Porous transport layer and solid polymer electrolyte membrane-type water electrolysis cell including same

Abstract

By means of a porous transport layer provided with a porous substrate comprising a conductive material, a first coating film that is formed on the surface of the conductive material constituting the porous substrate and contains a metal oxide, and a second coating film that is formed on the first coating film and contains a noble metal or a noble metal oxide having conductivity, and a solid polymer electrolyte membrane (PEM)-type water electrolysis cell provided with the porous transport layer, there are provided a low-cost porous transport layer that is both conductive and corrosion-resistant and has excellent long-term reliability, and a PEM-type water electrolysis cell provided with the porous transport layer.

Description

Porous transport layer and solid polymer electrolyte membrane water electrolysis cell comprising the same

[0001] The present invention relates to a porous transport layer, and more particularly to a component disposed between a bipolar plate (or power supply) and a catalyst layer in a solid polymer electrolyte membrane (PEM) type water electrolysis cell.

[0002] In recent years, hydrogen energy, which does not emit carbon dioxide, has attracted attention as a way to combat global warming. Hydrogen can be obtained by the electrolysis of water (hereinafter sometimes referred to as "water electrolysis"), and the PEM-type water electrolysis method, which has excellent responsiveness to the fluctuating output of renewable energy, is attracting attention.

[0003] A PEM-type water electrolysis cell uses PEM as the electrolyte and a cation exchange membrane that acts as a diaphragm. It comprises an electrode catalyst-equipped electrolyte membrane (CCM) in which platinum group catalysts that promote the electrolysis of water are integrally bonded to both sides of the PEM, with a porous transport layer on the outside and a bipolar plate further outside (see Patent Document 1).

[0004] When pure water is supplied to the anode side of the CCM and a DC current is passed between the two electrodes, a catalytic reaction occurs, and the pure water is decomposed into oxygen gas and hydrogen ions in the anode catalyst layer. The decomposed hydrogen ions move towards the cathode side through the PEM due to the electric field, and gain electrons in the cathode catalyst layer to produce high-purity hydrogen gas.

[0005] In PEM-type water electrolysis cells, perfluorocarbon sulfonic acid membranes are generally used, and since the temperature of the pure water supplied to the anode is between 60°C and 80°C, the anode chamber of the water electrolysis cell is exposed to a high-temperature, strongly acidic atmosphere.

[0006] Furthermore, during water electrolysis, the anode side becomes highly potential due to positive polarization, and the large amount of oxygen gas generated exposes the anode chamber to a highly oxidizing atmosphere, creating a highly corrosive environment for metal materials. For this reason, titanium (Ti), which has excellent corrosion resistance, is used for the porous transport layer on the anode side. However, when exposed to strong acid and a high oxidation potential, an oxide film of resistive components gradually forms and grows on the Ti surface, causing the voltage of the water electrolysis cell to rise rapidly, which has led to a problem of shortening the lifespan of the electrolysis cell.

[0007] Therefore, in order to solve this problem, various proposals have been made conventionally. For example, in Non-Patent Document 1 and Non-Patent Document 2, as shown in FIG. 2, a porous transport layer in which a noble metal such as platinum (Pt) or gold (Au) is plated on the surface of a sintered body or an expanded metal made of Ti particles or Ti fibers is described.

[0008] As described in Non-Patent Document 1 and Non-Patent Document 2, when the surface of a porous transport layer made of Ti is coated with a noble metal such as Pt or Au, the corrosion resistance is improved. However, Au described in Non-Patent Document 1 cannot withstand the high oxidation potential on the anode side and is gradually oxidized and dissolved, so the long-term corrosion resistance is insufficient.

[0009] On the other hand, Pt can withstand anodic oxidation dissolution. However, the plating method generally used as a method for coating Pt is likely to cause coating defects such as pinholes and cracks. Therefore, in the porous transport layer coated with Pt by the plating method, corrosion of Ti occurs due to the intrusion of sulfonic acid or oxygen gas partially desorbed from the PEM into the coating defects, or peeling of the Pt coating occurs due to the formation and growth of an oxide film of a resistance component on the Ti surface. There are problems in long-term reliability. In order to overcome this problem, it is necessary to make the thickness of the expensive Pt coating about 1 μm, which has a disadvantage in terms of economy.

[0010] From an economic point of view, a porous transport layer that does not use noble metals for the coating is disclosed in Patent Document 2. In Patent Document 2, in order to improve the corrosion resistance while maintaining conductivity, the porous transport layer is coated with titanium nitride (TiN), which is a conductive ceramic. However, a vacuum dry coating method such as a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method, which has low industrial productivity, is required. In addition, this method has a drawback that it is difficult to uniformly coat the entire surface of a large object, and surface defects such as pinholes are likely to occur. Therefore, the porous transport layer coated by this method is likely to have variations in quality, and the resistance component also increases due to dissolution and oxide film growth occurring at pinholes, so the disadvantage of poor long-term reliability has not been overcome.

[0011] As a method for compensating for the drawbacks of the vacuum dry coating method, Patent Document 3 discloses a method in which a porous transport layer is coated with a conductive ceramic film and then one side of the porous transport layer is coated with a noble metal or a noble metal oxide. However, all of the porous transport layers described in the prior art documents had the problem that a film for improving corrosion resistance was not formed even inside the porous transport layer. Since the oxygen gas generated on the anode surface passes through the inside of the porous transport layer together with high-temperature pure water and is discharged along the flow path of the bipolar plate, the inside of the uncoated porous transport layer is also exposed to a high-temperature, high-potential oxidizing atmosphere similar to the surface of the porous transport layer. Therefore, the growth of the oxide film also proceeds on the surface of the Ti material inside the porous transport layer. Since the growth of this oxide film gradually proceeds and reaches the surface of the porous transport layer, drawbacks such as an increase in the cell voltage or the possibility that the film for corrosion protection is peeled off by the gas pressure of oxygen gas have not yet been overcome, and the long-term reliability is poor.

[0012] Japanese Unexamined Patent Application Publication No. 2023-072818, Japanese Unexamined Patent Application Publication No. 2024-074184, Japanese Unexamined Patent Application Publication No. 2023-117048

[0013] Electrochemistry, 89(3), 240-246 (2021), Special Reports, Toshiba Review, Vol. 73, No. 3 (May 2018) 9-12, "Noble-Metal-Sparing Electrode for PEM Water Electrolysis"

[0014] The problem to be solved by the present invention is to provide a low-cost porous transport layer having excellent long-term reliability with both conductivity and corrosion resistance, and a PEM type water electrolysis cell using the porous transport layer.

[0015] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by forming a first film containing a specific metal oxide and a second film containing a specific noble metal or a noble metal oxide having conductivity on a porous substrate made of a conductive material, and have completed the present invention.

