Carbon fiber electrode material, fuel cell, liquid electrolytic device, redox flow battery, mobile device, and method for manufacturing carbon fiber electrode material

Abstract

The objective is to provide a carbon fiber electrode material that can form a uniform and thin MPL (microporous layer) on its surface, and a method for manufacturing the same. [Solution] The carbon fiber electrode material comprises a carbon fiber fabric formed from warp and weft threads, and a web made of multiple carbon fibers, wherein the web is positioned on one side of the carbon fiber fabric, and at least one end of the carbon fibers of the web is inserted into the weave of the carbon fiber fabric, so that the carbon fibers of the carbon fiber fabric and the carbon fibers of the web are attached to each other. The length of the carbon fibers of the web may be in the range of 20 mm to 150 mm. The thickness of the carbon fibers of the web may also be in the range of 5 μm to 10 μm.

Description

[Technical Field]

[0001] This invention relates to carbon fiber electrode materials used in fuel cells and the like, and to methods for manufacturing them. It also relates to fuel cells, liquid electrolytic devices, redox flow batteries, and mobile devices using the carbon fiber electrode material. [Background technology]

[0002] Conventionally, various technologies have been developed for carbon fiber electrode materials used in fuel cells, redox flow batteries, and liquid electrolytic devices. In particular, for gas diffusion layers in fuel cell applications, a papermaking structure using carbon fibers (carbon paper) has been mainly employed. This structure is manufactured by forming carbon fibers into a sheet using papermaking technology.

[0003] This allows for the creation of a component with gas permeability and a certain level of electrical conductivity. Furthermore, Patent Document 1 discloses a technology using carbon cloth (carbon fiber fabric). This technology aims to improve contact performance with the film electrode assembly by optimizing the weave size of the carbon cloth.

[0004] Furthermore, Patent Document 2 discloses a structure combining carbon paper and carbon cloth, which attempts to achieve both gas permeability and structural stability. Such technologies contribute to improving the performance of fuel cells. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-124645 [Patent Document 2] Japanese Patent Publication No. 2021-125376 [Overview of the project] [Problems that the invention aims to solve]

[0006] In conventional fuel cell applications, such as those disclosed in Patent Documents 1 and 2, a thin layer called an MPL (microporous layer) is formed on one side of the gas diffusion layer, which is placed between the gas diffusion layer and the catalyst layer. This layer plays a role in improving gas dispersibility, reducing contact resistance with the thin film, and protecting the thin film.

[0007] Furthermore, the MPL acts as a buffer to connect the coarse structure of the gas diffusion layer with the fine structure of the catalyst layer. This MPL is formed by applying a slurry of carbon powder or conductive filler and hydrophobic binder to the surface of the gas diffusion layer. However, in the gas diffusion layer disclosed in Patent Document 1, the application of the slurry is uneven, and insufficient pressure is applied to the catalyst layer in the center of the weave, resulting in increased contact resistance and a problem where the MPL becomes thicker.

[0008] This problem arose because the surface roughness and fiber arrangement of carbon cloth and carbon paper were not uniform, causing the applied slurry to flow out from the edges of the carbon cloth and carbon paper. Furthermore, the technology disclosed in Patent Document 2 had the problem of generating a large amount of carbon dioxide during the firing process that bonded the carbon paper and carbon cloth.

[0009] Therefore, the object of the present invention is to provide a carbon fiber electrode material and a method for manufacturing the same, on which a uniform and thin MPL can be formed on the surface. [Means for solving the problem]

[0010] The present invention (first invention) provides a carbon fiber electrode material having a carbon fiber fabric formed from warp and weft threads and a web consisting of a plurality of carbon fibers, wherein the web is arranged on one side of the carbon fiber fabric, and at least one end of at least some of the carbon fibers constituting the web is embedded in the weave of the carbon fiber fabric, so that the carbon fibers of the carbon fiber fabric and the carbon fibers of the web are attached to each other.

[0011] The second invention is a carbon fiber electrode material of the first invention, wherein the length of the carbon fibers in the web is in the range of 20 mm to 150 mm.

[0012] The third invention is a carbon fiber electrode material of the first invention, wherein the thickness of the carbon fibers in the web is in the range of 5 μm to 10 μm.

[0013] The fourth invention is a carbon fiber electrode material of the first invention, wherein the diameter of the carbon fibers in the carbon fiber fabric is in the range of 3 μm to 10 μm.

[0014] The fifth invention is a carbon fiber electrode material of the first invention, wherein the number of carbon fibers contained in the cross-section of the warp and weft single filaments of the carbon fiber fabric is in the range of 50 to 250.

[0015] The sixth invention is a carbon fiber electrode material of the first invention, wherein the opening ratio of the carbon fiber fabric is in the range of 5% to 75%.

[0016] The seventh invention is an electrode material in which a microporous layer is formed on at least one surface of the carbon fiber electrode material of the first invention.

[0017] The eighth invention is a method for manufacturing a carbon fiber electrode material, comprising: a first step of creating a web from cotton using a combing roller; a second step of unwinding a polyacrylonitrile fiber fabric below the web after the first step; a third step of sending compressed air from above the web toward the polyacrylonitrile fiber fabric while winding up the polyacrylonitrile fiber fabric after the second step; and a fourth step of performing flame-retardant treatment and carbonization treatment on the web and the polyacrylonitrile fiber fabric.

