Porous transport layer for electrolysis and electrolytic device

Abstract

The purpose of the present invention is to provide a porous transport layer for electrolysis which has high springiness, high conductivity, and high permeability. Provided is a porous transport layer for electrolysis which is a porous body having a thickness of 0.4-3.5mm and is configured in a manner such that: when divided into a plurality of layers each having a thickness of 3.9μm in the thickness direction, a high-fill region comprising continuous layers having a fill rate which is at least 1.05 times the average value (hereinafter referred to as the average fill rate X (%)) of the fill rate of each of the layers and a low-fill region comprising continuous layers having a fill rate which is at most 0.95 times the average fill rate X (%) are layered in an alternating manner across an interval between a layer A and a layer B; and the total number of high-fill regions and low-fill regions per 1mm of thickness is 7.0-39.0, inclusive.

Description

Porous transport layer for electrolysis and electrolytic device

[0001] This invention relates to a porous transport layer for electrolysis.

[0002] Hydrogen-based power generation systems are attracting attention as a means of reducing greenhouse gas emissions, and electrolysis is gaining attention as a hydrogen production system. Electrolysis, also known as electrolysis, is a method of producing hydrogen using only electricity and the liquid or gas being electrolyzed. Examples of liquids that can be electrolyzed include water, formic acid, and liquid ammonia, as well as gases such as carbon dioxide. In particular, research is being conducted extensively on the electrolysis of water. Types of water electrolysis methods include proton exchange type (PEM type) water electrolysis, anion exchange type (AEM type) water electrolysis, alkaline type water electrolysis, and solid oxide type water electrolysis. Among these, PEM type water electrolysis is characterized by its ability to utilize the technology of polymer electrolyte fuel cells (PEFCs) and to produce high-purity hydrogen.

[0003] The cell used in PEM-type water electrolysis is a laminate containing a membrane electrode assembly (MEA). The MEA consists of a solid polymer electrolyte membrane with an anode catalyst layer and a cathode catalyst layer bonded to both sides, further sandwiched between porous transport layers (PTLs). The MEA is further sandwiched between separators and assembled into a cell. The principle of PEM-type water electrolysis is that water supplied from the separator surface on the anode side reacts with oxygen and protons (H) in the anode catalyst layer of the membrane electrode assembly (MEA). ＋ It is decomposed into (H), and the proton moves from the anode side to the cathode side in the solid polymer electrolyte membrane, gaining electrons in the cathode catalyst layer and becoming hydrogen (H). ２ ) and is discharged from the separator on the cathode side. The porous transport layer is an important layer for promoting the transport of reactants and products and for efficiently carrying out electrochemical reactions.

[0004] Patent Document 1 describes a porous transport layer in which a titanium metal porous sintered body, which has excellent conductivity, mechanical strength, and durability, is used as a conductive porous substrate. However, due to the problem of high raw material costs, research is underway to replace the porous transport layer on the cathode side, where corrosion reactions are less likely to occur, with a carbon conductive porous substrate. Carbon conductive porous substrates have been conventionally applied to fuel cells. For example, Patent Document 2 discloses a technology to suppress fuel cell flooding and substrate bending by dividing a fuel cell substrate into three layers according to a certain definition, and designating them as X, Z, and Y layers from the surface on one side, and specifying that the packing density of each layer is in the order of X layer > Y layer > Z layer. Here, packing density is the ratio of the volume occupied by the constituent components of the conductive porous substrate to the volume of each layer, that is, the ratio of the volume excluding the pore portion of the conductive porous substrate.

[0005] Japanese Patent Publication No. 2023-76968, International Publication No. 2016 / 060044

[0006] For electrolytic porous transport layers used in electrolysis, it is crucial that they are porous materials possessing high springiness to absorb dimensional changes in the direction perpendicular to the plane (thickness direction) and conductivity to achieve high electrolytic efficiency. In particular, since electrolytic cells generally have a larger surface area than those for fuel cells, the porous transport layer needs to be subjected to uniform pressure over a large area to obtain sufficient in-plane gas or liquid permeability and conductivity perpendicular to the plane. This requires a greater thickness and sufficient springiness compared to fuel cell cells.

[0007] However, when the conductive porous substrate for fuel cells described in Patent Document 2 was used as a porous transport layer for electrolysis, it was prone to denting even with a high filling density of the surface layer, making it difficult to achieve both high springiness, high conductivity, and high gas or liquid permeability, which are required for a porous transport layer for electrolysis.

[0008] To solve the above problems, the present invention has the following configuration: (1) A porous material with a thickness of 0.4 to 3.5 mm, which, when divided into multiple layers of 3.9 μm thickness in the thickness direction, alternates between highly packed regions where layers have a packing rate of 1.05 times or more the average packing rate of each layer (hereinafter, average packing rate X (%)) and low packed regions where layers have a packing rate of 0.95 times or less the average packing rate X, in the section from layer A to layer B as defined below, and the total number of highly packed regions and low packed regions per 1 mm thickness is 6.0 to 39.0. <Definition of layer A and layer B> Layer A and layer B are the two layers closest to both surfaces among the layers having a packing rate of 50% or more the average packing rate of each layer.

[0009] (2) The porous transport layer for electrolysis according to (1), wherein the average packing rate X (%) is 15% or more and 55% or less. (3) The porous transport layer for electrolysis according to (1) or (2), wherein the porous body is made of a conductive porous body containing carbon fibers and a binder. (4) The porous transport layer for electrolysis according to (3), wherein one surface of the conductive porous body has a microporous layer containing carbon fine particles. (5) The porous transport layer for electrolysis according to any one of (1) to (4), wherein the total number of the high-packing region and the low-packing region per 1 mm thickness is 11.0 or more and 19.0 or less. (6) An electrolytic apparatus using the porous transport layer for electrolysis according to any one of (1) to (5) on the cathode side.

[0010] According to the present invention, a porous transport layer for electrolysis having high springiness, high conductivity, and high permeability can be provided, improving the electrolytic performance of an electrolytic device using it.

[0011] This is a schematic diagram of a PEM-type electrolytic cell containing the electrolytic porous transport layer of the present invention. This is a schematic diagram showing the packing density distribution in the thickness direction of the electrolytic porous transport layer of the present invention. This is a schematic diagram showing the procedure for measuring the packing density.

