FUEL CELL MEMBRANE ELECTRODE UNITS

Abstract

Fuel cell membrane electrode assembly (22) comprising: a polymer electrolyte membrane (PEM) (12); and a first and second electrode (50, 100), wherein the PEM (12) is located between the first and second electrode (50, 100), wherein the first electrode (50, 100) has a first catalyst material layer (56, 106) comprising a first catalyst material and having a first and second surface, wherein the first electrode (50, 100) has a first and second material layer adjacent to the first and second surfaces of the first catalyst material layer (56, 106), respectively, wherein the first material layer faces away from the PEM (12) and the second material layer faces the PEM (12), wherein the first material layer comprises a first graphene-based material layer (52, 102) with a first number of defects (58, 108, 60, 110) designed to allow the dissolution of the first catalyst material through the first material layer (52, 102). weaken,wherein the first catalyst material layer (56, 106) has several gaps (118, 120, 122) designed to change the shape of the first material layer, which comprises the graphene-based material layer (52, 102), over several operating cycles of a fuel cell (10) containing the fuel cell membrane electrode assembly.

Description

TECHNICAL AREA The present disclosure relates to fuel cell membrane electrode assemblies designed to attenuate catalyst dissolution while maintaining the transport of reactants and products from fuel cells. BACKGROUND Fuel cells have proven to be a promising alternative energy source for vehicles and other transportation applications. Fuel cells utilize a renewable energy carrier, such as hydrogen. They also operate without toxic emissions or greenhouse gases. A single fuel cell consists of a membrane electrode assembly (MEA) and two flow field plates. A single fuel cell typically delivers 0.5 to 1.0 V. Individual fuel cells can be stacked to form a fuel cell stack with a higher voltage and power output. Due to the relatively high cost of the materials used in the fuel cell stack, fuel cell technology has so far been used to a limited extent. One of the materials that accounts for a significant portion of the overall cost of the fuel cell stack is the catalyst material, such as platinum catalyst materials.The durability of the catalyst materials affects the overall cost of fuel cell technology. From DE 10 2020 209 427 A1, a fuel cell membrane electrode unit is known, comprising: a polymer electrolyte membrane (PEM); and a first and second electrode, wherein the PEM is located between the first and second electrode, wherein the first electrode has a first catalyst material layer with a first catalyst material and with a first and second surface, wherein the first electrode has a first and second material layer adjacent to the first and second surfaces of the first catalyst material layer, respectively, wherein the first material layer faces away from the PEM and the second material layer faces the PEM, wherein the first material layer comprises a first material layer based on graphene with a first number of defects designed to attenuate the dissolution of the first catalyst material through the first material layer. US 2013 / 0344413 A1 further discloses a fuel cell membrane electrode assembly comprising: a polymer electrolyte membrane (PEM); and a first and second electrode with a first and second bulk material, wherein the PEM is located between the first and second electrodes, the first bulk material comprising a first number of catalyst units distributed therein, the catalyst units each comprising a catalyst material layer with a catalyst material and with a first and second surface and a first and second material layer adjacent to the first and second surfaces of the catalyst material layer, respectively, the first material layer of each catalyst unit comprising a graphene-based material layer having multiple defects designed to attenuate the dissolution of the catalyst material through the graphene-based material layer. SUMMARY It is therefore the purpose of the present disclosure to provide a fuel cell membrane electrode assembly with a polymer electrolyte membrane (PEM) in which the durability of a catalyst material layer is increased, thereby reducing the technologically induced costs. The problem is solved by a fuel cell membrane electrode unit having the features of claims 1 or 8. Advantageous further developments are found in the dependent claims. According to one embodiment, a fuel cell membrane electrode assembly is disclosed, comprising a polymer electrolyte membrane (PEM) and a first and second electrode. The PEM is located between the first and second electrodes. The first electrode has a first catalyst material layer with a first catalyst material and a first and second surface. The first and second material layers are adjacent to the first and second surfaces of the first catalyst material, respectively. The first material layer faces away from the PEM, and the second material layer faces the PEM. The first material layer comprises a graphene-based material layer with multiple defects configured to attenuate the dissolution of the first catalyst material through the first material layer.The first catalyst material layer has several gaps designed to change the shape of the first material layer, which comprises the graphene-based material layer, over several operating cycles of a fuel cell containing the fuel cell membrane electrode assembly. According to a further embodiment, a fuel cell membrane electrode assembly is disclosed. The fuel cell membrane electrode assembly comprises a polymer electrolyte membrane (PEM) and a first and second electrode. The PEM is located between the first and second electrodes. The first electrode has a first catalyst material layer with a first catalyst material and with a first and second surface. The first electrode has a first and second graphene-based material layer adjacent to the first and second surfaces of the first catalyst material, respectively. The first graphene-based material layer faces away from the PEM, and the second graphene-based material layer faces the PEM. The first graphene-based material layer has a first number of defects, and the second graphene-based material layer has a second number of defects. The first number is greater than the second number. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a simplified side view of a fuel cell. Fig. 2 shows a simplified side view of an electrode configured to be used as the cathode and / or anode of a fuel cell. Fig. 3 shows a simplified side view of an electrode configured to be used as the cathode and / or anode of a fuel cell. Fig. 4 shows a simplified top view of a catalyst unit configured to be used in a cathode and / or anode of a fuel cell. Fig. 5 shows a simplified perspective top view of a catalyst unit configured to be used in a cathode and / or anode of a fuel cell. Fig. 6 shows a simplified side view of a membrane electrode unit not according to the invention, configured to be used in a fuel cell.Figure 7 shows a simplified side view of a membrane electrode assembly configured for use in a fuel cell. DETAILED DESCRIPTION This document describes embodiments of the present disclosure. It is understood, however, that the disclosed embodiments are merely examples and that further embodiments may take different and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or reduced in size to illustrate details of components. Therefore, specific details regarding structure and function disclosed in this document should not be interpreted as limiting, but merely as a representative basis to convey to a person skilled in the art the different uses of the embodiments.The person skilled in the art will understand that various features illustrated and described with respect to any one of the figures can be combined with features illustrated in one or more other figures to create embodiments not expressly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features according to the teaching of this disclosure may be desirable for applications or embodiments. Except in the examples or where otherwise expressly stated, all numerical quantities in this description indicating amounts of material or reaction and / or conditions of use are to be understood as modified by the word "approximately" and thus describe the scope of protection of the invention to the broadest extent. In general, practical implementation within the stated numerical limits is preferred. Unless expressly stated otherwise, percentages, "parts of," and ratios are by weight; the term "polymer" includes "oligomer," "copolymer," "terpolymer," and the like; the description of a group or class of materials as suitable or preferred for a particular purpose in connection with the invention implies that mixtures of any two or more of the elements of the group or class are equally suitable or preferred.If a molar mass specified for any polymer refers to the number-averaged molar mass; if the description of constituents refers chemically to the constituents at the time of their addition to any combination specified in the description, and does not necessarily exclude chemical interactions among the constituents of a mixture once they are mixed; if the first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation in this document, and applies analogously to regular grammatical variants of the abbreviation defined at the outset; and if, unless expressly stated otherwise, the measured value of a property is determined by the same method as previously or subsequently specified for the same property. This invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may naturally differ. Furthermore, the terminology used in this document serves only to describe embodiments of the present invention and is in no way intended to be limiting. The singular forms "ein," "eine," "der," "die," and "das," when used in the description and the attached claims, encompass plural reference objects unless the context clearly indicates otherwise. For example, when referring to a single component in the singular, a multitude of components should be considered to be included. The term "essentially" may be used in this document to describe disclosed or claimed embodiments. The term "essentially" may modify a value or relative property that is disclosed or claimed in this disclosure. In such cases, "essentially" may mean that the value or relative property it modifies is within ± 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or 10% of the value or relative property. Due to rising carbon dioxide emissions and the relatively high current dependence on non-renewable fossil fuels as energy sources in the transport sector, the need for the development and marketing of transport technologies that utilize clean and sustainable energy sources is constantly increasing. One promising technology is the fuel cell. A fuel cell uses oxygen from the air and compressed hydrogen as fuel sources, releasing only water and heat as byproducts. Widespread use of fuel cells would reduce carbon dioxide emissions. However, further technological developments are necessary for widespread deployment. One area for further technological development is improving the durability of the catalyst materials in the fuel cell. Catalyst materials are contained in a catalyst layer at