Anode-side separator and water electrolysis device

Abstract

To provide an anode side separator which can enhance conductivity.SOLUTION: An anode side separator according to the present invention is an anode side separator used in a water electrolysis apparatus, and includes a metal base material composed of titanium or stainless steel, and a conductive oxide film which is provided on the surface of the metal base material and contains indium tin oxide (ITO), wherein the degree of crystallization of the conductive oxide film is 20% or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an anode-side separator used in a water electrolysis apparatus and a water electrolysis apparatus equipped therewith. [Background technology]

[0002] In recent years, water electrolysis devices that produce hydrogen by electrolyzing raw materials such as water have been known, and these devices consist of stacked water electrolysis cells using electrolyte membranes such as solid polymer electrolyte membranes. In a water electrolysis cell, for example, an anode catalyst layer and a cathode catalyst layer are provided on one side and the other side of a solid polymer electrolyte membrane, respectively. An anode power supply and an anode-side separator are stacked on the anode catalyst layer, and a cathode power supply and a cathode-side separator are stacked on the cathode catalyst layer.

[0003] The anode separator is responsible for transmitting electricity to the anode catalyst layer, and therefore requires high conductivity. Furthermore, when using a metal substrate from the standpoint of strength, corrosion resistance becomes an issue because the metal substrate is prone to corrosion. For this reason, anode separators employ a configuration in which a conductive layer with high conductivity and excellent corrosion resistance is provided on the surface of the metal substrate. For example, the separator described in Patent Document 1 comprises a metal substrate made of titanium or the like, and a noble metal layer (conductive layer) made of Au directly laminated on the metal substrate, possessing high conductivity and high corrosion resistance, and the surface roughness of the metal substrate is adjusted to improve adhesion between the metal substrate and the noble metal layer. Furthermore, the component constituting the anode described in Patent Document 2 comprises an electrode substrate made of a metal such as aluminum, and a conductive oxide film that forms a nanostructure and is provided on the surface of the electrode substrate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-127707 [Patent Document 2] Japanese Patent Publication No. 2013-231208 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The anode separator described in Patent Document 1 has a noble metal layer on the surface of a metal substrate, which gives it excellent corrosion resistance, but it is expensive and difficult to adopt in actual products. To address this, as an anode separator with a conductive layer on the surface of a metal substrate, such as the component described in Patent Document 2, it has been considered to use a low-cost conductive oxide film on the surface of a metal substrate made of aluminum or the like, and in that case, a conductive oxide film with high conductivity is required. On the other hand, in water electrolysis devices, a high voltage of about 1.8V is usually applied to the water electrolysis cell. Therefore, corrosion resistance becomes an issue again in anode separators with a conductive oxide film on the surface of a metal substrate made of aluminum or the like.

[0006] Therefore, as an anode-side separator with a conductive oxide film provided on the surface of a metal substrate, a conductive oxide film containing indium tin oxide (ITO), which is assumed to have high conductivity among conductive oxides, has been proposed, and in this case, the durability of the conductive oxide film is also considered important.

[0007] This invention has been made in view of these points, and its purpose is to provide a highly conductive anode-side separator and a water electrolysis apparatus equipped therewith. [Means for solving the problem]

[0008] To solve the above problems, the anode-side separator of the present invention is an anode-side separator used in a water electrolysis apparatus, comprising a metal substrate made of titanium or stainless steel, and a conductive oxide film containing indium tin oxide (ITO) provided on the surface of the metal substrate, characterized in that the crystallinity of the conductive oxide film is 20% or more.

