Fuel cell unit cell

Abstract

The present invention relates to a fuel cell unit cell. A fuel cell unit cell according to one embodiment of the present invention may include a membrane electrode assembly portion comprising a membrane electrode assembly, a separator portion disposed opposite to the membrane electrode assembly portion, and a bonding film portion interposed between an outer periphery region of the membrane electrode assembly portion and a corresponding region of the separator portion to heat-fuse bond the membrane electrode assembly portion and the separator portion. The bonding film portion has a multilayer structure including a first skin layer, a core layer, and a second skin layer formed integrally by co-extrusion, wherein the core layer provides electrical insulation between the membrane electrode assembly portion and the separator portion, the first skin layer is heat-fused bonded to the separator portion, and the second skin layer is heat-fused bonded to the membrane electrode assembly portion, the bonding film portion includes a sealing pattern to form an airtight line in the outer periphery region of the membrane electrode assembly portion, and the separator portion may include a flat surface in which no groove processing is formed in the bonding region where the bonding film portion is heat-fused.

Description

Technology Field

[0001] The present invention relates to a fuel cell unit cell, and more specifically, to a fuel cell unit cell in which a multilayer co-extruded bonding film is interposed in the outer periphery region between a membrane electrode assembly and a separator plate and heat-fused, thereby replacing the gasket function with the bonding film and enabling unit cell stacking. Background Technology

[0003] Polymer Electrolyte Fuel Cell (PEMFC) stacks are typically manufactured by stacking and connecting multiple components, such as membrane electrode assemblies (MEAs), gas diffusion layers (GDLs), gaskets, and bipolar plates. In this structure, sealing is primarily provided by gaskets, which function to prevent the leakage of reaction gases within the stack while simultaneously electrically insulating the electrodes from the electrolyte.

[0004] However, conventional stack stacking manufacturing methods are subdivided into minimum units such as GDL, gasket, catalyst layer, and electrolyte membrane, which increases the number of parts to be managed during the assembly process and makes it prone to alignment errors, mixing, and deviations in fastening conditions during stacking. In particular, in existing graphite PEMFC stacks, hydrogen leakage due to gasket tolerances and damage to bipolar plates due to manufacturing errors occur, which are major impediments to improving mass production capabilities.

[0005] In addition, since gaskets are exposed to reaction gases, cooling water, humidified environments, and temperature changes, chemical durability, thermal durability, and sufficient mechanical strength are required.

[0006] Nevertheless, the risk of leakage is cited as a drawback of conventional gasket materials (e.g., rubber, silicone, etc.), and achieving an optimal design that satisfies target performance is difficult because elasticity, tensile strength, wear resistance, and chemical resistance vary by material. Furthermore, gas leakage prevention and insulation effects are linked to the gasket's compression ratio (thickness / fastening load / surface pressure), which can result in a trade-off relationship; thus, design and process control are required to maintain an appropriate compression ratio.

[0007] In other words, if a deviation in fastening load or accumulated tolerance occurs during the assembly process, damage to parts (e.g., breakage of separator) or performance degradation due to over-compression may occur in some cells, while sealing failure (gas leakage) due to insufficient compression may occur in other cells.

[0008] In addition, the existing stacking method has problems such as errors occurring during the stacking process because the gasket, catalyst, GDL, membrane, and separator must be managed separately during stacking, reduced mass production capabilities due to manufacturing errors and errors by the manufacturer, difficulty in changing stack capacity, difficult maintenance, and the risk of the entire stack being discarded in the event of failure.

[0009] Therefore, a method to resolve these problems is required. Prior art literature

[0011] Republic of Korea Registered Patent Publication No. 10-1272588 The problem to be solved

[0012] The present invention is an invention devised to solve the problems of the aforementioned prior art, and aims to provide a fuel cell unit cell that simplifies the outer circumference sealing structure between the membrane electrode assembly and the separator while ensuring airtightness, enables unit cell assembly and stacking to improve mass production efficiency, reduces the risk of gas leakage due to improved sealing, and aims to reduce production costs.

[0013] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0015] A fuel cell unit cell of the present invention for achieving the above-mentioned purpose comprises a membrane electrode assembly portion including a membrane electrode assembly, a separator portion disposed opposite to the membrane electrode assembly portion, and a bonding film portion interposed between an outer periphery region of the membrane electrode assembly portion and a corresponding region of the separator portion to heat-fuse bond the membrane electrode assembly portion and the separator portion, wherein the bonding film portion has a multilayer structure including a first skin layer, a core layer, and a second skin layer formed integrally by co-extrusion, wherein the core layer provides electrical insulation between the membrane electrode assembly portion and the separator portion, wherein the first skin layer is heat-fused bonded to the separator portion and the second skin layer is heat-fused bonded to the membrane electrode assembly portion, wherein the bonding film portion includes a sealing pattern to form an airtight line in the outer periphery region of the membrane electrode assembly portion, and wherein the separator portion includes a flat surface in which no groove processing is formed in the bonding region where the bonding film portion is heat-fused.

[0016] At this time, the first skin layer and the second skin layer may be co-extruded to have different materials, so that the bonding characteristics on the separator side and the bonding characteristics on the membrane electrode assembly side are distinguished from each other.

[0017] Additionally, the bonding film portion may further include a tie layer disposed at at least one position between the core layer and the first skin layer and between the core layer and the second skin layer.

[0018] At this time, the bonding film portion may be configured to be co-extruded such that the composition of the core layer changes compartmentally along the outer periphery region, thereby forming a plurality of compartments with different insulation functions and mechanical strengths.

[0019] In addition, the sealing pattern may include at least one of a lip pattern, a bead pattern, and a maze pattern.

[0020] At this time, the bonding film portion may be configured to include a through opening corresponding to a manifold position, and to have the sealing pattern disposed in the periphery area of ​​the through opening.

[0021] In addition, the core layer may include at least one of an insulating polymer matrix and an insulating inorganic filler dispersed in the insulating polymer matrix.

[0022] At this time, the bonded film portion may further include a barrier layer that reduces permeation to a reaction gas or cooling fluid.

[0023] In addition, the bonded film portion may further include at least one of a fiber reinforcement layer or a mesh reinforcement layer to reduce deformation due to long-term compressive load.

[0024] At this time, the bonding film portion may be configured to be pre-heat-fused to the separator portion to form a film-integrated separator and then laminated with the membrane electrode assembly portion, or to be pre-heat-fused to the membrane electrode assembly portion to form a film-integrated membrane electrode assembly and then laminated with the separator portion.

[0025] In addition, the bonding film portion may include at least one of a reference mark, a reference hole, and a reference slot for lamination alignment.

[0026] In addition, the bonded film portion may further include an identification mark recognizable by visual inspection or automatic inspection. Effects of the invention

[0028] The fuel cell unit cell of the present invention, designed to solve the aforementioned problems, reduces the risk of reaction gas leakage caused by tolerance accumulation, alignment errors, and sealing defects occurring in gasket-based stacked structures by interposing a co-extruded multilayer bonding film portion in the outer periphery region between the membrane electrode assembly portion and the separator portion and performing thermal fusion bonding. Furthermore, it stably secures electrical insulation between the membrane electrode assembly portion and the separator portion through the core layer of the bonding film portion and improves airtightness during long-term operation by forming an airtight line through a sealing pattern. Additionally, by configuring the bonding area of ​​the separator portion as a flat surface without groove processing, it enhances contact uniformity of the bonding surface and thermal fusion reliability. Moreover, by pre-thermally fusing the bonding film portion to the separator portion or the membrane electrode assembly portion to realize it as an integrated component, assembly and stacking at the unit cell level become possible, thereby providing the effects of process simplification, improved mass production capability, reduced production costs, and increased ease of maintenance.

