can also be used in various applications such as as a raw material for chemical products and in ironmaking processes. In particular, since the output of renewable energy fluctuates greatly depending on weather and other factors, it is difficult to directly connect it to conventional power transmission systems, and leveling of electric power is desired. In this respect as well, diverting surplus power generated from renewable energy to hydrogen production is desirable because it can eliminate waste in energy production.

[0004] However, in the case of alkaline water electrolysis, fluctuating power applied to the electrodes can cause electrode degradation, potentially leading to a decrease in electrolysis efficiency and a significant reduction in electrode durability. In particular, with catalysts coated with catalytic oxides on metal surfaces such as nickel, which are resistant to oxidizing environments, the coating may peel off due to power fluctuations. Furthermore, from a cost perspective, the use of lower-cost materials is required.

[0005] An example of an oxygen-evolving electrode used in alkaline water electrolysis is the one using a perovskite oxide described in Patent Document 1. In the technology described in Patent Document 1, the perovskite oxide is formed on a nickel-based metal substrate, and as a coating method, a catalyst layer is obtained by applying a precursor suspension to the nickel-based metal substrate and then firing it. However, it is generally considered difficult to achieve a coating with high adhesion between the fired oxide powder and the electrode, which is the current collector.

[0006] Patent Document 2 describes a technique for forming an electrode catalyst layer by coating a conductive substrate made of nickel or a nickel-based alloy with oxide precursors (a first solution and a second solution) and firing it, with the aim of improving catalyst performance. In the technique described in Patent Document 2, it is stated that the adhesive strength between the conductive substrate and the electrode catalyst layer becomes stronger through heat treatment, but the specific reaction is not clearly stated, and it is expected that the bonding will not be sufficient as the reaction will be carried out solely by thermal energy. Furthermore, the technique described in Patent Document 2 is based on the premise of using expensive precious metals such as iridium and ruthenium, which also presents the challenge of increased costs.

[0007] Patent Document 3 describes a technique in which gold plating is applied to prevent delamination between the catalyst material (nickel-sulfur plating) and the electrode substrate, thereby reducing plating stress and improving adhesion. However, the technique described in Patent Document 3 results in increased costs due to the gold plating.

[0008] Patent Document 4 describes a technique in which a carbonaceous material (carbon material, graphite) is used as a substrate, a metal salt, which is a precursor substance, is converted to a hydroxide form, and then converted from this hydroxide form to an oxyhydroxide form. However, in the technique described in Patent Document 4, if the carbonaceous material is not completely coated with the precursor substance, the uncoated portion of the carbonaceous material will react, making it difficult to maintain the substrate itself. Furthermore, from the viewpoint of electrical resistance, it is considered desirable for the substrate to be a metal rather than a carbonaceous material.

[0009] In the technologies described in Patent Documents 1 to 4, the catalyst layer is formed by coating and firing the catalyst layer precursor, making it difficult to obtain sufficient adhesion to withstand severe stresses such as voltage fluctuations.

[0010] Non-Patent Document 1 describes a method for enhancing catalytic performance by using stainless steel as an electrode and electrochemically treating the surface of the stainless steel (electrochemical surface oxidation treatment) to create nanofibers. In the method described in Non-Patent Document 1, the stainless steel itself, which is the base material, changes to become the catalyst layer, so there are no adhesion problems like those that occur when laminating dissimilar materials, and it is also economically preferable because it uses an inexpensive material such as stainless steel.

[0011] However, in the technology described in Non-Patent Document 1, when a catalyst layer formed by electrochemical treatment of the surface of stainless steel is subjected to water electrolysis, nanofiber formation may continue, potentially leading to uncontrolled leakage of metal ions (e.g., Fe and Cr) from the stainless steel electrode. These leaked metal ions are undesirable because they can adversely affect the counter electrode, for example, or make wastewater treatment more difficult by being present in the electrolyte. Therefore, electrode materials with better durability are required. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Special Publication No. 2024-518460 [Patent Document 2] Japanese Patent Publication No. 2017-190476 [Patent Document 3] Japanese Patent Publication No. 2010-150590 [Patent Document 4] Japanese Patent Publication No. 2008-138282 [Non-patent literature]

