Fuel cell membrane electrode assembly

Abstract

The invention relates to a fuel cell membrane electrode assembly. A fuel cell membrane electrode assembly comprising a polymer electrolyte membrane (PEM) and first and second electrodes. The PEM is located between the first and second electrodes. The first electrode comprises a first catalyst material layer comprising a first catalyst material and having first and second surfaces. The first electrode comprises first and second material layers 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 towards the PEM. The first material layer comprises a graphene-based material layer having a plurality of defects configured to mitigate leaching of the first catalyst material through the first material layer.

Description

Technical Field

[0001] The present disclosure relates to fuel cell membrane electrode assemblies configured to mitigate catalyst dissolution while maintaining the deliverability of fuel cell reactants and products. Background Art

[0002] Fuel cells have shown promise as an alternative power source for vehicles and other transportation applications. Fuel cells operate on renewable energy carriers, such as hydrogen. Fuel cells 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 outputs 0.5 to 1.0 V. Single fuel cells can be stacked together to form a fuel cell stack with higher voltage and power. Due to the relatively high cost of the materials in the fuel cell stack, the application of fuel cell technology is limited. One of the materials that accounts for a significant share of the total cost of the fuel cell stack is the catalyst material, such as platinum catalyst material. The durability of the catalyst material affects the overall cost of the fuel cell technology. Summary of the Invention

[0003] According to one embodiment, a fuel cell membrane electrode assembly is disclosed, comprising a polymer electrolyte membrane (PEM) and first and second electrodes. The PEM is positioned between the first and second electrodes. The first electrode comprises a first catalyst material layer comprising a first catalyst material and having first and second surfaces. The first electrode comprises first and second material layers 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 having a plurality of defects, the defects being configured to mitigate dissolution of the first catalyst material through the first material layer.

[0004] According to another embodiment, a fuel cell membrane electrode assembly is disclosed. The fuel cell membrane electrode assembly includes a polymer electrolyte membrane (PEM) and first and second electrodes. The PEM is positioned between the first and second electrodes. The first electrode includes a first catalyst material layer comprising a first catalyst material and having first and second surfaces. The first electrode includes first and second graphene-based material layers 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 of defects is greater than the second number of defects.

[0005] According to yet another embodiment, a fuel cell membrane electrode assembly is disclosed. The fuel cell membrane electrode assembly includes a polymer electrolyte membrane (PEM) and first and second electrodes, the first and second electrodes comprising first and second host materials. The PEM is positioned between the first and second electrodes. The first host material comprises a first number of catalyst units dispersed therein. Each catalyst unit comprises a catalyst material layer comprising a catalyst material and having first and second surfaces, and first and second material layers adjacent to the first and second surfaces of the catalyst material layer, respectively. The first material layer of each catalyst unit comprises a graphene-based material layer having a plurality of defects, the defects being configured to mitigate dissolution of the catalyst material through the graphene-based material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 A schematic side view of a fuel cell is depicted.

[0007] Figure 2 Depicted are schematic side views of electrodes configured for use as cathodes and / or anodes of fuel cells.

[0008] Figure 3 Depicted are schematic side views of electrodes configured for use as cathodes and / or anodes of fuel cells.

[0009] Figure 4 Depicted is a schematic top view of a catalyst unit configured for use in the cathode and / or anode of a fuel cell.

[0010] Figure 5 Depicted is a schematic top perspective view of a catalyst unit configured for use in the cathode and / or anode of a fuel cell.

[0011] Figure 6 Depicted is a schematic side view of a membrane electrode assembly configured for use in a fuel cell.

[0012] Figure 7 Depicted is a schematic side view of a membrane electrode assembly configured for use in a fuel cell. DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely examples and that other embodiments may take various alternative forms. The drawings are not necessarily to scale; some features may be enlarged or minimized to show details of components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to utilize the embodiments in various ways. As understood by those of ordinary skill in the art, the various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to arrive at embodiments that are not explicitly illustrated or described. The combination of illustrated features provides representative embodiments of typical applications. However, applications or implementations may require various combinations and modifications of features consistent with the teachings of the present disclosure.

