Metal porous body, fuel cell, and method for manufacturing metal porous body

Abstract

The metal porous body according to one aspect of the present disclosure is a sheet-like metal porous body, which includes a skeleton having a three-dimensional network structure, wherein the skeleton contains an alloy containing at least nickel (Ni) and chromium (Cr), the skeleton 11 is a solid solution with iron (Fe), the skeleton includes a chromium oxide (Cr2O3) layer as the outermost layer and includes a chromium carbide layer located below the chromium oxide layer, the thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and the thickness of the chromium carbide layer is 0.1 μm or more and 1 μm or less.

Description

Technical Field

[0001] The present disclosure relates to a metal porous body, a fuel cell, and a method for manufacturing a metal porous body. This application claims the priority of Japanese Patent Application No. 2018-168102 filed on September 7, 2018, and the entire disclosure of this application is incorporated herein by reference. Background Art

[0002] A conventionally known method for manufacturing a metal porous body having a high porosity and a large surface area involves forming a metal layer on the surface of a resin porous body such as a resin foam. For example, a metal porous body can be manufactured by subjecting a resin molded body including a skeleton having a three-dimensional network structure to a conductivity treatment so that the surface of the skeleton has conductivity, then performing electroplating to form a metal layer on the skeleton, and then burning out the resin molded body as needed.

[0003] The metal porous body has various applications, and some applications require the skeleton to have high corrosion resistance. Examples of known metal porous bodies having high corrosion resistance include metal porous bodies having a nickel-chromium alloy skeleton.

[0004] Japanese Patent Laid-Open No. 2012-149282 (Patent Document 1) teaches a method for manufacturing a metal porous body containing an alloy of nickel and chromium, which involves preparing a metal porous body including a nickel skeleton (hereinafter also referred to as "nickel porous body"), then performing plating to form a chromium layer on the surface of the skeleton, and then performing heat treatment to diffuse chromium.

[0005] Japanese Patent Laid-Open No. 08-013129 (Patent Document 2) teaches a method for manufacturing a metal porous body containing an alloy of nickel and chromium, which involves embedding a nickel porous body into a powder containing Al, Cr, and NH4Cl or their compounds, and then performing heat treatment in an atmosphere filled with Ar gas, H2 gas, and / or the like to cause diffusion penetration.

[0006] Citation List

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open No. 2012-149282

[0009] Patent Document 2: Japanese Patent Laid-Open No. 08-013129 Summary of the Invention

[0010] The metal porous body according to one aspect of the present disclosure is

[0011] A metal porous body, which is in a sheet shape and includes a skeleton having a three-dimensional network structure,

[0012] wherein

[0013] The framework contains an alloy containing at least nickel (Ni) and chromium (Cr), and the framework 11 is a solid solution with iron (Fe).

[0014] The framework includes a chromium oxide (Cr2O3) layer as the outermost layer and includes a chromium carbide layer located below the chromium oxide layer.

[0015] The thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and

[0016] The thickness of the chromium carbide layer is 0.1 μm or more and 1 μm or less.

[0017] A method for manufacturing a metal porous body according to an aspect of the present disclosure includes:

[0018] Preparing a porous body including a framework having a three-dimensional network structure and containing nickel as a main component, and the preparation includes:

[0019] Conductivizing the surface of the framework of the resin molded body by coating carbon powder on the surface of the framework of the resin molded body including a framework having a three-dimensional network structure;

[0020] Performing nickel plating to coat the surface of the framework of the resin molded body having conductivity thereby with nickel;

[0021] Subsequently removing the resin molded body by heat treatment in an oxidizing atmosphere; and

[0022] After removing the resin molded body, performing heat treatment in a reducing atmosphere containing water vapor to reduce the amount of carbon remaining in the nickel; and

[0023] Forming an alloy containing at least nickel and chromium to obtain a metal porous body, and the forming includes embedding the porous body into a powder containing chromium (Cr), aluminum oxide (Al2O3), and ammonium chloride (NH4Cl), and then performing heat treatment to initiate the diffusion penetration of chromium into the framework. Brief Description of the Drawings

[0024] Figure 1 is a schematic diagram of an exemplary metal porous body according to an embodiment of the present disclosure.

[0025] Figure 2 is a cross-sectional photograph of an exemplary metal porous body according to an embodiment of the present disclosure.

[0026] Figure 3 is an enlarged view schematically showing a partial cross-section of an exemplary metal porous body according to an embodiment of the present disclosure.