[0012] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. The following description will refer to the drawings as appropriate to facilitate understanding, but the drawings are illustrative and the present invention is not limited to the embodiments shown. Furthermore, the description of specific embodiments shown in the drawings can also be understood as a description of the present invention as a broader concept. Figure 1 is a schematic diagram of one embodiment of a PEM-type electrolytic cell including the electrolytic porous transport layer of the present invention. In the PEM-type electrolytic cell, an anode catalyst layer 2 and a cathode catalyst layer 4 are laminated on both sides of the electrolyte membrane 3, and an anode substrate 1 and an electrolytic porous transport layer 5 are arranged further outside. The electrolytic porous transport layer 5 of the present invention is located on the cathode catalyst layer 4 side and transports electrons and protons (H) in the cathode catalyst layer. ＋ Hydrogen (H) produced from ) ２ It plays the role of efficiently transporting the ) and discharging it from the cathode-side separator. The porous transport layer 5 for electrolysis of the present invention is a porous material that has high springability to absorb dimensional changes in the direction perpendicular to the surface (thickness direction) of the porous transport layer and conductivity to obtain high electrolysis efficiency. The porous transport layer 5 for electrolysis of the present invention will be described below.

[0013] [Porous Transport Layer for Electrolysis] The porous transport layer for electrolysis of the present invention is a porous material. Being porous allows for excellent gas or liquid permeability, enabling the discharge of hydrogen generated during electrolysis to the outside of the cell and the supply of liquids or gases necessary for the reaction. Furthermore, in order to obtain high electrolysis efficiency, it is preferable to use a porous material that has conductivity (referred to as a conductive porous material). As the porous material, it is preferable to use a porous material containing carbon fibers, such as carbon fiber paper, carbon fiber fabric, and felt-type carbon fiber nonwoven fabric. In particular, it is preferable to use a carbon fiber paper as the porous material because it has excellent properties for absorbing dimensional changes in the thickness direction of the electrolyte membrane, i.e., "springiness".

[0014] Furthermore, the electrolytic porous transport layer of the present invention preferably has a form in which a binder is applied to a porous body containing carbon fibers, that is, it preferably contains carbon fibers and a binder, and more preferably consists of a carbon fiber papermaking body in which carbon fibers are bound together with a binder. An example of a method for manufacturing a carbon fiber papermaking body will be described later, which improves the mechanical strength of the electrolytic porous transport layer and improves conductivity as the binder acts as a conductive path.

[0015] Carbon fibers used in the porous transport layer for electrolysis of the present invention include polyacrylonitrile (PAN), pitch, and rayon carbon fibers. Among these, PAN carbon fibers and pitch carbon fibers are preferred due to their excellent mechanical strength. Alternatively, a porous body may be prepared using flame-resistant yarn that becomes carbon fiber through a carbonization process, and a porous body containing carbon fibers may be prepared through a carbonization process. Furthermore, conventionally known natural fibers and synthetic fibers such as rayon fibers, acrylic fibers, and cellulose fibers may be mixed.

[0016] The carbon fibers used in this invention preferably have an average diameter of 3 to 20 μm, and more preferably 5 to 10 μm. When the average diameter of the single fibers is 3 μm or more, the diameter of the pores becomes larger, resulting in an electrolytic porous transport layer with excellent permeability of gas or liquid within the plane. On the other hand, when the average diameter of the single fibers is 20 μm or less, it becomes easier to control the thickness of the electrolytic porous transport layer within a preferred range.

[0017] When carbon fiber paper is used as an electrolytic porous transport layer, the average length of the carbon fiber single fibers is preferably in the range of 3 to 20 mm, and more preferably in the range of 5 to 15 mm. If the average length of the single fibers is 3 mm or more, the electrolytic porous transport layer will have excellent mechanical strength, electrical conductivity, and thermal conductivity. On the other hand, if the average length of the single fibers is 20 mm or less, a homogeneous electrolytic porous transport layer with little variation in density and fiber orientation can be obtained.

[0018] The basis weight of the porous transport layer for electrolysis in this invention is 120 to 1800 g / m². ２ Preferably, the basis weight is 120 g / m². ２The above conditions improve the mechanical strength and conductivity of the porous transport layer for electrolysis. On the other hand, if the basis weight is 1800 g / m² ２ The following conditions result in good permeability of liquids and gases in the thickness direction of the porous transport layer for electrolysis, thereby improving electrolysis performance: The basis weight of the porous transport layer for electrolysis is 350 to 1200 g / m². ２ This is preferable because it enhances these effects. The basis weight of the electrolytic porous transport layer can be adjusted by controlling the amount of constituent materials of the electrolytic porous transport layer, such as carbon fibers and carbonized resin compositions.

[0019] The thickness of the porous transport layer for electrolysis in this invention is 0.4 to 3.5 mm. Here, the thickness of the porous transport layer for electrolysis is the thickness measured by X-ray CT analysis described later. When the thickness is 0.4 mm or more, mechanical strength is maintained and handling in the manufacturing process is easy. Furthermore, by having the highly packed and low packed regions of this invention take a predetermined configuration, the springiness is increased and the in-plane uniformity of the fastening pressure within the cell of the electrolytic device is improved.

[0020] On the other hand, if the thickness of the porous transport layer for electrolysis is 3.5 mm or less, the permeability of liquids and gases in the thickness direction becomes good. Also, the conductive path in the thickness direction becomes shorter, resulting in good conductivity. These effects are enhanced when the thickness of the porous transport layer for electrolysis is 0.8 to 2.4 mm, making it more preferable. Generally, the thickness of the porous transport layer for electrolysis in this invention is larger than that of transport layers for fuel cells.

[0021] The electrolytic porous transport layer of the present invention has an internal structure in which regions with high packing density and regions with low packing density are alternately repeated along the thickness direction. Here, packing density refers to the ratio of the constituent components of the electrolytic porous transport layer (carbon fibers, binders, etc.) to the volume of the region to be measured. In other words, it is the occupancy rate of the portion of the electrolytic porous transport layer excluding the pores. Details of the method for measuring packing density will be described later.

[0022] The present invention is characterized by the distribution of packing density of each layer when the electrolytic porous transport layer is divided into 3.9 μm thickness intervals in the thickness direction. In this invention, the average value of the packing density of each layer divided into 3.9 μm thickness intervals is used, but layers with extremely low packing density near both surfaces contain irregular structures such as a single carbon fiber protruding from a section, so including them in the calculation would unnecessarily increase the error. To prevent this, first, layers A and B, which are located near both surfaces of the electrolytic porous transport layer, are defined as follows. That is, in this invention, layers A and B are defined as the two layers closest to both surfaces that satisfy the condition that when the layers obtained by dividing the electrolytic porous transport layer into 3.9 μm thickness intervals in the thickness direction are lined up in a row, the layers have a packing density of 50% or more of the average value of the packing density of the layers in the section from layer A to layer B. Here, the average value of the packing density of layer A, layer B, and all layers sandwiched between layer A and layer B is X1. The method for actually identifying layer A and layer B is as follows.

