Fuel cell manufacturing method for controlling antioxidant position

Abstract

A method of manufacturing a fuel cell and a fuel cell manufactured according to the method. The method may include: joining a sub-gasket provided with an air inlet and a hydrogen inlet to a side surface of a three-layer membrane electrode assembly (MEA) including an electrolyte membrane, a cathode located on one surface of the electrolyte membrane, and an anode located on the other surface of the electrolyte membrane; laminating a gas diffusion layer containing an antioxidant precursor on the cathode and the anode, and preparing a five-layer MEA; and applying a current to the five-layer MEA and moving an antioxidant derived from the antioxidant precursor to the electrolyte membrane.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a fuel cell and a fuel cell manufactured according to the method, the method causing metal ions contained in an antioxidant to locally migrate to a region of an electrolyte membrane where a large amount of chemical degradation occurs. Background Art

[0002] Generally, a polymer electrolyte membrane fuel cell (PEMFC) is applied as a fuel cell for a vehicle. In order for a PEMFC to exhibit a normal high output performance of at least several tens of kW under various driving conditions of the vehicle, the PEMFC should be able to operate stably within a wide current intensity range.

[0003] The reaction for generating electricity in a PEMFC occurs in a membrane electrode assembly (MEA) formed by a perfluorosulfonic acid ionomer-based membrane and electrodes of an anode and a cathode. Hydrogen supplied to the anode (oxide electrode of the PEMFC) is separated into hydrogen ions (protons) and electrons, and then the hydrogen ions migrate through the membrane toward the cathode (reduction electrode), and the electrons migrate to the cathode through an external circuit. Then, oxygen molecules, hydrogen ions, and electrons react together at the cathode to generate electricity and heat, while generating water (H 2 O) as a reaction by-product.

[0004] When an appropriate amount of water is present, the water generated during the electrochemical reaction in a PEMFC is desirably used to keep the MEA moist. However, when too much water is present, a flooding phenomenon occurs at high current intensities. The flooded water hinders the effective supply of reaction gases into the PEMFC, making the voltage loss very large. In the electrochemical reaction of such a PEMFC, when hydrogen ions at the anode migrate through the membrane to the cathode, the hydrogen ions usually combine with water molecules in the form of hydronium ions (such as H 3 O + ) to drag the water molecules. This phenomenon is called electro-osmotic drag (EOD). Additionally, when the amount of water accumulated at the cathode increases, some water may move in the reverse direction from the cathode to the anode, which is called back diffusion (BD). Therefore, in order to obtain excellent battery performance from a PEMFC, it is necessary to accurately understand the water movement phenomenon and effectively utilize the water in the PEMFC.

[0005] Generally, hydrogen and oxygen in air, which are reaction gases of a PEMFC, pass through an electrolyte membrane to promote the generation of hydrogen peroxide (H-O-O-H), and the hydrogen peroxide generates hydroxyl radicals (-OH) and oxygen-containing radicals (e.g., perhydroxyl radicals (-OOH)). These radicals attack the perfluorosulfonic acid-based electrolyte membrane to cause chemical degradation of the electrolyte membrane, thereby reducing the durability of the PEMFC. Conventionally, as a technique for mitigating the chemical degradation of the electrolyte membrane, methods of adding various antioxidants to the electrolyte membrane have been proposed. In addition, as the guaranteed ability time of the MEA increases, research has been conducted in the direction of increasing the ability of the antioxidant or increasing the absolute amount of the antioxidant.

[0006] However, due to technical limitations, the direction of improving the ability of the antioxidant requires a large amount of research time and investment. Therefore, industrially, most research has been conducted in the direction of increasing the absolute amount of the antioxidant in the electrolyte membrane. However, when only the absolute amount of the antioxidant is increased, metal ions representing antioxidation enter the electrolyte membrane in an amount exceeding a predetermined amount to chelate with sulfonic acid groups 3ea representing proton conduction. Therefore, there is a problem that the conductivity decreases and thus the ohmic loss increases. In addition, when only the absolute amount of the antioxidant is increased, there is the following problem: when the process of transferring the cathode / anode electrode is performed, the transferability deteriorates due to changes in surface characteristics, and the incidence of defects may increase rapidly.

[0007] Therefore, there is a need for an effective and economical method for manufacturing a fuel cell by introducing an antioxidant only into the electrolyte membrane where degradation frequently occurs at a high concentration. SUMMARY OF THE INVENTION

[0008] In a preferred aspect, there is provided a method for manufacturing a fuel cell and a fuel cell manufactured by the method, the method causing metal ions contained in an antioxidant to locally migrate to a region of the electrolyte membrane having a large amount of chemical degradation.

[0009] The object of the present invention is not limited to the above object, and other objects not mentioned in the present invention can be understood through the following description, and other objects of the present invention will also be obviously understood through the embodiments of the present invention. In addition, the object of the present invention can be achieved by the means described in the appended claims and their combinations.

