Fuel cell electrode catalyst layer coating

Abstract

The present invention relates to fuel cell electrode catalyst layer coatings. The fuel cell includes first and second electrode catalyst layers and a polymer electrolyte membrane (PEM) located therebetween, and a graphene-based material coated on the first and / or second surfaces of the first and / or second electrode catalyst layers. The graphene-based material has a plurality of defects, including a plurality of quadrivacancy (QV) defects formed by vacancies of at least four adjacent carbon atoms in the graphene-based material. The plurality of QV defects are configured to mitigate dissolution of the first and / or second catalyst material through the first and / or second surfaces of the first and / or second electrode catalyst layers.

Description

Technical Field

[0001] The present disclosure relates to defective two-dimensional materials (eg, graphene-based materials) coated onto the surface of a fuel cell electrode catalyst layer that are 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 comprises a membrane electrode assembly (MEA) and two flow field plates. A single fuel cell typically outputs 0.5 to 1.0 V, which is generally too low for vehicle and transportation applications. 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 a fuel cell stack is the catalyst material, such as a 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 is disclosed. The fuel cell includes a polymer electrolyte membrane (PEM) and first and second electrode catalyst layers containing first and second catalyst materials. The PEM is located between the first and second electrode catalyst layers. The first electrode catalyst layer has a first surface facing away from the PEM and a second surface facing the PEM. The second electrode catalyst layer has a first surface facing away from the PEM and a second surface facing the PEM. The fuel cell further includes a graphene-based material coated on the first and / or second surface of the first and / or second electrode catalyst layer. The graphene-based material has a plurality of defects. Each defect is formed by a vacancy of at least four adjacent carbon atoms in the graphene-based material. The plurality of defects are configured to reduce the dissolution of the first and / or second catalyst material through the first and / or second surface of the first and / or second electrode catalyst layer.

[0004] According to another embodiment, a fuel cell is disclosed. The fuel cell includes a polymer electrolyte membrane (PEM) and first and second electrode catalyst layers containing first and second catalyst materials. The PEM is located between the first and second electrode catalyst layers. The first electrode catalyst layer has a first surface facing away from the PEM and a second surface facing the PEM. The second electrode catalyst layer has a first surface facing away from the PEM and a second surface facing the PEM. The fuel cell further includes a two-dimensional layered material coated on the first and / or second surface of the first and / or second electrode catalyst layer. The two-dimensional layered material has a plurality of defects. Each defect is formed by a vacancy of at least four adjacent carbon atoms in the two-dimensional layered material. The plurality of defects are configured to reduce the dissolution of the first and / or second catalyst material through the first and / or second surface of the first and / or second electrode catalyst layer.

[0005] According to another embodiment, a fuel cell is disclosed. The fuel cell includes a polymer electrolyte membrane (PEM) and first and second electrode catalyst layers containing first and second catalyst materials. The PEM is located between the first and second electrode catalyst layers. The first electrode catalyst layer has a first surface facing away from the PEM and a second surface facing the PEM. The second electrode catalyst layer has a first surface facing away from the PEM and a second surface facing the PEM. The fuel cell includes a graphene-based material coated on the first and / or second surfaces of the first and / or second electrode catalyst layers. The graphene-based material has a plurality of defects. The plurality of defects include a plurality of quadrivacancy (QV) defects formed by vacancies of four adjacent carbon atoms in the graphene-based material. The plurality of defects also include a plurality of smaller defects formed by vacancies of three or fewer adjacent carbon atoms. The plurality of defects also include a plurality of larger defects formed by vacancies of five or more adjacent carbon atoms. The plurality of QV defects are configured to reduce the dissolution of the first and / or second catalyst material through the first and / or second surfaces of the first and / or second electrode catalyst layers. The plurality of small defects are configured to transport H2 through the graphene-based material. The plurality of larger defects are configured to transport H2, O2, and H2O through the graphene-based material. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0007] Figure 2 is a schematic diagram of a computing platform that can be used to perform DFT algorithms, calculations, and / or methods of one or more embodiments.

[0008] Figure 3 a to 3d depict schematic views of defective graphene sheets including monovacancies (MV), divacancies (DV), trivacancies (TV), and tetravacancies (QV), respectively.

[0009] Figure 4 a to 4h depict schematic views of the atomic structures of different adsorbate species (e.g., Pt, H2, O2, and H2O) interacting with MVs in graphene sheets.

[0010] Figure 5 a to 5d depict schematic views of the atomic structures of different adsorbate species (e.g., Pt, H2, O2, and H2O) interacting with DV in a graphene sheet.

[0011] Figure 6 a to 6d depict schematic views of the atomic structures of different adsorbate species (e.g., Pt, H2, O2, and H2O) interacting with TV in a graphene sheet.

[0012] Figure 7 a to 7d depict schematic views of the atomic structures of different adsorbate species (e.g., Pt, H2, O2, and H2O) interacting with QVs in a graphene sheet.