the anode and cathode of a fuel cell. Platinum catalysts are typically used as catalyst materials for the anode and / or cathode. Platinum catalysts dissolve, and Pt²⁺ ions migrate from the catalyst layer to other components in the fuel cell, such as the polymer electrolyte membrane (PEM). Catalyst degradation in a fuel cell occurs in one case via the dissolution of Pt at a high operating potential (e.g., above approximately 0.6, 0.7, and 0.8 volts relative to a standard hydrogen electrode (SHE)). In another case, catalyst degradation occurs when a fuel cell reaches an even higher potential than 0.8 volts (e.g., up to approximately 2 volts).This can occur due to transient operation, carbon corrosion, and / or gas shortages during start-up and shutdown, which can further accelerate the degradation of the catalyst and other fuel cell components. As the electrochemically active surface area (ECSA) of a fuel cell catalyst gradually decreases, a significant decline in oxygen reduction (ORR) activity can occur. Furthermore, dissolved catalyst metal ions can migrate to other fuel cell components, such as the polymer electrolyte membrane (PEM), potentially accelerating PEM degradation. There is a need for a solution to reduce dissolution and slow migration while maintaining the advantageous catalytic activity of the platinum catalyst. Aspects of this disclosure relate to the use of defective graphene-based materials as part of an electrode to increase the durability of catalyst materials, e.g., by reducing dissolution and slowing migration. In aspects of this disclosure, graphene-catalyst hybrid systems are used via controlled interfaces between atoms and molecules to suppress the dissolution of the metal in catalysts for PEM fuel cells.By using defective materials based on graphene, the electrochemically active surface (ECSA) is preserved and / or the degradation of the PEM is reduced, thereby extending the lifetime of the fuel cell stack for a given catalyst material loading. Fig. 1 shows a simplified side view of a fuel cell 10. The fuel cell 10 can be stacked to form a fuel cell stack. The fuel cell 10 has a polymer electrolyte membrane (PEM) 12, an anode 14, a cathode 16, and a first and second gas diffusion layer (GDL) 18 and 20. The PEM 12 is located between the anode 14 and the cathode 16. The anode 14 is located between the first GDL 18 and the PEM 12, and the cathode 16 is located between the second GDL 20 and the PEM 12. The PEM 12, the anode 14, the cathode 16, and the first and second GDL 18 and 20 form a membrane electrode assembly (MEA) 22. The first and second sides 24 and 26 of the MEA 22 are bounded by the flow fields 28 and 30, respectively. Flow field 28 supplies the MEA 22 with H₂, as indicated by arrow 32. Flow field 30 supplies the MEA 22 with O₂, as indicated by arrow 34.A catalyst material such as platinum is used in the anode 14 and the cathode 16. The catalyst material is usually the most expensive component of the MEA 22. Fig. 2 shows a simplified side view of an electrode 50 configured to serve as the anode 14 and / or cathode 16 of the fuel cell 10. The electrode 50 comprises a first and second material layer based on graphene 52 and 54, and a catalyst material layer 56. The catalyst material layer 56 is located between the first and second graphene-based material layers 52 and 54. At least one surface of the catalyst material layer 56 can be partially or completely coated with the graphene-based material. The graphene-based material of layers 52 and 54 can comprise graphene, graphene oxide (GO), reduced graphene oxides (rGO), and combinations thereof. The graphene-based material can also include other materials that capture dissolved metal ions during the operation of the fuel cell 10. The graphene-based material can contain oxygen-containing functional groups such as epoxy (-O-), carbonyl (=O), carboxy (-COOH), and / or hydroxy (-OH) to further optimize the transport and diffusion of Pt, H₂, O₂, and H₂O. In one embodiment, different types of graphene and various graphene oxides can be produced using the Hummer process. The graphene-based material can comprise a substantial amount of material capable of capturing dissolved metal ions. The substantial amount can be at one of the following values ​​or in a range between any two of the following values: 70, 75, 80, 85, 90, 95 and 100%.The remaining amounts may partially comprise an amorphous and / or crystalline graphene material. In one embodiment, the first and / or second graphene-based material layers 52 and 54 may comprise more crystalline graphene material than amorphous graphene material. Crystalline graphene material is an sp2-hybridized carbon that is less corrosive during start-up / shutdown of fuel cell 10 operation compared to an amorphous carbon, which is primarily an sp3-hybridized carbon. The graphene-based material may also be functionalized by cation or anion doping. In another embodiment, the graphene-based material may be a carbide, nitride, or fluoride material configured to optimize the selective diffusion of Pt, H₂, O₂, and H₂O.The coating made of graphene-based material can also provide a physical barrier against attack with RF and / or SO3, thus further preventing degradation of the PEMFC. In another embodiment, the graphene-based material can consist of a single layer or between two and five layers of sp2-hybridized carbon atoms. Amorphous carbon, e.g., with sp3 hybridization, can also be present. The ratio of sp2-hybridized to sp3-hybridized carbon atoms can depend on the operating conditions of the fuel cell. The graphene-based material can be a graphene layer applied in a planar orientation. The graphene-based layer can comprise a single