Metal porous body

Abstract

This metal porous body, which has a skeleton having a three-dimensional network structure, is in the form of a sheet including a first main surface and a second main surface on the reverse side from the first main surface. The metal porous body comprises a first metal porous body layer which includes the first main surface. The first metal porous body layer includes a first region sandwiched between a virtual plane S11 at a distance of 0.01 mm from the first main surface towards the first metal porous body layer and a virtual plane S12 at a distance of 0.10 mm from the first main surface towards the first metal porous body layer. The opening ratio A1 of the first region is 40% or less, with the opening ratio being measured by using a scanning electron microscope to observe a cross section along a line normal to the first main surface of the metal porous body. The transmitted-light area ratio of the first main surface is 2% or less, with the transmitted-light area ratio being measured by using a microscope to observe the first main surface in a state in which the metal porous body is irradiated with light from the second main surface side.

Description

Porous metal

[0001] The present disclosure relates to a porous metal body.

[0002] Hydrogen is attracting attention as a highly efficient clean energy source because it is suitable for storage and transportation and has a small environmental impact. Most hydrogen is produced by steam reforming of fossil fuels, but hydrogen production by water electrolysis is becoming increasingly important from the perspective of reducing the environmental impact. Because water electrolysis involves the consumption of electricity, various improvements to water electrolysis methods are being attempted in order to realize highly efficient hydrogen production systems.

[0003] In recent years, AEM (Anion Exchange Membrane) water electrolysis using an anion exchange membrane has been attracting attention (see, for example, Patent Document 1). Compared to currently mainstream alkaline water electrolysis and PEM (Polymer Electrolyte Membrane) water electrolysis, the advantages of AEM water electrolysis are that it can increase the current density compared to alkaline water electrolysis, it allows for more compact equipment, and it does not require a precious metal catalyst that is essential for PEM water electrolysis.

[0004] Japanese Patent Application Laid-Open No. 2022-26413

[0005] The metal porous body of the present disclosure is a metal porous body having a skeleton with a three-dimensional network structure, the metal porous body being in a sheet shape including a first main surface and a second main surface opposite the first main surface, the metal porous body comprising a first metal porous body layer including the first main surface, the first metal porous body layer including a first region sandwiched between an imaginary plane S11 that is 0.01 mm away from the first main surface toward the first metal porous body layer and an imaginary plane S12 that is 0.10 mm away from the first main surface toward the first metal porous body layer, the aperture ratio A1 of the first region being 40% or less, the aperture ratio being measured by observing a cross section of the metal porous body taken along a normal to the first main surface with a scanning electron microscope, the transmitted light area ratio of the first main surface being 2% or less, and the transmitted light area ratio being measured by observing the first main surface with a microscope while irradiating the metal porous body with light from the second main surface side.

[0006] Fig. 1 is a diagram illustrating a typical configuration example of a metal porous body according to embodiment 1. Fig. 2 is an enlarged schematic view of a cross section of a skeleton 11 of a metal porous body 10 shown in Fig. 1. Fig. 3 is a schematic view of a cross section of the skeleton 11 shown in Fig. 2 taken along line III-III. Fig. 4 is a cross-sectional view of an example of a metal porous body according to embodiment 1.

[0007] [Problem to be Solved by the Present Disclosure] In AEM-type water electrolysis, smoothness is required for the electrodes in contact with the electrolyte membrane to prevent damage to the electrolyte membrane. There are two types of electrolytic cell: the CCM method, in which a catalyst is applied to the AEM membrane, and the CCS method, in which a catalyst is applied to an electrode made of a conductive porous body such as a porous metal body. In the CCS method, increasing the contact area between the catalyst and the electrolyte membrane that contributes to the electrolytic reaction contributes to improving electric field performance. For this reason, there is a demand for porous metal bodies that can be coated with a larger amount of catalyst on their surfaces.

[0008] Therefore, an object of the present disclosure is to provide a porous metal body that has an improved surface smoothness to prevent damage to the electrolyte membrane and that allows a larger amount of catalyst to be applied to the surface.

[0009] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a porous metal body that has an improved surface smoothness, suppresses damage to an electrolyte membrane, and allows a larger amount of catalyst to be applied to the surface.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described below. (1) A metal porous body according to the present disclosure is a metal porous body having a skeleton with a three-dimensional network structure, the metal porous body being in the form of a sheet including a first main surface and a second main surface opposite to the first main surface, the metal porous body comprising a first metal porous body layer including the first main surface, the first metal porous body layer including a first region sandwiched between an imaginary plane S11 that is 0.01 mm away from the first main surface toward the first metal porous body layer and an imaginary plane S12 that is 0.10 mm away from the first main surface toward the first metal porous body layer, the aperture ratio A1 of the first region being 40% or less, the aperture ratio being measured by observing a cross section of the metal porous body taken along a normal to the first main surface with a scanning electron microscope, the transmitted light area ratio of the first main surface being 2% or less, The light transmittance area ratio is measured by observing the first main surface with a microscope while irradiating the metal porous body with light from the second main surface side.

