Patent Publication Number: US-6989215-B1

Title: Apparatus of high power density fuel cell layer with micro structured components

Description:
CROSS-REFERENCES TO RELATED APPLICATION(S) 
     The application herein claims priority from the provisional Patent Application 60/354,795 with a filing date of Feb. 6, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to fuel cells. More specifically the invention relates to a fuel cell layer comprising multiple cells formed within a channel formed using porous substrates. 
     BACKGROUND OF THE INVENTION 
     High power density fuel cells have long been desired. 
     Existing fuel cells generally are a stacked assembly of individual fuel cells, with each cell producing high current at low voltage. The typical cell construction involves reactant distribution and current collection devices brought into contact with a layered electrochemical assembly consisting of a gas diffusion layer, a first catalyst layer, an electrolyte layer, a second catalyst layer and a second gas diffusion layer. With the exception of high temperature fuel cells, such as molten carbonate cells, most proton exchange membrane, direct methanol, solid oxide or alkaline fuel cells have a layered planar structure where the layers are first formed as distinct components and then assembled into a functional fuel cell stack by placing the layers in contact with each other. 
     One major problem with the layered planar structure fuel cell has been that the layers must be held in intimate electrical contact with each other, which if intimate contact does not occur the internal resistance of the stack increases, which decreases the overall efficiency of the fuel cell. 
     A second problem with the layered planar structured fuel cell has been to maintain consistent contact between the layers for sealing and ensuring correct flows of reactants and coolants in the inner recesses of the layer structured fuel cell. Also if the overall area of the cell becomes too large then there are difficulties creating the contacting forces needed to maintain the correct fluid flow distribution of reactant gases over the electrolyte surface. 
     Existing devices also have the feature that, with the layered planar structure fuel cell since both fuel and oxidant are required to flow within the plane of the layered planar structured fuel cell, at least 4 and up to 10 but typically 8 distinct layers have been required to form a workable cell, typically a first flowfield, a first gas diffusion layer, a first catalyst layer, a first electrolyte layer, a second catalyst layer, a second gas diffusion layer, a second flowfield layer and a separator. These layers are usually manufactured into separate fuel cell components and then the layers are brought into contact with each other to form a fuel cell stack. When contacting the layers care must be taken to allow gas diffusion within the layers while preventing gas leaking from the assembled fuel cell stack. Furthermore, all electrical current produced by the fuel cells in the stack must pass through each layer in the stack, relying on the simple contacting of distinct layers to provide an electrically conductive path. As a result, both sealing and conductivity require the assembled stack to be clamped together with significant force in order to activate perimeter seals and reduce internal contact resistance. 
     The manufacture of the layers for existing fuel cell configurations is often expensive and difficult. The bipolar plates, which serve as oxidant and fuel flowfields as well as the separator are often constructed from graphite which is difficult to machine, adding significant cost to the fuel cell stack. The membrane electrode assembly (MEA) is usually constructed by first coating a solid polymer electrolyte with catalyst on either side and then pressing gas diffusion electrodes onto the electrolyte. The fuel cell assembly requires multiple individual bipolar plates and membrane electrode assemblies to be connected together in a serial manner. Usually discrete seals must be attached between neighbouring bipolar plates and membrane electrode assemblies and the whole stack of sealed bipolar and MEA layers must be held together under considerable compressive force. 
     A need has existed to develop alternative fuel cell designs that do not perpetuate the approach of assembling discrete layers in a serial manner. One way to meet this need is to build fuel cells using a micro-structured approach wherein microfabrication techniques and nano-structured materials can be combined to create novel devices not subject to the problems commonly associated with conventional fuel cell designs. The application of microscale techniques to fuel cells has a number of distinct advantages. Specifically, the potential for increased power density due to thinner layers and novel geometries, improved heat and mass transfer, improved and/or more precise catalyst utilization and reduced losses with shorter conductive path lengths will all make fuel cells more efficient and enable higher volumetric power densities. The opportunity to include ancillary systems into the fuel cell design and the potential for new applications to emerge present even more potential benefits. 
     A need has existed for a micro fuel cell capable of low cost manufacturing because of having fewer parts than the layered planar structure fuel cell. 
     A need has existed for a micro fuel cell having the ability to utilize a wide variety of electrolytes. 
     A need has existed for a micro fuel cell, which has substantially reduced contact resistance within the fuel cell. 
     A number of prior inventions have used microscale-manufacturing techniques with fuel cells. U.S. Pat. No. 5,861,221 presents a ‘membrane strip’ containing a number of conventional MEAs connected to each other in series by connecting the edge of the negative electrode of one MEA to the edge of the positive electrode of the next MEA. Two configurations are considered. The first constructs the ‘membrane strip’ by placing the MEAs together in a step-like configuration. The second constructs the ‘membrane strip’ by combining MEAs end-to-end with electrically conductive regions between them that connect the cells in series. In some follow-up work (U.S. Pat. No. 5,925,477) the same inventors incorporate a shunt between the electrodes to improve the electrical conductivity of the cell. The MEA&#39;s themselves are of conventional layered structure design, and the overall edge collected assembly continues to rely on conventional seals between neighbouring MEA&#39;s. 
     U.S. Pat. No. 5,631,099 and U.S. Pat. No. 5,759,721 use similar series connection concepts but apply a number of other microscale techniques to the fuel cell design. By doing so multiple fuel cells are formed within a single structure simultaneously. The fuel cells themselves still reside as layered planar devices mounted onto a carrier, with interconnection between neighbouring fuel cells requiring a penetration of the carrier layer. Most of the techniques discussed in these patents relate to the creation of methanol tolerant catalysts and the application of palladium layers to the catalyst to prevent methanol crossover within the cells. 
