Controlled release antioxidants for fuel cells.

Abstract

Microcapsule and microsphere controlled-release forms of antioxidants, such as cerium oxide, are disclosed for improving fuel cell durability and extending lifespan. Membrane electrode assemblies (MEAs) and polymer electrolyte membrane fuel cells (PEMFCs) employ controlled-release forms, and methods for mitigating or inhibiting cerium migration within fuel cells are also disclosed.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is a PCT international patent application claiming priority to and encompassing the entire subject matter of U.S. Provisional Patent Application No. 63 / 379,615, filed October 14, 2022, and U.S. Non-Provisional Patent Application No. 18 / 486,595, filed October 13, 2023.

[0002] FIELD OF THE DISCLOSURE This disclosure relates generally to fuel cells, and more particularly to the use of controlled release antioxidants to improve durability and extend the life of fuel cells. [Background technology]

[0003] The discussion of the background art provided herein is intended to generally provide a context for the present disclosure.

[0004] Fuel cell vehicles offer high energy efficiency and feature zero-emission powertrain platforms, making them a promising option for future transportation. Currently, commercially available fuel cell vehicles use polymer electrolyte membrane fuel cells (PEMFCs). Although PEMFC technology has been commercialized for decades, it still faces significant challenges: high material costs and significant performance gaps.

[0005] One issue with the use of PEMFCs is the need to extend the operational life of fuel cells in vehicles. Current fuel cells can typically provide an operational life of 5,000 hours. However, significantly longer lifespans would be beneficial for passenger cars and are necessary for the practical application of fuel cells in commercial vehicles and heavy trucks. According to the U.S. Department of Energy's 2050 targets, passenger cars will benefit from an operational lifespan of at least 8,000 hours, while heavy trucks, for example, require an operational lifespan of at least 25,000 hours, and more preferably 30,000 hours. Therefore, it is desirable to develop improved PEMFCs with longer lifespans. Summary of the Invention [Means for solving the problem]

[0006] This section provides a general overview of the disclosure and is not an exhaustive disclosure of its complete scope or all of its features.

[0007] In various embodiments, the present disclosure provides a membrane electrode assembly having an anode containing a first catalyst, a cathode containing a second catalyst, and a proton exchange membrane between the anode and cathode. At least one of the proton exchange membrane, anode, and cathode contains an antioxidant comprising cerium oxide particulates in a controlled-release form selected from microcapsules or microspheres configured to release cerium oxide over time. Yttrium-doped cerium oxide, zirconium-doped cerium oxide, and manganese oxide can also be employed as antioxidants within the scope of the present disclosure.

[0008] In another aspect, the present disclosure provides a fuel cell having a membrane electrode assembly including a proton exchange membrane, an anode including a first catalyst, and a cathode including a second catalyst. The proton exchange membrane is positioned between the anode and cathode. A first microporous layer contacts the anode, and a second microporous layer contacts the cathode. An anode diffusion layer contacts the first microporous layer, and a cathode diffusion layer contacts the second microporous layer. A first flow path contacts the anode diffusion layer, and a second flow path contacts the cathode diffusion layer. At least one of the proton exchange membrane, anode, cathode, first microporous layer, and second microporous layer contains a cerium oxide antioxidant in a controlled-release form selected from microcapsules or microspheres configured to release cerium oxide over time. Yttrium-doped cerium oxide, zirconium-doped cerium oxide, and manganese oxide can also be employed as antioxidants within the scope of the present disclosure.

[0009] In another aspect, the present disclosure provides a method for inhibiting cerium ion migration in a proton exchange membrane fuel cell (PEMFC), the PEMFC having a membrane electrode assembly (MEA). The MEA has a proton exchange membrane, an anode containing a first catalyst, and a cathode containing a second catalyst. The proton exchange membrane contains a perfluorosulfonic acid polymer and is positioned between the anode and cathode; a first microporous layer contacts the anode, and a second microporous layer contacts the cathode; an anode diffusion layer contacts the first microporous layer, a cathode diffusion layer contacts the second microporous layer, and a first flow path contacts the anode diffusion layer and a second flow path contacts the cathode diffusion layer. The method includes incorporating a predetermined amount of a cerium oxide antioxidant into the membrane electrode assembly in a controlled-release form selected from microcapsules or microspheres configured to release cerium oxide over time. Yttrium-doped cerium oxide, zirconium-doped cerium oxide, and manganese oxide may also be employed as antioxidants within the scope of the present disclosure.