[0011] According to the present disclosure, it is possible to provide a porous metal body that has an improved surface smoothness, suppresses damage to an electrolyte membrane, and allows a larger amount of catalyst to be applied to the surface.

[0012] (2) In the above (1), the metal porous body includes a second metal porous body layer provided in contact with the main surface opposite to the first main surface of the first metal porous body layer, and the second metal porous body layer includes a second region sandwiched between a first interface between the first metal porous body layer and the second metal porous body layer and an imaginary plane S13 that is 0.01 mm away from the first interface toward the second metal porous body layer, and the aperture ratio A2 of the second region may be the same as or greater than the aperture ratio A1.

[0013] This reduces the pressure loss of the porous metal body. When the porous metal body is used in an AEM water electrolysis device, the generated gas can be easily removed by the liquid flow.

[0014] (3) In the above (2), the ratio A2 / A1 of the opening rate A2 to the opening rate A1 may be 1.0 or more and 4.0 or less. This can reduce pressure loss in the porous metal body.

[0015] (4) In the above (2) or (3), the metal porous body includes a third metal porous body layer provided in contact with a fourth main surface of the second metal porous body layer opposite to a third main surface that is in contact with the first metal porous body layer, and the third metal porous body layer includes a third region sandwiched between a second interface between the second metal porous body layer and the third metal porous body layer and an imaginary plane S14 that is 0.01 mm away from the second interface toward the third metal porous body layer, and the aperture ratio A3 of the third region may be the same as or greater than the aperture ratio A1.

[0016] This reduces the pressure loss of the porous metal body. When the porous metal body is used in an AEM water electrolysis device, the generated gas can be easily removed by the liquid flow.

[0017] (5) In the above (4), the ratio A3 / A1 of the aperture ratio A3 to the aperture ratio A1 may be 1.0 or more and 4.0 or less. This can reduce pressure loss in the porous metal body.

[0018] (6) In any of (1) to (5) above, the first main surface includes a first opening defined by the skeleton, the first opening is an opening through which light passes when the light is irradiated onto the metal porous body from the second main surface side, the first opening includes a second opening, the circle equivalent diameter of the second opening is 35 μm or less, and the percentage (N2 / N1)×100 of the number N2 of the second openings to the number N1 of the first openings may be 50% or more.

[0019] This further increases the amount of catalyst that can be applied to the surface of the porous metal body.

[0020] (7) In any one of (1) to (6) above, the first main surface includes a first opening defined by the skeleton, the first opening is an opening through which light passes when the light is irradiated onto the metal porous body from the second main surface side, and the upper limit of the circle equivalent diameter of the first opening may be 60 μm or less.

[0021] This further increases the amount of catalyst that can be applied to the surface of the porous metal body.

[0022] [Details of the embodiment of the present disclosure] Specific examples of the metal porous body of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0023] In the present disclosure, the notation in the form of "A to B" means A or more and B or less, and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0024] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0025] [Embodiment 1: Metallic Porous Body] A metallic porous body according to one embodiment of the present disclosure is a metallic porous body having a skeleton with a three-dimensional network structure, the metallic porous body being in a sheet shape including a first main surface and a second main surface opposite to the first main surface, the metallic porous body comprising a first metallic porous body layer including the first main surface, the first metallic porous body layer including a first region sandwiched between an imaginary plane S11 that is 0.01 mm away from the first main surface toward the first metallic porous body layer and an imaginary plane S12 that is 0.10 mm away from the first main surface toward the first metallic porous body layer, the first region having an aperture ratio A1 of 40% or less, the aperture ratio being measured by observing a cross section of the metallic porous body taken along a normal to the first main surface with a scanning electron microscope, the transmitted light area ratio of the first main surface being 2% or less, The light transmittance area ratio is measured by observing the first main surface of the porous metal body with a microscope while irradiating the porous metal body with light from the second main surface side.

[0026] <Structure of Porous Metal Body> Fig. 1 is a diagram illustrating a typical configuration example of a porous metal body according to embodiment 1. Fig. 2 is an enlarged schematic view of a cross section of a skeleton 11 of a porous metal body 10 shown in Fig. 1. Fig. 3 is a schematic view of a cross section of the skeleton 11 shown in Fig. 2 taken along line III-III. Fig. 4 is a cross-sectional view of an example of a porous metal body according to embodiment 1.

[0027] The metal porous body 10 has a skeleton 11 with a three-dimensional network structure. The metal porous body 10 has an overall sheet-like appearance including a first main surface 1 and a second main surface 2 opposite to the first main surface 1. Pores 14 are formed inside the metal porous body 10 by the skeleton 11 with the three-dimensional network structure.

[0028] The skeleton 11 of the metal porous body 10 is composed of a skeleton main body 12 made of metal, and the interior 13 of the skeleton is hollow. At least some of the pores 14 formed by the skeleton 11 are interconnected pores that communicate with adjacent pores 14.

