Membrane electrode assembly for fuel cell and fuel cell comprising the same

Abstract

The present invention relates to a membrane electrode assembly for a fuel cell and a fuel cell comprising the same, and more particularly, to a membrane electrode assembly for a fuel cell and a fuel cell comprising the same, which prevents deterioration of an electrolyte membrane caused by radicals by forming an additional radical protection layer comprising fucoidan and a radical scavenger other than fucoidan between the polymer electrolyte membrane and the electrode layer, thereby greatly improving chemical resistance.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0001926, filed with the Korean Patent Office on January 5, 2024, the entire contents of which are incorporated herein by reference. The present invention relates to a membrane electrode assembly for a fuel cell and a fuel cell comprising the same. Background Technology

[0002] As a new generation of energy, fuel cells have attracted much attention. Polymer electrolyte fuel cells (PEMFCs) are fuel cells that use polymer membranes with hydrogen ion exchange properties as electrolytes.

[0003] As a battery that can directly convert the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon fuels such as methanol, ethanol, and natural gas into electrical energy through oxidation / reduction reactions, fuel cells have attracted much attention as a new generation of clean energy that can replace fossil fuels due to their high energy efficiency and low pollutant emissions.

[0004] Based on the state and type of electrolyte, fuel cells can be divided into alkaline electrolyte fuel cells, polymer electrolyte fuel cells, etc. Among them, polymer electrolyte fuel cells have attracted attention as portable, vehicle and home power devices due to their advantages such as operating temperature below 100℃, fast start-up and response, and excellent durability.

[0005] To summarize the reactions that occur in a polymer electrolyte fuel cell: First, when fuel such as hydrogen is supplied to the oxidation electrode, hydrogen ions (H+) are generated through the oxidation reaction of hydrogen at the oxidation electrode. + ) and electrons (e - The generated hydrogen ions are transferred to the reducing electrode through the polymer electrolyte membrane, while the generated electrons are transferred to the reducing electrode through an external circuit. Oxygen is supplied at the reducing electrode, where it reacts with hydrogen ions and electrons (e...). - They combine to form water through the reduction of oxygen.

[0006] On the other hand, there are still many technical barriers to the commercialization of polymer electrolyte fuel cells, and the factors that need to be improved include achieving high performance, long lifespan, and reducing production costs. Among these, the most influential structural element is the membrane electrode assembly, and the polymer electrolyte membrane is one of the core elements that has the greatest impact on the performance and cost of the membrane electrode assembly.

[0007] Electrolyte membrane degradation is classified into chemical / electrochemical degradation and mechanical degradation. Among them, chemical / electrochemical degradation refers to the degradation of the polymer membrane caused by free radicals / hydrogen peroxide generated within the battery attacking it, which is one of the main reasons for the shortened lifespan of fuel cells. Summary of the Invention

[0008] Technical issues

[0009] The purpose of this invention is to provide a membrane electrode assembly for fuel cells that improves the degradation caused by free radicals generated during fuel cell operation.

[0010] Another object of the present invention is to provide a fuel cell whose performance is improved by including the membrane electrode assembly.

[0011] Technical solution

[0012] According to a first embodiment of the present invention, a membrane electrode assembly for a fuel cell is provided, comprising: a polymer electrolyte membrane; a free radical protection layer disposed on at least one surface of the polymer electrolyte membrane and containing a free radical scavenger; and an electrode layer disposed on the free radical protection layer, wherein the free radical scavenger comprises alginate sulfate.

[0013] According to a second embodiment of the present invention, in the first embodiment, the free radical scavenger may further comprise one or more of transition metals, their ions, their salts, their oxides, their nitrides and their complexes, carotenoids, flavonoids, vitamins and glutathione.

[0014] According to a third embodiment of the present invention, in the first embodiment, the content of the fucoidan sulfate ester can be more than 0.2% by weight and less than 1.0% by weight, based on the total weight of the free radical protective layer containing fucoidan sulfate ester.

[0015] According to a fourth embodiment of the present invention, in the second embodiment, the free radical protective layer includes a first free radical protective layer and a second free radical protective layer, and at least one of the first free radical protective layer and the second free radical protective layer may contain fucoidan sulfate.

[0016] According to a fifth embodiment of the present invention, in the fourth embodiment, the first free radical protective layer is located on the polymer electrolyte membrane, the second free radical protective layer is located on the first free radical protective layer, and the content of free radical scavengers other than the brown algae polysaccharide sulfate in the first free radical protective layer may be higher than that in the second free radical protective layer.

[0017] According to a sixth embodiment of the present invention, in the fifth embodiment, the content of the first free radical protective layer and the content of the second free radical protective layer of brown algae polysaccharide sulfate may be the same or different.

[0018] According to a seventh embodiment of the present invention, in the fifth embodiment, the content of free radical scavengers other than brown algae polysaccharide sulfate in the first free radical protective layer may be more than 0.1% by weight and less than 20% by weight, based on the total weight of the free radical protective layer.