[0016] In other words, the present invention is as described in [1] to

[13] below. [1] A porous transport layer comprising: a porous substrate made of a conductive material; a first film containing a metal oxide formed on the surface of the conductive material constituting the porous substrate; and a second film containing a noble metal or a conductive noble metal oxide formed on the first film. [2] The porous transport layer according to [1], wherein the metal oxide is a metal oxide containing one or more metal elements selected from the group consisting of titanium, niobium, tantalum, molybdenum, and tungsten. [3] The porous transport layer according to [1] or [2], wherein the thickness of the first film is 10 nm or more and 30 nm or less. [4] The porous transport layer according to any one of [1] to [3], wherein the first film contains 0.1 mol% or more and 1.0 mol% or less of a metal or metal oxide containing one or more metal elements selected from the group consisting of platinum, ruthenium, and iridium. [5] The porous transport layer according to any one of [1] to [4], wherein the noble metal or conductive noble metal oxide contains one or more metal elements selected from the group consisting of platinum, ruthenium, and iridium. [6] The porous transport layer according to any one of [1] to [5], wherein the thickness of the second film is 100 nm or more and 300 nm or less. [7] The porous transport layer according to any one of [1] to [6], wherein the thickness of one side of the second film is 100 nm or more and 300 nm or less, and the thickness of the other side is 25 nm or more and 200 nm or less. [8] The porous transport layer according to any one of [1] to [7], wherein the grain size of the crystal grains of the noble metal or conductive noble metal oxide contained in the second film is 10 nm or more and 50 nm or less. [9] The porous transport layer according to any one of [1] to [8], wherein the porous substrate is a porous substrate made of titanium or a titanium alloy.

[10] The porous transport layer according to any one of [1] to [9], wherein the conductive material constituting the porous substrate is a conductive material comprising an aggregate of particles with a diameter of 5 μm or more and 150 μm or less.

[11] The porous transport layer according to any one of [1] to [9], wherein the conductive material constituting the porous substrate is a conductive material made from fibers having a cross-section with an equivalent circular diameter of 10 μm or more and 50 μm or less.

[12] A porous transport layer according to any one of [1] to

[11] , wherein the porosity of the porous substrate is 40% by volume or more and 80% by volume or less. The porosity is a value expressed as a percentage of the value obtained by [1 - {(mass of porous substrate) / ((true density of the material of the porous substrate) × (apparent volume of the porous substrate))}]. The apparent volume is the volume including voids.

[13] A solid polymer electrolyte membrane (PEM) type water electrolysis cell comprising the porous transport layer according to any one of [1] to

[12] .

[0017] According to the present invention, a porous transport layer can be obtained that maintains excellent corrosion resistance and conductivity for a long period of time, even when in contact with strongly acidic CCM in a water electrolysis cell and exposed to oxidizing oxygen gas and an anodic environment generated by high-temperature pure water as a raw material, and is inexpensive and easy to mass-produce.

[0018] This is a schematic enlarged cross-sectional view of the porous transport layer of the present invention. This is a schematic diagram showing the coating structure of a conventional porous transport layer. This is a schematic diagram showing the coating structure of the porous transport layer of the present invention. This is a schematic unfolded view of the PEM type water electrolysis cell of the present invention.

[0019] The embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0020] [1. Porous Transport Layer] The porous transport layer according to the present invention comprises a porous substrate made of a conductive material, a first coating containing a metal oxide formed on the surface of the conductive material constituting the porous substrate, and a second coating containing a noble metal or a conductive noble metal oxide formed on the first coating. Figure 1 is a schematic diagram showing how the first coating containing a metal oxide formed on the surface of the conductive material constituting the porous substrate and the second coating containing a noble metal or a conductive noble metal oxide formed on the first coating are formed in the porous transport layer of the present invention when the porous substrate is of the particle sintering type or fiber sintering type.

[0021] [2. Porous Substrate] The substrate consists of a porous substrate made of a conductive material. The porous transport layer is placed between the strongly acidic CCM and the bielectrode plates or power supply. Therefore, the porous substrate needs to have (a) high conductivity that allows electrons to be exchanged between the CCM and the bielectrode plates or power supply, (b) porosity that allows pure water raw material to be supplied to the CCM from the flow channels of the bielectrode plates or power supply and oxygen gas generated on the CCM to be quickly discharged, and (c) mechanical strength that does not deform even under the surface pressure inside the PEM type water electrolysis cell and does not impair its porosity. Conductivity here refers to the ability of electrons to move efficiently between the electrode catalyst and the bielectrode plates or power supply, and it is preferable that the resistance value is equivalent to that of a metal.

[0022] The material of the porous substrate is not particularly limited, as long as it has the above-mentioned functions. Examples of porous substrate materials include: (a) sintered metals and metal meshes made of various metals such as titanium (Ti) or Ti alloys, stainless steel, niobium (Nb), and tantalum (Ta); and (b) porous carbon sheets such as carbon paper and carbon nonwoven fabrics.

[0023] Among these, Ti or Ti alloys are lightweight and have excellent mechanical strength, so they can withstand the surface pressure during the formation of the first coating and inside the water electrolysis cell without compromising their porosity, and they also have excellent adhesion to the first coating.

[0024] Porous substrates can be made from particles or fibers made of Ti or Ti alloy. In the case of porous substrates made from particles of Ti or Ti alloy, it is preferable to be composed of aggregates of particles with a diameter of 5 μm or more in order to allow fluids (oxygen and water) to permeate through the porous transport layer, but it is particularly preferable to be composed of aggregates of particles with a diameter of 10 μm or more in order to ensure a sufficient amount of permeation. On the other hand, from the viewpoint of mechanical strength and thickness of the porous transport layer, it is preferable to be composed of aggregates of particles with a diameter of 150 μm or less, but it is particularly preferable to be composed of aggregates of particles with a diameter of 75 μm or less. Furthermore, these aggregates are preferably sintered. The diameter of these particles can be measured by known methods, for example, by observing the surface or cross-section using a microscope such as a scanning electron microscope (SEM).

[0025] In the case of a porous substrate using Ti or Ti alloy fibers as raw materials, it is preferable to use fibers having a cross-section with an equivalent circular diameter of 10 μm or more in order to allow fluids (oxygen and water) to permeate through the porous transport layer, but it is particularly preferable to use fibers having a cross-section with an equivalent circular diameter of 15 μm or more in order to ensure sufficient permeation. On the other hand, from the viewpoint of mechanical strength and thickness of the porous transport layer, it is preferable to use fibers having a cross-section with an equivalent circular diameter of 50 μm or less, but it is particularly preferable to use fibers having a cross-section with an equivalent circular diameter of 30 μm or less. The form of the Ti fibers may be either short fibers or long fibers, but a porous substrate made of long fibers, which have superior mechanical strength and are easier to control the porosity of, is preferable as a porous transport layer for the anode. Furthermore, these fibers are preferably sintered. Note that the equivalent circular diameter refers to the diameter of a circle having an area equal to the area of ​​the particle. The equivalent circular diameter of this fiber can be measured by known methods. For example, the porous substrate is cut to expose the cross-section of the fiber, and the average equivalent circular diameter can be determined by averaging the results of measurements taken under a microscope such as a scanning electron microscope (SEM) for five or more fields, with three or more fibers per field.