[0029] As shown in FIG. 3, the cross-sectional shape of the skeleton 11 can be modeled as a triangle with a hollow center (interior 13 of the skeleton).

[0030] The first main surface of the metal porous body can consist of only the skeleton 11 with a three-dimensional network structure, or can consist of the skeleton 11 with a three-dimensional network structure and pores 14. On the first main surface of the metal porous body, there is no filler that fills the pores 14 or a coating material that covers the skeleton 11 and the pores 14.

[0031] In the porous metal body 10 of the first embodiment, the composition of the skeleton is not particularly limited and may be appropriately selected depending on the intended use. Examples of the skeleton composition include nickel, nickel-chromium, nickel-cobalt, nickel-tin, copper, and aluminum.

[0032] The thickness of the porous metal body 10 of the first embodiment is not particularly limited and may be appropriately selected depending on the application. The thickness of the porous metal body 10 may be, for example, 0.1 mm or more and 10 mm or less, or 0.1 mm or more and 5 mm or less. The thickness of the porous metal body 10 can be measured, for example, using a digital thickness gauge.

[0033] 4 , the metal porous body 10 of embodiment 1 includes a first metal porous body layer 5 including a first main surface 1. The first metal porous body layer 5 includes a first region 15 sandwiched between an imaginary surface S11 that is 0.01 mm away from the first main surface 1 on the first metal porous body layer 5 side, and an imaginary surface S12 that is 0.10 mm away from the first main surface 1 on the first metal porous body layer 5 side. The first region 15 includes the imaginary surface S11 and the imaginary surface S12.

[0034] <Opening Ratio A1 of First Region> The opening ratio A1 of the first region of the metal porous body 10 of embodiment 1 is 40% or less. This increases the smoothness of the first main surface of the metal porous body. When the metal porous body is used as an electrode in an AEM water electrolysis device and the first main surface is disposed in contact with an electrolyte membrane, damage to the electrolyte membrane can be suppressed. Furthermore, when a catalyst is sprayed onto the first main surface, the catalyst is more likely to be retained on the first main surface, allowing a larger amount of catalyst to be applied to the first main surface. The upper limit of the opening ratio A1 of the first region may be 38% or less, 36% or less, or 30% or less, from the viewpoint of increasing the amount of catalyst applied to the first main surface. The lower limit of the opening ratio A1 of the first region is not particularly limited, but may be, for example, 20% or more, 25% or more, or 27% or more. The aperture ratio A1 of the first region may be 20% or more and 40% or less, 20% or more and 38% or less, 25% or more and 36% or less, or 27% or more and 30% or less.

[0035] In the present disclosure, the aperture ratio A1 of the first region is measured by observing a cross section of the porous metal body along the normal to the first main surface with a scanning electron microscope. Specifically, it is measured by the following procedure.

[0036] Step A1: The metal porous body is cut along an imaginary plane parallel to the normal to the first main surface to expose a cross section along the normal to the first main surface.

[0037] Step A2: The cross section of the metal porous body is observed using a scanning electron microscope to obtain an observation image. The observation magnification is appropriately set depending on the size of the measurement field of the scanning electron microscope and the size of the pores 14. For example, the observation magnification can be 100 times.

[0038] Step A3: On the cross section of the metal porous body in the observed image, draw an imaginary line L0 that is 0.01 mm away from the first main surface, an imaginary line L1 that is 0.05 mm away from the first main surface, and an imaginary line L2 that is 0.10 mm away from the first main surface. The lengths of the imaginary lines L0, L1, and L2 are each long enough to cross at least 10 pores 14. For example, when the observation magnification is 100x, the lengths of the imaginary lines L0, L1, and L2 can each be 1 mm or longer.

[0039] Step A4: For each of the imaginary lines L0, L1, and L2, calculate the percentage P1 (P1 = (LP / LT) x 100) of the total length LP of the pores 14 crossed by the imaginary lines relative to the length LT of the imaginary lines. Calculate the percentage P1 for each of the imaginary lines L0, L1, and L2. Calculate the average P11 of the three calculated percentages P1. In the present disclosure, the average P11 corresponds to the opening ratio A1 of the first region.

[0040] <Light Transmitted Area Ratio of First Main Surface> The light transmitted area ratio of the first main surface of the metal porous body 10 of embodiment 1 is 2% or less. This allows the catalyst to be easily retained on the first main surface when sprayed onto the first main surface, allowing a larger amount of catalyst to be applied to the first main surface. From the viewpoint of increasing the amount of catalyst applied to the first main surface, the upper limit of the light transmitted area ratio of the first main surface may be 1.9% or less, 1.8% or less, 1.7% or less, 1.5% or less, 1.0% or less, or 0.8% or less. The lower limit of the light transmitted area ratio of the first main surface may be 0% or more. The light transmitted area ratio of the first main surface may be 0% or more and 2% or less, 0% or more and 1.9% or less, 0% or more and 1.8% or less, 0% or more and 1.7% or less, 0% or more and 1.5% or less, 0% or more and 1.0% or less, or 0% or more and 0.8% or less.

[0041] In the present disclosure, the light transmitted area ratio of the first principal surface is measured by irradiating the metal porous body with light from the second principal surface side and observing the first principal surface with a microscope. Specifically, the measurement is performed by the following procedure.

[0042] Step B1: While irradiating the metal porous body with light from the second main surface side, the first main surface is observed with a microscope to obtain an observation image. The observation magnification is set appropriately depending on the size of the measurement field of the microscope. For example, the observation magnification can be 10 to 1000 times. The size of the observation image is, for example, rectangular, and if pores are present in the first main surface, each of its length and width may be 10 times or more longer than the maximum opening diameter of the pores. The microscope used is a "VHX-7000" (trademark) manufactured by KEYENCE Corporation.

[0043] Step B2: The observed image is binarized using the image processing software provided with the microscope to obtain a binarized image. The brightness threshold for binarization can be determined appropriately depending on the state of the image being used. For example, if there are 256 gradations, the center value of 128 can be used.

[0044] In the binarized image, areas through which light is transmitted are displayed in white. The percentage of the area S1 of the light-transmitting area relative to the area S of the entire binarized image is calculated as (S1 / S) x 100.

[0045] Step B3: Obtain the observation images of step B1 at three non-overlapping locations, and perform step B2 based on each observation image to obtain the percentage (S1 / S) x 100. Calculate the average of the percentages (S1 / S) x 100 of the three observation images. In the present disclosure, the average of the percentages (S1 / S) x 100 of the three observation images corresponds to the transmitted light area ratio of the first principal surface.

[0046] <Circle-equivalent diameter of first opening> The first main surface of the porous metal body 10 of embodiment 1 may include a first opening defined by a skeleton. The first opening is an opening through which light passes when the porous metal body is irradiated with light from the second main surface side.

[0047] The upper limit of the equivalent circle diameter of the first openings may be 60 μm or less, 55 μm or less, or 50 μm or less, from the viewpoint of improving the smoothness of the first main surface and increasing the amount of catalyst applied to the first main surface. The lower limit of the equivalent circle diameter of the first openings is not particularly limited, but may be, for example, 1 μm or more. The equivalent circle diameter of the first openings may be 1 μm or more and 60 μm or less, 3 μm or more and 55 μm or less, or 5 μm or more and 50 μm or less. This means that when the catalyst is applied toward the first main surface by spraying, the catalyst forms a catalyst layer on the first main surface and is easily retained on the first main surface, allowing a larger amount of catalyst to be applied to the first main surface.

[0048] In the present disclosure, the upper limit of the circle-equivalent diameter of the first opening is measured by the following procedure.

[0049] Step C1: Identify the light-transmitting areas on the first principal surface using the same method as steps B1 and B2 of the method for measuring the light-transmitting area ratio of the first principal surface. Each of the light-transmitting areas corresponds to a first opening.

[0050] Step C2: For each of the first openings identified in Step C1, the equivalent circle diameter is determined using image processing. Specifically, the contour length CL and area S of each first opening are determined, and the equivalent circle diameter r is calculated from r = 2 × S / CL. The largest equivalent circle diameter of the first opening is identified in the observation image.

[0051] Step C3: Observation images of step B1 are obtained at three non-overlapping locations, and steps C1 and C2 are performed based on each observation image to identify the largest equivalent circle diameter of the first opening. In the present disclosure, the largest equivalent circle diameter r of the first opening among the three observation images corresponds to the upper limit of the equivalent circle diameter of the first opening.

[0052] <Percentage of the number N2 of second openings relative to the number N1 of first openings (N2 / N1) × 100> The first main surface of the metal porous body 10 of embodiment 1 includes first openings, the first openings include second openings, the circle equivalent diameter of the second openings is 35 μm or less, and the percentage of the number N2 of second openings relative to the number N1 of first openings (N2 / N1) × 100 may be 50% or more.

[0053] The lower limit of the percentage (N2 / N1) x 100 may be 50% or more, 51% or more, 53% or more, 55% or more, or 60% or more, from the viewpoint of reducing the pressure loss of the metal porous body and facilitating the transport of the electrolyte to the catalyst-coated layer on the first main surface and the discharge of gas generated in the catalyst-coated layer. The upper limit of the percentage (N2 / N1) x 100 is not particularly limited, but may be, for example, 100% or less, 90% or less, 80% or less, or 75% or less. The percentage (N2 / N1) x 100 may be 50% or more and 100% or less, 51% or more and 90% or less, 53% or more and 80% or less, 55% or more and 75% or less, or 60% or more and 75% or less.

[0054] In the present disclosure, the percentage (N2 / N1) x 100 is measured by the following procedure.