     WO 01/95406 describes a single membrane device that is segmented to create multiple MEA structures. Complex bipolar plates that are difficult to manufacture provide both fuel and oxidants to both sides of the MEA layer. U.S. Pat. No. 6,127,058 describes a similar structure, but instead of complex manifolding of reactant gases, only one reactant is supplied to either side of the MEA layer. Series interconnection of the fuel cells formed within the single MEA layer is achieved through external current collectors arranged around the perimeter of the device providing electrical connection from the top of the MEA layer to the bottom of the MEA layer. Such perimeter electrical connections are inefficient. 
     Some prior art fuel cells attempt to reduce size and fabrication costs by applying microfabrication techniques. For example the Case Western Reserve University device forms multiple fuel cells on a carrier substrate using thin layer processes similar to those used in printing and semiconductor fabrication (Wainwright et al. “A microfabricated Hydrogen/Air Fuel Cell” 195 Meeting of the Electrochemical Society, Seattle, Wash., 1999). In these designs the fuel cells remain of conventional planar design, with the exception that the fuel cells are built-up on a base substrate. The cathodes must be formed on top of the planar electrolytes and then must be connected to neighbouring anodes with an explicit interconnect. 
     All the cells presented above use current collection on the edge of the electrode. This significantly increases the internal cell resistance of these cells. Each of these cells is also based on solid polymer electrolytes as this is the only electrolyte that allows for easy manufacture. Furthermore, all of the cells presented above achieve a micro fuel cell design by forming multiple fuel cells within a single electrolyte plane. 
     The concept of using non-planar electrolytes has been considered in the past. GB 2,339,058 presents a fuel cell with an undulating electrolyte layer. In this configuration a conventional layered MEA is constructed in an undulating fashion. This MEA is placed between bipolar plates. This design increases the active area that can be packed into a given volume. However, this design still relies on the expensive and complicated layered structure with explicit seals and requires compressive force to maintain internal electrical contact and sealing. JP 50903/1996 presents a solid polymer fuel cell having generally planar separators with alternating protruding parts serving to clamp a power generation element (apparently an MEA) into a non-planar but piecewise linear shape. As with GB 2,339,058, this document continues to rely on the expensive and complicated layered structure but this design also puts undue stress on the MEA by forcing it into a non-planar arrangement using the separator plates. 
     In addition to non-planar designs, some prior art presents tubular configurations. U.S. Pat. No. 6,060,188 presents a cylindrical fuel cell with a single MEA layer formed into a cylinder. Fuel or oxidant is delivered to the interior recess of the cylinder with the other reactant delivered on the exterior. Within this design, each cylindrical structure creates a single cell, with current flowing through the annular cylindrical wall that is the fuel cell. A method of providing series electrical interconnection between fuel cells or of sealing individual fuel cells is not disclosed. This design is reminiscent of tubular designs for solid oxide fuel cells that are well known. 
     A need has existed to develop fuel cell topologies or fuel cell architectures that allow increased active areas to be included in the same volume, i.e. higher density of active areas. This will allow fuel cells to be optimized in a manner different than being pursued by most fuel cell developers today. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a specific fuel cell layer architecture that is of an integrated design in which the functions of gas diffusion layers, catalyst layers, and electrolyte layers are integrated into a single substrate. This integrated design enables simpler manufacturing processes and scaling of the design. 
     The invention is also a fuel cell layer with a fuel plenum, an oxidant, and a plurality of fuel cells. The fuel cell has a porous substrate, a channel, an anode and a cathode formed in opposite channel walls, an electrolyte contacting the anode and the cathode preventing transfer of fuel to the cathode and transfer of oxidant to the anode, a coatings to prevent fuel or oxidant from entering a portion of the porous substrate, a first sealant barrier disposed on the first side and the second sealant barrier disposed on the second side, and a positive and a negative electrical connection disposed on said second side. Multiple fuel cells are connected and the fuel cell assembly generates a current to drive an external load. 
     The fuel cell layer is created by forming an assembly of single channel fuel cells to create a layer with an anode side and a cathode side enclosing a plurality of fuel cells that are series connected within the layer. When microscopic dimensioned channels are used the result is a very high power density arrangement of fuel cells in a confined volume. 
     A number of variations on the design of the fuel cell layer are envisioned. Some of the variations include having the fuel and oxidant plenums dead-ended, having the fuel cell layer enclosing a volume, having the porous substrate in a non-planar, or alternately planar, configuration and having the fuel cell layer enclose a volume in a cylindrical shape. The substrate can be formed from a variety of conductive and non-conductive porous media. 
     Dimensionally, the channels can have a dimension ranging from 1 nanometer to 10 cm in height, 1 nanometer to 1 mm in width and from 1 nanometer to 100 meters in length. A single fuel cell of the invention is contemplated of being capable of producing between approximately 0.25 volts and approximately 4 volts. 
     Between 1 and 5000 fuel cells are contemplated as usable in one fuel cell layer in this design, however in a preferred embodiment, the fuel cell layer has between 75 and 150 joined fuel cells. This fuel cell layer is contemplated to be capable of producing a voltage between 0.25 volts and 2500 volts. A fuel cell with more channels will be capable of producing higher voltages. 
     Electrolyte usable in this invention can be a gel, a liquid or a solid material. It is contemplated that the electrolyte can be between 1 nanometer and 1.0 mm in thickness, or alternatively simply filling each channel from first wall to second wall without a gap. Having a thin channel, and therefore a thin electrolyte, increases the efficiency of the fuel cell. 