[0014] Except in the examples or where otherwise expressly indicated, all numerical quantities in this specification indicating amounts of materials or reaction conditions and / or conditions of use should be understood as being modified by the word "about" to describe the broadest scope of the invention. It is generally preferred to practice within the numerical limits stated. In addition, unless expressly indicated to the contrary, percentages, "parts" and ratio values ​​are by weight; the term "polymer" includes "oligomers," "copolymers," "terpolymers," etc.; a group or class of materials described as suitable or preferred for a given purpose in connection with the present invention means that mixtures of any two or more members of the group or class are also suitable or preferred; the molecular weight provided for any polymer is the number-average molecular weight; descriptions of ingredients in chemical terms refer to the ingredients when added to any combination specified in the specification and do not necessarily exclude chemical interactions between the ingredients of the mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and unless expressly indicated to the contrary, measurements of properties are determined by the same techniques as previously or subsequently mentioned for the same property.

[0015] The present invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may, of course, vary. Furthermore, the terminology used herein is used only to describe embodiments of the present invention and is not intended to be limiting in any way.

[0016] As used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to a component in the singular is intended to include plural components.

[0017] The term "substantially" may be used herein to describe the disclosed or claimed embodiments. The term "substantially" may modify a numerical value or relative characteristic disclosed or claimed in the present disclosure. In such cases, "substantially" may mean that the numerical value or relative characteristic it modifies is within ± 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of that numerical value or relative characteristic.

[0018] Due to rising CO2 emissions and the transportation industry's current high reliance on non-renewable fossil fuels as an energy source, there is a growing demand for the development and commercialization of transportation technologies that utilize clean and sustainable energy. One promising technology is the fuel cell. Fuel cells use oxygen from the air and compressed hydrogen as fuel sources, while emitting only water and heat. Widespread adoption of fuel cells will reduce CO2 emissions. However, widespread adoption requires further technological development. One area of ​​further technological development is improving the durability of catalyst materials used in fuel cells.

[0019] The catalyst material is contained in the catalyst layer of the anode and cathode of the fuel cell. Platinum catalyst is often used as the catalyst material of the anode and / or cathode. 2+ Ions migrate from the catalyst layer to other components in the fuel cell, such as the polymer electrolyte membrane (PEM). One catalyst degradation pathway in a fuel cell involves Pt dissolution at high operating potentials (e.g., greater than approximately 0.6, 0.7, and 0.8 volts vs. standard hydrogen electrode (SHE)). In another catalyst degradation pathway, the fuel cell reaches potentials even higher than 0.8 volts (e.g., up to approximately 2 volts). This may occur due to unstable operation, carbon corrosion, and / or gas starvation during startup and shutdown, where degradation of the catalyst and other fuel cell components may be accelerated. A significant decrease in oxygen reduction (ORR) activity may occur when the electrochemically active surface area (ECSA) of the fuel cell catalyst gradually decreases. In addition, dissolved catalyst metal ions may migrate toward other fuel cell components, such as the polymer electrolyte membrane (PEM), which may accelerate PEM degradation.

[0020] Solutions are needed to reduce dissolution and slow migration while maintaining the beneficial catalytic activity of platinum catalysts. Aspects of the present disclosure relate to the use of defective graphene-based materials as part of an electrode to improve the durability of the catalyst material, such as reducing dissolution and slowing migration. Aspects of the present disclosure use hybrid graphene-catalyst systems to inhibit metal dissolution of the catalyst in a PEM fuel cell environment through controlled atomic and molecular interfaces. The use of defective graphene-based materials maintains electrochemical surface active area (ESCA) and / or mitigates PEM degradation, thereby extending the life of the fuel cell stack at a given catalyst material loading.

[0021] Figure 1 A schematic side view of a fuel cell 10 is depicted. Fuel cells 10 can be stacked to create a fuel cell stack. Fuel cell 10 includes a polymer electrolyte membrane (PEM) 12, an anode 14, a cathode 16, and first and second gas diffusion layers (GDLs) 18 and 20. PEM 12 is positioned between anode 14 and cathode 16. Anode 14 is positioned between first GDL 18 and PEM 12, and cathode 16 is positioned between second GDL 20 and PEM 12. PEM 12, anode 14, cathode 16, and first and second GDLs 18 and 20 form a membrane electrode assembly (MEA) 22. First and second sides 24 and 26 of MEA 22 are defined by flow fields 28 and 30, respectively. Flow field 28 supplies H2 to MEA 22, as indicated by arrow 32. Flow field 30 supplies O2 to MEA 22, as indicated by arrow 34. Catalyst material, such as platinum, is used in anode 14 and cathode 16. Catalyst material is typically the most expensive component of MEA 22.

[0022] Figure 2 Depicted is a schematic side view of an electrode 50 configured for use as the anode 14 and / or cathode 16 of the fuel cell 10. The electrode 50 includes first and second graphene-based material layers 52 and 54 and a catalyst material layer 56. The catalyst material layer 56 is positioned between the first and second graphene-based material layers 52 and 54. At least one surface of the catalyst material layer 56 may be partially or completely coated with the graphene-based material.