[0018] The ninth invention is a method for manufacturing a carbon fiber electrode material, comprising: a first step of producing a web from air-laid cotton by a commingling roller; a second step of unwinding a woven fabric made of polyacrylonitrile fibers below the web after the first step; a third step of attaching the web to the side of the woven fabric made of polyacrylonitrile fibers while spraying a polyvinyl alcohol solution from above the web after the second step; a fourth step of drying and integrating the web and the woven fabric made of polyacrylonitrile fibers by spraying hot air from above the web after the third step; and a fifth step of performing a flame-retardant treatment and a carbonization treatment on the web and the woven fabric made of polyacrylonitrile fibers.

[0019] The tenth invention is a fuel cell having the carbon fiber electrode material of the first to sixth inventions or the electrode material of the seventh invention.

[0020] The eleventh invention is a liquid electrolysis device having the carbon fiber electrode material of the first to sixth inventions or the electrode material of the seventh invention.

[0021] The twelfth invention is a redox flow battery having the carbon fiber electrode material of the first to sixth inventions or the electrode material of the seventh invention.

[0022] The thirteenth invention is a moving body equipped with the fuel cell of the tenth invention.

Advantages of the Invention

[0023] The first invention has a structure in which a web composed of a plurality of carbon fibers is attached to one side of a carbon fiber woven fabric. Since both are fixed, a slurry for forming a thin and uniform MPL can be easily applied, and the gas permeability and the adhesion to the electrode catalyst layer are greatly improved. As a result, in a fuel cell, a reduction in flow path resistance and a suppression of contact resistance are achieved, the drainage of generated water is good, and an improvement in the overall power generation performance of battery systems such as fuel cells and membrane electrolysis is made possible.

[0024] The second invention relates to the carbon fiber electrode material of the first invention, and by setting the length of the carbon fibers in the web to a range of 20 mm to 150 mm, the adhesion with the carbon fiber fabric is optimized, and a good balance of gas permeability and rigidity is ensured. As a result, the discharge efficiency of generated water is improved, and the durability and performance as an electrode for a fuel cell are enhanced.

[0025] The third invention further improves the balance between gas permeability and electrical resistance of the entire electrode by setting the thickness of the carbon fibers in the web to a range of 5 μm to 10 μm in the carbon fiber electrode material according to the first invention. In other words, because the carbon fibers in the web are relatively thin, the degree of unevenness on the surface to which the MPL is applied is reduced, and the MPL can be made thinner. The operating environment of automotive fuel cells has a temperature range of -30 to 80°C and a humidity range of 30 to 85%, and even if expansion and contraction strain occurs in the electrolyte membrane, the cushioning properties of the electrode material absorb this strain, and the contact pressure is maintained so that the contact resistance does not decrease.

[0026] The fourth invention allows for a reduction in the thickness of the carbon fiber fabric in the carbon fiber electrode material of the first invention by setting the diameter of the carbon fibers in the carbon fiber fabric to a range of 3 μm to 10 μm. This further improves the balance between the gas permeability and electrical resistance of the entire electrode.

[0027] The fifth invention allows for a reduction in the thickness of the carbon fiber fabric in the carbon fiber electrode material of the first invention by setting the number of carbon fibers contained in the single-fiber cross-sections of the warp and weft threads of the carbon fiber fabric to a range of 50 to 250. This further improves the balance between the gas permeability and electrical resistance of the entire electrode.

[0028] The sixth invention relates to the carbon fiber electrode material of the first invention, in which the opening ratio of the carbon fiber fabric is set to a range of 5% to 75%, thereby ensuring gas diffusion in the direction perpendicular to the surface of the carbon fiber fabric. This further improves the gas permeability of the entire electrode.

[0029] The seventh invention involves forming a microporous layer on the carbon fiber electrode material of the first invention, resulting in an electrode substrate with a thin and uniform microporous layer, which significantly improves adhesion to the electrode catalyst layer.

[0030] The eighth invention involves a process of uniformly adhering the web to a polyacrylonitrile fiber fabric using compressed air, thereby improving the bonding between materials and suppressing peeling and shifting. This ensures consistent product uniformity and quality, improves production efficiency, and creates a process suitable for mass production. Furthermore, since no binders or chemicals are used, the environmental impact is reduced.

[0031] The ninth invention employs a series of steps in which a cotton batting is formed into a web, attached to a polyacrylonitrile fiber fabric, and then hot-air dried. This method not only ensures the uniformity and adhesion of the carbon fiber electrode material but also improves the efficiency and reproducibility of the entire manufacturing process. Furthermore, the resulting carbon fiber electrode material achieves improved performance, such as reduced rigidity in the thickness direction and reduced electrical resistance, making it suitable for a wide range of battery systems.

[0032] The tenth invention is a fuel cell having the carbon fiber electrode material of the first to sixth inventions or the electrode material of the seventh invention, which enables an improvement in overall power generation performance.

[0033] The eleventh invention is a liquid electrolytic apparatus having a carbon fiber electrode material from the first to sixth inventions or an electrode material from the seventh invention, which enables an improvement in overall electrolysis performance.

[0034] The twelfth invention is a redox flow battery having the carbon fiber electrode material of the first to sixth inventions or the electrode material of the seventh invention, which enables an improvement in overall power generation performance.