     The fuel cell layer of the invention can be used by first, connecting a fuel source to a fuel plenum inlet; second, connecting a fuel plenum outlet to a re-circulating controller; third, connecting an oxidant plenum inlet to an oxidant source; fourth, connecting an oxidant plenum outlet to a flow control system, fifth, connecting a positive electrical connection and a negative electrical connection to an external load; sixth, flowing fuel and oxidant to the inlets; and finally, driving load with electricity produced by the fuel cell. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       A specific embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of a first embodiment of the inventive fuel cell; 
         FIG. 1   a  is a cross-sectional detailed view of the anode with the catalyst at a first depth in the porous substrate; 
         FIG. 1   b  is a cross sectional detailed view of the anode with the catalyst at a second depth in the porous substrate; 
         FIG. 1   c  is a cross sectional detailed view of the cathode; 
         FIG. 2  is a cross-sectional view of a dead ended embodiment of the inventive fuel cell; 
         FIG. 2   a  is embodiment of the fuel cell according to the invention with the fuel and oxidant plenums being solid with flow channels contained therein; 
         FIG. 3  is a cross-sectional view of another embodiment of a dead ended fuel cell; 
         FIG. 3   a  is an embodiment of the invention with an oxidant plenum open to the ambient environment; 
         FIG. 3   b  is an embodiment of the invention with a fuel plenum open to the ambient environment; 
         FIG. 4  is a cross-sectional view of a fuel cell layer formed by combining multiple fuel cells of the type described in  FIG. 1 ; 
         FIG. 4   a  is a cross sectional view of a multiple porous substrate fuel cell layer with the fuel plenum open to the ambient environment; 
         FIG. 4   b  is a cross sectional view of a multiple porous substrate fuel cell layer with the oxidant plenum open to the ambient environment; 
         FIG. 4   c  is a cross sectional view of a fuel cell layer with up to 5000 fuel cells; 
         FIG. 5  is a cross-sectional view of a fuel cell with multiple fuel cells of the type described in  FIG. 1  formed within a single substrate; 
         FIG. 5   a  is another embodiment of a fuel cell with multiple cells; 
         FIG. 6  is a perspective view of a fuel cell layer containing multiple fuel cells of the type described in  FIG. 1 ; 
         FIG. 7  is another detailed perspective view of the fuel cell of the invention with undulating channels; 
         FIG. 8  is a perspective view of a cylindrical version of a fuel cell according to the invention; 
         FIG. 8   a  is a cross-sectional view of an embodiment of the fuel cell of  FIG. 1  in which the substrate is irregularly shaped; 
         FIG. 9  is a cross sectional view of a cylindrical version of a fuel cell according to the invention; 
         FIG. 10  is another embodiment of the inventive fuel cell of the invention with the channels in the form of a set of stacked annular rings; 
         FIG. 11  is another embodiment of the inventive fuel cell with the channels in the form of a spiral around the cylinder; and 
         FIG. 12  is a perspective view of a bi-level fuel cell structure. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The present invention relates to a microstructure fuel cell having a substrate, which is preferably porous, an assembly of fuel cells having a single or multiple substrate structure and methods for manufacturing such fuel cells and fuel cell layers. 
     The invention relates to a specific fuel cell architecture that is of an integrated design in which the functions of gas diffusion layers, catalyst layers, and electrolyte layers are integrated into a single substrate. This architecture makes it possible to fold together the various ‘layers’ of which a working fuel cell is formed and produce linear, curvilinear, undulating or even fractal shaped electrolyte paths that allow for higher volumetric power density to be achieved by increasing the electrochemically active surface area. In addition, by forming the various fuel cell layers within a single substrate the problem of simple contacting of fuel cell components to create electrical connections is eliminated, thus creating the potential for lower internal cell resistances to be achieved. The cell layers themselves can be constructed in planar, non-planar or involute configurations providing further advantages in increasing surfaces areas and providing flexibility in applications. This integrated design enables simpler manufacturing processes and scaling of the design. 
     Unlike existing fuel cell designs, the present invention, in one embodiment, provides convoluted electrolyte layers, which do not smoothly undulate. Other embodiments of the invention include shapes that are essentially non-smooth. Utilizing such non-smooth electrolyte paths allows for greater overall surface areas for the fuel cell reactions to be packed into a given volume than can be achieved when planar electrolyte layers are employed as in conventional fuel cell designs. The present invention also allows for significantly decreased distances between separate electrolyte layers, thereby allow for a greater surface area in a given volume than conventional designs. 
     The present invention contemplates the use of a design inspired by fractal patterns, which provides long electrolyte path lengths. The invention includes a method for building fuel cells and “stacks” that are not dependent on the layered process and which do not require the post-manufacturing assembly of distinct layered components. The conventional relationship between MEA layers and bipolar plates is eliminated, as is the reliance on multiple discrete layered structures. The invention also contemplates a design with individual fuel cells turned on their side relative to the overall footprint of the assembled fuel cell device. The invention contemplates building multiple fuel cells with an integrated structure on a single substrate using parallel manufacturing methods. 