[0010] In yet another aspect, the present disclosure provides a vehicle having a fuel cell as described herein.

[0011] Further areas of applicability of the above-described techniques and various ways of enhancing them will become apparent from the description provided herein. The description and specific examples in this summary are for illustrative purposes only and are not intended to limit the scope of the disclosure. [Brief explanation of the drawings]

[0012] The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein: [Figure 1] FIG. 1 is a cross-sectional view of an exemplary membrane electrode (MEA) assembly of the present disclosure. [Figure 2] 1 is a cross-sectional view of a portion of an exemplary fuel cell of the present disclosure. [Figure 3] 1 is a cross-sectional view of a portion of an exemplary fuel cell of the present disclosure. [Figure 4]1 is a schematic cross-sectional view of a portion of an exemplary fuel cell of the present disclosure. [Figure 5] 1 is an illustration of an antioxidant microcapsule controlled release form of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of the controlled release profile of antioxidants using microcapsules of the present disclosure, using CeO2 / Ce ions as an example. [Figure 7] 1 is an illustration of an antioxidant microsphere controlled release form of the present disclosure. [Figure 8] FIG. 1 is a schematic diagram of the controlled release profile of antioxidants using microspheres of the present disclosure, using CeO2 / Ce ions as an example. [Figure 9A] 1 is a scanning electron microscope (SEM) image showing urea-formaldehyde CeO2 (UF / CeO2) microcapsules of the present disclosure. [Figure 9B] 1 is a scanning electron microscope (SEM) image showing a cross-section of a microcapsule of urea-formaldehyde CeO2 (UF / CeO2) of the present disclosure. [Figure 9C] FIG. 1 is a scanning electron microscope (SEM) image showing a cross-section of a microcapsule of urea-formaldehyde CeO2 (UF / CeO2) of the present disclosure. [Figure 10] Illustrated decomposition of the polymer shell of the microcapsules and release of the radical quencher, i.e., CeO2. [Figure 11] NMR spectrum results of a benzenesulfonic acid decomposition test. [Figure 12] 1 is a graph showing the concentrations of benzenesulfonic acid and H2O2 remaining after decomposition.

[0013] It should be noted that the diagrams described herein are intended to illustrate the general characteristics of the methods, algorithms, and devices in the present technology to describe particular aspects. These diagrams may not precisely reflect the characteristics of any given aspect, and are not necessarily intended to define or limit particular embodiments within the scope of this technology. Furthermore, particular aspects may incorporate features from a combination of diagrams. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present disclosure provides improved chemical stability for proton exchange membrane fuel cell (PEMFC) components by providing antioxidants for quenching radicals that can damage the proton exchange membrane and adversely affect fuel cell life. The antioxidants described herein are designed to control the timing of the release of the radical quencher to extend life, thereby improving fuel cell life. In particular, the antioxidants of the present disclosure are designed to protect the radical quencher with a polymer shell or polymer complex structure, such as microspheres, that allow for controlled release of the radical quencher.

[0015] A PEMFC cell is a device that converts chemical energy of hydrogen into electricity through an electrochemical reaction with oxygen. Figure 1 shows a typical example of a fuel cell 100. The fuel cell 100 has a membrane electrode assembly (MEA) 110 with a proton exchange membrane 120 positioned between an anode 130 and a cathode 140. A first microporous layer 150 contacts the anode 130. An anode gas diffusion layer 170 contacts the first microporous layer 150, and a first flow path 190 contacts the anode gas diffusion layer 170. A second microporous layer 160 contacts the cathode 140. A cathode gas diffusion layer 180 contacts the second microporous layer 160, and a second flow path 200 contacts the cathode gas diffusion layer 180. Although not shown in Figure 1, the anode bipolar plate may contact the first flow path 190, and the cathode bipolar plate may contact the second flow path 200.

[0016] The proton exchange membrane (PEM) is understood to be a structure in which the anode catalyst layer and cathode catalyst layer are arranged to have proton conductivity with respect to each other. This structure may have an anode gas diffusion layer 170 and a cathode gas diffusion layer 180 in contact with the anode catalyst layer and the cathode catalyst layer, respectively. The anode and cathode gas diffusion layers 170 and 180 are configured so that hydrogen and oxygen gases diffuse into the anode and cathode catalyst layers, respectively, and water products diffuse away from the cathode catalyst layer.