[0013] [Non-Patent Document 1] Naoto Todoroki, "Formation of Nanostructured Catalyst Layers on Stainless Steel and their Application to Oxygen Generation Electrodes for Alkaline Water Electrolysis," Materia, Vol. 62, No. 6 (2023), pp. 368-374. [Overview of the project] [Problems that the invention aims to solve]

[0014] This technology was proposed in light of the conventional situation and provides an electrode member with good durability. [Means for solving the problem]

[0015] As a result of diligent research, the inventors of this case have found that the above problem can be solved by forming a conductive oxide layer with excellent electrical conductivity on a metal substrate, and then forming a metal layer mainly composed of iron on this conductive oxide layer.

[0016] The electrode member relating to this technology is constructed by laminating a metal substrate, a conductive oxide layer having a film thickness of 1 nm or more and less than 200 nm, and a metal layer containing at least 50% by weight of iron in this order.

[0017] The method for manufacturing an electrode member according to this technology comprises step A, forming a conductive oxide layer with a thickness of 1 nm or more and less than 200 nm on a metal member, and step B, forming a metal layer containing at least 50% by weight of iron on the conductive oxide layer, thereby forming an electrode member in which a metal substrate, a conductive oxide layer, and a metal layer are laminated in this order. [Effects of the Invention]

[0018] According to the present technology, an electrode member with excellent durability can be provided. [Brief Description of the Drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration example of an electrode member. [Figure 2] FIG. 2 is a cross-sectional view showing a configuration example of an electrode member subjected to electrochemical treatment. [Mode for Carrying Out the Invention]

[0020] [Electrode Member] The electrode member according to the present technology is formed by laminating a metal base material, a conductive oxide layer having a film thickness of 1 nm or more and less than 200 nm, and a metal layer containing at least 50% by weight of iron in this order.

[0021] As will be described in detail later, the electrode member according to the present technology can be subjected to a predetermined electrochemical treatment to convert the entire thickness of the metal layer into a catalyst layer (a nanofiber layer containing iron as a main component), and sufficient catalytic performance can be obtained by this catalyst layer.

[0022] In addition, the electrode member according to the present technology can have excellent durability particularly by including the conductive oxide layer having a film thickness of 1 nm or more and less than 200 nm. This can suppress the elution of metal ions from the metal layer, and for example, can suppress the mixing of metal ions (e.g., Cr ions) into the electrolytic solution. Further, since the electrode member has excellent durability, waste liquid treatment, electrode replacement and the like can be suppressed, and for example, costs associated with the use of the electrode member can be reduced.

[0023] FIG. 1 is a cross-sectional view showing a configuration example of an electrode member 1. The electrode member 1 is formed by laminating a metal base material 2, a conductive oxide layer 3 having a film thickness of 1 nm or more and less than 200 nm, and a metal layer 4 containing at least 50% by weight of iron in this order.

[0024] <Metal Base Material> The metal substrate 2 is a substrate made of metal. The metal substrate 2 only needs to be made of an electrically conductive metal, and is not particularly limited in terms of the type of metal. The metal constituting the metal substrate 2 may be a single type or two or more types. The metal substrate 2 may be a single layer or composed of two or more layers.

[0025] From the viewpoint of reducing the cost of electrode member 1, the metal substrate 2 is preferably made of a metal such as iron, copper, aluminum, or steel (e.g., stainless steel). Since electrode member 1 is used in electrochemical reactions, if the metal substrate 2 is not sufficiently covered by the conductive oxide layer 3, corrosion of the metal substrate 2 may occur. Therefore, from the viewpoint of suppressing such unintended corrosion of the metal substrate 2, it is preferable to use stainless steel, which has strong corrosion resistance, as the metal substrate 2.

[0026] When the metal substrate 2 is stainless steel, the stainless steel may be austenitic, austenitic-ferritic, ferritic, or martensitic. For example, austenitic stainless steel (SUS316 as an example) can be used.