graphene monolayer. In further embodiments, the number of graphene monolayers in the graphene-based layer can be one of the following numbers or a range between any two of the following: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15. The graphene-based material can be configured to mitigate the degradation of the catalyst material in electrode 50. A reduction in Pt degradation can bring one or more of the following advantages: (1) less reduction in the size of the ECSA and (2) prevented migration of Pt2+ ions to the interface between the PEM 12 and the electrode 50 or into the PEM 12, thereby preventing degradation of the PEM. The addition of the graphene-based material enhances electron transport due to the increased conductivity of the catalyst layer. In one embodiment, the first and second graphene-based material layers 52 and 54 are in direct contact with the catalyst material layer 56. In another embodiment, the first and second graphene-based material layers 52 and 54 are loosely bonded, for example, at a small distance from the catalyst material layer 56. This small distance can be one of the following values ​​or a range between any two of the following: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, and 10 nm. When Pt ionizes to Pt²⁺(aq) and dissolves, the graphene-based material coating can trap the dissolved Pt species. One or both surfaces of the catalyst material layer 56 can be coated with the graphene-based material using various methods. The graphene-based material can be applied to the catalyst material layer 56 during or after the synthesis of the electrode 50, either as a thin film or via dispersion (e.g., using graphene ink). The graphene can be in the form of layers, flakes, powders, and / or combinations thereof. A coated electrode can be produced using solid-state processes, solution-based processes, or deposition processes with subsequent secondary heat treatment in the presence of oxidizing or reducing agents (e.g., air, O₂, N₂, Ar, H₂, or mixtures thereof).A graphene-based film can be grown on a metal foil using chemical vapor deposition (CVD). This is followed by cleaning with an organic solvent and electropolishing under acidic voltage. The material can then be rinsed and heat-treated in a reducing environment (e.g., using an Ar:H₂ gas mixture) to promote graphene growth. After CVD growth, the sample can be combined with a polymer (e.g., polymethyl methacrylate (PMMA)) and subsequently etched or rinsed. The composite film can then be transferred to the catalyst material layer 56. In another embodiment, a graphene film consisting of a single layer or multiple layers can be grown on strong metal substrates in addition to metal foils. Graphene films can be mechanically supported by supplementing the graphene with a polymer film layer using spin coating, dip coating, or other coating processes. The graphene-polymer film stack can be removed from the metal substrate using a wet process in an electrochemical bath and transferred to a catalyst substrate. Once the graphene-polymer film stack is applied to the catalyst substrate, the polymer support can be removed using a wet chemical or dry plasma etching process. A cleaning process may be necessary prior to graphene deposition on the metal substrate.After polymer removal, an additional purification step may be necessary to obtain high-quality graphene-metal catalyst composites. During the transfer process, the smoothness and crystallization of the starting metal substrate are crucial for the expected extent of graphene defects. After the transfer process is complete, the roughness of the underlying catalyst metals (e.g., nanoparticles) primarily contributes to the final extent of the graphene defects. In one embodiment, the shape of the graphene-based material corresponds to the contour of the surface of the catalyst material layer, for example, the roughness of platinum nanoparticles. The number of defects in the graphene-based material, the shape of folds in the graphene-based material, and the shape of the interface between the first and / or second graphene-based material layers 52 and 54 and the catalyst material layer 56 can lead to different surface morphologies, depending on the surface roughness of the catalyst material layer 56.Depending on the number of defects, the shape of the graphene-based material layer and the interface shape, the folding and / or the totality of graphene defects, several activation cycles can be carried out to enable proper diffusion and relatively fast transport of H2, O2 and H2O, thus achieving the desired activity for the oxygen reduction reaction (ORR). Using various methods, a surface of the catalyst material layer 56 can be coated with further two-dimensional layered materials. Non-restrictive examples of further two-dimensional layered materials include graphyne, borophene, germanene, silicon, Si₂BN, stanine, phosphorene, bismuthene, molybdenite, as well as transition metal dichalcogenides (TMDCs) (e.g., MOS₂, WSe₂, HfS₂, etc.), multilayer transition metal carbides and carbonitrides (MXenes) with a general formula Mn+1XnTx, where M represents transition metals (e.g., Ti, Mo, W, Nb, Zr, Hf, V, Cr, Ta, and Sc), X represents carbon and / or nitrogen, and Tx represents functional groups on the surface (e.g., =O, -OH, or -F), and combinations thereof. Other two-dimensional layered structural materials can be used to completely or partially replace the graphene-based materials in the catalyst layer coating of the electrodes. The catalyst material of layer 56 can be pure Pt, a Pt-M alloy (where M is another metal from the periodic table), another platinum group metal (PM) (e.g., Ru, Rh, Pd, Os, or