[0029] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims. Brief explanation of the drawing

[0031] FIG. 1 is an exemplary diagram showing the overall structure of a fuel cell unit cell according to an embodiment of the present invention. FIG. 2 is an exploded perspective view showing the combination relationship of each component of a fuel cell unit cell according to an embodiment of the present invention. FIG. 3 is an exemplary diagram showing the detailed structure of a bonding film portion in a fuel cell unit cell according to an embodiment of the present invention. FIG. 4 is an exemplary diagram showing the structure of a bonded film portion to which a tie layer is applied in a fuel cell unit cell according to an embodiment of the present invention. FIG. 5 is an exemplary diagram showing a sealing pattern in a fuel cell unit cell according to an embodiment of the present invention. FIG. 6 is an exemplary diagram showing the arrangement of a through opening and a sealing pattern of a bonding film portion in a fuel cell unit cell according to an embodiment of the present invention. FIG. 7 is an exemplary diagram showing the structure of a bonded film portion to which a barrier layer, a fiber reinforcement layer, and a mesh reinforcement layer are applied in a fuel cell unit cell according to an embodiment of the present invention. FIG. 8 is an exemplary diagram showing a bonded film portion to which a reference mark, a reference hole, a reference slot, and an identification mark are applied in a fuel cell unit cell according to an embodiment of the present invention. Specific details for implementing the invention

[0032] Preferred embodiments of the present invention, in which the objectives of the present invention can be specifically realized, will be described below with reference to the attached drawings. In describing these embodiments, the same names and reference numerals are used for identical components, and additional explanations thereof will be omitted.

[0033] FIG. 1 is an exemplary diagram showing the overall structure of a fuel cell unit cell according to an embodiment of the present invention. FIG. 2 is an exploded perspective view showing the coupling relationship of each component of a fuel cell unit cell according to an embodiment of the present invention.

[0034] Referring to FIGS. 1 and 2, a fuel cell unit cell according to one embodiment of the present invention may include a membrane electrode assembly part (100), a separator part (200), and a bonding film part (300). The fuel cell unit cell may be a basic unit constituting a fuel cell stack. FIG. 1 may illustrate a fuel cell unit cell in a state where each component is assembled. FIG. 2 may illustrate an exploded perspective view showing the connection relationship of each component.

[0035] The membrane electrode assembly (100) may be a component in which an electrochemical reaction occurs in a fuel cell. The membrane electrode assembly (100) may include a membrane electrode assembly (MEA) in which an anode electrode and a cathode electrode are bonded to both sides of a polymer electrolyte membrane. The membrane electrode assembly (100) may further include a gas diffusion layer (GDL). The gas diffusion layer (GDL) may be placed on the outer side of each electrode of the membrane electrode assembly. The gas diffusion layer (GDL) may serve to uniformly diffuse the reaction gas. The gas diffusion layer (GDL) may serve to discharge the generated water. The membrane electrode assembly (100) may be placed opposite the separator (200). The outer periphery of the membrane electrode assembly part (100) can be sealed by the bonding film part (300).

[0036] In one embodiment of the present invention, the outer surface of the gas diffusion layer of the membrane electrode assembly (100) may be extended to partially overlap with the bonding film portion (300). During the heat fusion bonding process, a portion of the second skin layer (330) of the bonding film portion (300) may be melted. A portion of the melted second skin layer (330) may be impregnated into the porous structure of the gas diffusion layer. A portion of the melted second skin layer (330) may penetrate into the pores and harden. A portion of the hardened second skin layer (330) may form a mechanical interlocking effect. The mechanical interlocking effect may improve bonding strength. The impregnation structure of the second skin layer (330) may block a reaction gas leakage path formed along the plane direction of the gas diffusion layer. The impregnation structure of the second skin layer (330) may improve airtightness.

[0037] The separator section (200) may be positioned opposite the membrane electrode assembly section (100). The separator section (200) may serve as a partition separating unit cells from each other in a fuel cell stack. The separator section (200) may include a flow path that supplies hydrogen fuel and air (oxygen) to the electrodes of the membrane electrode assembly section (100). The separator section (200) may serve as a conductor that transfers electrons generated by an electrochemical reaction to an external circuit. The separator section (200) may include a cooling flow path that releases reaction heat to the outside.

[0038] The separator plate portion (200) may include a flat surface in the bonding area where the bonding film portion (300) is heat-fused. A separate groove may not be formed on the flat surface. A sealing pattern (340) that performs a sealing function may be integrally formed on the bonding film portion (300), and accordingly, the bonding area of ​​the separator plate portion (200) may be configured to be flat in correspondence with the sealing pattern (340). At this time, by applying a flat surface in which no groove is formed in the bonding area of ​​the separator plate (200), the actual contact area between the bonding film (300) and the separator plate (200) is increased and the contact pressure is uniformly distributed within the surface, thereby reducing the possibility of local overheating or non-bonding (poor contact) occurring at the bonding interface during heat fusion, and mitigating phenomena such as the bonding film (300) becoming locally thin or tearing due to the corners or steps of the groove and the concentration of creep deformation under long-term compressive loads, thereby improving the continuity of the outer sealing line and reducing the risk of leakage, and suppressing the transmission of processing tolerances and surface roughness deviations caused by groove processing to the bonding interface, thereby reducing deviations in bonding quality and improving bonding reliability. In addition, the flat bonding area structure of the separator plate (200) can simplify the processing process of the separator plate (200), and thereby bring about improved productivity and cost reduction effects.

[0039] In one embodiment of the present invention, the material constituting the separator portion (200) may have electrical conductivity, corrosion resistance, mechanical strength, and gas impermeability. For example, the separator portion (200) may be graphite, a carbon composite, surface-coated stainless steel, titanium or its alloy, an aluminum alloy, a nickel alloy, or a conductive polymer composite. However, the embodiments of the present invention are not limited thereto. Depending on the material of the separator portion (200), the material of the first skin layer (310) of the bonding film portion (300) may be selected. The selection of the material of the first skin layer (310) may be made considering the bonding strength.

[0040] The bonding film portion (300) may be interposed between the outer periphery of the membrane electrode assembly portion (100) and the corresponding area of ​​the separator portion (200). The bonding film portion (300) may serve to integrally bond the membrane electrode assembly portion (100) and the separator portion (200) through a heat fusion process that applies heat and pressure. The bonding film portion (300) may replace conventional separable gaskets. The bonding film portion (300) may perform a sealing function to prevent leakage of reaction gas. The bonding film portion (300) may perform an electrical insulation function between the membrane electrode assembly portion (100) and the separator portion (200). The integrated bonding structure may reduce the number of parts. Reducing the number of parts may simplify the assembly process. Simplifying the assembly process may lower the possibility of alignment errors. Simplifying the assembly process may improve production efficiency.

[0041] In one embodiment of the present invention, the bonding film portion (300) can be applied in two ways. In the first way, the bonding film portion (300) can be pre-heat-fused to the separator portion (200) to form a film-integrated separator. The film-integrated separator can be laminated with the membrane electrode assembly portion (100) to form a final bond. In the second way, the bonding film portion (300) can be pre-heat-fused to the membrane electrode assembly portion (100) to form a film-integrated membrane electrode assembly. The film-integrated membrane electrode assembly can be laminated with the separator portion (200) to form a final bond. The stepwise assembly method can modularize each process step. Modularization of process steps can facilitate quality control. Modularization of process steps can increase mass production capability.

[0042] In one embodiment of the present invention, the outer edge of the bonding film portion (300) may have a shape that alleviates stress concentration. For example, the outer edge may have a tapered shape in which the thickness of the outer edge gradually decreases toward the outside. Alternatively, the outer edge may have a rounded shape in which the corners are rounded. The tapered shape or the rounded shape can alleviate stress concentration at the sealing end. Stress concentration can occur due to thermal expansion and contraction or mechanical vibrations that occur during fuel cell operation. Alleviating stress concentration can prevent cracking or delamination of the bonding portion. Preventing cracking or delamination of the bonding portion can improve the long-term durability and reliability of the unit cell.

[0043] As illustrated in FIG. 1, the bonding film portion (300) may have a multilayer structure. The bonding film portion (300) may include a first skin layer (310), a core layer (320), and a second skin layer (330). The multilayer structure may be designed to impart different functions and characteristics to each layer. The multilayer structure may be formed into a single film by a co-extrusion method. The co-extrusion method may physically or chemically bond each layer. The co-extrusion method may be a method of manufacturing a multilayer film by simultaneously extruding different molten resins through a single die. The co-extrusion method may control the thickness of each layer. The co-extrusion method may secure interlayer adhesion without using interlayer adhesive.

[0044] The first skin layer (310) and the second skin layer (330) may be layers located at the outermost edge of the bonding film portion (300) and serving as an adhesive. The first skin layer (310) may be heat-fused and bonded facing the flat bonding area of ​​the separator portion (200). The second skin layer (330) may be heat-fused and bonded facing the outer periphery area of ​​the membrane electrode assembly portion (100). The first skin layer (310) and the second skin layer (330) may be melted during the heat-fusion process. The melted skin layers may seep into the surface of the opposing member to form a physical and chemical bond. The physical and chemical bond can achieve airtightness and bonding strength.