[0019] According to the eighth embodiment of the present invention, in the fifth embodiment, the thickness ratio of the first free radical protective layer to the second free radical protective layer can be from 10:1 to 1:10.

[0020] According to a ninth embodiment of the present invention, in the first embodiment, the free radical protective layer may comprise carbon nanofibers.

[0021] According to a tenth embodiment of the present invention, in the fifth embodiment, carbon nanofibers may be included only in the first free radical protective layer.

[0022] According to the eleventh embodiment of the present invention, in the first embodiment, the thickness of the free radical protective layer can be more than 10 nm and less than 2000 nm.

[0023] According to the twelfth embodiment of the present invention, in the first embodiment, the electrode layer may include a catalyst layer disposed on the surface of the electrode substrate.

[0024] According to a thirteenth embodiment of the present invention, a fuel cell is provided, including the membrane electrode assembly for a fuel cell described in the first embodiment.

[0025] Unless otherwise expressly stated otherwise, the features described in the above embodiment may be combined with other embodiments.

[0026] Invention Effects

[0027] The free radical protection layer of this invention can effectively block free radicals flowing into the polymer electrolyte membrane, thereby improving the chemical resistance and durability of the membrane electrode assembly, and ultimately improving the lifespan and performance of the fuel cell. Attached Figure Description

[0028] Figure 1 A cross-sectional view of a membrane electrode assembly according to an embodiment of the present invention is shown for illustrative purposes.

[0029] Figure 2 A cross-sectional view of a membrane electrode assembly according to another embodiment of the present invention is shown for illustrative purposes.

[0030] Figure 3This is a schematic diagram illustrating the overall structure of a fuel cell according to an embodiment of the present invention. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can readily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0032] Figure 1 A cross-sectional view is provided for the purpose of briefly illustrating a membrane electrode assembly according to an embodiment of the present invention. (Refer to...) Figure 1 To illustrate, the membrane electrode assembly 100 includes a polymer electrolyte membrane 50 and electrode layers 20 and 20' respectively disposed on two surfaces of the polymer electrolyte membrane 50, and also includes free radical protective layers 10 and 10' located on at least one surface of the polymer electrolyte membrane 50 and disposed between the electrode layers 20 and 20' and the polymer electrolyte membrane 50.

[0033] Figure 1 An embodiment of a membrane electrode assembly 100 is shown in which free radical protective layers 10, 10' are formed on both surfaces of a polymer electrolyte membrane 50, but it may also be provided on only one surface on the cathode side or the anode side.

[0034] One embodiment of the present invention includes a membrane electrode assembly for a fuel cell, comprising: a polymer electrolyte membrane 50; free radical protection layers 10, 10' formed on at least one surface of the polymer electrolyte membrane and containing a free radical scavenger; and electrode layers 20, 20' formed on the free radical protection layers, wherein the free radical scavenger contains alginate sulfate.

[0035] According to one embodiment of the present invention, the polymer electrolyte membrane 50 is not particularly limited as long as it is used in a fuel cell, and the ion conductor contained in the polymer electrolyte membrane can be one or more of conventional hydrocarbon polymers or fluorinated polymers. The hydrocarbon polymer can be any known hydrocarbon polymer, for example, poly(aryl ether) sulfonated derivatives (SPAEs), poly(aryl sulfides) (SPASs), polyimides (SPIs), polybenzimidazoles (PBIs), polyphenylene oxides (PPs), or polyether ether ketones (PEEK). Furthermore, the fluorinated polymer can be any known fluorinated polymer, for example, Nafion, Aciplex, Flemion, polyvinylidene fluoride, hexafluoropropylene, trifluoroethylene, polytetrafluoroethylene, or copolymers thereof.

[0036] According to one embodiment of the present invention, the thickness of the polymer electrolyte membrane can be 5 to 200 μm in the absence of humidification.

[0037] According to one embodiment of the present invention, the free radical protection layers 10, 10' contain a free radical scavenger to prevent free radicals generated from the electrode layers 20, 20' from flowing into the polymer electrolyte membrane 50, thereby inhibiting the degradation of the electrolyte membrane caused by free radicals.

[0038] According to one embodiment of the present invention, the free radical protection layers 10, 10' may contain a free radical scavenger in an interfacial adhesive layer that can be formed between the polymer electrolyte membrane 50 and the electrode layers 20, 20'.

[0039] The free radical scavenger of the present invention essentially comprises fucoidan sulfate, and may further comprise inorganic compounds and other free radical scavengers besides fucoidan sulfate. Fucoidan sulfate, extracted from seaweed, is a sulfated heterosaccharide with a backbone primarily composed of L-fucose linked by α-1,2 or α-1,3 glycosidic bonds. Fucoidan sulfate acts as a free radical scavenger through antioxidant activity and also possesses hydrogen ion conductivity due to the presence of sulfate groups.