Ir), Ag, Au, Cu, Fe, Mn, Ni, Co, W, Mo, Sn, Ti, PGM-M, Pt-PGM-M, or combinations or alloys thereof. The thickness of the catalyst material layer 56 can vary depending on the catalyst loading required to meet different fuel cell requirements and / or on the size of the layer. The thickness (t) of the metal catalyst layer, as shown in Fig. 2, can be one of the following values ​​or in a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 20 nm. The catalyst material of layer 56 can be a nanostructured catalyst material, thus providing a larger accessible electrochemically active surface area (ECSA).The larger ECSA delivers a higher catalytic output per unit mass of catalyst material used. The first material layer based on graphene 52 exhibits defects 58 and 60. The second material layer based on graphene 54 exhibits defects 62, 64, and 66. Defects 58, 60, 62, 64, and / or 66 can be designed to (1) trap dissolved metal ions (e.g., Pt²⁺(aq) ions) from the catalyst material layer 56 and / or (2) provide a diffusion pathway (e.g., a channel) for fuel cell reactants (e.g., H₂, O₂, and / or H₂O). Defects 58, 60, 62, 64, and / or 66 can significantly increase the weak binding energies in unaffected graphene. Non-restrictive examples of defects include single vacancies (mono-vacancy, MV), double vacancies (divacancy, DV), triple vacancies (tri-vacancy, TV), quad vacancies (quad-vacancy, QV), graphene holes, Stone Wales defects (SW defects), and / or commonly occurring oxygen-containing functional groups such as hydroxide (-OH), epoxy (-O-), carbonyl (=O), and / or carboxyl (-COOH) groups. Non-restrictive examples of methods for producing such defects include synthesis, annealing, and ion bombardment. In another embodiment, graphene defects can be holes. Multiple carbon atoms can be removed (e.g., creating larger vacancies), thus rearranging the defective graphene structure. The number of defects per unit volume of either the first or second graphene-based material layer can be one of the following values ​​or in a range between any two of the following values: 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13%. The number of defects per unit volume can vary depending on the durability requirements and / or the operating conditions for the fuel cell 10. As a non-restrictive example, if the fuel cell 10 is to operate at a relatively high potential above approximately 0.6, 0.7, or 0.8 VRHE (or in any other transient state resulting in an abrupt increase in the fuel cell potential), more defects may be necessary to trap dissolved metal ions from the catalyst material layer 56 during degradation. According to Fig.1. The first and / or second material layers based on graphene 52 and 54 can exhibit different selectivities for metal ions, H₂, O₂, and H₂O. In one embodiment, the second material layer based on graphene 54 can serve as a support material for the catalyst material layer 56, and the first material layer based on graphene 52 can be designed to trap dissolved metal ions and / or provide a diffusion pathway (e.g., a channel) for fuel cell reactants. In this embodiment, fewer defects may be required in the second material layer based on graphene 54 than in the first material layer based on graphene 52. Fig. 3 shows a simplified side view of an electrode 100 configured to serve as the anode 14 and / or cathode 16 of the fuel cell 10. The electrode 100 comprises a first and second material layer based on graphene 102 and 104, and a catalyst material layer 106. The catalyst material layer 106 is located between the first and second material layers based on graphene 102 and 104. The first material layer based on graphene 102 has defects 108 and 110. The second material layer based on graphene 104 has defects 112, 114, and 116. The defects 108, 110, 112, 114 and / or 116 can be designed to (1) capture dissolved metal ions (e.g. Pt2+(aq) ions) from the catalyst material layer 56 and / or (2) provide a diffusion path (e.g. channel) for fuel cell reactants (e.g. H2, O2 and / or H2O). The thickness (t) of the metal catalyst layer, as shown in Fig. 3, can be at one of the following values ​​or in a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 20 nm. The catalyst material layer 106 has a lower catalyst loading compared to the catalyst material layer 56, resulting in gaps such as gaps 118, 120, and 122 in the catalyst material layer 106, as shown in Fig. 3. In one embodiment, the gaps can be created by the surface tension between metal catalyst nanoparticles. In another embodiment, the graphene-based material can be homogenized in a homogenizer at a relatively high rotational speed. Relatively larger gaps can be formed, as shown in Fig. 3. The volume of each gap can be independently selected from one of the following values ​​or within a range between any two of the following values: 1 nm³, 50 nm³, 100 nm³, 200 nm³, 500 nm³, 750 nm³, and 1 µm³.The percentage of gap to volume occupied by catalyst materials can be one of the following values ​​or in a range between any two of the following values: 25%, 30%, 40%, 50% and 60%. In one or more embodiments, one or more of the gaps provide a diffusion path (e.g., a channel) for fuel cell reactants (e.g., H₂, O₂, and / or H₂O). The gaps can allow for the redeposition of the metal catalyst. Furthermore, the gaps can form an interface between the catalyst material layer 106 and the first and second graphene-based material layers 102 and 104 with lower interfacial resistance. Due to the gaps, the first and second graphene-based material layers 102 and 104 can develop folds after a certain number of fuel cell cycles (e.g., change the shape of the graphene-based material layers in a region above or below a gap). The number