Titanium porous material, titanium laminate, water electrolysis device, method for electrolyzing water, and method for producing hydrogen

Abstract

The present invention provides a titanium porous material, a titanium laminate, a water electrolysis device, a method for electrolyzing water, and a method for producing hydrogen, all of which exhibit excellent breathability or liquid permeability in the thickness direction. [Solution] 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. For holes present in a cross-section along the thickness direction, the average value of the aspect ratio calculated as the ratio of the thickness direction length of the holes to the width direction length of the holes within a 200 μm × 200 μm field of view in the cross-section is 3.2 or more.

Description

[Technical Field]

[0001] This 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. [Background technology]

[0002] A porous titanium body manufactured by sintering titanium powder or the like possesses permeability or liquid permeability due to its pores, as well as electrical conductivity. Furthermore, it exhibits high corrosion resistance due to the formation of a passive film on its surface.

[0003] Such porous titanium materials are being considered for use in porous transport layers (PTLs) and other applications in polymer electrolyze membrane (PEM) type water electrolysis devices, where corrosion can occur. In particular, hydrogen produced in PEM type water electrolysis devices using electricity derived from renewable energy is called green hydrogen and is attracting great attention in recent years as efforts toward realizing a decarbonized society accelerate.

[0004] In this regard, Patent Document 1 describes a titanium porous material that is "relatively thin, in the form of a sheet, is not easily damaged during handling, and has at least one smooth surface, and a method for manufacturing a titanium porous material," with the objective of "providing a titanium porous material that is in the form of a sheet, has a thickness of 0.3 mm or less, a fracture bending strain of 0.005 or more, and for the three-dimensional surface properties of at least one surface, has 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 properties of 0.93 or more, and an arithmetic mean curvature Spc of the peaks of 4.8 (1 / μm) or less."

[0005] On the other hand, Patent Documents 2 and 3 state that "when electron beams or lasers are used as energy sources, 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 fabricate relatively small diameter pores on the order of 100 μm. For this reason, it is not possible to manufacture a porous metal body with a high porosity and low fluid pressure loss," and then propose a "metal component having a three-dimensional ordered skeletal structure."

[0006] More specifically, Patent Document 2 describes a metal member having a three-dimensional ordered skeletal structure with a porosity in the range of 50% to 95%, wherein the three-dimensional ordered skeletal structure has a skeleton and a plurality of pores extending in a first direction, and in a cross section perpendicular to the first direction, a laminated structure is formed in which rows of pores in which the pores and the skeleton are arranged alternately are periodically stacked, and the phases of the pores and the skeleton coincide in adjacent rows of pores in the stacking direction.

[0007] Furthermore, Patent Document 3 describes a metal member having a three-dimensional ordered skeletal structure in which the porosity is in the range of 50% to 95%, wherein the three-dimensional ordered skeletal structure has a skeleton and a plurality of pores extending in a first direction, and in a cross section perpendicular to the first direction, a laminated structure is formed in which rows of pores in which the pores and the skeleton are arranged alternately are periodically stacked, and the phases of the pores and the skeleton are shifted between adjacent rows of pores in the stacking direction. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2023 / 145375 [Patent Document 2] Japanese Patent Publication No. 2024-035329 [Patent Document 3] Japanese Patent Publication No. 2024-035330 [Overview of the project] [Problems that the invention aims to solve]

[0009] Incidentally, in PEM-type water electrolysis devices, it is required that gas or liquid can easily pass through the thickness direction of the sheet-like titanium porous material used as the porous transport layer. Patent documents 1 to 3 do not focus on such requirements, and there is room for improvement in titanium porous materials from the standpoint of enhancing their permeability or permeability in the thickness direction.

[0010] The object of this invention is to provide a titanium porous body, a titanium laminate, a water electrolysis device, a method for electrolyzing water, and a method for producing hydrogen, all of which can exhibit excellent permeability or liquid permeability in the thickness direction. [Means for solving the problem]

[0011] The titanium porous body of this invention is made of a powder sintered body, 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 × 200 μm field of view in the said cross-section is 3.2 or more.

[0012] In the above-mentioned porous titanium material, it is preferable that the average length of the pores in the width direction within the field of view is 70 μm or less.

[0013] The above-mentioned porous titanium material preferably has a porosity of 30% or more and 55% or less.

[0014] The above-mentioned porous titanium material preferably has a standard deviation of aspect ratio of 0.3 to 3.0.