[0017] The first microporous layer 150 and the second microporous layer 160 are primarily composed of a water-repellent resin and a conductive material. In some embodiments, carbon or polytetrafluoroethylene (PTFE) is used for the first microporous layer 150 and the second microporous layer 160.

[0018] The anode gas diffusion layer 170 and cathode gas diffusion layer 180 contact the anode 130 and cathode 140, respectively, and are made of a gas-permeable and electrically conductive material, which may be a carbon porous material such as carbon paper, carbon cloth, or glassy carbon. In other examples, porous metal bodies are used. In some embodiments, the gas permeability, or the rate at which reactive gases pass through the anode or cathode diffusion layer, is substantially uniform across the entire surface of the diffusion layer according to this embodiment. In some embodiments, carbon paper or carbon cloth is utilized.

[0019] The first flow channel 190 is provided for flowing a fuel gas over the surface of the negative electrode diffusion layer. The second flow channel 200 is provided for flowing an oxidizing gas over the surface of the positive electrode diffusion layer. In some embodiments, the first and second flow channels are formed from carbon resin, stainless steel, titanium, a titanium alloy, or a conductive ceramic material.

[0020] The fuel gas is typically hydrogen, which may be stored in a storage tank. Optionally, the hydrogen may be stored as a metal hydride or may be hydrogen obtained by reforming a hydrocarbon fuel.

[0021] The oxidizing gas is typically an oxygen-containing gas, and in some embodiments, the oxidizing gas is ambient air.

[0022] As shown in FIG. 2 , a fuel cell having a proton exchange membrane 120, an anode 130, a cathode 140, an anode gas diffusion layer 170, and a cathode gas diffusion layer 180 may further include an anode current collector 210 and a cathode current collector 220 in electrical communication with the anode and cathode catalyst layers, respectively, and configured to connect to an external circuit 230.

[0023] FIG. 3 shows an example of a fuel cell 300 having a polymer electrolyte membrane 310, an anode catalyst layer 320, and a cathode catalyst layer 330. An anode microporous layer 340 is in contact with the anode catalyst layer 320. An anode gas diffusion layer 360 is in contact with the anode microporous layer 340. A cathode microporous layer 350 is in contact with the cathode catalyst layer 330. A cathode gas diffusion layer 370 is in contact with the cathode microporous layer 350. An anode bipolar plate 380 is in contact with the anode gas diffusion layer 360, and a cathode bipolar plate 390 is in contact with the cathode gas diffusion layer 370. The flow of hydrogen and air within the cell is shown in FIG. 3. Hydrogen (H2) is supplied to the anode side of the fuel cell, and an oxygen source (such as ambient air) is supplied to the cathode side of the fuel cell. Figure 3 shows water and excess air exiting the cathode side of the fuel cell, and unreacted hydrogen exiting the anode side of the fuel cell.

[0024] The anode bipolar plate 380 and cathode bipolar plate 390 can be independently made of metal (e.g., titanium or stainless steel) or carbon structure (e.g., graphite). Some metallic bipolar plates use a carbon film coating on some or all of the bipolar plate surfaces. U.S. Pat. No. 10,283,785, incorporated herein by reference, teaches the use of amorphous carbon membranes in bipolar plates. In a fuel cell, fuel gas and oxygen gas should be supplied separately to the entire electrode surface without mixing with each other. Therefore, the bipolar plates must be gas-tight. Furthermore, the bipolar plates must have good electrical conductivity to collect electrons produced by the reaction and, when multiple sub-cells are stacked, to function as electrical connectors for connecting adjacent sub-cells. Furthermore, because the electrolyte membrane surface is highly acidic, the bipolar plates provide excellent corrosion resistance. The primary purpose of the bipolar plates in a PEMFC stack is to supply fuel (hydrogen) and oxygen to the cells and manage the flow of generated heat and water. It is also used as a backing medium for stacking individual fuel cells.

[0025] FIG. 4 is another example of a membrane electrode assembly (MEA) 110 having a proton exchange membrane 120, an anode 130, and a cathode 140.

[0026] The proton exchange membrane 120 is configured to support proton transport across the membrane (i.e., proton conduction) and to be electrically insulating. The proton exchange membrane 120 may be a pure polymer membrane or a composite membrane and may be formed from any suitable material, such as a perfluorosulfonic acid polymer, other fluoropolymer, hydrocarbon polymer, or any other suitable material. The MEA 110 further includes an anode 130 having an anode catalyst layer configured to electrocatalyze the anode hydrogen decomposition reaction.

[0027] [ka]

[0028] The anode catalyst layer can be formed substantially from anode catalyst particles of platinum or platinum alloy supported on carbon such as carbon black.

[0029] The MEA 110 further includes a positive electrode 140 configured to catalyze the oxygen reduction reaction.

[0030] [ka]

[0031] The cathode catalyst layer may comprise platinum or platinum alloy cathode catalyst particles supported on carbon, such as carbon black. In some implementations, the cathode catalyst particles are platinum-cobalt alloys. In some such implementations, the weight ratio of platinum to cobalt may be about 3:1 to about 15:1. In some embodiments, the ratio is about 10:1.

[0032] In some embodiments, the proton exchange membrane is a perfluorosulfonic acid (PFSA) polymer ion exchange membrane. PFSA polymers are commercially available. Non-limiting examples of PFSA polymers include the product lines sold under the trade names Nafion® (sold by Chemours) and Aquivion® (sold by Solvay). The anode and cathode catalyst layers are made of a gas-permeable, electrically conductive material that supports a catalyst (e.g., platinum or a platinum alloy) that promotes the electrochemical reaction of hydrogen and oxygen, and are made of a carbon support having the catalyst supported thereon. The anode and cathode layers are opposite sides of the proton exchange membrane.

[0033] The first catalyst and the second catalyst are each independently a platinum or platinum alloy catalyst. In some embodiments, the platinum or platinum alloy is supported on a conductive support such as carbon. Suitable carbon conductive supports include, but are not limited to, carbon black, graphite, activated carbon, and carbon nanotubes. Platinum alloys include platinum-cobalt alloys. Examples of such alloys are described in U.S. Patent No. 7,940,080.

[0034] In some embodiments, the anode catalyst layer and / or cathode catalyst layer may comprise a solid ionomer, such as a fluorinated polymer, such as perfluorosulfonic acid (PFSA), such as Nafion®, sold by Chemours. Other commercially available examples include Flemion® (AGC Corporation), Aciplex® (Asahi Kasei Corporation), and Fumion® (Fumatec).

[0035] In some embodiments, the anode and / or cathode catalyst particles may have an average largest dimension of 2 to 5 nm. In some embodiments, the anode and / or cathode catalyst particles comprise porous particles that increase the surface area for catalytic activity.

[0036] To extend the life of PEMFCs beyond the typical operating life of 5000 hours, antioxidants are used to react with the free radicals generated from the catalytic reactions in PEMFCs. For example, cerium oxide is used as a reservoir of cerium ions, which act as an antioxidant. More specifically, the addition of Ce to the proton exchange membrane, electrodes, or gas diffusion layers can prevent chemical degradation to the membrane or ionomer in PEMFCs. 3+ and Ce 4+are commonly used. In particular, cerium ions are thought to mitigate chemical attack from free radicals on membranes and other components within fuel cells. Without wishing to be bound by any particular theory, it is believed that cerium(III) ions are oxidized by hydroxyl radicals (HO*) to form tetravalent cerium(IV) ions and water, which are then rapidly reduced by hydroperoxyl radicals (HOO*) or hydrogen peroxide (H2O2) to regenerate cerium(III). Yttrium-doped cerium oxide, zirconium-doped cerium oxide, and manganese oxide can also be employed as antioxidants.

[0037] Cerium ions (Ce 3+ and Ce 4+ Although the use of cerium ions can prevent damage to the PEM, some cerium ions migrate to other parts of the fuel cell during radical quenching reactions. Some of the cerium ions leach out of the PEMFC with water. The resulting cerium ions in the fuel cell can poison the catalyst and reduce the ionic conductivity of the ionomer and PEM. The most common ionomer and polymer is perfluorosulfonic acid (PFSA). Either of these events can cause a decrease in fuel cell performance and efficiency. Furthermore, the fouled membrane has reduced mechanical stability, negatively impacting the fuel cell's lifespan.

[0038] Maintaining a desirable cerium ion concentration in fuel cells for mitigating free radicals in heavy-duty vehicle applications requires the addition of larger amounts of antioxidants to the fuel cell stack, i.e., the multiple stacked membrane electrode assemblies (MEAs) that make up the PEMFC. However, without a release strategy, the cerium ion concentration in the fuel cell stack increases, reducing fuel cell performance and durability. This leads to higher initial material costs (larger stacks) and increased fuel (H) costs for customers. In some embodiments, the present disclosure relates to controlled release techniques for controlling antioxidant concentrations, such as cerium ion concentrations in membrane electrode assemblies (MEAs), to enable the operational life required for heavy-duty vehicle fuel cells and other vehicle fuel cells. Yttrium-doped cerium oxide, zirconium-doped cerium oxide, and manganese oxide can also be employed as antioxidants within the scope of the present disclosure.