[0026] The porosity of a porous substrate is not particularly limited, and the optimal porosity can be selected according to the purpose. Generally, if the porosity of a porous substrate is too low, it becomes difficult for water, the raw material, to flow through the porous substrate, and the smooth discharge of oxygen gas produced by the electrochemical reaction may not be possible. Therefore, a porosity of 40 volume% or more is preferable for a porous substrate. On the other hand, by setting the porosity of the porous substrate to 85 volume% or less, the true volume of the porous substrate increases, making it possible to conduct electricity with low electrical resistance, but from the viewpoint of ensuring mechanical properties, it is more preferable to set it to 80 volume% or less. The porosity is a value expressed as a percentage of the value obtained by [1 - {(mass of porous substrate) / ((true density of the material of the porous substrate) × (apparent volume of the porous substrate))}]. The apparent volume is the volume including voids.

[0027] The shape of the porous substrate is not particularly limited as long as it can be used in a PEM-type water electrolysis cell or the like, but examples include square, rectangular, circular, and elliptical shapes. The thickness of these porous substrates is not particularly limited as long as it can be used in a PEM-type water electrolysis cell or the like, but for example, the thickness is 0.04 to 1.0 mm, preferably 0.08 to 0.5 mm.

[0028] [3. First Coating] The first coating formed on the conductive material surface constituting the porous substrate is a coating containing a metal oxide. The metal oxide is preferably a metal oxide containing one or more metal elements selected from the group consisting of Ti, Nb, Ta, molybdenum (Mo), and tungsten (W), and Ti, Mo, and W are particularly preferred as they exhibit relatively higher conductivity and corrosion resistance.

[0029] Furthermore, the first coating may contain, in addition to the metal oxide, a metal or metal oxide containing one or more metal elements selected from the group consisting of platinum (Pt), ruthenium (Ru), and iridium (Ir). A first coating containing a metal or metal oxide containing one or more metal elements selected from the group consisting of Pt, Ru, and Ir is suitable as the first coating because it has high corrosion resistance in the corrosive environment inside a water electrolysis cell and also has high conductivity. From the viewpoint of long-term reliability against the high oxidation potential on the anode side and conductivity, it is particularly preferable to include at least one of Ir oxide and Pt.

[0030] Furthermore, if the amount of metal or metal oxide containing one or more metal elements selected from the group consisting of Pt, Ru, and Ir in the first coating is too small, sufficient conductivity may not be obtained. Therefore, it is preferable that the amount of metal or metal oxide containing one or more metal elements selected from the group consisting of Pt, Ru, and Ir in the first coating be 0.1 mol% or more, but it is more preferable that it be 0.2 mol% or more to obtain a sufficient effect of conductivity. On the other hand, if the amount of metal or metal oxide containing one or more metal elements selected from the group consisting of Pt, Ru, and Ir in the first coating is too large, a localized galvanic effect may occur, and sufficient corrosion resistance may not be obtained. Therefore, it is preferable that the amount of metal or metal oxide containing one or more metal elements selected from the group consisting of Pt, Ru, and Ir in the first coating be 1.0 mol% or less, but it is more preferable that it be 0.8 mol% or less to obtain a sufficient effect of corrosion resistance.

[0031] The thickness of the first coating is not particularly limited, and the optimal thickness can be selected according to the purpose. Generally, if the thickness of the first coating is too thin, sufficient corrosion resistance may not be obtained. Therefore, the first coating needs to cover the entire porous substrate, and a thickness of 10 nm or more is preferable. On the other hand, if the thickness of the first coating is too thick, the voltage of the water electrolysis cell will increase due to a decrease in conductivity, which may cause oxidative dissolution due to the anode potential of the bipolar plates, power supply, and the porous transport layer itself, and is also economically unfeasible. Therefore, a thickness of 30 nm or less is preferable for the first coating. This film thickness can be measured by known methods, for example, by measurement using X-ray fluorescence analysis (XRF) or by measuring the value from cross-sectional images taken using a transmission electron microscope (TEM).

[0032] To prevent the growth of an oxide film on the surface of the porous substrate and to stably maintain the conductivity and corrosion resistance of the porous transport layer over a long period of time, it is preferable to form the first film over the entire surface of the conductive material constituting the porous substrate. That is, the first film is formed not only on one or both surfaces of the porous substrate, but also on the surface of the conductive material present inside the porous substrate.

[0033] The first coating can be formed using known chemical solution precipitation methods such as the sol-gel method or thermal decomposition method, or by thermal oxidation.

[0034] [4. Second Coating] The first coating described above does not necessarily have sufficient corrosion resistance to contact with strongly acidic CCM or resistance to high oxidation potential, and there is a risk that the resistance will increase due to corrosion of the first coating or the growth of oxide film on the porous substrate surface. Therefore, as shown in Figure 3, this phenomenon is prevented and long-term reliability is improved by further forming a second coating with superior corrosion resistance. The second coating requires long-term reliability against oxidation potential on the anode side, corrosion resistance that can withstand contact with strongly acidic CCM, and high conductivity. For this reason, the second coating is preferably a thin film containing a noble metal or a conductive noble metal oxide, and is formed on the first coating formed on the porous substrate.

[0035] The second coating is a coating containing a noble metal or a conductive noble metal oxide. The noble metal or conductive noble metal oxide is Pt, platinum oxide (PtO ２), Ir, iridium oxide (IrO ２ ), Ru, ruthenium oxide (RuO ２ ), a noble metal containing any one or more metal elements selected from the group consisting of, or a noble metal oxide having conductivity is preferred. In particular, from the viewpoints of oxidation resistance, conductivity and corrosion resistance, Pt, IrO ２ is preferred.

[0036] In addition to the noble metal or the noble metal oxide having conductivity, the second coating may contain other additives to an extent that does not impair the conductivity in order to improve oxidation resistance and corrosion resistance. Other additives include (a) inevitable impurities, (b) titanium oxide (TiO ２ ), tantalum oxide (Ta ２ O ５ ), tungsten oxide (WO ３ ), cerium oxide (CeO ２ ), etc. It may contain any one of these, or may contain a mixture of two or more. The addition amount of other additives is preferably 0.1 mol% or more and 30 mol% or less from the viewpoint of conductivity.

[0037] The thickness of the second coating is not particularly limited, and an optimum thickness can be selected according to the purpose. Generally, if the thickness of the second coating is too thin, sufficient corrosion resistance may not be obtained. Therefore, the thickness of the second coating is preferably 100 nm or more. On the other hand, from an economic viewpoint, there is no need to make the second coating thicker than necessary, and it is preferably 300 nm or less. This film thickness can be measured by a known method. For example, it can be measured from a cross-sectional image taken using a transmission electron microscope (TEM).

[0038] The grain size of the precious metal or conductive precious metal oxide crystal grains can be selected to be optimal according to the target thickness of the second coating. If the grain size of the precious metal or conductive precious metal oxide crystal grains is too small, the second coating can cover the entire first coating, but it may result in an amorphous structure with poor corrosion resistance. Therefore, a grain size of 10 nm or larger is preferable for the precious metal or conductive precious metal oxide crystal grains. On the other hand, if the grain size of the precious metal or conductive precious metal oxide crystal grains is too large, when the thickness of the second coating is set within the above range, many areas of the first coating will be exposed, and sufficient corrosion resistance cannot be ensured. Therefore, a grain size of 50 nm or smaller is preferable for the precious metal or conductive precious metal oxide crystal grains. This grain size can be measured by known methods, for example, from a cross-sectional image taken using a transmission electron microscope (TEM).

[0039] To ensure the corrosion resistance of the first coating and to stably maintain the conductivity and corrosion resistance of the porous transport layer over a long period of time, it is preferable to form the second coating on the entire surface of the first coating which is formed on the entire surface of the conductive material constituting the porous substrate.

[0040] The second coating is preferably formed over the entire surface of the first coating, but it is not necessary to have a uniform thickness over the entire area. On the side in contact with the CCM, which is exposed to strong acid and high potential, it is necessary to maintain conductivity and corrosion resistance for a long period of time, so the thickness of the second coating is preferably 100 nm to 300 nm. The thickness of the second coating on the other side in contact with the bipolar plate (or power supply), where the acidity is slightly reduced, may be thinner than the side in contact with the CCM from an economic standpoint, but a thickness of 25 nm or more is preferred in order to suppress the growth of oxide film on the porous substrate surface and maintain conductivity. On the other hand, the thickness of the second coating on the other side in contact with the bipolar plate (or power supply) is preferably 300 nm or less, as a certain thickness is sufficient to maintain conductivity, but from an economic standpoint, 200 nm or less is more preferable, and 100 nm or less is particularly preferable.

[0041] The second coating can be formed using known chemical solution deposition methods such as the sol-gel method or the thermal decomposition method.

[0042] [5. Applications] The porous transport layer according to the present invention can be used as a porous transport layer for the anode or a porous transport layer for the cathode in a PEM-type water electrolysis cell, but is particularly suitable as a porous transport layer for the anode. Since the anode chamber in a PEM-type water electrolysis cell is exposed to a strongly acidic, high-potential, and oxidizing atmosphere, applying the porous transport layer according to the present invention to the porous transport layer for the anode can greatly improve the durability of the PEM-type water electrolysis cell.

[0043] [6. Method for Manufacturing a Porous Transport Layer] The method for manufacturing a porous transport layer according to the present invention comprises a first step of forming a first film containing a metal oxide over the entire porous substrate, and a second step of forming a second film containing a noble metal or a conductive noble metal oxide on the first film.

[0044] [6.1. First Step] First, a first coating containing metal oxide is formed on the entire porous substrate using a thermal oxidation method or a chemical solution deposition method such as a sol-gel method or a thermal decomposition method (first step). When forming a first coating containing an oxide of the same metal as the metal constituting the porous substrate, a thermal oxidation method can be used. In the thermal oxidation method, the first coating is formed by heating the porous substrate at a high temperature while passing a gas containing an oxidizing gas such as oxygen through a heat treatment furnace.

[0045] In the thermal oxidation method, it is preferable to select the optimal heat treatment temperature according to the purpose. Generally, if the heat treatment temperature is too low, the heat treatment cannot be completed within a practical time. Therefore, the heat treatment temperature is preferably 250°C or higher, and more preferably 350°C or higher. On the other hand, if the heat treatment temperature is too high, the first coating may grow beyond an appropriate thickness, increasing resistance, or the porous substrate may be damaged, reducing mechanical strength. Therefore, the heat treatment temperature is preferably 650°C or lower, and more preferably 550°C or lower.

[0046] The heat treatment time for the thermal oxidation method is selected according to the heat treatment temperature. Generally, the higher the heat treatment temperature, the shorter the time required to complete the formation of the first coating. The suitable heat treatment time is usually around 10 to 60 minutes, although this also depends on the heat treatment temperature.

[0047] When forming a first coating having a metal oxide containing one or more metal elements selected from the group consisting of Ti, Nb, Ta, Mo, and W, a chemical solution deposition method can also be used. The type of chemical solution deposition method is not particularly limited as long as it is a method that can form a thin and uniform first coating over the entire porous substrate. Examples include the sol-gel method, thermal decomposition method, complex polymerization method, hydrothermal method, solvothermal method, and colloid method. In particular, the sol-gel method and thermal decomposition method are suitable as methods for forming the first coating because they offer excellent solution stability and allow for the simple formation of a uniform thin film.

[0048] The solution used in the chemical solution precipitation method may be commercially available or synthesized by known methods. Examples of commercially available solutions include TiO2 from Kojunka Kagaku Co., Ltd. ２ Examples of coating materials include solutions synthesized by known methods, such as those described in Japanese Patent Publication No. 2001-340757 and the literature by Renkakuji et al. (Seiichi Renkakuji, Yuko Nakamura, Light Metals 38 (2002) Vol. 52, No. 1).

[0049] To form the first coating, the above-described solution is applied to the interior of the porous substrate. The method of applying the solution is not particularly limited, and conventionally known methods can be used, such as spray coating, atomization, curtain flow coating, dip coating, brush coating, and roller coating. However, spray coating, dip coating, brush coating, and roller coating are preferred because they can reliably apply the solution to the interior of the porous substrate and allow for easy control of the film thickness. After applying the solution, the coating film is dried to remove the solvent. The drying temperature varies depending on the type of solvent, but is usually within the range of 80 to 200°C.

[0050] Next, the coated film is heat-treated to crystallize into a metal oxide. While it is preferable to select the optimal heat treatment temperature according to the purpose, generally, if the heat treatment temperature is too low, the heat treatment cannot be completed within a practical time. Therefore, the heat treatment temperature in this step is preferably 250°C or higher, and more preferably 350°C or higher. On the other hand, if the heat treatment temperature is too high, an oxide film may form on the surface of the metal material constituting the porous substrate, increasing resistance, or the porous substrate may be damaged, reducing its mechanical strength. Therefore, the heat treatment temperature is preferably 650°C or lower, and more preferably 550°C or lower. The heat treatment time required for crystallization is usually about 1 to 120 minutes, and while the firing atmosphere is not particularly limited, air or oxygen is usually used.

[0051] [6.2. Second Step] Next, a second film containing a noble metal or a conductive noble metal oxide is formed on the first film using a chemical solution deposition method such as the sol-gel method or the thermal decomposition method (second step). The type of chemical solution deposition method is not particularly limited as long as it is a method that can form a thin and uniform film on the first film. Examples include the sol-gel method, thermal decomposition method, complex polymerization method, hydrothermal method, solvothermal method, and colloid method. In particular, the sol-gel method and the thermal decomposition method are suitable as methods for forming the second film because they have excellent solution stability and can easily form a uniform thin film.

[0052] The solution used in the chemical solution precipitation method can be the same as the solution used in the chemical solution precipitation method for forming the first film.

[0053] To form a second film, the above-described solution is applied onto the first film. The method of applying the solution is not particularly limited, and conventionally known methods can be used, such as spray coating, atomization, curtain flow coating, dip coating, brush coating, and roller coating. However, spray coating, dip coating, brush coating, and roller coating are preferred because they can reliably coat the first film inside the porous substrate and allow for easy control of the film thickness. After applying the solution, the film is dried to remove the solvent. The drying temperature varies depending on the type of solvent, but is usually within the range of 70 to 200°C.

