Ni-coated substrate for separator of anion exchange membrane water electrolysis device, and method for producing same

Abstract

Provided is an Ni-coated substrate for a separator of an anion exchange membrane water electrolysis device, which exhibits excellent corrosion resistance in the usage environment of a separator of an anion exchange membrane water electrolysis device, which exhibits excellent contact resistance properties with a porous transport layer, and which has excellent productivity.　An Ni-coated substrate for a separator of an anion exchange membrane water electrolysis device according to the present invention comprises a metal substrate and an Ni coating layer on a surface of the metal substrate. The thickness h (μm) of the Ni coating layer satisfies formula (1), and is 1 μm or less. (Fe+Cr×2-Ni×8) / (100×h)<10 … (1) Fe, Cr and Ni in formula (1) indicate the content values (mass%) of the elements contained in the metal substrate, and take a value of 0 if the element in question is not contained.

Description

Ni-coated substrate for separators in an anion exchange membrane type water electrolysis apparatus and method for manufacturing the same

[0001] The present invention relates to a Ni-coated substrate for separators in an anion exchange membrane type water electrolysis apparatus and a method for producing the same.

[0002] In recent years, from the perspective of protecting the global environment, CO2 has been a focus, and CO2 is a substance with excellent hydrogen generation efficiency. ２ Development is underway on water electrolysis devices that do not emit pollutants. Water electrolysis devices produce H₂ from water and electricity through an electrochemical reaction. ２ and O ２ It generates. The water electrolysis device has an electrolyte membrane (ion exchange membrane), two electrode catalyst layers (hydrogen generation electrode and oxygen generation electrode), and O ２ and H ２ It is constructed with a basic structure consisting of a diffusion layer and a cell sandwiched between two separators.

[0003] Water electrolysis devices are classified into alkaline water electrolysis (AWE), proton exchange membrane (PEM), anion exchange membrane (AEM), and solid oxide electrolyte cell (SOEC) types, depending on the type of electrolyte membrane used, and development is progressing for each type.

[0004] Among these water electrolysis devices, anion exchange membrane type water electrolysis devices, which use anion exchange membranes as the electrolyte membrane, are particularly promising because they do not require expensive precious metal catalysts in the electrode catalyst layer and are resistant to load fluctuations, among other advantages, and are expected to become more widespread in the future.

[0005] An anion exchange membrane type water electrolysis apparatus uses an anion exchange membrane to convert water and electricity into H ２ and O ２ This is how it extracts the anion. In an anion exchange membrane type water electrolysis apparatus, the anion exchange membrane is sandwiched between an electrode catalyst layer, a porous transport layer (e.g., Ni fibers), and a separator, forming a single component (a so-called single cell). Then, electricity is passed between the separator on the oxygen generation electrode side and the separator on the hydrogen generation electrode side to electrolyze water.

[0006] Also, when putting a water electrolysis device into practical use, it is common to configure a water electrolysis stack by connecting dozens to hundreds of such single cells in series for use.

[0007] For the separator used in a water electrolysis device, in addition to the role as a partition wall (a) separating single cells, (b) a conductor for transporting electrons, and (c) a function as a flow path through which water and generated O ２ and H ２ flow respectively, excellent durability and electrical conductivity are required.

[0008] Here, the durability is determined by corrosion resistance. The reason is that when the separator corrodes and metal ions elute, the durability of electrolyte membranes such as ion exchange membranes decreases, and the water electrolysis characteristics deteriorate.

[0009] Also, regarding electrical conductivity, it is desired that the contact resistance between the separator and the porous transport layer is low, that is, the contact resistance characteristics are excellent. The reason is that when the contact resistance between the separator and the porous transport layer increases, the electrolysis efficiency of the water electrolysis device decreases. That is, it can be said that the smaller the contact resistance between the separator and the porous transport layer, the more excellent the water electrolysis characteristics.

