Titanium porous body, titanium laminate, water electrolysis device, water electrolysis method, and hydrogen production method

Abstract

A titanium porous body according to the present invention comprises a powder sintered body and is formed in a sheet shape having a thickness of 200 μm or greater. In the titanium porous body, holes present in a cross-section extending along the thickness direction have an average aspect ratio of 3.2 or higher, the aspect ratio being calculated as a ratio of the thickness-direction length of a hole to the width-direction length of the hole, within a visual field measuring 200 μm × 200 μm in the cross-section.

Description

Titanium porous body, titanium laminate, water electrolysis device, water electrolysis method, and hydrogen production method

[0001] The present invention relates to a titanium porous body, a titanium laminate, a water electrolysis device, a method for electrolyzing water, and a method for producing hydrogen.

[0002] Porous titanium bodies produced by sintering titanium powder or the like have air or liquid permeability and electrical conductivity due to the pores, and also have high corrosion resistance due to the formation of a passivation film on the surface.

[0003] Porous titanium having such properties is being considered for use in porous transport layers (PTLs) in polymer electrolyte membrane (PEM)-type water electrolysis devices, which are in environments where corrosion may occur. In particular, hydrogen produced in PEM-type or other water electrolysis devices using electricity derived from renewable energy is called "green hydrogen," and great expectations are being placed on it in recent years as efforts to realize a decarbonized society accelerate.

[0004] In this regard, Patent Document 1 aims to "provide a porous titanium body in the form of a relatively thin sheet that is resistant to breakage during handling and has at least one smooth surface, and a method for producing the porous titanium body," and describes "a sheet-like porous titanium body having a thickness of 0.3 mm or less, a bending strain at fracture of 0.005 or more, and the three-dimensional surface texture of at least one surface having an arithmetic mean height Sa of 2.5 μm or less, a maximum height Sz of 30 μm or less, an aspect ratio Str of the surface texture of 0.93 or more, and an arithmetic mean curvature of the peaks Spc of 4.8 (1 / μm) or less."

[0005] On the other hand, Patent Documents 2 and 3 state that "when an electron beam or laser is used as an energy source, it is difficult to control the melting range of the metal powder raw material, and it is not possible to form pores with high precision. In particular, it is extremely difficult to periodically form pores with relatively small diameters on the order of 100 μm. As a result, it is not possible to manufacture a metal porous body with a high porosity and low fluid pressure loss," and then propose a "metal member having a three-dimensional regular skeletal structure."

[0006] More specifically, Patent Document 2 describes "a metal component having a three-dimensionally ordered skeletal structure with a porosity in the range of 50% to 95%, the three-dimensionally ordered skeletal structure having a skeleton and a plurality of pores extending in a first direction, wherein in a cross section perpendicular to the first direction, pore rows in which the pores and the skeletons are alternately arranged are periodically stacked to form a layered structure, and the phases of the pores and the skeletons in the pore rows adjacent to each other in the stacking direction are consistent."

[0007] Furthermore, Patent Document 3 describes "a metal component having a three-dimensionally regular skeletal structure with a porosity in the range of 50% to 95%, the three-dimensionally regular skeletal structure having a skeleton and a plurality of pores extending in a first direction, wherein in a cross section perpendicular to the first direction, pore rows in which the pores and the skeletons are alternately arranged are periodically stacked to form a layered structure, and the pores and the skeletons are out of phase with each other in the pore rows adjacent to each other in the stacking direction."

[0008] International Publication No. 2023 / 145375 Japanese Patent Application Laid-Open No. 2024-035329 Japanese Patent Application Laid-Open No. 2024-035330

[0009] In a PEM-type water electrolysis device, the porous titanium sheet serving as a porous transport layer is required to allow gas or liquid to pass easily in the thickness direction. Patent Documents 1 to 3 do not address this requirement, and there is room for improvement in terms of increasing the air permeability or liquid permeability of the porous titanium sheet in the thickness direction.

[0010] An object of the present invention is to provide a titanium porous body, a titanium laminate, a water electrolysis apparatus, a method for electrolyzing water, and a method for producing hydrogen, which are capable of exhibiting excellent air or liquid permeability in the thickness direction.