[0035] The 13th invention is a mobile vehicle equipped with a fuel cell from the 10th invention, which enables improved fuel efficiency. [Brief explanation of the drawing]

[0036] [Figure 1] This is a magnified photograph (magnification: 250x) of the carbon fiber electrode material of the present invention, taken from the carbon fiber fabric side. [Figure 2] This is a magnified photograph (magnification: 250x) of the carbon fiber electrode material of the present invention, taken from the web side. [Figure 3] This is a magnified photograph (magnification: 250x) of the carbon fiber electrode material of the present invention, taken from the web side (when transmitted light is shone from the carbon fiber fabric side). [Figure 4] This is a schematic cross-sectional view of the carbon fiber electrode material 1 of the present invention. [Figure 5] This is a schematic cross-sectional view of carbon fiber electrode materials, etc., within a fuel cell stack. [Figure 6] This is a schematic overall diagram of the carbon fiber electrode material manufacturing apparatus 10 of the present invention. [Figure 7] This is a schematic diagram of the test specimen manufacturing process in the example. [Modes for carrying out the invention]

[0037] A carbon fiber electrode material according to one embodiment of the present invention will be described with reference to the drawings. Figure 1 shows a magnified photograph (magnification: 250x) of the carbon fiber electrode material according to one embodiment of the present invention taken from the carbon fiber fabric side, Figure 2 shows a magnified photograph (magnification: 250x) of the same carbon fiber electrode material taken from the web side, Figure 3 shows a magnified photograph (magnification: 250x) of the same carbon fiber electrode material taken from the web side when transmitted light is shone on the carbon fiber fabric side, Figure 4 shows a schematic cross-sectional view in the thickness direction of the carbon fiber electrode material 1 of the present invention, and Figure 5 shows a schematic cross-sectional view of the carbon fiber electrode material, etc., inside a fuel cell stack.

[0038] The carbon fiber electrode material 1 of the present invention comprises a carbon fiber fabric 2 formed from warp threads 2A and weft threads 2B, as shown in Figures 1 and 2, and a web 3 consisting of a plurality of carbon fibers. The web is arranged on one side of the carbon fiber fabric, as shown in Figures 2 and 3, and at least one end of at least some of the carbon fibers constituting the web 3 is in contact with the carbon fiber fabric 2, penetrating the weave of the carbon fiber fabric 2, as shown in Figure 4.

[0039] The following describes in detail the "carbon fiber fabric," "diameter of carbon fibers in the carbon fiber fabric," "number of carbon fibers in the carbon fiber fabric," "opening ratio of carbon fibers in the carbon fiber fabric," "web," "length of carbon fibers in the web," and "thickness of carbon fibers in the web," which form the carbon fiber electrode material of the present invention.

[0040] <Carbon fiber fabric> Carbon fiber fabric (carbon cloth), as shown in Figure 1, is a woven fabric composed of warp and weft threads, and functions as a base material that combines strength and flexibility. In this invention, this carbon fiber fabric adheres to the carbon fibers of the web and acts as a stable support when the slurry forming the MPL is applied. The density and weave spacing of the carbon fiber fabric can be adjusted to allow the carbon fibers of the web to penetrate properly and to ensure adhesion between the carbon fibers of the web and the carbon fiber fabric. Furthermore, uniformity is required of the carbon fiber fabric, and it is necessary to minimize weave coarseness and fiber variation. This achieves both gas permeability and electrical conductivity.

[0041] <Diameter of carbon fibers in carbon fiber fabric> In this invention, the diameter of the carbon fibers constituting the carbon fiber fabric is preferably 3 μm or more and 10 μm or less. A carbon fiber diameter of 10 μm or less allows for a thinner carbon fiber fabric, thus providing a carbon fiber fabric suitable for fuel cell applications. If the carbon fiber diameter is less than 3 μm, the strength and productivity of the carbon fiber fabric may deteriorate.

[0042] <Number of carbon fibers in carbon fiber fabric> In the present invention, it is preferable that the warp and weft threads constituting the carbon fiber fabric each contain 50 to 250 carbon fibers in the cross-section of the single filaments constituting the warp and weft threads. By having 250 or fewer carbon fibers, more preferably 150 or fewer, in the cross-section of the single filaments constituting the warp and weft threads, the carbon fiber fabric can be made thinner. If the number of carbon fibers in the warp or weft threads is less than 50, the strength and productivity of the carbon fiber fabric may deteriorate. Furthermore, it is preferable that the warp and weft threads are spun carbon fiber yarns. When using double yarn as the spun yarn, it is preferable that the total number of carbon fibers contained in the cross-section of each single filament constituting the double yarn is 50 to 250.

[0043] <Open area ratio of carbon fiber fabric> In the present invention, the carbon fiber fabric preferably has an opening ratio of 5% or more and 75% or less. An opening ratio of 5% or more is preferable because it yields a carbon fiber fabric with excellent gas diffusion in the direction perpendicular to the surface. If the opening ratio of the carbon fiber fabric exceeds 75%, the web becomes more prone to slippage, and the yield decreases. Here, the opening ratio of the carbon fiber fabric is the value defined by the following formula, where the warp pitch is Tp, the weft pitch is Yp, the warp width is Tw, and the weft width is Yw. Opening ratio [%]=(Tp-Tw)×(Yp-Yw) / Tp / Yp×100.

