Composite powder, method for producing composite powder, gas diffusion layer, membrane electrode assembly, and fuel cell

Abstract

Provided is a composite powder for use in a gas diffusion layer that has sufficient gas permeability and water discharge properties while maintaining the inside of an MEA in a water-containing state. The composite powder contains a polymer resin and at least one of fibers and particles, and the average porosity of the composite powder is 50-98 vol%.

Description

Technical Field

[0001] This disclosure relates to composite powders made by combining polymer resins with particles and fibers, methods for manufacturing composite powders, and gas diffusion layers, membrane electrode assemblies, and fuel cells using the same. Background Technology

[0002] Gas diffusion layers possess gas permeability and gas diffusion properties, for example, in fuel cells. In a polymeric electrolyte fuel cell, one side of a hydrogen-ion-conducting polymeric electrolyte membrane is exposed to fuel gases such as hydrogen, while the other side is exposed to oxygen. Water is synthesized through a chemical reaction via the electrolyte membrane, and the energy generated in this reaction is extracted as electricity.

[0003] A single cell of a polymeric electrolyte fuel cell has a membrane electrode assembly (hereinafter referred to as MEA) and a pair of conductive membranes disposed on both sides of the MEA. The MEA has a hydrogen ion-conducting polymeric electrolyte membrane and a pair of electrode layers sandwiching the electrolyte membrane. The pair of electrode layers has: a catalyst layer formed on both sides of the polymeric electrolyte membrane, which is mainly composed of carbon powder carrying a platinum group catalyst; and a gas diffusion layer formed on the catalyst layer, which has the functions of current collection, gas permeability and waterproofing.

[0004] The gas diffusion layer in the MEA uniformly supplies gas from the separator to the catalyst layer. Additionally, the gas diffusion layer functions as a conductive path for electrons between the catalyst layer and the separator. Furthermore, the gas diffusion layer requires high water resistance to rapidly remove any residual moisture generated in the catalyst layer through the battery reaction, allowing it to escape from the MEA and out of the system, while preventing the pores of the gas diffusion layer from becoming clogged by generated water.

[0005] Therefore, a gas diffusion layer (MPL, or microporous layer) is typically formed on porous carbon paper or carbon felt based on carbon fiber to manage the generated water. The carbon paper or carbon felt is waterproofed by impregnating it with a highly waterproof resin. In addition, the MPL is composed of conductive particles such as carbon black and a highly waterproof resin, which serves to rapidly drain any excess water generated in the catalyst layer from the MEA to the outside of the system and prevent the necessary amount of water from escaping.

[0006] For example, Patent Document 1 discloses a method for manufacturing a mixed powder by spray drying a solution containing PTFE and conductive particles, and forming a gas diffusion layer by sheeting the mixed powder.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 6-316784 Summary of the Invention

[0008] The problem that the invention aims to solve However, in Patent Document 1, the PTFE and conductive particle mixed powder is granulated by spray drying, thus promoting PTFE fibrosis due to temperature rise and shear. Furthermore, due to shrinkage and agglomeration during heating and drying, only powders with small pores can be produced. Consequently, in the gas diffusion layer made using the PTFE and conductive particle mixed powder described in Patent Document 1, the fibrosis of PTFE within the mixed powder is promoted, resulting in insufficient PTFE binding the powder particles together and reduced membrane strength. Additionally, due to the small pores in the mixed powder, only membranes with small pores can be produced. Therefore, fuel cells using gas diffusion layers with small pores made from conventional mixed powders, especially in high current density regions where large amounts of water are generated during power generation, are prone to water retention in the fine pores of the carbon fiber substrate, potentially hindering gas diffusion. Furthermore, the durability of gas diffusion layers with low membrane strength, as described in conventional mixed powders, is reduced, and they may break down during prolonged operation.

[0009] The purpose of this disclosure is to provide a composite powder that, when used in a gas diffusion layer, provides a gas diffusion layer with sufficient gas permeability and water expulsion capability.

[0010] Methods for solving problems The composite powder involved in this disclosure is a composite powder containing at least one of a polymer resin, a fiber, and a particle, and the average porosity of the composite powder is above 50% and below 98%.

[0011] The gas diffusion layer disclosed herein has a porous membrane comprising the aforementioned composite powder.

[0012] The membrane electrode assembly disclosed herein includes the aforementioned gas diffusion layer, a pair of electrodes, and an electrolyte membrane.

[0013] The fuel cell disclosed herein includes the aforementioned membrane electrode assembly and current collector.

[0014] The method for manufacturing composite powder disclosed herein includes: a step of stirring and mixing a polymer resin with at least one of fibers and particles using a dispersing solvent to obtain a mixed solution of at least one of polymer resin, fibers, and particles; a step of spraying the mixed solution in the form of droplets into a chamber that is internally cooled to a temperature below the melting point of the dispersing solvent to obtain composite powder in which the droplets are frozen; and a step of sublimating the dispersing solvent contained in the frozen composite powder to obtain dried composite powder.

[0015] The method for manufacturing composite powder disclosed herein includes: a step of stirring and mixing a polymer resin and at least one of fibers and particles with a dispersing solvent to obtain a compound of at least one of polymer resin, fibers and particles; a step of obtaining a frozen compound formed by freezing the compound; a freeze-pulverizing step of pulverizing the frozen compound to obtain frozen powder; and a drying step of removing the dispersing solvent from the frozen powder to obtain composite powder.

[0016] Another example of the method for manufacturing composite powder disclosed herein includes: a step of stirring and mixing a polymer resin with at least one of fibers and particles using a dispersing solvent to obtain a compound of polymer resin, fibers, and particles; a step of obtaining a frozen compound obtained by freezing the compound; a step of obtaining a frozen mixture obtained by mixing the frozen compound with a polymer resin; a freeze-pulverizing step of pulverizing the frozen mixture to obtain a frozen composite powder; and a drying step of removing the dispersing solvent from the frozen composite powder to obtain the composite powder.

[0017] The method for manufacturing the gas diffusion layer disclosed herein includes a step of rolling the composite powder using rollers and sheeting it to obtain a gas diffusion layer comprising sheets.

[0018] Invention Effects According to the composite powder disclosed herein, when used as a gas diffusion layer, it is possible to manufacture a gas diffusion layer that maintains the interior of the MEA in a water-containing state and has sufficient gas permeability and water expulsion capability. Attached Figure Description

[0019] Figure 1 This is an example of a flowchart of a method for manufacturing composite powder using the freeze granulation method in Embodiment 1.

[0020] Figure 2 This is a schematic cross-sectional view showing the cross-sectional structure of the spray freezing granulation device.

[0021] Figure 3 This is an example of a flowchart illustrating the method for manufacturing composite powder using the freeze-pulverization method in Embodiment 2.

[0022] Figure 4 This is an example of a flowchart illustrating the method for manufacturing composite powder using the freeze-pulverization method in Embodiment 3.

[0023] Figure 5 This is an example of a flowchart illustrating the method for manufacturing composite powder using the freeze-pulverization method in Embodiment 4.

[0024] Figure 6 This is an SEM image of the composite powder from Example 1.

[0025] Figure 7 The image shown is an SEM image of the composite powder from Example 1.

[0026] Figure 8 This is an SEM image showing unfibrillated PTFE particles in the composite powder of Example 1.

[0027] Figure 9 This is a SEM image showing the unfibrillated PTFE particles in the composite powder of Reference Example 1.

[0028] Figure 10 This is a diagram showing the pore distribution of the composite powders in Examples 1-2.

[0029] Figure 11 This is a diagram showing the pore distribution of the composite powder in Reference Example 1.

[0030] Figure 12 This is a schematic cross-sectional view showing the cross-sectional structure of the polymer electrolyte fuel cell unit involved in Embodiment 1.

[0031] Figure 13 This is a schematic perspective view showing the structure of the polymer electrolyte type fuel cell stack according to Embodiment 1. Detailed Implementation

[0032] The general outline of this disclosure is as follows.

[0033] The first method involves a composite powder that comprises at least one of a polymer resin, a fiber, and a particle, and the average porosity of the composite powder is above 50% and below 98%.

[0034] Based on the above composition, porous membranes with high porosity can be fabricated by using powders with high porosity.

[0035] The second method involves a composite powder that, in the first method described above, is held in a cross section by two concentric geometric circles, an circumscribed circle and an inscribed circle. The average value of the sphericity (AB) obtained by dividing the difference (AB) between the maximum radius A of the concentric circumscribed circle (the largest geometric circle) and the minimum radius B of the concentric inscribed circle (the smallest geometric circle) of the composite powder by the maximum radius A can satisfy the following equation (1).