[0010] In one aspect, a method of manufacturing a fuel cell is provided, the method comprising: joining a sub-gasket provided with an air inlet and a hydrogen inlet to a side of a three-layer membrane electrode assembly (MEA), the three-layer membrane electrode assembly including an electrolyte membrane, a cathode on one surface of the electrolyte membrane, and an anode on the other surface of the electrolyte membrane; laminating a gas diffusion layer containing an antioxidant precursor on at least one of the cathode and the anode, and preparing a five-layer MEA; and applying a current to the five-layer MEA and moving an antioxidant derived from the antioxidant precursor to the electrolyte membrane.

[0011] The gas diffusion layer may include a substrate and a microporous layer on the substrate, the microporous layer may be on at least one of the cathode and the anode, and the antioxidant precursor may be included in the microporous layer.

[0012] As used herein, "microporous layer" refers to a porous material including pores or holes having a size less than 2 nm. Exemplary microporous substrates may include closed pores or open pores within a predetermined size (e.g., less than 2 nm), the predetermined size being measured by the maximum diameter of the pores.

[0013] The antioxidant precursor may include an oxide of an antioxidant.

[0014] The antioxidant precursor may include CeO 2 and MgO 2 or at least one of them.

[0015] The antioxidant may be in an ionic state.

[0016] The antioxidant may include one or more selected from Ce 3+ 、Ce 4+ 、Mg 2+ and Mg 3+ or more of them.

[0017] The microporous layer may contain an antioxidant precursor in a content range of about 165 μg / cm 2 to about 210 μg / cm 2 of it.

[0018] The thickness range of the microporous layer may be about 10 μm to about 100 μm.

[0019] The current may be applied to the gas diffusion layer at an intensity range of about 50 A to about 250 A.

[0020] The current may be applied to the gas diffusion layer under conditions of a temperature range of 30 °C to about 90 °C, a humidity range of about 30% to about 100%, and an application time of the current of more than 3 hours.

[0021] The method described herein, and the antioxidant derived from the antioxidant precursor included in the gas diffusion layer may be included in the electrolyte membrane.

[0022] The antioxidant can be mainly distributed in a portion of the electrolyte membrane corresponding to the gas diffusion layer adjacent to the air inlet of the adjacent sub-gasket in the thickness direction.

[0023] The antioxidant can be contained in the electrolyte membrane in a content range of about 0.1 μm / cm 2 to about 20 μm / cm. 2

[0024] Other aspects of the present invention are discussed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments shown in the accompanying drawings, which are given by way of example only hereinafter and thus do not limit the present invention, wherein:

[0026] Figure 1 shows an exemplary method of manufacturing a fuel cell according to an exemplary embodiment of the present invention;

[0027] Figure 2A shows an exemplary gas diffusion layer including an antioxidant precursor according to an exemplary embodiment of the present invention, the gas diffusion layer being arranged in contact with each of the cathode and the anode;

[0028] Figure 2B shows an exemplary three-layer membrane electrode assembly (MEA) after arranging a gas diffusion layer including an antioxidant precursor in contact with each of the cathode and the anode according to an exemplary embodiment of the present invention;

[0029] Figure 3 shows an exemplary gas diffusion layer according to an exemplary embodiment of the present invention;

[0030] Figure 4A is a mapping image showing the distribution of cerium ions before and after a durability test of an exemplary MEA in a fuel cell manufactured according to an exemplary embodiment of the present invention;

[0031] Figure 4B is a plan view showing the distribution of cerium ions in the plane of an exemplary electrolyte membrane after applying a current satisfying the conditions of the present invention to a fuel cell manufactured according to an exemplary embodiment of the present invention;

[0032] Figure 4C is a plan view showing the distribution of cerium ions through a cross-section of an exemplary electrolyte membrane after applying a current satisfying the conditions of the present invention to a fuel cell manufactured according to an exemplary embodiment of the present invention;

[0033] Figure 5A and Figure 5B ​Shows the distribution of cerium ions in the plane of the electrolyte membrane in the fuel cells according to Comparative Examples 1-1 and 1-2;

[0034] Figures 6A to 6C Shows the distribution of cerium ions in the plane of the electrolyte membrane in the fuel cells according to Comparative Examples 2-1 to 2-3;

[0035] Figures 7A to 7C Shows the distribution of cerium ions in the plane of the electrolyte membrane in the fuel cells according to Comparative Examples 2-1 to 2-3;

[0036] Figure 8A Is a graph showing the cell performance before the durability test of the fuel cells according to Examples 1-1 to 1-5;

[0037] Figure 8B Is a graph showing the cell performance after the durability test of the fuel cells according to Examples 1-1 to 1-5;

[0038] Figure 8C Is a bar graph showing the comparison of the cell performance before and after the durability test of the fuel cells according to Examples 1-1 to 1-5; and

[0039] Figure 9 Is a graph showing the analysis of the amount of cerium ions (antioxidant) with respect to the current holding time of the fuel cell according to Example 1-1.

