Diffusion layer

Abstract

To provide a diffusion layer that is excellent in corrosion resistance and electrical conductivity, and furthermore is low-cost.SOLUTION: The diffusion layer comprises: a porous substrate composed of electrical conductive material; a first coating film formed on one surface of the substrate and including a metal nitride having an electrical conductivity of 5×105 S / m or higher; and a second coating film formed on the other surface of the substrate and including a precious metal, a precious metal alloy including two or more precious metal elements, and / or a precious metal oxide having electrical conductivity. The metal nitride preferably has composition represented by MxN, wherein M is one or more metal elements selected from the group consisting of Nb, Ti, Ta, Zr, and V, 0.7≤x≤1.3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a diffusion layer, and more particularly to a diffusion layer used in a gas diffusion layer of a polymer electrolyte fuel cell (PEFC) or a gas diffusion layer of a polymer electrolyte membrane (PEM) water electrolysis device. [Background technology]

[0002] A polymer electrolyte fuel cell comprises a membrane electrode assembly (MEA) in which electrodes (catalyst layers) containing a catalyst are bonded to both sides of an electrolyte membrane. A gas diffusion layer (GDL) is disposed on the outside of the MEA, and a separator (also called a current collector) with a gas flow path is disposed on the outside of that. A polymer electrolyte fuel cell typically comprises a structure (fuel cell stack) in which multiple unit cells each consisting of an MEA, a gas diffusion layer, and a separator are stacked. When a fuel gas and an oxidant gas are supplied to the anode and cathode of such a fuel cell, respectively, water is produced at the cathode and electricity is simultaneously generated.

[0003] On the other hand, PEM water electrolysis devices have a structure similar to that of polymer electrolyte fuel cells, but they operate in the opposite direction to polymer electrolyte fuel cells. That is, when water is supplied to the oxygen electrode and electricity is applied between the electrodes, electrolysis of water proceeds, and hydrogen and oxygen can be extracted.

[0004] In a PEM water electrolysis device, the gas diffusion layer is also called a porous transport layer (PTL). In the present invention, the term "diffusion layer" refers to these collectively, that is, to the member inserted between the MEA and the separator, regardless of the application of the MEA.

[0005] In polymer electrolyte fuel cells and PEM water electrolysis systems, polyperfluorocarbon sulfonic acid membranes are typically used as electrolyte membranes. Therefore, the diffusion layers are exposed to a strongly acidic atmosphere during use. If the surface of the diffusion layer oxidizes during use, a high-resistance layer forms on the contact surface with the electrode (catalyst layer) or separator, inhibiting the electrode reaction or electrolysis reaction.

[0006] Therefore, various proposals have been made in the past to solve this problem. For example, Non-Patent Document 1 discloses an anode gas diffusion layer for a PEM water electrolysis cell made of Pt-coated porous titanium. The document states that, since the anode side has a high potential, the surface of the anode gas diffusion layer made of titanium needs to be coated with Pt in order to improve durability.

[0007] As described in Non-Patent Document 1, coating the surface of porous titanium with Pt improves the corrosion resistance of the anode gas diffusion layer. However, the method described in Non-Patent Document 1 is expensive because it uses an expensive precious metal (Pt).

[0008] Furthermore, plating has traditionally been used to coat the anode gas diffusion layer with platinum. (a) Because it is a wet process, it requires a multi-step process, including pre-treatment (e.g., roughening the surface) to make it easier to plate, and post-treatment such as cleaning. (b) It is a wasteful and expensive process due to low utilization of expensive precious metal raw materials. (c) In order to completely cover the entire surface of the porous Ti substrate with a Pt coating, the thickness of the Pt coating needs to be about 1 μm. There were problems such as: Furthermore, there has been no example proposed to date of a diffusion layer that can be manufactured without using a high-cost process while significantly reducing the amount of expensive materials such as precious metals used. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Special feature SPECIAL REPORTS, Toshiba Review, Vol.73, No.3 (May 2018) 9-12, "Precious metal saving electrode for PEM water electrolysis" Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is to provide a diffusion layer that is excellent in corrosion resistance and conductivity and is also low in cost. [Means for solving the problem]

