Gas diffusion layer and fuel cell comprising same

Abstract

Disclosed are a gas diffusion layer and a fuel cell comprising same. The gas diffusion layer has a horizontal gas permeability (InP) of 10 to 100×10-12m2 and a vertical gas permeability (ThP) of 0.02 to 1×10}-12m2.

Description

Gas diffusion layer and fuel cell containing the same

[0001] A gas diffusion layer and a fuel cell including the same are disclosed. More specifically, a gas diffusion layer having a controlled ratio of horizontal gas permeability to vertical gas permeability and a fuel cell including the same are disclosed.

[0002] A fuel cell is a device that produces electrical energy by electrochemically reacting fuel and oxygen. Since it is not a heat engine, it has a high efficiency exceeding the Carnot limit efficiency and emits only water vapor as a byproduct.

[0003] Polymer electrolyte membrane fuel cells (PEMFCs) have lower operating temperatures and higher efficiency than other types of fuel cells, higher current and power densities, shorter start-up times, and faster response to load changes.

[0004] In addition, the polymer electrolyte membrane fuel cell includes a membrane electrode assembly (MEA) in which a fuel electrode (anode) and an air electrode (cathode) are formed by bonding gas diffusion layers (GDLs) on both sides of a catalyst coated membrane (CCM) on which a catalyst layer is applied on both sides of a polymer electrolyte membrane.

[0005] Bipolar plates are attached to both sides of the membrane electrode assembly (MEA). Here, the gas diffusion layer (GDL) is manufactured by coating a microporous layer (MPL) on a carbon substrate made of a porous carbon material such as carbon cloth, carbon felt, and carbon paper.

[0006] The microporous layer is composed of various sizes of carbon particles such as flake graphite, spherical graphite, acetylene black, furnace black, activated carbon, and CNT, and a fluorine-based resin such as PTFE, FEP, and PFA that binds them. The fluorine-based resin not only acts as a binder that binds the carbon particles, but also discharges water generated in the catalyst layer toward the separator due to its water-repellent properties. In other words, the microporous layer uses the principle of osmosis to evenly distribute hydrogen and air between the small pores and transport them to the catalyst layer, thereby causing a uniform electrochemical reaction in the catalyst layer. At this time, the interfacial structure of the catalyst layer and the microporous layer directly affects the electrochemical performance. The catalyst layer includes nano-sized precious metal catalyst particles such as platinum and ruthenium supported on a carbon support, and an ionomer, a proton-conducting polymer that binds them. The catalyst layer, where oxidation / reduction reactions occur, possesses hydrophilic properties due to the hydrogen ion conductivity of the ionomer, while simultaneously possessing hydrophobic properties due to the porous structure of the support. The interfacial structure between the catalyst layer and the microporous layer is crucial for ensuring smooth gas flow within the catalyst layer and rapid discharge of generated water toward the microporous layer.

[0007] In particular, the electrochemical performance of MEA stacks is significantly improving, driven by advancements in MEA manufacturing technology and the introduction of bipolar plates that facilitate gas discharge. Consequently, the energy density of MEA stacks has increased at the same operating voltage, and the operating current density has even doubled. However, as the current density increases, the required amounts of hydrogen and air also increase, leading to a proportional increase in water production.

[0008] Conventional MPLs disperse carbon particles and fluorinated resin in a dispersion medium consisting of a solvent and a dispersant, and apply the resulting slurry to a carbon substrate to a consistent thickness. The dispersant is then removed through a drying and sintering process, followed by melting the fluorinated resin to achieve water repellency. Because these conventional MPLs are formed using a mixture of carbon particles and fluorinated resin in equal proportions, they exhibit consistent water repellency throughout the MPL's thickness. The water generated through the electrochemical reaction concentrates at the interface between the catalyst layer and the MPL, and from there, it sequentially migrates toward the carbon substrate and the separator along the MPL's thickness, before being discharged to the outside. However, as the current density increases, if the water concentrated at the catalyst layer and MPL interface cannot be rapidly discharged toward the GDL and separator, the water overflows at the interface between the catalyst layer and the MPL, forming a water layer. This sequentially floods the MPL-impregnated section and the carbon substrate section. This impedes the supply of reaction gases to the catalyst layer, rapidly degrading the electrochemical performance of the MEA stack. Additionally, the water layer formed at the interface between the catalyst layer and the MPL can induce a reverse potential and a corrosion reaction of the carbon, rather than an electrochemical reaction that generates electricity. This can cause corrosion of the catalyst support and the MPL, leading to increased resistance and reduced durability.

[0009] One embodiment of the present invention provides a gas diffusion layer in which the ratio of horizontal gas permeability to vertical gas permeability is controlled.