[0040] It should be understood that the drawings are not necessarily drawn to scale, but rather present a somewhat simplified representation of the various features showing the basic principles of the present invention. Certain design features of the present invention disclosed herein, including for example specific dimensions, orientations, positions, and shapes, will be determined in part by the particular design application and use environment.

[0041] In the drawings, throughout the several views of the drawings, reference numerals refer to the same or equivalent parts of the present invention. Detailed Description of the Invention

[0042] Referring to the drawings, the above and other objects, features, and advantages of the present invention will become more apparent from the following description of the preferred embodiments. However, the present invention is not limited to the embodiments disclosed herein and may be implemented in different ways. The embodiments disclosed herein are provided to make the present invention thorough and complete and to fully convey the spirit of the present invention to those skilled in the art.

[0043] When describing the accompanying drawings, like reference numerals denote like components. In the drawings, dimensions of structures are shown at an enlarged scale for clarity of the present invention. Although terms such as first, second, third, etc. may be used herein to describe various components, these components should not be limited by these terms. The terms are only used for the purpose of differentiating one component from another. For example, without departing from the scope of the present invention, a first element may be termed a second element, and similarly, a second element may be termed a first element. Unless the context clearly dictates otherwise, the singular forms include the plural forms.

[0044] It should also be understood that the words "comprises", "comprising", "has" specify the presence of the features, integers, steps, operations, components, elements, or combinations thereof described herein, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, elements, or combinations thereof. Additionally, when a part of a layer, film, region, plate, etc. is referred to as being "on" another part, this includes not only the case where the part is "directly on" the other part, but also the case where another part is present between the part and the other part. Conversely, when a part of a layer, film, region, plate, etc. is referred to as being "under" another part, this includes not only the case where the part is "directly under" the other part, but also the case where another part is present between the part and the other part.

[0045] Unless otherwise indicated, all numbers, values, and / or expressions indicating amounts of ingredients, reaction conditions, polymer compositions, and combined products used herein are approximate values reflecting various measurement uncertainties, where various uncertainties arise when obtaining these values in other things that are essentially different, and thus it should be understood that all numbers, values, and / or expressions are modified by the term "about". Additionally, unless specifically stated or obvious from the context, the term "about" used herein should be understood to be within the normal tolerances in the art, for example, within two standard deviations of the average value. "About" can be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless clearly known from the context otherwise, all numerical values provided herein are modified by the term "about".

[0046] Additionally, when a numerical range is disclosed herein, unless otherwise indicated, such numerical range is continuous and the numerical range includes all values from the minimum value to the maximum value. Additionally, when the numerical range refers to integers, unless otherwise indicated, all integers from the minimum value to the maximum value are included.

[0047] In this specification, when describing the range of a variable, it should be understood that the variable includes all values within the range (including the endpoints described within the range). For example, it should be understood that the range from "5 to 10" includes the values 5, 6, 7, 8, 9, and 10, as well as any sub-ranges (e.g., from 6 to 10, from 7 to 10, from 6 to 9, from 7 to 9, etc.), and also includes any values between reasonable integers within the range (e.g., 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9, etc.). Additionally, for example, it should be understood that the range "10% to 30%" includes all integers (including the values 10%, 11%, 12%, 13%, etc. up to 30%), as well as sub-ranges 10% to 15%, 12% to 18%, 20% to 30%, etc., and also includes any values between reasonable integers within the range (e.g., 10.5%, 15.5%, 25.5%, etc.).

[0048] It should be understood that the term "vehicle" or "vehicular" or other similar terms used herein include general motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including various boats and ships, and aircraft, etc., and also include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels obtained from resources other than petroleum). As mentioned herein, a hybrid vehicle is a vehicle having two or more power sources, for example, a vehicle having both gasoline power and electric power.

[0049] Method for manufacturing a fuel cell

[0050] Figure 1 is a schematic flowchart showing a method of manufacturing a fuel cell according to an embodiment of the present invention. As Figure 1 shown, the method of manufacturing a fuel cell may include the following steps: joining a sub-gasket (provided with an air inlet and a hydrogen inlet) to the side surface of a three-layer membrane electrode assembly (MEA) including an electrolyte membrane, a cathode located on one surface of the electrolyte membrane, and an anode located on the other surface of the electrolyte membrane (S10); laminating a gas diffusion layer containing an antioxidant precursor on the cathode and the anode, and preparing a five-layer MEA (S20); and applying a current to the five-layer MEA and causing an antioxidant derived from the antioxidant precursor to move to the electrolyte membrane (S30).