[0013] Figure 8A Graph showing the relative energy change as Pt moves away from the QV in the z direction.

[0014] Figure 8B Schematic top view showing the Pt atomic structure at different distances from the graphene sheet including the QV.

[0015] Figure 8C Schematic side view showing the Pt atomic structure at different distances from the graphene sheet including the QV.

[0016] Figure 9 Includes plotting the relative energy (eV) for H2 on a graphene sheet with QV vs. the distance of H2 (in the z direction) from the QV 's curve graph.

[0017] Figure 10A Includes plotting the relative energy (eV) for O2 on a graphene sheet with QV vs. the distance of O2 (in the z direction) from the QV 's curve graph.

[0018] Figure 10B Included is a plot of relative energy (eV) for H2O on a graphene sheet with QV vs. the distance of H2O (in the z direction) from the QV. 's curve graph.

[0019] Figure 11 is a schematic view showing the chemical structure of a graphene sheet with various defects.

[0020] Figure 12is a schematic view of a catalyst layer surface including wrapped islands of defective graphene material. DETAILED DESCRIPTION

[0021] 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 particular 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 accompanying drawings may be combined with the features illustrated in one or more other drawings to derive embodiments that are not explicitly illustrated or described. The combination of illustrated features provides representative embodiments of typical applications. However, specific applications or implementations may require various combinations and modifications of features consistent with the teachings of the present disclosure.

[0022] 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 use 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 the 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.

[0023] 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 specific embodiments of the present invention and is not intended to be limiting in any way.

[0024] As used in the specification and the appended claims, the singular forms "a," "an," "the," and "said" include plural referents unless the context clearly dictates otherwise. For example, reference to a component in the singular is intended to include plural components.

[0025] The term "substantially" may be used herein to describe embodiments disclosed or claimed. The term "substantially" may modify a numerical value or relative characteristic disclosed or claimed in this 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.

[0026] 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.

[0027] 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. The platinum catalyst is subjected to dissolution and Pt 2+ Ions migrate from the catalyst layer to other components in the fuel cell, such as the polymer electrolyte membrane (PEM). A solution is needed to reduce dissolution and slow migration while maintaining the beneficial catalytic activity of the platinum catalyst. Aspects of the present disclosure relate to the use of defective graphene-based materials as part of the catalyst layer to improve the durability of the catalyst material, i.e., reduce dissolution and slow migration. Aspects of the present disclosure use hybrid graphene-catalyst systems to inhibit metal dissolution of the catalyst in a PEM fuel cell environment by controlling the 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.

[0028] Figure 1A schematic diagram of a fuel cell 10 is depicted. Fuel cells 10 can be stacked to produce a fuel cell stack. Fuel cell 10 includes a polymer electrolyte membrane (PEM) 12, an anode catalyst layer (CL) 14, a cathode catalyst layer (CL) 16, and first and second gas diffusion layers (GDLs) 18 and 20. PEM 12 is positioned between anode CL 14 and cathode CL 16. Anode CL 14 is positioned between first GDL 18 and PEM 12, and cathode CL is positioned between second GDL 18 and PEM 12. PEM 12, anode CL 14, cathode CL 16, and first and second GDLs 18 and 20 form a membrane electrode assembly 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 CL 14 and cathode CL 16. The catalyst material is typically the most expensive component of the MEA 22 .

[0029] At the anode CL 14, the catalyst material catalyzes the hydrogen oxidation reaction (HOR) (H2→2H + +2e - ), which establishes electron flow through conduit 36 (e.g., wire). At cathode CL 16, the catalyst material catalyzes the oxygen reduction reaction (ORR) (1 / 2O2 + 2H + +2e - → HO), with electrons supplied from conduit 36. HO (and heat) from the ORR exits the fuel cell 10 via the second flow field 30 as indicated by arrow 38. The loading of catalyst material in the cathode CL 16 is higher than that in the anode CL 14 because the kinetics of ORR are significantly slower than those of HOR. As low as 0.025 mg Pt / cm 2 The loading of the anode CL 14 may result in a kinetic loss of HOR of less than or equal to 20 mV. 0.1, 0.2, 0.3 or 0.4 mg Pt / cm 2 The loading of cathode CL 16 may result in a kinetic loss greater than or equal to 400 mV.

[0030] During operation of the fuel cell 10, the catalyst material at the anode CL 14 and cathode CL 16 may degrade, causing the fuel cell 10 to experience an increase in kinetic overpotential over time. Various phenomena can contribute to the degradation of the catalyst material in the fuel cell. Variations in the catalyst loading in the cathode CL 16 during operation of the fuel cell 10 may result in variations in cathode potential, such as variations to any of the following values or ranges: 0.7, 0.8, 0.9, and 0.95 V. Such variations in cathode potential may contribute to degradation of the catalyst material in the cathode CL 16. Startup and shutdown effects or localized fuel starvation effects may contribute to degradation of the catalyst material in the anode CL 14. Because a significant reduction in catalyst material loading can significantly contribute to achieving the cost targets of the fuel cell 10, identifying systems, structures, and methods for reducing catalyst material degradation will help meet both start-of-life (BOL) and end-of-life (EOL) performance targets.