[0039] As used herein, "controlled release" refers to the gradual, delayed, and / or slow release of an antioxidant at a predetermined interval or over a period of time. "Controlled release" also includes "sustained release," "extended release," and / or "delayed release." In the present disclosure, controlled release of an antioxidant is achieved by providing the antioxidant in a controlled-release form selected from microcapsules or microspheres. As shown in FIG. 5, a microcapsule 400 of the present disclosure comprises a core material 410 containing antioxidant microparticles, such as cerium oxide microparticles; and a polymeric shell 420 surrounding the core material, the polymeric shell having a predetermined thickness for controlling the release of the antioxidant. The core may be a pure solid, containing microparticles such as CeO2, or a mixture of microparticles and water, such as CeO2 / water. The core material within the capsule may also be referred to as the internal phase, fill, or filler, and the shell may also be referred to as the wall, coating, or matrix. The polymeric shell completely surrounds or encapsulates the core material, including the cerium oxide particles, isolating the core material from the external environment, and the polymeric shell controls or delays the exposure or release of the cerium oxide particles to the PEM, electrode, and / or gas diffusion layer. Figure 6 illustrates an example controlled release profile of an antioxidant using CeO2 / Ce ions. Figure 6 also shows that the thickness of the polymeric shell can be varied, e.g., increased, for a subset of microcapsules to further delay the release of the antioxidant over time.

[0040] In some examples, the thickness of the polymer shell ranges from about 50 nm to about 9 μm. The overall loading of cerium ions can be controlled to a predetermined level so that fuel cell performance does not decrease significantly over time. The microspheres and microcapsules of the present disclosure have particle sizes ranging from 100 nm to 10 μm. The microspheres and microcapsules of the present disclosure must be small enough to fit into the catalyst layer (~10 μm) and microporous layer (<40 μm). Particles that are too large, for example, larger than 10 μm, can significantly impact the integrity of the catalyst layer or microporous layer.

[0041] As shown in Figure 7, microspheres 500 of the present disclosure have antioxidant microparticles 510, such as cerium oxide microparticles, embedded or dispersed within a polymer 520, such as a matrix, selected to control the release of the antioxidant microparticles 510 over time. Figure 6 illustrates the controlled release profile of an antioxidant using CeO2 / Ce ions as an example, demonstrating that release can be customized by optimizing the polymer composition and antioxidant loading in the microspheres.

[0042] The microcapsules of the present disclosure can be formed by any suitable microencapsulation technique. Microencapsulation is generally a process in which small individual particles form a core material and are surrounded by a continuous membrane or shell of polymeric material. The core material is completely coated or surrounded by the shell, isolating it from the external environment. The microspheres of the present disclosure can be formed by spray drying, a microencapsulation technique in which particles or core material are suspended or dissolved in a melt or polymer solution and entrapped within the dried particles. Other suitable microencapsulation techniques include, but are not limited to, simple or complex droplet formation, including suspension polymerization, dispersion polymerization, emulsion polymerization, interfacial condensation polymerization / polyaddition, interfacial crosslinking, ionic polymerization, and sol-gel polymerization, solvent evaporation, ionic gelation, thermal gelation, sonochemical processes, layer-by-layer adsorption, flash nanoprecipitation, electrospray, in situ polymerization, and interfacial polymerization.

[0043] The microspheres of the present disclosure can also be formed by mixing or incorporating antioxidant particles into a polymer matrix to form a composite. As used herein, "composite" refers to a material made up of two or more constituent materials with different physical or chemical properties. When forming the microspheres of the present disclosure, the antioxidant particles are uniformly dispersed within the matrix. In some instances, the antioxidant particles are dissolved or suspended in the polymer matrix.

[0044] Polymers that can be slowly degraded by free radicals to release the radical quencher can be used for the polymer shell and / or polymer matrix. Suitable polymers include, but are not limited to, natural polymers, synthetic polymers, and natural and synthetically produced polymers. Suitable natural polymers include, but are not limited to, gelatin, chitosan, starch, gum arabic, gum, albumin, cysteine, alginate, silk fibroin, and wax. Suitable synthetic polymers include, but are not limited to, polycaprolactone, poly(methyl methacrylate), poly(lactic acid), poly(glycol alcohol), polyolefins, cellulose and cellulose derivatives; thermosetting resins, including, but not limited to, melamine formaldehyde resins, urea-formaldehyde resins, polyurea-formaldehyde resins, and phenol-formaldehyde resins; polyamides, polyureas, polyurethanes, poly(urea-urethanes), polyurethane / chitosan, polyesters, polystyrenes, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU), polyether ketone (PEEK), and derivatives and combinations thereof.