[0023] The graphene-based materials of layers 52 and 54 may include graphene, graphene oxide (GO), reduced graphene oxide (rGO) and combinations thereof. The graphene-based materials may also include other materials that capture dissolved metal ions during the operation of the fuel cell 10. The graphene-based materials may contain oxygen functional groups, such as epoxy (-O-), carbonyl (=O), carboxyl (-COOH) and / or hydroxyl (-OH) to further optimize the transport and diffusion of Pt, H2, O2 and H2O. In one embodiment, different graphene and graphene oxide can be obtained by the Hummer method. The graphene-based materials may include a significant amount of materials that can capture dissolved metal ions. A significant amount can be any of the following values ​​or within the range of any two of the following values: 70, 75, 80, 85, 90, 95 and 100%. The remaining amount may partially include amorphous and / or crystalline graphene materials. In one embodiment, the first and / or second graphene-based material layers 52 and 54 may contain more crystalline graphene material than amorphous graphene material. 2 type carbon, which is less corrosive during the start-up / shutdown process of the fuel cell 10 than amorphous carbon, which is mainly sp 3The graphene-based material can be further functionalized by cation or anion doping. In another embodiment, the graphene-based material can include a carbide material, a nitride material, or a fluoride material configured to optimize the selective diffusion of Pt, H2, O2, and H2O. The graphene-based material coating can also provide resistance to HF and / or SO3 - physical barriers to further prevent PEMFC degradation.

[0024] In another embodiment, the graphene-based material may be formed from sp 2 Amorphous carbon, such as sp 3 Types may also exist. 2 Type carbon atoms and sp 3 The ratio of carbon atoms of different types may be based on the operating conditions of the fuel cell.

[0025] The graphene-based material can be a graphene sheet applied in a planar orientation. The graphene-based sheet can include a single graphene monolayer. In other embodiments, the number of graphene monolayers in the graphene-based sheet can be any of the following values ​​or a range between any two of the following values: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15. The graphene-based material can be configured to mitigate degradation of the catalyst material in the electrode 50. Mitigation of Pt degradation can provide one or more of the following benefits: (1) reduced ECSA loss, and (2) prevention of Pt degradation. 2+ The ions migrate to the interface between the PEM 12 and the electrode 50 or into the PEM 12, thereby inhibiting PEM degradation.

[0026] The addition of graphene-based materials can enhance 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 can be 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 bound, for example, at a short distance from the catalyst material layer 56. The short distance can be any of the following values ​​or within a range of any two of the following values: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, and 10 nm. When Pt is ionized into Pt 2+ (水溶液) When the Pt species are dissolved into the solution, the graphene-based material coating can capture the dissolved Pt species.

[0027] Various methods can be used to coat the graphene-based material onto one or both surfaces of the catalyst material layer 56. The graphene-based material can be deposited onto the catalyst material layer 56 in the form of a thin film or via a dispersion (e.g., using graphene ink) during the synthesis of the electrode 50 or after the electrode 50 is fabricated. Graphene can be in the form of sheets, flakes, powders, and / or combinations thereof. The coated electrode can be fabricated using solid-state, solution-based, or deposition techniques, followed by a secondary heat treatment in the presence of an oxidizing or reducing agent (e.g., air, O2, N2, Ar, H2, or a mixture thereof). A film of the graphene-based material can be grown on a metal foil using chemical vapor deposition (CVD), followed by cleaning with an organic solvent and electropolishing with an acid under an applied voltage. Thereafter, the material can be rinsed and heat-treated in a furnace in a reducing environment (e.g., using an Ar:H2 gas mixture) to grow the graphene. After CVD growth, the sample can be combined with a polymer (e.g., poly(methyl methacrylate) (PMMA)) and then etched or rinsed. The composite membrane may be transferred to the catalyst material layer 56 .

[0028] In another embodiment, a monolayer or several layers of graphene film can be grown on a thick metal substrate except for metal foil. The graphene film can have mechanical support provided by adding a polymer film layer on the graphene using spin coating, dip coating or other coating methods. The graphene / polymer film stack can be removed from the metal substrate using an electrochemical bath wet method and can be transferred to a catalyst substrate. Once the graphene / polymer film stack is applied to the catalyst substrate, the polymer support can be removed by wet chemistry or dry plasma etching. A cleaning process may be required before graphene is deposited on the metal substrate. Additional cleaning processes may be required after removing the polymer to obtain high-quality graphene-metal catalyst composites. For the transfer process, the smoothness and crystallinity of the starting metal substrate will determine the expected graphene defect level. After the transfer process is completed, the roughness of the catalyst metal (e.g., nanoparticles) below will be the main influencing factor to the final graphene defect level.