[0040] According to one embodiment of the present invention, the brown algae polysaccharide sulfate is uniformly distributed throughout the free radical protective layers 10 and 10', which not only helps to improve hydrogen ion conductivity, but also effectively blocks the inflow of free radicals into the electrolyte membrane.

[0041] According to one embodiment of the present invention, preferably, in addition to fucoidan sulfate, the free radical protective layers 10 and 10' also contain antioxidants as free radical scavengers. These additional free radical scavengers may be one or more selected from transition metals (e.g., cerium (Ce), manganese (Mn), etc.), their ions, salts, oxides, nitrides and complexes, carotenoids (e.g., lutein, lycopene, carotene, etc.), flavonoids (e.g., catechins, anthocyanins, etc.), vitamins (e.g., ascorbic acid, tocopherol, etc.), and glutathione. Preferably, CeZrO2 may also be included.

[0042] According to one embodiment of the present invention, the content of the fucoidan sulfate, based on the total weight of the free radical protective layer comprising fucoidan sulfate, can be 0.2 to 1.0% by weight. If the content exceeds this range, battery performance will be reduced; if it is below this range, the improvement in durability will be negligible due to reduced free radical scavenging effect. The chemical resistance and durability of the membrane electrode assembly can be improved by adjusting the content of the fucoidan sulfate within the above range, ultimately improving the lifespan and performance of the fuel cell.

[0043] According to one embodiment of the present invention, the free radical protective layers 10 and 10' can be formed as a single layer or as a stack of two or more layers.

[0044] According to one embodiment of the present invention, the free radical protection layer 10 includes a first free radical protection layer 11 and a second free radical protection layer 12, wherein at least one of the first free radical protection layer 11 and the second free radical protection layer 12 may contain alginate sulfate.

[0045] Reference Figure 2 , Figure 2 The following embodiment is shown: free radical protective layers 10 and 10' are formed on both surfaces of the polymer electrolyte membrane 50, and each free radical protective layer 10 and 10' is formed by a stacked structure of a first free radical protective layer 11 and 11' and a second free radical protective layer 12 and 12'.

[0046] According to one embodiment of the present invention, the first free radical protective layers 11, 11' and the second free radical protective layers 12, 12' may each independently contain alginate sulfate or alginate sulfate combined with an additional free radical scavenger. Specifically, for example, the first free radical protective layers 11, 11' in contact with the polymer electrolyte membrane 50 may contain CeZrO2, while the second free radical protective layers 12, 12' may contain only alginate sulfate as a free radical scavenger.

[0047] According to one embodiment of the present invention, the first free radical protective layer 11 is located on the polymer electrolyte membrane 50, and the second free radical protective layer 12 is located on the first free radical protective layer 11. The content of free radical scavengers other than the fucoidan sulfate in the first free radical protective layer 11 may be higher than that in the second free radical protective layer 12. Specifically, the first free radical protective layer 11 may contain CeZrO2.

[0048] The densities of free radical scavengers, excluding fucoidan sulfate, in the first free radical protective layer 11 and the second free radical protective layer 12 can be different, such as... Figure 2As shown, when the first free radical protection layer 11 is located on the electrolyte membrane 50 side and the second free radical protection layer 12 is located on the electrode layer 20 side, preferably, the density of free radical scavengers other than alginate sulfate in the first free radical protection layer 11 is higher than that in the second free radical protection layer 12. Alginate sulfate has hydrogen ion conductivity, but the hydrogen ion conductivity of free radical scavengers other than alginate sulfate is usually significantly reduced or nonexistent. To improve hydrogen ion conductivity, it is necessary to adjust the content of free radical scavengers other than alginate sulfate. Therefore, considering both hydrogen ion conductivity and free radical scavenging rate, preferably, after free radicals are first scavenged in the second free radical protection layer 12 (where the density of free radical scavengers other than alginate sulfate is relatively low), free radicals are then scavenged together with the free radical scavengers other than alginate sulfate in the first free radical protection layer 11.

[0049] According to one embodiment of the present invention, the content of brown algae polysaccharide sulfate in the first free radical protective layer 11 and the second free radical protective layer 12 may be the same or different.

[0050] According to one embodiment of the present invention, the content of free radical scavengers other than fucoidan sulfate in the first free radical protective layer, based on the total weight of the free radical protective layer, can be 0.1–20% by weight. Specifically, based on the total weight of the free radical protective layer, the content of free radical scavengers other than fucoidan sulfate in the first free radical protective layer can be 0.2–19% by weight, 0.3–18% by weight, 0.4–17% by weight, 0.5–16% by weight, 0.6–15% by weight, 0.7–14% by weight, 0.7–13% by weight, 0.8–12% by weight, 0.9–11% by weight, 1–10% by weight, 2–9% by weight, 3–8% by weight, 4–7% by weight, or 5–6% by weight. If the content exceeds the above range, the battery performance will be reduced; if the content is less than the above range, the free radical scavenging ability will be reduced.

