In the figures, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the figures are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve figure legibility. Further, the particular shapes of the elements, as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the figures.
Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including but not limited to”.
The present invention is generally related to bipolar plates for fuel cells, such as phosphoric acid fuel cells, solid oxide fuel cells, and, in particular, polymer electrolyte membrane fuel cells. The present bipolar plates may also be employed in electrolyzers having an electrode assembly structure.
Referring to
Anode and cathode frames 16,18 are provided with manifold openings for the supply of reactants and exhaust of reaction products, as well as the supply and exhaust of coolant; namely, fuel supply manifold opening 40 and fuel exhaust manifold opening 42, oxidant supply manifold opening 44 and oxidant exhaust manifold opening 46, and coolant supply manifold opening 48 and coolant exhaust manifold opening 50.
In the case of metallic bipolar flow field plates, the flow field plates are typically joined by welding around the manifold openings and the flow field area. However, crevice corrosion may occur at the exposed weld joints during fuel cell operation, particularly in the manifold openings. By forming the manifold openings in the frames, welding of the metallic plates is not necessary, thereby reducing or eliminating crevice corrosion. One of ordinary skill in this field will understand that the manifold openings may be appropriately sized and at any number of positions, and thus the manifold openings are limited to the sizes and positions shown in any of the figures.
In addition, each of anode and cathode frames 16,18 may further contain a manifold seal groove 54 on their respective active surfaces. Manifold seal groove 54 is adaptable for receiving elastomeric and/or compressible seals that provide a gas-tight seal around when in contact with an electrode assembly (not shown) and/or with corresponding manifold openings of adjacent flow field plates (not shown).
Furthermore, anode and cathode frames 16,18 may include adhesive seal grooves 58 on their respective inactive surface around the circumference of anode and cathode flow field plates 12,14 and/or around the manifold openings for receiving adhesive for gluing the anode and cathode frames together to form a sealed bipolar flow field plate assembly. In some embodiments, seal grooves 58 have a complex cross-sectional shape, such as that described in U.S. Pat. No. 6,777,127. In further embodiments, adhesive seal grooves 58 may be omitted from one or both of the anode and cathode frames and/or the inner frame(s), as desired. In further embodiments, manifold seal grooves 54 and/or adhesive seal grooves 58 may be omitted from one or both of the anode and cathode frames and/or the inner frames, as desired.
Any suitable adhesive may be used for attaching anode and cathode frames 16,18 to peripheral edges 28 of anode and cathode flow field plates 12,14, and/or for attaching anode and cathode inner frames 20,22 to peripheral edges 28 of anode and cathode flow field plates 12,14. Suitable adhesives are compatible in the frame and plate materials employed, and are stable under fuel cell operating conditions. For example, in polymer electrolyte membrane fuel cell applications, an epoxy (e.g., acrylic-based or cyanoacrylic-based) may be used to join anode frame 16 to anode flow field plate 12, anode inner frame 20 to anode flow field plate 12, cathode frame 18 to cathode flow field plate 14, and/or cathode inner frame 22 to cathode flow field plate 14. Likewise, any suitable adhesive may be used for attaching the inactive surface of anode frame 16 to the inactive surface of cathode frame 18 and, thus, attaching anode plate assembly 30 to cathode plate assembly 36.
An adhesive may also be applied around each of the manifold openings of the anode and cathode frames to prevent leakage of the reactant and product fluids, as well as the coolant fluid, when attaching anode plate assembly 30 to cathode plate assembly 36. In one embodiment, and adhesive is used to adhesively attach the components to form a sealed anode or cathode plate assembly, and/or a sealed bipolar flow field plate. A person of ordinary skill in this field may readily select a suitable adhesive material for a this application.
In addition, anode and cathode flow field plates 12,14 further comprise a plurality of through-holes 76 as shown in
As shown in
While port 60 is shown as perpendicular with respect to active surface 24, port 60, as well as any of ports 62, 64, and/or 66, may be angled as described in, for example, U.S. Pat. No. 6,232,008.
In the embodiment illustrated in
In one embodiment, anode frame 16 and anode inner frame 20 are provided with fluid ports 60,62, while cathode frame 18 and cathode inner frame 22 are provided with fluid ports 64,66. Inner frames 20,22 may also contain transition flow fields 74 (which are out of view in
By forming the manifold openings in manifold frame 78, a very smooth surface is provided around inner perimeter 80 of manifold openings 40,42,44,46,48,50, and may eliminate the need for glue joints at the edges of the manifold openings. In some applications, this may assist in reducing or preventing any accumulation of water therein, thereby avoiding problems related to the freezing of water at subzero temperatures and the associated problems of cold temperature fuel cell start-up. Furthermore, manifold frame 78 may be formed with features in the manifold openings that aid in the delivery and/or removal of the reactant and product fluids, as well as the coolant fluids to and/or from the manifold openings. Although
In any of the above embodiments, anode and cathode flow field plates 12,14 may be a metallic material that has high electrical and thermal conductivity, as well as high corrosion and chemical resistance, and is compatible with the operating environment within the fuel cell. For example, the anode and cathode flow field plates may be a composite material that has a metallic or polymeric layer on the surface of a metal substrate, such as a metal carbide, metal nitride, or metal oxide, on a stainless steel or aluminum substrate. Alternatively, the anode and cathode flow field plates may comprise a metal substrate that has been surface-treated to provide high corrosion resistance and high electrical and thermal conductivity. Again, although a certain materials have been described above, it should be understood that the selection of a particular material for the flow field plate is not essential to the present invention, as a person of ordinary skill in the art will be able to select a suitable material for a given application.
In any of the above embodiments, anode and cathode frames 16,18 and anode and cathode inner frames 20,22 are a rigid, electrically-insulating material, such as a thermoplastic or a thermoset that can withstand the operating conditions of the fuel cell. In some embodiments, the rigid, electrically-insulating material is an engineered plastic with a low coefficient of thermal expansion, high chemical stability, and high temperature resistance such as, for example, Lexan® and Ultem®. Preferably, the frames should be thin, for example, less than 50 microns, to minimize the thickness of the flow field plate.
All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety.
While particular elements, embodiments, and applications of the present invention have been shown and described, it will be understood that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings.