Polymer electrolyte membrane fuel cell unit cell and method of manufacturing the same

Abstract

One embodiment of the present invention discloses a polymer electrolyte membrane fuel cell comprising: a polymer electrolyte membrane; a catalyst layer disposed to face both sides of the polymer electrolyte membrane; a gas diffusion layer disposed on one side of the catalyst layer; one or more carbon nanotube sheet layers disposed between the at least one catalyst layer and the gas diffusion layer, having flow channels formed therein for moving reaction gases and products; and at least one separator plate in contact with one side of the gas diffusion layer.

Description

Technology Field

[0001] Embodiments of the present invention relate to a polymer electrolyte membrane fuel cell unit cell and a method for manufacturing the same. Background Technology

[0002] The gradual increase in fossil fuel consumption due to rising global energy demand has accelerated global warming, and the importance and development of eco-friendly energy sources are being highlighted as a means to overcome this. In particular, the Paris Agreement held in 2015 became a turning point that triggered rapid changes in the energy system, and the development of alternative energy sources is continuously underway to achieve the goals set forth in the agreement.

[0003] Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are expected to be a next-generation energy source for transportation and portable devices because they are environmentally friendly as they utilize hydrogen among alternative energy sources to produce energy, and they can achieve a short energy conversion process, high power density, and operation at relatively low temperatures of 40-120°C.

[0004] However, these PEMFCs require improvement in terms of power density, durability, and cost. Power density, one of the important parameters of a PEMFC, is closely related to volume or weight, and the bipolar plates (BP) commonly used in PEMFCs account for a high proportion, approximately 80% of the total volume and 60% of the weight within the stack. Meanwhile, in terms of cost, they account for more than 30% of the total cost of the stack.

[0005] Therefore, it is necessary to develop a technology that can achieve high volumetric output while being cost-effective compared to conventional technology by improving the separator area through weight reduction and thinning using low-cost materials. The problem to be solved

[0006] Embodiments of the present invention aim to provide a polymer electrolyte membrane fuel cell unit cell capable of improving performance even under various humidity conditions, and a method for manufacturing the same.

[0007] Embodiments of the present invention aim to provide a polymer electrolyte membrane fuel cell unit cell capable of improving power density and a method for manufacturing the same. means of solving the problem

[0008] According to one aspect, a polymer electrolyte membrane fuel cell unit cell is provided, comprising: a polymer electrolyte membrane; a catalyst layer disposed to face both sides of the polymer electrolyte membrane; a gas diffusion layer disposed on one side of the catalyst layer; one or more carbon nanotube sheet layers disposed between the at least one catalyst layer and the gas diffusion layer, having a flow channel formed therein for moving reaction gas and product; and at least one separator plate in contact with one side of the gas diffusion layer.

[0009] According to one embodiment, the carbon nanotube sheet layer is disposed between a catalyst layer and a gas diffusion layer disposed on one of the two sides of the polymer electrolyte membrane, and the separator plate may be in contact with the gas diffusion layer of the catalyst layer disposed on the other side of the polymer electrolyte membrane.

[0010] According to one embodiment, the fluid channel may have a shape that bends repeatedly.

[0011] According to one embodiment, the thickness of the flow channel may be 0.3 to 0.7 mm.

[0012] According to one embodiment, the flow channel formed in the carbon nanotube sheet layer may be formed by laser engraving.

[0013] According to another aspect, a method for manufacturing a polymer electrolyte membrane fuel cell unit cell is provided, comprising the steps of: forming a catalyst layer by coating a catalyst on both sides of a polymer electrolyte membrane; forming a gas diffusion layer on one side of the catalyst layer; forming a carbon nanotube sheet layer by inserting a carbon nanotube sheet having a flow channel formed between the catalyst layer and the gas diffusion layer; and forming a separator on one side of the gas diffusion layer.

[0014] According to one embodiment, the step of forming the carbon nanotube sheet layer may include: preparing a carbon nanotube sheet; and forming a flow channel on the carbon nanotube sheet.

[0015] According to one embodiment, the step of preparing the carbon nanotube sheet may include the step of purifying the carbon nanotube sheet by heat treatment and acid treatment.

[0016] According to one embodiment, the step of forming a flow channel on the carbon nanotube sheet can be formed by imprinting the shape of the flow channel on the carbon nanotube sheet with a laser.

[0017] According to one embodiment, the step of forming the catalyst layer may be to form the catalyst layer by coating a solution containing a catalyst on both sides of the polymer electrolyte membrane. Effects of the invention

[0018] The polymer electrolyte membrane fuel cell unit cell of the embodiments of the present invention includes a carbon nanotube sheet with a flow channel formed therein as an intermediate layer, so that performance can be improved even under various humidity conditions.

[0019] The polymer electrolyte membrane fuel cell unit cell of the embodiments of the present invention includes a carbon nanotube sheet with a flow channel formed therein as an intermediate layer to replace the separator, thereby reducing the thickness of the cell and improving power density.

