Porous composite

Abstract

A porous composite according to the present invention comprises a substrate having a primary surface and a nickel layer disposed on at least a portion of the primary surface. The substrate is formed from either a nickel porous body having a three-dimensional network construction or a nickel mesh structure. The nickel layer has an arithmetical mean height Sa as defined by ISO 25178 of 5 μm or less.

Description

porous composite

[0001] The present disclosure relates to porous composites.

[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 composite porous body of the present disclosure is a porous composite comprising: a substrate having a first main surface; and a nickel layer provided on at least a portion of the first main surface, wherein the substrate is made of a nickel porous body or a nickel mesh structure having a three-dimensional network structure, and the nickel layer has an arithmetic mean height Sa defined in ISO 25178 of 5 μm or less.

[0006] FIG. 1 is a cross-sectional view of an example of a porous composite according to Embodiment 1. FIG. 2 is a diagram illustrating a typical configuration example of a nickel porous body. FIG. 3 is an enlarged schematic view of a cross section of the nickel porous body shown in FIG. 2. FIG. 4 is a schematic view of a cross section of the skeleton 11 shown in FIG. 3 taken along line IV-IV. FIG. 5 is a diagram showing an example of an SEM image of a cross section of the porous composite according to Embodiment 1. FIG. 6 is a diagram showing a schematic SEM image of a cross section of a nickel mesh structure. FIG. 7 is a diagram showing an example of an SEM image of a cross section of the nickel layer of the porous composite according to Embodiment 1.

[0007] [Problem to be Solved by the Present Disclosure] In AEM-type water electrolysis, an anion exchange membrane and an electrode made of a conductive porous body are arranged side by side. If the surface of the porous body is rough, protrusions on the surface of the porous body may pierce the anion exchange membrane, causing problems such as a micro-short circuit or through-holes in the anion exchange membrane, which may lead to cross-leakage of oxygen and hydrogen. To avoid these problems, one possible solution is to thicken the anion exchange membrane. However, thickening the anion exchange membrane increases the resistance of the water electrolysis cell, which increases the voltage during water electrolysis and increases power consumption. Therefore, there is a need for a technology that can provide electrodes with reduced surface roughness to prevent problems with the anion exchange membrane.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a porous composite that is used as an electrode for an AEM water electrolysis device and has reduced surface roughness.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) A porous composite of the present disclosure is a porous composite comprising: a substrate having a first main surface; and a nickel layer provided on at least a portion of the first main surface, wherein the substrate is a nickel porous body having a three-dimensional network structure or a nickel mesh structure, and the nickel layer has an arithmetic mean height Sa defined in ISO 25178 of 5 μm or less.

[0010] According to the present disclosure, it is possible to provide a porous composite that is used as an electrode for an AEM-type water electrolysis device and has reduced surface roughness. In the present disclosure, ISO 25178 is, more specifically, ISO 25178-2:2012.

[0011] (2) In the above (1), the nickel layer may have a plurality of pores therein, and the average opening diameter of the nickel layer may be 0.1 μm or more and 50 μm or less.

[0012] This improves the smoothness of the surface of the nickel layer, making it less likely to pierce the anion exchange membrane.

[0013] (3) In the above (1) or (2), the average thickness of the nickel layer may be 0.5 μm or more and 100 μm or less.

[0014] This allows the strength of the nickel layer itself to be maintained in an AEM water electrolysis device using the porous composite as an electrode. Also, material transport of the electrolyte solution, generated gas, and the like becomes smoother between the substrate portion of the porous composite and the anion exchange membrane, improving the electrolysis efficiency of the AEM water electrolysis device.

[0015] (4) In any one of the above (1) to (3), the nickel layer may have a plurality of pores therein, and the porosity of the nickel layer may be 40% or more and 75% or less.

[0016] As a result, in an AEM water electrolysis device using the porous composite as an electrode, material transport such as the electrolyte and generated gas is smoother between the substrate portion of the porous composite and the anion exchange membrane, improving the electrolysis efficiency of the AEM water electrolysis device.

[0017] (5) In any one of the above (1) to (4), the porous composite may have an average thickness of 50 μm or more and 500 μm or less.

[0018] As a result, in an AEM water electrolysis device using the porous composite as an electrode, material transport such as electrolyte and gas within the electrolysis cell becomes smoother, the electrolysis device can be made smaller, and the uniformity of material transport within the electrolysis cell is improved, thereby improving the electrolysis efficiency of the AEM water electrolysis device.

[0019] (6) In any one of the above (1) to (5), the substrate may have an average opening diameter of 50 μm or more and 800 μm or less.

