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Integrally molded gasket for a fuel cell assemblyRelated Patent Categories: Chemistry: Electrical Current Producing Apparatus, Product, And Process, Fuel Cell, Subcombination Thereof Or Methods Of Operating, Catalytic Electrode Structure Or Composition, Having An Inorganic Matrix, Substrate Or SupportIntegrally molded gasket for a fuel cell assembly description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070003821, Integrally molded gasket for a fuel cell assembly. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention generally relates to fuel cells. More particularly, the present invention relates to an integrally molded gasket seal for a fuel cell membrane electrode assembly. BACKGROUND OF THE INVENTION [0002] Electrochemical fuel cells facilitate chemical reactions between hydrogen and oxygen to generate electrical current. The chemical reactions take place in one or more membrane electrode assemblies ("MEA"). Each MEA typically includes an ion exchange membrane disposed between two electrodes, which are also referred to as gas diffusion layers. Between each electrode and the membrane is a catalyst, the location of which defines an electrochemically active area of the MEA. [0003] One electrode functions as a cathode and the other electrode functions as an anode. Typically, hydrogen is supplied to the anode and oxygen is supplied to the cathode. The hydrogen and oxygen are directed to the electrodes in separate manifolds. [0004] The membrane acts as a barrier to isolate the hydrogen and oxygen to prevent short-circuiting of the MEA. The membrane restricts passage of oxygen and hydrogen, but permits protons to pass between the anode and the cathode. In many MEA's, the membrane extends laterally beyond the perimeter of each electrode layer. Extending the membrane beyond the two electrodes helps to prevent passage of oxygen and hydrogen between the electrodes at the perimeter edges of the electrodes, which can short-circuit the MEA. [0005] To further isolate the hydrogen and oxygen molecules, a gasket seal is provided around the perimeter edge of the electrodes and over the portion of the membrane that extends beyond the electrodes. To enhance the effectiveness of the seal, the seal is impregnated within the electrodes, which are typically porous and have a uniform density. The seal is made of an elastomeric material and can include multiple beads or protrusions to further increase the effectiveness of the seal. [0006] In operation, hydrogen gas (H.sub.2) supplied to the anode reacts with the catalyst to split the H.sub.2 molecule into two H.sup.+ ions and two electrons. The electrons are conducted via the anode to an external circuit to provide current to the circuit that can be used for a variety of purposes, such as to power and turn a motor. The circuit next directs the electrons to the cathode side of the fuel cell. [0007] Simultaneously, oxygen gas (O.sub.2) supplied to the cathode reacts with the catalyst to form two oxygen atoms. Each of the oxygen atoms have a strong negative charge. This negative charge attracts the H.sup.+ ions through the membrane. The H.sup.+ ions combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule (H.sub.2O). [0008] A single MEA produces only a small voltage. To increase the amount of voltage produced, multiple MEAs are often combined in a fuel cell stack in a manner that is commonly known in the art. The multiple MEA's are typically separated by flow field plates, which are commonly referred to as separator plates. [0009] While existing MEAs are suitable for their intended use, they are subject to improvement. For example, portions of the elastomeric seal sometimes enter the MEA active area during the manufacturing process as the elastomer is impregnated within the MEA. The presence of elastomer in the active area is undesirable because it restricts movement of gases and other particles in the active area, thereby decreasing the effective size of the active area and decreasing the efficiency of the fuel cell. Therefore, there is a need for a device and method that prevents portions of the seal from entering the active area during the impregnation process. [0010] Existing MEA's also experience problems due to the size of the gasket seal or the distance that the seal extends above or below the MEA. For example, if the seal is too large and thus protrudes too far above or below the MEA then the seal will not properly fit between the MEA and the neighboring separator plates of a fuel cell stack. Further, such large seals exert more stress on the seal/MEA interlock than smaller seals due to numerous factors, such as their volume and increased exposure to outside forces that can highly strain the seal, thus making it more likely that larger seals, rather than smaller seals, will become detached from the MEA or damage the MEA. Still further, larger seals may permit more hydrogen permeation as compared to smaller seals. On the other hand, larger seals are more effective than smaller seals at preventing gross leakage from the MEA into the surrounding environment. Thus, there is a need for a seal that realizes the advantages associated with both large and small seals, while at the same time overcomes the disadvantages of each. SUMMARY OF THE INVENTION [0011] The present invention provides for a fuel cell membrane electrode assembly (MEA) comprising first and second gas