[0020] According to the method for manufacturing a polymer electrolyte membrane fuel cell unit cell of the embodiments of the present invention, a carbon nanotube sheet having a flow channel formed therein is formed as an intermediate layer, thereby enabling the manufacture of a polymer electrolyte membrane fuel cell with improved performance even under various humidity conditions.

[0021] According to the method for manufacturing a polymer electrolyte membrane fuel cell unit cell of the embodiments of the present invention, a carbon nanotube sheet having a flow channel formed therein is formed as an intermediate layer to replace the separator, thereby allowing for the reduction of the cell thickness and the improvement of power density, thereby enabling the manufacture of a polymer electrolyte membrane fuel cell. Brief explanation of the drawing

[0022] FIG. 1 is a cross-sectional view schematically showing the configuration of a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the configuration of a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention. FIG. 3(a) is a schematic diagram showing the manufacturing process of a carbon nanotube sheet according to one embodiment of the present invention. FIG. 3(b) is a schematic diagram showing an example of a carbon nanotube sheet according to one embodiment of the present invention. FIG. 4 is a schematic diagram showing an example of the internal structure of a carbon nanotube sheet after heat treatment and acid treatment according to one embodiment of the present invention. FIG. 5 is a schematic diagram illustrating the process of imprinting a flow channel on a purified carbon nanotube sheet using a laser according to one embodiment of the present invention. FIGS. 6(a) and 6(b) are schematic diagrams showing the structure of a polymer electrolyte membrane fuel cell unit cell according to one embodiment and a comparative example of the present invention. FIGS. 7(a) and 7(b) are cross-sectional views schematically showing the structure of a polymer electrolyte membrane fuel cell unit cell according to one embodiment and a comparative example of the present invention. FIG. 8(a) is an FE-SEM image showing the surface structure of a carbon nanotube sheet before heat treatment and acid treatment according to one embodiment of the present invention. FIG. 8(b) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after heat treatment and acid treatment according to one embodiment of the present invention. Figure 8(c) is an FE-SEM image showing the surface structure of a carbon nanotube sheet before heat treatment and acid treatment, enlarged from Figure 8(a). Figure 8(d) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after heat treatment and acid treatment, enlarged from Figure 8(b). FIG. 9(a) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after a flow channel is laser-engraved according to one embodiment of the present invention. Figure 9(b) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after the flow channel is laser-engraved, enlarged from Figure 9(a). FIG. 9(c) is an enlarged FE-SEM image of the rib region after the flow channel of a carbon nanotube sheet according to one embodiment of the present invention has been laser-engraved. FIG. 9(d) is an enlarged FE-SEM image of the channel region after the flow channel of a carbon nanotube sheet according to one embodiment of the present invention has been laser-engraved. FIGS. 10(a) to 10(d) are graphs showing polarization curves of a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention under relative humidity conditions of 100%, 80%, 60%, and 40%. FIGS. 11(a) to 11(d) are graphs showing the results of electrochemical impedance spectroscopy of a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention under conditions of relative humidity of 100%, 80%, 60%, and 40%. Specific details for implementing the invention

[0023] The above-mentioned objectives, means, and resulting effects of the present invention will become clearer through the following detailed description in conjunction with the attached drawings, and accordingly, a person skilled in the art to which the present invention pertains will be able to easily implement the technical concept of the present invention. Furthermore, in describing the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted.

[0024] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form as appropriate unless specifically stated otherwise in the text. In this specification, terms such as "comprising," "providing," "making arrangements," or "having" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0025] In this specification, terms such as "or", "at least one," etc., may represent one of the words listed together or a combination of two or more. For example, "or B", "at least one of and B" may include only one of A or B, or may include both A and B.

[0026] In this specification, descriptions following "e.g." should not limit the embodiments of the invention according to various embodiments of the invention, such as variations including tolerances, measurement errors, limits of measurement accuracy, and other commonly known factors, as the information presented, such as cited characteristics, variables, or values, may not exactly match.

[0027] In this specification, where it is stated that a component is 'connected' or 'connected' to another component, it should be understood that it may be directly connected or connected to the other component, or that there may be other components in between. On the other hand, when it is mentioned that a component is 'directly connected' or 'directly connected' to another component, it should be understood that there are no other components in between.

[0028] In this specification, where a component is described as being 'on' or 'in contact' with another component, it should be understood that it may be in direct contact with or connected to the other component, but that another component may exist in between. Conversely, where a component is described as being 'immediately above' or 'in direct contact' with another component, it should be understood that no other component exists in between. Other expressions describing the relationship between components, such as 'between' and 'directly between,' may be interpreted in the same way.

[0029] In this specification, terms such as 'first,' 'second,' etc., may be used to describe various components, but such components should not be limited by these terms. Furthermore, these terms should not be interpreted as limiting the order of each component, but may be used for the purpose of distinguishing one component from another. For example, 'first component' may be named 'second component,' and similarly, 'second component' may be named 'first component.'

[0030] Unless otherwise defined, all terms used in this specification may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0031] Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited by the following embodiments.

[0033] FIG. 1 is a cross-sectional view schematically showing the configuration of a unit cell of a polymer electrolyte membrane fuel cell according to one embodiment of the present invention.

