Titanium porous body, titanium laminate, water electrolysis cell, and method for producing hydrogen

Abstract

The present invention relates to a titanium porous body which is in a sheet form having a thickness of not more than 700 μm, which has a porosity of 30-60%, and which has a bubble point diameter of not more than 20 μm, wherein, among two main surfaces of the titanium porous body, the main surface having the higher surface roughness Rz has a surface roughness Rz of not less than 5 μm.

Description

Titanium porous material, titanium laminate, water electrolysis cell, and hydrogen production method

[0001] This invention relates to a titanium porous body, a titanium laminate, a water electrolysis cell, and a method for producing hydrogen.

[0002] Titanium porous materials possess the characteristics of metal porous materials, such as air permeability, liquid permeability, and electrical conductivity, along with the high corrosion resistance unique to titanium. Titanium porous materials are being explored for use in fields such as electrode materials and filters that can withstand highly corrosive environments, and their application in water electrolysis cells using polymer electrolyte membranes (PEMs) is particularly anticipated.

[0003] As an example of a porous metal body, for instance, International Publication No. 2013 / 140941 (Patent Document 1) describes a three-dimensional mesh metal porous body for current collectors, characterized in that it consists of a sheet-like three-dimensional mesh metal porous body, the porosity of the sheet-like three-dimensional mesh metal porous body is 90% or more and 98% or less, and the 30% cumulative pore diameter (D30) of the sheet-like three-dimensional mesh metal porous body, calculated by measuring the pore diameter using the bubble point method, is 20 μm or more and 100 μm or less.

[0004] International Publication No. 2013 / 140941

[0005] The porous metal material described in Patent Document 1 is a porous metal material for use as a current collector in a lithium-ion secondary battery. The porous metal material described in Patent Document 1 has a very high porosity and a large surface area per unit area, which increases the contact area between the current collector and the active material, allowing for effective utilization of the active material, improving the battery capacity, and reducing the amount of conductive additive to be mixed.

[0006] However, for example, a PEM-type water electrolysis cell includes an anode, an electrolyte membrane, and a cathode. If a sheet-like porous metal material with extremely high porosity, such as that described in Patent Document 1, is used as the porous transport layer (PTL) on the anode side, it is thought that the contact area between the catalyst layer and the PTL will be insufficient due to the excessively high porosity, resulting in insufficient water electrolysis efficiency.

[0007] Therefore, one embodiment of the present invention aims to provide a titanium porous material suitable for use in water electrolysis cells. Another embodiment of the present invention aims to provide a titanium laminate, a water electrolysis cell, and a method for producing hydrogen using the titanium porous material.

[0008] In a PEM-type water electrolysis cell, the porous transport layer on the anode side plays a role not only in diffusing fluids such as water and oxygen but also in conducting electric current to the catalyst layer. Therefore, it is thought that the larger the contact area or the more contact points between the surface of the porous transport layer and the surface of the catalyst layer, the easier it is for electric current to flow to the catalyst layer. Furthermore, from the viewpoint of uniformly supplying water to the catalyst layer, it is preferable that the porous transport layer has many fine pores formed on its surface. If the porous transport layer has many pores on its surface and supplies water to the catalyst layer, it is thought that water will be electrolyzed efficiently without having to spread the water in the catalyst layer. Moreover, if many fine pores are formed on the surface of the porous transport layer, the electrolyte membrane is less likely to penetrate into the porous transport layer, and the electrolyte membrane is less likely to be damaged. However, even if many fine pores are formed on the surface of the porous transport layer, if relatively large pores exist inside the porous transport layer, the flow of fluids such as water and oxygen inside the porous transport layer may be disturbed, which may hinder the supply of water to the catalyst layer and the discharge of oxygen from the porous transport layer.

[0009] Therefore, the inventors diligently studied to achieve the above objectives and found that a sheet-like titanium porous material having a specific thickness, in which the porosity, bubble point diameter, and surface roughness Rz are controlled, is suitable for use in water electrolysis, particularly as a porous transport layer on the anode side, thus completing the present invention.

[0010] Embodiments of the present invention can be described in the following [1] to [7]. [1] A titanium porous body, which is in the form of a sheet with a thickness of 700 μm or less, has a porosity of 30% or more and 60% or less, has a bubble point diameter of 20 μm or less, and of the two main surfaces of the titanium porous body, the main surface with the larger surface roughness Rz has a surface roughness Rz of 5 μm or more. [2] The titanium porous body according to [1], wherein the bubble point diameter is 10 μm or less. [3] The titanium porous body according to [1] or [2], wherein the main surface with the larger surface roughness Rz has a surface roughness Rz of 15 μm or more. [4] The titanium porous body according to any one of [1] to [3], which is a sintered body of powder. [5] A titanium laminate in the form of a sheet, comprising a plurality of titanium gas-liquid permeable layers, each having pores and allowing gas and / or liquid to pass through, wherein at least one of the gas-liquid permeable layers is the titanium porous material described in any of [1] to [4]. [6] A water electrolysis cell comprising the titanium porous material described in any of [1] to [4] or the titanium laminate described in [5]. [7] A method for producing hydrogen, comprising performing electrolysis of water using the water electrolysis cell described in [6].