[0045] The present disclosure is also directed to a method of inhibiting or mitigating cerium ion migration in a proton exchange membrane fuel cell (PEMFC), which involves loading a membrane electrode assembly with a predetermined amount of a cerium oxide antioxidant in a controlled release form selected from microcapsules or microspheres configured to release cerium oxide over time, as described herein.

[0046] Importantly, by using the emission control concepts described herein, longer fuel cell lifetimes can be achieved without significantly sacrificing fuel cell performance, and in some instances, the fuel cell operational lifetime is greater than 5,000 hours, at least 8,000 hours, at least 15,000 hours, at least 20,000 hours, at least 25,000 hours, or at least 30,000 hours.

[0047] The present disclosure is also applicable to various other aspects, such as vehicles powered by fuel cells, power generation systems that provide fuel cell power, and other items that include fuel cells. In some examples, the vehicle may be a car or truck. In some examples, the power generation system may be stationary. [Example]

[0048] Various aspects of the present disclosure are further illustrated by the following examples, which are provided to illustrate specific embodiments of the present disclosure and should not be construed as limiting the scope of the present disclosure to any particular aspect.

[0049] Example 1: Synthesis and properties Microcapsules of the present disclosure were synthesized with cerium oxide (CeO) nanoparticles as the core and a urea-formaldehyde polymer shell surrounding the core material. The urea-formaldehyde polymer was obtained by the following reaction of urea and formaldehyde: The CeO encapsulation was prepared by in situ polymerization. Urea, ammonium chloride, and resorcinol were added to deionized (DI) water and stirred at room temperature for 30 minutes. Next, CeO nanoparticles as the core material were added to the solution. The pH of the solution was adjusted to 3.5 by adding NaOH solution. Then, formaldehyde solution was added and stirred for 30 minutes. The temperature of the beaker was increased to 55°C on a hot plate for 4 hours to form encapsulated CeO.

[0050] [ka]

[0051] The diameter of the CeO2 particles was ~10-30 nm, and the encapsulated CeO2 was 0.7-1.7 μm. A urea-formaldehyde polymer shell protects the CeO2 core. The core-shell particle structure can be seen in the scanning electron microscope (SEM) image in Figure 9A. Cross-sections of microcapsules cut by ion beam are shown in Figures 9B and 9C. The black scattering mode in the SEM reveals the CeO2 core (bright) and the urea-formaldehyde (UF) polymer shell (dark). In the UF / CeO2 microcapsules, all CeO2 nanoparticles are covered by the UF shell (Figures 9A-9C).

[0052] Example 2: Benzenesulfonic acid decomposition test results The synthesized UF / CeO microcapsules were submerged in a sample containing benzenesulfonic acid and a certain amount of water, as shown in Figure 10. The benzenesulfonic acid and UF polymer shell of the microcapsules 102 were attacked by free radicals generated from H2O2, leading to the decomposition of the polymer shell. During the decomposition of the polymer shell, a radical quencher, i.e., cerium oxide (CeO2), was released 103. The remaining benzenesulfonic acid was determined by integrating the benzenesulfonic acid peak and the water peak in the NMR spectrum, as shown in Figures 11A, 11B, and 11C. Since the water concentration in the sample was fixed, the concentration of benzenesulfonic acid could be determined as follows:

[0053] [ka]

[0054] Figure 12 shows that, according to the present disclosure, approximately 60% of the benzenesulfonic acid remains from the CeO2 and approximately 38% of the benzenesulfonic acid remains from the UF / CeO2 microcapsules. Because there is no CeO2 to directly quench the radicals, the UF / CeO2 microcapsules are unable to slow the decomposition of benzenesulfonic acid, as evidenced by the low amount of benzenesulfonic acid remaining. As a result, more H2O2 is consumed. Therefore, the urea-formaldehyde (UF) shell slows the release of CeO2. Naturally, the thickness of the polymer shell can be varied to control the release of the antioxidant over time.