[0031] The main degradation pathway of Pt related to the two degradation phenomena specified above is the dissolution of Pt to form Pt 2+ (水溶液) ions. This dissolution leads to a loss of active electrode area and a subsequent decrease in ORR activity. In addition, the generated Pt 2+ (水溶液) The ions dissolve and subsequently migrate toward the PEM 12, which may increase the likelihood of hydrogen peroxide generation and potentially accelerate degradation of the PEM 12. Therefore, if the dissolution of Pt from pure Pt or Pt-based catalysts (and the dissolution of any other transition metals in Pt-M alloys) or other catalyst materials disclosed herein can be controlled, it would be beneficial to inhibit the long-term degradation of the fuel cell 10.

[0032] In one embodiment, first principles density functional theory (DFT) algorithms, calculations, and / or methods are used to model the atomic-scale interactions of graphene with fuel cell reactants (H2 and O2) and products (H2O) and catalyst materials (Pt). These algorithms, calculations, and / or methods demonstrate that defective graphene can serve as a selective diffusion barrier for Pt compared to other species present that must diffuse through the fuel cell 10. Thus, as described herein, structures for incorporating defective graphene into the cathode CL 16 and / or anode CL 14 are disclosed to enhance the durability of the MEA 22 and enable a reduction in Pt loading. The use of defective graphene with vacancies can significantly enhance the weak binding energy in pristine graphene. Non-limiting examples of graphene vacancies include monovacancy (MV), divacancy (DV), and Stone-Wales (SW) defects. Non-limiting examples of methods for creating these defects include synthesis methods, annealing methods, and ion bombardment. Furthermore, the removal of more carbon atoms (eg, creating larger vacancies) can be achieved to rearrange the defective graphene structure.

[0033] The DFT algorithms, calculations and / or methods of one or more embodiments utilize a computer platform, such as Figure 2 5. The computing platform 50 shown in FIG. 5 is executed. The computing platform 50 may include a processor 52, a memory 54, and a non-volatile memory 56. The processor 52 may include one or more devices selected from a high-performance computing (HPC) system, including a high-performance core, a microprocessor, a microcontroller, a digital signal processor, a microcomputer, a central processing unit, a field programmable gate array, a programmable logic device, a state machine, a logic circuit, an analog circuit, a digital circuit, or any other device that manipulates signals (analog or digital) based on computer-executable instructions located in the memory 54. The memory 54 may include a single storage device or multiple storage devices, including but not limited to random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache memory, or any other device capable of storing information. The non-volatile memory 56 may include one or more permanent data storage devices, such as a hard drive, an optical drive, a tape drive, a non-volatile solid-state device, cloud storage, or any other device capable of permanently storing information.

[0034] The processor 52 can be configured to read and execute computer-executable instructions located in the DFT software module 58 of the non-volatile memory 56 and embodying the DFT slab model algorithms, calculations, and / or methods of one or more embodiments. The software module 58 can include an operating system and application programs. The software module 58 can be written or interpreted by a computer program created using various programming languages and / or technologies, including, but not limited to, Java, C, C++, C#, Objective C, Fortran, Pascal, JavaScript, Python, Perl, and PL / SQL, alone or in combination.

[0035] When executed by the processor 52, the computer-executable instructions of the DFT software module 58 may cause the computing platform 50 to perform one or more of the DFT algorithms and / or methods disclosed herein. The non-volatile memory 56 may also contain DFT data 60 that supports the functions, features, calculations, and processes of one or more embodiments described herein.

[0036] The program code embodying the algorithms and / or methods described herein can be distributed independently or collectively as various forms of program products. The program code can be distributed using a computer-readable storage medium having computer-readable program instructions thereon so that a processor executes aspects of one or more embodiments. Intrinsically non-transitory computer-readable storage media may include volatile and non-volatile, as well as removable and non-removable tangible media executed in any method or technology for storing information (such as computer-readable instructions, data structures, program modules or other data). The computer-readable storage medium may further include RAM, ROM, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other solid-state storage technology, portable compact disc read-only memory (CD-ROM) or other optical memory, cassettes, magnetic tape, disk storage or other magnetic storage devices or any other medium that can be used to store the required information and can be read by a computer. The computer-readable program instructions can be downloaded from the computer-readable storage medium to a computer, another type of programmable data processing device or another device, or downloaded to an external computer or external storage device via a network.

[0037] The computer-readable program instructions stored in a computer-readable medium can be used to instruct a computer, other types of programmable data processing devices or other equipment to work in a particular manner so that the instructions stored in the computer-readable medium generate an article of manufacture comprising instructions for performing the functions, actions and / or operations specified in the flow chart or diagram. In certain alternative embodiments, the functions, actions and / or operations specified in the flow chart and diagram can be reordered, processed serially and / or processed in parallel according to one or more embodiments. In addition, any flow chart and / or diagram may include more or fewer nodes or blocks than those illustrated according to one or more embodiments.