of cycles can be one of the following values ​​or a range between any two of the following values: 2000, 2500, 3000, 3500, and 4000.In one embodiment, one or more of the cavities can be filled with one or more conductive materials, which are not the catalyst material. The other conductive materials can include amorphous carbon black and / or conductive polymers. The electrode 100 also has first and second openings 124 and 126. The openings 124 and 126 can be designed to provide a diffusion path (e.g., a channel) for fuel cell reactants (e.g., H₂, O₂, and / or H₂O). Some of the catalyst material in the form of dissolved metal ions may be lost through one or more of the first and second openings 124 and 126 if the fuel cell 10 is operated at a relatively high potential. In general, however, the diffusion of metal ions (e.g., Pt²⁺) is considerably lower due to attractive forces between the dissolved metal ions and the first and second material layers based on graphene 10² and 10⁴, as illustrated with the dissolved metal ions 119. Electrodes 50 and / or 100 can be used as thin-film electrodes, in which one or more graphene-based materials are transferred to or directly deposited onto a thin Pt catalyst film. Non-limiting examples of applications for this type of thin-film design include mobile communications, small power electronics, military, and / or aerospace applications. Fig. 4 shows a simplified top view of a catalyst unit 70 configured for use in the anode 14 and / or cathode 16 of the fuel cell 10. The catalyst unit 70 comprises a first and second material layer based on graphene 72 and 74, and the catalyst material layer 76. The catalyst material layer 76 is located between the first and second material layers based on graphene 72 and 74. The first material layer based on graphene 72 exhibits regularly repeating graphene-based materials, for example, regions 78 and 80. Shadowed regions such as regions 82 and 84 represent the formation of graphene-based defects based on oxygen-containing functionalized groups (e.g., -O-, =O, -COOH, and -OH).Areas that do not exhibit regularly repeating graphene-based materials or graphene-based defects based on oxygen-containing functionalized groups are gaps such as gaps 86 and 88. The gaps can be empty spaces and / or graphene holes. As shown in Fig. 4, the catalyst unit 70 has a width 90, a length 92, and a thickness 94. The width 90, length 92, and thickness 94 can all be independently varied depending on the requirements of the PEMFC (e.g., stack size, power requirements, operating regime, etc.). The width 90 can be one of the following values ​​or a range between any two of the following: 10 nm, 100 nm, 1 µm, 10 µm, and 100 µm. The length 92 can be one of the following values ​​or a range between any two of the following: 10 nm, 100 nm, 1 µm, 10 µm, and 100 µm. The thickness 94 can be at one of the following values ​​or in a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 20 nm. Fig. 5 shows a simplified perspective top view of a catalyst unit 150 configured for use in the anode 14 and / or cathode 16 of the fuel cell 10. The catalyst unit 150 comprises a graphene-based material layer 152 and a catalyst support material layer 154. The catalyst material layer 156 lies between the graphene-based material layer 152 and the catalyst support material layer 154. The graphene-based material layer 152 exhibits regularly repeating graphene-based materials, for example, regions 158 and 160. Shadowed regions such as regions 162 and 164 represent the formation of graphene-based defects based on oxygen-containing functionalized groups (e.g., -O-, =O, -COOH, and -OH).Areas that do not exhibit regularly repeating graphene-based materials or graphene-based defects based on oxygen-containing functionalized groups are gaps such as gaps 166 and 168. The gaps can be empty spaces and / or graphene holes. The specified percentage can be at one of the following values ​​or in a range between any two of the following values: 5%, 10%, 15%, 20%, and 25%. The catalyst support material layer 154 can be formed from an amorphous carbon material (e.g., carbon with sp3 hybridization), one or more metal oxides (e.g., MOx, where M = Ti, Sn, W, Mo, Ge, Ta, etc.), or combinations thereof. The catalyst support material layer 154 can be located closer to the PEM 12 than the graphene-based material layer 152. In a further embodiment, the catalyst support material layer 154 can be arranged between the first and second graphene-based material layers, and the outer surface of the graphene-based material contacts a catalyst support material layer 154. As shown in Fig. 5, the catalyst material layer has gaps such as gaps 170 and 172. In one or more embodiments, one or more of the gaps constitute a diffusion path (e.g., a channel) for fuel cell reactants (e.g., H₂, O₂, and / or H₂O). The gaps can also form the interface between the catalyst material layer 106 and the first and second graphene-based material layers 152 and 154 with lower interfacial resistance. Due to the gaps, the first and second graphene-based material layers 152 and 154 can form folds after a certain number of fuel cell cycles (e.g., change the shape of the graphene-based material layers in a region above or below a gap). The number of iterations can be one of the following values ​​or in a range between any two of the following values: 2000, 2500, 3000, 3500 and 4000.In one embodiment, one or more of the cavities can be filled with one or more conductive materials, which are not the catalyst material. The other conductive materials can include amorphous carbon black and / or conductive polymers. As shown in Fig. 5, the catalyst unit 150 has a width 174, a length 