[0045] In one embodiment of the present invention, the first skin layer (310) and the second skin layer (330) may be co-extruded to have different materials. The separator portion (200) and the membrane electrode assembly portion (100) may have different materials and surface characteristics. Adhesive properties may be imparted to each bonding interface. For example, if the separator portion (200) is made of a metal material, the first skin layer (310) may be composed of a modified polyolefin-based resin having adhesion to the metal. If the outer periphery of the membrane electrode assembly portion (100) is composed of a polymer frame, the second skin layer (330) may be composed of a polyamide-based resin having compatibility with the polymer frame. Bonding reliability can be improved by imparting different bonding characteristics.

[0046] For example, the thermoplastic resin constituting the first skin layer (310) and the second skin layer (330) may be a modified polyolefin, thermoplastic polyurethane (TPU), ethylene vinyl acetate (EVA), polyamide, polyester, fluoropolymer, ionomer, or styrenic block copolymer. However, embodiments of the present invention are not limited thereto. The selection of the material may be determined by considering the material of the bonding target, the required bonding temperature and pressure, and the chemical durability against the internal environment of the fuel cell.

[0047] The core layer (320) may be located between the first skin layer (310) and the second skin layer (330). The core layer (320) may form the structural basis of the bonding film portion (300). The function of the core layer (320) may be to provide electrical insulation between the separator portion (200) and the membrane electrode assembly portion (100). Electrical insulation can prevent short circuits. The core layer (320) may provide mechanical rigidity and shape stability to the entire film. The core layer (320) may suppress deformation caused by stack fastening pressure. The core layer (320) may serve to maintain a constant sealing thickness.

[0048] The core layer (320) may be composed of a composite material in which an insulating inorganic filler is dispersed in an insulating polymer matrix. For example, the insulating polymer matrix may be polypropylene (PP), high-density polyethylene (HDPE), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyimide (PI), or epoxy resin. However, embodiments of the present invention are not limited thereto. For example, the insulating inorganic filler may be silica, alumina, boron nitride, mica, talc, glass fiber, or barium titanate particles. However, embodiments of the present invention are not limited thereto. The addition of inorganic fillers can contribute to improving dielectric breakdown strength, thermal conductivity, mechanical stiffness, and dimensional stability.

[0049] In one embodiment of the present invention, the composition of the core layer (320) may be co-extruded so as to vary compartmentally along the outer periphery. The compartmental compositional variation of the core layer (320) may be implemented using a designed co-extrusion die. The co-extrusion die may supply materials of different compositions to specific locations in the film. For example, the core layer (320) in the area around the through-opening (H) through which the stack fastening bolt passes may be composed to include a reinforcing filler content. The reinforcing filler may be glass fiber. The reinforcing filler may increase mechanical rigidity. Other areas of the core layer (320) may be composed to include an insulating ceramic filler content. The insulating ceramic filler may improve electrical insulation properties. Multiple compartments with different insulating functions and mechanical rigidity may be formed. Multiple compartments may locally improve the performance of the bonded film portion (300).

[0050] As illustrated in FIG. 2, the bonding film portion (300) may include a sealing pattern (340) on the surface of the bonding film portion (300). The sealing pattern (340) may be a linear or planar structure protruding from the surface of the bonding film portion (300). When heat-fusion bonding occurs, the sealing pattern (340) may be pressed against the surfaces of the separator portion (200) and the membrane electrode assembly portion (100). As the sealing pattern (340) is pressed, it may form local contact pressure. The contact pressure may fill in fine surface irregularities. The contact pressure may induce a tight seal. The contact pressure may form a sealing line in the outer periphery of the membrane electrode assembly portion (100). The sealing line may prevent reaction gas or cooling water from leaking out.

[0051] The shape of the sealing pattern (340) can be designed to improve airtightness performance. For example, the sealing pattern (340) may be a single or multiple lip pattern, a bead pattern with a semicircular cross-section, a labyrinth pattern that elongates the leakage path, a dotted pattern, a wave pattern, a grid pattern, or a concentric circle pattern. However, embodiments of the present invention are not limited thereto. A multi-seal structure can be formed by arranging two or more sealing lines in parallel. A multi-seal structure can ensure that other lines maintain airtightness even if a defect occurs in one line. A multi-seal structure can serve as a double safety device. A multi-seal structure can improve reliability.

[0052] A fuel cell unit cell may include a manifold for supplying and discharging reaction gas and cooling water. The manifold may correspond to a through-opening (H) shown in the drawing. The through-opening (H) may be formed by penetrating the membrane electrode assembly portion (100), the bonding film portion (300), and the separator portion (200). The bonding film portion (300) may include a through-opening (H) corresponding to the location of the manifold. To prevent each fluid from mixing with one another or leaking to the outside, a sealing structure may also be required in the periphery area of ​​the through-opening (H). A sealing pattern (340) may be arranged along the outer periphery of the unit cell. A sealing pattern (340) may also be arranged along the periphery of each through-opening (H).

[0053] FIG. 3 is an exemplary diagram showing the detailed structure of a bonding film portion in a fuel cell unit cell according to an embodiment of the present invention.

[0054] Referring to FIG. 3, the fuel cell unit cell may include a bonding film portion (300) interposed between a membrane electrode assembly portion (100) and a separator portion (200). Regarding the membrane electrode assembly portion (100), details that overlap with those described in FIG. 1 and FIG. 2 may be omitted. The membrane electrode assembly portion (100) may be placed on one side surface of the bonding film portion (300) and bonded by a heat fusion process. Regarding the separator portion (200), details that overlap with those described in FIG. 1 and FIG. 2 may also be omitted. The separator portion (200) may be placed on the other side surface of the bonding film portion (300) and configured to face the membrane electrode assembly portion (100).

[0055] The bonding film portion (300) can perform the function of physically bonding the membrane electrode assembly portion (100) and the separator portion (200) and sealing them airtightly. Additionally, the bonding film portion (300) can have the function of ensuring electrical insulation between the two components. The bonding film portion (300) may have a multilayer structure formed integrally by a co-extrusion method. Specifically, the bonding film portion (300) may include a first skin layer (310), a core layer (320), and a second skin layer (330). An interface layer in which polymer chains are mutually diffused may be formed at the boundary surface of each layer by the co-extrusion process. This interface layer can effectively prevent interlayer delamination, thereby improving the structural stability of the bonding film portion (300).

[0056] The core layer (320) is located in the center of the bonding film portion (300) and can serve to maintain the overall shape and provide mechanical rigidity. The core layer (320) may be made of a resin having a melting point higher than that of the resin constituting the first skin layer (310) and the second skin layer (330). In this case, the core layer (320) maintains a solid state even at the temperature at which the first skin layer (310) and the second skin layer (330) melt during the heat fusion bonding process, thereby suppressing deformation of the bonding film portion (300) and supporting its shape. Additionally, the core layer (320) may be formed of a material having an elastic modulus higher than that of the first skin layer (310) and the second skin layer (330). Through this, excessive thickness deformation caused by the compressive load applied during unit cell stacking can be suppressed, and a constant sealing pressure can be maintained.

[0057] Additionally, the core layer (320) may be configured to include a porous polymer structure so as to absorb the thickness tolerance of the separator plate (200) that occurs during unit cell stacking through local compressive deformation of the core layer (320). This allows for the uniformization of the fastening force applied to the entire stack, thereby preventing stress concentration in a specific unit cell, and elastically accommodating the difference in thermal expansion of each component that occurs during thermal cycle operation, thereby preserving the airtightness for a long period.

[0058] The core layer (320) can perform an electrical insulation function between the separator portion (200) and the membrane electrode assembly portion (100). To this end, the core layer (320) may be composed of an insulating polymer matrix or a composite material in which an insulating inorganic filler is dispersed in the matrix. For example, the insulating polymer matrix may be polypropylene, polyethylene, polyvinyl chloride, polystyrene, polycarbonate, polyethylene terephthalate, or polyimide. However, embodiments of the present invention are not limited thereto. The thickness ratio of the core layer (320) to the total thickness of the bonding film portion (300) may be formed to be greater than the combined thickness ratio of the first skin layer (310) and the second skin layer (330). This thickness ratio setting can contribute to sufficiently securing the dielectric breakdown voltage between the separator part (200) and the membrane electrode assembly part (100).

[0059] In one embodiment of the present invention, the bonding film portion (300) may include an additive to suppress chemical decomposition caused by peroxide radicals generated during fuel cell operation. For example, a radical scavenger containing cerium (Ce) or manganese (Mn) may be dispersed and contained within the core layer (320) or the first skin layer (310) and the second skin layer (330). Such a radical scavenger may serve to improve the long-term durability of the bonding film portion (300). Additionally, the core layer (320) may include a colored coloring agent, and the first skin layer (310) and the second skin layer (330) may be formed of a transparent or translucent material. This configuration allows for visual identification of whether the position of the core layer (320) has deformed or the state of the melt flow of the skin layer after heat fusion bonding, thereby facilitating process quality control.

[0060] The first skin layer (310) and the second skin layer (330) may each be layers located on both surfaces of the bonding film portion (300) to perform an adhesive function. The first skin layer (310) may be heat-fused to the separator portion (200), and the second skin layer (330) may be heat-fused to the membrane electrode assembly portion (100). The first skin layer (310) and the second skin layer (330) may be co-extruded to have different materials. Through this, the bonding characteristics on the separator portion (200) side and the bonding characteristics on the membrane electrode assembly portion (100) side can be optimized to match the surface characteristics of the respective substrates.

[0061] The first skin layer (310) and the second skin layer (330) can be formed from a resin having a higher Melt Flow Index (MFI) than the core layer (320). Under the thermal fusion bonding temperature conditions, the first skin layer (310) and the second skin layer (330) can have higher fluidity than the core layer (320). Therefore, the first skin layer (310) and the second skin layer (330) can easily diffuse to the surface of the separator part (200) and the membrane electrode assembly part (100) to fill fine irregularities and form strong adhesion. In particular, the first skin layer (310) can have a thickness greater than the arithmetic mean roughness (Ra) of the surface of the separator part (200). In this case, when heat-fusion bonding is performed, the molten first skin layer (310) completely fills the fine irregularities on the surface of the separator (200) and adheres to it, thereby suppressing the occurrence of pores at the interface and maximizing sealing performance.

[0062] At this time, the thickness of each layer of the bonding film portion (300) can be determined according to the required functional priority. Specifically, the thickness of the core layer (320) can be primarily set as the base thickness, taking into account the target dielectric breakdown voltage between the separator portion (200) and the membrane electrode assembly portion (100) and the shape stability when stacking. Meanwhile, it is preferable that the thicknesses of the first skin layer (310) and the second skin layer (330) be set to a minimum thickness greater than that which can completely fill the arithmetic mean roughness (Ra) or fine irregularities on the surface of the corresponding separator portion (200) or membrane electrode assembly portion (100) to form an airtight interface. Therefore, even when the surface roughness of the separator plate (200) is relatively large, the thickness of the core layer (320) is first secured to a level necessary for maintaining the insulation performance and rigidity, and then the thickness of the skin layer is adjusted to be greater than the surface roughness of the substrate in conjunction with this, thereby simultaneously satisfying insulation reliability and airtightness performance without conflict in the interlayer thickness ratio.

[0063] In one embodiment of the present invention, the material and surface characteristics of the first skin layer (310) may be designed to improve adhesion with the separator portion (200). For example, if the separator portion (200) is made of a metal material, the first skin layer (310) and the second skin layer (330) may include a polyolefin-based resin grafted with maleic anhydride. Such a resin may contribute to forming adhesion by increasing chemical affinity for the metal surface. Additionally, the surface of the first skin layer (310) may be modified by plasma treatment or corona treatment. Such surface treatment may increase wetting tension by introducing polar functional groups to the surface. As a result, adhesion may be improved by increasing surface energy. The first skin layer (310) may be designed to maintain an amorphous or low-crystalline state before thermal fusion bonding, and then increase in crystallinity during the cooling process after thermal fusion bonding. This phase change induces shrinkage stress upon cooling, which can enhance the mechanical interlocking effect and contribute to securing the final bonding strength.

[0064] FIG. 4 is an exemplary diagram showing the structure of a bonded film portion to which a tie layer is applied in a fuel cell unit cell according to an embodiment of the present invention.

[0065] Referring to FIG. 4, a detailed cross-sectional structure of a bonding film portion (300) of a fuel cell unit cell according to one embodiment of the present invention may be illustrated. Regarding the membrane electrode assembly portion (100), details that overlap with those described in FIG. 1 to 3 may be omitted. The membrane electrode assembly portion (100) may form a region where the electrochemical reaction of the fuel cell takes place. Regarding the separator portion (200), details that overlap with those described in the preceding drawings may also be omitted. The separator portion (200) may be arranged opposite the membrane electrode assembly portion (100). The separator portion (200) may perform the role of providing a flow path for reaction gas and collecting generated electricity. The bonding film portion (300) may be interposed between the membrane electrode assembly portion (100) and the separator portion (200). The bonding film portion (300) can physically bond the membrane electrode assembly portion (100) and the separator portion (200). The bonding film portion (300) can electrically insulate the membrane electrode assembly portion (100) and the separator portion (200). The bonding film portion (300) can perform the function of ensuring airtightness of the reaction region.

[0066] The bonding film portion (300) may include a first skin layer (310), a core layer (320), a second skin layer (330), and a tie layer (350). Details regarding the first skin layer (310), the core layer (320), and the second skin layer (330) that overlap with those described in FIG. 3 may be omitted. In the embodiment illustrated in FIG. 4, the bonding film portion (300) may have a five-layer structure in which a tie layer (350) is additionally disposed between the core layer (320) and the first skin layer (310), and between the core layer (320) and the second skin layer (330), respectively. The multilayer structure may be formed integrally through a co-extrusion process. Each layer may be designed to perform a unique function. By introducing the tie layer (350), the interfacial adhesion between heterogeneous materials within the bonding film portion (300) can be improved. The improved interfacial adhesion can prevent delamination. The tie layer (350) can play a role in improving overall structural stability and durability.

[0067] The tie layer (350) may be a functional adhesive layer introduced to strengthen the internal interface adhesion of the bonding film portion (300). The tie layer (350) may be located between the core layer (320) and the skin layers (310, 330), which have chemically different properties. The tie layer (350) may enhance compatibility between the two layers. The tie layer (350) may form a physical and chemical bond. For example, if the core layer (320) is composed of an engineering plastic resin for high rigidity and insulation, and the skin layers (310, 330) are composed of a polyolefin resin for thermal fusion with an external member, the two layers may have low chemical affinity and may easily peel off during direct bonding. The tie layer (350) may act as a bonding medium between dissimilar materials. The tie layer (350) may ensure the integrity of the bonding film portion (300). The tie layer (350) can ensure long-term reliability.

[0068] In one embodiment of the present invention, the tie layer (350) may be made of a modified polyolefin resin. The modified polyolefin resin constituting the tie layer (350) may include both a first functional group that reacts with the resin constituting the core layer (320) and a second functional group that reacts with the resin constituting the skin layer (310, 330). The tie layer (350) may form a chemical bond with the core layer (320) and the skin layer (310, 330). For example, the first functional group may be a carboxyl group or an epoxy group capable of reacting with the terminal group of the polyamide or polyester resin of the core layer (320). The second functional group may be an alkyl chain structure capable of forming a physical entanglement or covalent bond with the polyolefin resin of the skin layer (310, 330). The chemical bond may provide interfacial bonding strength beyond simple physical adhesion. Chemical bonding can suppress interlayer delamination even under thermal and mechanical stresses generated during fuel cell operation.

[0069] In one embodiment of the present invention, the tie layer (350) can influence the overall mechanical properties and flexibility of the bonding film portion (300). The balance between the stiffness and flexibility of the bonding film portion (300) can be controlled by adjusting the thickness, composition, elastic modulus, etc., of the tie layer (350). For example, a relatively flexible material can be applied to the tie layer (350) to improve the cushioning ability against external shocks or vibrations. The improved cushioning ability can contribute to enhancing the durability of the fuel cell stack. Conversely, the stiffness can be increased by adding a specific filler to the tie layer (350). Increased stiffness can improve the shape stability of the bonding film portion (300). Increased stiffness can reduce creep deformation under compressive loads. In addition to functioning as a simple adhesive layer, the tie layer (350) can serve as an element that realizes the multifunctionality of the bonding film portion (300). For example, the modified polyolefin resin constituting the tie layer (350) may be maleic anhydride grafted polypropylene, glycidyl methacrylate grafted polyethylene, acrylic acid grafted ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ionomer, ethylene-propylene-diene monomer (EPDM)-based adhesive, or styrene-butadiene-styrene (SBS) block copolymer-based adhesive. However, embodiments of the present invention are not limited thereto.