[0055] Step D1: Determine the equivalent circle diameter for each of the first openings using the same method as steps C1 and C2 in the method for measuring the upper limit of the equivalent circle diameter of the first openings. Openings with an equivalent circle diameter of 35 μm or less correspond to the second openings.

[0056] Step D2: In the entire observation image, count the number n1 of first openings (regardless of their equivalent circular diameter) and the number n2 of second openings with an equivalent circular diameter of 35 μm or less, and calculate the percentage (n2 / n1)×100.

[0057] Step D3: Observation images of step B1 are obtained at three non-overlapping locations, and steps D1 and D2 are performed based on each observation image to calculate the percentage (n2 / n1) × 100. In the present disclosure, the average of the percentages (n2 / n1) × 100 of the three observation images corresponds to the percentage (N2 / N1) × 100 of the number N2 of second openings relative to the number N1 of first openings.

[0058] 4 , the metal porous body 10 of Embodiment 1 includes a second metal porous body layer 6 provided in contact with the main surface opposite to the first main surface 1 of the first metal porous body layer 5, and the second metal porous body layer 6 may include a second region 16 sandwiched between a first interface 8 between the first metal porous body layer 5 and the second metal porous body layer 6 and an imaginary plane S13 that is 0.01 mm away from the first interface 8 toward the second metal porous body layer 6. The second region 16 does not include the third main surface 3 of the second metal porous body layer 6 facing the first metal porous body layer 5, but includes the imaginary plane S13.

[0059] <<Opening Ratio A2 of Second Region>> The opening ratio A2 of the second region of the porous metal body 10 of embodiment 1 may be the same as or larger than the opening ratio A1 of the first region.

[0060] The lower limit of the ratio A2 / A1 of the aperture ratio A2 to the aperture ratio A1 may be 1.0 or more, 1.2 or more, or 1.5 or more, from the viewpoints of reducing pressure loss in the metal porous body and facilitating transport of the electrolyte to the catalyst-coated layer on the first main surface and smooth discharge of gas generated in the catalyst-coated layer. The upper limit of the ratio A2 / A1 may be 4.0 or less, 3.0 or less, or 2.7 or less, from the viewpoints of balancing the catalyst coating amount on the first main surface with transport of the electrolyte and gas discharge on the second main surface. The ratio A2 / A1 may be 1.0 or more and 4.0 or less, 1.2 or more and 3.0 or less, or 1.5 or more and 2.7 or less.

[0061] The aperture ratio A2 may be, for example, 25% or more and 80% or less, 35% or more and 75% or less, or 40% or more and 70% or less.

[0062] In the present disclosure, the aperture ratio A2 of the second region is measured by observing a cross section of the metal porous body taken along the normal to the first main surface with a scanning electron microscope. Specifically, it is measured by the following procedure.

[0063] Step E1: An observation image of the cross section of the porous metal body is obtained using the same method as steps A1 and A2 in the method for measuring the opening ratio A1 of the first region.

[0064] Step E2: On the cross section of the second metal porous body layer in the observed image, draw an imaginary line L3 that is 0.003 mm away from the first interface, an imaginary line L4 that is 0.006 mm away from the first interface, and an imaginary line L5 that is 0.01 mm away from the first interface. The lengths of the imaginary lines L3, L4, and L5 are each long enough to cross at least 10 pores 14.

[0065] Step E3: For each of the imaginary lines L3, L4, and L5, calculate the percentage P2 (P2 = (LP / LT) x 100) of the total length LP of the pores 14 crossed by the imaginary lines relative to the length LT of the imaginary lines. Calculate the percentage P2 for each of the imaginary lines L3, L4, and L5. Calculate the average P22 of the three calculated percentages P2. In the present disclosure, the average P22 corresponds to the opening ratio A2 of the second region.

[0066] 4 , the metal porous body 10 of Embodiment 1 includes a third metal porous body layer 7 provided in contact with the fourth main surface 4 of the second metal porous body layer 6 opposite to the third main surface 3 that is in contact with the first metal porous body layer 5, and the third metal porous body layer 7 may include a third region 17 sandwiched between a second interface 9 between the second metal porous body layer 6 and the third metal porous body layer 7 and an imaginary plane S14 that is 0.01 mm away from the second interface 9 toward the third metal porous body layer 7. The third region does not include the main surface of the third metal porous body layer 7 facing the second metal porous body layer 6, but includes the imaginary plane S14.

[0067] The aperture ratio A3 of the third region of the metal porous body 10 of the first embodiment may be the same as or larger than the aperture ratio A1.

[0068] The lower limit of the ratio A3 / A1 of the aperture ratio A3 to the aperture ratio A1 may be 1.0 or more, 1.2 or more, or 1.5 or more from the viewpoint of reducing pressure loss of the metal porous body. The upper limit of the ratio A3 / A1 may be 4.0 or less, 3.3 or less, or 3.0 or less from the viewpoint of balancing the catalyst coating amount on the first main surface with electrolyte transport and gas discharge on the second main surface. The ratio A3 / A1 may be 1.0 or more and 4.0 or less, 1.0 or more and 3.3 or less, or 1.0 or more and 3.0 or less.