[0010] Another embodiment of the present invention provides a fuel cell comprising the gas diffusion layer.

[0011] One aspect of the present invention is:

[0012] Horizontal gas permeability (InP) is 10 to 100×10 -12 m 2 , and the vertical gas permeability (ThP) is 0.02 to 1×10 -12 m 2It provides a gas diffusion layer.

[0013] The above horizontal gas permeability (InP) and the above vertical gas permeability (ThP) can satisfy the following mathematical equation 1:

[0014] [Mathematical Formula 1]

[0015] 10 ≤ InP / ThP ≤5,000.

[0016] The above gas diffusion layer may include a carbon substrate and a microporous layer disposed on the carbon substrate.

[0017] The above carbon substrate may include carbon fibers, carbon powder, and carbides of thermosetting resins.

[0018] The above carbon substrate may have pores having an average diameter of 200 μm or less.

[0019] The above microporous layer may include carbon particles, a water-repellent binder resin, and a thickener.

[0020] The above microporous layer may have pores with a major diameter of 100 to 300 nm.

[0021] Another aspect of the present invention is:

[0022] A fuel cell including the above gas diffusion layer is provided.

[0023] A gas diffusion layer according to one embodiment of the present invention has a ratio of horizontal gas permeability to vertical gas permeability in a controlled range, thereby enabling a fuel cell including the gas diffusion layer to exhibit high performance even when operated in a low-humidity, high-temperature, and pressurized environment.

[0024] Figure 1 is a drawing for explaining a method for measuring horizontal gas permeability.

[0025] Figure 2 is a drawing for explaining a method for measuring vertical gas permeability.

[0026] Hereinafter, a gas diffusion layer and a fuel cell including the same according to one embodiment of the present invention will be described in detail.

[0027] In this specification, “in-plane gas permeability of a gas diffusion layer” means gas permeability passing in a direction parallel to the smooth surface (widest surface) of the gas diffusion layer, and “through-plane gas permeability of a gas diffusion layer” means gas permeability passing in a direction perpendicular to the smooth surface of the gas diffusion layer.

[0028] Also in this specification, the Mean Pore Diameter is the average value of the total pore size, calculated as the weighted average of the pore size and the volume of the pore:

[0029] Average diameter (D) mean ) = (Σ(di * Vi)) / (Σ(Vi))

[0030] Here, di represents the size of a specific pore, and Vi represents the amount of mercury intrusion into that pore. The average diameter reflects the overall pore size, but if the data is asymmetric or has a multimodal distribution, it may not clearly indicate the size of a specific pore.

[0031] In addition, in this specification, "modal pore diameter" means the pore size corresponding to the highest peak in the pore distribution curve, which can be understood as the same concept as the mode. Specifically, the pore size on the x-axis corresponding to the maximum value on the y-axis (Log Differential Intrusion) in the measured pore size distribution data is defined as the modal diameter. The modal diameter indicates the dominant pore size in the pore size distribution, which is closely related to the functional characteristics under actual operating conditions. On the other hand, the average diameter is calculated based on the entire pore size distribution, and therefore may not accurately reflect the actual dominant pore size in the multimodal distribution.

[0032] For example, the following pattern can be observed in the pore size distribution:

[0033] (1) Single peak distribution: If a distinct peak appears around 100 nm in the pore size distribution curve, the x-axis value of the peak is defined as the major diameter.

[0034] (2) Multimodal distribution: When peaks appear at around 100 nm and 300 to 600 nm, the x-axis value of the peak position with a larger y-axis (Log Differential Intrusion) value is defined as the major diameter.

[0035] [Main diameter measurement method]

[0036] Mercury Intrusion Porosimetry (MIP) is used to measure the major diameter. The MIP method for measuring the major diameter is as follows:

[0037] (1) Mercury penetration into the pores: Mercury is penetrated into the pores by applying external pressure.

[0038] (2) Calculation of the relationship between pressure and pore diameter: The relationship between pressure (P) and pore diameter (d) is calculated according to the Washburn equation:

[0039] d = -(4 × surface tension × cos contact angle) / P

[0040] Here, “surface tension” represents the surface tension of mercury, and “contact angle” represents the contact angle between mercury and the pore wall.

[0041] (3) Data processing: The measured data is processed in the following format:

[0042] x-axis: pore size (logarithmic scale)

[0043] Y-axis: Mercury injection amount by pore size (Log Differential Intrusion)

[0044]

[0045] The gas diffusion layer according to one embodiment of the present invention has a horizontal air permeability (InP) of 10 to 100×10 -12m 2 , and the vertical air permeability (ThP) is 0.02 to 1×10 -12 m 2 If the horizontal air permeability (InP) and the vertical air permeability (ThP) are each within the above range, the fuel cell including the gas diffusion layer can exhibit high performance even when operated in a low-humidity, high-temperature, and pressurized environment.