[0036] (AB) / A≤0.5…Equation (1) With the above composition, the composite powder is a spherical powder, which has high fluidity and can produce a highly uniform film when forming a film.

[0037] In the third method, the composite powder involved in the first or second method above has a fiberization degree of less than 80% for the polymer resin.

[0038] It is known that polymeric resins such as polytetrafluoroethylene (PTFE) can become fibrous by applying shear force. If the PTFE in the powder becomes fibrous, there will be insufficient PTFE fibers connecting the powder particles when making a membrane from the powder, resulting in reduced membrane strength. Therefore, based on the above structure, by suppressing the degree of fibrosis of the polymeric resin to below 80%, a membrane with high strength can be produced.

[0039] In the fourth method, the composite powder involved in any of the first to third methods mentioned above can have a cohesion of less than 30%.

[0040] In the fifth method, the composite powder involved in any of the first to fourth methods mentioned above has a deformation strength of more than 1 kPa and less than 60 kPa.

[0041] Regarding the composite powder involved in the sixth method, in any of the first to fifth methods mentioned above, the interior of the composite powder may have pores with a pore volume of 0.60 mL / g or more, in which the pore radius is 0.055 μm or more and 0.4 μm or less in the Log differential pore volume diagram determined by mercury intrusion porosimetry.

[0042] Based on the above composition, a membrane with large pores and controlled pore radius can be produced by fabricating a membrane from powder with large pores and controlled pore radius.

[0043] In the seventh method, the composite powder may be made of polytetrafluoroethylene (PTFE) in any of the first to sixth methods mentioned above.

[0044] In the seventh method, the composite powder involved in the eighth method may contain more than 1 wt% and less than 40 wt% polytetrafluoroethylene.

[0045] In the ninth method, the composite particles involved can be conductive particles or conductive fibers in any of the first to eighth methods mentioned above.

[0046] The composite powder involved in the tenth method may contain 5 wt% or more and less than 35 wt% conductive particles and 35 wt% or more and less than 80 wt% conductive fibers, as described in the ninth method above.

[0047] The composite powder involved in the eleventh method can have an average particle size of more than 1 μm and less than 1000 μm in any of the first to tenth methods mentioned above.

[0048] The gas diffusion layer of the twelfth type has a porous membrane containing composite powders from any of the first to eleventh types described above.

[0049] The gas diffusion layer of the thirteenth method has a porous membrane containing the composite powder of any of the first to eleventh methods, and has the following pores: in the Log differential pore volume diagram determined by mercury porosimetry, the pore volume of pores with a radius of 0.055 μm or more and 0.4 μm or less is 0.60 mL / g or more.

[0050] The gas diffusion layer of the fourteenth method has a porous membrane containing the composite powder of any of the first to eleventh methods described above, and has the following pores: in the Log differential pore volume diagram measured by mercury porosimetry, it has two peaks, the pore volume of pores with a pore radius of 0.055 μm or more and 0.4 μm or less is 0.60 mL / g or more, and the pore volume of pores with a pore radius of 0.4 μm or more and 10 μm or less is 0.10 mL / g or more.

[0051] The gas diffusion layer of the fifteenth embodiment has a porous membrane containing the composite powder of any of the first to eleventh embodiments described above, with an internal porosity of 0.5% or less for particles larger than 10 μm.

[0052] The membrane electrode assembly of the sixteenth embodiment includes a gas diffusion layer, a pair of electrodes, and an electrolyte membrane, as described in any of the twelve to fifteenth embodiments above.

[0053] The fuel cell of the seventeenth embodiment includes the membrane electrode assembly and current collector of the sixteenth embodiment described above.

[0054] Based on the above configuration, by using a gas diffusion layer with high membrane strength, large porosity, and controlled pore radius in the fuel cell, the introduction of reactant gases and the discharge of water generated by the reaction can be controlled, thereby improving output and durability.

[0055] The method for manufacturing composite powder according to the eighteenth method includes: a step of stirring and mixing a polymer resin with at least one of the fibers and particles using a dispersing solvent to obtain a mixed solution of the polymer resin with at least one of the fibers and particles; a step of spraying the mixed solution in the form of droplets into a chamber that is internally cooled to a temperature lower than the melting point of the dispersing solvent to obtain a composite powder with frozen droplets; and a step of sublimating the dispersing solvent contained in the frozen composite powder to obtain a dried composite powder.

[0056] Based on the above configuration, a frozen composite powder can be obtained by spraying the mixed solution into a cooling chamber and freezing it. Then, by sublimating the dispersing solvent contained in the frozen composite powder, the dispersing solvent can be removed while maintaining the space where it was present, thus producing a powder with large pores. Furthermore, since no shear force is applied to the polymer resin, the fibrosis of the polymer resin can be suppressed.

[0057] The nineteenth method involves a method for manufacturing composite powder in which the polymer resin may include polytetrafluoroethylene (PTFE) as described in the eighteenth method above.

[0058] The method for manufacturing composite powder involved in the twentieth embodiment may further include a step of heating the dried composite powder at a temperature above 100°C and below 400°C, as described in the eighteenth or nineteenth embodiment above.

[0059] Based on the above composition, polytetrafluoroethylene (PTFE) softens upon heating and readily becomes fibrous. Simultaneously, heating causes the mixed particles and fibers to expand, thereby promoting the fibrosis of PTFE.

[0060] The method for manufacturing composite powder according to the twenty-first method includes: a step of stirring and mixing a polymer resin with at least one of fibers and particles using a dispersing solvent to obtain a compound of polymer resin with at least one of fibers and particles; a step of obtaining a frozen compound obtained by freezing the compound; a step of pulverizing the frozen compound to obtain a frozen powder; and a drying step of removing the dispersing solvent from the frozen powder to obtain the composite powder.

[0061] Based on the above structure, by pulverizing the moisture in the compound while it is frozen, pulverization can be achieved without destroying the voids present in the frozen moisture. Therefore, particles with large voids can be produced. Furthermore, since no shear force is applied to the polymer resin, fibrosis of the polymer resin can be suppressed, maintaining its shape.

[0062] In the method for manufacturing composite powder involved in the twenty-second method, the moisture content of the compound can be 20-80% in the twenty-first method mentioned above.

[0063] In the method for manufacturing composite powder involved in the twenty-third method, the temperature in the freeze-pulverization process can be -150~-10℃, as described in the twenty-first or twenty-second methods above.

[0064] In the twenty-fourth scheme, the method for manufacturing composite powder involves sublimating the dispersing solvent contained in the frozen powder during the drying process, as described in any of the twenty-first to twenty-third schemes above, to obtain a dried composite powder.

[0065] In the method for manufacturing composite powder according to the twenty-fifth method, in any of the twenty-first to twenty-fourth methods mentioned above, the drying process may be further heated at a temperature of 100°C or higher and 400°C or lower.

[0066] In the method for manufacturing composite powder involved in the twenty-sixth method, in any of the twenty-first to twenty-fifth methods mentioned above, the drying process can be an evaporation method of water heated under atmospheric pressure.

[0067] In the method for manufacturing composite powder involved in the twenty-seventh method, in the aforementioned twenty-sixth method, the drying temperature in the drying process can be above 100°C and below 400°C.

[0068] The method for manufacturing composite powder according to the twenty-eighth method includes: a step of stirring and mixing a polymer resin with at least one of fibers and particles using a dispersing solvent to obtain a compound of polymer resin, fibers and particles; a step of obtaining a frozen compound obtained by freezing the compound; a step of obtaining a frozen mixture obtained by mixing the frozen compound with a polymer resin; a freeze-pulverizing step of pulverizing the frozen mixture to obtain a frozen composite powder; and a drying step of removing the dispersing solvent from the frozen composite powder to obtain the composite powder.

[0069] The manufacturing method of the gas diffusion layer in the twenty-ninth method includes a step of rolling and sheeting the composite powder involved in any of the first to eleventh methods to obtain a gas diffusion layer containing a sheet.

[0070] By rolling the composite powder between rollers and applying shearing as described above, the unfibered PTFE is fiberized and sheeted to obtain a gas diffusion layer that serves as a self-supporting membrane.

[0071] Hereinafter, with reference to the accompanying drawings, the composite powder and its manufacturing method, gas diffusion layer, membrane electrode assembly, and fuel cell of the embodiments of the present disclosure will be described in detail.

[0072] Furthermore, the embodiments described below are general or specific examples. The numerical values, shapes, materials, constituent elements, arrangement of constituent elements, connection methods, steps, and order of steps shown in the following embodiments are examples and are not intended to limit this disclosure. Additionally, constituent elements in the following embodiments that are not described in the independent claims representing the highest-level concept are described as arbitrary constituent elements. In the figures, substantially identical components are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified.