[0054] In forming the second coating, it is preferable that the thickness of one side of the second coating is 100 nm or more and 300 nm or less, and the thickness of the other side is 25 nm or more and 200 nm or less. In other words, it is preferable that the porous transport layer has different thicknesses on the front and back sides of the second coating. For example, when the porous transport layer is used in a PEM type water electrolysis cell, the porous transport layer is provided between the CCM and the bipolar plate (or power supply), so one side of the second coating refers to the side that is in contact with the CCM, and the other side refers to the side that is in contact with the bipolar plate (or power supply).

[0055] Specifically, in forming the second film, it is preferable to create a gradient in the film thickness within the cross-sectional direction of the porous transport layer, such that the thickness of the side in contact with the CCM is 100 nm to 300 nm, and the thickness of the other side in contact with the bipolar plate (or power supply) is 25 nm to 200 nm. Suitable methods for applying the solution to create the gradient in the second film include spray application, brush application, and roller application. By controlling the spray pressure, brush pressure, roller pressure, etc., and applying the solution from the side in contact with the CCM, the application is repeated until the solution has spread evenly to the other side in contact with the bipolar plate (or power supply), thereby creating a gradient in the second film.

[0056] By doing so, the second coating is thicker on the CCM side, improving corrosion resistance, while the second coating is thinner on the dual electrode plate (or power supply) side, reducing the amount of precious metals used.

[0057] Next, a heat treatment is performed to crystallize the coating film into a metal oxide. This heat treatment can be carried out under the same conditions as the heat treatment used to crystallize the coating film formed on the porous substrate for the first coating formation into a metal oxide.

[0058] [7. PEM-type water electrolysis cell] In one embodiment of the present invention, the PEM-type water electrolysis cell includes PEM and a porous transport layer according to the present invention. The form of the porous transport layer according to the present invention is described in the section "Porous transport layer" above. The PEM-type water electrolysis cell may include a plurality of porous transport layers. In the PEM-type water electrolysis cell, the porous transport layer according to the present invention is preferably a porous transport layer for the anode. The PEM-type water electrolysis cell may further include a porous transport layer other than the porous transport layer according to the present invention.

[0059] In forming the second coating of the porous transport layer according to the present invention, it is preferable that the thickness of one side of the second coating is 100 nm or more and 300 nm or less, and the thickness of the other side is 25 nm or more and 200 nm or less. In other words, it is preferable that the porous transport layer has different thicknesses on the front and back sides of the second coating. When the porous transport layer is used in a PEM type water electrolysis cell, the porous transport layer is provided between the CCM and the bipolar plate (or power supply), so one side of the second coating refers to the side that is in contact with the CCM, and the other side refers to the side that is in contact with the bipolar plate (or power supply).

[0060] PEM can be selected from known electrolyte membranes used in PEM-type water electrolysis. For example, a perfluorocarbon membrane having sulfonic acid groups can be used. An example of a perfluorocarbon membrane having sulfonic acid groups is the Nafion membrane (a registered trademark manufactured by DuPont).

[0061] The PEM-type water electrolysis cell may further include other components. These other components may be selected from known components of PEM-type water electrolysis cells. Examples of other components include a catalyst layer, a gasket, a sealing material, and a bipolar plate (or power supply).

[0062] The catalyst in the catalyst layer can be selected from known catalysts used in PEM-type water electrolysis. Examples of catalyst components include Pt, Au, silver (Ag), palladium (Pd), palladium oxide (PdO), Ir, and IrO. ２ , rhodium (Rh), rhodium oxide (Rh ２ O ３ ), Ru, RuO２ , tin (Sn), tin oxide (SnO ２ ), iron (Fe), iron(Fe)(Tetr) oxide ３ O ４ ), cobalt (Co), cobalt(Co)(Co) ３ O ４ ), nickel (Ni), Mo, molybdenum oxide (MoO ３ ), W, WO ３ , vanadium (V), vanadium pentoxide (V ２ O ５ Examples include carbon black, TiO2, and their alloys and composite oxides. The catalyst may be in the form of particles. The catalyst layer may contain a catalyst supported on a support. Examples of supports include carbon black and TiO2. ２ Examples include particles.

[0063] The bipolar electrode (or power supply) can be selected from known bipolar electrode (or power supply) used in PEM-type water electrolysis. Examples of components of the bipolar electrode (or power supply) include metals such as Ti and stainless steel.

[0064] The arrangement of each component in a PEM-type water electrolysis cell may be determined by referring to known PEM-type water electrolysis cells. In the PEM-type water electrolysis cell of the present invention, as shown in Figure 4, the PEM is preferably located between the anode catalyst layer and the cathode catalyst layer, the PEM and catalyst layers are preferably located between the porous transport layer for the anode and the porous transport layer for the cathode, and the PEM, catalyst layer and porous transport layer are preferably located between the two bipolar plates (or power supply). The PEM-type water electrolysis cell of the present invention offers excellent long-term reliability and low cost.

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way to these examples, and various modifications are possible without departing from the spirit of the invention.

[0066] [1. Sample Preparation] [1.1. Preparation of Porous Transport Layer] (Example 1) (1) A sintered body made of Ti fibers having a cross-section equivalent to a circular diameter of 20 μm, with a porosity of 56%, was used as the substrate. This porous substrate was a 25 mm × 25 mm square with a thickness of 0.2 mm.

[0067] (2) Step to form the first coating The degreased substrate from (1) is heat-treated at 500°C for 30 minutes, and TiO is added to the substrate so that the film thickness is approximately 30 nm. ２ A first coating was formed consisting of the following. The thickness of the first coating was measured by X-ray fluorescence analysis (XRF).

[0068] (3) Steps to form the second coating A coating solution, which is a platinum precursor solution with a molar concentration of 0.3 M, was prepared by adding hydrochloric acid and 1-pentanol to platinum(IV) chloride and then dissolving it by stirring for 24 hours. On the first coating formed in (2), the platinum precursor solution was applied using a brush application method from the side in contact with the CCM (front surface), controlling the brush pressure to ensure uniform distribution throughout the porous substrate. After removing the solvent by a drying step at 130°C, a second coating made of Pt was formed by heat treatment at 500°C for 30 minutes. Next, the platinum precursor solution was similarly applied from the opposite side (back surface) to ensure uniform distribution throughout the porous substrate. After removing the solvent, heat treatment was performed to form the second coating. This process of forming the second coating by application from both the front and back surfaces was repeated on the fiber surface where the first coating was formed, which was exposed on both the front and back surfaces, until the thickness of the second coating reached approximately 200 nm. The thickness of the second coating was calculated from cross-sectional images taken using a transmission electron microscope (TEM). Furthermore, TEM images confirmed that the grain size of the Pt crystals was between 10 nm and 50 nm.