[0051] According to one embodiment of the present invention, the density of free radical scavengers other than alginate sulfate in the second free radical protective layer 12 is lower than that in the first free radical protective layer 11. Therefore, in the same unit volume, the content of free radical scavengers other than alginate sulfate in the second free radical protective layer 12 is less than that in the aforementioned first free radical protective layer 11.

[0052] In the case of the first radical protection layer 11, if the density of the radical scavenger other than alginate sulfate is higher than the aforementioned range, the efficiency of the fuel cell will be significantly reduced due to a substantial decrease in hydrogen ion conductivity. If the density of the radical scavenger other than alginate sulfate is lower than the aforementioned range, a considerable amount of free radicals will flow into the electrolyte membrane, causing problems in suppressing electrolyte membrane degradation. Preferably, compared to the first radical protection layer 11, the second radical protection layer 12 has a lower density of radical scavenger other than alginate sulfate. In extreme cases, it may contain only alginate sulfate as a radical scavenger.

[0053] According to one embodiment of the present invention, the weight ratio of the free radical scavenger, including alginate sulfate, contained in the first free radical protective layer 11 to the free radical scavenger other than alginate sulfate contained in the second free radical protective layer 12 may be 1:5 to 1:20. Specifically, the weight ratio of the free radical scavenger, including fucoidan sulfate, contained in the first free radical protective layer 11 to the free radical scavenger other than fucoidan sulfate contained in the second free radical protective layer 12 can be 1:6 to 1:20, 1:7 to 1:20, 1:8 to 1:20, 1:9 to 1:20, 1:10 to 1:20, 1:11 to 1:20, 1:12 to 1:20, 1:13 to 1:20, 1:14 to 1:20, 1:15 to 1:20, 1:16 to 1:20, 1:17 to 1:20, 1:18 to 1:20, or 1:19 to 1:20. When the weight ratio of the free radical scavenger, including alginate sulfate, contained in the first free radical protective layer 11 to the free radical scavenger, excluding alginate sulfate, contained in the second free radical protective layer 12 meets the above-mentioned range, the degradation caused by free radicals can be improved.

[0054] According to one embodiment of the present invention, the thickness ratio of the first free radical protective layer 11 to the second free radical protective layer 12 can be from 10:1 to 1:10. Preferably, it can be from 5:1 to 1:5, more preferably, it can be from 2:1 to 1:2, or 2:1.

[0055] According to one embodiment of the present invention, the free radical protective layer 10 may comprise carbon nanofibers. The free radical protective layer 10 may comprise a polymeric form of fucoidan sulfate without requiring an additional support, or it may comprise an additional carbon support to improve durability. For example, the carbon support may be carbon nanofibers, specifically, a support formed from carbon nanosheets.

[0056] According to one embodiment of the present invention, carbon nanofibers may be included only in the first radical protection layer. Since carbon nanofibers have excellent conductivity, they are preferably not distributed throughout the entire radical protection layer 10, but only in a portion thereof, thus blocking the conduction of electricity generated in the electrode layer to the electrolyte membrane. Specifically, the second radical protection layer 12, which is in contact with the electrode layer 20, preferably does not contain carbon nanofibers, while only the first radical protection layer 11 contains carbon nanofibers. Therefore, the second radical protection layer 12 can also function as an insulating layer.

[0057] According to one embodiment of the present invention, the thickness of the free radical protective layer can be 10–2000 nm. Specifically, the thickness of the free radical protective layer can be 50–1800 nm, 60–1800 nm, 80–1700 nm, 100–1600 nm, 120–1600 nm, 140–1500 nm, 160–1400 nm, 170–1300 nm, 180–1200 nm, 190–1100 nm, or 200–1000 nm. Furthermore, the thicknesses on the cathode side and the anode side can be the same or different. If the thickness of the free radical protective layer is less than the above range, it will be difficult to prevent free radicals from flowing into the polymer electrolyte membrane 50 due to its excessive thinness. If it is greater than the above range, the hydrogen ion conductivity of the membrane electrode assembly will be significantly reduced due to the free radical protective layer, resulting in a sharp decrease in the efficiency of the fuel cell.

[0058] According to one embodiment of the present invention, the electrode layer may include a catalyst layer formed on the surface of the electrode substrate.

[0059] Reference Figure 2 Electrodes 20 and 20' include electrode substrates 40 and 40' and catalyst layers 30 and 30' formed on the surface of the electrode substrates 40 and 40'. In order to facilitate the diffusion of substances in the electrode substrates 40 and 40' between the electrode substrates 40 and 40' and the catalyst layers 30 and 30', a microporous layer (not shown) containing conductive particles such as carbon powder and carbon black may also be included.

[0060] In the membrane electrode assembly 100, the electrode 20 disposed on one surface of the polymer electrolyte membrane 50 and which undergoes an oxidation reaction that causes the fuel transferred through the electrode substrate 40 to the catalyst layer 30 to generate hydrogen ions and electrons is called the anode electrode, and the electrode 20' disposed on the other surface of the polymer electrolyte membrane 50 and which undergoes a reduction reaction that causes the hydrogen ions supplied through the polymer electrolyte membrane 50 to react with the oxidant transferred through the electrode substrate 40' to the catalyst layer 30' to generate water is called the cathode electrode.

[0061] The catalyst layers 30 and 30' of the anode electrode 20 and cathode electrode 20' contain a catalyst. Any catalyst that participates in the battery reaction and can be used as a conventional fuel cell can be used. Preferably, platinum-based metals can be used.

[0062] Platinum-based metals may include platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), platinum-M alloys (where M is selected from one or more of palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), gallium (Ga), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), gold (Au), zinc (Zn), tin (Sn), molybdenum (Mo), tungsten (W), lanthanum (La), and rhodium (Rh), non-platinum alloys, and combinations thereof. More preferably, combinations of two or more metals selected from the platinum-based catalyst metal group may be used, but are not limited thereto, and any platinum-based catalyst metal available in this art may be used without limitation.

[0063] Specifically, the platinum alloy can be selected from Pt-Pd, Pt-Sn, Pt-Mo, Pt-Cr, Pt-W, Pt-Ru, Pt-Ru-W, Pt-Ru-Mo, Pt-Ru-Rh-Ni, Pt-Ru-Sn-W, Pt-Co, Pt-Co-Ni, Pt-Co-Fe, Pt-Co-Ir, Pt-Co-S, Pt-Co-P, Pt-Fe, Pt-Fe-Ir, Pt-Fe-S, Pt-Fe-P, Pt-Au-Co, Pt-Au-Fe, Pt-Au-Ni, Pt-Ni, Pt-Ni-Ir, Pt-Cr, Pt-Cr-Ir, and combinations thereof, and can be used alone or in combination of two or more.

[0064] Furthermore, non-platinum alloys can be selected from Ir-Fe, Ir-Ru, Ir-Os, Co-Fe, Co-Ru, Co-Os, Rh-Fe, Rh-Ru, Rh-Os, Ir-Ru-Fe, Ir-Ru-Os, Rh-Ru-Fe, Rh-Ru-Os, and combinations thereof, and can be used alone or in combination of two or more.

[0065] This catalyst can be used as the catalyst itself or supported on a carrier.

[0066] The carrier can be selected from carbon-based carriers, porous inorganic oxides such as zirconium oxide, alumina, titanium dioxide, silicon dioxide, cerium dioxide, and zeolites. The carbon-based carrier can be selected from, but is not limited to, graphite, superconducting carbon black (super P), carbon fiber, carbon sheet, carbon black, Ketjen Black, superconducting acetylene black (Denka black), acetylene black, carbon nanotubes (CNTs), carbon spheres, carbon ribbons, fullerene, activated carbon, carbon nanofibers, carbon nanowires, carbon nanospheres, carbon nanoangles, carbon nanocages, carbon nanorings, ordered nano- / meso-porous carbon, carbon aerogels, mesoporous carbon, graphene, stable carbon, activated carbon, and combinations thereof. Any carrier available in this technical field may be used without restriction.

[0067] The catalyst particles can be located on the surface of the support or can penetrate into the interior of the support, filling the internal pores of the support.

[0068] When using a noble metal supported on the support as a catalyst, commercially available catalysts or catalysts prepared by supporting the noble metal on the support can be used. The process of supporting the noble metal on the support is well known in the art, and therefore a detailed description thereof is omitted in this specification, which is readily understood by those skilled in the art.

[0069] The content of catalyst particles relative to the total weight of the catalyst electrodes 30 and 30' can be 20-80% by weight. If the content is less than 20% by weight, there may be a problem of reduced activity. If the content is greater than 80% by weight, the active area may be reduced due to the agglomeration of catalyst particles, which will reduce the catalytic activity.

[0070] Furthermore, the catalyst electrodes 30, 30' may include an adhesive to improve their adhesion and hydrogen ion transfer. Preferably, an ion-conducting conductor with ion conductivity is used as the adhesive; the description of the ion-conducting conductor has been given above and will not be repeated.

[0071] However, the ionic conductor can be used as a single substance or in mixtures, and alternatively, it can be used with a non-conductive compound to further improve adhesion to the polymer electrolyte membrane 50. Preferably, the amount used is adjusted to suit the intended use.

[0072] The non-conductive compound may be selected from one or more of polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene (ETFE), trifluorochloroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), dodecylbenzenesulfonic acid, and sorbitol.

[0073] The content of the binder relative to the total weight of the catalyst electrodes 30 and 30' can be 20-80% by weight. If the content of the binder is less than 20% by weight, the generated ions cannot be transferred well. If it is greater than 80% by weight, it will be difficult to supply hydrogen or oxygen (air) due to insufficient pores, which will reduce the active area that can react.