[0011] The titanium porous body of this invention is made of a powder sintered body and is in the form of a sheet with a thickness of 200 μm or more, and for the pores present in a cross section along the thickness direction, the average aspect ratio, calculated as the ratio of the thickness direction length of the pore to the width direction length of the pore within a 200 μm x 200 μm field of view on the cross section, is 3.2 or more.

[0012] In the above-mentioned porous titanium body, the average width of the pores within the field of view is preferably 70 μm or less.

[0013] The porous titanium body preferably has a porosity of 30% or more and 55% or less.

[0014] The titanium porous body preferably has a standard deviation of the aspect ratio of 0.3 to 3.0.

[0015] The porous titanium body preferably has a ten-point average roughness Rz of 20 μm or less on at least one surface of the porous titanium body. The porous titanium body preferably has a thickness of 200 μm or more and 1000 μm or less. The porous titanium body preferably has an average aspect ratio of 3.2 or more and 20 or less. The porous titanium body preferably has an average widthwise length of pores within the field of view of 5 μm or more and 70 μm or less.

[0016] The porous titanium body can be used in the porous transport layer of a PEM-type water electrolysis device.

[0017] The titanium laminate of the present invention is in the form of a sheet, stacked and bonded together at the titanium bonding surfaces adjacent to each other in the stacking direction, and comprises a plurality of titanium gas-liquid permeable layers, each having pores that allow gas and / or liquid to pass through, at least one of the gas-liquid permeable layers being any one of the porous titanium bodies described above.

[0018] The titanium laminate of the present invention is in the form of a sheet, and is laminated by bonding adjacent titanium bonding surfaces together in the lamination direction, and comprises a plurality of titanium gas-liquid permeable layers, each having pores that allow gas and / or liquid to pass through, and at least one of the gas-liquid permeable layers that forms the surface of the laminate is a porous titanium body as described above, with at least one porous body surface having a ten-point average roughness Rz of 20 μm or less, and the surface of the laminate is the surface of the porous body.

[0019] The water electrolysis device of the present invention is a PEM type having a cell including a cathode, an electrolyte membrane, a porous transport layer, and an anode stacked together, wherein the porous transport layer includes any one of the titanium porous bodies described above.

[0020] The method for electrolyzing water according to the present invention uses the water electrolysis device described above.

[0021] The method for producing hydrogen of the present invention involves decomposing water using the above-described electrolysis method to produce hydrogen.

[0022] The porous titanium body of the present invention can exhibit excellent air or liquid permeability in the thickness direction.

[0023] An embodiment of the present invention is described in detail below. The titanium porous body according to one embodiment of the present invention is a sheet-like body made of a sintered powder compact having a thickness of 200 μm or more. The titanium porous body has pores present in a cross section along the thickness direction, and the average aspect ratio (thickness length of pore / width length of pore) calculated as the ratio of the thickness length of the pore to the width length of the pore within a 200 μm × 200 μm field of view on the cross section is 3.2 or more.

[0024] Thus, when the average aspect ratio is 3.2 or more, the pores inside the porous titanium body tend to extend in the thickness direction or to be elongated in the thickness direction. As a result, when a gas or liquid is passed through the porous titanium body in the thickness direction, it is expected that the gas or liquid will pass mainly through the pores extending in the thickness direction, making it easier for the gas or liquid to pass through the porous titanium body in the thickness direction. As a result, the porous titanium body can exhibit excellent air or liquid permeability in the thickness direction.

[0025] (Titanium porous body) The titanium porous body is made of titanium. If it is made of titanium, a titanium porous body having high electrical conductivity at a certain relative density can be obtained. The titanium content of the titanium porous body is preferably 97% by mass or more, and more preferably 98% by mass or more. The upper limit of the titanium content is not limited to this, but may be, for example, 99.8% by mass or less, or 99% by mass or less. This titanium content refers to the purity of titanium taking into account not only the metal components but also impurities such as gas components such as oxygen. Therefore, the titanium content can be calculated by subtracting the total content of impurities, including metal components and gas components, from 100% by mass.

[0026] The titanium porous body may contain Fe as an impurity, and the Fe content may be, for example, 0.25 mass% or less. The titanium porous body may also contain Ni, Cr, Al, Cu, Zn, and Sn as unavoidable impurities resulting from the manufacturing process. It is preferable that the content of each of Ni, Cr, Al, Cu, Zn, and Sn is less than 0.10 mass%, and that the total content of these elements is less than 0.30 mass%. Metal components other than titanium in the titanium porous body can be measured by inductively coupled plasma (ICP) atomic emission spectroscopy.