[0038] As generated by the DFT software module 58, Figure 3 Figures 3a through 3d depict schematic views of a defective graphene sheet 100 including a monovacancy (MV) 102, a divacancy (DV) 104, a trivacancy (TV) 106, and a tetravacancy (QV) 108, respectively. Carbon atoms 110 are represented by circles, and bonds 112 between carbon atoms 110 are represented by lines. MV 102 is formed by removing a single carbon atom from the original graphene sheet. DV 104 is formed by removing two adjacent carbon atoms from the original graphene sheet. TV 106 is formed by removing three adjacent carbon atoms from the original graphene sheet. QV 108 is formed by removing four adjacent carbon atoms from the original graphene sheet.

[0039] DFT calculations were performed using the Perdew–Burke–Eenzerhof (PBE) formula with the generalized gradient approximation using the projected augmented wave method to structurally relax graphene, thereby forming the defective graphene sheet 100. DFT calculations using the PBE formula can be performed using the Vienna ab initio simulation package (VASP). In one embodiment, the plane wave basis cutoff energy is set to 520 eV. The k-point per reciprocal atom (KPPRA) value can be any of the following values or a range between any two of the following values: 1000, 1500, 2000, 2500, 3000, 3500, and 4000. The KPPRA value can vary with the supercell size.

[0040] The energy penalty (in eV / carbon atom) associated with creating a graphene defect compared to a pristine graphene sheet can be calculated. The energy penalty (in eV / carbon) for creating a vacancy in a graphene sheet can be determined using the following equation (1):

[0041] E 惩罚 =[(E 0,最终 +n xμC )–E 0,石墨烯 ]] / n (1)

[0042] where E0 is the calculated DFT internal energy, n is the number of vacancies, and μ C is the chemical potential of carbon (-9.217 eV).

[0043] Table 1 below shows the energy penalties in eV for MV, DV, TV, and QV.

[0044] MV DV TV QV Energy Penalty 6.310 1.811 2.353 1.249 .

[0045] Based on this data, MV is the most difficult to form of the four phases listed in Table 1. Furthermore, the high-energy MV phase is the most reactive with other species, such as hydrogen atoms. For these reasons, DV is preferred over MV. TV has a slightly higher energy penalty than DV, but is still more stable than MV. Based on the energy penalty data in Table 1, QV is the most stable of the graphene defects listed in Table 1.

[0046] The reactivity of defective graphene species (e.g., MV, DV, TV, and QV) with Pt, H2, O2, and H2O was tested and determined as generated by the DFT software module 58 that performs DFT calculations. The reactivity can be measured by the reaction enthalpy (eV). Equation (2) can be used to determine the reaction enthalpy.

[0047] ΔE rxn =E 0,最终,经吸附 –(μ 被吸附物 +E 0,缺陷化_石墨烯 ) (2)

[0048] where E0 is the calculated DFT internal energy of the atomic structure before and after adsorption, and μ 被吸附物 is the chemical potential of the different adsorbate species (e.g., Pt, H2, O2, and H2O). In one embodiment, the chemical potentials used are as follows: Pt (-6.097 eV), H2 (-6.762 eV), O2 (-9.046 eV), and H2O (-14.886 eV). In this embodiment, μ Pt is the DFT bulk energy of Pt metal, μ H2 is the DFT energy of H2 gas, μ O2 is the DFT energy of O2 gas, and μ H2O is the DFT energy of bulk H2O (e.g. solid ice). Depending on the choice of chemical potential used, the relative reaction enthalpy may shift by a constant value. For example, Pt 2+ (水溶液) Additional terms may be involved, such as ionization and solvation corrections. rxn ) is a negative number, the corresponding reaction occurs spontaneously, and vice versa.

[0049] Table 2 shows the chemical reactivity using equation (2).

[0050] Reaction enthalpy (eV) Pt <![CDATA[H2]]> <![CDATA[O2]]> <![CDATA[H2O]]> MV +22.871 -2.078 -5.013 -0.751 DV +4.599 +4.321 +0.102 +3.291 TV +0.550 -3.557 +0.870 +0.916 QV +4.385 +0.541 +4.895 +1.597 .