[0074] Porous conductive substrates can be used as the electrode substrates 40 and 40' to facilitate the supply of hydrogen or oxygen. Examples include carbon paper, carbon cloth, carbon felt, or metal cloth (referring to a porous membrane made of fibrous metal cloth or a cloth formed of polymer fibers with a metal film formed on its surface), but these are not limited to these. Furthermore, it is preferable to use electrode substrates 40 and 40' that are waterproofed with a fluorinated resin to prevent a decrease in reactant diffusion efficiency due to water generated during fuel cell operation. The fluorinated resin can be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, perfluoroalkyl vinyl ether, perfluorosulfonyl fluoroalkoxy vinyl ether, fluorinated ethylene propylene, polychlorotrifluoroethylene, or copolymers thereof.

[0075] In addition, a microporous layer may be included to enhance the diffusion of reactants in the electrode substrates 40 and 40'. This microporous layer may typically contain conductive powder with small particle size, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, carbon nanohorns, or carbon nanorings.

[0076] The microporous layer is prepared by coating a composition comprising conductive powder, binder resin, and solvent onto the electrode substrates 40 and 40'. Preferably, the binder resin can be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, perfluoroalkyl vinyl ether, perfluorosulfonyl fluoroalkoxy vinyl ether, polyvinyl alcohol, cellulose acetate, or copolymers thereof. Preferably, the solvent can be alcohols such as ethanol, isopropanol, n-propanol, and butanol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. The coating process can be screen printing, spraying, or blade coating, depending on the viscosity of the composition, but is not limited to these methods.

[0077] One embodiment of the present invention includes a fuel cell comprising a membrane electrode assembly for a fuel cell.

[0078] Figure 3 This is a schematic diagram illustrating the overall structure of the fuel cell.

[0079] Reference Figure 3 The fuel cell 200 includes: a fuel supply unit 210 for supplying a mixed fuel consisting of fuel and water; a reforming unit 220 for generating a reforming gas containing hydrogen by reforming the mixed fuel; a stack 230 for generating electrical energy by causing the reforming gas containing hydrogen supplied by the reforming unit 220 to undergo an electrochemical reaction with an oxidant; and an oxidant supply unit 240 for supplying an oxidant to the reforming unit 220 and the stack 230.

[0080] The fuel cell stack 230 has multiple individual cells that generate electrical energy by inducing an oxidation / reduction reaction between a reforming gas containing hydrogen supplied by the reforming unit 220 and an oxidant supplied from the oxidant supply unit 240.

[0081] Each cell refers to a single cell that generates electrical energy, comprising: a membrane electrode assembly (MEA) for oxidizing / reducing oxygen in a reforming gas containing hydrogen and an oxidant; and a separator (also called a bipolar plate, hereinafter referred to as "separator") for supplying the reforming gas containing hydrogen and the oxidant to the MEA. Separators are positioned on both sides of the MEA. The separators located on the outermost sides of the stack are also specifically referred to as end plates.

[0082] In the separator, one end plate includes: a tubular first supply pipe 231 for injecting reforming gas containing hydrogen supplied by the reforming unit 220; and a tubular second supply pipe 232 for injecting oxygen. The other end plate includes: a first discharge pipe 233 for discharging the unreacted reforming gas containing hydrogen remaining in the plurality of single cells to the outside; and a second discharge pipe 234 for discharging the unreacted oxidant remaining in the single cells to the outside.

[0083] In the fuel cell, except for the membrane electrode assembly 100 of one embodiment of the present invention, the separator, fuel supply section and oxidant supply section constituting the power generation unit are the same as those used in conventional fuel cells. Therefore, detailed descriptions of them are omitted in this specification.

[0084] Example

[0085] The embodiments of the present invention are described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0086] Preparation example: Preparation of membrane electrode assembly

[0087] Comparative Example 1

[0088] A cathode electrode composition was prepared by dispersing a Pt / C cathode catalyst (88 wt%) and a Nafion / H₂O / 2-propanol solution (12 wt%) as a binder using stirring and ultrasonic methods. The prepared cathode electrode composition was then coated onto a Teflon release film and dried to prepare the cathode electrode. At this point, the catalyst loading of the cathode electrode was approximately 0.40 mg / cm³. 2 .

[0089] An anode electrode composition was prepared by dispersing an 88 wt% Pt / C anode catalyst with a 12 wt% Nafion / H₂O / 2-propanol solution as a binder using stirring and ultrasonic methods. The prepared anode electrode composition was then coated onto a Teflon release film and dried to prepare the anode electrode. At this point, the catalyst loading of the anode electrode was approximately 0.10 mg / cm³. 2 .

[0090] An interfacial adhesive layer composition comprising 5% by weight of fluorinated ionomer PFSA with an EW of 700-800 g / eq and 95% by weight of H2O / 2-propanol solution was prepared.

[0091] The above-prepared composition for forming the interfacial adhesive layer was applied at approximately 0.12 mg / cm³. 2 An amount of material is sprayed onto the electrode prepared above, forming an interfacial adhesive layer with a thickness of approximately 800 nm on the electrode surface.

