Abstract:
A spirally-wound fuel cell assembly is disclosed. The spirally-wound fuel cell assembly includes an enclosure. Multiple cell assemblies are disposed in electrical contact with each other and provided in the enclosure. Each of the cell assemblies has at least one membrane electrode assembly including a negative electrode, a positive electrode and a proton conductive membrane sandwiched between the negative electrode and the positive electrode. An oxidant channel is provided in each of the cell assemblies for receiving an oxidant gas. A fuel gas pathway is defined around the cell assemblies for receiving a fuel gas. A method of fabricating a fuel cell assembly is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fuel cells. More particularly, the present invention relates to a spirally-wound fuel cell assembly which has a high operational efficiency and occupies a relatively small volume. 
     BACKGROUND OF THE INVENTION 
     Fuel cell technology potentially provides clean and efficient energy for stationary and traction applications. In order to be amenable to common usage, a fuel cell is best implemented in a form which provides reasonably high reaction efficiency near ambient temperatures, preferably below 100 degrees Celsius. However, the state-of-the-art of catalyst and membrane technology requires substantial working area between the electrodes to achieve commercially useful current at a reasonable potential at these temperatures. Current art commonly specifies large, flat electrodes to achieve the high surface area; however, this implementation requires precision-made plates, large rectangular seals, and complex reagent flow fields in order to function. These designs lead to a high-cost product with low reliability. 
     One known technique for improving the used surface area per unit volume of a fuel cell involves spirally winding the electrode assembly of the fuel cell. However, this technique does not include a mechanism to separate the fuel gas from the oxidizer, which is a necessary element for safe and efficient operation of the fuel cell. The technique presumes that the combustible fuel and oxidizer streams leading into the fuel cell are mixed prior to being introduced to a catalytic surface. Moreover, the technique does not afford a method for control over the fuel-oxidizer-inerts mixture, which changes dynamically throughout discharge. 
     One method used in the production of high surface area electrodes in commercially viable packages involves spirally winding the electrode elements around a core mandrel, which often also serves as one of the terminals. While this is a common and easily automated technique used in the commercial battery industry, the nature of fuel cells is such that active material immobilization (a presumption of wound electrodes) is not possible. Moreover, the typically low efficiency of the fuel cell reactions generates an additional requirement that the substantial quantity of waste heat due to polarization be removed. 
     Therefore, a spirally-wound fuel cell assembly which has high operational efficiency and occupies a relatively small volume of space is needed. 
     SUMMARY OF THE INVENTION 
     The present invention is generally directed to a spirally-wound fuel cell assembly. The spirally-wound fuel cell assembly includes an enclosure and multiple cell assemblies disposed in electrical contact with each other in the enclosure. Each of the cell assemblies has at least one membrane electrode assembly including a negative electrode, a positive electrode and a proton conductive membrane sandwiched between the negative electrode and the positive electrode. An oxidant channel is provided in each of the cell assemblies for receiving an oxidant gas. A fuel gas pathway is defined around the cell assemblies for receiving a fuel gas. 
     The present invention is further directed to a method of fabricating a fuel cell assembly. The method includes providing a mandrel tube for receiving a fuel gas, providing multiple cell assemblies each having at least one membrane electrode assembly and an oxidant channel defined by the membrane electrode assembly or assemblies for receiving an oxidant gas, forming a fuel gas pathway around the cell assemblies by winding the cell assemblies around the mandrel tube, and establishing fluid communication between the mandrel tube and the cell assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an illustrative embodiment of a spirally-wound fuel cell assembly according to the present invention; 
         FIG. 2  is a longitudinal sectional view of the spirally-wound fuel cell assembly shown in  FIG. 1 ; 
         FIG. 3  is a sectional view of a portion of an electrode assembly component of the spirally-wound fuel cell assembly; 
         FIG. 4  is a side perspective view of a portion of the electrode assembly; 
         FIG. 5  is an edge perspective view of a portion of the electrode assembly; and 
         FIG. 6  is a perspective view of multiple electrode assemblies rolled and connected to each other in the spirally-wound fuel cell assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, an illustrative embodiment of the spirally-wound fuel cell assembly according to the present invention is generally indicated by reference numeral  36 . As shown in  FIG. 2 , the spirally-wound fuel cell assembly  36  includes multiple cell assemblies  18  which are physically and electrically connected to each other in a layered configuration and rolled in a generally cylindrical configuration. As shown in  FIG. 3 , each cell assembly  18  includes a pair of membrane electrode assemblies (MEAs)  17  which are connected to each other at multiple depressions  4  along the cell assembly  18 , as further shown in  FIGS. 4 and 5 . As shown in  FIG. 3 , each MEA  17  includes a porous, chemically inert conductive layer  2  which serves as a negative electrode or cathode in the spirally-wound fuel cell assembly  36 . The negative electrode  2  has a high aspect ratio and is coiled to form multiple trough surfaces  1  and depressions  4 , as shown in  FIGS. 3-5 . A porous, chemically inert conductive layer  11 , which serves as a positive electrode or anode in the spirally-wound fuel cell assembly  36 , matches the outer bounds of the depressions  4  and is coined to nest with the trough surfaces  1  of the negative electrode  2 . 