[0027] The oxygen content of the porous titanium body is not particularly limited, but may be 0.5% by mass or more and 2.0% by mass or less. If the drying step and / or the binder removal step are carried out in an oxygen-containing atmosphere, as in the production method described below, the oxygen content of the porous titanium body may increase to some extent. The oxygen content can be measured by inert gas fusion-infrared absorption spectroscopy.

[0028] The titanium porous body may have a purity corresponding to pure titanium grades 1 to 4, typically grades 1 to 2, of JIS H 4600 (2012), excluding the oxygen content.

[0029] The thickness of the sheet-shaped porous titanium body is 200 μm or more. For example, a porous titanium body of this thickness may be required for the porous transport layer of a PEM-type water electrolysis device. However, if the thickness is too large, the PEM-type water electrolysis device may become large. The thickness of the porous titanium body may be, for example, 1000 μm or less, 500 μm or less, 400 μm or less, or 300 μm or less.

[0030] The thickness is measured at five points in total, four points on the periphery and one point in the center of the titanium porous body, using a digital thickness gauge with a flat probe having a diameter of 10 mm and a measurement accuracy of 0.001 to 0.01 mm, such as a digital thickness gauge (model number 547-321) manufactured by Mitutoyo Corporation, and the average of these measurements is used. When the sheet-like titanium porous body has a rectangular shape in plan view, the four peripheral points are the four corners.

[0031] The projected surface area of ​​the sheet-like porous titanium body in a plan view is not particularly limited. 2 or more, for example, 600,000 mm 2 Porous titanium bodies with a relatively large projected surface area can be cut and used as needed, making them suitable for mass production. The projected area here refers to the area of ​​the surface of the porous titanium body projected onto a plane.

[0032] The term "sheet-like" in reference to a porous titanium body refers to a plate or foil shape having a thickness small relative to its dimensions in a plan view. The shape of the porous titanium body in a plan view is not particularly limited, but may be a square, a rectangle with an aspect ratio of 1:1 to 1:3, a rhombus, or other polygonal shape. The corners of a polygonal porous titanium body may be chamfered.

[0033] Porous titanium bodies are composed of sintered powders in which titanium powder particles are bonded together, and may have a three-dimensional network structure in which pores are formed between the bonded titanium powder particles. For example, porous titanium bodies may have a skeleton with a three-dimensional network structure similar to that of titanium sponge. Note that porous titanium bodies manufactured using titanium fibers tend to have a three-dimensional network structure similar to that of nonwoven fabric. In many cases, the skeleton of porous titanium bodies, which is composed of titanium powder particles bonded together, is solid rather than hollow.

[0034] The porosity of the titanium porous body is preferably 30% or more and 55% or less, more preferably 30% or more and 50% or less, and even more preferably 35% or more and 50% or less. If the porosity is within this range, breakage during handling can be suppressed while ensuring the required breathability or liquid permeability depending on the application. When the porosity is 30% or more, good breathability or air permeability can be obtained. On the other hand, when the porosity is 55% or less, cracks are less likely to occur during handling.

[0035] The porosity ε of the porous titanium body is determined by the ratio of the apparent density ρ' calculated from the volume and mass determined from the width, length, and thickness of the porous titanium body, to the true density ρ (4.51 g / cm) of titanium constituting the porous titanium body. 3 ) and calculate using the formula: ε = (1 - ρ' / ρ) x 100.

[0036] A titanium porous body has one or more pores in a cross section obtained by cutting the body along the thickness direction. When observing the pores in the cross section obtained by cutting the body along the thickness direction, the average aspect ratio of the pores within a 200 μm × 200 μm field of view is 3.2 or greater. Here, the aspect ratio is calculated as the ratio of the length of the pore along the thickness direction (referred to as the "thickness length") to the length along the width direction (referred to as the "width length"). The width direction refers to the direction perpendicular to the thickness direction in the cross section. Titanium porous bodies, particularly powder sintered bodies, tend to have a three-dimensional network structure with irregularly arranged pores. Among these pores, those extending in the thickness direction contribute to excellent air permeability and liquid permeability in the thickness direction. Therefore, the pores for which the aspect ratio is calculated have a thickness length of 70 μm or greater.

