Abstract:
High power density generators are formed with a flexible multi-layered structure. The structure includes a fuel layer with a separate fuel cell stack adjacent to each side of the fuel layer. The structure can be flexible and formed into a variety of shapes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of U.S. patent application Ser. No. 11/257,738 filed Oct. 25, 2005 now U.S. Pat. No. 7,811,690 entitled “Proton Exchange Membrane Fuel Cell” and U.S. patent application Ser. No. 11/270,848 filed Nov. 9, 2005 now U.S. Pat. No. 7,901,816 entitled “Water Reclamation In A Micropower Generator”. 
    
    
     FIELD 
     The invention pertains to solid state electrical generators. More particularly, the invention pertains to multi-layer, high power density generators. 
     BACKGROUND 
     One type of known fuel cell incorporates a proton exchange membrane in combination with electrodes located on each side of the membrane, along with various gas diffusion layers and associated hydrophobic and hydrophilic coatings. One form of such a power generator has been disclosed in U.S. Patent Application entitled “Proton Exchange Membrane Fuel Cell”, application Ser. No. 11/257,738, filed Oct. 25, 2005, assigned to the Assignee hereof. The disclosure of that applicant is hereby incorporated by reference. Another form of a power generator which incorporates a multi-layer fuel cell produces electricity and water as a by-product. The water can be reclaimed and used to produce additional hydrogen gas through a reaction with a solid hydrogen producing fuel. Such a power generator and fuel cell are disclosed in U.S. Patent Application entitled “Water Reclamation in a Micropower Generator”, application Ser. No. 11/270,848, filed Nov. 9, 2005. That application is assigned to the Assignee hereof and incorporated herein by reference. 
     While known solid state power generators are useful and appropriate for their intended purpose, there continue to be outstanding unmet needs for higher power density generators, as opposed to energy density, than have heretofore been available. There continues to be a need for high power density solid generators which are suitable for micro- or nano-applications. Preferably such power generators would be light weigh, relatively inexpensive, valveless and would exhibit sufficient power for high power, light weight applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric type view of a power generator in accordance with the invention; 
         FIG. 2  is a sectional view taken along plane  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a view of a power generator in accordance with the invention which incorporates an array of fuel cells; and 
         FIG. 4  is a view of the generator of  FIG. 3  taken along the plane  4 - 4 . 
     
    
    
     DETAILED DESCRIPTION 
     While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated. 
     Power generators in accordance with the invention exhibit higher power density without a need for either an onboard source of water or valves to regulate the hydrogen generating chemical reaction. In one aspect of the invention a rectangular shaped generator can be formed almost entirely of fuel cell stacks with a thin layer of fuel between the stacks. Such a power generator can be expected to have a very high power density (in excess of 10 watts/liter) in view of the large fuel cell area. 
     The above described power generators could be implemented with a plurality of flexible layers and could be used flat, for example as wing of an ultra-light air vehicle or rolled into a cylindrical configuration. In yet another aspect of the invention, such generators can be expected to be inherently light in weight as a result of the high specific energy of fuel and capable, when configured appropriately, of producing power levels which could be used to energize ultra-light air vehicles. 
     In yet another aspect of the invention a three-layer power generator incorporates a relatively thin flexible sheet, a fuel layer such as lithium aluminum hydride or other chemical hydride which can generate oxygen when exposed to water vapor. The fuel layer in a disclosed embodiment is sandwiched between two fuel cell stacks. Each of the stacks incorporates at least one proton exchange membrane, gas diffusion layers, electrodes and associated hydrophobic and hydrophilic coatings as would be understood by those of skill in the art. The composite power generator is flexible and can be formed into a planar, substantially cylindrical or other shapes as required for a particular application. 
     In yet another aspect of the invention, the multi-layer power generator recycles water generated by the electrochemical reactions in the associated fuel cells and uses the water to generate hydrogen thereby obviating any need for onboard source of water. Further, the reactions regulate themselves and thus require no regulating valves. 
     Power generators in accordance with the invention can be implemented in an array with a common fuel layer. Members of a plurality of fuel cells formed on each side of the fuel layer can be interconnected in series to increase output voltage. Multiple stacks can be interconnected in parallel, in cylindrical or planar form, to achieve increased output power. 
     In yet another aspect of the invention, the oxygen flow needed to generate the high power densities, where the stacks are closely arranged, can be achieved by forcing ambient atmosphere through the stacks. This can be accomplished in an aircraft for example by passing air flow generated by a rotor or wings past the stacks. In other applications the same effect can be achieved using a fan or a pump. 
       FIG. 1  illustrates a high power density, ultra-light power generator  10  in accordance with the invention. The generator  10  incorporates a fuel layer  12  such as for example lithium aluminum hydride or other chemical hydride which produces hydrogen when exposed to water vapor. The fuel layer  12  which could be elongated and have a rectangular shape generally as indicated in  FIG. 1  has associated therewith fuel cell stacks  14  and  16 , one of each side thereof. It will be understood that all of the layers  12 ,  14  and  16  of the generator  16  are flexible and can be formed into a planar, substantially planar, curved, such as cylindrical, configuration all without limitation. 
     Those of skill will also understand that the layers  12 - 16  of the generator  10 , while indicated generally in a rectangular form in  FIG. 1  are not limited to any particular shape. The generator  10  can assume a variety of physical configurations all without limitation and without departing from the spirit and scope of the invention. 
       FIG. 2  is a sectional view taken along plane  2 - 2  of  FIG. 1 .  FIG. 2  illustrates the relationship between the various layers of the generator  10 . 
     Each of the fuel cell stacks  14 ,  16  incorporates a multi-layer planar fuel cell having an anode, cathode, a proton exchange membrane and other layers as would be understood by those of skill in the art which are useful or desirable in implementing such fuel cell stacks. One of the advantages of fuel generator such as the generator  10  results from the fact that the fuel cell stacks  14 ,  16  can be formed with a large area. This can produce a very high power density for a limited amount of time depending on the amount of fuel available. 
       FIGS. 3 and 4  taken together illustrate one particular form of a generator  30  in accordance with the invention. Generator  30  incorporates a series connected array of fuel cells  32   a  formed on one side of a fuel layer  36  and a second plurality of fuel cells  32   b  formed on the other side of the fuel layer  36 . Each of the members of the plurality  32   a  and the plurality  32   b  can be interconnected in series to generate a higher output voltage between connections  40   a, b  than could be easily achieved with a single fuel cell. 
     It will be understood that the fuel cells of the array  30  are spaced apart from one another by intervening layers of insulation  34   a, b, c  and  d . It will also be understood that the number of fuel cells present in the array  30  is not a limitation of the present invention. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.