[0023] In this invention, dividing the material into 3.9 μm thick sections in the thickness direction is determined by factors such as image acquisition conditions and measurement resolution, but is not necessarily limited to a thickness of 3.9 μm. A thickness of approximately 3.9 μm is acceptable as long as it provides sufficient accuracy to obtain a distribution curve that reflects the characteristics of the filling density distribution in each layer. In other words, by dividing the material into 3.9 μm thick sections in the thickness direction according to this invention, the distribution state of the filling density in each layer is sufficiently reflected, and a filling density distribution curve (reference numeral 14 in Figure 3) can be obtained.

[0024] First, when the porous transport layer for electrolysis is divided in the thickness direction into 3.9 μm intervals, the layers located on the outermost surfaces are designated as layer a and layer b, respectively. Next, the average value X1 of the packing density of the layers in the interval from layer a to layer b is calculated (Step 1). At this time, if the packing density of layers a and b is 50% or more of X1, layers a and b are defined as layers A and layer B. If the packing density of layer a is less than 50% of X1, the layer one level inward from layer a is designated as the new layer a. Similarly, if the packing density of layer b is less than 50% of X1, the layer one level inward from layer b is designated as the new layer b. Then, the average value X2 of the packing density of each layer in the interval from the new inner layer a to the new inner layer b is calculated (Step 2). If the packing density of layers a and b is 50% or more of X2, the new layers a and b are defined as layers A and layer B. Layers A and B can be uniquely defined by repeating steps 1 and 2 above until they are defined. The X1 or X2 determined in this way will be the same value as the average packing density of each layer, i.e., the average packing density X. Note that when the porous transport layer for electrolysis is divided into 3.9 μm thick sections, a layer less than 3.9 μm thick may remain on one of the surface sides. In this case, this layer less than 3.9 μm thick is not considered. This is because the outermost layer is a layer with an extremely low packing density, containing only a few protruding carbon fibers.

[0025] Figure 2 is a schematic diagram showing the packing efficiency distribution in the thickness direction of the electrolytic porous transport layer of the present invention. In Figure 2, layers 15 divided at 3.9 μm intervals are shown from one surface to the other, i.e., in the thickness direction 7 of the electrolytic porous transport layer. Figure 2 is a magnified view of the layers near the surface, excluding the central part of the film of the electrolytic porous transport layer. In Figure 2, reference numeral 15 is attached in one place, but the space between the dotted lines in Figure 2 corresponds to each layer divided at 3.9 μm intervals. Here, if the vertical axis is the value of the packing efficiency of each layer and the packing efficiency of each layer is plotted, a packing efficiency distribution curve 14 is obtained. As described above, the packing efficiency distribution curve 14 reflects the distribution state of the packing efficiency of each layer. The average packing efficiency X can be obtained by methods such as integrating the packing efficiency distribution curve 14. Layers A and B are the layers on both sides that have a packing efficiency of 50% or more of the average packing efficiency.

[0026] As illustrated in Figure 2, for layers a and b as described above, the average value X1 including the leftmost and rightmost layers is calculated, and it is determined whether it is 50% or more. Since the filling rates of the rightmost and leftmost layers in Figure 2 are less than 50% of X1, the innermost layers are designated as new layers a and b, and the average value X2 for the interval is calculated, and it is determined whether it is 50% or more of the average value X2. The layer one layer inward from the leftmost end of Figure 2 is 50% or more, so layer A is determined, and the layer one layer inward from the rightmost end is less than 50%, so the further inner layer is designated as layer b, and the determination is repeated. In this way, layers A (indicated by 8) and layer B (indicated by 9) in Figure 2 are determined. Figure 2 shows the average filling rate X (indicated by 10), 50% of the average filling rate X (indicated by 11), 1.05 times the average filling rate X (indicated by 12), and 0.95 times the average filling rate X (indicated by 13), which are the average values ​​of the filling rates of each layer in the interval from layer A to layer B.

[0027] The average packing density X mentioned above is preferably 15-55%, and more preferably 25-45%. When the average packing density X is 15% or more, the overall mechanical strength and conductivity of the porous transport layer for electrolysis are excellent. On the other hand, when the average packing density is 55% or less, the permeability of the porous transport layer for electrolysis is improved.

[0028] The electrolytic porous transport layer of the present invention has a structure in which, in the section from layer A to layer B, there are 6.0 to 39.0 high-packing regions per 1 mm thickness, where layers with an average packing density of 1.05 times or more are continuous, and low-packing regions where layers with an average packing density of 0.95 times or less are continuous. In Figure 2, each high-packing region consists of 2 to 3 layers, and each low-packing region also consists of 2 to 3 layers. However, since Figure 2 is simplified for illustrative purposes, the actual number of layers constituting each high-packing region or low-packing region is not limited to this. Here, the average packing density X is the average value of the packing density (%) of each layer. A region in which layers greater than 0.95 times the average packing density X (%) but less than 1.05 times the average packing density X are continuous is defined as a medium-packing region. If there are only medium-packing regions between two or more high-packing regions and no low-packing regions, these multiple high-packing regions and medium-packing regions are considered as one high-packing region. Similarly, if two or more low-filled regions do not have an intermediate-filled region in between, they are considered as a single low-filled region. By creating a structure in which high-filled and low-filled regions alternately repeat via intermediate-filled regions, a good porous transport layer for electrolysis is obtained that combines the high strength and high conductivity characteristics of high-filled regions with the high springiness and high permeability characteristics of low-filled regions. In the porous transport layer for electrolysis of the present invention, if the total number of high-filled and low-filled regions is 6.0 or more and 39.0 or less per 1 mm thickness, it is possible to achieve both high springiness that absorbs dimensional changes in the direction perpendicular to the plane (thickness direction) of the porous transport layer and high electrolysis efficiency. Furthermore, it is more preferable that the total number of high-filled and low-filled regions per 1 mm thickness is 11.0 or more and 19.0 or less.

[0029] [Method for Measuring Filling Rate] The method for measuring the filling rate will be explained with reference to Figure 3. A sample piece of the electrolytic porous transport layer (dimensions: 10 mm long x 5 mm wide) is set in the three-dimensional X-ray CT scanner "TDM1000H-CF" (manufactured by Yamato Scientific Co., Ltd.), and a 3D image of "4 mm x 4 mm x thickness [mm]" is created by scanning 360° with the vertical axis as the axis of rotation. Here, the axis of rotation is set in one direction of the surface of the object being measured, but the axis of rotation can be any direction of the object being measured. Furthermore, the method is not limited to using the three-dimensional X-ray CT scanner exemplified here, as long as a 3D image can be obtained. At this time, each slice image constituting the 3D image should have a thickness of 3.9 μm. Next, the filling rate in the slice image is calculated. At this time, the filling rate of each slice image can represent the filling rate of each layer divided into 3.9 μm thicknesses. First, in each obtained slice image, binarization is performed to distinguish between the void areas where the electrolytic porous transport layer does not exist and the areas occupied by the constituent components of the electrolytic porous transport layer. For example, using the image processing program "ImageJ" (homepage: https: / / imagej.net / ij / ), each obtained slice image is divided into 1 to 255 brightness levels, and the point where the separation of the two peaks obtained when a grayscale histogram is drawn is used as the brightness threshold for binarization (Otsu's binarization method).