[0046] The above horizontal air permeability (InP) can be appropriately controlled by adjusting the weight ratio of the thermosetting resin to the carbon fibers included in the carbon substrate, which will be described later. Specifically, as the weight ratio of the thermosetting resin to the carbon fibers included in the carbon substrate decreases, the horizontal air permeability (InP) can increase.

[0047] The above vertical air permeability (ThP) can be appropriately controlled by adjusting the content ratio of the thickener added during the formation of the microporous layer, which will be described later. Specifically, as the content ratio of the thickener added during the formation of the microporous layer decreases, the vertical air permeability (ThP) can increase.

[0048] The above horizontal air permeability (InP) and the above vertical air permeability (ThP) can satisfy the following mathematical expression 1:

[0049] [Mathematical Formula 1]

[0050] 10 ≤ InP / ThP ≤5,000.

[0051] When the horizontal air permeability (InP) and the vertical air permeability (ThP) satisfy the above mathematical expression 1, the fuel cell including the gas diffusion layer can exhibit high performance even when operated in a low-humidity, high-temperature, and pressurized environment.

[0052] The above gas diffusion layer may include a carbon substrate and a microporous layer disposed on the carbon substrate.

[0053] The above carbon substrate may include carbon fibers, carbon powder, and carbides of thermosetting resins.

[0054] The above carbon fibers may have a length of 3 mm to 25 mm or 3 mm to 30 mm, and one type, two types, or three or more types of carbon fibers may be mixed and used.

[0055] The carbon powder may include activated carbon, carbon black, acetylene black, Ketjen black, Denka black, carbon whiskers, activated carbon fibers, vapor-grown carbon fibers (VGCF), carbon aerosol, carbon nanotubes, carbon nanofibers, carbon nanohorns, natural graphite, synthetic graphite, or a combination thereof.

[0056] The thermosetting resin may include a phenol resin, a polyurethane resin, a polyimide resin, a melamine resin, an epoxy resin, or a combination thereof.

[0057] The above carbon substrate may be carbon paper, carbon fiber, carbon felt or carbon sheet, but the present invention is not limited thereto.

[0058] Additionally, the carbon substrate may have pores having an average diameter of 200 μm or less.

[0059] Additionally, the carbon substrate may further include a water-repellent binder resin described below.

[0060] The above microporous layer may include carbon particles, a water-repellent binder resin, and a thickener.

[0061] The carbon particles may include activated carbon, carbon black, acetylene black, Ketjen black, Denka black, carbon whiskers, activated carbon fibers, vapor-grown carbon fibers (VGCF), carbon aerosols, carbon nanotubes, carbon nanofibers, carbon nanohorns, natural graphite, synthetic graphite, or a combination thereof.

[0062] The above water-repellent binder resin may include polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, a fluorinated ethylene-propylene (FEP) copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkoxy (PFA), polychlorotrifluoroethylene, an ethylene-tetrafluoroethylene (ETFE) copolymer, polyfluorovinylidene (PVDF), a PVDF-based copolymer, or a combination thereof.

[0063] The thickener may include cellulose, methylcellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch, agar, azodicarbonamide, calcium, polyacrylate, polymethacrylate, polymethylmethacrylate, polyvinyl alcohol, polyvinylpyrrolidone, polyisobutene, polytetrahydrofuran, or a combination thereof.

[0064] As long as the above thickener performs a thickening function, it can be used without limitation in the form of a thickener such as solid, liquid, spherical, or fibrous.

[0065] The above microporous layer may have pores with a major diameter of 100 to 300 nm.

[0066] Another aspect of the present invention provides a fuel cell comprising the gas diffusion layer described above.

[0067] Hereinafter, a method for manufacturing a gas diffusion layer according to one embodiment of the present invention will be described in detail.

[0068] (1) Manufacturing of carbon substrates

[0069] 1) Carbon fiber structure (carbon fiber pre-web) formation process

[0070] First, a carbon fiber web is formed. To this end, a conventional papermaking method using wet dispersion can be used to obtain a carbon fiber structure with an isotropic structure in which carbon fibers are randomly arranged, i.e., a carbon fiber preweb. Specifically, the carbon fiber preweb can be manufactured using a wet nonwoven process. That is, a single type or two or more types of carbon fibers with different lengths are sufficiently dispersed and mixed in a dispersion medium in an opening machine, and the carbon fiber dispersion thus obtained is supplied to a paper machine and laminated on a wire mesh (belt) of the paper machine. At this time, the carbon fiber dispersion may include a dispersant to lower the surface energy of the carbon fibers, but this is not essential. The dispersion may further include binder short fibers in addition to the carbon fibers. The above binder single fiber may be one or two or more types selected from the group consisting of, for example, polyvinyl alcohol (PVA) single fiber, low-melting point (LM) polyester single fiber, polyethylene (PE) single fiber, polypropylene (PP) single fiber, cellulose single fiber, and pitch single fiber.