[0051] Figure 4 4a to 4h depict schematic views showing the atomic structures of different adsorbate species (eg, Pt, H 2 , O 2 , and H 2 O) before and after adsorption onto a graphene sheet 158 including MV 160 . Figure 4 4a, 4c, 4e and 4g show the Pt atomic structure 150, H2 atomic structure 152, O2 atomic structure 154 and H2O atomic structure 156 located on the MV 160 of the graphene sheet 158 before structural relaxation using DFT calculation. Figure 4 In b, the Pt atomic structure 150 has been removed from the MV 160 of the graphene sheet 158 and attached to the carbon site 162. In addition, two additional carbon atoms 164 have been attached to other carbon rings, thereby making Figure 4 a's MV 160 becomes Figure 4 TV 166 is shown in b. As can be seen in Table 2, this reaction is very endothermic (+22.871 eV), so it is unlikely that this reaction will occur. In the case of H2 atomic structure 152, O2 atomic structure 154, and H2O atomic structure 156, Figure 4 c, 4e and 4g of the H2 atomic structure 152, O2 atomic structure 154 and H2O atomic structure 156 as shown Figure 4 d, 4f, and 4h show dissociation around MV 160. These dissociation reactions occur spontaneously, as shown in the chemical reactivity in Table 2. As shown in Table 1, MVs are rarely observed, likely due to a calculated energy penalty of greater than 6 eV.

[0052] Figure 5 5a to 5d depict schematic views of the atomic structures of different adsorbate species (eg, Pt, H 2 , O 2 , and H 2 O) after adsorption onto a graphene sheet 208 having DVs 210 . Figure 5 5a, 5b, 5c and 5d show a Pt atomic structure 200, a H2 atomic structure 202, an O2 atomic structure 204 and a H2O atomic structure 206 located on a graphene sheet 208 having a DV 210. Figure 5 As shown in Figures 5a, 5b, and 5d, the Pt atomic structure 200, the H2 atomic structure 202, and the H2O atomic structure 206 are respectively stable (e.g., do not dissociate) when located on a graphene sheet 208 having a DV 210. Figure 5As shown in Figure c, O2 atomic structure 204 dissociates into a carbon ring in graphene sheet 208. Since DFT calculations indicate that O2 atomic structure 204 reacts with DV 210 in graphene sheet 208, this defective graphene sheet may not be suitable for oxygen diffusion through the DV. Furthermore, all DFT-calculated reaction enthalpies in Table 2 for the DV are positive, indicating that a certain amount of energy is required for these reactions to occur.

[0053] Figure 6 a to 6d depict schematic views of the atomic structures of different adsorbate species (eg, Pt, H 2 , O 2 , and H 2 O) after adsorption onto a graphene sheet 258 having DV 260 . Figure 6 6a, 6b, 6c and 6d show a Pt atomic structure 250, an H2 atomic structure 252, an O2 atomic structure 254 and an H2O atomic structure 256 located on a graphene sheet 258 having a TV 260. Figure 6 As shown in Figures 6b and 6c, the H2 atomic structure 252 and the O2 atomic structure 254 each dissociate onto the carbon of the graphene sheet 258 having TV 260. Therefore, in one or more embodiments, the graphene sheet 258 having TV 260 may not be suitable for diffusion of hydrogen and oxygen gas species through the TV. The reaction enthalpy of TV and H2 is very negative (-3.557 eV), meaning that this type of reaction occurs spontaneously.

[0054] Figure 7 a to 7d depict schematic views of the atomic structures of different adsorbate species (eg, Pt, H 2 , O 2 , and H 2 O) after adsorption onto a graphene sheet 308 with QVs 310 . Figure 7 7a, 7b, 7c and 7d show a Pt atomic structure 300, an H2 atomic structure 302, an O2 atomic structure 304 and an H2O atomic structure 306 located on a graphene sheet 308 having a QV 310. Figure 7 As shown in Figures 7b, 7c, and 7d, the H2 atomic structure 302, the O2 atomic structure 304, and the H2O atomic structure 306, respectively, do not dissociate onto the graphene sheet 308 having the QV 310. In addition, the DFT-calculated reaction enthalpies of the QVs in Table 2 are positive, meaning that a certain amount of energy is required for these dissociation reactions to occur. Therefore, this means that the dissociation probability of the H2 atomic structure 302, the O2 atomic structure 304, and the H2O atomic structure 306 is low. Figure 7As shown in FIG. 1 , the Pt atomic structure 300 in a dissolved form is captured by the QV. In other embodiments, the QV may capture catalyst materials other than Pt. For example, the QV may capture a Pt-M catalyst, where M is a transition metal such as Co, Fe, or Ni. The Pt captured on the QV can still act as a catalyst material because the Pt is in contact with the graphene-based material that serves as a conductor. Less Pt migrates toward the PEM 12, thereby reducing the loss of electrochemical surface active area (ECSA). Since less Pt is redeposited on the PEM 12, less PEM 12 degradation occurs. Preventing ECSA loss and PEM degradation can increase the life of the fuel cell 10. During a negative sweep, the Pt on the graphene defects can be ionized, released, and redeposited in the anode CL 14 and / or cathode CL 16 of the fuel cell 10.

[0055] DFT calculations were used to examine the relative energy changes when different adsorbate species (eg, Pt, H 2 , O 2 , and H 2 O) were brought relatively close to or away from the QV. These calculations were used to simulate various environments within the fuel cell 10 . Figure 8A Graph showing the relative energy change as Pt moves away from the QV in the z direction. Figure 8A Included is a plot of relative energy (eV) vs. distance of Pt (in the z direction) from the QV for Pt on a graphene sheet with a QV Graph 350. Figure 8A As shown in , the binding energy of Pt to QV is strong (>-3.0 eV) near the graphene sheet. Figure 8B A schematic top view of a Pt atomic structure 352 is shown at different distances from a graphene sheet 354 including QVs 356 . Figure 8C A schematic side view of a Pt atomic structure 352 is shown at different distances from a graphene sheet 354 including a QV 356 .