[0070] In one embodiment of the present invention, the tie layer (350) may be formed on both sides of the core layer (320). Alternatively, the tie layer (350) may be selectively formed at at least one location between the core layer (320) and the first skin layer (310) and between the core layer (320) and the second skin layer (330). For example, if the material compatibility between the first skin layer (310) and the core layer (320) is good but the compatibility between the second skin layer (330) and the core layer (320) is low, the tie layer (350) may be placed only between the core layer (320) and the second skin layer (330). Selective application can reduce the manufacturing cost of the bonding film portion (300). Selective application may be advantageous for securing the necessary performance. The tie layers (350) placed on both sides may have different compositions or thicknesses. The first skin layer (310) and the second skin layer (330) may be composed of different materials, and in this case, an asymmetrical bonding film portion (300) requiring different levels of adhesive strength can be implemented. Tie layers (350) having different compositions or thicknesses can be applied to implement the asymmetrical bonding film portion (300).

[0071] FIG. 5 is an exemplary diagram showing a sealing pattern in a fuel cell unit cell according to an embodiment of the present invention.

[0072] Referring to FIG. 5, an embodiment of a sealing pattern (340) that can be formed on a bonding film portion (300) may be illustrated. The sealing pattern (340) may be formed integrally on the surface of the bonding film portion (300). The sealing pattern (340) may serve to maximize airtightness at the interface between the membrane electrode assembly portion (100) and the separator portion (200). The sealing pattern (340) can concentrate stress in a specific area when the fuel cell unit cell is compressed by a clamping force. This allows for the formation of high local contact pressure. This high contact pressure can form a main airtight line that prevents reaction gas or cooling fluid from leaking out. The material of the sealing pattern (340) may have elasticity and resilience. This allows the sealing performance to be continuously maintained even under a compressed state for a long time.

[0073] The sealing pattern (340) may include various types depending on its shape and function. For example, the sealing pattern (340) may include a lip pattern (340a), a bead pattern (340b), and a maze pattern (340c). In one embodiment of the present invention, the sealing pattern (340) may include at least one of the lip pattern (340a), the bead pattern (340b), and the maze pattern (340c). Each of these patterns may have a unique sealing mechanism. The patterns may be selectively applied according to the required specifications of the fuel cell unit cell. Additionally, sealing performance can be improved through a hybrid structure that combines two or more patterns. The application of the sealing pattern (340) may contribute to simplifying the structure of the separator part (200). The application of the sealing pattern (340) may eliminate the need to machine a separate groove in the bonding area of ​​the separator part (200). This allows the manufacturing process of the separator (200) to be simplified. In addition, production costs can be reduced.

[0074] FIG. 5(a) may illustrate an example in which a lip pattern (340a) is applied. The lip pattern (340a) may have a structure protruding in the form of one or more continuous lines along the outer sealing area of ​​the bonding film portion (300). As illustrated in the drawing, the lip pattern (340a) may have a double structure in which two closed curve lines are arranged in a concentric circle. Each line may function as an independent sealing barrier. This multi-barrier structure can improve the reliability of airtightness.

[0075] The lip pattern (340a) may have a shape with a narrow cross-section and height. The lip pattern (340a) can concentrate high pressure in a very narrow linear contact area upon compression. This high-pressure linear contact can fill fine gaps on the surfaces of the membrane electrode assembly (100) and the separator (200). This can be effective in preventing leakage of hydrogen gas with small molecular size. In the double structure, the outer lip can serve as a primary sealing line. The inner lip can serve as a secondary sealing line, i.e., a backup, functioning as a double safety device. The space between the two lips can act as a buffer area to capture trace amounts of gas passing through the primary line. This can alleviate the pressure gradient applied to the secondary line.

[0076] In one embodiment of the present invention, the shape parameters of the lip pattern (340a) can be optimized according to the operating pressure, temperature, and required durability of the fuel cell. For example, the height, width, spacing, and cross-sectional shape of the lip can be optimized according to the operating pressure, temperature, and required durability of the fuel cell. For example, in a high-pressure environment, the height of the lip can be increased to secure the amount of deformation. This can increase the contact pressure. The cross-sectional shape of the lip may be square. Additionally, the cross-sectional shape of the lip may be round to relieve stress concentration. Furthermore, the cross-sectional shape of the lip may be triangular to maximize initial sealing performance.

[0077] FIG. 5(b) may illustrate an example in which a bead pattern (340b) is applied. The bead pattern (340b) may have a structure in which a plurality of independent protrusions, i.e., beads, having a shape such as a hemispherical or cylindrical shape, are arranged at regular intervals along a sealing line. Each bead may function as an independent pressure concentration point. These points may come together to form an overall sealing line. The bead pattern (340b) may have greater structural flexibility compared to a continuous lip pattern (340a).

[0078] The flexibility of the bead pattern (340b) can be advantageous in compensating for assembly tolerances or fine differences in flatness of the part surface. Each bead can adhere to the surface irregularities of the mating part while deforming locally. This characteristic can improve responsiveness to mechanical deformations, such as thermal expansion and contraction, that occur during the operation of the fuel cell stack. Through this, the bead pattern (340b) can contribute to maintaining airtightness even during long-term operating cycles.

[0079] In one embodiment of the present invention, the shape, size, arrangement density, and arrangement method of the beads constituting the bead pattern (340b) may be changed. For example, increasing the density of the beads can form a denser sealing line. This can enhance airtightness. Additionally, the beads may be arranged in two rows instead of one. A zigzag pattern in which the beads are arranged in an alternating pattern may be applied. Such a zigzag pattern can make the gas leakage path long and complex. This can bring about the effect of further improving sealing performance.

[0080] FIG. 5(c) illustrates an example in which a maze-like pattern (340c) is applied. The maze-like pattern (340c) can utilize the principle of increasing fluid flow resistance by geometrically maximizing the length of the leakage path. In the example illustrated in the drawing, multiple concentric closed curve lines can be superimposed. This allows for the formation of a complex path. Gas attempting to leak out must pass through this long, winding maze structure.

[0081] The maze-like pattern (340c) can achieve a sealing effect through the pressure drop that occurs as the fluid travels along a long path. The longer the path and the narrower the cross-sectional area, the greater the flow resistance can be. Accordingly, even if the initial pressure is high, the pressure can be significantly reduced when reaching the end of the path. This principle enables the control of leakage. The maze-like pattern (340c) can be applied to applications requiring long-term durability and stability.

[0082] In one embodiment of the present invention, the maze pattern (340c) may have a complex structure other than a structure of concentric circles. For example, flow resistance may be increased by placing an obstacle in the middle of the channel. Additionally, flow resistance may be increased by locally changing the width and depth of the channel. Furthermore, the lip pattern (340a) and the maze pattern (340c) may be combined. The lip pattern (340a) can perform primary pressure sealing. The maze pattern (340c) can perform secondary flow resistance sealing. Through this, a multi-mechanism sealing structure can be realized.

[0083] FIG. 6 is an exemplary diagram showing the arrangement of a through opening and a sealing pattern of a bonding film portion in a fuel cell unit cell according to an embodiment of the present invention.

[0084] Referring to FIG. 6, a bonding film portion (300) of a fuel cell unit cell according to an embodiment of the present invention may be illustrated. Details regarding the bonding film portion (300) that overlap with those described in FIG. 1, FIG. 3, and FIG. 4 may be omitted. The bonding film portion (300) may be interposed between the membrane electrode assembly portion and the separator portion. The bonding film portion (300) may perform the role of ensuring airtightness and providing electrical insulation. In FIG. 6, the bonding film portion (300) may be specifically illustrated as including a structure for fluid supply and discharge.

[0085] The bonding film portion (300) may include a through opening (H) corresponding to the location of the manifold. The through opening (H) may be an opening formed in the bonding film portion (300) to communicate with the manifold, which is a fluid passage formed by penetrating the fuel cell stack. For operation, the fuel cell stack may need to supply and discharge fuel gas such as hydrogen, oxidant gas containing oxygen, and cooling fluid to remove reaction heat to each unit cell. A common flow path for distributing and collecting these fluids may correspond to the manifold. Therefore, the through opening (H) may function as a passage that allows the reaction gas and cooling fluid to pass through the bonding film portion (300) and smoothly flow into or out of the flow path of the separator portion.