[0034] Referring to FIG. 1, according to one aspect, a polymer electrolyte membrane fuel cell unit cell (100) of the present invention comprises: a polymer electrolyte membrane (110); a catalyst layer (120) disposed to face both sides of the polymer electrolyte membrane (110); a gas diffusion layer (130) disposed on one side of the catalyst layer (120); one or more carbon nanotube sheet layers (140) disposed between the at least one catalyst layer (120) and the gas diffusion layer (130), having flow channels formed therein for moving reaction gas and products; and at least one separator plate (150) in contact with one side of the gas diffusion layer (130).

[0035] For example, the catalyst layer (120) may be formed as a first catalyst layer and a second catalyst layer facing each other on both sides of the polymer electrolyte membrane (110), and the gas diffusion layer (130) may be arranged as a first gas diffusion layer provided on one side of the first catalyst layer and a second gas diffusion layer provided on one side of the second catalyst layer. A carbon nanotube sheet layer (140) may be arranged between the first catalyst layer and the first gas diffusion layer and between the second catalyst layer and the second gas diffusion layer. Alternatively, the carbon nanotube sheet layer (140) may be arranged between the first catalyst layer and the first gas diffusion layer or between the second catalyst layer and the second gas diffusion layer. That is, a carbon nanotube sheet layer (140) may be inserted as an intermediate layer between the catalyst layer (120) and the gas diffusion layer (130).

[0036] According to one embodiment of the present invention, a carbon nanotube sheet layer (140) may be disposed between a catalyst layer (120) and a gas diffusion layer (130) disposed on either side of the polymer electrolyte membrane (110). That is, the carbon nanotube sheet layer (140) may be disposed between a catalyst layer (120) and a gas diffusion layer (130) formed on one side of the polymer electrolyte membrane (110) with respect to the polymer electrolyte membrane.

[0037] Additionally, when the carbon nanotube sheet layer (140) is placed between the catalyst layer (120) and the gas diffusion layer (130) placed on either side of the polymer electrolyte membrane (110), the separator plate (150) may be placed to be in contact with the gas diffusion layer (130) of the catalyst layer (120) placed on the other side of the polymer electrolyte membrane (110).

[0038] That is, when the carbon nanotube sheet layer (140) is placed between the catalyst layer (120) and the gas diffusion layer (130) formed on one side of the polymer electrolyte membrane (110) with respect to the polymer electrolyte membrane (110), a separator plate (150) may be placed to contact the gas diffusion layer (130) placed on one side of the catalyst layer (120) formed on the opposite side of the polymer electrolyte membrane (110).

[0039] According to the structure described above, a polymer electrolyte membrane fuel cell unit cell (100) according to one embodiment of the present invention may have a structure in which a separator plate (150) in contact with a gas diffusion layer (130) is disposed on one side based on the polymer electrolyte membrane (110), and no separator plate is formed on the other side.

[0040] For example, a polymer electrolyte membrane fuel cell unit cell (100) may be arranged or stacked in the order of a separator (150), a gas diffusion layer (130), a catalyst layer (120), a polymer electrolyte membrane (110), a catalyst layer (120), a carbon nanotube sheet layer (140), and a gas diffusion layer (130).

[0041] Specifically, the carbon nanotube sheet layer (140) may be positioned between the catalyst layer (120) and the gas diffusion layer (130) on the anode (oxidation electrode) side and the separator plate (150) may be positioned to be in contact with the gas diffusion layer (130) on the cathode (reduction electrode) side, or the carbon nanotube sheet layer (140) may be positioned between the catalyst layer (120) and the gas diffusion layer (130) on the cathode (reduction electrode) side and the separator plate (150) may be positioned to be in contact with the gas diffusion layer (130) on the anode (oxidation electrode) side.

[0042] In a polymer electrolyte membrane fuel cell unit cell (100) according to one embodiment of the present invention, a carbon nanotube sheet layer (140) may be disposed between a catalyst layer (120) and a gas diffusion layer (130) on the negative electrode side, and a separator (150) may be disposed to be in contact with a gas diffusion layer (130) on the positive electrode side. That is, a carbon nanotube sheet layer (140) with a flow channel formed between the catalyst layer and the gas diffusion layer (130) on the negative electrode side is disposed to replace the separator on the negative electrode side, and the separator (150) may be formed only on the positive electrode side.

[0043] Meanwhile, FIG. 2 schematically illustrates another exemplary embodiment of the unit cell (100) of the polymer electrolyte membrane fuel cell shown in FIG. 1.

[0044] Referring to FIG. 2, the components of the polymer electrolyte membrane fuel cell unit cell (100) described above in FIG. 1 may be formed in the opposite order. For example, the polymer electrolyte membrane fuel cell unit cell (100') may be arranged or stacked in the order of a gas diffusion layer (130'), a carbon nanotube sheet layer (140'), a catalyst layer (120'), a polymer electrolyte membrane (110'), a catalyst layer (120'), a gas diffusion layer (130'), and a separator (150'), but is not limited thereto.