[0010] To date, an anion exchange membrane type water electrolysis device using a Ni metal plate as a separator has been researched and developed. The separator made of this Ni metal plate has the advantages of relatively low contact resistance and high corrosion resistance in a high-alkali environment. However, the separator made of a Ni metal plate (separator made of a Ni metal plate) has the disadvantage of being very expensive, and it is considered to be a cause that hinders the future spread of anion exchange membrane type water electrolysis devices.

[0011] Therefore, attempts have been made to apply a relatively inexpensive material instead of the Ni metal plate as the separator material. In particular, various studies have been conducted towards the practical application of a separator made of stainless steel from the viewpoints of cost and durability.

[0012] For example, Patent Document 1 discloses a technique for producing stainless steel for alkaline water electrolysis treatment apparatus that contains fluorine in a film formed on the surface of a substrate by either an immersion treatment in which a substrate made of stainless steel is immersed in an aqueous solution containing hydrofluoric acid or an inorganic compound containing fluorine, or an electrolytic treatment in which the substrate is electrolyzed in the aqueous solution.

[0013] Furthermore, Patent Document 2 discloses a bipolar plate for a water electrolyzer containing an anion exchange membrane, made of stainless steel (SS304, SS316, SS430, etc.) coated with a layer of metal containing any metal such as nickel, gold, or a combination thereof.

[0014] Furthermore, Patent Document 3 discloses a technique for suppressing a decrease in the sealing performance of the anodic solution and anodic chamber gas in an alkaline water electrolytic cell by providing a nickel plating layer on the first frame that defines the anodic chamber.

[0015] Japanese Patent Publication No. 2020-164915, Japanese Patent Publication No. 2023-538279, International Publication No. 2023 / 054576

[0016] However, the technology disclosed in Patent Document 1 does not clarify the properties related to conductivity, and it is unclear whether the technology disclosed in Patent Document 1 can be applied to the separator material of an anion exchange membrane type water electrolysis apparatus.

[0017] Furthermore, the technology disclosed in Patent Document 2 does not show specific examples of coating technology, and Patent Document 2 does not clarify the type of coating, coating thickness, material combination, etc., that are suitable as a separator material for an anion exchange membrane type water electrolysis apparatus.

[0018] Furthermore, the technology disclosed in Patent Document 3 requires a nickel plating layer with a thickness of 27 μm or more. However, nickel is a critical metal, and resource conservation is desired for this element, and the material cost is also high. Therefore, in order to ensure the desired corrosion resistance and conductivity for the separator material of an anion exchange membrane type water electrolysis apparatus, as well as to reduce coating costs and improve productivity (shortening the coating processing time), further thinning is required. Moreover, the required properties differ between the separator material and the frame material. For this reason, it is not possible to determine whether the frame material with a nickel plating layer in the alkaline water electrolysis cell disclosed in Patent Document 3 is suitable as a separator material for an anion exchange membrane type water electrolysis apparatus, and the optimal range of nickel plating layer thickness suitable for the separator material is also unclear.

[0019] Thus, when using a metal substrate such as stainless steel as the separator material for an anion exchange membrane type water electrolysis device, the Ni coating layer formed on its surface is required to be thin (thin film) while simultaneously achieving both corrosion resistance and conductivity. However, it is difficult to say that these two conditions are adequately met in practice.

[0020] The present invention was developed in view of the above-mentioned circumstances, and aims to provide a Ni-coated substrate for separators in an anion exchange membrane type water electrolysis apparatus that has excellent corrosion resistance, excellent contact resistance characteristics with the porous transport layer, and excellent productivity in the separator usage environment of an anion exchange membrane type water electrolysis apparatus.

[0021] Furthermore, the present invention aims to provide a method for manufacturing a Ni-coated substrate for the separator of the above-mentioned anion exchange membrane type water electrolysis apparatus.

[0022] To solve the above problems, the inventors used various metal plates as the metal substrate (metal base) for the separator material of an anion exchange membrane type water electrolysis apparatus, and diligently investigated various Ni coating layer formation treatments for these metal plates. As a result, the following findings were obtained.