[0086] When fuel cell stacks are stacked, the manifold holes in the separator portions included in each unit cell and the through-holes (H) in the bonding film portions (300) can be precisely aligned. Through this alignment, a continuous manifold flow path can be formed that penetrates the entire stack. For example, a through-hole (H) connected to a hydrogen supply manifold can allow hydrogen to be supplied to the anode flow path of the separator portion. Additionally, a through-hole (H) connected to an air supply manifold can allow air to be supplied to the cathode flow path. If an error occurs in the position or size of the through-holes (H), fluid flow may be obstructed. This may result in insufficient fuel supply to specific cells, which can cause cell performance degradation and reduced durability.

[0087] The number, location, and shape of the through-openings (H) can be determined according to the design specifications of the fuel cell stack. For example, the bonding film portion (300) may include through-openings (H) for hydrogen supply, hydrogen discharge, air supply, air discharge, coolant inflow, and coolant outflow, respectively. These through-openings (H) can generally be placed in the corner or edge area of ​​the bonding film portion (300). This allows for avoiding interference with the fastening structure of the stack and increasing fluid distribution efficiency. Additionally, the shape of the through-openings (H) can be designed not only as a circle but also as an ellipse, square, or streamlined shape. This allows for configuration to minimize flow resistance and reduce pressure drop.

[0088] Regarding the sealing pattern (340), details that overlap with those described in FIG. 5 may be omitted. As shown in FIG. 6, the sealing pattern (340) can be placed not only in the outer periphery of the bonding film portion (300) but also in the periphery of each through-opening (H). The sealing pattern (340) placed in the outer periphery can maintain airtightness between the internal active area of ​​the fuel cell unit cell and the external environment. This can serve to prevent reaction gas from leaking out. At the same time, the sealing pattern (340) placed in the periphery of the through-opening (H) can perform the function of individually sealing each manifold flow path.

[0089] A sealing pattern (340) formed around a through opening (H) can provide an isolation sealing function that prevents different types of fluids from mixing. For example, a hydrogen supply manifold and an air supply manifold may be placed adjacent to each other. If leakage occurs between the two manifolds, a flammable mixed gas may be formed. The sealing pattern (340) around the through opening (H) can block such internal leakage, thereby ensuring the safety of the fuel cell system. Additionally, the sealing pattern (340) can prevent reaction gas from leaking into the coolant flow path or coolant from leaking into the reaction gas flow path. This prevents electrode flooding or catalyst poisoning, thereby ensuring the performance and lifespan of the stack.

[0090] In one embodiment of the present invention, the process of integrally forming a through opening (H) and a sealing pattern (340) in a bonding film portion (300) can improve production efficiency. For example, the through opening (H) can be precisely formed through press processing or laser cutting after the film extrusion process. Subsequently, the sealing pattern (340) can be formed through a heat compression molding or embossing process. At this time, during the process of forming the sealing pattern (340), the first skin layer (310) and the second skin layer (330), which have a relatively high melt flow index (MFI) and a low melting point, flow locally along the pattern shape of the mold due to the heat and pressure applied to the bonding film portion (300), causing a change in thickness and forming a protruding pattern. In this process, the core layer (320), which has a relatively high melting point and high rigidity, is not completely melted but remains in a solid or semi-melted state and acts as a structural support for pattern formation, thereby maintaining the insulation thickness of the entire multilayer film and simultaneously inducing the formation of a precise sealing pattern on the surface of the skin layer. As a result, the formed sealing pattern (340) is realized through thickness variation caused by material flow of the skin layer itself, so high local contact pressure is formed at the bonding interface without a separate gasket member, thereby maximizing airtightness performance.

[0091] This integrated structure can reduce the number of parts by replacing gaskets, which were previously separate components. In addition, it can contribute to increasing mass production yield by preventing errors such as misalignment or omissions that may occur during the assembly process.

[0092] FIG. 7 is an exemplary diagram showing the structure of a bonded film portion to which a barrier layer, a fiber reinforcement layer, and a mesh reinforcement layer are applied in a fuel cell unit cell according to an embodiment of the present invention.

[0093] Referring to FIG. 7, the bonding film portion (300) of a fuel cell unit cell according to one embodiment of the present invention may have a multilayer structure including additional functional layers to improve durability and functionality. The bonding film portion (300) may be positioned between the membrane electrode assembly portion (100) and the separator portion (200) to bond and seal them. The bonding film portion (300) illustrated in FIG. 7 may include a first skin layer (310), a core layer (320), and a second skin layer (330) as a basic structure, and additionally may include a barrier layer (360), a fiber reinforcement layer (371), and a mesh reinforcement layer (372).

[0094] Regarding the membrane electrode assembly (100), details that overlap with those described in FIGS. 1 and 2 are omitted. The membrane electrode assembly (100) is positioned on one side of the bonding film (300) and can be integrally bonded with the second skin layer (330) of the bonding film (300) through a heat fusion process. Regarding the separator plate (200), details that overlap with those described in FIGS. 1 and 2 are omitted. The separator plate (200) is positioned on the other side of the bonding film (300) and can be integrally bonded with the first skin layer (310) of the bonding film (300) through a heat fusion process.

[0095] The bonding film portion (300) may include a first skin layer (310), a barrier layer (360), a fiber reinforcement layer (371), a mesh reinforcement layer (372), a core layer (320), and a second skin layer (330). The first skin layer (310) is located at the outermost edge of the bonding film portion (300) and can be in direct contact with and heat-fused to the separator portion (200). The second skin layer (330) is located at the opposite outermost edge of the bonding film portion (300) and can be in direct contact with and heat-fused to the membrane electrode assembly portion (100). The core layer (320) is located between the first skin layer (310) and the second skin layer (330) and can serve as a structural support and an electrical insulator for the bonding film portion (300).

[0096] The first skin layer (310) and the second skin layer (330) may include a thermoplastic resin and melt upon thermal fusion bonding to provide adhesion to the surfaces of the separator plate (200) and the membrane electrode assembly (100), respectively. In particular, to improve adhesion to the separator plate (200) made of a metal material, the first skin layer (310) and the second skin layer (330) may include a polyolefin-based resin grafted with maleic anhydride. The polar groups of maleic anhydride can form a strong interaction with the oxide layer on the metal surface to increase interfacial adhesion strength. Additionally, the thickness of the first skin layer (310) may be designed to be greater than the arithmetic mean roughness (Ra) of the surface of the separator plate (200). Through this, the first skin layer (310) that is melted during heat fusion can completely fill the fine irregularities on the surface of the separator plate (200) to form a hermetic bonding interface and suppress the occurrence of leakage paths.

[0097] In one embodiment of the present invention, the first skin layer (310) and the second skin layer (330) may be formed from a resin having a higher Melt Flow Index (MFI) than the core layer (320). Since the higher the Melt Flow Index, the higher the fluidity of the resin under the same temperature conditions, the skin layer resin can have higher fluidity than the core layer (320) and diffuse to the surface of the separator part (200) and the membrane electrode assembly part (100) during thermal fusion bonding. Through this difference in fluidity, the skin layer resin can rapidly diffuse to the surface of the bonding target, thereby securing a large contact area and achieving stable bonding. Additionally, the surface of the first skin layer (310) may be surface modified by plasma treatment or corona treatment. Such surface treatment can increase surface energy by introducing polar functional groups to the surface. As a result, the wetting tension can be configured to have increased surface energy compared to the untreated state.

[0098] In one embodiment of the present invention, the first skin layer (310) may maintain an amorphous or low-crystalline state before thermal fusion bonding. The first skin layer (310) may be configured to increase its degree of crystallization during the cooling process after thermal fusion bonding to ensure bonding strength.

[0099] The core layer (320) supports the core structure of the bonding film portion (300) and can be responsible for electrical insulation between the separator portion (200) and the membrane electrode assembly portion (100). The core layer (320) may be made of a resin having a melting point higher than the melting point of the resin constituting the first skin layer (310) and the second skin layer (330). As a result, while the first skin layer (310) and the second skin layer (330) are melting at the heat fusion bonding temperature, the core layer (320) remains in a solid state, thereby ensuring the shape stability of the entire bonding film portion (300) and preventing excessive compression or deformation. Additionally, the core layer (320) may be formed of a material having an elastic modulus higher than that of the first skin layer (310) and the second skin layer (330). A high elastic modulus suppresses excessive thickness deformation caused by compressive loads applied during unit cell lamination, thereby maintaining a constant sealing pressure and ensuring long-term airtightness reliability.