[0027] The shape of the metal substrate 2 may be a flat plate, or it may have a porous structure in order to increase the area for electrode reaction. A porous structure is, for example, when the metal substrate 2 is plate-shaped, a shape in which through holes are formed over a part of the main surface or over the entire main surface in a plan view of the metal substrate 2. A specific example of a shape having a porous structure is a shape having a mesh structure. A shape having a mesh structure is, for example, when the metal substrate 2 is plate-shaped, a shape in which lattice-like (lattice pattern) through holes are formed over the entire main surface in a plan view of the metal substrate 2.

[0028] The thickness of the metal substrate 2 can be, for example, 0.1 to 10 mm. If the metal substrate 2 is composed of two or more layers, it is preferable that the total thickness satisfies the above range.

[0029] <Conductive oxide layer> The conductive oxide layer 3 is formed to be in contact with one surface of the metal substrate 2, for example, as shown in Figure 1. The conductive oxide layer 3 serves to ensure conductivity between the metal substrate 2 and the metal layer 4, and also protects the metal substrate 2 from oxidizing environments. The conductive oxide layer 3 can be constructed using known conductive oxides. In particular, from the viewpoint of protecting the metal substrate 2 from oxidizing environments, it is preferable that the conductive oxide layer 3 be constructed of a conductive oxide having acid and alkali resistance, such as tin oxide (SnO2). Tin oxide can maintain a solid state over a wide range of liquids and has excellent chemical stability.

[0030] If the conductive oxide layer 3 is composed of tin oxide, the conductive oxide layer 3 may further contain other elements, as long as it does not impair acid resistance or alkali resistance. For example, to further improve the electrical conductivity of the conductive oxide layer 3, the conductive oxide layer 3 may further contain fluorine or antimony in addition to tin oxide. For example, the conductive oxide layer 3 may have tin oxide as its main component and may further contain other elements in a range not exceeding 10 atomic percent relative to the tin element of the tin oxide.

[0031] The thickness (film thickness) of the conductive oxide layer 3 is preferably 1 nm or more and less than 200 nm. A thickness of 1 nm or more in the conductive oxide layer 3 effectively protects the metal substrate 2 from the oxidizing environment, thereby improving the durability of the electrode member 1. Furthermore, from the viewpoint of more reliably coating the metal substrate 2 and more effectively protecting the metal substrate 2 from the oxidizing environment, the thickness of the conductive oxide layer 3 is more preferably 20 nm or more, but may also be 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, or 60 nm or more.

[0032] Furthermore, although the conductive oxide constituting the conductive oxide layer 3 has electrical conductivity, it has a higher resistivity compared to metals, and therefore the energy loss due to electrical resistance is greater than that of metals. For this reason, by keeping the thickness of the conductive oxide layer 3 to less than 200 nm, the metal substrate 2 can be effectively protected from the oxidizing environment, and the catalytic performance of the electrode member 1 can be improved by suppressing an excessive increase in electrical resistance. The upper limit of the thickness of the conductive oxide layer 3 may be 150 nm or less, 120 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, or 50 nm or less.

[0033] The conductive oxide layer 3 may be a single layer or composed of two or more layers. If the conductive oxide layer 3 is composed of two or more layers, it is preferable that its total thickness satisfies the range described above.

[0034] <Metal layer> The metal layer 4 is a layer that, for example, transfers electrons in contact with the alkaline electrolyte and functions as a catalyst for oxygen evolution in alkaline water electrolysis. For example, when the metal layer 4 is used on the oxygen evolution electrode side of alkaline water electrolysis, the oxygen evolution reaction (OER) shown in equation 1 below occurs in the metal layer 4.

[0035] Formula 1: [ka]

[0036] Normally, overvoltage (OER) does not occur at theoretical potentials; OER proceeds when a high overpotential with a favorable potential is applied. As will be described in detail later, electrochemical treatment of electrode member 1 forms a catalyst layer on the surface of metal layer 4. The catalyst layer is intended to reduce this overpotential.

[0037] Generally, precious metal oxides are often used in catalyst layers. From the perspective of reducing costs, it is preferable to use oxides or hydroxides made from metals that are cheaper than precious metal oxides (for example, iron, nickel, etc.). Also, if the iron content in metal layer 4 is too low, there is a risk that the catalyst layer (a nanofiber layer mainly composed of iron) that metal layer 4 transforms into may not be sufficiently formed. Therefore, metal layer 4 contains iron as its main component, that is, it contains at least 50% by weight of iron. The iron content of metal layer 4 may be 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, or 80% by weight or more.