[0051] The preparation step (S10) of the three-layer MEA joined with the sub-gasket includes the following process: preparing a three-layer MEA including a cathode located on one surface of the electrolyte membrane and an anode located on the other surface of the electrolyte membrane, and then joining a sub-gasket provided with an air inlet and a hydrogen inlet to the side surface of the three-layer MEA.

[0052] The electrolyte membrane according to the present invention can be a conventional electrolyte membrane that can be used in the present invention (e.g., perfluorosulfonic acid-based compounds and fluorine-based polymer compounds having a sulfonic acid group at the end group). Preferably, the electrolyte membrane can be Nafion and polytetrafluoroethylene (PTFE)-based polymers (polymers having MSC, LSC, and SSC group side chains in the Teflon main chain), but the electrolyte membrane is not limited to containing specific components.

[0053] The cathode located on one surface of the electrolyte membrane is a conventional cathode that can be used in the present invention, e.g., transition metal series (e.g., Pt / C, PtM x N y / C (M or N = Ni), Co, and Fe, noble metal-based catalysts other than Pd), and ionomers of PFSA-based polymer materials used as catalysts and binders in the electrode, but the cathode is not limited to containing specific components.

[0054] The anode located on the other surface of the electrolyte membrane is a conventional anode that can be used in the present invention, e.g., anodic voltage protection catalysts (e.g., Pt / C and IrO x )), and ionomers of PFSA-based polymer materials used as catalysts and binders in the electrode, but the anode is not limited to containing specific components.

[0055] The sub-gasket can be joined to the side of the three-layer MEA. The sub-gasket according to the present invention is not particularly limited as long as it can avoid MEA fluttering below 20 microns to improve working efficiency and can prevent edge failure of the MEA. Preferably, the sub-gasket can be formed in the edge region of the side of the three-layer MEA to seal the side end of the three-layer MEA. The shape of the sub-gasket can vary according to the general shape that can be used in the present invention (e.g., the shape of the five-layer MEA), and can include one or more of rectangular, square, oval, circular, and combinations thereof, but the shape of the sub-gasket is not limited to a specific shape.

[0056] The sub-gasket according to the present invention can be provided with an air inlet and a hydrogen inlet. Preferably, the portions near the air inlet and hydrogen inlet of the separator to be laminated can be referred to as the air inlet and hydrogen inlet of the sub-gasket.

[0057] The method of manufacturing a fuel cell according to the present invention has the following advantages: It is possible to selectively and concentratively introduce an antioxidant only into "the portion corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket in the thickness direction (the position where deterioration often occurs in the electrolyte membrane)" at a high concentration by applying specific current application conditions to the cell.

[0058] As Figure 2A and 2BAs shown, the steps (S20) for preparing the five-layer MEA include the following process: laminating a gas diffusion layer containing an antioxidant precursor on at least one of the cathode and the anode, and preparing a five-layer MEA (sub-gaskets not shown).

[0059] Figure 3 is an enlarged perspective view showing the gas diffusion layer according to the present invention. As Figure 3 shown, the gas diffusion layer according to the present invention may include a substrate and a microporous layer located on the substrate. The microporous layer may be located on at least one of the cathode and the anode, and preferably may be located on both the cathode and the anode. The microporous layer may include: i) one or more polymer materials selected from polypropylene oxide, polystyrene, polyarylether, and polyimide, and ii) a carbon material including a polymer material containing one or more PFSA groups.

[0060] The thickness of the microporous layer may be about 10 μm to about 100 μm. When the thickness of the microporous layer is less than about 10 μm, due to the too high density of the antioxidant content in the microporous layer, aggregation may occur, and thus there is a disadvantage that the structure of the microporous layer may be damaged due to the load applied when stacking unit cells. On the contrary, when the thickness is greater than about 100 μm, the density of the antioxidant content is too small, and thus there are the following disadvantages: when a current is applied for a certain time, an appropriate dissolved amount of antioxidant ions is not eluted, and the single cell spacing increases in the region with a thickness above a specific value, resulting in an increase in volume when stacking unit cells.

[0061] The microporous layer may include an antioxidant precursor. Preferably, the antioxidant precursor may include an oxide of an antioxidant, or particularly include one or more selected from CeO 2 and MgO 2 . The microporous layer may include an antioxidant precursor in a content range of about 165 μg / cm 2 to about 210 μg / cm 2 , preferably in a range of about 165 μg / cm 2 to about 190 μg / cm 2 . When the content of the antioxidant precursor is less than about 165 μg / cm 2 , there are the following disadvantages: the saturation amount of cerium ions is small, so the durability improvement effect is not significant, and when the content of the antioxidant precursor is greater than about 190 μg / cm 2 , due to the saturation amount of cerium ions being higher than a certain level, there is a disadvantage in terms of production cost.

[0062] The manufacturing method of the fuel cell according to the present invention has the following advantages: It is possible to apply an electric current to the gas diffusion layer under specific conditions, so that an antioxidant derived from an antioxidant precursor is placed in the electrolyte membrane, preferably in a portion of the electrolyte membrane corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket along the thickness direction.