     Specifically, it is contemplated to use a porous substrate for the fuel cell through which reactant gas will diffuse with little driving force. The substrate may or may not be electrically conductive. If it is conductive, it is contemplated to insulate at least a portion of the substrate, which typically would separate the anode from the cathode, this insulation may be formed by the electrolyte separating the anode from the cathode and, if necessary, an optional insulating structural member may be added. More specifically, the fuel cell is contemplated to have: (a) a fuel plenum comprising fuel; (b) an oxidant plenum comprising oxidant; (c) a porous substrate communicating with said fuel plenum, and said oxidant plenum further comprising a top, a bottom, a first side, and a second side; (d) a channel formed using said porous substrate, wherein said channel comprises a first channel wall and a second channel wall; (e) an anode formed from a first catalyst layer disposed on the porous substrate of said first channel wall; (f) a cathode formed from a second catalyst layer disposed on the porous substrate of said second channel wall; (g) electrolyte disposed in at least a portion of said channel contacting the anode and the cathode preventing transfer of fuel to the cathode and preventing transfer of oxidant to the anode; (h) a first coating disposed on at least a portion of said porous substrate to prevent fuel from entering at least a portion of said porous substrate; (i) a second coating disposed on at least a portion of said porous substrate to prevent oxidant from entering at least a portion of said porous substrate; (j) a first sealant barrier disposed on the first side and the second sealant barrier disposed on the second side; (k) a positive electrical connection disposed on said first side; (l) a negative electrical connection disposed on said second side; and wherein the resulting fuel cell generates current to drive an external load. 
     Referring to  FIG. 1 , which is a cross-sectional view of one embodiment of the invention, a fuel cell  8  has an optional fuel plenum  10  containing fuel  11 . A porous substrate  12  is adjacent the optional fuel plenum  10 . The fuel plenum can have an optional fuel plenum inlet  18 . The fuel plenum can also have an optional fuel plenum outlet  20 . An optional oxidant plenum  16  containing oxidant  13  is adjacent the porous substrate  12 . The oxidant plenum can have an optional oxidant plenum inlet  52 . The oxidant plenum can also have an optional oxidant plenum outlet  54 . If no oxidant plenum is used the fuel cell uses the ambient environment as a source of oxidant. 
     The porous substrate  12  can have a shape that is rectangular, square or orthogonal or alternatively, it can be irregularly shaped. In this embodiment it is pictured as being formed within a single plane, although non-planar substrates or multiple substrate configurations are envisioned. 
     A channel  14 , formed using the porous substrate, can be straight or of arbitrary design. If of arbitrary design the channel is referred to throughout this application as “undulating.” If multiple channels are present at least one may be undulating. The channel  14  has a first channel wall  22  and a second channel wall  24 . Additionally the porous substrate  12  has a top  100 , bottom  102 , first side  104  and a second side  106 . 
     Said channel can comprise an undulating channel, a straight channel or an irregular channel. If undulating, the channel can be sinusoidal in shape and if undulating, the channel may be of a shape that is in at least three planes. 
     An anode  28  is created on or alternately in the surface of the first channel wall  22 , although the anode could be embedded in the wall as well. Anode  28  is created using a first catalyst layer  38  on or into the surface of the first channel wall  22 . 
     A cathode  30  is formed on the surface or alternately in the second channel wall  24 . Like the anode  28 , the cathode  30  could be embedded in the second channel wall  24 . Cathode  30  is created using a second catalyst layer  40 . 
       FIGS. 1   a ,  1   b  and  1   c  provide details of the cathode and anode of the fuel cell.  FIG. 1   a  shows the anode  28  at a first depth within the porous substrate  12 ,  FIG. 1   b  shows the anode  28  at a second depth within the porous substrate  12  and  FIG. 1   c  shows the cathode  30 . 
     The catalyst layers can be deposited on the first and channel walls or can be formed in the channel walls. In one embodiment the first and second catalyst layers are disposed in the porous substrate to at least a minimum depth to cause catalytic activity. 
     Referring back to  FIG. 1 , an electrolyte  32  is disposed in the channel  14 . 
     A first coating  34  is disposed on at least a portion of the porous substrate  12  preventing fuel from entering at least a portion of the porous substrate  12 . A second coating  36  is disposed on at least a portion of the porous substrate  12  preventing oxidant from entering at least a portion of the porous substrate  12 . 
     A first sealant barrier  44  is disposed on the first side of the porous substrate and a second sealant barrier  46  is disposed on the second side of the porous substrate. The sealant barriers can optionally be disposed within a sealant barrier channel  43 . 
     A positive electrical connection  50  is engaged with the porous substrate  12  on the first side of the porous substrate. 
     A negative electrical connection  48  is engaged with the porous substrate  12  on the second side of the porous substrate. 
     The resulting fuel cell generates current  56  to drive an external load  58 . 
       FIG. 2  is another embodiment of the invention showing a dead ended version of the fuel cell  108  specifically excluding the fuel outlet  20  and the oxidant outlet  54  of the  FIG. 1  embodiment. 
     In the embodiments of the invention depicted in  FIGS. 2 and 2   a , it is contemplated that the electrolyte  32  can be mounted in the channel  14  at an angle  76 , preferable at an angle, which is perpendicular to the longitudinal or horizontal axis  74  of the predominant portion of the porous substrate  12 . 
     In  FIG. 2  an optional support member  26  separates first channel wall  22  from second channel wall  24  however the support member is not required in every embodiment. Some alternatives envision multiple support members as shown in  FIG. 2   a . Between one and  50 , or more support members are contemplated herein. 
     Now referring to  FIG. 2   a , a fuel cell is shown with a solid fuel plenum  10  with flow fields  126  and a solid oxidant plenum  16  with flow fields  126 . It is also envisioned that the fuel plenum comprises a permeable material containing the fuel. The oxidant plenum can also comprise a permeable material. It is understood that the fuel plenum and oxidant plenum need not be constructed in the same manner and a variety of combinations of oxidant and fuel plenum configurations can be used. The fuel plenum and the oxidant plenum can each have a variety of shapes, round, elliptoid, rectangular or square. It is particularly contemplated that the fuel plenum has a rectangular cross-section. 