     A negative catalyst layer  3  is coated on the negative electrode  2 . The negative catalyst layer  3  may be electrodeposited, deposited using chemical vapor deposition (CVD), painted or otherwise provided on the negative electrode  2 . A positive catalyst layer  10  is coated on the positive electrode  11 . The positive catalyst layer  10  may be electrodeposited, deposited using chemical vapor deposition (CVD), painted or otherwise provided on the positive electrode  11 . A proton-conductive membrane  14  is sandwiched between the negative catalyst layer  3  on the negative electrode  2  and the positive catalyst layer  10  on the positive electrode  11 . In formation of each MEA  17 , the negative electrode  2 , the negative catalyst layer  3 , the proton-conductive membrane  14 , the positive catalyst layer  10  and the positive electrode  11  are pressed and bonded together according to techniques which are known by those skilled in the art. 
     In each cell assembly  18 , two of the MEAs  17  are juxtaposed in such a manner that the MEAs  17  are joined to each other at the depressions  4 . Between the depressions  4 , the MEAs  17  are spaced-apart from each other to form an oxidant channel  12 . As shown in  FIG. 3 , at each depression  4 , the MEAs  17  are joined to each other along an abutting surface  9 , by any suitable technique such as welding or riveting, for example. As shown in  FIG. 2 , adjacent cell assemblies  18  are physically and electrically attached to each other in a layered configuration in the spirally-wound fuel cell assembly  36 , at a physical/electrical interface  16  between the trough surfaces  1  of the adjacent cell assemblies  18 . The depression surface  5  of each depression  4  may be punched through to form a gas flow opening (not shown) to permit the flow of a fuel gas directly from one side to the other side of each cell assembly  18 . The short ends (not shown) of each cell assembly  18  are taper-pinched closed. 
     As shown in  FIG. 3 , at each long end of each cell assembly  18 , a spacer  8 , having a gas passage  7 , is provided between the positive electrodes  11  of the MEAs  17  to secure the MEAs  17  in the cell assembly  18 . Each spacer  8  forms a conductive interface  6 , allows the passage of oxidant gases via the gas passage  7 , and maintains the desired spacing between the MEAs  17 . Each spacer  8  may be perforated and stamped metal, cast metal, a metalized porous ceramic or a high-porosity open-cell metal foam, for example. 
     As shown in  FIG. 2 , a cathode tube  19 , which is a conductive metal strip, is inserted between the spacer  8  and the positive electrode  11  of each cell assembly  18  to serve as a positive current collection tab, with electrical contact being provided at an electrical contact  19   a . The cathode tube  19  may be welded or otherwise attached to the surface of the positive electrode  11 . 
     As shown in  FIGS. 2 and 6 , in the spirally-wound fuel cell assembly  36 , a non-conductive elastomer seal  15  is provided between the long ends of adjacent cell assemblies  18 , with a sealing surface  15   a  provided between each elastomer seal  15  and each cell assembly  18 . The connected cell assemblies  18  are rolled around a conductive, close-ended perforated mandrel tube  25 , the open end of which is connected to a fuel source (not shown). Vent openings  26  are provided along the length of the mandrel tube  25  to permit the flow of a fuel gas from the interior to the exterior of the mandrel tube  25 , thereby forming a fuel gas pathway  13  between and on the outsides of the physically and electrically connected cell assemblies  18 . Optionally, a boss (not shown) may be added to the mandrel tube  25  to provide additional assembly robustness. The innermost cell assembly  18  is electrically connected to the mandrel tube  25  at multiple points of electrical contact  28 . The electrical contacts  28  are maintained by either winding pressure or by application of a weld at the electrical contacts  28 . The exterior surface of the mandrel tube  25  may be coated with an insulating polymer  25   a  to reduce the possibility of a short circuit. 
     As shown in  FIGS. 1 and 2 , the layered and rolled cell assemblies  18  are inserted into a cylindrical, open-ended enclosure  21 , which may be a non-conductive material such as high-density polyethylene, for example. The closed negative end of the enclosure  21  accommodates the mandrel tube  25 . The opposite, open end of the enclosure  21  is provided with an oxidizer delivery tube  30 . Additionally, the enclosure  21  may be provided with oxidant exhaust openings  23  or may be fitted with a dedicated oxidant exhaust tube (not shown). As shown in  FIG. 2 , annular fuel vents  24  and a concentric flexible tube  29  may be provided on the exterior of the enclosure  21  to provide a one-way valve, and thus, facilitate purging or circulation of the fuel gas stream. 