[0011] According to one embodiment of the present invention, a titanium porous material suitable for use in water electrolysis cells can be provided. Furthermore, according to another embodiment of the present invention, a titanium laminate, a water electrolysis cell, and a method for producing hydrogen can be provided using the titanium porous material.

[0012] The following describes in detail the titanium porous body, titanium laminate, water electrolysis cell, and hydrogen production method according to embodiments of the present invention.

[0013] (Titanium porous material) The titanium porous material according to one embodiment of the present invention is a sheet-like material with a thickness of 700 μm or less, a porosity of 30% or more and 60% or less, a bubble point diameter of 20 μm or less, and of the two main surfaces of the titanium porous material, the main surface with the larger surface roughness Rz has a surface roughness Rz of 5 μm or more.

[0014] The sheet-like titanium porous material described above has a small bubble point diameter and one of its main surfaces is relatively smooth. For example, when used as a porous transport layer on the anode side of a PEM-type water electrolysis cell, it can secure a contact area or contact points with the catalyst layer, making it easy to pass current to the catalyst layer. Furthermore, because the titanium porous material has a small bubble point diameter and a relatively large porosity, it is thought to have a large number of through-pores. Therefore, it has high diffusion efficiency for fluids such as water and oxygen, and for example, when used as a porous transport layer on the anode side of a PEM-type water electrolysis cell, it is possible to effectively supply water to the catalyst layer and discharge oxygen from the porous transport layer. In addition, although the titanium porous material has a small bubble point diameter and one of its main surfaces is relatively smooth, it is preferable that the other main surface has a relatively large surface roughness Rz. In particular, when the titanium porous material is a powder sintered body, a larger surface roughness Rz tends to result in larger openings on the main surface. Therefore, for example, when used in the porous transport layer on the anode side of a PEM-type water electrolysis cell, it is expected that good diffusion of fluids such as water and oxygen can be ensured, and that fluids such as water and oxygen can also diffuse well in the direction along the main surface. However, since the main surface with a larger surface roughness Rz may damage the electrolyte membrane, it is preferable to position it so that it is the main surface opposite to the electrolyte membrane side. For these reasons, the above-described sheet-like titanium porous material is recognized as a titanium porous material suitable for use in water electrolysis cells, particularly for use in the porous transport layer on the anode side.

[0015] In this specification, the surface of a sheet-like porous titanium material and the surface located on the opposite side in a plan view may be referred to as the "main surface" because they have a larger apparent area. Furthermore, the porous titanium material has two main surfaces with different surface roughness Rz. Here, the main surface with the smaller surface roughness Rz (smooth surface) may be referred to as "one main surface" or "one main surface," and the main surface with the larger surface roughness Rz (rough surface) may be referred to as "the other main surface" or "the other one main surface."

[0016] A titanium porous body has pores on its surface and inside, and may have a three-dimensional network structure inside. Preferably, the titanium porous body is a sintered powder body, more specifically, 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. Furthermore, from the viewpoint of smoothing the surface of a sheet-like titanium porous body, it is preferable that the titanium porous body is a sintered powder body. As an example, a titanium porous body may have a sponge-like three-dimensional network structure skeleton. While titanium fibers can also be used in titanium porous bodies, those manufactured using titanium fibers tend to have a non-woven three-dimensional network structure, and the skeletal structure differs between titanium porous bodies made of powder sintered bodies and those made of fiber sintered bodies. When a titanium porous body is a fiber sintered body, the ends of the fibers tend to protrude from the surface of the titanium porous body, potentially damaging the electrolyte membrane when used, for example, in a porous transport layer of a water electrolysis cell. Furthermore, it is preferable that the inside of the titanium skeleton of the titanium porous body is solid rather than hollow.

[0017] 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.

[0018] 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.

[0019] 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. In the manufacturing method described later, if drying and / or debinding is carried out in an oxygen-containing atmosphere, the oxygen content of the titanium porous material may increase to some extent. The oxygen content can be measured by the inert gas melting-infrared absorption method.

[0020] The carbon content of the titanium porous material is not particularly limited, but may be between 0.01% by mass and 0.25% by mass. The carbon content can be measured by combustion-infrared absorption spectroscopy.

[0021] The nitrogen content of the titanium porous material is not particularly limited, but may be between 0.01% by mass and 0.15% by mass. The nitrogen content can be measured by the inert gas fusion-thermal conductivity method.

[0022] 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 oxygen, carbon, and nitrogen content.