[0069] The aperture ratio A3 of the third region of the metal porous body 10 of the first embodiment may be the same as or larger than the aperture ratio A2.

[0070] The lower limit of the ratio A3 / A2 of the aperture ratio A3 to the aperture ratio A2 may be 1.0 or more, 1.2 or more, or 1.5 or more, from the viewpoint of reducing pressure loss of the metal porous body. The upper limit of the ratio A3 / A2 may be 4.0 or less, 3.3 or less, or 3.0 or less, from the viewpoint of balancing the catalyst coating amount on the first main surface with the electrolyte transport and gas discharge on the second main surface. The ratio A3 / A2 may be 1.0 or more and 4.0 or less, 1.0 or more and 3.3 or less, or 1.0 or more and 3.0 or less.

[0071] The aperture ratio A3 may be, for example, 30% or more and 95% or less, 35% or more and 90% or less, or 45% or more and 90% or less.

[0072] In the present disclosure, the aperture ratio A3 of the third region is measured by observing a cross section of the porous metal body taken along the normal to the first main surface with a scanning electron microscope. Specifically, it is measured by the following procedure.

[0073] Step F1: An observation image of the cross section of the porous metal body is obtained using the same method as steps A1 and A2 in the method for measuring the opening ratio A1 of the first region.

[0074] Step F2: Draw an imaginary line L6 that is 0.003 mm away from the second interface, an imaginary line L7 that is 0.006 mm away from the second interface, and an imaginary line L8 that is 0.01 mm away from the second interface on the cross section of the third metal porous body layer in the observed image. The lengths of the imaginary lines L6, L7, and L8 are each set to a length that crosses at least 10 pores 14.

[0075] Step F3: For each of the imaginary lines L6, L7, and L8, calculate the percentage P3 (P3 = (LP / LT) x 100) of the total length LP of the pores 14 crossed by the imaginary lines relative to the length LT of the imaginary lines. Calculate the percentage P3 for each of the imaginary lines L6, L7, and L8. Calculate the average P33 of the three calculated percentages P3. In the present disclosure, the average P33 corresponds to the opening ratio A3 of the third region.

[0076] <Method for producing a metal porous body> The method for producing a metal porous body of embodiment 1 can include a first step of preparing a metal porous body material having a skeleton with a three-dimensional network structure, and a second step of performing two-stage pressing on the metal porous body material to obtain a metal porous body.

[0077] <First Step> A metal porous body material having a skeleton with a three-dimensional network structure is prepared. The metal porous body material is used in a sheet-like shape as a whole. The average pore size of the metal porous body material may be appropriately selected depending on the application of the metal porous body 10. For example, the average pore size of the metal porous body material may be 50 μm or more and 5000 μm or less, 100 μm or more and 1000 μm or less, or 200 μm or more and 700 μm or less.

[0078] The average pore diameter of a porous metal material is defined by the following formula [1]. In formula [1], n c is the average number of pores 14 per inch (25.4 mm = 25,400 μm) obtained by observing the main surface of the porous metal material in at least 10 fields using a microscope or the like. Average pore diameter = 25,400 μm / n c Formula [1] The number of pores 14 is measured in accordance with the method for determining the number of pores (number of cells) in a flexible foam material specified in JIS K6400-1:2004, Appendix 1 (Reference).

[0079] Two or more porous metal materials having different average pore diameters may be prepared.

[0080] As the porous metal material, "Aluminum Celmet" (trademark) manufactured by Sumitomo Electric Industries, Ltd., or copper or nickel "Celmet" (trademark) can be used.

[0081] <<Second Step>> Next, the porous metal material is subjected to two-stage pressing to obtain a porous metal body. Specifically, the porous metal material is pressed in the thickness direction using a roll press. In the first stage of pressing, the porous metal material is pressed to 1.5 to 2.0 times the final desired thickness of the porous metal layer, and in the second stage of pressing, the porous metal material is pressed to the desired thickness. The pressing pressure, pressing speed, and number of pressings may be selected depending on the size and properties of the porous metal material. For example, a 10 cm wide sample can be pressed at a linear pressure of 10 kN and a speed of 10 cm / min.

[0082] When two or more sheets of porous metal material are prepared in the first step, the first-stage pressing may be performed separately for each sheet of porous metal material. Alternatively, the first-stage pressing may be performed simultaneously by stacking two or more sheets of porous metal material with their main surfaces facing each other. Alternatively, for example, a porous metal material that has been pressed in the first stage and an unpressed porous metal material may be stacked together, and the second-stage pressing may be performed in this stacked state. The order, timing, and number of pressings may be adjusted depending on the final desired structure, but it is preferable to perform one or more pressings in the final stacked state. By two-stage pressing, the opposing main surfaces of two or more porous metal materials are directly bonded to each other, resulting in a porous metal material in which two or more porous metal materials are integrated. It is presumed that the bonding of the two porous metal materials occurs when at least a portion of the skeletons of the two porous metal materials become intertwined at the interface between the two opposing porous metal materials. In the resulting porous metal body, no adhesive or the like is present at the interface between the two opposing porous metal materials.