       FIG. 3  is a cross-section of another embodiment of a dead ended version of the fuel  110  that excludes both the fuel inlet  18  and the fuel outlet  20  as well as the oxidant inlet  52  and the oxidant outlet  54  of the embodiment of  FIG. 1 .  FIG. 3   a  shows an embodiment of the fuel cell where the oxidant plenum  16  is entirely removed. In such an embodiment the cell would use the ambient environment as an oxidant supply.  FIG. 3   b  shows an embodiment of the fuel cell where the fuel plenum  10  is removed entirely. In this configuration the fuel cell uses the ambient environment as a fuel supply. 
       FIG. 4  shows a first fuel cell  66  formed from a substrate  12  that is made adjacent a second fuel cell  114  formed from a second substrate  62 . The first and second fuel cells may be formed from either the association of multiple substrates or, as shown in  FIG. 5 , the first fuel cell  66  and the second fuel cell  114  may be formed by creating multiple channels  14  within a single substrate  12 . 
     In  FIG. 4 , a plurality of fuel cell structures are formed using separate porous substrates and they are then connected to each other at said sealant barriers  44  forming a fuel cell layer. In this figure a first fuel cell  66  is connected to a second fuel cell  114 . Multiple fuel cells can be connected together in this manner to create a fuel cell layer  64  with a fuel side  116  and an oxidant side  118 . The details in the figure can be easily understood by referring to the items numbers in the description of  FIG. 1  and will therefore not be elaborated here. 
     In this embodiment it is envisioned that the fuel cell be connected in series, in parallel or in combinations thereof to allow the fuel cell layer to produce current to drive an external load. 
       FIG. 4   a  shows a fuel cell layer with the fuel plenum open to the ambient environment.  FIG. 4   b  shows a fuel cell layer with the oxidant plenum open to the ambient environment. In this figure at least one optional support member  26  is shown on at least one of said fuel cells. 
       FIG. 4   c  shows an embodiment of said fuel cell layer wherein up to 5000 cells are connected together in the manner explained for  FIG. 4 . 
     In  FIG. 5 , the same fuel cell structures are formed in a single porous substrate  12 . In this embodiment a plurality of fuel cells are created within the porous substrate in the same manner as described for  FIG. 1 . Since, in this case, the fuel cells are formed within a single substrate the sealant barriers and electrical connections associated with each fuel cell are not required. Instead a first sealant barrier  44  is disposed on the first side of the porous substrate, a second sealant barrier  46  is disposed on the second side of the porous substrate and a plurality of third sealant barriers  45  are disposed between said fuel cells. The sealant barriers provide gas impermeable separators between the fuel cells within the fuel cell layer. 
     It is understood that the same embodiments shown for the multiple substrate structure in  FIGS. 4   a ,  4   b  and  4   c  can be used with the single substrate structure shown in  FIG. 5 . Additionally the porous substrate  12  in  FIG. 5 , has first side  104  and a second side  106 . 
     This association of two fuel cells, either by the structure of  FIG. 4  or the structure of  FIG. 5 , can be extended to place an arbitrary number of fuel cells in association with each other. In both embodiments, the ends of the multiple structures are sealed with a sealant barrier  44  and a second sealant barrier  46 . In both embodiments, negative electrical connection  48  is attached on one end of the multiple fuel cell assembly and positive electrical connection  50  is attached on the other end of the multiple fuel cell assembly to allow the multiple fuel cell assembly to drive an external electrical load. 
     The association of multiple fuel cells produces a fuel cell layer  64  having a fuel side  116  that is brought into association with a fuel plenum  10  and an oxidant side  118  that is brought into association with an oxidant plenum  16 . 
     If the substrate material from which the fuel cells within the fuel cell layer  64  is formed is conductive, then electrical current produced by the individual fuel cells is able to flow directly through the substrate material and the sealant barriers  44  to create a bipolar fuel cell structure within the formed fuel cell layer. If the substrate material from which the fuel cells within the fuel cell layer are formed is not electrically conductive then the first coating  34  and second coating  36  should both be made of an electrically conducting material and formed so that the first coating  34  is in electrical contact with the anode  40  while second coating  36  is in electrical contact with cathode  38 . The first coating  34  and the second coating  36  are also made in electrical contact with the conductive sealant barrier  44 . In either case, with a conductive or non-conductive substrate the electrical current produced by the fuel cell can be transported to the positive and negative electrical connections. 
     An alternate configuration for the fuel cell layer is shown in  FIG. 5   a . In this configuration the first coating  34  is extended to connect the anode of the first fuel cell to the cathode of the second fuel cell. The second coating  36  is likewise extended to contact the anode of the first fuel cell. The first coating on the end and the second coating on the end can be used to connect the fuel cells on the ends to the positive electrical connection  50  and the negative electrical connection  48 . In this configuration portions of the first coating are porous to allow fuel to reach the anode and portions of the second coating are porous to allow oxidant to reach the cathode. In this configuration neither the porous substrate nor the sealant barrier need be electrically conductive. It is also envisioned that only the first coating be extended to provide electrical contact between the cells or that only the second coating be extended to provide electrical contact between the cells. 