[0073] Furthermore, the various elements shown in the accompanying drawings are merely schematic illustrations for the purpose of understanding this disclosure, and the dimensions and appearance may differ from the actual objects.

[0074] (Implementation Method 1) <Composite Powder> The composite powder of Embodiment 1 comprises at least one of a polymer resin, a fiber, and particles. In this Embodiment 1, for example, polytetrafluoroethylene (PTFE) is used as the polymer resin, carbon fiber as the fiber, and carbon particles as the particles. The types and compositions will be described later, but the combination of polymer resin, fiber, and particles is not limited to the examples described above.

[0075] The average particle size of the composite powder is, for example, 1 μm or more and 1000 μm or less. While it varies depending on the formed film and porosity, it is preferably smaller than the target film thickness. Furthermore, if the average particle size decreases, the cohesive force increases, reducing operability; therefore, the average particle size is preferably 1 μm or more. The method for calculating the average particle size of the composite powder is described. The average particle size of the composite powder can be measured, for example, using a Microtrac MT3000II particle size distribution measuring device. The average particle size refers to the particle size at which the cumulative value (D50) of the particle size distribution, determined by laser diffraction and scattering, reaches 50% of the total number of particles. The laser diffraction and scattering method determines the particle size by utilizing the difference in the intensity distribution of diffracted and scattered light when a laser beam is irradiated onto the particles, based on the particle size.

[0076] The average porosity of the composite powder is above 50% by volume and below 98% by volume. Average porosity refers to the volume ratio of voids within the particles. Submicron-sized pores can be measured using nitrogen adsorption, but when pore sizes span a wide range, they can be measured using electron microscopy, mercury intrusion porosimetry (JIS R1655 "Method for Determination of Pore Size Distribution in Molded Bodies Based on Mercury Intrusion Porosimetry for Fine Ceramics," derived from the relationship between the pressure and mercury volume when mercury penetrates the voids), etc. The average porosity can be calculated using the following formula based on the pore volume obtained by mercury intrusion porosimetry and the true density of the material.

[0077] ((pore volume × true density) / (1 + pore volume × true density)) × 100 [volume %] However, the average porosity calculated above sometimes includes the voids between powder particles. Therefore, a certain load can be applied to the powder to form it, and the formed body can be measured.

[0078] In this embodiment 1, the average porosity of the powder is calculated using the pore volume measured by mercury porosimetry (JIS R1655). Regarding powder filling, the powder in its unloaded state is filled into the measuring container. The calculated range for the pore radius is set to 0.001 μm to 100 μm. The calculated range for the pore radius sometimes also includes the voids between powder particles, thus an optimal range can be set based on the particle size of the powder, etc. If the average porosity decreases, the voids in the formed film also decrease; therefore, 50% by volume or more is preferred. Furthermore, if the average porosity of the powder is too large, powder cannot be formed; therefore, 98% by volume or less is preferred.

[0079] In a cross-section, when the composite powder is held between two concentric geometric circles, one circumscribed and one inscribed, the maximum radius A of the concentric circumscribed circle (the largest geometric circle) and the minimum radius B of the concentric inscribed circle (the smallest geometric circle) of the composite powder are calculated when the interval between the two concentric circles is minimized. The average value of the sphericity of the composite powder, expressed as (AB) / A (the difference between the maximum radius A and the minimum radius B) divided by the maximum radius A, is 0.5 or less, satisfying the following equation (1), and thus it is approximately spherical.

[0080] (AB) / A≤0.5…Equation (1) Regarding the spherical shape, the sphericity, expressed as (AB) / A, can be calculated from electron microscope images. Excluding powder particles damaged by impacts during manufacturing, the average sphericity (AB) / A of at least five composite powder samples is calculated. If the average sphericity of the composite powder satisfies Equation (1), high fluidity can be obtained, and a uniform film can be formed.

[0081] In the composite powder, the degree of fibrillation of PTFE, the polymer resin, is 80% or less. More preferably, it is 60% or less. The PTFE raw material is in the form of particles, but by applying shear to make it fibrillated, it can form a self-supporting film. The method for calculating the degree of fibrillation of the polymer resin in the composite powder is described. The degree of fibrillation of the polymer resin in the composite powder is calculated by measuring phase separation results using EDX images from a SEM. For example, phase separation can be performed using Oxford Instruments software AZtec 4.3.

[0082] The phase analysis is described here. The EDX image measurement results have a spectrum for each pixel. By calculating and processing the spectrum of each pixel obtained from the EDX image measurement, a phase analysis image can be obtained by grouping pixels with similar spectra. Based on this phase analysis image, the area ratio of each phase in the image field of view and the composition ratio of the quantitative analysis based on the spectrum can be calculated. In this embodiment 1, firstly, focusing on the fluorine (F) contained in the polymer resin PTFE and the carbon (C) contained in the conductive particles and conductive fibers as carbon materials, the phases are grouped into two phases: the CF phase, which is mainly composed of fluorine (F), and the C phase, which is mainly composed of carbon (C). PTFE fibers are so fine that they are difficult to observe with SEM, and the amount detected per unit area is small. Therefore, the F concentration in the C phase, which is mainly composed of C, is related to the amount of PTFE fibers. Regarding the degree of fibrillation, the F concentration of the whole surface is further calculated by the following formula (2).

[0083] PTFE fiberization degree: (C phase area ratio × C phase F concentration) / overall F concentration... Equation (2) If the fibrosis of PTFE in the composite powder increases, there will be insufficient PTFE fibers connecting the composite powder particles when making a membrane, resulting in reduced membrane strength. Therefore, by suppressing the degree of PTFE fibrosis to below 80%, it is possible to produce a membrane with high strength.

[0084] <Cohesion> The agglomeration degree of the composite powder is 30% or less, more preferably 20% or less. By reducing the agglomeration degree, the flowability is improved, and clogging and deviation can be suppressed during film fabrication. The method for calculating the agglomeration degree of the composite powder is described. The agglomeration degree of the composite powder can be measured, for example, using a powder tester PT-X manufactured by Hosokawa Micron Co., Ltd. When a certain amount of vibration is applied to powder with a smaller mesh size than the sieve, the powder particles agglomerate into larger particles, or the powder adheres to the sieve mesh and does not fall off the sieve. The result of quantifying this phenomenon is the agglomeration degree. The agglomeration degree is calculated according to the following steps. First, based on the average of the loose bulk density and the dense bulk density (average bulk density), three types of sieves and vibration times corresponding to them are calculated.

[0085] Loose bulk density can be determined by gently filling a container with powder using a vibrating sieve (e.g., sieve mesh 710 μm, frequency 60 Hz, amplitude 1.0 mm, time 50 seconds). Closed bulk density can be determined in the same manner as loose bulk density, after gently filling the container with powder and then tapping it lightly (e.g., stroke 18 mm, number of taps 50 times).

[0086] The selection of the mesh size for the three types of sieves used for cohesion determination was carried out as follows. For example, when the average bulk density of the powder is 0.4~0.9 g / cm³. 3For samples with mesh sizes of 75μm, 150μm, and 250μm, three types of sieves were used. Additionally, the average bulk density of the powder was less than 0.4 g / cm³. 3 In the case of samples with mesh sizes of 150 μm, 250 μm, and 355 μm, three types of sieves were used. Furthermore, the average bulk density of the powder was greater than 0.9 g / cm³. 3 In the case of samples with mesh sizes of 45μm, 75μm, and 150μm, three types of sieves were used. In any case, the sieve was selected such that all the sample powder passed through the bottom sieve. For example, in this case, since the average bulk density of the powder was less than 0.4 g / cm³... 3 Therefore, three types of sieves with mesh sizes of 150μm, 250μm, and 355μm were selected.

[0087] The time T[s] for vibrating the sieve is calculated using the following formula (3) based on the average of the loose and compacted bulk densities (average bulk density).

[0088] T = 20 + (1.6 - ρ) / 0.016 … Equation (3) ρ: The average of the loose packing density and the compacted packing density (average packing density) The cohesion degree is calculated as follows. First, sieves with three different mesh sizes are stacked from bottom to top in order of increasing mesh size. Next, w[g] (usually 2g) of powder is placed on the top sieve, and the sieve is vibrated with an amplitude of 1mm for a specified time based on the bulk density. Then, the powder remaining on each sieve is weighed. The cohesion degree is calculated using the following formula (4).