[0015] The above-mentioned titanium porous material preferably has a ten-point average roughness Rz of at least one porous surface of 20 μm or less.

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

[0017] The titanium laminate of this invention is in sheet form, and is laminated by bonding titanium bonding surfaces adjacent to each other in the lamination direction, and includes a plurality of titanium-made gas-liquid permeable layers each having pores and allowing gas and / or liquid to permeate, and at least one of the gas-liquid permeable layers is any of the above titanium porous bodies.

[0018] Also, the titanium laminate of this invention is in sheet form, and is laminated by bonding titanium bonding surfaces adjacent to each other in the lamination direction, and includes a plurality of titanium-made gas-liquid permeable layers each having pores and allowing gas and / or liquid to permeate, and among the plurality of gas-liquid permeable layers, at least the gas-liquid permeable layer forming one surface of the laminate is a titanium porous body having a ten-point average roughness Rz of the surface of at least one porous body of 20 μm or less as described above, and the surface of the laminate is the surface of the porous body.

[0019] The water electrolysis device of this invention is a PEM type including a cell in which a cathode, an electrolyte membrane, a porous transport layer, and an anode are laminated, and the porous transport layer includes any of the above titanium porous bodies.

[0020] The method for electrolyzing water of this invention is to use the above water electrolysis device.

[0021] The method for producing hydrogen of this invention is to decompose water using the above electrolysis method to generate hydrogen.

Effects of the Invention

[0022] According to the titanium porous body of this invention, excellent air permeability or liquid permeability in the thickness direction can be exhibited.

Modes for Carrying Out the Invention

[0023] Embodiments of this invention will be described in detail below. One embodiment of this invention is a titanium porous body made of a powder sintered body and is in the form of a sheet having a thickness of 200 μm or more. For the pores present in the cross-section along the thickness direction of this titanium porous body, the average aspect ratio (length in the thickness direction of the pore / length in the width direction of the pore), calculated as the ratio of the length of the pore in the thickness direction to the length of the pore in the width direction within a 200 μm × 200 μm field of view in that cross-section, is 3.2 or more.

[0024] Thus, when the average aspect ratio is 3.2 or higher, it can be said that the pores inside the titanium porous material tend to have a shape that extends in the thickness direction or a shape that is elongated in the thickness direction. As a result, when a gas or liquid is flowed through the titanium porous material in the thickness direction, the gas or liquid is expected to pass mainly through the pores that extend in the thickness direction, making it easier for the gas or liquid to pass through the titanium porous material in the thickness direction. Consequently, the titanium porous material can exhibit excellent permeability or liquid permeability in the thickness direction.

[0025] (Titanium porous material) The titanium porous material is made of titanium. If made of titanium, a titanium porous material with high electrical conductivity at a certain relative density can be obtained. The titanium content of the titanium porous material 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 metal components but also impurities such as gaseous components like oxygen. Therefore, the titanium content is determined by subtracting the total content of metal components and impurity components, including gaseous components, from 100% by mass.

[0026] The titanium porous material may contain Fe as an impurity, and the Fe content may be, for example, 0.25% by mass or less. The titanium porous material 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 be less than 0.10% by mass, and that their total content be less than 0.30% by mass. The metal components other than titanium in the titanium porous material can be measured by inductively coupled plasma (ICP) emission spectrometry.

[0027] The oxygen content of the titanium porous material is not particularly limited, but it may be between 0.5% by mass and 2.0% by mass. If the drying and / or debinding processes are carried out in an oxygen-containing atmosphere, as in the manufacturing method described later, the oxygen content of the titanium porous material may increase to a certain extent. The oxygen content can be measured by the inert gas melting-infrared absorption method.

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

[0029] The thickness of the sheet-like titanium porous material shall be 200 μm or more. For example, a titanium porous material of this thickness may be required for the porous transport layer of a PEM-type water electrolysis device. However, if the thickness is too high, it may lead to an increase in the size of the PEM-type water electrolysis device. The thickness of the titanium porous material 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: four points on the periphery and one point in the center of the porous titanium material. This measurement is taken using a digital thickness gauge with a flat probe of Φ10 mm and a measurement accuracy of 0.001 to 0.01 mm, such as the Mitutoyo Digital Thickness Gauge (model number 547-321), and the average of these measurements is used. If the sheet-like porous titanium material is rectangular in plan view, the four points on the periphery should be the four corner points.