[0045] According to the structure described above, the proportion of the separator in the polymer electrolyte membrane fuel cell unit cell is reduced, thereby improving the volumetric power density of the fuel cell. In addition, as the cell thickness of the polymer electrolyte membrane fuel cell unit cell decreases, the movement paths of reactants and charges within the polymer electrolyte membrane fuel cell are shortened, which can improve the electrochemical performance of the fuel cell.

[0046] The polymer electrolyte membrane (110, 110') may include one or more selected from the group consisting of fluorine-based polymers, ketone-based polymers, benzimidazole-based polymers, amide-based polymers, and imide-based polymers. Additionally, the polymer electrolyte membrane (110, 110') may include one or more selected from the group consisting of fluorosulfonic acid polymers, perfluorocarbon sulfonic acid polymers, polyimide, polyvinylidene fluoride, polyethersulfone, polyphenylene sulfide, polyphenylene oxide, polyphosphazine, polyethylene naphthalate, polyester, polyetherketone, polysulfone, meta-polybenzimidazole, para-polybenzimidazole, poly[2-5-benzimidazole], and phosphoric acid-doped polybenzimidazole, but is not limited thereto, and is not limited to any known polymer electrolyte membrane applied to a polymer electrolyte membrane fuel cell.

[0047] The catalyst layer (120, 120') is arranged to face both sides of the polymer electrolyte membrane (110, 110'), and the catalyst layer may include one or more materials selected from the group consisting of platinum, palladium, ruthenium, osmium, cobalt, gold, tin, molybdenum, rhodium, iridium, bismuth, copper, nickel, iron, yttrium, and chromium, but is not limited thereto, and is not limited to any known catalyst layer material applied to a polymer electrolyte membrane fuel cell unit cell.

[0048] The gas diffusion layer (130, 130') is generally composed of a microporous layer and a gas diffusion backing layer, and due to this porous structure, it provides a pathway for the movement of reactants and products within a polymer electrolyte membrane fuel cell unit cell and plays a role in improving the dispersion of reactants and water management. Although not limited thereto, the microporous layer may include carbon black and polytetrafluoroethylene (PTFE), and the gas diffusion backing layer may be a carbon substrate, one of carbon paper, carbon fiber woven fabrics, or carbon fiber non-woven fabrics.

[0049] In a polymer electrolyte membrane fuel cell unit cell (100) according to one embodiment of the present invention, a carbon nanotube sheet layer (140, 140'), which is a functional layer, is inserted as an intermediate layer between a catalyst layer (120, 120') and a gas diffusion layer (130, 130'), and a flow channel through which reaction gas and products move is formed on the surface of the carbon nanotube sheet layer (140, 140'). In addition, a rib without a channel is formed between the formed flow channels.

[0050] The fluid channel may have a shape that is repeatedly bent. Alternatively, the fluid channel may have a shape that is repeatedly folded. For example, the fluid channel may have a shape that includes a straight section and a bent section or folded section extending from the straight section, with these parts repeating. The fluid channel may be in a serpentine shape, a single serpentine shape, or a multiple serpentine shape. Although not limited thereto, the shape of the fluid channel may be a shape in which the straight section of the fluid channel and the bent section or folded section extending from the straight section have the same thickness.

[0051] The flow channels formed in the carbon nanotube sheet layers (140, 140') can have a long flow path by having a shape that is repeatedly bent or folded, which allows the reaction gas to be distributed uniformly, thereby increasing reaction uniformity and allowing the reaction product to flow smoothly without stagnation, thus improving stability. Accordingly, the performance of the polymer electrolyte membrane fuel cell can be improved.

[0052] Although not limited thereto, the thickness of the above-mentioned flow channel may be 0.3 to 0.7 mm, 0.3 to 0.6 mm, 0.4 to 0.6 mm, or 0.4 to 0.5 mm. The thickness of the above-mentioned flow channel refers to the width of the flow channel. If the thickness of the flow channel is less than 0.3 mm, the flow of gas and products moving through the flow channel is not smooth, which may result in insufficient fuel supply inside the fuel cell, making it difficult for a uniform reaction to occur, and flooding may occur as the generated water cannot be discharged. Additionally, if the thickness of the above-mentioned flow channel exceeds 0.7 mm, the area of ​​the ribs between the channels may decrease, which may reduce electrical conductivity, and the reaction product, water, may be easily discharged, which may cause the polymer electrolyte membrane to fail to sufficiently retain moisture, thereby degrading the performance of the fuel cell.

[0053] Although not limited to this, the flow channels formed in the carbon nanotube sheet layers (140, 140') may be formed by laser engraving.

[0054] Meanwhile, a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention may further include a gasket disposed along the periphery of a gas diffusion layer or a gas diffusion layer and a carbon nanotube sheet layer. For example, in an area where a separator is disposed, the gasket may be disposed along the periphery of the gas diffusion layer, and in an area where a separator is not disposed, the gasket may be disposed along the periphery of the gas diffusion layer and the carbon nanotube sheet layer.