[0023] The titanium porous material is in sheet form. "Sheet form" in the context of titanium porous material means a plate-like or foil-like material with a small thickness relative to its dimensions in plan view. However, as mentioned above, titanium porous material has pores on its surface and inside, and may have a three-dimensional network structure, especially inside. The shape of the titanium porous material in plan view is not particularly restricted, but may be square, rectangular with an aspect ratio of 1:1 to 1:3, rhombic, or other polygonal shapes. Polygonal titanium porous material may have chamfered corners.

[0024] The thickness of the sheet-like porous titanium material is 700 μm or less. Alternatively, the thickness of the sheet-like porous titanium material may be 500 μm or less, or 300 μm or less. While there is no particular lower limit, the thickness of the sheet-like porous titanium material may be, for example, 60 μm or more, or 100 μm or more.

[0025] The thickness is measured at five points in total: four points on the periphery and one point in the center of the titanium porous 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 titanium porous material is rectangular in plan view, the four points on the periphery are replaced with the four corner points.

[0026] The projected area of ​​the main surface of the sheet-like titanium porous material is not particularly limited. For example, the projected area of ​​this surface may be 250 mm². 2 That's all, for example, 600,000 mm 2 The following may apply: A titanium porous material with a sufficiently large projected surface area can be cut and used as needed, making it suitable for mass production. Here, "projected surface area" refers to the area obtained by projecting the main surface of the titanium porous material onto a plane.

[0027] The porosity of the titanium porous material is 30% or more and 60% or less. When using a titanium porous material as the porous transport layer of a water electrolysis cell, it is necessary to ensure mechanical strength while appropriately diffusing fluids such as water and oxygen gas. To appropriately diffuse fluids such as water and oxygen gas, it is preferable that the porosity of the titanium porous material be 30% or more. On the other hand, if the porosity is too high, it may become difficult to ensure mechanical strength, so it is preferable that the porosity of the titanium porous material be 60% or less. For example, if the porosity of the titanium porous material is too high, depending on the pressure applied when assembling the water electrolysis cell, excessive deformation may occur, leading to uneven or inhibited fluid diffusion. Also, if the porosity of the titanium porous material is too high, there is a risk that PEM may enter the pores of the titanium porous material and be damaged by compression in the stacking direction of the water electrolysis cell, or that the contact area between the catalyst layer and PTL will be insufficient, resulting in insufficient water electrolysis efficiency. The porosity of the titanium porous material may be 55% or less, or 50% or less. Furthermore, the porosity can be adjusted by appropriately adjusting the sintering conditions and other factors in the manufacturing method described later.

[0028] 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.

[0029] The bubble point diameter of the titanium porous material is 20 μm or less. Because the titanium porous material has a relatively large porosity of 30% to 60% while having a small bubble point diameter of 20 μm or less, it is thought that the titanium porous material contains numerous through-pores, resulting in high fluid diffusion efficiency. For example, when used as a porous transport layer in a water electrolysis cell, it is thought to facilitate homogeneous diffusion of water into the catalyst layer. Furthermore, it is thought that oxygen generated in the catalyst layer can be easily removed. The bubble point diameter of the titanium porous material may be 10 μm or less, or 5 μm or less. While there is no particular lower limit, the bubble point diameter of the titanium porous material may be, for example, 0.5 μm or more.

[0030] In this specification, "bubble point diameter" refers to the maximum pore diameter obtained by measuring the through-pore diameter distribution using the gas permeation method (capillary flow method). The pore diameter of a titanium porous material may also be evaluated by the mercury intrusion method, but in pore diameter distribution measurement by the mercury intrusion method, closed pores that do not penetrate the titanium porous material are also measured in addition to pores that penetrate the titanium porous material. Considering the objective of the present invention, which is to provide a titanium porous material suitable for use in porous transport layers, it can be said that pore diameter distribution measurement by the gas permeation method, which measures pores that penetrate the titanium porous material, is a more suitable evaluation method than pore diameter distribution measurement by the mercury intrusion method. Furthermore, it is considered that among titanium porous materials with equivalent porosity, the larger the bubble point diameter, the greater the variation in the cross-sectional dimensions of the pores formed inside the titanium porous material, and conversely, the smaller the bubble point diameter, the smaller the variation in the cross-sectional dimensions of the pores formed inside the titanium porous material tends to be.

[0031] Furthermore, in this specification, "bubble point" refers to the pressure at which bubbles first form on one of the main surfaces of a sheet-like porous titanium material when it is thoroughly wetted and pressurized with a gas with low solvent solubility from the opposite side of the main surface. The pore diameter obtained from this bubble point is called the "bubble point diameter." Through-pore diameter distribution measurement by gas permeation can be performed in accordance with JIS K 3832-1990 "Test method for bubble points of precision filtration membrane elements and modules." However, the measurement is performed using POROFIL Wetting Fluid (manufactured by Anton Paar Japan) as the highly wettable liquid used to fill the porous titanium material.