[0020] This allows smooth material transport of electrolyte, gas, and the like within the electrolysis cell in an AEM-type water electrolysis device using the porous composite as an electrode, improving the electrolysis efficiency of the AEM-type water electrolysis device.

[0021] (7) In any one of the above (1) to (6), the cross-sectional porosity of the substrate may be 50% or more and 95% or less.

[0022] This allows smooth material transport of electrolyte, gas, and the like within the electrolysis cell in an AEM-type water electrolysis device using the porous composite as an electrode, improving the electrolysis efficiency of the AEM-type water electrolysis device.

[0023] [Details of the embodiment of the present disclosure] Specific examples of the porous composite of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0024] 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.

[0025] 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.

[0026] [Embodiment 1: Porous Composite] A porous composite according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a porous composite comprising: a substrate having a first main surface; and a nickel layer provided on at least a portion of the first main surface, wherein the substrate is made of a nickel porous body or a nickel mesh structure having a three-dimensional network structure, and the nickel layer has an arithmetic mean height Sa defined in ISO 25178 of 5 μm or less.

[0027] In the porous composite of embodiment 1, the nickel layer has a reduced surface roughness and an arithmetic mean height Sa of 5 μm or less as defined in ISO 25178. When the porous composite is used in an application involving contact with an anion exchange membrane, such as AEM-type water electrolysis, the nickel layer has a arithmetic mean height Sa of 5 μm or less, which prevents protrusions on the surface of the porous composite from piercing the anion exchange membrane, thereby preventing problems such as micro-short circuits and the formation of through-holes in the anion exchange membrane that allow cross-leakage of oxygen and hydrogen.

[0028] Furthermore, by making the arithmetic mean height Sa of the nickel layer 5 μm or less, the protrusions on the surface of the porous composite are prevented from piercing the anion exchange membrane, which contributes to making the anion exchange membrane thinner and ultimately leads to improved electrolysis efficiency.

[0029] AEM-type water electrolysis is divided into the CCM method, in which a catalyst is applied to an anion exchange membrane, and the CCS method, in which a catalyst is applied to an electrode made of a conductive porous material. In the CCS method, increasing the contact area between the catalyst and the anion exchange membrane, which contributes to the electrolysis reaction, contributes to improving electrolysis performance.

[0030] In the porous composite of Embodiment 1, the arithmetic mean height Sa of the nickel layer is 5 μm or less, and therefore when a catalyst is applied to the nickel layer to form a catalyst layer, the surface irregularities of the catalyst layer are reduced. Therefore, when the porous composite of Embodiment 1, with a catalyst applied to the nickel layer, is used in CCS-type AEM-type water electrolysis, it is possible to increase the contact area between the catalyst and the anion exchange membrane.

[0031] <Porous Composite Structure> As shown in FIG. 1 , a porous composite 30 of embodiment 1 includes a substrate 5 having a first main surface 1 and a nickel layer 20 provided on at least a portion of the first main surface 1.

[0032] The lower limit of the average thickness of the porous composite may be 50 μm or more, 100 μm or more, or 150 μm or more, from the viewpoint of enabling smooth substance transport within an electrolysis cell in an AEM-type water electrolysis device using the porous composite as an electrode. The upper limit of the average thickness of the porous composite may be 500 μm or less, 400 μm or less, or 300 μm or less, from the viewpoint of reducing the size of the electrolysis device and improving the uniformity of substance transport within the electrolysis cell. The average thickness of the porous composite may be 50 μm or more and 500 μm or less, 100 μm or more and 400 μm or less, or 150 μm or more and 300 μm or less.

[0033] In the present disclosure, the average thickness of a porous composite is measured by the following method. The thickness is measured at any five points on the porous composite using a commercially available digital thickness gauge (Teclock Corporation). The average of the thicknesses at the five points is calculated. In the present disclosure, this average corresponds to the average thickness of the porous composite.

[0034] <Substrate> In the porous composite 30 of embodiment 1, the substrate 5 is made of a nickel porous body 10 having a three-dimensional network structure or a nickel mesh structure. The substrate 5 has a sheet-like appearance as a whole, including a first main surface 1 and a second main surface 2 opposite to the first main surface 1.

[0035] <<Nickel Porous Body>> Fig. 2 is a diagram illustrating a typical configuration example of a nickel porous body 10. Fig. 3 is an enlarged schematic diagram showing a cross section of the nickel porous body 10 shown in Fig. 2. As shown in Fig. 3, the nickel porous body 10 has a skeleton 11 with a three-dimensional network structure. Pores 14 are formed inside the nickel porous body 10 by the skeleton 11 with the three-dimensional network structure.