[0037] The larger the average aspect ratio, the easier it is for gases and liquids to flow in the thickness direction of the porous titanium body, improving the air permeability or liquid permeability of the porous titanium body in the thickness direction. Furthermore, when the pores extend in the thickness direction, the skeletons that define the pores and are adjacent to them also tend to extend columnarly in the thickness direction, which is thought to have the advantage of improving the compression resistance of the porous titanium body in the thickness direction. From this perspective, it is preferable that the average aspect ratio of the pores be 4.0 or more, and even more preferably 5.0 or more.

[0038] As described above, the pores inside the titanium porous body are elongated and extend in the thickness direction, and it is also desirable that they have a certain degree of width. In other words, it is preferable that the average aspect ratio of the pores is not too large. This is because relatively wide pores reduce the viscous resistance that gases and liquids passing through them experience from the skeleton surrounding the pores, which is expected to further improve air permeability or liquid permeability. Specifically, it is preferable that the average aspect ratio of the pores be 20 or less, and more preferably 15 or less.

[0039] The standard deviation of the aspect ratio of the porous titanium body may be, for example, within a range of 0.3 to 3.0. The standard deviation of the aspect ratio may be within a range of 0.3 to 2.5, or within a range of 0.3 to 2.0.

[0040] The average value and standard deviation of the pore aspect ratio can be determined as follows. First, a sheet-shaped porous titanium body is immersed in a liquid resin, and then the resin is cured to impregnate the pores of the porous titanium body. This resin can be a two-component type. The base resin and the curing agent are mixed at a predetermined ratio, such as 200:1, and stirred with a glass rod for at least 5 minutes before being used to impregnate the pores of the porous titanium body. After impregnation, the mixture is degassed in a vacuum chamber for 5 minutes and allowed to stand overnight. Next, the porous titanium body is cut at a desired position along the thickness direction and then polished to expose the cross section of the porous titanium body. The cross section is then observed with an optical microscope. The field of view is 200 μm × 200 μm. The magnification can be appropriately determined depending on the size of the pores and skeleton present in the cross section, but can be 100x to 500x, for example. For example, titanium porous bodies with small pores or skeletons, such as those manufactured using titanium powder with a relatively small average particle size D50, can be easily observed at a magnification of approximately 400x. On the other hand, titanium porous bodies with large pores or skeletons can be easily observed at a relatively low magnification of 100x to 200x. All pores with a thickness length of 70 μm or more within the above field of view are observed, and the thickness and width lengths of each pore are measured. Pores partially outside the field of view are considered to have a length extending to the edge of the field of view. Pores extending through the field of view in the thickness and / or width directions are considered to have a thickness and / or width length of 200 μm, which is the dimension of the field of view. The aspect ratio (thickness length / width length) of each pore can be calculated by dividing the thickness length by the width length. If multiple pores with a thickness length of 70 μm or more are present within the field of view, the aspect ratios of all of those pores are calculated. This calculation of the aspect ratio of the hole is carried out for any 10 different fields of view, and the aspect ratios of all the holes are found, and the average value and standard deviation value are calculated.

[0041] In a cross section of the titanium porous body taken along the thickness direction, the average widthwise length of the pores is preferably 70 μm or less. When the widthwise length of the pores is short, the dimensions of the pores exposed on the sheet surface of the titanium porous body (also referred to as the "porous body surface") tend to be small, and in this case, the porous body surface is likely to be smooth. When a titanium porous body with high surface smoothness is used as a porous transport layer in a PEM-type water electrolysis device, the porous transport layer is less likely to damage the electrolyte membrane against which it is pressed. Therefore, the average widthwise length of the pores is preferably 60 μm or less, more preferably 50 μm or less, even more preferably 35 μm or less, and even more preferably 30 μm or less. On the other hand, from the viewpoint of reducing the viscous resistance that gases and liquids passing through the titanium porous body in the thickness direction experience from the skeleton surrounding the pores, thereby further improving the breathability or liquid permeability, the average widthwise length of the pores is preferably 5 μm or more, even more preferably 8 μm or more, and even more preferably 10 μm or more. To calculate the average widthwise length of the holes, the widthwise lengths of the holes whose aspect ratios have been calculated are measured in 10 fields of view in the same manner as in the method for calculating the average aspect ratio described above, and the average value is calculated.