[0031] The projected surface area of ​​a sheet-like porous titanium material in a plan view is not particularly limited. This projected surface area is, for example, 250 mm². 2 That's all, for example, 600,000 mm 2 The following may apply: A titanium porous material with a sufficiently large surface projection area can be cut and used as needed, making it suitable for mass production. Here, "projection area" refers to the area obtained by projecting the surface of the titanium porous material onto a plane.

[0032] In relation to porous titanium materials, "sheet-like" refers to a plate-like or foil-like material with a small thickness relative to its dimensions in plan view. The shape of the porous titanium material in plan view is not particularly restricted, but it may be square, rectangular with an aspect ratio of 1:1 to 1:3, rectangular, rhombic, or other polygonal shapes. Polygonal porous titanium materials may have chamfered corners.

[0033] A porous titanium material is composed of a powder sintered body in which titanium powders are bonded together, and may have a three-dimensional network structure with pores formed between the bonded titanium powders. For example, a porous titanium material may have a sponge-like three-dimensional network structure skeleton. A porous titanium material manufactured using titanium fibers tends to have a nonwoven fabric-like three-dimensional network structure. In most cases, the inside of the skeleton composed of bonded titanium powders in a porous titanium material is solid, not hollow.

[0034] The porosity of the titanium porous material 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. Within this range of porosity, it is possible to ensure the required air permeability or liquid permeability according to the application while suppressing damage during handling. When the porosity is 30% or more, good air permeability or liquid permeability is obtained. On the other hand, when the porosity is 55% or less, cracking during handling becomes less likely.

[0035] The porosity ε of a titanium porous material is calculated from the volume obtained from the width, length, and thickness of the titanium porous material, as well as the apparent density ρ' calculated from the mass, and the true density ρ (4.51 g / cm³) of the titanium constituting the titanium porous material. 3 Using ), it is calculated by the formula: ε = (1 - ρ' / ρ) × 100.

[0036] A porous titanium material has one or more pores in the cross-section obtained by cutting along the thickness direction. When observing the pores that appear in the cross-section obtained by cutting along the thickness direction, the average aspect ratio of the pores within a 200 μm × 200 μm field of view is 3.2 or higher. Here, the aspect ratio is calculated as the ratio of the length of the pore along the thickness direction ("thickness direction length") to the length along the width direction ("width direction length"). The width direction refers to the direction perpendicular to the thickness direction in the above cross-section. When a porous titanium material is a powder sintered body, it has a three-dimensional network structure and the pores tend to be irregularly arranged. Of such pores, those that extend in the thickness direction contribute to excellent air permeability and liquid permeability in the thickness direction. Therefore, the pores for which the above aspect ratio is determined are those with a thickness direction length of 70 μm or more.

[0037] The larger the average aspect ratio, the easier it is for gases and liquids to flow in the thickness direction of the titanium porous material, potentially improving its permeability or permeability in the thickness direction. Furthermore, if the pores extend in the thickness direction, the framework adjacent to and partitioning the pores is also more likely to extend columnarly in the thickness direction, which is considered to have the advantage of increasing the compressive resistance of the titanium porous material in the thickness direction. From this viewpoint, it is preferable that the average aspect ratio of the pores be 4.0 or higher, and more preferably 5.0 or higher.

[0038] The pores inside the titanium porous material should, as described above, be elongated and extending in the thickness direction, and it is also preferable that they have a certain width. In other words, it is preferable that the average aspect ratio of the pores is not too large. If the pores are relatively wide, the viscous resistance that the gas or liquid passing through them experiences from the surrounding framework will be reduced, and further improvements in air permeability or liquid permeability can be expected. Specifically, it is preferable that the average aspect ratio of the pores be 20 or less, and more preferably 15 or less.

[0039] Furthermore, the standard deviation of the aspect ratio of the titanium porous material may be in the range of, for example, 0.3 to 3.0. The standard deviation of the aspect ratio may also be in the range of 0.3 to 2.5, or in the range of 0.3 to 2.0.