[0036] The skeleton 11 of the nickel porous body 10 is composed of a skeleton main body 12, and the interior 13 of the skeleton 11 is hollow. At least some of the pores 14 formed by the skeleton 11 are interconnected pores that communicate with adjacent pores 14.

[0037] The nickel porous body 10 may contain 80% by mass or more of nickel. In the present disclosure, the composition of the nickel porous body 10 refers to the composition of the skeletal main body 12. In other words, it can also be expressed that the skeletal main body 12 of the nickel porous body 10 contains 80% by mass or more of nickel. The nickel porous body 10 may contain other components in addition to nickel. The other components may be at least one selected from the group consisting of iron, cobalt, chromium, phosphorus, boron, and carbon. The total content of the other components in the nickel porous body 10 may be 0.1% by mass or more and 20% by mass or less. The total content of the other components in the nickel porous body 10 is measured by ICP (Inductively Coupled Plasma) emission spectroscopy.

[0038] Fig. 4 shows a schematic cross section of the skeleton 11 taken along line IV-IV 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).

[0039] <Nickel Mesh Structure> The nickel mesh structure may be a woven fabric, a nonwoven fabric, a punched sheet, or the like. The nickel mesh structure may contain 80% by mass or more of nickel. The nickel mesh structure may contain other components in addition to nickel. The other components may be at least one selected from the group consisting of iron, cobalt, chromium, phosphorus, boron, and carbon. The total content of the other components in the nickel mesh structure may be 0.1% by mass or more and 20% by mass or less. The total content of the other components in the nickel mesh structure is measured by ICP atomic emission spectroscopy.

[0040] <Average Opening Diameter of Substrate> In an AEM water electrolysis device using the porous composite as an electrode, the average opening diameter of the substrate 5 may be 50 μm or more and 800 μm or less, 100 μm or more and 700 μm or less, or 150 μm or more and 600 μm or less, from the viewpoint of improving the substance transport efficiency of the electrolytic solution, gas, and the like in the substrate and smoothing the substance transport in the electrolysis cell.

[0041] In the present disclosure, when the substrate 5 is a nickel porous body, the average opening diameter of the substrate 5 is measured by the following procedure: Step A1: The porous composite 30 is cut along an imaginary plane parallel to the normal to the main surface to expose a cross section of the substrate 5 along the normal to the main surface.

[0042] Step A2: A cross section of the substrate 5 is observed using a scanning electron microscope (SEM) at an appropriate magnification that allows the opening structure of the substrate 5 to be photographed within the field of view, thereby obtaining an SEM image of the cross section of the substrate 5. The boundary between the substrate 5 and the nickel layer 20 can be confirmed in the SEM image. The position of the boundary corresponds to the position of the first main surface 1 of the substrate 5.

[0043] Step A3: In the SEM image of the cross section of the substrate 5, three imaginary lines are drawn to divide the substrate into four equal parts in the thickness direction. The imaginary lines are designated as imaginary line L1, imaginary line L2, and imaginary line L3, in that order from the nickel layer side. The lengths of the imaginary lines L1, L2, and L3 are the lengths across the field of view.

[0044] Step A4: For each of the imaginary lines L1, L2, and L3, measure the number N1 (pores) of pores crossed by the imaginary lines and the total length LT (μm) of the pores. Calculate LT (μm) / N1 (pores) for each of the three imaginary lines. Calculate the average A1 of LT (μm) / N1 (pores) for the three imaginary lines.

[0045] Step A5: SEM images of step A2 are obtained at three non-overlapping locations, and steps A3 and A4 are performed based on each SEM image to calculate an average A1. An average A2 of the three averages A1 is calculated. In the present disclosure, this average A2 corresponds to the average opening diameter of the substrate 5.

[0046] FIG. 5 is an example of an SEM image of a cross section of the porous composite of embodiment 1. In FIG. 5, line LS1 indicates the first main surface of the substrate 5, and line LS2 indicates the second main surface of the substrate 5. In FIG. 5, imaginary lines L1, L2, and L3 are shown as white lines. In FIG. 5, the number of pores intersected by imaginary line L1 is 14, and the total length of the pores is 1727 μm. The number of pores intersected by imaginary line L2 is 12, and the total length of the pores is 1701 μm. The number of pores intersected by imaginary line L3 is 14, and the total length of the pores is 1815 μm. Based on this, the average opening diameter of the substrate 5 shown in FIG. 5 is calculated to be 131.1 μm. In FIG. 5, the pores correspond to the area sandwiched between the arrows and the area sandwiched between the arrows and the outer edge of the measurement area. The length of the pores corresponds to the length of the black lines on the imaginary lines. The hollow space inside the skeleton 11 is not measured as a pore portion.