[0055] In addition, it may further include a current collector provided on the outer surface of the separator or gas diffusion layer and an end plate provided on the outer surface of the current collector.

[0056] Although not limited thereto, a polymer electrolyte fuel cell unit cell according to one embodiment of the present invention may be applied to a polymer electrolyte fuel cell stack comprising a plurality of unit cells.

[0058] According to another aspect, a method for manufacturing a polymer electrolyte membrane fuel cell unit cell of the present invention comprises the steps of: forming a catalyst layer by coating a catalyst on both sides of a polymer electrolyte membrane; forming a gas diffusion layer on one side of the catalyst layer; forming a carbon nanotube sheet layer by inserting a carbon nanotube sheet having a flow channel formed between the catalyst layer and the gas diffusion layer; and forming a separator plate in contact with one side of the gas diffusion layer.

[0059] The step of forming a catalyst layer is to form a catalyst layer by coating a solution containing a catalyst on both sides of the polymer electrolyte membrane. Although not limited thereto, the coating may be a method of directly coating the catalyst layer on the polymer electrolyte membrane, and the coating may be carried out by one of spray coating, doctor blade coating, slot-die coating, and comma roll coating.

[0060] The step of forming a gas diffusion layer on one surface of the catalyst layer may include the step of manufacturing the gas diffusion layer. The gas diffusion layer is composed of a microporous layer and a gas diffusion support layer, and can be manufactured by attaching the gas diffusion support layer onto the microporous layer, and the manufactured gas diffusion layer can be disposed on and attached to one surface of the catalyst layer.

[0061] FIG. 3(a) is a schematic diagram showing the manufacturing process of a carbon nanotube sheet according to one embodiment of the present invention, FIG. 3(b) is a schematic diagram showing an example of a carbon nanotube sheet according to one embodiment of the present invention, and FIG. 4 is a schematic diagram showing an example of the internal structure of a carbon nanotube sheet after heat treatment and acid treatment according to one embodiment of the present invention.

[0062] According to one embodiment of the present invention, the step of forming a carbon nanotube sheet layer may include the step of preparing a carbon nanotube sheet and the step of forming a flow channel on the carbon nanotube sheet.

[0063] Referring to FIGS. 3(a) and (b), the step of preparing the carbon nanotube sheet may include the step of synthesizing carbon nanotubes to manufacture the carbon nanotube sheet. The synthesis of the carbon nanotube sheet may involve synthesizing carbon nanotubes using a precursor solution containing a carbon source and hydrogen gas, etc., and the synthesized carbon nanotubes may be multi-walled carbon nanotubes, but are not limited thereto.

[0064] Although not limited to this, the method for manufacturing the carbon nanotube sheet may be one of direct spinning, forest spinning, wet spinning, or powder pressing.

[0065] According to one embodiment, the step of preparing the carbon nanotube sheet may include the step of purifying the carbon nanotube sheet by heat treatment and acid treatment.

[0066] Referring to FIG. 4, residual catalyst and amorphous carbon may be included as byproducts during the synthesis process of carbon nanotube sheets. Since these impurities can cause a degradation in the performance of polymer electrolyte membrane fuel cells, a process of purifying the carbon nanotube sheets is required before forming flow channels on the carbon nanotube sheets. Accordingly, amorphous carbon can be removed by heat-treating the carbon nanotube sheets, and the carbon nanotube sheets can be purified by acid-treating the heat-treated carbon nanotube sheets to remove impurities such as iron.

[0067] FIG. 5 is a schematic diagram illustrating the process of imprinting a flow channel on a purified carbon nanotube sheet using a laser according to one embodiment of the present invention.

[0068] Referring to FIG. 5, the step of forming a flow channel on a carbon nanotube sheet can be performed by imprinting the shape of the flow channel on the carbon nanotube sheet with a laser. In the step of forming a flow channel on a carbon nanotube sheet according to one embodiment of the present invention, by imprinting the shape of the flow channel on the carbon nanotube sheet using a laser, the flow channel can be formed more finely, and it may be easier to laser process only the portion forming the channel. In addition, the carbon nanotube sheet can be processed non-contactually, thereby preventing deformation or damage to the carbon nanotube sheet.

[0069] Meanwhile, the step of forming the carbon nanotube sheet layer may further include the step of inserting a carbon nanotube sheet having a flow channel formed between the catalyst layer and the gas diffusion layer formed on one side of the polymer electrolyte membrane. That is, in the step of forming the gas diffusion layer on one side of the catalyst layer described above, a carbon nanotube sheet having a flow channel formed can be inserted and bonded before the gas diffusion layer is attached and disposed on one side of the catalyst layer.

[0070] According to one embodiment of the present invention, a carbon nanotube sheet having a flow channel formed between a catalyst layer and a gas diffusion layer disposed on one side of a polymer electrolyte membrane can be inserted, and on the other side of the polymer electrolyte membrane, a separator plate can be formed to contact the catalyst layer disposed on the other side and the gas diffusion layer formed on one side of the catalyst layer.