[0027] Figure 4A photograph of a polyurethane foam resin, which is an exemplary resin molded body including a skeleton having a three-dimensional network structure.

[0028] Figure 5 A schematic diagram of a fuel cell according to an embodiment of the present disclosure.

[0029] Figure 6 Shows Figure 5 A cross-sectional schematic diagram of the structure of the single cell shown. Detailed Description

[0030] [Problems to be Solved by the Present Disclosure]

[0031] In recent years, for various batteries such as fuel cells and power storage devices such as capacitors, further improvement in power and capacity (miniaturization) has been required.

[0032] As the gas diffusion layer of a fuel cell, a carbon structure body and / or a stainless steel (SUS) structure body are generally used. Each of the carbon structure body and the SUS structure body has grooves as gas channels. Each groove has a continuous linear shape with a width of about 500 μm. The grooves occupy about half of the area of the boundary between the carbon structure body or the SUS structure body and the electrolyte, so the porosity of the gas diffusion layer is about 50%. Such a gas diffusion layer included in a conventional fuel cell does not have a very high porosity and has a large pressure loss, so a conventional fuel cell cannot have both a reduced size and increased power at the same time.

[0033] To solve this problem, the inventors of the present invention studied replacing the carbon structure body or the SUS structure body used as the gas diffusion layer of a fuel cell with a metal porous body including a skeleton having a three-dimensional network structure. By including a metal porous body with a high porosity as the gas diffusion layer, a fuel cell can have enhanced gas diffusion performance and higher gas utilization efficiency. For example, in a polymer electrolyte fuel cell (PEFC) including a metal porous body as the gas diffusion layer, the metal porous body is exposed to a strong acid generated by a membrane electrode assembly (MEA), so it needs to have high corrosion resistance.

[0034] A metal porous body including a nickel-chromium alloy skeleton has high corrosion resistance, so it can be used as the gas diffusion layer of a fuel cell.

[0035] The same as the method taught in Patent Document 1, when manufacturing a metal porous body by plating, from the environmental point of view, it is necessary to use a trivalent chromium plating solution. However, when using a trivalent chromium plating solution, the film formation rate is as low as about 0.3 μm / h, so it takes a long time to manufacture a metal porous body with a chromium alloy ratio of 20% or more. Therefore, there is room for improvement in productivity.

[0036] To solve this problem, the inventors of the present invention studied the use of a metal porous body manufactured by diffusion penetration in the same manner as the method taught in Patent Document 2 as a gas diffusion layer of a fuel cell. This study found room for improvement; when the metal porous body is used as the gas diffusion layer, water (H2O) generated due to power generation needs to be quickly discharged from the pore portions.

[0037] In view of the above circumstances, the present disclosure has been devised, and an object of the present invention is to provide a metal porous body having excellent corrosion resistance and including a skeleton having a highly hydrophobic surface.

[0038] [Advantageous Effects of the Present Disclosure]

[0039] The present disclosure can provide a metal porous body having excellent corrosion resistance and including a skeleton having a highly hydrophobic surface.

[0040] [Description of Embodiments]

[0041] First, each aspect of the present disclosure will be described.

[0042] (1) The porous body according to one aspect of the present disclosure is

[0043] a sheet-like metal porous body including a skeleton having a three-dimensional network structure,

[0044] wherein

[0045] the skeleton contains an alloy containing at least nickel (Ni) and chromium (Cr), and the skeleton 11 is a solid solution with iron (Fe),

[0046] the skeleton includes a chromium oxide (Cr2O3) layer as the outermost layer and includes a chromium carbide layer located below the chromium oxide layer,

[0047] the thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and

[0048] the thickness of the chromium carbide layer is 0.1 μm or more and 1 μm or less.

[0049] According to the aspect of (1) above, a metal porous body is provided at low cost, which has excellent corrosion resistance and has fewer fine particles adhering to the surface of its skeleton.

[0050] (2) Preferably, the porosity of the metal porous body according to (1) above is 60% or more and 98% or less.

[0051] According to the disclosure of (2) above, a metal porous body having a very high porosity is provided.

[0052] (3) Preferably, the average pore diameter of the metal porous body according to the above (1) or (2) is 50 μm or more and 5000 μm or less.

[0053] According to the disclosure of the above (3), a metal porous body is provided, which exhibits stronger gas diffusion performance and effectively discharges water generated due to power generation when used as a gas diffusion layer of a fuel cell.

