Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
  • H01M8/2465—Details of groupings of fuel cells
  • H01M8/247—Arrangements for tightening a stack, for accommodation of a stack in a tank or for assembling different tanks
  • H01M8/248—Means for compression of the fuel cell stacks
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0258—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
  • H01M8/241—Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
  • H01M8/2465—Details of groupings of fuel cells
  • H01M8/2483—Details of groupings of fuel cells characterised by internal manifolds
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M2008/1095—Fuel cells with polymeric electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present disclosure relates to a fuel cell stack assembly in which the mechanism for securing the fuel cell stack in its compressed, assembled state includes a spring bar loading a disc spring at its inner diameter and a compression band which circumscribes the fuel cell stack assembly.
• Solid polymer electrochemical fuel cells generally employ a membrane electrode assembly ('MEA') consisting of a polymer electrolyte membrane ( 1 PEM') (or ion exchange membrane) disposed between two electrodes comprising porous, electrically conductive sheet material and an electrocatalyst disposed at each membrane/electrode layer interface to induce the desired electrochemical reaction.
• 'MEA' membrane electrode assembly
• 1 PEM' polymer electrolyte membrane
• electrocatalyst disposed at each membrane/electrode layer interface to induce the desired electrochemical reaction.
• the MEA is disposed between two electrically conductive separator or fluid flow field plates.
• Fluid flow field plates have at least one flow passage formed therein to direct the fuel and oxidant to the respective electrodes, namely, the anode on the fuel side and the cathode on the oxidant side.
• fluid flow field plates are provided on each of the anode and cathode sides. The plates also act as current collectors and provide mechanical support for the electrodes.
• Two or more fuel cells can be connected together in series to form a fuel cell stack to increase the overall voltage of the assembly.
• a fuel cell stack typically further includes manifolds and inlet ports for directing the fuel and the oxidant to the anode and cathode flow field passages respectively.
• the fuel cell stack also usually includes a manifold and inlet port for directing a coolant fluid, typically water, to interior passages within the fuel cell stack to absorb heat generated by the exothermic reaction in the fuel cells.
• the fuel cell stack also generally includes exhaust manifolds and outlet ports for expelling the unreacted fuel and oxidant gases, as well as an exhaust manifold and outlet port for the coolant stream exiting the fuel cell stack.
• the peripheral edge location of the tie rods in conventional fuel cell designs has inherent disadvantages. It requires that the thickness of the end plates be substantial in order to evenly transmit the compressive force across the entire area of the plate. Also, the peripheral location of the tie rods can induce deflection of the end plates over time if they are not of sufficient thickness. Inadequate compressive forces can compromise the seals associated with the manifolds and flow fields in the central regions of the interior plates, and also compromise the electrical contact required across the surfaces of the plates and MEAs to provide the serial electrical connection among the fuel cells which make up the stack. End plates of substantial thickness however, contribute significantly to the overall weight and volume of the fuel cell stack, which is particularly undesirable in motive fuel cell applications.
• each of the end plates must be greater in area than the stacked fuel cell assemblies.
• the amount by which the end plates protrude beyond the fuel cell assemblies depends on the thickness of the tie rods, and more importantly on the diameter of the washers, nuts and any springs threaded on the ends of tie rods, since preferably these components should not overhang the edges of end plate.
• the use of external tie rods can increase stack volume significantly.
• the fuel cell stack compression mechanisms described above typically utilize springs, hydraulic or pneumatic pistons, pressure pads or other resilient compressive means which cooperate with the tie rods, which are generally substantially rigid, and end plates to urge the two end plates towards each other to compress the fuel cell stack. These compression mechanisms undesirably add weight and/or volume and complexity to the fuel cell stack.
• Tie rods typically add significantly to the weight of the stack and are difficult to accommodate without increasing the stack volume.