[0038] The metal layer 4 may contain elements other than iron, for example, one or more elements selected from the group consisting of nickel, chromium, molybdenum, carbon, manganese, silicon, nitrogen, phosphorus, sulfur, titanium, and niobium. For example, from the viewpoint of further improving the performance of the catalyst layer, the metal layer 4 may contain chromium and carbon as elements other than iron, may contain chromium and nickel, or may contain chromium, nickel, and carbon.

[0039] A specific example of the metal layer 4 is a sputtered film formed by sputtering stainless steel as a target. As the stainless steel, austenitic, austenitic-ferritic, ferritic, and martensitic stainless steels can be used. Examples of stainless steels that can be used include SUS316 (e.g., with an iron content of 62% by weight or more), SUS304 (e.g., with an iron content of 66% by weight or more), SUS310S (e.g., with an iron content of 50% by weight or more), SUS440C (e.g., with an iron content of 77% by weight or more), and SUS430 (e.g., with an iron content of 80% by weight or more).

[0040] The thickness of the metal layer 4 is not particularly limited, but from the viewpoint of making the catalyst layer modified by the metal layer 4 function more effectively, it is preferably 20 nm or more, may be 25 nm or more, may be 30 nm or more, may be 35 nm or more, may be 40 nm or more, may be 45 nm or more, or may be 50 nm or more. Here, if the metal layer 4 is too thick, it is thought that the area deep from the surface of the metal layer 4 will not substantially function as a catalyst. For this reason, the upper limit of the thickness of the metal layer 4 is preferably 80 nm or less, may be 75 nm or less, may be 70 nm or less, may be 65 nm or less, may be 60 nm or less, may be 55 nm or less, or may be 50 nm or less. For example, the thickness of the metal layer 4 can be 20 nm or more and 80 nm or less, or 20 nm or more and 50 nm or less.

[0041] As described above, the electrode member 1 has good durability because it is constructed by laminating a metal substrate 2, a conductive oxide layer 3 with a film thickness of 1 nm or more and less than 200 nm, and a metal layer 4 containing at least 50% by weight of iron in this order. Therefore, the electrode member 1 can suppress the elution of metal ions from the metal layer 4, for example, the contamination of the electrolyte with metal ions.

[0042] An example of the configuration of the electrode member 1 is a metal substrate 2 which is, for example, stainless steel with a thickness of 0.1 to 10 mm, a conductive oxide layer 3 which is tin oxide with a film thickness of 20 nm to 100 nm, and a metal layer 4 which is a sputtered film with a film thickness of 20 nm to 80 nm, which is sputtered onto stainless steel as the target. By making the metal substrate 2 stainless steel and the metal layer 4 which is a sputtered film, the durability of the electrode member 1 can be improved and the manufacturing cost of the electrode member 1 can be reduced.

[0043] The electrode member 1 is not limited to the configuration described above, and may have other configurations as long as they do not impair the effects of this technology. For example, the electrode member 1 may have a predetermined metal material laminated between the metal substrate 2 and the conductive oxide layer 3 for the purpose of improving their adhesion.

[0044] Figure 2 is a cross-sectional view showing an example of the configuration of an electrochemically treated electrode member 1A. By performing a predetermined electrochemical treatment, the electrode member 1 can be transformed into an electrode member 1A in which the metal layer 4 is transformed into a catalyst layer 5 over its entire thickness. Compared to an electrode member 1 in which the metal layer 4 is not transformed into a catalyst layer 5, such an electrode member 1A can lower the overpotential of the oxygen evolution reaction shown in the above-mentioned formula 1, and oxygen evolution becomes easier. Because the electrode member 1A has good oxygen generation performance in water electrolysis, it can be suitably used, for example, on the oxygen evolution electrode (working electrode) side of alkaline water electrolysis.

[0045] The conditions for the electrochemical treatment performed on the electrode member 1 are not particularly limited, but for example, if the metal layer 4 is a layer consisting of a sputtered film obtained by sputtering stainless steel as the target, it is preferable to use the conditions described in Non-Patent Document 1 above, and for example, the conditions for the electrochemical treatment described in the examples described later can be used.