[0011] In order to solve the above problems, the diffusion layer according to the present invention comprises: a porous substrate made of a conductive material; A conductive film having a conductivity of 5×10 formed on one surface of the substrate 5 a first coating containing a metal nitride having a surface roughness of S / m or more; a second coating formed on the other surface of the substrate and containing a precious metal, a precious metal alloy containing two or more kinds of precious metal elements, and / or a conductive precious metal oxide; The gist is that it is equipped with the following. [Effects of the Invention]

[0012] Although the separator-side surface of the substrate is exposed to a strongly acidic atmosphere, it does not directly contact the MEA, so it does not require the same high oxidation resistance as the MEA-side surface. Furthermore, certain metal nitrides have inferior oxidation resistance compared to noble metals, but they possess sufficient corrosion resistance and electrical conductivity to protect the separator-side surface. Furthermore, metal nitride coatings can be deposited using a relatively low-cost sputtering method. Therefore, by forming a first coating containing a metal nitride on the separator-side surface of the substrate and a second coating containing a precious metal, a precious metal alloy, or a precious metal oxide on the MEA-side surface, a diffusion layer with excellent corrosion resistance and conductivity, as well as low cost, can be obtained. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the relationship between current density and cell voltage for the PEM water electrolysis cells obtained in Example 1 and Comparative Examples 1 to 3. [Figure 2] FIG. 10 is a diagram showing the relationship between the thickness of a TiN coating and the contact resistance of the TiN coating after voltage application. [Figure 3] FIG. 1 is a graph showing the relationship between the amount x of Zr contained in a ZrxN coating and the contact resistance of the ZrxN coating after voltage application. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will be described in detail below. [1. Diffusion layer] The diffusion layer according to the present invention comprises: a porous substrate made of a conductive material; A conductive film having a conductivity of 5×10 formed on one surface of the substrate 5 a first coating containing a metal nitride having a surface roughness of S / m or more; a second coating formed on the other surface of the substrate and containing a precious metal, a precious metal alloy containing two or more kinds of precious metal elements, and / or a conductive precious metal oxide; It is equipped with:

[0015] [1.1. Base material] The substrate is a porous member made of a conductive material. As mentioned above, the diffusion layer is inserted between the MEA and the separator. Therefore, the substrate (a) Electrical conductivity sufficient to allow electrons to be exchanged between the MEA and the separator; (b) Porosity sufficient to allow the supply of raw materials and fuel from the separator to the MEA and the discharge of reaction products from the MEA to the separator. It is necessary to have the following.

[0016] The material of the substrate is not particularly limited as long as it exhibits the above-mentioned functions. Examples of the material of the substrate include: (a) Metal mesh, foam metal or sintered metal made of various metals such as titanium or titanium alloy, stainless steel, aluminum or aluminum alloy, (b) Porous carbon sheets such as carbon paper and carbon nonwoven fabric; etc.

[0017] Among these, titanium and titanium alloys form a passive film mainly composed of TiO2 on their surface under oxidizing conditions, which has the advantage that titanium ions and other substances are less likely to be eluted even when part of the substrate surface is exposed. Stainless steel has the advantages of being inexpensive and easy to process. Aluminum, aluminum alloys, and polymeric materials have the advantages of being inexpensive, lightweight, and easy to process.

[0018] [1.2. First coating] [1.2.1. Materials] The first coating contains a metal nitride. In the present invention, the term "metal nitride" refers to a metal nitride containing a metal element M and having a conductivity of 5×10 5 This refers to nitrides with a value of S / m or more. In order to exchange electrons with the separator, the higher the electrical conductivity of the metal nitride constituting the first coating, the better. The electrical conductivity is preferably 8×10 5 S / m or more, more preferably 1×10 6 S / m or more.

[0019] The metal nitride is preferably a compound having a composition represented by the following formula (1). M x N …(1) however, M is at least one metal element selected from the group consisting of Nb, Ti, Ta, Zr, and V; 0.7≦x≦1.3.

[0020] The metal element M is preferably Nb, Ti, Ta, Zr, or V. Metal nitrides containing these metal elements M all exhibit relatively high corrosion resistance and relatively high electrical conductivity. The metal nitride may contain any one of these metal elements M, or may contain two or more of them.