[0044] <Web> The web is an important component in the carbon fiber electrode material of the present invention that assists in the uniform formation of the MPL (microporous layer), and is formed from multiple carbon fibers. As shown in Figures 2 and 3, the web is arranged on one side of the carbon fiber fabric, and at least one end of at least some of the carbon fibers constituting the web enters the weave of the carbon fiber fabric, fixing the weave by cross-linking the weave. It is sufficient that at least one end of the web's carbon fibers enters the weave of the carbon fiber fabric, so it is acceptable for both ends of the web's carbon fibers to enter different weaves of the carbon fiber fabric and be fixed (attached) in that way. Because at least one end of the web's carbon fibers enters the weave of the carbon fiber fabric, the surface on which the web's carbon fibers exist is flat, so it prevents leakage from the weave when slurry is applied to form the MPL, and makes it possible to form the MPL thin and uniform in thickness without impairing the surface roughness. In this application, "web" refers to a sheet in which fibers are arranged in a spiderweb-like pattern.

[0045] Furthermore, because the web consists of intertwined carbon fibers, the adhesion between the carbon fibers is improved, ensuring the overall structural stability. By creating a structure in which the carbon fibers of the web penetrate the weave of the carbon fiber fabric, some of the web's carbon fibers are incorporated into the interior of the carbon fiber fabric, resulting in the following effects: The movement and displacement of the web's carbon fibers are reduced, and by applying MPL, the web and carbon fiber fabric adhere even more stably. In addition, by arranging the web's carbon fibers more densely than the carbon fiber fabric, the thickness of the MPL can be made thinner and more uniform. Moreover, direct contact between the web's carbon fibers and the carbon fiber fabric improves electrical conductivity and mechanical stability.

[0046] Furthermore, if the structure is such that both ends of the web's carbon fibers penetrate and adhere to different weaves of the carbon fibers, the web's carbon fibers adhere closely to the carbon fiber fabric, forming a stronger structure. This structure improves gas permeability and mechanical durability, and also enhances the effect of preventing leakage through the back during slurry application. These characteristics contribute to improving the reliability and performance of the carbon fiber electrode material of the present invention.

[0047] <Length of carbon fiber in the web> The length of the carbon fibers in the web is preferably in the range of 20 mm to 150 mm. Within this range, not only are the carbon fibers more easily penetrated into the weave of the carbon fiber fabric, but gas permeability and electrical conductivity are also improved. If the carbon fibers are too short, they are more likely to slip through the weave, which may reduce the yield. On the other hand, if they are too long, the number of carbon fibers that penetrate into the weave of the carbon fiber fabric decreases, which may result in unstable adhesion to the carbon fiber fabric. Note that the length of the carbon fibers in the web does not need to be between 20 mm and 150 mm, as long as the length of the carbon fibers is substantially between 20 mm and 150 mm. If 90% or more of the single yarns are between 20 mm and 150 mm in length, the spun yarn is composed of carbon fibers between 20 mm and 150 mm in length.

[0048] <Width of carbon fiber in the web> The thickness of the carbon fibers in the web is preferably in the range of 5 μm to 10 μm. In the method of manufacturing the carbon fiber electrode material of the present invention, a method is sometimes used in which a web composed of precursor fibers and a fabric are integrated, and then fired by flame-retardant treatment or carbonization treatment to produce carbon fibers. However, if the thickness of the single filaments of the acrylic raw cotton constituting the web and the carbon fiber fabric are not significantly different, it is easier to optimize the aforementioned firing conditions. Furthermore, this thickness range is selected to achieve both gas permeability and structural stability. If the thickness of the carbon fibers exceeds 10 μm, the interwoven yarns of the carbon fiber fabric become thicker, and the carbon fiber fabric also becomes thicker, which can increase the resistance in the thickness direction and reduce the power generation efficiency.

[0049] Furthermore, the carbon fiber electrode material of the present invention is preferably used in a configuration in which a separator is arranged on the carbon fiber fabric side, and an MPL (microporous layer) and MEA (membrane electrode assembly) are arranged on the single-fiber carbon fiber side, as shown in Figure 5. Therefore, as long as the thickness of the carbon fibers is within the above range, the carbon fiber fabric side maintains cushioning properties (stretch and recoverability) as an electrode material relative to the separator, and on the carbon fiber side of the web, an appropriate gap is secured between adjacent carbon fibers, enabling the formation of a uniform and thin MPL and excellent gas permeability.

[0050] Next, the method for manufacturing the carbon fiber electrode material of the present invention will be described with reference to the drawings. A schematic overall view of the carbon fiber electrode material manufacturing apparatus 10 of the present invention is shown in Figure 6. The first aspect of the method for manufacturing the carbon fiber electrode material of the present invention comprises a total of four steps: a first step of creating a web W1 from cotton C using a combing roller 12; a second step of unwinding a polyacrylonitrile fiber fabric W2 below the web W1 after the first step; a third step of sending compressed air from above the web W1 toward the polyacrylonitrile fiber fabric W2 while winding up the polyacrylonitrile fiber fabric W2 after the second step; and a fourth step of performing flame-retardant treatment and carbonization treatment on the web W1 and the polyacrylonitrile fiber fabric W2. The details of the first to fourth steps described above will be explained below.

[0051] <Step 1: Website Creation> The first step involves extracting a large number of cotton fibers C from the impinger 11 of the carbon fiber electrode material manufacturing apparatus 10 and processing them with a combing roller (carding machine) 12 to produce a uniform, thin web W1. In this step, it is important to improve the overall strength and uniformity of the web W1 by aligning the fibers of the cotton fibers C. Appropriate speed and pressure settings of the combing roller 12 affect the quality of the web W1 produced, so proper control is important. This web W1 is the basis for bonding with the polyacrylonitrile fiber fabric W2 in the next step, so uniformity is necessary.