[0046] For example, if the metal layer 4 in electrode member 1 is made of a sputtered film obtained by sputtering stainless steel as a target, the catalyst layer 5 in electrode member 1A can be made of nickel or iron. Here, a larger thickness of the catalyst layer 5 is considered preferable as a catalyst because it increases the surface area. However, from the viewpoint of the electrical conductivity of the hydroxide produced by the electrochemical treatment of electrode member 1, for example, if the thickness of the catalyst layer 5 exceeds a certain level, the increase in the resistance of the hydroxide is thought to exceed the gain in catalytic efficiency.

[0047] [Method for manufacturing electrode members] Next, a method for manufacturing the electrode member 1 will be described. The method for manufacturing the electrode member according to this technology comprises step A, which involves forming a conductive oxide layer 3 with a film thickness of 1 nm or more and less than 200 nm on a metal member 2, and step B, which involves forming a metal layer 4 containing at least 50% by weight of iron on the conductive oxide layer 3, thereby forming an electrode member 1 in which the metal substrate 2, the conductive oxide layer 3, and the metal layer 4 are laminated in this order.

[0048] In step A, a conductive oxide layer 3 with a thickness of 1 nm or more and less than 200 nm is formed on the surface of the metal member 2, for example, using a sputtering apparatus. In step A, the conductive oxide layer 3 made of tin oxide can be formed by using, for example, a tin oxide target. The preferred conditions for the metal member 2 and the conductive oxide layer 3 are the same as those for the metal member 2 and the conductive oxide layer 3 in the electrode member 1 described above.

[0049] In step B, a metal layer 4 is formed on the surface of the conductive oxide layer 3, for example, using a sputtering apparatus. In step B, a metal layer 4 containing at least 50% by weight of iron can be formed by using, for example, stainless steel as a target. The preferred conditions for the metal layer 4 are the same as those for the metal layer 4 in the electrode member 1 described above.

[0050] Thus, in the manufacturing method of the electrode member 1, an electrode member 1 can be formed by steps A and B, in which a metal substrate 2, a conductive oxide layer 3, and a metal layer 4 are laminated in this order. As described above, the electrode member 1 has good durability.

[0051] Furthermore, the electrode member 1 formed by processes A and B can be subjected to electrochemical treatment to become electrode member 1A, in which the metal layer 4 is transformed into a catalyst layer 5 over its entire thickness. However, even if the electrochemical treatment of electrode member 1 is stopped midway and a portion of the metal layer 4 remains, the actual water electrolysis is performed under conditions exceeding those of the electrochemical treatment. As a result, the entire metal layer 4 becomes the catalyst layer 5, and there is a risk that the chromium and iron that leak out at that time may dissolve into the water electrolysis and have adverse effects. The electrochemical treatment may be performed during the manufacture of electrode member 1, or it may not be performed during the manufacture of electrode member 1 but may be performed when electrode member 1 is in use. The catalyst layer 5 is considered to be vulnerable to pressure, for example, because its fine nanostructure is self-supporting. Therefore, by performing the electrochemical treatment when electrode member 1 is in use, it is possible to prevent the catalyst layer 5 from being destroyed by stacking during the transport of electrode member 1. Also, since the electrochemical treatment can be performed with a general water electrolysis apparatus, there is no need to perform it during the manufacture of electrode member 1.

[0052] As a specific example of the manufacturing method for the electrode member 1, a conductive oxide layer 3 is formed on the surface of a metal substrate 2 (electrode), and then a metal material mainly containing iron is deposited on the surface of the conductive oxide layer 3 to obtain the electrode member 1. By subjecting this electrode member 1 to electrochemical treatment, even when inexpensive materials such as stainless steel are used for the metal substrate 2 and metal layer 4, stable catalytic performance can be maintained for a long period of time, and the oxygen evolution potential can be kept low, making oxygen evolution easier. Therefore, energy efficiency in green hydrogen production can be further improved. [Examples]

[0053] The following describes some embodiments of this technology. However, this technology is not limited to these embodiments.