[0040] The mean and standard deviation of the aspect ratio of the pores can be determined as follows. First, a sheet of porous titanium is immersed in a liquid resin, and then the resin is cured to impregnate the pores of the porous titanium with the resin. A two-part resin can be used, in which the main component and the hardener are mixed in a predetermined ratio such as 200:1, stirred with a glass rod for at least 5 minutes, and then used to impregnate the pores of the porous titanium. After impregnation, the resin can be degassed in a vacuum chamber for 5 minutes and left overnight. Next, the porous titanium is cut along the thickness direction at an arbitrary position, then polished to expose the cross-section of the porous titanium. The cross-section is then observed with an optical microscope. At this time, the field of view is set to 200 μm × 200 μm. The magnification can be appropriately determined according to the size of the pores and skeleton present in the cross-section, but can be 100x to 500x, etc. For example, in the case of a porous titanium material with small pores and a small framework, such as one manufactured using titanium powder with a relatively small average particle size D50, it is easier to observe at a high magnification of around 400x. On the other hand, in the case of a porous titanium material with large pores and a large framework, it can be easily observed even at relatively low magnifications such as 100x to 200x. Within the field of view described above, all holes with a thickness length of 70 μm or more are to be observed, and the thickness and width lengths of each hole are measured. Holes that are partially outside the field of view are considered to have a length extending to the edge of the field of view. Furthermore, holes that extend through the field of view in the thickness and / or width directions are assumed 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 hole can be calculated by dividing the thickness length by the width length. If there are multiple holes with a thickness length of 70 μm or more within the field of view, the aspect ratio is calculated for all of them. This aspect ratio calculation is performed for any 10 different fields of view, and the average and standard deviation values ​​of the aspect ratios of all such holes are calculated.

[0041] In a cross-section along the thickness direction of the titanium porous material, the average length of the pores in the width direction is preferably 70 μm or less. When the length of the pores in the width direction is short, the dimensions of the pores exposed on the sheet surface of the titanium porous material (also called the "porous material surface") tend to be smaller, and in this case, the porous material surface tends to be smoother. When a titanium porous material with high surface smoothness is used as a porous transport layer in a PEM-type water electrolysis device, it is less likely to damage the electrolyte membrane to which the porous transport layer is pressed. For this reason, it is preferable that the average length of the pores in the width direction be 60 μm or less, more preferably 50 μm or less, more preferably 35 μm or less, and 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 material in the thickness direction receive from the framework around the pores, thereby achieving further improvement in permeability or liquid permeability, it is preferable that the average length of the pores in the width direction be 5 μm or more, more preferably 8 μm or more, and more preferably 10 μm or more. To determine the average width of the hole, measure the width of the hole for which the aspect ratio was determined in 10 fields of view, using the same method as described above for calculating the average aspect ratio, and then calculate the average of these measurements.

[0042] The ten-point average roughness Rz of at least one surface of the titanium porous body is preferably 20 μm or less, and more preferably 15 μm or less, 10 μm or less, 7 μm or less, and 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 its surface facing the electrolyte membrane. The ten-point average roughness Rz of the surface is measured using, for example, a Mitutoyo SJ-210 according to ISO 4287-1997. In the "metal members having a three-dimensional ordered 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 here. A titanium porous body, which is a powder sintered body, tends to have smaller pores opening on the porous body surface, resulting in a small ten-point average roughness Rz and excellent surface smoothness. Furthermore, as mentioned earlier, the titanium porous body of this embodiment has a large aspect ratio of the pores in the cross-section in the thickness direction, resulting in high surface smoothness while also exhibiting excellent permeability or liquid permeability in the thickness direction.

[0043] The above-mentioned porous titanium material can be manufactured, for example, as follows: A paste made by mixing relatively fine titanium powder, such as dehydrogenated titanium powder (HDH titanium powder), with an organic solvent or organic binder and defoaming it is applied to a sheet. This sheet can then be heated at predetermined temperatures to sequentially dry, degrease, and sinter the titanium powder. This yields a powder sintered body having a three-dimensional network structure. The powder sintered body may be cut to predetermined dimensions if necessary to adjust its size.

[0044] The paste described above preferably contains titanium powder, an organic binder, and an organic solvent, and is free of water and 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 (for example, Orgatics TC-401 from Matsumoto Fine Chemical Co., Ltd., or Prenact 44 from Ajinomoto Fine Techno Co., Ltd.) to the paste. This is thought to increase the bonding between the organic binder and the titanium powder, and to increase the tendency for the components to volatilize in the thickness direction from the paste applied in a sheet, thereby making it easier to manufacture a titanium porous body having pores inside as described above.

[0045] Furthermore, the paste can be applied to a polyethylene terephthalate (PET) film with a release agent using a knife coater. By using a knife coater in this process, the direction of volatilization of components from the paste and the orientation of the pores inside the titanium porous material can be adjusted to the desired specifications.