[0055] The preceding description is merely illustrative in nature and is not intended to limit the present disclosure, its application, or uses. As used herein, the phrase "at least one of A, B, and C" should be construed to mean the logical (A or B or C), using the non-exclusive logical "OR." It is understood that various steps within a method can be performed in different order without altering the principles of the present disclosure. The disclosure of ranges includes the disclosure of all ranges and subranges within the overall range.

[0056] Headings (such as "Background" and "Summary") and subheadings used herein are intended to provide a general overview of the topics in the disclosure only and are not intended to limit the disclosure of the technology or any aspect thereof. The description of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments including different combinations of the stated features.

[0057] As used herein, the terms "have" and "include" and variations thereof are intended to be open-ended, such as describing a series of items or a list, so as not to exclude other similar items that may be useful in the devices and methods of the technology. Similarly, the terms "can" and "may" and variations thereof are intended to be open-ended, so that a statement that an embodiment can or may have particular elements or features does not exclude other embodiments of the technology that do not include those elements or features.

[0058] As used herein, the term "about" in the context of the concentration of a formulation component typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0059] The broad teachings of the present disclosure can be implemented in a variety of forms. Thus, while the present disclosure includes specific examples, the true scope of the present disclosure should not be so limited, as other modifications will become apparent to those skilled in the art upon studying this specification and the following claims. Reference herein to an aspect, or various aspects, means that a particular feature, structure, or characteristic described in connection with an embodiment or a particular system is included in at least one embodiment or aspect. The appearance of the phrase "in one aspect" (or variations thereof) does not necessarily refer to the same aspect or embodiment. Also, it should be understood that the various method steps described herein need not be performed in the same order as depicted, and that not every method step is required in every aspect or embodiment.

[0060] The foregoing description of the embodiments has been provided for purposes of explanation and illustration. It is not intended to be exhaustive or to limit the present disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, may be interchangeable and used in selected embodiments even if not specifically shown or described. This may be modified in various ways. Such modifications should not be considered a departure from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. an anode including a first catalyst; a positive electrode including a second catalyst; a proton exchange membrane between the negative electrode and the positive electrode; A membrane electrode assembly having At least one of the proton exchange membrane, the negative electrode, and the positive electrode comprises an antioxidant comprising cerium oxide microparticles in a controlled release form selected from microcapsules or microspheres configured to release cerium oxide over time.

2. The cerium oxide antioxidant is in the form of microcapsules, the microcapsules comprising: a core containing cerium oxide microparticles; a polymeric shell surrounding the core, the polymeric shell having a predetermined thickness for controlling the release of the cerium oxide over time; The membrane electrode assembly of claim 1 ,

3. The cerium oxide antioxidant is in the form of microspheres, the microspheres comprising: comprising cerium oxide microparticles dispersed within a polymer matrix; 10. The membrane electrode assembly of claim 1, wherein the polymer is selected to control the release of the cerium oxide particulates over time.

4. 3. The membrane electrode assembly of claim 2, wherein the polymer shell or matrix is ​​selected from the group consisting of gelatin, chitosan, starch, gum arabic, rubber, albumin, cysteine, alginate, silk fibroin, wax, polycaprolactone, poly(methyl methacrylate), poly(lactic acid), poly(glycol alcohol), polyolefin, cellulose, melamine formaldehyde resin, urea-formaldehyde resin, polyurea-formaldehyde resin, phenol-formaldehyde resin, polyamide, polyurea, polyurethane, poly(urea-urethane), polyurethane / chitosan, polyester, polystyrene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU), polyether ketone (PEEK), and derivatives and combinations thereof.

5. 3. The membrane electrode assembly of claim 2, wherein the polymer shell has a thickness of about 50 nm to about 9 μm.

6. The membrane electrode assembly according to claim 1 , wherein the proton exchange membrane contains a perfluorosulfonic acid polymer.

7. 1. A polymer electrolyte membrane fuel cell (PEMFC) having a plurality of stacked membrane electrode assemblies (MEAs), A polymer electrolyte membrane fuel cell, wherein each of the plurality of MEAs comprises an MEA according to claim 1, and wherein the fuel cell has an operational life of at least 8000 hours.