[0100] In one embodiment of the present invention, the bonding film portion (300) may include an interface layer in which polymer chains of each layer are mutually diffused at the interface between the first skin layer (310) and the core layer (320) and at the interface between the second skin layer (330) and the core layer (320) by a co-extrusion process. This interface layer may be configured to prevent interlayer delamination.

[0101] In one embodiment of the present invention, the core layer (320) may be designed to occupy a significant portion of the total thickness of the bonding film portion (300) to sufficiently secure the dielectric breakdown voltage. For example, the thickness ratio occupied by the core layer (320) may be formed to be greater than the combined thickness ratio of the first skin layer (310) and the second skin layer (330) to secure the dielectric breakdown voltage between the separator portion (200) and the membrane electrode assembly portion (100). Additionally, the core layer (320) may include insulating inorganic fillers having a platelet structure. During the co-extrusion process, the platelet fillers may be arranged in layers within the core layer (320) according to the direction in which the resin flows. This arrangement structure may have the effect of improving gas blocking performance by diverting the path through which reactive gases, such as hydrogen or oxygen, attempt to pass through the film, thereby increasing the length of the transmission path.

[0102] In one embodiment of the present invention, the core layer (320) may include a component for suppressing chemical decomposition caused by peroxide radicals generated during fuel cell operation. For example, a radical scavenger containing cerium (Ce) or manganese (Mn) may be dispersed and contained within the core layer (320) or the skin layers. Such a radical scavenger converts harmful radicals into stable substances, thereby preventing the cleavage of polymer chains and significantly improving the long-term durability of the bonding film portion (300). Additionally, the core layer (320) may include a colored coloring agent, and the first skin layer (310) and the second skin layer (330) may be formed from a transparent or translucent material. Through this, after heat fusion bonding, the quality of the bonding process can be easily inspected by visually identifying whether the position of the core layer (320) has been deformed or the state of the melt flow of the skin layer from the outside.

[0103] The barrier layer (360) is disposed inside the bonding film portion (300) and can effectively block reaction gas or cooling fluid from passing through the film. Hydrogen, oxygen, water, etc., may be present in the internal environment of the fuel cell. Minimizing leakage and crossover of these fluids may be important for performance and safety. The barrier layer (360) may include a polymer resin with excellent gas barrier properties. For example, the barrier layer (360) may be ethylene vinyl alcohol (EVOH), polyamide, polyvinylidene chloride, polyacrylonitrile, polyethylene naphthalate, liquid crystal polymer, or cyclic olefin copolymer. However, embodiments of the present invention are not limited thereto.

[0104] In one embodiment of the present invention, the barrier layer (360) may be located inside the core layer (320). Some barrier resins, such as EVOH, may have characteristics such as reduced gas barrier performance or dimensional expansion when they absorb moisture. If the barrier layer (360) is positioned to surround the outer part of the core layer (320), which has relatively low moisture permeability, the arrival of external moisture to the barrier layer (360) can be delayed. Additionally, the core layer (320) can contribute to maintaining the shape stability of the entire bonding film portion (300) by physically suppressing dimensional changes of the barrier layer (360).

[0105] Fiber reinforcement layers (371) and mesh reinforcement layers (372) may be introduced to improve the mechanical strength and long-term dimensional stability of the bonding film portion (300). The fuel cell stack may be operated for a long time by being fastened under constant pressure. The sealing member may be subjected to continuous compressive loads. Under these conditions, the polymer material may exhibit a creep phenomenon in which it gradually deforms over time. This creep phenomenon can lead to a decrease in sealing pressure and a reduction in airtightness. Fiber reinforcement layers (371) or mesh reinforcement layers (372) can ensure long-term reliability by reducing deformation caused by such long-term compressive loads.

[0106] In one embodiment of the present invention, the fiber reinforcement layer (371) and the mesh reinforcement layer (372) may have a structure in which they are embedded within the core layer (320). When manufacturing the bonding film portion (300) by a co-extrusion process, the resin of the core layer (320) in a molten state may flow through and fill the fiber bundles of the fiber reinforcement layer (371) or the mesh pores of the mesh reinforcement layer (372). After undergoing a cooling and solidification process, an integrated composite structure can be formed in which the core layer (320) and the reinforcement layers are physically and strongly bonded. This structure allows the reinforcement layers to effectively share the load against external stress. Furthermore, it can prevent interlayer delamination, thereby maximizing the overall mechanical durability of the bonding film portion (300). For example, the fiber reinforcement layer (371) may include glass fibers, carbon fibers, aramid fibers, etc., and the mesh reinforcement layer (372) may include a high-strength polymer or metal mesh.

[0107] FIG. 8 is an exemplary diagram showing a bonded film portion to which a reference mark, a reference hole, a reference slot, and an identification mark are applied in a fuel cell unit cell according to an embodiment of the present invention.

[0108] Referring to FIG. 8, a bonding film portion (300) of a fuel cell unit cell according to an embodiment of the present invention may be illustrated. Regarding the bonding film portion (300), details that overlap with those described in FIG. 1, FIG. 3, FIG. 4, FIG. 6, and FIG. 7 may be omitted. FIG. 8 may show an example of components formed in the bonding film portion (300). The components formed in the bonding film portion (300) can achieve precise alignment during the assembly process of the fuel cell stack. In addition, the components formed in the bonding film portion (300) can track the production history of each part. The bonding film portion (300) may include an alignment structure that functions as a standard for accurately stacking a plurality of unit cells including a membrane electrode assembly portion (100) and a separator portion (200). In addition, the bonding film portion (300) may include identification information to increase the efficiency of manufacturing and quality control.

[0109] The bonding film portion (300) may include at least one of a reference mark (381), a reference hole (382), and a reference slot (383) for stacking alignment. The alignment structures can enable an automated stacking device to accurately recognize and position each component. Precise alignment can ensure that the flow paths inside the fuel cell stack are connected without blockage. In addition, precise alignment can contribute to maximizing the overall performance and efficiency of the stack by ensuring that the active areas of each cell overlap accurately. Misalignment can cause local pressure deviations, which may lead to gas leakage. Furthermore, misalignment can cause over-compression of the gas diffusion layer (GDL), which may lead to performance degradation. The reference mark (381), reference hole (382), and reference slot (383) can play an essential role in ensuring the reliability of the stack.

[0110] The reference mark (381) may be a visual pattern formed on the surface of the bonding film portion (300). The reference mark (381) may be used as a reference for an automated device equipped with a vision system to optically recognize the position and orientation of the bonding film portion (300). For example, a camera may photograph the bonding film portion (300) being transported via a conveyor belt. Image processing software may analyze the coordinates of the reference mark (381) to calculate the error between the current position and the target position. An actuator, such as a robotic arm, may fine-tune the position of the bonding film portion (300) based on the calculated error. The actuator may position the bonding film portion (300) in the correct position. The optical alignment method may be non-contact. The non-contact method can prevent damage to the film. Additionally, the optical alignment method can be advantageously applied to high-speed processes.

[0111] In one embodiment of the present invention, the reference mark (381) may be implemented in various forms. For example, the reference mark (381) may be a crosshair mark, a circular mark, a square mark, a doughnut-shaped mark, a checkerboard pattern, a fiducial mark, an L-shaped mark, or a triangle mark. However, the embodiments of the present invention are not limited thereto. The shape, size, and color of the reference mark (381) may be designed to maximize the recognition rate of the vision system. For example, recognition accuracy may be improved by using a color with a distinct contrast with the surrounding area. Alternatively, recognition accuracy may be improved by printing with a material having high reflectivity under lighting of a specific wavelength. The reference mark (381) may be formed on the bonding film portion (300) through inkjet printing, laser marking, screen printing, or photolithography.

[0112] The reference hole (382) may be a physical hole formed by penetrating the bonding film portion (300). The reference hole (382) may be used to perform mechanical alignment by combining with an alignment pin installed on an assembly jig. When stacking multiple bonding film portions (300), membrane electrode assembly portions (100), and separator portions (200), the alignment pin may be passed sequentially through the reference hole (382) formed in each part. The alignment pin may ensure that all parts are fixed at the same reference position. The mechanical alignment method may be less affected by external lighting or surface contamination compared to the optical alignment method. The mechanical alignment method can ensure high repeatability. The reference hole (382) may generally be machined into a circular shape. The reference hole (382) may serve as a reference point that simultaneously fixes the position in the X-axis and Y-axis directions.