[0023] (1) When a thick Ni coating layer is applied to the metal substrate, excellent corrosion resistance and contact resistance characteristics can be obtained. On the other hand, a thick Ni coating layer reduces productivity and leads to increased costs. Also, a thick Ni coating layer makes it easier for the Ni coating layer to peel off when processing it into the desired separator shape.

[0024] (2) Next, when the Ni coating layer was made thinner (thinned), the number of defects in the Ni coating layer increased, the area of ​​the metal substrate exposed increased, and the corrosion resistance decreased. Furthermore, it was found that when the Ni coating layer was made thin, the effect of reducing contact resistance was not sufficiently obtained.

[0025] (3) First, in order to ensure the desired corrosion resistance even when the Ni coating layer is thinned, the inventors investigated the stability of various metal substrates in a high-alkali, high-potential environment prior to the formation of the Ni coating layer. As a result, the inventors concluded that if the component composition of the metal substrate can be made such that a stable film is formed in a high-alkali, high-potential environment, then the desired corrosion resistance can be ensured even when the Ni coating layer is thinned in the above environment.

[0026] Specifically, the inventors considered that, assuming a steel sheet as the metal substrate, it would be desirable to be able to stably and densely form a Ni oxide film that is thermodynamically more stable in the above environment than Fe and Cr, which are the main constituent elements of the steel sheet. To achieve this, they concluded that it would be necessary to relatively increase the Ni content of the steel sheet and further control the Cr content to an appropriate range.

[0027] However, the steel sheet used as the metal substrate is selected from various types depending on the mechanical properties required when processing it into the desired separator shape. Therefore, it is necessary to consider the appropriate thickness of the Ni coating layer for the steel sheet used as the metal substrate.

[0028] (4) Next, the inventors applied a Ni coating layer to various steel sheets and then attempted to thin the Ni coating layer. As a result, they found that by appropriately controlling the thickness of the Ni coating layer according to the component composition of the metal substrate (steel sheet), particularly the Ni content, it is possible to ensure excellent corrosion resistance even in high-alkali, high-potential environments, and furthermore, to ensure the desired contact resistance characteristics.

[0029] (5) Furthermore, when electricity derived from renewable energy sources such as solar power and wind power is used in water electrolysis devices, these power sources fluctuate depending on weather conditions and time of day, which can lead to large potential fluctuations in the water electrolysis device. In such a highly alkaline environment and a high-load environment with large potential fluctuations, the separator material is also subjected to a high load, requiring even greater corrosion resistance from the Ni coating layer. We have found that even in such a high-load environment, excellent corrosion resistance can be ensured by creating multiple layers of Ni coating.

[0030] This invention is based on the above findings. In other words, the gist of this invention is as follows:

[0031] [1] A Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus, comprising a metal substrate and a Ni coating layer on the surface of the metal substrate, wherein the thickness h (μm) of the Ni coating layer satisfies the following formula (1) and is 1 μm or less: (Fe + Cr × 2 - Ni × 8) / (100 × h) < 10 ... (1) Here, Fe, Cr, and Ni in formula (1) represent the content (mass%) of each element contained in the metal substrate, and 0 is used if none are contained. [2] The Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus according to [1], wherein the metal substrate contains 4 mass% or more of Ni. [3] The Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus according to [1] or [2], wherein the Ni coating layer is multilayered. [4] A method for manufacturing a Ni-coated substrate for a separator of an anion exchange membrane type water electrolysis apparatus, comprising a metal substrate and a Ni coating layer on the surface of the metal substrate, comprising: a step of setting the range of thickness h (μm) of the Ni coating layer to be formed on the surface of the metal substrate to a range that satisfies the following formula (1) and is 1 μm or less; and a step of forming the Ni coating layer on the surface of the metal substrate with a thickness within the set range, wherein the method for manufacturing a Ni-coated substrate for a separator of an anion exchange membrane type water electrolysis apparatus is: (Fe + Cr × 2 - Ni × 8) / (100 × h) < 10 ... (1) Here, Fe, Cr, and Ni in formula (1) represent the content (mass %) of each element contained in the metal substrate, and 0 is used if none is contained.