[0032] The measurement of through-pore diameter distribution by gas permeation is as follows: First, a highly wettable liquid is packed into a sheet-like porous titanium material. Next, gas pressure is applied to push out the packed liquid. When the gas pressure is small, the liquid trapped in the pores remains within the pores due to the equilibrium between pressure and surface tension, so no gas flows. When the gas pressure exceeds the capillary pressure, the liquid is discharged from the pores, and the pores become empty. At this time, the pores become empty in order from the largest to the smallest. The gas passes through the empty pores, and its flow rate and pressure are measured. Here, the equilibrium equation for capillaries is expressed as follows: 2πrγ cosθ = πr 2 In the formula hρg, r = radius of the capillary, γ = surface tension of the liquid, θ = contact angle between the liquid and the capillary wall, h = height, ρ = density of the liquid, and g = acceleration due to gravity. Pressure P = hρg (capillary pressure), and the equilibrium equation for the capillary is expressed as follows based on Washburn's equation: Pr = 2γcosθ. When a highly wettable liquid is filled into a titanium porous material and the contact angle is assumed to be 0°, the relationship between pressure and the diameter of the through-pore (d) can be simplified as follows: d = 4γ / P. In this specification, the bubble point diameter can be determined from this simplified relationship between pressure and pore diameter: d = 4γ / P. Thus, since the pressure at which the liquid filled in the pores is discharged correlates with the diameter of the pores penetrating the titanium porous material, the pore diameter can be evaluated by measuring that pressure. Furthermore, since the flow rate increases as the number of pores penetrating the titanium porous material increases, the pore diameter distribution for the through-pores can also be calculated from the difference in flow rate.

[0033] In this specification, for example, the POROMETER 3G micro model manufactured by Anton Paar Japan can be used as the through-pore diameter distribution analyzer, and a perfluoro compound [for example, POROFIL Wetting Fluid manufactured by Anton Paar Japan (composition: perfluoro compound, mainly a compound with 12 carbon atoms, boiling point: >150°C)] can be used as the highly wettable liquid to fill the titanium porous body, and air (atmosphere) can be used as the gas to push out the filled liquid.

[0034] The titanium porous material preferably has a difference between the bubble point diameter and the average flow diameter of 2.0 μm or less, 1.0 μm or less, 0.8 μm or less, or 0.5 μm or less. A smaller difference between the bubble point diameter and the average flow diameter reduces the variation in the size of the through-pores present in the titanium porous material. For this reason, the lower limit of this difference is not particularly limited, but the difference between the bubble point diameter and the average flow diameter of the titanium porous material may be, for example, 0.01 μm or more.

[0035] The average flow diameter of the titanium porous material is smaller than the bubble point diameter, but may be, for example, 15 μm or less, or 12 μm or less. The lower limit is not particularly limited, but the average flow diameter of the titanium porous material may be, for example, 0.4 μm or more.

[0036] In this specification, the mean flow pore size (MFP) is the pore size obtained from the results obtained by measuring the through-pore size distribution by gas permeation. When a graph is drawn with the gas flow rate on the vertical axis and the gas pressure on the horizontal axis, a dry curve, a wet curve, and a curve plotted at the point where the flow rate of the dry curve is 1 / 2 (hereinafter referred to as the "1 / 2 flow curve") are plotted, the pore size is determined from the pressure at the intersection of the 1 / 2 flow curve and the wet curve using the above relation: d = 4γ / P. Here, the dry curve shows the relationship between flow rate and pressure measured when measuring the through-pore size distribution by gas permeation on a dry titanium porous body without filling it with liquid, and the wet curve shows the relationship between flow rate and pressure measured when measuring the through-pore size distribution by gas permeation on a titanium porous body filled with a highly wettable liquid. The average flow diameter can be determined in accordance with ASTM E1294-89 (Reapproved 1999) "Standard Test Method for Pore Size Characteristics of Membrane Filters Using Automated Liquid Porosimeter".

[0037] The porous titanium body has two main surfaces with different surface roughness Rz, and the main surface with larger surface roughness Rz has a surface roughness Rz of 5 µm or more. As described above, the porous titanium body has a bubble point diameter of 20 µm or less. While one main surface thereof is relatively smooth, it is preferable that the other main surface has a certain level of high surface roughness Rz. Particularly when the porous titanium body is a powder sintered body, the main surface with larger surface roughness Rz tends to have larger openings present on the main surface. Therefore, when the surface roughness Rz of the main surface with larger surface roughness Rz is 5 µm or more, for example, when the porous titanium body is used as a porous transport layer of a water electrolysis cell, it can be expected to ensure good diffusion of fluids such as water and oxygen, and good diffusion of fluids such as water and oxygen can also be expected in the direction along the main surface. This makes it easier for fluids such as water and oxygen to enter the porous transport layer. The main surface with larger surface roughness Rz preferably has a surface roughness Rz of 10 µm or more, or 15 µm or more. The upper limit is not particularly limited, and can be appropriately set according to the diffusion capacity for water and oxygen required of the porous titanium body. The surface roughness Rz of the main surface with larger surface roughness Rz may be, for example, 80 µm or less. For example, when a porous titanium body is used for the porous transport layer of a water electrolysis cell, the main surface having a larger surface roughness Rz is preferably a main surface located on the opposite side to the main surface in contact with the electrolyte membrane, or in contact with the catalyst layer when the catalyst layer is disposed on the surface of the electrolyte membrane.