[0021] In formula (1), x represents the ratio of the number of metal element M atoms to the number of N atoms. If x is too small, a single phase may not be formed, and a mixture with components that are inferior in electrical conductivity and corrosion resistance may result. Therefore, x is preferably 0.7 or more. x is preferably 0.8 or more, and more preferably 0.9 or more. On the other hand, if x is too large, a metallic phase may be formed, resulting in a decrease in corrosion resistance. Therefore, x is preferably 1.3 or less. x is preferably 1.2 or less, and more preferably 1.1 or less.

[0022] Any of the metal nitrides having the predetermined composition has high corrosion resistance in a fuel cell environment or a water electrolysis device environment, and also has high electrical conductivity, making it suitable for the first coating. The first coating may contain any one of these metal nitrides, or may contain two or more of them. The metal nitride constituting the first coating preferably contains one or more elements selected from the group consisting of Nb, Ti, and Zr as the metal element M. All of these metal nitrides have both high corrosion resistance and high electrical conductivity.

[0023] The first coating preferably consists essentially of metal nitride, but may contain other phases as long as they do not impair the high corrosion resistance and high electrical conductivity. Other phases include, for example: (a) unavoidable impurities, (b) highly corrosion-resistant materials other than metal nitrides; etc.

[0024] 1.2.2. Thickness The thickness of the first coating is not particularly limited, and an optimum thickness can be selected depending on the purpose. Generally, if the thickness of the first coating is too thin, sufficient corrosion resistance may not be obtained. Therefore, the thickness of the first coating is preferably 30 nm or more. The thickness of the first coating is preferably 40 nm or more, and more preferably 50 nm or more. On the other hand, if the thickness of the first coating is too thick, adhesion to the substrate decreases, and peeling or cracking may occur. Therefore, the thickness of the first coating is preferably 500 μm or less. The thickness of the first coating is preferably 300 nm or less, and more preferably 200 nm or less.

[0025] [1.2.3. Location of first coating] The first coating is formed on one surface of the substrate. In the present invention, "one surface" refers to the separator-side surface of a polymer electrolyte fuel cell or a PEM water electrolysis device. The first coating may be formed on the entire one surface of the substrate, or on only a portion of the one surface.

[0026] The separator typically has a flow path for the flow of fuel for power generation, oxidant, raw materials for electrolysis, or reaction products. The diffusion layer typically does not contact the separator over the entire surface of one of the surfaces, but only the protrusions that form the flow path. Even if a high-resistance layer is formed on the surface of one of the surfaces of the substrate that does not contact the separator, this does not significantly impede the exchange of electrons. Therefore, the first coating may be formed only on the surface of one of the surfaces that contacts the separator.

[0027] To prevent an increase in contact resistance due to the formation of a high-resistance layer, the first coating preferably covers 90% or more of the surface of the substrate that comes into contact with the separator. The first coating preferably covers 95% or more, and more preferably 99% or more, of the surface that comes into contact with the separator. The first coating preferably completely covers the surface that comes into contact with the separator.

[0028] [1.3. Second coating] [1.3.1. Materials] The second coating contains a precious metal, a precious metal alloy containing two or more precious metal elements, or a conductive precious metal oxide. The second coating is formed on the MEA-side surface of the substrate. The reason why the second coating is made of a precious metal, a precious metal alloy, or a precious metal oxide is that the second coating is required to have higher corrosion resistance than the first coating.

[0029] Specific examples of the material for the second coating include: (a) a noble metal consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, or Os; (b) Precious metal alloys containing two or more precious metal elements, such as Pt-Pd alloys, Pt-Rh alloys, Pt-Ir alloys, Pd-Ir alloys, and Pt-Au alloys; (c) Conductive noble metal oxides such as platinum oxide, rhodium oxide, iridium oxide, and palladium oxide etc. The second coating may contain any one of these, or may contain a mixture of two or more of them. In particular, the second coating is preferably made of Pt or Au, since these have high corrosion resistance and electrical conductivity.

[0030] The second coating preferably consists essentially of a precious metal, a precious metal alloy, and / or a precious metal oxide, but may contain other phases as long as they do not impair the high corrosion resistance and high electrical conductivity. Other phases include, for example: (a) unavoidable impurities, (b) Highly corrosion-resistant materials other than precious metals, precious metal alloys, and precious metal oxides; etc.