[0009] Furthermore, the water electrolysis apparatus of the present invention is characterized by comprising the anode-side separator described above. [Effects of the Invention]

[0010] According to the present invention, conductivity can be increased. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic exploded cross-sectional view showing the configuration of a water electrolysis cell, which is a constituent unit of the water electrolysis apparatus according to the first embodiment, equipped with an anode-side separator according to the first embodiment. [Figure 2] This is an enlarged view of the X portion in Figure 1. [Figure 3] This graph shows the change in contact resistance before the durability test with respect to the crystallinity of the conductive oxide film of the anode-side separator in the comparative example and Examples 1-5. [Figure 4] This graph shows the change in contact resistance after durability testing with respect to the crystallinity of the conductive oxide film of the anode-side separator in the comparative example and Examples 1-5. [Modes for carrying out the invention]

[0012] First, the outline of the anode-side separator and water electrolysis apparatus according to the embodiment will be described by illustrating the first embodiment. Figure 1 is a schematic exploded cross-sectional view showing the configuration of a water electrolysis cell, which is a constituent unit of the water electrolysis apparatus according to the first embodiment, equipped with the anode-side separator according to the first embodiment. Figure 2 is an enlarged view of portion X in Figure 1.

[0013] As shown in Figure 1, the water electrolysis apparatus 100 according to the first embodiment is constructed by stacking multiple sets of water electrolysis cells 20. The water electrolysis cell 20 is a solid polymer type water electrolysis cell comprising a membrane electrode assembly 10 and an anode-side separator 12 and a cathode-side separator 14 according to the first embodiment that sandwich the membrane electrode assembly 10.

[0014] A membrane-electrode assembly 10 comprises a solid polymer electrolyte membrane 2, an anode catalyst layer 4a and a cathode catalyst layer 4c respectively provided on one main surface 2a and the other main surface 2c of the solid polymer electrolyte membrane 2, an anode current collector 6a laminated on a main surface 4aa of the anode catalyst layer 4a, and a cathode current collector 6c laminated on a main surface 4cc of the cathode catalyst layer 4c. An anode-side separator 12 is laminated on a main surface 6aa of the anode current collector 6a, and a cathode-side separator 14 is laminated on a main surface 6cc of the cathode current collector 6c.

[0015] As shown in FIG. 1 and FIG. 2, the anode-side separator 12 comprises a metal base material 8 made of pure titanium, and a conductive oxide film 9 containing indium tin oxide (ITO) provided over the entire surface 8s of the metal base material 8. The crystallinity of the conductive oxide film 9 is 40% or higher. In the anode-side separator 12, a fluid passage 12p is formed by providing grooves 8g for a fluid passage on a main surface 8a side of the metal base material 8 facing the solid polymer electrolyte membrane 2, and a water supply port 12f and a drainage port 12d communicating with the fluid passage 12p are provided.

[0016] The cathode-side separator 14 comprises a metal base material 16 made of any one of titanium, stainless steel, and aluminum. In the cathode-side separator 14, a fluid passage 14p is formed by providing grooves 16g for a fluid passage on a main surface 16a side of the metal base material 16 facing the solid polymer electrolyte membrane 2, and a hydrogen outlet 14d communicating with the fluid passage 14p is provided.

[0017] The anode-side separator 12 and the cathode-side separator 14 have the function of transmitting electricity to the anode catalyst layer 4a and the cathode catalyst layer 4c via the anode current collector 6a and the cathode current collector 6c respectively, and at the same time electrically connecting to adjacent water electrolysis cells (not shown). In a water electrolysis apparatus 100, a plurality of sets of water electrolysis cells 20 are laminated in the opposing direction of the anode-side separator 12 and the cathode-side separator 14, and clamped from both sides in the lamination direction by end plates (not shown).

[0018] When producing hydrogen gas by electrolyzing raw material water by using such a water electrolysis apparatus 100, first, raw material water is supplied from the water supply port 12f of the anode-side separator 12 to the fluid passage 12p. At the same time, electricity is transmitted to the anode catalyst layer 4a and the cathode catalyst layer 4c via the anode power feeder 6a and the cathode power feeder 6c respectively by the anode-side separator 12 and the cathode-side separator 14. Thereby, the raw material water is electrolyzed in the anode catalyst layer 4a, thereby generating hydrogen ions (H + ), electrons, and oxygen gas (O 2 ) are generated. Next, due to the potential difference between the anode catalyst layer 4a and the cathode catalyst layer 4c, hydrogen ions permeate through the solid polymer electrolyte membrane 2 which is a cation-permeable membrane, and move from the anode catalyst layer 4a side to the cathode catalyst layer 4c side. Then, hydrogen ions receive electrons from the cathode catalyst layer 4c and are molecularized, whereby hydrogen gas (H 2 ) is obtained in the fluid passage 14p of the cathode-side separator 14. The hydrogen gas is taken out from the hydrogen outlet 14d. On the other hand, the oxygen gas obtained in the fluid passage 12p of the anode-side separator 12 is discharged from the drain port 12d together with most of the raw material water.