[0030] In other words, the void portions of the electrolytic porous transport layer have a dark brightness, while the constituent materials of the electrolytic porous transport layer, such as carbon fibers or binders, have a bright brightness. Therefore, binarization separates the void portions from the constituent materials of the electrolytic porous transport layer. The packing rate [%] is defined as the percentage of the total area of ​​each slice image that is occupied by the bright side after binarization, i.e., the constituent materials of the electrolytic porous transport layer. Next, as shown in Figure 3(a), the packing rate of each slice image (packing rate of each layer) is plotted on a graph where the horizontal axis is the thickness direction of the electrolytic porous transport layer 7 and the vertical axis is the packing rate of each layer 16 to confirm the distribution of the packing rate. In this distribution, as described above, layer A (reference numeral 8) and layer B (reference numeral 9) are defined, and the average packing rate X (reference numeral 10) and 50% of the average packing rate X (reference numeral 11) are determined (Figure 3(b)).

[0031] By the above method, the average value X of the filling rate of the porous transport layer for electrolysis, and the number of high-filling regions and low-filling regions can be clarified. Since the regions including layer A or layer B at both ends are always low-filling regions, the number of low-filling regions is the value obtained by adding 1 to the number of high-filling regions. Next, by multiplying the number from layer A to layer B by 3.9 μm which is the thickness of each layer, the thickness of the porous transport layer for electrolysis can be calculated, and thus, the number n of high-filling regions and low-filling regions per 1 mm thickness can be calculated. In the present invention, the "thickness" when measuring the filling rate refers to the unpressurized thickness measured during X-ray CT analysis, that is, when unpressurized, which is different from the "thickness under pressure" of the measurement method described later.

[0032] [Microporous layer] Next, the microporous layer of the present invention will be described. The microporous layer can be laminated on at least one surface of the porous transport layer for electrolysis, and the microporous layer is preferable from the following viewpoints. The roles of the microporous layer include moisturizing the electrolyte membrane, reducing the interfacial electrical resistance between the catalyst layer and the porous transport layer for electrolysis, and suppressing damage to the electrolyte membrane by carbon fibers protruding from the porous transport layer for electrolysis. The microporous layer is preferably a layer containing carbon fine particles and a binder resin. Carbon black is preferably used as the carbon fine particles. The binder resin is not particularly limited and may be selected from various thermoplastic resins and thermosetting resins. In particular, fluororesins, phenol resins, polyvinylpyrrolidone, etc. having a fluoroalkyl chain with high durability and easy adjustment of water management such as moisturizing and drainage are preferably used.

[0033] The basis weight of the microporous layer of the present invention is preferably 10 to 35 g / m ２ When the basis weight of the microporous layer is 10 g / m ２ or more, it covers the carbon fibers protruding from the surface of the porous transport layer for electrolysis, so that the carbon fibers can be prevented from damaging the electrolyte membrane. Also, drying of the electrolyte membrane can be prevented. When the basis weight of the microporous layer is 35 g / m ２ or less, the permeability of liquid and gas in the thickness direction becomes good.

[0034] [Method for Manufacturing an Electrolytic Porous Transport Layer] As described above, it is preferable to use a carbon fiber papermaking body as the electrolytic porous transport layer of the present invention. Below, an example of a method for manufacturing the electrolytic porous transport layer of the present invention is described, using a carbon fiber papermaking body, but the present invention is not limited in any way by the following description. The method for manufacturing the electrolytic porous transport layer of the present invention preferably includes a papermaking step of making a slurry containing carbon fibers, a resin impregnation step of applying resin to the carbon fiber papermaking body obtained in the papermaking step, a molding step of laminating the pre-impregnated bodies obtained in the resin impregnation step and pressing them together by high temperature and pressure while adjusting the thickness, and a firing step of carbonizing the laminated pre-impregnated bodies.

[0035] [Papermaking Process] As the porous transport layer for electrolysis in the present invention, it is preferable to use a carbon fiber papermaking body prepared by dispersing carbon fiber bundles in an aqueous solution, and then forming a sheet from the prepared slurry using a wet papermaking method. The aqueous solution in which the carbon fibers are dispersed preferably contains an antifoaming agent, a surfactant, and a thickening agent. The antifoaming agent suppresses foaming during stirring and is not particularly limited, but urethane-based, polyoxyalkylene-based, and silicone-based agents are preferred. The surfactant is effective in defibrillating the carbon fiber bundles and is not particularly limited, but polyethylene glycol-based and polyethylene oxide-based agents are preferred. The thickening agent thickens the aqueous solution and is effective in suppressing physical contact between the carbon fibers and is not particularly limited, but polyethylene oxide-based and polyacrylic acid-based agents are preferred.

[0036] The viscosity of the aqueous solution used to disperse the carbon fibers is preferably 5 to 50 mPa·s, and more preferably 8 to 20 mPa·s, considering the dispersibility of the carbon fibers and the drainage during papermaking. A viscosity of 5 mPa·s or higher allows for a highly viscous aqueous solution, which can suppress the re-aggregation of carbon fibers. A viscosity of 50 mPa·s or lower allows for a faster unraveling of the carbon fiber bundles, as well as improved drainage during papermaking, which can prevent breakage during transport and poor adhesion of the binder resin.

[0037] A slurry can be obtained by dispersing a carbon fiber bundle in the above aqueous solution. As a method for obtaining a wet body that serves as a base substrate for a carbon fiber paper sheet from the slurry, there is a wet papermaking method in which a papermaking machine such as a Fourdrinier papermaking machine, a cylinder papermaking machine, or an inclined papermaking machine is used to separate the carbon fibers and the aqueous solution in the slurry and form the carbon fibers into a sheet. Among these, it is particularly preferable to use an inclined papermaking machine because it is easy to control fiber orientation and it is possible to suppress re-aggregation by lowering the carbon fiber concentration in the slurry. In the wet papermaking method, a wet body having a desired basis weight and thickness can be obtained by adjusting the concentration of the slurry fed into the papermaking machine, the flow rate of the slurry, and the speed of the papermaking wire. The wet papermaking method includes single-layer papermaking and multi-layer papermaking in which two or more wet bodies are laminated. Considering production stability and production cost, single-layer papermaking is preferred.

[0038] In general, a binder resin is applied to the wet body obtained by the above method in order to maintain the shape as a carbon fiber paper sheet. For this application, for example, a method of applying a binder resin to the wet body can be adopted, and in that case, various commercially available coating devices can be used. As the coating method, methods such as a spray coater, a curtain coater, and a die coater can be used. The coating methods exemplified above are merely examples and are not necessarily limited to these.