[0054] (4) The fuel cell according to one aspect of the present invention is

[0055] a fuel cell including the metal porous body according to any one of the above (1) to (3) as a gas diffusion layer.

[0056] According to the disclosure of the above (4), a small-sized high-power fuel cell is provided.

[0057] (5) The method for manufacturing a metal porous body according to one aspect of the present disclosure includes:

[0058] preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component, and the preparation includes:

[0059] conducting a surface conductivity treatment on the skeleton of the resin molded body by coating carbon powder on the surface of the skeleton of the resin molded body including a skeleton having a three-dimensional network structure;

[0060] performing nickel plating to coat the surface of the skeleton of the resin molded body having conductivity thus obtained with nickel;

[0061] subsequently removing the resin molded body by heat treatment in an oxidizing atmosphere; and

[0062] after removing the resin molded body, performing heat treatment in a reducing atmosphere containing water vapor to reduce the amount of carbon remaining in nickel; and

[0063] forming an alloy containing at least nickel and chromium to obtain a metal porous body, and the formation includes embedding the porous body into a powder containing at least chromium (Cr), alumina (Al2O3) and ammonium chloride (NH4Cl), and then performing heat treatment to cause the diffusion penetration of chromium into the skeleton.

[0064] According to the aspect of the above (5), a method for manufacturing a metal porous body is provided, which can provide a metal porous body having excellent corrosion resistance and including a skeleton with a highly hydrophobic surface.

[0065] [Detailed description of each aspect]

[0066] In the following, a more detailed description of specific examples of each of the metal porous bodies, fuel cells, and methods for manufacturing metal porous bodies according to an aspect of the present disclosure will be given. It is intended that the scope of the invention be defined by the claims, rather than by the examples given below, and includes all modifications and variations within the meaning and scope equivalent to the claims.

[0067] <Metal porous body>

[0068] Figure 1 FIG. is a schematic view of an exemplary metal porous body according to an embodiment of the present disclosure. As Figure 1 shown, the metal porous body 10 according to an embodiment of the present disclosure includes a framework 11 having a three-dimensional network structure and a sheet-like outer shape. The framework 11 defines a pore portion 14, and the pore portion 14 is a communication pore that connects the surface of the metal porous body 10 to the inside of the metal porous body 10.

[0069] Figure 2 FIG. is a cross-sectional photograph of the framework 11 having a three-dimensional network structure of the metal porous body 10 according to an embodiment of the present disclosure. Figure 3 FIG. schematically shows Figure 2 an enlarged view of the cross-section of the metal porous body 10 shown in FIG. When the shape of the framework 11 has a three-dimensional network structure, the framework 11 of the metal porous body 10 has a hollow interior 13, and the hollow interior 13 generally looks as Figure 3 shown in FIG. The framework 11 is made of an alloy film 12.

[0070] The framework 11 may contain an alloy containing at least nickel (Ni) and chromium (Cr), and may be a solid solution with iron (Fe). Nickel is the main component of the framework 11, which means that nickel is contained in the framework 11 at the highest ratio compared to all other components. Chromium in the framework 11 may exist as an alloy Cr2Ni3 with nickel, or may exist as chromium oxide (Cr2O3), or needless to say, it may exist as an alloy with other metal components. Iron may exist as a solid solution with the alloy components of the framework 11 or the metal components of the framework 11.

[0071] Preferably, the chromium content of the framework 11 is about 5% by mass or more and about 45% by mass or less. When the chromium content of the framework 11 is 5% by mass or more, a metal porous body having excellent corrosion resistance and not causing nickel to dissolve in a strong acidic atmosphere can be provided. When the chromium content of the framework 11 is 45% by mass or less, a metal porous body having excellent tensile strength can be provided at a lower manufacturing cost. From these viewpoints, the chromium content of the framework 11 is preferably about 10% by mass or more and about 45% by mass or less, more preferably about 20% by mass or more and about 40% by mass or less.

[0072] The iron content of the framework 11 is preferably about 50 ppm or more and about 5000 ppm or less, more preferably about 100 ppm or more and about 3000 ppm or less, and still more preferably about 200 ppm or more and about 2000 ppm or less. When the iron content of the framework 11 is 50 ppm or more, a spinel-type composite oxide FeCr2O4 can be formed under the FeO layer, thereby suppressing the detachment of the above-mentioned chromium oxide from the surface of the framework 11. When the iron content of the framework 11 is 5000 ppm or less, an increase in the resistance of the metal porous body can be suppressed.