• the associated fasteners add to the number of different parts required to assemble a fuel cell stack.
• Disc springs are conventionally contacted over their inner diameter under load.
• National Disc Springs catalogue and manual of the Rolex Company National Disc Spring Division of 385 Hillside Avenue, Hillside N.J. teaches that such disc springs should contact the load imposing surface with the disc spring's outer diameter.
• loading the disc spring by the outer diameter requires a greater amount of material to load the outer diameter resulting in greater weight and volume, increased cost of material, and reduced power density and efficiency, especially in automotive applications.
• a fuel cell stack assembly comprising: a first end plate; a second end plate; a plurality of fuel cells interposed between the first and second end plates, a first spring bar; a second spring bar; a first disc spring having an inner and outer diameter, interposed between the first end plate and the first spring bar, wherein the first spring bar loads the first disc spring at the first spring bar's inner diameter; a second disc spring having an inner and outer diameter, interposed between the second end plate and the second spring bar, wherein the second spring bar loads the second disc spring at the second spring bar's inner diameter; and a compression band circumscribing the first spring bar, the second spring bar, the plurality of fuel cells, the first end plate and the second end plate, the compression band urging the first spring bar toward the second spring bar, thereby applying compressive force upon the plurality of fuel cells.
• a fuel cell stack assembly comprising: a first end plate; a second end plate; a plurality of fuel cells interposed between the first and second end plates; a spring bar; a disc spring having an inner and outer diameter, interposed between the first end plate and the spring bar, wherein the spring bar loads the disc spring at the disc spring's inner diameter; and a compression means urging the spring bar toward the first end plate and second end plate, thereby applying compressive force upon the plurality of fuel cells.
• the end plate may be adapted to receive a disc spring.
• Figure 1 is a partially exploded perspective view of a prior art fuel cell stack.
• Figure 2 is a perspective view of a prior art fuel cell stack.
• Figure 3 is a side cross-sectional view of a prior art end plate assembly.
• Figure 4B is a side cross-sectional view of fuel cell stack according to another embodiment.
• Figure 5 is a partial perspective view of fuel cell stack according to one embodiment.
• Figure 6 is a perspective view of fuel cell stack according to one embodiment.
• Figure 8A is a side cross-sectional view of spring bar according to another embodiment.
• Figure 8B is a bottom view of spring bar according to one embodiment.
• Figure 8C is a perspective view of spring bar according to one embodiment.
• FIG. 1 illustrates a prior art fuel cell stack assembly 10, including a pair of end plates 15, 20 and a plurality of fuel cells 25 interposed therebetween.
• Tie rods 30 extend between end plates 15 and 20 to retain and secure fuel cell stack assembly 10 in its assembled state with fastening nuts 32.
• Springs 34 on the tie rods 30 interposed between the fastening nuts 32 and the end plate 20 apply resilient compressive force to the stack of fuel cells 25 in the longitudinal direction.
• Reactant and coolant fluid streams are supplied to and exhausted from internal manifolds and passages in the fuel cell stack assembly 10 via inlet and outlet ports (not shown) in end plate 15.
• Each fuel cell 25 includes an anode flow field plate 35, a cathode flow field plate 40, and MEA 45.
• End plate 35 has a plurality of fluid flow passages 35a formed in its major surface facing MEA 45.
• Figure 2 illustrates a prior art fuel cell stack assembly 110 including end plate assemblies 115 and 120 and a plurality of fuel cells 125 interposed between end plate assemblies 115, 120.
• Compression bands 130 extending tightly around the end plate assemblies 115, 120 and fuel cells 125 retain and secure fuel cell stack assembly 110 in its assembled state.
• End plate assemblies 115, 120 preferably have rounded edges 115a, 120a to reduce the stress on compression band 130.
• a person of ordinary skill in the art may choose to employ one or a plurality of disc springs. Where a single disc spring 450 is employed, it is arranged such that spring bar 440 loads the disc spring 450 at its inner diameter while the outer diameter contacts end plate 414. A plurality of disc springs may be employed to achieve a desired combined spring constant or spring travel. Where a plurality of disc springs is employed in the form of a spring stack, the disc springs may be arranged such that the outermost disc spring in the spring stack is loaded by the spring bar 440 by the outermost disc spring's inner diameter.