[0039] A carbon fiber paper sheet can be obtained by drying the wet body to which the binder resin has been applied. When drying, it is preferably dried at a temperature of 100 to 180 ° C, and generally used multi-cylinder dryers, Yankee dryers, hot air drying, etc. can be used. Among them, it is preferable to perform hot air drying while conveying while being supported by a heat-resistant belt, a heat-resistant mesh, a heat-resistant felt, etc. The drying methods exemplified are merely examples and are not necessarily limited to these.

[0040] In the carbon fiber paper sheet, the basis weight of the carbon fiber is preferably in the range of 10 to 50 g / m ２ more preferably in the range of 15 to 35 g / m ２ even more preferably in the range of 20 to 30 g / m ２It is even more preferable that the weight of the carbon fibers in the carbon fiber paper is 10 g / m². ２ When these conditions are met, the porous transport layer for electrolysis obtained from the carbon fiber papermaking body will have excellent mechanical strength. Furthermore, the basis weight of the carbon fibers in the carbon fiber papermaking body should be 50 g / m². ２ The permeability of the porous transport layer for electrolysis obtained from the carbon fiber paper is increased when the following conditions are met. Here, the basis weight of the carbon fibers in the carbon fiber paper is determined by the mass of the residue obtained by removing organic matter from a carbon fiber paper cut into 10 cm squares, held in an electric furnace at 450°C under a nitrogen atmosphere for 15 minutes, and the area of ​​the carbon fiber paper (0.01 m²) of the carbon fiber paper. ２ It can be found by dividing by ).

[0041] [Resin Impregnation Process] In the method for producing the electrolytic porous transport layer of the present invention, one preferred embodiment is to impregnate a carbon fiber papermaking body with a resin composition that serves as a binder. In the present invention, the binder contained in the electrolytic porous transport layer refers to components other than carbon fibers in the electrolytic porous transport layer, and mainly plays a role in binding the carbon fibers together. Examples of binders include resin compositions or carbides thereof that are impregnated into the carbon fiber papermaking body. In the present invention, a carbon fiber papermaking body impregnated with a resin composition that serves as a binder may be referred to as a "pre-impregnated body". In the present invention, the resin composition used when producing the pre-impregnated body is an impregnation resin to which a solvent or the like is added as needed. Examples of impregnation resins include thermosetting resins and thermoplastic resins. The resin composition may also contain additives such as carbon powder or surfactants as needed.

[0042] The carbonization yield of the impregnating resin contained in the above resin composition is preferably 40% by mass or more. Carbonization is the process by which carbon remains when a substance is burned in an oxygen-free state, and the carbonization yield is expressed as the ratio of the carbon content remaining after carbonization to the mass of the impregnating resin before carbonization. When the carbonization yield is 40% by mass or more, the porous transport layer for electrolysis tends to have excellent mechanical properties and conductivity. There is no particular upper limit to the carbonization yield of the impregnating resin contained in the resin composition, but it is usually around 60% by mass.

[0043] Preferred impregnating resins in the above resin composition include thermosetting resins such as phenolic resins, epoxy resins, melamine resins, and furan resins. Among these, phenolic resins are particularly preferred due to their high carbonization yield. Additives that may be added to the above resin composition as needed include carbon powder, which can improve the mechanical properties, electrical conductivity, and thermal conductivity of the porous transport layer for electrolysis. Examples of carbon powders that can be used include carbon black such as furnace black, acetylene black, lamp black, and thermal black; graphite such as flake graphite, scaly graphite, clay graphite, artificial graphite, expanded graphite, and flake graphite; carbon nanotubes; carbon nanofibers; and milled carbon fibers. The impregnating resin and carbon powder together are referred to as the "resin component."

[0044] The above resin composition may optionally contain various solvents to enhance its impregnation into carbon fiber paper. Examples of solvents include methanol, ethanol, and isopropyl alcohol.

[0045] When impregnating a carbon fiber papermaking body with a resin composition, it is preferable to impregnate the pre-impregnated body with the resin composition in an amount of 30 to 400 parts by mass, and more preferably 50 to 300 parts by mass, per 100 parts by mass of carbon fibers. When the amount of resin impregnation per 100 parts by mass of carbon fibers in the pre-impregnated body is 30 parts by mass or more, the electrolytic porous transport layer will have excellent mechanical properties, electrical conductivity, and thermal conductivity. On the other hand, when the amount of resin impregnation per 100 parts by mass of carbon fibers in the pre-impregnated body is 400 parts by mass or less, the permeability of the electrolytic porous transport layer will be high.

[0046] In the present invention, methods for impregnating a carbon fiber papermaking body with a resin composition include immersing the carbon fiber papermaking body in a resin composition, coating the carbon fiber papermaking body with a resin composition, and forming a layer made of a resin composition on a release film and transferring the layer made of the resin composition to the carbon fiber papermaking body. Among these, the method of immersing the carbon fiber papermaking body in a resin composition is particularly preferred due to its excellent productivity. By using this method, the resin composition can be attached to the entire carbon fiber papermaking body, thereby attaching a binder to the entire resulting porous transport layer for electrolysis, and thus further improving the strength of the porous transport layer for electrolysis.

[0047] A pre-impregnated body can be obtained by impregnating a carbon fiber paperboard with a resin composition and then drying it as needed. To obtain the pre-impregnated body, multiple pre-impregnated bodies A and B with different filling rates can be produced by two resin impregnation processes with different conditions, and by stacking them alternately as ABAB..., an electrolytic porous transport layer with a structure in which high-filled and low-filled regions alternately can be obtained. Alternatively, by adjusting the resin impregnation conditions and drying conditions, a structure can be created in which high-filled and low-filled regions are combined in the thickness direction within a single pre-impregnated body, and by stacking multiple such pre-impregnated bodies, an electrolytic porous transport layer with a structure in which high-filled and low-filled regions alternately can also be obtained. The above method may be used to obtain an electrolytic porous transport layer with a structure in which high-filled and low-filled regions alternately, or other methods may be used.

[0048] Methods for creating a structure in which a single pre-impregnated body has both high-filling and low-filling regions in the thickness direction include, for example, immersing a carbon fiber paper body in a resin composition containing a resin component that acts as a binder, and then, before drying, absorbing excess resin composition from one surface to create a gradient in the thickness direction; squeezing the pre-impregnated body between two rolls with different surface structures to create a difference in the amount of resin composition adhering to one surface and the other; and adjusting the amount of solvent volatilized from both surfaces during drying after resin impregnation to adjust the amount of resin composition migrating to both surfaces, thereby increasing the amount of resin composition adhering to the surfaces near both of the pre-impregnated body compared to the center. When adjusting the amount of solvent volatilized from both surfaces, for example, drying with one side placed on a plate increases the amount of resin composition migrating to the side opposite the plate, creating a gradient where the filling rate increases from the plate side to the other surface. Furthermore, after obtaining a pre-impregnated body, the amount of resin composition adhering to one surface of the pre-impregnated body can be controlled to be different by applying an additional resin composition to only one surface of the pre-impregnated body using a spray or gravure roll.