[0038] In the present specification, surface roughness Rz refers to the maximum height Rz of a roughness curve, and is measured in accordance with ISO 4287-1997, for example, using an SJ-210 manufactured by Mitutoyo Corporation.

[0039] The aforementioned porous titanium body can be produced, for example, by the following method. That is, titanium powder is mixed with an organic solvent, an organic binder or the like to obtain a defoamed paste, the paste is applied into a sheet shape, followed sequentially by drying, binder removal (hereinafter also referred to as "degreasing") and sintering, whereby the porous titanium body can be produced. Each step can be performed by heating at a predetermined temperature. By such a production method, a powder sintered body having a three-dimensional network structure can be obtained. The powder sintered body may be cut into predetermined dimensions if necessary for adjusting the dimensions.

[0040] The above paste preferably contains titanium powder, an organic binder and an organic solvent, and preferably contains neither water nor a foaming agent. The titanium powder is not particularly limited, but it is preferable to use finely powdered hydrogenation dehydrogenation titanium powder (HDH powder). The average particle diameter of the titanium powder is preferably 10 µm or more and 150 µm or less, more preferably 10 µm or more and 45 µm or less. In the present specification, the average particle diameter of titanium powder refers to D50 (volume basis) obtained from a particle size distribution determined by laser diffraction method. Polyvinyl butyral (PVB) can be used as the organic binder, and isopropyl alcohol (IPA) can be used as the organic solvent, respectively.

[0041] The mass ratio of the organic binder to the organic solvent contained in the paste may be appropriately determined. For example, the ratio of the mass Ms of the organic solvent to the mass Mb of the organic binder (Ms / Mb) is preferably 2.0 or more and 4.5 or less. Further, the paste may contain, for example, 7.0 g or more and 20.0 g or less (7.0 g to 20.0 g) of the organic binder and 30.5 g or more and 60.0 g or less (30.5 g to 60.0 g) of the organic solvent per 100 g of titanium powder.

[0042] The paste can be produced, for example, by mixing titanium powder, an organic solvent, an organic binder, and optional components appropriately used as needed, with a planetary centrifugal mixer. Here, all of the above materials may be mixed together, or a part may be mixed first, and then the remainder is added and mixed. For example, it is also possible to mix the organic solvent and the organic binder first, and then add the titanium powder and perform mixing.

[0043] In a planetary centrifugal mixer, the container charged with the above materials is revolved, and at the same time, the container itself rotates on its axis. The rotation directions of the rotation on its axis and the revolution can be appropriately set. For example, the revolution may be clockwise, and the rotation on its axis may also be clockwise. By performing defoaming while mixing the materials charged into the container under reduced pressure using the planetary centrifugal mixer, the bubble point diameter of the finally obtained porous titanium body can be reduced.

[0044] A known rotary-orbit mixer can be used. A cylindrical container with a lid that can be opened and closed can be used as the mixing container for the rotary-orbit mixer. Furthermore, the mixing container is preferably made of resin from the viewpoint of avoiding metal contamination originating from the container. The titanium porous body may be incorporated into the anode side of a water electrolysis cell and used in an extremely harsh environment that is highly acidic and highly oxidizing. If the titanium porous body is manufactured using a paste that contains metal contamination originating from the container, there is a risk that the metal from the container will leach out of the titanium porous body when used in a water electrolysis cell. The resin used for the mixing container is not particularly limited, but examples include polypropylene resin and polyethylene resin. Furthermore, it is preferable that the container does not contain stirring blades. This is because it is desirable to suppress metal contamination originating from the stirring blades.

[0045] The rotational and revolutionary mixer allows for appropriate adjustment of the container's rotational and revolutionary speeds and the mixing time. For example, it is preferable that the revolutionary speed of the container of the rotational and revolutionary mixer be faster than the rotational speed, and it is even more preferable to set the revolutionary speed of the container of the rotational and revolutionary mixer to twice the rotational speed (in rpm). Furthermore, it is preferable that the mixing time be 5 minutes or longer. This allows for more reliable removal of foam.

[0046] Furthermore, from the viewpoint of efficiently mixing and degassing, the container may be tilted when using a rotational mixer. In this case, the angle of inclination of the rotation axis (corresponding to the central axis of a cylindrical or similar container) relative to the orbital axis can be set as appropriate, but for example, it is 45°. Normally, the orbital axis is parallel to the vertical direction.