• FIG. 4B shows a cross section of fuel cell stack assembly 410b where a single disc spring 450a is employed at one end whereas three disc springs 450b-450d are employed at the opposite end.
• the spring bar 440 By loading disc spring 450a, 450b by spring bar 440 at the inner diameter 451 a, 451 b of the disc spring 450, the spring bar 440 is not required to have a width sufficient to span the outer diameter 452a, 452b of the disc spring 450a, 450b. That is, spring bar 440 may be made narrower than the outer diameter 452a, 452b of the disc spring 450a, 450b. By comprising less width and therefore, less material, spring bar 440 may be made resiliently flexible to further provide biasing properties to the assembly, improving sealing and electrical contact between the individual fuel cells 425. Furthermore, the lightweight and compact structure reduces the overall weight and volume of the fuel cell stack assembly increasing efficiency, cost and power density. For example, Figure 5 shows end plate 414, spring bar 440, disc spring 450a and compression band 430 where spring bar 440 is deflected under the compressive load.
• Spring bar 440 may be made of any suitable material including aluminum, steel, plastics and composite fiber based material such as Kevlar ® . Where it is desirable for spring bar 440 to be resilient to deflection, as described above, spring bar 440 may similarly be made of aluminum, steel, plastics and composite fiber based material such as Kevlar ® . A person of ordinary skill in the art may select an appropriate material for the spring bar 440. Spring bar 440 may be made by any suitable method known in the art including, for example, casting, machining and injection molding.
• the fuel cell stack assembly may be configured with one or a plurality of compression bands circumscribing the fuel cell stack.
• disc springs and corresponding spring bars may be employed at one end or both ends of the fuel cell stack assembly.
• a person of ordinary skill in the art may readily choose the appropriate number of compression bands, disc springs and spring bars for a particular application.
• Figure 6 illustrates another embodiment of fuel cell stack assembly 410c where a plurality of compression bands 430a, 430b, spring bars 440a, 440b and disc springs 450a, 45Oe are employed.
• a compression means may be a band formed from rolled stainless steel (for example, 301 grade, 0.025 inch thickness, 2.5 inch width, tensile strength 26,000 psi) strapping, which is pre-welded to the desired length (circumference).
• a compression means is made of an electrically conductive or semi conductive material, strips of electrically insulating material (not shown) may be interposed between compression means and the edges of the fuel cells.
• the ends of the compression means may be joined after it is wrapped around the stack, in which case, to ensure a tight fit, it may be again desirable to over-compress the stack in a fixture until one or more bands are fitted. If the length of compression means is adjustable, it may be fitted and subsequently tightened.
• the longitudinal dimension of the stack can vary, even for a fixed stack design, due to slight differences in the thicknesses of stack components. Also, during use the longitudinal dimension of the stack tends to change. In some cases, for example if the length of compression band is not readily adjustable, it may be desirable to use spacer layers to increase the stack length, for example, during initial stack assembly and/or after prolonged use. This approach can be used to ensure that the desired compressive force is applied to the stack, without the need to prepare and inventory compression bands of many slightly differing lengths.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Fuel Cell (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

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Cited By (1)

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Citations (6)

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• 2007
  • 2007-12-20 US US11/961,883 patent/US20090162726A1/en not_active Abandoned
• 2008
  • 2008-12-16 WO PCT/US2008/087038 patent/WO2009085776A1/en not_active Ceased
  • 2008-12-16 EP EP08867837.0A patent/EP2232623B1/en not_active Not-in-force
  • 2008-12-16 JP JP2010539713A patent/JP5468551B2/ja not_active Expired - Fee Related
  • 2008-12-16 CN CN2008801220336A patent/CN101904039B/zh not_active Expired - Fee Related

Patent Citations (6)

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