[0047] It has been confirmed that, for the same porous composite, there is almost no variation in the measurement results when the average pore size of the substrate is measured in different measurement regions. Because the substrate is sheet-like, slight waviness may be present at the boundary between the substrate 5 and the nickel layer 20 in the cross-sectional SEM image. In such cases, the line LS1 shown in the cross-sectional SEM image does not exactly coincide with the boundary between the substrate 5 and the nickel layer 20. However, as long as the line LS1 is located approximately at the boundary between the substrate 5 and the nickel layer 20, it has been confirmed that this has almost no effect on the measurement results of the average pore size of the substrate 5.

[0048] In the present disclosure, when the substrate 5 is a nickel mesh structure, the average opening diameter of the substrate 5 is measured by the following procedure. The porous composite 30 is cut along an imaginary plane parallel to the normal to the main surface to expose a cross section of the substrate 5 along the normal to the main surface. The cross section of the substrate 5 is observed using a scanning electron microscope at an appropriate magnification that allows the opening structure of the substrate 5 to be photographed within the field of view, and an SEM image of the cross section of the substrate 5 is obtained. Figure 6 is a diagram schematically showing an SEM image of the cross section of a nickel mesh structure.

[0049] In an SEM image of the cross section of the nickel mesh structure, a single imaginary straight line L61 is drawn across the thickest part of the cross section of the metal wire 16 that constitutes the mesh. The number N1 (pores 14) that the imaginary line crosses and the total length LT (μm) of the pores 14 are measured, and LT (μm) / N1 (pores) is calculated.

[0050] SEM images of the cross section of the nickel mesh structure are taken at three non-overlapping locations, and LT (μm) / N1 (pieces) is calculated based on each SEM image using the above procedure. The average of the three LT (μm) / N1 (pieces) is calculated. In the present disclosure, this average corresponds to the average opening diameter of the substrate 5.

[0051] It has been confirmed that, for the same porous composite, there is almost no variation in the measurement results even when the average opening diameter of the substrate is measured in different measurement regions.

[0052] <Cross-sectional porosity of substrate> The lower limit of the cross-sectional porosity of the substrate 5 may be 50% or more, 55% or more, or 65% or more from the viewpoint of reducing pressure loss in the porous composite 30 and smoothing material transport such as the electrolyte and gas within the electrolytic cell, thereby improving the electrolysis efficiency of the AEM water electrolysis device. The upper limit of the cross-sectional porosity of the substrate 5 may be 95% or less, 85% or less, or 75% or less from the viewpoint of ensuring appropriate compressive strength. The cross-sectional porosity of the substrate 5 may be 50% or more and 95% or less, 55% or more and 85% or less, or 65% or more and 75% or less.

[0053] In the present disclosure, the cross-sectional porosity of the substrate 5 is measured by the following procedure: Step B1: The porous composite 30 is cut along an imaginary plane parallel to the normal to the main surface to expose a cross section of the substrate 5 along the normal to the main surface.

[0054] Step B2: A cross section of the substrate 5 is observed using a scanning electron microscope at an appropriate magnification that allows the porous structure of the substrate 5 to be photographed, and an SEM image is obtained.

[0055] Step B3: In the SEM image of the cross section of the substrate 5, a rectangular measurement area is set that includes an area large enough to measure the cross-sectional porosity of the substrate 5. Using image processing software, the percentage (S1 / SA) of the area S1 of the pores relative to the area SA of the entire measurement area is calculated as (S1 / SA) x 100.

[0056] Step B4: SEM images of step B2 are obtained at three non-overlapping locations, and step B3 is performed based on each SEM image to determine the percentage (S1 / SA) x 100. The average of the three percentages (S1 / SA) x 100 is calculated. In the present disclosure, this average corresponds to the cross-sectional porosity of the substrate 5.

[0057] It has been confirmed that, for the same porous composite, there is almost no variation in the measurement results even when the cross-sectional porosity of the substrate is measured by changing the measurement area.

[0058] <Average Thickness of Substrate> The average thickness of the substrate 5 may be, for example, 0.04 mm or more and 0.5 mm or less, or 0.1 mm or more and 0.3 mm or less. The method for measuring the average thickness of the substrate 5 is as follows. An SEM image of a cross section of the substrate 5 is obtained using the same method as steps A1 and A2 of the method for measuring the average opening diameter of the substrate 5. In the SEM image, the distance from the first main surface 1 to the second main surface 2 of the substrate 5 is measured at any five points. The average of the distances at the five points is calculated. In the present disclosure, this average corresponds to the average thickness of the substrate 5.