[0092] A PFSA fluoropolymer electrolyte membrane with a thickness of 15 μm was sandwiched between the cathode electrode and the anode electrode prepared above, and then subjected to a test at 160 °C and 20 kgf / cm². 2 After hot pressing for 3 minutes under heat and pressure conditions, the membrane electrode assembly with the cathode electrode and anode electrode bonded to the polymer electrolyte membrane is prepared.

[0093] Comparative Example 2

[0094] Except that a PES hydrocarbon polymer electrolyte membrane was used instead of the fluorinated polymer electrolyte membrane in Comparative Example 1, the membrane electrode assembly was prepared in the same manner as in Comparative Example 1.

[0095] Example 1

[0096] Except that the composition for forming the interfacial adhesive layer in Comparative Example 1 contains 0.5% by weight of brown algae polysaccharide sulfate, the membrane electrode assembly was prepared in the same manner as in Comparative Example 1.

[0097] Example 2

[0098] Except that, in Example 1, the interfacial adhesive layer forming composition containing 5% by weight of a free radical scavenger (CeZrO2) is further sprayed onto the electrode on which the interfacial adhesive layer is formed to form a two-layer interfacial adhesive layer, the membrane electrode assembly is prepared in the same manner as in Example 1. In this case, the thickness ratio of the first free radical protective layer to the second free radical protective layer is 2:1 (thickness of the first free radical protective layer: 600 nm, thickness of the second free radical protective layer: 300 nm).

[0099] Example 3

[0100] Except that the composition for forming the interfacial adhesive layer in Comparative Example 2 contains 0.5% by weight of brown algae polysaccharide sulfate, the membrane electrode assembly was prepared in the same manner as in Comparative Example 2.

[0101] Example 4

[0102] Except that, in Example 3, the interfacial adhesive layer forming composition containing 5% by weight of free radical scavenger (CeZrO2) is further sprayed onto the electrode on which the interfacial adhesive layer is formed to form a two-layer interfacial adhesive layer, the membrane electrode assembly is prepared in the same manner as in Example 3. In this case, the thickness ratio of the first free radical protective layer to the second free radical protective layer is 2:1.

[0103] Experimental Example: Comparison of Physical Properties of Membrane Electrode Components

[0104] The electrode area is 25 cm² 2 The membrane electrode assembly (MEA) was assembled into a single cell. An electrical load was applied step-by-step and allowed to stabilize. The flow rate, temperature, and humidity were controlled in the MEA evaluation workstation (SciTech Korea) to measure the performance of the MEA under single-cell temperature of 65°C and humidity of 100%.

[0105] Table 1 below compares the current density (A / cm) when the battery voltage is 0.6V. 2 Accelerated durability assessment employed the open-circuit voltage holding (OCV) method within the electrochemical aging process. Under conditions of 90°C, 30% RH, and 50 kPa pressure per cell, the voltage decay rate relative to the initial open-circuit voltage (OCV) was calculated by measuring the individual cell voltage after a specified time. Hydrogen permeability was determined using linear sweep voltammetry (LSV). A potentiostat (Bio Logics) was used, with the voltage varied within the range of 0.2–0.8 V at a scan rate of 0.5 mV / s, while simultaneously measuring the hydrogen permeation current.

[0106] The LSV method involves supplying hydrogen and nitrogen to the anode and cathode respectively, and measuring the current generated by hydrogen crossover. When the voltage is increased at a specified rate (linear sweep), the crossover hydrogen reacts on the catalyst on the cathode side, releasing electrons. The amount of hydrogen that has passed through the membrane can be determined by measuring the amount of these electrons.

[0107] Table 1 Hydrogen permeability increase rate: The rate of increase in hydrogen permeability relative to the initial hydrogen permeability after maintaining the open-circuit voltage for 400 hours. Increased gas permeability leads to a decrease in open-circuit voltage (OCV), resulting in reduced fuel efficiency due to the amount of fuel consumed that cannot participate in the electrochemical reaction. Hydrogen permeating the polymer membrane at the anode encounters oxygen at the cathode, generating H₂O, H₂O₂, HO₂, etc., under the action of a platinum catalyst, or is discharged unreacted. As these reactions proceed, they, along with the reduction of oxygen at the cathode (as part of the original reaction), create a mixed potential, thereby reducing OCV. Hydrogen permeating the membrane encounters oxygen, generating H₂O₂ or oxygen free radicals under the action of a platinum catalyst. These hydrogen peroxides or free radicals attack the polymer in the electrolyte membrane, causing membrane degradation and pinhole formation. These pinholes further increase gas permeability, thereby accelerating the generation of hydrogen peroxide and free radicals, exacerbating membrane degradation. The permeability of the electrolyte membrane significantly impacts the performance and lifespan of PEMFCs; therefore, measuring the gas permeability of the PEMFC membrane is crucial. Thus, the degree of electrolyte membrane degradation is analyzed by measuring the aforementioned hydrogen permeability.

[0108] Compared to Example 1, Comparative Example 1, which uses a fluorinated polymer electrolyte membrane and includes a free radical protective layer containing alginate sulfate, shows a reduction of approximately 3 times in the increase rate of hydrogen permeability and approximately 2.8 times in the battery voltage decay rate.