[0069] (Example 2) A solution of titanium tetraisopropoxide mixed with ethanol was slowly hydrolyzed by dropping a mixed solution containing ethanol and water, prepared to a hydrochloric acid concentration of 8.26 mol%, onto the mixture. The mixture was then stirred for 30 minutes to prepare TiO2. ２ TiO2 is produced by a dip coating method in which a porous substrate is immersed in a sol, and after removal, it is dried for 5 minutes. ２ A gel film is prepared and heat-treated at 300°C for 2 hours to create a TiO film with a thickness of approximately 30 nm. ２ A first coating consisting of was formed. These steps involved nitrogen (N ２ The experiment was carried out in an airflow at room temperature. A porous transport layer was prepared in the same manner as in Example 1, except that the first film was formed by the sol-gel method.

[0070] (Example 3) Iridium(III) chloride trihydrate was dissolved by adding 1-pentanol and stirring for 4 hours to prepare a coating solution which is an iridium oxide precursor solution with a molar concentration of 0.3 M. Using a spray coating machine, the precursor coating solution, which had been left to stand in a cool, dark place at 4°C for at least 2 days, was applied to the side (surface) of the porous substrate that was in contact with the CCM, while controlling the spray pressure and stroke to ensure uniform distribution throughout the porous substrate. After removing the solvent by drying at 130°C, the solution was heat-treated at 380°C to produce IrO ２ A second coating was formed consisting of the above. Next, the coating solution was similarly applied to the entire porous substrate from the opposite side (back side), and after solvent removal, heat treatment was performed to form the second coating. This process of forming the second coating by coating from both the front and back sides was repeated on the fiber surface where the first coating was formed, which was exposed on the front and back sides, until the thickness of the second coating reached approximately 200 nm.

[0071] (Example 4) RuO was prepared in the same manner as in Example 3, except that the coating solution was a ruthenium oxide precursor solution with a molar concentration of 0.3 M, obtained by adding 1-pentanol to ruthenium(II) chloride n hydrate and then dissolving it by stirring for 4 hours. ２ The process of forming a second coating consisting of the above was repeated on the fiber surface where the first coating was formed, which was exposed on the front and back surfaces, until the thickness of the second coating reached approximately 200 nm.

[0072] (Example 5) Platinum(IV) chloride, hydrochloric acid, 1-pentanol, DISPERBYK-161 (manufactured by BYK) as a dispersant, and CeO2 with a particle size of less than 25 nm. ２ (IV) nanopowder (manufactured by Sigma-Aldrich) was added, and the mixture was stirred for 24 hours to prepare a 0.5% cerium oxide (CeO) solution with a total metal molar concentration of 0.3 M. ２ ) - Using a coating solution which is a platinum mixed precursor solution, CeO ２ A porous transport layer was fabricated in the same manner as in Example 1, except that a second coating made of Pt with a film thickness of approximately 200 nm was formed.

[0073] (Example 6) After adding 1-butanol to tungsten hexachloride, the mixture was dissolved by stirring for 1 hour to form a 0.1 M molar concentration WO for first film formation.３ A precursor solution, the coating solution, was prepared. Next, the coating solution was applied to a porous substrate by a brush application method, and after solvent removal by a drying process at 130°C, it was fired at 450°C to produce WO ３ A first coating with a thickness of 30 nm was formed. In the second coating formation process, chloroplatinic acid (IV) and tungsten hexachloride were weighed out so that the molar ratio of platinum to tungsten was 99.5:0.5, 1-pentanol was added, and the mixture was dissolved by stirring for 24 hours to form tungsten oxide (WO) with a total metal molar concentration of 0.3 M. ３ A coating solution, which is a platinum mixed precursor solution, was prepared. Then, the same procedure as in Example 1 was followed, except that this coating solution was used. ３ A porous transport layer was fabricated by forming a second coating made of Pt with a thickness of approximately 200 nm.

[0074] (Example 7) A mixture of penta-n-butoxytantalum, acetylacetone, and 1-butanol was refluxed under nitrogen at 50°C, and a 1-butanol mixture containing water was slowly added dropwise to allow hydrolysis and polycondensation reactions to proceed. Then, 1-butanol and water were removed by vacuum distillation to obtain tantalum oxide (Ta) at a molar concentration of 0.1 M. ２ O ５ A precursor solution, the coating solution, was prepared. Next, the coating solution was applied to a porous substrate by brush application, and after removing the solvent by a drying process at 130°C, it was fired at 400°C to produce Ta ２ O ５ A first coating with a thickness of approximately 13 nm was formed. In the second coating formation process, first, a platinum precursor solution with a molar concentration of 0.6 M was prepared by adding hydrochloric acid and 1-butanol to platinum(IV) chloride and then dissolving it by stirring for 24 hours. Next, a solution of penta-n-butoxytantalum, acetylacetone, and 1-butanol was refluxed under nitrogen at 50°C, and a 1-butanol mixed solution containing water was slowly added dropwise to allow hydrolysis and polycondensation reactions to proceed. Then, 1-butanol and water were removed by vacuum distillation to obtain a tantalum pentoxide (Ta) solution with a molar concentration of 0.3 M. ２ O ５ A precursor solution was prepared. Platinum precursor solutions were prepared so that the molar ratio of platinum to tantalum was 99:1, and tantalum pentoxide (Ta２ O ５ ) Weigh out the precursor solution and dilute it with 1-butanol to obtain a 0.5% tantalum pentoxide (Ta) with a total metal molar concentration of 0.3 M. ２ O ５ A coating solution, which is a platinum mixed precursor solution, was prepared. Then, in the same manner as in Example 1, except that this coating solution was used, ２ O ５ A porous transport layer was fabricated by forming a second coating made of Pt with a thickness of approximately 200 nm.

[0075] (Example 8) In the first coating formation step, the same procedure as in Example 7 was followed except that niobium-n-butoxide was used. ２ O ５ A first coating with a thickness of approximately 18 nm was formed. In the second coating formation step, niobium pentoxide (Nb) was prepared in the same manner as in Example 7, except that niobium-n-butoxide was used, with a molar concentration of 0.3 M. ２ O ５ A precursor solution was prepared. Platinum precursor solutions were prepared separately so that the molar ratio of platinum to niobium was 99:1, and niobium pentoxide (Nb ２ O ５ ) Weigh out the precursor solution and dilute it with 1-butanol to obtain a 0.5% niobium pentoxide (Nb) solution with a total metal molar concentration of 0.3 M. ２ O ５ A coating solution, which is a platinum mixed precursor solution, was prepared. Then, in the same manner as in Example 1, except that this coating solution was used, Nb ２ O ５ A porous transport layer was fabricated by forming a second coating made of Pt with a thickness of approximately 200 nm.

[0076] (Example 9) In the first coating formation step, the process was carried out in the same manner as in Example 6, except that molybdenum 2-ethylhexanoate was used. ３ A first coating with a thickness of approximately 26 nm was formed. In the second coating formation process, chloroplatinic acid (IV) and molybdenum hexachloride were weighed out so that the molar ratio of platinum to molybdenum was 99.5:0.5, 1-pentanol was added, and the mixture was dissolved by stirring for 24 hours to form molybdenum oxide (MoO) with a total metal molar concentration of 0.3 M. ３A coating solution, which is a platinum mixed precursor solution, was prepared. Then, MoO was prepared in the same manner as in Example 1, except that this coating solution was used. ３ A porous transport layer was fabricated by forming a second coating made of Pt with a thickness of approximately 200 nm.