diffusion layers and an ion exchange membrane disposed between the diffusion layers. Each diffusion layer includes an inner surface facing the membrane, an outer surface opposite the inner surface, and a side surface defining a perimeter of the diffusion layers. An outboard region extends about the diffusion layers at the perimeter. The outboard region surrounds an inboard region. The outboard region has a low density region proximate to the side surface and a high density region between the low density region and the inboard portion. A seal is mounted at the low density region. The high density region prevents portions of the seal from entering the inboard region during the manufacturing process, thereby damaging the MEA. [0012] Another aspect of the invention provides for a fuel cell membrane assembly having a first gas diffusion layer, a second gas diffusion layer, an ion exchange membrane disposed between the first and second gas diffusion layers, and a seal. Each one of the first and second gas diffusion layers include the following: an inner surface facing the ion exchange membrane; an outer surface opposite the inner surface; and a side surface between the outer surface and the inner surface defining a perimeter of the first and the second layers respectively. The seal has a first rim integral with a second rim. The first rim is mounted to the outer surface and the side surface of each of the first layer and the second layer. The second rim is laterally offset from the first and the second layers. The seal impregnates the first gas diffusion layer and the second gas diffusion layer to provide a barrier between the first and the second gas diffusion layers that is at least substantially impermeable to gas. The first rim has a smaller volume than the second rim. [0013] A further aspect of the invention provides for a first support plate, a second support plate, and a membrane electrode assembly positioned between the first support plate and the second support plate. The membrane electrode assembly includes a first electrode, a second electrode, an ion exchange membrane, and a seal. The first electrode is adjacent to the first support plate. The second electrode is opposite the first electrode and adjacent the second support plate. The ion exchange membrane is disposed between the first electrode and the second electrode. Each one of the first electrode and the second electrode include: an inner surface facing the ion exchange membrane; an outer surface opposite the inner surface, the outer surface of the first electrode faces the first support plate and the outer surface of the second electrode faces the second support plate; a side surface between the outer surface and the inner surface defining a perimeter of the first and the second electrodes respectively; an outboard region extending about a periphery of each of the first electrode and the second electrode at the perimeter; and an inboard region at least substantially surrounded by the outboard region. The outboard region includes a low density region proximate to the side surface and a high density region that is inboard of, and adjacent to, the low density region. The seal impregnates the low density region of the outboard region to provide a barrier between the first and the second gas diffusion layers that is at least substantially impermeable to gas. [0014] Yet an additional aspect of the invention provides for a method for manufacturing a fuel cell membrane electrode assembly having an ion exchange membrane affixed between a first gas diffusion layer and a second gas diffusion layer. The method comprises the following steps: positioning the first and the second gas diffusion layers between two halves of a thermo-mold assembly, each mold half having a protruding region that mirrors the location of a high density region to be formed in the first and second gas diffusion layers at an outboard region that extends about a periphery of the first and second diffusion layers; closing the mold halves under heat such that the protruding regions of the mold halves compress the first and the second diffusion layers at the high density regions to increase the density of the first and second diffusion layers at the high density regions; injecting an elastomeric material that is heated to a liquid within a cavity of the closed mold, the cavity located about the periphery of the membrane electrode assembly at a low density region that is outboard of the high density region, the liquid elastomer flows within the first and second diffusion layers at the low density region; and curing the liquid elastomeric material to form an elastomeric seal that is impregnated within the first and second diffusion layers at the low density region and extends around side surfaces at the periphery of the first and second diffusion layers. [0015] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0016] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: [0017] FIG. 1 is an exploded perspective view of a fuel cell assembly according to the teachings of the present invention comprising a membrane electrode assembly (MEA) disposed between two support plates; [0018] FIG. 2 is a perspective view of the MEA of FIG. 1; [0019] FIG. 3 is an exploded view of the MEA of FIG. 1 illustrated without the gasket seal for clarity; and [0020] FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2. 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