[0019] The effects of the anode-side separator 12 and the water electrolysis apparatus 100 as described above will be explained. Here, we will explain the problems of a water electrolysis apparatus 100 that, as in the prior art, uses an anode-side separator in which a conductive oxide film containing indium tin oxide is provided on the surface of a metal substrate made of a general-purpose metal other than titanium and stainless steel (e.g., aluminum) instead of the anode-side separator 12 according to the first embodiment. In a water electrolysis apparatus, when an anode-side separator in which a conductive oxide film is provided on the surface of a metal substrate is generally used, the conductive oxide film is porous, so the raw water supplied to the fluid passage permeates the conductive oxide film, resulting in contact between the conductive oxide film and the metal substrate, which contain different metals, in the raw water. As a result, a corrosion cell is formed between the conductive oxide film and the metal substrate and the raw water, causing current to flow and dissimilar metal contact corrosion. Furthermore, in a water electrolysis apparatus, when raw water is electrolyzed, a high voltage of, for example, about 1.8V is usually applied to the water electrolysis cell of the constituent unit, so the anode-side separator is exposed to a high-voltage environment. In such situations, when using an anode separator made of a general-purpose metal other than titanium or stainless steel as the metal substrate, the corrosion resistance of the metal substrate is accelerated due to galvanic corrosion, as these general-purpose metals do not have sufficient corrosion resistance. This raises concerns about the corrosion resistance of the anode separator.

[0020] In contrast, in the anode-side separator 12 according to the first embodiment, the pure titanium used in the metal substrate 8 has significantly higher corrosion resistance than general-purpose metals other than titanium and stainless steel. Therefore, in the water electrolysis apparatus 100 according to the first embodiment, even when the conductive oxide film 9 and the metal substrate 8, which contain different metals, are in contact in the raw water, and the anode-side separator 12 is exposed to a high-voltage environment, for example, when a high voltage of about 1.8V is applied to the water electrolysis cell, corrosion of the metal substrate 8 due to galvanic corrosion can be suppressed. Furthermore, in the anode-side separator 12 according to the first embodiment, the indium tin oxide contained in the conductive oxide film 9 provided as a conductive layer on the surface 8s of the metal substrate 8 is less expensive than precious metals such as Au contained in the precious metal layer provided as a conductive layer on the surface of the metal substrate in conventional separators. Therefore, the anode-side separator 12 can reduce costs compared to conventional separators.

[0021] Furthermore, conductive oxide films containing indium tin oxide, such as the conductive oxide film 9 provided on the surface 8s of the metal substrate 8 in the anode-side separator 12 according to the first embodiment, are expected to provide high conductivity among conductive oxide films, but their conductivity and durability depend on the degree of crystallinity. The conductive oxide film 9 according to the first embodiment has a degree of crystallinity of 40% or more, resulting in higher conductivity compared to films with a degree of crystallinity of less than 20%, such as amorphous films. Therefore, the conductivity of the anode-side separator can be increased. Moreover, the conductive oxide film 9 is more energetically stable than films with a degree of crystallinity of less than 40%, so dissolution is suppressed when used in a water electrolysis device, resulting in higher durability. Therefore, the durability of the anode-side separator can be improved. Thus, the electrolysis performance of the water electrolysis device 100 can be sufficiently increased, and the durability of the water electrolysis device 100 can be improved.