[0071] At this time, the areal weight and thickness of the carbon fibers can be controlled by the amount of carbon fibers supplied to the paper machine and the papermaking speed. The structure of the carbon fiber pre-web manufactured in this way may be identical between the contact surface and the opposite surface that contacts the wire mesh, or it may have a structure with a gradient of pores in the thickness direction.

[0072] 2) Thermosetting resin impregnation and molding curing process

[0073] Next, a mixture containing a thermosetting resin and carbon powder is impregnated into the carbon fiber preweb and dried. The carbon powder serves to increase the electrical conductivity between the thermosetting resin and the binder single fibers and the carbide and the carbon fibers. Specifically, after the carbon fiber preweb forming process, the carbon fiber structure (carbon fiber preweb) is impregnated with a slurry containing a thermosetting resin (optionally, binder single fibers) and carbon powder and then dried to obtain an impregnated carbon fiber preweb.

[0074] The thermosetting resin may be, for example, one type selected from among epoxy resins or phenolic resins, specifically, novolac or resol type phenol formaldehyde resins, or a mixture of two or more types thereof. Examples of applicable thermosetting resins include those commercially available under the trade names or product names of KC-510 (Gangnam Hwaseong, Korea), TD-787 (Gangnam Hwaseong, Korea), KC-5024 (Gangnam Hwaseong, Korea), KC-3750, KC-5565, Bekelite PF786SW2 (Hexion), PF7870SW (Hexion), PF786SW2 (Hexion). However, the present invention is not limited to the above products, and a resol or novolac type phenolic resin having a carbon residue of 10 wt% or more after the carbonization process can be particularly applicable.

[0075] The above carbon powder may be at least one selected from the group consisting of carbon black, Ketjen black, acetylene black, furnace black and thermal black, graphite or thermally expandable graphite, carbon aerosol, carbon nanotubes, carbon nanofibers, carbon nanohorn powder and natural or synthetic graphite powder. Specific examples thereof include natural graphite powder or synthetic graphite powder commercially available under trade names or product names such as Cond 5, 8 (Samjung C&G, Korea), SFG4 (Immerys, EU) and ES350F5 (Samsung C&G, Korea); Or expanded graphite, etc. can be applied, and carbon black can be obtained under the product name 150G (Immerys, EU) or Vulcan Xc-72R (Cabot, USA), Ketjen black (Akzonovel), Denka black, carbon whiskers, etc., and in addition, carbon nanofibers, vapor-grown carbon fibers (VGCF), etc. can be applied, and are not limited to the above products.

[0076] The dispersion medium of the above slurry mainly uses water, and in some cases, a dispersant may be used to increase the dispersing power.

[0077] The above dispersant may be at least one selected from the group consisting of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants, or a combination thereof. Specifically, the dispersant may be, but is not limited to, cationic surfactants such as alkyltrimethylammonium salts, alkyldimethylbenzylammonium salts, and phosphate amine salts; anionic surfactants such as polyoxyalkylene alkyl ethers, polyoxyethylene derivatives, alkylamine oxides, and polyoxyalkylene glycols; amphoteric surfactants such as alanine, imidazolium betaine, amidepropyl betaine, and aminodipropionate; and nonionic surfactants such as alkylaryl polyether alcohol. Commercially available anionic surfactants include HOSTAPAL and EMULSOGEN from Clariant, Dispersbyk from BYK, and Dispers from TEGO, while nonionic surfactants include Triton X-100. The dispersant used should be a substance that can be thermally decomposed and removed at a temperature of 250 to 400°C.

[0078] The weight ratio of the thermosetting resin to the carbon powder can be controlled to be 95:5 to 60:40, and preferably 90:10 to 70:30.

[0079] After impregnating and drying the carbon fiber structure (carbon fiber pre-web) as above, the carbon fiber web is subjected to a temperature of 100 to 200°C and a pressure of 3 to 20 kgf / cm 2 By applying heat and pressure under the pressure of a thermosetting resin, the thermosetting resin is cured, and the resulting carbon fiber web is compressed and flattened. In this molding curing process, two or more sheets of dried carbon fiber web, for example, 2 to 6 sheets, specifically 2 to 3 sheets, are overlapped and laminated, and then molding cured, thereby increasing the density of the gas diffusion layer, and a flat and level high-density carbon fiber web laminate can be obtained.