[0031] 1.3.2 Thickness The thickness of the second coating is not particularly limited, and an optimum thickness can be selected depending on the purpose. Generally, if the thickness of the second coating is too thin, sufficient corrosion resistance may not be obtained. Therefore, the thickness of the second coating is preferably 30 nm or more. The thickness of the second coating is preferably 40 nm or more, and more preferably 50 nm or more. On the other hand, if the thickness of the second coating is too thick, adhesion to the substrate decreases, and peeling or cracking may occur. Furthermore, if the thickness of the second coating is too thick, costs increase. Therefore, the thickness of the second coating is preferably 500 μm or less. The thickness of the second coating is preferably 300 nm or less, and more preferably 200 nm or less.

[0032] [1.3.3. Location of second coating] The second coating is formed on the other surface of the substrate. In the present invention, "the other surface" refers to the surface on the MEA side of a polymer electrolyte fuel cell or a PEM water electrolysis device. The diffusion layer usually has a size equal to or larger than that of the catalyst layer of the MEA. Furthermore, no gap is usually intentionally formed between the MEA and the diffusion layer. Therefore, the second coating is preferably formed over 90% or more of the other surface of the substrate. The second coating preferably covers the entire surface of the other surface.

[0033] To suppress an increase in contact resistance due to the formation of a high-resistance layer, the second coating preferably covers 90% or more of the surface of the other surface of the substrate that comes into contact with the MEA. The second coating preferably covers 95% or more, and more preferably 99% or more, of the surface that comes into contact with the MEA. The second coating preferably completely covers the surface that comes into contact with the MEA.

[0034] [1.4. Usage] The diffusion layer according to the present invention comprises: (a) Anode-side gas diffusion layer or cathode-side gas diffusion layer for a polymer electrolyte fuel cell (b) Oxygen electrode side gas diffusion layer or hydrogen electrode side gas diffusion layer for PEM water electrolysis device It can be used for the following purposes: The diffusion layer according to the present invention is particularly suitable as an oxygen electrode-side gas diffusion layer in a PEM water electrolysis device. Because the oxygen electrode-side gas diffusion layer is exposed to a high potential, applying the diffusion layer according to the present invention to the oxygen electrode-side gas diffusion layer can improve the durability of the PEM water electrolysis device.

[0035] [2. Manufacturing method of diffusion layer] The method for manufacturing a diffusion layer according to the present invention includes the steps of: a first step of forming a first coating containing a metal nitride on one surface of a substrate using a dry coating method (A); a second step of forming a second coating film containing a precious metal, a precious metal alloy containing two or more kinds of precious metal elements, and / or a conductive precious metal oxide on the other surface of the substrate using a dry film formation method (B); It is equipped with:

[0036] [2.1. 1st step] First, a first coating containing a metal nitride is formed on one surface of a substrate using a dry coating method (A) (first step). In the present invention, the type of dry coating method (A) is not particularly limited as long as it is capable of forming a first coating that is pinhole-free, thin, and uniform in thickness. Examples of dry coating methods (A) include sputtering, PVD, ion plating, and vapor deposition. In particular, sputtering is suitable as a method for forming the first coating because it allows a thin and uniform first coating to be formed at low cost and also makes it easy to form a film over a large area.

[0037] [2.2. 2nd process] Next, a dry film formation method (B) is used to form a second coating containing a precious metal, a precious metal alloy containing two or more precious metal elements, and / or a conductive precious metal oxide on the other surface of the substrate (second step). In the present invention, the type of dry film formation method (B) is not particularly limited as long as it is capable of forming a second coating that is pinhole-free, thin, and uniform in thickness. Examples of dry film formation methods (B) include sputtering, PVD, ion plating, and vapor deposition. Dry film formation method (B) may be the same as or different from dry film formation method (A). In particular, sputtering is suitable as a method for forming the second coating because it allows a thin and uniform second coating to be formed at low cost and also makes it easy to form a film over a large area.