[0042] The ten-point mean roughness Rz of at least one surface of the titanium porous body is preferably 20 μm or less, more preferably 15 μm or less, 10 μm or less, 7 μm or less, or 5 μm or less. When the surface roughness of at least one surface of the titanium porous body is small, damage to the electrolyte membrane can be effectively suppressed by incorporating the titanium porous body in a PEM-type water electrolysis device with the surface facing the electrolyte membrane. The ten-point mean roughness Rz of the surface is measured, for example, using an SJ-210 manufactured by Mitutoyo Corporation according to ISO 4287-1997. It should be noted that with the "metal member having a three-dimensional regular skeletal structure" described in the aforementioned Patent Documents 2 and 3, it is difficult to reduce the surface roughness while orienting the internal pores in a predetermined direction, as in the embodiment described herein. Titanium porous bodies, which are powder sintered bodies, tend to have small pores opening to the surface of the porous body, resulting in a small ten-point mean roughness Rz and excellent surface smoothness. Furthermore, as mentioned above, the porous titanium body of this embodiment has a large aspect ratio of the pores in the cross section in the thickness direction, and therefore has high surface smoothness and excellent air or liquid permeability in the thickness direction.

[0043] The porous titanium body described above can be produced, for example, as follows. A relatively fine titanium powder, such as hydrogenated dehydrogenated titanium powder (HDH titanium powder), is mixed with an organic solvent, an organic binder, and the like to form a paste that has been defoamed. The paste is then applied to a sheet, which is then dried, degreased, and heated at predetermined temperatures to sequentially sinter the titanium powder. This produces a powder sintered body with a three-dimensional network structure. The sintered powder body may be cut to a predetermined size if necessary to adjust its dimensions.

[0044] The paste preferably contains titanium powder, an organic binder, and an organic solvent, but does not contain water or a foaming agent. Polyvinyl butyral (PVB) can be used as the organic binder, and isopropyl alcohol (IPA) can be used as the organic solvent. It is also preferable to add a titanium-based coupling agent (e.g., Orgatix TC-401 manufactured by Matsumoto Fine Chemical Co., Ltd., or Plainact 44 manufactured by Ajinomoto Fine-Techno Co., Ltd.) to the paste. This enhances the bonding between the organic binder and the titanium powder, which is thought to increase the tendency for components to volatilize in the thickness direction from the paste applied in sheet form. As a result, it becomes easier to produce a titanium porous body having pores therein, as described above.

[0045] The paste can also be applied to a polyethylene terephthalate (PET) film with a release agent using a knife coater, which allows the direction of volatilization of the paste components and the orientation of the pores inside the porous titanium body to be adjusted as desired.

[0046] (Titanium Laminate) The titanium laminate is in the form of a sheet and includes multiple titanium gas-liquid permeable layers. The multiple gas-liquid permeable layers are bonded to each other at the titanium bonding surfaces adjacent to each other in the stacking direction. The interfaces of the multiple gas-liquid permeable layers are preferably substantially free of metals other than titanium or titanium-free compounds, since this allows for the desired high conductivity to be achieved at low cost. This is because joining the gas-liquid permeable layers by providing a layer containing another metal, such as platinum, to suppress an increase in electrical resistance at the interface would result in increased costs. Each of the multiple gas-liquid permeable layers has pores that allow gas and / or liquid to pass through. Titanium laminates used as porous transport layers in PEM-type water electrolysis devices can be permeable to gas and / or liquid in the stacking direction (sheet thickness direction) or in other directions, such as directions perpendicular to the stacking direction. Here, the sheet surface of a sheet-like titanium laminate is also referred to as the "laminate surface."

[0047] At least one of the gas / liquid-permeable layers is the porous titanium body described above, which has a thickness of 200 μm or more and an average aspect ratio of pores present in a cross section along the thickness direction, calculated as the ratio of the thickness direction length of the pore to the width direction length of the pore within a 200 μm × 200 μm field of view on the cross section, of 3.2 or more.

[0048] When the ten-point average roughness Rz of at least one surface of the porous titanium body is 20 μm or less, the porous titanium body is preferably used as at least one gas-liquid permeable layer forming the surface of one of the gas-liquid permeable layers of the laminate, and the porous body surface is preferably used as the laminate surface. In this case, by pressing the laminate surface (porous body surface) with the smaller surface roughness against the electrolyte membrane, damage to the electrolyte membrane can be suppressed.