[0080] 3) Carbonization and graphitization process

[0081] Next, the carbon substrate is heated in an inert atmosphere at a carbonization temperature of 500 to 1,000°C without applying a load to the carbon fiber web laminate to carbonize the thermosetting resin and the binder single fibers. Continuing the carbonization process, in a continuous process, the carbonized carbon fiber web laminate is heated in an inert atmosphere at a graphitization temperature of 1,600 to 2,800°C without applying a load to the carbon fiber web laminate to graphitize the carbonized carbon fiber web laminate to obtain a carbon substrate for a gas diffusion layer. Specifically, the carbon fiber web laminate is heated at a temperature of 100 to 200°C and a pressure of 3 to 20 kgf / cm. 2 By applying heat and pressure under the pressure of a thermosetting resin, the carbon fiber web laminate is cured and the carbon fiber web laminate is compressed and flattened. Specifically, the carbon fiber web laminate that has undergone the above-described heat curing process is subjected to a high-temperature heat treatment in an inert atmosphere, thereby carbonizing and graphitizing the thermoplastic resin, etc. contained in the carbon fiber web laminate, thereby obtaining a carbon substrate for a gas diffusion layer.

[0082] 4) Water-repellent treatment of carbon substrate

[0083] The carbon substrate manufactured above can be treated to be water-repellent by impregnating an aqueous dispersion of a water-repellent binder resin into the substrate and then drying it.

[0084] (2) Preparation of composition for forming microporous layer

[0085] A composition for forming a microporous layer is prepared by mixing a water-repellent binder resin, carbon powder, a dispersant, a thickener, and a solvent. Since the water-repellent binder resin, the carbon powder, the dispersant, and the thickener are each the same as those described above, a detailed description thereof will be omitted herein.

[0086] The composition for forming the above microporous layer can be manufactured, for example, through a step of (a) adding carbon powder to a solution containing a dispersant and milling or mixing at high speed to homogeneously disperse the carbon powder; and (b) adding a water-repellent binder resin to the mixture obtained in step (a) and mixing at low speed to homogeneously disperse the carbon powder.

[0087] For example, the composition for forming a microporous layer may include 1 to 5 parts by weight of a dispersant, 7 to 30 parts by weight of carbon powder, and 3 to 20 parts by weight of a water-repellent binder resin, based on 100 parts by weight of the total solid content of the composition for forming a microporous layer. The amount of the solvent may be 45 to 89 parts by weight of the solvent, based on 100 parts by weight of the total solid content of the composition for forming a microporous layer.

[0088] The above solvent may be, for example, a basic solvent such as water, n-propanol, or isopropanol, and may further be used by mixing a high-boiling-point solvent such as ethylene glycol, propylene glycol, dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), or butyl acetate. For example, a high-boiling-point solvent may be mixed with water and used.

[0089] In order to manufacture the composition for forming the microporous layer, after adding the water-repellent binder resin, the water-repellent binder resin may be modified by the dispersant in the composition for forming the microporous layer or by the shear force of the mixer when mixed, so the types of the dispersant and mixer can be appropriately selected.

[0090] (3) Manufacturing of gas diffusion layer

[0091] The composition for forming a microporous layer manufactured in the above (2) is applied onto the water-repellent treated carbon substrate and then dried to manufacture a gas diffusion layer in which a microporous layer is formed on the water-repellent treated carbon substrate.