[0071] Specifically, a carbon nanotube sheet layer may be placed between the catalyst layer and the gas diffusion layer on the anode (oxidation electrode) side and a separator plate may be formed to be in contact with the gas diffusion layer on the cathode (reduction electrode) side, or a carbon nanotube sheet layer may be placed between the catalyst layer and the gas diffusion layer on the cathode (reduction electrode) side and a separator plate may be formed to be in contact with the gas diffusion layer on the anode (oxidation electrode) side. In a method for manufacturing a polymer electrolyte membrane fuel cell according to one embodiment of the present invention, it may be more suitable to place a carbon nanotube sheet layer between the catalyst layer and the gas diffusion layer on the cathode (reduction electrode) side and form a separator plate to be in contact with the gas diffusion layer on the anode (oxidation electrode) side.

[0072] Although not limited to this, the step of forming a separator on one side of the gas diffusion layer may be performed after the carbon nanotube sheet layer is placed and bonded between the catalyst layer and the gas diffusion layer.

[0073] Meanwhile, a method for manufacturing a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention may further include the step of forming a unit cell comprising a polymer electrolyte membrane, a catalyst layer, a gas diffusion layer, a carbon nanotube sheet layer, and a separator, and arranging and combining other components constituting the polymer electrolyte membrane fuel cell, such as a gasket, a current collector, and an end plate, to manufacture a polymer electrolyte membrane fuel cell, but is not limited thereto.

[0075] [Example]

[0076] Examples

[0077] 1. Preparation and purification of carbon nanotube sheets

[0078] Carbon nanotube (CNT) sheets were synthesized using a direct spinning method in a chemical vapor deposition (CVD) chamber. The precursor solution was prepared by using acetone (99.7%, Samchun Chemicals, Republic of Korea) and ethylene glycol (Samchun Chemicals, Republic of Korea) as carbon sources, and mixing ferrocene (catalyst precursor, 98%, Sigma-Aldrich, USA) and teraphine (catalyst activator, 99%, Sigma-Aldrich, USA). Subsequently, carbon nanotubes were synthesized by injecting the mixed precursor solution and hydrogen gas (99.99%) into a vertical CVD chamber preheated to 1450°C at flow rates of 0.6 sccm and 2200 sccm, respectively. The synthesized carbon nanotubes were rolled onto rollers and collected into a sheet structure to produce carbon nanotube sheets.

[0079] To remove amorphous carbon from the prepared carbon nanotube sheets, heat treatment was performed in a furnace at 550°C for 30 minutes. The heat-treated carbon nanotube sheets were acid-treated by immersing them in an oil bath with 11.32 M HCl (Sigma-Aldrich, United States of America) for 30 minutes to remove impurities such as iron catalysts, and then washed with distilled water and ethanol, followed by drying in an oven for 12 hours to complete the purification.

[0080] 2. Carbon nanotube sheet channel imprinting

[0081] After designing a serpentine-shaped flow channel, the designed flow channel shape was input into a laser engraving machine (marking machine). The focal length of the laser engraving machine was adjusted to 10.4 cm, the power was set to 0.4 W, and the number of etching passes was adjusted to 50. To accurately engrave the channel shape, a carbon nanotube sheet was placed and fixed on a fixed platform, and then the laser engraving process was performed on the carbon nanotube sheet using the designed flow channel shape.

[0082] 3. Preparation of catalyst layer coated electrolyte membrane

[0083] The catalyst ink was prepared by mixing 40 wt% Pt / C (Alfa Aesar, United Kingdom), 5 wt% Nafion solution (Dupont CO., United States of America), isopropyl alcohol (Daejung Chemical Co., LTD., Republic of Korea), and deionized water, and the mixture was ultrasonically treated for 30 minutes to ensure uniform dispersion. The prepared catalyst ink was placed on a hot plate set at 80 ℃ using a spray method. ® It was uniformly coated on a 211 membrane (Dupont Co., United States of America). Both the anode and cathode were fabricated using the same method, and both electrodes were 5 cm in diameter. 2 0.12 mg / cm² to prepare the active region 2 It was set to Pt loading.

[0084] 4. Fabrication of Polymer Electrolyte Membrane Fuel Cell Unit Cells

[0085] FIGS. 6(a) and 6(b) are schematic diagrams showing the structure of a polymer electrolyte membrane fuel cell unit cell according to one embodiment and a comparative example of the present invention, and FIGS. 7(a) and 7(b) are cross-sectional views showing the structure of a polymer electrolyte membrane fuel cell unit cell according to one embodiment and a comparative example of the present invention.

[0086] For example, FIGS. 7(a) and 7(b) may each be illustrated with the order of the components of the unit cell shown in FIGS. 6(a) and 6(b) reversed.

[0087] Referring to FIGS. 6(a) and FIGS. 7(a), the polymer electrolyte membrane fuel cell unit cell comprises a catalyst layer coated on both sides of the membrane, a cathode catalyst layer, and an anode catalyst layer, and includes a gas diffusion layer (GDL) on one side of each catalyst layer. A carbon nanotube sheet with an engraved flow channel and a thickness of 30 μm is inserted between the interface of the cathode catalyst layer and the anode gas diffusion layer. Additionally, a bipolar plate (BP) is positioned to be in contact with the anode gas diffusion layer formed on one side of the anode catalyst layer.