[0047] Also, the volume of the mixing container (V A The total volume (V) of the materials to be put into the mixing container relative to the volume (V) B The proportion (V) B / V A The following can be adjusted as appropriate, taking into consideration mixing, degassing, etc.

[0048] Furthermore, during mixing (and degassing), the inside of the container is controlled to a reduced pressure atmosphere, such as a certain degree of reduced pressure or vacuum. When a reduced pressure atmosphere is maintained, the pressure inside the container is preferably -0.02 MPa or less in relative pressure.

[0049] The paste can be applied onto a polyethylene terephthalate (PET) film with a release agent using a roll coater or the like. In this process, smaller titanium particles tend to be oriented towards the film, while larger particles tend to be oriented towards the surface of the applied paste layer. This makes it possible to produce a porous titanium body with main surfaces having different surface roughnesses.

[0050] (Titanium Laminate) The titanium laminate according to one embodiment of the present invention is a sheet-like titanium laminate comprising a plurality of titanium gas-liquid permeable layers, each having pores and allowing gas and / or liquid to pass through, wherein at least one of the gas-liquid permeable layers is the titanium porous body according to the above-described embodiment of the present invention.

[0051] 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, the titanium laminate used as a porous transport layer in a water electrolysis cell may be one that allows gas and / or liquid to permeate in the lamination direction (sheet thickness direction) or in other directions such as perpendicular to the lamination direction. Here, the sheet surface of the sheet-shaped titanium laminate is also called the "laminated surface."

[0052] Of the above-mentioned gas-liquid permeable layers, at least one gas-liquid permeable layer is a titanium porous material according to the above-described embodiment. The titanium porous material according to the present embodiment has excellent surface smoothness because it has a small bubble point diameter and is less likely to damage the electrolyte membrane, so it can be used to form a sheet-like titanium laminate with the titanium porous material on the surface.

[0053] Other gas-liquid permeable layers may also be titanium porous materials according to the embodiment of the present invention described above, but are not limited to such titanium porous materials. For example, sheet-like titanium porous materials with higher porosity, titanium expanded metal layers, titanium mesh layers, titanium perforated metal layers, titanium lotus metal layers, etc., may also be used. There are no particular limitations on the method of joining multiple gas-liquid permeable layers, but various methods such as sintering (diffusion bonding), laser fusion bonding, and spot welding can be employed.

[0054] The thickness of the other gas-liquid permeable layer is preferably 100 μm to 960 μm. By making the thickness of the other gas-liquid permeable layer somewhat thicker, the permeability or liquid permeability can be further improved, and by not making it too thick, it becomes possible to miniaturize the water electrolysis cell and improve the electrolysis efficiency per unit area.

[0055] The thickness of each gas-liquid permeable layer can be measured by observing the thickness at five points in the cross-section in the thickness direction of the resin-embedded and polished titanium laminate using a scanning electron microscope (SEM), and adopting the average value. Since each gas-liquid permeable layer in the titanium laminate has different required functions, the thickness of each gas-liquid permeable layer can be determined by identifying areas where differences in pore size can be observed in the lamination direction and observing those areas with an SEM.

[0056] When the titanium laminate is incorporated as a PTL on the anode side of a water electrolysis cell, it is preferable that it be made of metallic titanium to ensure excellent corrosion resistance and appropriate electrical conductivity.

[0057] As an example of a method for manufacturing a titanium laminate, one method involves preparing a titanium porous body according to one embodiment of the present invention and preferably another titanium sheet material as materials to be used for the gas-liquid permeable layer, and then laminating these to produce a titanium laminate. For example, a titanium porous body according to one embodiment of the present invention can be manufactured, and then a titanium laminate can be produced by placing, for example, a sheet-like titanium porous body with a higher porosity, a titanium expanded metal layer, a titanium mesh layer, a titanium perforated metal layer, or a titanium lotus metal layer on the titanium porous body and diffusion bonding them by sintering. Furthermore, if the gas-liquid permeable layer of the titanium laminate is composed of a sintered body of powder or fibers, it is also possible to produce a titanium laminate by laminating powder or fibers onto a dried sheet-like paste (green body) and then sintering it. It is also possible to produce a titanium laminate by laminating green bodies together, and then degreasing and sintering them.

[0058] (Water electrolysis cell) A water electrolysis cell according to one embodiment of the present invention is a water electrolysis cell that includes a titanium porous body or a titanium laminate according to one embodiment of the present invention described above.