[0029] In one embodiment, the shape of the graphene-based material follows the contours of the surface of the catalyst material layer, such as the roughness of the platinum nanoparticles. The amount of defects in the graphene-based material, the shape of the wrinkles 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 may result in 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 shape of the interface, the wrinkles, and / or the number of graphene defects, several activation cycles may be performed to enable appropriate diffusion and relatively rapid transport of H2, O2, and H2O to achieve the desired oxygen reduction reaction (ORR) activity.

[0030] Various methods can be used to coat other two-dimensional layered structured materials onto the surface of the catalyst material layer 56. Non-limiting examples of other two-dimensional layered structured materials include graphene, borophene, germanene, organosilicon, Si2BN, stanine, phosphorene, bismuthene, molybdenite, and transition metal dichalcogenides (TMDCs) (e.g., MOS2, WSe2, HfS2, etc.). ） 、General formula M n+1 X n T x Layered transition metal carbides and carbonitrides (MXenes), where M represents a transition metal (e.g., Ti, Mo, W, Nb, Zr, Hf, V, Cr, Ta, and Sc), X represents carbon and / or nitrogen, and T x Represents surface terminations (e.g., =O, -OH, or -F), and combinations thereof. Other two-dimensional layered structured materials can be used to replace all or part of the graphene-based materials in the electrode catalyst layer coating.

[0031] The catalyst material of layer 56 can be pure Pt, a Pt-M alloy (where M is another metal from the periodic table), other platinum group member (PGM) metals (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 specifications and / or sizes. Figure 2 The thickness (t) of the metal catalyst layer depicted in FIG5 can be any of the following values ​​or 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, thereby providing an increased accessible electrochemically active surface area (ECSA). The increased ECSA results in higher catalytic activity per unit mass of catalyst material used.

[0032] The first graphene-based material layer 52 includes defects 58 and 60. The second graphene-based material layer 54 includes defects 62, 64, and 66. The defects 58, 60, 62, 64, and / or 66 may be configured to (1) capture metal ions (e.g., Pt 2+ (水溶液) ions), and / or (2) provide diffusion paths (e.g., channels) for fuel cell reactants (e.g., H2, O2, and / or H2O). Defects 58, 60, 62, 64, and / or 66 can significantly enhance the weak binding energy in pristine graphene.

[0033] Non-limiting examples of defects include monovacancies (MV), divacancies (DV), trivacancies (TV), tetravacancies (QV), graphene holes, Stone-Wales (SW) defects and / or common oxygen functional groups such as hydroxyl (-OH), epoxy (-O-), carbonyl (=O) and / or carboxyl (-COOH). Non-limiting examples of methods for making these defects include synthesis methods, annealing methods and ion bombardment. In another embodiment, the graphene defect can be a hole. The removal of more carbon atoms (e.g., making larger vacancies) can be achieved to rearrange the defective graphene structure.

[0034] The number of defects per unit volume of the first or second graphene-based material layer may be any of the following values ​​or within a range of 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 may vary depending on the life requirements and / or operating conditions of the fuel cell 10. As a non-limiting example, if the fuel cell 10 is required to operate at a voltage above approximately 0.6, 0.7, or 0.8 V, the number of defects per unit volume may be any of the following values ​​or within a range of any two of the following values: 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13%. RHE When operating at a relatively high potential (or any other non-steady-state condition that causes a sudden increase in the potential of the fuel cell), more defects may be necessary to capture metal ions dissolved from the catalyst material layer 56 during the degradation process. Figure 1 , the first and / or second graphene-based material layers 52 and 54 may have different selectivities between metal ions, H2, O2, and H2O. In one embodiment, the second graphene-based material layer 54 may be a support material for the catalyst material layer 56, and the first graphene-based material layer 52 may be configured to capture dissolved metal ions and / or provide diffusion paths (e.g., channels) for fuel cell reactants. In this embodiment, fewer defects may be desired in the second graphene-based material layer 54 than in the first graphene-based material layer 52.