[0063] The step (S30) of moving the antioxidant to the electrolyte membrane includes the following process: applying an electric current to the five-layer MEA under specific conditions, and moving the antioxidant derived from the antioxidant precursor to the electrolyte membrane.

[0064] An electric current can be applied to the five-layer MEA. Preferably, the electric current can be applied after forming a unit cell (wherein separators are laminated on two surfaces of the five-layer MEA), or an electric current can be applied to a stack (wherein unit cells are laminated). However, the application of the electric current is not limited by a specific type.

[0065] Therefore, the method for manufacturing a fuel cell according to the present invention has the following advantages: An electric current can be applied to the five-layer MEA under specific conditions, and a high-concentration antioxidant derived from an antioxidant precursor can be selectively and concentratedly placed only in a high concentration in "the portion corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket along the thickness direction (the position where deterioration often occurs)".

[0066] That is, since the reaction surface (on which the electrolyte membrane, cathode, and anode of the five-layer MEA are in contact with each other) is formed in a rectangular shape, when an electric current is applied under specific conditions, the position where the antioxidant is distributed in the electrolyte membrane can vary according to the above specific conditions. In this case, when an electric current is applied to the five-layer MEA according to the current application conditions of the present invention, the antioxidant can be selectively and concentratedly placed only in a high concentration in "the portion corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket along the thickness direction (the position where deterioration often occurs)".

[0067] In particular, the electric current applied to the five-layer MEA can be applied in an intensity range of about 50 A to about 250 A, and preferably in a range of about 100 A to about 200 A. When the electric current is applied at a low intensity (for example, less than about 50 A), there are the following disadvantages: Since the amount of water generated at an extremely low current is too small, and there is no proper dissolution phenomenon of the target antioxidant (cerium) ions, it is difficult to migrate an appropriate amount from the gas diffusion layer (GDL) to the MEA. On the contrary, when the electric current is applied at a high intensity (for example, greater than about 250 A), there are the following disadvantages: Due to the long-term application of a high current relative to the amount of water generated, the electrode may be damaged.

[0068] Alternatively, it is preferable to apply a current under the conditions that the temperature range can be from about 30°C to about 90°C, the humidity range can be from about 30% to about 100%, and the time for applying the current can be more than about 3 hours. In particular, a current can be applied under the conditions that the temperature range can be from about 55°C to about 65°C, the humidity range can be from about 50% to about 100%, and the time for applying the current can be from about 3 hours to about 800 hours.

[0069] When the temperature is lower than the above range (e.g., lower than about 30°C), the migration rate of metal ions (antioxidants generated after the dissolution of antioxidant precursors) is too slow, resulting in the disadvantages of an increased constant current holding time and thus reduced efficiency. When the temperature is greater than the above range (e.g., greater than about 90°C), the temperature of the MEA rises rapidly, which may accelerate the deterioration in the material, the growth and aggregation of the size of metal nanoparticles in the material. Additionally, when the humidity is less than the above range (e.g., less than about 30%), in a dry environment where the MEA is not sufficiently wetted, the mobility of metal ions as antioxidants may decrease, there is a possibility of accelerating chemical deterioration, and the humidity cannot exceed 100% as the maximum humidity. Further, when the current holding time is less than the above range (e.g., less than about 3 hours), there are the following disadvantages: insufficient migration and migration deviation in the planar direction are not exhibited. When the current holding time is too long, after the current holding time is greater than the above range (e.g., greater than about 800 hours), there is a saturation stage, in which the amount of antioxidant moving to the electrolyte membrane does not increase to a certain level (10 μg / cm 2 ) or more, so there are disadvantages of deteriorated operation efficiency and economic feasibility.

[0070] According to various exemplary embodiments of the present invention, especially since the method includes moving an antioxidant derived from an antioxidant precursor to the electrolyte membrane, there are the following advantages: in the manufacturing operation, no additional operation is required to control the position of the antioxidant, thereby improving the efficiency of the process, and the antioxidant can be selectively and concentratedly placed only at the positions where deterioration often occurs in the electrolyte membrane at a high concentration, so there is an advantage of excellent economic feasibility due to cost reduction. Additionally, since position control can be performed in an ionic state rather than an oxide type, free radical scavenging is possible, thus having the advantage of high oxidation prevention efficiency.

[0071] Fuel cell

[0072] A fuel cell can be manufactured according to the method described herein. Thus, an antioxidant derived from an antioxidant precursor contained in the gas diffusion layer can be included in the electrolyte membrane. Preferably, the antioxidant can be mainly distributed in "the portion corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket in the thickness direction (the position where deterioration often occurs in the electrolyte membrane). Therefore, the antioxidant can be in an amount ranging from about 0.1 μm / cm 2 to about 20 μm / cm 2 and be included in the electrolyte membrane. The amount of the antioxidant contained in the electrolyte membrane can vary according to the driving time. Preferably, since the dissolution rate varies according to the initial content, the amount of the antioxidant can be the amount of the antioxidant in the antioxidant precursor contained in the gas diffusion layer and can vary according to the specific surface area of the antioxidant oxide contained in the gas diffusion layer.