     When multiple fuel cells are formed into a fuel cell layer, as described in  FIGS. 4 and 5  a series electrical connection of the individual fuel cells results. The summed voltages of the multiple fuel cells produce a potential difference between the positive and negative electrical connections at either end of the fuel cell layer. A larger number of fuel cells will enable the fuel cell layer to produce a higher voltage between the electrical connections. Any combination of conductive or non-conductive substrates, barriers and caps may be used so long as an electrically conductive path between neighbouring anodes and cathodes is created. In this manner either an edge collected or preferably a bipolar series electrical connection of each of the fuel cells in the fuel cell layer is achieved without the need to clamp distinct components together and without the use of independently formed layered components. Also, the direction of current flow in the fuel cell layer is overall in the plane of the fuel cell layer rather than being orthogonal to the fuel cell layer as is the case in most current designs. It is also envisioned to electrically connect the fuel cells within a fuel cell layer together in parallel or in a combination of series and parallel. 
       FIG. 6  is a cutaway perspective view of a fuel cell layer  64 . In this figure a first fuel cell  66  is separated from a second fuel cell  114  by a sealant barrier  44 . A third fuel cell  115  is separated from the second fuel cell  114  by another sealant barrier  44 . The layer has the same structure as the layers described in  FIGS. 4 and 5 . The single fuel cell layer  64  can contain as many sealant barriers and cells as desired. The determination of the spacing between individual fuel cells within the fuel cell layer is at the discretion of the designer, limited by pragmatic issues of manufacturability and mass transport issues within the porous substrate. 
     The overall structure of the fuel cell layer  64  creates a series connection of the individual fuel cells. Positive electrical connection  50  and negative electrical connection  48  allow an external load to be connected to the fuel cell layer, which produces a voltage that is a multiple of the single cell voltages produced within the fuel cell layer. 
       FIG. 7  shows a similar view as  FIG. 6  of the fuel cell layer  64  but in this Figure, each of the fuel cells  8  have a channel  14  with a less straight structure. Again, as with  FIG. 6 ,  FIG. 7  uses essentially the same structure as shown in  FIGS. 4 and 5 , but repeated multiple times creating a multi-cell structure. The less straight structure of the channels allows for increased electrochemically active areas for the anodes and cathodes formed on the channel walls. The less straight channels can be smoothly undulating or can be irregular in shape resembling a fractral structured path which is known to have extremely high area. Any arbitrary channel structure can be used with this invention allowing for the optimization of the area of the electrodes in each fuel cell. A preferred embodiment includes a plurality of thin channels that run parallel to each other and follow an irregular path that folds back on itself in a manner suggestive of a fractal pattern. Another preferred embodiment of the invention includes at least one channel that is in at least three planes. 
       FIG. 8  shows a perspective view of a cylindrical version 250 of a multiple fuel cell layer. In this version a multitude of non-planar fuel cells  208  are combined to create a fuel cell layer  64  that encloses a volume  210 . The enclosed volume  210  is used as the fuel plenum while oxidant is supplied by the environment outside the cell. It is also envisioned that the fuel be supplied by the environment outside the cylinder and that the enclosed volume  210  be used as an oxidant plenum. The cylindrical fuel cell  250  can either be constructed using a single porous substrate which is in the shape of a cylinder using the method discussed for combining cells in  FIG. 5  or with multiple porous substrates that are brought together into a cylinder using the method discussed for combining cells in  FIG. 4 . 
       FIG. 8   a  is a cross-section of a non-planar version of the fuel cell  208 . The fuel cell has a fuel plenum  10  with fuel inlet  18  and fuel outlet  20  and an oxidant plenum  16  with oxidant inlet  52  and oxidant outlet  54 . A non-planar porous substrate  212  is in communication with both the fuel plenum  10  and the oxidant plenum  16 . A channel  14  is formed within the non-planar porous substrate  212 . The channel  14  has an anode  40  and a cathode  38  constructed as described for  FIG. 1  and is filled with electrolyte  32 . The fuel cell has a support member  26  a first coating  34  and a second coating  36 . The negative electrical connector  48  is shown adjacent sealant barrier  46 . The positive electrical connector  50  is shown adjacent the optional sealant barrier  44 . Although in this figure an arc is used to show the non-planar nature of the fuel cell, any arbitrary configuration could be used. As with the fuel cells of  FIG. 1  the non-planar fuel cell can be combined to form a non-planar fuel cell layer with multiple cells and can be associated with fuel and optional oxidant plenums of various configurations. 
       FIG. 9  shows a cross sectional view of a cylindrical version of a fuel cell. In this case the non-planar substrate  212  is shaped in the form of a cylinder to enclose a volume  210 . The fuel cell in this figure is shown with fuel  11  in the enclosed volume  210  providing fuel to the fuel cell. In this configuration the ambient environment outside the cell supplies oxidant. It is also envisioned that oxidant be contained within the enclosed volume  210  and that the ambient environment supply the fuel. 
       FIG. 10  is another embodiment of a cylindrical fuel cell  251  having the channels  14  of the non-planar fuel cells  208  configured radially and orthogonal to the axis of the cylinder. It is understood that the fuel cells  208  within this figure can either be constructed or assembled, as described for  FIG. 4  or that they be formed within a single cylindrical substrate as described for  FIG. 5 . 
       FIG. 11  is another embodiment of a cylindrical fuel cell  252  having the channel  14  of the non-planar fuel cell disposed in a wound or spiral fashion around the perimeter of the cylinder. Although, in this figure, only a single spiral channel  14  is shown, multiple fuel cells with multiple channels could be formed using the porous substrate. 
     Although only cylindrical cells have been shown enclosing a volume it is contemplated herein that shapes such as extruded rectangles, squares, ovals, triangles and other shapes as well as non-extruded shapes such as cones, pyramids, football shaped objects and other shapes that enclose a volume are included as part of the invention. 