176, and a thickness (not shown). The width 174, length 176, and thickness can all be independently varied depending on the requirements of the PEMFC (e.g., stack size, power requirements, operating regime, etc.). The width 174 can be any of the following values ​​or any two of the following: 10 nm, 100 nm, 1 µm, 10 µm, and 100 µm. The length 176 can be any of the following values ​​or any two of the following: 10 nm, 100 nm, 1 µm, 10 µm, and 100 µm. The thickness can be at one of the following values ​​or in a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 20 nm. The electrodes 50 and / or 100 and the catalyst units 70 and 150 can be prepared using a chemical synthesis method and subsequently processed to a desired shape and size. Non-limiting examples of suitable chemical synthesis methods include focused ion beam scanning electron microscopy (FIB-SEM), electron beam lithography, laser writing, and photolithography. In further embodiments, the catalyst design can be obtained using a solution or deposition method until a desired size and shape are achieved. In the subsequent shaping and size-consolidation steps, the catalyst design can be formed as a square, nanowire, or strip. The square shape can have sides with one of the following values ​​or in a range between any two of the following values: 10 nm, 100 nm, 1 µm, 10 µm, and 100 µm.The width of the strip can be one of the following values ​​or in a range between any two of the following values: 2, 5, 10 or 15 µm. Figure 6, which is not part of the invention, shows a simplified side view of an MEA 200 configured for use in a fuel cell such as fuel cell 10. The MEA 200 has a cathode 202, a PEM 204, and an anode 206. The PEM 204 is located between the cathode 202 and the anode 206. The PEM 204 is an ionomer that forms an ionomer network 205. The PEM 204 is configured to conduct protons while simultaneously acting as an insulator for electrons and a barrier between fuel cell reactants (e.g., oxygen and hydrogen gas). The ionomer can be perfluorosulfonic acid based. A non-limiting example is Nafion from DuPont. The cathode 202 comprises a cathode bulk material 208. The catalyst units 70 and / or 150 can be distributed within the cathode bulk material 208. As shown in Fig. 6, the cathode bulk material 208 is an ionomer that forms an ionomer network 209 between the catalyst units 70 and / or 150. The anode 206 comprises an anode bulk material 210. The catalyst units 70 and / or 150 can be distributed within the anode bulk material 210. As shown in Fig. 6, the anode bulk material 210 is an ionomer that forms an ionomer network 211 between the catalyst units 70 and / or 150. The anode and / or cathode 202 and 206 can be formed by mixing the catalyst units 70 and / or 150 with one or more ionomers. The catalyst units 70 and / or 150 can be mixed using a solvent medium, e.g., a slurry in a homogenizer. The loading of catalyst units 70 and / or 150 in the cathode 202 and anode 206 can be selected independently depending on the operating conditions of the fuel cell. In one embodiment, the loading of catalyst units 70 and / or 150 in the cathode 202 is higher than in the anode 206 to overcome the ORR kinetics. The ratio of cathode loading to anode loading can be one of the following values ​​or in a range between any two of the following values: 2:1, 7:4, 3:2, 5:4, and 1:1. As previously described, both electrodes 50 and 100 and catalyst units 70 and 150 have at least one defective graphene-based layer. The size, type, and density of the defects can be controlled depending on the fuel cell's operating conditions (e.g., operating voltage and lifetime). In an embodiment used under higher power conditions, more graphene-based defects can be present than under lower power conditions, thus enabling the capture of more catalyst material and / or metal ions dissolved at a high potential (e.g., above approximately 0.6, 0.7, and 0.8 VRHE). Fig. 7 shows a simplified cross-sectional view of an MEA 250 configured for use in a fuel cell such as fuel cell 10. The MEA 250 has a cathode 252, a PEM 254, and an anode 256. The cathode 252 has a catalyst material layer 258 positioned between the first and second material layers 260 and 262. The first material layer 260 faces away from the PEM 254, and the second material layer 262 faces the PEM 254. In one embodiment, the first material layer 260 is a first material layer based on graphene 52 or 102, which is designed to (1) capture dissolved metal ions (e.g., Pt2+(aq) ions) from the catalyst material layer 56 and / or (2) provide a diffusion path (e.g., channel) for fuel cell reactants (e.g., H2, O2, and / or H2O), and the second carbon-based layer 262 is made of a support material such as an amorphous carbon material (e.g.,carbon with sp3 hybridization), one or more metal oxides (e.g. MOx, where M = Ti, Sn, W, Mo, Ge, Ta etc.) or combinations thereof are formed. The anode 256 has a catalyst material layer 264, which is arranged between the first and second material layers 266 and 268. The first material layer 266 faces away from the PEM 254 and the second carbon-based material layer 268 faces the PEM 254. In one embodiment, the first material layer 266 is a first material layer based on graphene 52 or 102, designed to (1) capture dissolved metal ions (e.g., Pt2+(aq) ions) from the catalyst material layer 56, and / or (2) provide a diffusion path (e.g., channel) for fuel cell reactants (e.g., H2, O2, and / or H2O), and the second material layer 268 is formed from a support material such as an amorphous carbon material (e.g., carbon with sp3 hybridization), one or more metal oxides (e.g., MOx, where M = Ti, Sn, W, Mo, Ge, Ta, etc.), or combinations thereof.