[0035] Figure 3 A schematic side view of an electrode 100 configured to function as an anode 14 and / or cathode 16 of a fuel cell 10 is depicted. The electrode 100 includes first and second graphene-based material layers 102 and 104 and a catalyst material layer 106. The catalyst material layer 106 is located between the first and second graphene-based material layers 102 and 104. The first graphene-based material layer 102 includes defects 108 and 110. The second graphene-based material layer 104 includes defects 112, 114, and 116. The defects 108, 110, 112, 114, and / or 116 may be configured to (1) capture metal ions (e.g., Pt) dissolved from the catalyst material layer 56. 2+ (水溶液) ions), and / or (2) providing diffusion paths (e.g., channels) for fuel cell reactants (e.g., H2, O2, and / or H2O). Figure 3The thickness (t) of the metal catalyst layer depicted in can be any of the following values ​​or a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 20 nm.

[0036] The catalyst material layer 106 has a reduced catalyst loading compared to the catalyst material layer 56, thereby introducing void spaces within the catalyst material layer 106, such as Figure 3 In one embodiment, the void spaces 118, 120, and 122 are shown in FIG. In one embodiment, the void spaces may be formed by surface tension between the metal catalyst nanoparticles. In another embodiment, the graphene-based material may be homogenized in a homogenizer at a relatively high RPM. Figure 3 The volume of each void space can be independently selected from any of the following values ​​or within the range of any two of the following values: 1 nm 3 , 50 nm 3 , 100 nm 3 , 200 nm 3 , 500 nm 3 , 750 nm 3 and 1 µm 3 The percentage of void space to volume occupied by the catalyst material can be any of the following values ​​or a range between any two of the following values: 25%, 30%, 40%, 50%, and 60%.

[0037] In one or more embodiments, one or more void spaces provide diffusion paths (e.g., channels) for fuel cell reactants (e.g., H2, O2, and / or H2O). The void spaces may allow for redeposition of metal catalysts. The void spaces may also shape the interface between the catalyst material layer 106 and the first and second graphene-based material layers 102 and 104 to have reduced interfacial resistance. Due to the void spaces, the first and second graphene-based material layers 102 and 104 may wrinkle after a certain number of fuel cell operations (e.g., the shape of the graphene-based material layers changes in the areas above or below the void spaces). The number of operations may be any of the following values ​​or a range between any two of the following values: 2000, 2500, 3000, 3500, and 4000. In one embodiment, the one or more void spaces may be filled with one or more conductive agents other than catalyst materials. Other conductive agents may include amorphous carbon black and / or conductive polymers.

[0038] The electrode 100 also includes first and second openings 124 and 126. The openings 124 and 126 can be configured to provide diffusion paths (e.g., channels) for fuel cell reactants (e.g., H2, O2, and / or H2O). While operating the fuel cell 10 at a relatively high potential, some 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. However, in general, as depicted by the dissolved metal ions 119, due to the attractive force between the dissolved metal ions and the first and second graphene-based material layers 102 and 104, the metal ions (e.g., Pt 2+ ) diffuses much more slowly.

[0039] Electrodes 50 and / or 100 can be used as thin film electrodes, wherein the one or more graphene-based materials are transferred or deposited directly onto a Pt catalyst thin film. Non-limiting examples of applications for this type of thin film configuration include mobile applications, low power electronic applications, military and / or aerospace applications.

[0040] Figure 4 A schematic top view of a catalyst unit 70 configured for use in the anode 14 and / or cathode 16 of the fuel cell 10 is depicted. The catalyst unit 70 includes first and second graphene-based material layers 72 and 74 and a catalyst material layer 76. The catalyst material layer 76 is located between the first and second graphene-based material layers 72 and 74. The first graphene-based material layer 72 includes regularly repeating graphene-based material, such as regions 78 and 80. Shaded regions, such as regions 82 and 84, depict the formation of graphene-based defects based on oxygen-functional groups (e.g., -O-, =O, -COOH, and -OH). Regions that do not include regularly repeating graphene-based material or graphene-based defects based on oxygen-functional groups are void spaces, such as void spaces 86 and 88. The void spaces can be vacancies and / or graphene holes.

[0041] like Figure 4 As shown in FIG, catalyst unit 70 has a width 90, a length 92, and a thickness 94. Width 90, length 92, and thickness 94 can each be independently varied based on the specifications of the PEMFC (e.g., stack size, power requirements, operating schedule, etc.). Width 90 can be any of the following values ​​or a range between any two of the following values: 10 nm, 100 nm, 1 μm, 10 μm, and 100 μm. Length 92 can be any of the following values ​​or a range between any two of the following values: 10 nm, 100 nm, 1 μm, 10 μm, and 100 μm. Thickness 94 can be any of the following values ​​or a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 20 nm.