[0049] [Molding Process] In manufacturing the electrolytic porous transport layer of the present invention, multiple pre-impregnated bodies manufactured by the above method are stacked and then heated and pressurized to thicken and partially crosslink the resin composition in the pre-impregnated bodies, and to adjust the final electrolytic porous transport layer to have a desired thickness and density. Methods of heating and pressurizing include applying pressure with a heated hot plate, roll, or belt. Additional heat treatment, such as with hot air, may be applied to further thicken and crosslink the resin composition in the pre-impregnated bodies. At this time, in order to achieve a desired design for the packing density distribution inside the final electrolytic porous transport layer, two types of pre-impregnated bodies with different packing densities may be stacked alternately, or multiple pre-impregnated bodies having both high-packing and low-packing regions in their internal structure may be stacked.

[0050] [Firing Process] In producing the porous transport layer for electrolysis of the present invention, firing is performed under an inert atmosphere such as nitrogen in order to carbonize the resin composition. A batch-type heating furnace or a continuous-type heating furnace can be used for this firing. The maximum firing temperature is preferably in the range of 1,300 to 3,000°C. If the maximum temperature is 1,300°C or higher, the carbonization of the impregnating resin in the pre-impregnated material progresses, and the porous transport layer for electrolysis becomes highly conductive. On the other hand, if the maximum temperature is 3,000°C or lower, the operating cost of the heating furnace is reduced. In this way, a porous transport layer for electrolysis consisting of carbon fibers and a binder with a predetermined packing density distribution can be obtained.

[0051] Next, a method for forming a microporous layer on an electrolytic porous transport layer will be described. The microporous layer can be formed by applying a coating solution for forming a microporous layer, which is a dispersion of carbon nanoparticles and a binder resin such as fluororesin in a solvent such as water, onto the electrolytic porous transport layer and then performing a heat treatment.

[0052] When preparing a coating solution for forming a microporous layer, it is preferable to add dispersants and thickeners to the solution, as this enhances the dispersion stability of carbon nanoparticles and binder resins. As a dispersant, nonionic surfactants are preferred due to their low metal content, and examples include polyoxyethylene octylphenyl ether-based "Triton®" X-100 (manufactured by Nacalai Tesque Co., Ltd.). In addition, it is effective to add a thickener to maintain the viscosity of the coating solution. Suitable thickeners include methylcellulose-based, polyethylene glycol-based, and polyvinyl alcohol-based agents. Furthermore, if necessary, it is also preferable to add fine particles to promote the electrolysis of water, such as iridium oxide, ruthenium oxide, and titanium oxide, and fine particles to deactivate radicals, such as cerium oxide and manganese oxide.

[0053] A mixture of the above components is kneaded using a homogenizer, planetary mixer, ultrasonic disperser, etc., to obtain a coating solution for forming a microporous layer. The coating solution for forming a microporous layer can be applied to the electrolytic porous transport layer using various commercially available coating devices. Suitable coating methods include screen printing, rotary screen printing, intaglio printing, gravure printing, spray coating, die coating, bar coating, blade coating, and roll knife coating.

[0054] After coating a microporous layer onto an electrolytic porous transport layer, the coating is dried at a temperature of 60 to 150°C, and then heated at a temperature of 250 to 380°C to promote the decomposition and removal of additives such as dispersants and thickeners, and the melting or hardening of the binder resin, thereby obtaining an electrolytic porous transport layer having a microporous layer on its surface. It is also preferable to appropriately perform treatments to impart properties such as water repellency or hydrophilicity to the electrolytic porous transport layer in order to improve the permeability of liquids and gases passing through the interior.

[0055] [Membrane Electrode Assembly] A membrane electrode assembly can be formed by bonding the porous transport layer for electrolysis of the present invention to at least the cathode side of an electrolyte membrane having catalyst layers on both sides. The electrolyte membrane is preferably one with high proton conductivity and oxidation resistance and low gas crossover. Electrolyte membranes made of fluorine-based polymers or hydrocarbon-based polymers are known and can be used. The membrane electrode assembly is preferably composed of different compositions for the cathode catalyst layer and the anode catalyst layer. For example, the cathode catalyst layer is preferably made of platinum as catalyst particles, while the anode catalyst layer is preferably made of noble metals such as iridium, ruthenium, rhodium, palladium, or oxides thereof.

[0056] [Electrolytic Apparatus] The electrolytic apparatus is one aspect of the present invention. The electrolytic apparatus of the present invention includes the porous transport layer for electrolysis of the present invention on the cathode side. It has an electrolytic cell having separators on both sides of a membrane electrode assembly that includes the porous transport layer for electrolysis of the present invention on the cathode side. The electrolytic apparatus of the present invention has high electrolytic performance and is preferably used for the electrolysis of liquids such as water.

[0057] Next, embodiments of the present invention will be specifically described by reference to the following examples. It should be noted that the present invention is not limited to the embodiments described below. First, the evaluation methods used in the examples are shown below.

[0058] <Measurement of Packing Ratio Distribution of Porous Transport Layer for Electrolysis> A sample of the porous transport layer for electrolysis (dimensions: 10 mm long x 5 mm wide) was set in a three-dimensional X-ray CT scanner "TDM1000H-CF" (manufactured by Yamato Scientific Co., Ltd.), and a 3D image of "4 mm x 4 mm x sheet thickness [mm]" was created by scanning 360° with the vertical axis as the rotation axis. The tube voltage was set to 60 kV and the tube current to 60 μA. At this time, each slice image constituting the 3D image was made to have a thickness of 3.9 μm. If there was a slice image with a thickness of less than 3.9 μm on one of the surface sides among the slice images constituting the 3D image, it was not considered in the subsequent steps. Next, in each obtained slice image, binarization was performed to distinguish between the void areas where the porous transport layer for electrolysis was not present and the areas occupied by the constituent components of the porous transport layer for electrolysis. Using the image processing program "ImageJ" (homepage: https: / / imagej.net / ij / ), each obtained slice image was divided into 1 to 255 brightness levels, and binarization was performed using the brightness threshold at the point where the separation of the two peaks obtained when plotting the grayscale histogram was highest (Otsu's binarization method). In other words, the image was divided into a dark side (voids) and a bright side (components of the electrolytic porous transport layer such as carbon fibers and binders). The packing rate [%] was defined as the percentage of the area occupied by the binarized bright side when the total area of ​​one slice image is set to 100%. Packing rate (%) = (Area of ​​the cross-sectional image occupied by components such as carbon fibers and binders) / (Total area of ​​the cross-sectional image) × 100 Next, the packing rates of each slice image were plotted from one surface to the other of the electrolytic porous transport layer, and a distribution map of the packing rate in the thickness direction of the entire electrolytic porous transport layer, composed of the packing rates of each layer with a thickness of 3.9 μm, was created. A distribution curve was obtained in which intervals with high and low packing densities alternated.