[0073] Therefore, even when using the antioxidant with low volume and high efficiency, the fuel cell according to the present invention can minimize the ohmic loss, thereby effectively improving the performance of the fuel cell. At the same time, there is an advantage that it can overcome the shortage of mass production caused by the appearance of steps when applying the existing transfer process.

[0074] Examples

[0075] The present invention will be described in more detail below through specific examples. The following examples are merely shown for understanding the present invention, and the scope of the present invention is not limited by the following examples.

[0076] Examples 1-1 to 1-5: Manufacturing fuel cells that meet current and other conditions

[0077] (S10): Prepare an ionomer (W.L.Gore & Associates GmbH) with an equivalent weight of 735 as the electrolyte membrane. Additionally, prepare an electrode with a thickness range of 7 μm to 8 μm and containing Pt / C catalyst, ionomer, and antioxidant Ce(NO 3 ) 3 ·6H 2 O as the cathode, and prepare an electrode with a thickness range of 1 μm to 2 μm and containing Pt / C catalyst, IrO 2 , ionomer, and antioxidant Ce(NO 3 ) 3 ·6H 2 O as the anode. The cathode and anode are disposed on one surface and the other surface of the electrolyte membrane, respectively, thereby preparing a three-layer MEA. Then, a sub-gasket equipped with an air inlet and a hydrogen inlet is disposed on the edge region of the side surface of the three-layer MEA to seal the side ends of the three-layer MEA.

[0078] (S20): By mixing CeO 2A gas diffusion layer is laminated on the cathode and the anode to prepare a five-layer MEA.

[0079] Specifically, a 70-μm substrate including carbon nanofibers is prepared. Additionally, a 20-μm microporous layer containing CeO 2 is prepared on the substrate to prepare the gas diffusion layer. Then, the prepared gas diffusion layer is disposed on each of the cathode and the anode to fabricate a five-layer MEA. In this case, an antioxidant precursor containing CeO 2 is included in the microporous layer in an amount of 165 μg / cm 2 .

[0080] (S30): A constant current of 130 A is applied to the five-layer MEA at atmospheric pressure for 200 hours. In this case, the temperature is maintained at 65 °C and the humidity is maintained at 50%. Finally, a fuel cell according to Examples 1-1 to 1-5 is fabricated.

[0081] Comparative Examples 1-1 and 1-2: Manufacturing conventional fuel cells without current and other conditions

[0082] A fuel cell in which a current collector electrode is applied to an M735 electrolyte membrane of W.L. Gore & Associates GmbH is used as Comparative Example 1-1. A fuel cell in which an FE electrode is applied to an M770 electrolyte membrane of W.L. Gore & Associates GmbH is used as Comparative Example 1-2.

[0083] Comparative Examples 2-1 and 2-3: Manufacturing fuel cells without current and other conditions

[0084] When comparing with Examples 1-1 to 1-5, a constant current of 0 A is applied under a pressure of 30 kPa. In this case, except that the temperature is maintained at 65 °C and the humidity is maintained at 50%, a fuel cell is fabricated in the same manner as in Examples 1-1 to 1-5.

[0085] Comparative Examples 3-1 to 3-3: Manufacturing fuel cells except under the current holding time condition

[0086] When comparing with Examples 1-1 to 1-5, a fuel cell is fabricated in the same manner as in Examples 1-1 to 1-5, except that the time for applying the constant current is less than 3 hours (2.5 hours).

[0087] Comparative Examples 4-1 to 4-5: Manufacturing off-the-shelf fuel cells

[0088] A three-layer MEA is fabricated by placing the cathode and anode electrodes on two surfaces of the electrolyte membrane and performing a heat fusing transfer process. Then, according to 270 cm 2The reaction area joins the sub-gasket coated with the polyurethane-based adhesive to both surfaces of the three-layer MEA to fabricate the five-layer MEA. Heat treatment is performed by hot pressing, and a fuel cell is prepared by stamping a manifold suitable for the structure and area of the separator.

[0089] Experimental Example 1: Analyzing the distribution of metal ions in fuel cells manufactured according to the present invention

[0090] Fuel cells are fabricated according to Example 1-1 and Comparative Examples 1-1 to 3-3, and the distribution of metal ions is compared based on the cross-section of the MEA and the plane of the electrolyte membrane.