[0042] Figure 5A schematic top perspective view of a catalyst unit 150 configured for use in the anode 14 and / or cathode 16 of a fuel cell 10 is depicted. Catalyst unit 150 includes a graphene-based material layer 152 and a catalyst support material layer 154. Catalyst material layer 156 is located between graphene-based material layer 152 and catalyst support material layer 154. Graphene-based material layer 152 includes regularly repeating graphene-based material, such as regions 158 and 160. Shaded regions, such as regions 162 and 164, depict the formation of graphene-based defects based on oxygen-functionalized groups (e.g., -O-, =O, -COOH, and -OH). Regions that do not include regularly repeating graphene-based material or graphene-based defects based on oxygen-functionalized groups are void spaces, such as void spaces 166 and 168. Void spaces can be vacancies and / or graphene holes. The specified percentage may be any of the following values ​​or a range between any two of the following values: 5%, 10%, 15%, 20%, and 25%.

[0043] The catalyst support material layer 154 may be made of amorphous carbon material (eg sp 3 The catalyst support material layer 154 may be formed from a plurality of metal oxides (e.g., MOx, where M = Ti, Sn, W, Mo, Ge, Ta, etc.), or a combination thereof. The catalyst support material layer 154 may be closer to the PEM 12 than the graphene-based material layer 152. In another embodiment, the catalyst support material layer 154 may be sandwiched between the first and second graphene-based material layers, with the outer surface of the graphene-based material in contact with the catalyst support material layer 154.

[0044] like Figure 5 As shown in , the catalyst material layer includes void spaces, such as void spaces 170 and 172. In one or more embodiments, the one or more void spaces provide diffusion paths (e.g., channels) for fuel cell reactants (e.g., H2, O2, and / or H2O). The void spaces can also shape the interface between the catalyst material layer 106 and the first and second graphene-based material layers 152 and 154 to have reduced interfacial resistance. Due to the void spaces, the first and second graphene-based material layers 152 and 154 may wrinkle after a certain number of fuel cell operations (e.g., the shape of the graphene-based material layer changes in the area above or below the void spaces). The number of operations can be any of the following values ​​or a range between any two of the following values: 2000, 2500, 3000, 3500, and 4000. In one embodiment, the one or more void spaces can be filled with one or more conductive agents other than catalyst materials. Other conductive agents can include amorphous carbon black and / or conductive polymers.

[0045] like Figure 5As shown in FIG, catalyst unit 150 has a width 174, a length 176, and a thickness (not shown). Width 174, length 176, and thickness can each be independently varied based on the specifications of the PEMFC (e.g., stack size, power requirements, operating schedule, etc.). Width 174 can be any of the following values ​​or a range between any two of the following values: 10 nm, 100 nm, 1 μm, 10 μm, and 100 μm. Length 176 can be any of the following values ​​or a range between any two of the following values: 10 nm, 100 nm, 1 μm, 10 μm, and 100 μm. Thickness can be any of the following values ​​or a range between any two of the following values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 20 nm.

[0046] The electrodes 50 and / or 100 and the catalyst units 70 and 150 can be manufactured using chemical synthesis methods and subsequently processed into the desired shape and size. Non-limiting examples of suitable chemical synthesis methods include focused ion beam scanning electrode microscopy (FIB-SEM), electron beam lithography, laser writing, and photolithography. In other embodiments, a solution-based or deposition method can be used to form the catalyst configuration until the desired size and shape are obtained. With respect to subsequent forming and sizing steps, the catalyst configuration can be formed into squares, nanowires, or strips. The side length of the square can be any of the following values ​​or within the range of any two of the following values: 10 nm, 100 nm, 1 μm, 10 μm, and 100 μm. The width of the strip can be any of the following values ​​or within the range of any two of the following values: 1, 2, 5, 10, or 15 μm.

[0047] Figure 6 A schematic side view of an MEA 200 configured for use in a fuel cell, such as fuel cell 10, is depicted. MEA 200 includes a cathode 202, a PEM 204, and an anode 206. PEM 204 is positioned between cathode 202 and anode 206. PEM 204 is formed from an ionomer that forms an ionomer network 205. PEM 204 is configured to conduct protons while providing a barrier between an electronic insulator and fuel cell reactants (e.g., oxygen and hydrogen). The ionomer can be based on perfluorosulfonic acid. A non-limiting example is Nafion, available from DuPont Company.