[0056] A relative energy of 0 eV indicates that the Pt is located in a vacuum away from the graphene sheet. In this embodiment, the Pt is used The distance between the graphene sheet and Pt can be 0.5, 0.6, 0.8, 0.9 and other distances can be used. It is observed that as Pt moves closer to the QV in the defective graphene sheet, the relative energy becomes more negative. This observation can be based on the following analysis. If Pt is released from the catalyst layer and moves away from the anode CL 14 and / or cathode CL 16 of the fuel cell 10, the introduction of a defective graphene sheet with QV will attract Pt atoms to form a Figure 7As shown in a, it falls at the center of the QV. As explained by the difference of more than 3 eV shown in Figure 8, there is a large thermodynamic driving force to drive Pt to move to the QV in the defective graphene. In one embodiment, a defective graphene sheet with QV defects is incorporated as a coating on the surface of the anode CL 14 and / or cathode CL 16 of the fuel cell 10, thereby hindering the dissolution of Pt by adsorbing Pt in the QV. If Pt is not released toward the PEM 12, polymer degradation can be inhibited or slowed down. Since graphene is also a conductor, the Pt that falls on the QV can still act as a catalyst (i.e., less ECSA loss, even if Pt is released from the main catalyst layer). In addition, the adsorbed Pt can be ionized into Pt during the negative scan of the potential. 2+ and released and may subsequently be redeposited in the anode CL 14 and / or cathode CL 16 along with other Pt metal.

[0057] While mitigating Pt degradation by introducing graphene defects, there is a need to efficiently transport reactants (eg, hydrogen and oxygen) and products (eg, formed water) to and from the graphene-coated catalyst layer (eg, from and to the gas diffusion layer). Figure 9 Shown are the relative energies of H2 away from the QV in the z direction. Figure 9 Includes plotting the relative energy (eV) for H2 on a graphene sheet with QV vs. the distance of H2 (in the z direction) from the QV The relative energy of 0eV is when H2 is located in a vacuum far away from the graphene sheet. Compared with Pt in Figure 8, Figure 9 The opposite phenomenon was observed for H2. Figure 9 DFT calculations in

[15] show that H2 binding becomes weaker (e.g., more positive binding energy) as one moves from vacuum toward the QV. This suggests that an energy penalty of at least ~0.5 eV is required for H2 to cross the QV. Since the fuel cell 10 operates within this voltage window, H2 diffuses through the QV if the operating voltage is above 0.5 V. Otherwise (<0.5 eV), the H2 molecules may experience a repulsive force when approaching the QV, thus moving away from it.

[0058] Figure 10A Shows the relative energy of O2 away from the QV in the z direction. Figure 10A Includes plotting the relative energy (eV) for O2 on a graphene sheet with QV vs. the distance of O2 (in the z direction) from the QV Graph 450 of . Figure 10B Shows the relative energy of H2O away from the QV in the z direction. Figure 10B Included is a plot of relative energy (eV) for H2O on a graphene sheet with QV vs. the distance of H2O (in the z direction) from the QV. As O2 approaches the graphene QV, it feels a repulsive force until ~1.4 eV (when O2 is 0.8 ). Similarly, H2O feels an energy barrier of up to ~2.5 eV when approaching the QV in graphene. The typical operating regime of the fuel cell 10 is 0.6 to 0.9 V. DFT calculations show that it is difficult for O2 and H2O to diffuse through the QV in graphene. In other words, when being transported from the electrode to other components of the fuel cell (such as membranes, gas channels, etc.), it may be more advantageous for O2 and H2O to bypass the QV. Unlike H2, in order for O2 and H2O to pass through the QV, the energy penalty is relatively large, up to ~1.4 and ~2.5 eV, respectively. This indicates that even if the fuel cell 10 is operated at up to ~1 V, O2 and H2O may not be able to diffuse through the QV (e.g., insufficient thermodynamic driving force). These species may feel a very high repulsive force when approaching the QV and therefore stay away from the QV.

[0059] Therefore, in one or more embodiments, graphene defects, such as QVs, are introduced to mitigate Pt degradation and promote oxygen and water transport to and from the electrodes. In one embodiment, the graphene sheet is filled with defects of four (4) (e.g., QVs) or more adjacent carbon atoms. The number of more adjacent carbon atoms omitted to create the defects can be any of the following values or a range between any two of the values: 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, and 25. Based on the DFT calculations herein, the QVs may allow some H2 transport depending on the operating voltage. However, the DFT calculations also indicate that O2 and H2O transport across the QVs may be more difficult.