[0092] Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

[0093] Example 1: Preparation of a gas diffusion layer

[0094] (1) Manufacturing of carbon substrates

[0095] 70 g of first carbon fibers (manufactured by Toray, product number: T300) having a carbon content of 95 wt%, a diameter of 7 μm, and a fiber length of about 6 mm, 30 g of second carbon fibers (manufactured by Toray, product number: T300) having a carbon content of 95 wt%, a diameter of 7 μm, and a fiber length of 12 mm, 1 g of a dispersant (Triton X-100), and 5 g of polyvinyl alcohol (PVA) short fibers (manufactured by Nycon, product number: RMS702) having a fiber length of 6 mm were added to 200 L of water, and uniformly dispersed for about 20 minutes by mechanical mixing at a speed of 1,500 rpm to obtain a dispersion for forming a carbon fiber preweb. After that, the dispersion was put into the agitator of the paper machine, and 300 L of water was additionally added and stirred, and then the dispersion was supplied to an inclined fourdrinier device equipped with a 120# wire mesh, and the water was removed with a vacuum pump. In this manner, by passing the wire mesh through the dispersion, carbon fibers were deposited on the wire mesh to form a nonwoven carbon fiber preweb. Thereafter, a slurry containing a phenol resin solution (weight average molecular weight: 4,000, solvent: N-methyl-2-pyrrolidone) and graphite particles (manufacturer: Asbury Carbons, model name: 5991) (phenol resin / graphite particle weight ratio = 50 / 50, total solid content in the mixture: about 20 wt%) was dispersed in the carbon fiber preweb at a concentration of 4 mg / cm 2was impregnated with an amount of . Subsequently, the carbon fiber preweb impregnated with the phenol resin and graphite particles was heated at a temperature of 1,400°C in a nitrogen atmosphere to carbonize the phenol resin and PVA components, thereby obtaining a carbon fiber web (thickness: 150 μm) containing a carbide that binds the carbon fibers. Thereafter, the carbon fiber web was immersed in a 5 wt% PTFE aqueous dispersion (Du Pont) so that the PTFE content became 10 wt% of the carbon substrate, and after drying, heat-treated at 350°C for 30 minutes in an air atmosphere to obtain a water-repellent carbon substrate.

[0096] (2) Preparation of composition for forming microporous layer

[0097] 1000 g of deionized water, 20 g of dispersant (Triton X-100), 82 g of carbon black (Vulcan XC-72), 20 g of thermally expandable graphite (Ecophit(R) G), 8 g of 60 wt% polytetrafluoroethylene (PTFE) aqueous dispersion, and 3.06 g of thickener (hydroxypropylmethylcellulose) (3 wt% based on the total weight of carbon black and thermally expandable graphite) were added and mechanically mixed to obtain a composition for forming a microporous layer.

[0098] (3) Manufacturing of gas diffusion layer

[0099] The composition for a microporous layer manufactured in the above (2) was applied to the water-repellent carbon substrate manufactured in the above (1), dried, and then heat-treated at 350°C for 30 minutes in an air atmosphere to obtain a gas diffusion layer.

[0100] Example 2: Preparation of a gas diffusion layer

[0101] (1) In the process of manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 5.2 mg / cm 2 A gas diffusion layer was manufactured in the same manner as in Example 1, except that the method was changed to .

[0102] Example 3: Preparation of a gas diffusion layer

[0103] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 2.5 mg / cm 2 A gas diffusion layer was manufactured in the same manner as in Example 1, except that the method was changed to .

[0104] Example 4: Preparation of a gas diffusion layer

[0105] (2) When preparing a composition for forming a microporous layer, a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methylcellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite).

[0106] Example 5: Preparation of a gas diffusion layer

[0107] (2) When preparing a composition for forming a microporous layer, a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite).

[0108] Example 6: Preparation of a gas diffusion layer

[0109] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 5.2 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite).

[0110] Example 7: Preparation of a gas diffusion layer

[0111] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 2.5 mg / cm 2(2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite).

[0112] Example 8: Preparation of a gas diffusion layer

[0113] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 2.5 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite).

[0114] Example 9: Preparation of a gas diffusion layer

[0115] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 5.2 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite).

[0116] Reference Example 1: Manufacturing of a gas diffusion layer

[0117] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 6.5 mg / cm 2(2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite).

[0118] Reference Example 2: Manufacturing of a gas diffusion layer

[0119] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 5.2 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.02 g (1 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 1.02 g (1 wt% based on the total weight of carbon black and thermally expandable graphite).

[0120] Reference Example 3: Manufacturing of a gas diffusion layer

[0121] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 2.5 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.02 g (1 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 1.02 g (1 wt% based on the total weight of carbon black and thermally expandable graphite).

[0122] Reference Example 4: Manufacturing of a gas diffusion layer

[0123] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 1 mg / cm 2(2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 1.53 g (1.5 wt% based on the total weight of carbon black and thermally expandable graphite).

[0124] Reference Example 5: Manufacturing of a gas diffusion layer

[0125] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 1 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite).

[0126] Reference Example 6: Manufacturing of a gas diffusion layer

[0127] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 2.5 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 8.16 g (8 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 8.16 g (8 wt% based on the total weight of carbon black and thermally expandable graphite).

[0128] Reference Example 7: Manufacturing of a gas diffusion layer

[0129] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 5.2 mg / cm 2(2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 8.16 g (8 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 8.16 g (8 wt% based on the total weight of carbon black and thermally expandable graphite).

[0130] Reference Example 8: Manufacturing of a gas diffusion layer

[0131] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 6.5 mg / cm 2 (2) When preparing the composition for forming a microporous layer, the amount of thickener (hydroxypropyl methylcellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite), and a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methyl cellulose) added was changed to 6.12 g (6 wt% based on the total weight of carbon black and thermally expandable graphite).