[0091] As Figure 4A shown, it is confirmed that before applying a current satisfying the conditions of the present invention, metal ions (i.e., cerium ions) as antioxidants are scarcely distributed in the electrolyte membrane. It can also be confirmed that after applying a current satisfying the conditions of the present invention, a large amount of cerium ions are distributed around the reinforcing layer in the electrolyte membrane.

[0092] Meanwhile, Figure 4B shows the distribution of cerium ions in the plane of the electrolyte membrane after applying a current satisfying the conditions of the present invention. As Figure 4B shown, it can be confirmed that in the electrolyte membrane of the MEA fabricated according to the present invention, metal ions above the average are distributed in the part corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket along the thickness direction (the position where deterioration often occurs). Additionally, Figure 4C shows a cross-section of the MEA at the air inlet in a mapped image. As Figure 4C shown, it can be confirmed that, in particular, in the electrolyte membrane, metal ions as antioxidants are distributed in the part corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket along the thickness direction (the position where deterioration often occurs).

[0093] Meanwhile, Figure 5A and Figure 5B show the distribution of cerium ions in the plane of the electrolyte membrane of the MEA according to Comparative Examples 1-1 and 1-2. As Figure 5A and 5B shown, it can be confirmed that in the plane of the electrolyte membrane without applying a current satisfying the conditions of the present invention, the metal ions are uniformly distributed without any deviation for each position. Meanwhile, Figure 6A and Figure 6C show the distribution of cerium ions in the plane of the electrolyte membrane of the MEA according to Comparative Examples 2-1 and 2-3. As Figures 6A to 6CAs shown, it can be confirmed that, in the case of the electrolyte membrane plane with a current applied outside the conditions of the present invention, metal ions are not particularly distributed in "the portion corresponding to the gas diffusion layer near the air inlet of the sub-gasket in the thickness direction (the position with a high deterioration rate)", and the metal ions are widely distributed in "the portion corresponding to the gas diffusion layer near the air inlet of the sub-gasket in the thickness direction and unrelated to the deterioration rate", making it difficult to control the position. Additionally, Figures 7A to 7C shows the distribution of cerium ions in the plane of the electrolyte membrane in the MEAs according to Comparative Examples 3-1 to 3-3. As Figures 7A to 7C shown, it can be confirmed that, in the case of the electrolyte membrane plane with a current applied for an insufficient current holding time within the conditions of the present invention, cerium ions do not sufficiently migrate into the electrolyte membrane and do not exhibit a migration deviation in the plane direction.

[0094] Therefore, according to various exemplary embodiments of the present invention, in the method for manufacturing a fuel cell, since no additional operation is required to control the position of the antioxidant during the manufacturing operation, the efficiency of the process can be improved. Additionally, compared with the conventional method of applying or distributing the antioxidant at a high concentration over the entire surface, the method for manufacturing a fuel cell according to various exemplary embodiments of the present invention can selectively and centrally place the antioxidant at a high concentration only in the positions where deterioration often occurs in the electrolyte membrane according to the operation mode, thus having the advantage of good economic feasibility due to reduced production costs. Additionally, the greatest advantage is that position control can be performed in an ionic state rather than in the cerium oxide type. Therefore, different from the low distribution force in the oxide type antioxidant, since the precursor itself has a structure that easily hydrates into an oxide, there is an advantage of a strong distribution force. Therefore, even when using the antioxidant with a low volume and high efficiency, the fuel cell manufactured according to various exemplary embodiments of the present invention and the method described herein can minimize the ohmic loss, thereby effectively improving the performance of the fuel MEA. At the same time, there is an advantage of being able to overcome the shortage of mass production due to the appearance of steps when applying the existing transfer process.

[0095] Experimental Example 2: Confirming the durability of metal ions in fuel cells manufactured according to the present invention

[0096] Fuel cells were manufactured according to Examples 1-1 to 1-5 and Comparative Examples 4-1 to 4-5 of the present invention, the cell performance of each fuel cell was evaluated, and the results are shown in Figures 8A to 8C and Table 1 below.

[0097] Table 1

[0098]

[0099] Table 1 shows the performance degradation rate (%) before and after the durability test. AsFigures 8A to 8C As shown in Table 1, it can be confirmed that the MEA manufactured according to the present invention has a lower performance degradation rate than Comparative Examples 4-1 to 4-5, and thus the durability is increased and improved.

[0100] Experimental Example 3: Analyzing the movement of antioxidants based on the current holding time of fuel cells manufactured by this method

[0101] A fuel cell is manufactured according to Example 1-1, and as the current holding time gradually increases, the migration amount of cerium ions, which is an antioxidant, into the electrolyte membrane of the fuel cell is analyzed, and the results are shown in Table 2 and Figure 9 .