[0022] In the anode-side separator according to the embodiment, as in the first embodiment, titanium or stainless steel, which have significantly higher corrosion resistance than other general-purpose metals, are used as the metal substrate. Therefore, corrosion of the metal substrate can be suppressed. In addition, a conductive oxide film containing indium tin oxide, which is less expensive than precious metals, is used as the conductive layer provided on the surface of the metal substrate. Therefore, costs can be reduced. In addition, the conductivity of the anode-side separator can be increased by having a crystallinity of 20% or more of the conductive oxide film. Furthermore, if the crystallinity of the conductive oxide film is 40% or more, the durability of the anode-side separator can be improved.

[0023] Next, the configuration of the anode-side separator and water electrolysis apparatus according to the embodiment, as well as the hydrogen gas production method according to the embodiment, will be described in detail.

[0024] 1. Anode-side separator The anode-side separator according to this embodiment is an anode-side separator used in a water electrolysis apparatus, comprising a metal substrate made of titanium or stainless steel, and a conductive oxide film containing indium tin oxide (ITO) provided on the surface of the metal substrate, wherein the crystallinity of the conductive oxide film is 20% or more. Here, "surface of the metal substrate" means the outer surface of the metal substrate, and may be one main surface of the metal substrate or the other main surface of the metal substrate. The metal substrate, conductive oxide film, and other aspects of the anode-side separator will be described in detail below.

[0025] (1) Metal base material The titanium used as the metal substrate is not particularly limited, but examples include pure titanium and titanium alloys. Pure titanium is not particularly limited, but examples include those specified in JIS H 4600:2012. Titanium alloys are not particularly limited, but examples include Ti-Al. Among titanium, pure titanium is preferred because it has particularly high corrosion resistance. Examples of stainless steel used as the metal substrate include austenitic stainless steel such as SUS304.

[0026] The shape of the metal substrate is not particularly limited, as long as it is the shape of a general metal substrate that constitutes an anode-side separator used in a general water electrolysis apparatus, and may also be a shape in which grooves for the fluid passage of the separator are provided in the metal substrate. If the water electrolysis apparatus is a water electrolysis apparatus that includes a solid polymer type water electrolysis cell, the shape in which grooves for the fluid passage are provided may be, for example, as in the first embodiment, a shape in which grooves for the fluid passage are provided on the main surface side of the metal substrate facing the solid polymer electrolyte membrane. The shape of the metal substrate may also be a flat plate shape in which grooves for the fluid passage are provided in the metal substrate. When the shape of the metal substrate is a flat plate shape, for example, it constitutes a flat type separator with separated fluid passages. The surface roughness Rz of the metal substrate is, for example, in the range of 0.05 μm or more and 0.8 μm or less, and is preferably in the range of 0.1 μm or more, and particularly preferably in the range of 0.3 μm or more. The thickness of the metal substrate is not particularly limited and can be set according to the material of the metal substrate, taking into consideration strength and processing, but is, for example, in the range of 0.08 mm to 1 mm.

[0027] (2) Conductive oxide film The conductive oxide film is not particularly limited as long as it contains indium tin oxide (ITO) and is provided on the surface of the metal substrate. If the water electrolysis apparatus is a water electrolysis apparatus that includes a solid polymer type water electrolysis cell, the conductive oxide film is preferably provided on at least the main surface of the metal substrate facing the solid polymer electrolyte film, as in the first embodiment, but it may also be provided on the entire surface of the metal substrate.

[0028] The crystallinity of the conductive oxide film is not particularly limited as long as it is 20% or higher, but 40% or higher is preferable. This is because the conductive oxide film becomes more energetically stable, its dissolution is suppressed when used in a water electrolysis device, and its durability is increased, thus improving the durability of the anode-side separator.