[0083] The inventors have discovered that by performing two-stage pressing, it is possible to obtain a metal porous body of embodiment 1 in which the opening ratio A1 of the first region is 40% or less and the transmitted light area ratio of the first main surface is 2% or less.

[0084] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0085] [Preparation of Metal Porous Body] A sheet-shaped metal porous body material made of nickel having a three-dimensional mesh structure skeleton was prepared. For each sample, one, two, or three sheets of metal porous body material (first metal porous body material, second metal porous body material, third metal porous body material) were prepared. The average pore size and thickness of the metal porous body material prepared for each sample are as shown in Table 1.

[0086] Next, the metal porous body material was pressed to obtain a metal porous body. For samples prepared with two or three metal porous body materials, the metal porous body materials were stacked so that the main surfaces of the metal porous body materials faced each other to obtain a laminate, and then pressed. When three metal porous body materials were used, the first metal porous body material, the second metal porous body material, and the third metal porous body material were stacked in the above order and pressed.

[0087] The pressing was carried out in the thickness direction of the metal porous material using a roll press. The overall thickness of the metal porous material after the first pressing step and the overall thickness of the metal porous material after the second pressing step are shown in the "First Step" and "Second Step" columns of "Pressing" in Table 1, respectively. Samples marked with "-" in the "Second Step" column in Table 1 did not undergo the second pressing step.

[0088]

[0089] [Measurement of Metal Porous Body] For each sample of metal porous body, the thickness of the first metal porous body layer corresponding to the first metal porous body material, the second metal porous body layer corresponding to the second metal porous body material, and the third metal porous body layer corresponding to the third metal porous body material was measured. The measurement was performed by observing the cross section of the metal porous body with a microscope at a magnification of 100x. The thickness of each of the first metal porous body layer, the second metal porous body layer, and the third metal porous body layer was measured at three locations, and the average was calculated to represent the thickness of each of the first metal porous body layer, the second metal porous body layer, and the third metal porous body layer. The results are shown in the "First Metal Porous Body Layer," "Second Metal Porous Body Layer," and "Third Metal Porous Body Layer" columns of Table 2. Furthermore, the "Laminate" column of Table 2 also shows the thickness of the entire laminate.

[0090]

[0091] For each sample of the metal porous body, the aperture ratio A1 of the first region, the aperture ratio A2 of the second region, the aperture ratio A3 of the third region, the transmitted light area ratio of the first main surface, the upper limit of the circle-equivalent diameter of the first apertures, and the percentage (N2 / N1) x 100 of the number N2 of second apertures relative to the number N1 of first apertures were measured. Specific measurement methods were as described in embodiment 1. Furthermore, A2 / A1 and A3 / A1 were calculated based on the measurement results. The results are shown in Table 3.

[0092]

[0093] [Evaluation of Porous Metallic Body] <AEM-Type Water Electrolysis Catalyst Coating> The amount of catalyst that could be applied to the surface of each sample was evaluated. The specific evaluation method is as follows. Catalyst ink was applied to the first principal surface of each sample. A commercially available platinum-supported carbon powder, which is a catalyst for AEM-type water electrolysis, was used as the catalyst contained in the catalyst ink. The catalyst ink was prepared by mixing platinum-supported carbon powder with a 10 wt % polytetrafluoroethylene (PTFE) dispersion solution (solvent: pure water) at a ratio that would result in a concentration that could be applied. The percentage of the area of ​​the catalyst region relative to the area of ​​the entire field of view (hereinafter also referred to as "catalyst region percentage") was measured using SEM-EDX. The results are shown in the "AEM-Type Water Electrolysis Catalyst Coating" column in Table 4. A larger value for the catalyst region percentage indicates a larger amount of catalyst that can be applied to the surface of the porous metal body.

[0094] <Pressure Loss> For each sample, the pressure loss was evaluated when air was passed through the porous metal body. The specific evaluation method is as follows. A measurement sample measuring 25 mmφ was prepared for each sample. The sample was tightly fixed in a pipe with an inner diameter of 25 mm, and air was allowed to flow through the pipe to measure the pressure loss when the air flowed perpendicular to the main surface of the measurement sample. The difference from the blank was taken, and when the air flow rate was 1 m / s, a pressure loss of 15 kPa or less was evaluated as "A," and a pressure loss of more than 15 Pa was evaluated as "B." The evaluations are shown in the "Pressure Loss" column of Table 4.

[0095]

[0096] [Discussion] The porous metal bodies of Samples 1 to 12 were obtained by two-stage pressing and correspond to Examples. The porous metal bodies of Samples 101 to 106 were obtained by only first-stage pressing and correspond to Comparative Examples.