[0113] The reference slot (383) may be an elongated hole formed by penetrating the bonding film portion (300). The reference slot (383) may be used together with the reference hole (382). The reference slot (383) can increase the precision of alignment. Additionally, the reference slot (383) may serve to allow for deformation due to manufacturing tolerances or thermal expansion. Generally, one reference hole (382) and one reference slot (383) may be used as a pair. The reference hole (382) can fix the origin of the XY coordinates. The reference slot (383) may serve to prevent errors in the rotational direction. The alignment pin may move in the direction of the major axis of the reference slot (383). However, the movement of the alignment pin may be limited to the direction of the minor axis. The distance between the two reference points, the reference hole (382) and the reference slot (383), may change slightly due to thermal expansion, etc. The structure of the reference slot (383) can prevent excessive stress from being applied to the part. The method of using the reference hole (382) and the reference slot (383) together can avoid over-constraint. In addition, the method of using the reference hole (382) and the reference slot (383) together can achieve stable alignment.

[0114] In one embodiment of the present invention, the reference mark (381), reference hole (382), and reference slot (383) may be used in combination. For example, a two-stage alignment process may be adopted. First, the vision system may obtain a coarse alignment using the reference mark (381). Then, an alignment pin may be inserted into the reference hole (382) and the reference slot (383). The alignment pin may secure a final fine alignment. The combined alignment method can satisfy both the efficiency of a high-speed process and the precision of mechanical alignment. The alignment structures may be positioned in the outer region of the bonding film portion (300). The arrangement of the alignment structures may be designed so as not to affect the active region of the fuel cell unit cell. Additionally, the alignment structures may be arranged asymmetrically. Asymmetrical arrangement can perform a poka-yoke function that fundamentally prevents errors in which the top / bottom or left / right sides of the parts are reversed during the assembly process.

[0115] The bonding film section (300) may further include an identification mark (390) recognizable by visual inspection or automatic inspection. The identification mark (390) may serve to enable traceability by assigning unique information to each bonding film section (300). The information included in the identification mark (390) can be automatically scanned at each process stage of the production line. The scanned information can be stored in a Manufacturing Execution System (MES) database and utilized for quality control. For example, a defect may be found in the bonding film section (300) of a specific lot. Through the identification mark (390) information, all products belonging to the same lot can be quickly identified and traced. Necessary measures can be taken through identification and tracing.

[0116] The identification mark (390) may be configured to include various information. For example, the identification mark (390) may include a unique product serial number, production lot number, manufacturing date and time, production line information, raw material supplier information, quality inspection results, product specification code, etc. The information included in the identification mark (390) can increase the transparency of the manufacturing process. In addition, the information included in the identification mark (390) can facilitate cause analysis in the event of a problem. Even after the fuel cell stack is shipped to the market, maintenance history, usage time, failure information, etc., can be recorded and managed through the identification mark (390). Information management through the identification mark (390) can enable management throughout the entire lifecycle of the product. The identification mark (390) may be implemented in a form that can be easily recognized by an automated optical reader or scanner.

[0117] In one embodiment of the present invention, the identification mark (390) may be implemented as various types of codes. For example, the identification mark (390) may be a one-dimensional barcode, a two-dimensional code such as a QR code (Quick Response code), a Data Matrix code, a PDF417 code, an Aztec code, a MaxiCode, or a serial number composed of human-readable characters or numbers. However, the embodiments of the present invention are not limited thereto. Two-dimensional codes such as Data Matrix or QR codes can store a large amount of information in a small area. Data recovery may be possible even if a part of the two-dimensional code is damaged. Two-dimensional codes can guarantee a high recognition rate even in harsh manufacturing environments. The identification mark (390) may be permanently engraved on the surface of the bonding film portion (300) through methods such as laser engraving, inkjet marking, or thermal transfer printing.

[0118] In one embodiment of the present invention, the identification mark (390) may include an electronic identification means such as a Radio-Frequency Identification (RFID) tag or a Near Field Communication (NFC) tag. The electronic tag may be embedded within the multilayer structure of the bonding film portion (300) or attached to the surface. The electronic tag can simultaneously read or write multiple identification information from a distance in a non-contact manner. The use of the electronic tag can maximize process automation and data management efficiency. For example, information on all unit cells stacked inside can be scanned at once through a reader from the outside of the completed fuel cell stack. Through scanning, configuration information of the stack can be verified. In addition, data generated during operation can be recorded on the tag. The recorded data can be utilized for real-time status monitoring and predictive maintenance.

[0120] As described above, preferred embodiments according to the present invention have been examined. It is obvious to those skilled in the art that, in addition to the embodiments described above, the present invention may be embodied in other specific forms without departing from the spirit or scope thereof. Therefore, the embodiments described above should be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the description above but may be modified within the scope of the appended claims and their equivalents. Explanation of the symbols

[0122] 100 : Membrane electrode assembly part 200 : Separator part 300 : Bonding film section 310: 1st skin layer 320 : Core layer 330: Second skin layer 340 : Sealing pattern 340a : Rib pattern 340b: Bead pattern 340c : Maze pattern 350 : Taiping 360 : Barrier layer 371 : Fiber reinforcement layer 372 : Mesh reinforcement layer 381: Standard Mark 382 : Standard hole 383 : Standard slot 390: Identification Mark H: Penetrating opening

Claims

Claim 1 A membrane electrode assembly portion comprising a membrane electrode assembly and a gas diffusion layer (GDL); a separator portion disposed opposite to the membrane electrode assembly portion; and a bonding film portion interposed between the outer periphery region of the membrane electrode assembly portion and the corresponding region of the separator plate portion to heat-fuse bond the membrane electrode assembly portion and the separator plate portion; wherein the bonding film portion has a multilayer structure including a first skin layer, a core layer, and a second skin layer formed integrally by co-extrusion, the core layer provides electrical insulation between the membrane electrode assembly portion and the separator plate portion, the first skin layer is composed of a modified polyolefin-based resin and heat-fuse bonded to the separator plate portion made of metal material, the second skin layer is composed of a polyamide-based resin and heat-fuse bonded to the membrane electrode assembly portion, the bonding film portion includes a sealing pattern to form an airtight line in the outer periphery region of the membrane electrode assembly portion, the separator plate portion includes a flat surface in which no groove processing is formed in the bonding region where the bonding film portion is heat-fused, and a portion of the second skin layer that is melted during heat-fusion is impregnated into the porous structure of the gas diffusion layer (GDL) and hardened, A fuel cell unit cell configured to form a mechanical interlocking structure to block a reaction gas leakage path formed along the plane direction of the gas diffusion layer, wherein the sealing pattern includes at least one of a lip pattern, a bead pattern, and a maze pattern, wherein the bonding film portion includes a through opening corresponding to a manifold position and is configured such that the sealing pattern is also disposed in the periphery area of ​​the through opening, and further includes at least one of a fiber reinforcement layer or a mesh reinforcement layer to reduce deformation due to long-term compressive load, and is configured to be laminated with the membrane electrode assembly portion after forming a film-integrated separator by pre-heat-fusion to the separator portion, or to be laminated with the separator portion after forming a film-integrated membrane electrode assembly by pre-heat-fusion to the membrane electrode assembly portion. Claim 2 A fuel cell unit cell according to claim 1, wherein the first skin layer and the second skin layer are co-extruded to have different materials, so as to be configured such that the bonding characteristics on the separator side and the bonding characteristics on the membrane electrode assembly side are distinguished from each other. Claim 3 A fuel cell unit cell according to claim 1, wherein the bonding film portion further comprises a tie layer disposed at at least one position between the core layer and the first skin layer and between the core layer and the second skin layer. Claim 4 A fuel cell unit cell according to claim 1, wherein the bonding film portion is co-extruded such that the composition of the core layer changes compartmentally along the outer circumference region, thereby forming a plurality of compartments having different insulation functions and mechanical strengths. Claim 5 delete Claim 6 delete Claim 7 A fuel cell unit cell according to claim 1, wherein the core layer comprises at least one of an insulating polymer matrix and an insulating inorganic filler dispersed in the insulating polymer matrix. Claim 8 A fuel cell unit cell according to claim 1, wherein the bonding film portion further comprises a barrier layer that reduces permeation to a reaction gas or cooling fluid. Claim 9 delete Claim 10 delete Claim 11 In claim 1, the bonding film portion comprises at least one of a reference mark for lamination alignment, a reference hole, and a reference slot, for a fuel cell unit cell. Claim 12 A fuel cell unit cell according to claim 1, wherein the bonding film portion further comprises an identification mark recognizable by visual inspection or automatic inspection.

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