[0038] [2.3. Third step] The method for producing a diffusion layer according to the present invention includes the steps of: a third step of heat-treating the first coating at a temperature of 500°C to 800°C in an inert atmosphere or a reducing atmosphere to improve the crystallinity of the metal nitride; It may further comprise:

[0039] When the first coating is formed using the dry film formation method (A), the crystallinity of the first coating may decrease, resulting in a decrease in electrical conductivity. On the other hand, if a heat treatment is performed after the first coating is formed, the crystallinity of the first coating may be improved. Furthermore, the crystallinity of the metal nitride may be improved by the heat treatment, which may further improve the electrical conductivity of the first coating. Therefore, the first coating may be heat-treated as needed.

[0040] It is preferable to select the optimum conditions for the heat treatment temperature depending on the purpose. Generally, if the heat treatment temperature is too low, the heat treatment cannot be completed within a practical time. In addition, the crystallinity of the metal nitride may not be improved. Therefore, the heat treatment temperature is preferably 500°C or higher. The heat treatment temperature is preferably 600°C or higher, and more preferably 650°C or higher. On the other hand, if the heat treatment temperature is too high, the substrate may be damaged. Therefore, the heat treatment temperature is preferably 800° C. or less. The heat treatment temperature is preferably 780° C. or less, and more preferably 740° C. or less.

[0041] The heat treatment time is selected optimally depending on the heat treatment temperature. Generally, the higher the heat treatment temperature, the shorter the time required to complete the crystallinity improvement treatment of the metal nitride. The suitable heat treatment time is usually about 2 to 10 hours, although it depends on the heat treatment temperature.

[0042] [3. Effect] The diffusion layers used in polymer electrolyte fuel cells and PEM water electrolysis systems are exposed to a strongly acidic atmosphere during use, and therefore require high corrosion resistance. To solve this problem, a platinum coating was formed on both sides of the diffusion layer substrate using a plating method. However, to form a pinhole-free coating using the plating method, the platinum coating needed to be approximately 1 μm thick. Therefore, conventional diffusion layers were expensive.

[0043] In contrast, the separator-side surface of the substrate is exposed to a strongly acidic atmosphere but does not come into direct contact with the MEA, so it does not require as high oxidation resistance as the MEA-side surface. Metal nitrides are less resistant to oxidation than noble metals, but they possess both corrosion resistance and electrical conductivity sufficient to protect the separator-side surface. Furthermore, coatings containing metal nitrides can be deposited using a relatively low-cost sputtering method. Therefore, by forming a first coating containing a metal nitride on the separator-side surface of the substrate and a second coating containing a precious metal, a precious metal alloy, and / or a precious metal oxide on the MEA-side surface, a diffusion layer with excellent corrosion resistance and conductivity, as well as low cost, can be obtained.

[0044] The diffusion layer according to the present invention achieves high corrosion resistance and high conductivity despite using a smaller amount of expensive precious metal than conventional diffusion layers, and therefore can provide a low-cost fuel cell system and water electrolysis system. Furthermore, since the coating is formed by a low-cost dry film formation method (for example, sputtering) rather than a high-cost plating method, not only the material cost but also the process cost is low. [Example]

[0045] (Example 1, Comparative Examples 1 to 3) 1. Sample Preparation [1.1. Preparation of oxygen electrode side diffusion layer] 1.1.1. Example 1 A Ti mesh was used as the substrate. NbN and Pt were used as sputtering targets for the first and second coatings, respectively. The targets were loaded into a sputtering target holder, and a NbN coating was formed on one side of the Ti mesh (the side facing the separator) by sputtering, and a Pt coating was formed on the other side (the side facing the MEA). The thicknesses of the NbN coating and the Pt coating were each 100 nm.

[0046] 1.1.2. Comparative Example 1 A Pt coating was formed on both sides of the Ti mesh by plating, with a thickness of 1 μm.

[0047] 1.1.3. Comparative Example 2 NbN films were formed on both sides of the Ti mesh by sputtering under the same conditions as in Example 1.

[0048] 1.1.4. Comparative Example 3 The uncoated Ti mesh was used as the oxygen electrode diffusion layer.