[0089] Cohesion = (w1 + (3 / 5)w2 + (1 / 5)w3) × 100 / w Equation (4) w: Sample amount (e.g., 2g) w1: Residual amount on the upper sieve (e.g., opening size 350μm) w2: Residual amount on the middle section sieve (e.g., opening size 250μm) w3: Residual amount on the lower sieve (e.g., opening size 150μm) <Deformation Strength> The deformation strength of the composite powder is 1 kPa or more and 60 kPa or less. More preferably, it is 5 kPa or more and 30 kPa or less. By reducing the deformation strength, a film can be formed with a weaker force. If the deformation strength is too small, the powder particles will adhere to each other before film formation, and a uniform film cannot be formed. The method for calculating the deformation strength of the composite powder is described. The deformation strength of the composite powder can be measured, for example, using the NS-A300 microparticle crushing force measuring device manufactured by Nanoseeds. For the determination of deformation strength, pick up a particle of the powder, apply a force F continuously to the particle, calculate the force F10% at 10% of the initial particle size of the particle, and take the deformation strength σ10% expressed by the following formula (5) as the deformation strength.

[0090] σ10%=F10% / A…Equation (5) σ10%: Deformation strength (Pa) relative to 10% of the compressive displacement of the particle size. F10%: Test force (N) for 10% of the compressive displacement of the particle size. A: Represents the area (the area of ​​the equivalent circle calculated based on the particle size measured before compression) (m²) 2 ) The particle size used in the data was measured for each particle using image analysis software (WinROOF) based on images taken at the time of measurement. The particle size used for particle strength calculations was the diameter (length) of the particle held between the indenter and the plane to which the particle adheres.

[0091] In the Log differential pore volume diagram of the composite powder determined by mercury intrusion porosimetry (JIS R1655), the pores with a pore radius of 0.055 μm or more and 0.4 μm or less have a pore volume of 0.60 mL / g or more.

[0092] By using the composite powder and the manufacturing method described later, a gas diffusion layer can be manufactured, and fine pores with peak values ​​in the range of pore radius of 0.055 μm or more and 0.4 μm or less can be formed in the gas diffusion layer 3.

[0093] <Types of conductive particles 31, conductive fibers 32, and polymer resins 33> The conductive particles 31 can be, for example, carbon materials such as carbon black, graphite, and activated carbon. Carbon black, which has high conductivity and large pore volume, is preferred. Alternatively, acetylene black, Ketjen black, furnace black, and Vulcan can be used as carbon black. Acetylene black with low impurity content or Ketjen black with large specific surface area and high conductivity is preferred. Fullerenes such as fullerene 60 can also be used as conductive particles.

[0094] The size of the conductive particles, for example, has a D50 of 10 nm or more and 5 μm or less. Furthermore, it can be 10 nm or more and 500 nm or less, or even 10 nm or more and 100 nm or less. When the conductive particles are carbon black, for example, the primary particle size is 10 nm or more and 500 nm or less, or it can be 10 nm or more and 100 nm or less, and the size of the aggregates (primary aggregates) can be 100 nm or more and 500 nm or less. When the conductive particles are graphite or activated carbon, for example, the D50 is 1 μm or more and 5 μm or less.

[0095] The conductive fiber 32 contributes to improving the conductivity and mechanical strength of the gas diffusion layer 3. The material of the conductive fiber 32 is not particularly limited; for example, carbon fibers such as carbon nanotubes can be used.

[0096] The average fiber diameter of the conductive fiber 32 is preferably 50 nm or more and 300 nm or less. By making the average fiber diameter of the conductive fiber 32 50 nm or more, the conductivity of the gas diffusion layer 3 can be improved more effectively, and the mechanical strength of the gas diffusion layer 3 can be further improved. As a result, the gas diffusion layer 3 can have sufficient strength as a self-supporting film. In addition, by making the average fiber diameter of the conductive fiber 32 300 nm or less, the diameter will not become too large, so the pore volume in the porous component 30 can be easily and sufficiently ensured. As a result, the gas diffusion properties of the gas diffusion layer 3 can be further improved.

[0097] The average fiber length of the conductive fiber 32 is preferably 0.5 μm or more and 50 μm or less. By making the average fiber length of the conductive fiber 32 0.5 μm or more, the conductivity of the gas diffusion layer 3 can be improved more effectively, and the mechanical strength of the gas diffusion layer 3 can be further improved. In addition, by making the average fiber length of the conductive fiber 32 50 μm or less, the fiber will not become too long, so the conductive fiber 32 will not clump and break during manufacturing, and the gas diffusion of the gas diffusion layer 3 can be further improved.

[0098] Examples of polymeric resins 33 include PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVDF (polyvinylidene fluoride), ETFE (tetrafluoroethylene-ethylene copolymer), PCTFE (polychlorotrifluoroethylene), and PFA (polyvinyl fluoride-perfluoroalkyl vinyl ether copolymer). Among these, PTFE is preferred as the polymeric resin 33 from the viewpoints of heat resistance, water resistance, and chemical resistance. PTFE can be used in the form of a raw material, such as a dispersion or powder. Dispersions are preferred due to their excellent dispersibility.

[0099] The polymer resin 33 functions as an adhesive to bond the conductive particles 31 and conductive fibers 32 together. In addition, the polymer resin 33 is waterproof, and therefore also prevents water from being trapped in the pores inside the gas diffusion layer 3 and thus hindering gas permeation.

[0100] Furthermore, in the gas diffusion layer 3, conductive particles 31 are present in the gaps between the conductive fibers 32, and the conductive fibers 32 and conductive particles 31 can be well bonded by the fibrous polymer resin 33, so the gas diffusion layer 3 can have sufficient strength.

[0101] <Composition of composite powder used in gas diffusion layer> The composite powder used in the gas diffusion layer preferably contains 5 wt% or more and less than 35 wt% of conductive particles 31. That is, the proportion of conductive particles 31 relative to the overall gas diffusion layer 3 is preferably 5 wt% or more and less than 35 wt%. In the gas diffusion layer made of composite powder, the proportion of conductive particles 31 is 5 wt% or more, thereby ensuring that the amount of conductive particles 31 filling the gaps between the conductive fibers 32 is sufficient, and thus the volume resistivity of the gas diffusion layer 3 is not likely to become high. In addition, by having a proportion of conductive particles 31 of less than 35 wt%, the gaps between the conductive fibers 32 are not excessively reduced, thereby further improving water expulsion and gas diffusion.

[0102] The composite powder used for the gas diffusion layer preferably contains 35 wt% to 80 wt% of conductive fibers 32. That is, the proportion of conductive fibers 32 relative to the overall gas diffusion layer 3 is preferably 35 wt% to 80 wt%. In the gas diffusion layer made of the composite powder, the proportion of conductive fibers 32 is 35 wt% or more, so the gaps between the conductive fibers 32 are not excessively reduced, thus improving water expulsion and gas diffusion. Furthermore, by having a proportion of conductive fibers 32 of 80 wt% or less, the amount of particles filling the gaps between the conductive fibers 32 is sufficient, thus preventing the bulk resistivity of the gas diffusion layer 3 from becoming too high.

[0103] The composite powder used for the gas diffusion layer preferably contains 1 wt% to 40 wt% of polymeric resin 33. That is, the proportion of polymeric resin 33 relative to the total composite powder is preferably 1 wt% to 40 wt%. In the gas diffusion layer made from the composite powder, by ensuring that the proportion of polymeric resin 33 is 1 wt% or more, the polymeric resin 33 fully functions as a binder, thereby improving the tensile strength of the gas diffusion layer. Therefore, even under the pressure of gas generation and the swelling and contraction of the electrolyte membrane, the gas diffusion layer is less prone to fracture, improving the durability of the fuel cell. Furthermore, by ensuring that the proportion of polymeric resin 33 is 40 wt% or more, the volume resistivity of the gas diffusion layer is less likely to increase, thus improving battery performance.

[0104] <Gas Diffusion Layer> The gas diffusion layer 3 comprises conductive particles 31, conductive fibers 32, and polymer resin 33. It should be noted that the gas diffusion layer 3 is preferably a self-supporting membrane supported by the conductive particles 31, conductive fibers 32, and polymer resin 33. It should be noted that a self-supporting membrane refers to a membrane with a self-supporting structure.

[0105] The gas diffusion layer 3 has the following fine pores: in the Log differential pore volume distribution map determined by mercury porosimetry, there are peaks in the range of pore radius above 0.055 μm and below 0.4 μm.

[0106] Here, the fine pores inside the gas diffusion layer 3 will be explained.