[0032] According to the present invention, in the environment where the separator of an anion exchange membrane type water electrolysis device is used, it is possible to provide a Ni-coated substrate for the separator of an anion exchange membrane type water electrolysis device, which has excellent corrosion resistance, excellent contact resistance characteristics with a porous transport layer, and excellent productivity.

[0033] According to the present invention, a separator for an anion exchange membrane type water electrolysis device having excellent corrosion resistance and contact resistance characteristics can be obtained, and thus an anion exchange membrane type water electrolysis device having excellent durability can be obtained at low cost. For the evaluation of corrosion resistance and contact resistance characteristics, reference can be made to the description of the examples.

[0034] Hereinafter, the present invention will be specifically described.

[0035] The Ni-coated substrate for the separator of the anion exchange membrane type water electrolysis device of the present invention (hereinafter, also simply referred to as the Ni-coated substrate) includes a metal substrate and a Ni coating layer provided on the surface of the substrate.

[0036] (1) Metal substrate The metal substrate (metal base) is not particularly limited, but it is preferable to use a metal plate. The metal plate is not particularly limited, but a steel plate is preferable, and specifically, a stainless steel plate, a steel plate made of ordinary steel, etc. are preferable. As the stainless steel plate, a ferritic stainless steel plate, an austenitic stainless steel plate, and a duplex stainless steel plate can be preferably used.

[0037] For example, suitable stainless steel sheets include SUS430 (Cr content: 16% by mass), SUS443J1 (Cr content: 21% by mass), SUS304 (Cr content: 18% by mass, Ni content: 8% by mass), SUS316L (Cr content: 17% by mass, Ni content: 12% by mass, Mo content: 2% by mass), and SUS329J1 (Cr content: 24% by mass, Ni content: 4% by mass). Furthermore, the metal substrate preferably contains 4% by mass or more Ni from the viewpoint of stability in high-alkaline, high-potential environments. A Ni content of 6% by mass or more is more preferable. In particular, SUS304 containing about 8% by mass Ni has high corrosion resistance and good workability in high-alkaline environments. Therefore, SUS304 is particularly advantageous as a metal substrate for separators in anion exchange membrane type water electrolysis devices used in highly alkaline, high-potential environments where strict corrosion resistance is required. Furthermore, from the standpoint of material cost, the metal substrate preferably contains 16% by mass or less of Ni.

[0038] Furthermore, in an anion exchange membrane type water electrolysis apparatus, considering the space and weight when the water electrolysis stack is constructed, the thickness of the metal plate used as the metal substrate for the separator is preferably in the range of 0.05 to 0.50 mm. If the thickness of the metal plate is less than 0.05 mm, the production efficiency of the metal plate decreases. On the other hand, if the thickness of the metal plate exceeds 0.50 mm, the space and weight when the water electrolysis stack is constructed increases. The thickness of the metal plate is more preferably 0.10 mm or more. Also, the thickness of the metal plate is more preferably 0.30 mm or less.

[0039] (2) Ni coating layer In the present invention, by providing a Ni coating layer on the surface of the metal substrate, excellent corrosion resistance and contact resistance characteristics are achieved simultaneously. Regarding the reason why the corrosion resistance and contact resistance characteristics are improved by providing a Ni coating layer on the surface of the metal substrate, the inventors of the present invention consider as follows. That is, Ni can ensure high corrosion resistance by forming a stable oxide film in a high-alkali, high-potential environment. Also, since it has high conductivity, it is considered that low contact resistance can be maintained. In the present invention, the high-alkali environment means an environment with a pH of 12 or more. Also, in the present invention, the high-potential environment means an environment with a potential of 0.6 V (vs SSE) or more.