[0049] The other gas / liquid permeable layer may also be the porous titanium body described above, but is not limited to such a porous titanium body and may be, for example, a titanium expanded metal layer or titanium mesh layer in which regular pores of a certain size are formed penetrating through the thickness direction, a titanium punched metal layer, a titanium lotus metal layer, etc. The method for joining multiple gas / liquid permeable layers is not particularly limited, and various methods such as sintering, laser fusion joining, and spot welding can be used.

[0050] (PEM-type water electrolysis device, water electrolysis method, hydrogen production method) A PEM (Polymer Electrolyte Membrane) water electrolysis device includes a cell including at least a cathode, an electrolyte membrane, a porous transport layer, and an anode stacked together. Here, the electrolyte membrane and the porous transport layer are sandwiched in this order between the cathode and the anode from the cathode side to the anode side. A porous transport layer may also be provided between the cathode and the electrolyte membrane. In addition, in a stack, multiple cells may be formed by sandwiching a bipolar plate between the cathode and the anode.

[0051] The anode and cathode are often made of a highly conductive metal such as copper. The porous transport layer on the anode side includes the porous titanium body described above. This porous transport layer may include the titanium stack described above, and the titanium stack may include the porous titanium body described above. To enhance electrical conductivity, the porous titanium body may be coated on at least one surface with, for example, a noble metal, more specifically, a platinum group metal (platinum, ruthenium, rhodium, palladium, osmium, iridium, typically platinum). This coating may be applied to one or both of the electrolyte membrane-side and anode-side surfaces of the porous titanium body. The porous transport layer on the cathode side is made of, for example, carbon or graphite.

[0052] The electrolyte membrane, which may also be referred to as a proton exchange membrane, may typically include a sulfonic acid cation exchange membrane made of a fluororesin. An anode catalyst layer made of iridium oxide (IrO) or the like may be provided between the electrolyte membrane and the anode. Meanwhile, a cathode catalyst layer made of platinum (Pt) or the like may be provided between the electrolyte membrane and the cathode. Each catalyst layer may be bonded to the electrolyte membrane by coating or pasting, and an electrolyte membrane provided with such a catalyst layer may be referred to as a catalyst-coated membrane (CCM). However, the anode catalyst layer and / or cathode catalyst layer may be bonded to the anode- or cathode-side porous transport layer, or simply sandwiched between the anode- or cathode-side porous transport layer and the electrolyte membrane. Such a catalyst layer may be provided in any suitable form, for example, on the surface of the electrolyte membrane or porous transport layer, or may be provided as a separate component between the electrolyte membrane and the porous transport layer.

[0053] Separators may be provided between the anode and the anode-side porous transport layer, and between the cathode and the cathode-side porous transport layer. The cathode-side separator and the anode-side separator may each be made of titanium or stainless steel, and their surfaces may be coated with a precious metal such as a platinum group metal. To reduce the size of the device, the separator may be integrated with the anode or cathode, respectively, and in such cases, the separator material is used. As described above, separators may be arranged as appropriate depending on the requirements for the cell or stack.

[0054] In PEM-type water electrolysis devices, a plurality of cells such as those described above are often stacked to form a stack, which is then placed inside the device. When forming a stack, for cells other than the endmost cells, the cathode-side separator and cathode of the cell, as well as the anode and anode-side separator of the adjacent cell, can be replaced with bipolar plates, allowing the cells to be connected and stacked together. Here, the innermost cell includes an electrolyte membrane and a porous transport layer stacked between two bipolar plates. The bipolar plates may be made of the same material as the separators.

[0055] By using the water electrolysis device, water can be electrolyzed. More specifically, when a voltage is applied between the anode and cathode of the cell, water (HO) supplied to the anode side is mainly converted into 2HO → 4H + + O2 + 4e - The oxidation reaction produces hydrogen ions (H + ) and oxygen (O2). The hydrogen ions pass through the electrolyte membrane and - passes through an external circuit and moves to the cathode side, and 2H + +2e - →Hydrogen (H2) is produced by the reduction reaction of H2. Therefore, looking at the reaction as a whole, water is decomposed into oxygen and hydrogen. This allows hydrogen to be produced.