[0107] The micropores inside the gas diffusion layer 3 have the following three functions. First, they diffuse the fuel gas and oxidant gas flowing in the gas flow path of the diaphragm towards the catalyst 2. Second, they control the generated water from the reaction, keeping the catalyst layer 2 and the polymer electrolyte membrane 1 moist, and allowing any remaining generated water to be rapidly discharged to the outside through the micropores. Third, when the generated water alone is insufficient to keep the catalyst 2 and the polymer electrolyte membrane 1 moist, they transport moisture from the humidified fuel gas and oxidant gas towards the catalyst layer 2 and the polymer electrolyte membrane 1, ensuring proton conductivity.

[0108] If the gas diffusion layer 3 has pores with a radius of 0.055 μm or more and 0.4 μm or less, sufficient water vapor permeability can be ensured within the pores of this size, while the permeability of condensate and mist is suppressed. Therefore, the catalyst layer 2 and the polymer electrolyte membrane 1 can be maintained in a suitable water-containing state, and any remaining moisture can be quickly discharged as water vapor.

[0109] The pores with a radius of 0.055 μm or more and 0.4 μm or less are formed by the gaps between the conductive fibers 32. Therefore, by having more conductive fibers 32 constituting the gas diffusion layer 3 than conductive particles 31, the peak value of the pore radius in the gas diffusion layer 3 can be formed in the range of 0.055 μm or more and 0.4 μm or less.

[0110] The pore volume of pores with a radius of 0.055 μm or more and 0.4 μm or less is preferably 0.60 mL / g or more. If the pore volume is less than 0.60 mL / g, gas diffusivity decreases, especially in the high current density region, resulting in reduced battery performance.

[0111] The pore volume of pores with a radius of 0.055 μm or more and 0.4 μm or less is preferably 0.80 mL / g or more. When the pore volume is 0.80 mL / g or more, under high humidification or high current density regions, the drainage path of residual generated water inside the MEA and the gas diffusion path from the separator can be adequately ensured, thereby further improving battery performance.

[0112] Furthermore, the gas diffusion layer 3 can have the following pores: in the Log differential pore volume diagram measured by mercury porosimetry, it has two peaks, with a pore volume of 0.60 mL / g or more for pores with a pore radius of 0.055 μm or more and 0.4 μm or less, and a pore volume of 0.1 mL / g or more for pores with a pore radius of 0.4 μm or more and 10 μm or less. As described above, the pores with a pore radius of 0.055 μm or more and 0.4 μm or less are formed by the gaps between the conductive fibers inside the composite powder.

[0113] On the other hand, the pores with a radius of 0.4 μm or more and 10 μm or less are pores generated by the interfaces between the composite powders, etc., and have the function of discharging condensate generated in the gap between the catalyst layer 2 and the gas diffusion layer 3 through capillary phenomenon, or condensate generated by water vapor condensation in the submicron pores of the composite powder 34 inside the gas diffusion layer 3 to the outside.

[0114] For pores with peaks in the range of 0.4 μm to 10 μm, the pore volume is 0.1 mL / g or higher. When the pore volume is less than 0.1 mL / g, the drainage of condensate generated inside the gas diffusion layer sometimes decreases, resulting in reduced gas diffusivity.

[0115] It should be noted that the method for determining the pore size distribution and pore volume of the gas diffusion layer 3 can be performed by mercury porosimetry after drying the gas diffusion layer 3 at 120°C for 4 hours as a pretreatment.

[0116] Porosity The volume ratio of voids larger than 10 μm inside the gas diffusion layer 3, i.e., the porosity, is less than 0.5% (volume %).

[0117] In the voids larger than 10 μm inside the gas diffusion layer, water vapor condenses and remains as liquid water, becoming the main reason for hindering gas diffusion. Therefore, by making the porosity of the voids larger than 10 μm inside the gas diffusion layer 3 less than 0.5%, liquid water is less likely to remain inside the gas diffusion layer, which improves gas diffusion, especially during power generation in high current density regions.

[0118] Here, the reason why the porosity of the voids with a size of 10 μm or more inside the gas diffusion layer 3 is less than 0.5% will be explained.

[0119] In conventional carbon paper and carbon felt substrates with MPL (Metal-Plastic Composite) layers, the substrate contains voids ranging from several μm to tens of μm in size, which act as gaps between the carbon fibers, making it easy for liquid water to accumulate. On the other hand, MPL layers are formed by coating a mixture of carbon black and PTFE onto the substrate surface using a mold or sprayer, resulting in pores with a diameter of tens of nm, representing the gaps between primary aggregates (aggregates) of the carbon black. However, when forming MPL layers using molds or sprayers, numerous voids larger than 10 μm are formed within the MPL due to substrate unevenness, coating defects, and solvent shrinkage during drying.

[0120] On the other hand, the gas diffusion layer 3 of this disclosure is obtained by rolling a composite powder with an average porosity of 50% to 98% by volume and a deformation strength of 1 kPa to 60 kPa by a roller. The powder has a high porosity, but since it is a composite powder that is easily deformable, the powder particles are tightly packed together by rolling, which can significantly reduce the number of voids larger than 10 μm.

[0121] It should be noted that the porosity of voids larger than 10 μm within the gas diffusion layer was determined using the following method.

[0122] Methods: Observation using X-ray CT Device: Xradia 620 Versa (manufactured by Carl Zeiss) Tube voltage: 80kV Observation field of view: approximately 1.0 mm (resolution: 1 μm / pixel) Porosity calculation: The X-ray CT image was binarized using ImageJ to calculate the volume of voids larger than 10 μm and the volume outside the voids. The porosity (volume %) inside the GDL was calculated as (volume of voids larger than 10 μm) / (volume of voids larger than 10 μm + volume outside the voids). Additionally, the porosity (area %), representing the proportion of the area of ​​voids larger than 10 μm exposed on the surface of the gas diffusion layer, was calculated as (area of ​​voids larger than 10 μm exposed on the surface of the gas diffusion layer) / (surface area of ​​the gas diffusion layer).

[0123] <Membrane Electrode Assembly: MEA> Figure 12 This is a schematic cross-sectional view showing the cross-sectional structure of the polymer electrolyte fuel cell unit involved in Embodiment 1.

[0124] The membrane electrode assembly (MEA) 20 has a polymer electrolyte membrane 1, a catalyst layer 2, and a gas diffusion layer 3. An anode catalyst layer 2a and a cathode catalyst layer 2b (together forming catalyst layer 2) are formed on both sides of the polymer electrolyte membrane 1, which selectively transports hydrogen ions. An anode-side gas diffusion layer 3a and a cathode-side gas diffusion layer 3b (together forming gas diffusion layer 3) are respectively disposed on its outer side.

[0125] The polymeric electrolyte membrane 1 may be made of, for example, a perfluorocarbon sulfonate polymer, but there are no particular limitations as long as it has proton conductivity.

[0126] Catalyst layer 2 can be a layer containing carbon materials carrying catalyst particles such as platinum and a polymer electrolyte.

[0127] <Fuel Cells> Figure 13 This is a schematic perspective view showing the structure of the polymer electrolyte type fuel cell stack according to Embodiment 1.

[0128] like Figure 13 As shown, the fuel cell 100 is formed by stacking one or more battery cells 10 as basic units, and by using current collectors 11, insulating plates 12 and end plates 13 arranged on both sides of the stacked battery cells 10 to compress and fasten them under a specified load.

[0129] The current collector 11 is formed of a gas-impermeable conductive material. For example, copper or brass is used for the current collector 11. A current extraction terminal (not shown) is provided on the current collector 11, from which current is extracted during power generation.

[0130] The insulating board 12 is formed of an insulating material such as resin. For example, fluorinated resin or PPS resin is used for the insulating board 12.

[0131] The end plate 13 secures and holds the stacked battery cell 10, current collector 11, and insulating plate 12 with a specified load via a pressure mechanism (not shown). The end plate 13 is made of a high-rigidity metal material such as steel.

[0132] Figure 12 This is a schematic cross-sectional view showing the cross-sectional structure of the battery cell 10. In the battery cell 10, a membrane electrode assembly (hereinafter also referred to as MEA) 20 is sandwiched between the anode-side separator 4a and the cathode-side separator 4b. Hereinafter, the anode-side separator 4a and the cathode-side separator 4b will be referred to together as separator 4. Other constituent elements will also be described in the same way when multiple constituent elements are described together.

[0133] A fluid flow path 5 is formed in the diaphragm 4. A fluid flow path 5 for fuel gas is formed in the anode-side diaphragm 4a. A fluid flow path 5 for oxidant gas is formed in the cathode-side diaphragm 4b. The diaphragm 4 can be made of carbon-based or metallic materials.

[0134] The fluid flow path 5 is a groove formed in the diaphragm 4. Ribs 6 are provided around the fluid flow path 5.