[0040] And in the present invention, it is extremely important to control the film thickness of the above Ni coating layer within the following range according to the component composition of the metal substrate.

[0041] The thickness h (μm) of the Ni coating layer satisfies the following formula (1) and is 1 μm or less. (Fe + Cr×2 - Ni×8) / (100×h) < 10... (1) Here, Fe, Cr, and Ni in formula (1) represent the content (mass%) of each element contained in the metal substrate, and are set to 0 if not contained.

[0042] The above formula (1) defines the allowable lower limit for the thickness h of the Ni coating layer. By controlling the thickness h of the Ni coating layer within the range that satisfies the above formula (1), even when the Ni coating layer is made thinner, the corrosion resistance and contact resistance characteristics in the separator usage environment of the anion exchange membrane type water electrolysis device can be maintained. Regarding the reason, the inventors of the present invention consider as follows.

[0043] That is, usually, as the film thickness of the Ni coating layer decreases, the number of defects leading from the surface of the Ni coating layer to the metal substrate increases in the Ni coating layer. As a result, the metal substrate corrodes through the defects. On the other hand, if the film thickness of the Ni coating layer is controlled within the above range considering the corrosion resistance of the metal substrate, optimization of the corrosion resistance of the metal substrate and the defects of the Ni coating layer can be achieved, and as a result, the desired corrosion resistance can be obtained.

[0044] If the thickness h of the Ni coating layer does not satisfy equation (1) above, the number of defects in the Ni coating layer increases, and the corrosion resistance deteriorates easily. On the other hand, if the thickness h of the Ni coating layer exceeds 1 μm, the processing cost for forming the Ni coating layer increases, and the productivity of the Ni coated substrate decreases. Therefore, the upper limit of the thickness h of the Ni coating layer is set to 1 μm. Preferably, the thickness h of the Ni coating layer is 0.5 μm or less. The thickness of the Ni coating layer can be determined by the method described in the examples.

[0045] To form the Ni coating layer on the surface of the metal substrate, methods such as plating or physical vapor deposition (PVD) can be used. In particular, plating is preferred. In this case, the metal substrate is immersed in a plating bath adjusted to an appropriate composition using a conventionally known plating method, and electroplating or electroless plating is performed. The thickness (film thickness) of the Ni coating layer can be adjusted by the residence time in the plating bath, i.e., the plating time, in the case of plating. In the case of PVD, it can be adjusted by the deposition time, etc. The Ni coating layer may be composed of Ni or a Ni alloy. When the Ni coating layer is formed from a Ni alloy, other components besides Ni include Fe, etc. The Ni coating layer is a layer mainly composed of Ni. As an example, the Ni content in the Ni coating layer is 85% or more. Preferably, the Ni content in the Ni coating layer is 90% or more, more preferably 95% or more.

[0046] In the present invention, the Ni coating layer may be formed on one side of the metal substrate or on both sides. Furthermore, the Ni coating layer may be formed before processing the metal substrate into the desired separator shape or after processing it into the desired separator shape. Also, the Ni coating layer may be a single layer or a multilayer (two or more layers). If the Ni coating layer is multilayer, the thickness of the Ni coating layer is the sum of the thicknesses of all the Ni coating layers.

[0047] Furthermore, after forming the Ni coating layer, heat treatment may be applied to improve adhesion with the metal substrate. This forms an alloy layer at the interface between the Ni coating layer and the metal substrate, thereby improving adhesion between the Ni coating layer and the metal substrate.

[0048] Furthermore, by using multiple layers of Ni coating, corrosion resistance can be further improved in highly alkaline environments and high-load environments with large potential fluctuations. As mentioned above, if the Ni coating is thin, defects can exist that lead from the Ni coating to the metal substrate, and the metal substrate corrodes through these defects. By using multiple layers of Ni coating, defects that lead from the Ni coating to the metal substrate can be further reduced.