[0052] <Step 2: Unwinding the fabric> The second step involves placing a polyacrylonitrile fiber fabric W2 below the web W1 produced in the first step. This polyacrylonitrile fiber fabric W2 is supplied with appropriate tension using an unwinding machine 13 and continuously recovered by a winding machine 14 via feed rollers 17 and 18. The purpose of this step is to prepare the web W1 and the polyacrylonitrile fiber fabric W2 to become one. Precise control of the unwinding speed and tension of the polyacrylonitrile fiber fabric W2 is necessary because they greatly affect the adhesion to the web W1 and the finished product.

[0053] <Step 3: Web adhesion using compressed air> In the third step, a compressed air adhesion process is performed to ensure that the web W1, which is positioned above the polyacrylonitrile fiber fabric W2 unwound in the second step, adheres securely to the surface of the polyacrylonitrile fiber fabric W2. In this step, a compressed air supply device (air jet device) 16A is used to generate an airflow directed from above the web W1 downwards toward the polyacrylonitrile fiber fabric W2. Here, a mesh member 19 is placed on the lower surface of the polyacrylonitrile fiber fabric W2 to support the polyacrylonitrile fiber fabric W2 from below, allowing the generated airflow to pass through (preventing the airflow from being reflected by the polyacrylonitrile fiber fabric W2). This airflow has the effect of pressing the web W1 against the polyacrylonitrile fiber fabric W2 with a constant pressure, eliminating any fine air layers or gaps between the web W1 and the polyacrylonitrile fiber fabric W2.

[0054] Furthermore, the flow velocity and pressure of the compressed air are adjusted according to the material properties of the web W1 and the polyacrylonitrile fiber fabric W2, as well as the winding speed of the polyacrylonitrile fiber fabric W2. In addition, in this third step, the action of the compressed air promotes the appropriate entanglement of the fibers of the web W1 and the mechanical bonding with the fibers of the polyacrylonitrile fiber fabric W2. At this time, the polyacrylonitrile fiber fabric W2 is taken up with appropriate tension by the winding machine 14, thereby maintaining uniform adhesion between the web W1 and the polyacrylonitrile fiber fabric W2. Through this process, integration of the web W1 and the polyacrylonitrile fiber fabric W2 is achieved. Although not shown here, when winding up the polyacrylonitrile fiber fabric W2 to which the web W1 is attached, a slippery sheet can be wound up to prevent the web W1 from reattaching to the other side (the side that is not attached) of the polyacrylonitrile fiber fabric W2.

[0055] <Fourth step: Finishing with flame-retardant treatment and carbonization treatment> To convert the polyacrylonitrile fiber matrix material of the carbon fiber electrode material obtained after the third step described above into carbon fibers, flame-retardant treatment and carbonization treatment are performed. This flame-retardant treatment and carbonization treatment remove the organic components from the matrix material of the carbon fiber electrode material obtained after the third step, leaving the carbon components in high purity. In the flame-retardant treatment, oxidation is performed in an oxygen atmosphere at 200-250°C or below for several hours, and in the subsequent carbonization treatment, the material is held at 1200°C or above for 10 minutes in an atmosphere where oxygen is blocked, for example, inert gas (such as nitrogen or argon), to bake it into highly conductive carbon fibers. At this stage, by sandwiching it between plates with heat-resistant, smooth surfaces and ensuring a certain gap, a webmed carbon fiber fabric with a smooth surface can be obtained.

[0056] Next, a second aspect of the method for manufacturing the carbon fiber electrode material of the present invention will be described with reference to the drawings. The second aspect of the method for manufacturing the carbon fiber material electrode includes a total of five steps: a first step of creating a web W1 from cotton using a combing roller 12; a second step of unwinding a polyacrylonitrile fiber fabric W2 below the web W1; a third step of attaching the web W1 to the polyacrylonitrile fiber fabric W2 by blowing a polyvinyl alcohol solution onto the web W1 from above; a fourth step of drying and integrating the web W1 and the polyacrylonitrile fiber fabric W2 by blowing hot air onto the web W1 from above; and a fifth step of performing flame-retardant treatment and carbonization treatment on the web W1 and the polyacrylonitrile fiber fabric W2. The details of the third and fourth steps in the second aspect will be described below. Note that the first, second, and fifth steps in the second aspect are the same as the first, second, and fourth steps in the first aspect described above, so a detailed explanation will be omitted.

[0057] <Step 3: Web attachment> In the third step, the polyvinyl alcohol solution is sprayed onto one surface of the polyacrylonitrile fiber fabric W2 from above using a coater 15, thereby adhering the web W1 to the fabric. The polyvinyl alcohol solution acts as an adhesive, used to firmly bond the two materials together. When spraying, it is important to ensure uniform application and appropriate amount of the polyvinyl alcohol solution (0.2-0.4% aqueous solution of polyvinyl alcohol), which ensures uniform adhesion across the entire interface between the web W1 and the polyacrylonitrile fiber fabric W2.

[0058] <Step 4: Drying of polyacrylonitrile fiber fabric> In the fourth step, the web W1 and the polyacrylonitrile fiber fabric W2 are dried together by blowing hot air from above the web W1 using a dryer 16B. This step evaporates the water in the polyvinyl alcohol solution and completely fixes the adhesion between the two materials. The drying temperature and the speed of the hot air blowing must be appropriately adjusted to prevent uneven drying and deformation of the materials due to excessive heat. Once drying is complete, the base material for the carbon fiber electrode is formed.