[0059] It has been confirmed that, for the same porous composite, there is almost no variation in the measurement results even when the measurement area is changed when measuring the average thickness of the substrate.

[0060] <Nickel layer> In the porous composite 30 of Embodiment 1, the surface of the nickel layer 20 is the surface to which a catalyst is applied when the porous composite 30 is used for CCS-type AEM-type water electrolysis. In Fig. 1 , the nickel layer 20 is provided over the entire first main surface 1, but this is not limited thereto. When the porous composite 30 is used for CCS-type AEM-type water electrolysis in a state where a catalyst is applied to the nickel layer 20, the region where the nickel layer 20 is provided may be part of the first main surface 1, as long as the catalyst can be present in the region facing the anion exchange membrane.

[0061] The nickel layer 20 may contain 80% by mass or more of nickel. The nickel layer 20 may contain other components other than nickel. The other components may be at least one selected from the group consisting of iron, cobalt, chromium, phosphorus, boron, and carbon. The total content of the other components in the nickel layer 20 may be 0.01% by mass or more and 20% by mass or less. The content of the other components in the nickel layer 20 is measured by ICP atomic emission spectroscopy.

[0062] The nickel layer 20 can be made of a nickel sintered body.

[0063] <Arithmetic Mean Height Sa of Nickel Layer> The upper limit of the arithmetic mean height Sa of the nickel layer 20 as defined in ISO 25178 is 5 μm or less, may be 4 μm or less, or may be 3 μm or less. The lower limit of the arithmetic mean height Sa of the nickel layer 20 is not particularly limited and may be 0 μm or more, or from a manufacturing standpoint, may be 0.5 μm or more. The arithmetic mean height Sa of the nickel layer 20 may be 0 μm or more and 5 μm or less, 0 μm or more and 4 μm or less, or 0.5 μm or more and 5 μm or less. If the arithmetic mean height Sa of the nickel layer 20 exceeds 5 μm, the protrusions on the surface of the porous composite may puncture the anion exchange membrane. Furthermore, if deep holes exist on the surface of the nickel layer 20 and a catalyst is applied to the nickel layer, the catalyst embedded in the deep holes may not function, resulting in catalyst loss. Furthermore, holes may be formed in the catalyst layer itself, which is formed by applying a catalyst to a nickel layer, and the perforated areas may not function as catalysts.

[0064] In the present disclosure, the arithmetic mean height Sa defined in ISO 25178 is measured by the following procedure. The surface of the nickel layer 20 is observed with a laser microscope at an appropriate magnification that allows the uneven surface structure to be observed. The measurement area is the entire field of view. The surface of the nickel layer 20 is the main surface of the nickel layer 20 opposite the main surface facing the first main surface 1 of the substrate 5, and is shown as the third main surface 3 in FIG. 1 . The arithmetic mean height Sa defined in ISO 25178 of the measurement area is measured. For the measurement, a laser microscope "VK-X3000" (trademark) manufactured by Keyence Corporation is used. The arithmetic mean height Sa is measured in three measurement areas that do not overlap each other. The average of the arithmetic mean heights Sa of the three measurement areas is calculated. In the present disclosure, this average corresponds to the arithmetic mean height Sa of the nickel layer 20.

[0065] It has been confirmed that, for the same porous composite, there is almost no variation in the measurement results even when the measurement area is changed when the arithmetic mean height Sa of the nickel layer is measured.

[0066] <Average Opening Diameter of Nickel Layer> In the porous composite 30 of embodiment 1, the nickel layer 20 may have a plurality of pores therein. In an AEM-type water electrolysis device using the porous composite as an electrode, the lower limit of the average opening diameter of the nickel layer 20 may be 0.1 μm or more, 1 μm or more, or 2 μm or more from the viewpoint of smooth transport of substances such as electrolyte and gas within an electrolysis cell. The upper limit of the average opening diameter of the nickel layer 20 may be 50 μm or less, 25 μm or less, or 10 μm or less from the viewpoint of improving the surface smoothness of the nickel layer, preventing protrusions on the surface of the porous composite from piercing the opposing anion exchange membrane, and maintaining the surface smoothness of a catalyst layer formed by coating the nickel layer. The average opening diameter of the nickel layer 20 may be 0.1 μm or more and 50 μm or less, 1 μm or more and 2 μm or more and 10 μm or less.

[0067] In the present disclosure, the average opening diameter of the nickel layer 20 is measured by the following procedure: Step C1: The porous composite 30 is cut along an imaginary plane parallel to the normal to the main surface to expose a cross section of the nickel layer 20 along the normal to the main surface.