[0049] [1.2. Preparation of water electrolysis cell] An oxygen electrode catalyst sheet was fabricated by adding an ionomer to the oxygen electrode catalyst IrO2, and a hydrogen electrode catalyst sheet was fabricated by adding an ionomer to the hydrogen electrode catalyst platinum / carbon (Pt / C). Next, an oxygen electrode catalyst sheet and a hydrogen electrode catalyst sheet were transferred onto both sides of the electrolyte membrane by thermal transfer to fabricate a membrane electrode assembly (MEA). Furthermore, an oxygen electrode diffusion layer and an oxygen electrode flow path block (separator) were placed on one side of the MEA, and a hydrogen electrode diffusion layer and a hydrogen electrode flow path block (separator) were placed on the other side.

[0050] The oxygen electrode side diffusion layer used was the diffusion layer prepared in [1.1.]. In Example 1, the diffusion layer was installed so that the Pt coating was in contact with the MEA. The oxygen electrode side flow path block used a Pt-plated Ti material. Furthermore, the hydrogen electrode side diffusion layer and the hydrogen electrode side flow path block were each made of carbon material. After assembling the PEM water electrolysis cell, the airtightness was inspected by a differential pressure test, and then the cell was subjected to a water electrolysis evaluation test.

[0051] 2. Test Method Water electrolysis was carried out with the PEM water electrolysis cell temperature kept constant at 80°C. Furthermore, the current density was set to 3.0 A / cm 2 The change in cell voltage when the voltage was increased to

[0052] [3. Results] Fig. 1 shows the relationship between the current density and the cell voltage for the PEM water electrolysis cells obtained in Example 1 and Comparative Examples 1 to 3. The following can be seen from Fig. 1. (1) Example 1 exhibited a low voltage almost equivalent to that of Comparative Example 1, which used a conventional Pt-plated diffusion layer. In the case of Example 1, the current density was 3.0 A / cm 2 The voltage at this temperature was approximately 1.7 V, demonstrating excellent cell characteristics. It was confirmed that even with an increase in current density, there was no increase in resistance due to corrosion, and electrical conductivity and corrosion resistance were maintained.

[0053] (2) By changing the method for forming the Pt coating from plating to sputtering, the thickness of the Pt coating could be reduced to 1 / 10. Furthermore, by coating only one side with Pt, the amount of Pt used could be halved. As a result, the total amount of Pt used could be reduced to 1 / 20. The coated area using the sputtering method was about one-fifth of that using the plating method. In other words, in Example 1, equivalent water electrolysis performance could be achieved with an amount of Pt used that was about two orders of magnitude less than that used in Comparative Example 1.

[0054] (3) When a Ti mesh diffusion layer with NbN sputtered on both sides was used (Comparative Example 2), the current density was 3.0 A / cm 2 The voltage rose to about 2.0 V. In the case of the uncoated Ti mesh diffusion layer (Comparative Example 3), the cell voltage increased rapidly with increasing current density. This is thought to be because corrosion formed a highly resistive oxide layer on the surface, increasing the resistance.

[0055] Examples 2 to 5 1. Sample Preparation A Ti substrate (0.1 × 100 × 50 mm: manufactured by Nilaco Corporation) was used as the substrate. TiN (Example 2), VN (Example 3), ZrN (Example 4), or TaN (Example 5) was used as the target. A metal nitride coating was formed on the surface of the Ti substrate using a sputtering method. The atmosphere during sputtering was an Ar atmosphere, and the film thickness was approximately 100 nm.

[0056] 2. Test Method 2.1. Voltage application A 1 L separable flask was charged with 800 mL of 0.01 N sulfuric acid solution and the sample, and the flask was then placed on a mantle heater. The sulfuric acid solution and the sample were then heated to 80°C using the mantle heater. While the sample temperature was maintained at 80°C, a voltage of 2.0 V was applied to the sample for 6 hours.

[0057] [2.2. Contact resistance] To measure the change in resistance before and after voltage application, the contact resistance of each sample was determined. A load cell was used to apply a pressure of 1 MPa to the sample (1 cm x 2 cm), and a current of 0 to 0.5 A was applied perpendicular to the sample surface, measuring the voltage. The contact resistance was calculated from the voltage value.

[0058] [3. Results] The contact resistance after voltage application is shown in Table 1. It was found that in all of Examples 2 to 5, there was no large change in resistance before and after voltage application, and low contact resistance was exhibited even after voltage application.