[0097] It was confirmed that the porous metal bodies of Samples 1 to 12 had an aperture ratio A1 of 40% or less, which was smaller than the aperture ratio A1 of the porous metal bodies of Samples 101 to 106. This indicates that the porous metal bodies of Samples 1 to 12 have smooth surfaces and can suppress damage to the electrolyte membrane.

[0098] It was confirmed that the porous metal bodies of Samples 1 to 12 had a larger amount of catalyst that could be applied to the surface of the porous metal bodies than the porous metal bodies of Samples 101 to 106.

[0099] It was confirmed that the porous metal bodies of Samples 1 to 12 had smaller pressure loss than the porous metal bodies of Samples 101 to 104. This shows that the porous metal bodies of Samples 1 to 12 allow the electrolyte solution used in AEM-type water electrolysis and generated gases such as oxygen and hydrogen to pass through smoothly.

[0100] From the above, it is presumed that when the porous metal bodies of Samples 1 to 12 are used as electrodes in an AEM water electrolysis device, damage to the electrolyte membrane can be suppressed, which in turn leads to a thinner electrolyte membrane and improved electrolysis performance. Furthermore, when the porous metal bodies of Samples 1 to 12 are used as electrodes in a CCS-type AEM water electrolysis device, in particular, it is presumed that the amount of catalyst on the surface can be increased, further improving electrolysis performance.

[0101] Furthermore, the metal porous body of the present disclosure is considered to be effective not only as an electrode for an AEM water electrolysis device, but also in other applications where surface smoothness, porosity, and electrical conductivity are simultaneously required, and is presumed to be effective, for example, as a current collector for an anode-supported solid oxide fuel cell.

[0102] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined and modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0103] 1 First main surface, 2 Second main surface, 3 Third main surface, 4 Fourth main surface, 5 First metal porous layer, 6 Second metal porous layer, 7 Third metal porous layer, 8 First interface, 9 Second interface, 10 Metal porous body, 11 Skeleton, 12 Skeleton main body, 13 Interior of skeleton, 14 Pore portion, 15 First region, 16 Second region, 17 Third region.

Claims

1. A metal porous body having a three-dimensional network-like structure skeleton, wherein the metal porous body is in a sheet shape including a first main surface and a second main surface opposite to the first main surface, the metal porous body includes a first metal porous body layer including the first main surface, the first metal porous body layer includes a first region sandwiched between a virtual surface S11 having a distance of 0.01 mm from the first main surface to the first metal porous body layer side and a virtual surface S12 having a distance of 0.10 mm from the first main surface to the first metal porous body layer side, an aperture ratio A1 of the first region is 40% or less, the aperture ratio is measured by observing a cross-section along the normal line of the first main surface of the metal porous body with a scanning electron microscope, a transmitted light area ratio of the first main surface is 2% or less, and the transmitted light area ratio is measured by observing the first main surface with a microscope in a state where the metal porous body is irradiated with light from the second main surface side.

2. The metal porous body according to claim 1, further including a second metal porous body layer provided in contact with a main surface of the first metal porous body layer opposite to the first main surface, the second metal porous body layer includes a second region sandwiched between a first interface between the first metal porous body layer and the second metal porous body layer and a virtual surface S13 having a distance of 0.01 mm from the first interface to the second metal porous body layer side, and an aperture ratio A2 of the second region is the same as or larger than the aperture ratio A1.

3. The metal porous body according to claim 2, wherein a ratio A2 / A1 of the aperture ratio A2 to the aperture ratio A1 is 1.0 or more and 4.0 or less.

4. The metal porous body according to claim 2 or 3, further including a third metal porous body layer provided in contact with a fourth main surface opposite to a third main surface of the second metal porous body layer in contact with the first metal porous body layer, the third metal porous body layer includes a third region sandwiched between a second interface between the second metal porous body layer and the third metal porous body layer and a virtual surface S14 having a distance of 0.01 mm from the second interface to the third metal porous body layer side, and an aperture ratio A3 of the third region is the same as or larger than the aperture ratio A1.

5. The metal porous body according to claim 4, wherein a ratio A3 / A1 of the aperture ratio A3 to the aperture ratio A1 is 1.0 or more and 4.0 or less.

6. The first major surface includes a first opening defined by the skeleton, the first opening being an opening through which light passes when the metal porous body is irradiated with light from the second major surface side, the first opening including a second opening, the equivalent circle diameter of the second opening being 35 μm or less, and the percentage (N2 / N1)×100 of the number N2 of the second openings with respect to the number N1 of the first openings being 50% or more. The metal porous body according to any one of claims 1 to 5.

7. The first major surface includes a first opening defined by the skeleton, the first opening being an opening through which light passes when the metal porous body is irradiated with light from the second major surface side, and the upper limit of the equivalent circle diameter of the first opening being 60 μm or less. The metal porous body according to any one of claims 1 to 6.

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