[0135] Example The embodiments of this disclosure will be described below.

[0136] (Material) The materials used in the manufacture of the test pieces of each embodiment and comparative example are described below.

[0137] [Conductive Particle 31] • Li-400 (Made by Denka) [Conductive Fiber 32] • VGCF (Showa Denko system, VGCF-H) [Polymer Resin 33] • PTFE dispersion (manufactured by Daikin), average particle size 0.25 μm [Method for manufacturing composite powder] First, use Figures 1-5 The method for manufacturing the composite powder of Embodiment 1 will be described.

[0138] Figure 1 This is a flowchart illustrating an example of the method for manufacturing composite powder using the freeze granulation method in Example 1 of this invention.

[0139] Figure 2 This is a schematic diagram of a spray freezing granulation device.

[0140] Figure 3 This is a flowchart illustrating an example of the method for manufacturing composite powder using the freeze-pulverization method in Embodiment 2.

[0141] Figure 4 This is a flowchart illustrating an example of the method for manufacturing composite powder using the freeze-pulverization method in Embodiment 3.

[0142] Figure 5 This is a flowchart illustrating an example of the method for manufacturing composite powder using the freeze-pulverization method in Embodiment 4 of this invention.

[0143] [Method for manufacturing composite powder in Example 1-1] The following example illustrates the method for manufacturing the composite powder in Example 1-1. Figure 1 As illustrated, the method for manufacturing the composite powder according to this embodiment includes: step (S1), mixing polymer resin 33, conductive fiber 32, and conductive particles 31 with a dispersing solvent (here, water and surfactant); step (S2), spraying the mixed solution into a cooling chamber to form a frozen composite powder; and step (S3), sublimating the freezing solvent within the frozen particles to form a dried composite powder. It should be noted that... Figure 1 The flowchart shows the manufacturing method of the composite powder of Examples 1-2 described later, which includes a heating step (S4), but the heating step (S4) is not necessary.

[0144] The method for manufacturing the composite powder of Example 1-1 will be described in more detail below.

[0145] In step S1, carbon particles 31, carbon fibers 32, and PTFE 33 are mixed in a ratio of 15:65:20 wt%, and then water and a surfactant are used to prepare a solution with a solid component concentration of 20 wt%. This solution is then mixed using a planetary mixer. Regarding the solid component concentration, a sprayable viscosity of 5000 mPa·s and a temperature below 25°C are acceptable, preferably 1 wt% or more and 50 wt% or less. In mixing the solution in step S1, in addition to a planetary mixer, a mixing agitator, kneader, roller mill, etc., can be used. Furthermore, by appropriately selecting the solid component concentration and mixing method, the mixing state and the fiberization of PTFE can be controlled.

[0146] In step S2, Figure 2In the spray freezing granulation apparatus shown, a mixed solution is sprayed at a feed rate of 5 kg / h within a -50°C cooling chamber to produce frozen particles. The spraying mechanism can be, for example, a two-fluid nozzle, a single-fluid pressurized nozzle, a three-fluid nozzle, a four-fluid nozzle, an ultrasonic nozzle, or a centrifugal sprayer. The cooling medium used in the cooling chamber can be liquid nitrogen, nitrogen gas, liquid argon, argon gas, liquid helium, helium gas, dry ice, carbon dioxide gas, or a cooling gas obtained by cooling the atmosphere. Furthermore, the cooling temperature only needs to be below the freezing temperature of the solution used; considering cooling efficiency, a temperature of -10°C to -150°C is preferred. Additionally, the particle size of the frozen particles depends on the raw materials, the concentration of the solid components in the solution, the spraying mechanism, and the cooling temperature, and can be controlled from 1 to 1000 μm in terms of average particle size D50.

[0147] In step S3, the frozen dispersion solvent, i.e., water, contained in the frozen particles is removed by sublimation at an insoluble temperature under reduced pressure. Sublimation can be performed under reduced pressure or normal pressure as long as the frozen water remains insoluble. By sublimating the water, the space in which the water exists can be preserved, allowing for the production of powders with large pores. If the water content is below 5 wt%, it is difficult to agglomerate and can be treated as a powder.

[0148] [Methods for manufacturing composite powders in Examples 1-2] The following example illustrates the manufacturing method of the composite powder in Examples 1-2. Figure 1 As illustrated, the method for manufacturing composite powder according to this embodiment includes: step (S1), mixing polymer resin 33, conductive fiber 32 and conductive particles 31 with a dispersing solvent (here, water and surfactant); step (S2), spraying the mixed solution into a cooling chamber to form frozen composite powder; step (S3), sublimating the freezing solvent in the frozen particles to form dried composite powder; and a further heat treatment step (S4).

[0149] The method for manufacturing the composite powders of Examples 1-2 will be described in more detail below.

[0150] Steps 1-3 are performed in the same manner as in Example 1-1.

[0151] In step S4, the moisture-removed composite powder is further heated at 300°C for 3 hours. Heating softens the PTFE, making it easier to fiberize. Simultaneously, the thermal expansion of the carbon particles 31 and carbon fibers 32 promotes PTFE fiberization, and by maintaining the thermally expanded carbon particles 31 and carbon fibers 32, the porosity can be further increased. PTFE fiberization can be controlled by adjusting the time between 100°C (for easy fiberization) and 400°C (for PTFE decomposition).

[0152] [Method for manufacturing composite powder in Example 2] The following example illustrates the manufacturing method of the composite powder in Example 2. Figure 3 As illustrated, the method for manufacturing the composite powder in this embodiment includes: a step (S11) of stirring and mixing a polymer resin 33, a conductive fiber 32 and a conductive particle 31 with a dispersing solvent (here, water and a surfactant) to obtain a compound; a step (S12) of obtaining a frozen compound formed by freezing the above compound; a freeze-pulverizing step (S13) of pulverizing the frozen compound to produce frozen particles; a step (S14) of sublimating the freezing solvent in the frozen particles to form a dry composite material; and a step (S15) of further performing a heat treatment.

[0153] The method for manufacturing composite powders will be explained in more detail below.

[0154] In step S11, carbon particles 31, carbon fibers 32, and PTFE 33 are mixed in a ratio of 15:65:20 wt%, and then water and a surfactant are used to prepare a compound with a solid content concentration of 30 wt%. This compound is then mixed using a planetary mixer. The solid content concentration is preferably 20-80 wt%, more preferably 20-50 wt%. By reducing the solid content concentration, the solvent is filled into the voids, resulting in a powder with larger voids. In the mixing of the solution in step S1, in addition to a planetary mixer, a mixing agitator, a kneader, a roller mill, etc., can be used. Furthermore, by appropriately selecting the solid content concentration, mixing method, etc., the mixing state and the fiberization of PTFE can be controlled.

[0155] In step S12, the mixture is immersed in liquid nitrogen and frozen to produce a frozen mixture. The cooling medium used for freezing can be liquid nitrogen, nitrogen gas, liquid argon, argon gas, liquid helium, helium gas, dry ice, carbon dioxide gas, or a cooling gas obtained by cooling the atmosphere, a cryogenic chamber, etc. Depending on the solvent, the cooling temperature only needs to be below the freezing temperature of the solution used; however, considering cooling efficiency, -10°C to -150°C is preferred. Furthermore, the freezing rate can be slow cooling or rapid freezing. Slow cooling allows the ice crystals to crystallize larger, creating larger pores.

[0156] In step S13, the frozen mixture is pulverized using a cooled pulverizer to produce frozen particles. Pulverization methods can include impact pulverization using needles or hammers, cutting pulverization, rotary pulverization, etc. Furthermore, the cooling medium used in the pulverization process can be liquid nitrogen, nitrogen gas, liquid argon, argon gas, liquid helium, helium gas, dry ice, carbon dioxide gas, or a cooling gas obtained by cooling the atmosphere. Additionally, the average particle size of the frozen particles depends on the raw materials, freezing state, pulverization method, and pulverization conditions, and can be controlled from 1 to 1000 μm in terms of average particle size D50.

[0157] In step S14, the frozen water contained in the frozen particles is removed by sublimation at an insoluble temperature under reduced pressure. Sublimation can be performed under reduced pressure or normal pressure as long as the water remains insoluble. By sublimating the water, the space where the water exists is preserved, allowing for the production of powders with large pores. If the water content is below 5 wt%, it is difficult to agglomerate and can be treated as a powder.