[0073] Intentionally or unavoidably, the framework 11 may further contain other components other than nickel, chromium or iron. Examples of these other components include manganese (Mn), silicon (Si), aluminum (Al) and zirconium (Zr). In particular, when the framework 11 contains silicon in the form of SiO2, it has the effect of suppressing the detachment of chromium oxide from the surface of the framework 11, whereby the metal porous body has excellent hydrophobicity.

[0074] The outermost layer of the framework 11 is a chromium oxide layer 121, which is a layer containing chromium oxide (Cr2O3). A chromium carbide layer 122 is formed under the chromium oxide layer 121, and the chromium carbide layer 122 is a layer containing chromium carbide. When the outermost layer of the framework 11 is the chromium oxide layer 121, the metal porous body has excellent hydrophobicity. When the framework 11 includes the chromium carbide layer 122, the metal porous body has excellent hardness.

[0075] The thickness of the chromium oxide layer 121 as the outermost layer of the framework 11 is 0.1 μm or more and 3 μm or less. When the thickness of the chromium oxide layer 121 is 0.1 μm or more, the metal porous body can have stronger hydrophobicity. When used as, for example, a gas diffusion layer of a fuel cell, since the surface of the framework 11 of the metal porous body has high hydrophobicity, water generated by power generation can be efficiently discharged. When the thickness of the chromium oxide layer 121 is about 3 μm, due to the saturation of the hydrophobic effect of the chromium oxide layer 121, the thickness of the chromium oxide layer 121 can be 3 μm or less. When the thickness of the chromium oxide layer 121 is about 3 μm or less, an increase in the manufacturing cost of the metal porous body can be suppressed.

[0076] In the skeleton 11, a chromium carbide layer 122 is formed under the outermost chromium oxide layer 121 (in other words, the chromium carbide layer 122 is formed on the side closer to the inside of the skeleton than the chromium oxide layer 121), and the thickness of the chromium carbide layer 122 is 0.1 μm or more and 1 μm or less. Since chromium carbide has high hardness, when the thickness of the chromium carbide layer 122 in the skeleton 11 is 0.1 μm or more, the skeleton 11 has high hardness. When the thickness of the chromium carbide layer 122 is 1 μm or less, the thickness of the chromium oxide layer 121 can be increased without embrittling the skeleton 11. From these viewpoints, the thickness of the chromium carbide layer 122 is more preferably 0.1 μm or more and 0.5 μm or less, and further preferably 0.1 μm or more and 0.3 μm or less.

[0077] The chromium carbide in the chromium carbide layer 122 can exist in two states: Cr7C3 and Cr 23 C6. Chromium carbide can exist at the grain boundaries of the chromium oxide crystals in the chromium oxide layer 121.

[0078] The skeleton of the metal porous body can be analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence (XRF), and / or X-ray diffraction (XRD) to confirm the presence of the chromium oxide layer 121 and the chromium carbide layer 122 in the skeleton 11.

[0079] The porosity of the metal porous body 10 according to the embodiments of the present disclosure can be appropriately selected according to the use of the metal porous body. The porosity of the metal porous body 10 is calculated by the following equation.

[0080] Porosity (%) = [1 - {Mp / (Vp × dp)}] × 100

[0081] Mp: Mass of the metal porous body [g]

[0082] Vp: Volume of the metal porous body based on the outer shape [cm 3

[0083] dp: Density of the metal of the metal porous body [g / cm 3

[0084] For example, when the metal porous body 10 is used as a gas diffusion layer of a fuel cell, it is preferable that the gas diffusion performance is excellent and the pressure loss is small. In this case, the porosity is preferably 60% or more and 98% or less, more preferably 70% or more and 98% or less, and further preferably 90% or more and 98% or less.

[0085] ​​The average pore diameter of the metal porous body 10 according to the embodiments of the present disclosure can be appropriately selected according to the use of the metal porous body. The average pore diameter of the metal porous body 10 refers to the value obtained by the following method: observing the surface of the metal porous body 10 in at least ten fields of view with a microscope or the like; counting the average number (nc) of pore portions 14 per inch (25.4 mm = 25400 μm); and calculating by the following formula.

[0086] Average pore diameter (μm) = 25400 μm / nc

[0087] For example, when the metal porous body 10 is used as a gas diffusion layer of a fuel cell, the average pore diameter of the metal porous body 10 can be selected by considering the diffusibility and pressure loss of the gas passing through the pore portion 14. More specifically, when used as a gas diffusion layer of a fuel cell, the average pore diameter of the metal porous body is preferably 50 μm or more and 5000 μm or less, more preferably 100 μm or more and 1000 μm or less, and still more preferably 200 μm or more and 700 μm or less.