[0109] Furthermore, comparing the results of Comparative Example 2 and Example 3 using PES hydrocarbon polymer electrolyte membranes, the hydrocarbon polymer electrolyte membranes, especially those including a free radical protective layer containing brown algae polysaccharide sulfate, exhibited superior anti-deterioration properties. Specifically, in Example 3, the increase in hydrogen permeability was reduced by about 2 times or less, and the battery voltage decay rate was also reduced by about 2.9 times.

[0110] Furthermore, based on the results of Examples 1 and 2, when a free radical protective layer containing brown algae polysaccharide sulfate is stacked with an additional free radical protective layer, the increase rate of hydrogen permeability is reduced by about 6.5 times or less, and the battery voltage decay rate is also reduced by about 3.3 times compared to the monolayer case.

[0111] Furthermore, based on the results of Examples 3 and 4, when a free radical protective layer containing brown algae polysaccharide sulfate is stacked with an additional free radical protective layer, the increase rate of hydrogen permeability is reduced by about 5 times or less, and the battery voltage decay rate is also reduced by about 1.8 times compared to the monolayer case.

[0112] The preferred embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited thereto. Various modifications and improvements made by those skilled in the art using the basic concepts of the present invention as defined in the appended claims should also fall within the scope of the present invention.

[0113] Explanation of reference numerals in the attached figures

[0114] 10, 10': Free radical protective layer

[0115] 11, 11': First free radical protective layer

[0116] 12, 12': Second radical protective layer

[0117] 20, 20': Electrode layer

[0118] 30, 30': Catalyst layer

[0119] 40, 40': Electrode substrate

[0120] 50: Polymer electrolyte membrane

[0121] 100: Membrane electrode assembly

[0122] 200: Fuel Cell

[0123] 210: Fuel Supply Department

[0124] 220: Reorganization Department

[0125] 230: Fuel cell stack

[0126] 231: First Supply Management

[0127] 232: Second Supply Pipe

[0128] 233: First discharge pipe

[0129] 234: Second discharge pipe

[0130] 240: Oxidant Supply Department

Claims

1. A membrane electrode assembly for a fuel cell, characterized in that, include: Polymer electrolyte membrane; A free radical protective layer, disposed on at least one surface of the polymer electrolyte membrane, and comprising a free radical scavenger; and An electrode layer is disposed on the free radical protective layer. The free radical scavenger includes brown algae polysaccharide sulfate.

2. The membrane electrode assembly for fuel cells according to claim 1, characterized in that, The free radical scavenger also contains one or more of the following: transition metals, their ions, their salts, their oxides, their nitrides and their complexes, carotenoids, flavonoids, vitamins, and glutathione.

3. The membrane electrode assembly for fuel cells according to claim 1, characterized in that, The content of the fucoidan sulfate is 0.2% by weight or more and 1.0% by weight or less, based on the total weight of the free radical protective layer containing fucoidan sulfate.

4. The membrane electrode assembly for fuel cells according to claim 2, characterized in that, The free radical protection layer includes a first free radical protection layer and a second free radical protection layer, and at least one of the first free radical protection layer and the second free radical protection layer contains alginate sulfate.

5. The membrane electrode assembly for fuel cells according to claim 4, characterized in that, The first free radical protective layer is located on the polymer electrolyte membrane, and the second free radical protective layer is located on the first free radical protective layer. The content of free radical scavengers other than the brown algae polysaccharide sulfate in the first free radical protective layer is higher than that in the second free radical protective layer.

6. The membrane electrode assembly for fuel cells according to claim 5, characterized in that, The content of brown algae polysaccharide sulfate in the first free radical protective layer and the second free radical protective layer may be the same or different.

7. The membrane electrode assembly for a fuel cell according to claim 5, characterized in that, Based on the total weight of the free radical protective layer, the content of free radical scavengers in the first free radical protective layer, excluding brown algae polysaccharide sulfate, is more than 0.1% by weight and less than 20% by weight.

8. The membrane electrode assembly for fuel cells according to claim 5, characterized in that, The thickness ratio of the first free radical protective layer to the second free radical protective layer is 10:1 to 1:

10.

9. The membrane electrode assembly for a fuel cell according to claim 1, characterized in that, The free radical protective layer comprises carbon nanofibers.

10. The membrane electrode assembly for a fuel cell according to claim 5, characterized in that, Carbon nanofibers are contained only in the first free radical protective layer.

11. The membrane electrode assembly for a fuel cell according to claim 1, characterized in that, The thickness of the free radical protective layer is greater than 10 nm and less than 2000 nm.

12. The membrane electrode assembly for a fuel cell according to claim 1, characterized in that, The electrode layer includes a catalyst layer disposed on the surface of the electrode substrate.

13. A fuel cell, characterized in that, Includes the membrane electrode assembly for fuel cells as described in claim 1.

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