[0059] In the obtained infill density distribution curve, first, the two layers closest to both surfaces that satisfy the condition of having an infill density of 50% or more of the average infill density of the layers in the interval from layer A to layer B were designated as layer A and layer B. The average infill density of all layers in the interval from layer A to layer B was defined as the average infill density X. The method for actually identifying layer A and layer B was as follows: First, the layers closest to both surfaces in the slice image were designated as layer a and layer b, respectively. Next, the average infill density X1 of the layers in the interval from layer a to layer b was calculated. At this time, if the infill density of layer a and layer b is 50% or more of X1, then layer a and layer b were defined as layer A and layer B (procedure 1). If the infill density of layer a is less than 50% of X1, the layer one level inward from layer a was designated as the new layer a, and if the infill density of layer b is less than 50% of X1, the layer one level inward from layer b was designated as the new layer b. Then, the average value X2 of the filling density of each layer in the interval from the new inner layer a to the new inner layer b was calculated (Step 2). If the filling density of layers a and b was 50% or more of X2, the new layers a and b were defined as layers A and B. Steps 1 and 2 above were repeated until layers A and B were defined. The X1 or X2 determined in this way is the same value as the average value of the filling density of each layer, i.e., the average filling density X.

[0060] Next, in the section from layer A to layer B, the number of high-filled regions, where layers with a filling rate of 1.05 times or more the average filling rate X are continuous, and the number of low-filled regions, where layers with a filling rate of 0.95 times or less the average filling rate X are continuous, were counted. A high-filled region, where layers with a filling rate of 1.05 times or more the average filling rate X are continuous, refers to a region in which multiple layers divided into 3.9 μm sections have a filling rate of 1.05 times or more the average filling rate X. However, if two or more high-filled regions have only an intermediate region (a region in which layers with a filling rate greater than 0.95 times the average filling rate X but less than 1.05 times the average filling rate X are continuous) between them and no low-filled regions, these multiple high-filled regions and intermediate-filled regions were considered as one high-filled region. Similarly, if two or more low-filled regions do not have an intermediate-filled region between them, they were also considered as one low-filled region.

[0061] Next, the thickness (mm) of the electrolytic porous transport layer was calculated by multiplying the number of layers from layer A to layer B by the thickness of each layer, which is 3.9 μm. Furthermore, the frequency of high-packed regions (units / mm) and low-packed regions (units / mm) were calculated by dividing the number of high-packed regions and low-packed regions obtained by the thickness. The number was rounded to the first decimal place by two decimal places. At one level, the above measurements were performed on 10 samples of electrolytic porous transport layers, and the average packing rate X, the number of high-packed regions and low-packed regions, the thickness, the frequency of high-packed regions, and the average frequency of low-packed regions were calculated for each sample. Note that the "thickness" when measuring the packing rate is indicated as the unpressurized thickness measured during X-ray CT analysis, i.e., without pressure, and is different from the "pressurized thickness" in the measurement method described later.

[0062] <Measurement of basis weight of the porous transport layer for electrolysis> Cut a 10 cm square piece of the porous transport layer for electrolysis to make a sample, and measure its mass [g] over the area of ​​the sample (0.01 m²). ２ This was obtained by dividing by ().

[0063] <Measurement of Pressurized Thickness and Spring Properties of the Porous Transport Layer for Electrolysis> The pressurized thickness and spring properties of the porous transport layer for electrolysis were measured by surface pressure cycle tests at 0.03 MPa and 3 MPa. A digital micrometer was installed on two flat metal fixtures, upper and lower, attached to a Shimadzu Corporation "Autograph®" AGS-X, to measure the distance between the fixtures. A 30 mm square sample was placed in the center of the flat metal fixture, and a surface pressure cycle test was performed, starting at 0.03 MPa, increasing to 3 MPa, and then depressurizing back to 0.03 MPa. During this time, the distance between the upper and lower fixtures at each pressure was continuously measured. The thickness when the pressure was increased from 0.03 MPa to 1 MPa was defined as the pressurized thickness of the porous transport layer for electrolysis. Furthermore, the difference between the thickness at 2 MPa and the thickness at 1 MPa during the depressurization process after increasing the pressure to 3 MPa was defined as the spring properties of the porous transport layer for electrolysis. Measurements were taken for five samples, and the average values ​​were used as the pressurized thickness and springiness of the porous transport layer for electrolysis. Springiness was judged to be better the greater the difference between the thickness at 2 MPa and the thickness at 1 MPa.

[0064] <Measurement of Electrical Resistance of Porous Transport Layer for Electrolysis> The electrical resistance under pressure was measured using Shimadzu Corporation's "Autograph®" AGS-X. A sample of the porous transport layer for electrolysis, cut to a 22.4 mm square, was placed on the lower of two electrical resistance measuring jigs. The upper electrical resistance measuring jig was lowered and a load was applied until it reached 1 MPa. Next, a current of 1 A was applied from a DC power supply connected to the electrical resistance measuring jig. At this time, the voltage value was read from a digital multimeter, and the electrical resistance value was calculated from the measured value and the measured area. Measurements were taken for five samples, and the average value was taken as the electrical resistance of the porous transport layer for electrolysis.

[0065] <Measurement of In-Plane Air Permeability of Porous Transport Layer for Electrolysis> A donut-shaped sample of the porous transport layer for electrolysis, with an outer diameter of 40 mm and an inner diameter of 12 mm, was cut and placed between two flat plate fixtures attached to a Shimadzu Corporation "Autograph®" AGS-X, and the in-plane air permeability was measured. A hole for injecting compressed air from the outside was provided in the center of the upper fixture, and air was introduced into the donut-shaped sample sandwiched between the upper and lower fixtures from the inner diameter side of the sample, passed through the plane of the sample, and exited from the outer diameter side of the sample. At this time, a regulator and flow meter were provided upstream of the incoming air, and the flow rate was measured while setting the pressure to an arbitrary value. When the sample was sandwiched at 1 MPa, and the air pressure was P (kPa) and the flow rate at that time was Q (L / min), the in-plane air permeability of the sample (μm) was calculated from the rate of change (ΔQ / ΔP) using the following formula. ３ The in-plane air permeability (μm) was determined. Measurements were taken for five samples, and the average value was taken as the in-plane air permeability of the porous transport layer for electrolysis. ３ )=(ΔQ / ΔP)×(1.8 / (2×60×π))×(ln(40 / 12))×10 ７ ...(Formula 1).