[0088] The thickness of the metal porous body 10 according to the embodiments of the present disclosure is not particularly limited and can be appropriately selected according to the use of the metal porous body. For example, the thickness of the metal porous body 10 can be measured with a digital thickness gauge.

[0089] In many cases, when the thickness of the metal porous body is 0.1 mm or more and 3.0 mm or less, the metal porous body can be lightweight and have high strength. From these viewpoints, the thickness of the metal porous body 10 is more preferably 0.3 mm or more and 2.5 mm or less, and still more preferably 0.4 mm or more and 2.0 mm or less.

[0090] <Fuel cell>

[0091] The fuel cell according to the embodiments of the present disclosure can have the same structure as a conventional fuel cell, provided that it includes the above-described metal porous body according to the embodiments of the present disclosure as a gas diffusion layer. The type of the fuel cell is not particularly limited and can be a polymer electrolyte fuel cell or a solid oxide fuel cell. The conductive metal porous body 10 can serve as both a gas diffusion layer and a current collector in the fuel cell.

[0092] The fuel cell according to the embodiments of the present disclosure includes a gas diffusion layer having high gas diffusibility, and thus has higher gas utilization efficiency. Therefore, miniaturization and power improvement of the fuel cell can be achieved simultaneously. In addition, in the fuel cell according to the embodiments of the present disclosure, the metal porous body used as the gas diffusion layer includes a skeleton 11 having excellent hydrophobicity, so that the water generated by power generation can be quickly discharged from the pore portion 14.

[0093] In the following, reference will be made to Figure 5 and Figure 6 to give a more specific description of an exemplary fuel cell according to an embodiment of the present disclosure.

[0094] Referring to Figure 5 , the fuel cell 40 including the metal porous body 10 according to the present embodiment has a stacked structure composed of a plurality of single cells 41 and is, for example, a polymer electrolyte fuel cell. As Figure 6 shown, the single cell 41 includes an ion exchange membrane 42, catalyst layers 43a, 43b, gas diffusion layers 44a, 44b, and separators 45. For example, the ion exchange membrane 42 is a polymer electrolyte membrane containing an aqueous electrolyte solution. A catalyst layer 43a is provided on the first major surface of the ion exchange membrane 42. A gas diffusion layer 44a is provided on the side of the catalyst layer 43a opposite to the side having the ion exchange membrane 42. A catalyst layer 43b is provided on the second major surface of the ion exchange membrane 42 opposite to the first major surface. A gas diffusion layer 44b is provided on the side of the catalyst layer 43b opposite to the side having the ion exchange membrane 42. The combination of the catalyst layer 43a and the gas diffusion layer 44a constitutes a hydrogen electrode 46, and the combination of the catalyst layer 43b and the gas diffusion layer 44b constitutes an oxygen electrode 47. The structure composed of the gas diffusion layer 44a, the catalyst layer 43a, the ion exchange membrane 42, the catalyst layer 43b, and the gas diffusion layer 44b stacked and fixed together is called a membrane electrode assembly (MEA). The MEA is sandwiched between two separators 45.

[0095] The gas diffusion layers 44a, 44b serve as a dual role of a platform for battery reactions and a current collector. Therefore, they need to have an appropriate porosity and an appropriate mechanical strength. Therefore, it is preferable to use the metal porous body 10 according to the present embodiment.

[0096] Referring to Figure 6 , when hydrogen is introduced into the hydrogen electrode 46 and oxygen is introduced into the oxygen electrode 47 in the single cell 41, the reaction “H2 → 2H + + 2e - ” occurs on the hydrogen electrode 46 and the reaction “1 / 2O2 + 2H + + 2e - → H2O” occurs on the oxygen electrode 47. Protons (H + ) are generated on the hydrogen electrode 46 and diffuse through the ion exchange membrane 42 as Figure 6 shown and thus move to the oxygen electrode 47 side. On the oxygen electrode 47, the protons react with oxygen to generate water (H2O).

[0097] <Manufacturing method of the metal porous body>

[0098] The method for manufacturing a porous metal body according to an embodiment of the present disclosure includes the following preparation step and alloy formation step.