[0068] Step C2: The cross section of the nickel layer 20 is observed using an SEM at an appropriate magnification that allows the opening structure of the nickel layer 20 to be photographed within the field of view, thereby obtaining an SEM image of the cross section of the nickel layer 20. The boundary between the substrate 5 and the nickel layer 20 can be confirmed in the SEM image. The position of the boundary corresponds to the position of the first main surface 1 of the substrate 5.

[0069] Step C3: In the SEM image of the cross section of the nickel layer 20, three imaginary lines are drawn to divide the nickel layer into four equal parts in the thickness direction. The imaginary lines are designated as imaginary line L11, imaginary line L12, and imaginary line L13, in that order from the substrate side.

[0070] Step C4: For each of the imaginary lines L11, L12, and L13, measure the number of pores N11 (number of pores) crossed by the imaginary lines and the total length of the pores LT1 (μm). Calculate LT1 (μm) / N11 (number of pores) for each of the three imaginary lines. Calculate the average A11 of LT1 (μm) / N11 (number of pores) for the three imaginary lines.

[0071] Step C5: SEM images of step C2 are obtained at three non-overlapping locations, and steps C3 and C4 are performed based on each SEM image to calculate the average A11. The average A12 of the three average A11s is calculated. In the present disclosure, the average A12 corresponds to the average opening diameter of the nickel layer 20.

[0072] FIG. 7 is an example of an SEM image of a cross section of the nickel layer of the porous composite of embodiment 1. In FIG. 7, line LS3 indicates the surface of the nickel layer, and line LS4 indicates the boundary between the substrate 5 and the nickel layer. In FIG. 7, imaginary lines L11, L12, and L13 are shown as white lines. In FIG. 7, the number of pores crossed by imaginary line L13 is 7, and the total pore length is 18.4 μm. Similarly, the number of pores crossed by imaginary line L12 is 7, and the total pore length is 22.4 μm. The number of pores crossed by imaginary line L11 is 12, and the total pore length is 35.2 μm. Based on this, the average opening diameter of the nickel layer 20 shown in FIG. 7 is calculated to be 2.9 μm. In FIG. 7, the pores correspond to the area between the arrows and the area between the arrows and the outer edge of the measurement area. The pore length corresponds to the length of the black line on the imaginary line.

[0073] It has been confirmed that, for the same porous composite, the average opening diameter of the nickel layer is measured with different measurement areas, and the measurement results show almost no variation.

[0074] <Porosity of Nickel Layer> In the porous composite 30 of embodiment 1, the nickel layer 20 may have a plurality of pores therein. The lower limit of the porosity of the nickel layer 20 may be 40% or more, 45% or more, or 55% or more, from the viewpoint of smoothing material transport of the electrolyte and generated gas between the substrate portion of the porous composite and the anion exchange membrane in an AEM water electrolysis device using the porous composite as an electrode and improving the electrolysis efficiency of the AEM water electrolysis device. The upper limit of the porosity of the nickel layer 20 may be 75% or less, 70% or less, or 65% or less, in order to provide appropriate compressive strength. The porosity of the nickel layer 20 may be 40% or more and 75% or less, 45% or more and 70% or less, or 55% or more and 65% or less.

[0075] In the present disclosure, the porosity of the nickel layer 20 is measured by the following procedure: Step D1: The porous composite 30 is cut along an imaginary plane parallel to the normal to the main surface to expose a cross section of the nickel layer 20 along the normal to the main surface.

[0076] Step D2: The cross section of the nickel layer 20 is observed using a scanning electron microscope at an appropriate magnification that allows the pores in the nickel layer 20 to be photographed, and an SEM image is obtained.

[0077] Step D3: A rectangular measurement area that includes an area large enough to measure the porosity of the nickel layer 20 is provided in the SEM of the cross section of the nickel layer 20. Using image processing software, the percentage of the pore area S11 to the total area SA1 of each measurement area is calculated as (S11 / SA1) x 100.

[0078] Step D4: The SEM images of step D2 are obtained at three non-overlapping locations, and step D3 is performed based on each SEM image to determine the percentage (S11 / SA1) x 100. The average of the three percentages (S11 / SA1) x 100 is calculated. In the present disclosure, this average corresponds to the porosity of the nickel layer 20.

[0079] It has been confirmed that, for the same porous composite, even when the porosity of the nickel layer is measured in different measurement areas, there is almost no variation in the measurement results.