[0059] <Gas diffusion layer> A carbon fiber electrode material of the present invention, in which a microporous layer is formed by applying a microporous layer coating solution to one side, is suitably used as a gas diffusion layer.

[0060] The microporous layer coating solution may contain a dispersion medium such as water or an organic solvent, or a dispersion aid such as a surfactant. Water is preferred as the dispersion medium, and a nonionic surfactant is preferred as the dispersion aid. It is preferable if the microporous layer coating solution contains conductive fine particles, as this allows for the acquisition of a microporous layer with excellent conductivity. It is also preferable if the microporous layer coating solution contains a water-repellent resin, as this allows for the acquisition of a microporous layer with excellent drainage properties for discharging water generated by electrochemical reactions in the fuel cell to the separator, and with excellent mechanical strength. Coating of the microporous layer coating solution onto a porous carbon sheet can be carried out using various commercially available coating devices. Coating methods such as screen printing, rotary screen printing, spray atomization, intaglio printing, gravure printing, die coater coating, bar coating, and blade coating can be used, but die coater coating is preferred because it allows for the quantification of the coating amount regardless of the surface roughness of the porous carbon sheet. The coating methods exemplified above are merely examples and are not necessarily limited to these.

[0061] <Membrane electrode assembly> A membrane electrode assembly can be formed by bonding the carbon fiber electrode material of the present invention to at least one side of an electrolyte membrane having catalyst layers on both sides. When using a carbon fiber electrode material with a microporous layer formed on it to serve as a gas diffusion layer, it is preferable to arrange it so that the microporous layer side is in contact with the catalyst layer side, as this facilitates back diffusion of the generated water and increases the contact area between the catalyst layer and the gas diffusion layer, thereby reducing contact electrical resistance. Platinum is usually used as the catalyst for the catalyst layer. It is preferable to use a perfluorosulfonic acid-based polymer material with high proton conductivity, oxidation resistance, and heat resistance for the electrolyte membrane.

[0062] <Fuel cell> A fuel cell is one aspect of the present invention. The fuel cell of the present invention is a fuel cell having the carbon fiber electrode material of the present invention. That is, it refers to a fuel cell having separators at both ends of the membrane electrode assembly described above. The separator has a flow path to allow fuel gas to flow into the anode-side gas diffusion layer and oxidizing gas to flow into the cathode-side gas diffusion layer. The separator and the flow path can be of any shape that allows fuel gas and oxidizing gas to flow in and out. A fuel cell stack can be constructed by stacking multiple of the above fuel cells.

[0063] <Liquid electrolyzer> A liquid electrolytic apparatus is one aspect of the present invention. The liquid electrolytic apparatus of the present invention has the carbon fiber electrode material of the present invention. That is, it has a liquid electrolytic cell having separators on both sides of the above-mentioned membrane electrode assembly.

[0064] <Redox flow battery> A redox flow battery is one aspect of the present invention. The redox flow battery of the present invention uses the carbon fiber electrode material of the present invention as the positive electrode and / or negative electrode. The carbon fiber electrode material of the present invention can be used as an electrode in either a flow-through type or a flow-by type cell.

[0065] <Mobile> A mobile body is one aspect of the present invention. The fuel cell in the present invention is a fuel cell installed in a mobile body such as an automobile, ship, or railway, and can be used as a power source for said mobile body. In other words, the mobile body of the present invention refers to a mobile body equipped with the fuel cell of the present invention. [Examples]

[0066] (Example 1) First, a twill weave fabric was woven using a yarn made by combining acrylic spun yarn (1 / 200 Nm) and polyvinyl alcohol (PVA) 85T filament, with 95 warp and weft threads per inch. This fabric was then immersed in 75°C hot water to dissolve and remove the PVA threads, resulting in a white fabric equivalent to A3 size (297 mm x 420 mm) consisting only of yarns with a low twist count and a twist angle of 18 degrees.

[0067] Next, 38mm long acrylic spun yarn is fed as raw cotton into the beating machine 11 shown in Figure 6, and a combing roller (carding machine) 12 is used to process it to a basis weight of 6g / m². 2 A flat web was formed. This web was placed on a white fabric the size of an A3 sheet of paper. Furthermore, this combination was placed on a stainless steel mesh (gap: 1 mm) the size of a B4 sheet of paper (257 mm x 364 mm), and the fabric and stainless steel mesh were slowly submerged in a stainless steel rectangular tray the size of an A3 sheet of paper filled to a depth of 20 mm with a 0.3% PVA aqueous solution. After that, the stainless steel mesh was slowly lifted up in the same manner as papermaking, so that the ends of the acrylic spun yarn of the web would be tucked into the weave by the water flow. A schematic diagram of the production of the test specimen used in this embodiment is shown in Figure 7.

[0068] By drying in this state, the PVA adhesive effect caused the web to adhere to the white fabric from the stainless steel mesh, and it was confirmed that it could not be easily peeled off. This web-attached fabric (the base material of the test specimen) was sandwiched between carbon plates, with a gap of one web of free thickness, and placed horizontally in a hot air furnace, where it was subjected to flame-retardant treatment in air (at a temperature range of 200-250°C for 2-4 hours).

[0069] Subsequently, a carbonization treatment was performed in a nitrogen atmosphere at 1,200°C for 10 minutes to complete the carbon fiber fabric (carbon fiber electrode material) with the web attached. The physical properties of the obtained carbon fiber electrode material were as follows.