     After insertion of the layered, rolled and connected cell assemblies  18  in the enclosure  21 , the cathode tubes  19  are formed into a cathode tab bundle  20 . As shown in  FIG. 1 , the oxidizer delivery tube  30  is typically fitted to a cap  22 , which is preferably an insulating material, to close the open end of the enclosure  21 . The cap  22  is attached to the open end of the enclosure  21  typically along an annular weld  27 , thereby ensuring that the cathode tab bundle  20  is inserted through the interior of the oxidizer delivery tube  30 . The cathode tab bundle  20  may be welded or otherwise attached to the interior of the delivery tube  30 . As shown in  FIG. 2 , the enclosure  21  may be a conductive material such as nickel-coated mild steel to increase electrical connectivity via a friction fit  28   a , provided that the cap  22  is formed of an insulating material or provided that the cap  22  and enclosure  21  are separated from each other by a gas-sealing and electrically-insulating material (not shown). The oxidizer delivery tube  30  is an electrically conductive material and is connected to an oxidizing gas source (not shown). 
     In use of the invention, the spirally-wound fuel cell assembly  36  is capable of automotive or stationary applications. The mandrel tube  25  is connected to a fuel gas source (not shown) which contains a fuel gas  38  such as hydrogen. The oxidizer delivery tube  30  is connected to an oxidant gas source (not shown) which contains an oxidant gas  40 , such as oxygen, for example. The fuel gas  38  flows from the fuel gas source and through the mandrel tube  25  and the vent openings  26 , respectively, where the fuel gas  38  contacts the negative electrode  2  ( FIG. 3 ) on the innermost cell assembly  18 . Some of the fuel gas  38  flows beyond the innermost cell assembly  18  progressively to the outer cell assemblies  18  in the spirally-wound fuel cell assembly  36 , typically through the fuel gas openings (not shown) provided in the depression surfaces  5  ( FIG. 3 ) of each cell assembly  18 . Simultaneously, the oxidant gas  40  flows from the oxidant gas source (not shown), through the oxidizer delivery tube  30  and into the oxidant channels  12  of each cell assembly  18  through the spacer  8  of each cell assembly  18 . Because the oxidant channels  12  of each cell assembly  18  are connected to each other around the depressions  4 , the oxidant gas is able to flow freely throughout the oxidant channels  12  or each cell assembly  18 . 
     At each cell assembly  18 , the fuel gas  38  flows through the porous negative electrode  2  and contacts the negative catalyst layer  3  on the negative electrode  2 . At the negative catalyst layer  3 , the typically hydrogen fuel gas is split into protons and electrons. The electrons are distributed through an external circuit (not shown), which typically drives an electric motor (not shown), and return to the positive catalyst layer  10  on the positive electrode  11 . The protons flow from the negative catalyst layer  3 , through the proton conductive membrane  14  and to the positive catalyst layer  10 . 
     At the positive catalyst layer  10 , the electrons returning from the external circuit are joined with the protons from the proton conductive membrane  14  to form exhaust water. The unreacted oxidant gas  40  distributes the exhaust water from the oxidant channels  12 , through the gas passages  7  at the exhaust end of the cell assemblies  18 . The unreacted oxidant gas  40  and the exhaust water are discharged from the spirally-wound fuel cell assembly  36  through the oxidant exhaust openings  23  of the enclosure  21 . 
     It will be appreciated by those skilled in the art that the spirally-wound fuel cell assembly  36  of the present invention is amenable to efficient fabrication since the fuel cell assembly operations include easily-automated steps. The cell component materials are well-known in the art and in conventional manufacturing disciplines. The spirally-wound fuel cell assembly incorporates a large electrode surface area in a relatively small volume. The spiral configuration of the cell assemblies are retained in a cylindrical enclosure, which has excellent shape retention under internal isostatic pressure. 
     The flow resistance for the oxidant gas feed is low due to massively parallel cross-current pathways. This provides a uniform and high oxidizer concentration and the ability to use associated inerts to cool the fuel cell. The oxidant gas pathway may be tuned for optimum water management through changes to the flow resistance of the spacers. Electrical pathways are maximized without an increase in the gas flow resistance. The construction of the cell assemblies allows for simple scale-up of voltage through a series connection of multiple cells or current through an increase in surface area of the electrodes. Kinetic resistance due to diffusion through ancillary structures (i.e. GDL) is minimized. If non-conductive active materials are used, a common manifold may be used to allow series voltage. The fuel cell concept is easily optimized through any combination of component dimensions. 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.