[0054] <Example 1> After cutting a SUS316 plate to be used as a substrate into 20mm x 50mm pieces, the surface of the cut SUS316 plate was polished using emery paper and alumina powder. The polished SUS316 plate was ultrasonically cleaned in a beaker filled with pure water for 10 minutes to remove the abrasive material. The ultrasonically cleaned SUS316 plate was dried in an oven at 100°C. This yielded a metal substrate 2 with a thickness of 0.5mm.

[0055] The dried and cleaned substrate was placed in an RF sputtering apparatus (apparatus name: SPV-420, manufactured by Toei Kagaku Sangyo Co., Ltd.) and evacuated. The ultimate vacuum level was 10. -3 After confirming that the pressure was below Pa, argon and oxygen gases were introduced, and a voltage was applied to a tin oxide target placed on the cathode inside the RF sputtering apparatus to generate a discharge and perform sputtering, forming a tin oxide layer as a conductive oxide layer 3 on the surface of the metal substrate 2. The deposition rate was measured in advance, and the discharge was stopped when the thickness of the conductive oxide layer 3 reached 50 nm.

[0056] Subsequently, without introducing air, a voltage was applied to a SUS316 target placed on another cathode within the same RF sputtering apparatus to discharge and sputter, forming a metal layer 4 on the surface of the conductive oxide layer 3. The deposition rate was measured in advance, similar to the conductive oxide layer, and the discharge was stopped when the thickness of the metal layer 4 reached 50 nm. This resulted in obtaining an electrode member 1 in which a metal substrate 2, a conductive oxide layer 3, and a metal layer 4 containing at least 50% by weight of iron were laminated in this order.

[0057] Electrode member 1 was removed from the RF sputtering apparatus, and a sample was prepared by coating all parts except the surface to be evaluated as an electrode (10 mm x 10 mm) and the connection terminals with silicone resin to prevent contact with the electrolyte.

[0058] <Example 2> The sample was prepared under the same conditions as in Example 1, except that the thickness of the conductive oxide layer 3 was changed to 20 nm.

[0059] <Example 3> The sample was prepared under the same conditions as in Example 1, except that the thickness of the conductive oxide layer 3 was changed to 100 nm.

[0060] <Example 4> The sample was prepared under the same conditions as in Example 1, except that the thickness of metal layer 4 was changed to 20 nm.

[0061] <Example 5> The sample was prepared under the same conditions as in Example 1, except that the thickness of metal layer 4 was changed to 80 nm.

[0062] <Example 6> The sample was prepared under the same conditions as in Example 1, except that the target used for depositing the metal layer 4 was changed to SUS304.

[0063] <Example 7> The sample was prepared under the same conditions as in Example 1, except that the target used for depositing the metal layer 4 was changed to SUS310S.

[0064] <Example 8> The sample was prepared under the same conditions as in Example 1, except that the target used for depositing the metal layer 4 was changed to SUS440C.

[0065] <Example 9> The sample was prepared under the same conditions as in Example 1, except that the target used for depositing the metal layer 4 was changed to SUS430.

[0066] <Comparative Example 1> After cutting a SUS316 plate to be used as a substrate into 20mm x 50mm pieces, the surface of the cut SUS316 plate was polished using emery paper and alumina powder. The polished SUS316 plate was ultrasonically cleaned in a beaker filled with pure water for 10 minutes to remove the abrasive material. The ultrasonically cleaned SUS316 plate was dried in an oven at 100°C. This yielded a metal substrate 2 with a thickness of 0.5mm. For the metal substrate 2, a sample was prepared by coating all parts except the surface to be evaluated as an electrode (a 10mm x 10mm window) and the connection terminals with silicone resin to prevent contact with the electrolyte.

[0067] <Comparative Example 2> After cutting a SUS316 plate to be used as a substrate into 20mm x 50mm pieces, the surface of the cut SUS316 plate was polished using emery paper and alumina powder. The polished surface of the cut SUS316 plate was ultrasonically cleaned in a beaker filled with pure water for 10 minutes to remove the abrasive material. The ultrasonically cleaned SUS316 plate was dried in an oven at 100°C. This yielded a metal substrate 2 with a thickness of 0.5mm.