[0029] The thickness of the conductive oxide film is not particularly limited, but is, for example, within the range of 0.05 μm to 0.8 μm, and preferably within the range of 0.3 μm or more. This is because a thickness of 0.05 μm or more of the conductive oxide film enables the uniform formation of the conductive oxide film. Furthermore, a thickness of 0.3 μm or more of the conductive oxide film ensures sufficient corrosion resistance of the anode-side separator when the surface of the metal substrate becomes rough after going through the pressing process. On the other hand, a thickness of 0.8 μm or less of the conductive oxide film suppresses the delamination of the conductive oxide film from the metal substrate due to residual stress.

[0030] (3) Method for manufacturing the anode separator The method for manufacturing the anode separator is not particularly limited, but examples include a method in which a metal substrate made of titanium or stainless steel is prepared, and a conductive oxide film containing indium tin oxide (ITO) is deposited on the surface of the metal substrate by sputtering. In this manufacturing method, the method for achieving a crystallinity of 20% or more or 40% or more of the conductive oxide film is not particularly limited, but methods such as adjusting the deposition conditions such as the target used, cathode power and deposition time during deposition by sputtering, and heat-treating the conductive oxide film after deposition are used.

[0031] Methods for adjusting the film deposition conditions during film deposition by sputtering include, for example, appropriately selecting the type of target to be used according to the sputtering equipment used for film deposition, and setting the cathode power and deposition time. Examples of target types include composite materials containing In2O3 and SnO2, in which the weight ratio of In2O3 and SnO2 is set to various ratios.

[0032] Methods for heat-treating a conductive oxide film after its formation include, for example, heat-treating the conductive oxide film in an atmospheric furnace under predetermined atmospheric furnace temperature and heat treatment time conditions, and heat-treating the conductive oxide film in an argon furnace under predetermined argon furnace temperature and heat treatment time conditions.

[0033] 2.Water electrolysis device The water electrolysis apparatus according to the embodiment is not particularly limited as long as it is equipped with an anode-side separator according to the embodiment, but a water electrolysis apparatus including a solid polymer type water electrolysis cell using a solid polymer electrolyte membrane, such as the water electrolysis apparatus according to the first embodiment, is preferred.

[0034] Examples of solid polymer type water electrolysis cells include, as in the water electrolysis cell according to the first embodiment, a membrane electrode assembly and an anode-side separator and a cathode-side separator that sandwich the membrane electrode assembly. Examples of such solid polymer type water electrolysis cells include, for example, a membrane electrode assembly comprising a solid polymer electrolyte membrane, an anode catalyst layer and a cathode catalyst layer provided on one main surface and the other main surface of the solid polymer electrolyte membrane, an anode power supply laminated on the main surface of the anode catalyst layer and a cathode power supply laminated on the main surface of the cathode catalyst layer, with the anode-side separator laminated on the main surface of the anode power supply and the cathode-side separator laminated on the main surface of the cathode power supply.

[0035] Solid polymer electrolyte membranes block the flow of electrons and gases, and also block hydrogen ions (H + It has the function of moving ions from the anode catalyst layer side to the cathode catalyst layer side. The solid polymer electrolyte membrane is not particularly limited, but for example, it is composed of a polymer electrolyte resin which is a solid polymer material such as perfluorosulfonic acid (PFSA) ionomer, and consists of an ion exchange membrane in which the polymer membrane having ion conductivity is the electrolyte.

[0036] The anode catalyst layer has the function of generating hydrogen ions, electrons, and oxygen gas from raw water. The anode catalyst layer is not particularly limited, but for example, it consists of a catalyst and an ionomer, and is formed by coating the catalyst with the ionomer. The catalyst is not particularly limited, but for example, a supported catalyst is formed by supporting platinum group metals such as platinum or alloys thereof on carrier particles. The carrier particles are not particularly limited, but for example, carbon carrier particles such as carbon black are used. The ionomer is, for example, a polymer electrolyte resin which is a solid polymer material such as a fluorine-based resin of the same quality as the solid polymer electrolyte membrane, and has proton conductivity due to the ion exchange groups it possesses. Unlike the anode catalyst layer, the cathode catalyst layer generates hydrogen ions and electrons into hydrogen gas (H 2 It has the function of making the cathode catalyst layer a catalyst. The cathode catalyst layer is not particularly limited, but for example, it consists of a catalyst and an ionomer, and is formed by coating the catalyst with the ionomer. The catalyst and ionomer are the same as those of the anode catalyst layer.