8. a membrane electrode assembly having a proton exchange membrane, an anode including a first catalyst, and a cathode including a second catalyst, the proton exchange membrane being positioned between the anode and the cathode; a first microporous layer in contact with the negative electrode; a second microporous layer in contact with the positive electrode; a negative electrode diffusion layer in contact with the first microporous layer; a positive electrode diffusion layer in contact with the second microporous layer; a first flow path in contact with the negative electrode diffusion layer; a second flow path in contact with the positive electrode diffusion layer; A fuel cell having:

1. A fuel cell, wherein at least one of the proton exchange membrane, the anode, the cathode, the first microporous layer, and the second microporous layer comprises a cerium oxide antioxidant in a controlled-release form selected from microcapsules or microspheres configured to release cerium oxide over time.

9. At least one of the proton exchange membrane, the negative electrode, the positive electrode, the first microporous layer, and the second microporous layer comprises a cerium oxide antioxidant in the form of microcapsules, the microcapsules comprising: a core containing cerium oxide microparticles; a polymeric shell surrounding the core, the polymeric shell having a predetermined thickness for controlling the release of the cerium oxide over time; 9. The fuel cell of claim 8, wherein

10. At least one of the proton exchange membrane, the anode, the cathode, the first microporous layer, and the second microporous layer comprises a cerium oxide antioxidant in the form of microspheres, the microspheres comprising: comprising cerium oxide microparticles dispersed within a polymer matrix; 9. The fuel cell of claim 8, wherein the polymer is selected to control the release of the cerium oxide particulates over time.

11. 10. The fuel cell of claim 9, wherein the polymer shell is selected from the group consisting of gelatin, chitosan, starch, gum arabic, rubber, albumin, cysteine, alginate, silk fibroin, wax, polycaprolactone, poly(methyl methacrylate), poly(lactic acid), poly(glycol alcohol), polyolefin, cellulose, melamine formaldehyde resin, urea-formaldehyde resin, polyurea-formaldehyde resin, phenol-formaldehyde resin, polyamide, polyurea, polyurethane, poly(urea-urethane), polyurethane / chitosan, polyester, polystyrene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU), polyether ketone (PEEK), and derivatives and combinations thereof.

12. 10. The fuel cell of claim 9, wherein the polymer shell has a thickness of about 50 nm to about 9 μm.

13. 9. The fuel cell of claim 8, wherein the proton exchange membrane comprises a perfluorosulfonic acid polymer.

14. A vehicle comprising the fuel cell of claim 8.

15. 1. A method for inhibiting cerium ion migration in a proton exchange membrane fuel cell (PEMFC), comprising: The PEMFC includes a membrane electrode assembly having a proton exchange membrane, an anode including a first catalyst, and a cathode including a second catalyst, the proton exchange membrane including a perfluorosulfonic acid polymer, and positioned between the anode and the cathode; a first microporous layer in contact with the negative electrode; a second microporous layer in contact with the positive electrode; a negative electrode diffusion layer in contact with the first microporous layer; a positive electrode diffusion layer in contact with the second microporous layer; a first flow path in contact with the negative electrode diffusion layer; a second flow path in contact with the positive electrode diffusion layer; and The method comprises:

1. A method comprising: loading a predetermined amount of a cerium oxide antioxidant into a membrane electrode assembly in a controlled release form selected from microcapsules or microspheres configured to release cerium oxide over time.

16. The cerium oxide antioxidant is in the form of microcapsules, the microcapsules comprising: a core containing cerium oxide microparticles; a polymeric shell surrounding the core, the polymeric shell having a predetermined thickness for controlling the release of the cerium oxide over time; 16. The method of claim 15, comprising:

17. The cerium oxide antioxidant is in the form of microspheres, the microspheres comprising: comprising cerium oxide microparticles dispersed within a polymer matrix; 16. The method of claim 15, wherein the polymer is selected to control the release of the cerium oxide microparticles over time.

18. 17. The method of claim 16, wherein the polymeric shell is selected from the group consisting of gelatin, chitosan, starch, gum arabic, rubber, albumin, cysteine, alginate, silk fibroin, wax, polycaprolactone, poly(methyl methacrylate), poly(lactic acid), poly(glycol alcohol), polyolefin, cellulose, melamine formaldehyde resin, urea-formaldehyde resin, polyurea-formaldehyde resin, phenol-formaldehyde resin, polyamide, polyurea, polyurethane, poly(urea-urethane), polyurethane / chitosan, polyester, polystyrene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU), polyether ketone (PEEK), and derivatives and combinations thereof.

19. 17. The method of claim 16, wherein the polymer shell has a thickness of from about 50 nm to about 9 μm.

20. 16. The method of claim 15, wherein the proton exchange membrane comprises a perfluorosulfonic acid polymer.

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