[0068] The dried and cleaned substrate was placed in the RF sputtering apparatus and evacuated. The ultimate vacuum level was 10. -3 After confirming that the pressure was below Pa, argon and oxygen gases were introduced, and a voltage was applied to a tin oxide target placed on the cathode inside the RF sputtering apparatus to generate a discharge and perform sputtering, forming a tin oxide layer as a conductive oxide layer 3 on the surface of the metal substrate 2. The deposition rate was measured in advance, and the discharge was stopped when the thickness of the conductive oxide layer 3 reached 50 nm. As a result, a laminate was obtained in which the metal substrate 2 and the conductive oxide layer 3 were stacked.

[0069] The laminate was removed from the RF sputtering apparatus, and the sample was prepared by coating all parts except the surface to be evaluated as an electrode (10 mm x 10 mm window) and the connection terminals with silicone resin to prevent contact with the electrolyte.

[0070] <Comparative Example 3> The sample was prepared under the same conditions as in Example 1, except that the thickness of the conductive oxide layer 3 was changed to 200 nm.

[0071] <Comparative Example 4> The sample was prepared under the same conditions as in Example 1, except that the tin oxide target for forming the conductive oxide layer 3 was changed to a silicon oxide target.

[0072] [Electrochemical treatment] Each prepared sample was subjected to electrochemical treatment. The electrochemical treatment involved immersing the sample in 1M KOH at 75°C with a current density of 30 mA / cm².2 constant current electrolysis was performed for 5 hours.

[0073] [Evaluation] <OER(Oxygen Evolution Reaction) potential> The OER potential was evaluated by cyclic voltammetry. After washing the electrochemically treated sample with water, it was immersed in 1 M KOH and used as the working electrode. A platinum electrode (length: 5.7 cm, electrode part diameter: 0.5 mm, manufactured by BAS Inc.) was used as the counter electrode. For the reference electrode, Ag + / AgCl was used for measurement, and the result was converted to a reversible hydrogen electrode potential (RHE). After preparing the cell, after 100 cycles of sweeping (cyclic voltammetry) in the range of 0.9 to 1.5 V (RHE) at a sweep rate of 50 mV / s, the potential was increased from the low voltage side (0 V) at 5 mV / s until oxygen evolution occurred and the current density reached 10 mA / cm 2 , the potential obtained was taken as the OER overpotential. The results are shown in Table 1. The OER overpotential is preferably less than 1.80 V, more preferably 1.60 V or less, and still more preferably less than 1.55 V.

[0074] <Cr in Aqueous Solution> After measuring the OER overpotential, the current density was fixed at 100 mA / cm 2 and electrolysis (constant current electrolysis) was performed at a constant current density for 100 hours. Then, the electrolyte was collected and the elution of Cr was confirmed by ICP (Inductively Coupled Plasma) optical emission spectrometry. The results are shown in Table 1. In Table 1, "Not detected" refers to the case where Cr could not be confirmed in the electrolyte; "Detected" refers to the case where Cr was confirmed in the electrolyte; "Not implemented" refers to the case where the constant current electrolysis evaluation was not performed (could not be performed).

[0075]

Table 1

[0076] [Evaluation Results] From the results of Examples 1 to 9, it was found that the electrode member 1, in which a metal substrate 2 (SUS316 plate), a conductive oxide layer 3 (tin oxide layer) with a film thickness of 1 nm or more and less than 200 nm, and a metal layer 4 (sputtered film sputtered with stainless steel as the target) containing at least 50% by weight of iron are laminated in this order, can maintain a low overpotential of 1.51 to 1.60 V (RHE) oxygen evolution potential after electrochemical treatment, and that it has good durability as no Cr was detected in the electrolyte after 100 hours.

[0077] Specifically, from the results of Examples 1 to 5, it was found that electrode member 1, in which the conductive oxide layer (tin oxide layer) has a thickness of 20 nm or more and less than 200 nm, and the metal layer is a sputtered film that targets stainless steel (SUS316), can maintain a low overvoltage of 1.51 to 1.60 V (RHE) after electrochemical treatment, and also exhibits good durability.