[0037] The anode and cathode power supply members are not particularly limited as long as they are conductive members with gas permeability, but for example, they are composed of conductive porous materials, specifically porous metallic materials such as sintered titanium powder, or porous fibrous materials such as carbon fibers or graphite fibers.

[0038] The anode-side separator is as described in section "1. Anode-side separator" above. The cathode-side separator may be a metal substrate made of titanium, stainless steel, aluminum, etc. The shape of the metal substrate of the cathode-side separator is not particularly limited as long as it is a general shape. The thickness of the metal substrate of the cathode-side separator is not particularly limited and can be set according to the material of the metal substrate, taking into consideration strength and processing.

[0039] 3. Method for producing hydrogen gas The hydrogen gas production method according to the embodiment is not particularly limited, as long as it is a method of producing hydrogen gas by electrolyzing raw materials such as water using the water electrolysis apparatus according to the embodiment, but for example, a method using pure water as a raw material may also be used. [Examples]

[0040] The anode-side separator and water electrolysis apparatus according to the embodiment will be described in more detail below with reference to examples, comparative examples, and reference examples.

[0041] 1. Evaluation of the change in contact resistance with respect to the crystallinity of the conductive oxide film on the anode-side separator. Anode-side separators were fabricated for comparative examples and examples. The crystallinity of their conductive oxide films and their contact resistances before and after the durability test were calculated, and the change in contact resistance before and after the durability test with respect to the crystallinity of the conductive oxide film was evaluated.

[0042] [Comparative Example] First, a flat metal substrate made of pure titanium was prepared. Next, the native oxide film and other materials were removed from one main surface (film deposition surface) of the metal substrate by reverse sputtering. Then, using a sputtering apparatus (UHSP-PL2060TO) manufactured by Shimadzu Corporation, a conductive oxide film containing indium tin oxide (ITO) was deposited on one main surface of the metal substrate to a thickness of 100 nm under the following conditions. This created an anode-side separator.

[0043] Target material: Composite material containing In2O3 (90% by weight) and SnO2 (10% by weight) Cathode power: 4.4kW (DC) Deposition time: 20 seconds Preheating: None

[0044] [Example 1] An anode-side separator was fabricated in the same manner as in the comparative example, except that the cathode power and deposition time during the deposition of the conductive oxide film were set to 3 kW (DC) and 80 seconds, respectively.

[0045] [Example 2] An anode-side separator was fabricated in the same manner as in the comparative example, except that the cathode power and deposition time during the deposition of the conductive oxide film were set to 1.5 kW (DC) and 180 seconds, respectively.

[0046] [Example 3] An anode-side separator was fabricated in the same manner as in the comparative example, except that the cathode power and deposition time during the deposition of the conductive oxide film were set to 4 kW (DC) and 60 seconds, respectively.

[0047] [Example 4] Similar to the comparative example, a metal substrate was prepared, and a conductive oxide film was deposited on one main surface of the metal substrate. Then, the metal substrate and the conductive oxide film were placed in an atmospheric furnace and heat-treated at 350°C for 5 minutes to produce an anode-side separator.

[0048] [Example 5] Similar to the comparative example, a metal substrate was prepared, and a conductive oxide film was deposited on one main surface of the metal substrate. Then, the metal substrate and the conductive oxide film were placed in an argon furnace and heat-treated in the argon furnace at 250°C for 5 minutes to produce an anode-side separator.

[0049] [Crystallization of conductive oxide film] For the conductive oxide films of the anode-side separators in the comparative examples and Examples 1-5, X-ray diffraction spectra were measured using powder X-ray diffraction (XRD). Then, the diffraction lines (peaks) due to crystalline material and the scattered light (haloes) due to amorphous material in the X-ray diffraction spectra were fitted, and the integrated intensity of each part was determined. The degree of crystallinity was then calculated using the following equation (1).