[0059] [Table 1]

[0060] Example 6 1. Sample Preparation A Ti substrate (0.1 × 100 × 50 mm: manufactured by Nilaco Corporation) was used as the substrate. TiN was used as the target. A TiN coating was formed on the surface of the Ti substrate by sputtering. The sputtering atmosphere was an Ar atmosphere, and the film thickness was approximately 10 to 1000 nm.

[0061] [2. Test Method and Results] The contact resistance after voltage application was determined in the same manner as in Example 2. Figure 2 shows the relationship between the thickness of the TiN film and the contact resistance of the TiN film after voltage application. From Figure 2, when the thickness of the TiN film is 30 nm or more and 500 nm or less, the contact resistance was 10 mΩcm even after voltage application. 2 It can be seen that the following low contact resistance is maintained (that is, high corrosion resistance and high conductivity are maintained even after voltage application).

[0062] Example 7 1. Sample Preparation The substrate was a Ti substrate (0.1 × 100 × 50 mm, manufactured by Nilaco Corporation). The target was Zr x N (x = 0.3 to 1.6) was used. Zr was deposited on the surface of the Ti substrate by sputtering. x The sputtering atmosphere was Ar, and the film thickness was approximately 100 nm.

[0063] [2. Test Method and Results] The contact resistance after voltage application was determined in the same manner as in Example 2. x The amount of Zr contained in the N coating, x, and Zr after voltage application x Figure 3 shows the relationship between the contact resistance of the N coating and the contact resistance of the N coating. When 0.3≦x≦1.6, the contact resistance after voltage application is 50mΩcm. 2 Furthermore, when 0.5≦x≦1.4, the contact resistance after voltage application is 20 mΩcm 2 Furthermore, when 0.7≦x≦1.3, the resistance remains below 10 mΩcm even after voltage application. 2 It can be seen that the following low contact resistance is maintained (that is, high corrosion resistance and high conductivity are maintained even after voltage application).

[0064] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0065] The diffusion layer according to the present invention can be used as a gas diffusion layer for a polymer electrolyte fuel cell, a gas diffusion layer for a polymer electrolyte membrane (PEM) water electrolysis device, or the like.

Claims

1. a porous substrate made of a conductive material; A conductive film having a conductivity of 5×10 formed on one surface of the substrate 5 a first coating containing a metal nitride having a viscosity of S / m or more; a second coating formed on the other surface of the substrate, the second coating including a precious metal, a precious metal alloy including two or more kinds of precious metal elements, and / or a conductive precious metal oxide; A diffusion layer comprising:

2. The diffusion layer according to claim 1 , wherein the metal nitride has a composition represented by the following formula (1): M x N …(1) however, M is at least one metal element selected from the group consisting of Nb, Ti, Ta, Zr, and V; 0.7≦x≦1.

3.

3. 3. The diffusion layer according to claim 2, wherein M is at least one metal element selected from the group consisting of Nb, Ti, and Zr.

4. The diffusion layer according to claim 1 , wherein the first coating has a thickness of 30 nm to 500 nm.

5. The diffusion layer according to claim 1 , wherein the first coating covers all or part of one surface of the substrate.

6. The diffusion layer according to claim 1 , wherein the second coating is made of Pt or Au.

7. The diffusion layer according to claim 1 , wherein the second coating has a thickness of 30 nm to 500 nm.

8. The diffusion layer according to claim 1 , wherein the second coating covers 90% or more of the other surface of the substrate.

9. 9. The diffusion layer according to claim 1, wherein the substrate is made of titanium or a titanium alloy.

10. The diffusion layer according to any one of claims 1 to 9, which is used as a gas diffusion layer for a polymer electrolyte fuel cell (PEFC) or a gas diffusion layer for a polymer electrolyte membrane (PEM) water electrolysis cell.

11. The diffusion layer according to claim 10 , wherein the first coating covers 90% or more of the surface of the substrate that comes into contact with the separator.

12. 12. The diffusion layer according to claim 10, wherein the second coating covers 90% or more of the surface of the other surface of the substrate that comes into contact with the membrane electrode assembly.

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