[0078] The results from Examples 6 and 7 show that even when the nickel content in the metal layer 4 in Example 1 is varied, a low overvoltage can be maintained and durability is good.

[0079] From the results of Examples 8 and 9, it was found that the electrode member 1 having a metal layer 4 sputtered onto a nickel-free stainless steel (SUS440C, SUS430) target exhibited slightly higher overvoltage after electrochemical treatment compared to the electrode member 1 having a metal layer 4 sputtered onto a nickel-containing target as in Example 1, but was able to maintain a low overvoltage and exhibited good durability.

[0080] In Comparative Example 1, Cr was detected in the electrolyte after 100 hours, indicating poor durability. This is thought to be because Comparative Example 1 used a sample in which the conductive oxide layer 3 and metal layer 4 were not formed on the metal substrate 2, causing the metal substrate 2, which serves as the electrode, to continue to dissolve. Furthermore, in the case of Comparative Example 1, if long-term operation (electrolysis) is performed, Cr ions will leach into the electrolyte, making wastewater treatment difficult.

[0081] The sample in Comparative Example 2 could not undergo electrolytic treatment (evaluation of OER overpotential) because the voltage exceeded the rating. Specifically, after electrochemical treatment, the sample in Comparative Example 2 was observed up to 2.0V after cyclic voltammetry by raising the potential, but no increase in current was confirmed, and oxygen generation did not occur. Therefore, constant current electrolysis evaluation was not performed on the sample in Comparative Example 2. This is thought to be because the sample used in Comparative Example 2 did not have a metal layer 4 containing at least 50% by weight of iron formed.

[0082] In Comparative Example 3, oxygen evolution was confirmed at 1.8V in the OER potential evaluation after electrochemical treatment of the sample. However, this was a high overpotential and did not demonstrate any practical advantage. This is thought to be due to the use of a conductive oxide sample with a film thickness of less than 200 nm in Comparative Example 3.

[0083] In Comparative Example 4, no current flowed even after electrochemical treatment, making it impossible to evaluate the OER potential and constant current electrolysis. This is thought to be because Comparative Example 4 used a sample with a non-conductive SiO2 layer instead of a conductive oxide layer 3 with a film thickness of 1 nm or more and less than 200 nm. [Explanation of Symbols]

[0084] 1 Electrode member, 1A Electrode material after electrochemical treatment, 2 Metal base material, 3. Conductive oxide layer, 4 metal layers, 5 Catalyst layer

Claims

1. Metal substrate and A conductive oxide layer having a film thickness of 1 nm or more and less than 200 nm, An electrode member comprising a metal layer containing at least 50% by weight of iron, laminated in this order.

2. The electrode member according to claim 1, wherein the conductive oxide is tin oxide, or the conductive oxide contains other elements not exceeding 10 atomic percent relative to the tin element of tin oxide.

3. The electrode member according to claim 1 or 2, wherein the nickel content in the metal layer is 40% by weight or less.

4. The electrode member according to claim 1 or 2, wherein the metal layer is made of a sputtered film obtained by sputtering stainless steel as the target.

5. The electrode member according to claim 1 or 2, wherein the thickness of the metal layer is 20 nm or more and 80 nm or less.

6. The electrode member according to claim 1 or 2, wherein the metal substrate is stainless steel.

7. The electrode member according to claim 1 or 2, wherein the metal substrate has a porous structure.

8. The electrode member according to claim 1 or 2, wherein the metal substrate has a mesh structure.

9. An electrode member according to claim 1 or 2, used on the oxygen generation electrode side of alkaline water electrolysis.

10. The electrode member according to claim 1 or 2, wherein the thickness of the conductive oxide layer is 1 nm or more and 100 nm or less.

11. The electrode member according to claim 1 or 2, wherein the thickness of the conductive oxide layer is 20 nm or more and 100 nm or less.

12. Step A involves forming a conductive oxide layer on a metal member, the layer having a thickness of 1 nm or more and less than 200 nm. The process includes step B of forming a metal layer containing at least 50% by weight of iron on the conductive oxide layer. A method for manufacturing an electrode member, comprising forming an electrode member in which the above-mentioned metal substrate, the above-mentioned conductive oxide layer, and the above-mentioned metal layer are laminated in this order.

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