[0060] Figure 11 is a schematic view showing the chemical structure of a graphene sheet 500 having various defects. The graphene sheet 500 includes a number of QVs 502. The QVs 502 may be configured to capture dissolved Pt. The graphene sheet 500 includes a number of defects 504 (e.g., MV, DV, and TV) that are smaller than the QV. The smaller defects 504 may be configured to selectively allow H2 to be transported through the graphene sheet 500, while not allowing O2 and H2O to be transported through the graphene sheet 500. The graphene sheet 500 includes a number of defects 506 that are larger than the QV. The defects 506 may be formed by wrinkling of the graphene sheet 500. The larger defects 506 may be configured to allow H2, O2, and H2O to be transported through the graphene sheet 500. Based on DFT calculations, during the lateral diffusion of Pt in the xy direction, Pt is attracted to one of the QVs 502, which is as shown in FIG. Figure 11As shown in FIG, Pt is trapped in the QVs 502. Therefore, due to the attraction toward the QVs 502, the diffusion of Pt is relatively slow. Therefore, the escape of Pt ions through the larger defects is mitigated compared to the transport of H2, O2, and H2O.

[0061] The graphene-based material used as the surface coating for the anode CL 14 and / or cathode CL 16 may include a number of small defects (e.g., smaller than QV), a number of QV defects, and a number of large defects (e.g., larger than QV) per unit volume. The number of small defects per unit volume of the graphene-based material may be any of the following values or within a range of any two of the following values: 0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0%. The number of QV defects per unit volume of the graphene-based material may be any of the following values or within a range of any two of the following values: 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0%. The number of large defects per unit volume of the graphene-based material may be any of the following values or within a range of any two of the following values: 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0%. The ratio of smaller defects to QV defects to larger defects per unit volume can be any of the following ratios or a range between any two of the following ratios: 0:0:0, 3:5:6, and 1:1:1.

[0062] In another embodiment, graphene material having beneficial defects may be wrapped onto the surface of anode CL 14 and / or cathode CL 16 to form a geometry that differs from the planar geometry of a continuous graphene sheet. Figure 12 Schematic view of a catalyst layer surface 550 including encapsulated defective graphene material islands 552, 554, and 556. In one embodiment, graphene nanosheets (GNFs) can be dispersed in a catalyst material ink. The catalyst material and GNFs can be mixed in a slurry containing ethyl cellulose. For example, slurries are prepared using 70, 10, 10, and 10 weight percent of a Pt catalyst, nano-GNFs, ethyl cellulose, and an ionomer in a liquid solvent, respectively. Ultrasonic treatment can be performed to distribute the particles and prevent nanoparticle aggregation. The slurry samples can be cast, dried, and subsequently assembled into electrodes for a fuel cell 10.

[0063] like Figure 12As shown by arrows 558 and 560 in FIG, H2, O2, and H2O are transported between the encapsulated defective graphene material islands 552, 554, and 556, while the dissolved Pt ions are trapped by the graphene defects. The attractive and repulsive forces with Pt, H2, O2, and H2O can be further tuned by including different types of hydrogen (-H) and oxygen functional groups (e.g., -O-, =O, -OH, and / or -COOH) in the graphene sheet by forming reduced graphene oxide (rGO) or graphene oxide (GO). The percentage of hydrogenated functional groups (-H) in the graphene-based material can be any of the following values or within a range of any two of the following values: 0, 5, 10, 15, 20, 25, and 30%. The percentage of oxidized functional groups (e.g., —O—, ═O, —OH, and / or —COOH) in the graphene-based material can be any of the following values or ranges between any two of the following values: 0, 5, 10, 15, 20, 25, 30, 25, and 40%.

[0064] In one embodiment, a graphene-based material may be coated on a surface of anode CL 14 and / or cathode CL 16, such as the surface of anode CL 14 and / or cathode CL 16 facing away from PEM 12. The surface(s) may be partially or completely coated with the graphene-based material. The catalyst material of anode CL 14 and / or cathode CL 16 may 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), PGM-M, Pt-PGM-M, or a combination thereof. The graphene-based material may be a graphene sheet applied in a planar orientation relative to the coated surface of anode CL 14 and / or cathode CL 16. The graphene sheet may include a single graphene monolayer. In other embodiments, the number of graphene monolayers in the graphene substrate 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 anode CL 14 and / or cathode CL 16. 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 anode CL 14 and / or cathode CL 16 or migrate into the PEM 12, thereby inhibiting PEM degradation. The addition of graphene-based materials can enhance electron transport due to the increased conductivity of the catalyst layer. In one embodiment, the coating of graphene-based material can be in direct contact with the catalyst material in the anode CL 14 and / or cathode CL 16. In another embodiment, the coating of graphene-based material is loosely associated, for example, at a certain short distance from the anode CL 14 and / or cathode CL 16. The short distance can be any of the following values or within the range of any two of the following values: 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 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.