       FIG. 12  is a cutaway perspective view of a bi-level fuel cell layer structure  254  with two fuel cell layers, a first fuel cell layer  64  and a second fuel cell layer  112  each comprising an anode side and a cathode side wherein said first fuel cell layer  64  is stacked on top of said second fuel cell layer  112  such that the anode side  264  of the first fuel cell layer and the anode side  268  of the second fuel cell layer adjoin. 
     In this Figure, a seal  130  is disposed between the first and second fuel cell layer to form a fuel plenum  124 . The two positive electrical connections are connected to positive connector  120  and the two negative electrical connections are connected to negative connector  122  so that the individual fuel cell layers are now connected in an electrically parallel configuration. The resulting assembly is a bi-level fuel cell layer structure  254  having a top  70  and a bottom  72 , the top and bottom being the cathode sides of the respective fuel cell layers. The resulting structure is an enclosed plenum air breathing fuel cell that achieves a series electrical connection of the individual fuel cells in each fuel cell layer and a parallel electrical connection of the two fuel cell layers. Only fuel is required to be fed to the interior of the structure and electrical current flows within the two fuel cell layers independently of one another. There is no electrical connection between the two fuel cell layers except at the parallel connection of the positive and negative electrical connections at either end of the fuel cell layers in the structure. 
     It is also envisioned that the fuel cell layers be placed cathode to cathode thereby creating a common plenum that can be filled with oxidant. In this configuration the fuel cell sandwich uses the ambient environment as a fuel supply. 
     Although various materials could be used for the porous substrate of the invention, one usable material could be a conductive material. Materials such as a metal foam, graphite, graphite composite, at least one silicon wafer, sintered polytetrafluoroethylene, crystalline polymers, composites of crystalline polymers, reinforced phenolic resin, carbon cloth, carbon foam, carbon aerogel, ceramic, ceramic composites, composites of carbon and polymers, ceramic and glass composites, recycled organic materials, and combinations thereof are contemplated as usable in this invention. 
     The channel is contemplated to have up to 50 optional support members separating the walls of the channel. The support members can be located at the extreme ends of the channel, such as forming a top or bottom, or can be located in the middle portion of the channel, or be oriented at an angle to the center of the channel. It is contemplated that the support member can be an insulating material. If an insulating material is used, it is contemplated that silicon, graphite, graphite composite, polytetrafluoroethylene, polymethylmethacrylate, crystalline polymers, crystalline copolymers, cross-linked polymers thereof, wood, and combinations thereof can be usable in the invention. 
     Dimensionally, the channel can have a dimension ranging from 1 nanometer to 10 cm in height, 1 nanometer to 1 mm in width and from 1 nanometer to 100 meters in length. 
     A single fuel cell of the invention, optionally within a fuel cell layer, is contemplated of being capable of producing between approximately 0.25 volts and approximately 4 volts. Between 1 and 5000 fuel cells are contemplated as usable in one fuel cell layer in this design, however in a preferred embodiment, the fuel cell layer has between 75 and 150 joined fuel cells. This fuel cell layer is contemplated to be capable of producing a voltage between 0.25 volts and 2500 volts. A fuel cell with more channels will be capable of producing higher voltages. 
     The invention can be constructed such that the fuel comprises a member of the group: pure hydrogen, gas containing hydrogen, formic acid, an aqueous solution comprising a member of the group: ammonia, methanol, ethanol and sodium borohydride, and combinations thereof. The invention can be constructed such that the oxidant comprises a member of the group: pure oxygen, gas containing oxygen, air, oxygen enriched air, and combinations thereof. 
     Electrolyte usable in this invention can be a gel, a liquid or a solid material. Various materials are contemplated as usable and include: a perfluoronated polymer containing sulphonic groups, an aqueous acidic solution having a pH of at most 4, an aqueous alkaline solution having a pH greater than 7, and combinations thereof. Additionally, it is contemplated that the electrolyte layer can be between 1 nanometer and 1.0 mm in thickness, or alternatively simply filling each undulating channel from first wall to second wall without a gap. 
     The fuel cell is manufactured using a first and second coating on the porous substrate. These coatings can be the same material or different materials. At least one of said coatings can comprise a member of the group: polymer coating, epoxies, polytetrafluoroethylene, polymethylmethacrylate, polyethylene, polypropylene, polybutylene, and copolymers thereof, cross-linked polymers thereof, conductive metal, and combinations thereof. Alternatively, the first or second coating can comprise a thin metallic layer such as a coating of gold, platinum, aluminum or tin as well as alloys of these or other metals or metallic combinations. 
     The first and second catalyst layers that are contemplated as usable in the invention can be a noble metal, alloys comprising noble metals, platinum, alloys of platinum, ruthenium, alloys of ruthenium, and combinations of these materials. It is contemplated that ternary alloys having at least one noble metal are usable for good voltage creation. Platinum-ruthenium alloys are also contemplated as usable in this invention. The catalyst layers should each have a catalyst loading quantity wherein the amount of catalyst may be different for each layer. 
     The material for said optional sealant barriers contemplated herein can be selected from the group comprising: silicon, epoxy, polypropylene, polyethylene, polybutylene, and copolymers thereof, composites thereof, and combinations thereof. 