[0046] (Titanium laminate) The titanium laminate is in sheet form and comprises multiple layers of titanium gas-liquid permeable layers. The multiple layers of gas-liquid permeable layers are laminated by bonding adjacent titanium bonding surfaces in the lamination direction. It is preferable that there are substantially no metals other than titanium or compounds that do not contain titanium at the interface of the multiple layers of gas-liquid permeable layers, as this allows for the achievement of the required high conductivity at low cost. This is because adding layers containing other metals such as platinum to bond the gas-liquid permeable layers together in order to suppress the increase in electrical resistance at the interface would lead to increased costs. Each of the multiple layers of gas-liquid permeable layers has pores, allowing gas and / or liquid to permeate. In addition, for titanium laminates used as porous transport layers in PEM-type water electrolysis devices, those that allow gas and / or liquid to permeate in the lamination direction (sheet thickness direction) or in other directions such as perpendicular to the lamination direction may be used. Here, the sheet surface of the sheet-shaped titanium laminate is also called the "laminated surface."

[0047] Of the above-mentioned gas-liquid permeable layers, at least one gas-liquid permeable layer is the titanium porous material described above. This titanium porous material has a thickness of 200 μm or more, and for pores present in a cross-section along the thickness direction, the average aspect ratio calculated as the ratio of the thickness direction length of a pore to the width direction length of a pore within a 200 μm × 200 μm field of view in that cross-section is 3.2 or more.

[0048] If the ten-point average roughness Rz of at least one porous surface of the titanium porous material is 20 μm or less, it is preferable that the titanium porous material be used as a gas-liquid permeable layer forming at least one of the multiple gas-liquid permeable layers, and that the porous material surface be the laminate surface. In this case, if the laminate surface (porous material surface) with low surface roughness is pressed against the electrolyte membrane, damage to the electrolyte membrane can be suppressed.

[0049] Other gas-liquid permeable layers may also be made of the aforementioned titanium porous material, but are not limited to such titanium porous material. For example, they may be titanium expanded metal layers or titanium mesh layers, titanium perforated metal layers, titanium lotus metal layers, etc., in which holes of a certain size that penetrate in the thickness direction are regularly formed. There are no particular limitations on the method of joining multiple gas-liquid permeable layers, but various methods such as sintering, laser fusion joining, and spot welding can be employed.

[0050] (PEM-type water electrolysis device, water electrolysis method, hydrogen production method) A PEM (Polymer Electrolyte Membrane) type water electrolysis apparatus comprises a cell containing at least a cathode, an electrolyte membrane, a porous transport layer, and an anode, all stacked together. In this configuration, the electrolyte membrane and the porous transport layer are sandwiched between the cathode and the anode, in that order from the cathode side towards 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 constructed by sandwiching a bipolar plate between the cathode and the anode.

[0051] The anode and cathode are often made of highly conductive metals such as copper. The porous transport layer on the anode side contains the titanium porous material described above. This porous transport layer may also contain the titanium laminate described above, and the titanium laminate may contain the titanium porous material described above. To enhance electrical conductivity, at least one surface of the titanium porous material may be coated 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 surface and the anode side surface of the titanium porous material. The porous transport layer on the cathode side is made of, for example, carbon or graphite.

[0052] The electrolyte membrane, also known as a proton exchange membrane, typically includes a sulfonic acid cation exchange membrane made of a fluororesin. An anode catalyst layer, such as iridium oxide (IrO2), may be provided between the electrolyte membrane and the anode. On the other hand, a cathode catalyst layer, such as platinum (Pt), may be provided between the electrolyte membrane and the cathode. Each catalyst layer may be bonded to the electrolyte membrane by coating or bonding, and an electrolyte membrane with such catalyst layers may be called a catalyst-coated membrane (CCM). However, the anode catalyst layer and / or cathode catalyst layer may be bonded to the porous transport layer on the anode or cathode side, or they may simply be sandwiched between the porous transport layer on the anode or cathode side and the electrolyte membrane. Such catalyst layers can be provided in an appropriate form; for example, they may be provided on the surface of the electrolyte membrane or porous transport layer, or they may be provided as a separate component between the electrolyte membrane and the porous transport layer.