[0059] A water electrolysis cell generally includes an anode, a cathode, and an electrolyte membrane between the anode and cathode, with the anode and cathode being electrically connected. Here, a catalyst layer and a porous transport layer may be included between the electrolyte membrane and the anode or cathode. The catalyst layer on the anode side may be called an oxygen evolution catalyst layer, and the catalyst layer on the cathode side may be called a hydrogen evolution catalyst layer. The catalyst layer, on both the anode and cathode sides, is usually located between the porous transport layer and the electrolyte membrane. It is preferable that the water electrolysis cell includes a titanium porous body according to one embodiment of the present invention or a titanium laminate according to one embodiment of the present invention as the porous transport layer on the anode side. In the titanium porous body according to one embodiment of the present invention, it is preferable that the main surface with the lower surface roughness faces the electrolyte membrane side, and the main surface with the higher surface roughness faces away from the electrolyte membrane side, among the two main surfaces with different surface roughness. This can suppress damage to the electrolyte membrane. The porous titanium material or titanium laminate used in the porous transport layer on the anode side may be coated on at least one surface with a precious metal, more specifically a platinum metal (platinum, ruthenium, rhodium, palladium, osmium, iridium, typically platinum), to enhance electrical conductivity. This coating may be applied to one or both of the surfaces of the porous titanium material or titanium laminate that face the electrolyte membrane and the surface opposite the electrolyte membrane. Carbon materials such as graphite may be used in the porous transport layer on the cathode side.

[0060] The electrolyte membrane is preferably a polymer electrolyte membrane (PEM). A water electrolysis cell in which the electrolyte is constituted by a PEM may be referred to as a PEM-type water electrolysis cell. The electrolyte membrane may also be referred to as a proton exchange membrane, and typically may include a sulfonic acid cation exchange membrane made of fluororesin, or the like. Iridium oxide (IrO₂) or the like can be used for the catalyst layer on the anode side. Platinum (Pt) or the like can be used for the catalyst layer on the cathode side. Each catalyst layer may be bonded onto the electrolyte membrane by coating, attaching or the like, and the electrolyte membrane provided with such catalyst layers may be referred to as a Catalyst Coated Membrane (CCM). However, the anode-side catalyst layer and / or the cathode-side catalyst layer may be bonded onto the anode-side or cathode-side porous transport layer, and may also be simply sandwiched and disposed between the anode-side or cathode-side porous transport layer and the electrolyte membrane. Such a catalyst layer may be provided in an appropriate form, for example, it may be provided on the surface of the electrolyte membrane or the porous transport layer, or may be provided as a separate member between the electrolyte membrane and the porous transport layer.

[0061] The water electrolysis cell may be used alone, or may be used by integrating a plurality of cells. A structure constituted by a plurality of water electrolysis cells may be referred to as a stack. Further, the water electrolysis cell (including the form of a stack) itself may be referred to as a water electrolysis apparatus, or the water electrolysis apparatus may be referred to as including the water electrolysis cell and additional members.

[0062] (Method for Producing Hydrogen) The method for producing hydrogen according to one embodiment of the present invention is a method for producing hydrogen, which includes performing electrolysis of water using the water electrolysis cell according to one embodiment of the present invention described above.

[0063] By using the water electrolysis cell described above, electrolysis of water can be performed. More specifically, for example, when a voltage is applied between the anode and the cathode of the water electrolysis cell, water (H₂O) supplied to the anode side mainly reacts according to 2H₂O→4H + +O₂+4e - is decomposed into hydrogen ions (H + ) and oxygen (O₂) by the oxidation reaction of . Hydrogen ions pass through the electrolyte membrane, and e- These elements travel through an external circuit, moving to the cathode side, and then 2H occurs at the cathode. + +2e - →Hydrogen (H2) is produced through the reduction reaction of H2. Therefore, looking at the reaction as a whole, water is decomposed into oxygen and hydrogen. This allows for the production of hydrogen.

[0064] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these embodiments.

[0065] (Paste Materials and Composition) Pastes were prepared using the following materials and composition, except for Comparative Example 3. • Titanium powder: HDH powder was used. The average particle size of the HDH powder by volume was 14 μm or 26 μm. • Organic binder: Polyvinyl butyral (PVB) • Organic solvent: Isopropyl alcohol (IPA) • Composition: The mass ratio of titanium powder, organic binder, and organic solvent was adjusted so that, per 100 g of titanium powder, the organic binder was 7.0 g or more and 20.0 g or less, and the organic solvent was 30.5 g or more and 60.0 g or less.

[0066] (Manufacturing Example) A sheet-like porous titanium material with a thickness of 100 μm or more and 250 μm or less was manufactured as follows. Mixing and degassing: To be described later. Coating: The paste was applied in a sheet-like manner to a polyethylene terephthalate (PET) resin substrate with a mold release agent using a roll coater. Drying: Drying was carried out in an air atmosphere at 100°C for 180 minutes. After peeling off the resin substrate, the sheet-like dried paste was transferred to a graphite setter. Degreasing: The sheet-like dried paste was degreased in an air atmosphere at 360°C for 360 minutes. Sintering: After degreasing, the material was sintered in a reduced pressure atmosphere (1.0 × 10⁻⁶). -3 A sheet-like porous titanium material was produced by sintering under the conditions of Pa or less, 775°C, and 90 minutes.