[0158] In step S15, the powder, after moisture removal, is further heated at 300°C for 3 hours. Heating softens the PTFE, making it easier to fiberize. Simultaneously, the thermal expansion of the carbon particles 31 and carbon fibers 32 promotes PTFE fiberization. At the same time, maintaining the thermal expansion of the carbon particles 31 and carbon fibers 32 further increases the porosity. PTFE fiberization can be controlled by adjusting the time between 100°C (for easy fiberization) and 400°C (for PTFE decomposition).

[0159] [Method for manufacturing composite powder in Example 3] The following example illustrates the manufacturing method of the composite powder in Example 3. Figure 4 As illustrated, the method for manufacturing the composite powder in this embodiment 3 includes: a step (S11) of stirring and mixing a polymer resin 33, a conductive fiber 32 and a conductive particle 31 with a dispersing solvent (here, water and a surfactant) to obtain a compound; a step (S12) of obtaining a frozen compound obtained by freezing the above compound; a step (S13) of pulverizing the frozen compound to obtain frozen powder; and a step (S24) of heating the frozen powder under atmospheric pressure to obtain a dried composite powder.

[0160] Steps S11-13 are performed in the same manner as in Example 2.

[0161] In step S24, the frozen powder is heated at 300°C for 3 hours under atmospheric pressure to remove the solvent, thereby obtaining a dry composite powder. The heating temperature and time can be set to 100-400°C and 0.1-6 hours, which are sufficient to remove the solvent and prevent PTFE from melting. By removing moisture through a liquid state, surface tension acts on the particle surface, resulting in smooth particle shapes and improved flowability.

[0162] [Method for manufacturing composite powder in Example 4] The following example illustrates the method for manufacturing the composite powder in Example 4. Figure 5 The example includes: a step of mixing a frozen compound, which is prepared in the same manner as in Embodiments 2 and 3, with a polymer resin to obtain a frozen mixture (S33); a step of pulverizing the frozen mixture to obtain a frozen composite powder (S34); a step of sublimating the freezing solvent in the frozen composite powder to form a dry composite powder (S35); and a step of further heating to obtain a dry composite powder (S36).

[0163] Steps S11 and S12 are performed in the same way as in embodiments 2 and 3.

[0164] In step S33, the frozen compound and polymer resin 33 are mixed while cooling to prepare a frozen mixture, with the solid content of the frozen compound being equal to the polymer resin at a ratio of 90:10 wt%. The polymer resin can be a resin obtained by freezing dry powder or dispersion. The preferred mixing ratio is 99:1 to 70:30 wt% (solid content of the compound: polymer resin). If the polymer resin ratio is too high, the membrane resistance increases when formed; conversely, if the ratio is too low, the membrane strength decreases.

[0165] In step S34, the frozen mixture is pulverized using a cooled pulverizer to obtain frozen powder. Pulverization methods can include impact pulverizers using needles or hammers, cutting blade pulverizers, rotary blade pulverizers, and shredders. Furthermore, the cooling medium used in the pulverization process can be liquid nitrogen, nitrogen gas, liquid argon, argon gas, liquid helium, helium gas, dry ice, carbon dioxide gas, or a cooling gas obtained by cooling the atmosphere. By simultaneously freezing and pulverizing the frozen mixture of polymer resin and frozen compound, a pulverized frozen compound and a frozen mixture of polymer resin with suppressed fibrosis can be obtained. Additionally, by applying shear force during pulverization, the pulverized polymer resin can adhere to the surface of the pulverized frozen compound. Furthermore, the average particle size of the frozen powder depends on the raw materials, freezing state, pulverization method, and pulverization conditions, and can be controlled to be 1~1000 μm in terms of average particle size D50.

[0166] In step S35, the frozen water contained in the frozen composite powder is removed by sublimation at an insoluble temperature under reduced pressure. Sublimation can be performed under reduced pressure or normal pressure as long as the water remains insoluble. By sublimating the water, the space where the water exists can be preserved, allowing the production of powders with large pores. If the water content is below 5 wt%, it is difficult to agglomerate and can be treated as a powder.

[0167] In step S36, the frozen composite powder, after moisture removal, is further heated at 300°C for 3 hours. Heating softens the PTFE, making it easier to fiberize. Simultaneously, the thermal expansion of the carbon particles 31 and carbon fibers 32 promotes PTFE fiberization. At the same time, maintaining the thermal expansion of the carbon particles 31 and carbon fibers 32 further increases the porosity. By controlling the time between 100°C (for easy PTFE fiberization) and 400°C (for PTFE decomposition), the fiberization of PTFE can be controlled.

[0168] Alternatively, it can be dried in S36 instead of S35.

[0169] [Refer to the method for manufacturing composite powder in Example 1] First, surfactants and dispersing solvents were added to carbon particles 31, carbon fibers 32, and PTFE 33 in a ratio of 15:65:20 wt%, and the mixture was kneaded using a planetary mixer. Next, the kneaded mixture was calcined in a hot air furnace at 300°C for 4 hours to remove the surfactants and dispersing solvents. Then, the calcined mixture was pulverized using a shredder to produce composite powder.

[0170] [Manufacturing method of gas diffusion layer] The composite powder was fed into a roller press and sheeted with a pressing force of 0.5 ton / cm to create a gas diffusion layer. The thickness of the gas diffusion layer was 160 μm.

[0171] The raw material composition of the examples and reference examples, as well as the evaluation results of the resulting composite powders and gas diffusion layers, are shown in Table 1 below.

[0172] [Table 1]

[0173] (Manufacturing of a single-cell evaluation unit) A catalyst-supported carbon (TEC10E50E manufactured by Tanaka Precious Metals Industry Co., Ltd., 50% by mass of Pt) with platinum particles as electrode catalyst supported on carbon powder and a hydrogen ion-conducting polymeric electrolyte solution (Nafion dispersion) was dispersed in a mixed dispersion medium of ethanol and water (mass ratio 1:1) to prepare an ink for forming a cathode catalyst layer. The polymeric electrolyte was added in such a way that the mass of the polymeric electrolyte in the catalyst layer after coating was 0.4 times the mass of the catalyst-supported carbon.

[0174] The obtained cathode catalyst layer forming ink was spray-coated onto one surface of a polymer electrolyte membrane (GSII, 120mm × 120mm, manufactured by Gore-Tex Co., Ltd., Japan), with a platinum loading of 0.3 mg / cm³. 2 The cathode catalyst layer is formed in a manner that...

[0175] Next, similar to the cathode electrode, a platinum loading of 0.1 mg / cm³ was applied. 2 The anode catalyst layer is formed in a certain way.

[0176] Carbon paper manufactured by SGL was used as the gas diffusion layer on the anode side.

[0177] The gas diffusion layers of Example 1 and Reference Example 1 were bonded to the cathode catalyst layer as cathode-side gas diffusion layers. Additionally, the anode-side gas diffusion layer was bonded to the anode catalyst layer. Thus, an MEA was obtained.

[0178] Next, a fuel cell as a prototype was fabricated using a membrane with flow paths. First, the fabricated MEA was clamped between an anode-side membrane (with fluid flow paths for fuel gas supply and cooling water flow paths) and a cathode-side membrane (with gas flow paths for oxidant gas supply). Fluororubber gaskets were then placed around the anode and cathode, thus creating a single cell. The effective electrode (anode or cathode) area was 36 cm². 2 This single cell was used as a test piece. (Evaluation Test) The following evaluation tests were conducted on Examples 1-2 and Reference Example 1.

[0179] [Unit Voltage] The cell voltage was measured under the following conditions. The cell temperature of the test piece was controlled at 75°C. Hydrogen was supplied as fuel gas to the anode gas path, and air was supplied to the cathode gas path. The stoichiometry of hydrogen was 1.5, and the stoichiometry of air was 1.8. Both the fuel gas and air were humidified to a dew point of 75°C for high-humidification power generation and 45°C for low-humidification power generation before being supplied to the cell. The current density was measured from 0 A / cm². 2 Up to 2.0A / cm 2Every 0.5A / cm 2 Hold for 3 minutes and measure 2.0 A / cm. 2 The unit voltage at that time.

[0180] Figure 6 The image is an SEM image of the composite powder in Example 1. The maximum radius A of the circumscribed circle, i.e. the largest geometric circle, is 3.2 μm, and the minimum radius B of the inscribed circle, i.e. the smallest geometric circle, is 3.1 μm. Their difference (AB) is 0.1 μm. Therefore, the sphericity (AB) / A is 0.03, which satisfies the above equation (1).

[0181] Figure 7 Referring to the SEM image of the composite powder in Example 1, the maximum radius A of the circumscribed circle, i.e. the largest geometric circle, is 3.22 μm, and the minimum radius B of the inscribed circle, i.e. the smallest geometric circle, is 1.4 μm. Their difference (AB) is 1.82 μm. Therefore, the sphericity (AB) / A is 0.56, which does not satisfy the above equation (1).