Claims

Fuel cell membrane electrode assembly (22) comprising: a polymer electrolyte membrane (PEM) (12); and a first and second electrode (50, 100), wherein the PEM (12) is located between the first and second electrode (50, 100), wherein the first electrode (50, 100) has a first catalyst material layer (56, 106) comprising a first catalyst material and having a first and second surface, wherein the first electrode (50, 100) has a first and second material layer adjacent to the first and second surfaces of the first catalyst material layer (56, 106), respectively, wherein the first material layer faces away from the PEM (12) and the second material layer faces the PEM (12), wherein the first material layer comprises a first graphene-based material layer (52, 102) with a first number of defects (58, 108, 60, 110) designed to allow the dissolution of the first catalyst material through the first material layer (52, 102). weaken,wherein the first catalyst material layer (56, 106) has several gaps (118, 120, 122) designed to change the shape of the first material layer, which comprises the graphene-based material layer (52, 102), over several operating cycles of a fuel cell (10) containing the fuel cell membrane electrode assembly. Fuel cell membrane electrode assembly according to claim 1, wherein the number of defects (58, 108, 60, 110) is designed to trap the first catalyst material in the number of defects (58, 108, 60, 110). Fuel cell membrane electrode assembly according to claim 1, wherein the second material layer comprises a second material layer based on graphene (54, 104) with a second number of defects (62, 112, 64, 114, 66, 116) designed to attenuate the dissolution of the first catalyst material through the second material layer (54, 104). Fuel cell membrane electrode assembly according to claim 1, wherein the first and / or second material layer is applied to the first or second surface of the first catalyst layer as a first or second thin film. Fuel cell membrane electrode assembly according to claim 1, wherein the first catalyst material comprises pure Pt, a Pt-M alloy (where M is a metal other than Pt), platinum group metals (PGM), PGM-M, Pt-PGM-M or combinations thereof. Fuel cell membrane electrode assembly according to claim 1, wherein the graphene-based material layer comprises (52, 102, 54, 104) graphene, graphene oxide, reduced graphene oxides or combinations thereof. Fuel cell membrane electrode assembly according to claim 1, wherein the second material layer (54, 104) is a catalyst support layer designed to support the first catalyst material layer (56, 106). Fuel cell membrane electrode assembly comprising: a polymer electrolyte membrane (PEM) (12); and a first and second electrode (50, 100), wherein the PEM (12) is located between the first and second electrode (50, 100), wherein the first electrode (50, 100) has a first catalyst material layer (56, 106) with a first catalyst material and with a first and second surface, wherein the first electrode (50, 100) has a first and second material layer based on graphene (52, 102, 54, 104) adjacent to the first and second surfaces of the first catalyst material, respectively, wherein the first material layer based on graphene (52, 102) faces away from the PEM (12) and the second material layer based on graphene (54, 104) faces the PEM (12), wherein the first material layer based on graphene (52, 102) has a first number of defects (58, 108, 60, 110) and the second material layer based on graphene (54,104) has a second number of defects (62, 112, 64, 114, 66, 116) and the first number is greater than the second number. Fuel cell membrane electrode assembly according to claim 8, wherein the second number of defects (62, 112, 64, 114, 66, 116) is designed to trap the first catalyst material in the first number of defects (58, 108, 60, 110). Fuel cell membrane electrode assembly according to claim 8, wherein the first catalyst material comprises pure Pt, a Pt-M alloy (where M is a metal other than Pt), platinum group metals (PGM), PGM-M, Pt-PGM-M or combinations thereof. Fuel cell membrane electrode assembly according to claim 8, wherein the first number of defects (58, 108, 60, 110) comprises graphene-based vacancies and / or graphene-based defects based on one or more oxygen-containing functionalized groups. Fuel cell membrane electrode assembly according to claim 11, wherein the graphene-based vacancies comprise quad vacancy (QV) defects. Fuel cell membrane electrode assembly according to claim 8, wherein the first number of defects (58, 108, 60, 110) forms a first number of channels configured to allow one or more fuel cell reactants to diffuse.

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