[0080] <Average Thickness of Nickel Layer> The lower limit of the average thickness of the nickel layer 20 may be 0.5 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, or 30 μm or more from the viewpoint of maintaining the strength of the nickel layer itself. The upper limit of the average thickness of the nickel layer 20 may be 100 μm or less, 90 μm or less, or 80 μm or less from the viewpoint of smooth material transport of the electrolyte and generated gas between the substrate portion of the porous composite and the anion exchange membrane. The average thickness of the nickel layer 20 may be 0.5 μm or more and 100 μm or less, 5 μm or more and 100 μm or less, 10 μm or more and 100 μm or less, 20 μm or more and 90 μm or less, or 30 μm or more and 80 μm or less.

[0081] The method for measuring the average thickness of the nickel layer 20 is as follows. An SEM image of a cross section of the nickel layer 20 is obtained using the same methods as steps C1 and C2 of the method for measuring the average opening diameter of the nickel layer 20. In the SEM image, the distance from the surface of the nickel layer 20 to the boundary between the nickel layer 20 and the substrate 5 is measured at any five points. The average of the distances at the five points is calculated. In the present disclosure, this average corresponds to the average thickness of the nickel layer 20.

[0082] It has been confirmed that, for the same porous composite, there is almost no variation in the measurement results when the average thickness of the nickel layer is measured in different measurement areas.

[0083] <Method for manufacturing porous composite> A description will be given of an example of a method for manufacturing the porous composite of Embodiment 1. The method for manufacturing the porous composite can include the steps of preparing a substrate material, preparing a nickel microporous sheet, roll-pressing the substrate material and the nickel microporous sheet in a stacked state to obtain a laminate, and heating the laminate to obtain the porous composite.

[0084] <Step of Preparing Substrate Material> A nickel porous body or a nickel mesh structure having a three-dimensional network structure is prepared as the substrate material. The nickel porous body or nickel mesh structure used has an overall sheet shape.

[0085] The average pore diameter of the nickel porous body 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.

[0086] The average pore diameter of the nickel porous body is defined by the following formula [1]. In formula [1], n c is the average number of pores per inch (25.4 mm = 25,400 μm) obtained by observing at least 10 fields of view of the main surface of the nickel porous body using a microscope or the like. Average pore diameter = 25,400 μm / n c Formula [1] The number of pores is measured in accordance with the method for determining the number of pores (number of cells) in flexible foamed materials specified in JIS K6400-1:2004, Appendix 1 (Reference).

[0087] As the nickel porous body, for example, "Nickel Celmet" (trademark) manufactured by Sumitomo Electric Industries, Ltd. can be prepared.

[0088] As the nickel mesh structure, for example, a plain weave of nickel wire can be prepared.

[0089] <Step of Preparing Nickel Microporous Sheet> The nickel microporous sheet can be prepared by the following procedure. Nickel powder, a binder, and pure water are mixed to obtain a slurry. The slurry is applied to a support. For example, a polytetrafluoroethylene (PTFE) sheet can be used as the support. The slurry applied to the support is dried and then peeled off from the sheet to obtain a nickel green sheet. The drying conditions can be, for example, 30 minutes at 80°C in the atmosphere.

[0090] The nickel green sheet is sintered to obtain a nickel microporous sheet. Sintering conditions can be, for example, 900°C for 10 minutes in a hydrogen atmosphere. The thickness of the nickel microporous sheet can be, for example, 0.5 μm to 100 μm.

[0091] <Step of Obtaining a Laminate> Next, the substrate material and the nickel microporous sheet are roll-pressed together to obtain a laminate. The roll-press conditions can be set to an appropriate roll gap based on the thicknesses of the substrate material and the nickel microporous sheet. For example, the roll gap can be set to about 80% of the desired thickness of the porous composite.

[0092] <<Step of Obtaining Porous Composite>> Next, the laminate is heated to obtain a porous composite. Heating conditions can be, for example, 900°C for 10 minutes in a hydrogen atmosphere. This results in a porous composite in which the substrate and the nickel microporous sheet are bonded together.

[0093] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0094] [Samples 1 to 18] <Production of porous composite> <Step of preparing substrate material> As the substrate material, a nickel porous body (nickel content 99.9% by mass, referred to as "Ni porous body" in Table 1) having a three-dimensional mesh structure or a nickel mesh structure (nickel content 99.9% by mass, referred to as "Ni mesh structure" in Table 1) was prepared. The type of substrate material used in each sample, the average pore size of the substrate material, and the thickness of the substrate material are as shown in Table 1.

[0095] <Step of Preparing Nickel Microporous Sheet> Nickel powder, a binder, and pure water were mixed to obtain a slurry. The average particle size of the nickel powder used in each sample is as shown in Table 1. The average particle size of the nickel powder was measured using a Fisher sub sieve sizer. "Polyvinyl Alcohol 500" (trademark) manufactured by Kishida Chemical Co., Ltd. was used as the binder. The mixing ratio of nickel powder to binder was nickel powder:binder = 95:5 on a dry mass basis. Pure water was added to the mixture of nickel powder and binder to obtain a slurry.