[0088] A separator was formed only on the anode, and a unit cell was fabricated with a BP-less structure in which a carbon nanotube sheet layer was introduced as a functional layer on the cathode side without a separator. In other words, a carbon nanotube sheet layer with a flow field (flow channel) formed between the catalyst layer and the gas diffusion layer on the cathode side was inserted to replace the separator on the cathode side. The graphite anode separator utilized a single serpentine flow field shape with a flow field thickness of 0.5 mm.

[0089] Meanwhile, in the anode region where the separator is formed, a gasket (not shown) was placed along the periphery of the gas diffusion layer, and in the cathode region where the separator is not placed, a gasket (not shown) was placed along the periphery of the gas diffusion layer and the carbon nanotube sheet layer. In addition, a current collector (not shown) was placed outside the separator on the anode side and the gas diffusion layer on the cathode side, and an end plate (not shown) was placed on one side of each current collector to be positioned at the outermost edges of both sides of the unit cell, and the polymer electrolyte membrane fuel cell unit cell was manufactured by assembly.

[0090] The end plate was made of aluminum and anodized to prevent the risk of current leakage and to improve corrosion resistance. The current collector was made of beryllium copper and coated with gold to improve electrical conductivity. 36BB (Sigracet, Germany) was used for the gas diffusion layer, and a PTFE gasket (Tommyheco Co., Ltd., Republic of Korea) was used for proper sealing.

[0092] Comparative example

[0093] Referring to FIGS. 6(b) and FIGS. 7(b), a polymer electrolyte membrane fuel cell unit cell was manufactured by utilizing and assembling the same configuration as in the example, except for the channel imprinting of the carbon nanotube sheet, the insertion of the channel-imprinted carbon nanotube sheet layer, and the presence or absence of the reduction electrode separator.

[0094] The graphite separator utilized a single serpentine flow field shape with a flow channel thickness of 0.5 mm and was applied to both the oxidation and reduction electrode regions.

[0096] [Experimental Example]

[0097] Experimental Example 1. Analysis of the surface structure of purified carbon nanotube sheets

[0098] To confirm changes in the structural characteristics of the surface of a carbon nanotube sheet due to heat treatment and acid treatment, a field emission scanning electron microscope (FE-SEM) was used, and measurements were performed at 10,000 X and 30,000 X, respectively. FIG. 8(a) is an FE-SEM image showing the surface structure of a carbon nanotube sheet before heat treatment and acid treatment according to one embodiment of the present invention, and FIG. 8(b) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after heat treatment and acid treatment according to one embodiment of the present invention. FIG. 8(c) is an FE-SEM image showing the surface structure of a carbon nanotube sheet before heat treatment and acid treatment, enlarged from FIG. 8(a), and FIG. 8(d) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after heat treatment and acid treatment, enlarged from FIG. 8(b).

[0099] Referring to FIGS. 8(a) to (d), it can be seen that when heat treatment and acid treatment are performed on carbon nanotube sheets, amorphous carbon and iron catalyst, which are byproducts generated during the synthesis of carbon nanotubes, are significantly removed. Through this, when the purified carbon nanotube sheets are utilized in the unit cell of a polymer electrolyte membrane fuel cell, an improved interface can be provided in terms of contact within the unit cell, thereby improving electrical conductivity within the cell. In addition, it is possible to prevent the phenomenon where the pores through which reactants move during the operation of the fuel cell are blocked by byproducts.

[0100] Experimental Example 2. Analysis of the surface structure of channel-imprinted carbon nanotube sheets

[0101] FE-SEM was used to confirm structural differences in the surface of carbon nanotube sheets used in channels and ribs due to laser engraving, and measurements were performed at 10,000 X and 30,000 X, respectively.

[0102] FIG. 9(a) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after a flow channel is laser-engraved according to one embodiment of the present invention, and FIG. 9(b) is an FE-SEM image showing the surface structure of a carbon nanotube sheet after a flow channel is laser-engraved, enlarged from FIG. 9(a). FIG. 9(c) is an FE-SEM image showing the rib region after a flow channel is laser-engraved according to one embodiment of the present invention, enlarged from the rib region, and FIG. 9(d) is an FE-SEM image showing the channel region after a flow channel is laser-engraved according to one embodiment of the present invention.

[0103] Referring to Figures 9(a) and 9(b), the flow channels of the carbon nanotube sheet were formed into channels (dark areas) and rib areas (bright areas) after laser engraving. Referring to Figures 9(c) and 9(d), when the flow channels were laser-engraved on the carbon nanotube sheet layer, the corresponding areas showed a phenomenon where the carbon nanotube fibers became thinner and partially destroyed compared to the rib areas that were not laser-engraved; however, it can be confirmed that the destruction of the fibers did not occur completely because the laser could not penetrate beyond a certain depth.