[0049] When forming a multilayer Ni coating on the surface of a metal substrate, the plating method or PVD method described above can be used. For example, when forming two Ni coating layers, the desired thickness of the Ni coating layer can be set using equation (1) above, and after forming a predetermined thickness of the Ni coating layer in the first plating step, the remaining thickness can be formed in the second plating step. The same applies when forming three or more Ni coating layers. That is, the formation of a Ni coating layer of the desired thickness can be done by dividing the plating or PVD process into three or more steps. Note that, from the viewpoint of corrosion resistance, two Ni coating layers are preferable. Also, from the viewpoint of film formation cost, three or fewer Ni coating layers are preferable.

[0050] A method for manufacturing a Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus according to one embodiment of the present invention may include the steps of: setting the range (target value) of the thickness h (μm) of the Ni coating layer to be formed on the surface of a metal substrate to a range (target value) that satisfies the above-mentioned formula (1) and is 1 μm or less; and forming a Ni coating layer on the surface of the metal substrate with a thickness within the set range.

[0051] The separators in anion exchange membrane type water electrolysis devices are used in harsh environments such as at a temperature of 80°C and in a 1 M (mol / L) KOH aqueous solution (pH: 12 or higher). Therefore, excellent corrosion resistance is required under these conditions (high alkaline environment). Furthermore, when cells are connected to form a water electrolysis stack, the contact resistance between the separator and the porous transport layer must be as low as possible. In light of these required characteristics, the following two evaluations were performed on the samples described later.

[0052] (1) Evaluation of corrosion resistance (stability in the separator usage environment) A sample (test area: 20 mm x 15 mm, both sides) was immersed in a 1 M KOH aqueous solution at a temperature of 80°C, and the sample was maintained at a potential of 1.2 V (vs. SSE) for 24 hours using Ag / AgCl (saturated KCl) as the reference electrode. The Fe and Cr content (elution amount) in the aqueous solution after 24 hours was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Based on the values ​​of Fe and Cr elution amounts after 24 hours, the corrosion resistance after 24 hours in the separator usage environment of the anion exchange membrane type water electrolysis device was evaluated according to the following criteria: ○ (Pass): The elution amount of both Fe and Cr after 24 hours is less than 30 μg / L × (Fail): The elution amount of at least one of Fe and Cr after 24 hours is 30 μg / L or more

[0053] (2) Evaluation of Contact Resistance Characteristics The contact resistance between the sample and the porous transport layer (Ni fiber material, manufactured by Bekart Totsuna Metal Fiber Co., Ltd.) was measured before and after the above corrosion resistance evaluation. The load was set to 1.0 MPa, and the contact resistance was measured after holding for 30 seconds and evaluated according to the following criteria. At this time, it was assumed that the electrical resistance in the thickness direction of the sample and the porous transport layer was sufficiently smaller than the contact resistance. ○ (Pass): Contact resistance of 5.0 mΩ・cm ２ The following is a failing grade (×): Contact resistance is 5.0 mΩ·cm ２ super

[0054] Furthermore, the separator of an anion exchange membrane type water electrolysis device may be required to exhibit excellent corrosion resistance even under the aforementioned environmental conditions (high alkaline environment) and when potential fluctuations are large. Therefore, for some of the samples described later, in addition to the evaluations in (1) and (2) above, the following two further evaluations were performed.