[0096] The slurry was applied to a support made of a PTFE sheet using an applicator. After drying, the applied slurry was peeled off from the support to obtain a nickel green sheet. The drying conditions were air at 80°C for 30 minutes.

[0097] The nickel green sheet was roll-pressed as needed and then sintered to obtain a nickel microporous sheet. The sintering conditions were 900°C for 10 minutes in a hydrogen atmosphere. The thickness of the nickel microporous sheet for each sample is shown in the "Nickel microporous sheet thickness" column in Table 1.

[0098] <Step of Obtaining Laminate> Next, the substrate material and the nickel microporous sheet were laminated together and roll-pressed to obtain a laminate. For each sample, the roll gap during roll-pressing is as shown in the "Roll Gap" column in Table 1.

[0099] <Step of Obtaining Porous Composite> Next, the laminate was heated at 900° C. for 10 minutes in a hydrogen atmosphere to obtain a porous composite.

[0100]

[0101] [Measurement of porous composite] For each sample of composite porous body, the average pore size of the substrate, the cross-sectional porosity of the substrate, the arithmetic mean height Sa of the nickel layer as defined in ISO 25178, the average pore size of the nickel layer, the average thickness of the nickel layer, the porosity of the nickel layer, and the average thickness of the porous composite were measured. Specific measurement methods were as described in embodiment 1. The results are shown in Table 2.

[0102]

[0103] [Evaluation] The composite porous bodies of Samples 1 to 9, 11 to 13, and 15 to 18 have nickel layers with an arithmetic mean height Sa of 5 μm or less as defined in ISO 25178, and therefore correspond to Examples. The composite porous bodies of Samples 10 and 14 have nickel layers with an arithmetic mean height Sa of more than 5 μm as defined in ISO 25178, and therefore correspond to Comparative Examples.

[0104] The composite porous bodies of Samples 1 to 9, Samples 11 to 13, and Samples 15 to 18 have an arithmetic mean height Sa of 5 μm or less, and have reduced surface irregularities. Therefore, when the composite porous bodies of Samples 1 to 9, Samples 11 to 13, and Samples 15 to 18 are used in applications involving contact with an anion exchange membrane, protrusions on the surface of the porous composite are prevented from piercing the anion exchange membrane, preventing problems such as micro-short circuits and the formation of through-holes in the anion exchange membrane that allow oxygen or hydrogen to cross-leak. Furthermore, when a catalyst is applied to the nickel layer of the composite porous bodies of Samples 1 to 9, Samples 11 to 13, and Samples 15 to 18 to form a catalyst layer, the surface irregularities of the catalyst layer are also reduced. Therefore, when the porous composites of Samples 1 to 9, Samples 11 to 13, and Samples 15 to 18 are used as electrodes of a CCS-type AEM water electrolysis device with a catalyst applied to the nickel layer, it is possible to increase the contact area between the catalyst and the anion exchange membrane, and the electrolysis performance of the AEM water electrolysis device is improved.

[0105] 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 or 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.

[0106] 1 First main surface, 2 Second main surface, 3 Third main surface, 5 Substrate, 10 Nickel porous body, 11 Skeleton, 12 Skeleton main body, 13 Inside of skeleton, 14 Pore portion, 16 Metal wire, 20 Nickel layer, 30 Porous composite.

Claims

1. A porous composite comprising a substrate having a first main surface and a nickel layer provided on at least a part of the first main surface, wherein the substrate is a nickel porous body having a three-dimensional network structure or a nickel mesh structure, and the arithmetic mean height Sa defined in ISO 25178 of the nickel layer is 5 μm or less.

2. The porous composite according to claim 1, wherein the nickel layer has a plurality of pores inside, and the average pore diameter of the nickel layer is 0.1 μm or more and 50 μm or less.

3. The porous composite according to claim 1 or 2, wherein the average thickness of the nickel layer is 0.5 μm or more and 100 μm or less.

4. The porous composite according to any one of claims 1 to 3, wherein the nickel layer has a plurality of pores inside, and the porosity of the nickel layer is 40% or more and 75% or less.

5. The porous composite according to any one of claims 1 to 4, wherein the average thickness of the porous composite is 50 μm or more and 500 μm or less.

6. The porous composite according to any one of claims 1 to 5, wherein the average pore diameter of the substrate is 50 μm or more and 800 μm or less.

7. The porous composite according to any one of claims 1 to 6, wherein the cross-sectional porosity of the substrate is 50% or more and 95% or less.

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