[0070] • Basis weight: 72g / m² 2 • Thickness at a pressure of 1 MPa: 190 μm • Resistance in the thickness direction at a pressure of 1 MPa: 11 mΩ / cm 2 Next, polytetrafluoroethylene (PTFE) and carbon black were mixed in a mass ratio of 1:3.3 to prepare a water-soluble MPL (microporous layer) ink containing a dispersant and thickener. This ink was thinly applied to the surface to which the carbon fiber electrode material web was attached, and after drying, it was heat-treated in a hot air furnace at 370°C for 5 minutes. As a result, the additional basis weight of the MPL was 8 g / m². 2 Therefore, the resistance in the thickness direction (at a pressure of 1 MPa) is 14 mΩ / cm 2 That's what happened.

[0071] Furthermore, the side of this carbon fiber electrode material that was not coated with MPL was floated on the surface of a 4% PTFE aqueous solution, transferred to blotting paper to remove excess liquid, dried, and then subjected to a firing treatment at 370°C for 5 minutes to apply a water-repellent treatment. This MPL-coated carbon fiber electrode material was then cut to 1 cm 2 The specimens were cut to the required size and incorporated into a standard 1D cell using hydrogen and oxygen electrodes for power generation testing. During this process, 0.1 g / m² of Nafion® material with a thickness of 30 μm was used. 2 A polymer film coated with a platinum catalyst was used. The detailed conditions for this power generation test followed the methods described in the "NEDO PEFC Cell Evaluation and Analysis Protocol 2023".

[0072] To evaluate the gas diffusion resistance value in actual power generation by 1D cells, after the conditioning operation, gases of 1% oxygen (99% nitrogen) and hydrogen were respectively fed in under the conditions of being humidified at 60 °C and 80%. After repeating the condition of changing from 0.9 volts to 0.1 volts 5 times, the current was measured at 0.2 volts. When this power generation amount was defined as humidified power generation, an output of 0.28 A / cm 2 was obtained. Also, the condition of the input gas (45 °C · 145%) was defined as over-humidified power generation. After repeating the condition of changing from 0.9 volts to 0.1 volts 5 times in the same manner as in the humidified power generation and then measuring the current at 0.2 volts, as a result, an output of 0.26 A / cm 2 was obtained. This is a power generation state with only 1% oxygen and excessive moisture at a humidity of 145%. However, in this example, it was found that water has good drainage and flooding is unlikely to occur. Here, "flooding" refers to a state where, due to the generation of moisture by the fuel cell reaction at the air electrode of the fuel cell, when the humidification becomes excessive (over-humidification), water droplets adhere to the electrode surface, and as a result, the supply of gas to the electrode is hindered. Also, various parameters were measured according to the following measurement methods. The results are shown in Table 1.

[0073] <Measurement method> [Length of carbon fibers in the web] A part of the web was removed from the carbon fiber electrode material, the carbon fibers were extracted, and the lengths were confirmed. Five carbon fibers were taken out from five arbitrary locations, and the average value was calculated as the length of the carbon fibers in the web.

[0074] [Thickness of carbon fibers in the web] The diameters of five arbitrary points of the carbon fibers in the web were measured at a magnification of 2,500 times using magnifying equipment such as a microscope, and the average value was calculated as the thickness of the carbon fibers in the web.

[0075] [Diameter of carbon fibers in the carbon fiber fabric] The diameters of five arbitrary points of the warp and weft were measured at a magnification of 2,500 times using magnifying equipment such as a microscope, and the respective average values were calculated as the diameter of the warp and the diameter of the weft.

[0076] [Number of carbon fibers contained in the cross-section of warp and weft single filaments in a carbon fiber fabric] Using magnification equipment such as a microscope, the cross-sections of five warp and weft single filaments were examined at 500x magnification. The average number of carbon fibers contained in each cross-section was calculated as the number of carbon fibers in the warp and weft single filaments, respectively. The cross-sections of the warp and weft were revealed by cutting the carbon fiber fabric with a sharp blade.

[0077] [Open area ratio of carbon fiber fabric] The warp pitch Tp, weft pitch Yp, warp width Tw, and weft width Yw were measured under 200x magnification using a microscope or other magnification equipment, and the aperture ratio was derived using the following formula. Opening ratio [%]=(Tp-Tw)×(Yp-Yw) / Tp / Yp×100 This measurement was performed at five arbitrary points, and the average value was defined as the aperture ratio.

[0078] [Pressurized thickness of carbon fiber fabrics and carbon fiber electrode materials] The compression test mode of Shimadzu Corporation's "Autograph®" AGS-X was used to measure the compressed thickness of carbon fiber fabric and carbon fiber electrode material. The carbon fiber fabric and carbon fiber electrode material were cut to a size of 20 mm x 20 mm, sandwiched between smooth metal rigid electrodes, and the thickness of the carbon fiber fabric and carbon fiber electrode material was measured when an average pressure of 1.0 MPa was applied.

[0079] [Electrical resistance of carbon fiber fabrics and carbon fiber electrode materials] The electrical resistance of carbon fiber fabrics and carbon fiber electrode materials was measured using the compression test mode of the "Autograph®" AGS-X manufactured by Shimadzu Corporation. The carbon fiber fabrics and carbon fiber electrode materials were cut to a size of 20 mm x 20 mm, sandwiched between gold-plated, smooth metal rigid electrodes, and subjected to an average pressure of 1.0 MPa. The electrical resistance per unit area was calculated by measuring the voltage between the upper and lower electrodes when a current of 1 A was passed through them.