[0055] (3) Evaluation of corrosion resistance in high-load environments (stability in high-load separator usage environments with large potential fluctuations) A sample (test area: 20 mm x 15 mm, both sides) was immersed in a 1 M KOH aqueous solution at a temperature of 80°C. Using Ag / AgCl (saturated KCl) as the reference electrode, a cycle test was performed in which the sample was held at a potential of 1.2 V (vs. SSE) for 10 seconds and then at a potential of -0.9 V (vs. SSE) for 10 seconds, with this being considered one cycle, and this cycle was repeated 4000 times. The Fe and Cr content (elution amount) in the aqueous solution after the cycle test was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Based on the values ​​of Fe and Cr elution after this cycle test, the corrosion resistance after the cycle test in high-load separator usage environments of the anion exchange membrane type water electrolysis device was evaluated according to the following criteria. ◎ (Better): Fe and Cr elution levels are both less than 30 μg / L after 4000 cycles ○ (Better): Fe and Cr elution levels are both less than 100 μg / L after 4000 cycles, AND at least one of Fe and Cr elution levels is 30 μg / L or higher △: At least one of Fe and Cr elution levels is 100 μg / L or higher after 4000 cycles

[0056] (4) Evaluation of contact resistance characteristics after corrosion resistance evaluation in a high-load environment The contact resistance between the sample and the porous transport layer (Ni fiber, manufactured by Bekart Totsuna Metal Fiber Co., Ltd.) after the corrosion resistance evaluation in the high-load environment described above was measured. The load was set to 1.0 MPa, and the contact resistance was measured after holding for 30 seconds and evaluated according to the following criteria. At this time, it was assumed that the electrical resistance in the thickness direction of the sample and the porous transport layer was sufficiently smaller than the contact resistance. ◎ (better): Contact resistance of 20.0 mΩ・cm ２ Below ○ (Excellent): Contact resistance of 20.0 mΩ·cm ２ Super, 40.0mΩ・cm ２ Below, △: Contact resistance of 40.0 mΩ·cm ２ super

[0057] Example 1 SUS304 (Cr content: 18% by mass, Ni content: 8% by mass), SUS329J1 (Cr content: 24% by mass, Ni content: 4% by mass), SUS316L (Cr content: 17% by mass, Ni content: 12% by mass), SUS430 (Cr content: 16% by mass), and mild steel, all with a thickness of 0.1 mm, were used as metal substrates. After performing appropriate pretreatment such as degreasing on the metal substrates, a Ni coating layer with the thickness shown in Table 1 was formed on the metal substrates using the following plating bath composition and plating conditions to obtain a sample (Ni-coated steel sheet for separators in an anion exchange membrane type water electrolysis apparatus). Furthermore, for some metal substrates, two plating processes were performed using the following plating bath composition and plating conditions to form a two-layer Ni coating, and a sample (Ni-coated steel sheet for separators in an anion exchange membrane type water electrolysis device) was obtained (in the table, a single-layer Ni coating is indicated as "single layer," and a two-layer Ni coating is indicated as "double layer").

[0058] Using the samples thus obtained, various properties were evaluated in accordance with the procedure described above.

[0059] The thickness (film thickness) of the Ni coating layer was controlled in advance by investigating its relationship with the plating time. For comparison, samples without a Ni coating layer (indicated by "-" in the film thickness h column of Table 1) were also prepared, and their various properties were evaluated in the same manner as described above.

[0060] The thickness of the Ni coating layer was measured using the following method. First, the sample prepared as described above was cut into approximately 10 mm x 10 mm sections. Next, the cut samples were processed with a focused ion beam to create thin films for cross-sectional observation. Then, the thickness (film thickness) of the Ni coating layer was measured by observing the prepared thin films for cross-sectional observation with a transmission electron microscope (TEM). The thickness of the Ni coating layer was measured by taking the average of the thickness (film thickness) of the prepared thin films for cross-sectional observation at three arbitrary points.

[0061] (Plating bath composition and plating conditions for Ni coating layer) <Ni plating bath composition> Nickel chloride: 240 g / L Hydrochloric acid: 125 mL / L <Ni plating conditions> Temperature: 50°C Current density: 4 A / dm ２

[0062] Furthermore, when the Ni coating layer was to be multilayered, the first plating with the above plating bath composition and plating conditions formed a Ni coating layer with half the desired thickness, and then the second plating with the following plating bath composition and plating conditions formed the remaining thickness of the Ni coating layer to obtain the sample. <Ni plating bath composition (second plating)> Nickel sulfate: 300 g / L Nickel chloride: 40 g / L Boric acid: 30 g / L <Ni plating conditions (second plating)> Temperature: 50°C Current density: 1 A / dm ２ In addition, in the present invention, any known plating method, such as the PVD method, can be used as long as it can form the desired Ni coating layer, even if it is not the plating method described above.