[0050] X = Ic / (Ic + Ia) × 100 (1) (In equation (1), "X" represents the degree of crystallinity, "Ic" represents the integrated intensity of the peak region, and "Ia" represents the integrated intensity of the halo region.)

[0051] [Contact resistance before durability testing] Test samples were cut from the anode-side separators of the comparative examples and Examples 1-5, and the contact resistance [mΩ·cm] of the test samples before the durability test was measured. 2 The following was calculated: Specifically, a carbon sheet (TGP-H-060 manufactured by Toray Industries, Inc.) was placed on the conductive oxide film side of the test sample, and a constant load (1 MPa) was applied using a measuring jig. The current from the power supply was adjusted so that the current flowing through the test sample was 1 A, and the voltage applied to the test sample was measured with a voltmeter to calculate the contact resistance between the test sample and the carbon sheet.

[0052] [Contact resistance after durability testing] Durability tests (potential constant corrosion tests) were performed on the anode-side separators of the comparative examples and Examples 1-5 in accordance with the Japanese Industrial Standards (JIS) electrochemical high-temperature corrosion test method for metal materials (JIS Z 2294:2004). Specifically, a test sample was cut from the anode-side separator and immersed in an etching solution (dilute sulfuric acid aqueous solution) whose temperature was adjusted to 80°C using temperature-controlled water and whose pH was adjusted to 4 by the amount of sulfuric acid. In this state, a potential difference of 2V was created between the counter electrode, which was made of a platinum plate, and the test sample (sample electrode) by electrically connecting them, and the test sample was corroded. The potential of the test sample was kept constant with a reference electrode during the test. The test duration was 60 hours. A Hokuto Denko HZ-Pro was used as the test apparatus for the test.

[0053] For the test samples after the durability tests of the comparative examples and Examples 1-5, the contact resistance was calculated using the same method as the method used to calculate the contact resistance before the durability tests.

[0054] [evaluation] Table 1 below shows the crystallinity calculated for the conductive oxide films of the anode-side separators of Comparative Example and Examples 1 to 5. Table 1 below also shows the contact resistance calculated for the test samples before the durability test and the test samples after the durability test of Comparative Example and Examples 1 to 5. Figure 3 is a graph showing the change in contact resistance before the durability test with respect to the crystallinity of the conductive oxide film of the anode-side separators of Comparative Example and Examples 1 to 5. Figure 4 is a graph showing the change in contact resistance after the durability test with respect to the crystallinity of the conductive oxide film of the anode-side separators of Comparative Example and Examples 1 to 5.

[0055] [Table 1]

[0056] As is clear from Table 1 and Figure 3 above, in the anode-side separators of Comparative Example and Examples 1 to 5, when the crystallinity of the conductive oxide film is 19.8% or more, the contact resistance before the durability test is 10 mΩ·cm 2 or less, and did not exceed the range of the standard value, but the contact resistance after the durability test was 10 mΩ·cm 2 or more, and sometimes exceeded the range of the standard value. On the other hand, when the crystallinity of the conductive oxide film is 38.2% or more, the contact resistance after the durability test is also 10 mΩ·cm 2 or less, and did not exceed the range of the standard value.

[0057] Note that, as a result of observing the test samples after the durability test of the anode-side separators of Comparative Example and Examples 1 to 5 by visual inspection and an optical microscope, discoloration was observed in the conductive oxide film in the test samples after the durability test of Comparative Example and Example 1, so it is considered that indium tin oxide contained in the conductive oxide film dissolved. In contrast, no discoloration was observed in the conductive oxide film in the test samples after the durability test of Examples 2 to 5, so it is considered that the dissolution of indium tin oxide contained in the conductive oxide film was suppressed. Furthermore, it was confirmed that corrosion of the metal base material did not occur in any of the test samples after the durability test of Comparative Example and Examples 1 to 5.