[0102] Table 2

[0103]

[0104] As shown in Table 2 above and Figure 9 it can be confirmed that after the time of applying current to the fuel cell according to Example 1-1 exceeds 3 hours, the amount of cerium ions contained in the electrolyte membrane is 1.3 μm / cm 2 , and as the current holding time increases, the amount of cerium ions migrating into the electrolyte membrane gradually increases. It can be confirmed that after 400 hours, the increase in the amount of cerium ions gradually decreases, and after 800 hours, the amount of cerium ions reaches a saturated state, where the amount of cerium ions does not increase to a certain level (10 μg / cm 2 ) or more, so there is almost no increase. In addition, in the fuel cell according to the present invention, it can be confirmed that current can preferably be applied under the conditions of a temperature range of 30°C to 90°C, a humidity range of 30% to 100%, and a current application time of more than 3 hours, and more preferably, when current is applied under the conditions of a temperature range of 55°C to 65°C, a humidity range of 50% to 100%, and a time range of 3 hours to 800 hours, the antioxidant can be moved onto the electrolyte membrane in the most effective and economical manner.

[0105] According to various exemplary embodiments of the present invention, the method for manufacturing an MEA for a fuel cell can selectively and intensively place an antioxidant only at positions where deterioration often occurs in the electrolyte membrane at a high concentration according to an operation mode, thereby having the advantages of being economically feasible due to reduced manufacturing costs and being able to improve and enhance the durability of the electrolyte membrane.

[0106] According to various exemplary embodiments of the present invention, since no additional operation is required to control the position of the antioxidant during the manufacturing operation, the efficiency of the process can be improved. Additionally, compared with the conventional method of applying or distributing the antioxidant at a high concentration over the entire surface, the method of manufacturing a fuel cell according to the present invention can selectively and concentrically place the antioxidant at a high concentration only in the positions where deterioration frequently occurs in the electrolyte membrane according to the operation mode, thereby having the advantage of good economic feasibility due to reduced production costs. Additionally, the greatest advantage is that position control can be performed in an ionic state rather than in a cerium oxide type. Therefore, unlike the low distribution force in the oxide type antioxidant, since the precursor itself has a structure that easily hydrates into an oxide, there is an advantage of a strong distribution force. Accordingly, even when using the antioxidant in a low volume and with high efficiency, the membrane electrode assembly (MEA) of the fuel cell manufactured according to various exemplary embodiments of the present invention can minimize ohmic loss, thereby effectively improving the performance of the fuel MEA. At the same time, there is an advantage of being able to overcome the shortage of mass production due to the occurrence of steps when applying the existing transfer process.

[0107] The effects of the present invention are not limited to the above effects. It should be understood that the effects of the present invention include all effects that can be inferred from the above description.

Claims

1. A method for manufacturing a fuel cell, comprising the following steps: joining a sub-gasket provided with an air inlet and a hydrogen inlet to a side surface of a three-layer membrane electrode assembly, the three-layer membrane electrode assembly including an electrolyte membrane, a cathode located on one surface of the electrolyte membrane, and an anode located on the other surface of the electrolyte membrane; laminating a gas diffusion layer containing an antioxidant precursor on at least one of the cathode and the anode, and preparing a five-layer membrane electrode assembly; and applying a current to the five-layer membrane electrode assembly and causing an antioxidant derived from the antioxidant precursor to move to the electrolyte membrane, wherein the current is applied to the gas diffusion layer in an intensity range of 50 A to 250 A, wherein the current is applied to the gas diffusion layer under conditions of a temperature range of 30 °C to 90 °C, a humidity range of 30% to 100%, and an application time of the current of more than 3 hours.

2. The method according to claim 1, wherein, the gas diffusion layer includes a substrate and a microporous layer located on the substrate; the microporous layer is located on at least one of the cathode and the anode; and the microporous layer contains an antioxidant precursor.

3. The method according to claim 1, wherein, the antioxidant precursor includes an oxide of the antioxidant.

4. The method according to claim 3, wherein, The antioxidant precursor includes CeO 2 and MgO 2 at least one of them.

5. The method according to claim 1, wherein, the antioxidant is in an ionic state.

6. The method according to claim 5, wherein, The antioxidant comprises one or more selected from Ce 3+ , Ce 4+ , Mg 2+ and Mg 3+ .

7. The method according to claim 2, wherein, The microporous layer contains an antioxidant precursor in a content range of 165 μg / cm 2 to 210 μg / cm 2 .

8. The method according to claim 2, wherein, the thickness range of the microporous layer is 10 μm to 100 μm.

9. A fuel cell manufactured by the method according to claim 1, wherein, the electrolyte membrane includes an antioxidant derived from the antioxidant precursor.

10. The fuel cell according to claim 9, wherein, the antioxidant is mainly distributed in a portion of the electrolyte membrane corresponding to the gas diffusion layer adjacent to the air inlet of the sub-gasket along the thickness direction.

11. The fuel cell according to claim 9, wherein, The content range of the antioxidant in the electrolyte membrane is 0.1 μm / cm 2 to 20 μm / cm 2 .

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