     One method for making the fuel cell contemplates the following steps:
         a. forming a porous substrate having a top and bottom having a first side and a second side;   b. coating at least a portion of said top with a first coating;   c. coating at least a portion of said bottom with a second coating;   d. forming a channel using the porous substrate, wherein said channel comprises a first channel wall and a second channel wall;   e. forming an anode by depositing a first catalyst layer on said first channel wall;   f. forming a cathode by depositing a second catalyst layer in said second channel wall;   g. disposing electrolyte in at least a portion of the channel contacting the anode and the cathode;   h. attaching a positive electrical connection on one end to the first side of said porous substrate, and attaching a negative electrical connection on one end to said second side of said porous substrate;   i. attaching a fuel plenum to the porous substrate forming a fuel cell;   j. attaching an oxidant plenum to the porous substrate;   k. disposing a sealant barrier around at least a portion of said fuel cell; and   l. loading said fuel plenum with fuel and said oxidant plenum with oxidant.       

     The sequence of operations described may be varied and steps combined as required to suit the particular material requirements and fabrication processes used. As well, the method can comprise forming between one and 250 or more channels in said porous substrate. 
     Another method for forming a fuel cell envisioned in the invention contemplates the following steps:
         a. repeating steps a through h of the method above as many times as needed prior to joining the porous substrate to the fuel plenum forming at least one additional fuel cell;   b. securing the porous substrate at the sealant barriers to at least on additional fuel cell at its sealant barrier forming a fuel cell layer and extending said fuel cell layer securing additional formed fuel cells to the fuel cell layer at respective sealant barriers;   c. attaching the positive electrical connections and the negative electrical connections of the fuel cell layer together;   d. attaching the joined fuel cells to said fuel plenum; and   e. attaching the joined fuel cells to said oxidant plenum.       

     The positive electrical connections and the negative electrical connections of said fuel cells within the fuel cell layer can be connected in series, in parallel or in a combination of series and parallel. 
     Yet another method for making a fuel cell layer is contemplated which has the steps of:
         a. forming a porous substrate comprising a top and bottom, a first side and a second side;   b. coating at least a portion of said top with a first coating;   c. coating at least a portion of said bottom with a second coating;   d. forming a plurality of distinct channels using the porous substrate, wherein each distinct channel comprises a first channel wall and a second channel wall;   e. forming a plurality of anodes by depositing a plurality of first catalyst layers on said first channel walls;   f. forming a plurality of cathodes by depositing a plurality of second catalyst layers in said second channel walls;   g. disposing electrolyte in at least a portion of each distinct channel;   h. disposing a first sealant barrier on at least a portion of said first side;   i. disposing a second sealant barrier on at least a portion of said second side;   j. forming a plurality of third sealant barriers between each of said distinct channels creating a plurality of independent fuel cells adjacent each other in the porous substrate;   k. attaching a positive electrical connection to the first side of said porous substrate;   l. attaching a negative electrical connection to said second side of said porous substrate;   m. attaching a fuel cell positive electrical connection to each independent fuel cells   n. attaching a fuel cell negative electrical connection to each independent fuel cell forming a fuel cell layer; and   o. disposing a sealant barrier around at least a portion of said fuel cell layer.       

     In any of the methods described above a number of different methods of forming said porous substrate are contemplated herein. The porous substrate can be formed by a method that is a member of the group comprising: casting and then baking, slicing layers from a pre-formed brick, molding, extruding, and combinations thereof. The formed porous substrate may be non-planar or enclose a volume. 
     If at least one of the coatings is deposited with thin film deposition techniques, the technique may include a member of the group comprising: sputtering, electroless plating, electroplating, soldering, physical vapor deposition, chemical vapor deposition. If at least one of the coatings is an epoxy coating the coating can be disposed on said substrate by a method selected from the group: screen printing, ink jet printing, spreading with a spatula, spray gun deposition, vacuum bagging and combinations thereof. A mask can be used when applying said coatings to said porous substrate. If required, a portion of the coating can be removed prior to adding the electrolyte. 
     The channel can be formed in the porous substrate by a method selected from the group comprising: embossing, ablating, etching, extruding, laminating, embedding, melting, molding, cutting, and combinations thereof. If etching is used, the etching can be by a method selected from the group comprising: laser etching, deep reactive ion etching, and alkaline etching. Alternatively, it is anticipated the channels can be formed by micro-milling using laser cutting, high pressure waterjets, micro-dimensioned rotary tools or mechanical dicing saws. 
     Within the invention it is envisioned to deposit the electrolyte in said channel using a method that is a member of the group comprising: pressure injection, vacuum forming, hot embossing, and combinations thereof. 
     The variations for making the apparatus can be implemented into any of the methods described above. For example, the method can contemplate using a conductive material for the sealant barrier and/or an insulation material for the support member. 
     The fuel cell of the invention can be used by first, connecting a fuel source to a fuel plenum inlet; second, connecting a fuel plenum outlet to a re-circulating controller; third, connecting an oxidant plenum inlet to an oxidant source; fourth, connecting an oxidant plenum outlet to a flow control system, fifth, connecting a positive electrical connection and a negative electrical connection to an external load; sixth, flowing fuel and oxidant to the inlets; and finally, driving load with electricity produced by the fuel cell. 
     If a dead-ended version of the fuel cell is used the operation is much simpler. First, the fuel inlet is connected to a fuel supply, second, the oxidant inlet is connected to an oxidant supply, third, the positive electrical connection and the negative electrical connection are connected to an external load; and finally, the load is driven with electricity produced by the fuel cell. 
     The method of the invention can further comprise the step of sealing the plenum outlets and inlets after the fuel and oxidant is loaded into their respective plenums creating a dead ended fuel cell. The fuel cell can then be connected to an external load using the positive and negative electrical connections and used to drive the external load. 
     It is envisioned within this invention to use any combination of fuel and oxidant inlets and outlets to operate the fuel cell. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.