[0099] The preparation step is

[0100] a step of preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component, and the preparation step includes:

[0101] conducting a surface conductivity treatment on the skeleton of the resin molded body by coating carbon powder on the surface of the skeleton of the resin molded body including the skeleton having a three-dimensional network structure;

[0102] performing nickel plating to coat the surface of the skeleton of the resin molded body having conductivity thus obtained with nickel;

[0103] subsequently removing the resin molded body by heat treatment in an oxidizing atmosphere; and

[0104] after removing the resin molded body, performing heat treatment in a reducing atmosphere containing water vapor to reduce the amount of carbon remaining in the nickel.

[0105] The alloy formation step is

[0106] a step of forming an alloy containing at least nickel and chromium to obtain a porous metal body, and the formation includes embedding the porous body in a powder containing chromium (Cr), alumina (Al2O3), and ammonium chloride (NH4Cl), and then performing heat treatment to cause the diffusion penetration of chromium into the skeleton.

[0107] Hereinafter, a detailed description of these steps will be given.

[0108] (Preparation step)

[0109] The preparation step is a step of preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component. The porous body has a sheet-like shape. Since the porous metal body according to an embodiment of the present disclosure is obtained by forming an alloy of chromium and nickel contained in the above porous body, the structure of the porous body prepared as the porous body can be the same as the structure required for the porous metal body (for example, porosity and average pore diameter). As the porous body, a porous body including a skeleton that usually has a hollow interior and defines a pore portion can be prepared, such as a porous metal body. The definition of the porosity and average pore diameter of the porous body is the same as the definition of the porosity and average pore diameter of the porous metal body.

[0110] The expression "(skeleton) contains nickel as a main component" means that the skeleton of the porous body is made of a metal in which nickel has the highest amount.

[0111] A porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component can be obtained (for example) by the following method.

[0112] - Conductivization treatment step -

[0113] First, a sheet-shaped resin molded body (hereinafter may be simply referred to as "resin molded body") including a skeleton having a three-dimensional network structure is prepared. As the resin molded body, polyurethane resin, melamine resin, etc. can be used. Figure 4 A photograph of a polyurethane foam resin including a skeleton having a three-dimensional network structure.

[0114] Next, the surface of the skeleton of the resin molded body is conductivized by coating carbon powder on the surface of the skeleton of the resin molded body. Examples of the carbon powder used in the conductivization treatment include powders of amorphous carbon such as carbon black and powders of carbon such as graphite.

[0115] - Plating step -

[0116] In the plating step, nickel electroplating is performed using a resin molded body whose surface of the skeleton already has conductivity as a substrate. Nickel sputtering and / or electroless nickel plating can be used instead of electroplating to form a nickel film. However, from the viewpoints of productivity and cost, electroplating is preferred.

[0117] Nickel electroplating can be performed by known techniques. Known or commercially available plating baths such as Watts bath, chloride bath, or sulfamate bath can be used. Nickel electroplating can be performed by immersing the resin molded body obtained by the conductivization treatment in the plating bath, connecting the obtained resin molded body to the cathode, connecting the nickel counter electrode plate to the anode, and passing direct current or pulsed intermittent current.

[0118] - Resin molded body removal step -

[0119] After the plating step, the resin molded body having a nickel coating film on the surface of the skeleton is heat-treated in an oxidizing atmosphere to remove the resin molded body used as the substrate. For example, in an oxidizing atmosphere such as air, by heating to a temperature of about 600 °C or more and about 800 °C or less, preferably about 600 °C or more and about 700 °C or less, the resin molded body can be removed. By this step, the resin molded body used as the substrate is burned out, and a porous body containing nickel as the main component is obtained.

[0120] - Carbon removal step -

[0121] Although the resin molded body removal step can remove the resin molded body used as a base material, powders of amorphous carbon and / or powders of carbon for the electroconductification treatment may remain inside (hollow portion) of the skeleton (nickel-plated film) of the porous body containing nickel as a main component. This carbon powder can become a source of chromium carbide in the alloy formation step described below, where the alloy formation step includes forming an alloy containing nickel and chromium. When it is desired to reduce the content of chromium carbide in the skeleton of the metal porous body according to an embodiment of the present disclosure, it is preferable to reduce the amount of carbon powder by partially removing the carbon powder. When the amount of carbon remaining in the skeleton of the porous body containing nickel as a main component is 0.7 mass% or more, Cr7C3 is generated in the following alloy formation step (chromizing treatment). In addition, excessive supply of chromium generates Cr 23 C6.