[0132] Reference Example 9: Manufacturing of a gas diffusion layer

[0133] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 6.5 mg / cm 2 A gas diffusion layer was manufactured in the same manner as in Example 1, except that the method was changed to .

[0134] Reference Example 10: Manufacturing of a gas diffusion layer

[0135] (1) When manufacturing a carbon substrate, the amount of slurry of phenol resin and graphite particles impregnated into the carbon fiber pre-web is 1 mg / cm 2 A gas diffusion layer was manufactured in the same manner as in Example 1, except that the method was changed to .

[0136] Reference Example 11: Manufacturing of a gas diffusion layer

[0137] (2) When preparing a composition for forming a microporous layer, a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methylcellulose) added was changed to 1.02 g (1 wt% based on the total weight of carbon black and thermally expandable graphite).

[0138] Reference Example 12: Manufacturing of a gas diffusion layer

[0139] (2) When preparing a composition for forming a microporous layer, a gas diffusion layer was prepared in the same manner as in Example 1, except that the amount of thickener (hydroxypropyl methylcellulose) added was changed to 8.16 g (8 wt% based on the total weight of carbon black and thermally expandable graphite).

[0140]

[0141] Evaluation Example 1: Evaluation of gas permeability of a gas diffusion layer

[0142] The gas permeability of each gas diffusion layer manufactured in Examples 1 to 9 and Reference Examples 1 to 12 was evaluated using the following method, and the results are shown in Table 2 below.

[0143] (1) Horizontal gas permeability (InP) (m 2 ): The horizontal gas permeability (InP) of the gas diffusion layer (GDL) was evaluated using the following method.

[0144] 1) First, as illustrated in (a) of Fig. 1, a gas diffusion layer (GDL) was cut into a donut shape to prepare a GDL sample. Fig. 1 (a) shows a plan view (top), a cross-sectional view (center), and a perspective view (bottom) of the GDL sample.

[0145] 2) Then, as shown in (b) of Fig. 1, the GDL sample was placed on the lower plate of the CPRT-10L equipment of Living Care Co., Ltd. The CPRT-10L equipment of Living Care Co., Ltd. is a device configured to measure the thickness, resistance, and differential pressure changes of the GDL sample according to the pressure applied to the GDL sample (see Korean Patent No. 10-0902316).

[0146] 3) Then, as shown in (c) of Fig. 1, 50 sccm (standard cubic centimeter per minute) of dry air was flown while applying a pressure (P) of 1 MPa to the GDL sample through the upper plate, and the differential pressure (△P) between the inner hole of the GDL sample (i.e., the inner hole of the donut) and the outside was measured.

[0147] 4) The above differential pressure (△P) was applied to Darcy's law expressed in the following mathematical equation 2 to obtain the horizontal gas permeability (InP).

[0148] 5) Repeat the above steps 2) to 4) for 10 GDL samples to determine the gas permeability (k g ) (i.e., horizontal gas permeability (InP)) was evaluated, and the average value was taken.

[0149] [Equation 2]

[0150] U g = Q / A = - k g / μ g × △P

[0151] In the above mathematical expression 2, U g is the instantaneous flux of the gas (unit: m / s), and Q is the flow rate of the gas (unit: m 3 / s), and A is the cross-sectional area of ​​the GDL sample through which gas permeates after pressure (P) is applied (unit: m 2 ) and k g is the gas permeability (unit: m 2 ) and μ g is the kinematic viscosity of the gas (Pa·s), and △P is the differential pressure (unit: Pa) applied to the GDL sample. Here, the gas is dry air.

[0152] (2) Vertical gas permeability (ThP) (m 2 ): The vertical gas permeability (ThP) of the gas diffusion layer (GDL) was evaluated using the following method.

[0153] 1) First, as shown in (a) of Fig. 2, a gas diffusion layer (GDL) was cut into a cylindrical shape to prepare a GDL sample. Fig. 2 (a) shows a plan view (top), a cross-sectional view (center), and a perspective view (bottom) of the GDL sample.

[0154] 2) Then, as shown in (b) of Fig. 2, the GDL sample was placed on the lower plate of the CPRT-10L equipment of Living Care Co., Ltd.

[0155] 3) Then, as shown in (c) of Fig. 2, 50 sccm (standard cubic centimeter per minute) of dry air was flowed through the upper plate while applying a pressure (P) of 10 bar to the GDL sample, and the differential pressure (△P) between the lower and upper parts of the GDL sample was measured.

[0156] 4) Apply the above differential pressure (△P) to Darcy's law expressed in the above mathematical formula 2 to obtain the gas permeability (k g ) (i.e., vertical gas permeability (ThP)) was obtained.