[0058] 2. Evaluation of the change in contact resistance of the anode-side separator before and after heat treatment. For the anode-side separator, the change in contact resistance before and after heat treatment was evaluated when heat treatment was performed in an atmospheric furnace or an argon furnace.

[0059] (1) In the case of heat treatment in an atmospheric reactor First, the contact resistance of anode-side separators, prepared in the same manner as the comparative example, was calculated before heat treatment in an atmospheric furnace under various conditions (atmospheric furnace temperature and heat treatment time). Specifically, test samples were cut from the anode-side separators before heat treatment under various conditions, and the contact resistance of the test samples was calculated using the same method as the contact resistance calculation method described in "1. Evaluation of the change in contact resistance with respect to the crystallinity of the conductive oxide film of the anode-side separator" above. Next, the contact resistance of the same anode-side separators was calculated after heat treatment in an atmospheric furnace under various conditions. Specifically, test samples were cut from the anode-side separators after heat treatment under various conditions, and the contact resistance of the test samples was calculated using the same method as the contact resistance calculation method described above. Then, the change in contact resistance after heat treatment under various conditions compared to the contact resistance before heat treatment was calculated as the change in contact resistance due to heat treatment under various conditions (atmospheric furnace temperature and heat treatment time). The calculation results are shown in Table 2 below.

[0060] [Table 2]

[0061] (2) In the case of heat treatment in an argon furnace First, the contact resistance of an anode-side separator, prepared in the same manner as the comparative example, was calculated before heat treatment in an argon furnace under various conditions (argon furnace temperature and heat treatment time). Specifically, test samples were cut from the anode-side separator before heat treatment under various conditions, and the contact resistance of the test samples was calculated using the same method as described above. Next, the contact resistance of the same anode-side separator was calculated after heat treatment in an argon furnace under various conditions. Specifically, test samples were cut from the anode-side separator after heat treatment under various conditions, and the contact resistance of the test samples was calculated using the same method as described above. Then, the change in contact resistance after heat treatment under various conditions compared to the contact resistance before heat treatment was calculated as the change in contact resistance due to heat treatment under various conditions (argon furnace temperature and heat treatment time). The calculation results are shown in Table 3 below.

[0062] [Table 3]

[0063] (3) Evaluation As shown in Table 2 above, when heat treatment was performed in an atmospheric furnace under various conditions (atmospheric furnace temperature and heat treatment time), the contact resistance of the test sample could be reduced by heat treatment under all conditions except those where the atmospheric furnace temperature was too low and the heat treatment time was too short, and those where the atmospheric furnace temperature was too high and the heat treatment time was too long. Under all conditions except those where the atmospheric furnace temperature was too low and the heat treatment time was too short, it is thought that the crystallinity of the conductive oxide film was improved. Under the conditions where the atmospheric furnace temperature was too high and the heat treatment time was too long, it is thought that the effect of reducing contact resistance due to the improvement in the crystallinity of the conductive oxide film was offset by the oxidation of the conductive oxide film.

[0064] As shown in Table 3 above, when heat treatment was performed in an argon furnace under various conditions (argon furnace temperature and heat treatment time), the contact resistance of the test sample was reduced by heat treatment under all conditions except those where the argon furnace temperature was too low and the heat treatment time was too short. This suggests that the crystallinity of the conductive oxide film was improved.

[0065] Although embodiments of the anode separator and water electrolysis apparatus of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of Symbols]

[0066] 100: Water electrolysis device, 20: Water electrolysis cell, 10: Membrane electrode assembly, 12: Anode-side separator, 8: Metal substrate, 9: Conductive oxide film, 14: Cathode-side separator

Claims

1. an anode-side separator used in a water electrolysis apparatus, A metal base material made of titanium or stainless steel, The metal substrate comprises a conductive oxide film made of indium tin oxide (ITO) provided on its surface, The degree of crystallinity of the conductive oxide film is 40% or more. An anode-side separator characterized in that the thickness of the conductive oxide film is within the range of 0.05 μm to 0.8 μm.

2. A water electrolysis apparatus characterized by comprising the anode-side separator described in claim 1.

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