[0122] The carbon removal step can be performed by heat-treating the porous body containing nickel as a main component in a reducing atmosphere containing water vapor (H2O). The heat treatment can be performed at a temperature of 750 °C or higher. The heat treatment temperature is preferably high, but from the viewpoints of cost and the furnace body material of the reduction furnace, the heat treatment temperature can be 1000 °C or lower.

[0123] As the reducing gas, hydrogen, or a mixed gas of hydrogen and carbon dioxide or an inert gas can be used, or a combination of these gases can be used as needed. From the viewpoint of redox efficiency, it is particularly preferable that the reducing gas contains hydrogen. When the reducing gas contains water vapor (H2O), the carbon remaining inside the skeleton of the porous body containing nickel as a main component can be removed. The amount of water vapor (H2O) in the reducing gas can be about 0.01 L / m 2 or more and about 0.10 L / m 2 or less, and more preferably 0.02 L / m 2 or more and 0.05 L / m 2 or less.

[0124] Since this carbon removal step is performed in a reducing atmosphere, nickel oxidized in the resin molded body removal step can be reduced, thereby forming a dense metal film.

[0125] (Alloy formation step)

[0126] The alloy formation step is a step of forming an alloy containing nickel and chromium by diffusion permeation of chromium into the skeleton of the porous body containing nickel as a main component. The method for manufacturing a metal porous body according to an embodiment of the present disclosure uses the above porous body, in which the amount of carbon in the skeleton of the porous body is reduced. Therefore, this method can manufacture a metal porous body having a low chromium carbide content, a high Cr2Ni3 content, and a high Cr2O3 content.

[0127] The technique of diffusion infiltration with chromium can be a known technique. An exemplary technique includes embedding a porous body containing nickel as a main component into a powder containing at least chromium, alumina, and ammonium chloride, and then heating it to a temperature of about 800 °C or higher and about 1100 °C or lower in an atmosphere of an inert gas such as Ar gas or in an atmosphere of a gas having the same composition as the gas generated during heat treatment.

[0128] When performing chromium diffusion infiltration using an iron furnace or a stainless-steel furnace, a solid solution of the skeleton of the porous body with iron and / or manganese can be formed.

[0129] [Examples]

[0130] Hereinafter, a more detailed description of the present disclosure will be given in the form of examples. These examples are given for illustrative purposes, and the metal porous bodies and the like according to the present disclosure are not limited to those in these examples. The scope of the present invention is defined by the claims and includes all modifications and variations within the meaning and scope equivalent to the claims.

[0131] (Example 1)

[0132] [Preparation Steps]

[0133] A porous body including a skeleton having a three-dimensional network structure was prepared in the following manner.

[0134] -Conductivization Treatment Step-

[0135] As a resin molded body including a skeleton having a three-dimensional network structure, a polyurethane sheet having a width of 1 m and a thickness of 1.0 mm was used. The porosity of the resin molded body was 96% and the average pore diameter was 450 μm.

[0136] Carbon black (100 g) as amorphous carbon having a particle size of 0.01 μm or more and 0.20 μm or less was dispersed in 0.5 L of an aqueous solution of 10% acrylate resin, thereby preparing an adhesive coating of this ratio.

[0137] Then, the resin molded body was continuously immersed in the obtained coating, squeezed between rollers, and dried to form a conductive layer on the surface of the skeleton of the resin molded body. In this way, the conductivization treatment of the resin molded body was performed.

[0138] -Plating Step-

[0139] Nickel was attached in an amount of 500 g / m 2 to the obtained conductivized surface of the skeleton of the resin molded body by electroplating. Thus, a resin structure including a skeleton having a nickel coating on the surface was prepared.

[0140] -Resin Molded Body Removal Step-

[0141] Then, in order to remove the resin molded body from the obtained resin structure, the resin structure was heated to 700 °C in the atmosphere (in an oxidizing atmosphere). Thus, a porous body containing nickel as a main component from which the resin molded body had been removed was obtained.

[0142] - Carbon removal step -

[0143] Then, in order to remove the carbon powder remaining in the obtained porous body, the porous body was heated to 1000 °C in a reducing atmosphere composed of a gas made by adding water vapor (H₂O) to a mixed gas of H₂ and N₂ (cracked ammonia gas).

[0144] Thus, a porous body was obtained in which the residual amount of carbon in the skeleton was reduced. In addition, nickel was reduced and annealed.