[0048] Cathode 202 includes cathode body material 208. Catalyst units 70 and / or 150 may be dispersed within cathode body material 208. Figure 6 As shown in FIG, cathode body material 208 is an ionomer that forms an ionomer network 209 between catalyst units 70 and / or 150. Anode 206 includes anode body material 210. Catalyst units 70 and / or 150 may be dispersed within anode body material 210. Figure 6As shown in , the anode bulk material 210 is an ionomer that forms an ionomer network 211 between the catalyst units 70 and / or 150.

[0049] Anode and / or cathode 202 and 206 may be formed by mixing catalyst units 70 and / or 150 with one or more ionomers. Catalyst units 70 and / or 150 may be mixed using a solution-type medium, such as a slurry, in a homogenizer.

[0050] The loading of catalyst units 70 and / or 150 in the cathode 202 and anode 206 can be independently selected based 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 that in the anode 206 to overcome ORR kinetics. The ratio of cathode loading to anode loading can be any of the following values ​​or a range between any two of the following values: 2:1, 7:4, 3:2, 5:4 and 1:1.

[0051] As described above, electrodes 50 and 100 and catalyst units 70 and 150 each include at least one graphene-based layer having defects. The size, type, and density of the defects can be controlled depending on the fuel cell operating conditions (e.g., operating voltage and lifetime). In one embodiment suitable for use under high power conditions, more graphene-based defects may be present than under low power conditions to capture more catalyst material and / or to increase the number of defects at high potentials (e.g., above approximately 0.6, 0.7, and 0.8 V). RHE ) is the metal ions dissolved under the conditions of

[0052] Figure 7 A schematic cross-sectional view of an MEA 250 configured for use in a fuel cell, such as the fuel cell 10, is depicted. The MEA 250 includes a cathode 252, a PEM 254, and an anode 256. The cathode 252 includes a catalyst material layer 258 disposed between 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 graphene-based material layer 52 or 108 that is configured to (1) capture metal ions (e.g., Pt 254) dissolved from the catalyst material layer 56. 2+ (水溶液) ions), and / or (2) providing a diffusion path (e.g., a 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., sp 3 type carbon), one or more metal oxides (such as MOx, where M = Ti, Sn, W, Mo, Ge, Ta, etc.) or a combination thereof.

[0053] The anode 256 includes a catalyst material layer 264 disposed between 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 graphene-based material layer 52 or 108, which is configured to (1) capture metal ions (e.g., Pt) dissolved from the catalyst material layer 56. 2+ (水溶液) ions), and / or (2) providing a diffusion path (e.g., a channel) for fuel cell reactants (e.g., H2, O2, and / or H2O), and the second material layer 268 is made of a carrier material, such as an amorphous carbon material (e.g., sp 3 type carbon), one or more metal oxides (such as MOx, where M = Ti, Sn, W, Mo, Ge, Ta, etc.) or a combination thereof.

[0054] The following applications are related to this application: U.S. patent application serial number 16 / 544,511, filed on August 19, 2019, the entirety of which is incorporated herein by reference.

[0055] Although exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive, and it is understood that various changes can be made without departing from the spirit and scope of the present disclosure. As described above, the features of the various embodiments can be combined to form further embodiments of the present invention that are not explicitly described or illustrated. Although various embodiments may have been described as providing advantages or taking precedence over other embodiments or prior art embodiments in terms of one or more desired features, those of ordinary skill in the art will recognize that one or more elements or features can be sacrificed to achieve the desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, usability, weight, manufacturability, ease of assembly, etc. Therefore, if any embodiment is described as not as desirable as other embodiments or prior art embodiments in terms of one or more features, these embodiments are not outside the scope of the present disclosure and may be desirable for specific applications.

Claims

1. A fuel cell membrane electrode assembly comprising: polymer electrolyte membrane; and first and second electrodes, the polymer electrolyte membrane being located between the first and second electrodes, The first electrode includes a first catalyst material layer comprising a first catalyst material and having first and second surfaces, the first electrode including first and second material layers adjacent to the first and second surfaces of the first catalyst material layer, the first material layer facing away from the polymer electrolyte membrane and the second material layer facing the polymer electrolyte membrane, the first material layer being comprised of a first graphene-based material layer having a first number of defects, the defects being configured to mitigate dissolution of the first catalyst material through the first material layer, The first catalyst material layer includes a plurality of void spaces configured to change the shape of the first material layer composed of a graphene-based material layer through multiple operating cycles of a fuel cell containing the fuel cell membrane electrode assembly, wherein the volume of each void space is within 1 nm 3 to 1μm 3 and wherein the percentage of the volume occupied by the void space to the first catalyst material is in the range of 25% to 60%.