[0053] In addition, a separator may be provided between the anode and the porous transport layer on the anode side, and between the cathode and the porous transport layer on the cathode side, respectively. The separator on the cathode side and the separator on the anode side may be made of titanium or stainless steel, and in some cases, the surface thereof may be coated with a noble metal such as a platinum group metal. For miniaturization of the device, the separator may be integrated with the anode or the cathode, respectively. In the case of integration, the material of the separator is adopted. As described above, the separator may be appropriately arranged according to the requirements for the cell and the stack, etc.

[0054] In a PEM type water electrolysis device, a plurality of cells as described above are often stacked to form a stack and disposed therein. When forming a stack, for cells other than the cell located at the outermost end, the separator on the cathode side and the cathode in the cell, as well as the anode and the separator on the anode side in the cell adjacent to that cell, are replaced with bipolar plates, whereby the cells can be connected and stacked. Here, for the cells located inside, the electrolyte membrane and the porous transport layer are laminated and included between two bipolar plates. The bipolar plate may be made of the same material as the separator.

[0055] By using the above water electrolysis device, electrolysis of water can be performed. More specifically, for example, when a voltage is applied between the anode and the cathode of the cell, the water (H2O) supplied to the anode side mainly undergoes an oxidation reaction of 2H2O → 4H + + O2 + 4e - and is decomposed into hydrogen ions (H + ) and oxygen (O2). The hydrogen ions pass through the electrolyte membrane, and e - moves to the cathode side through an external circuit, respectively, and at the cathode, 2H + + 2e - → H2 reduction reaction produces hydrogen (H2). Therefore, overall, water is decomposed into oxygen and hydrogen. Thus, hydrogen can be produced.

Example

[0056] Next, we fabricated a prototype of the titanium porous body of this invention and confirmed its effects, which are described below. However, this description is for illustrative purposes only and is not intended to be limiting.

[0057] For samples No. 1-3, HDH titanium powder, as shown in Table 1, was mixed with the organic binder PVB and the organic solvent IPA. A titanium-based coupling agent, Orgatics TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd., was then 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 described above was applied in a sheet-like manner onto a PET film coated with a release agent using a knife coater, and then dried by heating at 160°C for 20 minutes. After drying, the dried material was peeled off the PET film and placed on a graphite setter, where it was sequentially degreased at 380°C for 8 hours and sintered at 850°C for 1 hour. This resulted in a sheet-like porous titanium material.

[0059] In No. 4, titanium fibers manufactured by chatter cutting were dry-deposited onto 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 framework.

[0060] For each of the titanium porous materials No. 1 to 4, the thickness, porosity, and ten-point average roughness Rz were determined according to the methods described above. The results are shown in Table 1.

[0061] [Table 1]

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

[0063] As shown in Table 3, the average aspect ratio of the pores was 3.2 or higher for titanium porous materials No. 1 and 2, but less than 3.2 for titanium porous materials No. 3 and 4.

[0064] [Table 2]

[0065] [Table 3]

Claims

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

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

3. The titanium porous body according to claim 1, wherein the porosity is 30% or more and 55% or less.

4. The titanium porous 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 porous body surface is 20 μm or less.

6. The titanium porous body according to claim 1, used in the porous transport layer of a PEM-type water electrolysis apparatus.

7. A sheet-like titanium laminate, The structure comprises multiple layers of titanium gas-liquid permeable layers, each having pores that allow gas and / or liquid to pass through, which are laminated by bonding adjacent titanium bonding surfaces in the lamination direction. A titanium laminate in which at least one of the gas-liquid permeable layers is a titanium porous body according to any one of claims 1 to 6.

8. A sheet-like titanium laminate, The structure comprises multiple layers of titanium gas-liquid permeable layers, each having pores that allow gas and / or liquid to pass through, which are laminated by bonding adjacent titanium bonding surfaces in the lamination direction. A titanium laminate in which, of the multiple gas-liquid permeable layers, at least one gas-liquid permeable layer forming the surface of the laminate is the titanium porous material described in claim 5, and the surface of the laminate is the porous material surface.

9. A PEM-type water electrolysis apparatus comprising a cell containing a cathode, an electrolyte membrane, a porous transport layer, and an anode in a stacked arrangement, The porous transport layer comprises a titanium porous body as described in any one of claims 1 to 6.

10. A method for electrolyzing water using the water electrolysis apparatus described in claim 9.

11. A method for producing hydrogen, comprising decomposing water using the electrolysis method described in claim 10 to generate hydrogen.

Images