[0157] 5) The vertical gas permeability (ThP) was evaluated by repeating the above processes 2) to 4) for 10 GDL samples, and the average value was taken.

[0158] Evaluation Example 2: Performance Evaluation of Fuel Cells

[0159] A total of 21 fuel cell cells were manufactured, each including the gas diffusion layers manufactured in Examples 1 to 9 and Reference Examples 1 to 12. The configuration and operating conditions of the fuel cell cells are summarized in Table 1 below. Thereafter, the 21 fuel cell cells were manufactured at 1.0 A / cm 2 and 2.0 / cm 2 The cell voltage was measured by driving each cell at a current density of 1.0 A / cm, and the results are shown in Table 2 below. In addition, 1.0 A / cm 2Cell voltage (V1) at a current density of 2.0 A / cm 2 The difference between the cell voltages (V2) at the current density (△V=V2-V1) is shown in Table 2 below.

[0160] Sample CCM (catalyst coated membrane) Active Area Cell Temp. Examples 1 to 9 / Reference Examples 1 to 12 Gore product 25 cm 2 80℃Relative Humidity Anode / CathodeH2 / O2molar ratioBack Pressure Anode / CathodeCompressibility50% / 50%1.3 / 1.6150kPa / 130kPa72.5%

[0161]

[0162] InP×10 12 (m 2 )ThP×10 12 (m 2 )InP / ThP cell voltage (@ 1.0A / cm 2 )Cell voltage (@ 2.0A / cm 2)△V(Volt) Example 1500.252000.7240.6230.101 Example 2100.25400.7250.6220.103 Example 31000.254000.7230.6210.102 Example 4500.022,5000.7240.6190.105 Example 5501500.7230.6170.106 Example 6101100.7220.6160.106 Example 710011000.7210.6150.106 Example 81000.025,0000.7260.6190.107 Example 9100.025000.7240.6170.107 Reference Example 17170.7210.5980.123 Reference Example 210250.7170.5820.135 Reference Example 31002500.7110.5670.144 Reference Example 420012000.7120.5890.123 Reference Example 52000.0210,0000.7250.5970.128 Reference Example 61000.0110,0000.7270.5750.152 Reference Example 7100.011,0000.7280.5660.162 Reference Example 870.023500.7260.5760.150Reference example 970.25280.7230.5990.124Reference example 102000.258000.7210.5910.130Reference example 11502250.7110.5770.134Reference example 12500.015,0000.7260.5710.155

[0163]

[0164] Referring to Table 2 above, when the gas diffusion layers manufactured in Examples 1 to 9 were used, the efficiency was 2.0 A / cm compared to when the gas diffusion layers manufactured in Reference Examples 1 to 12 were used. 2 The cell voltage (V2) at a current density of 1.0 A / cm is high. 2 Cell voltage (V1) at a current density of 2.0 A / cm 2 The difference between the cell voltages (V2) at the current density (△V=V2-V1) was found to be small. 2.0 A / cm 2 The cell voltage (V2) at a current density of 1.0 A / cm is high. 2 Cell voltage (V1) at a current density of 2.0 A / cm 2The smaller the difference (△V = V2-V1) between the cell voltages (V2) at the current density, the better the performance of the fuel cell.

[0165] While preferred embodiments of the present invention have been described above with reference to the drawings and examples, these are merely exemplary, and those skilled in the art will appreciate that various modifications and equivalent other embodiments are possible. Accordingly, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. Horizontal gas permeability (InP) is 10~100×10 -12 m 2 , and the vertical gas permeability (ThP) is 0.02 to 1×10 -12 m 2 Gas diffusion layer.

2. In paragraph 1, A gas diffusion layer in which the horizontal gas permeability (InP) and the vertical gas permeability (ThP) satisfy the following mathematical expression 1: [Mathematical Formula 1] 10 ≤ InP / ThP ≤5,000.

3. In paragraph 1, A gas diffusion layer comprising a carbon substrate and a microporous layer disposed on the carbon substrate.

4. In paragraph 3, The above carbon substrate is a gas diffusion layer including carbon fibers, carbon powder and carbide of a thermosetting resin.

5. In paragraph 3, The above carbon substrate is a gas diffusion layer having pores with an average diameter of 200㎛ or less.

6. In paragraph 3, The above microporous layer is a gas diffusion layer containing carbon particles, a water-repellent binder resin, and a thickener.

7. In paragraph 3, The above microporous layer is a gas diffusion layer having pores with a main diameter of 100 to 300 nm.

8. A fuel cell comprising a gas diffusion layer according to any one of claims 1 to 7.

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