[0077] (Example 10) 1-butanol was added to tetrakis(2-ethylhexanoate) titanium (IV), and then dissolved by stirring for 1 hour to form a molar concentration of 0.1 M TiO for the formation of the first coating. ２ A precursor solution, the coating solution, was prepared. Next, the coating solution was applied to a porous substrate by spray coating, and the solvent was removed by a drying process at 80°C. Then, after being held in an ozone gas atmosphere for 30 minutes, it was calcined in air at 450°C to produce TiO2. ２ A porous transport layer was fabricated in the same manner as in Example 1, except that a first coating with a thickness of approximately 30 nm was formed.

[0078] (Examples 11 and 12) A porous transport layer was fabricated in the same manner as in Example 1, except that the process of forming the second coating was repeated until the film thickness on the front and back surfaces reached 50 nm (Example 11) or 500 nm (Example 12).

[0079] (Examples 13 and 14) A porous transport layer was prepared in the same manner as in Example 1, except that a first coating was formed to a thickness of 10 nm (Example 13) or 50 nm (Example 14).

[0080] (Example 15) A porous transport layer was fabricated in the same manner as in Example 1, except that a sintered body comprising an aggregate of Ti particles with a particle size distribution of 20 to 45 μm in diameter and a Ti porous substrate with a porosity of 56% was used. This porous substrate was a 25 mm x 25 mm square with a thickness of 0.2 mm.

[0081] (Examples 16-19) A porous transport layer was fabricated in the same manner as in Example 1, except that a sintered body made of Ti fibers having a cross-section equivalent to a circle diameter of 20 μm was used, and a Ti porous substrate with a porosity of 35% (Example 16), 45% (Example 17), 78% (Example 18), or 85% (Example 19) was used.

[0082] (Examples 20-23) In the process of forming the second film in Example 1, the coating method was changed to a spray coating method. By controlling the stage temperature, spray pressure, and stroke of the spray coating machine, the platinum precursor solution was sprayed onto the porous substrate on which the first film had been formed only from the surface in contact with the CCM (front surface), so that four levels of difference in the amount of coating on the front and the opposite side (back surface) were created. After solvent removal, heat treatment was performed to form the second film. Except for repeating this process of forming the second film by coating from one side, four types of porous transport layers were prepared in the same manner as in Example 1, on the fiber surface on the side in contact with the CCM (front surface) where the first film had been formed, so that the film thickness of the second film was approximately 200 nm. The film thickness of the second film on the back surface of each prepared porous transport layer was measured, and the results were approximately 100 nm for Example 20, approximately 30 nm for Example 21, approximately 10 nm for Example 22, and 0 nm for Example 23.

[0083] (Comparative Example 1) A porous transport layer was prepared in the same manner as in Example 1, except that the step of forming the second coating (3) described in Example 1 was not performed.

[0084] (Comparative Example 2) A porous transport layer was fabricated in the same manner as in Example 1, except that a first film was formed using a plating method to a thickness of 200 nm, and the step of forming the second film (3) described in Example 1 was not performed. Furthermore, the Pt crystal grains formed by the plating method were confirmed to have a particle size of 400 nm from surface images taken with a scanning electron microscope (SEM). Note that this particle size is the diameter, and as shown in Figure 2, the first film is half embedded in the porous substrate, so the thickness of the first film is 200 nm.

[0085] (Comparative Example 3) A porous transport layer was prepared in the same manner as in Example 1, except that a second film made of TiN was formed using a gas nitriding method to a thickness of approximately 1000 nm. The nitriding treatment was carried out for 8 hours.

[0086] (Comparative Example 4) A porous transport layer was fabricated in the same manner as in Example 1, except that a first film made of TiN was formed using the sputtering method to a thickness of approximately 100 nm, and the step of forming the second film (3) described in Example 1 was not performed. The sputtering method was carried out under an argon (Ar) atmosphere.

[0087] Tables 1 and 2 show the conditions for preparing the porous transport layers in Examples 1 to 23 and Comparative Examples 1 to 4, the measured thicknesses of the first and second coatings, and the grain size of the noble metal or conductive noble metal oxide crystals contained in the second coating.

[0088]

[0089]

[0090] [Evaluation of each porous transport layer] [2.1. Contact Resistance] Samples (25 mm × 25 mm × t0.2 mm) prepared in the examples and comparative examples were sandwiched between Ti plates (25 mm × 80 mm × t5.0 mm), which are the power supply material, and then sandwiched on the outside with gold-plated copper plates, and set in a small press machine incorporating a load cell. The sample was pressed to a surface pressure of 1 MPa in the small press machine, and power was supplied to the gold-plated copper plates from a DC power supply, and a current of 1.56 A was passed perpendicular to the sample surface. The voltage value between the Ti plates at that time was read with a voltmeter, and the contact resistance value was calculated. The contact resistance values ​​of the samples from Examples 1 to 15 and Comparative Examples 1 to 4 are shown in Table 3.

[0091] (Results) As shown in Table 3, compared to Comparative Example 1, which had the same first coating as Example 1 but no second coating, and Comparative Example 3, which had a TiN-containing second coating, all of Examples 1 to 15 had a contact resistance value of 15 mΩ・cm. ２ The following was observed, confirming sufficient conductivity. In particular, in Examples 1 to 13 and 15, where the thickness of the first coating was 30 nm or less, the contact resistance value was 10 mΩ·cm. ２ The following was observed, and it was confirmed that it has good conductivity.

[0092]

[0093] [2.2. Corrosion Resistance Test] Each sample is used as the cathode, and IrO is used as the anode. ２ Using an electrode with a catalyst layer, a current density of 0.1 A / cm² was measured in a 1 M sulfuric acid aqueous solution at 30°C. ２ Electrolysis was performed to forcibly accelerate corrosion by cathode polarization of the sample. The electrolysis lifetimes of the samples in Examples 1 to 15 and Comparative Examples 1 to 4 are shown in Table 4. The electrolysis lifetime was defined as the time it took for the electrolysis voltage to rise by 1.0 V from the initial electrolysis voltage.

[0094] (Results) As shown in Table 4, Examples 1 to 15 all had an electrolytic life of 400 hours or more compared to Comparative Examples 1, 3, and 4, confirming that they possess sufficient corrosion resistance. Comparative Example 2, which does not have a second coating, and Example 11, which has a thin film thickness, also had relatively short electrolytic lives, suggesting that the second coating has the effect of preventing peeling of the first coating and damage to the substrate, thereby improving corrosion resistance. Furthermore, from Examples 1, 11, and 12, which have different second coating thicknesses, it was confirmed that good corrosion resistance can be obtained by making the thickness of the second coating 100 nm or more.