2. The fuel cell membrane electrode assembly of claim 1, wherein the number of defects is configured to trap the first catalyst material within the number of defects.

3. The fuel cell membrane electrode assembly of claim 1, wherein the second material layer is composed of a second graphene-based material layer having a second number of defects, the defects configured to mitigate dissolution of the first catalyst material through the second material layer.

4. The fuel cell membrane electrode assembly of claim 1, wherein the first and / or second material layer is applied as a first and / or second film, respectively, to the first and / or second surface of the first catalyst layer, respectively.

5. The fuel cell membrane electrode assembly of claim 1, wherein the first catalyst material comprises a platinum group metal, an alloy of a platinum group metal and another metal from the periodic table, or a combination thereof.

6. The fuel cell membrane electrode assembly of claim 5, wherein the platinum group metal is pure Pt. 7 . The fuel cell membrane electrode assembly of claim 1 , wherein the graphene-based material layer comprises graphene, graphene oxide, reduced graphene oxide, or a combination thereof.

8. The fuel cell membrane electrode assembly of claim 1, wherein the second material layer is a catalyst support layer configured to support the first catalyst material layer.

9. A fuel cell membrane electrode assembly comprising: polymer electrolyte membrane; and first and second electrodes, the polymer electrolyte membrane being located between the first and second electrodes, The first electrode includes a first catalyst material layer comprising a first catalyst material and having first and second surfaces, the first electrode includes first and second graphene-based material layers adjacent to the first and second surfaces of the first catalyst material, respectively, the first graphene-based material layer facing away from the polymer electrolyte membrane and the second graphene-based material layer facing the polymer electrolyte membrane, the first graphene-based material layer having a first number of defects and the second graphene-based material layer having a second number of defects, and the first number is greater than the second number, The first catalyst material layer includes a plurality of void spaces configured to change the shape of the first graphene-based material layer over multiple operating cycles of a fuel cell containing the fuel cell membrane electrode assembly, wherein the volume of each void space is within 1 nm 3 to 1μm 3 and wherein the percentage of the volume occupied by the void space to the first catalyst material is in the range of 25% to 60%.

10. The fuel cell membrane electrode assembly of claim 9, wherein the second number of defects is configured to trap the first catalyst material within the first number of defects.

11. The fuel cell membrane electrode assembly of claim 9, wherein the first catalyst material comprises a platinum group metal, an alloy of a platinum group metal and another metal from the periodic table, or a combination thereof.

12. The fuel cell membrane electrode assembly of claim 11, wherein the platinum group metal is pure Pt.

13. The fuel cell membrane electrode assembly of claim 9, wherein the first number of defects comprises graphene-based vacancies and / or graphene-based defects based on one or more oxygen-functionalized groups.

14. The fuel cell membrane electrode assembly of claim 13, wherein the graphene-based vacancies comprise tetravacancy defects.

15. The fuel cell membrane electrode assembly of claim 9, wherein the first number of defects form a first number of channels configured to diffuse one or more fuel cell reactants.

16. A fuel cell membrane electrode assembly comprising: polymer electrolyte membrane; and first and second electrodes comprising first and second host materials, the polymer electrolyte membrane being positioned between the first and second electrodes, the first host material comprising a first number of catalyst units dispersed therein, each catalyst unit comprising a catalyst material layer comprising catalyst material and having first and second surfaces, and first and second material layers 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 a plurality of defects, the defects being configured to mitigate dissolution of the catalyst material through the graphene-based material layer, The catalyst material layer includes a plurality of void spaces configured to change the shape of the first material layer composed of the graphene-based material layer through multiple operating cycles of the fuel cell containing the fuel cell membrane electrode assembly, wherein the volume of each void space is within 1 nm 3 to 1μm 3 and wherein the percentage of the volume occupied by the void space to the first catalyst material is in the range of 25% to 60%.

17. The fuel cell membrane electrode assembly of claim 16, wherein the second host material comprises a second number of catalyst units dispersed therein.

18. The fuel cell membrane electrode assembly of claim 17, wherein the first electrode is a cathode and the second electrode is an anode, and the first number is greater than the second number.

19. The fuel cell membrane electrode assembly of claim 18, wherein a ratio of the first quantity to the second quantity is in the range of 2:1 to 5:

4.

20. The fuel cell membrane electrode assembly of claim 16, wherein the first and second host materials are ionomers.

21. The fuel cell membrane electrode assembly of claim 20, wherein the second material layer of each catalyst unit is a catalyst support layer.

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