[0056] Next, a prototype of the porous titanium body of the present invention was produced and its effects were confirmed, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0057] For Nos. 1 to 3, the HDH titanium powder shown in Table 1 was mixed with the organic binder PVB and the organic solvent IPA, and then a titanium-based coupling agent, Orgatix TC-401 manufactured by Matsumoto Fine Chemical Co., Ltd., was added to prepare a paste. The mixing ratio, by mass, was titanium powder:PVB:IPA:titanium-based coupling agent = 60:7.3:30:0.6. This paste did not contain water or a foaming agent.

[0058] The paste was applied in sheet form to a PET film with a release agent using a knife coater, and then dried by heating at 160°C for 20 minutes. After drying, the dried product was peeled off from the PET film and placed on a graphite setter, where it was degreased at 380°C for 8 hours and sintered at 850°C for 1 hour. This produced a sheet-like porous titanium body.

[0059] In No. 4, titanium fibers produced by chatter cutting were dry-laid on a graphite setter using a sieve, and then sintered at 1000°C for 1 hour to obtain a porous titanium body with a nonwoven fabric-like skeleton.

[0060] The thickness, porosity, and ten-point average roughness Rz of each of the titanium porous bodies Nos. 1 to 4 were determined according to the methods described above. The results are also shown in Table 1.

[0061]

[0062] Furthermore, for each titanium porous body, the thickness direction length L and width direction length W of the pores present in the cross section along the thickness direction were measured, as described above, and the aspect ratio was calculated. The results are shown in Tables 2 and 3. Note that in visual fields 4, 5, and 7 to 10 of No. 1, there were multiple pores with thickness direction lengths of 70 μm or more within the visual field, and Tables 2 and 3 show the thickness direction length L and width direction length W of these pores.

[0063] As shown in Table 3, the average aspect ratio of the pores was 3.2 or more for the titanium porous bodies Nos. 1 and 2, but less than 3.2 for the titanium porous bodies Nos. 3 and 4.

[0064]

[0065]

Claims

1. A titanium porous body made of a powder sintered body, in the form of a sheet with a thickness of 200 μm or more, in which the average aspect ratio of the pores present in a cross section along the thickness direction, calculated as the ratio of the thickness direction length of the pores to the width direction length of the pores within a 200 μm x 200 μm field of view on the cross section, is 3.2 or more.

2. A porous titanium body according to claim 1, wherein the average width of the pores within the field of view is 70 μm or less.

3. The porous titanium body according to claim 1, which has a porosity of 30% or more and 55% or less.

4. The porous titanium body according to claim 1, wherein the standard deviation of the aspect ratio is within the range of 0.3 to 3.

0.

5. The titanium porous body according to claim 1, wherein the ten-point average roughness Rz of at least one surface of the porous body is 20 μm or less.

6. The titanium porous body according to claim 1, which has a thickness of 200 μm or more and 1000 μm or less.

7. The porous titanium body according to claim 1, wherein the average aspect ratio is 3.2 or more and 20 or less.

8. A porous titanium body according to claim 1, wherein the average width of the pores within the field of view is 5 μm or more and 70 μm or less.

9. The porous titanium body according to claim 1, which is used in a porous transport layer of a PEM-type water electrolysis device.

10. A sheet-like titanium laminate comprising a plurality of titanium gas / liquid permeable layers laminated and bonded together at adjacent titanium bonding surfaces in the stacking direction, each layer having pores that allow gas and / or liquid to pass through, at least one of the gas / liquid permeable layers being the porous titanium body according to any one of claims 1 to 9.

11. A sheet-like titanium laminate comprising a plurality of titanium gas / liquid permeable layers laminated and bonded together at adjacent titanium bonding surfaces in the stacking direction, each having pores that allow gas and / or liquid to pass through, at least one of the gas / liquid permeable layers forming the surface of the laminate is the porous titanium body defined in claim 5, and the surface of the laminate is the surface of the porous body.

12. A PEM-type water electrolysis device comprising a cell including a cathode, an electrolyte membrane, a porous transport layer, and an anode stacked together, wherein the porous transport layer comprises the titanium porous body according to any one of claims 1 to 9.

13. A method for electrolyzing water using the water electrolysis device according to claim 12.

14. A method for producing hydrogen, comprising decomposing water using the electrolysis method according to claim 13 to produce hydrogen.

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