[0145] <Alloy formation step>

[0146] In a stainless steel furnace, a mixed powder composed of 1 mass% of Al powder, 50 mass% of Cr powder, 0.5 mass% of NH₄Cl, and the balance of Al₂O₃ powder was prepared, and the porous body was embedded in the obtained mixed powder. Subsequently, heat treatment was carried out at 1000 °C for 10 hours to obtain Metal Porous Body No.1.

[0147] (Comparative Example 1)

[0148] Metal Porous Body No.A was obtained in the same manner as in Example 1, except that the carbon removal step was not carried out.

[0149] (Evaluation)

[0150] <Determination of the composition of the skeleton>

[0151] The composition and alloy components of the skeletons of Metal Porous Body No.1 and Metal Porous Body No.A were measured by EDX analysis and / or XRD analysis. The cross-section of the skeleton of each metal porous body was observed by SEM. In addition, the surface of the skeleton of each metal porous body was etched with nitric acid, and then the cross-section of the skeleton was observed by SEM. In this way, the presence of the chromium carbide layer was confirmed.

[0152] The results are shown in Table 1.

[0153] <Hydrophobicity>

[0154] Metal Porous Body No.1 and Metal Porous Body No.A were each left standing, and a drop of deionized water (about 0.03 ml to 0.05 ml) was placed on their main surfaces with a pipette. Visual observation was carried out from the side of the metal porous body, and the time until no residual water droplet was visible on the upper surface of the metal porous body (until all the water entered the pore part) was measured.

[0155] The results are shown in Table 1.

[0156] [Table 1]

[0157]

[0158] The metal porous body No. 1 has a high Cr2O3 content, so the skeleton has excellent hydrophobicity. Since the chromium carbide content is low, it is also found to have excellent flexibility.

[0159] On the contrary, compared with the metal porous body No. 1, the metal porous body No. A has a low Cr2O3 content, and the skeleton has low hydrophobicity. Since the chromium carbide content is high, the skeleton has excellent hardness but low flexibility.

[0160] List of reference numerals

[0161] 10 Metal porous body, 11 Skeleton, 12 Alloy film constituting the skeleton, 121 Chromium oxide layer, 122 Chromium carbide layer, 13 Inside the skeleton, 14 Hole part.

Claims

1. A metal porous body, which is in sheet form and includes a skeleton having a three-dimensional network structure, wherein the skeleton contains an alloy containing at least nickel and chromium, and the skeleton is a solid solution with iron, the skeleton includes a chromium oxide layer as the outermost layer and includes a chromium carbide layer located below the chromium oxide layer, the thickness of the chromium oxide layer is 0.1 μm or more and 3 μm or less, and the thickness of the chromium carbide layer is 0.1 μm or more and 0.5 μm or less, the chromium carbide layer contains Cr7C3, the skeleton contains silicon in the form of SiO2.

2. The metal porous body according to claim 1, wherein the porosity of the metal porous body is 60% or more and 98% or less.

3. The metal porous body according to claim 1 or 2, wherein the average pore diameter of the metal porous body is 50 μm or more and 5000 μm or less.

4. The metal porous body according to claim 1 or 2, wherein the chromium content of the skeleton is 5% by mass or more and 45% by mass or less.

5. The metal porous body according to claim 1 or 2, wherein the iron content of the skeleton is 50 ppm or more and 5000 ppm or less.

6. A fuel cell, which includes the metal porous body according to any one of claims 1 to 5 as a gas diffusion layer.

7. A method for manufacturing the metal porous body according to any one of claims 1 to 5, the method comprising: Preparing a porous body including a skeleton having a three-dimensional network structure and containing nickel as a main component, the preparation including: Conductivizing the surface of the skeleton of a resin molded body including a skeleton having a three-dimensional network structure by coating carbon powder on the surface of the skeleton of the resin molded body; Performing nickel plating to coat the surface of the skeleton of the resin molded body having conductivity thus obtained with nickel; Subsequently removing the resin molded body by heat treatment in an oxidizing atmosphere; and After removing the resin molded body, performing heat treatment in a reducing atmosphere containing water vapor to reduce the amount of carbon remaining in the nickel, such that the amount of carbon remaining in the skeleton of the porous body containing nickel as a main component is 0.7 mass% or more; and Forming an alloy containing at least nickel and chromium to obtain a metal porous body, the forming including embedding the porous body into a powder containing chromium, alumina, and ammonium chloride, and then performing heat treatment to cause diffusion penetration of the chromium into the skeleton.

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