[0065] Various methods can be used to apply graphene-based materials to the surfaces of anode CL 14 and / or cathode CL 16. The graphene-based material can be deposited onto the catalyst material in thin film form or via a dispersion (e.g., using graphene ink) during the synthesis of anode CL 14 and / or cathode CL 16, or after the anode CL 14 and / or cathode CL 16 are fabricated. The coated graphene-based material electrode catalyst layer 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 graphene-based material film 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 graphene. After CVD growth, the sample can be combined with a polymer (e.g., poly(methyl methacrylate) (PMMA)) followed by etching or rinsing. The composite film may be transferred to the surface of the anode CL 14 and / or cathode CL 16 .

[0066] Graphene-based materials may include graphene, graphene oxide (GO), reduced graphene oxide (rGO) and combinations thereof. Graphene-based materials may also include other materials that capture dissolved metal ions during operation of the fuel cell 10. 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. Graphene-based materials may include a significant amount of materials capable of capturing dissolved metal ions. A significant amount may 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 remainder may partially include amorphous and / or crystalline graphite materials. Graphene-based materials may be further functionalized by cation or anion doping. In another embodiment, the graphene-based material may 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 may also provide a selective diffusion barrier for HF and / or SO3. - physical barriers to further prevent PEMFC degradation.

[0067] Various methods may be used to coat other two-dimensional layered structured materials onto the surface of the anode CL 14 and / or cathode CL 16. Non-limiting examples of other two-dimensional layered structured materials include graphyne, borophene, germanene, organosilicon, Si2BN, stanine, phosphorene, bismuthene, molybdenite, and transition metal dichalcogenides (TMDCs) (e.g., MOS2, WSe2, HfS2, etc.), materials of the general formula M n+1 X n T x Layered transition metal carbides and carbonitrides (MXenes) wherein 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 a surface end (eg, =O, -OH, or -F), and combinations thereof. Other two-dimensional layered structure materials can be used to replace all or part of the graphene-based materials in the electrode catalyst layer coating.

[0068] 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 clearly described or illustrated. Although the 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 characteristics, those of ordinary skill in the art will recognize that one or more features or characteristics 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, to the extent that any embodiment is described as being less desirable than other embodiments or prior art embodiments in terms of one or more characteristics, these embodiments are not outside the scope of the present disclosure and may be desirable for specific applications.

Claims

1. A fuel cell comprising: Polymer electrolyte membrane PEM; first and second electrode catalyst layers comprising first and second catalyst materials, the PEM being positioned between the first and second electrode catalyst layers, the first electrode catalyst layer having a first surface facing away from the PEM and a second surface facing the PEM, and the second electrode catalyst layer having a first surface facing away from the PEM and a second surface facing the PEM; and A graphene-based material coated onto the first and / or second surfaces of the first and / or second electrode catalyst layers, the graphene-based material having a plurality of defects, the plurality of defects including a plurality of quadruple-vacancy QV defects formed by vacancies of four adjacent carbon atoms in the graphene-based material, a plurality of smaller defects formed by vacancies of three or fewer adjacent carbon atoms, and a plurality of larger defects formed by vacancies of five or more adjacent carbon atoms, the plurality of QV defects being configured to mitigate dissolution of the first and / or second catalyst material through the first and / or second surfaces of the first and / or second electrode catalyst layers, the plurality of small defects being configured to transport H2 through the graphene-based material, and the plurality of larger defects being configured to transport H2, O2, and H2O through the graphene-based material.

2. The fuel cell of claim 1, wherein the ratio of the number of smaller defects to the number of QV defects to the number of larger defects per unit volume is in the range of 3:5:6 to 1:1:

1.

3. The fuel cell of claim 1, wherein the graphene-based material is substantially planar relative to the first and / or second surface of the first and / or second electrode.

4. The fuel cell of claim 1, wherein the graphene-based material is at least partially wrinkled.

5. The fuel cell of claim 1, wherein the graphene-based material comprises one or more hydrogenated groups and / or one or more oxidized groups.

6. The fuel cell of claim 5, wherein the one or more oxidizing groups include -O-, =O, -OH and / or -COOH groups.

7. The fuel cell of claim 1, wherein the graphene-based material comprises graphene.

8. The fuel cell of claim 1, wherein the graphene-based material comprises graphene oxide, reduced graphene oxide, or a combination thereof.

9. The fuel cell of claim 1, wherein the graphene-based material is configured to trap the first and / or second catalyst material within the plurality of defects.

10. The fuel cell of claim 1, wherein the first and / or second catalyst material comprises pure Pt, a Pt-M alloy, wherein M is a metal other than Pt, a platinum group member PGM metal other than Pt, PGM-M, Pt-PGM-M, or a combination thereof.

11. The fuel cell of claim 1 , wherein the graphene-based material comprises one or more oxygen-based functional groups.

12. The fuel cell of claim 1, wherein the graphene-based material comprises a graphene sheet having a plurality of graphene layers.

13. The fuel cell of claim 12, wherein the number of graphene layers is in the range of 1 to 10.

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