[0095]

[0096] [2.3. Water Electrolysis Test] To evaluate the sample as a porous transport layer, a CCM was prepared to be incorporated into a PEM-type water electrolysis cell. The cathode catalyst ink was prepared by adding ultrapure water and Nafion dispersion to platinum carbon-supported catalyst powder, and then dispersing it by vibration stirring and ultrasonic stirring. The anode catalyst ink was made of high specific surface area IrO ２ After adding ultrapure water, ethanol, and Nafion dispersion to the powder, the ink was prepared by dispersing it using vibration stirring and ultrasonic stirring. Each catalyst ink was deposited onto a polyethylene terephthalate (PET) film substrate using the doctor blade method, and the solvent was removed by drying to obtain 25 mm x 25 mm PET films with each catalyst layer. The cation exchange membrane Nafion 115 was sandwiched between a PET film with an anode catalyst layer and a PET film substrate with a cathode catalyst layer, and further sandwiched between copper plates. By heating and pressurizing at 140°C and 2 MPa, each catalyst layer was transferred to Nafion 115, and a CCM was prepared.

[0097] A PEM-type water electrolysis cell was constructed by layering carbon paper on the cathode side and each sample on the anode side as porous transport layers on the fabricated CCM, and then sandwiching and tightening it with a platinum-clad Ti power supply and a carbon power supply. Ultrapure water at 80°C was circulated to the anode side of the water electrolysis cell at a rate of 30 ml / min using a magnetic pump, and a DC power supply of 25.0 A (current density 4 A / cm²) was used. ２ A water electrolysis test was conducted for 360 hours. Table 5 shows the contact resistance value before and after the test, the change in contact resistance value ΔR, and the rate of increase in contact resistance value for each sample.

[0098] (Results) As shown in Table 5, Examples 1 to 15 all showed a contact resistance increase rate of 50% or less compared to Comparative Examples 1 to 4, confirming that they have sufficient durability. In particular, Examples 1 to 13 and 15, in which the thickness of the first coating was 30 nm or less, maintained a contact resistance value of 10 mΩ・cm even after testing. ２ It was found to be less than [a certain value], and good conductivity was confirmed.

[0099]

[0100] [2.4. Porosity Change Test] A PEM-type water electrolysis cell was constructed by stacking the samples prepared in Example 1 or Comparative Examples 5-8 on the anode and cathode sides of a CCM prepared by the same method as in the above test, as porous transport layers, and then sandwiching and tightening them with a Pt-coated Ti power supply. Ultrapure water at 80°C was supplied to the anode side of the PEM-type water electrolysis cell at a rate of 30 ml / min using a magnetic pump and circulated, and a DC power supply of 12.5 A (2.0 A / cm²) was used. ２ A water electrolysis test was conducted for one hour. The cell voltage after the water electrolysis test is shown in Table 6.

[0101] (Results) As shown in Table 6, compared to Examples 18 and 19, Examples 1, 16, and 17, in which the porosity of the porous substrate was 40% to 80% by volume, all had a cell voltage of 1.9V or less, confirming their superior electrolytic performance.

[0102]

[0103] [2.5. Test using a porous transport layer with gradient film thickness] A PEM-type water electrolysis cell was constructed by laminating each sample prepared in Example 1 or Comparative Examples 9-12 onto the anode and cathode sides of a CCM prepared by the same method as in the above test, as a porous transport layer, and then sandwiching and tightening it with a Pt-coated Ti power supply. Ultrapure water at 80°C was supplied to the anode side of the PEM-type water electrolysis cell at a rate of 30 ml / min using a magnetic pump and circulated, and a DC power supply of 12.5 A (2.0 A / cm²) was used. ２ A water electrolysis test was conducted for one hour. The cell voltage after the water electrolysis test is shown in Table 7.

[0104] (Results) As shown in Table 7, compared to Examples 22 and 23, Examples 1, 20, and 21, in which the thickness of the back side of the second coating was 25 nm to 200 nm, all had a cell voltage of 1.9 V or less, confirming superior electrolytic performance.

[0105]

[0106] As described above, the porous transport layers of Examples 1 to 23 of the present invention had sufficient conductivity and corrosion resistance as porous transport layers for use in PEM-type water electrolysis cells. On the other hand, the porous transport layers of Comparative Examples 1 and 3 did not have good conductivity and corrosion resistance, and although the porous transport layers of Comparative Examples 2 and 4 had good conductivity, they had poor corrosion resistance. Therefore, the porous transport layers of Comparative Examples 1 to 4 were insufficiently suitable as porous transport layers for use in PEM-type water electrolysis cells.

[0107] 1: Anode power supply 2: Porous transport layer for anode 3: Anode catalyst layer 4: Cathode power supply 5: Porous transport layer for cathode 6: Cathode catalyst layer 7: PEM 8: Gasket

[0108] The porous transport layer according to the present invention can be used as a porous transport layer for the anode or a porous transport layer for the cathode of a PEM-type water electrolysis apparatus.

Claims

1. A porous transport layer comprising: a porous substrate made of a conductive material; a first coating containing a metal oxide formed on the surface of the conductive material constituting the porous substrate; and a second coating containing a noble metal or a conductive noble metal oxide formed on the first coating.

2. The porous transport layer according to claim 1, wherein the metal oxide is a metal oxide containing one or more metal elements selected from the group consisting of titanium, niobium, tantalum, molybdenum, and tungsten.

3. The porous transport layer according to claim 1, wherein the thickness of the first coating is 10 nm or more and 30 nm or less.

4. The porous transport layer according to claim 1, wherein the first coating contains 0.1 mol% to 1.0 mol% of a metal or metal oxide containing one or more metal elements selected from the group consisting of platinum, ruthenium, and iridium.

5. The porous transport layer according to claim 1, wherein the precious metal or conductive precious metal oxide is a precious metal or conductive precious metal oxide containing one or more metal elements selected from the group consisting of platinum, ruthenium, and iridium.

6. The porous transport layer according to claim 1, wherein the thickness of the second coating is 100 nm or more and 300 nm or less.

7. The porous transport layer according to claim 1, wherein the thickness of one side of the second coating is 100 nm or more and 300 nm or less, and the thickness of the other side is 25 nm or more and 200 nm or less.

8. The porous transport layer according to claim 1, wherein the particle size of the crystal grains of the noble metal or conductive noble metal oxide contained in the second film is 10 nm or more and 50 nm or less.

9. The porous transport layer according to claim 1, wherein the porous substrate is a porous substrate made of titanium or a titanium alloy.

10. The porous transport layer according to claim 9, wherein the conductive material constituting the porous substrate is a conductive material comprising an aggregate of particles with a diameter of 5 μm or more and 150 μm or less.

11. The porous transport layer according to claim 9, wherein the conductive material constituting the porous substrate is a conductive material made from fibers having a cross-section with an equivalent circular diameter of 10 μm or more and 50 μm or less.

12. The porous transport layer according to claim 9, wherein the porosity of the porous substrate is 40% by volume or more and 80% by volume or less. The porosity is a value expressed as a percentage of the value obtained by [1 - {(mass of porous substrate) / ((true density of the material of the porous substrate) × (apparent volume of the porous substrate))}]. The apparent volume is the volume including voids.

13. A solid polymer electrolyte membrane type water electrolysis cell comprising a porous transport layer according to any one of claims 1 to 12.

Images