[0080] (Comparative Example 1) In Comparative Example 1, the carbon fiber electrode material was prepared and various measurements were performed in the same manner as in Example 1, except that a web was not formed on the white fabric, resulting in a web-free fabric. The results are shown in Table 1.

[0081] (Comparative Example 2) Except for using carbon paper with a gas diffusion layer (MPL) (Type 24BC), manufactured by Company S and commercially available and installed in fuel cell vehicles, as the carbon fiber electrode material of the present invention, various measurements were performed in the same manner as in Example 1.

[0082] [Table 1]

[0083] As shown in Table 1, Example 1, despite having a smaller basis weight and similar resistance and thickness to Comparative Example 2, showed a significant difference in power generation under over-humidified conditions, which is an important indicator of fuel cell stack performance (twice the current could be extracted). In other words, when water vapor generated in the catalyst layer moves to the separator side, the structure of the carbon fiber electrode material of the present invention changes from dense to sparse in the thickness direction, as shown in Figures 1 to 5, and the so-called trumpet effect makes it difficult for the generated water vapor to condense. As a result, the important effect of generating power without causing flooding, even under over-humidified conditions simulating the inside of a fuel cell stack, was obtained.

[0084] In the carbon fiber electrode material of the present invention, the carbon fibers of the web are crosslinked into the weave, ensuring sufficient pressure for the MPL to press against the catalyst layer even in the center of the carbon fiber mesh from the separator side. Furthermore, as shown in Table 1, the thickness of the MPL protecting the polymer film can be reduced by approximately 50% or more compared to Comparative Examples 1 and 2 (gas diffusion layer manufactured by Company S) which lack a web, thereby reducing electrical resistance in the thickness direction. Due to the improved pressure of the MPL pressing against the catalyst layer by the web and the reduced thickness of the MPL, the carbon fiber electrode material of the present invention showed superior power generation under both over-humidified and humidified conditions compared to Comparative Example 1 which lacked a web.

[0085] Furthermore, it was found that the carbon fiber electrode material of the present invention functions as a cushion against expansion and contraction in the thickness direction within the fuel cell stack due to changes in temperature and humidity, contributing to the extended lifespan of the polymer membrane. In this example, the carbon fiber electrode material of the present invention was used for fuel cells, but similar effects can be observed with other electrode materials such as redox flow batteries and electrolysis devices. [Explanation of Symbols]

[0086] 1. Carbon fiber electrode material 2. Carbon fiber fabric 2A Warp 2B Weft 3 Web 10. Manufacturing equipment for carbon fiber electrode materials 11. Driving machine 12. Combing roller (card machine) 13. Unwinding machine 14. Winding machine 15 Applicator 16A Air Jet System 16B Dryer 17,18 Feed rollers 19 Mesh members C Wind cotton W1 Web W2 Polyacrylonitrile fiber fabric

Claims

1. A carbon fiber electrode material comprising a carbon fiber fabric formed from warp and weft threads, and a web consisting of a plurality of carbon fibers, wherein the web is positioned on one side of the carbon fiber fabric, and at least one end of at least some of the carbon fibers constituting the web is embedded in the weave of the carbon fiber fabric, and the carbon fibers of the carbon fiber fabric and the web are adhered to each other.

2. The carbon fiber electrode material according to claim 1, characterized in that the length of the carbon fibers in the web is in the range of 20 mm to 150 mm.

3. The carbon fiber electrode material according to claim 1, characterized in that the thickness of the carbon fibers in the web is in the range of 5 μm to 10 μm.

4. The carbon fiber electrode material according to claim 1, wherein the diameter of the carbon fibers in the carbon fiber fabric is 3 μm or more and 10 μm or less.

5. The carbon fiber electrode material according to claim 1, wherein the number of carbon fibers contained in the cross-section of the warp and weft single filaments of the carbon fiber fabric is 50 or more and 250 or less.

6. The carbon fiber electrode material according to claim 1, wherein the opening ratio of the carbon fiber fabric is 5% or more and 75% or less.

7. An electrode material having a microporous layer formed on at least one surface of the carbon fiber electrode material according to claim 1.

8. A method for manufacturing a carbon fiber electrode material, comprising: a first step of creating a web from cotton using a combing roller; a second step of unwinding a polyacrylonitrile fiber fabric below the web after the first step; a third step of sending compressed air from above the web toward the polyacrylonitrile fiber fabric while winding up the polyacrylonitrile fiber fabric after the second step; and a fourth step of performing flame-retardant treatment and carbonization treatment on the web and the polyacrylonitrile fiber fabric.

9. A method for manufacturing a carbon fiber electrode material, comprising: a first step of creating a web from cotton using a combing roller; a second step of unwinding a polyacrylonitrile fiber fabric below the web after the first step; a third step of adhering the web to the polyacrylonitrile fiber fabric by spraying a polyvinyl alcohol solution from above the web after the second step; a fourth step of drying and integrating the web and the polyacrylonitrile fiber fabric by blowing hot air from above the web after the third step; and a fifth step of performing flame-retardant treatment and carbonization treatment on the web and the polyacrylonitrile fiber fabric.

10. A fuel cell having the carbon fiber electrode material according to any one of claims 1 to 6 or the electrode material according to claim 7.

11. A liquid electrolytic apparatus having a carbon fiber electrode material according to any one of claims 1 to 6 or an electrode material according to claim 7.

12. A redox flow battery having a carbon fiber electrode material according to any one of claims 1 to 6 or an electrode material according to claim 7.

13. A mobile body equipped with the fuel cell described in claim 10.

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