[0066] (Example 1) Toray Industries, Inc.'s polyacrylonitrile-based carbon fiber "Torayca®" T300 (average fiber diameter: 7 μm) was cut to a length of 12 mm, dispersed in water, and continuously paper-made using a wet papermaking method. Furthermore, a 10% by mass aqueous solution of polyvinyl alcohol was spray-coated and dried, resulting in a basis weight of 30 g / m². ２ A carbon fiber paper was obtained. The amount of polyvinyl alcohol attached to the carbon fiber paper was 20 parts by mass per 100 parts by mass of carbon fibers. Next, a resin composition solution was prepared by mixing flake graphite (average particle size: 5 μm), phenolic resin (a mixture of resol-type phenolic resin and novolac-type phenolic resin in a mass ratio of 1:1), and methanol in a mass ratio of 5:10:85.

[0067] Next, the carbon fiber paper material was cut into 20 cm squares and immersed in an impregnation solution of resin composition filled in a tank. The amount of resin adhering to the material was then adjusted by sandwiching it between two metal rollers. At this time, a certain clearance was left between the two rollers, and the overall amount of resin composition adhering was adjusted by passing the immersed carbon fiber paper material between them. After that, it was placed on a hot plate at 100°C and heated for 5 minutes to dry, and a pre-impregnated body was prepared. A total of six pre-impregnated bodies were prepared using the above method.

[0068] Next, six of the obtained pre-impregnated materials were stacked and then held between parallel hot plates and molded at a temperature of 180°C for a total of 5 minutes while applying pressure. At this time, the pressure was adjusted so that the pressurized thickness after firing described below was 0.97 mm. In the following examples, unless otherwise specified, the same pressure as in this example was used. The obtained pre-impregnated materials after heating and pressurizing were introduced into a heating furnace maintained in a nitrogen gas atmosphere with a maximum temperature of 2,400°C and fired to obtain an electrolytic porous transport layer. The distribution of the packing density of the obtained electrolytic porous transport layer was measured according to the above <Measurement of Packing Density Distribution of Electrolytic Porous Transport Layer>. The average packing density X was 32%, with 6 high-filled areas and 7 low-filled areas. The thickness was 1.08 mm, and therefore, the total number of high-filled and low-filled areas was calculated to be 12.0 units / mm, the frequency of high-filled areas was 5.6 units / mm, and the frequency of low-filled areas was 6.5 units / mm. Table 1 shows the results for basis weight, pressurized thickness, spring properties, electrical resistance, and in-plane air permeability of the porous transport layer for electrolysis.

[0069] (Example 2) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that instead of drying the carbon fiber paper mass on a hot plate after impregnating it with the resin composition, the carbon fiber paper mass was secured to a 20 cm square metal frame with clips and dried in a 100°C hot air oven. The results are shown in Table 1.

[0070] (Example 3) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that when passing a carbon fiber paper roll, which had been immersed in a resin composition impregnation solution, between two metal rolls, one of the two rolls was a smooth metal roll and the other was a gravure roll with an uneven surface, and then the carbon fiber paper roll was air-dried at room temperature. The results are shown in Table 1.

[0071] (Example 4) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the pressure applied during molding was adjusted so that the thickness of the compressed layer after firing was 1.16 mm. The results are shown in Table 1.

[0072] (Example 5) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the pressure applied during molding was adjusted so that the thickness of the compressed layer after firing was 0.77 mm. The results are shown in Table 1.

[0073] (Example 6) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the composition of the resin composition solution consisted of flake graphite (average particle size: 5 μm), phenol resin (a mixture of resol-type phenol resin and novolac-type phenol resin in a mass ratio of 1:1), and methanol in a mass ratio of 3:7:90. The results are shown in Table 1.

[0074] (Example 7) An electrolytic porous transport layer was manufactured in the same manner as in Example 6, except that the pressure applied during molding was adjusted so that the thickness of the compressed layer after firing was 1.66 mm. The results are shown in Table 1.

[0075] (Example 8) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the composition of the resin composition solution consisted of flake graphite (average particle size: 5 μm), phenol resin (a mixture of resol-type phenol resin and novolac-type phenol resin in a mass ratio of 1:1), and methanol in a mass ratio of 10:20:70. The results are shown in Table 1.

[0076] (Example 9) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the pressure applied during molding was adjusted so that the thickness of the compressed layer after firing was 0.58 mm. The results are shown in Table 1.

[0077] (Example 10) Ten pre-impregnated bodies were prepared, and these ten pre-impregnated bodies were stacked. An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the pressure applied during molding was adjusted so that the thickness of the pressed material after firing was 1.52 mm. The results are shown in Table 1.

[0078] (Comparative Example 1) An electrolytic porous transport layer was manufactured in the same manner as in Example 1, except that the carbon fiber paper body was air-dried at room temperature after impregnation. The results are shown in Table 1. Electrical resistance was good, but springiness and in-plane air permeability deteriorated.

[0079]

[0080] 1: Anode substrate 2: Anode catalyst layer 3: Electrolyte membrane 4: Cathode catalyst layer 5: Porous transport layer for electrolysis 6: Separator 7: Thickness direction of the porous transport layer for electrolysis 8: Layer A 9: Layer B 10: Average packing density X 11: 50% of average packing density X 12: 1.05 times the average packing density X 13: 0.95 times the average packing density X 14: Packing density distribution curve 15: Layers divided every 3.9 μm 16: Packing density of each layer

Claims

1. A porous transport layer for electrolysis, having a thickness of 0.4 to 3.5 mm, which, when divided into multiple layers of 3.9 μm thickness in the thickness direction, alternates between highly packed regions where layers have a packing density of 1.05 times or more relative to the average packing density of each layer (hereinafter, average packing density X (%)) and low packed regions where layers have a packing density of 0.95 times or less relative to the average packing density X (%), in the section from layer A to layer B as defined below, and the total number of highly packed and low packed regions per 1 mm thickness is between 6.0 and 39.

0. <Definition of Layer A and Layer B> Layer A and Layer B are the two layers closest to both surfaces among the layers having a packing density of 50% or more relative to the average packing density of each layer.

2. The porous transport layer for electrolysis according to claim 1, wherein the average packing rate X (%) is 15% or more and 55% or less.

3. The porous transport layer for electrolysis according to claim 1 or 2, wherein the porous body is a conductive porous body containing carbon fibers and a binder.

4. The porous transport layer for electrolysis according to claim 3, having a microporous layer containing carbon fine particles on one surface of the conductive porous body.

5. The porous transport layer for electrolysis according to claim 1 or 2, wherein the total number of the highly packed regions and the low packed regions per 1 mm thickness is 11.0 or more and 19.0 or less.

6. An electrolytic apparatus using the porous transport layer for electrolysis described in any one of claims 1 to 5 on the cathode side.

Images