[0063] For each sample obtained as described above, the results of evaluating (1) corrosion resistance (stability in the separator usage environment) and (2) contact resistance are summarized in Table 1. Furthermore, for some samples, the results of evaluating (3) corrosion resistance in a high-load environment (stability in a high-load separator usage environment with large potential fluctuations) and (4) contact resistance after evaluation of corrosion resistance in a high-load environment are summarized in Table 2.

[0064]

[0065]

[0066] Table 1 makes the following clear: (a) In all of the samples of the inventive example, the amount of Fe and Cr eluted after 24 hours in the corrosion resistance evaluation was small, and good corrosion resistance was obtained even when exposed for a long time to a highly alkaline, high potential environment such as the separator environment of an anion exchange membrane type water electrolysis device. In addition, all of the samples of the inventive example obtained excellent contact resistance characteristics. (b) On the other hand, the samples of Comparative Examples No. 1, 12, and 16 all did not have a Ni coating layer formed, and therefore the desired corrosion resistance and contact resistance characteristics were not obtained. In particular, since samples No. 12 and 16 did not contain Ni in the steel plate, severe corrosion was observed during the corrosion resistance test, and precipitation was observed in the test aqueous solution. Therefore, the amount of Fe and Cr eluted could not be measured (indicated as "unmeasurable" in Table 1). In addition, the contact resistance could not be measured because the deterioration of the sample surface after the corrosion resistance test was severe (indicated as "unmeasurable" in Table 1). (c) In addition, Comparative Example No. In all of the samples 2, 13, and 17, the thickness of the Ni coating layer was not appropriate for the component composition in the steel sheet, and therefore the desired corrosion resistance and contact resistance characteristics were not obtained. (d) Furthermore, in the sample of Comparative Example No. 9, the thickness of the Ni coating layer exceeded the appropriate range, resulting in a plating treatment time of more than 10 minutes and reduced productivity.

[0067] Table 2 makes the following clear: (e) The sample of the inventive example with two Ni coating layers exhibits superior corrosion resistance even in corrosion resistance evaluation under high-load environments. Furthermore, the sample of the inventive example exhibits superior contact resistance characteristics even after corrosion resistance evaluation under high-load environments.

Claims

1. A Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus, comprising a metal substrate and a Ni coating layer on the surface of the metal substrate, wherein the thickness h (μm) of the Ni coating layer satisfies the following equation (1) and is 1 μm or less: (Fe + Cr × 2 - Ni × 8) / (100 × h) < 10 ... (1) Here, Fe, Cr, and Ni in equation (1) represent the content (mass%) of each element contained in the metal substrate, and 0 is used if none is contained.

2. The Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus according to claim 1, wherein the metallic substrate contains 4% by mass or more of Ni.

3. The Ni-coated substrate for a separator in an anion exchange membrane type water electrolysis apparatus according to claim 1 or 2, wherein the Ni-coated layer is multilayered.

4. A method for manufacturing a Ni-coated substrate for a separator of an anion exchange membrane type water electrolysis apparatus, comprising a metal substrate and a Ni coating layer on the surface of the metal substrate, the method comprising: setting the range of thickness h (μm) of the Ni coating layer to be formed on the surface of the metal substrate to a range that satisfies the following formula (1) and is 1 μm or less; and forming the Ni coating layer on the surface of the metal substrate with a thickness within the set range. (Fe + Cr × 2 - Ni × 8) / (100 × h) < 10 ... (1) Here, Fe, Cr, and Ni in formula (1) represent the content (mass%) of each element contained in the metal substrate, and 0 is used if none are contained.

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