[0067] <Example 1> Using titanium powder with an average particle size of 14 μm, a sheet-like porous titanium material was manufactured according to the above manufacturing example. A rotary-orbit mixer was used for mixing and degassing. The tilt angle of the rotation axis of the rotary-orbit mixer with respect to the orbital axis was set to 45°, the orbital speed of the container of the rotary-orbit mixer was set to twice the rotation speed (in rpm), and mixing was performed under reduced pressure conditions (relative pressure of -0.02 MPa or less). The manufactured sheet-like porous titanium material had a porosity of 41%, a bubble point diameter of 2.0 μm, and a surface roughness Rz of 12 μm on the main surface with the larger surface roughness Rz. The average flow diameter was 1.6 μm.

[0068] <Example 2> Using titanium powder with an average particle size of 26 μm, a sheet-like porous titanium material was manufactured according to the above manufacturing example. A rotary-orbit mixer was used for mixing and degassing. The tilt angle of the rotation axis of the rotary-orbit mixer with respect to the orbital axis was set to 45°, the orbital speed of the container of the rotary-orbit mixer was set to twice the rotation speed (in rpm), and mixing was performed under reduced pressure conditions (relative pressure of -0.02 MPa or less). The manufactured sheet-like porous titanium material had a porosity of 58%, a bubble point diameter of 9.1 μm, and a surface roughness Rz of 27 μm on the main surface with the larger surface roughness Rz. The average flow diameter was 8.6 μm.

[0069] <Comparative Example 1> Using titanium powder with an average particle size of 14 μm, a sheet-like porous titanium material was manufactured according to the above manufacturing example. A cylindrical container was used for mixing and degassing, with the axis of the cylindrical container positioned horizontally and rotated uniaxially. Mixing was performed at atmospheric pressure without reduced pressure. The manufactured sheet-like porous titanium material had a porosity of 43% and a bubble point diameter of 50 μm. The average flow diameter was 2.5 μm.

[0070] <Comparative Example 2> Using titanium powder with an average particle size of 26 μm, a sheet-like porous titanium material was manufactured according to the above manufacturing example. A rotating-orbit mixer was used for mixing and degassing. The inclination angle of the rotation axis of the rotating-orbit mixer with respect to the orbital axis was set to 45°, and the orbital speed of the container of the rotating-orbit mixer was set to twice the rotation speed (in rpm). Mixing was performed at atmospheric pressure without reducing the pressure. The manufactured sheet-like porous titanium material had a porosity of 59% and a bubble point diameter of 60 μm. The average flow diameter was 10.1 μm.

[0071] <Comparative Example 3> The composition of the above paste was changed to include the same amount of water instead of 10% by mass of the total mass of titanium powder, organic binder, and organic solvent, by replacing the organic binder and organic solvent with the same amount of water (however, the mass ratio of organic binder to organic solvent was the same in the composition of the above paste and the composition of the aqueous paste), and a sheet-like titanium porous body was manufactured under the following conditions following the manufacturing example of Example 1. A rotating-orbit mixer was used for mixing and degassing. The tilt angle of the rotation axis of the rotating-orbit mixer with respect to the orbital axis was set to 45°, the orbital speed of the container of the rotating-orbit mixer was set to twice the rotation speed (in rpm), and mixing was performed at atmospheric pressure without reduced pressure. Pinholes occurred when the paste was applied. The manufactured sheet-like titanium porous body had a bubble point diameter of 100 μm or more.

[0072] As can be seen from the above results, the titanium porous material produced in Examples 1 and 2 is a sheet-like titanium porous material with a thickness of 700 μm or less, a porosity of 30% or more and 60% or less, a bubble point diameter of 20 μm or less, and the main surface of the titanium porous material with the larger surface roughness Rz having a surface roughness Rz of 5 μm or more. It is recognized as a titanium porous material suitable for use in water electrolysis cells, particularly for use as a porous transport layer on the anode side.

Claims

1. A titanium porous body, which is in the form of a sheet with a thickness of 700 μm or less, has a porosity of 30% or more and 60% or less, has a bubble point diameter of 20 μm or less, and of the two main surfaces of the titanium porous body, the main surface with the larger surface roughness Rz has a surface roughness Rz of 5 μm or more.

2. The titanium porous body according to claim 1, wherein the bubble point diameter is 10 μm or less.

3. The titanium porous body according to claim 1 or 2, wherein the main surface with the larger surface roughness Rz has a surface roughness Rz of 15 μm or more.

4. A titanium porous body according to any one of claims 1 to 3, which is a sintered body of powder.

5. A titanium laminate in sheet form, comprising a plurality of titanium gas-liquid permeable layers, each having pores and allowing gas and / or liquid to pass through, wherein at least one of the gas-liquid permeable layers is a titanium porous body according to any one of claims 1 to 4.

6. A water electrolysis cell comprising a titanium porous body according to any one of claims 1 to 4 or a titanium laminate according to claim 5.

7. A method for producing hydrogen, comprising performing electrolysis of water using the water electrolysis cell described in claim 6.