[0182] Figure 8 This is a SEM image showing unfibrillated PTFE particles in the composite powder of Example 1. Figure 9 This is a SEM image showing unfibrillated PTFE particles in the composite powder of Reference Example 1.

[0183] like Figure 8 As shown, in the composite powder of Example 1, there are more unfibrillated PTFE particles, and the degree of fibrillation is less than 70%. On the other hand, as... Figure 9 As shown, in the composite powder of Reference Example 1, there are fewer unfibrillated PTFE particles and the degree of fibrillation exceeds 70%.

[0184] Figure 10 This is a diagram showing the pore distribution of the composite powders in Examples 1-2.

[0185] The average particle size D50 of the composite powders in Examples 1-2 is 80 μm, such as Figure 10 As shown, the average porosity, calculated from the pore volume of pores with pore radii of 0.001–100 μm within the powder body, is 95%, and the pore volume of pores with pore radii of 0.055–0.4 μm within the powder body is 1.1 mL / g. By rolling the composite powder from Example 1, the pore volume with a peak pore radius of 0.1–0.3 μm and a pore volume of pore radii of 0.055–0.4 μm is 0.75 mL / g.

[0186] Figure 11 This is a diagram showing the pore distribution of the composite powder in Reference Example 1.

[0187] The average particle size D50 of the composite powder in Example 1 is 65 μm, such as Figure 11 As shown, the pore volume of the fine pores with a pore radius of 0.055~0.4 μm inside the powder body is 0.72 mL / g. By rolling the composite powder of Reference Example 1, the peak pore radius is 0.1~0.3 μm, and the pore volume of the fine pores with a pore radius of 0.055~0.4 μm is 0.61 mL / g.

[0188] Therefore, compared with Reference Example 1, Example 1 confirms that the unit voltage during high humidification power generation is increased from 0.598 to 0.602V, while maintaining a substantially equivalent unit voltage of 0.620V during low humidification power generation.

[0189] Industrial applicability The use of the gas diffusion layer of the composite powder disclosed herein is particularly useful as a component for use in fuel cells, and can be applied to applications such as residential cogeneration systems, automotive fuel cells, mobile fuel cells, and backup fuel cells.

[0190] Explanation of reference numerals in the attached figures 100 fuel cells 1. Polymer electrolyte membrane 2 Catalyst layer 2a Anode catalyst layer 2b Cathode catalyst layer 3. Gas diffusion layer 3a Anode-side gas diffusion layer 3b Gas diffusion layer for cathode 4. Diaphragm 4a Anode-side diaphragm 4b Cathode-side diaphragm 5 Fluid flow path 6. Ribs 10 battery cells 11. Current collector 12 Insulation Board 13 end plates 20 Membrane electrode assembly 31 Conductive particles 32 Conductive Fibers 33. Polymer Resins

Claims

1. A composite powder comprising at least one of a polymer resin, a fiber, and a particle, wherein the average porosity of the composite powder is 50% by volume or more and 98% by volume or less.

2. The composite powder according to claim 1, wherein, When the composite powder is sandwiched between two concentric geometric circles (the circumscribed circle and the inscribed circle) in a cross-section, the average value of the sphericity (AB) obtained by dividing the difference (AB) between the maximum radius A of the largest geometric circle (the circumscribed circle of the composite powder, i.e., the largest geometric circle) and the minimum radius B of the smallest geometric circle (the inscribed circle of the composite powder, i.e., the smallest geometric circle) by the maximum radius A satisfies the following equation (1): (AB) / A≤0.5…Equation (1).

3. The composite powder according to claim 1, wherein, The degree of fibrosis of the polymer resin is below 80%.

4. The composite powder according to claim 1, wherein, The cohesion of the composite powder is below 30%.

5. The composite powder according to claim 1, wherein, The deformation strength of the composite powder is above 1 kPa and below 60 kPa.

6. The composite powder according to claim 1, wherein, The composite powder has fine pores inside, and in the Log differential pore volume diagram determined by mercury intrusion porosimetry, the pore volume of pores with a radius of 0.055 μm or more and 0.4 μm or less is 0.60 mL / g or more.

7. The composite powder according to claim 1, wherein, The polymer resin contains polytetrafluoroethylene.

8. The composite powder according to claim 7, wherein, The polytetrafluoroethylene contains more than 1 wt% and less than 40 wt%.

9. The composite powder according to claim 1, wherein, The particles are conductive particles, and the fibers are conductive fibers.

10. The composite powder according to claim 9, wherein, The conductive particles comprise 5 wt% or more and less than 35 wt%, and the conductive fibers comprise 35 wt% or more and less than 80 wt%.

11. The composite powder according to claim 1, wherein, The average particle size of the composite powder is greater than 1 μm and less than 1000 μm.

12. A gas diffusion layer having a porous membrane comprising the composite powder of any one of claims 1 to 11.

13. A gas diffusion layer having a porous membrane comprising the composite powder according to any one of claims 1 to 11, having pores such that, in a Log differential pore volume diagram determined by mercury intrusion porosimetry, the pore volume of pores with a radius of 0.055 μm or more and 0.4 μm or less is 0.60 mL / g or more.

14. A gas diffusion layer having a porous membrane comprising the composite powder according to any one of claims 1 to 11, having pores such that, in a Log differential pore volume diagram determined by mercury intrusion porosimetry, there are two peaks, the pore volume of pores with a radius of 0.055 μm or more and 0.4 μm or less is 0.60 mL / g or more, and the pore volume of pores with a radius of 0.4 μm or more and 10 μm or less is 0.10 mL / g or more.

15. A gas diffusion layer having a porous membrane comprising the composite powder of any one of claims 1 to 11, wherein the porosity of the interior at a depth of 10 μm or more is less than 0.5%.

16. A membrane electrode assembly comprising the gas diffusion layer of claim 12, a pair of electrodes, and an electrolyte membrane.

17. A fuel cell comprising the membrane electrode assembly and current collector as described in claim 16.

18. A method for manufacturing a composite powder, comprising: The process of stirring and mixing a polymer resin with at least one of the fibers and particles using a dispersing solvent to obtain a mixed solution of the polymer resin and at least one of the fibers and particles; The process of spraying the mixed solution as droplets into a chamber cooled to a temperature below the melting point of the dispersed solvent, thereby obtaining a composite powder formed by freezing the droplets; and The process of sublimating the dispersing solvent contained in the frozen composite powder to obtain a dried composite powder.

19. The method for manufacturing composite powder according to claim 18, wherein, The polymer resin contains polytetrafluoroethylene.

20. The method for manufacturing composite powder according to claim 18, wherein, It also includes a step of further heating the dried composite powder at a temperature above 100°C and below 400°C.

21. A method for manufacturing a composite powder, comprising: The process of stirring and mixing at least one of the polymer resins, fibers and particles with a dispersing solvent to obtain a compound of at least one of the polymer resins, fibers and particles; A process for obtaining a frozen compound by freezing the compound; The frozen mixture is pulverized to obtain frozen powder; and The drying process of removing the dispersing solvent from the frozen powder to obtain the composite powder.

22. The method for manufacturing composite powder according to claim 21, wherein, The moisture content of the mixture is 20-80%.

23. The method for manufacturing composite powder according to claim 21, wherein, The temperature in the freezing and pulverizing process is -150~-10℃.

24. The method for manufacturing composite powder according to claim 21, wherein, In the drying process, the dispersing solvent contained in the frozen powder is sublimated to obtain the dried composite powder.

25. The method for manufacturing composite powder according to claim 21, wherein, In the drying process, the temperature is further heated to above 100°C and below 400°C.

26. The method for manufacturing composite powder according to claim 21, wherein, The drying process is a method of evaporating water by heating under atmospheric pressure.

27. The method for manufacturing composite powder according to claim 26, wherein, In the drying process, the drying temperature is above 100°C and below 400°C.

28. A method for manufacturing a composite powder, comprising: The process of stirring and mixing at least one of the polymer resins, fibers and particles with a dispersing solvent to obtain a compound of at least one of the polymer resins, fibers and particles; A process for obtaining a frozen compound by freezing the compound; The process of obtaining a frozen mixture by mixing the frozen compound with a polymer resin; The frozen mixture is pulverized to obtain a frozen composite powder through a freeze-pulverization process; and The drying process of removing the dispersing solvent from the frozen composite powder to obtain the composite powder.

29. A method for manufacturing a gas diffusion layer, comprising the following steps: rolling the composite powder according to any one of claims 1 to 11 into a sheet to obtain a gas diffusion layer comprising the sheet.

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