[0104] Experimental Example 3. Measurement of Electrochemical Performance of Polymer Electrolyte Membrane Fuel Cells

[0105] The electrochemical performance of polymer electrolyte membrane fuel cells under relative humidity conditions was verified using a polarization curve.

[0106] FIGS. 10(a) to 10(d) are graphs showing polarization curves of a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention under relative humidity conditions of 100%, 80%, 60%, and 40%.

[0107] Referring to FIGS. 10(a) to 10(d), it can be confirmed that the cell of the example (CNT with channel 0.5 mm 1 set) with a carbon nanotube sheet layer imprinted with flow channels exhibits high power density under all relative humidity conditions. In particular, the 588 mW / cm² of the comparative example (Conventional) cell in a high humidity environment 2 839 mW / cm², a 43% improvement in performance 2 The performance was demonstrated. The example cell showed a greater improvement effect compared to the comparative example cell as electrochemical performance measurements were conducted under lower relative humidity conditions, and at the lowest relative humidity of 40%, it recorded 562 mW / cm². 2 As such, it showed a 128% improvement in performance compared to the comparative example, which is a general polymer electrolyte membrane fuel cell unit cell structure.

[0108] Experimental Example 4. Measurement of Ohmic Resistance and Charge Transfer Resistance

[0109] The ohmic resistance and charge transfer resistance of a polymer electrolyte membrane fuel cell were measured under relative humidity conditions using electrochemical impedance spectroscopy (EIS).

[0110] FIGS. 11(a) to 11(d) are graphs showing the results of electrochemical impedance spectroscopy of a polymer electrolyte membrane fuel cell unit cell according to one embodiment of the present invention under conditions of relative humidity of 100%, 80%, 60%, and 40%.

[0111] Referring to FIGS. 11(a) to 11(d), the example showed improvements in both ohmic resistance and charge transfer resistance under all relative humidity conditions, with ohmic resistance showing an improvement of 18% to 24% compared to the comparative example and charge transfer resistance showing an improvement of 38% to 60% compared to the comparative example. In particular, significant improvements were measured in each resistance under lower relative humidity conditions, which is because the thickness of the cell can be reduced by utilizing a thin carbon nanotube sheet layer as a functional layer along with the removal of the separator, thereby shortening the movement path of reactants and charges.

[0113] Although an embodiment of the present invention has been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the present invention as described in the claims, and such modifications and changes are also to be included within the scope of the rights of the present invention.

Claims

Claim 1 A polymer electrolyte membrane fuel cell comprising: a polymer electrolyte membrane; a catalyst layer disposed to face both sides of the polymer electrolyte membrane; a gas diffusion layer disposed on one side of the catalyst layer; one or more carbon nanotube sheet layers disposed between the at least one catalyst layer and the gas diffusion layer, having flow channels formed therein for moving reaction gases and products; and at least one separator plate in contact with one side of the gas diffusion layer. Claim 2 A polymer electrolyte membrane fuel cell according to claim 1, wherein the carbon nanotube sheet layer is disposed between a catalyst layer and a gas diffusion layer disposed on one of the two sides of the polymer electrolyte membrane, and the separator plate is in contact with the gas diffusion layer of the catalyst layer disposed on the other side of the polymer electrolyte membrane. Claim 3 A polymer electrolyte membrane fuel cell according to claim 1, wherein the flow channel has a repeatedly bending shape. Claim 4 A polymer electrolyte membrane fuel cell according to claim 1, wherein the thickness of the flow channel is 0.3 to 0.7 mm. Claim 5 A polymer electrolyte membrane fuel cell according to claim 1, wherein the flow channel formed in the carbon nanotube sheet layer is formed by laser engraving. Claim 6 A method for manufacturing a polymer electrolyte membrane fuel cell, comprising the steps of: forming a catalyst layer by coating a catalyst on both sides of a polymer electrolyte membrane; forming a gas diffusion layer on one side of the catalyst layer; forming a carbon nanotube sheet layer by inserting a carbon nanotube sheet having a flow channel formed between the catalyst layer and the gas diffusion layer; and forming a separator plate to be in contact with one side of the gas diffusion layer. Claim 7 A method for manufacturing a polymer electrolyte membrane fuel cell, wherein, in claim 6, the step of forming the carbon nanotube sheet layer comprises: a step of preparing a carbon nanotube sheet; and a step of forming a flow channel on the carbon nanotube sheet. Claim 8 A method for manufacturing a polymer electrolyte membrane fuel cell, wherein, in claim 7, the step of preparing the carbon nanotube sheet includes the step of purifying the carbon nanotube sheet by heat treatment and acid treatment. Claim 9 In claim 7, the step of forming a flow channel on the carbon nanotube sheet is formed by imprinting the shape of the flow channel on the carbon nanotube sheet with a laser, a method for manufacturing a polymer electrolyte membrane fuel cell. Claim 10 In claim 6, the step of forming the catalyst layer is to form a catalyst layer by coating a solution containing a catalyst on both sides of the polymer electrolyte membrane, in a method for manufacturing a polymer electrolyte membrane fuel cell.

Images